We have now reached the end of our series of articles on design considerations for injection moulding. Consider the points raised and then establish the design. Rutland Plastics would be happy to help with this aspect. We can advise on suitability for injection moulding and cost-saving options if required. If necessary, we can take a sketch and prepare full drawings for you.
Once your requirements are known the material can be selected. Again Rutland Plastics can advise on the most cost-effective solution combining material properties and design features.


Critical dimensions, surface finishes, flatness, etc. must be specified along with realistic tolerances.

Involving Rutland Plastics at an early stage can allow concurrent engineering to take place. This will result in less wastage of time and resources in producing a successful design. It is possible to start this process with just a sketch rather than a full CAD design. When a plastic part is being designed to replace an existing product or component manufactured in another material it is advisable to start the design from scratch using critical dimensions and features rather than trying to replicate the existing item.


  • Relatively easy to mould into complex shapes
  • Lightweight with good strength: weight or stiffness: weight ratios.  (Many consumers associate strength with weight which acts against plastics in some applications)
  • Can be transparent
  • Colours throughout material so scratching or chipping of the product is less apparent as there is not a different colour below the surface
  • Good chemical resistance for many plastics
  • Varied mechanical performance
  • Good thermal insulation


Copy of design services accordian 2

Answers to the following questions will aid the design process and help to ensure selection of the most appropriate material for the application:

  • Is the new part a replacement for an existing part or a completely new design?
  • If it is a replacement part can more than one existing part be incorporated into a single moulding?
  • Are there any special strength requirements?  If so:
    • Does it require impact strength?
    • Does it require strength for loading?
    • In either case, how much and is the impact/loading frequent or infrequent?
  • Is there likely to be exposure to chemicals?  If so, specify the chemicals and whether the exposure will be frequent or infrequent.
  • Is there likely to be exposure to UV light?
  • Will the part be exposed to extreme temperatures?  If so, specify maximum/minimum temperatures and whether exposure will be frequent or infrequent.
  • What is the life expectancy of the part?
  • Are there any specific aesthetic requirements?
  • What colour(s) are required?
  • Is the part assembled with other parts?  If so:
    • What type of joint is required?
    • Are the joints permanent or will there be a requirement for disassembly?
    • If disassembly is required will this be frequent or infrequent?Is there a requirement for the part to be recycled?
  • What are the anticipated quantities?
  • Is there a requirement for the part to be recycled?
  • What are the anticipated annual quantities?

Free design guide

Rutland Plastics has produced a free Design Guide to help you with all aspects of designing for plastic injection moulding.
Download free guide