Reglas de Diseño 2

MFGT 124Solid Design in ManufacturingProduct Evaluation for Cost, Manufacture, Assembly, and Other MeasuresProfessor Joe GreeneCSU, CHICO

Reference: The Mechanical Process, 3rd Edition, David Ullman, McGrall Hill New York (2003)Reference: Design for Manufacturability Handbook, J. Bralla, McGraw Hill (1999)

MFGT 124

Copyright 2003 Joseph Greene All Rights Reserved

Chap 12: Product Evaluation, Cost, DFMTopicsIntroductionCost Estimating in DesignValue EngineeringDesign for ManufactureDesign for Assembly EvaluationDesign for Reliability


Cost Estimating in DesignCost for manufactured partsDirect costsMaterial LaborToolingPurchased partsIndirect CostsOverhead- building, utilities, land, capital equipment, etc.Sales expense- advertising, sale promotions, rebates, low% financingProfit: typically 5-50%


Injection Molding CostsMany methods are used to determine the cost of injection molded partrough estimates based upon rules of thumb or experienceextremely detailed analysis based on costs for numerous plant functionsspreadsheet based analysis, IBIS and AssociatesPocket knife exampleMFGT 142: Cost estimating form for injection moldingAppendix: Blank Form

Part 1: Introduction SectionPart name, customer, molder, Tool source, date, estimator, approver


Injection Molding CostsPart 2: Resins and Additives CostsType and grade of resin, e.g., pocket knife is nylon 6,6 (Dupont Zytel)Cost of resin depending upon quantity, e.g., boxcar, gaylord, bagAdditives cost, e.g., colorants, fillers, stabilizers, etc. (black is $3/lb)Total Material Cost = (resin cost)*(resin fraction) + (additives cost)* (additives fraction)Example, Total Cost = $1.36 * 0.99 + $3.00 * 0.01 = $1.38 nylon and colorPart 3: Part CostsPart costs = material costs plus factory costsMaterial cost is materials plus scrap from runners, sprues, and part rejects.Example: Knife weighs 3.8 grams. The runners, sprues, and scrap is 5%. Total material uses us 3.8 + 0.05*3.8 = 4 grams. Cost = $1.38 * 4/454 lbs = $0.0122 per partFactory costs represent convenient price figure and is a factor*material costsExample: Factor = 1000. Then, factory costs = 1000 * $0.0122 = $12.00


Injection Molding CostsPart 4: Tooling CostsType of tooling material, e.g. steel, aluminum, kirksite.Number of cavities in tool, e.g., single cavity has 1 part, dual has 2, multicavity tool can have 4, 6, 8 pieces, or more.Number of slides or lifters in a tool to mold parts that have an internal flange or under cut.Number of years the tool is amortized for tool life, e.g., payoff tool in 1 year, 3 years, or five years. (Every company has different accounting practices.Internal (In-House) tool construction versus External (Outside) tool construction. Internal is usually less expensive per tool but has more overhead, thus need many jobs to reduce overhead costs.Example, knife handle$20,000 per tool (dual cavity, $5K internal, $15K external)Cost per part is $20,000/ 4million parts * 1000 (pieces) = $5 per 1000 pieces


Injection Molding CostsPart 5: Machine CostsCost of machine is dependent upon the time the machine is in use to make parts and whether the machine has an operator or not.Each machine will have two rates, e.g., automatic or manual.Rates are determined fromOriginal cost of machineOngoing operations costsSpecial equipment costs for particular jobs, e.g., special controllers or chillersCycle timeExample, KnifeCycle time is 30 seconds yields 240 parts per hour (120 per cavity)Hourly rate is $25 for manual with operator, and $15 on automatic Knife example needs operator to cut runner and sprue off partCost = $25 per hour / 240 parts per hour * 1000 = $104.17


Injection Molding CostsPart 6: Secondary Operations CostsMany parts are subject to other operations costs after moldingplaced or glued into an assembly, drilling of holes or attachments Rates are determined from some rate and cycle timeRate costs are dependent upon the type of machine used, $ per hourCycle time, parts per hourRunner and sprue removal are not considered secondary operations since they are removed at the press after molding.Example, KnifeSecuring the blade to the handle with screws after injection moldingCycle time is 10 seconds yields 60 parts per hour Cost = $7 per hour / 60 parts per hour * 1000 = $19.44 per 1000 piecesPart 7: Purchase Items CostsMany items are purchased and included in assemblyExample, Knife use Costs of blade and screw purchases Cost of blades = $1250 per 1000 piecesCost of screw = $2.00 per 1000 pieces


Injection Molding CostsPart 8: Packaging and Shipping CostsCosts for shipping cartons, bags, blister packages, foam materialsCosts for transportation can be includedExample, KnifeCosts for blister packages = $50 per 1000 piecesCost of carboard box = $0.70 per box that holds 1000 piecesTotal Factory Costs per 1000 pieces = $1443.51General Administration Costs = 10% = $144.35Marketing and Profit = 20% = $288.70Total Cost per 1000 parts =$1,876.16,or $1.88 per knife


Injection Molding Costs_ ExampleSpreadsheet: IBIS and Associates


Chart1

3.85

2.11

0.82

0.65

0.6

0.57

0.57

Part Volume

Piece Cost of Flying Disk

Sheet1

volumepiece cost

5,000$3.85

10,000$2.11

50,000$0.82

100,000$0.65

150,000$0.60

200,000$0.57

400,000$0.57

Sheet1

Part Volume

Piece Cost of Flying Disk

Sheet2

Sheet3

Inject Mold

----------

INJECTION MOLDING TECHNICAL COST MODELINJECTION MOLDING TCM: COST SUMMARY

IBIS Associates, Inc. Copyright (c) 1997IBIS Associates, Inc. Copyright (c) 1997

----------

Updated: 2/4/98per pieceper yearpercentinvestment

PRODUCT SPECIFICATIONSVARIABLE COST ELEMENTS----

Part NameToothbrushNAMEMaterial Cost$0.10$19,91927.0%

Weight30gramsWGTDirect Labor Cost$0.03$5,6487.6%

Maximum Wall Thickness12mmTHKMUtility Cost$0.00$7271.0%

Average Wall Thickness12mmTHKA

External Surface Area300sq cmSAREAFIXED COST ELEMENTS----

Projected Area300sq cmPAREAEquipment Cost$0.02$4,7006.4%$270,000

Tooling Cost$0.10$20,00027.1%$100,000

Number of Cavities8CAVBuilding Cost$0.00$3350.5%$48,115

Number of Actions in Tool1ACTMaintenance Cost$0.04$7,2159.8%

Surface Finish [3=best]2[1,2 or 3]FINOverhead Labor Cost$0.01$1,8102.4%

Cost of Capital$0.07$13,55518.3%

Annual Production Volume200(000/yr)NUM====

Length of Production Run5yrsPLIFETOTAL OPERATION COST$0.37$73,909100.0%$418,115

MATERIAL SPECIFICATIONS-----

Material TypeNylonMAT

Material Price$3.30$/kgPRICEINTERMEDIATE CALCULATIONS

Scrap Credit Value$0.00$/kgSCPRIPart NameToothbrush

Density1.2g/cm^3DENSMaterial DesignationNylon

Thermal Conductivity0.24W/mKTCONDProduct Weight30g

Heat Capacity1675J/kgKHTCAPRaw Material Price$3.30/kgPRICE

Melt Temp260CMTEMPMaterial Scrap Price$0.00/kgSCRAP

Tool Temp60CTTEMPMaterial Density1.2g/cm^3DENS

Eject Temp80CETEMP

Adjusted Material Scrap0.005SCR1

PROCESS RELATED FACTORSCumulative Rejection Rate0.001CREJ

Dedicated Investment0[1=Y 0=N]DEDEffective Production Volume200200/yrENUM

Operation Rejection Rate0.1%REJTool Complexity Factor21259CMPLX

Material Scrap Rate0.5%SCREnergy Adjustment Factor3.2EAF

Average Equipment Downtime20.0%DOWNClamping Force12704kNFORCE

Direct Laborers Per Station0.5NLABCooling Time252.8secCOOL

OPTIONAL INPUTSCALCULATEDCycle Time200.0secCTIME

Cycle Time200sec/cycleOCYCLE200.0

Equipment Cost per Station$150(000)OEQUIP$150,000Runtime for One Station13.9%RTIME

Tool Cost per Set$100(000)OTOOL$100,000Number of Parallel Stations0.14NSTAT

Productive Tool Life5yrsLTOOL

EXOGENOUS COST FACTORSEXOGTool Sets/Station1NTOOL

Direct Wages10/hrWAGE

Indirect Salary$50,000/yrSALARYEquipment Investment/Station$150,000/stationIEQUIP

Indirect:Direct Labor Ratio0.4ILABTooling Investment/Set$100,000/tool setITOOL

Benefits on Wage and Salary30.0%BENI

Working Days per Year260DAYSPower Consumption/Station1.3kWPOWER

Working Hours per Day24HRSBuilding Space/Station80.2sq mSPACE

Capital Recovery Rate15.0%CRR

Equipment Recovery Life8yrsELIFEEquipment Annuity$8,096/yrEINT

Building Recovery Life20yrsBLIFETooling Annuity$28,548/yrTINT

Working Capital Period3monthsWCPBuilding Annuity$1,059/yrBINT

Price of Electricity$0.051/kWhELECWorking Annuity$36,206/yrWINT

Price of Natural Gas$6.50/MBTUGAS

Price of Building Space$600/sq mPBLD#####

Auxiliary Equipment Cost20.0%AUX

Equipment Installation Cost50.0%INST

Investment Maintenance Cost5.0%MNT

-----

REGRESSION PARAMETERS

Cycle Time Constant8.87secCYC1

Cycle Time Cooling Coef1.35sec/secCYC2

Cycle Time Weight-Cav Coef0.0151sec/g/pcCYC3

Tool Pressure Constant200barsPRES1

Tool Pressure Coefficient224bar cm^1/2PRES2

Machine Cost Constant14829MCH1

Machine Cost Coefficient41/kNMCH2

Tool Cost Coefficient148TOOL1

Complexity Deformation Coef3909TOOL2

Complexity Actions Coef15477TOOL3

Complexity Surf Finish Coef1.56TOOL4

Tool Complexity Exponent0.25TOOL5

Weight Factor Exponent0.45TOOL6

Multi-Cavity Exponent0.4TOOL7

Baseline Tool Life1000000cyclesTLIFE

Electricity Requirement0.75kWh/kgELEC1

Floor Space Coefficient135sq mFLR1

Floor Space Scaling Exponent0.71FLR2

#####

&A

&L&D&C&A

Design for ManufacturingCost for manufacturing item is dependent uponType of machining operation: use general purposeMaterial selection: use common materialsProduction quantities: higher quantities = lower costDesign changes: keep the number smallDimensional accuracy: keep tolerances generous where allowable

Reference: Design for Manufacturability Handbook, J. Bralla, McGraw Hill (1999)


Sheet1

Sand Mold cating versus Die Casting

ProcessGray-Iron CastingAl Die Casting

Cost of ItemUnit CostCost of ItemUnit Cost

Tooling$5,000$0.10$35,000$0.70

Material$0.20$1.20$0.70/lb$1.40

Casting Setup0.30 h at $8/h$0.000.4h at $8/h$0.32

Casting Direct Labor0.80 h at $8/h$0.640.04h at $8/h$0.32

Machining: setup$50 for 5 ops$0.02$25 for 3 ops$0.01

Machining: direct labor0.05h at $8/h$0.400.03h at $8/h$0.24

------------------------------

Total unit cost$2.36$2.99

Sheet2

Sheet3

Design for ManufacturingCNC Factors versus manual methodsLead time is reducedComplex parts routinely producedOptimize process conditions for feed rates and speedsMath data taken right from computer to cutter


Sheet1

Lathe versus screw machines

ProcessTurret LatheAuto SingleAuto Multispindle

Cost of ItemUnit CostCost of ItemUnit CostCost of ItemUnit Cost

Tooling$350$0.35$680$0.68$680$1.00

Setup1h per 500 pieces$0.032h per 500 pieces$0.063h per 500 pieces$0.08

Direct labor2 min$0.67.6 min$0.05.2 min0.03

---------------------------------------------

Total unit cost$1.05$0.79$1.11

Sheet2

Sheet3

DFM PrinciplesUse of standardsUse of common componentsDesign to specifications and tolerancesUse of manufacturing guidelines in the early stages of design that maximize quality of manufactured partMinimize the use of materialsMinimize the use of floor space in plantLocate all necessary components near functional operationUse of automated machining for minimal errors


DFM Design RulesSimplify the design & reduce the number of parts required.Design for low labor cost operations, e.g., punch hole rather than drill.Make specific notes on drawings and avoid generalized statements, e.g., polish this surface.Dimensions should be made from specific surfaces and not points in space. (Dont dimension off a center of a circle)Minimize part weight whenever possible.Avoid sharp corners, use generous fillets and radii.Dimensions should be from one datum point rather than from a variety of points.Design part so that as many operations can be used without repositioning part


DFM Design RulesCast, molded, or stamped parts should be made with no stepped parting lines.Keep uniform wall thickness.Space holes so that they can be made in one operation without tooling weaknessFollow minimum draft requirements for cast or molded parts


DFM Quick ReferencesSurface finish from Various ProcessesNormal maximum surface roughness of common machined partsDimensional tolerances from machiningProcesses for flat surfacesProcesses for 2D contoured surfacesProcesses for hollow shapesCommonly used materials and metal working processesFormed metal parts


Material SelectionProper material selection is a major factor for a successful designed and manufactured product.Common engineering materialsCommon commercial forms of selected raw materialsUltimate tensile strength of selected materialsSpecific gravity (density) of selected materialsMelting point of selected materialsThermal conductivityCLTERelative Cost per unit weight and per unit volume


Ferrous MetalsHot-rolled steelProduced in a variety of cross sections and sizesRound bars from 6 to 250 mm in DSquare bars from 6 to 150mm per sideRounded corners squares 10 to 200 mm per sideFlat bars from 5 mm in thickness to 200 mm in widthAngles, channels, tees, zees and other sectionsOvals, half roundsSheets 1.5 mm (16guage) or thicker and platesCommon cross-sectional shapes for hot rolled steel


Ferrous MetalsHot rolled steelProcess and CharacteristicsEconomic QuantitiesDesign RecommendationsDimensional Factors and TolerancesCold-Finish steelDefinition and ApplicationsAvailable Shapes and SizesDesign RecommendationsStandard TolerancesStainless SteelDefinition and ApplicationsAvailable Shapes and SizesDesign RecommendationsStandard Tolerances


Hot-Rolled SteelProduced by passing a heated billet, bloom, or ingot of steel through a set of shaped rollers.Repeated passes, the rollers increase the length of the billet and change it to a cross section of specified shape and size. After rolling the shape is pickled (immersion in water, dilute sulfuric acid) to remove scale and then is oiledCharacteristicsProduced in a variety of cross sections and sizes, which the following are:Round bars from 6 (0.25in) to 250 mm in diameterSquare bars from 6 to 150 mm per sideRound-cornered squares, 10 to 200 mm per sideFlat bars from 5 mm in thickness and up to 200 mm in width (< 80 cm2 area)Angles, channels, tees with largest cross section dimension of 75 mmOvals, half rounds and other special cross sectionsSheets, 1.5 mm or thickerHot rolled steel is about 30% lower in price than cold-finish steel.HRS has more dimensional variation, rougher surface, mill scale, less straightness, less strength, and poorer machinability.


Hot Rolled Steel CharacteristicsCommon shapes

Hot rolled steel is employed in applications for which only a small amount of machining is required for which a smooth finish is not necessary.Examples are tie rods, welded frames, lightly machined shafts, cover plates, riveted and bolted racks, railroad cars, ships, bridges, buildingsHas low carbon content (< 0.25%)

PlatesSheetsStripsSquaresHalfOvalsTeesZeesAngles(unequal length)I-BeamsRoundsHalf roundsChannelsSeamless tubingAngles(equal length)


Economic QuantitiesStandard cross sections are suitable for all levels of production.Purchased from steel distribution warehouse or directly from millsSpecial cross section (Fig 2.2.2) hot-rolled steel are available in large quantities form high production levels of 100 tons minimumJack channels, studded T bars, U-harrow bars, hexagons, Diamonds, OvalsGrades for Further ProcessingMachining: moderately low-carbon grades (> 0.15%C) are best, otherwise it should be hardened and tempered.Carbon content between 0.15 to 0.30%, machinability is good.Machinability is good for Carbon content between 0.30 and 0.50% and better if prior annealed and partially speriodized.High carbon grades (>0.55%C) annealing must provide a completely spheriodized structureFor heavy machining, free machining grades require sulfur or leadForming: Low carbon grades are best. Lower the yield strength and higher ductility yields easier formingWelding: Low carbon grades are the best. Materials with 0.15%C or less are easier to weld. Weld-ability decreases with increasing carbon content or alloy content


Design RecommendationsGrade selection design criterion is to design for minimum strengthGrades with higher carbon content or low alloy content will provide lower cost parts than that can be made from plain low-carbon grades due to lighter sections can be used.Bending hot finished steel to help avoid fracturing material at bend: Bend line should be at right angles to grain direction from the rolling operation.Bend radius should be as generous as possible.To achieve a true surface from machining, Remove sufficient stock to get below the surface defects and irregularities.Include seams, scale, deviations from straightness or flatnessAISI (American Iron and Steel Institute)Machine allowance1.5mm per side for finished diameters or thicknesses from 40 to 75mm3.0mm per side for diameters or thicknesses over 75mm.


Dimensional Factors and TolerancesDimensional variations are considerably wider than with cold-finished material due to lack of secondary operationsStandard TolerancesAngles for Hot-Rolled steel: Tolerances for Thickness, Length of Leg, and Out-of-SquareNote: Longer leg of unequal angle determines the size for tolerance.Note: Out-of-Square tolerance in either direction is 1.5

Straightness Tolerance for Hot-Rolled Steel BarsNormal straightness Tolerance: in any 5-ft length or x length(ft) /4Special:1/8 in any 5-ft length or 1/8 x length (ft) /5


Sheet1

Specified length of leg, inThickness tolerance for thicknesses given (over/under), inTolerance for length of leg (Over/under), in

To 3/16Over 3/16 to 3/8Over 3/8

< 1 in0.0080.011/32

1 - 2 in0.010.010.0123/64

2 - 3in0.0120.0150.0151/16

Sheet2

Sheet3

Cold-Finish SteelDefinitionCold finished steel is more physically refined product than hot-rolled steel and:Higher surface finish, dimensional accuracy, and superior grain structureHigher tensile and yield strengthProducts include bars (round, square, hexagonal, flat, spherical), flat products (sheets, strips, or plates), tubular products, wire or various cross sectionsTypical ApplicationsCold finished steel is best for applications where the following are requiredGreater accuracy and smoother surface finishAdded mechanical properties, yield and tensile strength. 12% reduction in cross section yields 20% increase in tensile strength and 60% increase in yield strengthImproved machinability, formability, and freedom from surface scaleMill Processes used individually or in combinationCold drawing, cold rolling and machining.Can be subjected to heat treatments, e.g., stress relieving, annealing, normalizing, carbon restoration


Grades For Further ProcessingMachiningImproved due to increased hardness from drawing operationSulfur, lead, and tellurium are added to improve machiningCold Finished Steel Bar Formulations with Good Machinabilty

StampingCold-rolled sheet steel is better for stamping than hot finishedAbsence of scale, greater uniformity of stock thickness, better formabilitySurface finish is superiorGrade of steel required depends upon the severity of stampingDeep drawn parts may require Al kiln or drawing qualityLower carbon content (

Grades For Further ProcessingWeldingMaterial is fully weldable, especially low C, low-alloy steelDistortion is inherent to arc-welding, might be better with hot finish steelResistance weldament is great for cold-rolled steelPreferred material for arc and resistance welding is C < 0.35%BrazingBest accomplished with steels of lower C and alloy content.Ideal materials have C in range of 0.13 to 0.2% and Mn in 0.3 to 0.6%PlatingAll cold finish bars are suitable for platingAdditional polishing is required


Grades For Further ProcessingHeat TreatingCold working materials are heat treatable and widely used.Grades for heat treatment processesCarburizing: 8620, 4620, 1020, 1024, 9310Nitriding: 4140, 4340,8640Flame hardening: Medium carbon steels (0.35 0.70 %C)Cyaniding/carbonitriding: 1020, 1022, 1010Induction hardening: 1045,1038, 1144Other through-hardening: 4140, 4130PaintingAll cold finish bars are practical for paintingExtensive cleaning is not required


Shapes and SizesSome common shapes of Cold-finished Steel


Sheet1

Min thick or DMax thick or DNormal Length

ininft

Round bars0.1251210 to 24 ft

Square bars0.125610-12 ft

Hex bars0.125410-12 ft

Flats0.125 x .25 wide3 in x 8 in wide10-12 ft

Sheet0.015 x 13 wide0.179 in x 48 wide4 to 10 ft or coil

Tubing, round seamless.125 OD x .049 wall12 OD x .5 wall17-24 ft

Tubing, round welded.25 OD x .035 wall6 OD x .25 wall17-24 ft

Sheet2

Sheet3

Design RecommendationsDesign approach is to specify a size and shape of material that minimize subsequent machiningUse as-drawn or as-rolled surfaces and dimensionsOther RulesUse simplest cross-sectional shape possible; avoid holes & groovesWith special shapes, undercuts and reentrant angles can be produced but $$Use standard rather than special shapes.Avoid sharp corners & use the largest filets & radii (min 0.08mm)Grooves width should be less deep than 1.5 times the width.Keep section thickness as constant as possible, avoid abrupt changes should be avoided to reduce local stress concentrationsSpecify the most easily formed materials and lowest costWith tubular sections, welded rather than seamless types are more economical, especially if drawing after welding without mandrel


Design RecommendationsOther RulesAvoid undercuts and reentrant angles

PoorBetterAvoid sharp corners

PoorBetter


Stainless SteelDefinition and ApplicationsAlloys that posses unusual resistance to attack by corrosive mediaApplications include aircraft, railway cars, trucks, trailers,...AISI developed a 3digit numbering system for stainless steels200 series: Austenitic- Iron-Cr-Ni-MnHardenable only by cold working and nonmagnetic300 series: Austenitic- Iron-Cr-NiHardenable only by cold working and nonmagneticGeneral purpose alloy is type 304 (S30400)400 series: Ferritic- Iron-Cr alloy are not hardenable by heat treatment or cold workingType 430 (S43000) is a general purpose alloyMartensitic- Iron-Cr alloys are hardenable by heat treatment and magneticType 410 (S41000) is a general purpose alloy


Stainless SteelCorrosion of steels can be slowed with addition of Cr and Ni.Stainless steels have chromium (up to 12%) and Ni (optional)ferritic stainless: 12% to 25% Cr and 0.1% to 0.35% Carbonferritic up to melting temp and thus can not form the hard martensitic steel.can be strengthened by work hardeningvery formable makes it good for jewelry, decorations, utensils, trimaustenitic stainless: 16% to 26% Cr, 6% to 23% Ni,

Stainless SteelCold forming200 and 300 series: Excellent bending characteristicsWithstand a free bend of 180 with a radius equal to material thickness.As hardness increases, the bending becomes more restrictiveCan be stretched more than carbon steelExcellent stretch-forming characteristics, preferred 301 or 201 due to cold working induced high strength305 series exhibit excellent deep drawability400 series: Good bending characteristicsLess ductility than the 300 series with minimum radius equal to thickness.Cannot be stretched severely without thinning and fracturingCan be processed for deep drawability


Stainless SteelHot formingStainless steels are readily formed by hot operations, I.e., rolling, extrusion, and forgingMachiningMachining characteristics are substantially different than for carbon or alloy steelsStainless steel types are difficult to machine and are tough and gummy and tend to seize and gall.400 series- Easiest to machine, although produce a stringy chip200 and 300 series- Most difficult to machine due to gumminess and work-harden at a rapid rate.Ways to improve machinability: Specify that the bar for machining be in a slightly hardened condition.Order a Stainless steel that is chemically altered for machiningOrder a free-machining Stainless steel that has sulfur, selenium, Pb, CuTypes- 303, 303Se, 430F, 430F Se, 416, 416Se, 402F


Stainless SteelMachinability


Chart1

60

75

60

92

60

100

52

65

SS type

Ratings, %

Machinability of Stainless Steel

Sheet1

Machining Stainless

TypeRatings, %

30460

30375

43060

430F92

41060

416100

42052

420F65

Sheet1

SS type

Ratings, %


Sheet2

Sheet3

Sheet1

Machining Stainless

TypeRatings, %

30460

30375

43060

430F92

41060

416100

42052

420F65

Sheet1

SS type

Ratings, %


Sheet2

Sheet3

Stainless SteelWeldingWeld rod selection is important because the filler metal should have composition equivalent to or more highly alloyed than the base materialCr carbides can precipitate in the grain boundaries when stainless steels re heated and cooled during welding through a temperature range of 430C to 900C (800F to 1650F)This lessons the corrosion resistancePreventionLow carbon stainless steels are used, e.g., 304J, 316L, 317LStabilized with niobium or titanium to prevent precipitationAustenitic types are 321 and 347Ferritic types 409 and 439Soldering and BrazingStainless steel can be soldered readily as long as proper heat treating techniques are employed to avoid Cr Carbide precipitation


Stainless SteelDesign RecommendationsUse least expensive stainless Use rolled finishesUse thinnest gauge requiredUse thinner gauge continuously backedUse standard roll-formed sectionsUse simple sections for economy of formingUse concealed welds to eliminate refinishingUse stainless steel types that are especially suited to manufacturing processes, e.g., free machiningDimensional Factors Standard TolerancesProvided in the Steel Products Manual for Stainless SteelsComparable to to carbon and alloy steels


Dimensional Factors and TolerancesDimensional variations are considerably wider than with cold-finished material due to lack of secondary operationsStandard TolerancesAngles for Hot-Rolled steel: Tolerances for Thickness, Length of Leg, and Out-of-SquareNote: Longer leg of unequal angle determines the size for tolerance.Note: Out-of-Square tolerance in either direction is 1.5

Straightness Tolerance for Hot-Rolled Steel BarsNormal straightness Tolerance: in any 5-ft length or x length(ft) /4Special:1/8 in any 5-ft length or 1/8 x length (ft) /5


Sheet1

Specified length of leg, inThickness tolerance for thicknesses given (over/under), inTolerance for length of leg (Over/under), in

To 3/16Over 3/16 to 3/8Over 3/8

< 1 in0.0080.011/32

1 - 2 in0.010.010.0123/64

2 - 3in0.0120.0150.0151/16

Sheet2

Sheet3

Non-metallic PartsPlastics and ThermosetsProfessor Joe GreeneCSU, CHICO


DFM for Injection MoldingTypical characteristics of injection molding


DFM for Injection MoldingEffects of shrinkageParts are designed with shrinkage included early in the design and before tool buildShrink rates for common materialsMaterialMax ShrinkageAcetal2.5%Acrylic0.8%ABS0.8%Nylon1.5%PC0.7%PE5.0%PP2.5%PS0.6%PVC rigid0.5%PVC flexible5.0%


DFM for Injection MoldingDesign GuidelinesGate and Ejector pin locationsEdge, Fan, Submarine, Flash, Tunnel, Ring, Diaphragm, disk, or sprue gate Not on a show surface Not near a structural member or hole or fastenerMinimize flow lengthMinimize the number of weld linesGate thick to thinSuggested wall thicknessHave constant wall thickness in partHave transitions from thick to thin regions if have different thickness. Have gentle no sharp transitions


DFM for Injection MoldingDesign GuidelinesHolesHoles are possible with slides but can cause weld linesMin spacing between two holes or a hole and a sidewall should be 1DShould be located 3D or more from the edge of a part to min stressesThrough hole is preferred to a blind hole because core pin that produces hole can be supported at both ends and is less likely to bendHoles in bottom of part are better than holes in side, which requires retractable core pinsBlind holes should not be more than 2D deep. Use steps to increase the depth of a deep blind hole For through holes, cutout sections in the part can shorten the length of a small-diameter pin.Use overlapping and offset mold cavity projections instead of core pins to produce holes parallel to the die parting line (Perpendicular to the mold-movement direction)


Sprue GuidelinesThe sprue must not freeze before any other cross section. This is necessary to permit sufficient transmission of holding pressure. The sprue must de-mold easily and reliably.

Dco tmax + 1.5 mm Ds Dn + 1.0 mm 1 - 2 tan = Dco - Ds / 2L


Runner GuidelinesCommon runnersFull-round runner Trapezoidal runner Modified trapezoidal runner (a combination of round and trapezoidal runner)Half-round runner Rectangular runner


Gate DesignGate Design OverviewSingle vs. multiple gatesSingle gate is usually desirable because multiple gates have weld linesGate dimensionThe gate thickness is usually two-thirds the part thickness. The gate thickness controls packing timeChose a larger gate if you're aiming for appearance, low residual stress, and better dimensional stability.Gate locationPosition the gate away from load-bearing areas.Position the gate away from the thin section areas, or regions of sudden thickness change to avoid hesitation and sink marks


Gate DesignGate Design OverviewGate TypesManually trimmedRequires an operator to separate parts from runners during a secondary operationTypes include sprue, tab, edge, overlap, fan, disk, ring, film, diaphragm, spiderAutomatically trimmed gatesAutomatically trimmed gates incorporate features in the tool to break or shear the gateShould be used toAvoid gate removal as a secondary operationMaintain consistent cycle times for all shotsMinimize gate scarsTypes include Pin, Submarine, hot-runner, and valve


Gate DesignDesign RulesGate location Should be at the thickest area of the part, preferably at a spot where the function and appearance of the part are not impairedShould be central so that flow lengths are equal to each extremity of the partGate symmetrically to avoid warpage Vent properly to prevent air traps Enlarge the gate to avoid jetting Position weld and meld lines carefullyGate LengthGate length should be as short as possible to reduce an excessive pressure drop across the gate. Ranges from 1 to 1.5 mm (0.04 to 0.06 inches)The gate thickness is normally 50 to 80 percent of the gated wall section thickness. Pin and submarine gates range from 0.25- 2.0 mm (0.01- 0.08)The freeze-off time at the gate is the max effective cavity packing time.Fiber-filled materials require larger gates to minimize breakage of the fibers


Boosting structural integrity with ribs Structural integrity: the goal of every design The major component of designing for structural integrity, in many cases, is to design the structure to be stiff enough to withstand expected loads. Increasing the thickness to achieve this is self-defeating, since it will: Increase part weight and cost proportional to the increase in thickness. Increase molding cycle time required to cool the larger mass of material. Increase the probability of sink marks. Well-designed ribs can overcome these disadvantages with only a marginal increase in part weight. Typical uses for ribs Covers, cabinets and body components with long, wide surfaces that must have good appearance with low weight. Rollers and guides for paper handling, where the surface must be cylindrical. Gear bodies, where the design calls for wide bearing surfaces on the center shaft and on the gear teeth.Frames and supports.


Ribs Design RulesKeep part thickness as thin and uniform as possible. This will shorten the cycle time, improve dimensional stability, and eliminate surface defects. . If greater stiffness is required, reduce the spacing between ribs, which enables you to add more ribs. Rib geometry Rib thickness, height, and draft angle are related: excessive thickness will produce sinks on the opposite surface whereas small thickness and too great a draft will thin the rib tip too much for acceptable filling. Ribs should be tapered (drafted) at one degree per side. Less draft can be used, to one-half degree per side, if the steel that forms the sides of the rib is carefully polished. The draft will increase the rib thickness from the tip to the root, by about 0.175 mm per centimeter of rib height, for each degree of draft angle. The maximum recommended rib thickness, at the root, is 0.8 times the thickness of the base to which it is attached. The typical root thickness ranges from 0.5 to 0.8 times the base thickness.


Recommended Rib Design Parameters.See Figure 1 for recommended design parameters.


Ribs Design RulesLocation of ribs, bosses, and gussets Ribs aligned in the direction of the mold opening are the least expensive design option to tool. As illustrated in Figure 1, a boss should not be placed next to a parallel wall; instead, offset the boss and use gussets to strengthen it. Gussets can be used to support bosses that are away from the walls. The same design rules that apply for ribs also apply for gussets. Alternative configurations As shown in Below, ribs can take the shape of corrugations. The advantage is that the wall thickness will be uniform and the draft angle can be placed on the opposite side of the mold, thereby avoiding the problem of the thinning rib tip. Honeycomb ribbing attached to a flat surface provides excellent resistance to bending in all directions. A hexagonal array of interconnected ribs will be more effective than a square array,with the same volume of material in the ribs.


Design RulesBossesBosses are protruding pads that are used to provide mounting surface or reinforcements around holes.Use same guidelines as for ribsUndercutsRequire sliding cores, split molds, or stripping plateShallow undercuts may be strippable from mold without need for core pulls.Allowable undercut for common materials.


Screw ThreadsTry to Avoid screw threadsUse a core that is rotated after molding is complete to unscrew partPut axis of the screw at the parting line of the moldMake threads few, shallow, and of rounded form InsertsUseful and practical to provide reinforcement where stresses exceed the strength of the plasticSharp corners should be avoidedRecommended designs Lettering and surface decorationsLettering in the part should be raised Lettering should be perpendicular to the parting line of the mold, otherwise there will be an undercut.


Design RulesDraftDraft is needed to assist in demoldingCommon draft angles for materials

Corners: Radii and FilletsSharp corners should be avoided. They add stress to polymerFillets and radii should be generous as possible.Desirable minimum is 0.5 mmPreferable min is 1.0 mm


Design RulesSurface FinishSurface polish and textures are possible with plastic parts.High gloss are feasible but can accentuate sinks and blemishesDull, matte, or textured surfaces are preferred Flat SurfacesFeasible but prone to show irregularities than gently curved surfaces which are preferred.Molding parting lineThe line created when the two mold halves come togetherShould be straight as the two mold halves come together in one plane. Offset dies may help avoid appearance defects. For non-straight parting lines, add a bead or raised surface to clean flash on demold.


DFM for ThermosetsThermosets are processed withCompression molding- Medium pressure- 1 to 2 minute cycle timeInjection molding- High pressure - 0.2 to1 minute cycle timeExtrusion- Low pressure - continuousSRIM - Low pressure - 1 to 3 minutes cycle timeRIM - Low pressure - 1 to 3 minutes cycle timeRTM - Low pressure - 5 to 10 minutes cycle timeHand Lay-up - Low pressure - 1 to 8 hours cycle timeFilament Winding - Low pressure - 1 to 2 hours cycle timeTooling is very important in the manufacturing operations Tool materials are P-20 steel, aluminum, bronze, epoxy, polyester, and rubber


Thermosetting MaterialsEpoxyPolyester and vinyl esterPolyurethanePhenolic compoundsUrea compoundsMelamine compoundsPolyimidesBismaleimides


Design RecommendationsEffects of ShrinkageMaterialShrinkage during moldingPhenolic0.1-0.9Urea0.6-1.4Melamine0.8-12.Diallyl phthalate0.3-0.7Alkyd0.5-1.0Polyester0-0.7Epoxy0.1-1.0Silicones0-0.5


Design RecommendationsWall thicknessMaterialSuggested thickness, mmPhenolic1.5 -3Urea1.5 -3Melamine1.5-3Diallyl phthalate1.1 -2.4Alkyd2 -3Polyester1.1 -2.4Epoxy1 -2 Silicones1-2


Design RecommendationsToolingUndercutsParts must be designed so that they can be easily removed from the mold.If external undercuts are essential, straight draw is not possible, a side activated slide is required or split the mold with removable sectionsInternal Undercuts are difficult and should be avoidedMold Parting lineTwo mating mold surfaces must be sealed off to mold a flash free partContour and step partings lines are difficult and should be avoidedSharp cornersAll corners should have a radius or fillet at set-in sections of the mold or at the parting lineAvoid sharp cornersSpecify fillets and corner radii of 0.8mm to 1.1 mmHoles or openingsSteel pins or section are needed in the mold to incorporate holes or irregularly shaped openingsSpacing between holes and next to side walls should be as large as possible


Value EngineeringValue EngineeringDeveloped in the late 40s by General Electric and evolved in 80s.Customer-oriented approach to the entire design process.Value = (Worth of a feature, component, or assembly) / (Cost of it)Worth- functionality it provides to customer Value- function provided per dollar of costValue formulaStep 1: Determine what the feature does.Step 2: Identify the life-cycle cost of the feature.Includes manufacturing, energy, use costs, disposal costs, etc.Step 3: Identify the worth of the function to customer. Can use QFD technique (pg 134) Quality function deploymentStep 4. Compare worth to cost ratio of features and identify features that have low worth to cost ratio. Consider removing low ratio features and keeping high value features.


Quality EngineeringQuality EngineeringReliabilityPotential failures of a product can be identified and then the MTBFMTBF: Mean time between failuresAverage elapsed time between failures.


Sheet1

Mechanical failures per Million hrsElectrical failures per Million hrs

BearingMeter26

Ball13Battery

Roller200Lead acid0.5

Sleeve23Mercury0.7

Brake13Circuit board0.3

Clutch2Connector0.1

Compressor65Generator

Differential15AC2

Fan6DC40

Heat Exchanger4Heater4

Gear0.2Lamp

Pump12Incandescent10

Shock Absorbver3Neon0.5

Spring5Motor

Valve14Small HP8

Large4

Solenoid1

Switch6

Sheet2

Sheet3

Quality EngineeringQuality EngineeringDefects: Automotive Defects per 100 vehicles. JD Power 2003 resultsBased upon buyers reports of problems during the first 90 days of ownership

http://www.jdpower.com/cc/auto/auto.jspTop Rated Trucks Compact: Mazda B-Series Full size: Ford F Series Entry SUV: Honda CR-V Midsize SUV: Toyota Highlander Fullsize SUV: Chevy Suburban Luxury SUV: Lexus RX300Compact van: Olds Silhouette


Sheet1


BearingMeter26

Ball13Battery


Sleeve23Mercury0.7


Clutch2Connector0.1


Differential15AC2

Fan6DC40


Gear0.2Lamp



Spring5Motor

Valve14Small HP8

Large4

Solenoid1

Switch6

Car CompanyDefects per 100Car BrandsDefects per 100

Toyota115Lexus76

Porsche117Cadillac103

BMW124Infiniti110

Honda126Acura111

Industry Ave133Buick112

GM134Mercury113

Nissan135Porsche117

Ford136BMW118

DaimelerChrysler139Toyota121

Volkswagen141Jaguar122

Hyundai143Honda1287

Suzuki144Volvo128

Subaru143Chevrolet130

Mitsubishi148Audi132

Kia168Mercedes-Benz132

Industry Ave133

Olds134

Chrylser136

Ford136

Dodge137

Lincoln139

Nissan139

Pontiac142

Hyundai143

Volkswagen143

GMC144

Suzuki146

Jeep146

Subaru148

Saturn158

Saab160

Mini166

Kia168

Land Rover190

Hummer225

Sheet2

Sheet3

Sheet1


BearingMeter26

Ball13Battery


Sleeve23Mercury0.7


Clutch2Connector0.1


Differential15AC2

Fan6DC40


Gear0.2Lamp



Spring5Motor

Valve14Small HP8

Large4

Solenoid1

Switch6

Car CompanyDefects per 100Car BrandsDefects per 100

Toyota115Lexus76

Porsche117Cadillac103

BMW124Infiniti110

Honda126Acura111

Industry Ave133Buick112

GM134Mercury113

Nissan135Porsche117

Ford136BMW118

DaimelerChrysler139Toyota121

Volkswagen141Jaguar122

Hyundai143Honda128

Suzuki144Volvo128

Subaru143Chevrolet130

Mitsubishi148Audi132

Kia168Mercedes-Benz132

Industry Ave133

Olds134

Chrylser136

Ford136

Dodge137

Lincoln139

Nissan139

Pontiac142

Hyundai143

Volkswagen143

GMC144

Suzuki146

Jeep146

Subaru148

Saturn158

Saab160

Mini166

Kia168

Land Rover190

Hummer225

Sheet2

Sheet3

PatentsPatent office http://www.uspto.gov/


Reglas de Diseño 2

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