• Abstract • Organisation Profile • Bhel

CONTENTS

ABSTRACT

ORGANISATION PROFILE

BHEL HYDERABAD - AN OVERVIEW

CENTRIFUGAL COMPRESSORS

DEVELOPMENT OF MACHINE TOOLS

CNC PROGRAMMING

FEATURES OF SINUMERIK CNC SYSTEM ( TURNING CENTRES )

CNC MACHINE SPECIFICATION

FINISH TURNING OF IMPELLERS - DEVELOPED METHOD

CONCLUSION

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ABSTRACT

The basic function of the centrifugal compressor rotor is to impart the required compression energy to the gas.

The impeller is main part of the rotor. When the impeller is rotating at high speed, air is drawn through the eye of the impeller. The absolute velocity of the inflow air is axial. The magnitude and the direction of the entering relative velocity depend upon the linear velocity of the impeller at the radial position of the eye considered, as well as the magnitude and the direction of the entering absolute velocity. The impeller vanes at the eye are bent to provide shock less entrance for the entering flow at its relative entrance angle. The air then flows radially through the impeller passages due to centrifugal force. All the mechanical energy driving the compressor is converted into kinetic energy, pressure and heat due to friction.

Impellers are most stressed components of the compressors demanding highly precise manufacturing methods. The impellers are finish turned on CNC lathe to get the accurate profiles and required the surface finish. The dimensional accuracy of the impeller and the radius joining at the intersections of two surfaces should be smooth without under cuts.

Absolute programs are being used along with the machining cycles while finish turning on CNC lathe. The programmer is putting lot of efforts in calculating the co-ordinates and writing the programs. The efforts are continuous.

The finish machining of impeller is taken up as a project and efforts were put in learning the CNC programs and no of exercises are practiced to standardize the machining activity utilizing the CNC system features to the possible extent. Graphic simulation for the tool paths are verified and carried out the machining operations on regular piece and found OK. Profiles also checked with the templates given.

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ORGANISATION PROFILE

Bharat Heavy Electricals Limited is the largest engineering and manufacturing enterprise in India in the energy related / infrastructure sector today and ranks among the top twelve manufacturers of power equipment in the world.

Today BHEL has 14 Manufacturing Divisions, 4 Power Sector regional Centers, 8 Service Centers 18 regional offices and large number of Project Sites spread all over India and abroad enables the Company to promptly serve its customers and provide them with suitable products , systems and services efficiently and at competitive prices.

BHEL caters to core sectors of the Indian Economy viz, power Generation and Transmission, Industry, transportation, Renewable energy, Defence etc.

BHEL has already attained ISO 9000 and all the major units/divisions of BHEL have been upgraded to the latest ISO-9001: 2000 version quality standard certification for quality management. All the major units/divisions of BHEL have been awarded ISO-14001 certification for environmental management systems and OHSAS-18001 certification for occupational health and safety management systems.

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BHEL HYDERABAD AN OVERVIEW

BHEL - Hyderabad, a Manufacturing Unit located near Hyderabad

city. The major products of the Hyderabad unit are

- Gas Turbines

- Steam Turbines

- Compressors

- Generators and Exciters

- Heat Exchangers

- Pumps

- Oil Rigs

- Pulvarizers

- Switchgear etc.

The technology of BHEL - Hyderabad, for the products / systems is

on par with the latest / best in the world. BHEL- Hyderabad has

collaborations with leading companies in the world like M/s General

Electric-USA, M/s Siemens, Germany, M/s Nuovo Pignone-Italy etc.

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CENTRIFUGAL COMPRESSORS

ABSTRACT:

BHEL Hyderabad is the only organization in the public sector in India actively involved in manufacturing high-pressure centrifugal compressors for the industrial applications. These are employed for the use in Fertilizer industry, Steel Industry, Refineries, Petrochemical plants, Pipe Line, Gas booster for Gas Turbines etc.

BHEL started manufacturing compressors with technical know-how from Nuovo pignone of italy, the world leaders in compressor technology, BHEL - Hyderabad has been at the forefront of the latest developments in compressor Technology. BHEL’s endeavour is to offer quality products, designed to international standards, through dedicated service. A new addition to the wide range of Centrifugal Compressors is the integrally geared and packed SRL Compressors popularly known as ‘ API 672 Compressors ‘.

TYPES AND FEATURES OF BHEL’S RANGE OF CENTRIFUGAL COMPRESSORS

The entire product range of BHEL compressors is broadly divided into fourteen models of MCL & 2MCL casings and eight models of BCL & 2BCL casings, making it possible to choose the optimum size of casing for any capacity. For higher operating pressures, the casings of BCL & 2BCL type have been further graded into five pressure levels, enabling selection of right casing thickness.Features of different models are discussed below

A) Horizontally Split Compressor

MCL / 2MCL / 3 MCL / DMCL

These are multistage compressors for low and medium pressures with horizontally split casings. The horizontally split casing is either fabricated from plates or made of steel castings according to the duty of the compressor. The fabricated casing has several advantages and is preferred over cast construction. The journal bearings and thrust bearings are of the tilted pad type.

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MCL TYPE : These compressors can be utilized in fertilizer plants, ethylene plants, lube oil plants, refinery processes, city gas distribution etc.

2 MCL TYPE : These compressors are provided with intermediate suction and discharge nozzles.

B) Vertically Split Compressor ( Process )BCL / 2BCL / 3BCL / DBCL

C) Vertically split Compressor ( Pipeline )PCL Compressures for high pressures.

D) Integrally geared SRL 250 Compressors for low and medium pressures

Compressor Model Designation

2 BCL 40 7 / A2 = No of phases BCL = Constuctional feature 40 = Nominal Impeller dia ( cm ) 7 = No of ImpellersA = Pressure rating ( Up to 350 Atm )

Following are some of the developments in the recent past in the centrifugal compressors field.

- Multistage horizontal split casing design with design of 3D Impellers to maximize polytropic efficiency.

- Optimal design of impeller geometry adapted for low flow conditions (by slot welding technology for external welded impellers)

- Standard stage concept for optimum selection to suit any specific application.

- Fabrication of Casings- Compressors with high pressure ratios for process air service

( SRL type of compressors)- Compressor for highly corrosive service.- Some more features.

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Multistage horizontal split casing design with 3D impellers:

Larger plant capacities call for higher sizes of compressor models and hence increase the project costs. To make the models more competitive a careful study has been made in evolving 3D impellers with aerodynamic flow channels. Especially where the tip mach number is more than 0.85 e.g. for gases having high molecular weight or when operated at low temperatures (say 300 C) it is necessary to design the flow channel more aerodynamically. Any mismatch between the vane orientation and the flow direction results in higher incidence losses and thus affecting the overall efficiency of the machine, resulting in narrow operating range. By analytical study the flow channel can be made smoother which however results in 3 dimensional shape of impeller vane profile.

A computer package program for design of 3D impeller has been acquired from M/s NORTHERN RESEARCH CORPORATION USA. The program gives an optimum set of 3 dimensional co- ordinates for the impeller vane geometry. Acceptable geometry can be arrived at by observing velocity distributions in the passage.

Following are the merits in the design of 3D –impellers.

1. Higher polytropic efficiency:

The following data indicates qualitatively the improvement in efficiency of 3D -impellers over 2D- impellers.

Mach No inlet flow 2D impeller 3D impeller % improvement

coefficient efficiency efficiency in efficiency of

3D impeller over

2D impeller

0.85 0.08 75% 81.5 % ( 8.6 )

ii. Higher polytropic head coefficient:iii.

Mach No inlet flow 2D impeller 3D impeller % improvement

coefficient head co- head co-

efficient efficient

0.85 0.08 0.4875 0.566 16%

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From the above, it is clear that because of higher efficiency of 3D impellers the compressor power consumption will be low. The aspect of higher polytropic head combining with higher tip speeds results in less number of impellers for a given compressors ratio. Hence the design of the machine becomes more compact.

With the twisted blade geometry at the inducer portion conventional methods are not suitable for manufacturing 3D impellers. These impellers are manufactured by using five axis NC milling machining facility. Another method to produce impellers is by precision casting.

Though the manufacturing cost of the impellers are high, the difference in the cost between 2 dimensional impeller design and 3D impeller design gets compensated with in an tear because low operational cost and compactness of the machine in case of 3D impellers.

OPTIMAL DESIGN OF IMPELLER GEOMETRY ADOPTED FOR LOW FLOW CONDITIONS (EXTERNAL WELDED IMPELLERS):

Considering requirement of impellers handling low flows specially for high-pressure compressors a new chapter in manufacturing technology of impellers geometry is thus opened. This has incidentally helped in extending the range of operation of impellers.

The basic fact in the design of impellers is that higher the outlet vane angle higher the head coefficient and higher flow handling capacity. This means we have to employ low outlet angles for impeller vanes handling low flow. Generally for vanes angles less than 37.5 degrees, we require long channel passages. It is difficult to manufacture these impellers by any traditional methods. The efficiency and head realized in this case are definitely low.

External welded impeller manufacturing technology has over come the above difficulties. The steps of the manufacturing technology essentially are the following.

- Milling on vertical NC machines.- Milling of vanes on disc.- Corresponding slot milling on second forged disc.

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- Welding.- Matching of vane centerline with corresponding slot centerline

within an accuracy of 0.1 mm and fusion of parent material on to the vane material by TIG pulses.

- After the root fusion the remaining groove is filled with weld deposit by manual or automatic means.

FEATURES OF NEW DESIGN:

- Design of impeller geometry can be aimed for low flows with low vane angles without any sacrifice in efficiency (By way of having higher b2/D2 ratio)

- The operating range with these impellers is more than impeller employed with a compromise due to manufacturing constraint.

- Impellers calling for the design with outlet vane angles in the range of 15 to 180, results in long channel passages, hence appreciably better guidance for the flow.

- Because of no weld deposit in the gas passages the flow channels are clean. The improved surface finish has its own contributions to the overall efficiency.

STANDARD STAGE CONCEPT:

Centrifugal compressors belong to the ‘ Tailor made ‘ category product. However keeping in view of short delivery requirements cycles for the product and availability of powerful computer systems led to possibility of standardization of no. of components. In this effort the main focus is on the basic element of the compressor i.e. the impeller with diaphragm known as a stage.

The variety of industrial gases to be handled with molecular weights ranging from 3 to 120 makes the design more complex. Molecular weight is a very important factor affecting the operational speeds, geometry of impeller etc.

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Standard impeller are based on the following philosophy:

- Inlet capacity coefficient has been split into different ranges.

- For each range of capacity coefficient a family of impeller geometry is developed with different outlet angles yielding different levels of head coefficient.

- Series of impeller geometry in a family developed by further splitting the range of capacity coefficients. Acceptable geometry of the impeller is arrived at observing the basic necessities of relative velocity ratios and minimum disturbance of the flow angle with respect to the vane angle.

Impeller family Range of inlet capacity Outlet vane angle

Identification coefficient x 10-4 of the impeller

Geometry

B 189 – 1275 580

Q 180 – 564 450

F 43 – 210 150 – 160 - 170

Effective selections can be made by processing through computer by varying the parameters such as impeller diameter, speed, family of impeller group etc. The selection is accepted on the criteria of power absorbed and the range of operations.

Following are the merits in this concept.

- Storing of mass data of impeller geometry on computer system makes it convenient to generate different kinds of information required for predicting the critical speed of the machine, stresses in the impellers, vibrational amplitude. Through a plotter program it is possible even to generate the cross-section of the compressor stages.

- Selection of the impeller geometry is made, for which the performance is established through actual tests or extrapolated from the test results of the similar family. Thus makes the performance predictions more reliable.

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- Engineering cycle time is reduced to a greatest extent because of the fact pre-planning can be done for the engineering documents, tooling schedules preparation.

- Advance planning of raw materials like forgings and castings with minimum allowances for final finishing.

These impellers can be made by any one of the conventional methods viz. vane welding type, milling and welding type, electro erosion and the slot welding process.

COMPRESSORS WITH HIGH PRESSURE RATIO IMPELLERS

( SRL COMPRESSORS ):

Single and multistage compressors for low and medium pressures, are mainly used as blowers or boosters in industries, refineries and petrochemicals plants, when large volumes of gases have to be handled at low pressures and a packaged, integrally geared design is required for compactness and economy.

New series of SRL Compressors have been developed for process air requirement with high-pressure ratios. The new series of compressors use independent impellers, each of one being driven at its own optimum speed by means of an integral bull gear and pinion assembly. Overall pressure ratio with air can exceed 20:1.

These compressors can be designed and manufactured for supplying air-to-air separation unit.

COMPRESSORS FOR HIGHLY CORROSIVE SERVICE:

In addition to the introduction of the latest developments enumerated above a new compressor has been developed to handle highly corrosive gas. This is specifically significant, as it is a case of imported substitution.

The cross section of the compressor is a single stage over hung design since the pressure head required to be developed is low. The major components are made of austenite stainless steel material. The compressor is provided with single set of oil seals arrangement to seal the gas leaking from the shaft ends to atmosphere. An auxiliary seal oil system is provided to perform the

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duty. Bearing housing is rigidly clamped to the casing with suitable locations in the casing.

SOME MORE FEATURES:

- Provisions of two kinds of sealing at the shaft ends for the compressors handling cryogenic fluids are the recent necessities.

Mechanical seal arrangement to minimize the shaft end leakages of gas to outside atmosphere to the bare minimum during normal run of the compressor.

- For compressors handling toxic gasses tight shut off seals is one of the recent requirements. These seals arrest the gas leakage to outside atmosphere. When the unit is not in operation and where it is not afford to depressurize the system by venting.

COMPUTER AIDED DESIGN OF CENTRIFUGAL COMPRESSORS

It has often been said that the computer age will do for man’s mind what industrial revolution did for his muscle. High speed and high accuracy in problem solving made them an important design tool. Computer aided design ( CAD ) is a technique in which man and the computer are blended into a problem solving team, intimately coupling the best characteristics of each, so that this team works better than either alone. The main benefits that accrue out of CAD are

- Reduction in design cycle time

- Reliability of equipment

- Design optimization

APPLICATION OF CAD TO CENTRIFUGAL COMPRESSORS

Centrifugal compressors occupy an important position in process plants and they must be extremely reliable. Reliability of the equipment is built at the

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design stage itself. The design of compressor involves right from the evaluation of thermodynamic properties to rotor synchronous response complex mathematical equations. Also the calculation procedure is highly iterative. To carry out these calculations manually is not only time consuming but error prone. Application of CAD overcomes these short comings. The important aspects of computer program used in the design of centrifugal compressors are described below.

SOFTWARE FOR EVALUATING THERMODYNAMIC PROPERTIES OF GASES

One of the most important aspects in the design of centrifugal compressors is the correct evaluation of thermodynamic properties of gases or gas mixtures being handled. Till recently Mollier Charts were used for the above purpose. This method is tedious and time consuming. More over, it is difficult to obtain Mollier charts for gas mixtures.

To over come this difficulty an equation of state is used. An equation of state is a functional relationship between pressure, temperature and volume. An equation of state, theoretical or empirical makes possible easy interpolation ( and possible extrapolation). It condenses the availability PVT data to a great extent. Using and equation of state, the errors involved in the evaluation of derivatives and integrals are reduced, as taking slopes by graphical differentiation involve large errors and are tedious. The accuracy depends on how well the equation of state represents the PVT data.

The Benedict-webb-Rubins (BWR) equation of state is the best available in the field of gas and liquid for light hydrocarbons. This equation of state has 8 numerical constants varying for different gases. To predict more exactly the properties of simple components Starlings modification of BWR equation is used. This equation has 11 numerical constants.

For non-hydro carbons and hydrocarbons for which the eight coefficients of BWR equation are not available the generalized BWR euation as given by Cooper and Gold Frank is used. For gas mixtures the coefficients are obtained by mixing rules given by BISHNOI & BOBINSON.

A computer program based on above equations of state is being used. The input to the program consists of gas composition and ranges of pressure,

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temperature over which the properties are required. The graphical output of this program is used for the purpose.

SOFTWARE FOR SELECTION OF COMPRESSOR STAGES

Centrifugal compressors of BHEL-NP design employ standard tested stages. A stage is a combination of impeller, vane less diffuser and return vane channel. Depending upon the impeller blade outlet angle the stages are divided into different families as B,Q, F,G and H. In each family of impeller there are different types of stages. The polytropic efficiency of an impeller is expressed as a polynomial of inlet flow coefficient with 7 numerical constants. Each of these constants as a function of family, type, diameter and tip speed Mach number of impeller.

The head coefficient is expressed as a polynomial of product of inlet flow coefficient and specific volume ratio at inlet and outlet. The polynomial consists of 4 coefficients each of them is a function of family, type, diameter and tip speed Mach number of impeller.

From the tested data of a set of impellers in each family, the values of the above said coefficients are evaluated. This data is available as a direct access file on the computer. Part of the program consists of subroutines to evaluate gas properties.

The input program consists of the following

i) Inlet conditions of gasii) Discharge pressureiii) Gas compositioniv) Approximate speed and no. of stages in the trainv) Pressure drop across intercoolersvi) Impeller diametervii) Injection and extraction conditions

The program then selects the type of stages evaluates speed, phase polytropic efficiency and total power.

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SOFRWARE FOR DESIGN OF 3-DIMENSIONAL IMPELLERS

For impellers operating at high tip Mach numbers ( above 0.9) it is necessary to match the blade angle with flow angle to minimize losses. This results in a twisted impeller blade. To carry out the design of 3-dimensional impellers, a computer program developed by Northern research Engineering Corporation (NREC) is being used. The program calculates the relative velocity distribution along eight streamlines from hub to shroud based on prescribed loading method. The major input parameters are hub & shroud contours, blade thickness distribution, swirl distribution, blade blockage factor and outlet angle.

Output is in both tabular and graphical form giving the relative velocity distribution along 8 streamlines and blade shape in the form of line elements.

SOFTWARE FOR CALCULATION OF STRESSES IN CENTRIFUGAL IMPELLERS

The state of art in the present day centrifugal compressor design is to go in for high tip speeds. Calculation of stresses in the impeller is the basis for selecting the impeller material, type of heat treatment and interference for shrink fitting of impeller on to the shaft. A program based on the procedure given by B.P.C.H.O is being used.

The input to the program is the description of the impeller, tip speed and blade thickness distribution, blade root stresses, extension and deflection at various radii.

SOFTWARE FOR ROTOR DYNAMICS

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An important part of the standard design procedure for a rotor is the calculation of its critical speeds. As a first approximation undamped critical speeds are calculated using PROHL’method. In this method isotropic supports are considered. A rather more satisfying approach to the flexural analysis of the rotor consists in introducing damped in the vibration system and considering anisotropic linear supports. Such a model enables one to face the following problems.

a) Study of stationary vibrations due to unbalances that are present in the rotor. These vibrations are synchronous with the rotor rotation.

b) Study of stationary vibrations due to the presence of one or more forces, with constant intensity and all of them rotating uniformly at the same speed, generally different from rotor speed.

c) Study of natural damped mode of vibration of the rotor and calculation of stability parameter. Stability measures the attitude of

d) the very mode towards damping. A small or even negative value of this parameter indicates that the system is unstable.

With only one computer program, that was developed for this purpose, one can face three types of problems previously described. Most of the formulae used in the program were drawn from the theory that is illustrated by J.W.LUND. The input to the program consists of physical description of the rotor, geometric characteristics of bearing, speed range over which synchronous response is required.

Program output consists of bearing characteristics (stiffness and damping coefficients) vs sommerfield number, amplitude of vibration at various speeds.

Torsional critical speeds for the entire train is carried out by means of a program based on Holzers method.

SOFTWARE FOR PLOTTING OF DIAPHRAGM RETURN VANE CHANNEL AND FAMILY OF IMPELLERS:

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The flow entering the intermediate impeller of a compressor is made radial by deswirl vanes located upstream of the impeller.

Inlet angle of the vanes is obtained based upon the conditions of flow at the impeller outlet. The flow area varies linearly from inlet to outlet of return vane channel. A program based on above considerations calculates the vane profile.

The complete data pertaining to different types of impellers of a family is available as a direct access file. A computer program facilities plotting of complete series of impellers in a given family for a given diameter.

Accurate evaluation of thermodynamic properties, critical speeds, stresses contribute to the reliability of equipment. The next step is to generate component drawings and necessary information for machining on CNC machines.

COMPRESSOR COMPONENTS:

- Casing- Diaphragm- Rotor- End covers for barrel construction design - Sealing system

CASING:

The construction features of the two models in use are

- Horizontally split casing design- Vertically split casing design

Horizontally split type design :

The horizontal plane in the middle and consists of an upper and lower part. All necessary connections, such as suction and discharge nozzles,

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intermediate suction and discharge nozzles, wherever required, and lube oil inlet and drain connections are integral with the lower half. Internal parts can be accessed just by lifting the upper part which needs no major dismantling of piping. For inspection of bearings, there is no need to remove the upper

half. Only bearing cover removal is adequate. The MCL, 2MCL, 3MCL and DMCL compressors are of horizontal split design.

Vertically split type design :

These are used when the working pressure and type of gas demand such an arrangement. All internal parts are similar to the horizontally split type casing, but the diaphragm seals and the rotor bundle are inserted axially in a forged steel barrel casing. Ends are closed with end covers, the lower half of the bearing housing is integral with the end cover. By removing the end cover, it is possible to withdraw the complete internal assembly and have access to the internals like seals, diaphragms and rotor, without disturbing the outer casing. There is no need to remove end covers for bearing inspection. The BCL, 2BCL, DBCL, 3BCL and PCL type casings are of the vertical split design.

DIAPHRAGMS :

The function of the diaphragm is

i) To form the dynamic flow path of the gas inside the compressor. ii) To form the separation wall between one Compressor stage and the

subsequent one.iii) To convert the kinetic energy of the gas leaving the impeller into

pressure energy.

They are of three types.

1. Suction diaphragm2. intermediate diaphragm3. Discharge diaphragm

The diaphragm are generally made of cast steel. However, based on operating conditions, alloyed cast iron, forged steel or stainless steel

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materials are also used. In small and medium size casings, the diaphragms are fabricated from plates.

ROTOR:

The basic function of the centrifugal compressor rotor is to impart the required compression energy to the gas.

The rotor forms the heart of the centrifugal compressor, consisting of the shaft, Impellers, spacers, bushes, Balancing drum, thrust collar, Coupling hub and thrust bearing. The impellers are hot shrunk and keyed. The shrinking of impeller and balancing piston is necessary to ensure that the impeller does not get slackened due to the centrifugal forces during start up and normal running of the compressor. This would otherwise result in vibrations on the rotor system. Rotor must perform its function with a deflection less than the minimum clearance between rotating and stationary parts. The loads involved are the torques, the weight of the parts, and axial gas forces. The rotor, during assembly is balanced stage wise.

SHAFT:

The shaft is made out of forged alloy steel and the impellers, spacers and the balancing drum are shrunk fitted on it . Spacers of stainless steel material are used to protect the shaft against gas erosion and corrosion. The shaft is made by turning and grinding operations. journal bearing zones of the shaft is ground and burnished with the diamond burnishing technique to improve the surface finish and to keep the total run outs within the permissible limits.

IMPELLER:

When the impeller is rotating at high speed, air is drawn through the eye of the impeller. The absolute velocity of the inflow air is axial. The magnitude and the direction of the entering relative velocity depend upon the linear velocity of the impeller at the radial position of the eye considered, as well as the magnitude and the direction of the entering absolute velocity. The impeller vanes at the eye are bent to provide shock less entrance for the entering flow at its relative entrance angle. The air then flows radially

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through the impeller passages due to centrifugal force. All the mechanical energy driving the compressor is converted into kinetic energy, pressure and heat due to friction. The purpose of the diffuser/diaphragm is to convert the kinetic energy that leaves the impeller into pressure. The air leaving the diffusers is collected in a spiral passage from which it is discharged from the compressor.

Impellers are most stressed components of the compressors demanding highly precise manufacturing methods. Impellers are identified depending on the methodology used during manufacturing. The different types of impellers, which are being manufactured, are:

1) Welded type of impeller

Welding technology is adopted for the impellers having gas passage width more than 30 mm. In this type of impeller, disc and counter disc are machined out of two separate forgings and vanes are bent to the required shape out of plate. Vanes are welded to the disc and counter disc from inside, followed by stress relieving, testing of welded parts, heat treatment and machining to correct profiles.

2) Milled & welded type of impeller (Internal welded type)

This technology is adopted for the impellers having gas passage width varying from 7 to 30 mm. In this type of impellers, vanes are milled on to the disc (or counter disc) and then counter disc (or disc) is welded to the disc followed by heat treatment, testing, finish turning and balancing. The critical operation involved is the milling of vanes on disc (or counter disc) by special 3 dimensional milling machine.

3) Milled & welded type of impeller (External welded type)

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This is the latest technology, which has been adopted for impeller manufacturing. The impellers having low outlet angles, small radius of curvature of vanes and narrow gas passages, could not be manufactured as mentioned above because of the limitations involved in the impeller manufacturing techniques. Subsequently, new technology is developed established i.e. External welded impellers.

In this type the impellers are manufactured out of two separate forgings for disc and counter disc. The critical operations involved in manufacturing of external welded impellers are

i) Machining of vanes on counter disc and corresponding blind grooves on disc.

Milling is carried out on CNC machine center. This operation is critical in the sense that there should be perfect matching of the axis of the blind groove on disc and axis of vanes on the counter disc. This is being ensured by drilling peepholes on every blind groove.

ii) Welding of disc on to the counter disc

Disc is diametrically located on to the counter disc, coaxiality of groove and vanes axis is ensured through peepholes. The job is preheated and gas passages are closed by seal welding circumferentially to avoid the leakage of inert gas. Job is mounted on the special welding fixture, vanes curvature is centered w.r.t manipulator center and clamped. Root welding is done by TIG by fusing disc material on to the vanes and subsequently metal is filled up externally in the groove of disc by TIG pulse. This operation will be carried out special automatic welding machine having pulse generator and a special fixture.

4) Electro- eroded impeller:

This method is used where welding technology is not suitable for the impellers of small width gas passages. The impellers are manufactured out of a single forging. Gas passages are eroded in the forging & vanes are created by adopting EDM (Electrical discharge Machining) technique. The critical operation in manufacturing this type of impeller is the Electro-

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erosion of gas passages. Electrodes are machined to the shape similar to that of gas passages, and fed vertically downwards through a pilot hole. The pilot hole guides the electrode. Material is eroded by spark discharges between the electrode & the job across a gap usually filled with die electric medium and gas passages are created.

END COVERS :

BCL type of casing are closed at both ends with end covers which has got integral bearing and seal housing. End covers are always manufactured out of forgings.

DEVELOPMENT OF MACHINE TOOLS

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To stay in business, the main motive is profit. Better services offered on schedule, reliable, improved and consistent quality of product also mean profit.

Productivity in manufacturing is a parallel term to profit in business. Productivity is a positive difference between output and input. To increase the productivity therefore one has to maximize the output and while keeping the input as low as possible.

To meet the objective of consistency of quality particularly required in accurate and complex components calls for use of special purpose or automatic equipment. The cost of such equipment could only be met if the quantity of production and the productivity is very high.

Thus if quantity and quality and delivery schedule are prime importance, the answer is mass production.

However on the entire spectrum of production activities around 15-20% of demand desires the use of mass production. The remaining requirements can be met only by batch production.

Automation has been associated with advancement in technology. In the process of automation for small batch production, hydraulic tracer controlled machine tools and programmed special purpose machine tools have been evolved.

However these require cams, templates, stops, electrical trip dogs etc, calling for a longer set up time while changing over to new jobs.

These problems of automation of small lot (batch) production have been overcome by Numerical control machine tools to a great extent.

NC has long been considered a technology to produce engineering goods of good quality and accuracy.

NC is not a particular machining and forming method but only a better and effective way of controlling machine tool functions and performance independent of operator skill.

It does not substitute good tools or production engineering practices but supplements them both.

DEVELOPMENT OF MACHINE TOOLS

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GENERAL PURPOSE MACHINES (GPM)(CONVENTIONAL MACHINES)

SPECIAL PURPOSE MACHINES (SPM)(AUTOMATICS)

NUMERICAL CONTROL MACHINES

COMPUTER NUMERICAL CNTROL MACHINES

ADVANCED CAM TECHNIQUES LIKE FMS & CIM

Comparison of GPM / SPM / CNC :

GPM - Completely manualSPM - Built in automatic cycles / For mass production / Changes are difficultCNC - Highly flexible / Suitable for batch production / Job production as

per requirement

COMPUTER NUMERICAL CONTROL OF

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MACHINE TOOLS

By controlling the relative movements between the tool and the work piece geometrical shapes are machined. Control of these relative movements through coded letters numbers is known as Numerical Control of machine tools.

NC is simply a way of electronically controlling the operations of a machine. In conventional machine operator directly controlling the machine functions. Where as in NC machine a separate media which is in between machine and operator is controlling the machine functions. These NC machines do not have any memory of their own and hence capable of only executing a simple block of information fed to it at a time.

Hardware automation gave way to computer controlled automation in manufacturing process. Computer numerical control is the term used when the control system of an NC includes a computer. The availability of a dedicated computer permits new control features to be made available on CNC machines.

BASIC COMPONENTS OF NC

Program of instructions:

The program instructions is the detailed step by step of directions which tell the machine tool, what to do.

Machine control unit:

This consists of the electronics and hardware that read and interpret the program and convert it into mechanical actions of the machine tool.

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Program of instructions

MCU Machine tool

Machine tool:

It is the part of the NC system which performs the useful work.

OPERATING PRINCIPLE :

Conventional machine tool NC machine tool

Operators brain = NC controllerHands = DC servo drivesEyes = Feed back system

ADVANTAGES OF CNC MACHINES :

CNC machines offer the following advantages in manufacturing.

Higher flexibility. Increased machine utilization Increased productivity. Consistent quality. Reduced scrap rate. Reliable operation. Reduced non-productive time. Reduced man power. Shorter cycle time. Higher accuracy. Reduced lead time. Automatic material handling. Lesser floor space. Increased operational safety. Machining of advanced material. Savings in jigs and fixtures. Changes in the design can be easily incorporated. Ability to combine operations. Stored programs Editing facility near the machine Graphic simulation User written programs

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First step in CIM

CRITERIA FOR SELECTION OF COMPONENTS FOR NC MACHINING:

Number of operations per component - MANY Complexity of the operations carried out - HIGH Size of batches – MEDIUM Repetition of batches – OFTEN Labor cost of the component – HIGH Skill required by the operator – HIGH Ratio of cutting time to non cutting time – HIGH Variety of components to be produced - MORE Cost of special tooling involved – HIGH Design changes – FREQUENT Number of dimensions to be maintained – MANY Setup time and inspection time – HIGH Precision involved in the component – HIGH Time lag between the operations – HIGH Non- uniform cutting conditions - REQUIRED

EMERGING TRENDS AND NEW DEVELOPMENTS IN CNC TECHNOLOGY

Special purpose machine tools Coordinate measuring machine and Inspection probes Adaptive control Tool condition / collision monitoring DNC / Windows based CNC systems Work oriented program (WOP) / Conversational automatic

programming (CAP ) CAD / CAM Flexible manufacturing systems ( FMS ) Robotics Computer integrated manufacturing ( CIM )

Special purpose machine tools :

Because of the CNC technology new types of machines are being made like machining centers which are predominantly made for prismatic components. Turning centers are being made for machining components

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which have more of turning operations but also having operations which call for milling, drilling and tapping. These machines are also called CNC lathes with driven tools or live tools. These machines have turret which has independent drive, programmable through CNC system and some of the tool positions can have tools which will rotate. Using these machines, the operations like slotting, key way milling, drilling and tapping can be completed after completing the turning operations. Similarly, the machining centers are equipped with CNC controlled facing and turning attachments to complete the turning operations in the prismatic components.

Coordinate measuring machine and inspection probes :

One of the types of CNC machine is coordinate measuring machine and it is used mainly to inspect components which come out of CNC machines. The machine has a touch probe which will measure the dimensions as per program and can give out the deviations in the form of a chart or plot the actuals against the acceptance band. These machines can also be linked to the CNC machines to give suitable offsets to correct for the dimensional variations.

The use of in-process inspection probes is becoming more common in modern NC machine tool systems. These inspection probes are sophisticated dial indicators which can be mounted in the machine tool spindle or holder. In machines with automatic tool changers, the probe would be placed in the tool storage drum and loaded in to the spindle or holder when needed, just like any of the regular cutting tools. Sensors in the probe detect when contact has been made with a surface of the work part being checked. The software in the controller performs the necessary computations to interpret the signals from the probe.

The principal benefits that drive from the use of inspection probes are time savings and improved accuracy. Measurements taken with the probe are generally more accurate than traditional techniques used to measure part dimensions.

Adaptive controls

For machining operations, the term adaptive control denotes a control system that measures certain output process variables and uses them to

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control the process. Some of the process variables that have been used in adoptive control are spindle deflection ,torque, cutting temperature, Vibration, amplitude and horse power. The motivation for developing an adaptive machining system lies in trying to operate the process more efficiently. The typical measure of performance in machining have been removal rate cost per volume of metal removed.

Benefits of adaptive control machining:

1. Increased production rates2. Increased tool life3. Greater part protection4. Less operator intervention5. Easier part programming

Tool condition / Collision monitoring :

There is a possibility of collision of tool to work-piece or any stationary part of machine due to incorrect offsets. Anti-collision devices are used which will sense the collision by the load on the tool turret and stop the feed sufficiently fast to avoid permanent damage to the machine. Some times same or similar devices are used to find out the condition of the tool and give indication when the tool is worn out and needs replacement as blunt tool needs more power. An extension of this facility is to automatically change over to a sister tool ( a new tool of same type ) once the useful life of the tool is completed.

Direct numerical control ( DNC )

Direct numerical control is defined as a manufacturing system in which a number of machines are controlled by a computer through direct connection and in real time. The evolution in the configuration of DNC and its inclusion of computer numerical control have resulted in the introduction of the term “ Distributed numerical control “ for the initials DNC.

Advantages of DNC

- NC part programs are stored conveniently in files- Greater computational capability and flexibility

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- Reporting of shop performance

Work Oriented Programming ( WOP ) / Conversational automatic programming ( CAP ):

The WOP / CAP user interface has been designed to carry out the different types of machining like turning, drilling and milling by programming the

Tool geometry Work piece geometry Raw material contour Machining technology graphically

The programming process is usually carried by the machine operator. The WOP / CAP systems are designed to facilitate the part programming process by using an interactive mode to assist the operator through the programming steps. It queries the operator about the details of the machining job so that the operator types in the program responding to the sequence of questions. The system use shop language rather the alphanumeric codes. This removes some of the mystery usually surrounding the programming activity. Basically, the operator must able to read an engineering drawing and be familiar with the machining process. No extensive training is required in NC part programming.

The great advantage of WOP / CAP is its simplicity. It represents a relatively easy way for small shop to make the transition to numerical control.

The limitation is that the programs should be relatively short and simple. This means that the machining jobs should be uncomplicated. There are several reasons for this limitations. First, since there is no paper copy of the program, there is a limit on the length and complexity of program that the operator is capable of visualizing. Finally one of the biggest disadvantage is that the machine tool itself is not productive while programming is being accomplished. One way of overcoming this last disadvantage is by operating the machine tool in background mode.

The function program WOP / CAP allows

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The definition of work piece, tools, tool magazines and material lists Creation of tool geometry Programming of the machining technology Definition of a face or peripheral surface Graphic simulation of programmed traversing movements and Generation of a part program by the system using system built in

subprograms etc

Example : Shop turn interactive graphic package developed for turning centers with Sinumerik system.

CAD / CAM :

CAD / CAM is a term which means computer aided design and computer aided manufacturing.

It is the technology concerned with the use of digital computers to perform certain functions in design and manufacturing.

This technology is moving in the direction of greater integration of design and manufacturing.

CAD :

CAD can be defined as the use of computer systems to assist in the creation, modification, analysis, or optimization of a design.

The CAD soft ware consists of the computer programs to implement computer graphics on the system plus application ( soft wares ) programs to facilitate the engineering functions of the user company.

CAM :

CAM can be defined as the use of computer systems to plan, manage and control the operations of a manufacturing plant through either direct or indirect computer interface with the plants production resources.

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Flexible Manufacturing System

Computer control machines are the building blocks for FMS. Whereas through computer numerical we are able to improve the productivity of the individual machines by fairly high margin there is a tremendous scope to improve the actual utilization of the shop. This is possible through FMS by making the movement of components and their loading / unloading more efficient. It is the extension of CNC in to these areas which helps in improving the productivity of system in batch manufacturing.

Robotics:

In terms of control technology and programming, industrial robots share in common with numerical control machines. Robotics are used for moving parts and tools in the performance of industrial tasks. An important number of these tasks are concerned with the loading and unloading of production machines, including NC machines.

Computer Integrated Manufacturing ( CIM )

Computer – integrated manufacturing systems incorporate many of the individual CAD/CAM technologies and concepts. These include:

Computer numerical control ( CNC )Direct numerical control ( DNC )Computer process controlComputer integrated production managementAutomated inspection methodsIndustrial Robotics

CNC PROGRAMMING:

A program of instructions for a NC machine tool is termed as a part program. A NC part program is a series of coded instructions that direct the operations of a numerically controlled machine.

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These instructions contains all the machine and control functions necessary to make the machine perform a specific task.

The NC machine recovers the directions for operations from program. The program is prepared by listing coordinates values.

The coordinate values are prefixed with preparatory with preparatory codes to indicate the type of movement required from one coordinate to the next and supplemented with feed rate figures.

The coordinates are suffixed with miscellaneous codes for initiating the machine tool function like start, stop etc.

All these elements in a time of information form one meaningful command for the system / machine to execute and is called a block of information.

The preparation of a set of instructions to carry out the machining of a work piece is called part programming. This work is carried out by a part programmer. He prepares the planning sheet and write the instructions in a coded form which is acceptable to the controller of the machine tool.

Part programming is of three types

1. Manual part programming2. Computer assisted part programming using NC programming languages3. Generation of program using CAD / CAM package

1. Manual part programming:

While making the part program for a component the programmer first studies the drawing and decides upon the sequence of operations, cutting tools, speeds and feeds at various points, other necessary information like starting and stopping of machine tool etc.Manual programming is ideally suited for applications like drilling and turning .Regarding manual part programming further details are given at later pages.

2. Computer assisted part programming:

Most parts machined on NC systems are considerably more complex. In the more complicated and contouring applications, manual part programming, becomes an extremely tedious task and subject to errors. In

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these instances it is much more appropriate to employ the high speed digital computer to assist the part programming process.

Many part programming language systems have been developed to perform automatically most of the calculations which the programmer would otherwise be forced to do. This saves time and results in a more accurate and more efficient part program.

NC part programming languages :

NC part programming language consists of a software package plus the special rules, conventions, and vocabulary words for using that software. It to make it convenient for a part programmer to communicate the necessary part geometry and tool motion information to the computer so that the desired part program can be prepared. The vocabulary words are typically mnemonic and English like, to make the NC language easy to use.

APT programming language:

APT ( Automatically Programmed Tools ) is the most widely used of the more than 50 NC programming languages available. In APT programming, the work part is defined with geometric elements such as lines, planes, and circles. These lines, planes, and circles are “unbounded geometry” in the sense that the lines and planes are infinite and the circles are complete circles. The work part, of course, is bounded, so the APT geometry elements do not really provide an accurate and comprehensive definition of the part geometry. It is by means of a sequence of APT motion statements that the tool is directed around the actual surface of the part, ignoring the portions of the circles and lines that do not relate to the part.

The best known systems which are based on APT(APT compatible)are EXAPT, ADAPT, IFAPT, BASIC- APT, FAPT etc. Systems which have been developed by machine tool manufacturers include EASY-PROG, PROGRAMAT, H100 AND AUTOFIT.

APT is a powerful and versatile language, but has three potential disadvantages.

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The first is that the user must learn a language with its own syntax and grammar. Unless he already has computer programming experience , he is exposed to some concepts which are entirely alien to him.

A second disadvantage is that the part programmer must interpret the engineering drawings ( with the possibility of error ) and define the geometry of the part for APT .

The third disadvantage is that the programmer has to mentally visualize the tool path as he is programming.

2. Generation of part program using CAD / CAM packages.

In the CAD/CAM approach to geometric modeling, the part is defined by surfaces and edges that construct a solid geometric description of the part. The surfaces and edges do not extend infinitely in their respective directions. The term given to this method of part definition is “bounded geometry”. Which contrasts with the unbounded approach used in APT. Many of the concepts of APT geometry definition were utilized to develop the current geometric modeling technology of CAD/CAM. In many respects, developments in computerized geometric modeling have outpaced the APT geometry concepts.

Various CAD / CAM soft wares available in the market are

Pro Engineer Master Cam Unigraphics etc

IMPORTANCE OF MANUAL PROGRAMMING :

In manual part programming a programmer completes the programming task without any computer assistance. The only aids used are a scientific calculator, the programming instructions for the specific machine-tool controller/controller combination, a tape preparation device and experience. Programmers should always begin and conclude their training by manual part programming , since it is essential that they be able to readily understand, read, and modify part programs. A programmer must feel confident to correct programs both at the CNC machine and in the office.

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RESPONSIBILITIES OF THE CNC PROGRAMMER WHILE PREPARING THE MANUAL PART PROGRAM :

The programmer studies the engineering drawing and translates the operations to be performed into a manuscript in a prescribed format. The individual who programs the job for NC machine generally

Study the relevant component drawing thoroughly Chooses the NC machine tool to be used Identify the type of material to be machined Knows the specifications and functions of machine tool and features

of the CNC system Check the tooling required Establish the sequence of machining operations Determine the cutting parameters for the job/tool combination Prepares the program Decide the mode of storing the part program once it is completed

While preparing the part program, depends upon the availability of the features in the system, the below shown system features or the combination of different features can be used advantageously depending upon the amount of material to be removed, machining sequence, machine and the programmers convenience. Some of the CNC system features are listed below.

System features used in manual programming.

1. Work piece dimensioning, input system 2. Absolute coordinate system 3. Incremental coordinate system 4. Combination of Absolute and incremental5. Polar coordinate system ( Useful in machining centers )6. Programming with Constant RPM or constant Cutting Speed7. Tool nose radius compensation ( TNRC )8. Parametric programming ( Also called Variable programming )9. Blue print programming ( Also called Contour definition Programming )10. System built in machining cycles for stock removal in roughing and finishing cuts ( In turning, drilling and Threading ) 11. Developed, user sub programs ( Also called macros in Fanuc system )12. Subroutine nesting

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13. Mirroring one of the axis14. Programming with @ Functions

Some of the basic features exits readily in the machine switch on condition.

VARIOUS OPERATOR AND PROGRAM CONTROLS ON CONTROL PANNEL OF A CNC MACHINE

Manual program editing Back ground editing Single mode / Auto mode Cycle start Dry run Feed control ( 0 – 120 % ) Feed hold RPM control ( 50 – 120 % ) Reset Block search Optional stop Block skip MDI (Manual data input) Mirror image in selected Axis Reference Preset position Reposition incremental Jog continuous Chuck ON / OFF Direction of rotation Gear change Coolant ON / OFF Emergency Indicators for machine / system alarms Program verification by graphic simulation

RESPONSIBILITIES OF CNC MACHINE OPERATOR WHILE EXECUTING THE JOB :

Job loading and setting as per the job layout

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Program entering manually/ through punched tape / through DNC / calling from memory

Loading the required cutting tools into the turret / tool magazine as per the tools layout and entering the tool data into the memory

Fixing the work zero with reference to the machine zero Verification of correctness of the program from graphic simulation if

the system allows Machining the job in single mode as per the program. Dimensional

inspection while machining and correction of tool offset if necessary. Replacement of inserts, cutting tools whenever required.

Optimization of the program i.e. correction of feeds, speeds, idle movements etc

VARIOUS CNC SYSTEMS :

Various types are CNC systems are available in the market. These systems are having their own advantages and disadvantages.

SINUMERIK / HINUMERIK FANUC GE MARK ++ FAGOR GE-FANUC ANILAM KONGSBERG CRUSADOR LAXMI etc

The popular systems are Sinumerik from Siemens, Germany and Fanuc from Fanuc corporation , Japan.

FEATURES OF SINUMERIK CNC SYSTEM

It is a microprocessor CNC, continuous path control with integrated programmable logic controller ( PLC ). The system has linear axes control with simultaneous interpolation of two axes .

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Variable programming concept. Around 500 variables are available.

Graphic display of tool path to check the program errors. Background editing of programs i.e. while executing one program

another program can be entered without stopping the machining. Various built in machining cycles for easy programming. Block search facility. Memory capacity about 128 KB. Allows Blue print programming.

Meaning of alphabetical, Numerical and Special characters used in SINUMERIK system

Alphabetical characters

A - Angle 0-3590

B - Radius / ChamferD - Tool offsetF - Feed rateG - Preparatory functionH - Auxiliary functionI - Arc center offset in X- axisK - Arc center offset in Z- axisL - Sub program / Machining cycleM - Miscellaneous functionN - Block NumberP - Number of passesR - Assignable Parameters / VariablesS - Spindle speed in RPM or CCS in mts / minT - Tool numberX - Transversal axisZ - Longitudinal axisNumerical characters

0 – 9

Special characters

+ Addition

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- Subtraction* Multiplication/ Division= Equal to% Main Program fileLF End of Block@ At the rate function/ Slash

SYSTEM DIRECTORY

The CNC system directory consists of three ( 3 ) types of programs in memory

-Main programs ( % )-Sub programs ( L )-Machining cycles ( L )

MAIN PROGRAMS / PART PROGRAMS (%)

A part program comprises a complete string of blocks which define the sequence of a machining process on a numerically controlled machine tool. Subroutines and cycles may be components of the program

A part program comprises:

- The character for program start ( % )- A number of blocks with end of block character ( LF )- The character for program end ( M02 / M30 )

SUB PROGRAMS / SUBROUTINES ( L )

When a component has repetitive pattern machining at different places, subroutines programming can be used to reduce the effort of writing a detailed program. The program for repetitive machining can be stored in the memory as a separate program and can be called in the main program

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whenever needed. When the last block in the subroutine is executed, control will automatically return to the main program. Loop identification will be there for start of the subprogram and end of the sub program and calling of a sub program.

Subroutines can be called not only from a part program, but also from other subroutines. This process is referred to as subroutine nesting. Different controls allow nesting of subprograms up to different levels depending on the software capability. Usually nesting will be possible up to three levels. The sub programs either in absolute co-ordinates or incremental depends upon their usage.

STRUCTURE OF A PART PROGRAM

The part program is a set of instructions proposed to get the machined part from the desired blank and the machine tool. A part program defines a sequence of NC machining operations. The information contained in the program can be dimensional or non – dimensional like speed, feed, auxiliary functions, etc. The basic unit of a part program input to the control is called a block. Each block contains adequate information for the machine to perform a movement and functions. Blocks in turn are made up of words and each word consists of a number of characters. All blocks are terminated by the block end character. The maximum block length for each CNC is fixed.

BLOCK FORMATS :

Format is the sequence of words in which information appears in a program. Types of formats used in NC programming.

Word address format:

In word address format each word is identified by a letter eg: Letter N identifies the sequence number, word T identifies tool function etc

Tab sequential format :

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In tab sequential format, each word is separated from the other by a tab character. The words are identified by their respective positions in the block.

Word address format is used widely in CNC programming.

A block may contain any or all the following:

Optional block skip ( / ) Sequence or block number ( N ) Preparatory functions ( G ) Dimensional information (X, Y, Z, etc ) Dwell Decimal point ( . ) Feed rate ( F ) Spindle speed ( S ) Tool number ( T ) Tool offset function ( D ) Miscellaneous functions ( M ) Auxiliary function ( H ) Sub program number ( L ) Repetitive count ( P ) End of block ( LF )

Optional Block Skip character ( / ) :

A programmer may program all the operations of a particular family of components. The operator can omit certain operations in a program for a particular component. A particular operation may be required for a particular component and may not be required for another component. These blocks are programmed with the character / (Slash) as the first character. Whenever a program is read by the control unit, the blocks preceded by the / character are omitted ( not executed ) when a switch on the system is activated.

Block and Sequence Number ( N ) :

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A part program is constructed with a number of blocks. Block number represents the operation number in a program and is usually the first character.

The number of digits in a block number depends upon the control manufacturer ( usually it is four digits ). Block numbers are mainly used for the convenience of an operator in identifying the different operations. ( block numbers need not be consecutive and in most of the cases it is not must to have a block numbers ). Many times it is useful to give a single block number to a set of operations when they are related to each other. It is convenient for the block numbers within the original program to be in multiples of five so that additional blocks could be inserted during any editing that may needed.

The blocks in the program can be explained by means of remarks. A remark permits instructions for the operator to be displayed on the screen. The text of a remark is enclosed between the start- of- remark character “ ( “ and the end-of-remark character “ ) “.

The maximum number of characters allowed in a block is 120.

BLOCK NUMBERING :

The block number is used to identify each of the blocks that make up a program. The block number consists of the letter N followed by a figure between 0and 9999. Number must be written at the start of each block. It is advisable to avoid giving blocks consecutive numbers, so that new blocks can be interposed where required.

Preparatory function (G):

These are the codes which prepare the machine to perform a particular function like positioning, contouring, thread cutting and canning cycling. In general the following preparatory functions can be identified. Some of the preparatory functions ( G – codes ) exits in the system in machine switch on condition. These codes need not mention in the main program unless the other code is required.

LIST OF PREPARATORY FUNCTIONS ( G CODES )

G00 - Linear interpolation, at traverse rate / Rapid G01 - Linear interpolation, at defined feed rateG02 - Circular interpolation, clockwise

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G03 - Circular interpolation, counter clockwiseG06 - Spline interpolationG10 - Polar coordinate programming, rapid traverseG11 - Polar coordinate programming, linear interpolationG12 - Polar coordinate programming, circular interpolation, clockwiseG13 - Polar coordinate programming, circular interpolation, counter Clockwise

G04 - Dwell time under address X

G17 - Plane selection XY - planeG18 - Plane selection XZ - planeG19 - Plane selection YZ - plane

G33 - Thread cutting with constant lead

G40 - Tool nose radius compensation - CancelG41 - Tool nose radius compensation, leftG42 - Tool nose radius compensation, right

G53 - Suppress the zero offsetsG54 - Select zero offset 1G55 - Select zero offset 2G56 - Select zero offset 3G57 - Select zero offset 4

G70 - Input system in inchG71 - Input system in metric

G90 - Absolute dimension programmingG91 - Incremental dimension programmingG92 - Limitation of spindle speed S when using with G96G94 - Feed rate under address F mm/minG95 - Feed rate under address F mm/rev

G96 - Constant cutting speedG97 - Constant RPM

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Some of the G-codes exits in the switch on condition are G00,G40,G71,G90,G95 etc

TYPES OF INTERPOLATION :

a) Linear interpolationb) Circular interpolationc) Spline interpolation

Linear interpolation ( G01 ):

The tool must travel at a set feed rate along a straight line to the target position whilst machining the work piece at the same time. The controller calculates the tool path by means of linear interpolation.

Linear interpolation

- Paraxial- In two axes- In three axes- At the programmed feed rate- At the programmed spindle speed- To the target position programmed using absolute or incremental position data

Circular interpolation ( G02 / G03 ) :

The tool must traverse between two points on the contour in a circular arc, whilst simultaneously machining work piece. The controller calculates the tool path by means of circular interpolation. The action of preparatory function G02 and G03 is modal.

The center point of the circle is defined in one of the following ways.

a) By the interpolation parameters ( I,K )b) Directly using the radius ( B )

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G02X +

G03

Z +

Circular interpolation- Along a circular arc in a clockwise direction with G02- Along a circular arc in a counter clock wise direction with G03- About the programmed center point of the circle- From the starting position on a circular path to the programmed end position

Spline interpolation ( G06 ) :

Spline interpolation reduces the amount of programming when processing complex work piece contours and makes it possible to machine shapes that are not described by standard geometries.

A spline is a concatenation of contour elements which, at the points where they join together have the same function values, the same slope and the same curvature.

Dimensional Information (X,Y,Z etc ):

These give the coordinate positions of the tool. Movement of machine tool slides in one or more axes is determined by the dimensional data entered in the program.

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Feed rate word (F)

The feed rate or the rate at which the cutter travels through the material, is specified in mm/min or mm/rev.

Spindle Speed (S)

This may indicate either the spindle rpm or the constant cutting speed in m/min.

Tool number (T)

For machines having automatic tool changers or turrets, the T-word calls out a particular tool that has to be used for cutting.

D - Word

This word activates the cutter radius and length compensations. Tool compensation is a very useful feature in a control system and ensures that programming is independent of tool dimensions. The control system contains a memory in which both tool length and tool radius compensations are stored.

Miscellaneous functions ( M )

These are the operations associated with the machine for functions other than positioning or contouring, e.g. coolant on or off, spindle rotation, etc.

The following are the various miscellaneous functions in general.

LIST OF MISCELLANEOUS FUNCTION ( M-CODES)

M00 - Unconditional program stopM01 - Conditional program stopM02 - End of program with return to program startM03 - Spindle rotation, clockwiseM04 - Spindle rotation, counter clockwise

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M06 - Tool changeM05 - Spindle stopM08 - Coolant ONM09 - Coolant OFF M13 - Coolant ON with Spindle ONM15 - Coolant OFF with Spindle OFFM16 - Tool clampingM17 - End of subroutine ( written in the last block of the subroutine )M19 - Spindle orientationM24 - NeutralM25 - Speed range 1M26 - Speed range 2M27 - Speed range 3 M30 - End of program

Auxiliary functions ( H ):

One auxiliary function per block can be entered under address H for machine switching functions or movements not covered by numerical control.

End of block character ( LF ):

Each programmed block ends with End of block character i.e. LF .

PREPARATION OF MANUAL PART PROGRAM

While preparing the part program for a component the programmer first studies the drawing and decides upon the sequence of operations, cutting tools, speeds and feeds at various points, other necessary information like starting and stopping of machine tool etc.

The below shown system features or the combination of different features, which were discussed in earlier pages, can be used advantageously while preparing the program depending upon the amount of material to be removed, machining sequence, machine and the programmers convenience.

System features used in manual programming.

1. Work piece dimensioning, input system

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2. Diameter programming3. Absolute coordinate system 4. Incremental coordinate system 5. Combination of Absolute and incremental6. Polar coordinate system ( Useful in machining Centers )7. Programming with Constant RPM or Constant Cutting Speed8. Tool nose radius compensation ( TNRC )9. Parametric programming ( Also called Variable programming )10. Blue print programming (Also called Contour definition Programming )11. System built in machining cycles for stock removal in roughing and finishing cuts ( In turning, drilling and Threading ) 12. Developed, user sub programs ( Also called macros in Fanuc system )13. Subroutine nesting14. Mirroring one of the axis15. Programming with @ Functions

Some of the basic features exits readily in the machine switch on condition

WORK PIECE DIMENSIONING, INPUT SYSTEM

As a standard metric dimensioning input is being used in CNC system. This can be changed to FPS ie inches co-ordinate system by assigning G70 code.

DIAMETER PROGRAMMING

All lathe centers allow diameter programming system for programmers convenience. Diameter value is assigned against X- axis command.

ACTIVITY FLOW CHART FOR CNC MACHINES

RAW MATERIAL & ENGINEERING DRGS FOR THE COMPONENT TO BE MACHINED

SELECTION OF MACHINE TOOL / CNC SYSTEM

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SELECTION OF CUTTING TOOLS & PREPARATION OF MACHINING PLAN

DEVELOPMENT OF PART PROGRAMS

PROGRAM INPUT CNC SYSTEM

MACHINE TOOL CUTTING TOOLS SETTING AND LOADING INTO THE MAGAZINE

PROGRAM VERIFICATION AND MACHINING OF FIRST PIECE

OPTIMISATION OF PROGRAM

REGULAR PRODUCTION

FRONT TURNING LATHE( MACHINING BEFORE TURNING CENTER )

X -

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Z - Z +

X +

OPERATOR PLATFORM

REAR TURNING LATHE( MACHINING AFTER TURNING CENER )

51

X +

Z - Z +

X -

OPERATOR PLATFORM

CNC MACHINE REF CONCEPT ( REAR TURNING LATHE )

REF POINT CO-ORDINATE ( Z )

MACHINE REF POINT

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REF POINT CO-ORDINATE ( X )

SLIDE REF POINT

MACHINE ZERO POINT

TOOL

TOOL SETTING POINT OFFSET ( X )

TOOL OFFSET ( Z )

WORK PIECE ZERO POINT

ZERO OFFSET ( Z )/ G54 / G55 ETC

ABSOLUTE CO-ORDINATE SYSTEM

X+ P2 ( 65 , 90 )

P1 ( 45 , 50 )

45 65

Z - Z+

53

50

90

X -

INCREMENTAL CO-ORDINATE SYSTEM

X + P2 ( 20 , 40 ) W.R.T P1

P1 ( 45 , 50 ) 20 W.R.T P0

45 Z - P0 ( 0 , 0 ) Z+

50 40

X –

TOOL NOSE RADIUS COMPENSATION ( TNRC)

MAGNIFIED VIEW OF CUTTING TOOL RADIUS

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THEORITICAL TOOL TIP

EFFECT OF CUTTING TOOL RADIUS WHILE TURNING INCLIND AND RADIUS PORTIONS

55

TOOL LOCATION FOR TNRC

( AFTER TURNING CENTRE M/CS)

X +

56

4 8 3

5 7

Z +

1 6 2

PARAMETRIC PROGRAMMING WITH R – PARAMETERS / VARIABLES

Modern CNC systems offer the manual programmer increased computing power. Parametric programming allows the programmer to use canned cycles to save time. The cycles are uniquely written for the programmer and allows the programmer to design his own canned cycles.

Parameters, with address R, are used in a program to represent the numeric value of an address, and can be assigned to all functions except N.

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They are subdivided into transfer parameters, computing parameters. The number of R – parameters depends on the CNC system version used. The values are assigned to the parameters in the main program.

Parameter definition :

Parameter definition is used to assign certain numeric values with signs to the various parameters. They can be defined either in part programs or in subroutines

Example : R1 = 10 LF

Parameter calculation :

Parameter linkingAll four basic arithmetic operations are possible with parameters. The

linking sequence is however crucial to the result of the calculation.

Arithmetic operation Programmed arithmetic operation

Definition R1 = 100 Assignment R1 = R2 Negation R1 = - R2 Addition R1 = R2 + R3 Subtraction R1 = R2 – R3 Multiplication R1 = R2 * R3 Division R1 = R2 / R3

Value assignment amongst parameters :

The value of one parameter can be assigned to another parameter.

Example : R1 = R3 LF

Calculations using numbers and parameters :

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It is possible to add parameter to the value of an address or to subtract it from it. No sign signifies a positive number.

Example : X = 10 + R100 LF

It is possible to multiply, divide, add and subtract absolute numbers and R parameters.

Example : R10 = 15 + R11 LF

Parameter string :

All 4 basic arithmetic operations are permissible in any sequence. It is possible to link up to 10 parameters together in a parameter string. A parameter string is limited by the block length of 120 characters maximum.

Example : R1 = R2 + R3 - R4 * R5/R6

BLUE PRINT PROGRAMMING / CONTOUR DEFINITION PROGRAMMING:

Multi-point cycles for direct programming in accordance with the work piece drawing are provided for blueprint programming. The points of intersection of the straight lines are entered as coordinate values or via angles. The various straight lines may be joined together directly in the form of a corner, rounded via radii or chamfered. The geometrical calculation is performed by the controller. The end position coordinates may be programmed using either absolute or incremental position data.

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Angle ( A ) :

In the clockwise coordinate system the angle is always measured from the horizontal axis direction to the vertical axis direction.

Clock wise system for operating area after turning center :

+ X

+ Z

Clock wise system for operating area before turning center :

+ Z

+ X

PROGRAMMING WITH @ FUNTIONS :

By using @ funtions CNC programs and machining cycles can be generated manually without the help of computer. The elements used in with @ fuctions are

K ConstantR R Parameter

Conditional jump functions :

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A ) Absolute Jump

@ 100 K_________LF

Example : @ 100 K – 150 LF Absolute jump to the block 150 towards the beginning of the program

@ 100 K 200 LF Absolute jump to the block 200 towards the end of the program

B ) @ 121 R_______ R_______ K LF ( Equal )

C ) @ 122 R________R________K LF ( Not equal )

D ) @ 123 R________R________K LF ( Greater than )

E ) @ 124 R________R________K LF (Greater than or equal )

F ) @ 125 R________R________K LF ( Less than )

G ) @ 126 R________R________K LF ( Less than or equal )

While loops :

@ 131 to @ 136

Repeat loops :

@ 141 to @ 146

Data transfer :

@ 200 R________LF ( Delete variable )

@ 201 R________K______LF ( Load variable with value )

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Mathematical functions :

@ 610 R_______R_______LF ( Absolute value generation )

Example : R12 = - 34 LF

@ 610 R76 R12 LF ( R76 = 34 )

@ 613 R_______K_______LF ( Square root )

@ 614 R_______R_______R_______LF ( Square root from sum of squares )

@ 620 R LF ( Increment )

Example : If R70 = 1 Then @ 620 R70 LF( R70 = 2 )

@ 621 R LF ( Decrement )

Example : If R60 = 1 Then @ 621 R60 LF ( R60 = 0 )

@ 622 R LF ( Integer component )

Example : If R80 = 2.9 LF @ 622 R80 LF ( R80 = 2 )

TRIGONOMETRIC FUNCTIONS :

@ 630 R_______R_______LF ( Sine function )

Example : If R27 = 30 LF @ 630 R15 R27 LF ( R15 = 0.5 )

@ 631 R_______R_______LF ( Cosine function )

@ 632 R_______R_______LF ( Tangent function )

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@ 634 R_______R_______LF (Arc Sine )

Example : If R17 = 0.866 LF @ 634 R16 R17 LF ( R16 = 60 )

@637 R_______R_______R_______LF ( Angle from two vectorcomponents )

R35

R36Example : If R35 = 20 R36 = 30 @ 637 R17 R35 R36 LF (R17=146.31 0 )

@ 640 R______K_______LF ( Natural logarithm )

Example : If @ 640 R80 K 10 LF ( Natural logarithm value of 10 is Stored in R80 )

@ 641 R80 K2.5 LF ( Exponential of 2.5 = 12.182 is stored in R80 )

MACHINING CYCLES / CANNED CYCLES ( L )

Machining Cycles are permanently stored sub programs for use as standard machining process which have been created either by the machine manufacturer or by ourselves. They can be specially protected against misuse. These machining cycles can be adopted to any particular machining by writing in the parameters. A canned cycle ( fixed cycle ) defines a series of machining sequences for Turning, boring, Threading etc. The canned cycles are stored as subroutines in L93 to L97.

Various machining cycles available areL93 - Grooving cycleL95 - Stock removal cycle ( With undercuts )L96 - Stock removal cycle ( Without undercuts )L97 - Threading cycle etc

Details of one of the stock removal cycle, L96 cycle is given below.

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PROGRAMMING DETAILS OF PARAMETERS IN MACHINING CYCLE L96

Values to be assigned only to the parameters given below. No other parameters to be used for programming. R20 = Sub program number, where the profile details to be machined are

storedR21 = Starting point of the profile - X co-ordinateR22 = Starting point of the profile - Z co-ordinateR24 = Allowance for finishing, required in X axisR25 = Allowance for finishing, required in Z axisR26 = Depth of cut R27 = Tool nose radius compensation ( TNRC )R29 = Type of machiningL96 Machining cycleP = Number of times the machining cycle to be called

Type of machining

R29 = 31 TurningR29 = 32 FacingR29 = 21 Turning, finishing cut ( Tool moves w.r.t to final contour )R29 = 22 Facing, finishing cut ( Tool moves w.r.t to final contour )

MACHINE : SBCNC-60/2000 CNC LATHESUPPLIER : HMT - INDIAM/C COMMISSIONED IN MARCH-2002

MACHINE SPECIFICATIONS

SWING OVER BED : 600 mm

SWING OVER CARRIAGE : 800 mm

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DISTANCE BETWEEN CENTRES : 2000 mm

TYPE OF BED : SLANT BED

MAX WEIGHT OF THE WORK PIECE 1500 KGS CHUCKING CAPACITY MAXIMUM : 650 mm MINIUM : 30 mm

SPINDLE SPEED RANGE : 12 - 2000 RPM

SPINDLE DRIVE MOTOR : 37 KW / AC

TYPE OF TURRET / NO OF TOOLS : DISC TYPE / 12

TOOL SHANK HEIGHT : 32 MM

CONTROL SYSTEM : SINUMERIK

MEMORY CAPACITY : 128 KB

TOTAL FINISH TURNING DISC SIDE - I – SETUP

% 430 ( MAIN PROGRAM )

N005 G54( ENTER THE DRAWING DIMENSIONS AGAINST R1 TO R12 )N010 R1=N015 R2=N020 R3=

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N025 R4=N030 R5=N035 R6=N040 R7=N045 R8=N050 R9=N055 R10=N060 R11=N065 R12=

( RAW MATERIAL DIMENSIONS R31 TO R34 )N070 R31=N075 R33=N080 R34=

N085 R151 = R33 - R32 ( ADDITIONAL CALCULATION )

N090 L52 P1

N095 G0 X600 Z600 T1 D1 ( EXTL TURNING TOOL )N100 X = R31+ 10 Z =- R32 M0N105 Z=-R2+5N110 M25N115 G97 M4 S200N120 G95 G1 X=R1+0.25 F20N125 Z=-R12-5 F0.2 M8N130 L1 P1N135 G0 X600 Z600 M9N140 M5 M0N145 M25N150 M4 S200N155 G1 X=R1 Z=-R2+5 F20 D1N160 Z=-R12-5 F0.2 M8N165 L1 P1N170 Z5 F20 M8N175 M5 M0N180 M25N185 M4 S200N190 G1 X=R7+1.5 Z5 F20 D1N195 Z=-R120 F0.2 M8

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N200 L1 P1N205 G0 X600 Z600 M9N210 M5 M0N215 M25N220 M4 S200N225 G1 X=R7+0.5 Z5 F20 D1N230 Z=-R120 F0.2 M8N235 L1 P1N240 G0 X600 Z600 M9N245 M5 M0N250 M25N255 M4 S200N260 G1 X=R7 Z5 F20 D1 ( FINAL CUT )N265 Z=-R120 F0.2 M8N270 L1 P1N275 X=R1+4 Z=-R120+2 F20N280 G1 F0.2

N285 R20=430 R21=R1 R22=-R2 R24=0.05 R25=0.5 R27=40 R29 =22 L96 P1

N290 G0 X600 Z600 M9N295 M5 N300 M24 M0N305 M25N310 M4 S200 N315 G1 F0.3 M8 D1

N320 R20=430 R25=0.3 R29=22 L96 P1

N325 G0 X600 Z600 M9N330 M5 N335 M24 M0N340 M25N345 M4 S200N350 G1 F0.2 M8 D1

N355 R20=430 R25=0 R29=22 L96 P1

N360 G0 X600 Z600 M9

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N365 M5 M0N370 M25N375 M4 S200N380 G1 X=R7+4 Z0.5 F20 M8N385 X=R34-4 F0.2N390 L1 P1N395 G0 X600 Z600 M9N400 M5 M0N405 M25N415 M4 S200N420 G1 X=R7+4 Z0 F20 M8N425 X=R34-4 F0.2N430 L1 P1N435 G1 X=R7-6 Z2 F20N440 X=R7+2 Z-2 F0.2N445 G0 X600 Z600 M9N450 M5 M0

N455 G0 X600 Z600 T10 D10 ( BORE TURNING TOOL )N460 X=R7 Z5 M0N465 X=R9-5N470 M25N475 M4 S200N480 G1 Z=-R10-5 F0.3 M8N485 L3 P1N490 Z2N495 X=R9-2N500 Z=-R10-5 F0.3N505 L3 P1N510 Z2 N515 X=R9+5N520 X=R9-1 Z-1 F0.2N525 Z=-R10-5N530 L3 P1N535 Z5 M9N540 G0 X600 Z600 N545 M5 M0N550 M25N555 M4 S200N560 G1 X=R9+5 Z5 D10 F20

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N565 Z2 M8N570 X=R9 Z-0.5 F0.2N575 Z=-R10-5N580 L3 P1N585 Z5 M9N590 G0 X600 Z600N595 M5 M0

N600 G0 X600 Z600 T3 D13 ( INTL HUB LENGTH FACING TOOL )N605 X=R7 Z15 M0N610 X=R9-8N615 Z0 M0N620 Z=-R10-4N625 M25N630 M4 S200N635 G1 X=R11+6 F0.1 M8N640 L3 P1N645 X=R9-8 M9N650 M5 M0N655 M25N660 M4 S100N665 Z=-R10-2 D13N670 X=R11+6 F0.1 M8N675 L3 P1N680 X=R9-8 M9N685 M5 M0N690 M25N695 M4 S200N700 Z=-R10-1 D13N705 X=R11+6 F0.1 M8N710 L3 P1N715 X=R9-8 M9N720 M5 M0N725 M25N730 M4 S100N735 G1 X=R9-4 Z=-R10+3 F10 D13 M8N740 X=R9+2 Z=-R10 F0.1N745 X=R11+6N750 L3 P1N755 X=R9-6

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N760 Z5 F20 M9N765 G0 X600 Z600 M9N770 M5 M0N775 M24N780 M2

( SUB PROGRAMS FOR % 430 MAIN PROGRAM )

L1 ( EXTL TOOL RELIEF )G91 X4 Z2 F20G90 M17

L3 ( INTL TOOL RELIEF )G91 X- 4 Z-2 F20G90 M17

L52 ( PROFILE CALCULATION )

R32=R2+3@632 R101 R3@632 R102 R5R103=R1-R4R104=R103/2*R101R105=R4-R7R106=R105/2*R102R107=R104+R106R108=R2-R107@630 R111 R5@631 R112 R5R113=R8*R111R114=R8-R113R115=R8*R112R116=R114*R102R117=R107-R116R118=R117+R115R119=R118+1R120=R2-R119M17

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L430 ( PROFILE TURNING BY FACING )

G1 X=R1A=270+R3 A=270+R5 X=R7 Z=-R108 B=R6 B=R8G1 Z=-R120M17

TOTAL FINISH TURNING COUNTER DISC SIDE - II – SETUP

% 440 ( MAIN PROGRAM )

G54G97 G95( DRAWING DIMENSIONS R1 TO R14 )R1=R2=R3=R4=R5=

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R6=R7=R8=R9=R11=R12=R13=R14=( RAW MATERIAL DIMENSIONS R31 TO R34 )R31=R33=R34=

R151=R33-R32 ( ADDITIONAL CALCULATION )

L53 P1G0 X600 Z600 T1 D1X=R31+10 Z=-R32 M0Z=R151+2M25M4 S200G1 X=R7+14 F20F0.3 M8

R20=440 R21=R7 R22=R151 R24=1.5 R25=0 R26=2 R27=40 R29=31 L96 P1

G1 X=R7+0.5 Z=R151+2 F20Z=-R120 F0.2 M8L1 P1G0 X600 Z600 M9M5 M0M25M4 S200G1 X=R7 Z=R151+2 F20 ( FINAL CUT )Z=-R120 F0.2 M8X=R1+4 Z=-R120+2 F20G1 F0.3

R20=441 R21=R1 R22=-R2 R24=0 R25=1

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R26=2 R27=40 R29=22 L96 P1

G1 F0.2

R20=441 R25=0.5 R29=22 L96 P1

G0 X600 Z600 M9M5 M24 M0M25M4 S200G1 F0.2 M8

R20=441 R25=0 R29=22 L96 P1

G0 X600 Z600 M9M5M24 M0M25M4 S200G1 X=R7+4 Z=R151+2 F20 M8F0.3

R20=442 R21=R7+2 R22=0 R24=0 R25=0.5R26=2 R27=40 R29=32 L96 P1

G0 X600 Z600 M9M5 M0M25M4 S200G1 X=R7+4 Z=R151 F20F0.2 M8

R20=442 R25=0 R29=22 L96 P1

G0 X600 Z600 M9M5 M0

G0 X600 Z600 T10 D10 ( BORING TOOL )

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X=R7 Z5 M0M25M4 S150G1 X=R9-4 Z2 F20 M8F0.3

R20=443 R21=R140+3 R22=0 R24=0.25 R25=0 R26=1.5 R27=40 R29=33 L96 P1

G0 X600 Z600 M9M5 M0M25M4 S200G1 X=R9-4 Z5 F20 D10F0.2 M8

R20=443 R24=0 R29=23 L96 P1

G0 X600 Z600 M9M5 M0

G0 X600 Z600 T3 D3 ( TOOL HUB RADIUS )( DRAWING DIMENSIONS FOR HUB RADIUS )R201=R202=R203=R204=R205=R206= L72 P1 ( HUB RADIUS CALCULATION )

X=R7 Z5 M0M25M4 S150G1 X=R222 F10Z-=R211 M8G2 X=R205 Z-=R229 B=R204 F0.2G1 G91 Z2 F10G3 G90 X=R222 Z=-R211+2 B=R204

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G1 Z5 F20G0 X600 Z600 M9M5 M0

G0 X600 Z600 T03 D03 ( SEAL DIAS AND LENTH WITH 0.4 RADIUS INSERT )R35=R36=R37=R38=R39=R40=R41=R42=( ADDITIONAL CALCULATION )R43=R13-R39R44=R13-R40R45=R13-R41R46=R13-R42

X=R7+10 Z5 M0Z-5 M0Z5 M0X=R7-5 M0X=R7+10M25M4 S200G1 X=R35+1 F20Z2 M8Z=-R43+0.2 F0.2L1 P1G0 X600 Z600 M9M5 M0M25M4 S200G1 X=R35 Z5 F20 D3Z2 M8Z=-R43+0.2 F0.2L1 P1X=R7+2

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Z=-R43X=R35 F0.2L1 P1Z2X=R36+1Z=-R44+0.2 F0.2L1 P1G0 X600 Z600 M9M5 M0M25M4 S200G1 X=R36 Z5 F20 D3Z2 M8Z=-R44+0.2 F0.2L1 P1X=R35+2Z=-R44X=R36 F0.2L1 P1Z2X=R37+1Z=-R45+0.2 F0.2L1P1G0 X600 Z600 M9M5 M0M25M4 S200 G1 X=R37 Z5 F20 D3Z2 M8Z=-R45+0.2 F0.2L1 P1X=R36+2Z=-R45X=R37 F0.2L1 P1Z2X=R38+1Z=-R46+0.2L1 P1G0 X600 Z600 M9

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M5 M0M25M4 S200G1 X=R38 Z5 F20 D3Z2 M8Z=-R46+0.2 F0.2L1P1X=R37+2Z=-R46X=R38 F0.2L1 P1G0 X600 Z600 M9M5 M0M2

( SUB PROGRAMS FOR % 440 MAIN PROGRAM )

L53 ( PROFILE CALCULATION PROGRAM )

L52 ( Subprogram Nesting in L53 )

R121=R13-R14R122=R121-R12R123=R11-R12R124=R122/R123R125=R124*R11R126=R124*R12R127=R11*R11R128=R12*R12R129=R125*R125R130=R126*R126R131=R127-R129R132=R128-R130@613 R133 R131@613 R134 R132R135=R11*2R136=R9+R135R137=R133*2R138=R134*2R139=R136-R137

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R140=R139+R138R141=R12-R126M17

L440 ( SEAL DIA TURNING )

G1 X=R7 Z=-R120X=R7+12 M17

L441 ( PROFILE TURNING BY FACING )

G1 X=R1A=270+R3 A=270+R5 X=R7 Z=-R108 B=R6 B=R8G1 Z=-R120M17

L442 ( TOTAL LENGTH BY FACING )

G1 X=R9-10 Z0Z13 M17

L443 ( EYE PROFILE )

G1 X=R140 Z0G2 X=R139 Z=-R141 B=R12G2 X=R9 Z=-R121 B=R11G1 Z=-R121-10X=R9-2M17

L72 ( HUB RADIUS CALCULATION )

R208=0 ( NO ALLOWANCE IN X – OFFSET )R209=R206+R208R210=R201-R203R211=R210-2R212=R204*2R213=R209+R212R214=R204*R204

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R230=3 ( Z + OFFSET FOR FIRST CUT )R231=R202+R230R215=R231+R204R216=R215-R203R217=R216-2R218=R217*R217R219=R214-R218@613 R220 R219R221=R220*2R222=R213-R221R223=R213-R205R224=R223/2R225=R224*R224R226=R214-R225@613 R227 R226R228=R201-R215R229=R228+R227M17

CONCLUSIONS

PRESENT METHOD FOR FINAL MACHINING OF CENTRIFUGAL IMPELLER

As the external surface of the impeller consists of curved profiles and the details vary from impeller to impeller It requires lot of attention in calculating the co-ordinates manually or the programmer should take the Auto CAD assistance in calculating the co-ordinates required to write the CNC program.

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Thus the Impeller finish machining is being carried out with CNC program written in absolute pre-calculated co-ordinates and by using machining cycles etc.

DEVELOPED METHOD FOR FINAL MACHINING OF CENTRIFUGAL IMPELLER

The CNC system is provided with varied features like Variable programming, contour definition programming and Conditional jump functions etc. After studying the features through the manuals of the system, efforts are put to develop the finish turning program for impellers.

All the required Co-ordinates are calculated by using CNC system according to the construction geometry. System features like Contour definition is used conveniently. Part program for the finish machining is standardized. No modifications are required in the standard program.

Programming efforts are made zero for the same geometrical details and varied dimensions of the impeller.

Easy to incorporate the changes in the drawing dimensions of the impeller.

Machine operator enters, only the drawing values in the beginning of the program according to the variables assigned. Verify the simulation of the tool path accordingly and continues the machining operations.

Tool paths are optimized.

BIBILOGRAPHY

1. PRODUCT CATOLOGUES FROM BHEL

2. FUNDAMENTAL OF CAD / CAM

3. HMT MANUALS

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4. SINUMERIK SYSTEM MANUALS

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