Practical Concerns for Extrusion Die Design

A large die entrance angle may result in a zone of static material (analogous to the dead-metal zone in metal extrusion) at the periphery of the die. Static material may be a source of defects and should be avoided (Ref 1, 2, 3, 4, 5, 6). For industrial extrusions, die entrance angles are usually less than 25° and the (L/D) ratios range from 2-to-1 to 4-to-1 (Ref 1, 2, 3, 4, 5, 6). The tooling must have a smooth finish and should be inspected for wear, as extrusion pressure will increase with increasing surface roughness of the die (Fig. 13). Finally, uniform cross sections are an important aspect of tool and part design. Nonuniform cross sections can cause flow-rate differentials that will affect the flow characteristics of the part during extrusion, as well as causing variations in the final product (e.g., flaws, density gradients, etc.). Therefore, parts with sharp edges should be avoided, and for tube production the spider should be designed with a "bullet point" at the die entrance (Ref 1, 2, 3, 4, 5, 6).

Fig. 13 Influence of die land surface roughness on extrusion pressure. Top, extrusion pressure versus extrudate velocity for a variety of die land surface roughness. Bottom, roughness profiles (all dimensions in millimeters; s, smooth die had an internal diameter of 6.38 mm). Extrusion of Al2O3 powder; binder is clay, starch, and water; Do = 25.4 mm, D = 6.35 mm, L = 25.4 mm. Source: Ref 6

Fig. 13 Influence of die land surface roughness on extrusion pressure. Top, extrusion pressure versus extrudate velocity for a variety of die land surface roughness. Bottom, roughness profiles (all dimensions in millimeters; s, smooth die had an internal diameter of 6.38 mm). Extrusion of Al2O3 powder; binder is clay, starch, and water; Do = 25.4 mm, D = 6.35 mm, L = 25.4 mm. Source: Ref 6

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