Optimizing Wall Thickness in Injection Molding for Quality and Efficiency

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When producing injection molded parts, designers and engineers should follow strict guidelines to ensure the production of consistent products with minimal defects and minimum production costs. One of these guidelines involves the wall thickness of parts. Wall thickness in injection molded parts usually ranges from 1 mm to 1.5 mm depending on the type of plastic resin used, the parts requirements and other factors such as mold flow. It is essential for designers and engineers to design parts with a minimum wall thickness. This is because parts designed with thin walls take less time to cool thus saving on cycle times. Thin walls also consume less plastic material, saving on costs and increasing the efficiency of the injection molding process significantly. Generally, wall thickness is an important factor for designers to consider because it impacts the production speed, cost and the quality of the final part.  

Wall Thickness in Injection Molding 2

Section 1: The Importance of Proper Wall Thickness

Wall thickness refers to the distance between the inner side and the outer side of a plastic molded component. Wall thickness affects several aspects of the injection molding process including material use and the cooling time. For instance, parts designed with thin walls consume less plastic material than parts with thick walls. Additionally, parts designed with thin walls require less cooling time than parts with thick walls because of their small surface area and less material used in production. On the other hand, parts designed with thick walls are prone to warping during cooling, inconsistent cooling resulting in sink marks and inadequate filling during injection resulting in defective final parts. While thick walls offer additional strength, there are far much more advantages to designing parts with minimum thickness. Designing products with minimum wall thickness has several advantages including resistance to warping during cooling, reduced costs due to less material usage and fast production cycles, and production of lightweight parts for easy handling and shipping. For long production runs, optimal wall thickness is essential to ensure minimum material usages and fast production cycles. All these factors impact the overall efficiency of the injection molding process. It is therefore important for designers to use optimum wall thickness depending on the parts structural requirements, size and geometry and flow behavior of resins used to improve the efficiency of the injection molding process. 

Wall Thickness in Injection Molding 3

Section 2: Determining Optimal Wall Thickness

When determining the optimal wall thickness of a particular part, designers should consider the part’s size, geometry, structural requirements and resin flow behavior. 

Size: Large parts may require thick walls for the added strength and structural integrity. This can impact the volume of material used and result in increased cooling time. Parts with thick walls can also be prone to defects such as warping, sink marks and flow lines. 

Geometry:  This refers to the complexity of the shape and design of the part. Different parts are designed with varying draft angles, ribs, bends and corners sharpness. All these design specifications impact the size of the walls. designers should take into account the geometry of the part’s design before determining the optimum wall thickness.

Structural requirements: The intended application of each part should determine the structural requirements of the part, which affects the size of the wall thickness. Parts with high load and stress bearing requirements should be produced with thick walls in order to function effectively without failing. Designers should adjust their wall thickness keeping in mind material use and weight. 

Resin flow behavior: This refers to the behavior of the resin materials used in injection molding. Different resins have different viscosities which affect how the flow. Resins with high viscosity can be used for thick wall designs to ensure complete filling of the mold. Designers should also consider the resins uniformity in cooling and solidifying when determining wall thickness to prevent defects in final parts. 

  • Recommended wall thickness ranges for common injection molding resins.
ResinRecommended wall thickness
Liquid Crystal Polymer0.030–0.1200.76–3.05
Long-Fiber Reinforced Plastics0.075–1.0001.91–25.4
Polyethylene Sulfide0.020–0.1800.51–4.57

Section 3: Benefits of Thin Wall Injection Molding

Thin wall injection molding is the art of producing components with the thinnest possible walls without compromising on the structural integrity and functionality of the component. This production method offers several advantages over conventional techniques regarding the cost and cycle time of the injection molding process. Some of the benefits include:

  1. Increased precision in final parts: Using minimum wall thickness ensures manufactures can produce light weight plastic parts while maintaining the necessary strength and durability. 
  2. Faster cycle times and increased production rate: Thin wall injection molding uses advanced machinery with capabilities to produce large volumes within shorter timeframes. This increases the production rates while reducing the manufacturing costs in the long run. 
  3. Reduced material usage: Thin wall injection molding uses less material compared to other injection molding techniques, leading to less material wastage and overall cost saving. 
  4. Energy saving: The fast cycle times of thin wall injection molding allows manufacturers to save costs on energy used for production making this technique environment-friendly due to reduced carbon emissions.

Although thin wall injection molding has several benefits, there are also some challenges and considerations that manufacturers should consider when using this technique. 

One of the considerations is maintaining a uniform wall thickness. Variations in wall thickness could result in warping, structural weaknesses, sink marks and other defects that affect the overall quality of the final component. Manufacturers should design the mold carefully, paying close attention to gate location, wall thickness and runner size to ensure uniform wall thickness. 

The other consideration is injection speed and pressure. To achieve the desired precision and uniformity, high injection speed and pressure are required. This ensures that the plastic material flows evenly into the mold, preventing defects such as sink marks and warpage.

Finally, manufacturers should consider mold surface treatment before injection. This involves treating the mold core and surface with special coatings and finishes. Proper surface treatment improves the release of the part from the mold, preventing defects such as flashes and burrs. It also reduces the wear and tear on the mold, minimizing maintenance costs in improving the overall efficiency. 

Section 4: Achieving Uniform Wall Thickness

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Achieving a uniform wall thickness is important in injection molding because it determines the dimensions of the part, the performance and the manufacturing requirements. When parts are designed with inconsistent wall thickness, they are prone to defects such as warping, twisting and cracking.

Warping refers to the uneven shrinking of different parts of a component resulting in bending of the final component. This is caused by different cooling rates on various parts of the component due to inconsistent wall thickness.

Twisting: Just like warping, twisting is also caused by uneven cooling and solidifying of molten plastic due to inconsistent wall thickness. This causes the final component to bend and twist due to uneven internal pressure.

Cracking: This refers to the breaking or cracking of a part immediately or some time later after production. Inconsistent wall thickness may result in cracking due to uneven structural strength of the final component. 

Achieving and maintaining uniform wall thickness can be a challenging task, especially when producing intricate parts with complex geometries. However, manufacturers can use these design strategies to maintain uniform wall thickness throughout the injection molding process. 

  1. Avoid abrupt transitions to different wall thicknesses. When designing a part, use gradual transitions to smoothly switch from one thickness to the other.
  2. Use core outs in thick sections to maintain a uniform thickness.
  3. Use ribs and gussets to reinforce the part without increasing the overall wall thickness. 
  4. Design parts with slight curves and bosses to avoid large flat surfaces which are prone to warpage and sink marks.
  5. Use uniform draft angles for easy ejection of distortion or drag marks which may impact the wall thickness. 

Section 5: Managing Wall Thickness Transitions

Some parts may be designed with varying wall thickness at different sections. Transitioning from one wall thickness to the other can affect stress concentrations and cooling rate of the final part. Designers should design parts with smooth and gradual transition between these sections. Some of the guidelines for gradual thickness transitions include: 

  1. Using chamfers and fillets: Chamfers are angled edges where two surfaces meet while fillets are rounded corners and edges.
  2. Using rounded corners which enables molten plastic to flow easily into the mold and minimize differences in shrinkage as the plastic material cools.
  3. Tapering draft angles according to the part requirements for smooth transition between different wall thicknesses. 
  4. Extend the transition length to ensure the molten plastic has the longest possible transition length between the sections with different wall thicknesses.
  5. Consider the material properties of resins when designing the molds to ensure that during transitions, the materials flow into the mold easily.
  • Recommended limits on wall thickness variations to prevent defects in high shrinkage plastics.
Plastic MaterialMin. ThicknessRecommended Thickness of Small-sized Plastic PartsRecommended Thickness of Mid-sized Plastic PartsRecommended Thickness of Large-sized Plastic Parts


In conclusion, selecting the right wall thickness of a part is crucial for the success of the injection molding project. Wall thickness impacts several factors of the injection molding process including material usage, cycle times, cost and the overall efficiency of the process. As we have seen, different plastic materials require different wall thicknesses to ensure the production of high quality parts without compromising on structural integrity and functionality. When designing parts, designers should keep in mind the optimum wall thickness to ensure improved part quality and manufacturing efficiency. 


Gary Liao

Gary Liao

Gary Liao is the Engineering Manager of TDL Company and has more than 20 years of mold design experience.

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