Options
2002
Conference Paper
Titel
Process-integrated nondestructive testing of ground and case hardened parts
Abstract
Heat treatments and finishing processes are necessary to give materials under extreme load the desired strength, shape, and surface quality. Present quality management systems use tests that are performed according to relevant industry standards. However, these tests are time consuming, in many cases destructive, and are therefore not applicable for process-integrated non-destructive testing (PINT) or for fast post-process testing (FPPT). Non-destructive quality inspection (NDQI) equipment that is currently available uses optical, thermal, mechanical, electromagnetic, and acoustic methods for FPPT. Parameters like topography, microstructure, hardness, residual stresses, case depth, and cracks are the most important targets for NDQI. R&D has shown in the last five years that parameters such as hardness, residual stresses, and case depth can be determined simultaneously by using multi-parameter sensor systems. The key element for real-time quality inspection and process control are non-destructive sensor systems. In conventional machining, an incoming inspection and a final inspection after finishing are performed. Manufacturing with PINT / FPPT means no additional time for inspection is needed, except the sampling test for geometry. Very important material quality characteristics such as residual stresses, hardness, and case depth are determined while machining by using multi-parameter electromagnetic / acoustic sensor systems. This leads to a dramatic reduction of inspection time even though 100% of the machined output is checked. To verify the fundamental idea that "simultaneously measured physical properties of heat treated and machined surfaces will contain basic information about the complex microstructure and residual stress state", prototype units have been developed at the Fraunhofer-Institute Non-destructive Testing (IZFP), Saarbrücken. Tests have shown that hardness, case depth and residual stress gradient measurements can be performed with success and that complex grinding states and heat treatments can also be analysed with this multi-parameter approach.