DEVELOPING AND TESTING OF GRAPHICAL ENVIRONMENT FOR RAPID PROTOTYPING MACHINE MANAGEMENT

The present work is concerned with the polystyrene hotwire cutting: this technique can be applied to Rapid Prototyping and Rapid Manufacturing. Many software packages to manage numerical control cutting machines can already be found on the market but often those man/machine interfaces are complex and not intuitive; in some cases the cutting precision can also be improved. Given this, a simple software, which is able to import drawings in DXF or BMP format and to control a hotwire cutting machine, has been herein developed. The cut procedure starts from a DXF file, directly imported or obtained as vectorialization of a Bitmap file. Once provided the DXF, the shape to cut is displayed on the screen as a curve: then, the software extracts some key points from the curve minimizing the chordal tolerance. The raw block of polystyrene is placed on the table of the machine. The operator can set an eventual cutting offset, a scale factor and the positioning of the template to cut referred to the polystyrene block. The latter operation is done defining the coordinates of the lower edge of the rectangle that inscribes the shape to cut in a coordinate system centred in the position of the wire. Errors of cut are reduced by minimizing an objective function that evaluates the difference between the route resulting from the discrete movement of the stepper motors and the trajectory set by the software. A correction factor has also been introduced to manage the loss of precision due to the foam thickness dissolved by wire irradiation: its value is adapted to the cutting speed, which changes along the geometry of the shape to cut. The paper will describe the implementation of the software, the management of the cut trajectories, and the solutions to the problems that have been faced. The software has been tested on three case studies, with good results in terms of operator's approval and cut precision achieved. As a conclusion, it was noticed that using the traditional concepts of sketching and technical design (curves and trajectories theory, chordal tolerance, scaling and transformations algorithms) and the new theories of interfaces (man-machine interaction, usability), it is possible to build a powerful graphical environment, extremely simple and flexible. Future developments foresee the tapered cut and the capability to cut rigged surfaces.