Development of a transmission-illumination-based crack detection method using translucent tools for testing of thin-walled metal sheets and foils
2022-01-0275
03/29/2022
- Event
- Content
- The formability of thin-walled metallic sheets and foils is increasingly gaining in importance in the automotive industry and in medical and food packaging. As a result, the demand for methods to test the deep drawing and stretch forming capabilities of these materials is increasing significantly as well. In deep drawing and stretch forming, the in-situ crack detection is either performed manually by purely visual evaluation by the machine operator or automatically by a crack detection system. The automatic crack detection method commonly integrated in sheet metal testing machines functions by analyzing the drawing force during forming. However, friction, vibration, and machine noise are disturbance variables that prevent crack detection in thin sheets and foils. The same disturbance variables also prevent robust crack detection in thin sheets and foils by systems that analyze structure-borne sound. Crack detection systems that use reflected light methods, on the other hand, necessitate homogeneous illumination and are interfered by highly reflective as well as inhomogeneous sheet surfaces. In order to avoid the above-mentioned disadvantages of the currently existing crack detection methods, a method based on transmission-illumination was developed. Fundamental to this new development is the use of a translucent punch made from alumina-based ceramics, which incorporates a light source, and a camera connected to an image-processing unit. The detection process works as follows: the translucent punch penetrates the sheet and forms it accordingly. As soon as a crack is formed, light penetrates the fracture and falls onto the image sensor of the camera. The image-processing unit detects the jump in illumination and triggers the immediate stop of the forming process. Forming tests were conducted to confirm the stable and operator independent performance of the newly developed detection process and the toughness of the translucent punch.
- Citation
- Staupendahl, D., Schneider, J., and Wahlers , L., "Development of a transmission-illumination-based crack detection method using translucent tools for testing of thin-walled metal sheets and foils," SAE Technical Paper 2022-01-0275, 2022, .