Heavy-tonnage presses shape a wide range of metals in the metal stamping process. This can cause burrs, which are rough or raised areas on the surface of the part, or rough or sharp edges. Usually, the burr allowance for metal stampings is set at 5% of the thickness of the material. But more complicated parts may need a more complex stamping process or a method used after stamping to get rid of the burrs. The stamping parts supplier can advise on how to design the part to meet the necessary specifications and the expected burr, how it will affect the tolerances of the part and the best way to remove it if required.
What Causes One Side of a Stamped Part to Have a Burr?
The following things cause stamping parts to have a single-side burr:
• Die assembly error. If the punch is not perpendicular to the fixed plate or is worn out and loose, or if the locating pin is loose, the punch and die cannot be fixed in the right place.
• The guidance isn’t excellent. Because the die guide parts have too much fit clearance, the centre lines of the upper and lower dies don’t line up. This makes the stamping gap less uniform.
• Installation error. During the installation of a non-guide die, the upper and lower die supplied by the stamping parts supplier cannot be moved. This makes the gap between the dies uneven. The surface of the mould or the bottom plate isn’t clean, or the screw on the upper die isn’t tightened enough, which could cause the working part to tilt.
• When the die works, it changes shape. The punching mattress board has a leaking hole that is too large, the die’s lower template is too thin, and the female die’s rigidity is insufficient, to name a few.
• The space between the punch press’s guide rails is too big, and the bottom surface of the slide block and the working table don’t line up nicely. Or the slide block doesn’t move in a straight line with the working table.
• Since the “C” shaped bed is easily deformed for the open punch, the centre lines of the upper and lower dies do not align when the maximum resistance of the workpiece is greater than 80% of the nominal pressure of the punch press.
• When metal is stamped, the punch with the smaller diameter is tilted because sheet metal isn’t very flat.
• Die deformation during heat treatment or WEDM occurs if the material, heat treatment are not performed properly.
Conclusion
Having as few processes as possible is the most cost-effective way to work. So, whenever possible, you should go to a stamping parts supplier who can make clean parts that don’t have burrs. But it’s not possible with some materials and thicknesses. The burr is, of course, only on one side of the fabric. If it’s on the “inside” of your parts, for example, tell the producer which side is the “inside.”