Comparison between Six Model Six Punch Cold Heading Forming Machine and Multi station Cold Heading Machine
Source：http://www.rnbe.cn Author：冷鐓機(jī) Time：2015/3/21 Click：
The more accurate name for the six die six punch cold heading forming machine is "cylindrical cold forming machine", because this type of machine is not only used for processing nuts (in fact, if only processing nuts, five stations are sufficient), but also can implement upsetting, forward extrusion, backward extrusion, and closed extrusion (radial expansion) processes to process cylindrical parts with small aspect ratios, such as pipe joints and spark plugs. Corresponding to the "cylindrical cold forming machine", there is a so-called "rod cold forming machine", which is commonly known as the five station bolt cold heading machine.
Cold heading forming machine has two forms of mold arrangement: one is vertical arrangement, and the overall structure of the machine tool is lateral horizontal; One is a horizontal arrangement, where the overall structure of the machine tool is inclined horizontally. The side horizontal multi station cold heading machine is easy to operate and adjust, and workers can stand and operate without bending over. They can sit and observe the operation of the machine, which is more comfortable. The design concept of the side horizontal cold heading machine seems to focus on this advantage. However, compared to its series of drawbacks, this advantage is insignificant. The main disadvantages of the side horizontal cold heading machine are:
1、 The bed structure is asymmetrical in all directions, resulting in complex elastic deformation during operation and poor overall rigidity.
The axial component force of the forging resistance at each workstation is distributed on the vertical plane, and its resultant force deviates from the centerline of the machine tool, that is, from the center of the connecting rod pin, generating a huge torque on the slider. This torque almost entirely acts on the slider guide rail, causing significant destructive force on the guide rail. How much destructive power is this? For example, in a cold heading machine with a nominal pressure of 1200 kilonewtons, the resultant force of the forging resistance can cause a deviation of up to 5 centimeters from the centerline of the machine (which may be even greater when there is no workpiece at a workstation), and the torque acting on the guide rail is equal to 60 kilonewtons per meter. If the length of the slider is 1.5 meters, then this torque is equivalent to pressing a weight of 4 tons on one end of the slider and lifting it with a force of 40 kilonewtons (equivalent to 4 tons) on the other end. It goes without saying that both the slider and the guide rail will experience severe uneven wear, and the accuracy of the machine tool can be imagined.
3、 Due to structural reasons, the slider guide rail must be raised, which further exacerbates the friction between the slider and the guide rail.
4、 In order to improve the friction conditions between the slider and the guide rail, the designer had to lengthen the slider, which only increased its weight and reduced the overall stability of the machine.
5、 The ejection mechanism cannot be deployed on the same plane (longitudinal vertical plane) as the main transmission mechanism, making it impossible to achieve a compact design, resulting in a complex and massive structure.
6、 The clamp transmission mechanism also has the same drawbacks; The complex structure of the clamp box is not commensurate with its uncomplicated functions.
7、 When the clamp clamps the workpiece and rotates downwards, the workpiece is easily shaken and thrown off due to its own weight, especially for longer workpieces.
8、 When the clamp (or scissors) at the upper workstation drops the material, the workpiece may fall down and be pressed onto the lower workstation, damaging the mold and clamp.
9、 The height is too high, obstructing the workers' line of sight and deteriorating the working environment in the workshop.
10、 Mold assembly and disassembly are difficult, making it difficult to lift. Starting from the mid to late 1960s, and continuing until the 1970s, 1980s, and even early 1990s, side horizontal cold heading machines became popular in China and gradually formed a series. However, due to the aforementioned "ten major crimes", the side horizontal cold heading machine finally cannot escape the fate of being eliminated.
The design goal of the six die six punch cold heading forming machine three station machine is to process conventional/low strength products. With the widespread application of high-strength products and the emergence of a large number of irregular products, the functional defects of three station machines are increasingly exposed. The effective process for high-strength products is the secondary diameter reduction (large material with small deformation) process, while for irregular products, multiple upsetting strikes are required. Three station machines are difficult to implement these processes, so they are gradually being phased out and replaced by four - and five station machines. When choosing a multi station machine, if conditions permit, it is recommended to choose a four or five station machine, with at least four stations. Practice has proven that even for producing conventional products, a four station machine is more reasonable and economical than a three station machine. On the surface, there may seem to be a large number of four station molds, but in fact, the mold structure of the four station process is more reasonable, has a longer lifespan, is easier to manage, and is therefore more economical. For example, for a hexagonal bolt with a cutting edge, the three station cold heading process is: initial punching, precision punching and diameter reduction, and edge cutting. The second station precision punching lower die is a combination die, which includes a diameter reduction die core that is tightly matched with the die sleeve (cylindrical or conical) and has a fixed axial position, only suitable for one product length; To accommodate all product lengths within the functional range of the machine, multiple sets of molds must be readily available. The four station process is: initial punching, precision punching, diameter reduction, and edge cutting. The second station precision punching lower die does not include a diameter reduction die core, which greatly simplifies the structure. Although the third station diameter reduction die is also a combination die, the diameter reduction die core and die sleeve can be dynamically matched to adjust the axial position freely, so it can adapt to all product lengths within the functional range of the machine. In contrast, the four station process has fewer mold reserves, lower costs, and more convenient management. For cut edge hexagonal bolts, of course, an additional workstation will provide more, more convenient, and more reasonable choices for process design and mold design for other types of products.
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