Production of plastic injection moulding tools using selective laser sintering and high speed machining

Global manufacturing trend and competition challenge every industry to seek new manufacturing methods to improve their business processes and speed up the product development cycle [Conolly, 2004a and Knights, 2001]. Among the candidates, layer manufacturing (LM) technologies appear to be a potential solution [Plam, 2002, and Grimm, 2004]. Recent LM technologies have led to a demanding application for developing production tools to manufacture parts, known as rapid tooling (RT). Selective laser sintering (SLS) is one of the leading LM systems available today in RT to manufacture injection mould (core/cavity) inserts [Kruth, 1998, Chua, 1999, Dormal, 1999, and Grenda, 2005]. However, the current capabilities of the SLS in producing metal parts have not yet fulfil the requirements of the injection mould inserts, especially in dimensional accuracy and surface finish quality [Francis, 2002 and Dalgamo, 2001 a]. The aim of this research is to use indirect SLS and high speed machining (HSM) in developing production-quality plastic injection moulding (core/cavity) inserts. The idea is that the indirect SLS process is utilised to build a near-net-shape inserts, while HSM is then utilised to finish the inserts to production specifications. Benchmark studies have been carried out to characterise the capabilities of both SLS and HSM with reference to the typical requirements of injection mould inserts. Utilising the study results, new developments of the mould inserts have been implemented on three major industrial case studies. Their performances have been evaluated and measured by comparing them with its respective original inserts. Furthermore, a set of design rules has been derived from best practices of the case studies, and have been validated by developing a new design for each case studies inserts. The results have demonstrated that the indirect SLS process has a capability III manufacturing a near-net shape of the insert which requires further related finishing to achieve final production specifications. The insert performances in some case studies have indicated significant improvements in process productivity and energy consumption as well as economic benefits to using the inserts. Regarding the significant considerations in realising the design, a recommendation on further strategic design rules and manufacturing process are highlighted so that the development of the insert using the selected approach can be more effective and efficient. Moreover, a utilisation of computer analysis software and further durability trial is also highlighted in order to predict and evaluate the optimum overall performance

DIRECT METAL LASER SINTERING, USING CONFORMAL COOLING, FOR HIGH VOLUME PRODUCTION TOOLING#

Published ArticleExisting techniques to manufacture conventional tool steel inserts for the plastic injection moulding process are expensive and time-consuming. Complex mould inserts, difficult to manufacture with conventional processes, can be produced using Direct Metal Laser Sintering (DMLS) with Maraging tool steel (MS1). MS1 is an additive manufacturing (AM) material made available by Electro Optical Systems (EOS) GmbH. Contrary to material removal processes, DMLS can produce MS1 tool steel inserts directly from Computer-Aided Design (CAD) files suitable for high volume plastic injection moulding. Through DMLS it is possible to create conformal cooling channels inside the MS1 inserts that have advantages in reducing heat rapidly and evenly. This can result in a reduction of cycle times, cost per product as well as improving part quality by eliminating defects such as warpage and heat sinks. This paper will present a comparison between Finite Element Analysis (FEA) simulations of the injection mould inserts with actual mould trails of AM and conventional manufactured inserts. It also includes the design and manufacturing of conventional and DMLS inserts and compares the manufacturing costs and lead times. Using FEA simulations, the design of conformal cooling channels is optimised by comparing the mould temperature of different cooling channel layouts. Bestaande tegnieke vir die vervaardiging van matryse vir die plastiek-inspuit giet tegniek is duur en tyd rowend. Verder is dit nie altyd moontlik om konvensionele metodes vir die vervaardiging van matryse vir geomteries komplekse gietstukke te gebruik nie. Vir sodanige gietsukke kan invoegsels relatief vinnig vervaardig word, deur van direkte laser metal sinterings metodes (DLMS) met Maraging-staal (MS1) gebruik te maak. MS1 is ’n laag vervaardings materiaal wat onlangs deur Electro Optical Systems (EOS) GmbH beskikbaar gestel is. Dit is ’n pre-allooi, ultra hoë sterkte metaal met goeie meganiese eienskappe. In teenstelling met materiaal verwyderings prosesse (masjienerings prosesse), kan DMLS MS1 staal matryse of insetsels wat vir hoë volume produksie van plastiek gietsukke bruikbaar is, direk vanaf rekenaar-gesteunde ontwerp prosesse vervaardig word. Die gebruik van DMLS kan ook vir die ontwerp en vervaardiging van vorm getroue verkoelings kanale in matryse voorsiening maak, wat tot laer hitte asook die vinnige en eweredige verspreiding daarvan sal lei. Voorgenoemde behoort tot ’n aansienlike verlaging in produksie siklus tye te lei met ’n dien ooreenkomstige verlaging in die produksie koste asook ’n verbetering in die kwaliteit van die vervaardigde produkte a.g.v. die voorkoming van defekte soos kromtrekking en hitte-putte wat normaalweg deur oneweredige hitte verspreiding veroorsaak word

Automatic volume inspection for glass blow moulds

In the glass bottle mould making industry, volume control is done by measuring the amount of water needed to fill the mould. This process has several issues. Firstly, it requires a trained operator to properly seal the mould. Secondly, different operators will lead to different volume values. Another issue is related to the time and work necessary for the procedure, which can take up to 20 minutes for a single mould, making it unsuitable to inspect several moulds of the same series. These issues can be solved by automating the procedure. By using reverse engineering systems to obtain the internal cavity surfaces, comparative studies can be done, such as wear study, enabling the optimization of the moulds. The goal of this project is to establish a system to automate the inspection of the moulds which will result in the acquisition of the moulding surfaces. Then, the volume of the moulds and surface deviations in specific areas can be measured. The development of this project focused in two main areas: the development of a script, where the volume is calculated and the surface is inspected, from cloud points, to determine if the mould is in an acceptable state; and the study of technologies capable of acquiring the mould’s surface while simultaneously being automatable. As for this study, several case studies using laser and structured light are performed to understand the abilities and limitations of these technologies. The first study was done using polished cast iron moulds to determine the ability to acquire the surface and obtain the volume. Then, the ability to present proper comparative results is explored by using a set of unpolished cast iron moulds and then these same moulds once polished to verify if the used systems can obtain the deviations between the two situations. Finally, the validation of the technologies was done using a demo bronze mould, where surface deviations were inspected as well as a ring gauge where the inner cylinder was used for inspection. From these cases, the used laser scanner was able to obtain the volumes of the moulds as well as proper comparative results without spray. As for the used structured light system, it proved unable to acquire the surfaces of the moulds and of the ring gauge, requiring spray. Despite this performance, the system is quite automatable and a state-of-the-art structured light system, using blue light, could be used for this purpose. The laser is also a viable solution, but the cost and complexity to automate can be higher than the structured light system

A statistical analysis of nanocavities replication applied to injection moulding

The purpose of this paper is to investigate both theoretically and experimentally how nanocavities are replicated in the injection moulding manufacturing process. The objective is to obtain a methodology for efficiently replicate nanocavities. From the theoretical point of view, simulations are carried out using a submodeling approach combining Solidworks Plastics for a first macrosimulation and Fluent solver for a subsequent nanosimulation. The effect of the four main factors (melt temperature, mould temperature, filling time and cavity geometry) are quantified using an statistical 2 factorial experiment. It is found that the main effects are the cavity length, the mould temperature and the polymer temperature, with standardized effects of 5, 3 and 2.6, respectively. Filling time has a negative 1.3 standardized effect. From the experimental point of view, Focused Ion Beam technique is used for mechanizing nanocavities in a steel mould. The replication achieved in polycarbonate injection is quantified using an Atomic Force Microscope. It is observed how both the geometry and the position of the cavities in the mould affect its replication

Finite Element Thermal Analysis of Conformal Cooling Channels in Injection Moulding

The process cycle time in injection moulding process depends greatly on the cooling time of the plastic part, which is facilitated by the cooling channels in the injection mould. Effective cooling channel design in the mould is important because it not only affects cycle time but also the part quality. Traditional cooling channels are normally made of straight drilled holes in the mould, which have limitations in geometric complexity as well as cooling fluid mobility within the injectio n mould. Over the years, conformal cooling techniques are being introduced as effective alternative to conventional cooling. The main objective of this study is to determine an optimum design for conformal cooling channel of an injection moulded plastic part using finite element analysis and thermal heat transfer analysis. The part cooling time is optimized by conformal cooling channels in the mould using the ANSYS thermal a nalysis software. Analysis of virtual models showed that those with conformal cooling channels predicted a significant reduction of cycle time with expected improvement in part quality

Gas-assisted compression moulding of glass reinforced polypropylene

A new process of combining gas injection with compression moulding was developed and studied in this research work. The process is called Gas Assisted Compression Moulding (or GasComp). The principle is based on the injection of nitrogen gas during a conventional compression moulding cycle. The flow of the material due to the compressive force of the press is assisted by the injection of gas into the centre of the molten material. The gas assists in the flow by coring out the material, reducing the weight by up to 45 percent and increasing the dimensional stability of the component. Novel glass matt thermoplastic mould tools were designed and developed during the course of the research program for use with the process. These designs were of a flash compression mould tool design with a horizontal clamping face, rather than the conventional positive plug compression mould tool with a vertical shear edge. This created a fixed volume mould tool, which when used in conjunction with a short shot of material, would allow the gas to flow the material to fill the remaining volume. Several materials were investigated for their suitability with the process. Their characterisation showed that they contained different glass fibre contents and architectures. A material with a short, dispersed glass fibre content of 11 percent proved to consistently contain a significant gas cavity. The glass architecture proved to be the most significant contributing factor in the creation of a successful gas cavity. The most significant processing parameter in the creation of a large volume cavity proved to be the gas injection delay time. The gas pressure and gas ramp time affected the cavity shape, length and extent of gas fingering. The shrinkage was reduced in the presence of a gas cavity, along with the visible reduction of sink marks. The presence of other moulding features, such as hesitation marks, gas packing and the change in fibre orientation were also discussed

NOVEL TECHNIQUES FOR REDUCING COOLING TIME IN POLYMER INJECTION MOULDS USING RAPID TOOLING TECHNOLOGIES

In this research, thermal simulations and injection moulding experiments were performed to compare moulds having cooling channels of circular cross section and those with profiled cross section channels. Studies have been performed on the cooling time reduction in plastic injection moulding by different techniques utilizing thermal simulations and thermal measurements during experiments. Rapid Tooling (RT) technique, which is a manufacturing technique used to produce injection mould tools in a short period of time, has been applied in this research to fabricate injection moulds having circular and profiled conformal cooling channels. Injection moulding experiments for parts was done with these RT moulds using a vertical injection moulding machine. Manufacturing of mould patterns was done using 3-dimensional Printer Rapid Prototyping machine which used wax as the build material. Wax patterns were designed, fabricated and used to fabricate the mould cavity and channels. Aluminum Filled Epoxy material was used for the fabrication of mould cavities having circular conformal cooling channels and profiled conformal cooling channels. As the thermal conductivity of aluminum filled epoxy is much lower than metal moulds, another innovative concept which was embedding a metal insert around the cavity, was also applied for enhancing the heat dissipation. The metal insert was fabricated from aluminum. The concept was tested by fabricating moulds with aluminum inserts. All moulds were tested by injection moulding experiments with embedded thermocouples to measure the temperature of the cavity surface and temperatures were recorded with a data logger. Analysis of the temperature data indicated that the profiled channels had an increased heat dissipation and reduction of cooling time of about 17 percent over the circular channels. With the moulds having aluminum inserts, there was an impressive increase in cooling rate and the cooling time was further reduced by over 50 percent as compared to moulds without inserts

Stock market related pricing mechanisms for the tool and mould manufacturing industry

Tool and mould manufacturers typically prepare their quotation provide an accurate price of, for example, a die casting mould is a key competitive factor for such companies. However, particularly in the customised production area, calculating the quotations and tenders has been proven as extremely challenging and subjective matter. One main cause is that time dynamic costs are rarely taken into consideration sufficiently even though they have a major impact on the final quotation due to the large time frame between the moment of the initial quotation and the actual production start. They neglect can lead to a significant discrepancy of up to 40 percent between pre- And post-calculation and thus to a loss of the corporate added value. A novel method developed at the Institute of Production Engineering and Machine Tools (IFW), Leibniz Universität Hannover, aims to provide a framework which allows tool and mould manufacturer to prepare a more precise and reliable quotation by taking time-dependent dynamic costs into consideration. The prediction of the time dynamic costs takes place by using stock market pricing mechanisms. Subsequently, based on enterprise related knowledge aggregation, this method also accounts for the probability of occurrence of each quotation thereby minimising the discrepancy between the pre- and post-calculation