The design and development of a hydrostatic extrusion apparatus

doi:10.1016/S0924-0136(00)00593-8

Journal of Materials Processing Technology

Volume 104, Issue 3, 31 August 2000, Pages 226-235

https://doi.org/10.1016/S0924-0136(00)00593-8 Get rights and content

Abstract

The purpose of this research is to design and construct an experimental hydrostatic extrusion apparatus which has a maximum working pressure of 10 000 kg/cm², and to reduce the cost of this extrusion apparatus. The high-pressure extrusion container has been designed with two-layer pyramidal cylinders, and the material used was SKD61 which is cheap and readily available. Different materials and designs for high-pressure seals were tested and analyzed for the best combination performance. Problems in the extrusion processes using this device were analyzed and solved, which increased the reliability of the device. The results of extrusion experiments have established that this device is practicable.

Introduction

Progress of technology has caused the development of new materials to fulfill new engineering demands, e.g., new alloys, powder of ceramics and superconductors, etc. These new materials are often difficult to produce. Among the new processes that were developed in recent years to produce these new materials, hydrostatic extrusion appears to have the greatest potential. The difference between the conventional extrusion and hydrostatic extrusion is that the latter uses fluid (high-pressure fluid) as pressure-transmitting medium instead of direct contact. During the extrusion, this fluid transmits a hydrostatic pressure to the billet, which can largely increase the ductility of the extrusion materials. This fluid also acts as a lubricant between the die and billet and results in a near frictionless operation. Therefore the process is capable of extruding many difficult-to-deform materials. The extrusion machine can be divided into seven parts: (1) a high-pressure extrusion container, (2) a high-pressure seal, (3) a high-pressure source, (4) a high-pressure plunger, (5) a pressure intensifier device, (6) a manganin pressure gauge, and (7) back pressure equipment (Fig. 1). The cost of a typical hydrostatic extrusion device is very high compared to that of a traditional device, therefore, to design a practical and commercially viable device has become an important engineering topic.

The idea of hydrostatic extrusion was first established by Robertson [1], but the method was first experimented by Bridgman [2]. Later research and development work was carried out by Pugh [3] and his colleagues. They developed the back pressure system in 1964 [4], that can prevent the cracking of brittle material in simple hydrostatic extrusion. Following this, further research and experimentation was done at High Pressure Laboratory of the Academy Sciences of the USSR, as well as in the USA, and Japan.

The disadvantage of simple hydrostatic extrusion is that the extrusion speed is uncontrollable. Slater and Green [5] presented the way of “augmented hydrostatic extrusion” to overcome this problem. With this method, when the fluid pressure is insufficient to extrude the billet, an additional force is applied to the rear end of the billet by a solid ram. The extrusion speed can thus be well controlled. However, the length of the billet is then limited by buckling under the axial compressive force of the ram.

When Bridgman experimented with hydrostatic extrusion, he observed a severe fluctuation in the pressure, which was related to the “stick and slip phenomenon”. This happened because the fluid is compressible under the high pressure. When extrusion begins, there is a sudden drop in pressure and the extrusion process then stops until the pressure builds up again. Crawley [6] introduced a method to overcome the “stick and slip phenomenon”. He built a hydrostatic extrusion machine in which the volume of oil and the speed of the ram can be matched to prevent the occurrence of the phenomenon. Later, Duffill [7] designed a cross-bore arrangement hydrostatic extrusion machine which had a maximum design pressure of 40 t/in² (about 6200 atm pressure). The advantage of this arrangement is that the rams never need to be withdrawn from the ram chamber, which reduces the machine cycle time. These developments simplified the hydrostatic extrusion machine and decreased its cost.

Today, the usage of hydrostatic extrusion is still limited to special applications such as golden-wire making for the semiconductor industry. The main cause obstructing the development is the cost of the device. Therefore, the topics of this research are not only to design and construct a hydrostatic extrusion device but also to solve problems during its operation and to simplify the equipment by using commercially available materials.

Section snippets

High-pressure source

The high pressure of this experimental hydrostatic extrusion apparatus comes form the compressed fluid in a pressure container (Fig. 1). This cylindrical pressure container has an inner bore, 16 mm in diameter, fitted to a plunger. When a universal-testing machine with maximum capacity of 20.2 t is used to compress the fluid in the container through this plunger, a magnified fluid pressure as high as 10 000 kg/cm² (about 10 000 atm pressure) will be obtained in the pressure container.

High-pressure extrusion container

One of the most

Preliminary tests

After each component of the apparatus was built up and assembled according to the above design, preliminary tests that pressurize the system without the extrusion process are to be conducted. The set-up is shown in Fig. 4. In this research, a 10 000 kg/cm² hydrostatic pressure is designed for extrusion. Therefore, 20 110 kg force is applied to the high-pressure plunger by the universal tester. The results of this test show that no leakage and failure occur during the process, which verified that

The hydrostatic extrusion experiments

Hydrostatic extrusion experiments were conducted using the above apparatus to test its practicability as well as to observe the properties of materials after high-pressure extrusion. The processes of the experiments are discussed in the following sections.

Results and discussion

This section summarizes and discusses the results of the hydrostatic extrusion on two types of billets.

Conclusions

In this research, an experimental hydrostatic extrusion apparatus was designed, built and modified with emphases on both simplicity of structure and low cost with commercially available materials. Two types of billets were extruded using this apparatus to verify its practicability. Satisfactory testing results were obtained together with some information on the material behavior under hydrostatic pressure. While further investigations on the effects of hydrostatic extrusion parameters are going

Acknowledgements

The authors would like to thank the National Science Council of Taiwan, ROC for the grant NSC86-2212-E-009-015, under which the investigation was undertaken.

References (11)

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