Minimum wall thickness for injection moulding

Product wall thickness is a key consideration when designing products for plastic injection moulding.  Thicker walls will offer more strength, but they are also more likely to suffer from warping as the plastic cools in the mould.  Engineers and designers are usually more focussed on pushing the boundaries in the other direction, and using the minimum wall thickness for injection moulding they can get away with.  When mass-producing plastic parts there are a number of advantages to keeping them thin and light, and the longer the production run, the more significant these benefits become:

• Thinner parts require less material, reducing material costs
• Thinner parts cool quicker, thereby shortening the moulding cycle and reducing unit costs
• Thinner parts weigh less, potentially reducing shipping costs

Considerations

Generally, minimum wall thickness for injection moulding is dictated by strength and the structural requirements of the product or component.  We’ve also got to take the flow behaviour of the material into account, as there is a direct relationship between the maximum achievable flow length for a given wall thickness and injection pressure.  In both cases modern structural and flow analysis software will assist engineers in selecting the optimal wall thickness.

Just to add another variable into the mix, we can also use different types of plastics that have different strength and cooling properties!  However, as a rule, the minimum wall thickness for conventional injection moulding is 0.3mm, and even then it depends on the characteristic of the part itself.  Below this it is unlikely we would be able to guarantee the results.

Design Advice

From a moulding perspective, it’s good practice to keep wall thicknesses as uniform as possible.  This is because thinner walls cool (and therefore shrink) quicker than the thicker walls, which can cause warping to occur and result in internal stresses in the product, definitely what you don’t want when you’re pushing the boundaries of wall thickness!

When design considerations dictate that a uniform wall thickness is not possible, then the change in thickness should be as gradual as possible to avoid stress concentrations and abrupt cooling differences.

Pushing the Boundaries…

At Skar we like a challenge, and I like to think we’ve got as good a knowledge as you’ll find anywhere in the plastic injection moulding industry.  If you’ve got a challenging product you need to get into production we’d love to hear from you, call us now on 01473 828000 or email me.

Thanks for reading,

Brian.