Design for Manufacturing

Design for ManufacturingChapter 11EIN 6392, Product DesignSummer 2012

**Product Design and DevelopmentKarl T. Ulrich and Steven D. Eppinger4nd edition, Irwin McGraw-Hill, 2000.Chapter Table of Contents 1.Introduction2.Development Processes and Organizations3. Product Planning4.Identifying Customer Needs5.Product Specifications6.Concept Generation7.Concept Selection8. Concept Testing9.Product Architecture10. Industrial Design11.Design for Manufacturing12.Prototyping13.Product Development Economics 14.Managing Projects

**PlanningProduct Development ProcessConceptDevelopmentSystem-LevelDesignDetailDesignTesting andRefinementProductionRamp-UpHow can we emphasize manufacturing issues throughout the development process?

**OutlineDFX conceptDFM objectivesDFM methodMfg. cost estimationDFM impactsDFM examples

**Understanding Manufacturing Costs

**DefinitionDesign for manufacturing (DFM) is a development practice which emphasizes manufacturing issues throughout the product development process.Successful DFM results in lower production cost without sacrificing product quality.

**Three Methods to Implement DFMOrganization: Organize cross-functional teams Design Rules: Exercise best practices specialized by the firmCAD Tools: Apply CAD systems such as the Boothroyd-Dewhurst DFA software

**IntroductionDFM is part of DFXDFM often requires a cross-function teamDFM is performed through the development process

**Major DFM objectivesReduce component costsReduce assembly costReduce production support costs

**The DFM Process (5 steps)Estimate the mfg. costsReduce the costs of componentsReduce the costs of assemblyReduce the costs of supporting productionConsider the impact of DFM decisions on other factors.

**Estimate mfg. costsCost categoriesComponent vs. assembly vs. overheadFixed vs. variableMaterial vs. labor Estimate costs for standard partsCompare to similar part in useGet a quote from vendorsEstimate costs of custom made partsConsider material costs, labor costs, and tooling costsDepend on the production volume as wellEstimate costs of assembly Summing up all assembly operations (time by rate)Estimate the overhead costsA % of the cost drives

**Reduce the costs of componentsIdentify process constraints and cost driversRedesign components to eliminate processing stepsChoose the appropriate economic scale for the part processStandardize components and their processesAdhere the black-box component

**Reduce the costs of assemblyIntegrate parts (using the Boothroyd method)Maximize ease of assemblyConsider customer assembly (do-it-yourself) technology driven products

**Reduce the costs of supporting productionMinimize systematic complexity (such as plastic injection modeling for one step of making a complex product)Error proofing (anticipate possible failure modes in the production system and take appropriate corrective actions early in the development process)

**Considering impactsDevelopment timeDevelopment costProduct qualityExternal factors such as component reuse and life cycle costs

**Design for Manufacturing Example:1993 GM 3800cc V6 Engine Design

**DFM exampleExhibit 11-15 on Page 230Unit cost saving of 45%Mass saving of 66% (33 Kg.)Simplified assembly and service procedures.Improved emissions performanceImproved engine performanceReduce shipping costs (due to lighter components)Increased standardization across vehicle programs.

**Cost AppendicesMaterials costsExhibit 11-17 on page 235Component mfg. costsExhibits 11-18/21 on pages 236-239 Assembly costsPage 242 for common productsPage 243 for part handling and insertion times

**Design for X Design principlesPart shape strategies:adhere to specific process design guidelinesif part symmetry is not possible, make parts very asymmetrical design "paired" parts instead of right and left hand parts.design parts with symmetry.use chamfers and tapers to help parts engage.provide registration and fixturing locations.avoid overuse of tolerances.

**Design for X Design principlesStandardization strategyuse standard partsstandardize design featuresminimize the number of part typesminimize number of total parts.standardize on types and length of linear materials and code them.consider pre-finished material (pre-painted, pre-plated, embossed, anodized).combine parts and functions into a single part.

**Design for X Design principlesAssembly strategies 1design product so that the subsequent parts can be added to a foundation part.design foundation part so that it has features that allow it to be quickly and accurately positioned.Design product so parts are assembled from above or from the minimum number of directions.provide unobstructed access for parts and toolsmake parts independently replaceable.order assembly so the most reliable goes in first; the most likely to fail last.

**Design for X Design principlesAssembly strategies 2make sure options can be added easilyensure the product's life can be extended with future upgrades.use sub-assemblies, especially if processes are different from the main assembly.purchase sub-assemblies which are assembled and tested.

**Design for X Design principlesFastening strategies 1use the minimum number of total fastenersuse fewer large fasteners rather than many small fastenersuse the minimum number of types of fastenersmake sure screws should have the correct geometry so that auto-feed screwdrivers can be used.design screw assembly for downward motionminimize use of separate nuts (use threaded holes).consider captive fasteners when applicable (including captive nuts if threaded holes are not available).

**Design for X Design principlesFastening strategies 2avoid separate washers and lockwashers (make it be captivated on the bolt or nut so it can still spin with respect to the fastener)use self-tapping screws when applicable.eliminate fasteners by combining parts.minimize use of fasteners with snap-together features.consider fasteners that push or snap on.specify proper tolerances for press fits.

**Design for X Design principlesAssembly motion strategiesfastened parts are located before fastener is applied.assembly motions are simple.Assembly motions can be done with one hand or robot.assembly motions should not require skill or judgment.products should not need any mechanical or electrical adjustments unless required for customer use.minimize electrical cables; plug electrical sub-assemblies directly together.minimize the number of types of cable.

**Design for X Design principlesAutomation handling strategies 1design and select parts that can be oriented by automationdesign parts to easily maintain orientationuse parts that will not tangle when handled in bulk.use parts what will not shingle when fed end to end (avoid disks).use parts that not adhere to each other or the track.specify tolerances tight enough for automatic handling.avoid flexible parts which are hard for automation to handle.

**Design for X Design principlesAutomation handling strategies 2make sure parts can be presented to automation.make sure parts can be gripped by automation.parts are within machine gripper span.parts are within automation load capacity.parting lines, spruces, gating or any flash do not interfere with gripping.

**Design for X Design principlesQuality and test strategiesproduct can be tested to ensure desired qualitysub-assemblies are structured to allow sub-assembly testingtesting can be performed by standard test instrumentstest instruments have adequate access.minimize the test effort spent on product testing consistent with quality goals.tests should give adequate diagnostics to minimize repair time.

**Design for X Design principlesDF Maintenance strategies 1provide ability for tests to diagnose problemsmake sure the most likely repair tasks are easy to perform.ensure repair tasks use the fewest tools.use quick disconnect featuresensure that failure or wear prone parts are easy to replace with disposable replacementsprovide inexpensive spare parts in the product.ensure availability of spare parts.

**Design for X Design principlesMaintenance strategies 2use modular design to allow replacement of modules.ensure modules can be tested, diagnosed, and adjusted while in the product.sensitive adjustment should be protested from accidental change.the product should be protected from repair damage.provide part removal aids for speed and damage prevention.protect parts with fuses and overloads

**Design for X Design principlesMaintenance strategies 3protect parts with fuses and overloadsensure any sub-assembly can be accessed through one door or panel.access over which are not removable should be self-supporting in the open position.connections to sub-assemblies should be accessible and easy to disconnect.make sure repair, service or maintenance tasks pose no safety hazards.make sure sub-assembly orientation is obvious or clearly marked.

**Design for X Design principlesMaintenance strategies 4make sure sub-assembly orientation is obvious or clearly marked.provide means to locate sub-assembly before fastening.design products for minimum maintenance.design self-correction capabilities into productsdesign products with self-test capability.design products with test portsdesign in counters and timers to aid preventative maintenance.specify key measurements for preventative maintenance programsinclude warning devices to indicate failures.

**Design for X Design principlesAxomatic designAxiom 1In good design, the independence of functional requirements is maintained. Axiom 2Among the designs that satisfy axiom 1, the best design is the one that has the minimum information content.

**Design for X Design principlesAxiomatic design- corollariesDecouple or separate parts of a solution if functional requirements are coupled or become coupled in the design of products and processes.Integrate functional requirements into a single physical part or solution if they can be independently satisfied in the proposed solution.Integrate functional requirements and constraints.Use standardized or interchangeable parts whenever possible.Make use of symmetry to reduce the information content.Conserve materials and energy.A part should be a continuum if energy conduction is important.

**Design for X Design principlesDFA Method: Boothroyd and Dewhurst Apply a set of criteria to each part to determine whether, theoretically, it should be separated from all the other parts in the assembly. Estimate the handling and assembly costs for each part using the appropriate assembly process - manual, robotic, or high-speed automatic.

**Design for X Design principlesThree criteriaIs there a need for relative motion?Is there a need for different materialsIs there a need for maintenance?

**Design for Assembly RulesExample set of DFA guidelines from a computer manufacturer.1.Minimize parts count.2.Encourage modular assembly.3.Stack assemblies.4.Eliminate adjustments.5.Eliminate cables.6.Use self-fastening parts.7.Use self-locating parts.8.Eliminate reorientation.9.Facilitate parts handling.10.Specify standard parts.

**Design for AssemblyKey ideas of DFA:Minimize parts countMaximize the ease of handling partsMaximize the ease of inserting partsBenefits of DFALower labor costsOther indirect benefitsPopular software developed by Boothroyd and Dewhurst.http://www.dfma.com

**To Compute Assembly TimeHandling Time+ Insertion TimeAssembly Time

**Method for Part IntegrationAsk of each part in a candidate design:1.Does the part need to move relative to the rest of the device?2.Does it need to be of a different material because of fundamental physical properties?3.Does it need to be separated from the rest of the device to allow for assembly, access, or repair?If not, combine the part with another part in the device.

**Videocassette DFM Exercise2 billion worldwide annual volume7 major producers of 1/2 cassette shellsJVC licenses the VHS standard dimensions, interfaces, light path, etcVHS cassette shells cost ~$0.25 eachWhat is a $0.01 cost reduction worth?

**DFM Strategy is ContingentCorporateStrategyProductionStrategyProductStrategyDFMStrategy

*****