The main cause of operational noise in stamping machines is the impact between the punch and the workpiece, or between the stripper plate and the blank, as well as torsional and punching actions during the stamping process. The noise generated during the punching and shearing processes of a punch press can be quite significant.
Squealing noises often occur due to factors such as the thickness, hardness, geometry, striking speed, and die clearance of the stamped parts. As these values increase, so does the noise level. During the punching process, 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 impact speed increases, so does the noise level. This relationship has been studied and measured, and it's clear that punching thicker and harder materials results in higher noise levels compared to thinner and softer ones. For thick, ductile sheets, the impact noise is comparable in intensity to the sound of material fracture.
Figure 1 illustrates how impact velocity affects sound levels. Different stages of the stamping process generate varying types of noise. For example, blanking typically produces more noise than bending or deep drawing. In forming processes like embossing, pressure wave creation, flanging, bending, and deep drawing, the noise levels are generally lower.
To better understand the noise generation in blanking, let's take the punching process as an example. The blanking process can be divided into three main stages: elastic deformation, plastic deformation, and fracture separation. As the punch contacts the sheet metal, the punching force begins to rise. Elastic energy is stored as the material deforms. The punching force reaches its peak when the punch has penetrated about half the thickness of the sheet.
When the punch suddenly ruptures the sheet, the load on the punch is released abruptly. The accumulated elastic energy in the machine structure is then released in a very short time, causing vibrations and shocks between different components. Additionally, the high-speed movement of the slider disturbs the surrounding air, creating pressure waves that radiate as noise.
Other factors also contribute to increased noise levels. If the spacing between punches—whether left-right or front-back—is less than the factory specifications, the noise will increase. Similarly, if the installation density of the press is too high, noise levels will rise significantly. It's important to ensure adequate space in the press room to minimize noise buildup. Presses installed below 4 meters may lead to increased noise and reverberation, further contributing to a noisier environment.
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