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Difference between Feed Rate and Cutting Speed in CNC Machining

Difference between Feed Rate and Cutting Speed in CNC Machining

Through its automatic functions and ability to work on the materials accurately, computer numerical control (CNC) machining is a machine tool widely used by different industries. They rely on it in profitable manufacturing. However, maximizing the performance of a CNC requires knowledge of feed rate and cutting speed. These factors are interrelated, and a single error can lead to catastrophic outcomes. These are the critical parameters that are crucial to guarantee accurate and secure machining processes.

Do you know?

Balancing cutting speed and feed rate effectively can result in a higher tool lifespan. Proper optimization might contribute to a 15% to 25% extension in tool life, minimizing tool replacement frequency.

HiTop recognizes the significance of feed rate and cutting speed, and that’s precisely why this blog is dedicated to elucidating the distinction between the two. The aim is to provide clear insights into these crucial aspects, helping readers understand their separate roles in machining processes. Let’s delve into the details.

Feed Rate & Cutting Speed | Overview 

Feed Rate & Cutting Speed

Feed rate is the rate at which a cutting tool travels across or into a material during machining. It impacts the speed at which the tool advances and interacts with the workpiece, which in turn has an impact on the material removal rate. On the other hand, cutting speed is the velocity of the outmost cutting tool edge with respect to the material being machined. It is measured in rotations per minute (RPM) and indicates how fast the tool is spinning during milling.

What’s more?

Faster tool rotation and movement, linked to higher cutting speeds and feed rates, influence the speed and quality of material removal in manufacturing. These factors combined significantly affect the efficiency and precision of machining operations, making them crucial aspects to consider for achieving the best results in manufacturing.

What are the Characteristics of Feed Rate? 

To obtain the best machining results, it is essential to grasp the feed rate operation. It determines how fast the cutting tool traverses the material, influencing how fast the material is removed.

Let’s have a look at the characteristics

  1. Determines Tool Movement Speed:

The feed rate, which is the speed at which the cutting tool moves across or into the material, influences the general speed of the machining process.

  1. Directly Affects Material Removal:

The speed at which the tool advances determines how quickly material is removed, impacting the efficiency of the machining operation.

  1. Interconnected with Cutting Speed:

Feed rate and cutting speed are closely related, and both variables need to be optimized for the best quality of machining.

  1. Impacts Surface Finish:

The surface finish and overall quality of the machined part are impacted by the selected feed rate, which determines its smoothness.

  1. Tool Longevity:

Balancing the feed rate is crucial to extending the life of the cutting tool, as excessive speeds can lead to premature wear and reduce tool longevity.

  1. Critical for Chip Formation:

Creating well-formed chips and ensuring effective material removal without problems like chip clogging requires proper feed rates.

  1. Varies by Material and Tool:

Adjustments to the feed rate are necessary, depending on the specific material being machined and the type of cutting tool used.

What are the Characteristics of Cutting Speed?

The cutting speed, which influences material removal and surface finish, determines the angular velocity of the cutting tool. Measured in rotations per minute directly impacts the tool’s efficiency and lifespan. Below are some characteristics of cutting speed.

  1. Determines Tool Rotation Speed:

Cutting speed refers to the speed at which the outer edge of the cutting tool moves relative to the material, influencing the tool’s overall rotation during machining.

  1. Measured in RPM:

It is measured in rotations per minute (RPM), providing a quantifiable value for the speed of the tool’s rotation.

  1. Directly Impacts Material Removal Rate:

The rate at which material is being removed in machining, and thus the overall efficiency of the process, is directly affected by the cutting speed that is chosen.

  1. Influences Surface Finish:

The surface finish and final quality of the machined part are influenced by cutting speed, which affects its smoothness.

  1. Consideration for Tool Longevity:

Maintaining a balance in cutting speed is essential to prolong the lifespan of the cutting tool. Excessive speeds can cause premature wear, leading to a reduction in the tool’s lifespan.

  1. Interconnected with Feed Rate:

There is a significant correlation between cutting speed and feed rate, and the optimal balance of both is decisive in achieving the best machining results.

  1. Varies by Material and Tool Type:

The machining process requires adjustments that are dependent on the type of tool and the material being machined, as it defines the optimal cutting speed.

Why Are Speeds And Feeds Important In Machining?

Both are important for the several reasons listed below. 

  • The speed at which the cutting tool moves and rotates directly impacts the efficiency of material removal.
  • Ensuring appropriate speeds and feeds is crucial for accurately shaping the workpiece and preserving the tool’s durability by preventing excessive wear. 
  • Finding the right balance between cutting speed and feed rate is crucial for achieving optimal results and preventing issues like overheating or tool breakage. 
  • These parameters also play a key role in determining the surface finish of the machined part, impacting its overall quality. 
Graph Showing Speed and Feed Rate

Efficient, accurate, and safe machining operations require careful consideration of speeds and feeds.

Feed and Cutting Speed for Various Materials:

Cutting speed and feed rate of different materials for HSS tool

What is the Difference between Feed Rate and Cutting Speed?

It is important to know the differences between these two factors in machining. These two parameters play distinct yet interconnected roles in determining the efficiency and precision of the machining process. 

Let’s explore each factor to grasp how they shape the outcomes of material removal and overall machining operations.

Factor Cutting Speed Feed Rate
Tool Life & Cutting TemperatureHigher speeds lead to increased temperatures, affecting tool life.Higher feed rates increase cutting time, affecting temperature and tool life.
Surface Finishing & Feed MarksHigher speeds generally result in a smoother finish.Higher feed rates result in larger distances between tool passes, affecting scallop marks.
Role in ShapingActs as the generatrix, determining the motion that shapes the curve.Acts as the directrix, guiding the tool’s movement.
Chip DirectionDoesn’t impact chip direction.Often influences the actual flow of the chip direction.
Power ConsumptionHigher speeds increase cutting force and power usage.Doesn’t directly influence cutting force or power consumption.
MeasurementsVc (m/min or ft./min) – Speed of tool edge relative to material.s or f (mm/rev or mm/min) – Speed of tool movement across/into the material.
Table 2: Comparison between feed rate and cutting speed.
  1. Tool Life and Cutting Temperature:

These factors have a major effect on cutting temperature and tool life in machining. The higher cutting speeds may result in higher temperatures, which can influence the tool’s lifetime. Additionally, the feed rate determines how much time the tool spends cutting, which has an effect on temperature and, consequently, the tool’s life. 

  1. Surface Finishing and Feed Marks:

These two factors also influence surface finishing and feed marks in machining. The smoothness of the machined surface is influenced by cutting speed, typically leading to a smoother finish with higher speeds.

On the other hand, the feed rate influences the distance between tool passes, affecting the formation of scallop marks. 

  1. Directrix and Generatrix:

The terms “directrix” and “generatrix” refer to elements in geometry. The directrix is a fixed line used in defining a curve, while the generatrix is a line that moves to create the curve. 

In simpler terms, the directrix remains stationary, guiding the generatrix as it moves, helping define the shape of the curve. Understanding the roles of directrix and generatrix is fundamental in geometrical constructions and curve formations. In machining, the objective is to craft geometric surfaces with precise finishes and aesthetic appeal. To reach this objective, we should concentrate on cutting speed and feed rate, which are critical parameters.

The distinction is that the cutting speed acts as the generatrix, determining the motion that shapes the curve, while the feed motion serves as the directrix, guiding the tool’s movement.

  1. Chip Direction:

The deviation of chip direction from orthogonal is not affected by the cutting speed in machining. Still the feed rate decides the actual chip direction flow mostly. Making adjustments to the feed rate can often control how chips are formed during the machining process. 

  1. Power Consumption:

When machining, cutting speed affects cutting force and power consumption. Typically, higher cutting speeds lead to greater cutting force and higher power usage. 

On the other hand, the feed rate does not directly influence cutting force or power consumption. Recognizing this distinction is essential for managing power requirements and optimizing the efficiency of machining operations.

  1. Measurements:

The cutting speed Vc in meters per minute (m/min) or feet per minute (ft/min) constitutes the generatrix. It shows the speed of the tool’s outer edge motion compared to the material. The feed rate, denoted by s or f, is the directrix, and it is usually measured in millimeters per revolution (mm/rev) or millimeters per minute (mm/min). It means the speed at which the cutting tool travels across or into the material.

How do you determine the cutting speed and feed rate? 

Here is how you can determine:

Consult Machining Data:

Refer to machining data provided by tool manufacturers or machining handbooks. This data usually provides suggestions for how fast to feed and cut different materials with various types of tools.

Consider Material and Tool Properties:

Account for the machined material and the cutting tool’s characteristics. Different materials and tools may require adjustments in these factors.

Use Formulas:

Employ machining formulas related to feed per tooth, revolutions per minute (RPM), and other relevant parameters. These formulas help calculate the ideal feed rate and cutting speed based on the machining requirements. One example of using formulas is shown below.

Formulas for finding speed and feed rate

Perform Test Cuts:

Conduct test cuts on a scrap or sample material. Adjust feed rate and cutting speed incrementally while observing the results, ensuring the optimal balance for efficient material removal and desired surface finish.

Consider Machine Capability:

Take into account the capabilities of the machining equipment. Different machines may have varying capabilities, affecting the recommended feed rates and cutting speeds.

Seek Expert Advice:

Consult with experienced machinists or tooling experts if uncertainties persist. Their knowledge and services can provide valuable insights into selecting appropriate feed rates and cutting speeds for specific machining applications.

Factors to Consider for Feed Rate and Cutting Speed in CNC Machining:

When determining these factors, consider the following factors:

  1. Material Type:

Different materials require varying feed rates and cutting speeds. Consider the material properties, such as hardness and composition, to optimize machining parameters.

  1. Tool Material and Type:

The cutting tool’s material and type influence the recommended feed rate and cutting speed. Choose tools suitable for the material being machined.

  1. Machine Capability:

Take into account the capabilities of the CNC machine. Factors like spindle speed and power play a role in determining the appropriate feed rate and cutting speed.

  1. Workpiece Geometry:

The workpiece’s complexity and geometry affect the feed rate selection and cutting speed. Adjust parameters to accommodate intricate shapes and contours.

  1. Surface Finish Requirements:

Consider the desired surface finish of the machined part. Finer finishes may require adjustments in feed rate and cutting speed to achieve the desired result.

  1. Cutting Tool Condition:

Monitor the condition of the cutting tool. A well-maintained tool contributes to better machining performance. Adjust feed rates and cutting speeds based on tool wear.

  1. Tool Engagement:

Evaluate how much of the tool is engaged with the material. Adjust feed rates and cutting speeds to avoid excessive tool engagement, which can impact tool life and machining quality.

  1. Machining Strategy:

Select an appropriate machining strategy. Different operations, such as roughing and finishing, may require adjustments in feed rate and cutting speed.

  1. Coolant and Lubrication:

Consider the use of coolant or lubrication. Proper cooling can influence feed rates and cutting speeds, preventing overheating and improving tool life.

  1. Tool Manufacturer Recommendations:

Refer to recommendations provided by the tool manufacturer. Manufacturers often provide guidelines for feed rates and cutting speeds based on their tool specifications.

By carefully evaluating these factors, CNC machinists can optimize cutting and feeding to achieve efficient, high-quality machining results.

Some Technical Factors:

There are some other factors to consider. 

Non-Linear Path: 

In CNC machining, feed rates are usually associated with linear motion, where the tool moves straight. However, there are cases, like when machining outer or inner diameters, where feed rates follow an arc or circular path.

As the depth of the cut increases, the tool engagement angle grows, resulting in a non-linear path. 

When working on internal corners, the tool engages more deeply than external corners, contributing to the non-linear nature of the machining path. This consideration is vital for adjusting feeding to ensure effective tool engagement and precision during non-linear machining.

Spindle Speed Limit:

Be mindful of the spindle speed limit:

  • Check the CNC machine specs to know its maximum spindle speed.
  • Verify that the chosen spindle speed aligns with the cutting tool’s capabilities.
  • Consider the material being machined; some materials require specific spindle speeds.
  • Balance spindle speed to extend tool life; higher speeds can increase wear.
  • Find the spindle speed that optimally balances material removal efficiency and machining precision.

Considering these factors ensures CNC machining operates within optimal spindle speed limits, promoting efficiency and tool durability.

Interaction of Cutting Speed and Feed Rate:

When it comes to CNC machining, it’s important to consider how cutting speed and feed rate work together. These factors determine how quickly material is removed during machining. 

Moreover, tweaking these settings helps achieve the desired surface finish on the part being machined. The cutting tool’s life can be extended by striking the best balance between cutting speed and feed rate, ensuring consistent and dependable performance over time.

Conclusion:

Feed rate and cutting speed are essential factors in CNC machining, directly impacting how efficiently and effectively the process runs. While higher cutting speeds often mean faster material removal, it’s important to assess the tool material and machine capabilities carefully. On the other hand, the feed rate determines the depth of cut and, consequently, the amount of material removed with each pass.

HiTop Industrial – Hand Over Your Project to Experts

At HiTop, our CNC machining services are top-notch. You can trust us for expert guidance and reliable services. Discover precision and excellence with HiTop’s CNC machining solutions. We provide clear assistance to meet your machining needs. Contact us for accurate guidance and dependable services in CNC machining. We ensure a seamless experience for our clients, always delivering quality results.

Our commitment is to your satisfaction. Rely on us for all your CNC machining requirements, and let our expertise guide you to success. If you have any queries or want to arrange a consultation meeting, contact us and let our experts assist you in your project. 

Frequently Asked Questions:

What Is The Feed Rate And Speed Of CNC?

It’s the speed at which the cutting tool moves across the material. The speed, often measured in RPM (rotations per minute), is how fast the tool or workpiece rotates. Together, they determine how quickly material is removed during CNC machining.

What Is The Difference Between Feed Rate And SFM?

The feed rate refers to how fast the tool moves compared to the workpiece, while SFM (Surface Feet per Minute) indicates how fast the outer edge of the tool moves. SFM considers the tool’s diameter, helping control the cutting speed more precisely.

What Is The Difference Between Depth Of Cut And Feed Rate?

The depth of cut is how deep the tool cuts into the material. Feed rate is how quickly the tool moves across the workpiece. They are separate factors but impact machining together; adjusting one affects the other and influences material removal efficiency.

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