Punch tooling is often made of hardened steel or tungsten carbide. A die is located on the opposite side of the workpiece and supports the material around the perimeter of the hole and helps to localize the shearing forces for a cleaner edge. There is a small amount of clearance between the punch and the die to prevent the punch from sticking in the die and so less force is needed to make the hole. Nowadays a wide range of coatings are used to enhance its wear resistance and reduce galling so as to extend tool life. We began this article with a brief look at the most common punch and die treatments in the market. These may include:
- Diamond Coating
The idea here is to introduce properties of diamond to a punch and die system. Such tools are suitable for effervescent tablets. Diamond coated tools are generally abrasive resistant and durable. They don’t stick and their hardness is nearly 6 times more than the ordinary tablet presses.
- Galvanic Chrome Treatment
This tablet press tooling is suitable for most standard tablet press applications. In most cases, the coating is about 5 microns. The coating is one of the most popular types of treatment in most pharmaceutical industries. Another technique that is almost similar to the galvanic chrome treatment is the physical vapor deposition (PVD). Well, this procedure protects the tooling system of a tablet compression machine from wear and ensures better stability.
- Chrome Nitride Coating
The final surface of the tablet press tooling is better than the galvanic treatment. It has a high quality to price ratio with enhanced wear protection. Besides sticking, this coating is also useful in corrosion resistance.
This treatment is known for its smooth finish and higher surface hardness. Therefore, it is a perfect choice for most pharmaceutical tablet compression applications.
What’s more, numerous special materials and coatings has been developed to enhance both compression efficiency as well as extend tool life.
- Tungsten CarbideFor highly corrosive powder or granules, tungsten carbide die inserts are provided because tungsten is an extremely hard material which improves the life of the tooling by 3 to 5 times compared to a standard tooling material.
- Hard Chrome PlatingThis helps attain corrosion resistance due to some products or environment that has comparatively higher levels of humidity and this also helps in lubricity or in other words non-sticking of the fine granular powder on the punch surface.
- Bakelite ReliefIn this case an undercut is applied to the lower punch tip providing a deeper and sharper relief which helps in removal of granules adhered to the die wall. It is essential to remove the granules setting inside the die wall which otherwise might jam the lower punch inside the die bore.
Die punch is fundamental in ensuring maximum and efficient productivity of the tablet press machine. Therefore, selecting good material that combine extremely high wear resistance and compressive strength is critical.