The primary source of noise during the stamping process is the impact between the punch and the workpiece, or between the stripper plate and the blank. This includes both the punching and shearing actions, which are known to generate significant noise levels. The squealing sound produced by the press is influenced by several factors, such as the thickness, hardness, geometry of the material, the speed of the hammering, and the die clearance. As these parameters increase, so does the noise level.
When a punch press is in operation, the collision between the punch and the sheet metal, along with the interaction between the stripper plate and the blank, becomes more intense. As the speed of impact increases, so does the resulting noise. This impact noise can be measured separately from the sound generated when the material fractures. This measurement method has been successfully implemented in industrial settings. For instance, punching thick and hard materials tends to produce more noise compared to thin and soft materials. In the case of thick ductile sheets, the impact noise is comparable in magnitude to the fracture sound.
Figure 1 illustrates the effect of impact velocity on sound levels. The noise generated during punching and shearing varies significantly depending on the process. Sheet blanking typically produces more noise than bending or deep drawing, while other forming processes like embossing, pressure wave, flanging, bending, and deep drawing tend to generate less noise.
To better understand the noise generation in blanking, we can take punching as an example. The blanking process generally involves three stages: elastic deformation, plastic deformation, and fracture separation. As the punch makes contact with the sheet metal, the punching force begins to rise. At the same time, elastic energy is stored due to the deformation of the body and other structural components. The punching force reaches its peak when the punch has penetrated approximately half the thickness of the sheet.
The sudden rupture of the punch plate causes the punch to lose its load abruptly. The accumulated elastic energy within the structure is released rapidly, causing vibrations in the body and its components, leading to mechanical shocks. Additionally, the high-speed movement of the slider creates air pressure distortions around it, contributing to the overall noise.
Moreover, if the spacing between punches—whether left-right or front-back—is smaller than the manufacturer’s specifications, the noise level will increase. A densely packed setup in the press can also lead to a significant rise in noise. It is important that the space in the press room is not too cramped. If the truss is located below 4 meters, this can result in increased noise levels, reverberation, and overall acoustic discomfort.
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