Fundamentals of punch tool

Turrets hold a variety of tools and index to bring different punch tools into the workzone of the machine.

Each punch tool has a corresponding die that is located under the machine tool's worktable. The size and shape of the hole created in the sheet metal is determined by the geometry of the punch. Clearance between the punch and die is adjusted to reflect the material thickness.

When the punch press is actuated, a ram descends, causing the punch to knock out the material creating a slug. The die is designed to allow the slug to fall through. The stripper holds the sheet metal in place until the punch is fully withdrawn from the sheet.

Most sheet metal punch tools used in shops today are self-stripping. Instead of using the ram to push the punch through the material and pull it out, these tools are built with an internal spring that automatically retracts the punch. The ram then only needs to work in one direction. This saves cycle time and wear on the turret punch press.

Most of the more recent improvements in CNC punching technology have been focused around the need to improve productivity. While much effort has been directed to making the machines go faster, thereby reducing cycle time, additional consideration has been directed to looking at time savings across the entire sheet metal fabrication process.

These innovations have been demanded by job shops, and original equipment manufacturers are responding to their customers' demands for shorter order turn around, tighter tolerance specifications and delivery that coordinates with just-in-time inventory control systems.

Moreover, advancements in the simplification of sheet metal manufacturing, with the use of CNC and user friendly programming systems, has helped shops respond to the shortage of qualified workers. Many of the skills traditionally required to set up and operate punch presses are being incorporated in software and hardware that is designed to simplify the operation.

In the area of setup, tooling innovations have provided significant throughput improvements for fab shops by reducing the complexity of setting tools. Simplified punch length control is a technical improvement in tooling design that has had an impact on punch tool setup.

Part of the setup procedure for turret punch press tooling involves setting the stroke of the punch. This is especially critical when installing a punch that has been re-sharpened.

Grinding the punch removes metal and therefore affects overall length of the punch. To compensate, shims were used in the punch guide assembly to bring the tool back to its optimum length. That process obviously is time consuming.

Current tool design has made compensating the punch a much simpler job. These new tools use a push button adjusting system. Fine increments of 0.0001 inch eliminate the need for shims and make the tool setup consistent and fast.

In the stripper plate, rather than requiring screws or other fasteners to hold it in the guide, a push button locking system is used to secure the plate in the guide assembly. This system eliminates the need for installation tools, and together with shimless adjustment, can reduce setup by 15 minutes per tool. For a 30-tool capacity machine, that's significant.