ABS Injection Molding: A Guide to Material, Process, and Design

ABS is one of the most common thermoplastics used in manufacturing, offering a good balance of toughness, impact resistance, and affordability. Though ABS can be processed in several ways, including extrusion-style 3D printing, plastic injection molding of ABS is a go-to manufacturing process due to the relatively low melting point and good flow characteristics of the plastic.

Injection molded ABS parts can be found everywhere. Automotive dashboards, housings for household appliances, and even LEGO bricks are just some of the everyday items made using ABS injection molding, benefitting from the low-cost material’s desirable mechanical properties. Further applications can be found across a diverse range of industries, from healthcare to construction.

This article goes over the basics of ABS injection molding, looking at process parameters, material and filler options, surface finishing techniques, and more, drawing on our years of experience providing injection molding services to satisfied customers.

What is ABS?

Acrylonitrile butadiene styrene (ABS), first marketed in 1954 by the Borg-Warner Corporation, is a common thermoplastic polymer known for its impact resistance, toughness, and rigidity. It is made by polymerizing styrene and acrylonitrile in the presence of polybutadiene.

The three components of ABS contribute different material properties:

• Acrylonitrilegives the material a level of chemical resistance and heat stability.
• Butadiene creates toughness and impact resistance.
• Styrene provides rigidity and glossiness.

As a whole, the material is relatively strong, durable, and lightweight. And because it is a thermoplastic, it can be melted into shape and then remelted over and over without significant degradation. This makes it suitable for injection molding and other processes like blow molding, 3D printing, and material extrusion.

For injection molding, ABS is supplied in the form of plastic pellets. These are small, uniform granules made by extruding the material into long strands and then cutting it into smaller pieces. ABS pellets cost just a few dollars per kilogram—far less than other material forms like filament for 3D printing—and can be easily deposited into the hopper of the injection molding machine for melting.

The ABS Injection Molding Process

ABS injection molding is a fast and economical manufacturing process for making plastic parts in large quantities. Since injection molding machines are large and expensive pieces of equipment, the process is typically carried out by a dedicated manufacturer.

The process begins with the acquisition of ABS pellets, which are fed into the hopper of the injection molding machine. A reciprocal screw forces the thermoplastic resin pellets into a heated barrel, where they are melted at a temperature of around 180–240 °C. The molten ABS is then injected at pressure into the mold cavity, giving the material its shape.

The molten ABS cools and solidifies within the mold. Because the plastic has good flow properties, it can usually achieve fine details without issue.This makes ABS injection molding highly suitable for producing complex parts that require precise geometries and detailed surface textures. After solidification, the mold is opened and the part ejected using ejector pins. Depending on the size of the mold and other factors, overall injection molding cycle times can range from about 10 seconds to as long as two minutes.

Pros and Cons of ABS Injection Molding

ABS is a popular thermoplastic for injection molding, being fairly easy to work with and offering good mechanical properties. The only notable disadvantages of ABS injection molding relate to the material itself, not to the combination of material and process.

Advantages

• Good flow properties
• Good mechanical properties such as strength and toughness
• Fine features are possible as the material can easily fill the corners of the mold cavity
• Low-cost material
• Does not require particularly high temperatures
• Easy to post-process

Disadvantages

• Fairly low heat resistance
• Fairly low UV resistance

ABS Injection Molding Parameters

Compared to other thermoplastics, ABS injection molding parameters sit in the mid-range, with moderate temperatures and pressures, making the material easier to process than materials like polycarbonate (PC) or reinforced nylons. However, the parameters can vary depending on the ABS grade, part geometry, and other factors.

When it comes to the ABS injection molding temperature, note that the actual melt temperature of ABS will be slightly higher than the barrel temperature. The melt temperature can be measured with a pyrometer.

• Barrel temperature: 180–240 °C, with general-purpose ABS generally requiring slightly lower temperatures (180–230 °C) than heat-resistant ABS (190–240 °C). Flame-retardant grades may require a slightly lower temperature. The temperature will be highest at the front and lowest at the rear of the barrel.
• Mold temperature: 50–80 °C, striking a balance between the higher temperatures required for a good surface finish and the lower temperatures that can produce faster cycle times. Mold temperature controlis a good way to produce parts in the manner desired.
• Injection pressure: 10,000–20,000psi, with higher pressures required for heat-resistant grades or parts with thin walls and fine features.
• Injection rate: Slow to moderate.
• Moisture control: ABS pellets are hygroscopic and should be stored in a dry place. To prevent issues during molding, pellets can be dried for several hours at a temperature of around 80 °C.

ABS Materials for Injection Molding

ABS is available in a range of grades and varieties for injection molding, with different molecular structures and additives suiting different applications. In some cases, recycled ABS may be used.

• General-purpose ABS offers a balance of toughness, rigidity, and ease of processing.
• High-impact ABS contains extra butadiene rubber, providing improved impact resistance for parts that undergo high levels of stress.
• High-heat ABS has extra acrylonitrile, enhancing thermal stability, making it useful in industries like automotive.
• Flame-retardant ABS uses additives to decrease flammability and is often used in electrical devices.
• Transparent ABS is designed to provide a higher level of transparency for use in fields like healthcare.
• Metal plating ABS is a modified grade designed to adhere well to metal coatings, useful for items like shower heads.
• Healthcare-grade ABS provides biocompatibility and can be sterilized; such materials may have approval from agencies such as the US Food and Drug Administration.
• Recycled ABS is made principally from recycled ABS and often performs to a comparable level to virgin ABS.

Some of the major chemical producers of ABS injection molding pellets include LG Chem, SABIC, and the RTP Company.

Some ABS pellets are mixed with reinforcing agents. These can include glass fibers, which add stiffness and dimensional stability, and minerals such as calcium carbonate, which add rigidity and heat resistance. Flame-retardant ABS grades can be made with the addition of halogenated compounds, phosphorus-based chemicals, or inorganic compounds like aluminum hydroxide.

Common ABS blends include PC/ABS, which has a higher level of heat resistance than pure ABS, and PVC/ABS, which offers improved chemical resistance. ABS/Nylon blends can provide greater wear resistance than pure ABS.

ABS pellets can also be mixed with heat-stable pigments during molding to produce evenly colored batches of parts. Masterbatch concentrates produce better results than dry pigments, though both can be used.

Mold Materials for ABS

Injection molds for high-volume ABS production are usually made from hardened tool steels such as P20, H13, or S7. Shorter runs are suited to low-cost aluminum molds, though they wear faster than steel ones. Due to the good flow properties of ABS, molds can be relatively complex and contain fine features, allowing the production of complex parts with consistent dimensional accuracy.

Surface Finishing for ABS Moldings

After ejection, ABS moldings can be improved with post-processings steps, starting with trimming and deflashing to remove excess material before proceeding to finishing treatments to improve the surface finish quality of parts.

Different surface finishing methods can be used to achieve the desired surface roughness of ABS parts, with a diamond buff ideal for gloss and dry blasting preferred for rough textures. For large or medium-size batches of parts, adding texture to the metal mold is typically more cost-effective than post-processing the individual plastic moldings, as this only needs to be performed once.

ABS Injection Molding Design Guide

Engineers developing part designs for ABS injection molding must consider the limitations of the injection molding process and, to a lesser extent, the specific capabilities of ABS plastic within the context of the molding process. Design for Manufacturing (DFM) principles for molded ABS include wall thickness constraints and draft angles.

Design Rules

Wall Thickness

1.1–3.5 mm

All injection molded parts have a recommended wall thickness range. Too thin and the mold will be hard to fill and the part too fragile; too thick and the material may cool at an uneven rate throughout the mold cavity. ABS requires slightly thicker walls than other plastics like polyester, acetal, and acrylic, but less thick than polyurethane.

Draft Angle

0.5–1°

A draft angle is incorporated into injection molding designs so that parts can be ejected easily from the mold. As draft is essential to all molded plastic parts, the recommended angle here is not specific to ABS. The exception is parts with textured surfaces; since these introduce greater friction with the interior of the mold, a draft angle of 2–3° is recommended.

Radii

0.5–1 mm or 1/2 wall thickness

Sharp corners are not recommended for any injection molded part as they can cause stress and flow issues, and ABS is particularly sensitive due to its brittle nature. Instead, a rounded internal and external corner facilitates effective molding and ejection. The minimum radius should be about a quarter of the wall thickness, though increasing that value to half the wall thickness will provide superior strength.

Ribs

Rib height up to 3x wall thickness; rib thickness 1/2 wall thickness

Ribs are thin raised sections running perpendicular to the wall of a molding. They are used to increase strength without having to make the walls thicker, which typically requires more material and can lead to separate issues.

Bosses

Base thickness 1/2 wall thickness

Bosses are raised cylindrical features in which a fastener like a screw can be placed without damaging the part. For ABS parts, the maximum base thickness of the boss should be no more than about half of the part’s wall thickness.

Tolerance

0.1–0.3 mm

For most ABS moldings, tolerances should be no finer than about 0.1 mm. However, for very small or precise parts, it may be possible to specify a tolerance of 0.05 mm. In general, it is good practice to only call out tight tolerances where strictly necessary (for interlocking parts, for example) to avoid excess mold making costs.

Gates

Gates allow material to enter the mold cavity. As with other plastics, gates are best placed at thick sections of the part. Edge gates, pin gates, and submarine gates are common.

Vents

0.02–0.05 mm

Venting of molds helps to prevent gas traps—a cause of burns and voids. These must be fairly small, as ABS has good flow properties and can easily escape larger holes.

Helpful Software Features

Many CAD tools have injection molding–specific features to make it easier to design your ABS parts. These features may include:

• DFM analysis: Checks for wall thickness, draft angles, undercuts, and gate placement to ensure that the proposed design is moldable.
• Process analysis: Certain software packages can offer advanced features like mold flow analysis, simulating how the molten ABS will behave in the proposed mold cavity, as well as other features like shrinkage prediction and finite element analysis (FEA).
• Mold creation: Software may enable the user to automatically generate a two-part mold based on the 3D model of the part, complete with ejector pin placement and other features.
• CAM integration: Some platforms integrate with CAM software that controls the manufacturing equipment, though this is more relevant to manufacturers than designers.

Applications of ABS Injection Molding

As a highly versatile thermoplastic, ABS injection molding is deployed across a number of industries to make a wide range of products, from toys to car parts and construction materials. Typical applications include automotive components, consumer electronics housings, healthcare devices, and industrial parts. Here we look at some example ABS molded parts, sorted by industry.

• Automotive: Molded ABS parts are found in many vehicles, particularly for interior trim. Carmakers like Ford and Toyota are known to use ABS for parts like dashboard panels, glove compartments, and door trims, where parts are not subject to intense heat but still require a high level of toughness and dimensional stability, while BMW has used ABS/PC blends for glove compartments. Between 1968 and 1988, Citroen produced a highly unusual utility vehicle called the Mehari which featured colorful ABS exterior bodywork. One advantage of ABS injection molding in automotive is the ease of coloring, finishing, and texturing parts, particularly for aesthetic interior components.
• Consumer Electronics: Electronics companies often deploy injection molding of ABS for durable housings. For example, Dell and HP have used ABS/PC blends for laptop and computer monitor casings, combining scratch resistance with heat tolerance, while Canon and Epson are known to rely on ABS for printer housings due to its rigidity. Another popular consumer electronics product to feature an ABS housing is the PlayStation 4. (The newer PlayStation 5 uses a mix of ABS and polycarbonate.) Housings are suited to the injection molding process as they typically have fairly thin walls.
• Consumer Goods: Outside of electronics, many consumer goods like toys (including LEGO bricks), sporting equipment like plastic kayaks, and plastic musical instruments like recorders are made from molded ABS. Housings for kitchen appliances and vacuum cleaners are also good candidates for ABS materials. Vacuum company Dyson is known to use the material for some of its products, as the heat generated by a vacuum is well below the heat deflection temperature of ABS (around 80 °C).
• Healthcare: ABS is popular in healthcare for parts like medical housings and delivery systems, as it can be sterilized—though not through autoclaving, as the temperatures involved are too high. Philips Healthcare uses ABS for diagnostic device casings, as seen on the IntraSight unit. 3M employs ABS for inhalers and respiratory devices, taking advantage of the lightweight quality of the material. Molded ABS can also be used for drug delivery systems.
• Construction: In construction and various industrial fields, heat-resistant and flame-retardant grades of ABS may be used for parts like wall plates, electrical switches, and housings. ABS pipes and fittings are also common. In terms of industrial equipment, Stanley Black & Decker is one notable company to incorporatemolded ABS in tool housings and power equipment casings.

Injection Molding Companies

Engineers and product designers typically use third-party injection molding companies to manufacture parts or prototypes, given the size and cost of injection molding machinery. These companies are also typically specialists in mold making; product designers may not need expert knowledge of mold making to realize their 3D designs.

Injection molding companies typically operate a fleet of machines ranging in clamping forces, depending on the size of mold required.

Companies like 3ERP are able to realize a range of ABS injection molding projects, from prototypes to mass production. Our professional expertise allows us to handle DFM, mold making, production, and surface finishing, ensuring that final products meet the highest quality and precision standards..

Request a quote on your next project to see how we can help.

Frequently Asked Questions (FAQ)

How long do injection molds last for ABS?

When molding an easily processable material like ABS, molds can last a long time. A well-made steel mold may last hundreds of thousands or even a million cycles, while a low-cost aluminum mold will typically endure tens of thousands of cycles—ideal for low-volume molding.

How much on average for ABS injection molding?

As with all injection molding materials, the biggest ABS injection molding cost is the making of the mold. Simple aluminum molds cost a few thousand dollars, while steel molds generally cost upwards of $10,000—or far more for complex, multi-part molds. However, the cost per ABS injection is very low. Expect to pay more per part for short runs than mass production.

How to calculate shrinkage in ABS for injection molding?

ABS mold shrinkage is about 0.4–0.7%. Mold designers must apply this factor to cavity dimensions to ensure that the final moldings are not undersized.

Why do ABS pellets need to be dry?

ABS is a hygroscopic material, meaning it absorbs moisture from the air. If the ABS pellets have absorbed excess water before injection molding, vaporized water leads to problems like splay marks and voids. To prevent such issues, pellets can be dried at a moderate temperature (around 80 °C) before use.

How do you prevent warped ABS moldings?

Injection molding ABS is not especially difficult, but warping can be minimized by maintaining a consistent mold temperature, using uniform wall thickness, and cooling the finished moldings slowly.

Can molded ABS parts be used outdoors?

ABS is a reasonably good material for outdoor use, offering some degree of weather resistance. However, for highly demanding outdoor applications, a weather-resistant ABS grade may be used. Such materials are engineered to provide superior UV resistance and, therefore, will not degrade over time when exposed to sunlight.

Why choose ABS injection molding over ABS 3D printing?

Both technologies have their advantages. Extrusion-style FDM 3D printing is an excellent choice for making one-off rapid prototypes, and desktop 3D printers can be operated in non-industrial environments. On the other hand, injection molding is the better choice for making thin but strong parts with an excellent surface finish. In large quantities, injection molding is also significantly cheaper than 3D printing.

What about ABS blow molding?

Blow molding is a process used to make thin, simple parts like plastic bottles, using a preform within a mold that is inflated with air until it sticks to the walls of the mold. ABS can be used during blow molding and is suited to parts like electronics housings, pipes, and hosings. However, it lacks the transparency of other common blow molding thermoplastics and is more expensive than materials like high-density polyethylene (HDPE) and polypropylene (PP).

Are ABS moldings toxic?

Molded ABS is stable and typically considered non-toxic. However, it can release toxic fumes if burned. Uncoated ABS is also recyclable, and recycled ABS can be reused during the injection molding process.