metals

A. Diehl, D. Staud, U. Engel
Chair of Manufacturing Technology, University of Erlangen-Nuremberg Egerlandstr. 11, D-91058 Erlangen / Germany

Abstract

Ongoing miniaturisation leads to increasing complexity of micro parts linked with continuously decreasing development time. Hence, the demand for reliable material data and means to collect these data in a most efficient way is rising. Since the mechanical properties and thus material forming behaviour are dependent on the stress and strain conditions, the test methods have to be as close as possible to real conditions. Further, due to the so called size effects, data gathered from conventional length scale experiments cannot be used for the description of material used for parts with feature sizes in the micrometer range. In the present paper, the hydraulic bulge test as a means for the mechanical characterisation of thin metal sheets with thicknesses in the range of 25 μm to 500 μm is discussed and compared to data obtained by conventional tensile testing. Challenges due to the small sheet thickness are emphasized and the effect of strain rate on the flow curve is shown. The influence of geometric dimensions on the evaluation of the experiments is investigated by downscaling of the hydraulic bulge test. The material flow curves, as well as the forming limits are discussed in dependence of the sheet thickness.

S. Geißdörfer (a), A. Rosochowski (b), L. Olejnik (c), U. Engel (a)

(a) Chair of Manufacturing Technology, University of Erlangen-Nuremberg, Egerlandstrasse 11, 91058 Erlangen, Germany
(b) Department of Design, Manufacture and Engineering Management, University of Strathclyde, 75 Montrose Street, Glasgow, United Kingdom, G1 1XJ
(c) Institute of Materials Processing, Warsaw University of Technology, 85 Narbutta Street, 02-524 Warsaw, Poland

Abstract

Because of the well known virtues of low cost and high productivity, metal forming technology is well suited for mass production of metal micro-components. However, scaling down traditional metal forming processes proves to be problematic because, among other factors, the relatively coarse grain (CG) structure of micro-billets leads to nonuniform material flow and lack of repeatability during microforming. The aim of the presented study is to investigate a possibility of using an ultrafine grained (UFG) copper for micro-extrusion. The UFG version of Cu is produced by severe plastic deformation at room temperature using 4 and 8 passes of equal channel angular pressing (ECAP). The microstructure and compression properties of the UFG copper are investigated. For visualisation purposes, the microforming process of backward extrusion is carried out at room temperature using half cylindrical billets and transparent tools. The extrusion results, for billets subjected to 4 and 8 passes of ECAP, are compared in terms of the extrusion force, grain flow, shape representation and surface quality and show clearly that applying ultrafine grained material to microforming processes reduces scaling effects.

Mohamed Imbaby (a), Kyle Jiang (a), Isaac Chang (b)

(a) School of Mechanical engineering, University of Birmingham, Edgbaston, Birmingham, UK
(b) School of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham, UK

Abstract

316-L stainless steel has good mechanical properties and has been widely employed for making different devices. This paper presents a study for making micro 316-L stainless steel components by soft lithography in combination with powder metallurgical processes. The process involves producing deep and solid micro moulds using SU-8 photo resist, making soft replica of the moulds using silicon rubber (PDMS), forming green patterns by filling stainless steel slurry into the PDMS moulds. The green parts are de-moulded, de-bound, and finally sintered in tube furnace including nitrogen atmosphere to obtain the final micro parts. The resultant micro components show good quality micro parts with complex geometry. The density of the sintered parts reaches 91.5% of the theoretical one and the linear shrinkage of the micro components after sintering is investigated and it is found to be dependent on the percentage of the solid loading in the green patterns. The fabrication process is described in detail and the results of characterization in shrinkage and density have been analysed.

V. Piotter, K. Plewa, J. Prokop, A. Ruh, H.-J. Ritzhaupt-Kleissl, J. Hausselt
Forschungszentrum Karlsruhe, Institute for Materials Research III P.O. Box 3640, 76021 Karlsruhe, Germany

Abstract

Although microsystems technologies products have been steadily launched worldwide markets the development and improvement of manufacturing processes suitable for medium or large-scale production is still one of the most important prerequisites.
A well-known technology to meet such demands is micro injection moulding which has already reached an industrial viable status for polymeric materials. Nevertheless, there is still a lack of methods for the processing of materials with a wider range of properties.
A promising option to close this gap, development of the so-called MicroPIM process to facilitate the fabrication of metal and ceramic micro components was started.
Presently, the smallest dimensions achievable are 25-50μm of part thickness or minimum structural details of less than 5μm. Theoretical densities of up to 99% were achieved depending on the particular powder applied. As further improvement, the technology to produce rotational-symmetric parts by making use of a special head spindle system has been developed.
To enlarge the application possibilities of MicroPIM further, micro two-component injection moulding enables, for example, the fabrication of micro components consisting of two ceramic or metal materials with different physical properties and, not less important, significantly minimises assembly expenditure.

J-F. Charmeux (a), R. Minev (a), S. Dimov (a), E. Minev (a), S. Su (a), U. Harrysson (b)

a Manufacturing Engineering Center, Cardiff University, Cardiff, CF24 3AA, UK
b Fcubic, Kallarlyckevagen 6, 42935 Kullavik, Sweden

Abstract

The paper investigates the capability of a new technology, ‘Fcubic’, for a faster and less expensive production of investment casting shells directly from CAD data for the manufacture of micro-components. The technology utilises high resolution 3D printing heads for building shells using zirconia ceramics.

The capabilities of the ‘Fcubic’ process are compared to those of classical two-stage lost wax processes to produce metal micro-components. The tests are carried out on a machine incorporating units for centrifugal and pressure/vacuum casting specially developed to facilitate the replication of components with small features. In particular, this comparative study involved the manufacture of test parts in aluminium/zinc alloys and stainless steel with micro-features in the range of 250 to 700 μm and aspect ratios up to 2.4. The dimensional accuracy and the surface quality of the produced parts were measured. In addition, the production cost of the two different manufacturing routes was assessed to determine the economic viability of the ‘Fcubic’ direct shell technology for casting components incorporating micro-features.