Application of rapid prototyping technology in investment precision casting

In recent years, with the gradual improvement of China’s market economy system and the rapid improvement of the country’s comprehensive strength, aerospace and national defense science and technology began to become the national key development industry.  Space exploration, national defense construction and automobile production are inseparable from metal parts. These metal parts are not only the necessary material basis of the above industries, but also have the characteristics of complex structure and high degree of refinement.  The traditional casting technology of metal parts needs to complete the replication by designing the mother mold or the transition mold, which is time-consuming, costly and difficult to manufacture, but the formation of rapid prototyping technology solves this problem.  Rapid prototyping technology can quickly produce wax molds or vanishing investment molds in a short time, which enhances the efficiency and flexibility of precision casting.

Rapid prototyping technology and production process

Compared with the traditional manufacturing process, rapid prototyping technology at the same time integrates computer aided design technology, numerical control technology, material technology and many other new scientific and technological means, with high flexibility, low cost, convenience and other advantages.  Generally speaking, the process flow of rapid prototyping technology mainly includes three steps: using computer design software to form a three-dimensional solid model of the product to be produced, and converting the three-dimensional model into the standard STL format of RP file. If there is a mistake in the process of model conversion, the designer should check and repair it in time;  Sort out the data of each layer formed in the above links, and send it to the fast automatic forming machine;  In the rapid manufacturing process of the product, the technicians take the laser as the heating source of the rapid molding process of the product, take the material addition method, each layer is sintered or fused, and gradually connect each layer together, until the preparation of a complete part product.

Application of rapid prototyping technology in investment precision casting

2.1 Combination process of rapid prototyping and investment precision casting

Investment precision casting is the core component of parts manufacturing methods in China. It has a wide range of applications, with high accuracy, good repeatability and less workload.  Unlike other casting methods, precision casting is based on wax molds or other die that can be used for vanishing molds. Its casting efficiency depends on the structure and size of the casting. In general, precision casting takes several weeks to several months.  After the mold design and processing is completed, it cannot be put into use immediately, and further preparation of wax mold and shell is needed.  In the case of small production volume, die design and manufacturing often need to share high costs.

Rapid prototyping technology can solve the problem of traditional casting process to a large extent. It can directly form the wax mold without making the mold.  The wax mold made by laser rapid forming method is mainly made of paraffin powder, which is sintered layer by layer through laser beam.  This molding technology can be widely used in different materials, including paraffin powder, ceramic powder, metal powder, etc., using ceramic powder to prepare ceramic shell, using metal powder can be prepared metal mold.  The close integration of rapid prototyping technology and investment precision casting focuses on three situations: forming wax mold or vanishing mold, which is suitable for small batch casting of parts with complex structure;  Direct shell method, which is characterized by small batch;  Rapid molding wax mold, the method is mainly used in mass parts casting.

2.2 Wax mold size and assembly welding

Wax mold is the basis for rapid prototyping technology to be widely used, and it is very important in the concrete parts molding and casting.  In general, casting personnel should pay special attention to the size of wax mold and assembly welding.  First of all, the size of the wax mold design.  The size of the wax mould is affected by many factors, such as the shrinkage of the wax mould, the shrinkage of the alloy, the coefficient of expansion of the mould shell, and the technology available, so the foundry must consider it comprehensively.  Usually, the shrinkage rate of the wax mold needs to be determined by experiment.  The type of alloy or mold shell is also an important factor affecting the shrinkage of the line. In order to eliminate the influence of the two, the casting personnel should first determine the actual size of the casting, and then adjust the size of the wax mold to optimize the quality of the wax mold and the casting.  Secondly, the group welding of wax mold.  The wax mold prototype prepared by rapid prototyping technology has high quality requirements, not only can not produce any deformation, and the size is accurate without error.  Wax mold prototype after the corresponding clean treatment can be welded resistance, adhesion, etc.  Wax mold casting should adopt the same or similar properties of medium temperature wax to enhance the stability of wax mold adhesion.  In the assembly welding of wax mold, attention should be paid to the length and spacing of the inner gate in order to facilitate the feeding of riser.

2.3 Technical requirements for the preparation of type shell

Different from the traditional manufacturing process, the wax mold produced by rapid prototyping technology not only has strong coating performance, but also can be used for coating configuration, paste and sanding by the original process.  Under normal circumstances, the most common binder in our country is mainly silica sol or ethyl silicate, and the powder is the most widely used refractory.  Application of rapid prototyping technology in revestment precision casting, the use of sintered powder is melted to produce high temperature, the surroundings of the gas can’t flow, which makes the shell cannot adopt steam dewaxing technology, however, the use of pure oxygen environment, technicians can choose high temperature roasting method, so as to achieve the goal of removing wax models.

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Post time: May-28-2021