Process types of cold heading screws

Update:30 Jun 2020
Summary:

The cold heading screw process is an indispensable manu […]

The cold heading screw process is an indispensable manufacturing method for the automated production of irregularly shaped automobile fasteners, motorcycles, bicycles, and home appliances in mass production. Compared with the cutting process, the metal fiber (metal flow line) is along The shape of the product is continuous, and the crystal grains are not broken, so the strength of the product is improved, especially the mechanical property is excellent, and the raw material is saved. With the increasing call for environmental protection, fasteners have also paid more attention to environmental issues. Therefore, cold heading technology as a non-cutting shape increasingly pursues high strength and high added value.
1. Constrained punching Punching where the distance between the shape and the edge of the inner hole is less than the thickness of the plate, the inner diameter is greater than one-half the outer diameter, and the height is more than 1.5 times the inner diameter of the punching. The effect of constrained stamping is better. Due to the short distance between the shape and the edge of the inner hole, the force of the punching punch will affect the shape, and the size of the shape will also change. In order to prevent changes in the external dimensions, this part of the external shape must be kept in a restricted state. Due to the binding force, the stamping part is in a state of compressive stress. In this state of punching and compressive stress, the stamping effect of all bright bands can be obtained by taking an appropriate gap.


2. Cut and Extrusion Forming Usually, the head of the bolt is formed by cold heading plastic processing. The cut and extrusion process has more advantages than the expanding process. Before cutting and extruding, the blank must be shaped, and the blank can meet the technological requirements through shaping. The size of the blank must be paid attention to. The shape of the blank before extrusion should be determined according to the condition of the part. The shape of the blank that is conducive to the flow of material should be adopted. If the size of the blank is too large, that is, the cutting margin is too large, the required cutting force is large, which is easy to cause the life of the cutting die to be reduced, the possibility of accidental damage to the die is increased, and the raw material is consumed; the cutting margin is too small After cutting and extruding, the parts are easy to be cornered, the shape is incomplete, and satisfactory appearance quality cannot be obtained. The focus of the mold structure is on the design and processing of the cutting and extrusion film. The working size of the cutting edge is best controlled at the lower limit. The angle of the cutting and extrusion die should be appropriate. The cutting edge must be ground and polished. The roughness Ra0.025 to Ra0.050μm , With the highest lifespan.
3. Drawing and forging forming The combination of cold-extruded convex thick-walled parts and deep-drawn cup-shaped shaped parts are combined into one, using sheet material as the material, and formed by the combined forming method of deep drawing and compression. The forming characteristic of the fastener is the forming of the head protrusion and the increase of the wall thickness.
4. Partial forming There are two concepts of upsetting and pressing. One is the whole upsetting, that is, it has a force on the end surface of all products; the second is the local upsetting, that is, there is only the necessary part of the pressure. Overall forming, due to the large processing area and high forming load, requires a large-tonnage punching machine. For local forming, a lower load can be used to obtain the necessary plate thickness changes. It is widely used in the forming of holes and grooves. ① Step parts □ Taking joints as an example to illustrate the main points and applications of forming, engineering design: lathe machining-annealing-phosphorous saponification-extrusion according to the design drawing (semi-closed extrusion to form steps). ② Micro-partial forming ○ For the purpose of locking and chip removal, there are 1 to 3 scraping grooves for some set screws. Extrusion process can be used. The representative is the formation of scraping grooves for automobile assembly bolts.