DFM | Production
Figure 1: Mould modifi cations were required to successfully implement the unscrewing mechanism for this externally- threaded component
high, so it is important that they provide: Full automatic operation; High operational speeds; High volume capability. Achieving these performance criteria may require the addition of features on the component geometry that facilitates orientation of the parts and maintains them in the correct position for assembly or specifi c in-line testing procedures. Where moulded components have been stored in
dive in and unscrew the part from the cavity without causing any damage to it. When considering post
processes such as plating, painting, printing and the like it is very important to consider requirements for secure retention in the necessary jigs or handling equipment. Figure 2 shows a typical feature that allows a part to be clamped onto a painting jig without causing any damage to the visual surfaces and so that the whole of the surface that has to be painted can be covered in one pass. In this example it is also a gating feature, which will be cut off after painting. Considering this during early DFM allowed it to be included in the fi nal tooling / gating solution and enabled the manufacturer to run the fi nal painting process without any problems and at a high yield. Similarly, it is important to think about assembly line
requirements. Both automatic and manual assembly lines will have their own specifi c requirements when it comes to control and positioning of the components that are assembled in the fi nal product. Automatic lines are most often used where production volumes are
62 INJECTION WORLD | November/December 2013
Figure 2: This gating feature is also used to handle the part during painting
bulk boxes or bags, bowl feeders will typically be used to automatically orientate parts and to present them correctly to the assembly line. Vibratory action is used to move the components through the device and specifi c design features on the part are employed to spin or rotate it at a number of stations to align it correctly before it enters the assembly line. These design features may not have any purpose in the functionality of the product but need to be reviewed with automation and handling specialists at an early stage to ensure they will not negatively impact assembly, quality or function. Opting for a manual assembly method does not relieve the DFM team of the need to consider part features. In fact, it can be even more critical that features are incorporated that prevent parts being assembled incorrectly. The human factor is most often the most critical infl uence when it comes down to consistency and variances on the yield of an assembly line. Any feature in the component design that helps to make it ‘idiot- proof’ can pay off in revenue terms. A recent project undertaken by AST
involved the redesign of a part that was causing a production reject rate of
42% because an inner sub-assembly could be put together the wrong way around and could subsequently jam in service. It was established that this assembly mistake most often happened during the night shift. Adding just a simple, decentered guiding feature to the sub-assembly eliminated the problem immediately.
About the author: André Eichhorn is general manager of Germany-based AST Technology. This is the latest instalment in a series of articles in which he discusses how product manufactur- ing problems can be overcome at the start of a project by the application of Design for Manufacturing techniques. You can read the most recent articles in this series here, here and here.
www.injectionworld.com
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