Hans-Joachim Ritzhaupt-Kleissl

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.

Two-Component Tungsten Powder Injection Molding for Mass Production of He-Cooled DEMO Divertor Parts

Abstract Fusion technology as a possible and promising alternative energy source for the future is intensively investigated at Karlsruhe Institute of Technology (KIT). The KIT divertor design for the future DEMO fusion power plant is based on a modular concept of He-cooling finger units. More than 250,000 single parts are needed for the whole divertor system, where the most promising divertor material, tungsten, must withstand steady-state heat loads of up to 10 MW/m2. Powder injection molding (PIM) as a mass-oriented manufacturing method of parts with high near-net-shape precision has been adapted and developed at KIT for producing tungsten parts, which provides a cost-saving alternative compared to conventional machining. While manufactured tungsten parts are normally composed of only one material, two-component PIM applied in this work allows the joining of two different materials, e.g., tungsten with a tungsten alloy, without brazing. The complete technological process of two-component tungsten PIM of samples, including the subsequent heat-treatment process, is outlined. Characterization results of the finished samples, e.g., microstructure, hardness, density, and joining zone quality, are discussed.

Rheological Properties of Zirconia/Paraffin Feedstocks Used for Plastic Forming of Zirconia Micro Parts

Zirconia micro columns of approximately 200 μm x 200 μm width and with an aspect ratio of 6 were produced for flexure strength testing applications. A metal model whose size was corrected for the expected sintering shrinkage was milled and subsequently used for the preparation of a silicone rubber mold. Small volumes of zirconia feedstocks were prepared and placed into the molds by a suited plastic forming method. The feedstocks consisted of suspensions of submicron zirconia particles dispersed in hot paraffin. First results about the improvement of the shaping process by an adjustment of the rheological properties of the feedstock will be shown. Shaping of ceramic microparts by plastic forming methods Processes developed in the past for shaping of ceramic parts in the millimeter and micrometer ranges differ in terms of manufacturing expenditure, design freedom, and achievable aspect ratio. But they all have in common that production is based on a powder-technological molding process using a negative mold and subsequent thermal compaction [1]. Processes that have been proven to be especially suited for the fabrication of ceramic microparts are centrifugal casting [2], injection molding [3] and hot molding [4]. In contrast to high-pressure injection molding, where the feedstock is plastified by thermoplastics of high viscosity, hot molding and low-pressure injection molding of ceramics are based on the use of low-melting paraffins which allow molding at significantly lower temperatures and pressures [4]. Due to the small mold loads involved by these processes besides metal molding tools, plastic molds may be applied as well as molds cast from silicone rubber [5]. For the preparation of the feedstocks, paraffin and a dispersant are molten and then mixed with the ceramic powder. Zirconia feedstocks with a mean particle size of approximately 0,6 μm, for instance, usually have a solid content of about 50 vol.%. Low-pressure Injection Molding is performed in automatic or semi-automatic facilities, allowing the fabrication of larger series (Peltsman Corp., Minneapolis, USA, GOCERAM, Molndal, Sweden). For complete filling of the mold, the tool has to be evacuated prior to injection and the mold has to be heated up to a temperature that exceeds the melting point of the paraffin. Due to the elasticity of the silicone mold, it is also required to adapt the machine parameters in order to ensure sufficient dimensional accuracy [6]. Centrifugal casting. In most cases the same feedstock prepared for low pressure injection molding can also be used for centrifugal casting. In this technique the slip is not driven into the mold by pressure but by centrifugal forces. In contrast to the centrifugal casting described in [2], the centrifugation time is short and no sedimentation of the powder takes place, so it resembles the spin casting or investment casting of metals. Molds also have to be heated during filling and after filling they must be evacuated in a vacuum chamber before the solidification takes place. Centrifugal