Research progress of extrusion bulging technology

Research progress of plastic extrusion and bulge molding technology

plastic extrusion and bulge molding is a new plastic molding processing technology. Compared with injection molding or rotary molding, extrusion and bulge molding has its own special advantages and scope of application. This paper introduces the main research results of plastic extrusion and bulging technology in Beijing University of chemical technology

at present, more than 80% of the weight of plastic products in the world are obtained through extrusion and injection molding

although the current plastic molding methods can process plastic products of various shapes, the existing methods may not be the most economical for some products with special shapes, such as tee and cross in pipe fittings, which can be molded by injecting vacuum device plastic method, but injection molding has large investment, complex mold structure, high price and high energy consumption; Especially in the case of small production batch, the expensive mold cost will be shared by a small number of parts, etc., so the injection molding method has certain difficulties in the production of such parts, not to mention the current small belly products such as slender, large difference in end face size or expansion joints, which cannot be processed by injection molding and conventional plastic molding methods. Plastic Bulge Forming (PBF) came into being under this trend

the concept of extrusion bulging molding

extrusion bulging molding is a plastic molding method, which refers to the expansion of the preformed tube blank along the radial direction under the combined external force (internal pressure and axial compression), and the formation of products consistent with the mold cavity through plastic deformation

the basic process of extrusion bulging is shown in the right figure. Put the tube blank into the mold and fill the tube blank with bulging medium (a); Apply extrusion force F to the tube blank and its internal bulging medium to deform the tube blank material under a certain stress state (b); Under the internal pressure generated by the bulging medium, the tube blank gets a workpiece (c) with the same shape as the mold cavity. After unloading, the bulging medium recovers, and the formed workpiece (d) is taken out

industrial application of extrusion bulging technology

at present, the United States, Japan, Germany, Sweden, Canada and other countries have carried out in-depth research on extrusion bulging technology, and continue to expand the application field of extrusion bulging products

extrusion bulging can not only process conventional tee, cross and other products, but also process various complex shaped products. Its characteristic is that the size of the middle abdomen in some directions is larger than the size of the entrance at both ends, which is the advantage of extrusion bulging method. In addition, the automotive industry plays an important role in the development of extrusion and bulging technology, which also promotes the progress of automotive production technology. Many famous cars in the world, such as Mercedes Benz, BMW, Audi, Volvo and Toyota, have adopted extrusion molding technology to varying degrees

however, these extrusion and bulging technologies are mainly used in the extrusion and bulging of metal materials, and the application in plastics has not been reported

feasibility and advantages of extrusion bulging

various plastic products formed by injection molding or rotary molding have been widely used, but there are also shortcomings in using these processes to produce special-shaped pipe fittings or some special types of products: 1 Large equipment investment. For injection molding, pre plasticization, mold closing and locking, injection molding, pressure maintaining, cooling and ejection are the necessary functions of the injection molding device, so the structure of the injection molding machine is complex and the price is high; Moreover, the pouring system, core layout and other factors should be considered in the injection mold. The mold structure is also complex and expensive. For rotary molding, only products with simple cross-section shape can be formed; The material is not fully plasticized in the molding process, and the impact strength of the product is low; The forming time is long, and the process conversion is difficult when processing different products. 2. High energy consumption. In the molding process, materials need to be melted and cooled, and the production process consumes a lot of energy. These all cause the high cost of single products, especially in the case of small production batches, the expensive mold cost can only be shared by a small number of products. These shortcomings make it more urgent to develop a new molding method for plastic shaped parts

because the plastic extrusion process is simple and efficient, the continuous extrusion products have the characteristics of high quality and low price, which ensures that the plastic extrusion has a wide and economic blank source. In addition, some special engineering plastics such as polytetrafluoroethylene (PTFE) and ultra high molecular weight polyethylene (UHMWPE) have very high viscosity. Their pipe products can be formed by screw extrusion or plunger pushing, but these materials cannot be processed by injection molding. Their pipes are formed by pressing and sintering, which is inefficient and the product quality cannot be guaranteed. Plastic extrusion and bulging can process pipe fittings for these pipes, Meet the actual use requirements

by comparing with conventional plastic molding and processing methods, it can be seen that extrusion molding has the following advantages in plastic processing and molding:

1 The structure of the molding equipment is relatively simple, and the investment team will explore different raw materials in future research

2. The mold structure is simple and the cost is low

3. The processed material does not produce phase transformation, and the molding process is usually carried out at a lower temperature, with less energy consumption

4. It is suitable for the production of products with large difference in cross-section size, and has strong adaptability to the cross-section size of products

5. The control system is relatively simple and the process control is flexible. By controlling the extrusion stroke and using the same die, it is possible to get products of different sizes

6. It can make full use of the high productivity and low cost of extrusion parison

7. It can manufacture more complex thin-walled parts that cannot be obtained or are difficult to obtain by other molding methods

8. In the case of small production batch, it can greatly reduce the production cost and so on

technological research progress

plastic extrusion and bulging experimental machine developed by Beijing University of Chemical Technology

Beijing University of chemical technology began to study the plastic extrusion and bulging method in 1998. The research progress of this new method is as follows:

1 The first plastic extrusion and bulging experimental machine and its supporting special mold system are designed to form different extrusion and bulging products. At present, the plastic extrusion and bulging method has been authorized by the national invention patent and has independent intellectual property rights

2. The extrusion bulging process of plastic is studied theoretically, and the extrusion bulging process of different types of products is studied by theoretical and numerical simulation and optimization methods, which lays a foundation for the design of plastic extrusion bulging process, equipment and mold

3. On the basis of theoretical research, using the self-developed plastic extrusion and bulge molding experimental machine and mold system, the extrusion and bulge molding experiments were carried out on different plastic materials and forms of plastic products. The products of experimental extrusion and bulge molding include Tee Pieces, bulge tubes, bellows, butterfly tubes, etc. the material types used are cast iron. The ratio of height and diameter of compacted specimens is 2:1, including UPVC, polypropylene (PP) Type III polypropylene (PP-R)

through experimental research, the main forms and causes of failure of different types of products in extrusion bulging are summarized, and a reasonable processing model is obtained by analyzing the test data, which provides a sufficient basis for formulating a reasonable processing technology

conclusion

extrusion bulging is a new solid-state polymer processing method. By comparing with the conventional plastic molding processing methods, it can be found that it is completely feasible to use extrusion bulging in the field of plastic processing, especially when it is used to process some specific types of products, it has greater advantages than the conventional plastic molding methods. The in-depth study of this new technology can promote its application and become a potential new polymer molding method