With the demand of automobile industry for the production of complex and tortuous conveying pipes, the development of push force off-axis extrusion blow molding technology is called three-dimensional blow molding or 3D blow molding (or multi-dimensional extrusion blow molding MES in some countries). Due to the use of three-dimensional blow molding in the process of production of scrap greatly reduced, or even no scrap generated, so it is also known as less scrap or no scrap blow molding.

A common molding method of three-dimensional (3D) extrusion blow hollow plastics is that after the plastic parison is extruded, it is pre inflated and attached to one die wall. The extrusion head or die rotates the second or third axis according to the molding program. When the similar intestinal shaped blank is filled with the membrane cavity, the other side of the mold closes and hugs the blank to separate it from the subsequent blank The whole parison is inflated and pressed on the wall of the membrane cavity. In this way, it is not only less flash, but also there is no die line on the product, and it can be extruded in sequence, so that many parts with complex shapes can be easily processed by three-dimensional blow molding method.

The second molding method is mainly used to open and close the mold in sequence, negative pressure molding process. 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 parison is attracted by negative pressure air and moves along the curve of the inner cavity. After the blank is in place, the upper and lower sliding blocks of the mold are closed and blow molded. This molding method is more suitable for the products with regular pipeline shape.

The third method is to use robot or manipulator to hold the plastic parison and attach it to the mold, and blow it to form. It can also realize three-dimensional blow molding.

If using the conventional blow molding production process to produce curved pipe fittings, because the flat folding width of the billet is much larger than the projected width of the product, a large number of waste edges (some height above 50%) will be generated, and the blank clamping seam is longer, which will not only affect the appearance, but also affect the strength of the product.

Due to the special process of 3D blow molding, compared with the conventional blow molding process with flash, it has the following advantages.

  1. According to the formula of clamping force, P = 1.2p, P = QS, we can know that the projected area of 3D blow molding is much smaller than that of conventional blow molding, where p is the expanding force, q is the blowing pressure, s is the projected area on the clamping surface, so the clamping force is far less than the clamping force required by conventional blowing process.
  2. The amount of work needed to remove the flash is greatly reduced.
  3. There is no need to trim the outer diameter of the molded article.
  4. The quality of molding products has been improved, because the wall thickness distribution design, not less mold strength.
  5. Because of the decrease of flash material and extrusion time, the degradation probability of thermal sensitive material is reduced.
  6. Due to the large reduction of flash, smaller extruders can be used for production.

The above makes the pipe bending technology of this kind ideal. The parts that can be made by three-dimensional blow molding include: air duct of turbocharged diesel engine, special cooling medium pipe and fuel replenishment pipe. In some developed countries, 3D blow molding technology has replaced other technologies in some application fields, such as oil filling pipe, seamless door handle and other parts. In addition, three-dimensional blow molding technology has potential application value in the field of cross-country vehicle parts, furniture (chair back and chair leg), large-scale water pipe device, etc.; the three-dimensional blow molding technology has a very attractive development prospect.

The three-dimensional blow molding technology is suitable for manufacturing complex plastic pipe parts. The parts made will not have parting lines which are easy to cause damage, and have no flash. It can also improve the wall thickness uniformity of hollow blow molding parts. Three dimensional blow molding technology can promote the integration of parts without assembling parts, thus reducing the cost. At present, the technology is producing the product quality, production cost and production efficiency with sequential structure and sandwich structure. The molding technology will have a large application and development space in China.