Sheet metal processing is mainly the treatment of various metal materials, in the different materials, the processing is also different, so the need to use different processing technology. The deformation of heat treatment is an important process in the process of sheet metal processing. There are two types of heat treatment deformation: one is the change of size and the two is the change of the geometric shape of the part. Different methods of heat treatment, deformation and deformation prevention of parts size and geometry are also different.
In the process of heat treatment austenitizing, the longer the holding time is, the higher the temperature is, the more carbon is dissolved into austenite, and the larger the expansion is during martensitic transformation. When cooling, martensite expands the largest, followed by the upper bainite, and the volume of the lower bainite and the body is very small. At low temperature tempering, martensite shrinks and the amount of shrinkage is directly proportional to the supersaturated carbon content. When heated at room temperature of -200, part of austenite is transformed into martensite and expanded. However, the expansion of the martensite due to decomposition near 200 c has little change. In conventional heat treatment, the main reason for the change of the shape of the parts is the thermal stress and phase transformation stress during heat treatment and quenching. The heating rate is too fast, the parts are too large and the temperature of each part of the parts is different, which will lead to thermal deformation. During thermal insulation, the residual stress will be released and the deformation will be caused. When cooling, due to different parts of the cooling rate of different parts, will form thermal stress and deformation of parts. Even if the cooling speed is the same, the cooling surface is always fast and the heart is slow. Therefore, the surface of phase transformation causes plastic deformation of the core without phase transformation. If there is segregation of alloy components or decarburization, the stress of phase transformation will be more uneven and more likely to cause deformation of parts. In addition, if the thickness of the parts is uneven, the cooling rate will also be different.
In the heat treatment of forgings, the way to reduce the deformation of parts, one is to hang vertically as far as possible, two is vertically placed at the bottom of the furnace, three is supported by two points, the position of the fulcrum is between 1/3 and 1/4 in length, and four is flat on the heat-resistant steel.
In the cooling process of parts, the types, cooling properties and hardenability of quenching medium are related to deformation. The change of cooling performance can be adjusted by changing the viscosity, temperature, liquid surface pressure, additives and agitation. The higher the viscosity of quenching oil, the higher the temperature, the smaller the elliptical deformation. In the static state, the deformation is small.
The following methods can effectively reduce the deformation of sheet metal processing: (1) salt bath quenching; (2) high temperature oil quenching; (3) QSQ method; (4) vacuum quenching; three quenching of one groove. Salt bath quenching and high temperature oil quenching are similar, all are quenched at martensitic transformation temperature, so that the uniformity of martensitic transformation is increased. QSQ is double liquid quenching. By reducing the pressure of the liquid surface of the quenching medium, the pressure reduction process extends the phase of the steam film, and the cooling rate of the high temperature zone decreases and the cooling rate of the parts of the parts is uniform. The three section quenching structure is simple. First, the part from the quenching temperature oil is cold to a little higher than the Ms point. Then, the temperature of the part is kept in the atmosphere, the whole temperature of the part is uniform, then the oil is cooled, the martensite transformation is carried out evenly, and the irregularity of the deformation is greatly improved.
标签:   钣金加工 激光切割加工