What is feed rate?

Short Answer:

Feed rate is the distance that a cutting tool or workpiece moves during one revolution of the spindle or one stroke of the cutting operation. It is usually measured in millimeters per revolution (mm/rev) or millimeters per minute (mm/min). Feed rate plays an important role in determining the surface finish, tool life, and overall machining time.

A proper feed rate ensures smooth cutting, efficient chip removal, and reduced tool wear. If the feed rate is too high, it may cause rough surfaces and tool damage, while too low a feed rate can increase machining time and cause friction or tool rubbing.

Detailed Explanation :

Feed Rate

Feed rate is a basic but very important parameter in machining operations such as turning, drilling, milling, and grinding. It defines how fast the cutting tool or the workpiece moves in relation to the other during the machining process. The purpose of controlling the feed rate is to achieve the best combination of machining accuracy, surface finish, and production rate.

In simple terms, feed rate is the linear distance that the cutting tool travels along the workpiece for every revolution of the spindle. It determines how much material is removed in each pass of the tool. The selection of feed rate depends on factors such as the type of material, cutting tool material, machining process, and required surface finish.

Measurement of Feed Rate

Feed rate can be expressed in different forms depending on the operation:

  • mm/rev (millimeters per revolution): Used in turning and boring operations, where the tool advances a specific distance per revolution of the workpiece.
  • mm/min (millimeters per minute): Used in milling and drilling, where the feed is measured as the total distance moved per minute.
  • mm/tooth: In milling, feed per tooth represents how much material each tooth of the cutter removes.

For example, in a lathe machine, if the tool moves 0.2 mm per revolution of the workpiece, the feed rate is 0.2 mm/rev.

Formula for Feed Rate

Feed rate can be calculated using the following formula:

Where,

  • F = Feed rate (mm/min)
  • f = Feed per revolution (mm/rev)
  • N = Spindle speed (revolutions per minute or rpm)

This formula helps to determine how fast the tool should move to achieve the desired material removal rate without damaging the tool or workpiece.

Importance of Feed Rate

  1. Surface Finish: The feed rate affects the smoothness of the finished surface. A higher feed rate produces rougher surfaces, while a lower feed rate gives a smoother finish.
  2. Tool Life: Excessive feed rate increases cutting forces, temperature, and tool wear. Optimum feed rate ensures longer tool life.
  3. Machining Time: Increasing feed rate reduces machining time but may affect accuracy. Therefore, a balanced feed rate is necessary.
  4. Power Requirement: Higher feed rates require more cutting power; hence, the machine’s capacity should match the selected feed rate.

Factors Affecting Feed Rate

  1. Material of Workpiece: Harder materials require slower feed rates, while softer materials can be machined at higher feed rates.
  2. Tool Material and Geometry: Tools made from carbide or ceramic materials can withstand higher feed rates than high-speed steel tools. The tool’s geometry also influences chip formation and feed rate selection.
  3. Type of Machining Operation: Different operations such as turning, milling, or drilling have different feed rate ranges. For example, roughing operations use higher feed rates, while finishing operations use lower feed rates.
  4. Depth of Cut and Cutting Speed: Feed rate is related to these two parameters. Increasing depth of cut or cutting speed often requires adjusting the feed rate to maintain proper chip removal.
  5. Coolant and Lubrication: Proper cooling allows slightly higher feed rates by reducing friction and heat generation.

Effect of Improper Feed Rate

  • Too High Feed Rate:
    • Produces rough surface finish.
    • Increases tool wear and breakage.
    • Causes excessive cutting forces and vibration.
  • Too Low Feed Rate:
    • Leads to rubbing instead of cutting.
    • Increases machining time.
    • May cause work hardening in some materials.

Thus, selecting the right feed rate is essential to ensure efficient and high-quality machining.

Optimization of Feed Rate

Modern machining uses computer numerical control (CNC) systems to set and optimize feed rates. The CNC program includes feed rate commands (often represented by the letter “F”) to precisely control tool movement. With the help of sensors and automation, the machine can adjust the feed rate in real time depending on tool wear, temperature, or cutting load, ensuring better productivity and quality.

Conclusion:

Feed rate is the rate at which the cutting tool or workpiece moves during machining operations. It directly affects tool life, surface finish, and machining time. Selecting an appropriate feed rate ensures efficient cutting, better accuracy, and longer tool life. It must be chosen based on the type of tool, material, machine capacity, and operation type. Balanced feed rate helps in achieving both high productivity and quality machining results.