Die Design

This involves several steps like deciding number of stages (draws), finding intermediate shapes, die layout and finally the design of die elements. Important steps are explained as follows.

Deciding Number of Draws

This is an important decision taken by the CAPP system based on sheet metal type, sheet thickness, punch/Die clearance and radii and the type of drawing.

The CAPP system has a Knowledge Base which stores this knowledge in the form of Decision Tables and Inference Rules. To ensure that a cup can be drawn smoothly without failure, suitable drawing rate needs to be chosen based on the LDR-Limiting Draw Rate.

Table  shows the decision table data showing relationship between sheet thickness range and the LDR for mild steel full cup deep drawing for different stages in drawing.

           Table: Determination of Limit Drawing Rate for Full Cup Drawing

CAPP system contains many such Decision Tables in knowledge base to cater to various materials, drawing conditions and cup geometrics (simple cup, flanged cup, etc.)

Punch/Die Clearances

Clearance between Punch and Die determines the severity of draw, i.e. ironing or no ironing. Various rules and data based on experience/shop practices are stored into the CAPP system to design clearance between Punch and Die.

Where  t = sheet thickness,

D = Blank Diameter, and

d = Punch Diameter.

Punch/Die Profile Radii

The sizes of punch and die radii govern occurrence of fracture and wrinkling of part. Its selection is again based on the Decision Tables stored in Knowledge Base of the CAPP system.

Design/Selection of Punch/Die

CAPP system selects standard punch/die elements from the database based on some thumb rules stop practices. CAD models of Punch/Die elements are retrieved and the Die drawings and BOM are created.