Deformation temperature of 1. die forging

Heating is an important part of the die forging process. Die forging is often carried out at high and medium temperatures.

1. High temperature die forging

To prevent serious oxidation and decarburization on the surface of the blank during heating, it can be heated in a small, non-oxidizing open-flame furnace or a furnace that can effectively control the atmosphere. To prevent secondary oxidation during the cooling process of hot forgings, cooling can be carried out in a protected device. Forgings can also be placed in a grid sand box in order. When slow cooling is required, the company will cool the forgings in a hot sand box or asbestos powder.

2. Medium temperature die forging

Reducing the heating temperature can prevent strong oxidation and decarburization, as long as it has sufficient plasticity and appropriate deformation resistance, it can also achieve the purpose of die forging. Medium temperature die forging is a method of heating and forging in a temperature range that does not produce strong oxidation. Figure 8-4 shows the high temperature strength limit and high temperature oxidation performance curve of 45 8 steel. It can be seen that the intensity limit decreases sharply from 500 ℃ to 600 ℃, which is half of that at room temperature. 600 degrees above the strength limit is low, can be forging forming. Therefore, 45 8 steel in the range of 600 875 ℃, both low deformation resistance, and no strong oxidation, can make forgings to achieve a higher degree of dimensional accuracy and surface finish. Under the condition of warm forging, the working temperature of the die is generally about 400 degrees, and high-speed steel is more suitable for warm forging die material.

2. the accuracy of forgings

The main factors affecting the accuracy of die forgings are: rough volume deviation, elastic deformation of molds and forgings, temperature fluctuations of molds and blanks (forgings), mold accuracy and equipment accuracy.

When designing the forging drawing, only the dimensions of the main parts need to be guaranteed, and all dimensions are not required and should not be required. This is because the size of the blank and many factors in forming can not be accurately controlled, and plastic deformation is to comply with the volume invariant conditions, the use of some parts of the more relaxed requirements to adjust these errors.

1. Blank volume deviation

For open die forging, the volume deviation of the blank generally does not affect the size deviation of the forging. However, in closed die forging, assuming that the horizontal dimension of the die bore is unchanged and no flying spurs are produced, the volume deviation of the blank will cause the height dimension of the forging to change.

The reasons for the deviation of the blank volume are as follows: first, the blanking is not accurate; Second, the burning degree of each blank is inconsistent during heating. Therefore, to improve the accuracy of forgings, it is necessary to improve the accuracy of the material and improve the heating situation. At present, the blanking can control the weight deviation of the blank within 1% (the general blanking method is more than 3% ~ 5%). Secondly, in the forging drawing and process design, appropriate measures should be taken according to the possible variation range of the blank volume. For example, the dimensional tolerance of forgings in a certain direction; Or use open die forging to make excess metal flow into the flash groove; For some forgings with holes, punching core material can be used to adjust the volume deflection.

The dimensional accuracy of the die and the wear during use have a direct impact on the dimensional accuracy of the forgings. In different parts of the die cavity, the flow of metal and the pressure are different, and the degree of wear is also different.

In open die forging, the wear in the horizontal direction of the die bore will cause the reduction of the outer diameter and aperture size of the forging; the wear in the vertical direction of the die bore will cause the height dimension of the forging.

In closed die forging, the effect of die wear is shown in Figure 8-5, which will cause the horizontal dimension L(D) of the forging. If the blank volume is unchanged, and assuming no flash and good filling, the forging height dimension H will be reduced. In this case, the forging height dimension tolerance ΔH cannot be determined by the wear in the direction of the die height. When designing the die, the horizontal dimension of the die should be designed according to the corresponding dimension of the forging, while the height dimension of the die should be designed according to the corresponding dimension value of the forging, so that when the die wears out, the horizontal dimension of the forging reaches the value, while the height dimension reaches the value.

3. Elastic deformation of dies and forgings

Die forging, die and blank will produce elastic deformation. The size of the die chamber is affected by internal pressure; the blank is compressed and elastically deformed. After the external force is removed, the two elastic recovery occurs, so that the size of the forging changes. The dimensional change caused by elastic deformation can be calculated according to the elastic modulus, stress value and the size of the corresponding part of the two materials, but it is usually determined by process test.

4. Other factors

The surface quality of the blank (oxidation, decarburization and surface roughness, etc.) is the premise of forging. The accuracy and rigidity of the equipment have an important influence on the accuracy of forgings. The influence of the mold is more direct, such as the design accuracy of the mold cavity and whether the cold shrinkage is appropriate, the prediction of the mold temperature and its fluctuation, the rigidity and guiding accuracy of the mold, etc. With high-precision molds, it is also possible to form high-precision forgings on general equipment. Whether the process operation conforms to the specification, such as the deviation of heating temperature and lubrication, affects the difficulty of filling the die cavity with metal, thus causing the fluctuation of forging size.