Replication processes for metal and ceramic micro parts

To cover the demand for effective manufacturing of metal and ceramic micro components two process technologies are described. The first one can be regarded as a special variant of micro powder injection molding (MicroPIM): inmold-labeling using powder filled feedstocks. Its basic procedures are the backfitting of powder filled foils by an injected PIM-Feedstock and the subsequent co-debinding and co-sintering steps. For example, two-material ceramic parts with microstructured surfaces could be produced and compacted with mostly tight interfaces. The second process conduct combines two-component and insert injection molding with an electroforming process. Since all process steps involved are based on technologies suitable for series production, low product costs per unit will be realistic. Surface qualities and dimensional accuracies are comparable or even better than achieved if applying alternative processes like MicroPIM.     

Galvanic deposition in partially conductive plastic molds for manufacture of finely detailed microcomponents

Combining multicomponent injection molding and electroforming processes, a method for manufacturing medium and large quantities of high-quality metallic parts had been developed. Since the process steps involved are based on two technologies suitable for series production, low product costs per unit will be realistic. The high quality of the metallic microparts was verified, among other things, by means of demonstrator surface and dimensional measurements. Compared with competing methods (MicroPIM), significantly better or at least equal values were obtained. In addition, multi-material micro components containing e.g., ceramic inserts were manufactured successfully. There are certain potentials for optimizing the dimensional accuracy or scatter of the finished galvanic parts. Besides, 2C film injection molding, which allows replication of very fine exposed structures, has been examined successfully and will be developed further.     

Performance and simulation of thermoplastic micro injection molding

 Originally developed for the replication of high aspect ratio LIGA structures, micro injection molding is presently on its way to become an established manufacturing process. Enhanced technological products like micro optical devices are entering the market. New developments like the different kinds of injection molding with several components open up opportunities for increasing economic efficiency as well as for new fields of applications. Software tools for the simulation of the thermal household of the molding tool and/or the moldfilling process itself can provide useful but not wholly sufficient assistance for the optimization of micro injection molding. Received: 10 August 2001/Accepted: 24 September 2001     

Supporting design of primary shaped micro parts and systems through provision of experience

Nowadays, miniaturization is one observable trend in the development of new technical systems. Based on the miniaturization of existing macroscopic production technologies e.g. powder injection molding, a new process chain for the development of primary shaped microparts and systems is being developed in the collaborative research center 499 “design, production and quality assurance of molded micro components made of metallic and ceramic materials”. Because of the constantly evolving miniaturization and growing complexity of the developed microparts and systems, new development processes and methods are needed. Because of the mostly restrictive influence of the downstream phases (production and quality assurance) over the design phase, micro-specific design processes require well-founded knowledge about micro-specific manufacturing techniques (e.g. restrictions) which may be stored in form of design rules. However, many micro-specific aspects cannot be represented in design rules. In this paper the authors propose a new approach to ensure this other kind of knowledge.     

Powder injection moulding of metallic and ceramic micro parts

Industrial use of micro components is determined by the availability of efficient manufacturing techniques. While micro injection moulding of plastic is common practice, metal and ceramic powder injection moulding (PIM) still is under development. High-pressure and low-pressure injection moulding methods complement each other ideally, covering the entire spectrum from prototype to large-scale production. With high-pressure PIM, micro gear wheels with diameters <300 μm can be fabricated using LIGA mould inserts. Densities between 97 and 99% of the theoretical values are achieved. Apart from oxide ceramics, metal materials like copper or powder metallurgical steels like 17-4PH or 316L are often applied. Multi-component injection moulding requires less mounting steps and, hence, offers decisive advantages for effective production of interesting material combinations like electrically conductive/insulating or hard/ductile. Studies relating to the fabrication of immobile as well as mobile shaft-wheel components were performed. Other activities focussed on in-mould labelling with foils containing ultra-fine particles to improve surface quality and detail accuracy. Low-pressure injection moulding allows for the manufacture of small series within 1–4 weeks at low cost. However, the process has features which are not compatible with high-pressure PIM. Although use of a low-viscous feedstock is associated with various benefits, low-pressure injection moulding has not met with acceptance in micro moulding.     

Quality assurance in micro production

Quality assurance is essential for an efficient support of all developing and manufacturing processes and activities with the forefront objective to reach robust processes with a high throughput of parts meeting their functional requirements. Due to the lack of a broad base of experiences regarding the still developing manufacturing technologies in micro production an adequate quality assurance plays an even more important role in order to efficiently support the transition of micro production processes from non-robust to stable processes. Thereby, quality assurance faces particular challenges in micro production, which render a reasonable application of common quality methods difficult or even impossible. Consequently, it is essential to develop new concepts or adjust widely applied quality assurance methods in order to support and continuously improve the development- and manufacturing processes in micro production. Within the scope of the Collaborative Research Center (SFB) 499 “Design, production and quality assurance of primary shaped micro components manufactured in ceramic and metallic materials” the approach of the subproject working on the topic quality assurance is threefold: (i) An efficient and process-accompanying information management has been implemented and will be enhanced further on. (ii) Specifically adjusted preventive methods of quality assurance have been developed and applied. (iii) In order to implement an efficient operational quality assurance performance data of the manufacturing processes has been collected and provided. In the future this supply of data will be used to control and improve the manufacturing processes.     

The effects of metal particle size and distributions on dimensional accuracy for micro parts in micro metal injection molding

This study aims to develop processing techniques to improve dimensional accuracy of micro-size parts produced by micro metal injection molding (μ-MIM). Micro dumbbell specimens were molded by a micro injection molding machine, which can monitor the cavity pressure in injection molding process. The effects of particle size and distribution of metal powder on dimensional accuracy of micro dumbbell specimens at both grip parts were investigated. As the results, it is confirmed that the powder properties and sintering conditions to improve the dimensional accuracy of micro-MIM parts.     

Replication of large scale micro pillar array with different diameters by micro injection molding

The capillary force is always used as the driving force of microfluidic chips. In this study, the capillary force of blood smart diagnostic microfluidic chip which fabricated by micro-injection molding (μ-IM) is offered by the structure of micro pillar array. And the detection effect of blood smart diagnostic microfluidic chips is affected by the replication and height distribution of large scale micro pillar array. So the effect of process parameters on the micro-structure and the height distribution of micro pillar is studied. The mold design is also an important factor affecting micro parts properties. In this study, a steel mold insert with almost 15,500 micro blind cavities was fabricated by milling, electrical discharge machine and Femtosecond Laser process. Polymethyl methacrylate -Polystyrene copolymer (SMMA NAS 30) was used as the molding material. The single factor trail and orthogonal experiment approach were adopted to investigate the effect of several process parameters and the significant effect factors affecting the replication of micro pillar. And the height distribution of micro pillar array was investigated by scanning electron microscope (SEM) and universal tool-measuring microscope to measure the replication quality. The results reveal that the replication of micro pillar is sensitive to the flow direction of the polymer melt. The height of micro pillar increases with the increase of mold temperature and injection speed. Moreover, the height distribution of micro pillar along and against flow direction was tightly related to the thermomechanical history of material during the molding process.

     

The development of two-component micro powder injection moulding and sinter joining

Two-component micro powder injection moulding experienced significant progress in the recent past. Starting as a manufacturing method for integrating two different plastics, the extension of two-component injection moulding (2C-IM) from pure plastics to more resistant materials like ceramics or metals (2C-PIM) provided sophisticated and challenging applications. With the transfer of 2C-PIM to micro systems, two-component micro powder injection moulding (2C-MicroPIM) was established. Up to a certain extend sinter joining is an alternative to 2C-PIM. It allows for component assemblies to be moulded as separate low-complexity parts which are then joined into complex assemblies. This procedure considerably reduces the time and cost required to manufacture the injection moulding tools. This article gives an overview of the development of 2C-MicroPIM—from two component plastic devices to the production of complex two-component micro assemblies made of two ceramic or metallic materials and the state-of-the-art of science and technology of sinter joining.

     

The development of two-component micro powder injection moulding and sinter joining

Two-component micro powder injection moulding experienced significant progress in the recent past. Starting as a manufacturing method for integrating two different plastics, the extension of two-component injection moulding (2C-IM) from pure plastics to more resistant materials like ceramics or metals (2C-PIM) provided sophisticated and challenging applications. With the transfer of 2C-PIM to micro systems, two-component micro powder injection moulding (2C-MicroPIM) was established. Up to a certain extend sinter joining is an alternative to 2C-PIM. It allows for component assemblies to be moulded as separate low-complexity parts which are then joined into complex assemblies. This procedure considerably reduces the time and cost required to manufacture the injection moulding tools. This article gives an overview of the development of 2C-MicroPIM??from two component plastic devices to the production of complex two-component micro assemblies made of two ceramic or metallic materials and the state-of-the-art of science and technology of sinter joining.     

Fabrication of micro gear by micro powder injection molding

Micro components made from polymers can be easily processed but they may not be suitable for all applications. One example is where good mechanical properties are required. Thus, the fabrication of micro components from non-polymeric materials such as metals and ceramics is essential. In this paper, the fabrication of 316L stainless steel micro gear by micro powder injection molding is reported. The specifications of the green micro gear were: 10 teeth, module of 0.08, outer diameter of 1 mm and a length of 1 mm. Injection molding was conducted on a conventional injection molding machine with a small screw diameter of 14 mm. The green micro gear was well replicated. The debound micro gear retained its shape and the teeth were well defined. After sintering, the shape was also retained but with some surface irregularities. The process differences between μPIM and PIM, such as the use of smaller particle size and higher mold temperature are also highlighted.     

Metal-ceramic-composite casting of complex micro components

Metal-ceramic-composite casting has a huge potential as a new manufacturing method for the production of complex-shaped micro sized parts or microsystems consisting of different metals and ceramics. The fundamental advantage of this method is the capability of multi-component part fabrication in one step avoiding first time consuming joining or assembling techniques; second the used material combinations can fulfill complex functionalities and enhanced mechanical properties. One of the most challenging factors in micro composite casting is a stable mechanical bonding between the used individual materials. But under consideration of the different physical properties like thermal expansion coefficient as well as of the wettability of the ceramic inserts and of the applied metal casting material it is possible to manufacture form and force fitting microsystems. Within the framework of this feasibility study complex metal-ceramic micro composites have been realized successfully using the lost-wax casting process. Casting experiments were performed at different muffle preheating temperatures with Al-bronze of the type CuAl10Ni5Fe4 as casting material. The ceramic parts, respectively inserts cast around by metal are micro gear wheels (2.5 mm diameter) consisting of ZrO₂ and Al₂O₃.     

Polymethylmethacrylate/polyethyleneglycol-based partially water soluble binder system for micro ceramic injection moulding

In micro powder injection moulding polyethylene-wax binder systems have been widely established for many years enabling the fabrication of dense ceramic or metal micro structured parts. With respect to complete organic moiety removal a solvent debinding step prior to thermal decomposition using hexane as organic solvent has to be applied dissolving the wax prior to thermal decomposition of the polyethylene. The development of environmentally friendly binder systems must consider the substitution of any organic solvent or even the solvent pre-debinding. In this work a modified process chain, starting with a reactive feedstock mixture consisting of a thermally curable methylmethacrylate/polymethylmethacrylate resin, low molecular mass polyethyleneglycol and submicron-sized zirconia as ceramic filler, followed by feedstock polymerization at elevated temperature, pelletizing, injection moulding, debinding and sintering, will be presented. Prior to replication important feedstock properties like temperature and solid load dependent melt viscosity as well as the real solid load was measured guaranteeing a successful mould filling. Two different debinding strategies—with and without water-assisted predebinding—were pursued and the resulting sinter part densities as well as surface qualities were compared. Zirconia test specimen parts with a density around 99 % of the theoretical density could be obtained successfully.     

Influence of processing parameters on micro injection molded weld line mechanical properties of polypropylene (PP)

As a hot fabrication technology for micro scale parts, micro injection molding is receiving increasing market attention. Improving mechanical properties of micro parts should be an important issue in the micro injection molding process. The relation between weld line strength in micro injection molding parts and processing parameters is investigated. A visual mold with variotherm unit is designed and constructed, in which the micro tensile specimen with weld line are prepared. Polypropylene (PP) is used as the research material in this study, and six processing parameters were chosen as investigating factors, which were melt temperature, mold temperature, injection pressure, packing pressure, ejection temperature and injection speed. In order to achieve optimized processing parameters and their order of significance, Taguchi experiment method was applied in this presented study. The prediction formulation of the strength of micro weld line was built up by multiple regression analysis based on Chebyshev orthogonal polynomial. The results showed the influencing significance order of parameters from strong to week separately are mold temperature, melt temperature, injection speed, ejection temperature, packing pressure and injection pressure. And the tolerance of micro weld line prediction formulation was found to be lower than 21% through confirmation experiments.     

Hot embossing of micro and sub-micro structured inserts for polymer replication

Today replication of microstructured parts is state of the art in laboratory and commercial use. Beside the process of injection molding hot embossing enables the accurate replication of polymer structures in a broad variety of thermoplastic polymers even in the nanometer range. Characteristic for the most replication processes dealing with thermoplastic polymers is the use of microstructured mold inserts based on metals. In this paper we describe an alternative to the established mold inserts––the use of so called interstage mold inserts. These interstage mold inserts are replicated in high performance polymers and technical thermoplastics and can be fabricated many times by a previous replication step from a master even in the sub-micro range. Aspects like suitable material combinations, demolding behaviour, long time stability, production rate, and the quality of structures will be discussed. Because of the high flexibility the process of hot embossing is used for the fabrication of the microstructured interstage mold inserts and their replications.     

Automation of the powder injection molding process

Powder injection molding (PIM) offers a high potential for fabrication of micro-mechanical parts manufactured in metal or ceramic material providing a large variety of properties. To ensure an economical micro-PIM production in large lot sizes and high quality automation of the process beginning with demolding, handling, debinding and ending with sintering is a necessity. Within the field of automation research focus is to optimize critical processes like sprue separation, demolding and handling as well as the set-up of an autonomous and automated process-chain which are presented in this article.This work is based upon the Collaborative Research Centre SFB 499 funded by the German Research Foundation (DFG)     

Simulation of the filling process in molding components with micro channels

In micro molding of components with micro features, the ability for the polymer melt to flow into the micro channels is a crucial factor for successful molding. In this case, the molded volume is about the same as the conventional molding. The penetration distance into the microstructure depends on the flow rate and the cooling rate of the micro features, which is function of the geometric dimensions. In this study, a simplified model was established to estimate the injection distance into the micro channels of a mold insert. The effect of the mold temperature, injection rate, and micro channel dimension on the filling distance was investigated based on the model. The filling distance increases dramatically with respect to the increase of the channel width. In molding of components with micro features as those analyzed in this study, decrease of the part thickness could enhance the filling in the micro features.The authors would like to thank for the financial support from National Science Council in Republic of China under the contract number of NSC 91-2212-E006-131.     

Visualizing analysis for weld line forming in micro injection molding by experimental method

In micro injection molding, the melt flow behavior is important for the final product quality. However, the current process monitoring and measurement technology are not adequate enough to provide a direct analysis access. In the presented study, a glass insert mold designed for performing the direct visual analysis for melt flow phenomena in micro injection molding is introduced. The micro tensile specimen with 0.1 × 0.4 mm² (depth × width) cross section dimension is chosen as the objective part. The correlation between processing parameters (injection pressure, injection speed, mold temperature) and flow behavior was investigated and analyzed. The results show that the injection pressure put an obvious effect on the filling speed through micro cavity. Injection speed can influence the filling time dramatically also. Higher mold temperature brings positive influence with the flowing speed, due to the lower viscosity of polymers in higher mold temperature.     

Design and prototyping of a ceramic micro turbine: a case study

Within the framework of the Collaborative Research Center 499 (SFB 499) of the German Research Foundation (DFG), one task was the development of a zirconia micro turbine as a demonstrator tool to enhance the interaction of the participating workgroups. This case study describes the evolution of the demonstrator and experiences gained with the design and the manufacturing of a micro device. Although it was not the aim of this basic research project to develop a commercial product, the experiences are valuable for improving the performance of industrial product development processes for ceramic micro devices. The various parts of the zirconia micro turbine were prepared by a rapid prototyping process chain (RPPC) that allows for a fast and inexpensive manufacturing of ceramic parts with details down to the micron range. A first design concept was made to mainly demonstrate the shaping feasibility of the process in the micro range. However, some features affected the performance due to their low loading capacity. Thus, a modified design was improved for power output and durability. After optimization of the process chain, dense and homogenous ceramic micro parts could be manufactured. These parts were used for the assembling of a functional micro turbine demonstrator, which was powered by compressed air.     

A mechanism influencing micro injection molded weld lines of hybrid nano filled polypropylene

Nano fillers reinforced polymer composites have been widely applied in microsystem technologies. As one popular micro fabrication technology, micro injection molding is playing the key role in manufacturing micro scale parts made of nano thermoplastics composites. As a defect in micro injection molding parts hard to avoid, the weld line causes detrimental mechanical and physical properties, particularly in case of nano filled composites. In this study, the hybrid carbon nanofibers (CNFs)/TiO₂ nano particles (1:1) filled polypropylene (PP) was prepared by inner melts mixing process with various weight contents(10, 20, 30 and 35 wt%). Micro tensile samples with weld lines for all composites were formed by micro injection molding process at constant processing conditions. Mechanical properties of micro weld lines were tested by tensile test characterizing method. The results show that comparison with neat PP, the samples with weld lines made of hybrid nano PP composites are showing lower tensile strength and elongation percent, but higher E modulus. As increasing nano filler contents, the tensile strength and elongation of micro weld line samples are decreasing, while the E modulus is improved considerably.