Blow molding, also known as hollow blow molding, is a rapidly developing plastic processing method. During World War II, blow molding technology began to be used to produce low-density polyethylene bottles. In the late 1950s, with the birth of high-density polyethylene and the development of blow molding machines, blow molding technology was widely used. The volume of hollow containers can reach thousands of liters, and some production is already controlled by computers. Plastics suitable for blow molding include polyethylene, polyvinyl chloride, polypropylene, polyester, etc. The obtained hollow containers are widely used as industrial packaging containers. According to the production method of preforms, blow molding can be divided into extrusion blow molding and injection blow molding. New developments include multi-layer blow molding and stretch blow molding.

With the demand of the automotive industry for the production of complex and tortuous conveying pipelines, the development of off-axis extrusion blow molding technology is being driven. This technology is called 3D blow molding or 3D blow molding (also known as multi-dimensional extrusion blow molding MES in some countries). Due to the significant reduction or even absence of waste edges generated during the processing of 3D blow molding, it is also known as low waste or no waste edge blow molding.

A commonly used molding method for three-dimensional (3D) extrusion blown hollow plastics is that after the plastic mold is extruded, it is pre blown and tightly attached to one side of the mold wall. The extrusion head or mold rotates the second or third axis according to the molding program. When the intestinal shaped mold fills the membrane cavity, the other side of the mold closes and holds the mold tightly, separating it from the subsequent mold, This is when the entire blank is blown out and pressed against the wall of the membrane cavity to form. Using this method to produce air ducts or oil pipes similar to those on cars not only has fewer flash edges, but also has no clamping line on the product and can be sequentially extruded, making it easy to process and shape many complex shaped parts using 3D blow molding.

The second forming method mainly adopts a negative pressure forming process that can sequentially open and close the mold. It is to make the upper and lower ends of the mold into sliding blocks that can be opened and closed separately. During production, the mold is closed first. The tubular blank is attracted by negative pressure air and moves along the curve of the inner cavity inside the mold. After the blank is in place, the sliding blocks on the upper and lower ends of the mold are closed and blown into shape; This molding method is more suitable for forming products with regular pipeline shapes.

The third molding method mainly uses a robot or robotic arm to grip the plastic preform and attach it to the mold, blowing air to form it, and can also achieve three-dimensional blow molding.

If the conventional blow molding production process is used to produce curved pipe fittings, due to the flat folding width of the blank being much larger than the projection width of the product, a large amount of waste edges (some with a height of more than 50%) will be generated, and the gap between the blank and the workpiece is longer, which not only affects the appearance but also affects the strength of the product.

Due to the unique processing characteristics of 3D blow molding, it has the following advantages compared to conventional blow molding processes with waste edges.

1. According to the formula for selecting the clamping force, if the clamping force P is 1.2P and P is qs, it can be known that the projected area of 3D blow molding is much smaller than the flat folding width of conventional blow molding. P is the expanding force, q is the blowing pressure, and s is the projected area on the clamping surface. Therefore, the clamping force is much smaller than the required clamping force for conventional blow molding processes.

2. The workload of cutting edge materials is greatly reduced.

3. It is not necessary to trim the outer diameter of the formed item again.

4. The quality of formed items has been improved due to the wall thickness distribution design, which does not reduce the clamping strength.

5. Due to the reduction of leftover materials and less extrusion time, the probability of degradation of thermosensitive materials is reduced.

Due to the significant reduction of waste edges, smaller extruders can be used for production.

Due to the above characteristics of 3D blow molding, this method has become an ideal technology for manufacturing curved long conduits and pipelines for automobiles. Components that can be made using 3D blow molding include:; The air duct, special cooling medium duct, and fuel replenishment pipe of a turbocharged diesel engine. In some developed countries, 3D blow molding technology has replaced other technologies in certain application fields to make components such as oil injection pipes and seamless door handles. In addition, 3D blow molding technology also has potential application value in fields such as off-road vehicle components, furniture (chair backrests and legs), and large water pipe installations; The 3D blow molding technology has very attractive development prospects.

The 3D blow molding technology is suitable for manufacturing complex plastic pipeline parts. The resulting parts do not have easily damaged parting lines, and there are no flash edges. It can also improve the wall thickness uniformity of hollow blow molded components. 3D blow molding technology can promote the integration of parts without the need for assembly, thereby reducing costs. At present, this technology is moving towards the production of products with sequential and sandwich structures in terms of quality, production costs, and production efficiency. This forming technology will have significant application and development space in China.

The tubular plastic parison produced by extrusion or injection molding of thermoplastic resin is placed in the mold when it is hot (or heated to a softened state), and compressed air is immediately introduced into the parison after the mold is closed, causing the plastic parison to be blown and adhered to the inner wall of the mold. After cooling and demolding, various hollow products are obtained. The manufacturing process of blown film is very similar to hollow products in principle, but does not use molds. From the perspective of plastic processing technology classification, the forming process of blown film is usually included in extrusion. During World War II, blow molding technology began to be used to produce low-density polyethylene bottles. In the late 1950s, with the birth of high-density polyethylene and the development of blow molding machines, blow molding technology was widely used. The volume of hollow containers can reach thousands of liters, and some production is already controlled by computers. Plastics suitable for blow molding include polyethylene, polyvinyl chloride, polypropylene, polyester, etc. The obtained hollow containers are widely used as industrial packaging containers.