Of all the various design aspects, wall thickness has the most significant impact on the cost, production speed, and final quality of a part.
Proper Wall Thickness
While thick walls offer additional strength, there are some advantages to engineering thinner walls. In fact, the longer a production run, the more benefits that can be gained by keeping a part thin and light, so maintaining optimal wall thickness is particularly important for high-volume injection molding projects. Keeping walls as thin as possible allows for:
- Resistance to warping during the cooling process
- Reduced costs due to less material usage and faster manufacturing
- Reduced overall weight for ease of handling, management, and shipping
- Quicker cooling cycles for shorter, more efficient production run time
Wall thicknesses are not subject to any restrictions, but generally, the goal is to create the thinnest wall possible while taking into account the part’s structural requirements and overall size and geometry. The flow behavior and material qualities of the resin should also be considered.
Creating Uniform Wall Thickness
Consistent wall thickness is critical during the cooling process in injection molding; if some sections of a part are thinner than others, the part may be vulnerable to warping, cracking, twisting, and overall failure. Uniform wall thickness minimizes both shrinkage and residual stress in the final part.
If completely uniform walls simply aren’t an option, gradual thickness variations are essential to maintaining design stability. Wall thickness variations in high-mold-shrinkage plastics should never exceed 10%, even with gradual transitions to accommodate for potential stress concentrations.
Uniform wall thickness also allows for the most efficient, uniform flow of resin through a tool for ideal processing. Variations in wall thickness cause molten polymers to take preferential flows, leading to air trapping, unbalanced filling, and weld lines.
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