Punches manufacturing tolerances

Any clearance between the die wall and the punch affects the tableting behavior, as entrapped air will escape through the gap when pressure is applied. Fig. 9 presents the terminology. Table 1 summarizes manufacturing tolerances of punches and dies as well as the clearance between them. 

In the outsert technology, functional components out of thermoplastic polymers are injected into pre-punched holes of a metal blank. Therefore, the blank is inserted and fixed between the two halves of the injection mold. Sealing elements made from highly heat-resistant plastics (Figure 1.76) for example PEEK can help to compensate for the considerable manufacturing tolerances of metal parts [1, 3,15, and 32). 

The amount of clearance (space) between interacting parts like punch/die and barrel/turret guide, depends on the tolerance range (deviation from theoretical dimensions due to practical manufacturing reasons) of tooling dimensions. The clearance between the die wall and the punch tip affects the tableting process as well as the mechanical properties of the finished product while the powder is compressed, air needs to be released, and when the compressed tablet is moved upwards within the die bore, friction on the die walls is affected by the clearance. 

Tolerances for the surface finish of tooling are also specified by manufacturers and in international standards, see Fig. 23. Any roughness of the finishing is below 1 pm peak-to-valley height, and particularly punch-tip faces and die bore walls are polished to achieve lower tolerances. 

There is bound to be some variability in tablet weight during manufacture due to variation in the particle size of the material being compacted, flow property variation and machine parameters (e.g., small differences in the lengths of the lower punches). To allow for such variability, Pharmacopoeias set tolerances to ensure adequate control without providing a specification that is impossible to achieve in production. The European Pharmacopoeia (EP) test... 

Table 11.9. Standard Tolerance Guide for Punched Holes and Slots in High-Pressure Laminated Grades of Sheet Stock, Rods, and Tubes, as Classified by the National Electrical Manufacturers Association (NEMA)...

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