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Designing to Improve Plastic Strength

Plastic injection molded parts are typically tough and strong, capable of withstanding heavy loads, moderately high temperatures and the corrosive effects of acids and alkalis. Our injection moulding designers build strength into plastic parts in various ways and for numerous reasons. Strength can translate to different things depending on the part’s required purpose, we’ll explain strength, factors affecting a parts strength and how to improve strength in this article. 


Strength in Plastic Parts

Strength in plastic parts can translate to different things, depending on the parts purpose. We’ve categorised these into five sections:

  1. Deformation Resistance

Some plastic parts will be required to resist deformation to fulfil their purpose. For example, a plastic washing line clip to be able to flex and ‘deform’ enough to perform its job but not deform entirely that it becomes unusable.   

  1. Stress Resilience

When stress is applied to plastic parts they are usually required to withstand the stress applied and then return to their original shape once the stress is removed. This is possible when the stress applied is for short periods of time, but when stress is applied for longer periods of time plastic parts may not return to their original shape and this is referred to as creep.

  1. Load Bearing

The load a plastic part maybe subject to should be tested beyond expected load to ensure its viability. A good example is a plastic container, it is important to test that the container can carry a load far higher than expected.

We’ve discussed the importance of stress and load and explained creep in more detail in another article, read it here.

  1. Impact Strength

Some plastic parts are required to withstand impacts and should flex and return to their original shape when subject to certain levels of impact. For example plastic fenders on a boat are designed to withstand a low level of impact and return to their original shape.

  1. Environmental Strength

Environmental challenges can be temperature, humidity, exposure to chemicals and UV light and some plastic parts must withstand extreme temperatures, be flame retardant or endure long periods in very moist conditions.

What affects strength

When designing to add strength there are various considerations that should be applied during the design phase, this not only includes material selection but the actual design of the part. Extra thought must be given to the design when it comes to corners, walls, part thickness and whether the part has holes or inserts, as each of these affects a parts strength. We’ve covered these factors in more detail, read the article here.

How to improve strength in plastic parts 

A designer will need to establish the type of strength that you require and make the necessary adjustments to the design to achieve ultimate strength. A solution to achieve one type of strength may not work for another, for example adding glass fibers for strength would not work if the part was required to be flexible as it also makes the part brittle.


Contact a member of our team today and discuss how designing for strength can be achieved for your plastic part.


Get in touch today and talk to the specialists, click here.

Our team will be more than happy to help, advise and quote for your requirements.

Looking for more information? Check out our blog, News & Views for useful articles, tips and tricks on plastic injection moulding.