ABS is a commonly used injection molding material with three main ingredients: acrylonitrile, butadiene, and styrene. Each of these monomers imparts specific properties and provides ABS plastic with a robust combination of features.
The “A” in ABS, acrylonitrile, imparts hardness along with heat and chemical resistance.
The “B”, which stands for butadiene, provides toughness and impact resistance.
The “S”, for styrene, offers gloss, strength, and processability.
ABS is relatively inexpensive and supports color matching. It’s often used in consumer goods and electronic components, but isn’t the best choice for outdoor applications since it lacks strong resistance to sunlight and weather. However, ABS does support the use of additives that can increase its resistance to ultraviolet (UV) light.
For added strength, filler materials such as glass, nylon, acrylic, and stainless steel fibers can be added. Additives affect processing parameters, however, and different grades of ABS may contain different combinations of acrylonitrile, butadiene, and styrene. It’s important to understand the advantages and applications of ABS, but don’t stop there.
Advantages of ABS Injection Molding
If you’re wondering whether ABS plastic might be the right choice for your injection molded parts, consider some advantages of this popular polymer.
energy efficiency
versatility
dimensional stability
chemical resistance
strength and rigidity
cost
Energy Efficiency
The injection molding process is energy-intensive. Plastic pellets or granules are melted, and this molten material is injected at high pressure into a mold. ABS injection molding requires less energy because of its relatively low processing temperature, which reduces cycle times and overall costs since less heating and cooling are required.
Versatility
ABS is suitable for a wide range of applications. Examples include wall socket face guards, car bumpers, plastic tubing, kitchen utensils, consumer products, toys, and the keys on computer keyboards. ABS can also be used for outdoor applications, provided the polymer used has additives for increased resistance to sunlight.
Dimensional Stability
Injection molded parts need to be kept as close as possible to their required dimensions. With its excellent dimensional stability, ABS is a good choice for any volume of parts, but especially for high-volume runs where tooling can wear or processing conditions can change. Note that the addition of glass fiber further enhances the dimensional stability of ABS plastic.
Chemical Resistance
Injection-molded ABS is resistant to a range of corrosive chemicals such as diluted acids, alkalis, and aliphatic hydrocarbons. Examples of aliphatic hydrocarbons include propane, butane, petroleum oil, mineral oil, and diesel fuel. This makes ABS a good choice for many industrial and transportation-related applications.
Strength and Rigidity
ABS has excellent strength and rigidity. Because its material properties include impact and abrasion resistance, applications include injected molded parts subject to impact loads. However, ABS does not have good fatigue resistance, so this plastic isn’t a good choice for parts subjected to repeated load and unload cycles.
Cost
Compared to other injection molded plastics, ABS is relatively low in cost. Yet the specific cost of commodity plastics is subject to market fluctuations, and there are also cost differences between suppliers.
ABS Plastic Injection Molding Design Guidelines
All injection molded parts follow standard design guidelines to minimize defects and limit potential processing challenges, There are also some specific design considerations with ABS plastic:
wall thickness
radii
draft angle
part tolerances
Wall Thickness
Keep the wall thickness of ABS injection molded parts between 0.045 and 0.140” (1.14 to 3.56 mm). Also, remember that wall thickness needs to remain fairly constant. In other words, avoid abrupt and significant changes in the thicknesses of adjacent walls.
Radii
Avoid sharp corners to improve moldability and reduce stress concentrations — ABS is especially sensitive to sharp corners. Maintain a minimum radius equal to 25% of the wall thickness. For maximum strength, use a radius equal to 60% of the wall thickness.
Draft Angle
Like other injection molded plastics, ABS plastic molding parts need a draft angle between 0.5 and 1° to ensure that parts can be ejected easily from the mold and without damage.
Part Tolerance
Injected molded components have two main types of part tolerances: commercial and fine. For parts under 160 mm, commercial tolerances for ABS parts can range from 0.1 to 0.325 mm. Fine tolerances of 0.050 to 0.1 mm can be achieved for ABS parts equal to and smaller than 100 mm.
ABS Material Properties
Like other injection molded plastics, ABS can be characterized in terms of its typical material properties. Two physical properties, mold shrinkage and water absorption, are especially important because of their relationship to drying and processing. Mechanical properties such as tensile and flexural strength are important to consider during part design.
The table below lists the material properties of some common ABS grades:
| Polylac® (PA-765) | Cycolac™ (MG47) | Lustran® (348) | RTP (605) 30% GF | ||
| Physical | Density (g/cm3) | 1.19 | 1.04 | 1.06 | 1.27 |
| Shrinkage Rate (%) | 0.3–0.6 | 0.5–0.8 | 0.4–0.6 | 0.1–0.2 | |
| Rockwell Hardness (R) | 100 | 112 | 112 | – | |
| Mechanical | Tensile Strength at Yield (MPa) | 39 | 44 | 48.3 | 96.5 |
| Elongation (%) | 10 (Break) | 24 (Yield) | – | 1–2 (Yield) | |
| Flexural Modulus (GPa) | 1.8 | 2.3 | 2.69 | 8.27 | |
| Flexural Strength (MPa) | 55 | 70 | 75.8 | 134 | |
| Injection Molding | Drying Temperature (°C) | 87.8–93.3 | 80–95 | 79 | 82.2 |
| Drying Time (hrs) | 2–24 | 2–4 | 2–4 | 2 | |
| Melt Temperature (°C) | 232–249 | 220–260 | 246–274 | 204–238 | |
| Mold Temperature (°C) | 54.4–71.1 | 50–70 | 29–60 | 62.8–85 |
Table 1: Material properties of common ABS grades (Source: Matweb)
Table 2 below provides typical values for a generic ABS material that contains glass beads:
| Physical | Nominal Value |
| Mold Shrinkage – Flow (73 °F) | 4.0e-3* to 7.0e-3** inches |
| Water Absorption (24 hr., 73 °F) | 0.16 to 0.25% |
| Mechanical | Nominal Value |
| Tensile Modulus (73 °F) | 3,200 to 500 kpsi |
| Tensile Elongation (Break, 73 °F) | 2.0 to 10% |
| Flexural Modulus (73 °F) | 348 to 426 kpsi |
| Flexural Strength (73 °F) | 7,150 to 9,100 psi |
| Injection | Nominal Value |
| Drying Temperature | 176 to 180 °F |
| Drying Time | 2.0 to 9.0 hr. |
| Melt Temperature | 410 to 500 °F |
| Mold Temperature | 113 to 175 °F |
ABS Material Processing
Like other types of injection molded plastics, ABS needs to be processed properly to avoid part defects and processing issues. These are the key elements to consider:
viscosity
moisture
temperature control
injection pressure
injection speed
shrinkage
Viscosity
Melt temperature is a key processing consideration because of its relationship with viscosity, a measure of a fluid’s resistance to flow. If ABS pellets are melted beyond their plasticizing temperature, viscosity increases and the material becomes more difficult to mold. This behavior differs from that of other amorphous plastics where viscosity decreases beyond the plasticization temperature.
Moisture
ABS readily absorbs moisture. Therefore, it must be fully dried before processing, which adds time and costs. However, failing to remove moisture can result in molded parts with cloudiness, bubbles, or other surface defects. If parts require a surface with high gloss and high reflectivity, drying times greater than nine hours may be required.
Temperature Control
ABS that is overheated is subject to thermal decomposition: the heat-induced breakdown of chemical bonds. Typically, brown or burn marks on injection molded parts indicate that injection molding occurred at excessive temperatures. Sometimes, this is caused by problems with a machine’s temperature control.
If higher gloss on parts is required, a higher molding temperature must be maintained without damaging the material. Also, note that mold temperature is higher with ABS than with other commonly used injection molding materials. (Mold temperature differs from melt temperature.)
Injection Pressure
Because of the viscosity of ABS, higher injection pressures are usually needed; however, lower pressures may be suitable for smaller, simpler, or thicker ABS products.
A skilled injection molder will keep these two guidelines in mind:
If the injection pressure is too high, increased friction can cause molded parts to stick, which complicates their removal and adds production costs.
If the injection pressure is too low, mold shrinkage increases and can result in out-of-tolerance parts that won’t meet design requirements.
Injection Speed
Injection molding speed is also an important processing consideration for ABS plastic. If the speed is too fast, the plastic may burn or thermally decompose. The result is part defects such as weld lines, poor finish, or discoloration. If the injection molding speed is too slow, however, there may be an insufficient filling of the mold.
Shrinkage
All plastics undergo some degree of shrinkage during injection molding. With ABS, shrinkage rates range from 0.1 to 0.8%. This is on the lower end compared to other injection molded plastics, but it’s still an important consideration.
When ABS is heated into its molten form, its density decreases and its volume increases. After injection, the plastic is cooled inside the mold and this cooling causes the ABS to contract. Most shrinkage happens inside the mold, but some may occur after ejection.
To ensure the dimensional accuracy of parts, injection molds must be designed to account for a plastic’s anticipated shrinkage. Shrinkage can also be affected by injection pressure, melt and mold temperatures, and holding pressure. When you work with PROTO MFG, you’ll gain access to this type of injection molding expertise, including design for manufacturing (DFM) feedback.
PROTO MFG provides a wide range of manufacturing capabilities 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.
