2, the impact of die material selection
Choosing the right die material will prevent early die failure. The inclusions cause cracks inside the die, causing brittle fracture, which further expands to cause cracking of the die during further heat treatment and use. When the steel is subjected to hot working and annealing, the decarburized layer may remain after reworking. Due to the different inner and outer layers, the heat treatment cooling rate is inconsistent, causing cracks and causing cracking of the die. It contains high carbon and alloying elements and has many eutectic compounds. As a result, cracks along the banded carbides often appear during quenching. The cracks further expand during the use of the die, causing the die to crack.
3, the impact of die machining
The cavity portion of the die or the rounded portion of the punch is often left in the machining process because the feed is too deep, leaving a tool mark, causing stress concentration, and the crack at the corresponding portion is further expanded during quenching, causing the die to crack. During electromachining, the die is heated to a high temperature to change the structure, that is, the electroforming abnormal layer is repeatedly subjected to alternating stress, and the microcrack becomes a large crack, causing the die to be cracked and scrapped. Grinding can cause the surface of the grinding surface to overheat, or cause the surface to soften, the hardness is lowered, the die is severely worn during use, or the grinding crack is generated due to thermal stress, which eventually leads to early failure of the die.
4, the impact of die heat treatment specifications
The die shall be subjected to heat treatment such as quenching and tempering after machining. Improper selection of process parameters such as the temperature of the heating, the length of time, the size of the cooling rate, and the protective atmosphere all affect the durability of the die. The mold steel contains more carbon and more alloying elements, and the thermal conductivity is poor, and the heating speed cannot be too fast.
When oxidation occurs, the surface of the die is easily scratched and the size becomes small. It is easy to produce early fatigue cracks. When decarburization occurs, the surface hardness is significantly reduced, causing early wear; the quenching temperature is too high, which tends to cause grain growth. Steel exhibits brittleness, so cracks, chipping, breakage and the like often occur in the use of the die. On the contrary, the quenching temperature is too low, the compressive strength of the steel is also low, and the punch is prone to drumming and failure. For different die materials, different cooling speeds should be selected according to the required microstructure. For high alloy steels, due to the inclusion of more alloying elements, the hardenability is lower, oil cooling, air cooling, even austempering and grading can be used. Quenching and other processes. The strengthening treatment of the die surface is also an important way to improve the service life of the die. Nitriding, boronizing, carburizing and chrome plating all have certain effects. When the intensive process control is not strict or the strengthening method is not properly selected, it is impossible to obtain The expected effect, on the other hand, leads to the early failure of the die.
5, various operating conditions
For example, forging temperature, lubricant and lubrication methods, cooling rate, repair welding, preheating temperature and equipment conditions have a great impact on the durability of the die. It must be strictly controlled and properly used to obtain the high die life of the die material. The weld is prone to cracks during repair welding. Due to the tensile and compressive stress, the crack propagation shortens the die life.
6, the impact of the working temperature of the die
The working temperature of the die can be divided into several states such as low temperature, normal temperature or alternating temperature, and the temperature has a considerable influence on the wear resistance of the steel. Usually under 250 degrees, it is mainly oxidative wear, that is, the relative friction between the die butt joint or the die and the workpiece, forming an oxide film and repeatedly forming and peeling off, the wear amount is small; when it is between 250 degrees and 300 degrees, it becomes adhesive wear. The wear amount reaches the maximum value; above 300 degrees, it is converted into oxidative wear, and the wear amount tends to decrease. However, when the temperature is too high, the hardness of the die is obviously decreased, the sticking phenomenon is aggravated, and even a large area of ​​sintering and melt wear is formed.
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