Injection Molding

In gas-assisted injection molding, a pressurized inert gas (typically nitrogen gas) is injected into the mold right after the molten plastic, forcing the material into the mold walls and leaving a cavity where the gas once was. This gas allows for built-in hollow sections in a mold, but it also promotes cooling and prevents distortions by evening out wall thicknesses, especially in thick walls in an injection mold. Uses for gas-assisted injection molding include material reduction in large parts, hollow products, and other porous designs.
The benefits of this type of plastic injection molding revolve around its ability to reduce material usage and cooling time. The gas pocket will fill thicker sections, resulting in less warping and faster cooling times as the molten plastic flows towards the colder mold walls. The pressure also causes less shrinkage to occur when cooling and minimizes the chance of sink marks from appearing. Gas-assisted injection molding also requires lower clamping forces and overall residual stresses, leading to a more stable injection molding process.
Gas-assisted injection molding does not come without its limitations; it can only really be applied to single-cavity molds, otherwise, the gas channeling becomes too complicated (this is exacerbated if the multiple cavities are unique from each other). Also, some materials may react with the gas or become foggy due to the nature of the gas interfacing with the material's surface. Clear plastics are especially prone to this effect, and so are not usually capable of being gas-assisted injection molded.

In thin wall molding, parts maximize material and cost savings by utilizing thin wall thicknesses relative to the part’s overall size. Thin wall molding allows for 1-2mm thick walls that both decrease cycle time but increase needed injection pressure. Specialized thin wall injection molding machines have the highest precision specifications among injection molding machines, as thin-wall molding is often used for small parts. Uses for thin-wall injection molding are small, tight-tolerance applications like electronic parts, enclosures, medical device components, tubing, etc.
The advantages of thin-wall injection molding, as previously mentioned, are cost savings and speed. Thin wall plastic parts require less material, resulting in lower material costs and overall resource consumption when compared to traditional injection molding methods. Cycle time is also drastically reduced, and parts result in fewer emissions from shipping due to their decreased weight. A thin-wall injection mold can also be made of recyclable plastics, and thin-wall parts reduce weight (and therefore emissions) in fuel-based applications like heavy equipment and automotive vehicles.
The disadvantages of thin-wall injection molding are that thin wall injection molds and molding machines are more expensive, and their operation requires trained molding technicians. There is little room for error because thin wall injection molds require extreme precision and low tolerances. Technicians and designers must scour the project for sources of defects and potential optimizations, leading to longer lead times on molds and the overall project. Thin walls also require higher pressures, which means machines must be fitted with stress-resistant components that need to run smoothly over thousands and thousands of cycles.

Liquid silicone injection molding allows for the mass production of silicone rubber products. This type of injection molding is distinct from others in that silicone rubber is technically a thermoset rubber, therefore it will require vulcanization (the process that provides rubber its beneficial material properties like durability and flexibility). Opposite to typical injection molding where molten plastic is injected into a colder mold, cold silicone rubber is injected into a heated mold cavity and vulcanized. This injection molding technology requires specialized equipment such as mixers, metering units, perfectly sealed molds, and other components. Uses include products for sealing applications, connectors, over-molding for other plastic products, infant products, biocompatible medical products, baking equipment, insulating products, and more.
Liquid silicone injection molding has several unique advantages. The material does not require any melting and can be kept in its liquid form, ready to use. Silicone is generally quick to solidify and produces little to no burrs/waste if the machine is engineered correctly. This injection molding technology typically automates the injection process to reduce operator errors and offers a lower risk process as at no point is the material hot except inside the mold. Silicone products are one of the only biocompatible materials and are impressively resistant to chemicals, temperature, and electricity, making them a unique offering from an otherwise thermoplastic-laden injection molding selection.
Liquid silicone injection molding is not perfect; the vulcanization of silicone material is an irreversible process, meaning once a part is set, there is no going back. There is no recycling of silicone products, and if a mistake is made, the material cannot be turned back into stock as with other types of injection molding. Also, liquid silicone requires its own unique equipment that may be more difficult to procure and regularly maintain.

Structural foam molding allows for the mass-production of very large parts, thanks to the introduction of a composite material formed from a polymer mixed with an inert gas (such as nitrogen) or a chemical blowing agent. Material is kept separate in liquid state and then mixed inside the mold. The gas/ chemical blower is then added to the mixture, causing a change in the chemical reaction that results in the formation of a low-density, rapid expansion of foam. As the foam expands and cures, the interior retains its high porosity core while the surface interface between the foam and the mold collapses, forming a high-density protective skin on the outside of the part. The resulting injection mold is a lightweight, flexible, and strong foam product. Uses for structural foam molding include car roofs, housings for medical equipment, skis, interior and exterior automotive parts, and other large parts.
The advantages of structural foam injection molding lie in its ability to make large, lightweight, strong, and cost-effective parts. Structural foam parts can expand to the size of car roofs and other large products and use less material thanks to their inherent porosity. Also, this porous nature contributes to weight reduction with no tradeoff for strength; structural foam parts are strong, durable, and up to 8 times stiffer than solid polymers. Structural foam injection molding is easy to mold, as it easily conquers variable thickness walls, experiences less stress during the process, is resistant to warping, and has a lower incidence of damaging molds and machines. Structural foam parts are also quick to produce, easily painted, and are largely unaffected by temperature differentials.
The disadvantages of structural foam molding are mainly a result of the foam material, as surface finishes are rough, wall thicknesses cannot be under ¼ inch thick, and generally require more post-processing than other types of injection molding. Also, structural foam molding has lower production speeds than other injection molding techniques.

Probably the newest and most unique type of injection molding, metal injection molding allows for the production of injection-molded metal products. In the process, metal powder and binder are mixed and granulated. This so-called “feedstock” is then shot into an injection unit, where the raw product is molded. After molding, the part is cleaned in a solvent and thermally debonded of its binder material, leaving behind a fully metal (yet still porous) product. The debonded product is further strengthened in a sintering oven where metal particles coalesce into a solid matrix (typically under vacuum to reach high solid density), and the part is then ready for additional post-processing procedures like finishing, heat treatment, etc. This process is used to mass-produce small (<100g) metal components in a single step such as hand tool heads, mechanical components, linkages, automotive and aerospace parts, and more.
Metal injection molding has the advantage of being able to create metal parts that were previously impossible to produce using more traditional methods. Also, a high volume of parts can be molded in one step, which can rival the more common casting process for small metal parts. It also offers high fidelity features for the final product such as knurling, holes, and other fine details. Wall thicknesses can be made with narrow dimensional tolerances (hundreds of micrometers) and there is virtually no waste (a significant benefit when compared to all other metal manufacturing techniques).
The major downside to this injection molding technology is that it is somewhat expensive and limited to lower volumes and sizes of parts. The equipment needed for metal injection molding is quite expensive, and so far, the uses of metal injection molding are in high-end applications requiring incredibly complex and detailed metal parts.