The Importance of Uniform Wall Thickness in Injection Molding

The Importance of Uniform Wall Thickness in Injection Molding

Plastic injection molding is critical in producing durable and practical products, emphasizing the significance of maintaining consistent wall thickness.

Recognizing the value of this aspect can result in improved designs, minimized manufacturing flaws, and substantial financial advantages.

This comprehensive article delves into the principles, significance, and potential drawbacks of disregarding uniform wall thickness in injection molding. Prepare to expand your understanding and elevate the integrity of your products.

The Principles to Consider When Designing Injection Parts Walls

The Principles to Consider When Designing Injection Parts Walls

Designing injection parts walls requires careful consideration of several principles to ensure optimal results. By focusing on factors like sharp corners, adjacent wall thickness, draft angles, bosses, rims and bends, and ribs, designers can create structurally sound, aesthetically pleasing, and cost-effective parts.

The attainment of uniform wall thickness heavily relies on implementing these fundamental principles, which significantly contribute to the overall excellence of injection molded components.

In the following sections, we will delve into these principles, comprehending their utmost importance in the design process. By exploring these principles in detail, you will gain a deeper understanding of their significance and their impact on achieving uniform wall thickness.

1. Sharp Corners:

Sharp Corners

In the injection molding process, pointed angles can be a source of tension build-up and, in the worst-case scenario, result in the breakdown of the component.

It’s prudent to infuse arc measures in the plan to uphold the part’s solidity. Curved corners are conducive to smoother distribution of the material and assist in preserving a constant thickness of the wall.

2. Adjacent Wall Thickness:

Adjacent Wall Thickness

In the design stage of parts produced through injection molding, preserving an even thickness across neighboring walls is essential. Inconsistencies in the thickness can interfere with the cooling stage, paving the way for potential flaws such as distortion or sink marks.

Hence, maintaining a steady wall thickness is pivotal to ensure a top-tier final product. By emphasizing this detail, the completed components’ overall robustness and visual attractiveness can be significantly uplifted.

3. Draft Angles:

Draft angles are vital in the configuration of parts made through injection molding. They ease the removal of the piece from the mold, lessening the chances of damage or misshaping.

Generally, a single-degree taper serves the purpose, but this could fluctuate based on the substance used and the depth of the component.

4. Bosses:

Bosses are projections used for attachment and alignment purposes. To prevent sink marks and ensure proper filling, bosses should maintain the same wall thickness as the adjacent walls. Connection to the walls via ribs can also enhance strength.

5. Rims and Bends:

Rims and Bends

Rims and bends should adhere to uniform wall thickness to prevent premature cooling or material accumulation. Strategic design can optimize material flow and cooling rates, ensuring the integrity of these elements.

6. Ribs:

Ribs augment the robustness and steadiness of components formed through injection molding. Yet, keeping a certain proportion of wall thickness between the ribs and the nearby wall is essential to avert the formation of sink marks.

As a rule of thumb, the rib’s wall’s thickness should fall within 50 – 60% of the neighboring wall’s thickness. Moreover, it’s vital to confirm that the rib’s height does not exceed the thickness of the wall thrice.

By adhering to these principles during the design phase of injection molded parts, you can effectively mitigate the risk of manufacturing defects and significantly improve your product’s overall quality and performance.

Read Out: Draft Angle Guidelines for Injection Molding

Why is it Important to Maintain Uniform Wall Thickness?

Maintaining uniform wall thickness in injection molding cannot be overstated, as it significantly impacts multiple facets of the final product. It is pivotal in attaining a visually pleasing appearance, reducing defects, and ensuring consistent performance.

By prioritizing uniform wall thickness, manufacturers can enhance their injection-molded products’ overall aesthetics, functionality, and reliability.

1. Appearance:


Consistently maintaining uniform wall thickness in injection molding is crucial for creating a visually appealing product. Variations in wall thickness can result in visible defects like sink marks or warping, significantly compromising the overall visual appeal of the part.

Manufacturers can eliminate these unsightly flaws by ensuring uniformity in wall thickness and producing high-quality products that meet or exceed aesthetic expectations.

2. Gating Challenges:

Uniform wall thickness aids in effective gating system design, ensuring proper plastic flow melts throughout the part. If the wall thickness varies, it can lead to an imbalance in flow rates, potentially causing short shots or other defects.

3. Shear Stress:

Uneven wall thickness can cause increased shear stress in certain areas. This stress can degrade the plastic material and weaken the overall structural integrity of the product.

4. Cooling Rate:

The uniformity of wall thickness is a critical determinant in sustaining a steady cooling pace throughout the entire component during the injection molding process. If the thickness of the wall fluctuates, different segments of the element will cool at varying rates.

This discrepancy in cooling might result in problems like distortion or unstable dimensions, thereby impacting the product’s overall performance and quality.

5. Cost:


Uniform wall thickness can also result in cost savings. Uneven thickness often leads to additional material use and higher cycle times, increasing production costs.

By maintaining uniformity, material usage is optimized, and cycle times are reduced, leading to more cost-effective production.

Read More: 7 Types of Gates in Injection Molding: Ultimate Guide

Defects Caused by Uneven Wall Thickness

Defects caused by uneven wall thickness can significantly impact the quality and functionality of injection molded parts. Understanding and addressing these issues is crucial for achieving high-quality, visually appealing, and structurally sound products.

Let’s explore some of the most common defects that can arise due to uneven wall thickness:

1. Warpage:

Distortion, also known as warping – a deviation from the intended form, is a frequent issue triggered by the inconsistent thickness of the wall in injection molding.

A component with diverse wall thicknesses results in unequal cooling speeds, leading to the warping of the part as separate sections contract unevenly.

Such distortion not only impairs the aesthetic of the component but can also compromise its operational efficiency, leading to problems like poor fit or alignment issues during assembly.

2. Flow Lines:

Flow Lines

Flow lines refer to visible marks or designs appearing on the exterior of components produced through injection molding. These are usually due to the differences in the velocity at which the liquid plastic travels into diverse mold zones.

When the wall thickness isn’t constant, the molten plastic is prone to hasten into leaner sections while decelerating in bulkier areas. This disparity in flow velocity gives rise to the development of flow lines.

The speed variation could lead to flow lines as the plastic cools and solidifies at uneven rates. While these lines generally don’t influence the component’s structural stability, they could detract from its visual appeal, causing it to seem less polished or refined.

3. Sink Marks:

Sink Marks

Sink marks are depressions that manifest on the surface or subsurface of an injection molded part. They occur due to a disparity in the cooling and solidification process between the outer shell and the inner material.

When an area of the part has thicker walls, it takes longer to cool and shrink compared to the already solidified outer surface. As a result, the hardened surface is pulled inward, creating a sink mark.

These sink marks can have adverse effects on both the appearance and structural integrity of the part. More severe instances can even lead to failure points in the finished product.

Therefore, maintaining uniform wall thickness is essential to minimize the occurrence of sink marks and ensure the overall quality and performance of the injection molded parts.

4. Short Shots:

Short shots occur when the molten plastic fails to completely fill the mold cavity, leading to an incomplete or undersized part. Uneven wall thickness is a prevalent factor contributing to short shots.

When there are disparities in the wall thickness, it can create flow restrictions and uneven distribution of the molten plastic, preventing it from effectively reaching all areas of the mold cavity.

The molten plastic flows more quickly through thinner areas and can solidify before reaching the thicker sections, preventing complete fill. Short shots result in incomplete parts, wasting material and adding to production costs.

Choosing a Material for Plastic Injection Molding

The choice of materials in plastic injection molding stands as a pivotal determinant that substantially impacts the final characteristics, manufacturing feasibility, and the component’s overall efficacy.

Here are some general principles to bear in mind while picking materials for the injection molding procedure:

1. Determine Material Based on Use:

Determine Material Based on Use:

The material should be chosen based on the final use of the part. For example, polypropylene may be suitable for disposable items. At the same time, more durable plastics like ABS or nylon would be better for long-lasting, high-wear components.

2. Consider Material Properties:

Every material has different properties. Some are rigid and brittle, others flexible and durable. Consider the specific properties of each material and how these align with the needs of the final part.

3. Wall Thickness:

Wall Thickness

The selected material should accommodate the required wall thickness of the part. Different materials have varying flowability and cooling rates, impacting how well they can form and solidify in thin or thick sections.

4. Thermal Properties:

Materials with high thermal conductivity are suitable for thick-walled parts as they can efficiently dissipate heat during cooling, reducing warpage. On the contrary, low thermal conductivity materials work well for thin-walled parts.

5. Cost-effectiveness:

The material’s cost will directly impact the part’s overall production cost. It’s crucial to balance material properties and cost-effectiveness to ensure profitability.

MaterialsWall Thickness (mm)
ABS0.045 – 0.140
Acetal0.030 – 0.120
Acrylic0.025 – 0.500
Liquid Crystal Polymer0.030 – 0.120
Long-Fiber Reinforced Plastic0.075 – 1.000
Nylon0.030 – 0.115
Polycarbonate0.040 – 0.150
Polyester0.025 – 0.125
Polyethylene0.030 – 0.200
Polyphenylene Sulphide0.020 – 0.180
Polypropylene0.025 – 0.150
Polystyrene0.035 – 0.150
Polyurethane0.080 – 0.750
Rigid PVC0.090 – 0.250
Soft PVC0.025 – 0.150
Table 1. Recommended Wall Thickness for Different Materials

The material you choose for your plastic injection molding project will play a crucial role in the success of your product. Considering these general material thickness guidelines, you can make a well-informed choice that optimizes manufacturability and final part performance.

Design for Manufacturability

Design for Manufacturability (DFM) is an indispensable element of the injection molding procedure, aimed at refining the part’s design to boost manufacturing productivity, diminish expenses, and augment the overall quality.

Reflect on the ensuing crucial facets of DFM in injection molding:

  • The material used for the part should be suitable for the design and application of the part. DFM includes selecting a material that offers the necessary properties (e.g., strength, flexibility, thermal stability) while being cost-effective and easy to work with in the injection molding process.
  • Streamlining the part design to simplify and reduce complexity is crucial for achieving efficient and cost-effective manufacturing in injection molding. The molding process can be optimized by avoiding unnecessary complexity in features such as undercuts or thin, hard-to-fill sections.
  • The mold’s design, including its gate location, ejection system, and cooling channels, significantly impacts the part’s manufacturability. DFM encompasses optimizing these elements to ensure smooth production and high-quality results.
  • If the final product consists of multiple parts, DFM considers how these parts will be assembled. Designing parts for easy and efficient assembly can reduce manufacturing time and costs.

Check Out: It All Starts with Design: A Detailed Guideline on Insert Molding Design Guide

Kemal Plastic Injection Molding Services

Kemal Plastic Injection Molding Services

Kemal’s Plastic Injection Molding Services is your one-stop solution for high-quality, precision injection molded parts. With over two decades of experience in the industry, Kemal has honed a comprehensive understanding of injection molding processes and techniques.

Our services encompass everything from design consultation, where we guide you on optimizing your design for manufacturability and cost efficiency, to actual production, where we utilize advanced machinery and high-grade materials to bring your designs to life.

We cater to various industries, from automotive to medical devices, ensuring a versatile approach to meet unique client requirements.

We pride ourselves on providing cost-effective, timely solutions without compromising on quality. Our experienced team works hand-in-hand with clients, ensuring that every process stage is transparent and geared toward their success. Contact us for a seamless, efficient, and superior molding experience.


Wall thickness is crucial in injection molding. It affects physical properties, manufacturing, cost, and quality. Uniform thickness ensures consistent cooling, reduces defects, and minimizes material usage.

Material selection is vital in determining the properties of the final product, such as strength, durability, flexibility, and resistance to heat or chemicals.

Different materials have varied flow and cooling rates, directly influencing the part’s manufacturability, especially its wall thickness.

Uneven wall thickness can lead to several defects, including warpage (distortion due to inconsistent cooling rates), flow lines (streaks caused by variable flow speeds), sink marks (depressions resulting from delayed cooling in thicker areas), and short shots (incomplete parts due to premature solidification of the material).

The wall thickness is determined by the design of the mold. Therefore, it cannot be adjusted during the injection molding process.

Changes to wall thickness require modifications to the mold, which can be time-consuming and costly. Hence, optimizing the design for manufacturability before the mold is made is crucial.

Preventing uneven wall thickness starts with a well-designed part. CAD software and simulation tools can help identify potential problems before making the mold.

Smooth transitions between different wall sections and avoiding abrupt changes in thickness are additional factors that contribute to maintaining uniformity in wall thickness during injection molding.

Draft angles are slight angles applied to the vertical walls of the part design. They help facilitate the part’s removal from the mold after the injection molding process, reducing the risk of damage. They’re critical in parts with significant depth or recesses.

The gate is where the molten plastic enters the mold. If not correctly designed, it can lead to an uneven material flow, resulting in inconsistent wall thickness. It’s vital to place the gate at a location that allows for a balanced, uniform flow into all parts of the mold.


In conclusion, maintaining uniform wall thickness in injection molding is essential for creating quality, defect-free parts. A thoughtful design approach, careful material selection, and understanding of potential defects are crucial to success.

Are you ready to leverage these insights in your next injection molding project? Reach out to an experienced service provider like Kemal and embark on your journey towards flawless injection molded parts today.

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