What defects often appear in metal powder metallurgy preforming process?
In the process of metal powder metallurgy, the blank defects will be produced for various reasons, leading to the scrap of powder metallurgy parts. So, what defects often appear in the process of metal powder metallurgy billet?
1. The density of the billet does not meet the design requirements
In the production of metal powder metallurgy parts, the higher the material density, the higher the physical and mechanical properties. In other words, the density and distribution of metal POWDER metallurgy parts will determine the performance of the products. Therefore, in the process of metal powder metallurgy mold debugging and pressing, the density of the billet is a must be tested item. In density detection, attention should be paid to different structures and requirements of the billet to be treated differently.
2. The pressing size does not meet the requirements
2.1 Unqualified radial size or hole spacing
There may be a mold design or manufacturing problem. If the error can be eliminated by adjusting the process (i.e. by adjusting the powder composition, pressing density, sintering process, etc.). Can also be remedied, otherwise only scrap the mold.
2.2 The axial dimension is not qualified
The axial dimension can be adjusted and stabilized by adjusting the powder loading, changing the pressing pressure or prolonging the holding time of the cylindrical blank without steps. For step billet, the step height can be changed by adjusting the forming position of the combined die punching, the filling ratio of each platform and the running speed of the floating die punching.
3. Shape and position tolerance is out of tolerance
3.1 the straightness
The causes of straightness out of tolerance are: the straightness out of tolerance of the mold, the uneven density distribution of the blank, and the uneven wall thickness of the blank.
The causes of the parallelism are: the parallelism of the mold is out of sync, and the powder is not uniform.
The causes of coaxiality out-of-tolerance are: the precision of the mold is out-of-tolerance, the precision of the pressing tooling and equipment is low, the mold installation does not meet the requirements, and the dressing is not uniform.
In the case that the powder flow rate is appropriate, the mold precision meets the design requirements, and the precision of the pressing fixture and equipment meets the installation requirements, the shape and position tolerance is mainly related to the density distribution of the billet, and the density distribution of the billet is directly related to the powder filling effect when the pressing mode is determined.
4. the appearance is unqualified
High roughness, excessive burr, falling edge and Angle, hair-pulling and cracks are common appearance defects.