Milling Cutter Deflection Compensation Using Spindle Torque
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Solution Overview
Problem
Existing methods for compensating for milling cutter deflection during machining, such as measuring deviations on finished workpieces, are time-consuming and not justifiable for one-offs or small series, and require repeated procedures for each new workpiece, leading to contour errors and rejects.
Innovation Solution
A method that uses a relationship between a variable processed in the numerical control, such as the torque of the tool spindle, to determine and compensate for milling cutter deflection by performing a training cut on a test workpiece, saving the relationship, and applying position corrections proportional to the target positions of the machine tool axes, without the need for special sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If cutter deflection is compensated by measuring deviations on finished workpieces and incorporating them into modified machining programs, then manufacturing precision is improved, but productivity deteriorates due to scrap production and extreme time consumption
Solution Approach 1:
The patent performs a learning cut on a test workpiece before actual production to determine the relationship between torque and deflection. This preliminary action establishes correction values that are then applied during subsequent machining operations, eliminating the need for post-measurement and re-programming cycles.
Solution Approach 2:
The patent uses control-internal parameters (torque, feed rate, spindle speed) as feedback to continuously compensate for cutter deflection during machining. The numerical control system processes these parameters in real-time to determine correction values for axis positions, creating a closed-loop compensation system that improves precision without stopping production.
2Manufacturing precision
If traditional measurement and re-programming methods are used to compensate for cutter deflection, then manufacturing precision is improved, but loss of time increases due to repeated procedures for each new workpiece
Solution Approach 1:
The system performs self-characterization by automatically determining the torque-deflection relationship through a learning cut and storing these characteristics in the numerical control system. This self-service capability eliminates the need for manual measurement and programming adjustments for each new workpiece, as the system automatically applies compensation based on stored characteristics.
Solution Approach 2:
The patent changes the approach from geometric measurement parameters to process parameters (torque, feed rate, spindle speed) for detecting and compensating deflection. By monitoring torque variations during machining, the system can predict and compensate for deflection in real-time without physical measurement, reducing setup time while maintaining precision.
3Productivity
If control-internal parameters are used to infer deviations and compensate for them directly during machining, then productivity is improved by eliminating scrap and re-work, but device complexity increases due to requirements for specialized sensors and complex systems
Solution Approach 1:
The numerical control system uses its own existing control-internal parameters (torque, feed rate, spindle speed) that are already available during machining operations. By processing these existing parameters to infer deflection and determine correction values, the system achieves compensation without requiring additional specialized sensors or external measurement devices, thus avoiding increased device complexity.
4Manufacturing precision
If a learning cut is performed on a test workpiece to determine the torque-deflection relationship, then manufacturing precision is improved for subsequent workpieces, but loss of time increases due to the initial learning process
Solution Approach 1:
The learning cut is performed once as a preliminary action to characterize the specific milling cutter's behavior. The torque-deflection relationship determined during this initial cut is stored in the numerical control system and reused for all subsequent workpieces with the same cutter, making the initial time investment amortized over many production runs.
Solution Approach 2:
The system creates a digital model (copy) of the cutter's mechanical characteristics through the learning cut. This copied information about the cutter's deflection behavior under various torque conditions is stored and applied to subsequent machining operations, eliminating the need to physically measure each new workpiece and allowing the initial learning investment to benefit multiple productions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method significantly reduces milling cutter deflection errors by directly compensating for deflection forces during machining, improving contour accuracy and reducing rejects, especially for one-off or small series productions, by using internal control variables to apply proportional corrections based on the determined relationship between torque and deflection.
Implementation Method 1
a rotating milling tool is moved through the workpiece according to the specifications of a machining program. Material is removed until the workpiece has the desired shape
Implementation Method 2
This deflection force causes the cutter to deflect or bent. Deviations from the cutter's intended path due to the deflection force directly lead to contour errors
Implementation Method 3
Numerous tests have shown that the deflection force is, in many cases, directly proportional to the torque that the drive of a tool spindle must apply when milling a workpiece in climb milling
Implementation Method 4
The deflection force and the deflection or displacement of the milling cutter from its intended path are directly proportional according to Hooke's law
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A method of compensating for deflection (A) of a milling cutter (F) when machining a workpiece (W) with a multi-axis (X, Y) numerically controlled machine tool is disclosed, comprising the steps of: performing a training cut on a test workpiece ( W) with known geometry with the milling cutter (F) attached to a tool spindle in synchronism, determining a relationship between a variable (P4) proportional to the torque of a drive of the tool spindle and the deflection (A) of the milling cutter (F) normal to a surface of the test workpiece (W), the deflection (A) being determined by comparing the actual contour (2) of the test workpiece (W) with a target contour (1). The relationship for the cutter (F) is then saved and the workpiece (W) is machined with the cutter (F) synchronously, using the saved relationship to compensate for the deflection (A) of the cutter by adding a size (P4 ) proportional position correction to a target position of the axes (X, Y) of the machine tool.