Clothoid Stylus Tool Geometry for Low-Oil-Canning CNC Forming
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Solution Overview
Problem
Existing stylus tools for 3-axis CNC manufacturing suffer from 'oil canning' issues due to large forces at contact points and computationally expensive toolpath generation methods, which are time-consuming and inefficient.
Innovation Solution
A stylus tool with an axisymmetric forming surface generated by rotating a curved profile around the tool shank, where the curvature increases linearly with path length, and a toolpath generation method that inputs part and tool shapes to determine a tool offset surface for generating efficient toolpaths, reducing 'oil canning' and improving geometric accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a spherical stylus tool with hemispherical forming surface is used, then the tool can be manufactured with simple geometry, but it generates significant oil canning due to large forces at contact points
Solution Approach 1:
The patent applies a clothoid curve profile to generate the forming surface, which has continuously varying curvature rather than constant curvature like a sphere. The curvature radius changes along the path length according to the clothoid equation, allowing the tool to gradually adapt to surface changes and reduce concentrated forces that cause oil canning, while maintaining a mathematically defined smooth surface.
Solution Approach 2:
The patent changes the curvature parameter of the forming surface from constant (spherical) to variable (clothoid). The curvature radius is made a function of path length, allowing it to vary continuously. This parameter change enables the tool to adjust its contact characteristics dynamically, reducing oil canning while maintaining manufacturability through mathematical definition.
2Manufacturing precision
If discrete Minkowski sums are used to generate offset surfaces for toolpaths, then the toolpath can be generated with accurate tool compensation, but the computation is expensive and time consuming
Solution Approach 1:
The patent uses the axisymmetric property of the clothoid-forming surface to create a simplified 2D representation (the generating curve in the rz-plane) that captures all essential geometric information. This 2D copy is then used for offset surface calculation instead of processing the full 3D surface, dramatically reducing computational complexity while preserving accuracy.
Solution Approach 2:
The patent reduces the problem from 3D offset surface calculation to 2D curve offsetting by exploiting the axisymmetric nature of the tool. The forming surface is defined by rotating a 2D clothoid curve around the tool axis, so offset calculations can be performed on the 2D generating curve and then revolved to generate the complete offset surface, significantly reducing computational burden.
Data Source
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AI summary
The application provides a method of toolpath generation whereby the tool (200) may be any smooth convex axisymmetric shape. The tool includes a tool body (202) extending between a shank (204) and a head (206). The shank is configured to be mounted in a collet (150) which may optionally rotate. In the case of a stylus tool, the head has an axisymmetric forming surface used to press metal. In the case of a routing tool, the head has cutting surfaces which are enveloped by a smooth convex axisymmetric surface and the tool is used for milling a part. In a least one embodiment the tool is a stylus tool which has a forming surface (220) that has been generated from a portion of a clothoid curve.