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2.2 Progressive die configuration
The design configuration of a typical progressive die, as shown in Fig. 2, consists of two categories of parts. The first category is called the main parts, which include the upper die set, lower die set, die plate, punch plate, blank pressure plate, punch back plate, upper lifting, lower lifting, cam mechanism, blanking punch, bending punch, and dies required by each process station. The design of these parts totally depends on the specification of the progressive dies and the requirements of the clients. The second category is called the standard parts, such as the socket head cap screws, dowel pins, stripper blots, guide posts, and plain guide bushings. These standard parts are available from the market in different sizes.
Progressive dies for developing shells of mobile phones consist of the following basic process stations: piercing, blanking, drawing, bending, restriking, side punching, and cutting. These process stations should be positioned at equal distances based on the progressive pitch. We may also need to design a number of structural parts for each process station. Dowel pins are used to ensure that the strips stably move forward in the progressive die. Lifters are used to completely lift the products from the die faces in each process station. To improve spotting precision, a number
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of guide and position parts are used, including plain guide bushings and guide posts on the upper and lower die sets, respectively. When there is not enough space between adja-cent stations or there are some weak components, we need to add an idle station in between.
2.3 Designing the structural parts of progressive dies
Most progressive dies are one-off. Therefore, designers must consider both the technical requirements and the bud-get to offer an optimal die design to meet clients’ expecta-tions. Most die structures are very complex, and the design process of the progressive die consists of three stages: die design information, main parts design, and standard parts design.
Die design information is a minimum set of information required by the design system, including the strip layout with functional lines, sheet thickness, and progressive pitch.
& Strip layout with functional surface and lines: As shown in Fig. 3, strip layout with blanking line, die face, punch open line, piercing line, bending lines, side-punching line and cutting lines for blanking the raw material outline, drawing and restriking the shell shape, piercing the keyboard and screen holes, bending and side punching the earphone and charger holes, and cutting the shell outline
& Sheet thickness and progressive pitch: Sheet thickness is used to determine the clearance and tolerance of two matched parts for piercing, blanking, drawing, bending,
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Fig. 3 Strip layout with functional surface and lines for the outer shell of
restriking, side punching, and cutting processes. The progressive pitch is the distance to every stamping process.
The dimension of a progressive die is determined based on its strip layout with functional surface and lines, sheet thickness, and progressive pitch. Die design engineers are able to finish parts design once the dimension of the die is fixed.
In the main parts design stage, the main parts are deter-mined, including the shape and the dimension of the upper die set, lower die set, die plate, punch plate, blank pressure plate, punch back plate, upper lifting, lower lifting, cam mechanism, blanking punch, bending punch, and dies.