Mold surface processing for automotive panels

Covering parts mainly refer to the thin steel plate-shaped parts covering the engine, chassis or forming the cab, the surface and the interior of the car. Compared with ordinary stamping parts, covering parts have the characteristics of complex shapes, thin materials, high surface quality requirements, good rigidity, large structural dimensions, and mostly spatial curved surfaces. The stamping process of covering parts generally requires multiple processes such as blanking (or cutting), forming, trimming, punching and flanging. The forming process of the cover is mainly based on Deep Drawing (drawing), partially including bulging, flanging and bending. In most cases, forming is the key to manufacturing such parts, which directly affects product quality, material utilization, production efficiency and manufacturing costs.

Regarding mold materials, ordinary mold bases usually use HT300 or HT250; the molding part is usually produced in large and medium batches using alloy cast iron such as Macro cast iron or nodular cast iron, and small batches are used HT300; if the thickness of the trimming part is less than 1.0mm, air-cooled steel can be used (7CrSiMnMoV).

Deep drawing, trimming and flanging are the most basic processes, among which the drawing process is a more critical process, which directly affects product quality, material utilization, production efficiency and manufacturing costs.

There are many types of tools involved in the processing of cover molds. Face milling cutters, corn milling cutters, end milling cutters, drill bits and taps of different diameters are needed when processing guide plates, discharge plates, pressure plate grooves, supporting surfaces and ejector holes. Wait for the tool.
Of course, everyone is more concerned about the processing of the mold surface of the cover. For different purposes and different grades of cars, the expression of the surface quality is also different.

The cover itself is a thin metal plate, which deforms after being punched. If the design is not comprehensive enough, it is possible to trim the areas where the cover has a large error during the trial production. Compared with plastic molds, the accuracy level and surface roughness requirements of cover molds are not high. The cover mold is characterized by its large size and requires large-scale machine tools for processing.

With the increasingly fierce market competition, mold suppliers are becoming more and more sensitive to the cost of tools. In other words, for high-end tools, there are higher processing efficiency and service life requirements.

For rough machining of the profile, a ball end mill with a willow blade is commonly used. Major domestic panel mold manufacturers are using Seco’s R218.20 milling cutter, the diameter of the cutting part is 30mm, and the blade material is PVD-coated F25M. Due to the high rigidity design and two effective tooth numbers (K=2), this tool with high metal removal rate can withstand very high feed rates. R218.20 has a unique blade seat design with a positioning tenon, which can avoid the stress concentration of the locking screw and prevent the rotation of the blade. The chip removal space is large and contains a large arc surface, which makes the tool stronger at the center. There are two cutting edges that cut very lightly on the same insert. The high-strength blade and cutter body make this milling cutter have the greatest safety and reliability, making it suitable for unmanned production. The “S”-shaped curve of the cutting edge of the insert helps to reduce the cutting force and has a constant cutting rake angle along the cutting edge. The positive axial rake angle provides smooth cutting and allows the possibility of upward cutting, and strengthens the center to make it resistant to chipping. By using an adaptive relief angle along the cutting edge, a smooth geometric angle produces a very low cutting force, leading to an increase in tool life. Generally speaking, the life of the tool must reach more than ten hours.

For surface finishing, Seco’s Minim aster end mill is recommended. This kind of tool has a high reputation in the mold processing industry, and is also widely used in panel mold manufacturers. Seco’s MINIMASTER milling cutter is a universal and adaptable system. The toolholder materials include steel parts and high-density anti-vibration materials. It is a unique small-diameter end milling cutter system with interchangeable tool heads, which can be combined into different solutions, combining providing the most optimized reachability with maximum stability and safety.

The Minim aster system consists of a wide range of blades and shanks. There are more than 600 combinations of blades and shanks, with a diameter ranging from 6 to 20 mm. Minim aster is also an economical solution. For deep corners, it is very suitable to use Minim aster 6 and 8 end mills. The length of solid carbide milling cutters is often not enough.

The selection and correct use of tools is one aspect, and the efficiency of mold processing is also reflected in the functions and programming of the machine tool. When machining at a vertical angle, the linear velocity of the cutting point of the ball nose tool is zero, and the linear velocity of the cutting near the tip point is also very low, which affects the surface quality of the mold. If permitted by the machine tool, different machining inclination angles can be used according to different cavities, so that the inclination machining can achieve a more ideal cutting diameter and thus obtain a better linear speed.

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