Check out this case study. This is just one example of what computed tomography can do for you.
F. & G. Hachtel GmbH & Co. KG is a medium sized company in the plastic processing sector, located in Aalen, Germany. The company focuses on testing and the application of all technologies concerning injection molding as well as mold and tool making. Also an inherent part of the company profile is the application of industrial computed tomography.
For fast and optimized compensation of shrinkage and warpage of plastic injection molding parts, Hachtel uses a software product from WENZEL. The PointMaster V5 software allows the determination of exact correction parameters. The calculation is based on analyzed scanned data as a result of an actual to-nominal comparison. The actual geometry data is captured with a precise computed tomography system. The significant advantage of CT scanned data lies in the non-contact and holistic acquisition of outer and inner structures with a high resolution of detail.
Compensation of shrinkage and warpage is an ever present topic in the field of mold and tool making. With tools made strictly according to the drawings in most cases the parts produced are not true to size. This effect shows up particularly in complex plastic parts with high accuracy requirements.
Conventional methods for compensation of shrinkage and warpage are often time and cost intensive. There are several steps in the compensation procedure needed to reach the desired quality. The company F. & G. Hachtel GmbH & Co. KG integrated a system into their
process which reduces the required time for compensation of shrinkage and warpage in injection molding to a minimum.
Actual Data Acquisition with Computed Tomography
The process chain for compensation starts with a complete CT-Scan of the part.
Based on the 2D radiography images a 3D reconstruction is carried out. The 3-dimensional point cloud is used to calculate a surface-model in STL-format (Figure 2).
Subsequently the surface data is preprocessed; with STL-Modeling writing and ejection marks are removed. The data is smoothed and the number of triangles optimized afterwards.
This means, triangles on flat surfaces are enlarged and therefore the number of triangles reduced. On highly curved surfaces the number of triangles remains unchanged.
Subsequent to data processing a comparison of the scanned data and a CAD-model is carried out. The deviations of this actual-to-nominal comparison are displayed in colors. Figure 4 shows the deviations of a plastic box. This view shows the side wall of the box is shrunk to the inside.
With PointMaster, correction parameters according to these deviations are calculated. With this calculation method the deviations are not just simply mirrored, but the material properties are taken into account, also. The technical knowledge and experience of the toolmaker can optimally be included into this process.
In figure 5 the local differences between actual part (red) and nominal tool geometry (green) are shown. The blue intersection contour is the new contour to be manufactured.
When the tool geometry is changed according to this correction and the part is injection-molded with similar process parameters a more accurate part can be produced.
In a further procedure the STL data is reversed engineered into CAD surfaces (figure 6). Thus the compensated data can be imported to every conventional CAD/CAM system. This data is the basis for the tool design.
The following inspection of a part manufactured on the basis of the compensated tool design shows that even
after a single correction cycle parts true to size can be produced.