Introduction of drawing process and cold forging process

Drawing:

　　 The drawing process has two purposes, one is to change the size of the raw material; the other is to obtain the basic mechanical properties of the fastener through deformation strengthening. For medium carbon steel and medium carbon alloy steel, there is another purpose, that is The flake cementite obtained after the controlled cooling of the wire rod is cracked as much as possible during the drawing process to prepare for the subsequent spheroidization (softening) annealing to obtain granular cementite. However, some manufacturers do whatever they want to reduce the cost. Reduce the number of drawing passes, and the excessive reduction in surface area increases the work hardening tendency of the wire rod wire, which directly affects the cold heading performance of the wire rod wire. If the distribution of the reduction ratio of each pass is not appropriate, it will also cause torsion cracks in the wire rod wire during the drawing process. This kind of cracks distributed along the longitudinal direction of the wire and with a certain period are exposed during the cold heading process of the wire. In addition, if the lubrication is not good during the drawing process, it can also cause the cold drawn wire rod wire to regularly appear transverse cracks. The tangential direction of the wire rod wire exiting and winding die mouth is not concentric with the wire drawing die, which will increase the wear of the unilateral pass of the wire drawing die, make the inner hole out of round, and cause uneven drawing deformation in the circumferential direction of the wire. The roundness of the steel wire is too poor, and the cross-sectional stress of the steel wire is uneven during the cold heading process, which affects the cold heading qualification rate. During the drawing process of wire rod wire, the excessive surface reduction rate deteriorates the surface quality of the steel wire, while the excessively low surface reduction rate is not conducive to the crushing of flake cementite, and it is difficult to obtain as much granular cementite as possible. , That is, the spheroidization rate of cementite is low, which is extremely unfavorable to the cold heading performance of the steel wire. The bar and wire rod steel wire produced by the drawing method has a partial surface reduction rate directly controlled within the range of 10%-15%.

Cold forging: (Guide: Advantages of stainless steel tapping machine and technical parameters of stainless steel tapping machine)

　　Forming Generally, the forming of the bolt head adopts cold heading plastic processing. Compared with cutting processing, the metal fiber (metal remaining wire) is continuous along the product shape without cutting in the middle, thus improving the strength of the product, especially for machinery Excellent performance. The cold heading forming process includes cutting and forming, single-station single-click, double-click cold heading, and multi-station automatic cold heading. An automatic cold heading machine performs multi-station processes such as stamping, upsetting, extrusion and diameter reduction in several forming dies. The processing characteristics of the original blank used by the single-station or multi-station automatic cold heading machine are determined by the size of the bar material with a length of 5-6 meters or the size of the wire rod wire with a weight of 1900-2000KG, that is, the characteristics of the processing technology The cold heading does not use pre-cut single-piece blanks, but uses the automatic cold heading machine itself to cut and upset (if necessary) blanks from the bar stock and wire rod steel wire. Before extruding the cavity, the blank must be shaped. Through shaping, a blank that meets the process requirements can be obtained. Before upsetting, reducing diameter and forward extrusion, the blank does not need to be shaped. After the blank is cut, it is sent to the upsetting and shaping station. This station can improve the quality of the blank, can reduce the forming force of the next station by 15-17%, and can prolong the life of the mold. The bolts can be manufactured with multiple diameter reductions. 1. Use a semi-closed cutting tool to cut the blank. The easiest way is to use a sleeve-type cutting tool; the angle of the incision should not be greater than 3 degrees; and when the open-type cutting tool is used, the bevel angle of the incision can reach 5 -7 degrees. 2. When the short-sized blank is transferred from the previous station to the next forming station, it should be able to turn 180 degrees, so that it can play the potential of the automatic cold heading machine, process fasteners with complex structures, and improve the accuracy of parts. 3. Each forming station should be equipped with a punch ejecting device, and the die should be equipped with a sleeve type ejecting device. 4. The number of forming stations (excluding cutting stations) should generally reach 3-4 stations (more than 5 under special circumstances). 5. During the effective period of use, the structure of the main slider guide rail and process components can ensure the positioning accuracy of the punch and the die. 6. Terminal limit switches must be installed on the baffle that controls the selection of materials, and attention must be paid to the control of the upsetting force. The out-of-roundness of the cold-dial wire rod used in the manufacture of high-strength fasteners on the automatic cold heading machine should be within the diameter tolerance range, while the out-of-roundness of the wire for more precise fasteners should be limited to 1/ 2 Within the diameter tolerance range, if the wire diameter does not reach the specified size, cracks or burrs will appear in the upsetting part or the head of the part. If the diameter is smaller than the size required by the process, the head will be incomplete , The edges and corners or swelling parts are not clear. The accuracy that can be achieved by cold heading is also related to the selection of the forming method and the process used. In addition, it also depends on the structural characteristics of the equipment used, the process characteristics and its state, the accuracy of the mold, the life and the degree of wear. For high-alloy steel used in cold heading and extrusion, the working surface roughness of hard alloy molds should not be greater than Rau003d0.2um. When the roughness of the working surface of this type of mold reaches Rau003d0.025-0.050um, it has the highest life.

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