Micro assembly injection moulding

Injection moulding is established as one of the most common manufacturing processes of thermoplastics due to its high degree of automation and the short cycle times. Micro injection moulding is a rapidly growing technology that allows for the efficient production of very complex micro parts in high series. The “Market Analysis for Microsystems II 2002–2005” of the Nexus Task Force anticipates a yearly growth in the field of micro system technology of about 20% (Wechsung et al. 2002). This study identifies in addition to the continuous miniaturization the growing use of polymers in micro systems (Schneider et al. 2001). No other material group offers this wide range of material properties and permits to choose processing parameters and application properties according to necessities (Gächter 2000). While the production processes of micro technical components are mainly controllable, the assembly of these components to hybrid micro systems is a bottleneck to the industrial large scale production. The assembly itself represents a large fraction of the added product value and gains in importance with growing complexity and miniaturization of the systems.     

Energy efficiency benchmarking for injection moulding processes

Energy and resource efficiency is becoming an important strategy in manufacturing. In the automotive industry, the assessment of the environmental impact of a product in use-phase is common practice. In contrast, the manufacturing phase often lacks detailed data; potential for improvement gets lost. Analysis and comparative evaluation of how the production factor energy is used in manufacturing can be an impulse for parallel improvements regarding energy, material and process time efficiency. The paper presents a systematic approach to energy efficiency benchmarking in injection moulding, specifically addressing the impact of the mould. A knowledge base serves as a baseline for the process of data collection and evaluation. Additionally, energy efficiency benchmarking of single processes give insight into the effectiveness of improvement measures and allow to identify best practice process and product designs. The concept can be extended to predict energy consumption of production plants. An energy label for moulds is introduced.     

Geometrical algorithms for automated design of side actions in injection moulding of complex parts

This paper describes algorithms for generating shapes of side actions to minimize a customizable injection moulding cost function. Given a set of undercut facets on a polyhedral part and the main mold opening directions, our approach works in the following manner: first, we compute candidate retraction space for every undercut facet. This space represents the set of candidate translation vectors that can be used by the side action to completely disengage from the undercut facet. As the next step, we generate a discrete set of feasible, nondominated retractions. Then we group the undercut facets into undercut regions by performing state space search over such retractions. This search step is performed by minimizing the given moulding cost function. After identifying the undercut regions, we generate the shapes of individual side actions. We believe that the results presented in this paper will provide the foundations for developing fully automated software for designing side actions.     

New plastification concepts for micro injection moulding

Until now there are no suitable injection moulding machines available for the production of single micro parts, so injection moulders produce big, but precise sprues to achieve the necessary shot weight. Very often over 90 % of the polymer are wasted and this waste can be an important cost factor. Moreover, the big sprue increases cooling time and, along with that, cycle time. To open new dimensions for the minimum shot weight (<0.01 g), IKV, Aachen, Ferromatik Milacron Maschinenbau GmbH, Malterdingen, and Otto Männer Heißkanalsysteme GmbH, Bahlingen, with support of AGA Gas GmbH, Hamburg, have developed a new micro injection moulding machine. The very small amount of plastics needed is plasticised in an electrically heated cylinder and fed into the injection cylinder by a plunger. A second plunger with a diameter of just 2 mm injects the molten material into the cavity. It is driven by an electric motor and a precise linear drive. A central element for the operation of the machine is the nozzle. It is heated electrically and can be cooled down rapidly by injecting liquid CO₂ (TOOLVAC technology). In this way the gate is closed after the injection and the holding phase. The moulded part can be demoulded and a new injection moulding cycle starts. This processing technology reduces the sprue to about 15 to 20 mg. The ability to function of the thermal shut-off-nozzle could be proven theoretically by calculations with the IKV software CADMOULD/MEX. These calculations were verified by temperature measurements on a prototype machine. With the results of these investigations the design of nozzle and mould was optimized. After the injection unit and all the necessary drives and controlling devices have been integrated, the operation characteristics of the machine prototype are analysed. In the next step of the project, the focus is on improving the plasticising efficiency, because the prototype is equipped with a simply electrically heated plastification. For the thermal layout of the plasticising unit the recently developed 3D software SIGMASOFT was used. Moreover, different plasticising concepts are analysed, as there are a “Weißenberg”-extruder using the normal stress effect or plastification by ultrasonics. Especially the plastification by ultrasonics is a very promising idea for very small amounts of plastics and therefore analysed further. Ultrasonics are used successfully for wel- ding and riveting in plastics processing, as it is fast and neat bondings are produced. A test unit was built to prove the ability to operate as a plasticising device and to optimize the necessary components and processing parameters. The plastification results regarding homogenization and morphology of the molten mass have been evaluated by microscopy. The presentation will give detailed information about the trials and their results of the topics summed up above.     

New methacrylate-based feedstock systems for micro powder injection moulding

New methacrylate-based feedstocks have been developed according to fulfil the requirements of the micro powder injection moulding process chain, consisting of compounding, moulding and thermal post-processing for the realization of dense and warpage-free ceramic or metal parts. The different feedstock systems, consisting of polymethylmethacrylate (PMMA) as major binder component and microsized zirconia or stainless steel filler, were prepared by reactive compounding. The individual components—PMMA, solved in its monomer methylmethacrylate (MMA), additives and fillers—were mixed in a dissolver stirrer under ambient conditions and subsequently polymerized to a thermoplastic feedstock. Prior to injection moulding the mixtures’ flow properties were characterized by high pressure capillary rheometry as function of the composition, solid load and shear rate. After replication the obtained test specimen were debinded and sintered using optimized temperature programs. The achieved specimen densities reach 99% of the theoretical possible value for zirconia and 98.7% in case of stainless steel 17-4PH.     

Micro assembly injection moulding for the generation of hybrid microstructures

Based on the micro injection moulding process, which has been investigated at the IKV for several years, a process called micro assembly injection moulding is developed and investigated. It combines the joining of hybrid elements with the generation of functional structures. Micro assembly injection moulding is a quite diverse process with many influencing parameters. For basic studies of this process, a special mould technology with maximum flexibility and precision is used. The mould concept includes a special system for the positioning of inlay parts and complex sensor equipment (pressure, temperature endoscopic devices) for controlling and analysing the process. The processing aspects which have been investigated are the production of movable microstructures by using incompatible polymers, the generation of fluidic hollow structures by lost core technology and the overmoulding of wires and optical fibres. In all cases, the choice of the different materials, the temperature layout of the process and the mechanical strain of inlay parts play a significant role. Furthermore, the precision in positioning of inlay parts and the demoulding of hybrid structures are of great importance.The investigations are part of the SFB (Sonderforschungsbereich) 440 Assembly of Hybrid Micro Systems and were financially supported by the DFG (Deutsche Forschungsgemeinschaft).This paper was presented at the Conference of Micro System Technologies 2001 in March 2001.     

Optimization of the reactive injection moulding process

The aim of the paper is to discuss the possibility of applying a genetic algorithm (GA) in conjunction with the finite-volume (FV) FLUENT package to the optimisation of the reactive injection moulding (RIM) technological process. Firstly, the fundamental flow, heat, mass, and rheokinetic relations are examined, and the possibility of numerically simulating this class of problems is examined, with a view to optimising the parameters governing the progress of the process. Then, the optimisation objective is formulated, taking into account both the total curing time of the RIM process and the set of control parameters, called the degree of cure, that is used as a measure of the effectiveness of the technological process. From among the various parameters characterising the process, the temperatures of the heat sources (electric heaters placed around the mould) are chosen as the design variables (in discretised form). A 2-D planar problem is solved to illustrate the effectiveness of the proposed method.     

Micro assembly injection moulding with plasma treated inserts

Injection moulding is one of the most common manufacturing processes for thermoplastics. By injection moulding, polymer micro components can be produced in large numbers at low costs. Micro assembly injection moulding as a combination of multi-component injection moulding and micro injection moulding enables to avoid offline process steps, as joining is already accomplished in the mould by overmoulding. In case of joint hybrid micro structures, the bonding strength between two components affects the stability of the micro system and is thus important for the part quality. Investigations carried out at the Institute of Plastics Processing (IKV), Aachen, Germany, deal with methods to increase the bonding strength of a plastic and a non-plastic part joint. As shown in the following, a plasma treatment of the inserts is an appropriate approach for this aim.     

A GA/gradient hybrid approach for injection moulding conditions optimisation

Injection moulding conditions such as melt temperature, mould temperature and injection time are important process parameters. Optimisation of these parameters involve complex patterns of local minima, which makes it very suited for Genetic Algorithm (GA). However, once a minimal region is identified during the search process, the GA method is not efficient, even sometimes impossible, in reaching its minimum. This is because GA is opportunistic not deterministic. The crossover and mutation operation may lead the search out of the identified minimal region. Gradient methods, on the other hand, are very efficient in this regard and can guarantee a local minimum, but not a global one. In this paper, a strategy of using a hybrid of both methods in injection moulding conditions optimisation is proposed, so as to exploit their respective advantages. The hybrid optimisation process is elaborated and a case study is conducted to test the effectiveness and efficiency of the strategy and its implementation algorithm. The optimisation results from the hybrid approach are compared with those from the GA method alone to demonstrate the improvement.     

Automated process parameter resetting for injection moulding: a fuzzy-neuro approach

Optimal process parameter setting for injection moulding is difficult to achieve due to a large number of factors involved. Current practice in industry is to adjust the parameters based on the products' defects of test-run through trial and error. This process, however, requires enormous experience and is often time consuming. This paper reports an intelligent system employing fuzzy sets and neural networks which is able to predict the process parameter resetting automatically to achieve better product quality. The system is designed to be used in the test-run of injection moulding. Seven commonly encountered injection moulded product defects (short shot, flash, sink-mark, flow-mark, weld line, cracking, and warpage) and two key injection mould parameters (part flow length and flow thickness) are used as system input which are described using fuzzy terms. On the other hand, nine process parameter adjusters (pressure, speed, resin temperature, clamping force, holding time, mould temperature, injection holding pressure, back pressure, and cooling time) are the system output. A back-propagation neural network has been constructed and trained using a large number of {defects} {parameter adjusters} expert rules. The system is able to predict the exact amount to be adjusted for each parameter towards reducing or eliminating the observed defects. Testing in several real cases showed that the system produced satisfying results.     

Graph-based feature recognition for injection moulding based on a mid-surface approach

This paper presents a novel CAD feature recognition approach for thin-walled injection moulded and cast parts in which moulding features are recognised from a mid-surface abstraction of the part geometry. The motivation for the research has been to develop techniques to help designers of moulded parts to incorporate manufacturing considerations into their designs early in the design process. The main contribution of the research has been the development of an attributed mid-surface adjacency graph to represent the mid-surface topology and geometry, and a feature recognition methodology for moulding features. The conclusion of the research is that the mid-surface representation provides a better basis for feature recognition for moulded parts than a B-REP solid model. A demonstrator that is able to identify ribs, buttresses, bosses, holes and wall junctions has been developed using C++, with data exchange to the CAD system implemented using ISO 10303 STEP. The demonstrator uses a commercial algorithm (I-DEAS) to create the mid-surface representation, but the feature recognition approach is generic and could be applied to any mid-surface abstraction. The software has been tested on a range of simple moulded parts and found to give good results.     

Effects of material improvement and injection moulding tool design on the movability of sintered two-component micro parts

Two-component micro powder injection moulding (2C-MicroPIM) broadens the scope of possible microsystem applications since it facilitates the integration of two different materials and, hence, also two different functions in one micro assembly. As shown recently, not only two-component micro parts with fixed junctions can be produced, but, in principle, also parts with movable connections. This paper describes the difficulties associated with the realisation of shaft-to-collar connections with a movable junction. As an approach the gating concept of the injection moulding tool was changed. With the modified injection moulding tool, movable connections were obtained after sintering the micro parts to a maximum temperature of 1,450°C. Thus, the production of sintered movable connections does no longer require additional steps.     

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.     

Runner sizing and weld line positioning for plastics injection moulding with multiple gates

Weld line and warping are two critical defects for injection-moulded part. If weld lines are unavoidable due to multiple gates in a moulding, they should be positioned in the non-critical region. Instead of using flow leaders and deflectors to control the locations of the weld lines, this paper presents an approach to specify the locations of the weld lines by sizing the runners in a multi-gated injection moulding with the optimum gate locations. The methodology consists of three steps: partitioning the moulding into sub-mouldings based on the specified weld line location, determining the optimum gate location in each sub-moulding by minimizing the injection pressure and repositioning the weld lines to the desired locations by varying the runner sizes. Two examples are used to illustrate the approach.     

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.     

SVM performance assessment for the control of injection moulding processes and plasticating extrusion

The paper presents the application of a new and promising learning algorithm based on kernel methods, i.e. support vector machines (SVMs), for the control of injection moulding processes and plasticating extrusion. In particular, the main purpose of this work is to assess the effectiveness of the method when applied to such kinds of industrial processes, characterized by a large number of variables and strictly correlated by nonlinear relationships. First, we analyse the injection process by developing a simplified model, then we identify it by using a support vector machine. The reference of the control system is tracked through the design of a control block based on the structure of the SVM.     

Cost-effective design for injection molding

It is commonly agreed that a large proportion of the ultimate product cost is determined at product design stage. Therefore, a cost-effective design cannot be obtained unless all cost issues are resolved at early design stage. Therefore, instead of performing cost estimation after design, research presented in this paper aims to provide on-line cost evaluation and advisory to help product designers avoid cost-ineffective design. The objective can be obtained by (1) identifying factors that might affect product cost at each product design stage, (2) developing a design for cost effectiveness methodology that accommodates the concepts of concurrent engineering, and (3) developing a computer-based design for cost effectiveness system based on the proposed methodology. In this research, we focus on injection molding product design due to the advantages of injection molding process, such as high production rates, excellent quality and accuracy of the parts, and very long mold life. This paper first reviews and characterizes the conventional molding product development process with an emphasis on the identification of cost factors. Based on the results of process characterization, a cost model is developed, which depicts the relationships between cost factors and product development activities, as well as their relationships with product geometry. According to the product life cycle activities and the cost model, a design for cost effectiveness process is proposed. The process and the cost model are then employed for the development of a computer-based product design for cost effectiveness as one of the module of an integrated design for injection molding environment.     

Compounding, micro injection moulding and characterisation of polycarbonate-nanosized alumina-composites for application in microoptics

The addition of nanosized ceramics to polymers allows for a tailoring of the thermomechanical and optical properties of the used thermoplastic matrix polymers. In this work, the impact of nanosized γ-alumina filler to polycarbonate APEC2097 on the compounding process and the resulting physical properties is reported. Polymer degradation during compounding affects a plasticising effect and a reduction of the Charpy impact strength. The refractive indices of the polycarbonate-alumina-composites increase with increasing solid load. Due to nanoparticle agglomeration the optical transmittance drops with growing alumina content.     

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.