In response to the development trend of lightweight, high-performance, and energy-saving transportation vehicles, the technology of Tube Hydroforming or Internal High Pressure Forming has attracted great attention from industry and academia since the 1990s. It has developed and has become one of the mainstream manufacturing technologies in the international automotive industry, including: German double B, VW, AUDI, OPEL, American GM, FORD, CHRYSLER, Japan’s TOYOTA, HONDA, NISSAN, SUBARU, MAZDA, MITSUBISHI, South Korea’s KIA, Hyundai and others have been put into production or trial mass production. The main applications are chassis parts, body structure parts and exhaust system components. Applications in other industries are also expanding, and the prospects are very broad. Pipe fitting hydroforming technology has: weight reduction/energy saving, product integration, high rigidity, improved product performance/precision and innovation, and can reduce the number of semi-finished parts during the production process, and reduce the number of welding, mechanical processing and product assembly passes. Such as post-processing, effectively reduce production costs, shorten the processing cycle and other advantages. This article will discuss the processing principles, advantages, domestic and foreign industrial application status, technological development trends and industrial development trends of pipe hydroforming. 1. Technical principle The pipe fitting hydroforming technology is suitable for different-thickness and special-shaped hollow structure pipe fittings. As the name suggests, the pipe is first placed in a shaped mold, and high-pressure fluid (currently mainly water) is added to the pipe to match the shaft. Pressure is applied to compensate the pipe material, and the pipe material is pressed into the mold cavity to form. The hydraulic pressure required for forming is generally about 2000 Bar, even as high as 4000 Bar under special conditions. Applicable materials and scope of application: Excellent extensibility is the key to the hydroforming method. In principle, all materials suitable for cold forming are suitable for pipe hydroforming technology. At present, the main products are: carbon steel, special steel, stainless steel, aluminum Alloys, copper alloys, etc. are the mainstays. 2. Technical features The application of high-pressure technology in pipe fittings can reduce the number of structural parts, the number of welding passes and shorten the assembly time, achieving the goal of reducing weight and reducing costs. Its advantages vary from product to product, compared to traditional The advantages of production technology include: 1. Reduced weight: Compared with turning and boring, the hollow shaft of pipe hydroforming can be reduced by 40%~50%, some even up to 75%; if compared with stamping and welding parts, the hollow structure of pipe hydroforming on automobiles Pieces can be reduced by 20%~30%. 2. Reduce the number of semi-finished parts: In the forming process, large and complex 3D geometrical workpieces such as engine brackets, roof frames, door frames, etc. can be processed at one time. Compared with stamped and welded parts, the number of sub-frame parts is reduced from 6 to 1; the number of radiator bracket parts is reduced from 17 to 10. 3. Reduce mold costs: pipe hydroforming parts usually only need one set of molds, while stamping and welding parts are welded by multiple stamping parts, so multiple sets of stamping dies are required. 4. Reduce the amount of subsequent machining and assembly welding: Taking the radiator bracket as an example, the number of welding points is reduced from 174 to 20, the number of manufacturing passes is reduced from 13 to 6, and the production efficiency is increased by 66%. 5. Improve strength, rigidity and fatigue strength: The liquid has a cooling effect during the forming process, so that the workpiece is “cold-strengthened” to obtain a higher strength of the workpiece than the general stamping process. Take the radiator bracket as an example, the vertical direction is increased by 39%; the horizontal direction is increased by 50%. 6. Reduce production costs: Schuler Hydroforming Company analyzes the products that have been applied. Compared with the stamping and welding parts, the cost of pipe hydroforming parts is reduced by 15% to 20% on average, and the cost of molds is reduced by 20% to 30%. 7. Innovative: Overcoming the limitations of traditional manufacturing processes and applying to the design and development of new products. 3. Current status of domestic and foreign industrial applications Judging from the application development process in the past 10 years, the automotive industry is undoubtedly the largest application industry. Products have also expanded from dashboard brackets, engine brackets, radiator brackets, etc. to frame slides ( Frame Rail), engine sub-frame (Sub Frame) and other projects; in addition, in other vehicle industries, locomotive frame and rear arm (Rear Arm) were also officially used in off-road vehicles such as Harley and Yamaha in 2002. Among the models, the bicycle frame, rocker arm and upper tube also have the trajectory used by the manufacturer. As for faucets, valve products, spherical containers, superconducting accelerators, pipe fittings and other products, hydroforming technology is also used to meet their quality and consumer needs. The following is a detailed description of the related application products of hydroforming technology. The use of THF technology in the automotive industry by the automotive industry is one of the important milestones in automotive manufacturing technology in recent years. Generally speaking, the application of THF technology in automotive parts is as follows: A: A, B pillar B: IP beam C: Radiator support D: Engine cradle E: Roof rails F: Frame rails Exhaust system parts (Exhaust system parts) Considering heat-resistant and corrosive environments, most of them use stainless steel materials, products: engine tubes, catalytic converters, pressure tubes, tail pipes, connectors and manifolds. Chassis parts materials: low-carbon steel and medium-carbon steel, a small part of which uses aluminum alloy materials, products: frame rails, engine cradles, roof rails and bows, rear axle frames and radiator frames. Engine/power train components products: Suspension cross members, hollow camshafts, drive shafts and gear shafts. Body and safety parts The main products are Windshield headers, A/B/C pillars, space frame components, instrument panels, seat frames and shock absorber housings. In terms of local differences, major auto manufacturers in Germany, the United States, Japan, and South Korea have all introduced this technology. According to statistics from GM of the United States in 2002, the use of hydroforming technology can reduce approximately 12.3 million square feet of welded parts (approximately 145 tons of welding wire) and 2,000 tons of stamping waste (Scrap) each year. 3. 2 In the locomotive industry, the manufacturers of hydroforming components for locomotives belong to Harley and YAMAHA. For YAMAHA, its hydroforming technology is mainly applied to the swingarm of the 2002 WR250F (four-stroke off-road vehicle) to reduce weight and increase rigidity. As for Harley’s application, Harley’s Product Development Centre (Harley’s Product Development Centre) applied hydroforming technology to the frame of the 2002 V-Rod model to form a non-welded and rigid frame. Structure: The frame adopts 1.5-inch pipe fittings and is pre-bent into a complex three-dimensional structure by high-pressure forming. 3.3 The bicycle industry is mainly used in frame components, including: frame (Frame), top tube (Top Tube), front tube, joints, etc. At present, international leading brands have research and development in this direction. 3.4 Application of other industries in other industries: Examples of applications of THF parts outside the vehicle industry: bellows, vacuum system shock-absorbing components, valve sealing components, faucets, various handles, locomotives, valve housings.
. The research and development trend of pipe hydroforming technology The current research focus is on how to improve the competitiveness of hydroforming technology, including: reducing capital expenditure (initial equipment investment), increasing productivity and output, increasing material usage, rationalizing the process, and reducing defect rates As well as the development of integrated hydroformed parts, the main research and development projects are described as follows: 4.1 Pipe formability analysis technology is mainly for the establishment of basic data and experimental methods of material properties, including: bulging test, flow stress (K, n value) ), tube forming limit diagram (FLD), etc. 4.2 Application of CAD/CAE technology for pipe hydroforming In order to reduce costs, shorten product development timeline, and improve development success rate, CAD/CAE is becoming more and more important to new hydroforming technology. Numerical simulation can accurately reflect the hydroforming process of pipe fittings, predict forming defects, display the mold and forming conditions of the workpiece, and calculate the wall thickness distribution. Moreover, the matching relationship between internal pressure and axial displacement can be easily adjusted, and its influence on forming defects and wall thickness distribution can be studied to obtain the best loading curve. Therefore, the CAE simulation of pipe hydroforming has also attracted the attention of researchers and industry from all over the world. 4.3 Process and mold technology include: basic processing characteristics, design of process parameters necessary for forming (materials used, pipe wall thickness, product section geometry and minimum R angle, forming internal pressure, mold clamping force, internal pressure and axial displacement are reasonable Relationship and control methods, the stress and strain of the workpiece during the forming process, the measurement of geometric shapes, the friction characteristics of pipe hydroforming and the test method of pipe performance, etc.), mold design (precise control of mold closure, punch sealing, internal pressure and axial Load and forming time, etc.), mold manufacturing, etc. 4.4 Equipment technology In recent years, Germany has developed fast and short stroke presses to increase productivity. In addition, fast hydraulic filling devices have been researched to reduce the filling time of hydraulic pressure. As the shape of hydraulic parts of pipe fittings becomes more complicated towards 3D, the required forming pressure also varies. Therefore, the hydraulic equipment must include the integration of the following sub-system technologies and processes: The hydraulic and hydraulic pressure system of the press or other fixed-lock units that provide clamping force, especially the system technology related to the booster Side cylinder and punch seal and stroke control (position or force control) control technology (process control, data acquisition and sensor component integration, etc.).
5. Industry development trend Judging from the current application market of hydroforming technology, there is no doubt that the automobile industry will be the largest development market in the future. The most successful application of hydroforming technology should be the automobile chassis. The main reasons for its popularity are: high rigidity, high dimensional accuracy and stability, relatively corrosion resistance, fewer parts, simplified manufacturing process, and reduced cost. Therefore, the demand for pipe hydroforming components has increased dramatically and rapidly. This demand will force hydroforming equipment manufacturers and chassis system suppliers to accelerate the development of related technologies. In the future, the automobile body structure in the North American market may be replaced by hydroformed components. The reasons include: (1) Government regulations—Corporate Average Fuel Economy (CAFE): This regulation has allowed North American automobile manufacturers
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