EPT 221 Engineering Design

Manufacturing Process Selection

Objectives of Lecture

Differentiate and select primary, secondary , and tertiary processes

Understand and apply methods to select appropriate manufacturing processes

Estimate the costs of manufacturing a product.

How would we manufacture a mountain bike ?

TopTube

RearDerailleur

Front Brake

Rear Brake

SaddleSeatPost

Pedal

Handle Bar

DownTube

Fork

(Courtesy of Trek Bicycle, 2002)

Manufacturing process decisions

How do we choose the specific manufacturing processes?

How do the selected materials influence the choice of manufacturing processes?

Would product function or performance issues influence our choice of processes?

What criteria should we use to select processes? Which criteria are more important? Who will make the final decisions?

Parts undergo sequence of processes

Primary - alter the (“raw”) material’s basic shape or form. Sand castingRollingForgingSheet metalworking

Secondary - add or remove geometric features from the basic forms Machining of a brake drum casting (flat surfaces)Drilling/punching of refrigerator housings (sheet metal)Trimming of injection molded part flash

 Tertiary - surface treatments PolishingPaintingHeat-treatingJoining

Changes?

Part / Mfg. Process Considerations

1. Production Volume2. Part Size (overall)3. Shape Capability (features)/ geometric complexity boss/depression 1D boss/depression >1D holes undercuts (int./ext.) uniform walls cross sections - uniform/regular rotational symmetry captured cavities

Types of manufacturing processes

E xtrus ionF org ingR o ll ingB ar d raw ingW ire d raw ing

D eform ation

C en trifugalD ie cas t ingInvestm entP erm anen t m o ldS and cas t ing

C ast ing

B end ingB lank ingD raw ingP unch ingS hear ingS p inn ing

S hee tM etal

B low m old ingC ast ingC om press ion m o ld ingE x trus ionIn jec tion M old ingT herm oform ingT ransfe r m o ld ing

P o lym erP rocesses

B oringD ril lingF ac ingG rind ingM ill ingP lan ingT urn ingS aw ingE C M , E D M

M ach in ing

A nod iz ingH on ingP a in tingP la t ingP o lish ing

F in ish ing

A utom atedB ond ingB raz ingM anualR ive tingS o lde r ingW eld ing

A ssem bly

M anufac tu r ingP rocesses

How is the input material

changed?

Bulk Deformation

To change the shape or form of bulk material caused by compressive or tensile yielding.

Rolling Extrusion Drawing Forging

Rolling

Two or more cylindrical rollers plastically compress material, forming sheets, bars and rods.

Hot rolling requires less work but an oxidized surface finish

Cold rolling requires more work but increases the yield strength of the material and produces superior surface finish.

Rolling

slab

bloom

billet

sheetcoil

bar rod

structural

ingot

Extrusion

Heated metal plastically yields as it is pushed through a die, producing long pieces with a constant cross-section.

Size: 40-foot in length Economical production

quantities: 1,000 to 100,000 pieces

Materials: ductile metals (e.g. aluminum, steel, zinc, copper, magnesium)

Ram

Crosssections

Extrusion die

Billet

Drawing

Process of producing a wire, bar or tube by pulling on a material until it increases in length accompanied with a reduction in its cross-sectional diameter.

Size: bar size range 1/8 to 6 inches in cross-section, wire size range 0.001 to 3/8 inches.

Material: ductile metals (e.g. aluminum, steel, copper)

Pulling force

Crosssections

Drawing die

Billet

Forging (closed-die)

A process in which material is plastically compressed between 2 halves of a die set by hydraulic pressure or the stroke of a hammer.

Size: maximum size limit roughly 36 inches Economic production quantity: 1,000 to 100,000 pieces

Blockedpreform

Gutter

Ram pressure

Flash

Casting Processes

The process in which molten metal is poured into a cast to solidify.

Sand casting Die casting Investment casting

Sand casting (closed-mold)

Uses sand mold. The mold is destroyed to remove the part. Mold size ranges from inches to feet. (e.g. as mold cast for industrial

engine blocks as large as 12 feet in cross section and 30 feet long) Economical production quantity: very small i.e. 1 to 10 Material: all ferrous and nonferrous metals Parts produced have a granular surface finish.

Core RiserSprue

Runner

Drag

Flask

Cope

Gate

Partingline

Die casting

Molten metal is injected under high pressure into permanent die set usually made of steel.

Die casting is faster than sand casting but can more expensive.

Smoother surface finish than sand-cast parts.

Size: maximum part size 30 x 30 inches to parts less than an inch.

Economic production quantity: over 10,000

Material: low-melting-point metals (e.g. aluminum, zinc, magnesium, brass) Parting line

Plunger

Sprue

Moving die

Stationary die

Ejector pins

Moltenmetal

Investment casting (lost wax casting)

Molten metal solidifies in a ceramic cast made by coating a wax pattern with liquid slurry, then dried.

Wax is melted out and ceramic mold is destroyed after part solidifies.

Material: alloy of aluminum, zinc, magnesium, brass, steel, stainless steel.

Economic production quantity: less than 10,000 pieces

Investment casting

Wax patternis cast

Wax removedby melting

Molten metal solidifies in cast

Ceramic mold is removed

Ceramic mold(hardened slurry)4-part pattern tree

Polymer Processes Part shapes are created by solidification

of thermoplastic polymers or curing of thermosetting polymers.

Results in little waste of raw material and require few, if any, finishing operations

Compression molding Transfer Molding Blow molding Injection molding

Compression molding

Charge of thermoset or elastomer is formed between heated mold halves under pressure while the polymer cures.

Compression molds are simpler than injection molds (no sprue, runners, risers)

Size: minimum part size of the order of 1/8 to ¼ inch in cross-section Economic production volume: more than 10,000 pieces

Charge

Heated mold

Part

Ram Pressure

Transfer molding

Charge

Ram

Heatedmold

Sprue

Part

Ram pressure

Blow molding

Extruderair injector

parison

Part isremoved

Airblown into

parison

Mold halvesclose

Molten parison is extruded

Blow moulding

A molten parison of thermoplastic material injected with air, then expands to the shape of the mold.

Is used to produce hollow parts within thin walls.

Size: maximum size of about 3 feet in diameter

Injection moulding

Thermoplastic pellets are melted and injected under high pressure into a metal mold.

Size: maximum part size less than 24 x 24 inches, minimum part size are of the order of 1/8 to ¼ inch in cross-section

Economic production quantity: more than 10,000

Sheet Metalworking

The permanent deformation of thin metal sheets by bending and shearing forces produced by mechanical or hydraulic forces.

Often called stamping forces. Produces parts of moderate complexity. Size: less than 24x24inches Economic production quantity: more than 10,000 Material: alloys of steel and aluminum Bending Blanking Drawing Punching Shearing Spinning

Shearing : cutting or separating sheet metal along a straight line.

Blanking: shearing of a smaller, shaped piece, called a blank, from the stock.

Punching: produces slots, notches, extruded holes, and holes.

Embossing: forming plastic indentations to form ribs, beads, or lettering on the surface of metal.

Sheet metal drawing

Punch plastically deforms a blank sheet material into a die, forming cupped-, box-, or hollow-shaped parts

Products: soda cans, ammunition cartridge casings, and pots and pans.

Blank Drawn part

Clamp force

Blank holder

Die

PunchPunch ram

Solidification processes

Casting ProcessesSand CastingDie CastingInvestment CastingCentrifugal

Polymer ProcessesInjection MoldingBlow MoldingThermoFormingCompression Molding

solid Part molten material freezing

Flow (voids, flash)Cooling time (cycle time)TemperatureMold complexity Warpage Post processing Costs (materials, tooling, processing)

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Machining

The removing of material from the workpiece by a sharp cutting tool that shears away chips of material to create a desired form or features.

It is a subtractive process that produces manufactured waste and can, therefore be expensive.

Often used as a secondary process to true-up critical dimensions or surfaces or to smooth the surface finish.

Often used for low-volume production.

Machining processes

E xtrus ionF org ingR o ll ingB ar d raw ingW ire d raw ing

D eform ation

C en trifugalD ie cas t ingInvestm entP erm anen t m o ldS and cas t ing

C as t ing

B end ingB lank ingD raw ingP unch ingS hear ingS p inn ing

S hee tM etal

B low m old ingC as t ingC om press ion m o ld ingE x trus ionIn jec tion M old ingT herm oform ingT ransfe r m o ld ing

P o lym erP rocesses

B oringD ril lingF ac ingG rind ingM ill ingP lan ingT urn ingS aw ingE C M , E D M

M ach in ing

A nod iz ingH on ingP a in tingP la t ingP o lish ing

F in ish ing

A utom atedB ond ingB raz ingM anualR ive tingS o lde r ingW eld ing

A ssem bly

M anufac tu r ingP rocesses

Machining – removal of material…

Sawing –using a toothed blade.Milling – from a flat surface by a rotating cutter tool. Planing – using a translating cutter as workpiece feeds.Shaping - from a translating workpiece using a stationary cutter. Boring - increasing diameter of existing hole by rotating the workpiece.Drilling- using a rotating bit forming a cylindrical hole.Reaming – to refine the diameter of an existing hole.Turning - from a rotating workpiece. Facing - from turning workpiece using a radially fed tool. Grinding - from a surface using an abrasive spinning wheel.Electric discharge machining (EDM) - by means of a spark.

Machining process considerations

sawing, turning, boring, milling, drilling, grinding, ECM

material removed solid material machining

hardness, strength of materialshear forces = strong jigs & fixtures tool/bit wear, replacementsize of workpiece, fit machine?volume removedrate of removal, hp neededtolerances operator skill, CNCcosts (materials, tooling, processing)

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Finishing

Preparing the final surface for aesthetics and protection from the environment.

Cleaning: wire brushing is used to remove grit and scale, and chemical solutions, including acid baths, are used to remove oily films

Protection: polymers and ceramics requires little protection from the environment. Metals, however, require some surface treatment with oil-and-water based painting providing the least expensive coating. Steels are often plated with chrome, cadmium, or zinc). Aluminum alloys are usually anodized (a chemical surface treatment).

Finishing processes

E xtru s ionF org ingR o ll ingB ar d raw ingW ire d raw ing

D eform a tion

C en trifugalD ie cas t ingInvestm entP e rm anen t m o ldS and cas t ing

C as t ing

B end ingB lank ingD raw ingP unch ingS hea r ingS p inn ing

S hee tM etal

B low m o ld ingC as t ingC om press ion m o ld ingE x tru s ionIn jec tion M old ingT herm oform ingT ransfe r m o ld ing

P o lym erP rocesses

B oringD ril lingF ac ingG rind ingM ill ingP lan ingT urn ingS aw ingE C M , E D M

M ach in ing

A nod iz ingH on ingP a in t ingP la t ingP o lish ing

F in ish ing

A u tom atedB ond ingB raz ingM anualR ive t ingS o lde r ingW eld ing

A ssem bly

M anufac tu r ingP rocesses

protection?

Surface roughness

Assembly

The process of putting together all the components of a product before shipping.

Operation include handling, insertion, and/or attachment of parts.

Handling: grasping, moving, orienting, and placing parts, before insertion or attachment.

Attachment: either - Permanent: welding, brazing, soldering, adhesive bonding, rivets, eyelets, staples, shrink fits, press fits, or - Temporary: threaded fasteners such as screws, nuts and bolts, snap fits.

Assembly processes – fastening / joining of 2 or more components

E xtru s ionF org ingR o ll ingB ar d raw ingW ire d raw ing

D eform ation

C en trifugalD ie cas t ingInvestm entP erm anen t m o ldS and cas t ing

C as t ing

B end ingB lank ingD raw ingP unch ingS hear ingS p inn ing

S hee tM etal

B low m o ld ingC as t ingC om press ion m o ld ingE x tru s ionIn jec tion M old ingT herm oform ingT ransfe r m o ld ing

P o lym erP rocesses

B oringD ril lingF ac ingG rind ingM ill ingP lan ingT urn ingS aw ingE C M , E D M

M ach in ing

A nod iz ingH on ingP a in t ingP la t ingP o lish ing

F in ish ing

A u tom atedB ond ingB raz ingM anualR ive t ingS o lde r ingW eld ing

A ssem bly

M anufac tu r ingP rocesses

permanent?

Process / Material Screening

Product function is interdependent

Material Properties

ProductFunction

ManufacturingProcesses

ProductGeometry

Are materials compatible with mfg. process?

Material Properties

ManufacturingProcesses

compatiblematerials & processes

Material-Process Compatibility

ME 488 Design for Manufacture & Assembly Materials Compatibility

Processes Sh

ap

e A

ttrib

utes

Cast

Iron

Carbon S

teel

Alloy S

teel

Sta

inle

ss S

teel

Alu

min

um

& a

lloys

Copper &

alloys

Zin

c &

alloys

Magnesiu

m &

alloys

Titaniu

m a

nd a

lloys

Nic

kel &

alloys

Refr

acto

ry m

eta

ls

Therm

opla

stics

therm

osets

Solidification sand castinginvestment castingdie castinginjection moldingstructural foamblow molding - extrblow molding - injrotational molding

Bulk impact extrusionDeformation cold heading

closed die forgingpowder metalhot extrusionrotary swaging

Metal machined from stockRemoval ECM

EDM

Profile Generation Wire EDM

Sheet sheet metal bendingForming thermoforming

metal spinning© R. J. Eggert, BSU (Based on data from Boothroyd, Dewhurst & Knight) pg 47 revision 9/02/03

Legend Normal practiceLess commonNot applicable

Shape generation capability (of processes)

Manufacturing costs

Total Manufacturing Cost = Material + Tooling + Processing

raw mat’ls molds labor  fixtures electricity jigs supplies tool bits O/H

(deprec.)

TMC = M + T + P

Material costs per part, cM

Let M = total materials costs (raw, bulk) q = production quantity

Then material costs per part, cM is

cM = M/q = (cost/weight x weight) / number of parts

Let’s reorganize the variables in the equation above

cM = [cost/weight] [weight/number of parts] = (cost/weight) (weight/part), and therefore

cM = cost/part

Material cost per part (continued)

Let cw = material cost per unit weight, and wp = weight of finished part ww= weight of wasted material, scrap = ratio of wasted material weight / finished weight = ww / wp

Then the material cost per part, cM iscM = cw (wp + ww ) = cw (wp + wp ) cM = cw wp (1+ )

Tooling cost per part, cT

Let T= total cost of molds, fixtures per production run q = number of parts per run

Then tooling cost per part, cT

cT= T/q

e.g. sand casting cT = ($10,000/run) / (5000 parts/run) = $2.00/part

Processing cost per part, cP

Letct = cost per hour, (machine rate + labor)t = cycle time (hours per part)

then cP = ct t

e.g. sand casting cP = ($30/hr) (0.3 hrs/part) = $9/part

Total cost per part

Cost per part,

c = cM + cT + cP

c = cw wp (1+ ) + T/q + ct t (6.6)

e.g. sand casting

c = $1.05 + $2.00+ $9.00

c = $12.05 / part

Example Assume that our company is

considering making a part out of low-strength metals or thermoplastics. Three processes appear compatible with the required feature shapes: sand casting, injection, and machining. The marketing department estimates that the company should produce about 5,000 pieces. Data gathered to select the material and manufacturing process are shown in the table below. Determine the cost per part.

1

10

100

1000

0 1000 2000 3000 4000 5000 6000

Production quantity

Cos

t ($

/par

t)

A B C

Run quantity is important!

A-Sand casting B-Inj.Molding C-Machining

How can we lower the cost of parts?c = cw wp (1+ ) + T/q + ct t (6.6)

1) purchase less expensive materials,2) keep our finished part weight low3) produce little manufactured waste4) design simple parts that result in less expensive

tooling 5) make many parts production run (i.e. batch)6) choose a manufacturing process that has a low

cycle time & cost per hour

Goal: minimize the sum of the terms!(not any one term in particular)

Case Study- Aero engine

Summary

Manufacturing process decisions Deformation processes Casting processes Sheet metalworking Polymer processing Machining Finishing Assembly Material compatibilities / Process capabilities Material costs, Tooling costs, Processing

costs