Application of thermal arc spraying technology in

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Application of arc spraying technology in rapid tooling manufacturing process

Abstract: This paper mainly introduces the manufacturing process of LOM Prototype, the manufacturing process of rapid tooling based on LOM Prototype and other heat-resistant master molds, and the preparation process of mold filling materials. Based on the experiments of LOM Prototype and other heat-resistant master molds, the selection basis of arc spraying materials and the spraying process parameters of various materials are obtained, and some problems that should be paid attention to in the manufacturing process of rapid tooling are pointed out

key words: rapid mold arc spraying LOM Prototype process flow

in order to manufacture mold products quickly and cheaply, in recent years, rapid mold manufacturing technology based on LOM has become the focus of LOM application research and development abroad, and has evolved a complete set of rapid tool manufacturing technology (RT). Using this technology, the whole process of complex parts from drawings to mold manufacturing can be completed in a few days, or even 24 hours

at present, RT technology is mainly used to produce injection molds, die-casting molds, etc. these molds generally have complex core and cavity structures, and it is quite difficult to use traditional electromechanical processing. However, if LOM Prototype or sample is used as the master mold, the mold can be easily copied by metal spraying technology. This kind of mold has good machining performance, can be locally cut to obtain higher mold accuracy, and can produce plastic parts in batches and at low cost

1 LOM Prototype Production

laminated manufacturing technology (LOM technology) is a new advanced manufacturing technology developed abroad from the late 1980s to the early 1990s. It is a new discipline formed by the cross penetration of machinery, materials, NC, CAD, laser, chemical engineering and other disciplines. Although its development time is not long, its development speed is very rapid, And its importance to the manufacturing industry and its push action on today's manufacturing industry, combined with the 4-cylinder Volvo drive-e engine, have attracted more and more attention

the manufacturing process of LOM Prototype is: (1) model segmentation. For the parts whose size is larger than the table space of rapid prototyping equipment, they are divided into small-size parts according to their characteristics. (2) Base fabrication. In order to ensure that the prototype has high dimensional accuracy, complete shape and no dislocation, a certain thickness of substrate should be made on the workbench according to the size of the prototype, so that the prototype can be reliably connected with the workbench. (3) Prototyping. According to the actual situation of the production process, select the appropriate laser cutting speed, heating temperature, heating roller speed and pressure, paper feeding speed, laser energy coefficient and other parameters to start the prototype production. (4) Remove surplus materials and waste materials. Use appropriate tools to remove waste materials from the finished laminated blocks and peel off the prototype. (5) Post processing. In order to improve the surface quality of the prototype or meet the needs of further turning the mold, the prototype should be post processed, such as waterproof, moisture-proof, reinforcement and making its surface smooth. Figure 1 shows the processed LOM Prototype

2 rapid tooling manufacturing technology

metal spraying has several methods, such as arc spraying, flame spraying, plasma spraying and so on. Compared with other spraying methods, arc spraying has the advantages of high coating strength, low use cost, high production efficiency, stable quality and so on. 1 North and 1 South in addition, flame sprayed and plasma sprayed workpieces are directly heated by the flame and cannot be used to spray heat-resistant substrates (such as plastic, wood, paper, etc.); The heat received by the workpiece of arc spraying only comes from the heat energy carried by the particles. The high-speed compressed air flow that transmits the particles can also cool the substrate. The workpiece is heated lightly, has small deformation and thermal stress, so it can be sprayed on the heat-resistant LOM Prototype. It is these advantages of arc spraying that make it a hot spot in the research of mold spraying technology in recent years

2.1 selection of sprayed metal wires

metal wires used in arc spraying process can be divided into low melting point materials, medium melting point materials and high melting point materials according to the melting point. When using arc spraying technology to manufacture rapid tooling, the thickness of the cavity metal shell should be more than 3mm. After the molten metal particles with medium and high melting points are deposited on the master mold, they will release more heat, which will cause the master mold to undergo thermal deformation, reduce the replication accuracy of the mold cavity, and may cause the metal coating to warp or crack before reaching the required thickness; Low melting point metal or alloy wire has little thermal influence on the master mold, which can reduce the influence of molten metal particles on the master mold, reduce the thermal deformation of the master mold, and improve the accuracy of the mold. Therefore, when the calibration of zinc is completed, low melting point materials such as Babbitt alloy are more used in the manufacture of rapid tooling. However, the mold life of this low melting point material is low and can only be used for small batch trial production. To improve the life of the spraying mold, you can spray a layer of low melting point material on the master mold to enhance the heat resistance of the master mold, and then spray steel or other alloys with higher strength to enhance the strength of the mold, so as to improve the life of the mold

the mechanical and physical properties of some materials used for arc spraying are shown in Table 1

2.2 arc spraying process flow

the process flow of manufacturing concave and convex dies of injection molds, die-casting molds and other molds by arc spraying process is as follows:

(1) determine the size of the spraying base plate and the size of the mold frame according to the size of the mother mold

(2) fix the master mold on the spraying base plate, and paint release agent on the master mold and spraying base plate

(3) after the mold release agent is cooled and dried, the low melting point material is used for the first spraying, and the shell thickness is controlled at 0 mm; Then continue spraying with high melting point materials, and make the metal spraying layer reach mm, so that the manufacturing of the concave mold cavity shell of the mold is completed

(4) install the spraying shell into the female mold frame (equipped with cooling copper pipe), fill the mold base material, and cure for more than 10h

(5) turn over the die frame of the female mold, remove the spraying base plate, and brush the release agent on the parting surface and the other side of the master mold

(6) after the release agent is dried, repeat the spraying process in step 3, and spray for the second time to form the punch shell

(7) install the punch frame, install the punch cooling copper pipe, pour the filling material into the mold frame, and cure for more than 10 hours

(8) fix the guide and positioning device, separate the female mold and punch, take out the LOM Prototype, and complete the production of the female mold and punch. In the process of making metal spraying mold, the adjustment of spraying parameters is the key to the whole process. Various wires were tested on xdp-5 arc spraying equipment, and the spraying parameters of several wires finally obtained are shown in Table 2. The concave mold cavity formed by arc spraying process is shown in Figure 2

2.3 fabrication of filling materials for metal spray molds

after the convex and concave mold shells of the injection mold are manufactured by arc spraying technology, reinforcement materials are filled in the built mold frame, and the pouring system and cooling system are added. This system together with the mold base can form the injection mold. The most commonly used filling material for rapid tooling is the mixture of epoxy resin and aluminum powder. Adding aluminum powder to epoxy resin can play the role of filler modification and improve the mechanical, thermal and process properties of epoxy resin

the preparation process of filling material is:

(1) put the weighed epoxy resin in the container, add aluminum powder and stir slowly. If you need to add a large amount of aluminum powder as filling, you can use a mechanical mixer to stir. In order to reduce the risk of air entrainment, and thus become a member of the graphene like family, the speed of the mixer should be slow rather than fast, generally not more than 500r/min.

(2) the stirred mixture should be left standing for a period of time, so that the aluminum filler is completely wet, and the mixed air runs away completely

(3) install the cooling copper tube on the mold frame, add hardener to the mixture of epoxy resin and aluminum powder, and ensure that it is evenly mixed. After standing for min, it can be injected into the mold frame, and the sprayed shell and mold frame can be completely filled

3 conclusion

(1) the quality of LOM Prototype directly affects the quality of rapid tooling and products, so controlling the quality of LOM Prototype is one of the keys of product/mold rapid design and manufacturing technology

(2) in the process of arc spraying, the spraying parameters should be adjusted according to the metal materials used, and the water vapor in the compressed air should be removed by using the oil-water separator to ensure the uniformity of the spraying particles and the roughness of the spraying surface

(3) because there are many kinds of epoxy resin and its matching curing agent, there are great differences in curing time and curing effect, so the process parameters in manufacturing should be determined according to the actual situation, and diluent can be added for dilution modification if necessary

(4) pour the residual aluminum powder precipitated in the mixing container evenly into the mold frame to ensure that the aluminum powder completely enters the mixture. This process is faster because the pouring mixture will solidify within minutes. (end)

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