The three-dimensional curved surface parts of sheet metal have the structural characteristics of thin shell, because of its light weight, material saving, good mechanical properties, smooth geometric shape, often as the main parts, in various manufacturing fields such as civil products, military products and modern high-tech products. Widely used. Especially with the rapid development of modern industry and the continuous improvement of people's living standards, the demand for sheet metal forming parts is increasing. Especially in the aerospace, shipbuilding, automotive and other production industries, sheet metal forming plays a pivotal role. In the traditional sheet metal forming method, the mold forming method has occupied a leading position for many years because of its wide adaptability, high production efficiency, and suitability for mass production. However, with the development of the times, the speed of product upgrading is getting faster and faster, and the trend of multi-variety, small batch and individualization of sheet metal parts is becoming more and more obvious. The traditional mold design and manufacturing cycle is relatively long. Before it is put into use, it takes a long time to repeatedly test and repair the mold, and the mold material and processing cost are relatively high. Therefore, the traditional mold forming method is difficult to meet the current rapid development. Social needs. The development of new technologies and new equipment that can quickly adapt to product upgrading, high degree of automation, and wide adaptability has become an urgent need in the field of sheet metal forming.
Under this demand, many new technologies and methods for sheet metal forming have emerged. Mainly include: progressive forming of forming hammer, digital progressive forming, laser thermal stress forming, laser stamping forming, moldless multi-point forming and so on. These technologies are all supported by computer control systems to achieve moldless forming of the sheet and have great "flexibility". They overcome the shortcomings of traditional mold forming, save mold manufacturing costs, shorten the development cycle, and are especially suitable for the development of new products and small batch production, reflecting the concept of agile manufacturing. Our laboratory passed the introduction of the traditional overall model and author: Liu Jingping, male, master's degree in Qingdao University of Technology, research direction for mold manufacturing and rapid prototyping. Based on the research of various moldless forming technologies, a new sheet metal forming technology, an electromagnetic auxiliary sheet metal drawing rapid forming technology, is proposed based on the moldless multi-point forming technology. First introduce the dieless multi-point forming technology.
1 moldless multi-point forming technology
The moldless multi-point forming technology is an advanced manufacturing technology that combines flexible manufacturing technology and computer control technology based on the "discrete" idea. The basic idea is to discrete the traditional integral mold into a series of regularly arranged and height-adjustable unit bodies. By real-time control of the movement of each unit body, the forming surface can be freely constructed, thereby realizing the three-dimensional curved surface forming of the sheet.
We can see that in the overall mold forming, the sheet is formed by the curved surface of the mold, and in the multi-point forming, the envelope surface (or forming curved surface) of the unit punch is completed.
Since the position of each unit body can be adjusted according to the shape of the formed part, the forming surface can be changed each time the space position of each unit body is changed, which is equivalent to reconstructing the forming mold and having a large "flexibility". . The moldless multi-point forming technology has the advantages that the forming plate does not need to be separately arranged, the shape of the forming die is variable, the forming path is changed, the non-rebound forming is realized, and the small parts are formed into large parts, which is easy to realize automation. But it also has some unique defects: indentation, ladder effect and boundary effect. The most important defect is the indentation. According to the analysis of the forming mechanism of the multi-point forming indentation, the indentation is mainly caused by the high concentration of the contact pressure, the excessive deformation of the deformation and the unreasonable rigidity of the flexural deformation. For the forming mechanism of indentation, the multi-point forming technology has also taken some measures, such as the use of a large radius of curvature of the middle head, the use of elastic pads in the punch and sheet, and the use of multi-point press forming methods. Although these methods can suppress and reduce the indentation to a certain extent, the effect is not satisfactory.
The electromagnetic-assisted sheet metal stretch rapid prototyping technology proposed by our laboratory combines the advantages of multi-point forming and traditional integral mold forming, which can eliminate stepping effect and indentation. The following describes the electromagnetic assisted sheet metal stretch rapid prototyping technology.
2 Electromagnetically assisted sheet metal tensile rapid prototyping technology
2.1 System composition
Electromagnetically assisted sheet metal tensile rapid prototyping technology is developed on the basis of multi-point forming technology. Its working principle is similar to multi-point forming technology. Its working principle can be simply described as: firstly, the stepper motor drives the unit body to a specified position, and then uses the magnetic field to exert a powerful effect on the magnetic material powder and the smoothness of the magnetic field, and the magnetic material powder is used between the unit bodies. The pit is filled flat, and finally a large-strength clamping magnetic field is added, and the unit body and the magnetic material powder become a whole under the action of a strong magnetic field, and become a solid mold in the conventional sense. The idea of ​​electromagnetically assisted sheet metal tensile rapid prototyping technology is: the whole - discrete one, and the idea of ​​multi-point forming technology is: overall discrete. Therefore, this technology not only has the advantages of multi-point forming technology, but also has the advantages of high precision of conventional solid mold forming, smooth surface and beautiful appearance.
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