manish

Crankshaft Design of Escort EngineAuthors: Abhishek Badodekar (3), Anil Ingle(14), Anupam Gupta(19), AVSP Raghu Vamshi (27), Kishan P Rangaswamy(44), Naveen Tiwari(59)

ContentI.Engine Specification

2.     Design of Crank Shaft 3.     Material Selection 4. Manufacturing Process 5. Process Flow Chart of the Crankshaft

Design 6. Reference

Table of Contents

1..... Engine Specification. 4

2..... Design of Crank Shaft 4

3..... Material Selection. 9

3.1. Manufacturing Requirements. 9

3.2. Crankshaft Material 9

3.2.1. Manganese-molybdenum Steel 10

3.2.2. 1%-Chromium-molybdenum Steel 10

3.2.3. 2.5%-Nickel-Chromium-Molybdenum Steel 10

4. Manufacturing Process. 11

4.1. Forging. 11

4.2.      Turning. 12

4.3.      Drilling. 13

4.4.      Heat Treatment 13

4.5.      Shot Blasting. 14

4.6.      Grinding process. 14

4.6.1. Surface grinding. 14

4.6.2. Cylindrical grinding. 15

4.6.3. Outside diameter grinding. 15

4.6.4. Plunge grinding. 16

4.6.5. Centerless grinding. 16

5. Process Flow Chart of the Crankshaft Design. 17

6. Reference. 18

List of Figures

Figure 1 Part of a Crank Shaft 5

Figure 2 Manufacturing Process of a Crank Shaft 10

Figure 3 A Grinder 14

Figure 4 Surface grinder 14

Figure 5 A basic overview of Outside Diameter Cylindrical Grinding. 15

Figure 6   Centerless cylindrical grinder 15

Figure 7 A schematic of the centerless grinding process. 16

Figure 8 Flow Process Chart of Crank shaft design. 17

1.   Engine Specification

      Escorts – FT 45 Tractor

      Rated engine power 45 HP category

      No. of cylinders 3

      Bore x Stroke (m.m) 106.68x106.68

      Compression Ratio 10:1      

      Road Speed (At 2200 engine R.P.M. with rear tyre size 13.6x28)

2.   Design of Crank ShaftOur Calculation:

p = p0 (CR)^γ  where p0 is Pressure at Bottom Dead Center (BDC)

                                    CR is the Compression Ratio of the Engine,

                                     γ is the Specific Heat Ratio of the working fluid 

Assuming p0 as 1 bar and  γ=1.4( for Gasoline)

p= 1(10)^1.4 bar = 25.1 bar

                           = 25.1 * 10^5 pascal 

Diameter of the Bore is 106.68mm = .10668m 

Area of the Bore = (π/4)d² = 8.94 * 10^(-3) m² 

Force exerted on the Shaft = Pressure x Area

                                        = 25.1 * 10^5 * 8.94 * 10^(-3)

                                        = 22.4 * 10-

Cylinder bore diameter = D

Cylinder centre distance = 1.20 D

Big-end journals diameter = 0.65 D

Main-end journal diameter = 0.75 D

Big-end journal width = 0.35 D

Main-end journal width = 0.40 D

Web thickness = 0.25 D

Fillet radius of journal and webs = 0.04 D 

With reference to the above figure, we assume the following

                    dc = Diameter of the crankpin or big end bearing, 

                      lc = length of the crankpin or big end bearing = 1.3 dc

                      Pbc = Bearing pressure = 10

 N/mm2 

Load on the Crankpin = Pbc x dc x lc = 13 (dc)^2 

Since the Crankpin is designed to withstand maximum gas force FL, therefore

                     13 (dc)^2 = 22400 N – (Calculated Previously)

                      or, dc = 41.5mm 

Figure 1 Part of a Crank Shaft

Hence, Lc = 54mm (appox.) 

Design of a crankshaft

When crank is at dead centerThickness of the CrankWeb(t) is given by

 t = 0.4 ds to 0.6 ds

  (ds is diameter of shaft)

   = 0.22D to 0.32D

  (D is diameter of Bore)

   = 0.65 dc + 6.35 mm

 ( Diameter of the crankpin) 

The width of the CrankWeb is given by

w = 1.125 dc + 12.7 mm

w = 1.125 x 41.5 + 12.7

w = 59.38 

D is diameter of Cylinder Bore 

Assuming that Total Length of Crankshaft for a 3-cylinder =5D

                                                                                              = 5 x 106.68

                                                                                            = 533.4 mm = 0.5334 m 

Distance between the center of end of bearing to center of next cylinder, b1 = D

                                                                                                                                    = 106.68 mm 

Distance between center of the first cylinder to the end of the second bearing, b2  = 4D

                                                                                                                            = 4 x 106.68 mm

                                                                                                                             =  426.72 mm

Considering factor of safety as 3, maximum force, Fm = 3x Fp

                                                                                = 3 x 22.4 x10^3

                                                                                = 67.2 x 10^3 N

Reaction because of Piston Force on bearing 1, H1 = (b2 x Fm)/b

                                                                                  = (4D x  67.2 x 10^3)/5D

                                                                                  = 53.76 x 10^3 N 

Reaction because of Piston Force on bearing 2, H2 =  (b1 x Fm)/b

                                                                                  = (D x  67.2 x 10^3)/5D

                                                                                  = 13.44 x 10^3 N 

Assuming Weight of Fly Wheel is equal to 800Kg  

Assuming Belt tension, H2 = 3.5 KN  

H2` = H3` = H2/2 = 1.75 KN 

Design of CrankPin 

dc = Diameter of crankpin

lc  = length of the crankpin

σb = Max. allowable bending stress for crankpin = 75MPa (Carbon Steel) 

Max. bending moment of crankpin, Mc = H2  x b2 = 13.44 x 10^3 x 426.72 = 5735.12 Nm 

Mc = ( π/32)(dc^3) x σb , 

or, dc = 92 mm  

lc = Fp/(dc x Pb)

    = 22.4 x10^3 /(92 x 10) = 24.35 mm 

Design of Crank Web

Thickness of Web = 0.65dc + 6.35 = 66.15mm 

Width of the Web 125dc = 1. + 12.7 = 116.2mm 

Main Journal Diameter  

Engine Power = 45 HP = 33.5 KW 

Shaft Speed = 2200 RPM 

P = 2 π N T / 60 

T = (P X 60) / 2 π N

T = (33.5 x 1000 x 60) / (2 x  π x 2200) 

T = 145.4 Nm 

Assuming that crank shaft is made up of Mild steel

Hence Shear Stress (Γ) = 42 Mpa 

Torque transmitted by the shaft (T) =  ( π/16) x  Γ x d^3

                                                        where  Γ is shear stress of material used,

                                                                   d is the diameter of the shaft journal

or, d^3 = (T x 16)/( π x  Γ) = 17631 mm^3

or, d     = 26.02mm (Ref. 1) 

Shaft Design under flywheel 

C1 = C2 = C/2 where C is length of the Shaft of the Flywheel

Assuming C = 400mm

Mw = V3 x C1,

           where V3 = (½) x  Weight of Fly Wheel

       = 4000 x 0.2 = 800 Nm

Mt (Torsional Bending moment due to pulley) = 3500 x 0.2

                                                                           = 700 Nm

M = (Mw^2 + Mt^2)^0.5 = 1063 Nm

σ  = (32 x M)/(π x dsh^3)  or  dsh^3 = (32 x M) / (π x σ)

where  σ  is the shear stress capacity of the material being used (MS)

dsh^3 = (32 x 1063 x 1000) / (π x 42)

dsh = 63.6 mm ~ 64mm

The diameter of the shaft under the flywheel is 64 mm.

3.   Material SelectionCrankshafts meet the demands for high performance engines, lightweight design, component reliability and low through cost manufacturing. In converting the linear motion of the piston into rotational motion, crankshafts operate under high loads and require high strength. Elimination of the conventional heat treatment process by specifying Air cooled

steels offers manufacturers significant cost savings as well.  

Before making any Selection of the material for the crankshaft there are certain things to be taken care of.

      Steel composition and cleanness

      Forming, hot forging and hot machining

      Design criteria , cost weight , durability and packaging

      Heat treatment, through hardening and surface hardening

These above mentioned criteria in turn for the Performance requirement of the steel which is:

      High strength and stiffness to withstand the high loads in modern engines,      and to offer opportunities for downsizing and weight reduction

      Resistance to fatigue in torsion and bending

      Low vibration

      Resistance to wear in the bearing areas.

3.1. Manufacturing Requirements

      Consistent hardening response

      Good machinability in the hardened condition

       Predictable response to surface modification such as induction hardening, nitriding or fillet rolling.

3.2. Crankshaft MaterialThe crankshaft are manufactured from steel either by forging or casting. Forged crankshafts are stronger than the cast crankshafts, but are more expensive. Forging makes a very dense, tough shaft with a grain running parallel to the principal stress direction. Crankshafts are cast in steel, modular iron or malleable iron. The

major advantage of the casting process is that crankshaft material and machining costs are reduced because the crankshaft may be made close to the required shape and size including counterweights. Cast crankshafts can handle loads from all directions as the metal grain structure is uniform and random throughout. Counterweights on cast crankshafts are slightly larger than counterweights on a forged crankshaft because the cast metal is less dense and therefore somewhat lighter. Generally automobile crankshafts were forged in past to have all the desirable properties. However, with the evolution of the nodular cast irons and improvements in foundry techniques, cast crankshafts are now preferred for moderate loads. Only for heavy duty applications forged shafts are favoured. The selection of crankshaft materials and heat treatments for various applications are as follows. 

3.2.1. Manganese-molybdenum Steel 

This is a relatively cheap forging steel and is used for moderate-duty petrol-engine crankshafts. This alloy has the composition of 0.38% carbon, 1.5% manganese, 0.3% molybdenum, and rest iron. The steel is heat-treated by quenching in oil from a temperature of 1123 K, followed by tempering at 973 K, which produces a surface hardness of about 250 Brinell number. With this surface hardness the shaft is suitable for both tin-aluminium and lead-copper plated bearings. 

3.2.2. 1%-Chromium-molybdenum SteelThis forging steel is used for medium-to heavy-duty petrol- and diesel-engine crankshafts. The composition of this alloy is 0.4% carbon, 1.2% chromium, 0.3% molybdenum, and rest iron. The steel is heat-treated by quenching in oil from a temperature of 1123 K and then tempering at 953 K. This produces a surface hardness of about 280 Brinell number. For the use of harder bearings, the journals can be flame or induction surface-hardened to 480 Brinell number. For very heavy duty

applications, a nitriding process can produce the surface to 700 diamond pyramid number (DPN). These journal surfaces are suitable for all tin-aluminium and bronze plated bearings. 

3.2.3. 2.5%-Nickel-Chromium-Molybdenum SteelThis steel is opted for heavy-duty diesel-engine applications. The composition of this alloy is 0.31% carbon, 2.5% nickel, 0.65% chromium, 0.55% molybdenum, and rest iron. The steel is initially heat-treated by quenching in oil from a temperature of 1003 K and then tempered at a suitable temperature not exceeding 933 K. This produces a surface hardness in the region of 300 Brinell number. This steel is slightly more expensive than manganese-molybdenum and chromium-molybdenum steels, but has improved mechanical properties. 

From the above mentioned 3 materials we are choosing 1%-Chromium-molybdenum Steel because of the following reasons:

      It is cost efficient

      It has enormous hardness once heat treated

      It is being used for heavy vehicle.

4. Manufacturing Process     Figure 2, shows various manufacturing process involved in the designing of a crank shaft. All the processes are described here.

Figure 2 Manufacturing Process of a Crank Shaft

4.1. Forging         

  Forging is the shaping of metal using localized compressive forces. Forging is often classified according to the temperature at which it is performed: '"cold," "warm," or "hot" forging.  Forged parts usually require further processing to achieve a finished part.

  Industrial   forging is done either with presses or with hammers powered by compressed air, electricity, hydraulics or steam. These hammers may have reciprocating weights in the thousands of pounds. Smaller power hammers, 500 lb (230 kg) or less reciprocating weight, and hydraulic presses are common in art smithies as well.

There are certain advantages associated with Forging process. Some of them are mentioned below

  As the metal is shaped during the forging process, its internal grain deforms to follow

the general shape of the part. As a result, the grain is continuous throughout the part, giving rise to a piece with improved strength characteristics

  Iron and steel are almost always hot forged. Hot forging prevents the work hardening that would result from cold forming, which would increase the difficulty of performing secondary machining operations on the piece. Also, while work hardening may be desirable in some circumstances, other methods of hardening the piece, such as heat treating, are generally more economical and more controllable.

Some of forging processes are:

1.      Drop Forging

2.      Open –die drop Forging

3.      Impression-die drop Forging 

Forging operation is done on crankshaft to give the desired shape. It is the first operation which is done on the crankshaft .  

4.2.        Turning    Turning is the process whereby a single point cutting tool is parallel to the surface. It can be done manually, in a traditional form of lathe, which frequently requires continuous supervision by the operator, or by using a computer controlled and automated lathe which does not. This type of machine tool is referred to as having computer numerical control, better known as CNC. and is commonly used with many other types of machine tool besides the lathe.

    When turning, a piece of material (wood, metal, plastic, or stone) is rotated and a cutting tool is traversed along 2 axes of motion to produce precise diameters and depths. Turning can be either on the outside of the cylinder or on the inside (also known as boring) to produce tubular components to various geometries.

    A cam is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or

vice-versa. It is often a part of a rotating wheel (e.g. an eccentric wheel) or shaft (e.g. a cylinder with an irregular shape) that strikes a lever at one or more points on its circular path 

Facing and Centering is part of the turning process. It involves moving the cutting tool at right angles to the axis of rotation of the rotating work piece. This can be performed by the operation of the cross-slide, if one is fitted, as distinct from the longitudinal feed (turning). It is frequently the first operation performed in the production of the work piece, and often the last- hence the phrase "ending up".

performed  Facing & centring operation is performed by lathe machine .Facing operation is on material coming from the Forging stage and it is performed in order to obtain the  uniform    surface  ,the total length can be set to desired value, and to facilitate the remaining operations . In order to perform  turning operation, we should obtain the central line or axis line of the material and it can be done by Centring operation. Centring operation is performed   by lathe machine to get central line or rotation axis so that 

turning operation can be performed in an easy way.

After the facing& centring operation the desired length can be obtained and the material can be set to perform remaining operations.

4.3.        Drilling There are two types of Drilling process explained in this section:

1.      Centre Drilling:

The purpose of center drilling is to drill a hole that will act as a center of rotation for possible following operations. Center drilling is typically performed using a drill with a special shape, known as a center drill.

2.       Micro Drilling:Micro drilling refers to the drilling of holes less than 0.5 mm (0.020 in). Drilling of holes at this small diameter presents greater problems since coolant fed drills cannot be used and high spindle speeds are required.

High spindle speeds that exceed 10,000 RPM also require the use of balanced tool holders

4.4.        Heat Treatment     Heat treatment for a material is done so as to enhance the already existing features of the material, some of the reasons for the heat treatment are ductility, malleability, strength and hardness. In the material that we have chosen hardness is the prime most importance with the application surrounding the same. As mentioned earlier as the heat treatment process we will be doing the: 

Nitriding Surface-hardening Process 

    In this process the journals are heated to 773 K for a predetermined time in an ammonia gas atmosphere, so that the nitrogen in the gas is absorbed into the surface layer. The alloying elements such as chromium, aluminium, and molybdenum, present in the steel, from hard

nitrides. Aluminium nitrides form an intensely hard shallow case. Chromium nitrides diffuse to a greater depth than aluminium nitrides. The molybdenum increases hardenability, gives grain refinement, and improves the toughness of the core.    This process can use directly the journals ground to their final size as there is no quenching after nitriding thereby avoiding distortion unlike other surface-hardening processes. The slow rate of penetration of the surface makes the cost of the process high for example; it takes 20 hours to produce a case depth of about 0.2 mm. Doing so the surface hardness of the material would reach from 280 Brinell number to 480 , almost doubling.

4.5.        Shot Blasting    Shot blasting consists of attacking the surface of a material with one of many types of shots. Normally this is done to remove something on the surface such as scale, but it is also done sometimes to impart a particular surface to the object being shot blasted, such as the rolls used to make a 2D finish. This is a particularly effective

method for removing scale, rust, paint, and minor surface flaws from metal objects.

    It’s important to understand the properties of metal and the effects heat has on those properties. The smaller the grain size, the greater the strength; the larger the grain size, the lower the strength. When strength is important, every effort is made to ensure fine-grained steel.

         Cold rolling and hot rolling  

    To prevent cracking, the sheet steel is annealed, which involves protecting the steel from the atmosphere, heating it to a suitable temperature (usually around 1,000 degrees F) and then allowing it to cool slowly. This process may take several days. Often, the steel is cold rolled just a little to restore its high-strength properties, zinc coated and then shipped to the automaker for stamping and forming. Stamping and forming will further enhance the strength of the panel

4.6.        Grinding process 

           Grinding is an abrasive machining process that uses a grinding wheel as the cutting tool. It can produce very fine finishes and very accurate dimensions.

Figure 3 A Grinder

4.6.1. Surface grindingSurface grinding uses a rotating abrasive wheel to smooth the flat surface of metallic or non-metallic materials to give them a more refined look or to attain a desired surface for a functional

purpose. The surface grinder is composed of an abrasive wheel, a work holding device known as a chuck, either electromagnetic or vacuum, and a reciprocating table.

Typical work piece materials include cast iron and minor steel. These two materials don't tend to clog the grinding wheel while being processed. Other materials are aluminium, stainless steel, brass and some plastics.

Figure 4 Surface grinder

4.6.2. Cylindrical grindingCylindrical grinding (also called center-type grinding) is used in the removing the cylindrical

surfaces and shoulders of the workpiece. The workpiece is mounted and rotated by a workpiece holder, also known as a grinding dog or center driver. Both the tool and the workpiece are rotated by separate motors and at different speeds. The axes of rotation tool can be adjusted to produce a variety of shapes.

4.6.3. Outside diameter grindingOD grinding is grinding occurring on external surface of an object between the centers. The centers are end units with a point that allow the object to be rotated. The grinding wheel is also being rotated in the same direction when it comes in contact with the object. This effectively means the two surfaces will be moving opposite directions when contact is made which allows for a smoother operation and less chance of a jam up.

Figure 5 A basic overview of Outside Diameter Cylindrical Grinding

Figure 5, the curved arrows refer to direction of rotation

4.6.4. Plunge grindingA form of OD grinding, however the major difference is that the grinding wheel makes continuous contact with a single point of the object instead of traversing the object.

4.6.5. Centerless grinding

Figure 6   Centerless cylindrical grinder

Figure 7 A schematic of the centerless grinding process.

Centerless grinding is a form of grinding where there is no collet or pair of centers holding the object in place. Instead, there is a regulating wheel positioned on the opposite side of the object to the grinding wheel. A work rest keeps the object at the appropriate height but has no bearing on its rotary speed. The workblade is angled slightly towards the regulating wheel, with the workpiece centerline above the centerlines of the regulating and grinding wheel; this means that high spots do not tend to generate corresponding opposite low spots, and hence the roundness of parts can be improved. Centerless grinding is much easier to combine with automatic loading procedures than centered grinding; throughfeed grinding, where the regulating wheel is held at a slight angle to the part so that there is a force feeding the part through the grinder, is particularly efficient.

Centerless grinding is when the workpiece is supported by a blade instead of by centers or chucks. Two wheels are used. The larger one is used to grind the surface of the workpiece and the smaller wheel is used to regulate the axial movement of the workpiece. Types of centerless grinding include through-feed

grinding, in-feed/plunge grinding, and internal centerless grinding.

5. Process Flow Chart of the Crankshaft Design Figure 8, show the Flow Process Chart of the processes employed to design a Crank Shaft.

Figure 8 Flow Process Chart of Crank shaft