Multi Material Micro Manufacture Network of Excellence - metals

Investigation of the mechanical behaviour of thin metal sheets using the hydraulic bulge test

Wed, 30 Jul 2008 13:47:47 +0000

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.

Micro-extrusion of an ultrafine grained copper can

Wed, 30 Jul 2008 13:42:11 +0000

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.

Fabrication of stainless steel micro components using softlithography

Tue, 29 Jul 2008 15:35:19 +0000

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.

Manufacturing of Versatile Ceramic or Metal Micro Components by Powder Injection Moulding

Tue, 29 Jul 2008 14:04:56 +0000

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.

Capability study of the Fcubic direct shell process for casting micro-components

Tue, 20 May 2008 10:28:30 +0000

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.

Micro-machining of Metals, Ceramics and Polymers using Nanosecond Lasers

Tue, 20 May 2008 09:34:50 +0000

M.R.H Knowles, G. Rutterford, D. Karnakis, A. Ferguson
Oxford Lasers Ltd, Unit 8, Moorbrook Park, Didcot, OX11 7HP, UK

Abstract

Laser micro-processing is an enabling technology that facilitates component minaturization and improved performance characteristics. It is being applied across many industries – semiconductor, electronics, medical, automotive, aerospace, instrumentation, and communications. Laser ablation of metals, ceramics and polymers is a complex process and the exact nature of the interaction is specific to the material and laser processing parameters used. Ablation is usually a combination of evaporation and melt expulsion. In order to achieve the highest quality results it is often desirable to minimize the degree of melting involved and short pulse lasers show certain advantages in this respect. We discuss the benefits of high laser intensity (GW/cm)^2 on target for efficient laser micro-fabrication in metals and ceramics. At such high irradiance conditions, material properties are approaching their critical limits and ablation mechanisms are becoming even more complicated but can be exploited to our advantage in particular for high aspect ratio micro-drilling and micro-cutting.

Rapid prototyping of microstructured ceramic and metal parts using reaction molding techniques

Tue, 20 May 2008 08:20:48 +0000

T. Hanemann (a,b), K. Honnef (b), J. Hausselt (a,b)
a Forschungszentrum Karlsruhe, Institut f. Materialforschung III, D-76021 Karlsruhe, Germany
b Albert-Ludwigs-Universität Freiburg, Institut f. Mikrosystemtechnik (IMTEK), D-79110 Freiburg, Germany

Abstract

Different variants of reaction molding techniques like UV-embossing, UV-RIM, Photomolding, a.o., exploiting the rapid light induced photopolymerization of reactive resins are widely used in microsystem technologies for the fabrication of microoptical components or for rapid prototyping purposes. The solidification based on photocuring limits the suitable materials to transparent resins and yields only plastic microstructured parts. In this paper the further development of micro reaction molding with respect to a rapid prototyping of ceramic and metal parts will be described. As in the different variants of powder injection molding additional process stages have to be considered and individually optimized. First a free-flowing reactive resin based composite with a large filler load (microsized ceramic or metal powder) of at least 45 vol% has to be prepared. The addition of suitable thermal initiators allows the solidification of the composite subsequently after mold filling in a molding tool equipped with microstructured mold inserts. The mold filling and hence the accurate reproduction of surface details depend strongly on the composite’s viscosity, which is a function of the filler load. The further process stages like debinding and sintering have to be optimized with respect to the polymer based reactive resin used and the ceramic filler. Especially an improved process control of the composite formation prior to molding and the thermal debinding is crucial for the realization of ceramic or metal parts carrying a microstructured surface. The development of the whole process chain and some microstructured ceramic or metal parts will be presented.

Flexible Tool System for Creation of Surface Micro-Geometries

Mon, 19 May 2008 15:45:39 +0000

M. Rosochowska (a), K. Chodnikiewicz (a), R. Balendra (a), R. Smith (b)
a Design, Manufacture and Engineering Management, University of Strathclyde, Glasgow G1 1XJ, UK
b Pascoe Engineering Ltd. Glasgow G53 7TD, UK

Abstract

The performance of functional surfaces can be improved by incorporating a pattern of micro-geometrical features; research has shown that surface micro-geometries (smg’s) extend the range of the hydrodynamic lubrication regime, thus reducing friction. The incorporation of smg’s on functional surfaces in mechanical-engineering/bioengineering applications requires a fast, tolerance-insensitive technique; a novel technique, conforming to these requirements is the subject of this paper. The developed tool system enables the creation of smg’s of a range of depths of 0.5~25μm, up to a rate of 50Hz on undulating surfaces; this tool system works in conjunction with a 3-axis CNC machine. This is essentially a high-speed indentation process that uses piezoelectric actuation. Experimental results show that the tool system and associated controls enable the production of smg’s of high consistency of pattern, density and geometry. The use of diamond-tipped tools enables the creation of smg’s on hard (>60HRC) steel surfaces; current configurations permit the creation of smg’s on plain and cylindrical surfaces; more complex forms would require a 5-axis CNC machine. Experimental results show that the form-errors are of the order of 5% and the distribution error is 2%. However, to produce dimples of the required dimensions, it is essential to know the relationship between the dimple depth and forming force; these data were extracted using FE analysis.

Micro-stamping of Molybdenum Rhenium Components

Mon, 19 May 2008 15:40:43 +0000

N. Boudeaua (b), S. Thibauda (b), J.F. Michel (a)
a Department LMARC, FEMTO-ST Institute, 25000 Besançon, France
b ENSMM, 25030 Besançon cedex, France

Abstract

Optimizing productivity, parts quality, reducing production costs are objectives that companies must perpetually satisfy to remain competitive. An efficient solution, but complex to implement, consists in modifying completely the manufacturing process. That is the goal of these research works : it consists in manufacturing micro-electronic components by deep drawing which are currently rolled and welded leading to a strong rate of reject.

The objective of this work is to study the feasibility of skirts of Molybdenum Rhenium cathodes by micro-stamping. First, various nuances of Molybdenum Rhenium to low thickness (< 100 μm) have been characterized in their (large) plastic range of deformation.

Secondly, a forming process leading to no folds and no tears has been defined by means of finite element simulations.

Finally, a modular micro-stamping tool has been developed ; it includes the blanking process and the forming procedures. The different forming stages are determined from numerical simulations. The two first stages have been investigated experimentally and are presented.

Laser striation of groove patterns on metallic surfaces

Mon, 19 May 2008 15:37:06 +0000

C. Vincenta, G. Monteila, T. Barrièreb, J.C. Gelinb
a Laboratoire de Microanalyse des Surfaces, 25000 Besançon, France
b Institut FEMTO-ST, département mécanique appliquée, 25000 Besançon, France

Abstract

The aim of this work is to expose the machining of deterministic grooves by means of a laser Nd:YAG in a heterogeneous metallic material.

These grooves are defined by their cross section geometry and spatial distribution. For the cross section geometries, various profiles of the engraved lines are realised: hemispherical, rectangular, trapezoïdal and triangular. For the distribution or patterns of the grooves, they are classified in two categories: continuous lines and interrupted ones. The first pattern type allows the machining in the aeras where the crossing of the lines occurs to be studied. The second pattern type is dedicated to the measurement of the quality of the engraving process. The current dimensions of the grooves made on the metallic substrate are micrometric: typically up to 10 micrometers for the depth and up to 50
micrometers for the width.

In order to obtain the desired striation by laser machining, it is necessary to develop the adequate machining strategies. i.e., according to the slope of the surface to engrave on a horizontal plan, the direction of the laser beam has to use a varying slope: for a flat surface, the beam is machining vertically and for a tilted or vertical surface, the beam has various processing angles.

Moreover, this striation is engraved in a heterogeneous material, lamellar cast iron, leading to particular difficulties
arising during machining process. Accordingly to the material where the impact of the laser is located, graphite or
ferrous matrix, the engraved depth is different. However, an adjustment of the intensity of the current of lamp is carried out. It consists in comparing the machined depth with the required one after several laser machining passes.
Consequently, this adjustment allows us to obtain a correct machined average depth whatever the heterogeneity of
material is.

In addition the laser processing during the groove machining gives rise to burrs on the edges of the groove. The burrs elimination by fine grinding has been developed.

Multilayered and nanolayered hard nitride thin films for a better yield in micro machining

Mon, 19 May 2008 15:30:07 +0000

C. Ducros, B. Fillon, F. Sanchette
CEA Grenoble, Laboratoire de Technologies des Surfaces, 17 rue des Martyrs 38054 Grenoble Cedex, France

Abstract

TiN/AlTiN ; TiN/CrN and CrN/AlTiN multilayer coatings have been deposited by the cathodic arc evaporation technique. The period is in the range 7 – 200 nm for a total thichness of 3 μm. The period’s control of the nanoscaled hard films is achieved, a priori, by way of a simple geometrical calculation and, a posteriori, via both X-ray diffraction and transmission electron microscopy on cross-sections. Microstructure of the as-deposited coatings has been investigated by means of Xray diffraction and transmission electron microscopy in connection with the decrease of the period λ. For lower periods (multilayered coatings), the fcc structures, which derive from each nitride are observed while only the superlattice structure is found for nanoscale layered films (nanolayered coatings). Microstructure evolution with the period (defined as the sum of two elementary layers) is investigated for the three systems and the differences are comment. Mechanical and tribological properties are strongly dependant on coating structure. The best mechanical properties were obtained with TiN/AlTiN nanolayers with 7 nm periods and superlattice structure [1]. These coatings induced low main cutting force and low flank wear during Inconel 718 turning. Time life of superlattice TiN-AlTiN coated cutting tool is increased comparatively to CVD coated and AlTiN coated cutting tools actually used in production.

Simulating electroplated micro surfaces in 3-D

Mon, 19 May 2008 15:26:19 +0000

A H. J. Jeon (1), J Low (1), A. R. Mileham (1), A.N. Bramley (1), C. Johal (2)
1 Department of Mechanical Engineering, University of Bath, BA27AY, UK
2 Glacier Vandervell Bearings Ltd, Rugby, UK

Abstract

This paper describes the development, comparison and validation of a 3-D model of the electroplating process. It is based on the current density distribution that is generated using the Finite Element Method (FEM) and is used together with Faraday's law of electrolysis and various material and electrolyte values to determine the local plating depth. It has been developed initially to model the depth of the micro layer deposited on the work surface of an automotive engine’s "big end" shell bearing. Actual plating trials were conducted in a series of controlled laboratory experiments using an industrial type jig and industrial plating conditions. These consisted of a steel cathode (the bearing) and a lead anode. The results described here, in this paper, show good agreement between the 3-D simulation and the actual plating depth and profile and are considered to validate the model sufficiently for it to be used for electroplating tooling design and micro-electroforming.

A Friction Model for Microforming

Mon, 19 May 2008 15:23:28 +0000

H.J. Jeon, A.N. Bramley
Department of Mechanical Engineering, University of Bath, Bath BA2 7AY, UK

Abstract

For the simulation of metal forming processes, input data relating to the tool-workpiece interface is necessary. For microforming applications the tool/workpiece interface conditions tend to dominate the process and it has been found that traditional methods of modeling the interface are not realistic. This paper describes an approach that seeks to describe friction by modelling the geometric surface roughness of the tool as opposed to the use of the traditional empirical friction coefficient or factor. This finite element based model has been validated experimentally in terms of loads and metal flow using the ring test and actual surface measurements. It enables more accurate and also more flexible modeling of friction. As such it will be very suitable for microforming applications.

Discussion on Thin WEDM Error Analysis and Characterisation

Mon, 19 May 2008 15:19:45 +0000

A. Herreroa, L. Uriartea, J. Esmorisa, J.A. Sánchezb, L.N. Lopez de Lacalleb
a Fundación Tekniker, Avda. Otaola 20, 20600, Eibar, Spain
b Dpto. Ing. Mecánica, ETSII, Alameda Urquijo s/n, 48013, Bilbao, Spain

Abstract

The analysis of WEDM is still nowadays an important field of research due to the difficulties to measure the process characteristics: narrow gap (~10 mm), dirty environment (oil or deionised water), high frequency (>100 kHz), etc. Nevertheless, the WEDM technology has been improved thanks to the theoretical and empirical results of different research groups that have made use of state of the art technologies to measure temperature distributions, displacements, frequencies or electrical signals for spark characterisation. The accurate measurement of machined parts has also brought light to the machining process, being this aspect critical for the improvement of the EDM technology.

In the last years, the growing tendency to miniaturisation has promoted the research of production techniques capable to produce small components with very high precision. EDM technology, due to the low processing forces, was immediately identified as one applicable technology for the production of moulds and dies. The technological research in the field has been very important, reducing the minimum wire diameter from Ø0.1 mm to Ø0.02 mm, the machine components have evolved to provide a finer control of all process parameters, specially the wire traction force, the machine feed and the spark energy. Thanks to the research in WEDM, nowadays it is known that, during the process, electrostatic, electrodynamic, electromagnetic, dielectric and wire traction forces act on the wire. Many of these forces push and pull the part from the workpiece. The result of all these forces acting on the wire is an error of the machined shape that, in normal WEDM, is of only a few microns (3~20 mm depending on part height). This error is specially important when machining flat walls and machining corners in which the feeding direction change.

Despite using lower energy values, due to the origin of the different forces acting on the wire and the low tensile strength of wires smaller than Ø0.1 mm (considered as thin wires), the errors that can be found in miniature parts and microparts are bigger than the corresponding values in conventional WEDM. The present paper analyses the errors that appear when applying thin wire EDM (Ø0.03 mm) to the machining of 3 mm height components made of tungsten carbide, it presents the difficulties that are found when trying to characterise the errors in small components. A possible error analysis approach is presented and then the errors are discussed.

Micro-extrusion of ultra-fine grain aluminium

Mon, 19 May 2008 15:16:17 +0000

Micro-extrusion of ultra-fine grain aluminium
A. Rosochowski (a), W. Presz (b), L. Olejnik (b), M. Richert (c)
a Design, Manufacture and Engineering Management, University of Strathclyde, Glasgow G1 1XJ, UK
b Institute of Materials Processing, Warsaw University of Technology, 02-524 Warsaw, Poland
c Faculty of Non-Ferrous Metals, AGH University of Science and Technology, 30-059 Krakow, Poland

Abstract

Microforming of normal, coarse grain (CG) metals leads to scale problems which originate from the fact that the grain size becomes comparable to the part size. A possible way of dealing with these problems is replacing CG metals with ultra-fine grain (UFG) metals. UFG metals can be produced in bulk by severe plastic deformation (SPD). This paper describes using UFG aluminium 1070 for preliminary trials of micro extrusion of a cylindrical cup. The process of producing bulk UFG aluminium by SPD is explained and the material obtained characterised. The preparation of micro billets for the extrusion operation is discussed. Backward extrusion is carried out for two types of material, CG and UFG. This enables a comparison of the material behaviour and product characteristics.