Abstract: The characteristics of punch for cold heading roller are analyzed, and the punch is processed by cold extrusion process. The results show that the dimensional accuracy and service life of the cold extrusion roller punch have been greatly improved.
Key words: cold extrusion; Cold heading die; Roller punch
1 Cold extrusion process
Cold extrusion is a processing method to make parts by placing metal blanks in the cold extrusion die cavity at room temperature and applying pressure to the metal blanks through the punch fixed by the press to make the blanks produce plastic deformation. Cold extrusion is a non-cutting processing method, and its process features mainly include:
The size of the extrusion is accurate and the surface is smooth. The general dimension accuracy can reach 5~8 levels, and the surface roughness Ra can reach 0.4~0.8 μ m；
Save raw materials, and the material utilization rate of extrusion parts can reach more than 80%;
The production efficiency is very high, especially in mass production, which is several times or even several hundred times higher than that of cutting;
(4) It can process parts with complex shapes;
The extrusion has high strength and good rigidity.
2 Punch for cold heading roller
The cavity profile of the cold heading roller punch is relatively complex (Fig. 1), and the conventional machining process is turning and then polishing. Especially for some small size punch, due to the small size of the cavity, it can only be processed with the forming tool. The surface roughness of the forming surface processed by the forming tool is poor, especially for the part near the center, because the cutting speed is almost zero, the metal here is actually torn down, which will cause stress concentration of the punch in use, resulting in the failure of the punch block.
FIG.1
3 Cold extrusion process analysis
The current cold heading roller punch material is mostly GCr15, but the hole drop phenomenon is relatively serious in use. After analysis, it is believed that it is caused by the material and turning tool grain. Some large punch are processed by Cr12MoV, but the cost is high, and the forging is difficult, easy to crack, and easy to corrode and produce pitting during forming and quenching (except for vacuum furnace). In addition, the accuracy of the current cold heading machine is not high, and the phenomenon of upsetting cake occurs from time to time. To sum up, the cold extrusion process will be used to process the GCr15 material punch to prevent the occurrence of the hole phenomenon and improve the punch life.
Because the cold extrusion is in a three-dimensional compressive stress state, the microstructure of the metal material after extrusion is more compact, and the tiny pores, shrinkage porosity and microcracks are pressed. After the cold extrusion process is adopted, the surface roughness Ra of the punch forming part reaches 0.8 μ m. See Table 1 for the comparison of the effect of roller punch extrusion process and turning process.
Table 1
The cold extrusion processing punch will not cut the forging streamline of the forming part, so that the strength of the punch will be further improved. The streamline comparison between turning punch and extrusion punch is shown in Figure 2. The tooling required for cold extrusion of punch is shown in Figure 3.
FIG.2 AND FIG.3
In addition, in order to improve the extrusion performance of the material and prolong the service life of the extrusion die, the blank should be softened before extrusion. GCr15 blank shall be spheroidized and returned before extrusion, and its hardness shall be controlled between 174 and 192HB.
4 Conclusion
The size accuracy and service life of the roller punch processed by cold extrusion technology have been greatly improved. On the basis of understanding the principle and method of cold extrusion and the failure analysis of the failed punch, the cold extrusion method was used to replace the conventional turning forming for products such as 3020430205 and 32216. Compared with the original processing technology, the punch life was increased by 3-4 times on average, the uniformity of the punch cavity was also guaranteed, and the use effect was very good. With the continuous emergence of high-performance die materials and presses, the application of cold extrusion technology in machining will be more extensive.
More about WBM Carbide Cold Heading Dies:
WBM can produce different types and sizes Steel Ball Dies with quality assurance, include: carbide steel ball cold heading dies, Steel ball cold heading dies for national.
Materials: tungsten carbide or mold steel
Main parts for cold heading process: Quill (cut off die), cutter (cut off blade), punch, taper dies. No matter your material is case harden steel or through harden steel, our full set dies can run in a good lifetime.
High precision dies produced according to your drawing. And we can also provide tools design service according to your roller headers.
