POM vs ABS for High-Torque Injection Molding Parts

How to choose the right material for torque

High-torque injection molded parts fail in predictable ways. The material creeps under load. The part flexes at stress risers. The fastener hole elongates. You see the same pattern across gear housings, drive shafts, valve bodies, and actuator housings.

POM and ABS are both common choices. Both process well in injection molding. Both are widely available. The difference shows up under load.

POM, also called acetal, has a high yield strength and low creep. It holds shape under sustained torque. ABS has a lower stiffness and higher creep rate. It can deform over time, especially at elevated temperatures.

This section compares POM vs ABS for parts that must resist torque. It covers mechanical behavior, mold design, cost, and selection criteria.

How POM and ABS compare under load

Option	Best for	Limitations
POM (acetal)	High-torque parts, gears, drive components, valve bodies	Higher material cost, lower impact resistance at low temperatures
ABS	General structural parts, housings, lighter torque loads	Higher creep, lower stiffness, can deform under sustained load
Glass-filled POM	High stiffness, precision gears, high-torque applications	Higher cost, more brittle, requires careful mold design
Glass-filled ABS	Moderate torque with cost constraints	Higher creep than glass-filled POM, lower stiffness
Nylon 6 or 66	High wear, moderate torque, chemical exposure	Higher moisture absorption, dimensional variation

POM has a higher modulus of elasticity than ABS. It resists bending and torsion better. Under a constant torque load, POM creeps less. That means a POM gear or drive shaft holds its position over years of service. ABS flexes more. The part may still function, but tolerances drift.

Consider a small actuator housing that connects to a motor shaft. If the housing is made of plain ABS and the motor applies a constant torque, the housing may twist slightly over the first few months. The fastener holes may begin to stretch. The gap between the housing and the mating component may change. The assembly may still work, but the fit becomes loose. A POM housing under the same load would show far less movement. The geometry remains stable. The bolt holes keep their diameter.

ABS is tougher in impact. It handles drops and bumps better than POM. But torque is not an impact load. Torque is sustained. That changes the material ranking.

For a part that turns a handle, a valve, or a small drive shaft, POM is usually the safer choice. For a part that sees occasional shock, ABS may be better. For a part that must resist both torque and impact, glass-filled POM or nylon may be the answer.

Glass-filled variants change the equation. Adding short glass fibers to POM increases stiffness and reduces deflection. It also improves resistance to creep. The downside is brittleness. Glass-filled POM does not bend as much as plain POM. It transfers stress to the mold and the part geometry more directly. If the part has sharp internal corners, it may crack at the root. You must design the part with generous fillets.

Glass-filled ABS offers a middle ground. It is stiffer than plain ABS and cheaper than glass-filled POM. But it still creeps more than its POM counterpart. It is a reasonable choice for parts that see moderate torque but also need to survive handling damage.

Nylon 6 and nylon 66 offer different benefits. They have good wear resistance and decent stiffness. But they absorb moisture from the air. When a nylon part absorbs moisture, it swells. The dimensions change. A nylon gear may run fine in a dry environment but loosen in a humid one. You must account for this in the design.

How temperature changes the torque answer

Service temperature changes everything. At ambient conditions, the gap between POM and ABS is clear. At higher temperatures, ABS softens faster. Its yield strength drops. Creep increases.

If the part runs near 60 to 80 degrees Celsius, ABS may lose stiffness quickly. POM holds up better. If the part sees intermittent heat, such as a motor housing or a heated valve, the material choice becomes more complex.

Imagine a valve body that sits near a heater. The heater cycles on and off. The valve body is not directly heated, but the ambient temperature in the enclosure rises. Plain ABS may soften enough to allow the valve stem to flex. The seal may leak. The torque required to turn the valve may change. The user notices the valve feels loose or stiff depending on the temperature.

Check the maximum continuous service temperature. Check peak temperature. Check whether the part sits near a heat source or in direct sunlight. These factors can push the decision away from ABS even if the torque load is moderate.

Do not rely on room-temperature datasheet values alone. A material that works fine on a bench test may fail in service.

When selecting a material, ask about the thermal history of the part. Does it sit in a sunlit window? Does it run next to a motor that gets hot? Does it sit in a car dashboard that bakes in summer? If the part experiences heat, you must choose a material that retains its mechanical properties at that temperature. POM generally performs better in warm environments than ABS. If the temperature is very high, both may fail. In that case, you might need a thermoplastic polyester or a polyamide with heat resistance, but those are different materials with different processing requirements.

Also consider thermal cycling. If the part heats up and cools down repeatedly, the material fatigue becomes a concern. ABS may crack at stress risers over time. POM is more resistant to this kind of fatigue.

How mold design affects torque resistance

Material selection is only half the equation. Mold design determines how much of that material strength the part actually uses. A poorly designed part in a great material will still fail.

Gate location is the first thing to check. A gate that fills the part asymmetrically creates weld lines. Weld lines are stress concentrators. In a high-torque part, a weld line near a fastener hole or a gear tooth can become a crack initiation point.

Consider a circular housing with a single gate at the edge. The melt fills the cavity from the gate. The two sides of the cavity meet in the middle. The seam where they meet is a weld line. If that weld line runs across a bolt hole, the hole may crack under torque. The weld line is a weak point. The metal bolt pulls on the plastic, and the stress concentrates at the weld. The part breaks.

You can move the gate. You can use multiple gates. You can change the flow path. The goal is to keep weld lines away from high-stress areas.

Rib placement matters. Ribs add stiffness without adding material. A well-placed rib near a torque application point can double the local resistance to bending. A rib placed too close to the gate may cause sink marks. A rib that is too thin may not add strength.

Ribs should be placed parallel to the flow direction when possible. Perpendicular ribs are weaker. They create stress concentrations at the rib root. If you need a rib perpendicular to the flow, make the fillet radius larger. Use a thicker rib base.

Wall thickness must be uniform. Thicker sections cool slower. They shrink more. They create internal stress. In a torque part, that stress can crack the material over time.

For high-torque parts, design the part as a structural component, not just a container. Think about load paths. Keep fastener holes away from weld lines. Use generous fillets at corners. Avoid sharp transitions.

A prototype test will reveal problems that the drawing cannot. Run the prototype under real torque. Measure deflection. Check for creep over time. Then revise the mold or the material before committing to production.

If you use a steel mold, the surface finish affects the part too. A rough surface creates surface roughness that traps stress. A smooth surface allows the material to flow better and creates a stronger surface layer. For torque parts, a polished or semi-polished mold finish is often better.

Also consider the cooling system. If the mold cools unevenly, the part shrinks unevenly. That creates warpage. Warpage changes the geometry. The part may not fit properly. It may crack under load. The cooling channels must be designed to keep the part flat and stable.

How cost and lead time factor in

POM costs more than ABS. The material cost difference is usually moderate, but it adds up over a large production run. ABS is cheaper and more readily available. It may also have shorter lead times from suppliers.

Tooling cost is similar for both materials. A steel mold for POM and a steel mold for ABS will cost about the same. The difference is in the process. POM can be more sensitive to moisture. It must be dried properly before injection. If moisture control is poor, the part will have reduced strength and visible defects.

ABS is easier to process in many ways. It is forgiving. It does not require as strict a drying routine. But it does not hold torque as well.

If the part is low-volume, ABS may be the practical choice. If the part is high-volume and must last for years, the material premium for POM is usually worth it. The cost of a failed part in the field is far higher than the cost of better resin.

Consider the total cost of ownership. If the part fails in the field, you pay for replacement, shipping, and customer service. You may also face warranty claims. For a high-value application, such as an industrial actuator or an automotive component, the cost of failure is significant. For a low-cost consumer product, the material cost savings of ABS may outweigh the risk of failure.

Lead time also matters. If you need the part in two weeks, ABS may be easier to source. If you have three months, you can specify POM and allow time for drying and processing.

Also consider the supplier base. Some regions have more ABS suppliers than POM suppliers. This can affect price and availability. If you are in a region with limited POM availability, the cost may be higher due to shipping.

How to select the right material for your part

Use this sequence.

1. Define the torque load. Estimate the maximum torque and the duty cycle. Is the part constantly under load, or does it cycle on and off?
2. Define the service temperature. What is the maximum continuous temperature? What are the peak temperatures?
3. Define the service life. How many hours of operation? How many cycles?
4. Check for chemical exposure. Solvents, oils, and cleaners can weaken both materials, but they affect them differently.
5. Run a prototype. Test under real conditions. Measure deflection and creep.
6. Choose the material. If torque and stiffness dominate, choose POM. If impact and cost dominate, choose ABS. If both matter, consider glass-filled POM or nylon.

Do not skip the prototype. A torque part is a mechanical part. The drawing will not tell you if it will fail. The test will.

When defining the torque load, be specific. Do not just say “high torque.” Say “5 Newton-meters of constant torque for 8 hours a day.” Or “10 Newton-meters of peak torque for 5 seconds, repeated 10,000 times.” The duty cycle matters. A part that sees torque all the time is different from a part that sees torque only when the user presses a button.

For the service temperature, measure the actual temperature at the part. Do not guess. Use a thermometer in the assembly. If the part is inside a machine, the temperature may be higher than the ambient room temperature.

When checking chemical exposure, look at the datasheet for both materials. Some chemicals attack ABS more than POM. Others attack POM more than ABS. If the part touches oil, solvent, or cleaner, you must choose a material that resists that specific chemical.

The prototype test is the most important step. Build a sample in the chosen material. Put it in the actual assembly. Run it under real conditions. Measure the deflection with a dial indicator. Check for creep by measuring the dimension after 24 hours, 72 hours, and 7 days. If the part fails, change the material or the design. Do not move to production until the part passes.

When to use POM versus ABS

Choose POM when the part must resist sustained torque. Gears, drive shafts, valve bodies, actuator housings, and rotating handles are typical applications. POM holds shape. It resists creep. It maintains tolerances over time.

Choose ABS when the torque load is moderate and the part also needs impact resistance. Housings, covers, and components that see drops or bumps may work better in ABS. If the part does not sit under constant torque, ABS can be a reasonable choice.

Choose glass-filled POM when stiffness and precision matter. Gears with fine teeth, high-torque connectors, and precision drives benefit from the added stiffness. The trade-off is higher cost and more brittleness.

Choose glass-filled ABS when cost is a priority and the torque load is not extreme. It is a compromise. It is stiffer than plain ABS. It is cheaper than glass-filled POM. It is not as strong as either.

Choose nylon when wear and chemical resistance are the main concerns. Nylon has good wear properties. It is tougher than POM. But it absorbs moisture, which can affect dimensions. If the part operates in a wet environment, nylon may be the best fit.

The decision is not about which material is better. It is about which material fits the load, the temperature, the cost, and the service life.