Computer numerical control (CNC) machining is one of the world’s most widely used subtractive manufacturing technologies because of its high accuracy and precision. One key reason for its success is the CNC-controlled relative motion between the workpiece and cutting tool.
We can classify its motions as cutting and feed motions and measure them using cutting speed and feed rate.
But what is cutting speed, and how does it differ from feed rate? And how do these machining parameters contribute to the success of your manufacturing project? This article answers all of these questions and more.
What is the Difference Between Cutting Speed and Feed Rate?
To help you understand these two terms, let’s consider a simple analogy of a car moving at a linear speed of 60 km/hr with wheels rotating at 500 rpm. You’d agree that the wheels’ diameter and rotation are responsible for the car’s movement along a paved road. But when describing the vehicle’s speed to a friend, you’d explain it in terms of kilometers per hour.
Cutting speed can be compared to the linear velocity of the car, which depends on the wheels’ diameter and RPM. It measures the linear distance moved by the cutting tool against the machined part at a given time. Cutting speed is measured in millimeters per minute (mm/min), meters per minute (m/min), or feet per minute (ft/min).
In contrast, we can compare the feed rate to the wheels’ rotation in the car analogy. Feed rate is simply the distance the tool travels during one revolution of the part. We measure it in inch per revolution (inch/rev) or millimeter per revolution (mm/rev).
Still considering the car analogy, a wheel rotating at higher RPMs will likely consume more power and wear more quickly than wheels turning at lower RPMs. This wear is due to the friction and high temperatures between the tires and the road. Similarly, cutting speed affects the tool life, cutting temperature, and power consumption.
Feed rates also affect the tool life and power consumption during machining, but their effects are usually negligible compared to cutting force. Instead, feed rates are more likely to affect the machining time and surface finish of the machined part.
Choosing the Optimum Cutting Speed
To determine the optimum cutting speed for your machining project, you need to consider the workpiece hardness and the strength of the cutting tool.
Hardness describes the resistance of a material to deformation induced by abrasion, indentation, or scratching. Harder workpiece materials demand special attention during machining since they can easily reduce the performance life of cutting tools.
As a rule, the harder the workpiece material, the slower the cutting speed you should implement during machining. For example, materials like titanium will require a lower cutting speed compared to steel.
The strength of the cutting tool plays a role in the allowable cutting speeds for machining operations. For example, you can use high cutting speeds when machining with a cutting tool made of high-strength materials like diamond and carbon boron nitride, whereas tools made of high-speed steel demand lower cutting speeds.
Table 1 presents some of the common cutting tool materials and their allowable cutting speed range.
Learn More About: CNC Machining Materials
Chip Thinning and Optimum Feed Rate
Chip thinning is a manufacturing defect that occurs when you machine a workpiece such that the cut width is less than half the diameter of the cutting tool width. This reduces the chip load (the size or amount of material removed by the cutting tool per revolution), causing greater lead times.
One way to reduce the effect of chip thinning is to machine your workpiece at high feed rates. Doing this helps to improve your productivity and tool life.
CNC Machining with Gensun Precision Machining
Now that you understand the differences between feed rate vs. cutting speed, you’d agree that these two machining parameters are important during CNC machining. However, even after you choose the ideal cutting speed and feeds, the success of your project also depends on the machine shop you work with.
Gensun Precision is a leading provider of CNC machining services across Asia. Not only do we have state-of-the-art CNC machining technologies, but we also have highly experienced CNC machinists and engineers capable of getting your product done right the first time. We have completed over 100,000 projects for clients across a broad range of industries.
Learn more about our CNC Machining Services.