tool path generation for free form surfaces

7/28/2019 Tool Path Generation for Free Form Surfaces

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Tool path generation for free form

surfaces

using Bezier curves/surfaces


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1.Abstract

In the paper Presented by Young-Keun Choi & all, a tool pathgeneration method for multi-axis machining of free-form surfacesusing Bezier curves and surfaces. The tool path generation includestwo core steps. First is the forward-step function that determinesthe maximum distance, called forward step, between two cutter

contact (CC) points with a given tolerance. The second componentis the side step function which determines the maximum distance,called side step, between two adjacent tool paths with a givenscallop height. Using the Bezier curves and surfaces, we generatecutter contact (CC) points for freeform surfaces and cutter location(CL) data files for post processing. a Several parts are machined

using a multi-axis milling machine. As part of the validation process,the tool paths generated from Bezier curves and surfaces areanalyzed to compare the machined part and the desired part.


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2. Literature review

The tool paths generation can be classified into 3methods, iso-parametric, iso-planning, and iso-scallop height.

In iso-parametric method, Loney and Ozsoy(1987) and Broomhead and Edkins (1986) havestudied the tool-path generation using iso-parametric curve. They approximated tool pathinto surface using iso-parametric curve on the

surfaces. The forward step was calculated byquick and dirty method which is iterative andlengthy.


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In iso-planar machining, the tool-paths are along with the series ofplanes on the part. Bobrow (1985) and Huang and Oliver (1994)have developed iso-planar NC tool-paths generation. A part consistsof CSG (Constructive solid geometry) is sectioned by a series ofplanes to obtain cutter contact points. Since the calculations are

very tedious and sectioning plane is a non-trivial problem, thesemethods are not efficient to generate tool paths for free-formsurfaces. Huang and Oliver (1994) also have developed iso-planartool path generation methods based on non-constant scallop heighton the manufactured part. They implemented iso-planar machiningon parametric surfaces and determine a machining error using a

computational approach. However, calculations are also iterativeand lengthy.


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The last approach is iso-scallop machining. Sureshand Yang (1994) and Lin and Koren (1996) havestudied scallop height machining. They proposedalgorithm to generate tool path based on desired

accuracy on the manufactured part. Using thismethod, the accuracy of the manufactured part iscontrolled by user directly. In this method, theprimary goal is to generate shortest overall length

of tool path and least number of tool paths withpredetermined tolerance and scallop height ofthe manufacturing part.


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4. Proposed approach

Our method for tool path generation is similar to iso-scallopmachining in that we generate tool paths based onpredetermined tolerance and scallop height by using offsetof an iso-parametric curve on the designed part.

However, we propose a new and accurate method togenerate tool paths on the designed part. There areproblems to be solved in the generation of tool paths. Thefirst problem of cutting efficiency and cutting accuracy inmilling operation needs to be considered. The secondproblem is computing efficiency, since surface calculationsare generally iterative and lengthy. Last, true machiningerror will be verified. In order to obtain good accuracies wehave used exact mathematical representation of thesurface.


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July-Aug- Literature Serve

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5. Implementation and result

tool path generation for free form surfaces

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