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RT703 - 3.4.1 30 Keltool A process from 3D System combines...

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Unformatted text preview: 3.4.1 30 Keltool A process from 3D System combines the generation of an SLA model with the Keltool process to produce a mould in fused powered steel [16]. The SLA model for the final part is finished to a high quality by sanding and polishing. and then placed in a box where silicone rubber is poured around it to make an interim silicon rubber mould. This, tool, is placed in a box and silicon rubber poured around it so as to produce a copy of the SLA model in silicon rubber. This silicon rubber is then placed in a box and a propriety mixture of metal particles, such as tool steel, and a binder material is poured around it. cured. separated from the silicon rubber model and fired to fuse the metal particles and eliminate the binder. The fused part, which is about 70% steel and 30% void is then infiltrated with copper to give a solid mould which can be used in injection moulding. This process using a positive SLA master pattern, described as a reverse generatiOn process, beginning with an SLA model of the mould itself is also available. and requires one step less. It is claimed that in this process. the CAD solid model to injection-moulded production part can be completed in 4—6 weeks. Cost savings of around 25—40% can be achieved as compared with CNC machined steel tools. 4. Comparison of RT Techniques The RT technologies that are discussed are very different from one another. As they offer the manufacturer a wide variety of processes to choose from, a comparison between these tech- niques is necessary. in this section, a comparison is carried out of these techniques using the criteria of tool life. cost of tool development and tool development time. 4.1 Comparison on Tool Life From Table 1, it can be observed that the indirect soft tooling RT technologies have a short tool life of 10—200 pieces. This is because the tool for these technologies is made up of soft material such as silicon rubber, epoxy resins, ceramic. or plastic and as such. wears out quickly. The direct soft tooling RT technologies use relatively harder SLA resins and in the case Table 1.Comparison of RT by tool life. Tool life (number of pans) 10—200 201—2000 More than 2000 Silicon rubber mould Arc spray metal RapidTool tooling Spin casting with Direct AIM 3D Keltool vulcanised rubber mould Castable resin mould Laminated metal tooling SLS of sand casting moulds SL composite Castable ceramic mould Plaster mould Rapid Tooling Technology. Part I 607 of are spray metal tooling. use sprayed metal as the contacting surface with the fabricated parts and hence have a tool life of 201—2000 pieces. The RT technologies that use hard tooling are capable of producing many more parts before any signifi- cant wear of the tool is observed and as many as one million parts is claimed by some of these technologies. SLS of sand casting moulds is also placed under this category as it is an investment casting method and each laser sintered moulds is used only once and there is no loss of detail Owing to tool wear. 4.2 Comparison of Cost of Tool Development The cost of tool development (Table 2) for indirect soft tooling RT technologies, with the exception of arc spray metal tooling. is the lowest (5500-52000). The cost of tool development for these technologies applies not only to the RP master but also to the backing material for the tool. SLS of sand casting moulds is also included in this bracket as the cost of tool development for each investment casting mould is only about $500. For arc spray metal tooling, additional cost is needed for the fabrication of the tool steel bolster which is needed to sustain the high pressures during injection moulding. The total cost for this tool is about $5000 and hence it is placed in the next category, together with the direct soft tooling technologies. at SZOOI—SIOOOO. The cost of tooling for the direct soft tooling technologies is mainly due to the longer RP equipment machining time which equates to higher cost. For those hard tooling technologies. the cost of tool development is higher owing to the cost of the hard tool as well as the long tool. fabricating time on the RP equipment. 4.3 Comparison on Tool Development Time The direct soft tooling RT has the shortest tool development time as very little manual work is needed to produce these tools (see Table 3). If any manual work is needed for these tools. it is usually for the finishing operations such as cleaning. sanding and polishing. For the indirect soft tooling techno- logies, a tool development time of between 1 and 2 weeks is needed for the additional manual operations to produce the tool from the RP master. For the RT technologies that produce the hard tooling, the lead time is longer. as additional process time is needed for post-curing operations, such as firing. to produce the hard tool. Table 2. Comparison of RT by cost of tool development. Cost of tool development 5500-52000 52001—510 000 More than $10 000 SLS of sand casting moulds Silicon rubber mould Arc spray metal tooling Direct AIM RapidTool Laminated metal tooling Spin casting with 3D Keltool vulcanised nibber mould Castable resin mould Castable ceramic mould Plaster mould _—___—_.—_———————— SL composite ...
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