Introduction of Rapid Tooling
The rapid tooling technology with the adoption of rapid prototyping technology to develop and trial manufacture new product is fast growing recently. The traditional tooling manufacture methods are as follows: NC milling, forming grinding, electric spark machining, linear cutting, cast tool, electrolytic machining, electroforming, pressworking and photographic corrosion and so on. Since these technologies are complex, long periodic, high cost, the response speed of new product to the market is delayed. The traditional rapid tooling (such as low melting point alloy tool, electric cast tool, spray and coat tool) are difficult to meet the requirement of the customers because of their rough process, low precision, short lifetime. Especially, even the traditional rapid tooling cannot realize the real rapid because of the problems in design and manufacturing not corrected. Therefore, making rapid tooling with rapid prototyping, trial and low-value manufacture before final tool making, the success rate of product development can be greatly improved, and time and cost can also be saved effectively.
RP+RT technology offers a new concept and method for direct making tools from CAD model. It integrates the concept design and the process of tools into one CAD/CAM system, and provides well conditions for the application of concurrent engineering. The RT technology adopts the design and making method of early, multi-loop, rapid information feedback, combines various means of computer simulation and analog, which forms a complete set of brand new tool design and manufacturing system. The RP technology can solve great many of problems, which can be solved in much difficult condition or never be solved by traditional process (such as machining technology), obtain the complex shapes which all machine processes cannot do, directly manufacture complicated cavity according to the CAD model without NC machining. It needs only about one third of time period of traditional process from the concept design to the accomplishment of the manufacturing and obtains obvious effect in the improvement of quality, shortening of development period and the improvement of manufacturing flexibility. At present, making rapid tooling with rapid prototyping technology can be divided into two kinds, direct tooling and indirect tooling. More than 20 sorts of RT technologies have been applied in industry and examed by the market.
Within the RP field, the fastest developing, most active and most obvious increasing is rapid tooling technology, and this is the common opinion at the GARPA (Global Alliance of Rapid Prototyping Associations) in Paris France in May, 2000. Because of the hearty requirement of the market, new RT technologies and equipment are developed by many companies and well benefits are obtained. Because of the high technology content in these technologies, many scientific fields are involved, and the technology problems that are thought unable to be solved are solved before, these technologies are widely noticed. In 1999, the secondary RP market segment, which includes rapid tooling created directly from RP processes, grew 34.6% to an estimated more than 500 millions.
The Achievements of Rapid Tooling
Electroforming mould
Electrical Forming is one of the Rapid Tooling technologies which combines with RP and traditional Electrical Casting. The essence steps are, dealing with the surface of the rapid prototype, such as polishing, coating electrical layer on the pattern's surface, then place it in the electrical casting to form the metal layer, the inner surface of the metal layer copies the pattern's outer surface, and then by high temperature sinter to release the prototype, fill low melt point alloy or aluminum -epoxy composite into the crack between the frame of mold and metal layer, the electrical forming is formed at last.
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| Electroforming tooling for model of aerocraft tested in wind tunnel |
Silicone rubber model of ceramics mould
Using the silicone rubber mould obtained from LOM prototype or prototypes made by other RP technologies, through coat transferring that we can obtain the precise ceramics mold. Then it is poured with cast aluminum or black metal, the mold of meridian tire can be manufactured. Figure 9 shows the achievement that Tsinghua university cooperates with a plant in ShanDong province. Among these figures, (a) shows the LOM prototype of the tire, (b) shows the precise ceramics mold and (c) shows the alloy cast iron.
Someone adopted a process route similar to this process to manufacture mold rapidly. Yet, it uses gypsum mold. Figure 10 shows an example made by Korea technicians. First, they make LOM mould prototype by CAD model. Second, silica gel mold is manufactured from RP prototype. Last, precise gypsum mold is obtained through coat transferring. Last, it is poured accompany with pressurize vibration. Now, the mould of nave is obtained.
Powder metallurgy rapid mould
3D Systems also developed a powder metallurgy rapid mold process, which is named 3D Keltool. The fabrication process is: make a silicon rubber mold from SLA prototype as a intermediary mold, then inject tool steel powder mixed with resin binder into it. Once the material is solidified, a green part can be got out of the mold. The green part is then fired to burn away the binder, and a brown part with loose structure (about 30% space) is got. Then copper is infiltrated to achieve higher density and mechanical strength. Simple machining is applied to get higher precision (up to 0.04 mm). Thus a Keltool mold is achieved. The mold consists of 70% steel, 30% copper, with physical properties similar to that of P20 tool steel. The properties allow the mold to withstand pressures up to 20,000~ 25,000Pa and temperature up to 650C
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| (a) and (c) LOM prototype and casting part of the terne die; (c) and (d) LOM prototype and casting part of the cavity die |
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| Lom prototype (a) and its precise casting part (b) | ||
