The front or rear bumper of a car is a large, thin-walled, lightweight part that protects the vehicle. Its main purpose is to absorb energy when a vehicle is cornered. The bumper is also used to protect pedestrians. Various styles, materials, and finishes are available.
Automobiles are increasingly important in modern society. The safety of vehicles has received a lot of attention. The energy crisis has made it necessary for cars to be as lightweight as possible. The bumper must also protect the occupants of the vehicle. Fortunately, manufacturers have developed innovative ways to make auto bumpers. Injection molding is one such method.
Injection molding is a process that involves a special polyurethane compound. After this compound is introduced into a large bumper moulding, the plastic is injected through nozzles into the cavities. The mould’s temperature is regulated in several scopes, and the pressure is kept at a certain level.
The injection molding process is divided into four stages. The first stage is pretreatment. This includes surface treatment, which can ensure the appearance of the bumper. The second stage is injection pressure, which is 80,000 grams/cm for the sprue place and 90000 grams/cm for the rest of the product. This is the most critical stage, since it has the greatest influence on the quality of the final product.
The third stage is pressurize. This is the most crucial step, as it controls the strength of the plastic injected. Depending on the machine’s capacity, the maximum injection pressure may vary. It is important to have a proper cooling system for a quick and effective forming cycle. In addition, it is vital that the nozzle valves are not blocked by contaminants. If they are, the nozzle cannot provide adequate cooling, which can reduce the quality of the finished product.
The fourth and fifth stages are packing and demolding. The packaging pressure is between 5 and 10 seconds. The demolding angle is important for the precision of manufacturing. In general, the demolding angle should not be larger than 1.5 times the aperture. The minimum fillet of the typical part is R0.5. The parting surface should not be rounded. The inner parting line is a non-visible parting surface.
The sixth and seventh stages are circulating water cooling and die heating. The insulated runner plate is kept above the melt temperature by electric cartridge heaters. The dwell pressure is 85% of the filling maximum pressure.
The eighth and ninth stages are assembly and finishing. The mold’s assembly accuracy is high and the process is easy to control. A secondary timer can be used to set positive closure of each valve after a specified preset fill time. This is also helpful in preventing freezing. In addition, the secondary timers eliminate the need for overpacking at each gate.
The hot runner is another option. The advantages of this option include eliminating runners and sprue regrind, which reduces costs, and the mold is easier to clean. However, this option has a higher mold price. Moreover, it is more expensive to manufacture.
Post time: Nov-25-2023