山东Defects of powder metallurgy compacts

The other day, we received a request from Lianyungang Industry and Trade Technical School to provide them with bearing sleeve blanks directly sintered into semi-finished products. At first, they bought seamless steel tubes for cutting and then processed them on CNC lathes. Because the order volume reached 10000 pieces per year, the traditional manufacturing method was not economical enough, so they used powder metallurgy technology to produce.

Lianyungang Industry and Trade Technical School will provide graduates to Lianyungang Dongmu New Materials Co., Ltd. every year, so it has always maintained a close cooperation relationship. Through negotiation, Lianyungang Dongmu New Materials Co., Ltd. will provide blanks for the bushings this time, and then the school will finish the machining once.

Such cooperation mode is not new. Although Lianyungang Dongmu only produces powder metallurgy blanks, there will be many pressing defects in the production of blanks. It is mainly embodied in delamination, fragmentation and shear crack.

Delamination is a crack in the vertical pressing direction, which may be a very thin hair like crack, usually the severe one will cause partial or complete separation of the compact. The main reason for delamination is the elastic recovery of the female mold and the blank at the end of the pressing stroke. Figure 11-17 shows the formation and development process of delamination: ① flat pores are formed during compaction; ② When the pressure acting on the compact is released, the pores expand due to elastic recovery; ③ During the demoulding process, when the billet expands radially, several flat pores are merged.

The measures to prevent delamination are: ① effective lubrication to reduce the friction during demoulding to the extent of * * *; ② stay

Keep positive pressure on the blank during demoulding; ③ The upper part of the female mold has a slight taper, so that the compact will gradually swell during demoulding; ④ Reduce the pressing rate to avoid air interception; ⑤ The particle size distribution of mixed powder is appropriate.

For compacts with complex geometry, due to low green strength, improper lubrication and excessive demoulding pressure, the section of the compacts may be broken during demoulding.

For parts with worktops of different heights in the pressing direction, shear cracks may occur at the joints of different worktops when the moving rates of die punches forming different worktops are not completely synchronized.

Therefore, it is very important to produce the blank. After sintering, it will be transferred to Lianyungang Industry and Trade Technical School for machining. The unit price of this powder metallurgy product is calculated to be 12 yuan lower than that of the previous production, so 12W yuan can be accepted when it is supplied for one year. This fully reflects the advantages of powder metallurgy.