Bending - Metal sheet metal undergoes elastic deformation under the pressure of the upper or lower molds of the bending machine, and then enters plastic deformation. At the beginning of plastic bending, the sheet metal is free to bend. As the upper or lower molds apply pressure to the sheet metal, the inner surface of the V-shaped groove between the sheet metal and the lower mold gradually becomes closer, while the curvature radius and bending force arm also gradually decrease. Continue to apply pressure until the stroke ends, so that the upper and lower molds are in full contact with the sheet metal at three points. At this point, a V-shaped bending, commonly known as bending, is completed. This standard specifies the noise limits for the sound power level and sound pressure level of bending machinery. This standard is applicable to bending machinery, including various types of sheet metal bending machines and edge bending machines. 2 Normative References: The clauses in the following documents become clauses of this standard through reference in this standard. For dated reference documents, all subsequent amendments (excluding corrected content) or revisions are not applicable to this standard. However, parties to agreements based on this standard are encouraged to study whether the latest versions of these documents can be used. For undated references, the latest version applies to this standard. GB/T 23281-2009 Measurement Method for Sound Pressure Level of Forging Machinery Noise GB/T 23282-2009 Measurement Method for Sound Power Level of Forging Machinery Noise 3 Noise Limits The noise of bending machinery is divided into sound power level and sound pressure level requirements, and the noise limit requirements are given according to the type of bending machinery