dr. gsk - automotive manufacturing process

8/19/2019 Dr. GSK - Automotive Manufacturing Process

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UTOMOTIVE COMPONENTSM NUF CTURING

Associate Professor

Department of Automobile Engineering

MIT, Anna University


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MATERIALS

PROPERTIES


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Classes of MaterialsMetals

Stron , deformable and im act resistant, hard and do not breakreadily under high stressElectrical conductorsAlways opaque

CeramicsStron but not deformable, brittle, hi h hardness, stable at hi htemperaturesInsulatorsCan be transparent

PlasticsMade of h drocarbons carbon and h dro en atoms softercannot be shaped, cannot be used at high temperaturesInsulatorsCan be transparent


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Energy Bands

,Furthest band from the nucleus that has electrons in it, calledtheValence band,all keep their electrons tightly in place.Next band out from that is called the“Conduction band”andthere, theelectrons are free to roam around freely.In Metals -Valence band and a conduction band overlap, andelectricity flows freely and easily through them.

Insulators -Wide gap between the valence band and theconduction band, making it almost impossible for an electrono ge exc e enoug o ump rom one o e o er, so ey

block the flow of electricity.


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Energy Bands – Contd..

Materials that have a narrower a between the two bands andthey are calledSemiconductors.Sometimes they can act like metals, sometimes they can act likeinsulators, and sometimes they can have properties in between.When first discovered, they were considered useless because oftheir erratic, variable behavior — until physicists figured out themystery o t e an gap.When electrons get excited (by getting heated, or by being hitwith a particle of light, known as a photon), they can jump across

the gap.If an electron in a crystal gets hit by a photon that has enough,

to the conduction band, where it is free to form part of an electriccurrent.


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Energy Bands – Contd..

, .Silicon, a semiconductor, is the material of choice for solarcells in large part because of its bandgap.Silicon’s bandgap is just wide enough so that electrons caneasily cross it once they are hit by photons of visible light.The same process also works in reverse.When electricity passes through a semiconductor, it can emit

a photon, whose color is determined by the material’s bandgap.That’s the basis for light-emitting diodes, which areincreasingly being used for displays and computer screens,and are seen as the ultimate low-power light bulbs.


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Strength

.Strength of a componentis usually considered based on themaximum loadthat can be borne before failureis apparent.Strength of a materialis also themaximum nominal stressit

.Nominal stress is referred to in quoting the"strength" of amaterial and is always qualified by the type of stress, such astensile strength, compressive strength, or shear strength.


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Strength-Contd..

For most structural materials the difficult in findin com ressivestrength can be overcome by substituting the tensile strength valuefor compressive strength.This substitution is a safe assumption sincethe nominalcompression strength is always greater than the nominal tensile

compression and decreases in tension.Slip- When a force is applied to a metal, layers of atoms within

the crystal structure move in relation to adjacent layers of atoms.The smaller the grain size, the larger the grain boundary area.Decreasing t e grain size t roug co or ot wor ing o t e metatends to retard slip and thus increases the strength of the metal.


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Stress

,deformed, no matter how strong the metal or light the load.If the load is small, the distortion will probably disappearwhen the load is removed.

, , .If the distortion disappears and the metal returns to itsoriginal dimensions upon removal of the load, the strain iscalled elastic strain.

,the strain type is called plastic strain.


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Types of StressResidual Stress

stresses in a material.Weldingleaves residual stresses in the metals welded.

Structural Stressstresses produced instructural members because of theweightst ey support. e weig ts provi e t e oa ings.These stresses are foundin building foundationsandframeworks, as well as in machinery parts.

Pressure StressPressure stresses are stresses induced invessels containinpressurized materials.The loading is provided by the same force producing thepressure.


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Flow Stressstresses occur when amass of flowing fluidinduces adynamicressure on a conduit wall.

The force of the fluid striking the wall acts as the load.This type of stress may be applied in an unsteady fashion whenflow rates fluctuate.Water hammeris an example of a transient flow stress.

Thermal Stressstresses exist whenevertemperature gradientsare present in a

material.Different temperatures produce different expansions andsu ject materia s to interna stress.This type of stress is particularly noticeable in mechanismsoperating at high temperatures that are cooled by a cold fluid.


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Fatigue Stress

Stresses are due toc clic a licationof a stress.The stresses could be due tovibration or thermal cycling.The importance of all stresses is increased when the materialssupporting them are flawed.Flaws tend to add additional stress to a material. Also, whenoa ings are cyc ic or unstea y, stresses can e ect a materia moreseverely.Additional stresses associated with flaws and cyclic loading mayexceed the stress necessary for a material to fail.Stress intensity within the body of a component is expressed asone of three basic types of internal load.They are known astensile, compressive, and shear.


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Stress

type of stress in which the two sections of material on eitherside of a stress plane tend to pull apart or elongate

Compressive Stress .

press against each other through a typical stress planeShear Stress

Shear stress exists when two parts of a material tend to slideacross each other in an t ical lane of shear u on a licationof force parallel to that plane


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STRAIN

metal, aproportional dimensional change or distortionmusttake place.Such a proportional dimensional change (intensity or degreeof the distortion is calledstrainand is measured as the totalelongation per unit length of material due to some appliedstress.

The equation below illustrates this proportion or distortion.


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Types of Strain

Elastic strainis atransitory dimensional changethat exists onlywhile the initiating stress is applied and disappears immediatelyupon removal of the stress.Elastic strain is also called elastic deformation. TThe applied stresses cause the atoms in a crystal to move fromtheir equilibrium position.

All the atoms are displaced the same amount and still maintaintheir relative geometry.When the stresses are removed, all the atoms return to theiroriginal positions and no permanent deformation occurs.


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Elastic Deformation

When a lied stresses are not too lar e elastic deformationoccurs.Stress is proportional to strain – Hooke's law (applicable to bothtension and compression)Elastic deformation is reversibleW en materia is compresse in one irection, it usua y ten s toexpand in the other two directions perpendicular to the directionof compression.This phenomenon is called thePoisson effect.

Poisson's ratiois a measure of the Poisson effect.Poisson ratio is theratio of the fraction (or percent) of expansiondivided by the fraction (or percent) of compression, for smallvalues of these changes.


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Elastic DeformationThe Poisson's ratio of astable, isotropic linear elastic materialcannot beless than−1.0 nor greater than 0.5.

' . . .A perfectly incompressible materialdeformed elastically at small strainswould have a Poisson's ratio of exactly 0.5.Most steels and rigid polymers when used within their design limits(before yield) exhibit values of about0.3, increasing to0.5 for post-ield deformationwhich occurs lar el at constant volume.

Rubberhas aPoisson ratio of nearly 0.5.Cork's Poisson ratiois close to0: showing very little lateral expansion

when compressed.Some materials, mostly polymer foams, have anegative Poisson's ratio; if ,

thicker in perpendicular directions.Someanisotropic materialshave one or morePoisson ratios above 0.5insome directions.


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Plastic Deformation

stress is removed. It is usually accompanied by some elastic strain.The phenomenon of elastic strain and plastic deformation in amaterial are calledelasticity and plasticity, respectively.At room tem erature, most metals have some elasticit , whichmanifests itself as soon as the slightest stress is applied.Usually, they also possess some plasticity, but this may not

become apparent until the stress has been raised appreciably.Themagnitude of plastic strain, when it does appear, is likely to bemuch greater than that of the elastic strain for a given stressincrement.


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Resilience

This is usually measured by the modulus of resilience, whichis the strain energy per unit volume required to stress thematerial from, zero stress to the yield stress.

Resilience


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Toughness

it fractures.

Toughness


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Hardness

Hardness is a measure of a material’s resistance to localizedplastic deformation (a small dent or scratch).Quantitative hardness techniques have been developed wherea small indenter is forced into the surface of a material.The depth or size of the indentation is measured, andcorresponds to a hardness number.The softer the material, the larger and deeper the indentation

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MANUFACTURING

PROCESS


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Vehicle Body Materials

–weightIn 1950 and 60 – Mass Vehicle production started – HighdemandIn 1950 – Deep Drawing steel sheets with good formabilityIn 1960 –Anti Corrosive steel sheetsIn 1970 and 80 – Low fuel consumption –Due to severe oil

crisisIn Late 80’s – High strength steel sheets- reducing thethicknessIn 1990 – Safety and Environmental issues


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Sheet Metal Processes

Raw material: sheets of metal, rectangular, large

Raw material Processing: Rolling (anisotropic properties)

Processes:

ShearingPunchingBendingDeep drawingHydroforming


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Shearing

arge sc ssors act on, cutt ng t e s eet a ong a stra g t ne

Main use: to cut large sheet into smaller sizes for making parts.


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Shearing

Process for cuttin sheet metal to size out of a lar er stock such asroll stock.Shears are used as the preliminary step in preparing stock forstamping processes.Material thickness ranges from 0.125 mm to 6.35 mm (0.005 to0.250 in).The dimensional tolerance ranges from ±0.125 mm to ±1.5 mm(±0.005 to ±0.060 in).The shearing process produces a shear edge burr, which can beminimized to less than 10% of the material thickness.The burr is a function of clearance between the punch and the diew ic is nomina y esigne to e t e materia t ic ness , an t e

sharpness of the punch and the die.


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Blanking / Punching

operations that involve cutting the sheet metal along a closedoutline.If the part that is cut out is the desired product, the operationis called blankin and the roduct is called blank.If the remaining stock is the desired part, the operation iscalled punching.


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Blanking / Punching


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Cutting tool is a round/rectangular punch,that goes through a hole, or die of same shape

F ∝ t X edge-length of punch X shear strengthF ∝ t X edge-length of punch X shear strength

Punch

sheet

crack(failure in shear)

piece cut away, or slug

t

Punch

sheet

crack(failure in shear)

piece cut away, or slug

t

clearance

die

clearance

die


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Punching Main uses: cutting holes in sheets; cutting sheet to required shap

nesting of parts

typical punched part


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Typical bending operations and shapes

(a)

(b)


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Sheet metal bending

Planning problem: what is the sequence in which we do the bending operations?

Avoid: part-tool, part-part, part-machine interference


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Bending mechanics

Bending Planning what is the length of blank we must use?

This section isunder extension

Bend allowance, L b = α (R + kT)

This section isunder extensio n

Bend allowance, L b = α (R + kT)

R = Bend radius

Neutral axis

αL = Bend length

This section is

in compression

T = Sheet thickness

R = Bend radius

Neutral axis

αL = Bend length

This section is

in compression

T = Sheet thickness

Ideal case: k = 0.5 Real cases: k = 0.33 ( R < 2T) ~~ k = 0.5 (R > 2T)


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Deep Drawing

Tooling: similar to punching operation,Mechanics: similar to bending operation

die die die die die

punch punch punch punchblank

part

blank holder

die die die die die


part

blank holder

die die die die die


part

blank holder

a (c) (d) e)

Examples of deep drawn parts

a (c) (d) e)a (c) (d) e)

Examples of deep drawn parts

Common applications: cooking pots, containers, …


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Engine Components - Piston

temperature for approximately one hour.This process allows the die to readily accept the moltenmaterial when it is poured.

.The dies used are 5 piece and three piece. These dies aremade from cast iron with steel inserts for the gudgeon pinholes and the cores.

be located to give offset pins or square pins


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Celsius.This is well above the melting point of the aluminium, but below its boiling point.The material is then scooped up with a ladle from thecrucible (the pot that holdsthe molten material). This is then poured into the die throughthe sprue.The material is then allowed to cool before it is removedrom e e an p ace n o a n o o wa er. s wa er s

used to facilitate a more even settling of the hot metal.


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heat treatment plant overnight.This process tempers the casting and ensures the piston willhave improved qualities.

runner removed.This process takes little time and is fully automated.


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At this sta e of the iston manufacturin rocess the castin hasthe gudgeon pin hole rough machined and the locating bungmachined.The bung -This process is where the casting is machined on the base to allow placement of the casting in other machines.

.Turning of the casting is carried out on CNC (Computer NumericControl) machinery.

The castings are placed in the lathe on a bung and held in place bya solid rod through the gudgeon pin hole.A draw bolt is activated in the chuck which draws the rod towardthe chuck and holds the piston in place.


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,slotting, valve and crank relieving.

Drilling - Drilling includes all oil holes in places such as the.

Slotting - Slotting is where slots are placed in the skirt or inthe oil ring groove.


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This process is done on a mill and invloves setting the machine upfor the process, choosing the correct cutter and completing the job.Since there are so man different t es of valve reliefs it isimpossible to have a specialised machine set up to do one job.

Crank relievingCrank releivin is carried out on a specialised machine whichscallops the skirt of the piston to the required shape and depth byusing two opposed cutters placed on a common shaft.


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This process involves the final size being machined on thepiston.The grinder machines the skirt of the piston only and in the

.Cam grinding ensures the piston will "grow" evenly in the bore of the engine.A perfectly round piston will expand unevenly during use

(gudgeon pin bosses and ribbing used for strengthening).


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The final machining process for the piston is that of reaming.This process involves thepiston being placed in a bath of oiland reamed at different sizes to reach the final size required.

nce t e p n or ng process s on y roug t s necessary toream the pin bore a number of times to achieve the surfacefinishand size required.Reaming is not a fast process and is only partially automated(t ere are automatic ee s on t e reaming mac ines).Tolerances achieved on the finished reamed surface is 0.4Ra.


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Crank Shafts

motion, crankshafts operate under high loads and requirehigh strength.Crankshafts require the following characteristics:

modern engines, and to offer opportunities for downsizing andweight reduction

Resistance to fatigue in torsion and bendingLow vibrationResistance to wear in the bearing areas


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Manufacturing of forged steel cranks

, ,treatment.Controlled air cooling after forging is lower cost than thetraditional quench and temper and is now the preferredroute.Efficient and cost effective processing requires:

Consistent hardening responseGood machinability in the hardened condition

hardening, nitriding or fillet rolling


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Material Requirements

For ed steel crankshafts offer hi her stren th and stiffness than thecast iron alternative.Lower through cost, controlled air cooled steels are now preferredto traditional quench and tempered grades.Controlled hardenability steels ensure repeatability of mechanicalpropertiesOptimised sulphur content balances the conflicting benefits of lowsulphur for fatigue properties and high sulphur for improvedmachinability

Controlled carbon content produces consistent response toinduction hardeningontro e c romium an a uminium a itions ensure consistent

surface hardening through nitridingClean steels provide good fatigue resistance from a low overallinclusion content


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Connecting Rod

subsequently separated.Fracture splitting of the rod and cap is the latest majorindustry development and gives significant cost savingcompared with conventional machining.Connecting rods operate under high loads requiring:

High strength in both tension and compressionHigh fatigue strengthHighly efficient engines demand the lowest possible componentwei ht.

More slender rod designs must have:Materials with good rigidity / high strengthWeight consistency to facilitate engine balancing


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Manufacturing Requirements

,and cost.Cast iron rods are heavier and sintered powder products aremore expensive.

cost for most volume produced connecting rods.Lower through cost pressures demand:

Elimination of a heat treatment process

Low distortion on fracture splitting


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requirements without subsequent heat treatmentControlled hardenability steels ensure repeatability of mechanical properties

p m se su p ur con en a ances t e con ct ng benefits of low sulphur for fatigue properties and highsulphur for improved machinabilityControlled microstructure improves fracture splitting


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deliver fuel at high pressure for efficientcombustion, better fuel economy and lower emissions.High strength steels for nozzles, body holders and unit

maximum fatigue resistance.


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Performance Requirements

High mechanical strength to tolerate the high system pressuresResistance to the fatigue stresses imposed by the fuel deliverycycleDurabilit at hi h combustion tem eratures

Nozzle body holders are also subjected to high fatiguestresses from pulsating fuel pressures.

Additionally, weight and packaging constraints aredemandin smaller com onents.


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Materials Requirements

- ,conditionHigh strength and fatigue resistance after heat treatmentStrength at elevated temperatures

Nozzle body holder and unit injector bodies have more demandingmachinability requirements.

Bars with exceptional straightness which are stress anddefect free to avoid hole drift durin un drillinControlled resulphurised or leaded steels to furtherimprove machinability


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Nozzles

The 2Ni2Cr steel develo ed for in ector nozzles has been tailored tomeet the combined requirements of machinability, strength, fatigue andhigh temperature durability.This steel is in use in the latest common rail systems, operating atpressures of up to 1800 bar and temperatures in excess of 200°C.

Medium carbon steels, sometimes resulphurised and / or leaded (e.g.C45Pb) are used for the less demanding applications wheremachinability overrides fatigue considerations.Through hardening alloy steels (e.g. 42CrMo4) are needed for higherfuel pressure systems where fatigue strength is more critical.On heat treatment these steels develop the required mechanical strengthand retain adequate machinability.Special clean steel practices are necessary to minimise inclusion contentand further improve fatigue properties.


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dr. gsk - automotive manufacturing process

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