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The impact of material modification of cold heading machines on product quality

Time:

Dec 10,2020

The impact of material modification on the quality of cold heading machine products

The adjustment of material structure has a significant impact on product quality. The head defects of anchor bolt parts and the crack defects of cold heading machine parts are the main waste phenomena in the production process of cold heading machines. Part of the reason for these defects is caused by the material preparation process. According to the theory of metal plastic deformation, the bolt cold heading machine applies a certain pressure to the metal blank at room temperature, causing it to undergo plastic deformation in the mold cavity, forming according to specified shapes and sizes. The standard mechanical parts have a pair of bevel gears installed at one end of the crankshaft, with a cam device mounted on the driven bevel gear shaft, and a scissor slider vertically mounted on the roller shaft of the driven roller of the cam device. This utility model overcomes the shortcomings of the prior art, with a small running friction coefficient and impact force between the components of its feeding and cutting mechanism, making the equipment run smoothly, effectively reducing operating noise, and greatly improving product quality and productivity. The cold heading machine is a specialized device mainly used for mass production of fasteners such as nuts and bolts.

Causes and control of bolt fracture

According to the national standard GB3098.1, cold heading machine bolts should undergo a hardness test on the head that has not been heat-treated. In the test, the fracture phenomenon of the bolt head is referred to as fracture. There are two types of fractures: cracks caused by interlayers in the head and fractures at the joint between the head and the rod or adjacent parts.

The reason for cracking caused by interlayers in the workpiece head is relatively simple, generally due to improper cold heading machine processes. When the center position of the punching method and the concave method of the front punching process are improperly adjusted, the head and rod of the front punching piece have different axes, causing the head to form a significant tilt, resulting in waste during formation. If the diameter of the wire is small, it increases the forging ratio. Longitudinal bending is likely to occur during cracking, leading to disordered metal flow lines, separating the organic connections between grains, which can also cause fracture phenomena. For heads caused by improper cold heading machine processing, as long as the process design can be improved.

The fractured part of the head joint is due to the fidelity of the material restructuring process. Production practice and experimental research show that the cold deformation performance of steel plays a decisive role in the quality of the workpiece. The quality of steel consists of two aspects: first, the performance of the steel from the steel mill must meet the requirements for steel used in cold heading machines; on the other hand, the steel must be conducive to protecting or improving the performance of the cold heading machine during the restructuring process.

Common defects in the original structure of steel include: the presence of serious segregation zones in the steel, with a concentration of non-metallic elements such as carbon, phosphorus, and sulfur in the segregation zones, which reduces the cold deformation performance of the steel, leading to workpiece deformation. Generally speaking, boiling steel is prone to segregation. Defects such as shrinkage cavities, gas holes, inclusions, or coarse-grained overheated structures in the steel exhibit brittleness.

During the material restructuring process, due to improper process management, the factors causing steel defects include: hydrogen embrittlement during the pickling process and brittle fracture caused by overheating during the annealing process. When the tensile deformation in the material structure is within the critical deformation degree, and when the crystal annealing causes a larger grain thickness, head phenomena may also occur.

When the deformation of the head and the workpiece rod is significantly different, the degree of work hardening caused by this difference is large, and when the strength of the head joint is low, it may lead to fracture. For example, the thick tracking process of the grooved hex bolt is less destructive than the fine tracking process, and the process of the grooved cold drilling machine is smaller than that of the cold drilling machine.

This is due to the poor strength of the original head rod, with fewer interruptions in the production of medium and small products. This is because the materials used in small-sized products have improved performance after repeated rolling and drawing.

Introduce methods to ensure mechanical stability during the installation of cold heading machines.

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