Efficient laser hardening at an auto manufacturer

March 1, 2011
Drawing punches and cutting tools are subject to especially high wear and tear in convex radiuses and cutting edges. In order to increase the operating life of forming and cutting tools, companies are increasingly resorting to laser hardening.

STUTTGART, GERMANY–Drawing punches and cutting tools (FIGURE 1) are subject to especially high wear and tear in convex radiuses and cutting edges. In order to increase the operating life of forming and cutting tools, companies are increasingly resorting to laser hardening.

For near-surface hardening of tools, a laser beam is guided over the area to be hardened. The concentrated application of energy quickly heats the component. The subsequent dissipation of heat through the interior of the component causes it to quickly cool. This self-quenching effect leads to the desired, distortion-free hardening of the surface layer.

To fully develop the potential of laser hardening, the rectangular focal point must be aligned along the contour, and hardened areas must not be traversed more than once; otherwise, they would become tempered again. In addition, prolonged dwelling of the laser beam in the hardening area should be avoided.

For laser hardening, a rectangular pattern beam is oriented along the processing contour by a robot or machine. The laser hardening technology is provided by a Schuler (www.schulergroup.com) Pedilas 6-axis portal system equipped with a special Siemens 840D controller.

A German automobile manufacturer searched for an appropriate solution because a standard fully automated, offline programming solution for laser hardening was not available. Therefore Cenit AG was commissioned to develop a powerful system using its Fasttrim software for 3D laser processing as a basis. With this system, surfaces, curves, and points of Catia V5-based component geometries can be easily and quickly processed.

FIGURE 1. Areas to be hardened: Radiuses and cutting edges.

A process implementation kit (PIK) integrated into the Catia V5-based OLP system comprises a kinematics-based machine model, the postprocessor, and controller emulator, as well as process-specific adaptations of the user interface. For optimal technological implementation, a Visual Basic link to a Microsoft Access process database was implemented.

Through specific software extensions, such as for the creation of guide paths for the hardening, for example, the programming of convex tool radiuses and cutting edges is significantly speeded up.

Starting with the geometric and technological specifications, the tool paths are generated for the laser hardening (FIGURE 2). For example, the technical specifications for radii include the effective area of the laser, the safety margin between adjacent guide paths, information for detection of radius areas, the focal point distance, and look-ahead definitions.

The guide paths for constant and variable radii are automatically generated according to specifications. If the effective area of the laser does not extend beyond the radius width, one or more paths are bilaterally generated. Manual corrections are only necessary in the case of complex "suitcase corner areas" and areas outside the tolerance limits.

FIGURE 2. Automated technology: Quick generation of contours for laser hardening.

The hardening of cutting edges is a further contour type in Fasttrim which is based on the feature technology. In addition to the geometry and effective area of the laser, the lateral portion of the effective area relative to the cutting edge is also set. After selection of the cutting edge to be hardened, the guide path - a specially corrected center point path - is generated.

Fully automatic operations can be edited just as conveniently as in the standard software. Geometries can be modified and deleted. Start and end point on the guide path can be freely selected and easily defined with respect to approach and retraction movements. Events for additional control of the NC output can be distributed along the path at any time.

For simulation, multiply-traversed path areas or areas to be corrected are marked in red in the simulation, which helps to prevent unintentional tempering of hardened areas, increasing process reliability, and supports the user in the event of path corrections. Additional assurance is provided by the realistic motion simulation based on the Cenit Controller Emulator (CCE) for custom-tailored 6-axis control of the Siemens 840D.

A further important extension is the look-ahead function for coarse adjustment of axes to narrow or concave contour geometries to achieve minimal compensation movements. As a result, the axes have more time to adjust their orientation so that little or no feed interruption occurs. Furthermore, if a risk of collision is detected, the angle in the Z-direction is adjusted.

This programming solution for laser hardening offers a high degree of automation, time savings, and investment protection.

Adapted by ILS from the original by Dr.-Ing. Andreas Kach, Cenit AG, Stuttgart, Germany, who can be contacted at [email protected].

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