How to improve the impact resistance of automotive parts through injection molds?

1,Material selection and impact resistance performance
The basis for raising the impact resistance of automotive components is selecting plastic materials with high strength, great toughness, and good impact resistance. For structural components and collision parts like front/rear bumper beams and door side crash beams of vehicles, continuous fiber-reinforced thermoplastic composites (CFRT) for example have outstanding impact resistance and are extensively employed. By including continuous fiber reinforcement to the thermoplastic matrix, CFRT material considerably increases its mechanical qualities and impact resistance.
Apart from selecting high-performance plastic materials, material modification technologies help to increase the impact resistance of other materials. To plastic materials, for instance, adding impact modifiers, toughening agents, etc. can increase their toughness and impact resistance. Furthermore, by changing the composition and structure of the material, one can maximize its mechanical characteristics and impact resistance by means of blending modification and filling modification.
2, Influence of die structure design on impact resistance
One of the main links in the design of a mold construction is the parting surface design. Reasonable parting surface design helps to simplify the mold, eliminate thin-walled sections and sharp interior corners, so lowering the latter stage difficulty of mold manufacture and maintenance expenses. A good parting surface design can thus also lower the flow resistance of the melt during the filling process, enhance the filling effect, prevent either insufficient or too strong filling, and guarantee the dimensional correctness and appearance quality of the components.
Complex forms of automotive injection molded parts, such structures with inverted buckles, reinforcing ribs, etc., which call for the construction of appropriate demolding mechanisms such sliders and inclined tops. These tools should have enough wear resistance and strength to guarantee seamless functioning during movement, therefore preventing jamming-related damage of the mold. By means of a sensible demolding mechanism design, one can guarantee the integrity and usefulness of injection molded products by ensuring their damage free during the demolding process.
The lifetime of the mold and the quality of the injected molded products depend much on the design of the cooling system. A reasonable layout of cooling channels can ensure uniform cooling of the mold and reduce mold deformation caused by thermal stress. For molds of large injection molded parts for automobiles, such as bumper molds, the cooling channel should be designed according to the shape and wall thickness of the components, so that the cooling medium can effectively carry away heat and prevent local overheating from causing mold damage. Meanwhile, a reasonable cooling system design can also shorten the injection molding cycle and improve production efficiency.
Taking the design of a large thin-walled injection mold for the front bumper of a car as an example, the mold utilizes internal parting technology to assure the aesthetic appearance of the plastic parts. Before closing the mold, the top pin plate should be in a position 50mm away from the mold bottom plate to ensure that the A-plate does not touch the transverse small inclined top protruding from the large inclined top at the reverse buckle, and to ensure that the A-plate can smoothly complete the closing action by pressing the reset rod. When opening the mold, the A-plate and the ejector pin plate are first opened synchronously by 60mm to ensure that the plastic pieces and the transverse tiny oblique top are entirely removed from the reverse surface of the A-plate. Through this carefully constructed mold structure, high-quality production of car front bumpers has been successfully realized, ensuring high production efficiency of the mold and product stability.
3, The influence of molding process control on impact resistance performance
Control of the injection molding temperature
The flowability and filling effect of plastic melt depend much on the injection molding temperature. While too low temperatures can produce poor plastic flowability and increase mold wear, high injection molding temperature may induce plastic breakdown, generate corrosive fumes, and corrodes the surface of the mold. Accurate management of the temperature of the barrel, nozzle, and mold is therefore essential to guarantee that the plastic may smoothly fill the mold cavity without damaging the mold. For the often used polypropylene (PP) material for car interior components, for instance, its plasticizing temperature is usually between 180-240 ℃. PP material's molecular chains progressively loosen within this temperature range, and its fluidity rises to ready for the next injection operation.
Injection pressure and speed control
The lifetime of the mold and the quality of the injected molded goods depend much on the injection pressure and speed. Strong impact of plastic melt on the mold cavity may damage the mold surface; too high injection pressure can cause the mold to endure too great swelling force, which can readily lead to mold deformation or rupture. Finding the suitable mix of injection pressure and speed by means of trial molding and process improvement guarantees the quality of injection molded parts and increases the lifetime of the mold. To guarantee that the melt can uniformly and stably fill the mold cavity, it is imperative to modify the injection pressure and speed properly depending on the properties of the plastic material and mold utilized, in the injection molding process of precision molds for automobiles.
Case study concerning molding process optimization
Using the thin-walled front bumper beam of an automobile as an example, the structural dimensions of the bumper beam are rather large, with a saddle form, more reinforcing ribs, and high flow resistance when melted in the mold cavity, so making it difficult to fill. The filling issue has been effectively solved and the impact resistance of the anti-collision beam has been raised by means of optimal injection molding process parameters including changing injection temperature, injection pressure, and speed. Simultaneously, the suitable injection molding material PP+EPDM-T20 was chosen with low density, shrinkage rate of 1.0095, and high strength that satisfies manufacturing process criteria and thus guarantees the quality of the anti-collision beam.
4, Design of mold protection to ensure impact resistance performance
A collision resistant injection mold integrated structure can be utilized to prevent damage of the mold by collisions during transit, installation, and use. By means of improved shell, under the action of the insertion rod, plate body, protruding block, sliding rail, sliding plate, sleeve, spring, shaft seat, sliding rod, sliding block and reset spring, this structure achieves the effect of convenient anti-collision for the integrated structure of injection molds. Simultaneously, by tuning the elastic rod and buffer plate, the effect of convenient buffering of the integrated structure of the injection mold is obtained, so enhancing the stability and work efficiency of the integrated structure of the injection mold.
Should the mold be damaged during the collision process, it could lead to issues including mold deformation and enhanced wear, so influencing the dimensional accuracy and appearance quality of the injection molded parts and so lowering their impact resistance. Mold protection design can not only protect the mold itself from damage but also guarantee the quality and performance of injection molded parts. Consequently, one of the key guarantees to increase the impact resistance of automotive components is enhancing the design of mold protection.