Successful Formula for a Sheet Metal Punch and Die
Spectacular success is often achieved by implementing several small initiatives rather than a single major event. This principle applies to achieving success in a sheet metal punch and die. By doing many small things right, the punch and die manufacturers can put themselves on the road to higher productivity and profitability. Analyzing the punch and die that does the punching and examining the slugs that result could yield a continuous stream of benefits.
Punch and die Design
Punch and die design has four essential components: stripper, punch, die, and tool holder system. The success of sheet metal punch and die starts with the features built into these components by the punch and die manufacturer.
During the process of punching, the punch faces both compressive and tensile forces. The punch tip applies pressure as the punch contacts the surface of the sheet metal being punched until it overcomes the material’s tensile strength. And once the punch reaches the bottom of the stroke, it starts to retract from sheet metal. The upward punch movement and the workpiece scraping the punch flanks, apply significant tensile forces to the tip of the punch.
Successful punching depends on the design of the punch and die which can mitigate the effects of these unavoidable forces.
The stripper performs two important functions during the sheet metal punch and die process. The obvious one is to hold the sheet metal against the die as the punch approaches, penetrates, and retracts. The less obvious function is to grip the punch tip tightly in place as it punches the hole.
It is impossible to punch a hole successfully unless the punch and the die have a precise fit. Concentric and angular sheet metal punch and die alignment ensures that the punch can enter the die without making contact with it. Another consideration is the difference between dimensions of the punch and the die. It is called die clearance. Especially in tools with sharp corners such as squares and rectangles, uniform die clearance around the punch’s periphery is vital. The small radius in the corners of the die helps to maintain a uniform clearance.
The Toolholder System.
All toolholder systems guide the punch tip to the center of the die while holding the workpiece against the die’s top surface. Toolholding systems have precise internal and external features to provide orientation, concentric alignment, and angular alignment of the punch tip relative to the X, Y, and Z axes of the punch and die machine. Additionally, they have to provide reliable stripping at high speeds.
Guided and nonguided designs are two distinct tooling systems. A guided system is used to produce higher-quality parts with a greater interval between regrinds. Guided tool systems are designed to be more robust and the components last longer.
Optimizing the die clearance is the single most important contribution to the success of the punch and die process. When the die clearance is optimized, edge quality and tool life is improved and reduces cost per hit. Once you understand the punching process, achieving the correct die clearance is easy. Correct clearance aids in connecting the upper and lower fractures. This in effect frees the slug, releasing the punching force, and discharges the slug with minimum force and maximum efficiency.
One of the easiest ways to determining the efficiency of the punch and die operation is to look at the slugs. Since the slug is a mirror image of the hole, it helps you diagnose if the clearance is appropriate for the application. If the die and the machine is properly aligned, fracture plane and the burnished land are consistent around the slug. If you find that the burnished land is uneven, then it could mean that the tool is misaligned. A good slug could mean that the punch and die are operating at maximum efficiency. It also means that the interval between the regrinds is maximized and the cost of sheet metal punch and die is minimized.
Last but not least is to ensure simple maintenance is done at regular intervals. Proper punch and die maintenance include timely lubrication. According to the punch and die manufacturer’s recommendations, sharpening using grinding equipment designed for the job, and regular maintenance of the punch press ensures turret alignment.
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