Design for Manufacturing

1. Design for Manufacturing Chapter 11 EIN 6392, Product Design Summer 2012

2. Product Design and DevelopmentKarl T. Ulrich and Steven D. Eppinger4nd edition, Irwin McGraw-Hill, 2000. Chapter Table of Contents 1. Introduction 2. Development Processes and Organizations 3. Product Planning 4. Identifying Customer Needs 5. Product Specifications 6. Concept Generation 7. Concept Selection 8. Concept Testing 9. Product Architecture 10. Industrial Design 11. Design for Manufacturing 12. Prototyping 13. Product Development Economics 14. Managing Projects

3. Product Development Process Concept Development System-Level Design Detail Design Testing and Refinement Production Ramp-Up Planning How can we emphasize manufacturing issues throughout the development process?

4. Outline • DFX concept • DFM objectives • DFM method • Mfg. cost estimation • DFM impacts • DFM examples

5. Understanding Manufacturing Costs

6. Definition • Design 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.

7. Three Methods to Implement DFM • Organization: • Organize cross-functional teams • Design Rules: • Exercise best practices specialized by the firm • CAD Tools: • Apply CAD systems such as the Boothroyd-Dewhurst DFA software

8. Introduction • DFM is part of DFX • DFM often requires a cross-function team • DFM is performed through the development process

9. Major DFM objectives • Reduce component costs • Reduce assembly cost • Reduce production support costs

10. The DFM Process (5 steps) • Estimate the mfg. costs • Reduce the costs of components • Reduce the costs of assembly • Reduce the costs of supporting production • Consider the impact of DFM decisions on other factors.

11. Estimate mfg. costs • Cost categories • Component vs. assembly vs. overhead • Fixed vs. variable • Material vs. labor • Estimate costs for standard parts • Compare to similar part in use • Get a quote from vendors • Estimate costs of custom made parts • Consider material costs, labor costs, and tooling costs • Depend on the production volume as well • Estimate costs of assembly • Summing up all assembly operations (time by rate) • Estimate the overhead costs • A % of the cost drives

12. Reduce the costs of components • Identify process constraints and cost drivers • Redesign components to eliminate processing steps • Choose the appropriate economic scale for the part process • Standardize components and their processes • Adhere the black-box component

13. Reduce the costs of assembly • Integrate parts (using the Boothroyd method) • Maximize ease of assembly • Consider customer assembly (do-it-yourself) technology driven products

14. Reduce the costs of supporting production • Minimize 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)

15. Considering impacts • Development time • Development cost • Product quality • External factors such as • component reuse and • life cycle costs

16. Design for Manufacturing Example:1993 GM 3800cc V6 Engine Design

17. DFM example • Exhibit 11-15 on Page 230 • Unit cost saving of 45% • Mass saving of 66% (33 Kg.) • Simplified assembly and service procedures. • Improved emissions performance • Improved engine performance • Reduce shipping costs (due to lighter components) • Increased standardization across vehicle programs.

18. Cost Appendices • Materials costs • Exhibit 11-17 on page 235 • Component mfg. costs • Exhibits 11-18/21 on pages 236-239 • Assembly costs • Page 242 for common products • Page 243 for part handling and insertion times

24. Design for X – Design principles • Part shape strategies: • adhere to specific process design guidelines • if 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.

25. Design for X – Design principles • Standardization strategy • use standard parts • standardize design features • minimize the number of part types • minimize 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.

26. Design for X – Design principles • Assembly strategies 1 • design 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 tools • make parts independently replaceable. • order assembly so the most reliable goes in first; the most likely to fail last.

27. Design for X – Design principles • Assembly strategies 2 • make sure options can be added easily • ensure 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.

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

29. Design for X – Design principles • Fastening strategies 2 • avoid 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.

30. Design for X – Design principles • Assembly motion strategies • fastened 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.

31. Design for X – Design principles • Automation handling strategies 1 • design and select parts that can be oriented by automation • design parts to easily maintain orientation • use 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.

32. Design for X – Design principles • Automation handling strategies 2 • make 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.

33. Design for X – Design principles • Quality and test strategies • product can be tested to ensure desired quality • sub-assemblies are structured to allow sub-assembly testing • testing can be performed by standard test instruments • test 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.

34. Design for X – Design principles • DF Maintenance strategies 1 • provide ability for tests to diagnose problems • make sure the most likely repair tasks are easy to perform. • ensure repair tasks use the fewest tools. • use quick disconnect features • ensure that failure or wear prone parts are easy to replace with disposable replacements • provide inexpensive spare parts in the product. • ensure availability of spare parts.

35. Design for X – Design principles • Maintenance strategies 2 • use 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

36. Design for X – Design principles • Maintenance strategies 3 • protect parts with fuses and overloads • ensure 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.

37. Design for X – Design principles • Maintenance strategies 4 • make 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 products • design products with self-test capability. • design products with test ports • design in counters and timers to aid preventative maintenance. • specify key measurements for preventative maintenance programs • include warning devices to indicate failures.

38. Design for X – Design principles • Axomatic design • Axiom 1 • In good design, the independence of functional requirements is maintained. • Axiom 2 • Among the designs that satisfy axiom 1, the best design is the one that has the minimum information content.

39. Design for X – Design principles • Axiomatic design- corollaries • Decouple 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.

40. Design for X – Design principles • DFA 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.

41. Design for X – Design principles • Three criteria • Is there a need for relative motion? • Is there a need for different materials • Is there a need for maintenance?

42. 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.

43. Design for Assembly • Key ideas of DFA: • Minimize parts count • Maximize the ease of handling parts • Maximize the ease of inserting parts • Benefits of DFA • Lower labor costs • Other indirect benefits • Popular software developed by Boothroyd and Dewhurst. • http://www.dfma.com

44. To Compute Assembly Time Handling Time + Insertion Time Assembly Time

45. Method for Part Integration • Ask 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.

46. Videocassette DFM Exercise • 2 billion worldwide annual volume • 7 major producers of 1/2” cassette shells • JVC licenses the VHS standard • dimensions, interfaces, light path, etc • VHS cassette shells cost ~$0.25 each • What is a $0.01 cost reduction worth?

47. DFM Strategy is Contingent Corporate Strategy Product Strategy Production Strategy DFM Strategy