Custom plastic and hybrid gears for robots
A polymer gear is molded or machined from an engineering plastic such as acetal (POM), nylon (PA) or PEEK; a hybrid gear combines a polymer toothed rim with a metal hub or insert.
Pico can evaluate custom plastic gears and polymer-metal hybrid gears for robotics pilot projects, where weight, noise or cost targets may favor polymer over steel. We review the duty cycle before recommending a material.
At a glance
| Topic | How it works |
|---|---|
| Materials | Acetal (POM), nylon (PA), PEEK, and reinforced or lubricated grades |
| Gear types | Plastic spur, helical and internal gears, plastic planetary gear sets, hybrid gears |
| Where polymer is evaluated | Lighter-load stages, grippers and fingers, noise or mass targets |
| Prototype route | Machined from stock shapes, with no mold |
| Volume route | Molding or overmolding, which may come from outside molders |
| Country of origin | US manufacturing can be specified as required or preferred and is evaluated in the scope |
When does a plastic gear make sense in a robot?
Polymer trades load capacity and temperature range for lower mass, quieter running and less lubrication. The duty cycle decides whether that trade works.
Where polymer can fit
- Lighter-load reduction stages.
- Grippers, fingers and small wrist drives.
- Drives with noise or mass targets.
- Mechanisms that must run with little or no lubrication.
Where it usually does not
- High sustained torque, such as the main joints of an arm.
- High temperature, including heat from a nearby motor.
- Tight backlash that must hold as temperature and humidity change.
For main joints, compare metal reducers on robot joint gearboxes and reducers. Steel gears for the same transmission are covered on custom gears and gear sets for robotics.
Which plastic is best for gears: POM, nylon or PEEK?
No single plastic is best for every gear. The three common choices trade friction, moisture behavior, temperature resistance and cost:
| Material | Strengths for gears | Watch for |
|---|---|---|
| Acetal (POM) | Low friction, low moisture absorption, good dimensional stability and fatigue resistance | Homopolymer (POM-H) and copolymer (POM-C) grades differ; hard to bond with adhesives |
| Nylon (PA) | Tough, impact resistant, good wear resistance | Absorbs moisture, which changes its size and stiffness |
| PEEK | Highest temperature and chemical resistance of the three | Highest material cost; molding needs high process temperatures |
Reinforced and lubricated grades
Glass or carbon fiber adds stiffness and strength and lowers thermal expansion, but can wear the mating gear and makes molded shrinkage uneven. PTFE and other internal lubricants lower friction and wear, often at some cost in strength.
What is a polymer-metal hybrid gear?
A metal hub carries torque into the shaft and holds bore accuracy; a polymer rim carries the teeth for lower noise and mass. The joint between them is the critical design point.
Joining methods
- Overmolding onto a hub with lobes, knurls or holes that lock the polymer in place.
- Press-fit rim with anti-rotation features such as flats, keys or splines.
- Fastened or bonded rim on a flange of the hub.
Polymer and metal expand at different rates and the polymer can creep, so the anti-rotation feature must carry torque at both temperature extremes. Plastic planetary gears, such as polymer planets with a steel sun, are one option to evaluate in lighter-load custom planetary gearbox stages.
How do you design plastic gears for backlash and temperature?
A polymer gear changes size with temperature, and nylon also with humidity, far more than a steel gear. The mesh has to work across that whole range.
ΔL = α · L · ΔTLinear thermal expansion. α for unfilled engineering polymers is several times that of steel, so a polymer gear in a metal housing grows against a fixed center distance and loses backlash as it warms.
- Backlash: allow more than for steel, and check the mesh at the hot, cold, wet and dry limits.
- Creep: teeth and hubs deform slowly under sustained load, so check sustained torque, not only peak.
- Heat build-up: friction and hysteresis heat the teeth at speed, and polymers conduct heat poorly, so heat often limits continuous load.
- Mating gear: a steel mating gear helps carry heat away. Polymer-on-polymer pairs are often two different polymers, since like-on-like pairs tend to wear faster.
- Tooth form: a generous root fillet lowers root stress, and tip relief eases mesh entry for teeth that deflect more than steel.
How are plastic gears made at prototype and pilot quantities?
Prototypes are usually machined from stock rod or plate: no tooling, and the design can change between builds. Injection molding needs a mold and suits higher volumes. Molding may come from outside molders, and the scope states where each step happens.
| Route | Suits | Notes |
|---|---|---|
| Machined from stock | Prototypes and pilot batches | No mold; limited to grades sold as stock shapes |
| Injection molded | Higher volumes, stable design | Mold sized for shrinkage; uniform walls reduce warp |
| Overmolded on a hub | Hybrid gears at volume | Mold locates the hub; hub features set the torque path |
Molded parts have a skin, weld lines and shrinkage that machined parts do not, so the pilot plan states which process the test parts come from. A gear for a housed stage can be scoped with gearbox subassemblies and mechanical kits.
What should you send for a polymer gear inquiry?
- Torque (peak and continuous), speed and duty cycle.
- Temperature and humidity range.
- Lubrication: dry, initial grease or continuous.
- Mating gear material, and the gear data or drawing.
- Noise and life targets.
- Quantities for the first build and per year, timing, and any country-of-origin requirement.
Partial information is fine; we will ask for what is missing. Start a polymer gear project and choose polymer and hybrid concepts as the component.
Questions
Are plastic gears strong enough for a robot joint?
It depends on torque, speed, temperature and duty cycle. Polymer gears can suit lighter-load stages, such as grippers and small wrist or finger drives, while metal gears are the usual choice for high-torque main joints. We review your load case before recommending a material.
Do plastic gears need lubrication?
Many polymer gear pairs run dry or with light initial lubrication, which is one reason they are chosen. Lubrication can still reduce wear and heat in some duty cycles, so it is decided per application.
Can you make molded plastic gears at prototype quantities?
Prototypes are usually machined from stock polymer shapes, because molding needs a mold and makes sense at higher volumes. The pilot plan states which process the test parts come from.
Is Delrin the same as acetal?
Delrin is a trademark of its owner for an acetal homopolymer (POM-H). Acetal also comes as copolymer (POM-C) from several makers, and the grade affects strength, creep and processing.
Can you evaluate a hybrid gear with a metal hub?
Yes, for pilot projects. We review the duty cycle, the joining method and your weight, noise or cost targets before recommending a design or a build route.
Discuss a polymer or hybrid gear
Share the load case, environment, mating gear and your weight, noise or cost targets. We review the duty cycle before recommending a material or build route.
Start a project