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关键词：304不锈钢；冷拔；异型管 4093
General description of the design
This design topic is 40*25mm304 inner hexangular pipe process design. The diameter of 90mm solid billet processing into 40*25mm within six angle steel. The material use 304 stainless steel. The finished tube is a pipe with thick wall, so do not need to use rolling and steel pipe, reducing process during the forming process, the design adopts the perforation, drawing, including all kinds of intermediate process and to the end of pipe finishing the steps. In this design, completed the selection of equipment, pipe heating system, material, parameter calculation of perforation, perforation motor check, and complete the preparation of cold drawing table, drawing drawing force, cold-drawing machine power checking, design a variety of tooling. In the design process, mainly to solve the following questions:
（1）Work hardening characteristics of drawing process. At room temperature, the organization structure was changed during the deformation of the reinforced effect,it caused by work hardening，deformation structure was observed that strain induced martensite and deformation twinning has obvious influence on the flow stress of 304 austenitic stainless steel.It is the cause of low stacking fault energy of face-centered cubic structure of alloy and it has the strong ability of processing hardening. After cold drawing, due to work hardening, pipe material strength increased by 1.3 ~ 1.6 times, up to 2 times, the hardness increases and the ductility decreases 30%-35%,and difficult to carry out, so in the drawing process,we must use intermediate heat treatment to eliminate the work-hardening material plasticity, recovery and reduce the deformation resistance in order to continue drawing.
（2）Effect of heating system on the crystal boundary corrosion. Stainless steel occurs crystal boundary corrosion in stainless steel, because the carbon at low temperature to precipitate of Cr-rich carbides, makes the grain boundary and the chromium content decreased, it formatted a chromium depleted zone. This poor chrome area can easily be corrosion, leading to crystal boundary corrosion and stress corrosion cracking. Although stainless steel has excellent corrosion resistance, but used in the corrosive medium containing 450-900 ℃, it occurs crystal boundary corrosion. In order to improve the processing properties of 304 austenitic stainless steel, the cracks must be prevented in the processing process, in order to further deformation and good corrosion resistance, it must carry on the appropriate heat treatment for the stainless steel finished or semi-finished products, heat treatment methods are commonly used solution heat treatment. When the solution temperature is low, dissolution of carbide slower, not all dissolved in a relatively short period of time. In the corrosive media, in addition to chromium-rich carbide precipitates at grain boundary will be subject to erosion, the carbide grain interior also will be subject to erosion, resulting in the formation of pitting. But with the increase of solution temperature, carbide precipitation dissolution speed, it can completely dissolve in a relatively short period of time, so the pitting disappeared.
（3）Mold design process. The different wall shaped steel tube has three kinds, namely integral outer mold, combined external mold and outer mold. Due to integral mould has the advantages of simple structure, convenient use and replacement, good rigidity, product size precision, so it is the most widely used. When drawing inside tube, in order to ensure the surface quality of the pipe, it often use mold curved die and conical mandrel combination. Here, the deformation of wall reduction pipe is mainly through the mandrel diameter to achieve, the deformation process is from the inner surface of the outer wall of steel pipe penetration, to ensure the forming quality and eliminate the internal groove favorable.
（4）A groove in the phenomenon of drawing deformation. When drawing different wall shaped steel tubes with circular tube, because of the finished tube of wall thickness are different, so in the drawing forming process of deformation degree is not the same, the big part of wall reduction quantity，has large elongation, whereas small elongation rate. Actually the extension of large part of forcing extension small part has forced extension, extending small parts hinders expansion of large parts. Visible, in different wall shaped steel tube forming process, the former will make the steel pipe wall stretched, and the latter due to the additional lateral flow of metal, the metal part of small deformation of the transverse displacement and formatted internal groove. From the steel pipe of metal flow in the deformation zone of the thin wall part, the additional stress is compressive stress, additional stress of thick wall part is the tensile stress. It is not difficult to see in the size of metal flow like this on the shape, affecting energy consumption greatly. Therefore, drawing forming different wall shaped steel tube is the key to control the "right wall stretched" and eliminate the "inner groove phenomenon. Therefore, the design should be to reduce each pass inhomogeneous deformation of the tubular wall to reduce tension and prevent groove by multi-pass drawing.
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