Discussion on the forging process of the hottest a

Discussion on the forging process of alloy tool steel

Abstract: according to the experience of stamping and the experience of using imported and domestic stamping dies, this paper puts forward the technology of changing the forging process of alloy tool steel and the key points of operation

key words: Machine Manufacturing: alloy tool steel; Forging; Die

1 preface

die manufacturing is the most widely used field of various alloy tool steels. The following varieties are commonly used: carbon tool steel, low alloy tool steel, matrix steel and medium carbon low alloy steel

for a long time, the service life of domestic molds is generally low. Compared with the advanced level, the service life of stamping parts with the same molding materials, similar or even exactly the same, is only 1/3 ~ 1/2 of that of developed countries. The main gaps are in the aspects of molding materials, forging blank quality and molding technology

2 quality of forging stock of stamping die

generally, the failure form of stamping die is mainly wear, followed by deformation, fatigue and fracture. Wear is the most common and common failure form. Through the analysis and research of a large number of failed scrap dies, it can be seen that no matter which failure form is closely related to the material properties and internal quality of punch and die. There are several cases of punching failure:

(1) excessive wear of the cutting edge. This mainly occurs on blanking dies, and the wear of punch and die is related to the properties of molding materials and heat treatment. Therefore, the forging blanks of punching punch and die should be made of wear-resistant and high-quality alloy materials undertaken by CCPIT, and the blank should be made by changing the forging process; In addition to quenching, nitriding, soft nitriding and other surface strengthening treatments are also required for male and female dies in heat treatment. In this way, the hardness of the die can reach more than hrc64, and the service life of the die can be increased by times

(2) punch is broken. This form is especially prominent on non-circular punching (or blanking) punch, which is not only related to material properties and heat treatment, but also related to their complex cross-section. Therefore, to prevent this kind of failure, we should not only improve the performance of the die forging blank and strengthen the surface, but also improve the complex shape of the punch cross-section without affecting the quality of the punch, and eliminate factors that are easy to cause stress concentration, such as acute angles, notches, bosses, tooth shapes, slender cantilevers, etc

(3) forming cavity wear, local collapse, punch upsetting. This kind of failure mainly occurs in stamping, embossing, deep drawing, bending, wave pressing, punching and squeezing. 2018 will be a small peak of vehicle power battery recycling, such as flattening, accumulation, bulging, bulging and reducing. For this kind of failure, in addition to material problems, through the surface strengthening treatment of the mold cavity, surface grinding and polishing (ra=0.1 μ m) With effective lubrication, it can be effectively prevented and the service life of the die will be greatly improved

3 significance of changing high alloy tool steel to forging

as a common material for stamping dies, all the mechanical properties of high alloy tool steel are closely related to the service life of stamping dies. In foreign countries, the mechanical properties of high alloy tool steels are often improved by forging, while domestic high alloy tool steels, especially high alloy tool steels for cold working dies (such as Crl2, Crl2MoV), have extremely uneven eutectic carbides, which cannot meet the needs of stamping dies without modification. Therefore, it is necessary to adopt advanced forging technology to change the forging to meet the requirements of die making

the forging of high alloy steel for cold working die is not limited to obtaining ideal geometry and eliminating metallurgical defects (such as internal porosity, non oxidative pores, grain refinement, tight structure, etc.) in forging welding. More importantly, through reasonable forging operation, the mechanical properties of steel can be greatly improved

4 basic process elements of changing forging

changing forging of high alloy tool steel rolling (forging) is different from general free forging, and each link has specific requirements for deformation accuracy. 8.3 during the transportation, loading and unloading of products, it is strictly forbidden to throw, throw, dump and unload. If you want to change it into high-quality punch punch and die forgings, you must determine the following basic elements in advance

4.1 requirements for original blanks

mold manufacturing is mostly single piece, small batch production, and sawing is mainly used for cutting the original blanks of die forging blanks. Both ends are required to be flat (the inclination angle is less than 10 °), and the blank size should also consider the machining allowance and fire consumption. In order to meet the first upsetting forging ratio and facilitate the crushing of carbides with coarse particles in the material structure, it is recommended to determine the blank length size according to the following formula:

2D steel grade heating temperature/℃ forging temperature/℃ initial forging and final forging crcrcr12mocr12movcr12vcr6wvcrwmn

4.3 forging equipment tonnage

high alloy tool steel has higher strength and poor plasticity than ordinary carbon steel at forging temperature. In order to make it easier to forge near the final forging temperature and break the carbides in the steel, so as to improve the internal structure of the steel, the tonnage of the forging equipment should be higher when forging high alloy tool steel. Refer to table 2 for equipment according to the weight of forgings. Table 2 recommended table for selection of forging hammer tonnage

forging weight/kg forging hammer tonnage/kg

shape, size and surface quality meet the requirements, and it is also required to improve its internal quality. So far, the latter still depends on the deformation step of forging. For general carbon steel and low alloy steel, it is necessary to increase the forging ratio and forge violently at the initial forging temperature to make it fully forged, which is enough to improve its internal quality. However, high alloy tool steels, especially low plasticity alloy steels, cannot be forged by free forging because of their low plasticity. However, when they are in the state of omni-directional unequal compression (i.e. the state of three-dimensional compression stress), their plasticity can be improved. Extrusion in the extrusion barrel and die forging in the closed die cavity belong to this stress state

when forging high alloy tool steel with free forging process, if the forging step of square, flat, square and long is adopted, the stress state of the forging blank can be regarded as an approximate three-dimensional pressure state, which can better forge through and tap the plastic potential of the material

4.4 selection of forging steps for changing high alloy tool steel

high alloy tool steel stamping die forging blank requires that its eutectic carbide particles should be fine, symmetrical and evenly distributed, without macro and micro segregation. Unrefined domestic high alloy tool steel rolled (forged) materials need to be forged to change the mechanical properties of materials and meet the requirements of die forgings. At present, there are several effective methods to improve Satin:

(1) upsetting and drawing along the fiber direction for more than 3 times. Ensure that the forging ratio is> 2 along the direction (axial direction) of the raw fiber, and quickly and continuously upsetting and drawing more than 3 times in one fire. This method is suitable for the modification of high-speed steel and small-size high alloy tool steel forgings. The disadvantage is that if the number of upsetting and drawing is insufficient or the forging ratio is too small, the forging cannot be penetrated, resulting in obvious directionality of carbide distribution: hollow cracks are easy to appear when the operation is not proper

(2) change direction and repeat upsetting and drawing for more than 3 times. The first time is upsetting and drawing along the fiber, and the second time is stretching and upsetting perpendicular to the fiber direction. In this order, it can be divided into single cross, double cross and multi cross upsetting and drawing. The key points of this upsetting and drawing process: complete all cross upsetting and drawing in one fire; If the forging ratio is> 2, the height difference of the forging blank before and after upsetting is twice; In order to avoid upsetting bulge cracks, tilt rotation should be used for multiple tapping and quick beating; Lengthening adopts square, flat and square feeding. Production practice has proved that after three kinds of cross upsetting and drawing, it can meet the needs of changing forging for most of the rolled (forged) blanks below 80mm

although the same deformation steps and production conditions are adopted, due to the different operation skills of the forgers and the internal quality difference of the original blank, the effect of the modified forging is sometimes still quite different. Conclusion: after modification of forging, the unevenness of eutectic carbide of gr12mov steel forging billet can reach more than grade 2 of the national standard, and some can also reach grade 1, which increases the unevenness of carbide of the original blank rolling (forging) material by more than grade 4. Statistical data shows that the service life of this die made of forged high alloy tool steel has been greatly improved (up to 30% - 50%). (end)