Working Medium
The function of the working medium used in the hydraulic press is not only to transmit the pressure, but also to ensure that the working parts of the machine are sensitive, reliable, long-lived and less leaking.
The basic requirements of the hydraulic press for the working medium are:
① have suitable fluidity and low compressibility to improve the efficiency of transmission;
② can prevent rust;
③ have good lubrication performance;
④ easy to seal;
⑤ stable performance, long-term work rather than deteriorating.
The hydraulic press initially used water as the working medium, and later switched to an emulsion made by adding a small amount of emulsified oil to the water to increase lubricity and reduce rust. In the late 19th century, hydraulic presses using mineral oil as the working medium appeared. Oil has good lubricity, corrosion resistance and moderate viscosity, which is beneficial to improve the performance of hydraulic presses. In the second half of the 20th century, a new type of water-based emulsion appeared, and its emulsification form was "water-in-oil" instead of the original "oil-in-water". The external phase of "water-in-oil" emulsion is oil, its lubricity and anti-corrosion properties are close to oil, and its oil content is very small, and it is not easy to burn. However, the water-based emulsion is expensive, which limits its promotion.
Advantage
Compared with the traditional stamping process, the hydroforming process has obvious technical and economic advantages in reducing weight, reducing the number of parts and molds, improving stiffness and strength, and reducing production costs, and has been widely used in the industrial field, especially in the automotive industry. more and more applications. In the automotive industry, aviation, aerospace and other fields, reducing structural mass to save energy in operation is a long-term goal of people, and it is also one of the trends in the development of advanced manufacturing technology. Hydroforming is an advanced manufacturing technology to achieve lightweight structure. Hydroforming is also known as "internal high pressure forming". Its basic principle is to use the pipe as a blank, apply ultra-high pressure liquid inside the pipe, and apply axial thrust to both ends of the pipe blank to replenish the material. Under the combined action of the two external forces, the tube blank material undergoes plastic deformation, and finally adheres to the inner wall of the mold cavity to obtain a hollow part whose shape and precision meet the technical requirements.
For hollow variable-section structural parts, the traditional manufacturing process is to stamp and form two halves first, and then weld them into a whole, while hydroforming can integrally form hollow structural parts that vary along the cross-section of the component. Compared with stamping and welding processes, hydroforming techniques and processes have the following main advantages:
1. Reduce mass and save material. For typical parts such as automobile engine brackets and radiator brackets, hydroforming parts are 20% to 40% lighter than stamping parts; for hollow stepped shaft parts, the weight can be reduced by 40% to 50%.
2. Reduce the number of parts and molds and reduce mold costs. Hydroforming parts usually only need one set of dies, while stamping parts mostly require multiple sets of dies. The number of hydroformed engine bracket parts has been reduced from 6 to 1, and the number of radiator bracket parts has been reduced from 17 to 10.
3. It can reduce the amount of welding for subsequent machining and assembly. Taking the radiator bracket as an example, the heat dissipation area is increased by 43%, the number of solder joints is reduced from 174 to 20, the number of processes is reduced from 13 to 6, and the productivity is increased by 66%.
4. Improve the strength and stiffness, especially the fatigue strength. For example, the stiffness of the hydroformed radiator bracket can be increased by 39% in the vertical direction and 50% in the horizontal direction.
5. Reduce production costs. According to the statistical analysis of the applied hydroformed parts, the production cost of hydroformed parts is 15% to 20% lower on average than that of stamping parts, and the mold cost is reduced by 20% to 30%.
