Stamping parts are the basic components of the body skeleton, and their quality directly affects the quality of the entire vehicle. Stamping production is a batch and continuous production method. In order to ensure the continuous and stable production of qualified stamping parts, in addition to designing and manufacturing high-quality molds, appropriate positioning structures must also be selected. This article explains the principles and applicable ranges of several special positioning methods for stamping automotive parts in molds.
In the production process of automotive exterior parts, the sheet metal needs to go through multiple processes such as drawing, trimming, punching, flanging, and shaping. Each process requires positioning of the sheet metal or workpiece to determine the positioning benchmark of the stamping parts.
Since different processes use different raw materials (sheet metal, workpieces), the positioning methods also vary. The drawing process generally uses the edge of the sheet metal as the positioning benchmark and uses a positioning plate for positioning; the trimming and punching process generally uses the forming surface and the edge of the workpiece as the positioning benchmark, and uses the forming surface and positioning plate of the mold for positioning; the flanging and shaping process generally uses the positioning hole and forming surface on the stamping part as the positioning benchmark, and uses positioning pins for positioning.
The following are several special positioning methods for stamping parts in molds: weight-type positioning, supplement-type positioning, and pneumatic positioning.
Some stamping automotive parts of automobiles have a convex or Λ-shaped forming surface. Therefore, in the production process, there is a large height difference between the highest point of the sheet metal placed on the mold and the edge of the sheet metal. Under the action of gravity, the sheet metal and the forming surface of the mold are in close contact.
However, when the sheet metal is shifted, causing the positioning to fail, it will cause missing material, wrinkling, or cracking of the stamped part, affecting the quality of the stamped part and even damaging the mold.
To solve the above problem and ensure that the sheet metal is in the required position during the production process, a weight-type positioning method is selected to position the sheet metal.
The weight block can balance the weight of the sheet metal during the forming process and keep the sheet metal level during positioning.
The upper mold presses the sheet metal surface while the lower mold applies pressure from below, causing the sheet metal to deform, ensuring that the sheet metal is controllable during the deformation process, and placing the sheet metal in an accurate position during the stamping process, eliminating the problem of poor quality of the auto stamping parts caused by sheet metal deviation.
The use of holes and forming surfaces for positioning of the workpiece can improve the positioning accuracy of the workpiece, but not all automotive exterior parts have holes on the forming surface that can be used as the positioning benchmark during stamping production. For example, the engine hood outer panel and the car door outer panel have no holes, and the forming surface structure is smooth. If only the forming surface and trimming positioning of the workpiece are used during the production process, it will reduce the positioning accuracy of the stamped part and cannot guarantee the forming quality of the stamped part.
In this case, a supplement-type positioning can be selected. That is, two holes are punched in the stamping process area of the stamped part as the positioning holes for the subsequent process, and the positioning holes and forming surfaces in the supplement area are adjusted in the final process to make up for the lack of positioning holes in the stamped part.
In order to improve the production efficiency of stamping parts, more and more companies have adopted automated production methods. Factors that affect the production efficiency of automation include the shape of the auto stamping parts, the automation picking method, and the production trajectory.
Pneumatic positioning refers to setting the positioning plate of the stamped part on the cylinder piston, so that the positioning plate moves up and down with the cylinder piston according to the automation production rhythm. When the billet is placed on the mold before production, the cylinder piston lifts the positioning plate to a working state; after the process is completed, when the automation prepares to pick up the workpiece, the cylinder piston lowers, and the positioning plate follows to avoid the automation trajectory, thereby shortening the picking trajectory and improving production efficiency.
According to the characteristics of pneumatic positioning, this type of positioning is generally suitable for processes with shallow forming surfaces (that is, low automation picking heights), and should be set in the direction of the material out of the drawing process. In addition, pneumatic positioning is controlled by an automated program to control the air source, so the automation mode on the production site needs to be analyzed when designing this type of mold.
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