Slow wire walking, also called low-speed wire walking, is a kind of CNC machining machine tool that uses continuously moving fine metal wire as an electrode to pulse spark discharge on the workpiece to generate a high temperature of over 6000 degrees, ablate metal and cut into a workpiece. The principle of wire processing is the phenomenon that there is a gap between the wire electrode and the workpiece, and the metal is removed by continuous discharge. Since the slow-moving wire cutting machine adopts the method of wire electrode continuous feeding, that is, the wire electrode is processed during the movement, so even if the wire electrode is worn out, it can be continuously supplemented, so it can improve the machining accuracy of the parts and slow the wire. The surface roughness of the workpiece processed by the cutting machine can usually reach Ra=0.8μm and above, and the roundness error, linear error and dimensional error of the slow-moving wire cutting machine are much bett...
The Purpose Standardize the management of the scrapping of the company's metal stamping dies, prevent the loss of company assets, and formulate this system specially. Scope of application It is suitable for the management of the company's scrap molds. Definition If the molds listed in the assets of the company fall under one of the following circumstances, the use management department may apply for scrapping. 1. Molds that exceed the specified service life. 2. The mold is severely damaged by accidents or accidents, and molds that cannot be repaired or have no repair value. 3. Metal stamping dies that have not reached the service life, but due to safety, quality, efficiency and other issues, the repair still fails to meet the minimum requirements of the customer's product process or affects the production safety and efficiency. 4. Product customers have stopped placing orders or have not placed orders for molds in several years. 4. Responsibilities 1. Responsibilities of th...
KOVAR parts are commonly used as metal casing materials in the electronic packaging industry. Because they have a linear expansion coefficient close to that of molybdenum group glass, and can produce less sealing stress during the sealing (melting) process with molybdenum group glass, so To obtain good air-tightness, in order to make the metal tube and shell to achieve air-tight sealing, in the entire sealing process, the annealing process undoubtedly plays an important role as a link between the previous and the next. The internal stress generated during KOVAR machining also prepares the material structure for the implementation of the subsequent process-the sealing process of the metal parts. The main purpose of annealing Kovar shell before sealing is to: (1) Eliminate machining stress. When Kovar undergoes plastic machining deformation during cold working, about 10% to 15% of the applied energy is converted into internal energy, which is commonly referred to as internal stre...
Keywords:The characteristics and differences of quenching crack,forging crack and grinding crack are summarized by China Hardware
Quenching crack is a common quenching defect, and the causes are various. Because the defect of heat treatment starts from the product design, the work of preventing crack should start from the product design. The material should be chosen correctly, the structure design should be carried out reasonably, the technical requirements of heat treatment should be put forward, the process route should be arranged properly, the heating temperature, the holding time, the heating medium, the cooling medium, the cooling method and the operation mode should be selected reasonably.
material
Carbon is an important factor affecting the tendency of quenching cracking. With the increase of carbon content, the MS point decreases and the tendency of quenching crack increases. Therefore, under the condition of satisfying basic properties such as hardness and strength, lower carbon content should be selected as far as possible to ensure that it is not easy to crack.
The influence of alloying elements on quenching tendency is mainly reflected in the influence of hardenability, MS point, grain size growth tendency and decarbonization. Alloying elements affect the tendency of quenching through their influence on hardenability. Generally speaking, hardenability increases and hardenability increases, but at the same time, quenching medium with weak cooling ability can be used to reduce quenching deformation to prevent deformation and crack of complex parts. Therefore, for the parts with complex shapes, in order to avoid quenching cracks, it is a better plan to choose steel with good hardenability and use quenching medium with weak cooling capacity.
Generally speaking, the lower the MS point, the greater the quenching tendency of steel. When the MS point is high, the martensite generated by phase transformation may be self-tempered immediately, so as to eliminate part of the phase transition stress and avoid quenching. Therefore, when the carbon content is determined, steel with a small amount of alloying elements or elements that have little effect on the MS point should be selected.
When choosing steel, the sensitivity to overheating should be considered. Overheat sensitive steel, easy to crack, so in the selection of materials should be paid attention to.
Structural design of parts
Uniform section size. The parts with rapid change in section size will crack due to internal stress during heat treatment. Therefore, the design should try to avoid the abrupt change of section size. The wall thickness should be uniform. If necessary, holes can be opened in thick wall parts not directly related to the use. Holes should be made through holes as far as possible. For parts with different thicknesses, they can be designed separately and assembled after heat treatment.
Fillet transition. When the parts have edges, sharp corners, grooves and transverse holes, these parts are easy to produce stress concentration, resulting in parts quenching crack. To this end, the parts should be designed as far as possible not to occur stress concentration shape, in the sharp corners and steps processing into rounded corners.
Differences in cooling rate caused by shape factors. The cooling speed of parts quenching is different with the different shapes of parts. Even in different parts of the same part, there will be different cooling rates due to various factors. Therefore, excessive cooling differences should be avoided as far as possible to prevent quenching cracks.
Technical conditions for heat treatment
1.Use local quenching or surface hardening as far as possible.
2.Adjust the local hardness of the quenched parts according to the service conditions of the parts. When the local quenching hardness requirement is low, try not to force the whole hardness to be consistent.
3. Note the mass effect of steel.
4.Avoid tempering in the first type of tempering brittle zone.
Arrange process route and process parameters reasonably
When the steel material, structure and technical conditions are determined, the heat treatment process personnel will carry out process analysis, determine the reasonable process route, that is, the correct arrangement of preparation heat treatment, cold working and hot working process position and determine the heating parameters.
Quenching crack
At 1.500x, the crack was serrated, the initial crack was wide, and the end crack was fine to none.
Microscopic analysis: abnormal metallurgical inclusion, crack morphology is serrated extension; After corrosion with 4% nitric acid alcohol, no decarbonization phenomenon was observed. The microscopic morphology is shown in the following figure:
No abnormal metallurgical inclusions were found at the crack of the product, and no decarbonization phenomenon was found. The crack extended in serrated shape and had the typical characteristics of quenching crack.
Analysis conclusion:
The composition of the sample meets the standard requirements and corresponds to the composition of the original furnace number.
According to the microscopic analysis, no abnormal metallurgical inclusions were found at the crack of the sample, and no decarbonization phenomenon was found. The crack extended in serrated shape and had the typical characteristics of quenching crack.
Forging crack
Crack caused by typical material, edge of oxide.
Microscopic observations
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