Injection molding (IM) is considered a mainstream technology in the world’s manufacturing industry, and more than 30% of the world’s products are manufactured using injection molding technology. Since the equipment is expensive, it is typically used in batch production of plastic parts based on economies of scale—the more parts, the lower the unit cost. Other advantages of injection molding include high tolerances, repeatability, wide material selection, low labor costs, and standard post-processing. However, injection molding (IM) has its limitations, including its tendency to manufacture parts with relatively simple forms and geometries.
What is injection molding?
Back in 1872, brothers John and Isaiah Hyatt patented injection molding technology. However, the “golden age” of injection molding (IM) was after the mid-20th century, that is, after World War II. Due to the huge demand for low-cost, mass-produced parts, injection molding, on the one hand, can produce a large number of parts, and on the other hand, the cost of high-volume manufacturing is relatively low, so it has become a good choice.
How Injection Molding Works
Simply put, it can be thought of as using a cookie cutter to make cookies, where the molten plastic or other liquid material is the dough. You can see the detailed process in the video below: First, the material particles are melted and then pressed through a spiral barrel. Then, it is injected into a metal mold, and after cooling and solidification, the product is obtained from the mold with almost no post-processing required.
What is injection molding used for?
Injection molding (IM) technology is mainly used to manufacture plastic parts. Almost one-third of the objects you see around you today are mostly made using injection molding technology: equipment casings, boxes, office supplies, cups, etc.
Types of Injection Molding
There are many different types of injection molding, each with its pros and cons. The following are the general types:
Rotational molding
Using this technique, the material is placed in a mold and slowly rotated over a heating furnace. The material begins to melt and adhere to the inner surface of the mold, forming the object layer by layer. Rotational molding allows the fabrication of a variety of simple to complex shapes, such as industrial tanks, without the need for bonding or welding.
extrusion
In this method, molten material (usually plastic) is forced into a two-dimensional die-hole. It goes through a series of molds where it is melted to get its shape. When the product is ready, it forms a long, two-dimensional shape that can be cut into multiple parts. Metal injection molding is a metal processing process. After the blocks are formed from metal powder and binding material, they are formed and solidified using injection molding technology, and then the parts are post-processed at high temperatures. Finally, the binder is removed and the powder is sintered to obtain the product.
Reaction Injection Molding (RIM)
Using a thermoset polymer instead of plastic, after being pressed within a mold, the block is mixed with a catalyst and left to solidify. The most common reaction injection molding material is polyurethane.
Liquid Silicone Injection Molding
It is very similar to reaction injection molding (RIM): liquid silicone (rubber) is injected into the mold and solidifies. This technology can be used to evaluate different material configurations before full production.
Injection molding materials
There are thousands of materials used for injection molding, consisting primarily of various polymers and plastics (some thermoplastics and elastomers). All materials produce extremely low-viscosity melts that quickly fill complex mold cavities at low injection pressures. Combined with low injection pressure, the possibility of producing highly stressed parts is minimized. Commonly used injection molding materials include:
ABS
polyethylene
polyurethane
polycarbonate
polypropylene
Nylon (polyamide)
