Materials And Manufacturing Of The Crankshaft Engineering Essay
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Published: Mon, 5 Dec 2016
This paper reports presents the result of an analysis on materials and manufacturing of an engineering component the crankshaft. Crankshaft specifications, material selection & manufacturing processes are first analyzed using CES and then the design aspect & manufacturing process is discussed.
Crankshaft is a large component in the vehicle engine which converts linear energy into rotational energy by the displacement of the piston to a rotator motion.
Functions of crankshaft:
The crankshaft, connecting rods, piston constitute a crank mechanism which converts the linear motion of the piston to rotary motion. Thus the concept design of an engine is that the output would be rotation.
Generally the linear displacement of an engine is not smooth as the displacement is caused by combustion of gas in the combustion chamber. So the displacement has sudden shocks and using this input for other devices may cause damage to it. Thus crankshaft is used to change these sudden displacements to a smooth rotational output such that it can be input to other devices like pumps, generators and compressors. For this fly wheel is also used for smoothing the shocks.
The stresses which arise in a crankshaft are mainly due to bending and torsion.
The stresses can be:
Due to bending from combustion load
Due to axial bending from axial thrust variation
Due to high tensile hoop set up on the webs
Radial stress on the pins by the shrinkage of webs on journals
Due to transmission of variable torque producing twisting of main bearing and crankpins
Shear stress on the crankpin & bearing journals due
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MATERIAL REQUIREMENTS / SELECTION:
Crankshaft materials should have adequate strength, toughness, hardness and high fatigue strength.
The major crankshaft material competitors in the industry are forged steel and cast iron. Comparison of the performance of these materials is with respect to the CES Analysis.
Medium Carbon alloy:
Medium carbon alloy consists of predominantly iron and also small percentage of carbon (0,25% to 0.45% i.e. 25 to 45 points of carbon) and also several other combinations of alloying elements. The alloying elements used are magnesium, chromium, molybdenum, nickel, silicon, cobalt, vanadium and sometime aluminum and titanium.
The resultant alloy will have properties like harden ability, nitridability, surface and core hardness, ultimate tensile strength, ductility, impact resistance, corrosion resistance and tempering and brittle resistance.
The carbon content in this combination is the ultimate strength and hardness. This is an advantage as crankshafts operates under high loads and requires high strength.
Nodular Cast Iron:
This Cast Iron has 3 to 4% of carbon and 1.8 to 2.8% of silicon and graphite nodules. To achieve this 0.02 % residual cerium or 0.05% of residual magnesium or both are added and melted. Due to this Sulphur is removed and small spheroids are formed in the cast material.
The surface hardness of modular iron is greater than steel of similar strength, induction hardening can produce a surface with brinell number of 550 to 580.
Nodular cast iron has the advantageous properties like low melting point, good fluidility, cast ability, machinability, and wear resistance over mechanical properties of steel like relatively high strength, hardness, toughness, workability and harden ability.
Modular steel is better than Nodular Cast iron is justified by the graph produced by CES.
MANUFACTURING ROUTE SELECTION:
Crankshafts are manufactured from steel either by forging or casting.
crankshafts are stronger than the cast crankshaft but are more expensive. The process of forging makes a very dense, tough shaft with a grain running parallel to the principal stress direction.
The cost involved in material and machining of crankshaft using casting process is reduced as it makes use of required shape and size including counter weights.
The metal grain structure is uniform and random throughout and so cast crankshaft can handle loads from all directions. Counter weights on cast crankshaft are slightly larger than counterweights on forged crankshafts as the cast metal is less dense and so they are higher.
The evolution of the modular cast irons and improvements in techniques allows the manufacturers to prefer cast irons shafts for moderate loads. But for heavy duty applications forged shafts are favored.
DESCRIPTION OF SELECTED MANUFACTURING PROCESS:
Manufacturing process can be broken in to steps:
The manufacturing route for forged steel crankshaft is usually hot forging, machining, heat treatment, surface treatment and inspection.
Forging: Generally Hot Forging process id used to form crankshafts. The billet of suitable size is heated. The temperature would typically range from 1050 – 1250Â°c and the pressed into required shape by squeezing the billet between dies under very high pressure. Extreme deformation is also possible but requires different dies for shaping. Then the resultant product is removed by gas cutting.
Machining: Machining can be done using the following steps:
Centering: It is a process that decides suitability of the end product.
Turning: it is a process that processes journals, flanges, front axis, pins and recess for fillet rolling.
Induction Hardening: To increases hardness Pins, journals, oil seal part and flange are quenched by induction hardening machine.
Fillet Roll machining: this process is done to the journal and pins of the crankshaft use fillet rolling machine.
Milling: This process is used for surface roughness to be made accurate as per the drawing structure of that of the journal pin, edge axis and the flange by milling machines.
Balance; this process is used to balance by boring a hole through weight in order to stabilize pin weight to avoid vibrations.
Heat Treatment: The desired strength of the material is achieved by a process known as heat treatment.
Surface finishing: Steps involved in surface finishing;
Surface Hardening: to create a hardened surface the ion-nitriding process is done by exposing the cranks to a nitrogen mix. These nitrogen mixes reacts with the surface and thus gives hardened surface.
Shot ââ‚¬” Blasting: A process adopted to improve the surface quantity. In this process the surface of the material is attacked by different types of shots. The shots can be sand, steel balls or silicon carbide (granules). This is done to remove scale from the surface.
Computer Aided Grinding & Face Grinding: this process is used to improve the surface finish of crankshaft.
Final Washing: This is done using anti-corrosive oil.
Inspection: Using sophisticated Profilometer the crankshaft is inspected. For ensuring the quality of finishing product manual inspection is also done.
Advanced Analysis allowed the mass and the inertia crankshaft by still maintaining levels of balance, durability and torsional vibration.
30% mass reduction & 35% inertia reduction
Final product had high durability even after setting the revoluon limiter was set to 1600 rpm and despite the increase in twist due to torsional vibration.
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