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specifications, while global parameters are determined by both the design specifications and any relevant local param-eters. Taking the socket head cap screws shown in Fig. 6 as an example, the diameter (M) and pitch (P) of the screws are global parameters, while the other measures, such as V, X, W, L and l, are local parameters.
4.4 Skeleton mechanism construction
Once the parameters have been identified, a feature layer tree of the functional features for the main part of the progressive die is developed based on the design process, as shown in Fig. 10. Since various features of a progressive die can share a common functionality, all possible feature structures of a function must be pre-constructed when constructing the skeleton mechanism. When constructing a solid skeleton model of a die, only the selected functional features should be activated. All unselected functional fea-tures should be deactivated.
1896 Int J Adv Manuf Technol (2013) 68:1887–1899
When constructing skeleton mechanisms, design engineers should use all available preset sizes and constraints. All the dimensions are treated as parameters, whose values can be changed based on the design requirements. Since the values of the dimension parameters cannot be null or negative, every circumstance should be considered to avoid any potential problems, especially when there are cause-and-effect relation-ships among the various features. The number of constraints directly affects design flexibility. In most cases, the utilization of constraints can decrease the number of parameters and simplify the programming work. Therefore, an appropriate use of constraints is vital to the entire design process.
4.5 Programming
Programming aims to find all the relationships for each parameter that have been set up properly based on the input design information for such design as well as conforming to the design guidelines, design specifications, design process-es, and geometric operations. Then, the built-in modulus of the CATIA is used to convert the parameter relationship into a related program.
To facilitate the design process, programs are pided into three levels. Taking the cam mechanisms as an example, the
purpose of the first level is to select the main parts based on the design guidelines. This level of program takes advantage of two built-in modules of CATIA V5—Rule Editor and Formula Editor—to convert design guidelines into con-straints and formulas, which are used to determine the type, quantity, position, direction, and size of the main parts, as shown in Fig. 11a, b. The second level of the program is responsible for calculating the shape of the die. This level takes advantage of the built-in modules of CATIA V5 to construct the design table of the die based on the design specifications of each main part, so this level of program can use the design table to determine related independent and dependent parameters, as shown in Fig. 11c. The third level of the program is used to construct the model. Written by VB, this level of program is used to provide a modeling procedure of the main parts based on the type, quantity, position, direction, and dimension of the aforementioned two levels, as shown in Fig. 11d.
4Once the skeleton mechanisms of the progressive dies have been programmed, the standard parts need to be assembled into main parts. The progressive die contains a large number
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Fig. 12 Assembly design process of progressive dies
of standard parts, so it is necessary to plan a systematic process for the assembly design of the overall standard parts. Therefore, the assembly design operation could not only develop the procedural logic for the CAD system but also prevent mistakes in the assembly design.
To standardize the assembly design process, first, it is nec-essary to collect information related to various assembly design processes for progressive dies and then analyze all standard parts for each progressive die. It is also necessary to consider the design guidelines and specifications of the main parts. Then, it is possible to develop a flowchart for the assembly design process of a progressive die, as shown in Fig. 12.