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Prof. Dr.-Ing. Detlef Lohe 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. Jurgen Haubetaelt 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.

De la contraportada

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 following 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 are introduced to this field and led from the design and modeling aspects to tooling, molds, and micro injection molding as a powerful replication technology.<br> <br> From the Contents:<br> Design Environment and Design Flow<br> Modelling in Design<br> Modelling in Micro-PIM<br> Strategies for Manufacture of Mold Inserts<br> Micro End Milling in Hardened Steel<br> 3D Microstructuring of Mold Inserts by Laser Removal<br> Micro-EDM of Mold Inserts<br> Lithographic Fabrication of Mold Inserts<br> Material States, Surface Conditioning<br> Micro Injection Molding: Principles and Challenges<br> Micro-MIM<br> Micro-CIM<br> <br> Part II covers casting and forming techniques, automation, quality assurance, and component properties.

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Microengineering of Metals and Ceramics

John Wiley & Sons

Chapter One

A. Albers, J. Marz, Institute of Product Development (IPEK), University of Karlsruhe (TH), Germany

Abstract

The design flow for primary-shaped microcomponents and microsystems is presented. As a characteristic of microspecific design, the approach is predominantly driven by technology. To integrate the relevant technological demands and restrictions into the design synthesis for a realizable embodiment design in accordance with the specified function, design rules are defined. These represent mandatory instructions for the designer. To support the designer effectively the design rules are provided within a computer-aided design environment. In addition to an information portal, an embodiment design unit is built up on the basis of the 3D CAD system Unigraphics, which includes an application for knowledge-based engineering (KBE). The rule-based design methodology was used for the development and design of a microplanetary gear.

Keywords

design environment; design flow; target system definition; operation system; object system; design rule; knowledge-based engineering; methodological aid

1.1 Introduction 4 1.1.1 State-of-the-Art of Design Flows and Design Environments within Microtechnology 4 1.1.2 Mechanical Microproduction 5 1.2 Design Flow 6 1.2.1 Specific Issues Within the Design of Microsystems 6 1.2.1.1 Dominance of Technologies 6 1.2.1.2 Surface-to-Volume Ratio 6 1.2.1.3 Dynamics 7 1.2.1.4 Standardization 7 1.2.1.5 Validation 7 1.2.1.6 Enhanced Material Spectrum 7 1.2.1.7 Emphasis on Actuators 7 1.2.2 Microspecific Design Flow 7 1.3 Design Rules 9 1.3.1 Basics 9 1.3.1.1 Definition 9 1.3.1.2 Derivation of Design Rules 10 1.3.2 Design Rules Derived from Restrictions of Production Technology 11 1.3.2.1 Design Rules for Mold Insert Manufacturing 13 1.3.2.2 Design Rules for Replication Techniques 14 1.4 Design Environment 18 1.4.1 Information Unit 20 1.4.2 Embodiment Design Unit 20 1.4.2.1 Preparing Elementary Rules for Computer-aided Design Rule Check 21 1.4.2.2 Design Rule Check 24 1.5 Conclusion 27 1.6 References 27

1.1 Introduction

Microtechnology involves technologies for manufacturing and assembling predominantly micromechanical, microelectrical, microfluidic and microoptical components and systems with characteristic structures with the dimension of microns. In doing so, microproduction technologies take on a key role, since their process-specific parameters and boundary conditions determine the smallness and attainable quality features of the components. Owing to the ongoing progress in microtechnology and the increasing penetration of the market with medium-sized and large-batch products, development steps preliminary and subsequent to production are becoming more and more relevant for an effective design in compliance with the requirements. Therefore, the designer needs to be supported by a technological basic knowledge and know-how, regardless of individual persons.

1.1.1 State-of-the-Art of Design Flows and Design Environments within Microtechnology

Microtechnologies include silicon microsystem technology, the LIGA process and mechanical microproduction technology.

Silicon microsystem technology is the most widespread microtechnology throughout the world. It is based on the process technology of integrated circuits (ICs) and benefits from a comprehensive know-how from microelectronics. Unlike in microelectronics, microtechnological products integrate active and passive functional elements, which rely on at least two elementarily different physical, chemical or biochemical effects and working principles. In addition to sensors and information processing, particularly actuator functions are performed. The predominantly 2.5-dimensional and sometimes three-dimensional structures use silicon as substrate with its excellent mechanical properties. Along with others, all these characteristics of silicon micromechanical systems have required a specific design methodology ever since a critical level of development from research into industry was reached. Different design process models are known, which among other things integrate analytical and numerical simulation tools. Silicon-based micromechanical products are developed in an iterative sequence of synthesis and analysis steps. A specific difficulty lies in the deviation between the designed target structure and the actual structure after the optical lithography and etching process. Therefore, compensation structures are introduced into the design and simulation environment, adjusting the determined structure by dimensional add-on and auxiliary structures. Design rules are introduced as a methodological aid to represent this technological information. Design rules have been used in microelectronics since the early 1980s to enable very large-scale integrated (VLSI) circuits to be synthesized automatically to the extent of nearly 100%. Silicon microsystem technology has now reached a high degree of development status. A lot of research programs have led to design flow descriptions and collections of design rules.

Like silicon microsystem technology, the LIGA process utilizes mask-based process steps. The LIGA process approaches an obviously broader range of materials and is characterized by extremely high aspect ratios with at the same time the smallest lateral structure dimensions. LIGA permits the manufacture of mold inserts which can be used in replication techniques for large-batch parts (Chapter 8). In addition to thermoplastics, also metallic and ceramic materials are processed. To support the design and process, engineering design rules are utilized which give - depending on the process sequence - instructions for a design for manufacturing and for separating, manipulating and assembling components. Within different research programs, design environments for computer-aided design of LIGA microstructures embedding design rules were developed. The computer-aided design of LIGA microstructures still shows a high demand. A standardized model for methodological design flow in the LIGA process is lacking to date.

1.1.2 Mechanical Microproduction

To come up with a more cost-effective, medium-sized and large-batch suitable process for manufacturing microsystems, the potential of miniaturizing mechanical production technologies has been increasingly investigated in recent years. Predominantly staged production process sequences for manufacturing mold inserts by wear-resistant materials followed by a replication step show outstanding future prospects. Technologies such as micromilling and laser machining are suitable for manufacturing complex three-dimensional free-form surfaces (Chapters 5-7). By replication techniques such as micropowder injection molding, high-strength microcomponents and microsystems from metallic and ceramic materials can be produced in large quantities (Chapters 11 and 12).

When designing primary-shaped microparts with respect to function and manufacturing, it is necessary to incorporate boundary conditions and restrictions from process steps downstream to the product development into the design activities as early as possible. Thus, a design flow is introduced that uses design rules to support the designer effectively with respect to functional, geometric and capacitance demands. The process model and the method are embedded in a knowledge-based design environment.

1.2 Design Flow

1.2.1 Specific Issues Within the Design of Microsystems

In contrast to the procedures and methods commonly applied in mechanical engineering and precision engineering, product development of microtechnological systems requires attention to the following issues.

1.2.1.1 Dominance of Technologies

Going beyond the basic rules and guidelines of embodiment design microtechnology has a strong focus on parallelization of product and process development. Resulting from the rapid advances in existing production processes and the appearance of new technologies, the question of 'how to manufacture' becomes a conceptual part of product development. Microproduction technologies, materials and specific effects define the possible shape and function of new products.

1.2.1.2 Surface-to-Volume Ratio

Owing to the super-proportional rise in the surface-to-volume ratio in the range of the characteristic and functional dimensions of microcomponents, the global dimensions have a different ratio to local deviances. Higher level surface tolerances in macroengineering have the same significance as notch form deviation in microengineering. There is no longer a difference in magnitude between material microstructures and work-piece dimensions. The numbers of crystals and surface layers are relevant for the calculation of elastic properties.

1.2.1.3 Dynamics

As a consequence of their small volumes, microsystems have lower inertia. They can be operated in higher ranges of frequency and show high dynamics.

1.2.1.4 Standardization

Standards with regard to generic or product-specific dimensions do not exist for the design of microcomponents and systems.

1.2.1.5 Validation

Mostly, either no equipment for the measurement and testing of microcomponents is available at all or insurmountable physical obstacles occur (size of components, essential accuracy of the measuring equipment). Design can, therefore, only set requirements on what can be verified by means of measurement and with the use of testing equipment.

Compared with silicon microsystem technology, the LIGA process and the mechanical microproduction technologies show the following specific differences.

1.2.1.6 Enhanced Material Spectrum

Microsystem technologies with replication subprocesses possess an enhanced material spectrum. Totally new applications arise from it, making it necessary to characterize the materials with respect to their microstructures and properties. This is an important input for product development.

1.2.1.7 Emphasis on Actuators

Since the LIGA process and mechanical microproduction technologies do not rely on silicon as base material, there is enormous potential to develop actuators using a multitude of effects. Integrated in a superior system or as an integrated self-sufficient microsystem, actuators offer particularly energy and material interfaces to the macroscopic world. A microspecific design methodology has to be directed on methods and processes to calculate and design the relevant interface machine elements.

1.2.2 Microspecific Design Flow

Each design process starts with a definition of the target system. The target system definition is developed with the involvement of the customer and determines requirements and boundary conditions for the product that is to be developed(Fig. 1-1).

The target system definition helps to concretize the task and to clarify vague and unexpressed demands on the object system - the subsequent microproduct - prior to the beginning of the design. Along with the customer, a requirements list is generated, which describes the target system by quantitative and assessed criteria. To ensure that a fundamental criterion is not forgotten, checklists with main headings exist for drawing up a requirements list. The requirements list represents a dynamic document, which has to be examined continually with respect to up-to-dateness and inconsistencies during the design process. Moreover, the risk exists of specifying the task in an unchallenged or in an overextended way. An unchallenged specification might lead to a product ahead of schedule but without matching the real performance characteristics. On the other hand, an overextended specification might limit the solution space in such a manner that no solution could be developed. For the target system definition of microelectronic circuits, hardware description languages are standardized. The microsystem technology of primary shaping concentrates on energy- and material-converting microsystems with integrated information flow and with single functions from different physical, chemical and biochemical domains, so no formal methods and target system definition languages are available.

When conventionally developing products and systems of mechanical engineering and precision engineering, a conceptional phase would follow, in which basic partial solutions for functionally organized subsystems would be developed and systematically combined to the optimum basic solution with consideration of evaluation techniques. When developing microsystems, the approach is 'technology driven'. At the same time, the technology term describes all of those scientific disciplines as a whole that contribute to the product development process. This especially applies in production engineering and material sciences. Among material sciences, also research on new or specifically formed physical, chemical and biochemical effects has to be itemized. Effects are comprehended as both those which are intentionally used to transfer the target system into the object system by effects and active principles in order to fulfil a function (e.g. shape memory effect) and those which inevitably result from phenomena such as friction and wear.

Because of being driven by technology, parallelization of stages of conceptual and embodiment design occurs, which exceeds different levels of abstraction. While making conceptual decisions on system level related to function in a top-down approach, simultaneously structural details conditional on technology are being designed in a bottom-up way. In between, single components are preliminarily drafted (basic design). These structural details can be entirely finalized and annotated with all tolerance data and information relevant for production preparation. Already during the subsequent design stage, a complete component can be constituted in its final shape (detail design). The system comes to the stage of basic design. Eventually the system itself is finalized and refined into a detailed design documentation for transfer to production preparation. In doing so, the approach constantly changes between the view on the complete system and the smallest structural element ('meet-in-the-middle'), wherein the design space is restricted for the designer through boundary conditions and restrictions of the production processes. However, features that cannot be described as easily as geometric quantities also have an influence. These are characteristics of the materials themselves such as microstructure or mechanical properties and physical, chemical or biochemical effects made accessible by them. The latter can develop into disturbing effects when the dimensions become smaller, they can become less important or even emerge and therefore open up completely new applications. All of these 'technological' aspects therefore have to be integrated into the microtechnological design of structures, components and systems.

Therefore, it is necessary to make the multi-technological knowledge from the above-mentioned technologies directly available to the designer in the design process. This is achieved via the methodological aid of design rules.

1.3 Design Rules

1.3.1 Basics

1.3.1.1 Definition

Design rules are instructions derived from technological restrictions which have to be followed mandatorily for a realizable design.

(Continues...)

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