How Are Car Bumpers Made?

Why are the interior and exterior trim parts of the automotive industry mostly made of plastic materials? The reason is that plastic has excellent material properties and various processing methods. Different processes such as injection molding, blow molding, and blister molding can meet the molding requirements of different products, especially the complexity of auto parts. Injection molding of auto parts with different materials and sizes, such as bumpers, instrument panels, and car baffles.

Processing advantages of complex plastic parts for automobiles

1️⃣Plastic can be processed at one time, with short processing time and guaranteed accuracy.

2️⃣The elastic deformation characteristics of plastic products can absorb a large amount of collision energy, have a greater buffering effect on strong collisions, and protect vehicles and passengers. Plasticized dashboards and steering wheels are used on modern cars to enhance cushioning. The front and rear bumpers and body trim strips are all made of plastic to reduce the impact of objects outside the car on the body. Plastic also has the effect of absorbing and damping vibration and noise, which can improve ride comfort.

3️⃣Plastic has strong corrosion resistance, and local damage will not corrode.

4️⃣Plastics with desired properties are produced by adding different fillers, plasticizers and hardeners to suit the application requirements of different parts of the car. What's more convenient is that the plastic color can be adjusted to different colors through additives, saving the trouble of painting. Some plastic parts can also be electroplated.

Factors that need to be considered in injection molding

Due to the unique characteristics of plastic parts of complex parts of automobiles, the design of injection molding needs to fully consider the following factors, drying of materials, new requirements of glass fiber reinforced materials for screws, driving forms and mold clamping structure, etc.

1️⃣When the commonly used resin materials such as automobile bumpers and instrument panels are modified resins such as modified PP and modified ABS, the resin materials have different hygroscopic properties. In order to meet the moisture content requirements during molding (general requirements ≤ 0.2%), the resin raw materials must be subjected to hot air drying or dehumidification drying before entering the screw pre-plasticizing of the injection molding machine.

The hygroscopicity of the modified PP (PPEPDM) resin is relatively small, and a hot air dryer is generally used at 80-100℃for 2-3 hours. Modified ABS (PCABS) has strong hygroscopicity. Before molding and drying, a dehumidifying dryer should be used for dehumidification and drying. We fully consider the function of dehumidification and drying system in designing the molding system of complex plastic parts for automobiles.

2️⃣The material and structure of the screw of the injection molding machine used for molding non-glass fiber reinforced plastic parts are quite different from those of resins reinforced with chopped glass fibers. When designing the injection molding machine, attention should be paid to the alloy material of the screw barrel and the special heat treatment process to ensure its corrosion resistance and strength.

3️⃣Because auto parts are different from conventional products, its cavity surface is very complex, with unequal stress and uneven stress distribution, so the processing capacity it needs is mainly considered in the design. The processing capacity of the injection molding machine is reflected in the clamping force and the injection molding capacity (represented by the maximum theoretical injection volume). When the injection molding machine is molding a product, the clamping force must be greater than the mold opening force generated by the pressure of the mold cavity, otherwise the parting surface of the mold will be separated and overflow will occur.

In order to ensure reliable clamping, the process clamping force during injection molding must be less than the rated clamping force of the injection molding machine. The maximum theoretical injection volume of the injection molding machine matches the clamping force tonnage of the injection molding machine, which is the nominal injection volume of the injection molding machine before leaving the factory with polystyrene (PS) as the benchmark resin.

4️⃣Because the cavity surface of auto parts is very complex, the injection molding machine should consider its particularity in the design, and configure some special functional programs: such as multiple sets of core pulling function, timing control function, and injection molding machine supporting mold changing device function, supporting the function of picking up manipulator device, etc. These special functions have obvious advantages in the production of automotive plastic parts.

For example, in the bumper production process of this type of injection molding machine, in order to shorten the production cycle, the large plastic parts after the mold is opened and ejected are automatically taken out by the pick-up manipulator, and multiple sets of core-pulling make the large plastic products smoothly and integrally ejected out, there will be no top white or cracking phenomenon. At present, most of the 3-axis picking robots we use in this injection molding system are 6-axis picking robots.

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