EPT 221 Engineering Design Manufacturing Process Selection.
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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)
Add to your notes
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)
Add to your notes
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
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