Compensation for process variables in a numerically-controlled machining operation

• US 8,788,083 B2
• Filed: 07/22/2011
• Issued: 07/22/2014
• Est. Priority Date: 07/22/2011
• Status: Active Grant

• Current Assignee: Pratt & Whitney Canada Corporation (Rtx Corporation)
• Original Assignee: Pratt & Whitney Canada Corporation (Rtx Corporation)
• Inventors: Atabey, Fuat
• Primary Examiner(s): PATEL, RAMESH B
• Application Number:
  US13/188,604
• Publication Number:
  US 20130024021A1
• Time in Patent Office: 1,096 Days
• Field of Search: 700159-160, 700/163, 700174-175, 700/179, 700/184, 700/187, 298897-88972
• US Class Current: 700/175
• CPC Class Codes: G05B 19/404 characterised by control arrangements for compensation, e.g. for backlash, overshoot, tool offset, tool wear, temperature, machine construction errors, load, inertia G05B19/19, G05B19/41 take precedence
• CPC Class Codes: G05B 2219/37436 Prediction of displacement, relative or absolute, motion
• CPC Class Codes: G05B 2219/45147 Machining blade, airfoil
• CPC Class Codes: G05B 2219/49186 Deflection, bending of tool

Abstract

A method of machining a work part in a numerically-controlled machining process with a selected tool, includes steps of inspecting actual geometric parameters of the selected tool and predicting cutting forces and this tool deflections based on given tool/part engagement conditions and pre-measured static stiffness of the selected tool, then modifying a tool path of the numerically-controlled machining process to compensate for the predicted tool deflections, and finally machining the work part to a desired profile by use of the selected tool to follow the modified tool path.

Claims

1. A method machining an airfoil part in a numerically-controlled machining process with a selected tool, the numerically-controlled machining process being based on given tool-and-part engagement conditions, the method comprising:

a) inspecting actual geometric parameters of the selected tool;

b) predicting cutting forces in a computing program based on the given tool-and-part engagement conditions and using the inspected actual geometric parameters of the selected tool as inputs;

c) predicting tool deflections under the predicted cutting forces based on a pre-measured static stiffness of the selected tool;

d) modifying a tool path of the numerically-controlled machining process to compensate for the predicted tool deflections; and

e) machining the airfoil part to a desired profile by use of the selected tool to follow the modified tool path.

2. The method as defined in claim 1 wherein the selected tool is inspected immediately before every machining operation of a selected airfoil part.

3. The method as defined in claim 2 wherein the selected tool is inspected by a 3-dimensional scanner mounted on a machine performing the numerically controlled machining process.

4. The method as defined in claim 1 wherein the pre-measured static stiffness is measured when the selected tool is mounted to a spindle of a machine performing the numerically-controlled machining process.

5. The method as defined in claim 1 wherein the given tool-and-part engagement conditions comprise at least a pre-selected machine spindle speed, a pre-selected machining feed rate and material properties of the airfoil part.

6. The method as defined in claim 1 wherein the actual geometric parameters of the selected tool comprise at least a diameter of the tool, eccentricities of cutting edges about an central axis of the tool and asymmetries in tool shape.

7. The method as defined in claim 1 wherein steps a to d are performed in a process separate from step e.

8. An airfoil machining system having a numerically-controlled machine tool, the airfoil machining system comprising:

a storage medium containing data of a static stiffness of a cutting tool mounted on a spindle of the machine tool and data of given tool-and-part engagement conditions in the sequence of the desired operational steps;

a scanning apparatus for inspecting actual geometric parameters of the cutting tool, the scanning apparatus being operatively connected to the storage medium for sending data of the inspected actual geometric parameters of the cutting tool to the storage medium;

a computing apparatus capable of predicting cutting forces and tool deflections in a sequence of desired operational steps of the machine tool, based on the data stored in the storage medium; and

a numerically-controlled unit capable of controlling the machine tool in the sequence of the desired operational steps to provide a desired tool path.

9. The system as defined in claim 8 wherein the computing apparatus is operatively connected to the numerically-controlled unit, allowing calculation of a tool path compensation for the predicted tool deflections in order to provide the desired tool path.

10. The system as defined in claim 8 wherein the scanning apparatus comprises a 3-dimensional scanner.

11. The system as defined in claim 8 wherein the scanning apparatus is mounted on the numerically-controlled machine tool.

12. The system as defined in claim 8 wherein the actual geometric parameters of the selected tool comprise at least a diameter of the tool, eccentricities of cutting edges about an central axis of the tool and asymmetries in tool shape.

13. The system as defined in claim 8 wherein the given tool-and-part engagement conditions comprise at least a pre-selected machine spindle speed, a pre-selected machining feed rate and material properties of a work part to be machined.