How to calculate feed in CNC?

In CNC (Computer Numerical Control) machining, feed refers to the movement speed of the tool or workpiece during processing. It is a crucial parameter that significantly affects machining efficiency, surface quality, and tool life. The feed rate is commonly expressed in different ways:

• Feed per Revolution (mm/rev or ipr): This indicates the distance the tool moves per spindle revolution. It is commonly used in turning and drilling operations.

• Feed per Minute (mm/min or ipm): This represents the distance the tool moves per minute along the feed direction. It is widely used in milling operations.

• Feed per Tooth (mm/z or fz): For multi-tooth tools such as milling cutters, this refers to the distance each tooth moves per cutting pass.

A CNC Feeder plays a vital role in maintaining a consistent and optimized feed rate by automatically supplying raw materials into the CNC machine, ensuring stable machining performance.

Calculation Formulas

Relationship Between Feed per Revolution (f) and Feed per Minute (Vf)

The formula is:where:

• = Feed per minute (mm/min)

• = Feed per revolution (mm/rev)

• = Spindle speed (rpm)

For example, if the feed per revolution mm/rev and the spindle speed rpm: mm/min.

Relationship Between Feed per Tooth (fz), Feed per Revolution (f), and Number of Teeth (z)

The formula is:

If a milling cutter has 4 teeth and a feed per tooth mm/z: mm/rev.

Comprehensive Formula for Feed per Minute

For example, if a milling cutter has 5 teeth, a feed per tooth mm/z, and a spindle speed rpm: mm/min.

A CNC Feeder ensures that the stock material is consistently supplied at the correct feed rate, allowing for uninterrupted machining.

Factors Influencing Feed Rate Selection

1. Workpiece Material

Different materials have varying hardness and toughness, affecting feed rate selection. For instance:

• Soft materials (e.g., aluminum alloys): Higher feed rates can be used.

• Hard materials (e.g., hardened steel): Lower feed rates are necessary to prevent excessive tool wear.

A CNC Feeder can accommodate different material types, ensuring smooth and efficient machining.

2. Tool Material and Geometry

• High-speed steel tools: Lower heat and wear resistance, requiring a lower feed rate.

• Carbide tools: Higher durability, allowing for increased feed rates.

• Sharp cutting edges: Can handle higher feed rates, whereas dull tools require lower feed rates.

3. Machining Process Type

• Rough machining: Focuses on removing large amounts of material quickly, so higher feed rates are used.

• Finish machining: Prioritizes surface quality, requiring lower feed rates.

4. CNC Machine Performance

• Machines with high power and rigidity can sustain larger feed rates.

• A CNC Feeder integrated with the machine ensures steady material supply, optimizing feed consistency.

General Steps for Determining Feed Rate

1. Refer to Cutting Parameter Tables: Consult machining handbooks based on the workpiece and tool material to get recommended feed values.

2. Adjust Based on Machining Conditions: Consider rough or finish machining, tool geometry, and machine rigidity.

3. Test Cutting: Perform trial cuts to observe tool wear, surface quality, and cutting forces. Adjust feed rate as needed to optimize performance.

By integrating a CNC Feeder, machining operations can run continuously with precise feed control, enhancing productivity and ensuring high-quality results.