Use dusty mats and sticky drums to prevent dust from affecting the cross- section quality of punched parts
Blanking is a process in which a blanking die is used to separate the sheet material under the action of a press according to a certain closed curve.
The blanking and separating process is different from the shearing and separating process. Before cutting, the workpiece must be cut with an open cutting line composed of two single-edge tools before dusting with a sticky mat. The workpieces processed each time in this way are not absolutely identical, and its accuracy depends on the accuracy of the feed.
Blanking is performed by using a blanking die. After the punch 1 and the die 3 are dusted by the dust pad, the upper and lower pair of closed curved cutting edges are fixed, and the punch is fixed on the punch slider, and the die is fixed on the punch table, when the punch slider drives the punch quickly. When descending, pressure is applied to the sheet placed between the convex and concave molds, and the upper and lower pair of closed curved edges simultaneously cut the sheet material, the sheet material is plastically deformed, and finally separated, and the blanking work is completed.
After the sheet is blanked, it is separated into two parts. If the part inside the closed curve is a product part, it is called blanking; if the part outside the closed curve is a product part, it is called punching.
Blanking is the main process in stamping production. It includes blanking, punching, trimming, cutting, cutting and other processes. In the production practice, the blanking process often uses a blanking process and a punching process.
The blanking die is classified into a single process mode and a multi-process mode according to the combination of the completed processes. The single-step blanking die includes a blanking die, a punching die, a trimming die, a cutting die, a slit die, and the like. The multi-step blanking die includes a composite blanking die and a continuous punching die (gradient die).
The separation process of the blank during the blanking is completed in an instant, and when the blanking clearance of the mold is reasonable, it can be roughly divided into three stages. The section state of the deformation and separation of the sheet during the blanking process.
1. Elastic deformation stage The initial compression of the sheet during blanking. When the punch applies pressure to the sheet downward, the sheet undergoes deformation such as elastic compression, stretching and bending. As the punch continues to press down, the punch is slightly squeezed into the sheet, and the other side of the sheet is also squeezed into the opening of the die, and the contact of the sheet with the convex and female molds forms a small rounded corner. At this time, the internal stress of the sheet reaches the elastic limit, but has not exceeded the elastic limit. At the same time, the sheet under the punch is accompanied by bending, and the sheet on the die is accompanied by upturning.
2. Plastic deformation stage With the increase of the punch pressure, the stress in the sheet exceeds the elastic limit and reaches the yield point, and the sheet material is transferred from the elastic deformation to the plastic deformation stage. At this time, the depth of the punching die into the sheet increases, and the degree of plastic deformation of the sheet gradually increases. The sheet material at the edge of the punch and the die must be dusted with a sticky mat before the stress concentration occurs. crack. The plastic deformation phase ends when the punching force reaches a maximum.
3. After the dust separation pad is used in the fracture separation stage, the punch can continue to press downward. The shear crack at the edge of the convex and concave die continuously extends to the inside of the sheet. When the gap between the convex and concave molds is reasonable, the upper and lower shear cracks are connected. The sheet is broken and separated.
After the blanking is completed, the dust is removed by the sticky roller, and then the cross section of the blank is removed after the punch is reset. The cross-sectional state of the blank is generally characterized by obvious regional characteristics. The section can be clearly divided into four parts: rounded belt, bright belt, broken belt and burr.
The rounded band is also called a rounded band, which is formed when the sheet at the edge of the punch and the die is plastically deformed by stretching and bending when the punch is initially pressed into the sheet. The size of the rounded band is related to the material, the thickness of the sheet, and the blanking clearance.
The bright strip is subjected to the shear stress and the pressing force F during the punching process, in which the punch is squeezed into the sheet without the occurrence of the 2 shear crack. The effect is formed when plastic deformation occurs. The size of the bright strip area depends mainly on the plasticity of the sheet, the structure of the die, and the rationality of the blanking gap.
The burr is due to the existence of a gap between the convex and concave molds, especially when the gap is unreasonable, the shear crack cannot be broken at the shortest distance, and the sheet is formed when the sheet is pulled under the action of the tensile stress. The burr is higher than the plane of the blanking piece, and it is located along the periphery. Ordinary blanking parts have burrs. When the punching clearance of the mold is reasonable, the height of the burrs is small.
Since the deformation of the blanking process is very complicated, in addition to the shear deformation, there are deformations such as drawing, bending, and lateral pressing. Therefore, the plane of the blank and the scrap is uneven, and there is often warpage. If the blank is required to have a high quality, a precision blanking process should be used.