Do you know which technology is mostly used for mass production of identical plastic parts with good tolerance? So, Injection molding is the best technology for mass production. Injection molding is so popular because of the low cost per unit when manufacturing high volumes.

What is Injection molding? 

Injection molding is the best technology for the mass-production of identical plastic parts with good tolerances. In Injection Molding process polymer granules are first melted and then injected under pressure into a mold, where the liquid plastic cools and solidifies. The materials used in Injection Molding are thermoplastic polymers that can be colored or filled with other additives.

Majorly every plastic part around you was manufactured using injection molding: from car parts, to electronic enclosures, and to kitchen appliances etc. 

Materials used for injection molding: 

Majorly all thermoplastics can be injection molded. Some liquid silicones are also compatible with this process.

To modify their physical properties they can also be reinforced with fibers, rubber, minerals or flame retardant agents.

1. Polypropylene (PP): This plastic is the most common injection molding plastic and very good material for chemical resistance. Food-safe grades are also available. This material is not suitable for mechanical applications.
2. ABS: This material is common thermoplastic with high impact resistance with low-cost & low density. It is vulnerable to solvents.
3. Polyethylene (PE): This material is a very lightweight material.  Lightweight thermoplastic with good impact strength & weather resistance. This material is suitable for outdoor applications
4. Polystyrene (PS): This material cost is very low and available with food safe grades. Not suitable for mechanical applications.
5. Polyurethane (PU): Thermoplastic with high impact strength and good mechanical properties & hardness. This material is suitable for molding parts with thick walls.
6. Nylon (PA 6): Engineering thermoplastic with excellent mechanical properties and high chemical & abrasion resistance. Susceptible to moisture.
7. Polycarbonate (PC): PC has the highest impact strength then all other plastic with high thermal resistance, weather resistance & toughness. It can be colored or transparent.
8. PC/ ABS: This material is a blend of two thermoplastics resulting in high impact strength, excellent thermal stability, and high stiffness. 
9. POM ( Aceral/ Delrin): Engineering thermoplastic with high strength, stiffness & moisture resistance and self-lubricating properties. 
10. PEEK: This is a high-performance engineering thermoplastic with excellent strength and thermal & chemical resistance. This is majorly used to replace metal parts.
11. Silicon Rubber: Thermoset with excellent heat & chemical resistance and customizable shore hardness. Food-safe and medical grade available.

Injection Molding Surface Finishes: 

1. Glossy Finish:

In this finish the mold is first smoothed and then polished with a diamond buff, and it results in the mirror-like finish.  It is suitable for parts that require the smoothest surface finish for functional purpose.

2. Matte Finish:

In matte finish the mold is smoothed using fine stone powder to remove all the machine marks. It is suitable for parts with low visual appearance requirements but the machine marks are not acceptable.

3. Semi Gloss Finish:

To get the fine surface finish, the mold is smoothed with fine grit sandpaper and it is suitable for parts that require good visual appearance but not a high glossy look.

4. Textured Finish:

In this finish,  fine stone powder is used to smoothen the mold and then sandblasted. It is suitable for the parts that require a satin and dull textured surface finish.

5. As machined Finish: 

The mold is finished to the machinist’s discretion and it is more suitable for industrial or hidden components.

Application of Injection Molding: 

1. Automotive:

Most of the plastic components that are used in the interior of  a car are injection molded. The three most commonly used injection molding materials in the automotive industry are Polypropylene for non-critical parts, PVC for its good weather resistance and ABS for its high impact strength. Mostly the plastic parts of a car like bumpers, interior body parts and dashboards are made from one of these materials. 

2. Consumer Electronics:

Almost every mass produced consumer electronics device’s enclosures were made from the process of injection molding. For their excellent impact resistance and good electrical insulation, ABS and Polystyrene materials are preferred. 

3. Healthcare:

One of the most popular materials in the medical industry is medical grade silicone. Silicone belongs to a thermoset group but still it requires special machinery and process control to increase the cost. Many sterilizable and biocompatible materials are available for injection molding.

There are several reasons to choose injection molding technology. Injection molding has many applications for manufacturing, especially for producing high volume parts. While the tooling and molding can be expensive. But overall production cost will be less. Providing the ability to produce near-identical parts, injection molding is used for parts in a variety of material types.

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