Changing the wall thickness of different parts of the plastic part
Plastic part wall thickness is a crucial parameter in injection molding design, directly impacting the part’s mechanical properties, molding process, and appearance. Improperly designed variations in wall thickness can easily lead to defects such as sink marks, bubbles, and warping. Therefore, properly adjusting the wall thickness of different parts of a plastic part is key to ensuring product quality. During design, the optimal wall thickness range for each part must be determined based on the part’s usage scenario, stress conditions, and assembly requirements. Typically, thermoplastics have a wall thickness between 1 and 5 mm, while thermosets are slightly thicker, typically 2 to 6 mm.
When changing the local wall thickness of a plastic part, adhere to the principle of gradual transition to avoid sudden changes in wall thickness that create sharp or right angles. When a certain area of a plastic part needs to be thickened to improve strength, a ramp or arc transition should be used. The length of the transition section should be at least three times the wall thickness difference. This ensures smooth pressure transfer during the flow of the molten plastic and reduces the risk of inadequate filling or localized overheating caused by sudden changes in flow resistance. For example, at the junction of the rib and the main body of a plastic part, if the wall thickness suddenly increases from 3mm to 5mm, sink marks are likely to form at the corner. Using a ramp transition with a length of 6mm can effectively avoid such problems.
Variations in wall thickness significantly impact the cooling rate of plastic parts. Thick-walled areas cool longer, while thin-walled areas cool faster. This uneven cooling can easily lead to stress concentration within the part, causing warping. Therefore, when varying the wall thickness of different parts of a plastic part, CAE analysis software should be used to simulate the cooling time for each area, ensuring that the ratio of maximum to minimum wall thickness does not exceed 3:1. For parts where significant wall thickness variation is necessary, cooling holes or ribs can be added to thick-walled areas to increase cooling area and accelerate cooling. Furthermore, mold design can incorporate localized enhanced cooling, such as adding cooling water channels to thick-walled areas, to shorten cooling time and reduce molding cycle times.
From a mechanical performance perspective, the wall thickness of different parts of a plastic part must be adjusted to match the load conditions. Areas subject to high loads, such as gear teeth and bearing mating surfaces, require appropriate thickness increase to improve strength and wear resistance. Decorative areas subject to less stress can be thinned to reduce weight and save material. For example, the frame of a car instrument panel, which bears the weight of the entire instrument panel assembly, is designed with a 4mm wall thickness, while the decorative panels only require a 1.5mm thickness to meet operational requirements. Furthermore, the interior of thick-walled areas can be designed with a hollow structure to increase rigidity through internal support, saving material and reducing weight compared to simply increasing the thickness.
In actual production, changes to the wall thickness of plastic parts also need to consider the plastic’s fluidity. For plastics with poor fluidity, such as polyvinyl chloride and polycarbonate, if the wall thickness is too thin in a certain area (less than 1mm), it is easy to cause incomplete filling. In this case, the wall thickness of this area should be appropriately increased or the gate position should be optimized. Plastics with good fluidity, such as polyethylene and polypropylene, can be designed with thinner wall thicknesses, but attention should be paid to whether the strength of the thin-walled area meets the requirements. In addition, wall thickness adjustment must be compatible with the mold processing technology. Excessively thick areas will increase the mold processing difficulty and cost, while too thin areas may cause accelerated wear of the mold cavity and shorten the mold life. Therefore, the wall thickness design of different parts of the plastic part must comprehensively consider the molding process, material properties, usage requirements, and production costs. Through comparative optimization of multiple solutions, the optimal wall thickness distribution solution can be determined .
