Cold Isostatic Pressing Moulds

Cold Isostatic Pressing Moulds

How to Design the Mold for Cold Isostatic Pressing

In the cold isostatic pressing molding technology, according to the different molding methods, the casing and the mold are divided into the casing mold used by the wet bag method, the dry bag method, and the balanced pressing method. No matter what kind of mold, it is composed of four basic components: elastic mold, rigid mold, port sealing device and supporting device.

The cover, end plug and mold pad of the plastic mold are made of materials such as rubber or plastic. In cold isostatic pressing, the plastic mold not only plays the role of mold, but also plays the role of transmitting pressure to make the powder compact. The mold core, mold, etc. of the rigid mold are made of metal materials. The size and shape of the rigid mold remain unchanged during the molding process.

In the design of cold isostatic pressing molds in normal mass production, there are usually the following steps:

(1) Carry out small-scale simulation tests to determine the compression ratio during powder molding. The relationship between pressure and properties such as compact density and strength, and the basic data such as the shrinkage rate of the blank after sintering.

(2) According to the obtained test data. And consider the machining allowance and dimensional tolerances that need to be left after forming. Design the shape and size of the mold, and then check it through the actual measurement results. After repeated tests for many times until the shape, size and performance of the formed blank meet the technical requirements.

(3) Select the jacket material, determine the wall thickness of the jacket and the material of the metal mandrel, and determine the assembly method of the mold, the sealing of the charging port and the port, and the fixing device. If there is practical experience and data of this work, the design steps can be simplified. In short, in the design of the mold, we should not only pay attention to the rationality of the design, but also take into account the economical practicability of the mold.

The main factors affecting the package and mold design are as follows:

There are a series of factors to consider in jacket and mold design, among which the packing density of powder is the most critical. The uniformity of the filling density of the material in the mold and the size of the filling density are the main basis for the mold design.

The filling density of the material in the mold is affected by the following three aspects.

(1) Effect of powder properties on filling density. The influence of powder properties on filling density refers to the influence of powder particle shape, particle size composition and surface state on filling density. The packing density of regularly shaped spherical particle powder is higher than that of irregularly shaped dendritic particle powder. The packing density of powders with particle size distribution is higher than that of single particle size powders.

(2) The influence of the filling method of the powder. In practice, natural filling, artificial vibration, manual compaction, mechanical vibration, centrifugal filling, etc. are usually used. Among them, the natural filling density is the lowest. Mechanical vibration has the highest packing density. Although artificial vibration can obtain a high filling density, the filling is uneven, and the surface flatness of the green compact is poor.

(3) The influence of the mold itself. During the filling process, there is internal friction between the powder particles and external friction between the powder and the film, which limits the fluidity of the powder in the cavity. to this end. The filling port of the mold should be at the highest point of the cavity. In order to reduce the friction between the powder and the mold wall during the filling process, the surface of the mold wall should be as smooth and straight as possible. Didn't say anything about plastic Bao Kui. Supporting devices should be provided outside the sheath. It is beneficial to increase the packing density of powder.

Some cold isostatic pressing molds we made:

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