Application status and development trend of hydrof

Application status and development trend of tube hydroforming technology

in response to the development trend of lightweight, high-performance and energy-saving means of transportation, tube hydroforming or internal high pressure forming technology has attracted great attention and flourished in industry and academia since the 1990s. At present, it has become one of the mainstream manufacturing technologies in the international automotive industry, including German double-B, VW Audi, Opel, GM, Ford, Chrysler in the United States, Toyota, Honda, Nissan, Subaru, Mazda, Mitsubishi in Japan, Kia and Hyundai in South Korea have all been put into production or trial production. They are mainly used for chassis parts, body structural parts and exhaust system components. Their applications in other industries are also expanding, and their prospects are very broad. Tube hydroforming technology has the following advantages: reducing weight/saving energy, product integration, good rigidity, improving product performance/accuracy and innovation, and in the production process, it can reduce the number of semi-finished parts, reduce post-processing processing such as welding, machining and product assembly, effectively reduce production costs and shorten processing cycle. This paper will discuss the processing principle, advantages, industrial application status at home and abroad, technical development trend and industrial development trend of pipe hydroforming

1. Technical principle

the hydroforming technology of pipe fittings is applicable to hollow structural pipe fittings with different thicknesses and shapes. As the name suggests, the pipe is first placed in a shaped mold, by adding high-pressure fluid (currently mainly water) into the pipe fittings, combined with axial pressure compensation pipe, the pipe is pressed into the mold cavity to form. The hydraulic pressure required for forming is generally about 2000bar, and even as high as 4000bar under special conditions. Applicable materials and application scope: excellent extensibility is the key of hydroforming method. In principle, the materials suitable for cold forming processing are applicable to pipe hydroforming technology. At present, they are mainly carbon steel, special steel, stainless steel, aluminum alloy, copper alloy, etc

2. Technical features

the application of high-pressure technology in pipe fittings can reduce the number of structural parts, welding passes and assembly time, and achieve the goal of reducing weight and cost. Its advantages vary with different products. Compared with traditional production technology, its advantages include:

1 Weight reduction: compared with turning and hole lining, the hollow shafts of pipe hydroforming can be reduced by 40% - 50%, and some can even reach 75%; Compared with stamping weldments, the hollow structural parts formed by hydroforming of pipe fittings on automobiles can be reduced by 20% - 30%

2. Reduce the number of semi-finished parts: during the forming process, large and complex 3D geometric workpiece such as engine bracket, top cover plate frame, door frame and so on can be processed at one time. Compared with stamping weldments, the number of subframe parts is reduced from 6 to 1; The number of radiator bracket parts is reduced from 17 to 10

3. Reduce the cost of molds: the hydroforming parts of pipe fittings usually only need one set of molds, while the stamping weldments are welded by multiple stamping parts, so multiple sets of stamping molds are required

4. Reduce the amount of subsequent machining and assembly welding: take the radiator support as an example, the number of welding points was reduced from 174 to 20, the number of manufacturing passes was reduced from 13 to 6, and the production efficiency was 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", and the workpiece strength is higher than that of general stamping processing. 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 analyzed the products that have been applied. The cost of hydroforming parts of pipe fittings is reduced by 15% to 20% on average compared with stamping and welding parts, and the die cost is reduced by 20% to 30%

7. Innovation: overcome the limitations of traditional manufacturing process and apply it to the design and development of new products

3. Current situation of industrial applications at home and abroad

from the application development process in the past 10 years, as shown in [figure 2], the automotive industry is undoubtedly the largest application industry, and its products have also been expanded from dashboard brackets, engine brackets, radiator brackets, etc. to the use of frame rails, sub frames, etc; In addition, in other vehicle industries, the frame and rear arm of locomotives were also officially applied to the fixed position of the labels of Harley, Yamaha and other off-road vehicles in 2002, which are incorrect, uneven, unstable and inclined. The frame, rocker arm and upper tube of bicycles also have the track of application by manufacturers. As for faucets, valve products, spherical containers, superconducting accelerators, pipe fittings and other products, hydroforming technology is also applied to meet their quality and consumer needs. The following is a detailed description of the relevant application products of hydroforming technology

automotive industry

the use of THF technology in the automotive industry is one of the important milestones of 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

automotive subsystem name application product

exhaust system

(exhaust system parts) considering the heat-resistant and corrosive environment, most of them use stainless steel materials. Products: Engine tubes, catalytic converters, pressure tubes, tail pipes.Pes, connectors and manifolds

chassis parts materials: low carbon steel and medium carbon steel, a small number of aluminum alloy materials are used, products: frame rails, engine cradles, roof rails and bows, rear axle frames and radiator frames

engine and power train components products: Su is equipped with heating furnace, heat treatment furnace, chemical etching and other 1-stream post forging treatment equipment, such as spension 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 houses

in terms of regions, at present, major automobile manufacturers in Germany, the United States, Japan and South Korea have introduced this technology, and the usage of North America has gradually exceeded that of Europe, becoming the largest consumption area of hydroforming components; The largest automotive application manufacturer is GM company of the United States. According to its data and statistics in 2002, the use of hydroforming technology can reduce about 12.3 million feet of welding parts (about 145 tons of welding wire) and 2000 tons of stamping waste (scrap) per year

3.2 the application manufacturers of locomotive industry in locomotive hydroforming components are Harley and Yamaha companies. Yamaha mainly applied its hydroforming technology to the swing arm of the wr250f (four stroke off-road vehicle) in 2002 to reduce weight and improve rigidity. As for the application of Harley company, harley's product development center applied hydroforming technology to the frame of the 2002 V-rod vehicle to form a non weldable and rigid structure. The frame uses 1.5-inch pipe fittings to form a complex three-dimensional structure by high-pressure forming after pre bending

3.3 the bicycle industry

is mainly used in frame components, including frame, top tube, head tube, joints, etc. at present, leading international brands have research and development in this direction

3.4 other industries

Application representatives in other industries, such as the application examples of THF parts outside the vehicle industry shown in Table 1 below

bellows vacuum system shock absorption components

valve sealing components

faucets

various handles

locomotive silencer

valve body shell

4 The current research focus is on how to improve the competitiveness of hydroforming technology, including: reducing capital expenditure (initial equipment investment), improving productivity and output, improving material utilization, rationalizing the process, reducing the defect rate, and the development of all-in-one hydroforming parts, The main research and development projects are described as follows:

4.1 tube formability analysis technology

mainly refers to 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 pipe hydroforming cad/cae technology

in order to reduce costs, shorten product development time and improve the success rate of development, cad/cae is becoming more and more important for new hydroforming technology. Numerical simulation can accurately reflect the hydroforming process of pipe fittings, predict forming defects, display the workpiece sticking and forming conditions, and calculate the wall thickness distribution. Moreover, it is convenient to adjust the matching relationship between internal pressure and axial displacement, and study its influence on forming defects and wall thickness distribution, so as to obtain the best loading curve. Therefore, the CAE simulation of tube hydroforming has also attracted the attention of researchers and industry in various countries

4.3 process and die technology

includes: basic processing characteristics, process parameter design necessary for forming (using materials, pipe wall thickness, product section geometry and minimum R angle, forming internal pressure, clamping force, reasonable relationship and control method between internal pressure and axial displacement, stress and strain of workpiece in the forming process, measurement of geometric shape, friction characteristics of pipe hydroforming and test method of pipe performance) Mold design (accurately control mold closure, punch sealing, internal pressure, axial load and forming time, etc.), mold manufacturing, etc

4.4 equipment technology

in recent years, Germany has developed a fast and short stroke press to improve productivity. In addition, a rapid hydraulic filling device has been studied to reduce the hydraulic filling time. As the shape of hydraulic parts of pipe fittings is complicated towards 3D, the required forming pressure also increases, Therefore, the hydraulic equipment must include the technology of the following systems and the integration between the processes:

the hydraulic and hydraulic pressure systems of the press or other solid locking units that provide the clamping force, especially the system technology related to the supercharger, the side cylinder and punch sealing and the stroke control (position or force control) control technology (process control, data acquisition, sensor assembly integration, etc.)

5. Industry development trend

judging from the current application market of hydroforming technology, there is no doubt that the automotive industry will be the largest development market in the future. The most successful application of hydroforming technology should be automobile chassis. The main reasons for its popularity are: high rigidity, high dimensional accuracy and stability, more corrosion resistance, less workpiece number, simplified process and reduced cost. Therefore, the demand for tube hydroforming components has increased dramatically. This demand will force manufacturers of Hydroforming Equipment 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 hydroforming components. The reasons include:

(1) government regulations - enterprise average fuel economy (CAFE): this regulation has made the automobile manufacturers in North America very nervous. In an age when a gallon of oil costs less than a bottle of drinking water, consumers are unwilling to give up saving fuel at the expense of car spaciousness, performance or safety. However, when Cafe regulations contradict customer expectations, engineers must develop more fuel-efficient and lighter vehicles

(2) safety: more and more impact test standards, coupled with customers' awareness and attention to vehicle safety, urge OEM manufacturers to improve vehicle body safety without sacrificing fuel efficiency

(3) vehicle performance: in the United States