Design for assembly

PP is a tough and resilient plastic and many types of mechanical fastening techniques, (Section 7.2), can be easily used. However, PP is prone to creep and screws used under high stress for assembly may slack due to creep. In these cases, metal inserts should be preferred since they increase the load-bearing area in PP. Metal inserts may be moulded in or pressed in after injection moulding. However, the stress concentration effect on the impact strength due to sharp-edged inserts should be carefully considered. 

Moulded-in internal or external threads can be used with PP. The design of threads is important to avoid the possibility of thread jumping. Thread jumping may occur if high torque is applied to the screw. If this happens, the moulded thread is still usually unharmed and can still be used. Acme or buttress type threads can be used to decrease the possibility of thread jiunping. 

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An overview of eaeh of the main eommereial methods ean be found in Huang (1996), but in general, a number of design for assembly guidelines ean be highlighted (Leaney, 1996b) ... 

Fitting analysis. For this to be possible, an assembly sequence plan must be constructed and the difficulty of assembling each part in the sequence rated using the design for assembly analysis tables. Difficult assembly tasks and non-value added processes are revealed as candidates for correction by redesign. Simple concepts such as the ability to assemble in a layer fashion can result in major cost savings. 

Barnes, C. J., Dalgleish, G., Jared, G., Swift, K. G. and Tate, S. 1997 Assembly Sequence Structures in Design for Assembly. In Proceedings IEEE International Symposium on Assembly and Task Planning, Marina del Rey, California, 164-169. 

CSC Manufacturing 1995 Design for Assembly j Manufacturing Analysis Practitioners Manual, Version 10.5. Solihull CSC Manufacturing. 

CaC03 calcium carbonate (lime) DFA design for assembly... 

Mine Clearing Equipment. Devices used to actuate land mines without damage to personnel or equipment. Expl devices are typified by a group of linear shaped prefabricated structural sections, filled with composition expls, with a nose section and a towing and pushing attachment, designed for assembly into a device to be propelled by any standard tank. 

The primary structure of dendrotoxin-I is shown in Scheme 1. A design for assembling the segments in the synthesis of dendrotoxin-I is shown in Scheme 2JS1... 

The three essential technologies for assembly engineering explained in this section are product design for assembly, simultaneous engineering, and automation of connecting techniques. 

Various points concerning parts and product design for assembly are summarized below. 

In addition to the assembly design rules, a variety of methods have been developed to analyze component tolerance for assembly and design for assembly by particular assembly equipment. 

The suitability of a product design for assembly influences its assembly cost and quality. Generally, product engineers attempt to reduce the assembly process cost based on plans drawn by designers. The recent trend has been toward product assemblability from the early design phase in order to respond to the need for reduction in time and production costs. 

Design for assembly (DFA) usually results in simpler fixture design. Simple vertical stacking of parts, for example, generally allows minimal fixtures. 

A typical manufacturing analysis includes the investigation of design for assembly and service, in which the question is asked whether the task can be performed. Can the person reach into the opening while holding the part and assemble the pieces Can the object be reached by short and tall workers Is there sufficient clearance for the part and the hands Can the worker have an unobstructed view of the assembly so that it can be performed accurately Will the worker have sufficient strength to perform the assembly task, or wUl it require potentially injurious exertions ... 

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