Volker Piotter

Micro Powder Injection Molding

The availability of manufacturing processes suitable for medium and large-scale production of microscale devices is an important requirement for the economic success of microsystems technology. Powder injection molding is on its way to become such an established and economically viable process for manufacturing complex shaped metal or ceramic parts in quantity.

Micro powder-injection moulding of metals and ceramics

Development of micro-MIM/-CIM was started at Forschungszentram Karlsrahe with the aim of creating a process suitable for a wide range of materials as well as for medium-scale and large-scale production of micro components. Using enhanced machine technology and special tempering procedures, this process enables the manufacturing of metal and ceramic devices with smallest wall thicknesses of 50 Μm and structural details of less than 3 Μm. Using ultrafine ceramic powders (e.g. zirconia) and high-quality LIGA mould inserts, surface qualities ofRa = 40 nm or Rmax ≤ 3 mm could be obtained. Possible practical applications are demonstrated by components of micro-annular gear pumps made of zirconia for future handling of very small volumes of dangerous fluids and micro samples (tensile and bending specimens) suitable for mechanical testing of metals (316L, 17-4PH) and ceramic materials (A12O3, ZrO2) in the micrometre range.

Injection molding of LIGA and LIGA-similar microstructures using filled and unfilled thermoplastics

Micromolding is a key technology for the economic production of micro-components for microsystems. It is applied in several microstructuring techniques including the LIGA process which was invented and developed at Forschungszentrum Karlsruhe. Injection molding of multiple-use LIGA tool inserts produced by deep-etch x-ray lithography and electroforming allows the economic production of components for most applications using microsystems technology. Such microstructures are produced in small and large series and commercialized by Forschungszentrum Karlsruhe and the microParts Company, Dormund, Germany, cooperating within the framework of a license agreement. Special molding machines are applied for the production of single- or multi-stepped microstructures of a few micrometers in lateral dimension and structural details in the submicrometer range. Maximum aspect ratios of several ten up to 600 are achieved. In contrast to compact disc production, the machines are equipped with a special control unit, by means of which tool temperature is often kept above the melting temperatures of the plastics processed during injection. Evacuation of the tool cavity is required for the complete filling of the microstructurized nest area of the mold. Cycle time is mainly determined by the heating and cooling of the whole molding tool. Recently, novel techniques were developed for the production of ceramic LIGA or LIGA-similar microstructures at Forschungszentrum Karlsruhe, where further development of the LIGA technique has been performed for more than a decade. Using lost plastic microstructures and sometimes even metal tools, microstructures are made of structural (e.g., aluminum oxide, zirconium oxide) and functional ceramics (e.g., PZT). Current development activities are aimed at producing lost plastic molds for metal microstructures by injection molding. Molding tests with conductively filled thermoplastics have been carried out to manufacture lost molds for e.g. spin nozzles.

Recent developments in micro ceramic injection molding

Abstract Effective material application and miniaturization, both indispensable to modern product development and production, demand enhanced manufacturing processes suitable for both micro devices and economic series production. For micro parts made of polymeric materials, micro injection molding represents such a method and has already reached an industrially viable status. For manufacturing of ceramic products micro powder injection molding is a promising option because it combines the possibility of large-scale series production with a wide range of materials, thus possessing a considerable economic potential. An enhanced variant, micro two-component injection molding enables, for example, the fabrication of micro components consisting of two ceramic materials with different physical properties and, furthermore, significantly minimizes mounting expenditure.

Metal and ceramic micro components made by powder injection molding

To overcome the lack of micro manufacturing processes suitable for medium and large scale production as well as to process high resistive materials a special variant of micro injection molding is currently under development: micro powder injection molding (MicroPIM), which already enables the manufacturing of finest detailed components with structure sizes down to a few ten micrometer. In order to expand the scope of application of MicroPIM, tests are being conducted with pure tungsten powders or tungsten alloy powders. As further improvement, micro twocomponent injection molding allows, for example, the fabrication of micro components consisting of two ceramic materials with different physical properties.

Innovations in molding technologies for microfabrication

Micromolding is a key technology for the economic production of components for microsystems. It is applied in several manufacturing techniques including the LIGA process. Especially MicroInjection Molding allows cost-effective large-scale production of components for many applications to be used in microsystems technology. Using special molding machines, lateral dimensions in the micrometer range, structural details down to 200nm and maximum aspect ratios of more than 20 are achieved. Examples for applications are PSU-made housings for microfluidic systems or microcomponents made of PMMA for cardiac catheters. PC or LCP are appropriate materials for interconnection devices in microoptics and electronics. Other examples are injection molded lost plastic molds for electroforming or electroless plating of metal microstructures. An important economic factor is the optimization of the molding process and tool using different simulation techniques. Recently, novel techniques for manufacturing metal or ceramic microstructures were developed by adapting Powder Injection Molding to microtechnologies. Using commercially available feedstocks, microstructures were made of metals or ceramics. Rapid manufacturing of microcomponents is achieved by the so-called Photomolding process using reactive polymer resins as photocurable material and e.g. mold inserts fabricated by laser ablation. The addition of micro- or nanosized ceramics to the resin allows the molding of filled composite with enhanced mechanical properties. Subsequent debindering and sintering steps yield the pure ceramic microcomponents.

Innovative molding technologies for the fabrication of components for microsystems

Economic success of microsystems technology requires a wide range of materials as well as the related manufacturing processes. A suitable technology for medium/large scale production is micro injection molding which actually allows the manufacturing of plastic microstructures with 20 microns minimum thickness, structural details of approximately 0.2 microns or maximum aspect ratios of more than 20. These microstructures are, for example, applied as components in micro optics, micro fluidics or minimally invasive surgery. This is demonstrated by microparts that are currently available or will be available soon. For higher economic efficiency and cost reduction, fully electrical injection modeling machines of higher accuracy have been applied. Also, micro insert injection molding reduces mounting costs. Manufacturing of metal or ceramic microparts by powder injection modeling allows large-scale production of complex shaped microstructures with a wide range of materials. Typical examples are sintered structured like stepped LIGA- gear wheels with minimal dimensions of 50 microns in different metal and ceramic materials. Micro Precision Casting originating from conventional investment casting is a suitable process for small/medium-scale production. Examples are microturbine housings made of precious metal alloys. An approach similar to rapid prototyping applies photocurable reactive resins. Photoinduced molding of low viscous resins under ambient conditions leads to significantly reduced cycle times. Additionally, rapid testing of new composite materials can be performed easily. Microcomponents molded from polymers and different composites like dyes with nonlinear optical properties and nanosized ceramic powders will be presented.

Smoothed particle hydrodynamics simulation of shear-induced powder migration in injection moulding

We present the application of the smoothed particle hydrodynamics (SPH) discretization scheme to Phillips’ model for shear-induced particle migration in concentrated suspensions. This model provides an evolution equation for the scalar mean volume fraction of idealized spherical solid particles of equal diameter which is discretized by the SPH formalism. In order to obtain a discrete evolution equation with exact conservation properties we treat in fact the occupied volume of the solid particles as the degree of freedom for the fluid particles. We present simulation results in two- and three-dimensional channel flow. The two-dimensional results serve as a verification by a comparison to analytic solutions. The three-dimensional results are used for a comparison with experimental measurements obtained from computer tomography of injection moulded ceramic microparts. We observe the best agreement of measurements with snapshots of the transient simulation for a ratio Dc/Dη=0.1 of the two model parameters.

Micro PIM moves into the zone of industrial possibility

Increasing demand for ever-smaller devices presents challenges for materials science. German researchers are looking at the possibilities of micro powder injection moulding, and how to match the process to the needs of large-scale industrial production…

RibCon: micromolded easy-assembly multifiber connector for single- and multimode applications

The fabrication and the design of a new fiber connector for up to 16 single- or multimode fibers is presented. The connector features the following essential advantages: low cost fabrication by micro injection molding, easy assembly due to elastic alignment structures made possible using LIGA technology and bonding by UV-curing adhesive, and a hermaphroditic connector design in order to avoid damage of the precision part of the ferrule. The mean insertion loss is 0.35 dB with multimode fibers and as it turned out from first experiments 1.16 dB with singlemode fibers.