Milling Dies on Digitized Data

The blank is designed to have excess material to compensate for deviations in the imbedding and the casting processes. It also has excess material in the active areas to allow for machining and hand tuning of the tool, in order to produce the required form and surface quality of the part when stamped.

For machining, the blank is aligned and bolted down on the worktable of a horizontal milling machine. Generally the bottom is first machined flat. When the blank is turned the coarse contour of the tool is visible. Large blanks are often inspected and alignment marks manually applied on the blank before it is positioned on the milling machine. Based on the marks, the blank is positioned on the milling table, aligned and bolted down.

Casting-specific features are removed by cutting them off or milling them down in manual control. Then the first contact point of the milling tool and the blank is defined by letting the cutter work in the air, carefully bringing it to the blank manually. From this starting point the roughing is started. Because the cutting depth is not uniform, and cannot be predicted by the CAM software, a slow feedrate has to be used, with manual supervision and correction.

Processing time on the milling machine is a major cost, making any time reduction desirable. Digitized blanks, tool path generation, and optimized cutting can reduce the time required for milling significantly.

A cast blank, 1.5x1x0.5 meters in size (Fig. 1) was digitized using GOM's ATOS II scanner, which scans 1.6 by 1.2 meters (64" by 48") in one view. The part was digitized in six shots, in 15 minutes. On the left the digitizing setup is displayed and on the right, the digitized data is seen.

Fig. 1: Casting and digitized blank.

Fig. 2: Cast blank digitized using the ATOS II scanner with a measuring area of 1.6 by 1.2 meters (64" by 48") in one view.

Fig. 3: Digitized blank and optimized roughing.

Figure 3 shows the digitized blank and the optimized roughing using a ball cutter. By digitizing, the time for roughing was reduced from 12.5 hours to 6 hours, with Tebis milling software.

For digitizing the big cast blanks, markers with 12 mm dot diameter are applied on the blank, using self adhesive markers, or magnetic markers for magnetic blanks. Then a central view is captured, with typically eight or more markers visible in the measuring area. The exact center positions of all visible markers are automatically defined by the ATOS system and the area is digitized.

Then additional views are captured and automatically transferred into the existing scanned data if three or more markers can be defined in the new view, which were already defined in a previous ATOS scans.

Based on this technique, a blank of up to 5x3 meters can be digitized in one hour, while keeping the requested accuracy in the millimeter range (0.04"). The export data from the ATOS system is either a file in STL format or section data, in IGES or VDA format.

The ATOS export data can be directly imported in some CAM systems, such as TEBIS (SCAN module, www.tebis.com) or WorkNC (NCSpeed module from Sescoi Inc, www.worknc.com).

Based on the actual data, the form of the blank can now be fitted into the needed tooling geometry. Then an optimal fit can be defined with minimized processing time. In addition an optimized and collision free cutting path can be calculated, with ideal cutting parameters and minimized cutting time to generate the tool from the blank in a predictable, fast, safe and unmanned operation.

Fig. 4: Cast blank, 3x2x1 meters in size, digitized with ATOS II, with 30 shots in 45 minutes

The process has been tested at BMW, Mercedes and Audi, in Germany, in collaboration with TEBIS and SESCOI. In an actual case, the time on the milling machine could be reduced from 48 hours to eight hours.

Fig 5: Digitized blank with foundry relevant modifications (left) and optimized cutting paths produced by Tebis.

Automotive customers can request ready-to-use tools from suppliers using a digital description of the actual tooling form (Fig. 6). Based on this data, a quality control and traceability process can be started. Wear can be quantified, rework of the tool can be ordered and tested with a well-defined master form and, if needed, an accurate copy of the tool can be produced quickly.

Fig. 6: Tooling from the inner side of a hood.

The GOM scanner can also be used to scan the tool for this application. To get the needed high accuracy, the ATOS scanner with a measuring area of 1.6 by 1.2 meters is calibrated to digitize a smaller measuring area.

For digitizing tooling with high accuracy, a measuring area of the ATOS II scanner of 550x440 or 350x280 sq mm is recommended. Then markers with typically 5- or 3-millimeter dot diameter are attached to the tool and the TRITOP photogrammetry system from GOM is used to define the accurate position of these markers. Then the ATOS II digitizer is used to scan the tool and insert the digitized data into the grid defined by the markers. Using this (ATOS XL) technology, accuracy of a few hundredths of a millimeter per meter object size can be guaranteed.

The two cameras used in the ATOS scanners verify the calibration of the scanner in each measurement, a necessity when using transportable system in quality control applications.

If needed, a new recalibration of the scanner can be done in few minutes by the user. Also the change of the measuring area with calibration based on a certified artifact is done by the user in less than 10 minutes. Using this potential, a GOM digitizer can be adjusted to different customer needs and deliver accurate and efficient results.

For more information contact GOM mbH at www.gom.com.