Requirements of the Blank
Date: Mar,10 2020 View:
Requirements of the Blank
In the spinning, especially in the process of shear forming, the blank bears a lot of pressure from the spinning tool and core mold, then produces severe local deformation. Its surface and internal defects of the blank will be enlarged, causing the workpiece to be scrapped. In addition, the manufacturing accuracy of the blank, the heat treatment method, and the physical properties of the material will also affect the quality and economic effects of the spinning parts. Therefore, the requirements for spinning blanks are as follows:
1. Requirements for the inner and outer layers of the blank
(1) There must be no defects such as barriers, inclusions, cracks or looseness in the blank, otherwise the spinning parts are prone to defects such as fracture, internal cracks and micro-cracks. Therefore, for large blanks or blanks of spinning parts for important purposes, a flaw detection should be performed.
(2) The surface of the blank must not have mechanical damage such as scars, processing marks, scratches, and grooves, otherwise these defects and damage will be enlarged in the spinning deformation and even cause the spinning parts to crack. Some materials with sensitive surface defects (such as tungsten, Molybdenum alloys, ultra-high-strength steels, etc.) are particularly severe during processing.
The surface also requires smaller roughness (that is good smoothness), and generally has Ra12.5 to Ra3.2, otherwise the friction on the mold during spinning will be very serious.
Before spinning, the dirt and scales on the inner and outer surfaces of the blank should be removed and cleaned to avoid crushing the parts and contaminating the lubricant.
2.Requirements on blank dimensional accuracy
Since the deformation of the material during the spinning process is carried out by volume displacement, the uniformity of the wall thickness on any plane orthogonal to the axis of rotation is very important. For cylindrical parts, it is generally required that the deviation of the wall thickness of the blank is not greater than 0.1 to 0.2 mm. For conical parts and curved generatrix parts, the deviation of the flat blank and the preform blank will prevent the spinning process from strictly following the sine law. The side with too thick wall thickness will deviate too much from the sine law, which will cause the metal in front of the roller to easily accumulate, which will increase the tensile force of the deformed metal after the roller. The side with too thin wall will also deviate from the sine law, resulting in insufficient thinning, so that the metal fibers in the inner wall are subjected to high tensile stress, and cracks appear in the circumferential direction of the workpiece. Therefore, the wall thickness of the blank must be uniform, and designed and processed according to the requirements of sine rate reduction.
3. Requirements for the uniformity of the blank properties
The uneven metallographic structure and stress distribution of the blank will cause uneven deformation during spinning, which makes the spinning part bulge and break, and the material strength of different parts will also be different. In addition, the dimensional accuracy of the spinning parts will be reduced, and the accuracy such as roundness will also be reduced.
