Design for Manufacturing and Assembly

Transcription

1 Design for Manufacturing and Assembly

2 Design for Assembly Is a technique which can be used in many stages of product design and development such as product teardown, reverse engineering, improvement of product concept. Benefits of DFM SIMPLIFY the design of product Reduce the number of parts, and the cost of parts Reduce the time of manufacturing and assembly Increase quality and reliability of product

3 DFM Process

4 Manufacturing cost estimation In estimating manufacturing cost per unit of product, there are 3 cost categories Cost of parts Cost of assembly Overhead cost

5 Accuracy of manufacturing cost estimation Level 1 estimation relies on experience of expert engineer Takes less than 10 minutes for a system with 50 parts, and is within 20 % accuracy Level 2 estimation list the costs explicitly by relying on experience from similar product, expert experience, and vendor information Takes approx. 1 day for a system with 50 parts, and is within 5 % accuracy

6 Level 3 estimation Cost accounting cost calculation of every part Use database of material cost estimation and motion/ time study Take approx. 1 week for product with 50 parts and is within 1 % accuracy

7 How to reduce the cost of parts Understand manufacturing process capability Redesign the parts to eliminate manufacturing steps Choose production size suitable with manufacturing process

8 How to reduce the cost of assembly Even though assembly cost contributes only a small part of total manufacturing cost, assembly cost reduction is beneficial because of several indirect effects: Number of parts is reduced Process complexity is reduced Cost of manufacturing support is reduced A technique for reducing cost of assembly is design for assembly (DFA)

9 Design for Assembly System design Design for ease of handling Design for ease of insertion Design for fastening Design for manufacturing processes

10 System design MODULARITY - a module is a self-contained component that is equipped with standard interfaces that allow it to be integrated into a larger system (ก) (ข) (ค) Modules form building blocks that can be used interchangeably in different products. Design for modularity has several benefits: Easy to reassemble Easy to detect quality problems

11 Another way to achieve system design for assembly simple design, and eliminate unnecessary parts Steel support bracket Left: one-part product (simple, easy to manufacture) Right: several part product (joined by spot welding)

12 (a) Original design (b) Redesigned housing unit The redesigned part facilitates product assembly, as well as the servicing of the units.

13 A common electric outlet box.

14 13 parts, including screws, and must be assembled by tedious hand methods.

15 A one-piece plastic electric box is injection molded with the nails in place, and requires no assembly.

16 Criteria for analyzing unnecessary parts Boothroyd and Dewhurst (1994) suggests that unnecessary parts are those that answer No to the following questions: Does the part move relative to other parts in normal operating condition of product? Is it necessary that the part is made of different materials or isolated from other parts such as electrical insulation, heat insulation, or vibration reduction? Does the part have to be isolated from other parts otherwise it is impossible to assemble the products? If the answer is no, the part is unnecessary and can be integrated with other parts.

17 Another approach for system design reduce variability of parts

18 Handling Guidelines Maximize part symmetry (ก) Provide orienting features on non-symmetries (ข) Prevent nesting of parts Eliminate tangly parts Avoid sharp ends (ค) (ง) (จ) Provide orienting features ย ดหย นได on non-symmetries (ฉ)

19 Parts made symmetrical for easier orientation From Stoll (1999)

20 Adding external features (such as chamfers, slots, and flats) to facilitate orientation From Stoll ( 1999)

21 Provide orienting features on non-symmetries From Priest (2001)

22 Provide orienting features for label From Priest (2001)

23 Shingling or overlapping can be avoided by providing thicker contact edges, or vertical, or highly angled surfaces. (Stoll, 1999)

24 Insertion Guidelines (ก) Minimize resistance Provide chamfer (ข) Design parts that locks into place ต ดข ด ไม ต ดข ด ไม ต ดข ด Insert new parts into assembly (ค) from above (z axis) ย ดอย ก บท ได เอง (ง)

25 (a) top-down Z axis assembly (b) avoid multi-motion insertion (c) design assemblies as layered stacks with components positively located (d) provide alignment features for guiding components (Stoll, 1999)

26 Process in the open (Boothroyd, Dewhurst, and Knight, 1994)

27 Design features that facilitate inserting and mounting of components (Stoll, 1999)

28 Top-down assembly Note - Bottom of computer case is used as a conveyor pallet assembly fixture and support for parts. (From Priest, 2001)

29 Fastening guidelines Minimize the number of fasteners

30 Minimize the number of fasteners

31 Assembly Efficiency Assembly Efficiency (E ma ), DFA index E ma = N min t a / t ma N min = the theoretical minimum number of parts t a = 3 sec (average time used to assemble one part which is not difficult to handle, insert, or fasten together) t ma = approximate time to assemble the total number of parts into a product

32 Conclusion DFM is a technique which is aimed at reducing manufacturing cost by decreasing the number of parts in the design To do DFM, it is necessary to estimate manufacturing cost. DFA is part of DFM, invented by Boothroyd, Dewhurst and Knight. It is aimed at facilitating part assembly.

33 Eco-efficiency Reduction of raw material Reduction of energy usage Reduction of emission Increase of recyclability Increase of sustainable use of renewable resources Increase product durability Increase the useful functions of product and service

34 Regional and local environmental problems Acid rain Air pollution (smog) Water pollution

35 GLOBAL environmental problems 1. Biodiversity loss 2. Ozone depletion 3. Climate change

36 Design for Environment (DFE) is an umbrella term describing techniques used to incorporate an environmental component into products and services before they enter the production phase. DFE seeks to discover product innovations that will meet cost and performance objectives while reducing pollution and waste throughout the life-cycle.

37 DFE Techniques 1. Techniques that are used to identify the environmental impact of a product throughout its life cycle such as lifecycle assessment. 2. Techniques that help designers improve the environmental performance of their products. Design for recycling Design for disassembly Design for remanufacture Hazardous material minimization Design for finishing and labeling Design for energy efficiency Design for disposability

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39 DFE in System Design Design multifunctional products Aim for minimum number of parts Avoid the use of spring, cable, pulley Use modular design

40 Design for recycling Reduce material variability Reduce the use of high impact materials Use recycled materials Design for easy access of highest value materials Identify all materials in the product

41 Design for disassembly Design parts so that they are secure during disassembly. Avoid the use of metal inserts in plastic parts Other guidelines are similar to DFMA.

42 Fastening guidelines Minimize the number of fasteners Minimize the use of fastener-removing tools. Provide easy access to fasteners.

43 Fastening (ต อ) Use fasteners which are made of materials compatible with the parts. Avoid the use of adhesives unless compatible with the parts. Minimize the use of cables.

44 Design for remanufacturing/reuse Identify the parts which can be remanufactured. Identify the packages which can be remanufactured. Other guidelines are similar to design for disassembly

45 Hazardous material minimization Avoid the use of materials in the controlled lists Identify materials on all parts

46 Energy efficiency guidelines Specify best-in-class energy efficiency component Have subsystems power down when not in use Permit users to turn off systems in part or whole Make parts whose movement is powered as light as possible Insulate heated systems Avoid nonrechargable battery