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SEMNAR REPORT

DESIGN ASPECT OF ABRASIVE CUTTING

MACHINE

DESIGN

Design is undoubtedly a creative process, engineer with a ‘flair’ for design is as a

rule a man with a logical decision making ability by which he explores all possible

solutions to a given problem and arrives at an optimum after carefully analyzing all the

alternatives.

Until a decade, any design which was technically feasible is capable of being

manufactured, would generally go through to production irrespective of the time or cost

involved. However, the need to find practically new design solutions to keep ensuring

higher productivity has in recent times greatly increased the expenditure on design.

Design is progressively becoming a team activity as optimum solutions can be found

only by considering a large number of factors of diverse nature with which the designer

may not always be well conversant.

The block diagram shows how design is related to different engineering,

economic, natural, and social sciences.

In view of the heavy responsibilities on the designer and the large expenditure

involved in designing a new machine. It is necessary to streamline the design process so

that a sound design solutions is achieved with minimum expenditure.

The design process for designing a new machine tool as follows:

1. Requirement (Goal)

2. Precise definition of requirement after modification, expansion

3. Technical specification

4. Development of proper kinematic solution and selection of proper layout

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5. Design calculations for various units of machine tool.

6. Design of components and parts

7. Part and assembly drawings

8. Technical specifications

9. Prototype fabrication and testing

10. Production and marketing

The design process is carried out in three important stages

1. Design proposal

2. Preliminary design

3. Detailed design

At the end of each stage, the design must be subjected to a critical feasibility

analysis and a technical report prepared and submitted to the customer. The steps

involved in the design process will be elaborated as follows.

a) Requirement

The customer outlines the requirement by furnishing information about the parts

for machining of which he wants the machine tool to be designed. The information

should include the nomenclature of parts and their annual output, the dimensions and

shapes of surfaces to be machined, materials of the parts, machining tolerances, and the

quality of surface finish required. This information serves as the basis of for selecting

appropriate machining methods and cutting tools.

The customer, owing to his lack of specialist knowledge, may often not be in a

position to define his need exactly. The designer must first of all check that the

requirement of a new design is genuine and a suitable product does not already exist. A

consideration in undertaking a new design, in the presence of available solutions, may be

the need to make the product economically viable by reducing its cost. The designer

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must, therefore, make a preliminary assessment of the requirement to see whether it is

economically feasible. If necessary, he may, in consolation with the customer, modify or

expand the requirement to increase the market potential of the designed machine tool.

b) Technical specification

The technical specification is a listing of parameters that are essential for the

design. The information furnished by the customer about the parts forms the basis of

determining important machine tool specifications. In general, the designer should frame

the specifications in a manner that does not unnecessarily narrow the range of possible

solutions. It should be remembered that incorrect specifications are one of the major

sources of over design and redundant features in the finished product.

c) Selection of proper kinematic solution and layout

After technical specifications have been laid down, the designer explores the

combinations of relative motions that can ensure machining of surfaces of required

shapes and dimensions. The different possibilities are evaluated and those found

technically feasible are selected. Kinematic solution on the basis motion combination arenow developed. All these solutions are analyzed for their technical feasibility and

infeasible solutions are screened. A kinematic solution correlates the motion of the

workpiece and cutting tool and can be realized in a number of layouts of major machine

tool units. A technical feasibility analysis, keeping in mind the constrains of the

requirement and technical specifications, is again carried out to select the best possible

layout.

d) Design calculations

Design calculations cover the design of the major units of the machine tools.

These calculations are done in accordance with design procedures only for those

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versions that are found most suitable on the basis of the preceeding analysis. The final

version is selected comparing the economic feasibility of implementation of alternatives.

e) Drawings of components and assemblies

These drawings are made for the version that finally selected. The drawings must

be complete with dimensions, tolerances and manufacturing specifications (including the

manufacturing method to be employed). Special care should be taken during the stages

of design, calculations and detailed drawings to make use of standard components and

assemblies as far as possible.

It should be appreciated that design is essentially an iterative process. The

feedback that is received after prototype fabrication and testing, and particularly after

marketing the product must be carefully analyzed to make appropriate changes in

technical specifications and subsequent design. In the design process itself, the designer

should adopt a flexible attitude and be prepared to make modifications in the technical

specifications and even the requirement.

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GENERAL CONSIDERATIONS IN DESIGN OF ABRASIVE CUT OFF

MACHINE

Following are the general considerations in designing “Abrasive cut off

machine” and its components.

1. Type of load and stresses caused by the load:

The load, on a machine component, may act in several ways due to which the

internal stresses are set up. In our project, radial load acts on the bearings.

2. Motion of the parts of kinematics of the machine:

The successful operation of any machine depends largely upon the simplest

arrangement of the parts which will give the motion required.

In our project, motion required is rotary motion to abrasive cut off wheel. 1 H. P.

single phase motor is used as elector drive for providing rotary motion to a cut off wheel

shaft by means of v belt and pulley.

3. Selection of materials:

It is essential that a designer should have a through knowledge of the properties

of the materials and their behaviour under working conditions. Some of the important

characteristics of materials are strength, durability, flexibility, weight, resistance to heat

and corrosion, ability to cast, welded or hardened, machinability, electrical conductivity

etc.

C-20 and C-45 is selected as material for machine components.

4. Form and size of the parts:

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The form size are based on judgement. The smallest practicable cross – section

may be used, but it may be checked that the stresses induced in the designed cross –

section are reasonably safe. In order to design any machine part for form and size, it is

necessary to know the forces which the part must sustain.

5. Frictional resistance and lubrication

There is always a loss of power due to frictional resistance and it should be noted

that the friction of starting is higher than that of running friction. A careful attention

must be given to the matter of lubrication of all surfaces which move in contact with

others, whether in rotating or ball bearings.

6. Convenient and economical features:

In designing, the operating features of the machine should be carefully studied. If

parts are to be changed on account of wear or breakage, easy access should be provided

and the necessity of removing other parts to accomplish, this should be avoided if

possible.

7. Use of standard parts:

The use of standard parts of closely related to cost. These part should be used

whenever possible.

8. Safety of operation:

Machine is dangerous to operate. Any moving part of machine which is within

the zone of a worker is considered an accident hazard and may be cause of an injury.

Hence we have provided safety guard for belt and safety guard for cut off wheel, in such

way that they should in no way interface with operations of the machine.

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9. Workshop facilities:

A design engineer should be familiar with the limitations of his employer’s

workshop in order to avoid the necessity of having workdone in some other workshop.

10. No. of machines to be manufactured:

The number of machines to be manufactured affects the design in a number of

ways. The engineering and shop costs which are called fixed changes or overhead

expenses are distributed over the number of machines to be manufactured.

11. Cost of construction:

The cost of construction of machine is the most important consideration involved

in design. The aim of design engineer under all conditions, should be to reduce the

manufacturing costs to the minimum.

12. Assembling:

Every machine or structure must be assembled as a unit before it can function.

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GENERAL PROCEDURE IN MACHINE DESIGN

In designing a machine component, there is no rigid rule. The problem may be

attempted in several ways. The general procedure to solve a design problem is asfollows:

1. First of all make a complete statement of the problem, indicating the purpose for

which the machine is to designed.

2. Select the possible groups of mechanisms which will give the desired motion.

3. Find the forces acting on each member of the machine and the energy transmitted

by each other.

4. Select the material best suited for each member of the machine.

5. Find the size of each member for each member of the machine by considering the

forces acting and the permissible stresses of the material used. Each member

does not deflect or deform that the permissible limit.

6. Modify the size of the member to agree with the past experience and judgement

to facilitate manufacture.

7. Draw the detailed drawing of each component and the assembly of the machine

with complete specification for the manufacturing process suggested.

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Hardness Brinell or Rockwell hardness no.

Toughness Charpy or load impact value

Frictional properties Coefficient of friction

iv) Manufacturing considerations: Machinability of material is important

consideration in selection. Sometimes, expensive material is more

economical than a low priced one, which is difficult to machine. Where the

product is of a complex shape, casting properties are important. The

manufacturing process such as casting, rolling, extrension, welding and

machining govern the selection of material.

ENGINEERING REQUIREMENTS OF MATERIALS

Engg. Requirement of materials means as to what is expected from materials so

that the same can be successfully used for making engineering components.

1) Fabrication requirement: It means that material should be able to get shaped and

joined easily, fabrication requirements relate themselves with materials

Machinability, ductility, castability, heat treatment, weldability etc.

2) Service requirement: It implies that material selected for the purpose must stand

upto service demands like proper strength, wear resistance, corrosion resistance.

3) Economic requirement: It demands that engineering part should be made with

minimum overall cost which may be achieved by proper selection of both

technical and marketing variables.

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MOUNTING OF ABRASIVE WHEEL

Great care must be taken in mounting the abrasive wheels on the abrasive wheelspindle or shat. The abrasive wheel must be mounted correctly on the spindle for the

purpose of satisfactory operation and safety. The following points should be considered

while mounting abrasive wheel on the spindle.

1. First, the wheel should be visually and closely inspected just before mounting to

make sure that the wheel have not been damaged in transportation of wheel,

storage of wheel or other wise. The ringing test conducted on abrasive wheel. A

clean ringing, vibrating sound must be heard. When wheel is subjected to ringing

test. For this test, cut off wheel is put on order and it is subjected to slight

hammer blows.

2. The abrasive wheel should be easily fitted on the spindle. The wheel should not

be forced on the spindle.

3. There must be a flange on each side of the wheel to avoid local concentration of

pressure.

4. The washer should be used the nut. By using washer any unevenness of the

wheel surface is balanced and a tight joint is obtained.

5. The sides of the wheel and the flanges which clamp them should be flat and bear

evently all round.

6. The wheel guard should be placed and tightened before the machine started or

work. After mounting the abrasive wheel, the machine is started. The abrasive

wheel should be allowed to idle for a period of about 10 to 15 min.

7. The nut should be tightened to hold the wheel firmly. Undue tightness isnecessary and undesirable as excessive clamping strain liable to damage the

wheel.

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ADVANTAGES OF ABRASIVE CUT OFF MACHINE

1. Hard materials can be cut.2. Surface finish is better.

3. It is very fast and ideal for high volume production especially on small bar stock.

4. Machine is less time consuming than the other cutting process. As in hacksaw

machine there is reciprocating motion and one cutting stroke and one idle stroke.

But in abrasive cut off machine there rotary motion of cutting which continous

motion of cutting.

5. We can get desired accuracy and desired angle of cutting which we will not get

from the other cutting process.

6. Very less efforts are required to the operator.

7. Where mass production of identical workpieces are required, this machine plays

vital role.

8. Machine is flexible and shifted to anywhere, we are required to carry cut off

process.

9. For holding job, vice is used, so sufficient grip is there.

10. Upto 8 mm thickness pipe or rod can be cut off.

11. Whole assembly is mounted on table, so operation can done by sitting on the

chair.

12. It is very much economical because using the abrasive wheel, we can cut

different types of metals.

13. There is no danger of explosion, so operator can easily cut the metals withour

feeling danger.

14. Semiskilled or unskilled labour is sufficient.

15. Machine is very simple in construction.

16. Maintenance of machine is less.

17. Machine id portable and also weight is less.

18. Thin slender part like “I” beam, channel, small bar can be cut with less vibration.

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LIMITATIONS OF MACHINE

1. The power consumption is high.2. Heavy weight than other cutting equipments.

3. The machine makes noise while cutting.

4. Not suitable for thick large size solid bars.

5. Possibility of accidents when wheel breaks.

6. As wheel thickness is 3.2 mm, for cutting of any material more than 3.2 mm

material is wasted.

APPLICATION OF MACHINE

1. For making tables, benches, windows, we use these machines for cutting rods

and pipes.

2. This machines is also used to cut castings free of runners. Particularly for very

small investment castings.

3. For cut off long bars, small bars of castings in straight way as well as for angular

cuts.

4. Contour cutting can be done by this machine.

5. For cutting metal plates, sheets, strips, coils, tube, forging.

6. For cutting long cut extended bars into work piece lengths for milling, turning,

drilling processes.

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REFERENCES

1. Elements of workshop technology, Vol. II, Machine tools, S. K. Hajara

Choudhary, A. K. Hajara Choudhary, Nirjhar Roy, Media promoters &Publishers Pvt. Ltd., Ninth Edition, 1997

2. Material Science & Metallurgy, Prof. V. D. Kodgire, Everest Publishing House,

Tenth Edition, 2000

3. Design of machine elements, V. B. Bhandari, Tata McGraw Hill Publishing Co.

Ltd., Seventh Edition, 1999

4. A text book of machine design, R. S. Khurmi, J. K. Gupta, Twelth revised

edition, 1999, Eurasia Publishing House Pvt. Ltd.

5. Production Technology, HMT Bangalore, Tata McGraw Hill Publishing

Company Ltd.

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