State of the art in micro forming and investigations into micro deep drawing

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Abstract

Micro forming is an appropriate technology to manufacture very small metal parts, in particular for bulk production, as these are required in many industrial products resulting from microtechnology. This paper gives a review of the state-of-the-art in the micro forming of metals. The problems occurring in the miniaturisation of forming technologies such as micro massive forming and micro sheet metal forming are described. One of the problems is scaling effects, which e.g. occur in tribological aspects such as the friction coefficient, which increases with decreasing specimen size. Experimental investigations into micro deep drawing were carried out and the limit drawing ratio was determined. Furthermore, it was found that the friction coefficient in micro deep drawing at the flange and at the die radius are unequal and depend on the applied pressure.

Scaling effects not only appear within the process but also must be taken into account in all other areas of the forming process chain, finally demanding new solutions, especially on tool manufacturing and machine concepts. The laser is an innovative tool, which can be used for rapid tooling, building up millimetre high free-standing structures, or for the generation of near net shape structures by laser erosion. The laser technique represents an auspicious tool for the tool manufacturing industry to exploit the inherent potential of micro forming in the future.

Introduction

The estimated rise in turnover from 15 to 35 billion US$ in the last 7 years [1] shows a growing demand on micro technical products, which is mainly driven by a rising trend of miniaturisation of products. The demand of miniaturisation comes not only from consumers, who are wishing for more handy electronic devices and more integrated functions, but also from technical applications such as medical equipment, sensor technology and optoelectronics [2], [3]. All these products contain mechanical parts such as levers, connector pins, resistor caps, tiny screws, contact springs and chip lead-frames [3].

The manufacture of micro parts is very advanced in lithographic technologies, especially in LIGA-processes. Bulk production with high accuracy can be realised by these technologies, but costs are comparable high and the number of different materials is quite limited [2]. Thus, metal forming technologies become more and more established in the production of micro parts and a lot of research is currently being done in this field.

Section snippets

State of the art in micro forming

The forming of metals and thus the micro forming of metals can be divided in three sections: massive forming, sheet metal forming and profile forming. Technologies such as punching are not considered in this paper, because they belong to separating technologies. Micro forming processes are accompanied by specific tools, machines and simulations, which are also described in this paper.

Process chains

As mentioned above, micro forming processes have to be considered in their whole process chain to achieve sophisticated products. The interaction in such process chains demand a fundamental understanding of the technologies used, but also of the process conditions and the interfaces. A process chain consists of a starting point, several processes, and interfaces between the processes and the product. In this connection, interfaces are of great, often of underestimated, significance.

A

Experimental investigations in micro deep drawing

As a basic process of production, deep drawing provides a great application potential for the manufacturing of parts with complex shapes, but the smaller the dimensions of the part the more difficult the manufacturing. The reasons for this are:

  • (i)

    the ratio of surface to volume increases when the parts are minimised;

  • (ii)

    adhesion force, surface tension and so on will take more effect on smaller parts;

  • (iii)

    the influence of grains on micro forming parts will increase; and

  • (iv)

    the ratio of the closed lubricating

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