Solution to the cracking of powder metallurgy products

(1) materials integrated error

For a variety of reasons, metal powder additives are used. For example, adding a suitable lubricant mixed will enhance the compressibility, reduce demolding force. However, mixed powder added lubricant can inhibit the formation of bonding between particles, adhesives, impurity and residual air will be the bond formation have a negative effect.

(2) particle displacement

Bonding between particles initially mainly by the plastic deformation and the powder block movement formation, under ideal conditions, the densification process is a two-way, symmetrical and synchronous and will not happen between particles shifted side. Densification process after the shift will prevent the formation of bonding between particles, and can has been broken in forming the early formation of the bond.

(3) non normal plastic strain separation process

Particles will not recoverable plastic deformation. In addition to the recovery of plastic deformation will occur. The final forming stage, the pressure will reduce and eventually in the demoulding process is reduced to zero. Forming pressure vent out moment, compressive stress release, forming body embryo will suddenly from the plastic changes in the aptitude elastic stage. If the internal stress is less than the limit of the strength of the body, the crack will be generated.

(4) high tension and shearing force

Under the condition of powder metallurgy, if the forming body is formed by external or internal forces, the shear force is higher than the strength of the raw embryo, then it will crack.

(5) the cause of crack caused by material integration

Air left in the forming process of powder material, powder weight is approximately in accordance with a 2:1 ratio decreased. Inter granular pores filled with air must be in the forming process of extrusion, and must be completed in less time, the air must be from the powder matrix and design with the gap tolerance of very small mold assembly is extruded.

Powder metallurgy parts crack mainly occurred before the sintering process of pressing forming and processing process. Although crack may be in sintering becomes apparent, but the root cause of the cracks may is prior to sintering bonding between particles are relatively poor. Sintering caused by stress may crack "open", but this is likely to have been produced prior to sintering processing step. Few examples of incorrect product design may lead to sintering at higher stress level. Therefore, we should stress level may exceed the strength of the parts of the leading to mechanical failure.