The ATOS scanner generates a dense data set of the scanned form. This data can be exported as point cloud, section or stl data file. As many CAD/CAM software packages support the stl data format, scanner data can be used directly to create NC code for computer controlled machining.
The step to create CAD data (Reverse Engineering) which describe the complete form in multiple mathematical surfaces (patches) is the standard to define geometrically simple parts. It is also efficient to describe smoothly curved areas, but this method is very time consuming if complex forms have to be defined.
This Reverse Engineering process can thus be omitted if the scanner data is good enough in density and quality and if a direct copy of the existing model, is needed.
Therefore the traditional copy milling process can now be replaced by a faster and much more flexible process, including high end digitizing, stl data generation and direct interface into post treatment and NC code generation to the milling of a die.
In the actual case a series of 10 glass bowls with rich ornaments had to be reproduced in numbers, respecting a demanding time table. For this, 10 different moulds for glass molding in grey cast iron had to be produced by Forstek, Slovenia. The master patterns (i.e. the product) were similar, with different ornaments and different sizes. Each bowl had therefore to be copied into a die assembly to allow molding of the needed multiple glass copies. Enclosed, the needed steps to produce the mold assembly for a glass bowl with the dimensions of 230x230x150 mm are described.
In the traditional process, a negative copy would have been cast using an epoxy (araldite) material. Then the negative pattern would have been copy milled into a preformed block of grey cast iron using a copy milling machine.
The limitations of this process are:
- very slow process (no optimized milling possible)
- no potential for data modification and data storage
A very tough deadline and the large number of moulds needed, asked for a new process which is much faster compared to copy milling.
Faster milling is possible on CAD data. CAD data can be generated based on measured data, using Reverse Engineering methods. Thus a process using a digitizer, Reverse Engineering software and a CAM software can be a solution. The problem is the complex shape of the object. To create a CAD file defining the complex geometry of the glass bowl as shown in fig. 1 and 2 would take multiple days and create a massive file.
The lengthy Reverse Engineering process can be eliminated if a high end digitizer is used which produce a dense and accurate data file. Then the CAM (Computer Automated Manufacturing) process can be done directly on the stl data generated by the digitizer.
Pressed by the short delivery time and encouraged by the good success with the ATOS digitizer in other projects made by TECOS, Slovenian Tool and Die Development Centre, Forstek decided to go for a process based on high end scanning and direct milling. For the digitizing, some reference markers were applied and the glass bowl was sprayed using a fine Titanium Dioxide power mixed with alcohol.
