What is Uniform Wall Thickness?
Uniform wall thickness in injection molding refers to maintaining a consistent molding thickness across all walls of a plastic part， typically within 40-60% of each other. It doesn’t necessarily mean every wall must be exactly the same thickness but transitions between different thicknesses should be gradual. Uniform wall thickness injection ensures that the molten plastic flows evenly into all areas of the mold, reducing the risk of incomplete filling or air traps. It helps maintain uniform pressure throughout the mold, preventing areas of high stress that can lead to defects. Thick sections cool slower than thin sections and uneven wall thickness can cause differential cooling rates. The uniform thickness has even cooling and helps reduce the warping, distortion, or sink marks of parts. Parts with uniform wall moulding thickness have consistent mechanical properties, providing predictable strength and durability. Variations in wall thickness can create stress concentrations, leading to weak points in the part. Consistent wall thickness ensures even cooling, reducing the risk of internal stresses and ensuring the part maintains its shape. Parts with uniform thickness cool more predictably, allowing for optimized cycle times and increased production efficiency. Uniform wall thickness helps avoid overuse of material in thick sections, leading to material savings. Fewer defects mean lower scrap rates, reducing waste and cost.Selection the Optimal Wall thickness
Selecting the optimal wall thickness for plastic parts involves balancing several factors such as material properties, part function, manufacturing constraints, and cost considerations. The generally recommended wall thickness for plastic injection molded parts ranges from 1.0 mm to 30 mm, with 1.5 mm to 3.0 mm being the most common range 1 2 . However, the optimal thickness can vary depending on the specific material used and the size of the part. Here’s a chart summarizing recommended wall thicknesses for common plastic material:| Plastic material | Recommended wall thickness (in) | Recommended wall thickness (mm) |
|---|---|---|
| ABS | 0.045–0.140 | 1.14–3.56 |
| Acetal(POM) | 0.030–0.120 | 0.76–3.05 |
| Acrylic(PMMA) | 0.025–0.150 | 0.64–3.81 |
| Nylon | 0.030–0.115 | 0.76–2.92 |
| Polycarbonate(PC) | 0.040–0.150 | 1.02–3.81 |
| Polyethylene(PE) | 0.030–0.200 | 0.76–5.08 |
| Polyethylene Sulfide | 0.020–0.180 | 0.51–4.57 |
| Polypropylene(PP) | 0.025–0.150 | 0.64–3.81 |
| Polystyrene(PS) | 0.035–0.150 | 0.89–3.81 |
What is the minimum injection molding wall thickness?
The minimum injection molding wall thickness is the thinnest wall recommended for a molded plastic part. That is depending on the specific material and application. 1 mm is usually the thinnest that part walls get, although minimum wall thickness can be thinner for some materials. While technically possible to mold parts with walls thinner than 1 mm, staying above 1 mm helps avoid common issues associated with very thin walls, such as short shots, uneven cooling, warpages, cracks, and flow problems. This range is recommended because it achieves a balance between manufacturability and part quality.
What is the maximum injection molding wall thickness?
On the other hand, the maximum wall thickness of 5 mm is recommended to prevent problems like uneven cooling, increased internal stress, underfilling, warping, excessive dimensional deviations, longer cooling times, and higher production costs.
Defects Caused by Improper Injection Molding Wall Thickness
Here are some common challenges related to improper wall thickness in injection molding and strategies to address them:
- Warping and Shrinkage
Warping and shrinkage are primarily caused by uneven wall thickness leading to differential cooling and shrinkage, as well as excessive wall thickness causing internal stresses during cooling. Uniform wall thickness throughout the part, use gradual transitions when thickness changes are necessary, add ribs or gussets instead of thickening walls for strength, optimize cooling system design in the mold, and consider using materials with lower shrinkage rates will avoid these defects.
- Sink Marks
Sink marks occur due to thick sections cooling more slowly than surrounding areas and inadequate packing pressure or time. To avoid sink marks, reduce overall wall thickness where possible, use coring techniques to maintain uniform wall thickness in thick sections, increase packing pressure and time, add ribs or gussets instead of thick sections for strength, and optimize gate location and size.
- Flow Lines
Flow lines and weld lines are caused by abrupt changes in wall thickness or multiple gates. To minimize these defects, design for uniform wall thickness to promote even flow, use gradual transitions between different wall thicknesses, optimize gate location and number to control flow patterns, increase melt and mold temperatures to improve flow characteristics, and consider using materials with better flow properties.
How to Design for Uniform Injection Molding Wall Thickness?
Designing for uniform wall thickness is crucial in injection molding to ensure high-quality parts with minimal defects. Below are detailed strategies and guidelines for achieving uniform wall thickness in your designs:
1. Add Ribs and Gussets
- Ribs and Gussets
Ribs add strength and stiffness to a part without significantly increasing wall thickness. Gussets provide additional support to prevent bending and warping.
Ribs should be 50-70% of the main wall thickness and rib height should be less than three times the wall thickness. Space ribs apart by at least two times the wall thickness.
Align ribs with the flow direction of the molten plastic for better filling and strength.
Place gussets at corners and around bosses to reinforce these areas. Ensure gussets are not too thick to avoid creating thick sections.
2. Add Bosses
- Bosses in Injection Molding
Bosses are cylindrical features that reinforce fastener holes.
The wall thickness around bosses should be uniform and consistent with the rest of the part.
The height of a boss should be less than twice its diameter and use fillets where the boss meets the wall to avoid stress concentrations and improve material flow.
Reinforce bosses with ribs that blend smoothly into the main walls to distribute stress evenly.
3. Adding Draft Angles
- Draft Angles
Draft angles facilitate the easy removal of the part from the mold, reducing the risk of damage and defects.
A typical draft angle ranges from 1 to 3 degrees per side.
Ensure that all surfaces of the part have consistent draft angles to maintain uniform wall thickness and avoid areas of high stress.
4. Avoid Sharp Corners
- Injection Molding Conners
Use rounded corners with fillets and radii instead of sharp corners to reduce stress concentrations and improve material flow.
Ensure that the radius of internal corners is at least 0.5 times the wall thickness to maintain uniformity.
5. Gradual Thickness Transition
- Gradual Thickness Transition
Abrupt changes in wall thickness can lead to stress concentrations and defects such as warping and sink marks.
Use tapered transitions to gradually change wall thickness between different sections of the part.
Blend features such as ribs, bosses, and gussets smoothly into the main walls to avoid abrupt thickness changes.
Conclusion
Wall thickness is a critical aspect of injection molding design that significantly impacts part quality, performance, and manufacturability. Uniform wall thickness can prevent common defects such as warping, sink marks, voids, and uneven shrinkage. By understanding the impact of wall thickness on the final product and implementing these design guidelines, manufacturers can achieve better structural integrity, reduced production costs, and higher production efficiency.
