Plastic objects are of course found everywhere in our daily lives, but many people don’t know that there are different ways to form it for commercial or industrial use. Here are the seven most common methods, and what you need to know to decide which one is best for your next project.

Plastic Injection Molding
Plastic injection molding accounts for about 80% of the durable plastic items we find every day. Injection molding uses a mold or die made from aluminum or steel. The mold consists of a core side and a cavity side that is placed into a plastic injection molding machine. This machine heats the raw plastic resin pellets until they’re molten, injects them into the empty cavity of the mold under great pressure, and then opens to eject the finished part.

The advantage of PIM is that millions of identical parts can be made quickly, with excellent surface finish and at low cost. Molds however can be expensive and complex, depending on the part geometry. Careful engineering design of the mold is required to prevent defects and optimize part quality and processing speed.

Rotational (Roto) Molding
Rotational molding also uses a core and cavity mold tool, but the manufacturing process is quite different.

Plastic powder is poured into the cavity of the mold, and the mold placed in an oven. While being heated, the mold is slowly rotated on two axes. Gravity is used to stick the plastic to the tool walls and build up the correct thickness.

Then, the mold is removed from the oven and slowly cooled to prevent warpage. Full cooling can take several minutes, after which the tool is opened and the part removed for the next cycle.

Rotational molding is ideal for making large, hollow or concave shapes, often for outdoor use like canoes and tubs. The finished parts are stress-free and have no seams so they’re strong, and the tools are relatively simple and inexpensive to make.The downside is that tools don’t last more than a few thousand cycles before they need to be replaced, and the part finish quality is average at best so it’s not suited for precision forming.

Read more: The Plastic Forming & Manufacturing Process: Top 7 Techniques