Durability has a close relationship with the use of the die. If the durability is not good, it will cause the die to be damaged early and cannot be used normally. Therefore, when using a die, we must understand what factors will affect the durability of the die, which can not only improve The performance of the die can also extend the service life of the die.
Six factors affect the durability of the die:
1. The impact of unreasonable structural design
The die structure is the key to the durability of the die. Unreasonable structure can easily cause poor rigidity and uneven wall thickness distribution, as well as surface defects (such as surface oxidation, decarburization, cracks, scars), which will affect the performance of the material and cause early failure of the die .
2. The influence of die material selection
Choosing the right die material can prevent early failure of the die. Inclusions cause cracks in the die and cause brittle fracture. In further heat treatment and use, the cracks further propagate and cause the die to crack. When the steel is hot processed and annealed, sometimes there is still a decarburized layer after re-machining. Due to the different structure of the inner and outer layers, the heat treatment cooling rate is inconsistent, cracks occur, and the die cracks. Containing higher carbon and alloying elements, there are more eutectic compounds, resulting in cracks distributed along the band-shaped carbides often appear during quenching. The cracks further expand during the use of the die, causing the die to crack.
3. The influence of die machining
The cavity part of the die or the rounded part of the punch is often left with a knife mark due to too deep cutting during machining, which causes stress concentration, and the cracks in the corresponding part further expand during quenching, which causes the die to crack. During electrical machining, the die is heated to a high temperature to change the structure, that is, the abnormal layer of electrical machining is repeatedly affected by the alternating stress, and the microcracks become large cracks, causing the die to crack and be scrapped. Grinding process can cause overheating of the ground surface, or cause surface softening and decrease in hardness, which will cause severe wear of the die during use, or grinding cracks due to thermal stress, leading to early failure of the die.
4. The influence of die heat treatment specifications
The die should be quenched and tempered after machining. Improper selection of process parameters such as heating temperature, length of time, cooling rate, protective atmosphere, etc. will affect the durability of the die. Die steel contains more carbon and more alloying elements, has poor thermal conductivity, and cannot be heated too fast.
When oxidation occurs, the die surface is easily scratched, the size becomes smaller, and early fatigue cracks are likely to occur when used. When decarburization is caused, the surface hardness is significantly reduced, causing early wear; excessively high quenching temperature will easily cause grain growth and make Steel is brittle, so accidents such as cracks, chipping, and breakage often occur in the use of die. On the contrary, if the quenching temperature is too low, the compressive strength of steel is also low, and the punch is prone to bulging and failure. For different die materials, different cooling rates should be selected according to the required microstructure. For high alloy steels, because they contain more alloying elements, the hardenability is low. Oil cooling, air cooling, or even austempering and grading can be used. Quenching and other processes. The strengthening treatment of the die surface is also a very important way to improve the service life of the die. Nitriding, boronizing, carburizing and chromium plating have certain effects. When the strengthening process is not strictly controlled or the strengthening method is not selected properly, it is impossible to obtain The expected effect leads to the early failure of the die.
5. Various operating conditions
Such as forging temperature, lubricant and lubrication method, cooling rate, repair welding, preheating temperature and equipment conditions have a great influence on the durability of the die. It must be strictly controlled and used correctly in order to give full play to the performance of the die material and obtain a higher die life. Cracks are prone to appear in the weld during repair welding. Due to the effect of tensile and compression alternating stress, the crack propagation shortens the die life.
6. The influence of die working temperature
The working temperature of the die can be divided into several states such as low temperature, normal temperature or alternating temperature. Temperature has a considerable influence on the wear resistance of steel. Usually when the temperature is below 250 degrees, it is mainly oxidative wear, that is, the relative friction between the die butt or the die and the workpiece, forming an oxide film and repeatedly forming and peeling off, the amount of wear is small; when it is between 250 degrees and 300 degrees, it becomes adhesive wear , The wear amount reaches the maximum value; when the temperature is higher than 300 degrees, it is mainly converted to oxidative wear, and the wear amount tends to decrease. However, when the temperature is too high, the die hardness decreases significantly, the adhesion phenomenon increases, and even larger areas of sintering and melting wear are formed.