There are many criteria to consider when designing injection molds. The injection molding process is complex and the molds must be designed to properly form and release quality products on a consistent basis.
Outside of general design criteria, concerning shape, form and material type, it is beneficial to understand the following items, as well:
- What is the final function for the part?
- How does it interact with adjacent items in the assembly?
- What are the stresses applied when it is in use?
- How is the material interacting with the mold within the forming process?
The function of the part should always play a role in the design of a mold. For example, the dimensional tolerances of a children’s toy are much less critical than those of a mechanical component used in a larger assembly. Designing a molding process that will hold tolerances within a few thousandths of an inch adds unnecessary costs when tolerances of hundredths of an inch will not affect the functionality of the final part.
Conversely, if fit and precision tolerances are critical, any initial savings gained through lesser tooling and shorter processing times are quickly counteracted through reject parts that do not fit within their assembly. There is no singular answer for the way a mold or process should be designed, as each aspect is highly dependent on the end use of the part.
For products with multiple variations, the component’s interact with adjacent items in the assembly should be considered.
While many people think of “plastic” as one material, in reality, different thermoplastics exhibit very different material properties when molded. Different polymers melt, flow, and cure differently depending on their material make up.
Extensive knowledge about the material being molded should be applied with developing the tooling design and molding process. Depending on the material used for the molded part, the mold will be subjected to varying stresses, depending on the pressure and amount of heat required to create the part. CAD modeling is very beneficial in this aspect, as the maximum points of stress can be determined during the design phase by simulating the molding process. By engineering the weakest points to hold up to the stresses realized during molding, we can ensure that the mold will not wear prematurely.
Another related aspect of mold reliability is the number of parts that are expected to be produced from the mold. Based on the customer’s expected product life cycle we can create the optimal mold that will produce the desired number of parts without introducing unnecessary costs. At K&B Molded, we have 50 years’ of experience in the design and fabrication of custom molds used in plastic injection molding. Throughout that time we have served a diverse customer base which includes the HVAC, marine, automotive, and other OEM industries.
For more information about avoiding injection mold design mistakes and building a durable, long lasting mold, visit our blog or download our free guide to injection molding design.