Solutions for Excessive Wall Thickness in Injection Molding

 Excessive wall thickness is a common issue in the design or production of injection molded parts. It not only impairs product quality but also increases production costs and reduces production efficiency. The specific hazards are mainly reflected in the following aspects:

1. Frequent Molding Defects: Excessive wall thickness leads to uneven cooling rates of the melt, making it difficult for internal heat to dissipate. This easily causes defects such as sink marks, depressions, bubbles, and warpage. For example, when the thick-walled area shrinks during cooling, the surface material cannot be replenished in time, resulting in obvious sink marks; the incompletely cooled melt inside continues to shrink, which may generate internal bubbles and affect the structural integrity of the product.

2. Low Production Efficiency: Increased wall thickness prolongs the melt filling time and cooling cycle, significantly reducing the efficiency of injection molding. Under the same production conditions, the cooling time of thick-walled parts may be 2-3 times that of parts with reasonable wall thickness, leading to a substantial drop in output per unit time and increased production energy consumption.

3. Material Waste and Rising Costs: Excessive wall thickness means an increase in raw material usage, directly raising material costs. Meanwhile, the extended cooling time leads to higher energy consumption and accelerated mold wear, further driving up the overall production costs.

4. Poor Mechanical Properties: Excessive wall thickness may cause uneven crystallization inside the plastic and the occurrence of stress concentration, reducing the mechanical properties of the product such as impact strength and toughness, and affecting the service life and safety of the product.

To address the issue of excessive wall thickness, a comprehensive approach is required from multiple aspects such as design source optimization, process adjustment, and material adaptation, aiming to achieve the goal of "reducing thickness without compromising quality".

(I) Optimize Product Structure Design: Control Wall Thickness at the Source

Product design is the fundamental link to solve excessive wall thickness. On the premise of meeting usage requirements, unnecessary wall thickness should be reduced through scientific design while ensuring structural strength.

1. Adopt Uniform Wall Thickness Design: The ideal wall thickness of injection molded parts should be consistent, avoiding localized thick-walled areas. During design, a reasonable wall thickness range should be determined based on the product's application and stress conditions (typically, the reasonable wall thickness for thermoplastics is 1-4mm, which needs to be adjusted according to specific material properties). For parts of the product subject to high stress, methods such as adding reinforcing ribs and fillet transitions can be used instead of increasing wall thickness, which not only ensures strength but also avoids localized excessive thickness.

2. Incorporate Hollow Structures and Lightening Holes: For large-volume injection molded parts with no internal functional requirements, hollow design or lightening holes can be adopted to reduce the wall thickness of the core area. For example, for products such as home appliance casings and automotive interior parts, grid-like hollow structures can be arranged in non-stressed areas, which not only reduces material usage but also facilitates melt flow and cooling.

3. Optimize Transition Zone Design: The transition between areas of different wall thicknesses in the product should be smooth, avoiding right-angle or acute-angle abrupt changes. This prevents melt stagnation and accumulation during flow, while reducing defects caused by uneven cooling. The inclination angle of the transition zone is recommended to be controlled between 30°-60° to ensure smooth melt flow.

(II) Adjust Injection Molding Process Parameters: Adapt to Molding Requirements After Thickness Reduction

After optimizing the product structure, it is necessary to adjust the injection molding process parameters to ensure the smooth molding of the injection molded parts with reduced thickness and avoid problems such as insufficient filling and flash.

1. Improve Melt Fluidity: Appropriately increase the barrel temperature and mold temperature to reduce melt viscosity and enhance its flow capacity, ensuring that the melt can quickly fill the cavity with reduced thickness. The barrel temperature should be adjusted according to the plastic material (e.g., the temperature for PP material is usually 180-220℃, and for ABS material is 200-250℃), and the mold temperature is generally controlled at 40-80℃. This avoids material degradation caused by excessively high temperatures or poor fluidity due to excessively low temperatures.

2. Optimize Injection Pressure and Speed: Increase the injection pressure and injection speed to shorten the melt filling time and prevent insufficient filling caused by the reduced cavity wall thickness. The injection pressure is recommended to be increased by 10%-20% compared with the original parameters (adjustments should be made in combination with the mold bearing capacity). The injection speed can adopt segmented control: rapid filling in the early stage and slow pressure holding in the later stage, so as to reduce melt impact and flash generation.

3. Adjust Pressure Holding and Cooling Parameters: The cooling speed of injection molded parts with reduced thickness accelerates, so the pressure holding time and cooling time need to be adjusted accordingly. The pressure holding time can be shortened by 10%-15% to avoid product deformation caused by excessive pressure holding; the cooling time should be optimized according to the actual molding situation to ensure that the product temperature is lower than the heat distortion temperature when demolded, thereby reducing warpage.

(III) Select Suitable Materials and Improve Molds

1. Choose High-Flow Materials: For injection molded parts with thinner walls, it is recommended to select plastics with good fluidity, such as PP, PE, and ABS, or modified plastics (e.g., plasticizer-added modified PVC) to reduce molding difficulty. Avoid using materials with poor fluidity (such as PC and POM) for thin-walled products unless molding requirements can be met through process optimization or mold improvement.  

2. Optimize Mold Structure: Improve the mold’s gating system by increasing gate size and shortening runner length to reduce melt flow resistance. For example, adopt pin-point gates or fan gates to enhance melt filling efficiency; install cold slugs in the runner to prevent cold material from entering the cavity and affecting molding quality. Meanwhile, the mold cavity surface should be polished to reduce melt flow friction and improve filling effectiveness.  

3. Add Venting Systems: After wall thickness reduction, gas inside the cavity is more difficult to discharge, which may easily cause defects such as bubbles and burn marks on the product. Vent grooves should be arranged at the end of the mold cavity, dead corners of melt flow, and other positions. The recommended width of the vent groove is 0.01-0.03mm, and the depth is 0.5-1mm, ensuring timely gas discharge during the molding process.  

(IV) Strengthen Quality Inspection and Iterative Optimization  

1. Establish Wall Thickness Inspection Standards: Regularly inspect the wall thickness of injection molded parts during production using tools such as calipers and ultrasonic thickness gauges to ensure the actual wall thickness meets design requirements and avoid localized excessive thickness caused by production deviations.  

2. Conduct Mold Testing and Process Iteration: After adjusting the product structure and process parameters, conduct mold testing to verify the product’s filling condition, surface quality, and mechanical properties. If problems such as insufficient filling or sink marks occur, further optimize the structural design or process parameters until the qualified standard is achieved.  

3. Long-Term Monitoring and Feedback: Continuously monitor product quality during mass production, collect data on molding defects, and regularly analyze the causes to optimize the scheme. For example, if localized sink marks occur persistently, there may still be room for optimizing the wall thickness in that area, requiring re-adjustment of the structural design.

III. Precautions and Summary

To solve the problem of excessive wall thickness in injection molded parts, the principle of "design priority, process adaptation, and material matching" must be followed. The core is to minimize unnecessary wall thickness to the greatest extent on the premise of meeting product functions and mechanical properties. Meanwhile, the following points should be noted:

1. When optimizing the structure, do not excessively reduce the wall thickness. It is necessary to verify whether the product meets the usage requirements through strength tests to avoid quality problems such as product fracture and deformation caused by overly thin walls;

2. The adjustment of process parameters should be carried out step by step. Avoid drastic modifications at one time to prevent new molding defects such as flash and mold sticking;

3. Mold improvement should be combined with product structure and material characteristics. Avoid blindly adding gates or vent grooves, which may affect mold service life and product appearance.

In conclusion, solving the problem of excessive wall thickness in injection molded parts is a systematic project. It requires collaborative optimization from multiple aspects including design, process, materials, and molds. This not only addresses existing defects but also balances production efficiency and cost control, ultimately achieving a win-win situation for product quality and economic benefits.