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Lesson 249 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.
Must have book for Industrial Engineers. Do you have it?
Product Design for Manufacture and Assembly (To Improve Productivity and Reduce Costs), 3rd Edition
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.
Fundamentals of Metal Machining and Machine Tools
Winston A. Knight, Geoffrey Boothroyd
CRC Press, 08-Aug-2019 - Technology & Engineering - 602 pages
In the more than 15 years since the second edition of Fundamentals of Machining and Machine Tools was published, the industry has seen many changes. Students must keep up with developments in analytical modeling of machining processes, modern cutting tool materials, and how these changes affect the economics of machining. With coverage reflecting s
STANDARDIZATION
The first rule in designing for machining is to design using standard components as much as possible. Many small components, such as nuts, washers, bolts, screws, seals, bearings, gears, and sprockets, are manufactured for standard specifications in large quantities and should be employed wherever possible. The cost of these components will be much less than the cost of similar, nonstandard components. The designers need catalogues of the standard items available provided by various suppliers. Supplier information is provided in standard trade indexes, where companies are listed under products.
However, opportunities for creating economies by custom designs cannot be ignored. Many of the impressive successes brought about by the application of DFMA procedures were only made possible by breaking away from standardization. Taken to extremes, a slavish adherence to company "standards" will prevent innovation in design.
A second rule is to minimize the amount of machining by preshaping the workpiece. Workpieces can sometimes be preshaped by using castings or welded assemblies or by metal deformation processes, such as extrusion, deep drawing, blanking, or forging. Obviously, the justification for preforming of workpieces will depend on the required production quantity. But using castings is very popular. Other alternatives available are also to be kept in mind in designing parts.
Choice of Work Material
When choosing the material for a component, the designers must consider applicability, cost, availability, machinability, and the amount of machining required. The optimum choice will generally be a compromise between conflicting requirements.
SHAPE OF WORK MATERIAL
The choice of the shape of the work material (not custom made) depends mainly on availability in the market. Metals are generally sold in plate, sheet, bar, or tube form in a wide range of standard sizes.The designer should check on the standard shapes and sizes from the supplier of raw material and then design components that require minimal machining.
Even if standard components or standard preformed workpieces are not available, the designer should attempt to standardize on the machined features to be incorporated in the design. Standardizing on machined features means that the appropriate tools, jigs, and fixtures will be available, which can reduce manufacturing costs considerably. Examples of standardized machined features might include drilled holes, screw threads, keyways, seatings for bearings, splines, etc. Information on standard features can be found in various reference books.
Some undesirable features on rotational components.
1. Features impossible to machine.
2. Features extremely difficult to machine that require the use of special tools or fixtures.
3. Features expensive to machine even though standard tools can be used.
In considering the features of a particular design it should be realized that
1. Surfaces to be machined must be accessible when the workpiece is gripped in the work-holding device.
2. When the surface of workpiece is being machined, the tool and tool-holding device must not interfere with the remaining surfaces on the workpiece.
Regarding Tolerances
As a guide to the difficulty of machining to within required tolerances it can be stated that
Tolerances from 0.127 to 0.25mm (0.005 to 0.01 in.) are readily obtained.
Tolerances from 0.025 to 0.05mm (0.001 to 0.002 in.) are slightly more difficult to obtain and will increase production costs.
Tolerances 0.0127mm (0.0005 in.) or smaller require good equipment and skilled operators and add significantly to production costs.
SUMMARY OF DESIGN GUIDELINES
A summary of the main points a designer should keep in mind when considering the design of machined components.
Standardization
1. Utilize standard components as much as possible.
2. Preshape the workpiece, if appropriate, by casting, forging, welding, etc.
3. Utilize standard pre-shaped workpieces, if possible.
4. Employ standard machined features wherever possible.
Raw Materials
5. Choose raw materials that will result in minimum component cost (including cost of production and cost of raw material).
6. Utilize raw materials in the standard forms supplied.
Component Design
a. General
7. Try to design the component so that it can be machined on one machine tool only.
8. Try to design the component so that machining is not needed on the unexposed surfaces of the workpiece when the component is gripped in the work-holding device.
9. Avoid machined features the company is not equipped to handle.
10. Design the component so that the workpiece, when gripped in the work-holding device, is sufficiently rigid to withstand the machining forces.
11. Verify that when features are to be machined, the tool, toolholder, work, and work-holding device will not interfere with one another.
12. Ensure that auxiliary holes or main bores are cylindrical and have L/D ratios that make it possible to machine them with standard drills or boring tools.
13. Ensure that auxiliary holes are parallel or normal to the workpiece axis or reference surface and related by a drilling pattern.
14. Ensure that the ends of blind holes are conical and that in a tapped blind hole the thread does not continue to the bottom of the hole.
15. Avoid bent holes or dogleg holes. b. Rotational Components
16. Try to ensure that cylindrical surfaces are concentric, and plane surfaces are normal to the component axis.
17. Try to ensure that the diameters of external features increase from the exposed face of the workpiece.
18. Try to ensure that the diameters of internal features decrease from the exposed face of the workpiece.
19. For internal corners on the component, specify radii equal to the radius of a standard rounded tool corner.
20. Avoid internal features for long components.
21. Avoid components with very large or very small L/D ratios.
c. Nonrotational Components
22. Provide a base for work holding and reference.
23. If possible, ensure that the exposed surfaces of the component consist of a series of mutually perpendicular plane surfaces parallel to and normal to the base.
24. Ensure that internal corners normal to the base have a radius equal to a standard tool radius. Also ensure that for machined pockets, the internal corners normal to the base have as large a radius as possible.
25. If possible, restrict plane-surface machining (slots, grooves, etc.) to one surface of the component
26. Avoid cylindrical bores in long components.
27. Avoid machined surfaces on long components by using work material preformed to the cross section required.
28. Avoid extremely long or extremely thin components.
29. Ensure that in flat or cubic components, main bores are normal to the base and consist of cylindrical surfaces decreasing in diameter from the exposed face of the workpiece.
30. Avoid blind bores in large cubic components.
31. Avoid internal machined features in cubic boxlike components.
Assembly
32. Ensure that assembly is possible.
33. Ensure that each operating machined surface on a component has a corresponding machined surface on the mating component.
34. Ensure that internal corners do not interfere with a corresponding external corner on the mating component.
Accuracy and Surface Finish
35. Specify the widest tolerances and roughest surface that will give the required performance for operating surfaces.
36. Ensure that surfaces to be finish-ground are raised and never intersect to form internal corners.
Pub 1 Dec 2021
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