ABS Injection Molding: Definition, Applications, Process, and Techniques

ABS injection molding refers to the process of injecting molten ABS plastic into a mold at high pressures and temperatures. There are many ABS injection molding applications as it is a widely used plastic and can be found in the automotive, consumer product, and construction industries to name a few.

This article will cover the definition, applications, process, and techniques involved with ABS injection molding. LegoⓇ is one of the most recognizable products made from ABS and is shown in Figure 1 below:

What is ABS Injection Molding?

ABS (Acrylonitrile Butadiene Styrene) injection molding is one of the most popular methods for manufacturing ABS plastic products. ABS is a thermoplastic polymer that is durable and easy to work with. Injection molding is a process that involves injecting molten ABS into a mold cavity. The ABS part cools and is ejected. Injection molding is fast and efficient, and it can be used to create a wide variety of ABS products. Very few manufacturing technologies can achieve the same scale at the low costs offered by injection molding. 

For more information, see our guide on Plastic Injection Molding.

Why is ABS Used in Injection Molding?

ABS is widely used in injection molding because of its desirable properties. These include high strength, low melting temperature, recyclability, and good resistance to chemicals and heat. It is also relatively easy to process and can be molded into a variety of shapes and sizes. As a result, ABS is an ideal choice for applications in which strength and durability are required, such as: automobile parts, household appliances, tools, and medical devices. Overall, ABS is a versatile and popular choice for injection molding.

For more information, see our guide on ABS Plastic.

What Are the Applications of ABS Injection Molding?

ABS is used in many different industries. Some common industries and their relevant applications are listed below.

1. Consumer Products: ABS is widely used in the consumer industry. Typical products include LegoⓇ bricks and computer keyboard keys. ABS produces a smooth, shiny surface that is impervious to dirt impregnation. ABS will react well to the inclusion of pigments and can be easily painted or even electroplated if desired.
2. Construction Industry: ABS is used for housings on many power tools due to its durability. Power outlet fittings are also often manufactured from ABS.
3. Automotive industry: ABS is typically used for parts such as: dashboards, seat belt parts, door trim, and bumpers due to its low weight, durability, and strength.

What is the ABS Injection Molding Process?

The ABS injection molding process is the same as the process involved with injection molding in most other thermoplastics. The ABS injection molding process begins with pellets of ABS resin being fed into a hopper. The pellets are then melted and injected into a mold under high pressure. Once the molten ABS has cooled and solidified, the part is ejected from the mold and the process is repeated. The ABS injection molding process is relatively simple and efficient, making it ideal for high-volume production runs. ABS also has good dimensional stability and can be easily machined or drilled after molding.

What Are the ABS Injection Molding Techniques?

Listed below are some key techniques used for injection molding ABS:

1. Thin-Walled Parts: ABS has a relatively high viscosity, and as such injection pressures must be increased for thin-walled parts. Beyond its plasticizing temperature, the viscosity of ABS will increase with increased temperature. As such, only pressure can be increased for thin-walled parts. Molds must be specifically designed to handle these increased pressures.
2. Large Hollow Parts: Injection molding large, thin, or hollow parts is challenging. It may be beneficial to make use of water-assisted or gas-assisted injection molding which allows for the manufacture of large, thin-walled, or hollow parts. This technique uses high-pressure water or gas to press the molten plastic against the sides of the mold to produce uniform thickness and smooth internal volumes. 
3. Thick-Walled Parts: Manufacturing thick-walled parts with standard injection molding techniques can produce sink marks on the part. One method of getting around this is to make use of compression injection molding, which essentially deposits a specific amount of molten plastic into a mold to produce the final part. This technique also reduces internal stresses typical with injection molding. Alternatively, sink marks can be managed with thinner (or more uniform) mold walls or increased thermal transfer capacity in the mold.
4. Multi Material: If multi-material components are required, then techniques such as insert molding or overmolding can be used. ABS is often used for industrial tooling like cordless drills, which have their handles overmolded onto the ABS to improve tool grip. 

What Are the Advantages of ABS Injection Molding?

The advantages of ABS injection molding are:

1. High Productivity - Efficiency

Injection molding is a highly efficient and productive manufacturing technology and is the preferred method of manufacturing ABS parts. The process creates limited waste and can produce large volumes of parts with limited human interaction.

2. Design of Complex Parts

Injection molding can produce multi-featured, complex components that can include metal inserts or overmolded soft-grip handholds. The complexity of the parts is only limited by a set of well-established design for manufacturing (DFM) guidelines developed specifically for injection molding. 

3. Increased Strength

ABS is a strong, lightweight thermoplastic that is widely used in a number of industries due to these properties. As such, injection molding in ABS is ideal for applications that require increased durability and overall mechanical strength.

4. Flexibility of Color and Material

ABS is easily colored with a wide range of colors; this is evident with LegoⓇ bricks which are made from ABS. It must be noted however that ABS has poor weathering resistance and can be degraded by UV light and prolonged outdoor exposure. Fortunately, ABS can be painted and even electroplated with metal to improve its environmental resistance. 

5. Decreased Waste

Injection molding is inherently low-wastage production technology due to the large production volumes that injection molding was designed for. When millions of parts are made per year, any amount of wastage adds up to a significant cost over time. The only wastage is the material in the sprue, runners, and the flashing between mold halves. 

6. Low Cost of Labor

Due to the highly automated nature of injection molding, very limited human intervention is required. Reduced human intervention results in reduced labor costs. This reduced labor cost ultimately results in a low cost per part. 

What Are the Disadvantages of ABS Injection Molding?

The disadvantages of ABS injection molding are listed below:

1. High Tooling Costs and Extended Lead Times for Setup

Injection molding requires the design and manufacture of molds whose cost and manufacturing time increase with part complexity. As such, the initial investment in injection molding is high, and the cost must be weighed against the expected production volumes. Lower production volumes may not be economically viable. 

2. Partial Design Limitations

Injection molded part designs are limited by a set of rules that were painstakingly developed to improve injection molded part quality and consistency. These rules define wall thickness limitations, the location of reinforcing features like ribs, and the optimal hole location and size. As such, designs must be made to follow these rules to ensure optimal results. In some cases, these rules can make certain designs unfeasible.

3. Costly Small-Run Parts Are a Possibility

Due to the high initial investment cost when injection molding, there is a minimum part quantity required to break even on the costs expended on the design and manufacture of the mold. This break-even point is also dependent on the intended sale price of the final product. If the sale price is high—due to the part being used for a specialized application—it may be possible to have small-run manufacturing. However, low-cost parts require high volumes in the 10s of thousands to be cost-effective. 

What Are the Common Problems in ABS Injection Molding?

While ABS is one of the most widely used plastics for injection molding, there are still problems that present themselves when using this material, as listed below:

1. Viscosity: Unlike most other amorphous plastics, the viscosity of ABS increases when heated past its plasticizing temperature. This increase in viscosity means that the melt temperature of ABS must be kept at or below this temperature for optimal results as increased viscosity will make it more difficult to mold thin-walled components. 
2. Thermal Degradation: Apart from an unfavorable increase in viscosity with increased temperature, ABS tends to chemically degrade if kept at temperatures far above its plasticizing temperature.
3. Warping: Warping occurs when ABS plastic cools unevenly, resulting in distortion. Warping can be prevented by using a mold with evenly spaced cooling channels. Ejecting parts from the mold before they have had a chance to cool sufficiently can also result in warping.
4. Sink Marks: Sink marks can occur when the ABS plastic shrinks unevenly during cooling, causing sunken areas on the surface of the part. Other potential causes can be insufficient injection pressure or excessive temperature. Sink marks can be prevented by using a mold with high gate pressure, designing a part with uniform outer walls, and limiting internal strengthening ribs to around 50% of the thickness of the outer walls.

What Material is Used for Injection Molding?

Injection molding can be used with almost any thermoplastic. Thermoplastics can be filled with reinforcing additives like glass or carbon fiber fillers. Metals can also be injected if combined with a plastic filler material to allow the metal powder to flow through the mold. However, additional sintering is needed for metal injection molding.

For more information, see our guide on the 15 Most Common Plastic Injection Molding.

Summary

This article presented ABS injection molding, explained what it is, and discussed its different techniques. To learn more about ABS injection molding, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities, including injection molding and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

Copyright and Trademark Notice

1. LegoⓇ is a registered trademark for LEGO JURIS A/S CORPORATION DENMARK KOLDINGVEJ.

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