Process Characterisation including Process Chains

Micro-Injection Moulding: Factors Affecting the Replication Quality of Micro Features

B. Sha, S. Dimov, C. Griffiths and M. S. Packianather
The Manufacturing Engineering Centre, Cardiff University,Cardiff, CF24 3AA, United Kingdom.

Abstract

Micro-injection moulding is one of the key technologies for micro-manufacture because of its mass-production capability and relatively low component cost. The surface quality in replicating micro features is one of the most important process characteristics and constitutes a manufacturing constraint in applying injection moulding in a range of micro-engineering applications. This research investigates the effects of three processing and one geometric factor on the surface quality of micro features in three different polymer materials. In particular, the following factors are considered: barrel temperature, mould temperature, injection speed and placement density of micro features. In this investigation, the mould temperature was set in the conventional range. The study revealed that in general, increasing the barrel temperature, mould temperature and the injection speed improves the polymer melt fill in micro cavities. However, the effects of these factors on the process replication capabilities are not consistent for different polymer materials, and could be adverse in specific conditions. Varying the placement density of micro features does not affect the melt fills.

Keywords: micro-injection moulding; micro features; surface quality.

Laser polishing

T. Dobrev, D. T. Pham and S. S. Dimov
Manufacturing Engineering Centre, Cardiff University, Cardiff, CF24 3AA

Abstract

Laser milling with long pulses is generally associated with a high surface roughness, which prevents the broader use of this technology, especially in the manufacture of micro tools. In micro scale, achieving low surface roughness is very important, due to feature sizes. Laser polishing, also known as cleaning, is a novel technique for improving the surface quality of laser milled surfaces. It employs the same working principles as laser milling, but instead of having the target material in the focal point of the laser beam, an offset is introduced to the extent that there is not enough fluence for material removal. This paper reports on an investigation of the effects of laser polishing on two materials, industrial copper and stainless steel 316, used widely for the manufacture of micro cavities. The study provides an insight into the process behaviour during de-focused laser machining.

Keywords: micro, laser, polishing, cleaning, surface roughness

Size effects in the production of micro strip by the flat rolling of wire

K. van Putten, R. Kopp, G. Hirt
Metal Forming Institute, RWTH Aachen University, Intzestrasse 10, D-52056, Germany

Abstract

Comparison between down scaled flat rolling experiments of thin round wire and numerical simulation of those experiments have shown that the production process of manufacturing micro strip out of thin round wire is influenced by size effects. Decreasing the wire diameter into the microscopic domain is accompanied by decreasing yield stresses of the wire and turned out to be the dominating size effect for low rolling reductions. For high rolling reductions an increase of friction becomes of major influence. The plane strain compression test is applied as an experimental simulation of the rolling process. It is also used for further investigation of the determined size effects. An experimental set-up has been built, that allows scaled experiments on small and miniaturised specimens maintaining geometric similarity. Micro structural effects, such as the Hall-Petch effect and effects on the evolution of the surface roughness have been determined with this plane strain compression set-up.

Keywords: rolling, plane strain compression test, size effects, surface roughness, FEM simulation

Manufacturing and characterization of water repellent surfaces

A. De Grave, P. Botija, H.N. Hansen, P.T. Tang
Department of Manufacturing Engineering and Management, Technical University of Denmark
Produktionstorvet, Building 427 S, DK 2800, Lyngby, Denmark

Abstract

The leaves of some natural plants show a micro structure giving them the capacity of being cleaned from any undesired particles by rainfall. Thorough studies of the physical laws that lay behind this phenomenon, known as the lotus effect, has been conducted throughout the years, in order to obtain a set of useful characteristics for such surfaces. The problem of adapting this behaviour to artificially roughened surfaces could be addressed by providing design criteria for water-repellent and self-cleaning surfaces. They could then be engineered according to the actual performances desired for them. Using an enhanced design criteria, the production of patterned micro structured surfaces following two different process chains is reported in the present paper. The first is a combination of laser manufacturing and hot embossing on polystyrene. To compare geometry and functionality, a non-silicon based lithography technique using copper laminated epoxy is described as a second approach. Hydrophobization of some surfaces was attempted. Results of characterisation are shown. Drop deposition tests are performed on the obtained surfaces following two methods.

Keywords: water repellent surfaces, manufacturing processes chain, characterisation

Challenging the sustainability of micro products development

A. De Grave, S.I. Olsen
Department of Manufacturing Engineering and Management, Technical University of Denmark
Produktionstorvet, Building 427 S, DK 2800, Lyngby, Denmark

Abstract

Environmental aspects are one of the biggest concerns regarding the future of manufacturing and product development sustainability. Furthermore, micro products and micro technologies are often seen as the next big thing in terms of possible mass market trend and boom. Many questions are raised regarding the impact of size for recycling or environment. Indeed micro production is often seen as environmental friendly thanks to the small amount of material used. Such a statement can be misleading. In this article EcoDesign or Design for Environment (DFE) and Life Cycle Assessment (LCA) will be presented, together with some tools used in order to implement the concepts into design activities. Micro injection moulded components and MEMS are used as examples. Specificities of micro products will be investigated through a categorization in three levels: the end products, the whole production chain and the intermediate parts which can be in-process created. Possible future trends for micro products development scheme involving environmental concerns are given.

Keywords: Sustainability, Design for Environment, Life Cycle Assessment

Process parameter analysis on surface roughness and process forces in micro cutting

J. Fleischera, G. Lanzaa, M. Schlipfa, J. Kotschenreuthera, J. Petersa
a Institute of Production Science (wbk),Universität Karlsruhe (TH), Germany

Abstract

High precision engineering has a great technological potential regarding the manufacturing of microtechnical products. Due to its flexibility and the possibility of producing complex three-dimensional geometries in a broad variety of different materials, micro cutting is of special importance in the already mentioned field. However, milling and turning in micro dimensions follow special rules what is caused by size-effects. Successful micro cutting depends on reliable processes and therefore on the knowledge about parameter adjustments and process characterization. By means of micro cutting test series and statistical analyses, effects and interactions of process parameter variations for work piece material, cutting edge radii, cutting speed, and depth of cut were identified and mathematically quantified. The results show a significant influence of the mentioned factors on the response variables. Thus, a linear model for specific cutting force and surface roughness is proposed. Furthermore, the findings are compared to the empirical cutting model of Victor-Kienzle in macro dimensions.

Keywords: Micro Cutting, Process Characterization, Size Effects

On the use of hot embossing for the reproduction of the surface topography of mould microreliefs

M. Sahli a,b,c, C. Millot a, C. Roques-Carmes a , C. Khan Malek b and J.C.Gelin c
a Laboratoire de Microanalyse des Surfaces (LMS), ENSMM, 25030 Besançon Cedex, France
b Laboratoire FEMTO-ST, CNRS UMR 6174, Département LPMO, 25044 Besançon Cedex, France
c Laboratoire FEMTO-ST, CNRS UMR 6174, Département LMARC, 25030 Besançon Cedex, France

Abstract

This article describes the quality of reproduction of microcavities structured into mould substrates which were filled by the imposed flow of amorphous polymeric materials. The rheology of the selected materials (cyclic olefin copolymer, COC) depends on the experimental parameters (temperature, pressure) used for the hot embossing process. To support the experimental data, the polymers were qualified by their melt flow index, flow index and consistency. The efficiency of the filling procedure into microcavities with smaller and smaller size is described using the potentialities of a customized Scanning Mechanical Microscope (SMM).

Keywords: cyclic olefin copolymer (COC), rheology, viscosity, squeeze flow, hot embossing.

Mechanical properties and bending behaviour of metal foils

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

Abstract

Ongoing miniaturisation in various technical fields like electronics industry or micro systems technology is requesting precise forming processes for the production of small and thin components. Regarding these fields, thin metal foils are being used in micro-electro-mechanical systems, electronic components (e.g. leadframes) and in medical devices. As well as micro bulk metal forming processes, metal foils with thicknesses in the range of microns are subjected to the so called size effects. Previous investigations on various metal forming processes have shown the share of surface grains to be a decisive factor for the forming behaviour as it can be observed at micro foil forming. Besides this general valid size effect, every forming process inhibits specific size effects. In the case of bending processes large strain gradients are present, influencing the bending parameters and process accuracy (e.g. spring back). In the present paper, the mechanical properties and the bending behaviour of metal foils with thicknesses ranging from 25 μm to 500 μm are discussed in dependence of material properties, microstructure and foil thickness. Fundamental experiments are being performed, providing an experimental basis for future development of theoretical models describing strain gradient dependent forming behaviour of foil bending processes.

Keywords: metal foils, mechanical properties, spring back

Experimental study on the free-sintering process of a micro-porous HDPE membrane

D.B. Trifonov a,, Y.E. Toshev b
a Institute of Information Technologies, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
b Institute of Mechanics and Biomechanics, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria

Abstract

The paper presents an investigation of the possibilities for optimization of the free-sintering process of a microporous HDPE membrane to be used mainly for fine bubble aeration. The HDPE membranes have priority significance in fine bubble operation in wastewater treatment applications. Precision molded porous plastic media have many applications in the industry, medicine and consumer products market. Of the other hand fine pore HDPE membranes, developed of special HD-PE material, provide excellent chemical and thermal properties for the most challenging environments. Various types of laboratory experimental tools for forming the micro-porous HDPE membranes at various process conditions were developed. The two-stage compression molding methods were used for forming the porous membranes. Approach for changing the process parameters for the sintering of the membranes after the compression molding was developed. Some experiments were accomplished using different variants of the technological equipment at different combinations of the sintering process parameters. Тhe possibilities for obtaining of micro-porous membranes with different pore size and minimum pressure loss of the compressed air flow, passing through the membrane were investigated.

Keywords: micro-porous HDPE membrane, free-sintering, fine bubble aeration

Hybrid tooling: a review of process chains for tooling microfabrication within 4M

S. Azcarate 1, L. Uriarte 1, S. Bigot 2, P. Bolt 3, L. Staemmler 4, G. Tosello 5, S. Roth 6 and A. Schoth 7
1 Fundación Tekniker, Avda. Otaola 20, 20600, Eibar, Spain
2 M.E.C., School of Engineering, Cardiff University, Cardiff CF24 OYF, Wales, UK
3 TNO Industrial Technology, De Rondom 1, 5600 HE Eindhoven, The Netherlands
4 HSG-IMAT, Breitscheidstr. 2 b, 70174, Stuttgart, Germany
5 Department of Manufacturing Engineering and Management, DTU, 2800 Kgs. Lyngby, Denmark
6 Bayerisches Laserzentrum GmbH, Konrad-Zuse-Str. 4-6, D-91052 Erlangen, Germany
7 IMTEK, University of Freiburg, Georges-Koehler-Allee 103, EG-79110, Freiburg, Germany

Abstract

The current paper is based on the information gathered by the “Processing of Polymers” Division (Task 4.2 “Hybrid Tooling”) and “Processing of Metals” Division (Task 7.2 “Tooling”) within 4M Network activities. The aim of the task involves a systematic analysis of the partners' expertise in different technologies for processing tooling inserts for further replication in polymers. Firstly, the 4M partners current capabilities in individual tooling processes is briefly presented, and also the expected capabilities for year 2010 are analysed for each of the following processes: micromilling, micro-wire electrodischarge machining (ìWEDM), micro sinking electrodischarge machining (ìSEDM), laser micromachining, electrochemical micromilling (ìECM), and electrochemical milling with ultrashort pulses (ECF). Later the concept of 'hybrid tooling' as different process chains for tooling fabrication is introduced. Several examples of 'hybrid tooling' within 4M partners are presented. Considered materials are nickel for electroforming, stainless steel for ECF, and tool steel for the other processes. The paper results provide a global comparison between the previously mentioned processes, the current limitations of these technologies concerning feature sizes, surface finish, aspect ratios, etc. have been identified. The main conclusion drawn is the imperative requirement to combine individual processes ('hybrid tooling') to produce 3D free-form microshapes for tooling purposes.

Keywords: Hybrid tooling, Process chain, Micromanufacturing

Adapting ECF to steels used for micro mould inserts

L. Staemmler a, K. Hofmann b, M.-H. Kim b, D. Warkentin a, H. Kücka b
a Hahn-Schickard-Institute for Micro Assembly Technology (HSG-IMAT), Stuttgart, Germany
b University of Stuttgart, Institute of Micro- and Precision Engeneering (IZFM), Stuttgart, Germany

Abstract

Electrochemical machining with ultra short voltage pulses (ECF) is an innovative technique to machine electrochemically active materials particularly very hard materials at micrometer feature size. Since the ECF technique is an electrochemical process neither mechanical forces nor thermal load are applied to workpiece or tool. For that reason ECF it is an ideal technique for the production of microstructures. Especially the use of steel as the workpiece material makes the ECF technique a promising technique for the production of micro mould inserts, since steel is resistant against the wear that occurs due to the injection process. Therefore the abilities and the limits of the ECF process for different types of tool steels are shown and the process parameters have been optimised. Acetic acid has been proven to be a suitable electrolyte for the ECF-process of tool steels. In this electrolyte tool steels like 1.2767 or 1.2312 can be processed with the ECF technique at a high quality. But in lowalloyed steels like 1.1730 only a poor quality can be obtained.

Keywords: ECF, micro mould, steel

Microfluidics on foil

T. Veltena, H. Schucka, M. Richterb, G. Klinkb, K. Bockb, C. Khan Malekc, S. Polsterd, P. Bolte
a Fraunhofer Institute for Biomedical Engineering (IBMT), 66386 St. Ingbert, Germany
b Fraunhofer Institute for Reliability and Microintegration (IZM), 80686 Munich, Germany
c Laboratoire FEMTO-ST/Dpt. LPMO, UMR CNRS, 25044 Besançon, France
d Bayrisches Laserzentrum, 91052 Erlangen, Germany
e TNO Science & Industry, Eindhoven, The Netherlands

Abstract

The concept of microfluidics on foil opens up new opportunities for combining the advantages of having a flexible substrate with reel to reel processing which have the potential to be the basis for extremely cheap micro products. To reach this goal foil substrates must be combined with micro manufacturing technologies well adapted to these substrates. Some technologies are already available, some are subject of current research and some still have to be conceived. Here, technologies like reel to reel embossing, reel to reel laminating and laser ablation/cutting as well as laser welding will be discussed. A polymer electronics based alcohol sensor is presented and aspects of combining polymer (opto-)electronics and microfluidics on one foil based substrate will be discussed.

Keywords: microfluidics, foil, reel to reel

Application of SOI based sensors for MEMS wafer-level packaging

Farzan Alavian Ghavanini 1, Cristina Rusu 2, Katrin Persson 2, Peter Enoksson 1
1 Chalmers University of Technology, Solid State Electronics MC2, SE-41296 Göteborg, Sweden
2 The Imego Institute. Arvid Hedvalls backe 4, SE-41133 Göteborg, Sweden

Abstract

A method to evaluate MEMS wafer-level packaging by using sensors based on Silicon-on-Insulator (SOI) is developed. The SOI-MEMS technology has been used to create arrays of micromechanical stress and pressure sensors in the device layer of an SOI wafer. These sensors arrays will be used to evaluate the encapsulation characteristics of wafer-level packaging, by revealing the bonding-induced stress distribution as well as bonding quality. Mechanical resonance frequency and Q-factor of the sensors have been derived theoretically and were compared to the results of the Finite Element Modelling (FEM). The pressure sensor is designed to give Q-factor above 1000 at the pressures below 1 mbar and static capacitance of few pF. The resonance frequency of the stress sensor is designed for ca. 45 MPa as estimated for anodic bonding. The design, simulation and fabrication of the sensors are presented in this paper.

Keywords: wafer level packaging, anodic bonding, resonators, stress sensor, pressure sensor, SOI

Protective Coating of Zinc and Zinc Alloys for Industrial Applications

Y. Toshev a, V. Mandova b, N. Boshkov a, D. Stoychev a, P. Petrova , N. Tsvetkova a, G.
Raichevski a, Ch. Tsvetanov a, A. Gabev c, R. Velev b, K. Kostadinov a

a Bulgarian Academy of Sciences(BAS) - Institutes of Mechanics, Physical Chemistry and Polymers;
b TDP Group Ltd, Plovdiv, c Gabex Ltd, Sofia.

Abstract

Zinc and zinc-based electrogalvanized coatings have attracted remarkable interest because of the increasing demand for layers with better corrosion resistance. A new approach for improvement of the protective ability is the incorporation in the metal matrix of polymeric nanoparticles. The latter affect positively the protective properties of the nanocomposite coatings and result in increasing of their corrosion resistance in 5 % NaCl solution compared to the pure zinc and Zn-Co. The zinc coating process using the developed saturating mixtures excludes the phases of evaporation and condensation and the process is defined as hard-phase zinc coating. The hard phase zinc coating decreases the coating time 1, 5-2 times and powder dissipation with 20-25% compared to vapor-phase zinc coating. It does not require cooling the product together with the powder at the end of the process. The hard phase zinc coating has a high degree of automation and provides uniform coating of long-sized products and allows creating high-performing equipment. The prevention of the superficial roughness, during the hard phase zinc coating, leads to higher adhesion of varnishing coverings on the zinc-coated surface in comparison with vapor-phase zinc-coating.

Keywords: RAS activities, zinc coating, corrosion protection, nano composite layers

A Comparative Study of Three Technologies for Producing Castings with Micro/Meso-scale Features

J-F. Charmeux a, R. Minev a, S. Dimov a, E. Minev a and 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 capabilities of three different process chains for vacuum investment casting of parts with micro/meso-scale features. In particular, the capabilities of two layer-based manufacturing technologies, ThermoJet and PatternMaster, and a new direct shell printing technology developed by Fcubic are studied. The first two technologies create patterns out of a thermoplastic material that are suitable for casting parts utilising the classical two-stage lost-wax process while the 'Fcubic' process produces directly a casting tree in zirconia ceramics. The tests were carried out on a gravity casting machine on which overpressure/vacuum could be applied to facilitate the replication of components with micro/meso-scale features.

Keywords: investment casting, 3D printing, metal micro-components.

Influence of EDM machining on surface integrity of WC-Co

Mohammad Reza Shabgard, Atanas Ivanov, Andrew Rees
Manufacturing Engineering Centre, Cardiff University

Abstract:

This paper studies the effects of ultrasonic vibration of the tool electrode on the surface integrity of tungsten carbide (WC-10%Co) in the electro-discharge machining (EDM) process. Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX), optical microscopy, micro hardness testing and white light interferometery were employed in the investigation. The paper studies the composition, number and size of cracks on the surface layer, the topography of the machined surface and thickness of the defective layer.

Keywords: Electro-discharge machining (EDM), Ultrasonic assisted EDM, Ultrasonic vibration of tool, Tungsten carbide (WC-Co), Surface integrity, Surface topography.

Large Area Plastic Replication with Modular Molding Tools

M. Heckele 1, C. Mehne 2, R. Steger 3, P. Koltay 3, D. Warkentin 4
1 Institute for Microstructure Technoloyg(IMT), Karlsruhe Research Centre (FZK), Germany
2 Institute for Microstructure Technology, University of Karlsruhe, Germany
3 Department of Microsystems Engineering (IMTEK), Lab for MEMS Applications, University of Freiburg, Germany
4 Hahn-Schickhard Institute for Microassembly Technology (HSG-IMAT), Stuttgart, Germany

Abstract

Hot embossing of polymer microstructures has evolved over recent years from a simple lab technique to an established R&D technology. A multitude of technical applications demonstrate the high performance of this replication technique, which can provide more than first prototypes. Admittedly this technology is not recognized as a manufacturing process by industry. In this publication molding tool is presented which by its modular character can be easily integrated into existing hot embossing machines. Especially into a newly developed machine, which has been specially designed for the integration into a process chain. This modular molding includes a customized tool as well as a microstructured mold insert. The mold insert comprises discrete modules which can be changed for different applications or in case of partial damage. Finally the operator panels and equipment controls are based on standard PLC controls, which are known in manufacturing, and in this manner hot embossing optically becomes more trustworthy. The function and link-up of these components has been demonstrated using a “Dispensing Well Plate” with dimensions of 127.8 mm x 85.5 mm, to produce ambitious through hole nozzle components. With this continuous process chain it has been shown that hot embossing is ready for industrial implementation.

Keywords: Replication, Polymer, Tool, Mold Insert, Hot Embossing, Dispensing W ell Plate, Through Holes

Microforming of titanium - forming behaviour at elevated temperature

B. Eichenhüller, U. Engel
Chair of Manufacturing Technology, University of Erlangen-Nuremberg, Germany

Abstract

Titanium is applied in a wide range of technical applications, especially when high strength in combination with light weight or corrosion resistance is demanded. Titanium is also a popular material for implants in the field of medical technology due to its specific properties like the superb biocompatibility, the elastic behaviour matching that of the human bone, the radiological transparency and the galvanic neutrality. For the production of these partly small-sized implants manufacturing methods with high accuracy and close tolerances are necessary. When forming processes are used to manufacture the miniaturised medical components the size effects occurring with miniaturisation have to be considered. The size effects are amongst others responsible for an increased scatter of process parameters and a reduced accuracy, thereby reducing the process stability. Also the limited formability of titanium and titanium alloys at room temperature is a drawback of forming microparts made of titanium. The main objective of the present study is to investigate the forming behaviour of titanium at microscale and enlarge the formability by means of forming at elevated temperature.

Keywords: microforming, elevated temperature, titanium