Custom injection molding is among the least expensive processes available for producing large quantities of parts. Due to the initial investment of the mold however, there is a return on investment that needs to be considered when making the decision on what type of process to use.
If you anticipate needing tens or perhaps even hundreds of parts per year, injection molding may not be for you. You should consider other processes such as fabrication, polymer casting, of vacuum/thermo forming, depending on the geometry of the part.
If you do anticipate quantities that would justify the initial investment of an injection mold, you must also consider the shape of the part when determining what process to use. Below is a rundown of various processes and the geometry that best suits them:
Custom Injection Molding: A part with relatively consistent wall thickness, typically not thicker than 1/8″, and no internal voids.
Blow Molding: Think of a balloon being dangled inside of a cavity, injected with air, and formed in the shape of the cavity. Bottles, Jugs, Balls. Anything small with an internal void.
Vacuum (Thermal) Forming: Somewhat interchangeable with injection molding, this process starts with a sheet of heated plastic, and is vacuumed onto a form and cooled to create the desired shape. Packaging clamshells, lids, trays, blisters, as well as vehicle door and dash panels, refrigerator liners, utility vehicle beds, and plastic pallets.
Rotational Molding: Larger parts with internal voids. A slow but relatively efficient way to manufacture smaller quantities of large parts such as gas cans, oil tanks, bins and refuse containers, boat hulls.
Which ever process you find you need, it’s always important to crunch the numbers and find the return on investment (ROI) that works for your budget. As a rule of thumb, investors will look for a maximum of a 2-3 year time frame to recoup their money when investing in custom injection molding or any process of manufacturing.