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https://academia.edu/103626052/INTRODUCTION_TO_MODERN_INDUSTRIAL_ENGINEERING_Version_3_0
Lesson 248 of IEKC Industrial Engineering ONLINE Course Notes.
Engineering in Industrial Engineering - Machine work study or machine effort improvement, value engineering and design for manufacturing and assembly are major engineering based IE methods. All are available as existing methods.
Product Design for Manufacture and Assembly, Third Edition
Geoffrey Boothroyd, Peter Dewhurst, Winston A. Knight
CRC Press, 08-Dec-2010 - Technology & Engineering - 712 pages
https://books.google.co.in/books/about/Product_Design_for_Manufacture_and_Assem.html?id=W2FDCcVPBcAC
Note: It is important to read the books by Boothroyd to understand the full method of DFMA. The DFMA method is to be combined with Value Analysis and Engineering to do product industrial engineering. In the note only attempt is made to make readers aware of issues raised and solutions proposed by DFMA method.
Related Chapters from the Book
3. Product Design for Manual Assembly
4. Electrical Connections and Wire Harness Assembly
5. Design for High-Speed Automatic Assembly and Robot Assembly
6. Printed Circuit Board Design for Manufacture and Assembly 219
Product Design for Manual Assembly
Design Guidelines for Part Handling In general, for ease of part handling, a designer should attempt to:
1 . Design parts that have end-to-end symmetry and rotational symmetry about the axis of insertion. If this cannot be achieved, try to design parts having the maximum possible symmetry.
2. Design parts that, in those instances where the part cannot be made symmetric, are obviously asymmetric.
3. Provide features that will prevent jamming of parts that tend to nest or stack when stored in bulk.
4. Avoid features that will allow tangling of parts when stored in bulk.
5. Avoid parts that stick together or are slippery, delicate, flexible, very small, or very large or that are hazardous to the handler (i.e., parts that are sharp, splinter easily, etc.) .
Design Guidelines for Insertion and Fastening
For ease of insertion a designer should attempt to:
1. Design so that there is little or no resistance to insertion and provide chamfers to guide insertion of two mating parts. Generous clearance should be provided, but care must be taken to avoid clearances that will result in a tendency for parts to jam or hang-up during insertion.
2. Standardize by using common parts, processes, and methods across all models and even across product lines to permit the use of higher volume processes that normally result in lower product cost.
3. Use pyramid assembly—provide for progressive assembly about one axis of reference. In general, it is best to assemble from above.
4. Avoid, where possible, the necessity for holding parts down to maintain their orientation during manipulation of the subassembly or during the placement of another part. If holding down is required, then try to design so that the part is secured as soon as possible after it has been inserted.
5. Design so that a part is located before it is released. A potential source of problems arises from a part being placed where, due to design constraints, it must be released before it is positively located in the assembly. Under these circumstances, reliance is placed on the trajectory of the part being sufficiently repeatable to locate it consistently.
6. When common mechanical fasteners are used the following sequence indicates the relative cost of different fastening processes, listed in order of increasing manual assembly cost.
a. Snap fitting b. Plastic bending c. Riveting d. Screw fastening
7. Avoid the need to reposition the partially completed assembly in the fixture.
Although functioning well as general rules to follow when design for assembly is carried out, guidelines are insufficient in themselves for a number of reasons.
First, guidelines provide no means by which to evaluate a design quantitatively for its ease of assembly. Second, there is no relative ranking of all the guidelines that can be used by the designer to indicate which guidelines result in the greatest improvements in handling, insertion, and fastening; there is no way to estimate the improvement due to the elimination of a part, or due to the redesign of a part for handling, etc. It is, then, impossible for the designer to know which guidelines to emphasize during the design of a product.
Finally, these guidelines are simply a set of rules that, when viewed as a whole, provide the designer with suitable background information to be used to develop a design that will be more easily assembled than a design developed without such a background. An approach must be used that provides the designer with an organized method that encourages the design of a product that is easy to assemble. The method must also provide an estimate of how much easier it is to assemble one design, with certain features, than to assemble another design with different features.
ASSEMBLY EFFICIENCY
DFA index or "assembly efficiency" of a proposed design can be determined. In general, the two main factors that influence the assembly cost of a product or subassembly are
The number of parts in a product.
The ease of handling, insertion, and fastening of the parts.
The DFA index is a figure obtained by dividing the theoretical minimum assembly time by the actual assembly time. The equation for calculating the DFA index
Em3
where N^ is the theoretical minimum number of parts, ta is the basic assembly time for one part, and fma is the estimated time to complete the assembly of the product. The basic assembly time is the average time for a part that presents no handling, insertion, or fastening difficulties (about 3 s).
The figure for the theoretical minimum number of parts represents an ideal situation where separate parts are combined into a single part unless, as each part is added to the assembly, one of the following criteria is met:
1. During the normal operating mode of the product, the part moves relative to all other parts already assembled. (Small motions do not qualify if they can be obtained through the use of elastic hinges.)
2. The part must be of a different material than, or must be isolated from, all other parts assembled (for insulation, electrical isolation, vibration damping, etc.).
3. The part must be separate from all other assembled parts; otherwise the assembly of parts meeting one of the preceding criteria would be prevented. It should be pointed out that these criteria are to be applied without taking into account general design or service requirements.
For example, separate fasteners will not generally meet any of the preceding criteria and should always be considered for elimination. To be more specific, the designer considering the design of an automobile engine may feel that the bolts holding the cylinder head onto the engine block are necessary separate parts. However, they could be eliminated by combining the cylinder head with the block—an approach that has proved practical in certain circumstances. If applied properly, these criteria require the designer to consider means whereby the product can be simplified, and it is through this process that enormous improvements in assemblability and manufacturing costs are often achieved. To quantify the costs due to the effects of changes in design schemes, the DFA method incorporates a system for estimating assembly cost which, together with estimates of parts cost, will give the designer the information needed to make appropriate trade-off decisions.
SUMMARY OF DESIGN RULES FOR HIGH-SPEED AUTOMATIC ASSEMBLY
The various points made in the discussion of parts and product design for automatic assembly are summarized below in the form of simple rules for the designer.
Rules for Product Design
1. Minimize the number of parts.
2. Ensure that the product has a suitable base part on which to build the assembly.
3. Ensure that the base part has features that enable it to be readily located in a stable position in the horizontal plane.
4. If possible, design the product so that it can be built up in layers, each part being assembled from above and positively located so that there is no tendency for it to move under the action of horizontal forces during the machine index period.
5. Try to facilitate assembly by providing chamfers or tapers that help to guide and position the parts in the correct position.
6. Avoid expensive and time-consuming fastening operations, such as screw fastening, soldering, and so on.
Rules for the Design of Parts
1. Avoid projections, holes, or slots that cause tangling with identical parts when placed in bulk in the feeder. This may be achieved by arranging the holes or slots to be smaller than the projections.
2. Attempt to make the parts symmetrical to avoid the need for extra orienting devices and the corresponding loss in feeder efficiency.
3. If symmetry cannot be achieved, exaggerate asymmetrical features to facilitate orienting or, alternatively, provide corresponding asymmetrical features that can be used to orient the parts.
Designing Medical Devices For Manufacturability: A Complete Guide
https://www.europlaz.co.uk/medical-device-design-a-complete-guide/
Design for Manufacture and Assembly (DfMA) in Building Design
https://www.designingbuildings.co.uk/wiki/Design_for_Manufacture_and_Assembly_(DfMA)
Application
AN OVER-VIEW OF THE APPLICATIONS OF DFA (DESIGN FOR ASSEMBLY) TECHNIQUES ON AUTOMOBILE COMPONENTS FOR REDUCING ASSEMBLY
TIME AND COST
Shrey Arvind Jaiswal, Darius Gnanaraj S.
https://iopscience.iop.org/article/10.1088/1757-899X/1123/1/012003/pdf
Assembly Automation and Product Design - Geoffrey Boothroyd
CRC Press, 22-Jun-2005 - Science - 536 pages
Addressing design for automated and manual assembly processes, Assembly Automation and Product Design, Second Edition examines assembly automation in parallel with product design. The author enumerates the components, processes, performance, and comparative economics of several types of automatic assembly systems. He provides information on equipment
https://books.google.co.in/books?id=1uTLBQAAQBAJ
Design for Manual Assembly - DragonInnovation.com - Part 1
Design for Manufacturing Course 11
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https://www.youtube.com/watch?v=sheZ6bffiWU
https://pdfslide.net/technology/design-for-manufacturing-class-11-design-for-manual-assembly-part-2-boothroyd-dewhurst-method.html
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DFA Product Simplification 10 Basics
2 Jul 2013
Boothroyd Dewhurst, Inc.
An overview of the basics of the latest version of Design for Assembly
www.DFMA.com
https://www.youtube.com/watch?v=E7_afjJTAok
Design for Assembly Questions - Part 1 - Prof. Christoph Roser
https://www.allaboutlean.com/dfma-4/
Design for Assembly Questions - Part 2 - Prof. Christoph Roser
https://www.allaboutlean.com/dfma-5/
Design for Assembly Questions - Part 3 - Prof. Christoph Roser
https://www.allaboutlean.com/dfma-6/
Ud. 12.9.2022
Pub. 30.1.2021
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