1. Design for Assembly DFA

2. Goals of DFA Simplify product and assembly to –Save money –Improve quality –Improve reliability

3. Product Design for Manufacture and Assembly Boothroyd, Dewhurst, and Knight

4. Product Design for Manufacture and Assembly Boothroyd, Dewhurst, and Knight

5. Formal Techniques Boothroyd-Dewhurst http://www.dfma.com/ http://www.dfma.com/ Lucas http://www.teamset.com/design-for-assembly-2.html http://www.teamset.com/design-for-assembly-2.html Hitachi AEM

6. Boothroyd-Dewhurst First: Three main questions to see if parts are essential –Does the part move relative to other parts? –Must the part be a different material or isolated from other parts? –Must the part be separate to allow assembly?

7. Boothroyd-Dewhurst Examine the handling and insertion of each part and rate factors such as –Assembly time –Assembly cost

8. Lucas Method Point scale which gives relative measures of assembly difficulty in the form of –Design efficiency –Feeding/handling ratio –Fitting ratio

9. Cummins

10. General Electric

11. Bralla

21. When possible, avoid using countersunk screws for fastening (a). Any lateral (e.g. center-distance) or angular misalignment stresses the screw and changes Its height relative to the part surface. Square-shouldered heads located in oversize counterbores (b) are preferable. Stock Drive Products http://www.sdp-si.com/D220/D220cat.htm#T35

22. Bralla

24. The axial position of the bushing relative to the housing is overdetermined in (a). A one diameter hole, (b), eliminates this drawback. Stock Drive Products http://www.sdp-si.com/D220/D220cat.htm#T35 Avoiding Overspecification Of Dimensions Of Mating Parts

25. Stock Drive Products http://www.sdp-si.com/D220/D220cat.htm#T35

26. The design of the hinge (a) involves several interdependent dimensions with fairly close tolerances. In design (b) the lower hinge is axially floating and in design (c) the width of the middle (rolled) portion of the righthand member has been eliminated. In designs (b) and (C) the operation of the hinge remains reasonably efficient, but the need for close tolerances has been reduced. Stock Drive Products http://www.sdp-si.com/D220/D220cat.htm#T35

27. Product Design for Manufacture and Assembly Boothroyd, Dewhurst, and Knight

28. Long shafts and bushings are easier to assemble with a two- diameter construction. In such cases avoid having to match counterbore depth with the length of the reduced-diameter portion of the shaft (a). The depth of the counterbore should be slightly less than the length of the reduced-diameter portion of the shaft. Stock Drive Products http://www.sdp-si.com/D220/D220cat.htm#T35

29. The same principle applies in the assembly of a hollow shaft and bushing. In (a) the mating shaft lengths have to match and this requires close tolerances. In design (b) the length of the reduced- diameter section of the male shaft has been slightly reduced, thereby eliminating the need for close tolerances. Stock Drive Products http://www.sdp-si.com/D220/D220cat.htm#T35

30. Design For Accessibility In an assembly in which the bolt head is not readily accessible (a), an access hole for a wrench Is provided in design (b) or-better still-the bolt can be replaced by readily assembled threaded pins (c). Similarly a nut and bolt (a) should be located for easy accessibility as in (b) for tubular or Allen wrenches (the latter for a hexagonal socket head). Stock Drive Products http://www.sdp-si.com/D220/D220cat.htm#T35

31. Product Design for Manufacture and Assembly Boothroyd, Dewhurst, and Knight

32. Design For Ease Of Disassembly. When using dowel pins for alignment, avoid blind holes (a). The addition of a small-diameter exit hole (b) permits Introducing a punch for extracting the dowel pin. Better still, if possible, use a one- diameter bore (c); and if one part is too long for easy extraction, increase the diameter of the clearance hole (d), which does not require close tolerances. Stock Drive Products http://www.sdp-si.com/D220/D220cat.htm#T35

33. For the clamping of a housing with a nut and bolt, the thread on the reduced-diameter portion of the bolt should extend into the housing as in (b), so that the width of the housing does not have to match the length of the unthreaded portion of the bolt, as an (a). Design (b) avoid the possibility of the nut tightening against the bolt, rather than the housing. Stock Drive Products http://www.sdp-si.com/D220/D220cat.htm#T35

34. Allowing For Thermal Expansion To allow for the thermal expansion of a rotating shaft and avoid possible binding (a), it is preferable to mount the ball bearings In lapped holes (b) with one bearing held In postion by a split retaining ring and the other bearing allowed to float axially in the smooth machined bore. In the case of collars which control the axial positions of a shaft (a), it Is preferable to install the collars at one end of the shaft only, thereby allowing for thermal expansion (b). Stock Drive Products http://www.sdp-si.com/D220/D220cat.htm#T35

35. Product Design for Manufacture and Assembly Boothroyd, Dewhurst, and Knight