What is the difference between a ground ball screw and a rolled ball screw?

Ground Ball Screws vs. Rolled Ball Screws
Ground ball screws and rolled ball screws differ significantly in processing methods, precision, surface quality, mechanical properties, cost, application scenarios, and structural features. A detailed analysis is provided below:

 

1. Processing Method

Ground Ball Screws:
These utilize a complex machining process involving grinding to ensure precision. The process typically includes multiple steps, such as rough grinding and fine grinding, to achieve the required precision and surface quality.

Rolled Ball Screws:
These are formed in a single step using a chipless cold-forming method (rolling). Rollers plastically deform a round bar blank to create a long, threaded rod. Rolling processes can be hot or cold, with cold rolling offering increased strength, hardness, and longer service life.

 

2. Precision

Ground Ball Screws:
They offer higher precision grades, including C0, C1, C2, C3, C4, and C5. C0 represents standard precision, while C5 is suitable for ultra-high-precision applications like optical equipment and semiconductor processing machinery. Ground ball screws exhibit smaller lead errors and axial clearances, making them ideal for high-precision, high-speed, high-frequency, and heavy-load applications.

Rolled Ball Screws:
They have relatively lower precision grades, commonly C7, C8, and C10 (though German Rexroth reportedly achieves C5). While their lead errors and axial clearances are larger, they meet the requirements of most automated equipment and machinery.

 

3. Surface Quality

Ground Ball Screws:
The surface displays visible grinding marks, indicating high quality. However, machining defects such as chatter marks, cracks, tooth burns, or hard spots may occur, potentially affecting fatigue life.

Rolled Ball Screws:
The surface is smooth and shiny, often dazzling under reflected light. After rolling, a polishing process ensures a surface finish of up to Ra0.5 µm. The rolling process also avoids grinding-related defects, improving fatigue life.

4. Mechanical Properties

Ground Ball Screws:
Due to the grinding process, their mechanical properties may be slightly compromised. For example, tensile strength and fatigue strength may be lower than those of rolled ball screws.

Rolled Ball Screws:
Under strong rolling pressure, internal metal defects are compensated, and metal fibers become denser. This results in higher mechanical strength and fatigue life, with improvements in tensile strength, fatigue strength, and shear strength.

 

5. Cost and Delivery Time

Ground Ball Screws:
Manufacturing costs are relatively high, and delivery times are longer due to the complex, multi-step grinding process requiring sophisticated equipment.

Rolled Ball Screws:
Manufacturing costs are lower, and delivery times are shorter. The simpler rolling process enables mass production, reducing costs and accelerating delivery.

 

6. Application Scenarios

Ground Ball Screws:
Suitable for high-precision, high-speed, high-frequency, and heavy-load applications, such as high-speed machine tools, dynamic measuring devices, and precision instruments.

Rolled Ball Screws:
Ideal for most automation equipment and machinery, meeting general customer requirements in applications like general machine tools, automation devices, and standard instruments.