If you're designing a robotic joint actuator that needs to fit within a slender robotic arm, or an electric vehicle gearbox that must be lightweight and durable, you'll face a common problem – how to achieve more power in a smaller space?
Traditional solutions using spur gear transmissions can't solve this problem – they require large center distances and multiple stages to achieve high reduction ratios, resulting in bulky and cumbersome overall mechanisms.
A planetary gear system (also known as an epicyclic gear train) is your best option, offering the highest torque-to-weight ratio of all gear layouts. So how does it work? And how does the manufacturing process of the internal ring gear affect the performance of the entire system?
What is a Planetary Gear System?
A planetary gear system, which you can relate to the movement of our solar system, typically consists of four parts.
Sun gear
This is the center of the planetary gear system and usually serves as the input.
Planet gears
3-5 gears that rotate around the sun gear.
Planet carrier
Used to hold the planet gears in place, and usually serves as the output.
Ring gear (also called internal gear/ring gear)
The outermost gear, with teeth on the inside, which meshes with the planet gears and is usually fixed in place.
Why choose Planetary Gears?
High Torque
They achieve the best size-to-strength ratio, making them the most compact mechanical structure in terms of power-to-weight ratio.
Coaxial Transmission
The input and output shafts are on the same line, facilitating integration with motors and linear actuators.
High Efficiency
High-quality planetary gear sets can achieve single-stage transmission efficiencies of 95-98%.
High Stability
Radial forces cancel each other out, significantly reducing the load requirements on bearings and housings.
What are the manufacturing challenges of internal ring gears?
The key to manufacturing a high-precision planetary gear set lies in the manufacturing of its internal ring gear.
Why?
Processing limitations
The cutting tool must extend into the interior of the cylinder for machining, resulting in extremely limited space. Traditional hobbing is the most effective method.
Structural interference
In compact designs, the internal ring gear is often located at the bottom of a blind hole or close to the shaft shoulder (interference), leaving very little space for tool retraction.
Defects of old processes
Traditionally, internal ring gears were mainly machined by gear shaping. This process is inefficient and difficult to achieve the surface finish and tooth profile accuracy required for modern precision transmissions, often leading to large backlash and high noise levels.
Power Skiving for Internal Gear Rings
With advancements in manufacturing processes and equipment, Power Skiving is now commonly used for machining internal gear rings. Based on our practical experience using the Kashifuji Gear Skiving Machine KPS30 for machining internal gears, the advantages are as follows.
Speed and Cost
The machining speed is 3-5 times faster than traditional gear shaping, significantly reducing production costs.
Higher Accuracy (ISO Level 5)
It can achieve pitch and tooth profile accuracy comparable to gear grinding (ISO/DIN Level 5).
Geometric Freedom
It can machine internal gears within extremely small clearance spaces, even in deep blind holes.
Application scenarios for high-precision planetary gears
How to choose the right business partner?
When purchasing planetary gears, you can ask your supplier the following questions:
How do you manufacture the internal ring gear?
Can you perform integrated housing machining?
Do you provide DFM (Design for Manufacturability) support?
At Hansheng Automation, we are committed to providing our customers with one-stop planetary gear transmission solutions. Leveraging our extensive machining experience in precision planetary gearboxes and utilizing our factory's Kashifuji Gear Skiving Machine KPS30, we deliver high-precision, high-quality gears.
To learn more, please visit our Custom Planetary Gears page or contact our engineers for a free quote and DFM design evaluation.