Wall thickness in injection molding is the distance between the inner and outer surfaces of a part, typically ranging from 1 to 5 mm. Consistent thickness ensures uniform cooling and reduces defects. Walls are often tapered, with a draft angle of at least 0.5 degrees to aid in easy mold ejection and prevent damage.
Why Wall Thickness Matters?
First things first, why do we even care about wall thickness in injection molding? Well, it’s all about achieving the perfect balance between strength, durability, and cost. Too thick, and you’re wasting material and potentially creating injection molding defects. Too thin, and you risk warping, cracking, or even breaking your part.
Uniform Wall Thickness
Uniform wall thickness doesn’t mean all walls must be the same. Instead, walls should be consistent within 40% to 60% of adjacent walls’ thickness to avoid defects. Ribs and support structures can differ in thickness from the main walls.
Utilize CAD (Computer-Aided Design) software and DFM (Design for Manufacturing) principles to ensure optimal wall thickness. Modern CAD tools help adjust thickness and apply draft angles, facilitating effective injection molding design.
Wall Thicknesses for Common Injection Molding Materials
Here’s a guide to help you determine the optimal thickness for various plastic materials. For the best results, consult with an experienced injection molding manufacturer like BOYI.
| Resin | Recommended Wall Thickness |
|---|---|
| Long-Fiber Reinforced Plastics | 0.075–1.000 in (1.91–25.4 mm) |
| Nylon | 0.030–0.115 in (0.76–2.92 mm) |
| Polypropylene | 0.025–0.150 in (0.64–3.81 mm) |
| Polycarbonate | 0.040–0.150 in (1.02–3.81 mm) |
| Acrylic | 0.025–0.150 in (0.64–3.81 mm) |
| ABS | 0.045–0.140 in (1.14–3.56 mm) |
| Polyethylene Sulfide | 0.020–0.180 in (0.51–4.57 mm) |
| Acetal | 0.030–0.120 in (0.76–3.05 mm) |
| Polystyrene | 0.035–0.150 in (0.89–3.81 mm) |
| Polyester | 0.025–0.125 in (0.64–3.18 mm) |
| Liquid Crystal Polymer | 0.030–0.120 in (0.76–3.05 mm) |
| Polyethylene | 0.030–0.200 in (0.76–5.08 mm) |
| Polystyrene | 0.035–0.150 in (0.89–3.81 mm) |
| Polypropylene | 0.025–0.150 in (0.64–3.81 mm) |
| Acrylic | 0.025–0.150 in (0.64–3.81 mm) |
Key Considerations:
- Material Properties: Different plastics have varying optimal wall thicknesses due to their unique flow characteristics and cooling requirements.
- Part Design: Ensure wall thickness is consistent to avoid defects like warping and sink marks.
- Manufacturer Expertise: Collaborating with a skilled manufacturer can provide tailored recommendations based on specific project needs.
Consult with professionals to refine your design and select the optimal wall thickness for your injection molding project.
Design Tips for Optimal Wall Thickness
By following these tips, you can design parts with optimal wall thickness that balance strength, weight, and manufacturability.
- Analyze Material Properties: Choose a material that suits your product requirements and understand its shrinkage behavior.
- Plan for Uniformity: Design your part with consistent wall thickness wherever possible.
- Straight Pull Molds: Design your mold to allow for a “straight pull” or “up and down” motion during separation. This minimizes the need for complex actions like cams or core pulls, reducing costs.
- Draft Angles: Always include draft angles on all parts to allow for easy release from the mold. A minimum of 1/2 to 1 degree is typically recommended, with 1.5 to 2 degrees being the norm.
- Functional Holes: Adding holes for functionality or weight reduction can be tricky. Blind holes are more difficult to form without defects, so consider the depth-to-diameter ratio carefully.
- Avoid Complex Features: Complex features like undercuts can increase mold costs and make demolding more challenging. Simplify your design wherever possible.
- Prototype and Test: Don’t hesitate to prototype your design and test it under real-world conditions. This will help you identify potential issues early on and make necessary adjustments.
- Iterate Your Design: Based on test results, iterate your design to improve wall thickness consistency and overall product quality.
Materials Matter
Don’t forget about the material you’re using. Different resins have different properties and behaviors during injection molding.
Low-viscosity resins, particularly those that perform well at high shear rates, are ideal for thin-walled parts. Polystyrene resins with a viscosity range of 5-20 Pa-s (preferably 7-17 Pa-s) at a resin temperature of 220°C and a shear rate of 10,000-1 sec-1 are commonly used.
Common Issues and Solutions
Sink Marks
Sink marks occur when the plastic shrinks unevenly as it cools. This can be minimized by:
- Increasing wall thickness slightly in affected areas.
- Using materials with lower shrink rates.
- Adjusting cooling times and temperatures.
Warping
Warping is caused by uneven cooling and stresses in the part. Solutions include:
- Ensuring consistent wall thickness throughout the part.
- Adjusting mold temperatures and cooling rates.
- Adding reinforcing ribs or bosses to support thin sections.
Voids and Bubbles
Voids and bubbles can be caused by trapped air or insufficient plastic flow. Solutions might include:
- Increasing injection pressure and speed.
- Adjusting the gate location and size.
- Improving venting in the mold.
Conclusion
Determining the optimal wall thickness in injection molding is a balancing act that involves understanding material properties, design requirements, and manufacturing capabilities. By adhering to these guidelines, you can produce high-quality parts with the right balance of strength, functionality, and cost-effectiveness.
If you have any questions or need further assistance with your injection molding design, feel free to reach out!
FAQ
The minimum injection molding wall thickness is the thinnest recommended for a given plastic. Typically, 1 mm is the minimum, though some materials can be thinner.
The maximum injection molding wall thickness is typically limited to 5 mm to prevent defects like warping and underfilling. Thicker walls may be required for high loads or specific needs but can lead to issues if not carefully managed.
Injection molded walls typically range from 2 to 4 mm thick. The exact thickness depends on the material used and the part’s design requirements.
In injection molding, thick areas refer to parts with wall sections measuring 0.250 inches (6.35 mm) or greater.
Catalog: Injection Molding Guide
This article was written by engineers from the BOYI team. Fuquan Chen is a professional engineer and technical expert with 20 years of experience in rapid prototyping, mold manufacturing, and plastic injection molding.
