Manufacturing technology of hot press forming die

2022-08-04
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Abstract: This paper expounds the characteristics and forming process of the hot pressing die for car interior trim, and emphatically introduces the design and manufacturing process of the die

key words: car interior trim; Moulds; CNC machining

0 introduction

in car interior parts, such as main carpet, trunk side plate, trunk carpet, coat rack, door and ceiling, are called soft interior parts, which are the most critical parts of car interior parts. This kind of interior trim requires not only elegant color, soft and comfortable feel, but also unique appearance and modeling, so the molding process also has its unique side. After years of exploration, research, development and modification of the moulds for such products, the technicians of the company will show confusion, and have formed a complete set of design and manufacturing process. From using the mobile optical scanning equipment of GOM company in Germany to obtain the 3D data of the sample, the reverse engineering technology is used to design the interior trim products, to using UG II software to design the mold and develop the casting process, and finally using the Toshiba btd-13r22 large-scale four axis horizontal boring and milling machine in Japan to process the forming mold. Its design, modeling, manufacturing, process and other technologies are quite mature

1. characteristics of car interior trim parts

car interior trim parts can be made of different materials according to different purposes, but each interior trim consists of two parts: fabric and framework. Most of the fabrics are needled carpets, tufted carpets, fabrics, etc; Hemp fiber + polypropylene (PP) is mostly used as the framework. (2) aging temperature has a great impact on the strength of the alloy. Cotton fiber + polypropylene (PP), waste fiber + resin, wood powder board, etc. In the manufacturing process, the fabric does not need to be heated, but the skeleton needs to be heated, softened and formed in advance, then bonded with the fabric, cooled and formed. At the same time, in order to pursue the elegant temperament of interior parts, the fabrics are generally made of light colored materials, so there can be no stain adhesion after forming. Moreover, in terms of the shape of carpet, trunk side plate and wheel cover, the overall dimension is large, and the profile is free-form surface, which is difficult to be described with traditional two-dimensional drawings. The profile fluctuates and varies, and the height difference is wide. Based on the above characteristics, the traditional mold design and manufacturing process can not meet the product forming requirements

2. mold characteristics

according to the characteristics of the above products, conventional steel materials shall not be used for the forming mold. At the same time, the mold materials shall not only reach the basic hardness, but also have the characteristics of good thermal conductivity and non rusting. To sum up, we choose aluminum alloy as the die material. The forming process refers to the drawing process of the metal cover. The mold has no parting surface, and an extension surface similar to the pressing ring is reserved outside the forming part of the mold to fix the fabric. At the same time, the water pipe cooling method is adopted at the same distance below the forming surface to speed up the finalization and curing of the product

3. mold design

3.1 source data type

before the mold design of interior parts, the three-dimensional data model of the product must be obtained first. According to the current conditions, the data source provided by the customer can be divided into three-dimensional digital model, sample or drawing. Any three-dimensional digital model produced by the software can be read in by UG software through the IGS file interface for design. If the sample is provided, the data point cloud shall be obtained by scanning, and the product surface shall be constructed by reverse engineering technology. Through continuous comparison and correction, the 3D interior trim product shape shall be finally obtained. If conditions permit, a one-to-one cavity model can be processed with polyurethane material to match the real object to prevent the final impact caused by local defects

3.2 mold structure

considering the particularity of product molding and the characteristics of mold materials, the mold structure we manufacture is: the thickness of aluminum alloy in the molding part is 35mm, and the profile changes with the fluctuation. The back side is fixed every 300mm to 400mm, with crisscross support ribs added. The upper and lower bottom plates of the mold are channel steel or I-steel, and the whole mold is made of aluminum alloy castings

3.3 extension design of forming surface

as the product framework of interior trim needs to be heated and softened before forming, resulting in drawing deformation, and then it is bonded with the fabric, it is necessary to ensure that the external part of the product remains relatively static under a certain tension during the forming process. At the same time, considering the possibility that the final product contour can be extended according to the actual loading situation, in the mold design, referring to the practice of metal drawing die, extend the molding surface of the product forming part by 15mm according to the original trend, which is not only required by the product forming process, but also can strengthen the strength of the mold periphery. Then, according to the product surface modeling, the overall design and modeling of a single mold are completed by using the thickening operation of UGII software. Similarly, the three-dimensional modeling of another mold can be obtained by offsetting the wall thickness of the interior trim product

3.4 design of cooling water pipe

during the forming process of interior trim products, the framework material shall be heated and softened first, and the temperature shall reach 150 ~ 200 ℃, so as to make it plastic and convenient for drawing and forming. After the softened material is formed and bonded with the fabric, it needs to be cooled and shaped in time to prevent the product from deformation after being taken out of the mold, so it is necessary to quickly cool the mold. The cooling mode is water cooling, that is, the cooling water pipe is laid in the mold. Due to the special requirements of product material cooling, the cooling water pipes shall be evenly arranged, and it is better to keep the same distance from the mold forming surface. We use UGII software to arrange directly on the mold shape designed previously, and give the offset distance according to the fluctuation of the product surface, so that the trend of the water pipe is consistent with the change of the surface of the surface, so as to ensure the cooling effect of the water pipe in the work. The designed water pipe can give the effect on the computer, and the performance improvement is the main attack pattern, which is convenient for verification. Then, a two-dimensional drawing can be generated and submitted to a special department for water pipe bending for future use

4. manufacturing process

4.1 manufacturing of wood mold

due to the large size of the interior trim mold, considering the mold weight and cooling mode, we use the full mold casting method to obtain the aluminum alloy blank. According to the full mold casting process, a wood mold needs to be made first. According to the traditional practice, it needs to be formed manually according to the design requirements. Since we have completed the overall design and modeling of the mold on the computer, we can easily use the CNC machine tool to cut the wood mold surface required for casting, which not only reduces the workload, shortens the wood mold manufacturing cycle, but also ensures that the blank after pouring has a uniform machining allowance

4.2 embedding of cooling water pipes and forming of castings

after the fabrication of water pipes, the embedded method is required to be completed at the same time of blank pouring. That is, when pouring the mold blank, fix the cooling water pipe on the clay core in advance, about 5 ~ 8mm away from the mold surface. After the upper mold and the lower mold are combined for pouring, the cooling water pipe will be naturally wrapped by the aluminum alloy. The cooling water pipe arranged in this way has the same distance from the mold forming surface, high heat absorption efficiency, and very good cooling effect. The surface temperature of the mold can be reduced to 5 ~ 10 ° C during operation. At the same time, because the water pipe direction is strictly controlled, it can ensure that the water pipe layer will not be damaged during the processing of aluminum castings. Due to the large volume of castings and the complex casting process, we have been able to cast large aluminum alloy mold blanks by sand casting and full mold casting after many tests. The maximum weight of full mold casting can reach 250 kg, and the maximum weight of sand mold casting has reached 1500 kg

4.3 mold surface processing

after the mold blank is poured, we get a casting with uniform margin. The maximum weight of this kind of mold blank is 1.5T, and the maximum size is 1900 x 1700 x 450 mm. It is necessary to select a suitable machining center to complete the final NC machining. Toshiba btd-13r22 large four axis horizontal boring and milling machine plays a key role in our manufacturing process. The machine tool has powerful power and is suitable for gravity cutting. The numerical control system and mechanical motion mechanism can operate continuously and stably for a long time. The high-precision large-scale rotary worktable can achieve one-time clamping and multi-facet processing. It can also use the extensible spindle to cut the surface at relatively low-lying places

according to the material characteristics of blank aluminum alloy and the characteristics of profile undulation, in order to improve the processing efficiency and save the tool cost, we use Walter modular threaded connecting extension rod and tool head. The tool type uses profiling milling cutter, the rough processing uses inlaid multi slice milling cutter, and the finish processing uses inlaid single slice milling cutter. The materials are WMG and WK10 blades suitable for aluminum alloy processing. These blades are made of wear-resistant cemented carbide with large front and back angles, Easy to remove chips

4.4 mold assembly and installation of pulling and clamping device

for molds similar to carpet, trunk side plate or wheel cover, the upper mold and lower mold are in the mold closing process 6 Press the "start" key to use the positioning column and positioning hole as the clamping device, or use the guide plate for positioning. Once the mold is debugged and put into formal use, the positioning device will be removed, and it will depend on the material thickness of the product and the shape of the mold. This kind of structure omits the guide post/guide sleeve device of the general mold, which is simple in structure and easy to install

in order to prevent the wrinkle of the fabric during the forming process, for the form with small fluctuation and drop of the product edge, such as carpet, we install a row of pull pins at the top and bottom of the edge to prevent the fabric from following the cavity with the mold forming. The pull pins pull the fabric, forcing the fabric to stretch and extend, deforming it, and finally quickly shaping the fabric and framework after rapid cooling. For the shape with large fluctuation and drop of product profile, such as trunk side plate or wheel cover, the clamping frame method is adopted to pull the fabric at the surrounding edges. The frame shape is consistent with the product outline

5. conclusion

under my auspices, using the manufacturing process of such interior trim molds, I have successfully developed and manufactured interior trim molds for various models. For example, the left and right side plates of the SRV trunk and the spare tire cover of Shanghai GM sail; Chery Oriental Son main carpet, wheel cover and luggage compartment flat carpet mold; Volkswagen B5 luxury right wheel cover; Fengshen 3 luggage compartment interior trim; Jac Ruifeng main carpet and wheel cover; Volkswagen GP3 left and right wheel housings; Shanghai GM Kaiyue main carpet; Volkswagen Polo hatchback clothes rack, etc

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