G. Fu

A micro powder injection molding apparatus for high aspect ratio metal micro-structure production

A new variotherm molding apparatus is presented in this paper for the fabrication of high aspect ratio 316L stainless steel micro-structures using micro powder injection molding (μPIM) technology. The molding apparatus prototype includes an injection mold in which a silicon insert with an array of 24 × 24 (576) microcavities is mounted, a set of rapid tempering systems for the mold and a set of vacuum systems. The key advantage of this molding apparatus lies in the real-time monitoring and rapid adjustment of the mold cavity temperature during injection molding and part ejection, which makes molding and demolding of high aspect ratio green micro-structures possible. For example, incomplete filling occurs while injection molding micro-structures of 60 µm × height 191 µm with an aspect ratio of 3.2 using a conventional mold. In comparison, smaller micro-structures with higher aspect ratio are produced successfully in the case of the new molding apparatus, e.g. micro-structures of 40 µm × height 174 µm with an aspect ratio of 4.35 and 20 µm × height 160 µm with an aspect ratio of 8 were molded successfully.

The demolding of powder injection molded micro-structures : analysis, simulation and experiment

This paper studies the demolding of an array of powder injection molded micro-structures based on a variotherm mold. The demolding of the micro-structures array was analyzed both theoretically and experimentally. Finite element method (FEM) software ABAQUS was used to analyze and simulate the demolding of an array of 24 × 24 (total of 576) micro-structures. It was found that there exists a critical temperature at which the demolding force for the micro-structures array is a minimum. The stress distribution of the micro-structures and demolding force for the micro-structures during the course of demolding were analyzed for both demolding temperatures higher and lower than the critical temperature. Packing pressure and demolding temperature have an apparent impact on the demolding force. A series of demolding force measuring experiments at different packing pressures and demolding temperatures were conducted to verify the theoretical results.

Review of production of microfluidic devices: material, manufacturing and metrology

Microfluidic devices play a crucial role in biology, life sciences and many other fields. Three aspects have to be considered in production of microfluidic devices: (i) material properties before and after processing, (ii) tooling and processing methodologies, and (iii) measurements for process control. This paper presents a review of these three areas. The key properties of materials are reviewed from both the production and device performance point of views in this paper. The tooling and processing methodologies considered include both the direct tooling methods and the mold based processing methods. The response of material on the production parameters during hot embossing process are simulated for process control and product quality prediction purpose. Finally, the measurements for process control aspect discuss different measurement approaches, especially the defect inspection, critical dimensional measurements, bonding quality characterization and checking functionality. Simulation and experimental results are used throughout the paper to illustrate the effectiveness of such approaches.

Effects of Injection Molding Parameters on the Production of Microstructures by Micropowder Injection Molding

ABSTRACT Micropowder injection molding (μPIM) is a potential low-cost process for the mass production of metal or ceramic microstructures. In order to obtain good molded microstructures and to avoid molding defects, it is important to select suitable injection molding parameters. In this paper, the selection of injection molding conditions for the production of 316L stainless steel microstructures by μPIM is presented. Silicon mold inserts with 24 × 24 microcavities were injection molded on a conventional injection molding machine. The dimensions of each microcavity were Φ 100 μ m × depth 200 μm, giving an aspect ratio of 2. The distance between each microcavity was 200 μm. Five sets of experiments were conducted by varying one injection molding parameter at a time. The parameters included injection pressure, holding pressure, holding time, mold temperature, and melt temperature. Higher injection pressure and holding pressure were required during the injection molding process due to the small dimensions of the microcavities and the large number of microcavities (576 microcavities). High mold temperature was required for complete filling of the microcavities. Molded microstructures without visual defects were obtained using appropriate injection molding parameters. Catalytic debinding and sintering of the 316L stainless steel microstructures were successfully conducted.

Metallic mould inserts for fabrication of polymer microfluidic devices

In this paper, three metallic mould inserts for fabrication of polymer microfluidic devices were produced using different methods. Firstly, metallic glass mould insert was cut by high speed micro-milling. Secondly, 316L stainless steel mould insert was made by micro metal injection moulding (μMIM) using D50 = 4 μm powder. Finally, 316L stainless steel powder with a smaller particle size of D50 = 2 μm was used to produce mould insert in order to improve surface quality of the mould insert. The geometry and surface roughness of micro-features on the three mould inserts are viewed and compared.

Investigation of the Dimensional Variation of Microstructures Through the μMIM Process

In this paper, the dimensional variation of the microstructures throughout all the steps of the Micro Metal Injection Moulding (?MIM) process, that is, injection moulding, debinding and sintering, was investigated. The dimensions of the microstructures were measured using a Veeco interferometer. Based on the measured data, global warpage, surface roughness and dimensional shrinkage of the microstructures in different processing steps were compared. Further, a preliminary study on the effect of packing pressure on the three parameters (global warpage, surface roughness and dimensional shrinkage) throughout all the steps of the ?MIM process was conducted.