Über die Autorin bzw. den Autor

Prof. Dr.-Ing. Detlef Löhe studied mechanical engineering at the Technical University of Karlsruhe, Germany and obtained his Ph.D. in 1980. After heading the microstructure and mechancal behaviour working group there, he was appointed in 1991 as professor for materials science at Paderborn University, Germany, where he received an award for outstanding teaching achievements in 1994. In the same year, he returned to the Institute for Materials Science and Enginering I at Karlsruhe Technical University as its Director. He is Speaker of the Collaborative Research Centre 499 "Design, production and quality assurance of molded microparts constructed of metals and ceramics" and has been a Senator of the Deutsche Forschungsgemeinschaft (DFG) since 2003.
His research interests focus on metallic and ceramic materials properties and durability under different kinds of stress, component manufacture and behaviour, optimisation of heat treatment methods, and failure analysis.
 
Prof. Dr.-Ing. Jürgen Haußelt studied Physics and Materials Sciences at the University of Erlangen, Germany. After his doctorate and a research stay at Stanford University he joined Degussa AG in 1977, starting in metals research. After having worked as technical director in Degussa´s subsidiary in New York City, he returned to Germany in 1985 and was first in charge of metals research, then managed the entire materials development und process technology of Degussa´s corporate division "Metals". In 1993 he joined Forschungszentrum Karlsruhe as head of the Institute of Materials Research III. In addition, he was appointed professor at Freiburg University as Chair for Micromaterials Process Technology at IMTEK in 1996. In 1998 he became member of the supervisory board of Norddeutsche Affinerie AG, Hamburg.

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The gateway to the micro and nano worlds: AMN provides cutting-edge reviews and detailed case studies by top authors from science and industry, covering technologies, devices and advanced systems. Together, these have an immense innovative application potential that opens up with control of shape and function from the atomic level right up to the visible world without any technological gaps.<br> <br> This and the preceeding volume cover all angles of micro-scale parts and components engineering from both metallic and ceramic materials, a very promising field which is a strong source of innovation and development for micro process technology, aerospace applications, sensors, actors, medical and dental as well as many other applications.<br> <br> In this volume, readers find casting and electroforming replication techniques, automation and quality control issues, and the characterization of the microengineered components.<br> <br> From the Contents:<br> Micro Casting<br> Micro Electroforming of Metals<br> Further Ceramic Replication Techniques<br> Automation PIM<br> Assembly<br> Quality Assurance<br> Metallic Materials<br> Ceramic Materials<br> Tribological Characterization of Mold Inserts and Materials for Micro Components<br> Development of a Simulation Tool for Wear in Microsystems<br> <br> Part I covers the introduction to this field and leads from the design and modeling aspects to tooling, molds, and micro injection molding as a powerful replication technology.

Aus dem Klappentext

The gateway to the micro and nano worlds: AMN provides cutting-edge reviews and detailed case studies by top authors from science and industry, covering technologies, devices and advanced systems. Together, these have an immense innovative application potential that opens up with control of shape and function from the atomic level right up to the visible world without any technological gaps.
 
This and the preceeding volume cover all angles of micro-scale parts and components engineering from both metallic and ceramic materials, a very promising field which is a strong source of innovation and development for micro process technology, aerospace applications, sensors, actors, medical and dental as well as many other applications.
 
In this volume, readers find casting and electroforming replication techniques, automation and quality control issues, and the characterization of the microengineered components.
 
From the Contents:
Micro Casting
Micro Electroforming of Metals
Further Ceramic Replication Techniques
Automation PIM
Assembly
Quality Assurance
Metallic Materials
Ceramic Materials
Tribological Characterization of Mold Inserts and Materials for Micro Components
Development of a Simulation Tool for Wear in Microsystems
 
Part I covers the introduction to this field and leads from the design and modeling aspects to tooling, molds, and micro injection molding as a powerful replication technology.

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Microengineering of Metals and Ceramics

John Wiley & Sons

Chapter One

G. Baumeister, J. Hausselt, S. Rath, R. Ruprecht, Institute for Materials Research III (IMF III), Forschungszentrum Karlsruhe, Germany

Abstract

Microcasting is a metal forming process based on the well-known lost-wax - lost-mold technology of investment casting. The further development of this technique for casting structures in the range of some tens of micrometers requires special patterns, investments and casting parameters. First, this chapter describes the general casting process, highlighting differences from conventional dental and jewelry casting. Additionally, the parameters of a typical microcasting process are given. Next, some alloys used for microcasting and their chemical compositions, melting and casting temperatures and phase transitions during the solidification process are described in detail. Thereafter, the two basic investments used for microcasting and the influence of the investment on the surface roughness of the cast parts are discussed. Finally, cast microparts are shown and their properties such as microstructure, dimensional accuracy, surface roughness, mechanical properties, smallest achievable structure size and highest obtainable flow length and aspect ratio are presented.

Keywords

investment casting; dental casting; gold base alloy; bronze; CoCrMo alloy

13.1 Introduction 358 13.2 Investment Casting 359 13.2.1 General Process 360 13.2.1.1 Process Description 360 13.2.1.2 Pattern Design 362 13.2.1.3 Melting 363 13.2.1.4 Casting 364 13.2.1.5 Solidification 365 13.2.2 Vacuum Pressure Casting 365 13.2.3 Centrifugal Casting 367 13.2.4 Example of a Typical Casting Process 368 13.3 Casting Alloys 369 13.3.1 Introduction 369 13.3.2 Gold Base Alloy as an Example of Precious Metals 369 13.3.3 Bronze as an Example of Typical Casting Alloys 371 13.3.4 CoCrMo Alloy as an Example of High Strength Materials 372 13.4 Investment Materials 373 13.4.1 Introduction 373 13.4.2 Phosphate Bonded Investments 375 13.4.3 Plaster Bonded Investments 377 13.4.4 Influence of the Investment on the Surface Roughness 378 13.4.4.1 Coating the Pattern 379 13.4.4.2 Infiltrating the Mold 379 13.4.4.3 Modifying the Investment 380 13.5 Cast Microparts and Their Properties 381 13.5.1 Examples of Cast Microparts 381 13.5.2 Microstructure/Grain Size 383 13.5.3 Dimensional Accuracy 385 13.5.4 Surface Roughness 386 13.5.5 Mechanical Properties 387 13.5.6 Achievable Structure Size, Flow Length and Aspect Ratio 388 13.6 Conclusions 390 13.7 References 391

13.1 Introduction

Microcasting is the manufacturing process of small structures in the micrometer range or of larger parts carrying microstructures by using a metal melt which is cast into a microstructured mold. Fields of application are, e.g., instruments for minimal invasive surgery, dental devices and instruments for biotechnology. Additionally, the manufacturing of miniaturized devices for mechanical engineering is a desired outcome.

At present, two different techniques for casting structures in the micrometer range are known: capillary action microcasting and microcasting based on investment casting. The first manufacturing method was developed by Bach et al. and Moehwald et al. They applied capillary action microcasting for form filling of structures in the range of some micrometers. Similar to die casting, this technique uses a permanent mold which can be opened in order to remove the cast structure. The cavities in the mold are shaped by high-precision grinding. For casting, two different principles to fill these cavities exist: the suction principle and the displacement principle. In the first case the melt is sucked into a specially coated mold by the capillary pressure. In the second case the casting alloy is melted inside the divisible mold and fills the microstructured cavities owing to the capillary force. Subsequently pressure is applied to the mold to displace the excess melt through the slit. Owing to absorption of the coating during solidification, the casting detaches from the mold's surface, but at the same time the alloy composition changes slightly compared with the original material. In capillary action microcasting the castable geometries are limited to structures which can be filled by application of capillary forces. Microcasting based on the investment casting technique, which will be discussed in the following, does not suffer from these limitations.

13.2 Investment Casting

Microcasting, also named microprecision casting, is generally identified with the investment casting process, a casting technology also known as the lost-wax, lost-mold technique. This forming process excels in near net shape manufacturing and is an established technology with great freedom in design. It offers the chance to produce very complicated formed parts in metal even with undercuts. Another advantage of the investment casting process over other shaping processes is the rapidity of the casting procedure itself and the low loss of material due to the possibility of recycling the runners and sprues. However, the process cannot be fully automated, so it is best suited for small and medium series and for parts with highly complex shape. This is the reason why investment casting has, in addition to technical application, a high relevance for jewelry and dental casting. For both applications, precise manufacturing is achieved, especially by using precious alloys. For jewelry and dental casting, the sizes of the produced parts are in the millimeter up to the centimeter range with structural details in the millimeter and submillimeter ranges. Further development and improvement of these techniques allowed the casting of microparts with structural details even in the micrometer range, which was confirmed by the replication of small-scale LIGA structures (see Section 13.2.1.1) with high accuracy. The new microtechnology, derived from the conventional production process, requires different pattern materials, other investments, special alloys and other casting parameters compared with the standard investment casting process. Additionally, microcast parts cannot be machined mechanically after manufacturing. Sand blasting, as applied in dental and jewelry casting, cannot be used to remove residue of the investment, nor can surfaces be polished to increase their quality. Sand blasting would reduce the sharpness of the edges and therefore influence the accuracy of the part, and polishing is not possible because of their small size. Therefore, precious alloys are particularly suitable for microcasting, because here the investment can be removed chemically from the cast metal part using hydrofluoric acid without influencing the cast part. Recent progress in the development...