德语
Forging is an indispensable process in the production of hardware products in Gongxian County. How to choose excellent steel for hot forging molds to improve the service life of the mold, reduce production costs, and improve economic benefits has become a common concern for all production enterprises.
1. Working conditions of hot forged mold steel
1. Using tool hardware products as the guillotine. At present, most domestic manufacturers use hot forging forming process with a motorcycle press as the main machine, that is, the mold is loaded into the general mold frame of the press, and the high-temperature (about 1000℃) pre-forged blanks are continuously forged in the mold cavity. Due to the high forging speed (800-900 pieces/hour), the surface temperature of the mold cavity can reach about 500-600℃.
2. In order to shape the blank and achieve a predetermined dimensional accuracy, this module bears a large impact force, while the mold cavity bears three-way compressive stress.
3. During the thermal forming process of the blank, the flow of metal rubs against the surface of the mold cavity.
4. The mold cavity of the upper and lower dies is in a cooling state during empty stroke (natural air-cooling, compressed air blow-cooling or spraying, etc.), which corresponds to the heated state of the mold cavity during work, so the hot forging mold always works in the thermal alternating cycle state.
2. Common hot forging nose failure
1. When the thermally worn high-temperature metal flows plastically in the mold cavity, it resists relative friction with the mold cavity meter, resulting in loss of dimensional accuracy of the mold cavity and failure.
2. Thermal deformation is caused by the bed surface of the mold cavity, and the three-way compressive stress, and the mold cavity collapses and fails.
3. When the cracking mold is forged, cracks or fragments appear on the surface. Some micro-cracks are hidden in the substrate.
3. Causes of hot forging mold failure
1. Unreasonable design, such as improper preformed blank, clean the corners of the mold, inappropriate volume of the flicker groove (grooves) and bridge size.
2. Improper material selection. The mold material performance cannot meet the working conditions of the hot forging die.
3. Improper heat treatment, incorrect heat treatment process, failure of temperature control instrument, etc.
4. If the initial forging temperature of the forging is too low, the forging blank is deviated in the mold cavity, mold repeated strike, etc.
5. The forgings and the press do not match, such as the forging force far exceeds the deformation resistance of the forging.
6. Metallurgical quality problems of mold raw materials such as low-magnitude structure exceeding the standard, and the forging ratio of the cross-section of the steel ingot and the mold blank is too small, which is not enough to break the mesh carbide.
7. The mold management is chaotic such as no mold card, no inspection, or even mixed steel. In short, the cause of the failure of the mold is comprehensive and should be overcome in the process of design, material selection, manufacturing, and use.
4. Characteristic requirements for hot forging mold materials
Hot forging molds work under conditions where both mechanical load and temperature change cyclically, so the material selection must meet the following performance requirements as much as possible:
(1) High red hardness (high temperature wear resistance after printing) When the surface temperature of the mold cavity reaches 500~600℃, it still has a high hardness.
(2) High temperature strength mainly refers to the material having a higher yield point at a high temperature of 500600℃.
(3) For hot forging mold materials, the value of high impact toughness should be no less than.
(4) Hot forging mold materials with high fracture toughness should have a higher value to improve the control of the crack expansion rate of the mold (slow down the crack expansion).
(5) High thermal fatigue resistance Hot forging mold materials should have high resistance to alternating stress generated by hot and cold cycles. Judging from the current situation, it is difficult for hot forging mold steel to fully possess the above properties, but it is not advisable to unilaterally emphasize a certain performance. For example, mold steel with very good red hardness has poor impact toughness. After the mold is made, although it is not easy to wear and collapse, it will break prematurely, which is meaningless. Therefore, the material selection should comprehensively consider the above five properties.
5. Classification and selection of steel for hot forging molds
Hot forging die steel is usually divided into three categories: medium carbon low alloy, medium carbon medium alloy and medium carbon high alloy. In practical applications, due to the red hardness and low high-temperature strength of medium-carbon low-alloy hot forging die steel, it is generally only used as hammer forging die steel for air hammers. Especially 5 and 5 have poor hardenability and can only be used for medium and small hammer forging dies. 5: and 45 can be used for medium and large hammer forging dies.
Although medium-carbon high-alloy hot forging die steel has high red hardness and high-temperature strength, its low toughness and huge difference in thermal fatigue resistance are fatal flaws. Although quite a few companies still use this kind of material to make hot forging molds, the molds will fail due to cracking during use, which is very troublesome.
It is more suitable to choose hot forging dies for friction presses made of medium phosphorus Zhongtai gold hot forging chess tool steel. Because this type of steel has both strength and toughness and good overall performance, it can effectively overcome die failure caused by various factors and has good economic benefits.
6. Introduction to 328 steel
328 steel has been developed since the 1920s and has a history of seventy years. It was originally developed as a high-speed steel. However, due to failure, it was used as a hot work die steel and was retained. Its chemical composition is very close to the current 942, so it is called semi-high-speed steel.
This steel type contains 0.35% carbon (on average) and is a hypoeutectoid component. Due to Zhou 8, the precipitation point shifts to the left and has actually entered the eutectoid region, so it is classified as martensitic steel. Due to its high content, this steel has good red hardness and high temperature strength, so it has been used for decades and is still widely used in China. However, this steel type has two major insurmountable shortcomings;
1) Low impact toughness (due to the large atomic diameter, it dissolves into the crystal lattice and causes distortion, making the material brittle);
2) It has poor thermal fatigue resistance and weak resistance to crack expansion. This steel type is gradually being phased out internationally. The peak secondary hardening temperature of 328 steel is about 55~570°C, and the specific gravity is 8.35. The failure modes of the molds produced by it are collapse and fragmentation during use.
7. Introduction 3 (45) Gangmei
The 5 series hot work die steel used in China was developed in the 1930s. Due to its good overall performance, it was introduced to Europe in the 1950s and was widely used by industrialized countries in the 1960s. Large-scale special steel plants in the United States only produce !, 2, 3, and 211 steel grades, and its representative grade is 13.,
Its heat resistance is not as good as 328 steel. This is because tungsten carbide is not easy to aggregate and grow. 2=13 steel contains carbide-forming elements such as 0 and 0, giving it secondary hardening ability. It is far superior to 328 in terms of impact toughness, thermal fatigue and crack propagation resistance. The proportion of 13 steel is 7.71
The secondary hardening peak temperature of 13 steel is around 50°C. At 5°C, as the temperature continues to rise, its hardness drops sharply. Our factory began to conduct research on the direct use of 3 steel in 1986. In 1987, it was officially used in hot forging dies for some hand tool products. So far, most of the steel used in hot forging dies has been replaced by 8 steel, and considerable economic benefits have been achieved.
8. Analysis and comparison of 328 steel and 13 steel
The comparison between 328 steel and 13 steel in terms of material properties, heat treatment process, application and economic benefits is shown in the attached table.
9. Measures to improve the service life of hot forging dies
1. Design In addition to the correct cavity design of the forming mold, everything from raw materials to forgings is prefabricated.
2. The selection of hot forging mold materials is the basis for improving the life of the mold. You should be familiar with the performance and characteristics of various materials, and determine the most suitable material after analysis and comparison.
3. Metallurgical quality of mold materials Strictly speaking, the smelting quality of hot forging mold steel is no less than that of aviation materials.
11 things to pay attention to when designing two-color plastic molds, as well as the selection of soft rubber and hard rubber materials
1. Two-color mold design considerations:
1. Mold steel, available H13, 420H, 1.2344, NAK80, etc.
2. Leave an extra 0.07~0.13mm in the soft glue sealing position as pre-pressure. If it is a large area of sealing, you can reserve 0.2~0.25MM.
3. Hard glue must be supported by steel, especially the back side with soft glue, and the space should not be larger than 0.5MM.
4. The softening temperature of the bottom part and the rubber covering material must be at least 20 degrees apart, otherwise the bottom rubber part will melt.
5. If TPE is used, the exhaust depth is 0.01MM.
6. The shrinkage rate of soft rubber should be the same as that of hard rubber.
7. For TPE materials, the gate is not suitable for hidden ejector pins. Instead, a straight top can be used. The glue is inserted on the straight top. It is best to use a square shape. The fit between the straight top and the hole must be smooth, and the gap should be within 0.02MM, otherwise glue powder will easily be produced.
8. The runner should not be polished. Leaving lines can help the mold to come out. The front mold should be sun-dried, otherwise it will stick to the front mold.
9. The shrinkage rate of TPE will change the depth of skin lines.
10. What should I do if the product is defective?
(1) Front mold welding. (2) Add glue to the hard plastic front mold. (3) Add glue to the hard plastic back mold (4) Try not to weld the back mold, because the back mold must be completely consistent after rotating 180 degrees.
11. What to do with the soft adhesive front mold?
The software area of the hard plastic package should be undercut, or the hard plastic area should be roughened to prevent the soft adhesive from sticking to the front mold.
2. Brief description of two-color mold
Why do we often say "double color"?
1. "Double-color" is actually a kind of secondary injection molding. The product generally includes a main body (hard rubber) and an outsourcing (soft rubber) part. When manufacturing the mold, the hard rubber main body is manufactured first. The main hard rubber mold is designed according to normal design procedures, and the outsourcing (soft rubber) mold is designed. The hard rubber finished product should be used as a reference, and there is no need to add shrinkage. The rear mold part is basically the same as the hard rubber body. The front mold is different in that it has a rubber covering shape. During production, the hard rubber body is first produced, and then the hard rubber body is placed in the outer mold, and then the outer soft rubber injection molding is produced.
2. "Double-color" can also be called "coating". If the product output is not high, you can use a coating mold. First make a set of hard rubber molds, and then manually put the hard glue into the coating mold to form soft rubber.
3. The rear mold part of the soft package mold is the same as the main hard glue, with a small amount of space to avoid. The glue part must be glued with the main hard glue and there should be no empty space. It should be noted that the TPU material itself is easier to stick to the mold. If the product can be made into a sand surface, try to make it into a sand surface, so that it is easy to demould! The fluidity of TPU is relatively slow, and the cooling cycle will be relatively long. As long as you pay attention to the production process, there will be no big problem!
3. Two-color mold
The standard method for a two-color mold is to add shrinkage water to the soft glue in the mold design, which should be consistent with the hard glue. The male mold part of the two sets of molds is exactly the same, and the two mold cores of the female mold are different. The two sets of molds are installed on the same injection molding machine for injection molding (the height of the two sets of molds must be the same). After the first shot of hard glue is shot (the small nozzle is inserted into the glue), the mold is rotated 180 degrees, the second shot of soft glue is made, and then the product is ejected. This is called a two-color mold.
4. Commonly used hard rubber and soft rubber materials for encapsulation
Hard glue: ABS, AS (SAN), GPPS, HIPS (475), PA (PA6, PA66 and its modified materials), PC and its modified materials, PE, POM, PP, etc.
Soft rubber: TPE, TPR, TPU, TPV, TPEE, PVC, etc.
Source: Civilian Fitness Method, Psychological Crisis Strategy
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