Cases
"Copy and Paste" with roentgen rays and laser beam
Industrial Computer Tomography (CT) is gaining increasing significance in the quality assurance of casted parts. In measuring by way of CT both the inner contours and outer contours of an object can be grasped. The obtained three – dimensional data from the CT – scanned object is not only suitable for measurement tasks but also suitable for digitalizing objects for which no CAD models or technical drawings are available. In the case described here, an accurate copy of an original historical object could be constructed starting from CT – data.
Reverse Engineering gives new life to the past
The project was under guidance of the chair "Institute of Metal Forming and Casting" from TU Munchen (technological university of Munchen) in co – operation with several industrial partners. The objective of the project (requested by the research institute of Bavaria) was the construction of a fully functional cylinder head in the original material without the use of building plans or CAD models.
In order to demonstrate the feasibility of the Reverse Engineering process, a cylinder head from a BMW 328 (year of construction 1937 – 1939) was reconstructed from CT – Data with the aid of a Rapid Prototyping (RP) process. Motive for the choice of this complex cylinder head was the limited availability of this historical cast part, where in case of demand you have to take into account a delay of several years.
The followed method of Reverse Engineering, classifies into several chapters.
Establishing of the Objects Geometry by means of CT
The first step was the CT scanning of the disassembled cylinder head. The 550mm long cast part is being scanned in 1080 layers.
The matrix of the image measured 1024 x 1024 bit (8 bit depth). Out of the three – dimensional image from the cylinder head (the volume – or voxel model) cores (e.g. cooling channels) like inner and outer cores were extruded.
Creating of an STL Model
For further processing of these data the solid model was converted into a surface model (STL Model). After a curvature dependent triangle reduction of the STL data the file size of the data set was reduced to a useable 100 MB. The STL format formed the basis for changes in construction of the cylinder head and is the standard format for the production of sand cores by means of Selective Laser Sintering.
Preparation of an STL file for casting purposes
Because the scanned data only delivers a model of the finished cylinder head, all elements concerning the casting – like sprue, runner and gate – still had to be designed. First a feed point and gating system were designed. Because the cylinder head had to be machined on the functional surfaces after the casting process, tooling features – like shut off areas, tubes, inlets and outlets etc. – had to be foreseen. Therefore extra material needed to be added. This was realised by the offset function in Magics. Moreover one had to take into account the shrinkage after the hardening of the metal by an appropriate scaling factor.
Generation of the collection of cores
Construction of separate cores by means of Selective Laser Sintering
The RP technique of Selective Laser Sintering makes it possible to build sand cores directly out of STL data. As shape giving substance we used quartz sand and a thermo hardening binder which was locally cured by a laser beam. After this process the sand cores were post – cured in an oven.
Casting in the target material and post treatment
The complete assembled collection of cores was cast with an aluminium – silicon – alloy for heavily loaded cylinder heads. After demoulding and removing the cores, the functional surfaces of the cylinder head were machined on a five – axis milling machine.
An inspection on first sight as well as a CT control of the cast part showed that the obtained copy was a workable spare part for the desired BMW 328. The building time for the copy of the demanding cast cylinder head measures around 6 – 8 weeks.
Read more about Metal Casting
The main purpose of this project was to prove the feasibility of the Reverse Engineering process by means of a complex cast part. The described method is today the only available method to reconstruct objects with inner contours, without damaging the original part. More simple parts (e.g. smaller geometry’s) have shorter lead times and improve the cost – effectiveness of the above described method.
| In the project following companies were involved: BMW AG, Landshut; Hattinger Pruf – und Entwicklungsgesellschaft mbH (HAPEG), Hattingen; Knotenpunkt GbR, Balingen; Materialise GmbH, Munchen; VolumeGraphics GmbH, Heidelberg. |
We would like to thank all involved companies for their support to the implementation of this project.
Prof. Dr.–Ing. Hartmut Hoffmann
Dipl. – Ing. Timo Hanss
Dipl. – Ing. Heinz Steinbeiss
Lehrstuhl fur Umformtechnik und Giessereiwesen
TU Munchen
