Molding – Understanding the Difference Between Injection and Cast

Your project is unique to your needs and determining which process to use comes down to a few key differences in the production processes between urethane cast molding and injection molding.

First, let’s consider the similarities: Both processes allow for a multitude of colors, soft or rigid durometeres and the ability to “wrap” or cast around other materials. They both are also available as MR, UL, and FDA approved materials.

Now the differences:

1. Costs per unit are lower with injection molding due to the “hands off” nature of the process and high volumes. Hundreds of items are molded in a workday as opposed to a handful. Although tooling costs are higher in injection molding (hundreds to thousands of dollars), this is offset by the higher number of items output. Urethane molding is a much more labor intensive process so the cost per unit is higher but for smaller volumes or prototypes it’s usually the best option.

2. Production lead times vary from a couple of weeks to less than a month for cast and up to two months for injection molding.

3. Precision tolerance levels, while minute, are more accurate in the injection molding process than in cast. Urethane tolerances are +/-.010” for the first inch, and +/-.005” for every inch afterwards. Injection molding tolerances are +/.005” for the first inch, and +/-.002” for every inch afterwards.


Both urethane cast molding and injection molding offer excellent end results, but the choice of which method to use must be determined by understanding the number of units required, how quickly, and what tolerance is needed.

If you’re not sure which process is the most cost effective for your next application or part, give us a call.




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