Problems and solutions caused by the thin wall of the car bumper

The car bumper is one of the larger accessories on the car, it has three main functions: safety, functionality and decoration.
There are three main ways of car bumper lightweight: material lightweight, structural optimization design and manufacturing process innovation. Material lightweight generally refers to replacing the original materials under certain conditions, such as plastic for steel; bumper lightweight structure optimization design mainly has thin-wall technology; the new manufacturing process has micro-foam material and gas auxiliary molding and other new technologies.
Plastic bumper material selection plastic because of the light quality, good use performance, simple manufacturing, corrosion resistance, impact resistance, design freedom and other characteristics, is widely used in the automobile industry, and the proportion of more and more in the automobile materials. The amount of plastic used on a car has become one of the criteria to measure the development level of a country’s automobile industry. At present, the developed countries to produce a car for the use of plastic has reached 200kg, accounting for about 20% of the quality of the vehicle.
Plastic in China’s automobile industry is relatively late application, the amount of plastic in economic cars is only 50~60kg, senior cars have 60~80kg, some cars can reach 100kg, China in the production of medium-sized trucks, each car with about 50kg of plastic. Each car uses plastic for 5 to 10 percent of the car’s weight.
Bumper materials usually have the following requirements: good impact resistance, good weather resistance. Good paint attachment ability, good fluidity, good processing performance, low price. Accordingly, PP class materials are undoubtedly a better cost-effective choice. PP material is a kind of general plastic with good performance, but PP itself has poor low temperature performance and impact resistance, not wear resistance, easy aging and poor size stability, so modified PP is usually used as a car bumper production material. At present, the polypropylene automotive bumper specialized materials are usually PP as the main material, and add a certain proportion of rubber or elastomer, inorganic filler, color mother particles, additives and other materials after being mixed and processed.

It is easy to cause warping deformation, which is the result of internal stress release. Thin-walled bumpers cause internal stresses in various stages of injection molding.
Generally, it mainly includes orientation stress, thermal stress and mold release stress. Orientation stress is the internal attraction caused by the fibers, macromolecular chains or chain segments in the melt being oriented in a certain direction and caused by insufficient relaxation. The orientation is related to the product thickness, melt temperature, mold temperature, injection pressure, and pressure retention time. The higher the thickness, the lower the orientation; the higher the melt temperature, the lower the orientation, the lower the orientation; the higher the injection pressure, the higher the orientation; the longer the pressure retention time, the greater the orientation.
Thermal stress is due to the high temperature of the mold temperature and the lower temperature of the mold, and the faster cooling rate of the melt in the area close to the mold cavity. The release stress is mainly due to the insufficient strength and stiffness of the mold, the elastic deformation under the action of injection pressure and top output, and the unreasonable distribution arrangement of the product product is uneven. The bumper thin wall can also be difficult. Because the wall thickness gauge is small and has a small shrinkage, the product is tightly adhered to the mold; the pressure holding time control is difficult, and the thin wall thickness and reinforcement are easily damaged. Normal opening of the mold requires the syringe to provide sufficient mold opening force, which should be able to overcome the resistance of opening the mold.

There are several obstacles to be overcome in the process of mold opening

First of all, it is necessary to overcome the direct opening force. When the mold is opened, the plastic will have a certain adhesion force parallel to the opening direction, which is due to the cooling of the plastic parts when the mold cooling is insufficient, and the elastic expansion of the type cavity is not fully recovered. The size of this adhesion force is related to the nature of the plastic, the surface quality of the mold, the slope of the mold, etc. In addition, it is necessary to overcome the indirect mold opening resistance, that is, the motorized side core extraction process. It is also necessary to overcome the friction resistance caused by the movement of the mold moving template and the activity template. Then it is necessary to overcome the participation pressure of the cavity, when the pressure of the cavity may not be equal to the atmospheric pressure, and the pressure in the cavity is not equal to the external pressure.
In order to solve the above two major problems, the mold design needs to be improved appropriately. Select the appropriate mold material to improve the mold thermal strength and wear resistance. Reasonable mold structure design and manufacturing, appropriately increase the thickness of the push plate and the middle pad plate, improve the stiffness of the mold, reduce the elastic deformation of the mold. Improve the manufacturing and coordination accuracy of the core extraction mechanism and motion system, reduce the surface roughness of the type cavity, core and convex module components, and reduce the mold release force. With higher design and matching accuracy required, the linkage device is usually provided to prevent the relative displacement of the die core and the die cavity. The pouring system should be properly designed, and the flow channel design should overuse the plastic parts from thicker areas to thinner areas during injection. There will also need to be enough exhaust ports. In terms of the injection process, the internal stress of the plastic parts should be minimized, and the injection speed and the cooling speed should be reduced. Increasing the melt temperature and the mold temperature are therefore needed to be relaxed. Reasonable injection pressure, pressure retention time, and cooling time are also required.Huangyan Leiao Molding Co. , Ltd. is located in Huangyan District mould city, Taizhou, Taizhou province, which is “The hometown of Chinese mould”. The company is mainly engaged in the injection mold manufacturing, has many years of mold experience, mainly manufacturing and processing of bottle embryo mold, PET commodity mold, bottle cap mold, car interior and exterior decoration mold… … In the needle valve hot runner injection mold system has its own unique design and processing technology, based on the concept of “Integrity management”, with domestic and foreign customers to establish a long-term good relations of cooperation, I believe that Leiao will be your worthy of confidence in the cooperative enterprise.