This article will present an in-depth discussion on plastic gears.
The article will provide more detail on topics such as:
This section provides an overview of plastic gears, focusing on their manufacturing processes and how they work in various applications.
Plastic gears are toothed wheels made from advanced engineering plastics, primarily used to alter the speed ratio between a motor and its connected components. Among the popular engineering plastics for these gears are nylon, a form of polyamide resin, and polyacetal.
The method of producing plastic gears closely resembles that of metal gears, with the main difference being the material composition. Each gear's design is tailored to meet specific application needs, influencing the production technique used. Plastics do not possess the same strength as metals and are more affected by variations in temperature, impacting their stiffness and resilience. Additionally, plastic gears have a lower modulus of elasticity and mesh stiffness, causing more deflection under load.
Although there are similarities between metal and plastic gears, designing and engineering plastic gears require additional attention to their particular material characteristics.
Hobbing employs a hob—a cylindrical tool with teeth designed for cutting. During this process, a flat plastic disk is placed near the rotating hob. As it spins, the hob carves the gear teeth into the disk. By varying the hob's contact angle, different types of gears can be crafted.
This gear hobbing technique is economical due to its speed and efficiency, producing highly accurate spur gears, helical gears, splines, worm wheels, and sprockets.
Injection molding involves a steel mold that shapes the gear with precise dimensions. The mold's accuracy is crucial as it dictates the gear's final form. Molten plastic is injected under pressure to fill the mold cavity completely. Though costly, this process is ideal for large-scale production runs.
CNC machining is a flexible cutting technology that can produce virtually any gear type by removing layers of material from a plastic rod or disc, guided by G codes. Despite offering high precision, CNC machining is often slower and more expensive due to its limited production capacity per cycle.
This method is highly effective for crafting gears with exacting shapes and tight tolerances. Broaching, a technique integrated into CNC machining, shapes the gear teeth, bolstering both efficiency and accuracy in the manufacturing process.
Machining is more expeditious for smaller production volumes. However, for larger quantities, injection molding presents a more efficient solution. Despite its initial setup time and costs, the injection molding process allows for rapid scalability once the mold is in place, offering potential returns on initial investments.
Machining is usually more economical for small-scale productions of a few hundred parts. As the number of parts increases, machining becomes less cost-efficient. Conversely, injection molding significantly reduces the per-unit cost for mass production. While the initial cost of creating molds is higher, this expenditure is offset over large production runs, making injection molding more viable for mass manufacturing.
Machining provides a wide variety of material choices, enabling the creation of components from high-strength plastics that offer superior durability. This suitability for harder materials contrasts with injection molding, which primarily utilizes softer, pliable plastics such as thermoplastics and thermoset resins. Injection molding excels in crafting parts from materials that can be molded without losing integrity.
Machining prioritizes precision and accuracy with tight tolerances, attributed to the reliable control offered by computer programming. This minimizes variables that may impact the final product. In comparison, injection molding may introduce more defects like flow lines, voids, or warping, as it prioritizes mold tolerances over end products.
Injection molding is highly repeatable, advantageous for reproducing identical parts. However, altering designs incurs costs for creating new molds, reducing cost efficiency for continual design changes. Machining, conversely, offers enhanced flexibility, allowing for swift updates through CAD adjustments without incurring substantial costs.
```Plastic gear manufacturing has become a crucial component in a variety of industries thanks to the unique benefits that high-performance plastic gears provide, such as lightweight design, cost-efficiency, low noise, resistance to corrosion, and high adaptability. These advantages make plastic gears highly suitable for applications in the automotive industry, robotics, medical device manufacturing, industrial equipment, consumer electronics, milling, and mining. With growing demand for precision-molded plastic gears and gear components, choosing the right plastic gear making machine—and the manufacturer—becomes essential for maintaining quality, efficiency, and competitiveness in modern gear production processes.
Leading manufacturers in the United States and Canada offer advanced plastic gear molding equipment, including automatic and servo-driven injection molding machines, overmolding solutions, multi-shot molding technology, and high-precision CNC gear cutting machinery. Below is an overview highlighting top companies that specialize in the production and supply of plastic gear making machines for injection-molded and custom gear manufacturing:
Arburg delivers a wide range of injection molding machines perfectly suited for high-precision plastic gear production, with the Arburg Allrounder series being particularly notable. These modular machines are widely recognized for their exceptional flexibility, precision, and intelligent control systems utilized in gear molding and component manufacturing. Key features include high process repeatability, efficient energy usage, precise mold temperature regulation, and advanced servo-hydraulic technology, all of which ensure consistent part quality for engineered plastic gears, spur gears, and helical gears. The Allrounder series is favored by manufacturers due to its ability to support both high-volume automated gear molding and specialized, custom gear runs, while providing consistent process reliability and optimum cycle times. As a result, Arburg is a trusted partner for companies seeking scalable and reliable plastic gear injection molding solutions.
Engel stands out as a top manufacturer of injection molding equipment for plastic gear production, particularly with their Engel Victory series. This line is celebrated for its tie-bar-less design, offering maximum mold space and easy automation integration for multi-cavity gear molds and insert molding. Engel Victory machines feature servo-electric drives to deliver superior control, high energy efficiency, and the repeatability required for precision-molded plastic gears such as bevel, worm, planetary, and custom gears. The advanced multi-component technology available in the Victory series enables manufacturers to produce complex, multi-material, and high-strength gear assemblies. Engel's focus on digital solutions and intelligent process monitoring further strengthens their leadership in efficient, high-volume plastic gear manufacturing for the automotive, medical, and industrial sectors.
Sumitomo (SHI) Demag is renowned for delivering state-of-the-art all-electric injection molding machines like the IntElect Multi series, which are ideally suited for the precise and efficient production of plastic gears. The IntElect Multi series specializes in multi-component and overmolding applications frequently required in gear manufacturing. With ultra-high-speed operation, low maintenance, and advanced automation systems, these machines enable the production of intricate and detailed gear profiles—including internal gears and differential gears—consistently and to stringent quality standards. The IntElect Multi series also supports rapid mold changeovers and the processing of various engineering plastics, enhancing versatility for gear manufacturers who require flexibility for small-batch prototyping as well as high-volume manufacturing of plastic gearing components.
Milacron is a prominent supplier of precision injection molding equipment for gear manufacturing, offering the Elektron Multi-Shot series specifically designed for multi-material and multi-color gear molding. These machines are equipped with intuitive servo-electric drive technology, ensuring accurate shot control, high repeatability, and rapid cycle times—critical for mass production of precision-molded plastic gears, pulleys, and drive components. The Elektron Multi-Shot series stands out for its ability to support advanced automation, including integrated robotics for high-efficiency gear cell manufacturing. Milacron's commitment to engineering innovation and process optimization helps gear manufacturers achieve higher throughput, improved dimensional accuracy, and significant cost savings in their plastic gear production lines.
Nissei manufactures high-quality injection molding machines ideal for producing industry-standard plastic gears, with the NEX Series exemplifying their expertise. Designed for high-speed, energy-efficient operation, NEX Series machines deliver precision, dependability, and robust control for gear manufacturing environments. Featuring advanced injection unit technology, micro-molding capabilities, and user-friendly interfaces, Nissei NEX machines help gear manufacturers achieve stable, repeatable results for even the most demanding engineering plastic gears, miniature gears, and custom small module gear sets. Their reliability in both prototyping and high-volume gear production makes Nissei a preferred choice for OEMs and contract manufacturers in North America and globally.
These manufacturers are recognized industry leaders, offering advanced machinery tailored for a wide range of plastic gear manufacturing needs—from automotive transmissions and electric motors to high-precision instrumentation and consumer products. When selecting the best plastic gear making machine for your specific requirements, factors such as machine size, automation capabilities, energy efficiency, compatibility with engineering polymers, and technical support should be considered. For up-to-date model specifications, customization options, and expert guidance, it is advisable to contact manufacturers directly or consult their comprehensive product catalogs. Investing in reliable, state-of-the-art gear molding equipment ensures consistent product quality, reduces production downtime, and positions your business for growth in the rapidly evolving plastic gear market.
In the US, approximately 80% of gears are chosen from catalogs. While this approach is common, the optimal method is to collaborate with the customer’s engineers to design gears that address specific issues or design challenges, such as inertia or contamination. For instance, open gearing in industries like paper, food, or semiconductor processing can introduce substantial contaminants.
To engineer the ideal solution for an application, it is crucial to consider various operational parameters, including torque, RPMs, shock loads, backlash requirements, inertia, chemical exposure, and operational temperatures. Modifications to gear teeth or increasing gear width may be necessary to ensure that a plastic gear performs effectively in its intended application.
The face width of a gear tooth refers to the width of the tooth's top surface that is parallel to the gear's axis. Increasing the face width enhances the gear's bending and surface strength, contributing to its overall durability.
It is essential for the face width of a gear to be smaller than the space where it engages with another gear, a condition known as effective face width. This should not be confused with the face of a gear tooth, which is the surface above the pitch surface. Remember, the face width is specifically the top portion of the gear tooth that interfaces with the space between the teeth of a mating gear.
The size of a gear is represented by its module, which defines the gear's scale. The module is calculated as the ratio of the gear's diameter to the number of teeth. When selecting a gear, both the module and the number of teeth are crucial factors that determine the appropriate gear for the application.
The pressure angle of a gear is defined by the angle between two tangent lines that intersect at the inner circle of the gear and the top arc of a tooth. Traditionally, a pressure angle of 14.5° was the standard; however, advancements in technology have led to adjustments in this standard. A larger pressure angle results in larger and stronger gear teeth, enhancing the gear's durability and performance.
Backlash is the space between the meshing teeth of gears. It occurs when there is a slight gap, allowing movement or play. During gear design, it is possible to minimize backlash to ensure a tighter mesh between the teeth, which improves precision and efficiency in gear operation.
Temperature is a critical factor affecting the performance of plastic gears. Selecting appropriate materials during the design phase helps address temperature concerns. However, accurately predicting the working temperature of a gear can be challenging. It's beneficial to monitor gear operation to ensure that the temperature remains within safe limits. Many thermoplastics can function at temperatures up to 500 °F (260 °C).
The root, flank, and wear strength are crucial parameters for estimating gear life. These parameters, including root pulsating strength and flank strength, are influenced by the number of load cycles and vary depending on temperature and lubrication type (oil, grease, or dry running). For plastic gears, these factors significantly impact performance, whereas a single value is typically sufficient for steel gears.
Comparatively, Young's Modulus for plastic is approximately two magnitudes lower than for steel, with POM around 2800 N/mm² versus 206,000 N/mm² for steel. Similarly, the permissible bending stress for plastic is about one magnitude lower: 25 N/mm² compared to 250-450 N/mm² for steel. As a result, metal gears experience less relative deformation compared to plastic gears.
Despite this, plastic gears excel in shock absorption compared to metal gears. They often feature a mechanical stop design to minimize wear and tear on both the gear teeth and the motor, leading to longer wear periods and extended life expectancy. Metal gears tend to wear down more quickly than plastic ones.
Plastic gears typically do not require backlash adjustments like metal gears do. Most steel gears need regular backlash adjustments to counteract issues caused by gear and motor vibrations. In contrast, plastic gears can absorb these vibrations, which often extends their operational lifespan.
For gears like PowerCore, the size of injection-molded gears is constrained by the press size, typically up to about 5� to 6�. Unlike catalog gears, custom-designed gears developed in collaboration with engineers address specific challenges such as inertia or grease contamination, particularly in applications like paper, food, or semiconductor processing equipment.
Engineering a solution involves evaluating all operational parameters, including torque, RPM, shock load, backlash requirements, inertia, chemical exposure (especially in semiconductor applications), and operating temperature. Based on these factors, alternative solutions such as tooth modifications or increased gear width can be proposed to ensure the plastic gear performs effectively in the application.
Calculating gear life is a critical component of the engineering process. This calculation predicts the number of hours a gear will operate under specified conditions. Conversely, gears can be designed to meet specific longevity requirements, such as the five-year lifespan required by medical equipment manufacturers. Over the past two decades, this calculation has proven to be a reliable tool for assessing whether a plastic gear will be suitable for a given application, particularly when replacing metal gears.
| Input Data | ||
|---|---|---|
| z1 | 21 | Number Teeth Pinion |
| z2 | 210 | NUmber Teeth Gear |
| n1 | 1000 | RPM Pinion |
| n2 | 100 | RPM Gear |
| DP | 10 | Diametral Pitch |
| b | 1" | Face Width |
| g | 20° degrees | Pressure Angle |
| t | 65°C | Operating Temperature |
| P | 0.75 hp | Transmitted Power |
| Cs | 1.10 | Shock Load Factor |
| Geometry Data Output | ||
|---|---|---|
| dw1 | 2.10° | Pitch Pinion Diamter |
| dw2 | 21.00° | Pitch Diamter Gear |
| dk1 | 2.30° | Outside Diameter Pinion |
| dk2 | 21.20° | Outside Diameter Gear |
| Hk1 | 0.10° | Addendum Pinion |
| Hk2 | 0.10° | Addendum Gear |
| ea | 1.74 | Contact Ratio |
| i | 10.00 | Transmission Ratio |
| a | 11.55 | Center Distance |
| Operational Data Output | ||
|---|---|---|
| V | 2.79 m/sec | Pitch Line Velocity |
| T1 | 3.9 ft lbs | Torque at Pinion Shaft |
| T2 | 39.4 ft lbs | Torque at Gear Shaft |
| Load and Safety Data Output | ||
|---|---|---|
| Sb2 | 4.15 | Gear Tooth Root Stress Safety |
| Sg2 | 2.34 | Gear Tooth Flank Pressure Safety |
| SigmaW2 | 6.0 N/mm2 | Gear Tooth Root Stress |
| Kw2 | 0.6 N/mm2 | Gear Tooth Flank Pressure |
One of the advantages of using plastic for gear manufacturing is the broad range of polymers available. This includes various specialized polymer blends designed to enhance the strength and durability of plastic gears. Typically, crystalline plastics are favored due to their superior strength, durability, and resilience.
Polyoxymethylene (POM), also referred to as acetal, polyacetal, or polyformaldehyde, is a semicrystalline thermoplastic known for its suitability in creating precision components that demand stiffness, low friction, and dimensional stability. Produced through the polymerization of formaldehyde, POM is available in two main forms: homopolymer and copolymer, each offering distinct properties. Additionally, there are six different grades of polyacetal, each tailored with specific characteristics, though all share fundamental attributes of strength and dimensional stability.
PPS, or polyphenylene sulfide, is highly regarded as a high-performance thermoplastic due to its excellent temperature resistance and dimensional stability. Like polyacetal, PPS is a rigid, opaque semicrystalline thermoplastic with a melting point of 536 °F (280 °C). It is synthesized through a reaction between sodium sulfide and dichlorobenzene in a solvent. The primary reasons for choosing PPS in gear production are its exceptional strength, rigidity, and minimal degradation even at elevated temperatures.
Nylon is a polymer known for its toughness and wear resistance. Gears made from nylon are used in applications with increased torque and power, such as conveyors and automated equipment. A major factor in determining the use of nylon gears is the limited amount of noise and vibrations they produce.
Similar to nylon, polyamide is selected for gear production due to its capacity to handle high torque at low speeds. Polyamide gears can tolerate temperatures up to 248°F (120°C) and are well-suited for environments involving acids, gases, and saltwater. In specific applications, polyamide gears are preferred over metal gears because of their lighter weight and cost-effectiveness.
Polycarbonate is a clear thermoplastic renowned for its strength and resistance to impact and breakage. This eco-friendly polymer is processed into gears through pressure molding. Polycarbonate boasts impressive strength with a melting point of 311°F (155°C), though its cost is relatively high compared to other gear polymers. Common manufacturing methods for polycarbonate gears include extrusion and injection molding.
Polyurethane is an excellent material for gears due to its desirable properties. It operates with minimal noise and is highly resistant to chemicals and corrosion, providing zero backlash. Polyurethane is versatile, suitable for a range of gears including spur, helical, worm, and pinion types. Its durability and low noise levels make it a preferred choice over other plastics and metals for extended service life.
The six polymers mentioned are just a few examples of the many plastics used in gear production. The selection of a specific plastic depends on the application requirements, including necessary strength and expected service life. The adoption of plastic gears is increasing as advancements in plastic technology continue to enhance their performance and suitability as alternatives to metal gears.
There are various types of plastic gears, which include:
These types of gears are the most commonly used and are easily identifiable due to the teeth that extend from their perimeter. Their teeth and the shaft axis are aligned parallel to each other.
Plastic spur gears do not produce axial thrust force. They are designed to operate on parallel axes, transferring motion between two shafts that are aligned parallel to each other.
These applications are typically similar to those of plastic spur gears but without a steel core.
Injection molded spur gears are suitable for use in the same sectors as other plastic spur gears.
This type of gear has a conical shape with straight or spiral-cut teeth. Plastic bevel gears transfer motion between two intersecting axles, changing the rotation axis. These types of gears are mostly utilized in power tools and automotive applications. The spiral-cut version can be smoother and less noisy than other designs.
Plastic racks are designed to convert rotational motion into linear motion. The teeth are aligned along a straight bar, working with a cylindrical mating gear. With one gear axis fixed, plastic racks provide short oscillating strokes and are commonly used in steering systems, conveyors, and machinery for lifting applications.
Characteristics of Injected Molded Bevel Gears
These types of gears transmit power through right angles on shafts that are non-intersecting. Worm gears produce thrust load and are mostly suitable for high shock load applications. However, worm gears offer very low efficiency compared to other gears. Therefore, they are often used in lower horsepower applications.
Planetary gears feature teeth cut around the internal diameter of a central gear, with one or more spur gears meshing with these central teeth. This design allows the planetary gear to rotate around its internal diameter. Additionally, teeth can be arranged on the outside of the larger gear to accommodate additional gears running around its outer diameter. Planetary gears are frequently utilized in automotive gearboxes due to their compact design and efficient power transmission capabilities.
Helical gears differ from spur gears in that their teeth are angled relative to the shaft. This design results in multiple teeth engaging simultaneously during operation, which allows plastic helical gears to handle greater loads compared to plastic spur gears. The load is distributed across the teeth, enabling helical gears to operate more smoothly and quietly. However, plastic helical gears do produce a thrust load during operation, which must be taken into account. They are primarily used in enclosed gear drives due to their efficiency and quieter performance.
Plastic Helical Gears Applications
In these types of gears, two helical faces are positioned next to each other with a gap separating them. They are a variation of helical gears. The faces of the gears have identical helix angles opposite to each other. Double helical gears eliminate thrust loads and allow greater tooth overlap and a smoother operation. Double helical gears are also used in enclosed gear drives, just like helical gears.
Plastic Double Helical Gear Applications
Herringbone gears are similar to double helical gears but feature continuous helical faces without a gap between them. Their compact design makes them well-suited for high shock and vibration applications. However, due to the complexity of manufacturing and the associated high costs, herringbone gears are not as commonly used as other types of gears.
Plastic hypoid gears are akin to spiral bevel gears but differ in that their shafts do not intersect. In hypoid gears, the shafts are supported by bearings at each end, with the pinion positioned on a different plane than the gear. This arrangement allows for smooth operation despite the non-intersecting shafts.
Bull plastic gears are used in conjunction with pinion gears to transmit power. A bull gear can drive several pinion gears, allowing for speed adjustments through gear changes. Typically, one gear in the set is larger than the other, with the larger gear known as the bull gear and the smaller gears referred to as pinion gears.
This chapter will explore the benefits and drawbacks of using plastic gears.
One significant advantage of plastic gears is their capacity to handle increased loads due to their tooth bending and load-sharing characteristics. Bending stress can attempt to deform the gear teeth and shear them from the main body of the gear, which can lead to fatigue and breakage. Contact stress can also cause surface wear and eventual failure. In contrast, plastic gear teeth distribute the load across more teeth and deflect more under pressure. This load-sharing ability enhances the load-bearing capacity of plastic gears.
Typically, plastic gears are less costly to produce compared to metal gears. Moreover, plastic gears generally do not require additional finishing processes, which can result in cost savings of approximately 50% to 90% compared to their metal counterparts.
Plastic molding provides the flexibility to create a wider range of efficient gear geometries compared to metal. It is particularly suitable for producing complex shapes like internal gears, worm gears, and cluster gears, which can be prohibitively expensive to manufacture using metal.
Plastic gears can attain high precision levels through consistent material quality and meticulous control over the molding process.
Unlike metal gears, plastic gears are resistant to corrosion, making them suitable for use in environments such as water meters and chemical plant controls. Their inert nature also allows them to be employed in applications where metal gears might corrode or degrade.
Plastic gears are lighter than their metal counterparts of the same size. For instance, nylon and acetal have specific gravities around 1.4, whereas steel has a specific gravity of 7.85.
Plastic gears are capable of deflecting to absorb impact loads more effectively than metal gears. They also distribute localized loads caused by misalignment and tooth errors, reducing the impact on gear performance.
Plastic gears help reduce noise levels due to the noise-dampening properties of plastics, leading to quieter operation. This makes plastics ideal for applications where high precision and flexible materials are needed to achieve quieter drives.
Plastic gears possess inherent lubricity, making them suitable for applications such as printers, toys, and other uses where low-load and dry gears are essential.
More specifically, plastic gears offered by companies like PowerCore offer several advantages, including:
Despite these benefits, the disadvantages of plastic gears are far outweighed by their advantages.
Plastic gears are manufactured from two main methods: the injection molding process and the machining process. The type of manufacturing process depends on the volume of the parts needed to be produced and other factors like the required strength of the parts. As already mentioned, plastic gears offer many advantages over metal gears. Each type of plastic gear has a unique characteristic that makes it suitable for a particular application. Therefore, caution must be taken when selecting plastic gear for a particular application for successful and efficient performance.
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