Determination of the Heat Transfer Coefficient (HTC)
The thermal contact resistance between a cooled forming tool and the according heated metal blank is a determining factor in any press hardening process, as it highly influences the quality of all processed parts. Knowing its exact value enables a systematic temperature control of the sheet material and therefore the reliable anticipation of material properties that are influenced by microstructural transformations. As a consequence, parts can be formed that feature specific strength properties.
The designed test rig enables the exact determination of the heat transfer coefficient as a function of pressure and temperature for all metal combinations.
Aside from the physical disruption of a forming tool, tool wear is considered the most important failure mode in forming applications, as it has a direct impact on the dimension accuracy, shape and quality of the processed parts. Thus, its progress has to be monitored and - if possible - anticipated thoroughly. In this context, a tribometer is a laboratory test rig that simulates elementary relations between friction, wear and lubrication based on simplified sample geometries. While common tribometers (Pin/Disc or Pin/Flat) mostly realize recurring contact movements, the tribometric system designed at T&F it is always in contact with intact surface areas. The obtained information is therefore much more realistic and relevant - especially for forming applications.
As suggested by the name of the procedure, the Hole Expansion Test (HET) analyses the resistance to cracking of sheet materials when an existing hole is expanded. It therefore describes and evaluates the formability of material edges.
Current research focuses on the comparison of the cracking behaviour of laser cut and punched holes in different AHSS (Advanced High Strength Steel) grades. The applied test rig is built according to the standard ISO 16630:2009.