Elsevier

Computers & Graphics

Volume 27, Issue 1, February 2003, Pages 99-106
Computers & Graphics

Technical section
3D simulation of tool machining

https://doi.org/10.1016/S0097-8493(02)00248-0Get rights and content

Abstract

This paper describes a 3D tool machining simulation system. The initial tool and the grinding wheels are integrated with the machine tool. The application reads and interprets the CNC program code that controls the machine, it computes the positions and the motion of components and it translates the sequence of machining operations into Boolean operations. The machining is computed for 2D sections and, later, a 3D model of the tool is reconstructed. The application is ready to yield tool visualization, it gives measurements on sections and it can show an interactive animation of the whole process. A novel aspect of the simulation is that it is able to deal with 6-axes machines, whereas most of previous work is limited to 3- and 4-axes machines. In addition, it allows to interrupt the machining process and to show partially machined tools. A major contribution is the fact that the Boolean operations are performed in 2D and the 3D model is reconstructed from the cross sections, which provides user control on the resolution of the operations at a low cost.

Introduction

In mechanical industry, CNC (numerical control) machines have been in use for more than 20 years. Metal-cutting machines move according to the instructions of programs that command step-by-step linear or rotating servomotors and they yield better precision than that obtained with the old manual analogic machines.

There is a wide variety of papers on CNC in CAD, mainly centered on the automatic computation of tool paths, [7]. An integrated CAD/CAM system starts from a final tool design and yields the optimal trajectories of the tool and the grinding wheel, giving the CNC code as a final result. Machining simulation and verification wants to do exactly the opposite: to calculate the tool starting from the path with a triple goal, [3]: (i) to detect possible collisions between the tool or any of the grinding wheels and the rest of the machine tool, (ii) to check visually the efficiency of the trajectories; (iii) to verify that the surface of the resulting tool is effectively the desired surface. Using a simulation system decreases considerably the tool production cost because it avoids the trial-and-error process on the real machine with costly materials that is otherwise necessary.

Conventional CAD systems do not offer the function of simulating the mechanization of tools, for which specific applications are needed. This paper deals with a particular type of machine tools: bore and cutter grinders. Most of the existing simulation applications for these types of machines deal only with the machining of 2D cross sections of the tools and they are restricted to the main fluting operation [1]. 3D applications are rather recent [2], [13]. They provide a machining simulation for specific 5-axes machines and they are not applicable to general movements. The goal of this paper is to describe a novel application able to deal with any combination of movements up to 6 axes (Fig. 1). A major feature of the application is that, by opposition to the existing systems that construct one final tool, it is able to construct intermediate tools corresponding to the different steps of the machining. This feature provides better user control on the machining process and it facilitates updating locally the trajectories. In order to provide this flexibility, the system is based on a novel approach of the Boolean operations based on a double discretization of 4D space (3D+time). This algorithm is fast and it provides user control on simulation accuracy.

The paper is structured as follows. First, the requirements of the application are discussed. A general structure that fulfills these requirements is proposed for the simulation process. In Section 3, each step of the process is described, previous to the definition in Section 4 of the geometric model for the workshop objects. The results of the simulation are discussed in Section 5.

Section snippets

General structure of the application

The workshop is based on machine tools, which have up to 6 degrees of freedom: four in translation and two in rotation. It handles the motion of the bit to be machined, a tubular object made of sintered steel, called “the tool”, and the motion of the set of grinding wheels which will bite on it. The tool is placed on a spindle (the tool holder), that allows translation on three axes (X, Y and U) and rotation on two axes (W and A). The wheel spindle is another moving capstan that allows motion

Filter

The filtering module receives as input a tool machining program written following the CNC rules and regulations, and produces a sequence of lines that simplifies maximally the input sequence. The input CNC sequence is divided into blocks that correspond to each one of the logical machining operations (fluting, gashing, etc.). In each operation a single wheel and the tool are involved. Each instruction can be either a command controlling parameters of the machine, (rotation speed, rebalancing,

Geometric model

The tools have a tubular shape, which makes them suitable to be represented with a generalized cylinder based model. Each geometric model is defined as a set of planar contour curves centered in a sweeping axis. The contour curves are originally circular but they may acquire an irregular shape after machining. Evermore, during machining a contour can be broken into different connected contours, called shells. The representation of circular contours is parametric. They are stored at points where

Conclusions and future work

This paper describes an application that simulates tools machining, a recently developed field of great industrial interest. The main contributions of the package are:

  • A flexible and versatile architecture that allows simulation directly from CNC code, through a filtering and compilation preprocess, that minimizes geometric computations.

  • A geometric model of the workshop that evolves with time to facilitate real-time animations and high-quality visualizations.

  • A novel and efficient method to

Acknowledgements

We gratefully acknowledge the decisive help of Albert Mercade in the implementation of software for the application.

References (13)

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