How to Calculate Metal Removal Rate

Metal Removal Rate Calculator

Understanding Metal Removal Rate (MRR)

The Metal Removal Rate (MRR) is a critical parameter in machining operations, quantifying the volume of material removed per unit of time. A higher MRR generally indicates a faster and more efficient machining process, leading to reduced production times and costs. It is influenced by several factors related to the cutting tool, the workpiece material, and the machining parameters.

The formula used to calculate MRR is:

MRR = Cutting Speed × Feed Rate × Depth of Cut

Where:

• Cutting Speed (Vc): The speed at which the cutting tool moves relative to the workpiece. It is typically measured in meters per minute (m/min) or feet per minute (ft/min). Higher cutting speeds can reduce machining time but may also increase tool wear and require more robust machinery.
• Feed Rate (fr): The distance the tool advances into the material per revolution of the workpiece or cutting tool. It is commonly expressed in millimeters per revolution (mm/rev) or inches per revolution (in/rev). A faster feed rate removes more material but can also lead to a poorer surface finish and increased cutting forces.
• Depth of Cut (ap): The thickness of the material layer being removed by the cutting tool in a single pass. It is usually measured in millimeters (mm) or inches (in). A larger depth of cut can remove material more quickly but requires more power and can induce higher stresses on the tool and workpiece.

The resulting MRR is typically expressed in cubic millimeters per minute (mm³/min) or cubic inches per minute (in³/min). Optimizing these parameters is crucial for achieving efficient, cost-effective, and high-quality machining operations.

Example Calculation:

Let's consider a machining scenario with the following parameters:

• Cutting Speed = 120 m/min
• Feed Rate = 0.25 mm/rev
• Depth of Cut = 3 mm

Using the formula:

MRR = 120 m/min × 0.25 mm/rev × 3 mm

First, we need to ensure consistent units. Since cutting speed is in meters per minute and feed rate/depth of cut are in millimeters, we convert cutting speed to millimeters per minute:

120 m/min × 1000 mm/m = 120,000 mm/min

Now, calculate MRR:

MRR = 120,000 mm/min × 0.25 mm/rev × 3 mm

Note: The feed rate (mm/rev) needs to be converted to mm/min if the cutting speed is in m/min or mm/min. If the cutting speed is given in m/min, and the feed rate is in mm/rev, we must first convert cutting speed to mm/min and then multiply by the revolutions per minute if that were provided. However, the common interpretation of the MRR formula assumes direct multiplication of the three parameters after unit conversion for cutting speed. If we assume the feed rate is effectively the distance moved per minute for simplification in this context, or if we are implicitly considering rotational speed, the direct multiplication is often used in simplified MRR calculations.

A more precise MRR calculation often involves the rotational speed (N) of the spindle in RPM: MRR = Vc (mm/min) × fr (mm/rev) × ap (mm) Where Vc (mm/min) = Cutting Speed (m/min) * 1000 This formula directly uses the input values as typically presented.

Let's re-evaluate with the typical simplified approach for educational purposes, assuming the intent is to directly use the values after converting Vc to mm/min:

Vc = 120 m/min = 120,000 mm/min

MRR = 120,000 mm/min × 0.25 mm/rev × 3 mm = 90,000 mm³/min

So, the Metal Removal Rate in this example is 90,000 cubic millimeters per minute. This means that 90,000 cubic millimeters of material are being removed every minute during the machining operation.