Milling Material Removal Rate Calculator
Calculate efficiency for CNC Milling Operations
Understanding Material Removal Rate (MRR)
The Material Removal Rate (MRR) is a critical metric in CNC machining and milling that quantifies the volume of material removed from a workpiece per unit of time. It is a direct indicator of machining efficiency. A higher MRR generally implies higher productivity, provided that the cutting tool, spindle, and machine frame can withstand the cutting forces and power requirements.
The MRR Formula
The calculation for milling MRR is straightforward, relying on three primary variables: the Axial Depth of Cut, the Radial Depth of Cut (often called stepover or width of cut), and the Feed Rate.
Imperial Formula:
MRR (in³/min) = Ap × Ae × Vf
Metric Formula:
MRR (cm³/min) = (Ap × Ae × Vf) / 1000
- Ap (Axial Depth of Cut): The depth the tool engages the material along the spindle axis (Z-axis).
- Ae (Radial Depth of Cut): The width the tool engages the material perpendicular to the spindle axis (XY-plane).
- Vf (Feed Rate): The speed at which the tool moves through the material (Inches Per Minute or mm/min).
Why MRR Matters in Machining
Optimizing MRR is the key to reducing cycle times and increasing profitability in a machine shop. However, simply maximizing the variables isn't always the solution.
- Machine Power (HP): Every machine has a limit. High MRR requires significant spindle horsepower. If the MRR exceeds the machine's capabilities, it can stall the spindle or cause chatter.
- Tool Life: While High Efficiency Milling (HEM) strategies utilize high MRR by taking deep axial cuts with light radial cuts, traditional heavy roughing can wear tools prematurely if chip evacuation is poor.
- Surface Finish: Roughing operations focus on high MRR without regard for finish, while finishing passes sacrifice MRR for surface quality and dimensional accuracy.
Example Calculation
Suppose you are machining 6061 Aluminum with a 1/2″ endmill. You are taking a 0.5 inch axial depth of cut (Ap), a 0.2 inch radial width of cut (Ae), and running at a feed rate of 80 inches per minute (IPM).
MRR = 0.5 × 0.2 × 80 = 8.0 in³/min
This means you are removing 8 cubic inches of aluminum every minute.