Introduction and classification of hydroforming

●Hydroforming 

Hydroforming refers to a plastic processing technology that uses liquid or molds to shape workpieces, also known as hydraulic forming. Only a concave mold or a convex mold is required, and the liquid medium is used as a convex mold or a concave mold correspondingly, which saves the general mold cost and processing time, and the liquid as a convex mold can form many complex parts that cannot be formed by a rigid mold.

●Introduction to hydroforming

Hydroforming refers to the method of stamping sheet metal with liquid pressure instead of a rigid punch or die. It can carry out many stamping processes, such as bending, deep drawing, bulging of flat blanks, and bulging of spatial blank shapes. It can form various complex parts, such as bellows. And it has the advantages of good surface quality, reduced process, simplified mold, and no need for special stamping equipment. Because the liquid directly acts on the parts, it is difficult to seal, and the operation process is much more complicated than the general steel mold and rubber mold. Therefore, it is not widely used in mass production.

●Hydroforming classification

According to different liquid media used, hydroforming can be divided into hydraulic forming and hydraulic forming. The medium used in hydraulic forming is pure water or an emulsified liquid composed of water and a certain proportion of emulsified oil; the medium used in hydraulic forming is hydraulic transmission oil or engine oil. According to different blanks used, hydroforming can be divided into three types: pipe hydroforming, sheet hydroforming, and shell hydroforming.

Sheet and shell hydroforming use lower forming pressure, while pipe hydroforming uses higher pressure, which is also called internal high pressure forming or pipe hydroforming. The medium used in sheet hydroforming is mostly hydraulic oil, and the maximum forming pressure generally does not exceed 100MPa. The medium used in the hydroforming of the shell is pure water, and the maximum forming pressure generally does not exceed 50MPa. The medium used in internal high-pressure forming is mostly emulsion, and the maximum forming pressure used in industrial production generally does not exceed 400MPa.

The main characteristics of the modern hydroforming technology developed from the mid-1980s are manifested in two aspects: one is that only a female mold or a male mold is required, and the liquid medium is used as a male mold or a female mold accordingly, saving half of the mold cost and processing Time, and liquid as a punch can form many complex parts that cannot be formed by rigid punches. The shell hydroforming does not use any mold, so it is also called dieless hydroforming. The second is that liquid as a force transmission medium has real-time controllability. Through the hydraulic closed-loop servo system and the computer control system, the pressure can be accurately controlled according to a given curve to ensure that the process parameters are within the set values and are variable and adjustable over time. Greatly improve process flexibility. In addition to these characteristics, the three different hydroforming technologies of internal high-pressure forming, sheet metal hydroforming, and shell hydroforming have their characteristics, which will be introduced separately below.

Internal high-pressure forming

The main feature of the internal high pressure forming technology is that it can integrally form hollow parts with special-shaped cross-sections with a two-dimensional or three-dimensional curve. The initial circular cross-section of the pipe can be formed into rectangular, trapezoidal, elliptical, or other special-shaped closed cross-sections, as shown in the figure. . The traditional manufacturing process generally involves stamping and forming two or more halves and then welding them into a whole. In order to reduce welding distortion, spot welding is generally used, so the obtained section is not a closed section. In addition, the cross-sectional shape of stamping parts is relatively simple, and it is difficult to meet the needs of the structural design.

Internal high-pressure forming is an advanced manufacturing technology developed to adapt to the lightweight structure of vehicles such as automobiles and airplanes. There are two main approaches to lightweight structure: one is the material approach, which uses lightweight materials such as aluminum alloys, magnesium alloys, titanium alloys, and composite materials; the other is the structural approach, which uses hollow variable cross-sections, variable thickness thin-walled shells, and integral parts. structure. According to statistics, for certain weight reduction goals, in the aerospace field, the contribution of lightweight materials to reduce weight is about 2/3, and the contribution of structural weight reduction is about 1/3; and in the automotive industry, on the contrary, the main Use the structure to reduce weight. When the material is fixed, the main method of weight reduction is to design a reasonable light body structure. For structures that are mainly subjected to bending and torsion loads, hollow variable cross-section members are used, which can reduce the quality and make full use of the strength of the material.

Sheet metal hydroforming

Sheet metal hydroforming is an advanced metal forming process. This process has the characteristics of low mold cost, short mold manufacturing cycle, high forming limit, and high forming quality. It is one of the main process technologies for sheet flexible forming. It is suitable for parts with high deformation in the aerospace field that require multi-pass drawing to complete, such as fairings and other cylindrical parts with complex profiles, cones, etc.; it is also suitable for the automotive field with complex shapes The surface and part of the parts that require the pressing of a concave mold and a convex mold to be formed, such as automobile lamp reflectors, etc.; conventional forming is not easy to debug molds and parts that are prone to wrinkles and cracks, such as fenders. Besides, hydroforming is also suitable for processing many kitchen products, such as stainless steel tableware, containers, hand basins, and other deeper parts. The process technology mainly uses information technology support tools and uses a flexible mold to replace the traditional rigid punch or die, as shown in the figure.