Powder metallurgy (Powder metallurgy, referred to as PM) is a metallurgical technology in which metal powder (or a mixture of metal powder and non-metal powder) is used as a raw material to form metal products or materials through forming, sintering or hot forming. The powder metallurgy production process is similar to the production process of ceramic products, so people often call the powder metallurgy method “cermet method”.
With the rapid development of all walks of life, various requirements such as lightweight and compact design, more and more parts are becoming more and more complex, prompting the powder metallurgy molding process to face more challenges.
With the increase in the amount of PM, the requirements for the process are bound to be stricter. As the most critical equipment on the powder metallurgy part production line, the powder forming hydraulic press determines the quality of the powder compact and restricts the development of the powder metallurgy industry in China. . The high-performance powder press is a powder forming hydraulic press product based on electro-hydraulic ratio technology, but its technology is in a locked state.
At present, the larger powder metallurgy production plants have introduced advanced powder forming equipment and production lines from abroad, but the introduction alone cannot solve the problem fundamentally. Therefore, independent development of high-tech powder forming equipment is also the biggest development trend in the powder industry.
Powder metallurgy forming process
Forming is an important step in the powder metallurgy process. The purpose of forming is to produce a compact with a certain shape, size, density and strength. Compression molding is the most basic forming method.
The compression molding method has simple process, high efficiency, and is convenient for automated production. However, the pressure distribution of this method is not uniform, so that the density of the green body is not uniform, and cracking is prone to occur, leading to the appearance of defective products.
a. The uniformity of the density distribution of the compact: Because the powder body flows in all directions after being stressed in the die, it causes a side pressure perpendicular to the wall of the die. The side pressure causes friction, which will cause a significant pressure drop in the height direction of the compact.
Improvement measures: 1) Reduce friction, apply lubricating oil on the inner wall or use a mold with a smoother inner wall;
2) Two-way pressing is used to improve the unevenness of the density distribution of the green compacts;
3) Try to reduce the height-diameter ratio when designing the mold.
b. Demoulding integrity: due to the elastic expansion of the female mold during the pressing process, when the pressure is removed, the compact hinders the elastic contraction of the female mold, and the compact is subjected to radial pressure, causing the compact to receive reverse shear stress during the demolding process Some weak spots on the compact may be destroyed under the above-mentioned shear stress.
Improvement measures: In terms of structure, parts should avoid thin-walled, deep and narrow grooves, sharp edges, small and thin bosses and other shapes as much as possible.
From the above two points, a rough description of the impact of a single factor in the molding control process on product quality, but in practical applications, various influencing factors are mutual. During the research process, it is found that the factors that affect product quality at the same time are:
1. The influence of forming pressure on the quality of billet: the pressing force has a direct influence on the density. The existing pressure drop causes delamination and peeling during pressing, and cracks exist at the interface of the compact after demolding.
2. The effect of pressing speed on the quality of the compact: During powder compaction, the pressing speed affects the air discharge from the pores between the powders, and directly affects the uniformity of the compact density. The density difference of the compact is relatively large. The easier it is to produce cracks.
3. The influence of holding time on the quality of the compact: During the pressing process, there must be an appropriate holding time under the maximum pressing pressure, which can significantly increase the density of the compact.
The fully automatic powder metallurgy molding equipment newly developed by Chengdu Zhengxi Hydraulic Equipment Manufacturing Co., Ltd. is designed as a new domestic pioneering equipment integrating the advantages of mechanical presses and CNC servo hydraulic presses.
The floating template type composite mold base of the equipment can effectively control the consistency of the product and the qualified rate of the product. On the basis of satisfying the constant pressure pressing, the fixed process pressing mechanism of the mechanical press is added, which can not only serve as a limit but also as a fixed pressing mechanism. The double-layer protection of pressing and pressing greatly improves product accuracy and production efficiency.
Ms.Serafina
Tel/Wts/Wechat: 008615102806197
Post time: Jun-07-2021
