During the stamping process of zinc alloy commemorative coins, edge burrs are primarily caused by factors such as improper die clearance, blade wear, material fluidity variations, and uncontrolled process parameters. To effectively reduce burrs, comprehensive measures must be taken from four perspectives: die design, material selection, process optimization, and post-processing.
Die clearance is the key factor affecting burr formation on zinc alloy commemorative coins. If the clearance is too large, the zinc alloy material will tear due to excessive stretching during the punching process, resulting in thick, irregular burrs. If the clearance is too small, friction between the blade and the material will increase, triggering secondary shearing and producing fine but sharp burrs. Therefore, the clearance value must be precisely calculated based on the fluidity of the zinc alloy and the thickness of the commemorative coins, typically maintaining a value between 8% and 12% of the material thickness. For example, for zinc alloy commemorative coins with a thickness of 2mm, the die clearance should be set within the range of 0.16-0.24mm, and trial die adjustments should be performed to ensure uniform clearance between the upper and lower dies.
The condition of the blade directly impacts the punching quality of zinc alloy commemorative coins. When a die's cutting edge wears, its sharpness decreases, causing the material to tear rather than shear, resulting in filamentous or granular burrs. Therefore, the cutting edge radius should be regularly inspected. If the radius exceeds 0.05mm, it should be immediately repaired with a diamond file or a dedicated blunting tool. The choice of die material is also crucial. Hard working parts (such as the punch) must be made of tool steel and hardened to HRC60 or above to maintain long-lasting cutting edge sharpness. Zinc-based alloys can be used for the die, extending die life by automatically compensating for wear. However, care should be taken to control the depth of the collapse angle. If the collapse angle exceeds 0.5mm, it requires prompt repair.
The material properties of zinc alloys significantly affect burr formation. Materials with poor ductility, such as cast aluminum or high-carbon steel, tend to tear rather than shear during blanking, resulting in filamentous burrs. Therefore, it is important to select zinc alloys with good fluidity and moderate ductility, and to control the sheet thickness tolerance (e.g., within ±0.05mm) to reduce the risk of gap failure. Furthermore, surface defects such as rust or oxide layers can increase blanking resistance, increasing burr height by 20%-30%. Therefore, the sheet metal must be cleaned and surface treated before blanking.
Optimizing process parameters is key to reducing burrs on zinc alloy commemorative coins. Excessive punching speeds can lead to unstable flow of the zinc alloy material, causing tearing; insufficient pressing force can cause the material to wrinkle and tear, resulting in crescent-shaped burrs. Therefore, the punching speed should be adjusted according to the material type. For example, for aluminum, the punching speed should be controlled within 120 strokes/minute, and the pressing force should be ensured to exceed 30% of the material's tensile strength. Positioning errors are also a major cause of burr formation. Worn positioning pins or height deviations exceeding 0.1mm can cause offset blanking, resulting in localized gap abnormalities. Therefore, regular inspection of the positioning system and replacement of worn parts are necessary.
Post-processing is equally important for improving the edge quality of zinc alloy commemorative coins. For existing burrs, electrolytic deburring can be used. This process utilizes electrolysis to remove hidden areas or complex shapes. It offers high production efficiency and takes only a few to tens of seconds. Magnetic grinding is also an effective method. Using a magnetic field, a stainless steel needle acts as an abrasive, rotating and rubbing against the workpiece at a high frequency. This method is particularly suitable for removing burrs from small crevices such as the inner holes and corners of commemorative coins.
Reducing edge burrs in the stamping process of zinc alloy commemorative coins requires a coordinated approach involving die design, material selection, process optimization, and post-processing. By precisely controlling die clearance, maintaining cutting edge sharpness, selecting the appropriate zinc alloy material, optimizing process parameters, and employing efficient post-processing methods, burr generation can be significantly reduced, improving the edge quality and yield rate of commemorative coins.
