Abstract In this paper, based on the requirements of the design and manufacturing characteristics, a CAD-based CMM (coordinate measuring machine) software and analysis system for the sheet metal stamping die is developed. The system can analyze the NURBS die surface model in IGES format and generate the measuring program in DMIS format as well as the probe path simulation. Moreover, the proposed system has developed the window graphical interface which shows the measuring position and dimensional error through the integration of the die CAD model and measurement information. It can not only be used to diagnose the die quality, but also improve the shop floor process and provide the die polishing guidance. Real measurement of a set of industrial sheet stamping dies on a CMM validates the effectiveness of the developed system.69478

Keywords: Stamping die; Coordinate measuring machine; Die diagnosis

1. Introduction

Mold and die industries are mass technology and high value- added industries. The importance of the quality of the mold and die on industrial competitiveness is growing and the measur- ing technology has become an important issue. As compared to the traditional layout machine, the coordinate measuring machine (CMM), which is equipped with touch-trigger probe and can inspect the manufacturing errors of the dedicated prod- uct more precisely and rapidly using the computer numerical control method, has been used widely in the industry. However, most of the measured data remain as the identification of the qualified geometric dimensions or designed points, and cannot provide useful information for the die tryout.

The shapes of mold and die are often designed by sculptured or free-form surfaces with variable curvature by higher-degree polynomials. Conventionally, master models are necessary for die making process and hand engraved by the engraver. The final dies and molds are then machined on a contour milling machine, which uses a master model to guide the cutter. During the die making process, the final dies and stamps do not usually coincide with the curves traced on the drawing board due to the inaccuracy

∗ Corresponding author. Tel.: +886 4 8511888x2121; fax: +886 4 7554175.

E-mail address: chshe@mail.dyu.edu.tw (C.-H. She).

of machining and master model. The advent of computer-aided geometric design dramatically solved this problem. The dies and molds can be produced directly by the computer numerical control (CNC) machine together with the computer-aided design (CAD) and computer-aided manufacturing (CAM) software.

Measurements of free-form surfaces are difficult using a CMM with the teach mode since the surface normal direction of the probing point should be calculated to compensate the probe’s diameter. It is necessary to employ CAD-directed techniques to generate the probing points and probing paths. Various studies [1–4] have addressed the issue of developing a CMM inspection path planning and relatively few studies [5] have addressed the development of the CMM system dedicated for the stamping die to the best of the author’s knowledge. On the other hand, most of current commercial CMM packages such as PC-DMIS [6], CAPPS [7], CAMIO [8] and SILMA [9] support CAD-directed inspection planning. However, they are general purpose pack- ages designed for various components represented by free-form surfaces, and are expensive.

In this study, a CAD-based CMM software and analysis sys- tem for the sheet metal stamping die will be developed. The developed system can analyze the CAD model of the stamp- ing die with NURBS (non-uniform rational B-spline) surface in IGES (initial graphics exchange specification) format and gener- ate the neutral measuring program in DMIS (dimensional mea- suring interface specification) format. Moreover, the proposed

0924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2006.03.216