Improvement of hot forging manufacturing with PVD and DUPLEX coatings

The application of a DUPLEX treatment, which included low pressure pulsed plasma nitriding of AISI H11 tool steel dies and PVD BALINIT® FUTURA-TiN/TiAlN multilayered coating, was studied as a possible technology to improve the process of hot forging of steel components. The quality of the DUPLEX treatment was determined by laboratory analyses of coated test plates, which were treated together with the hot forging dies. Surface roughness, Vickers microhardness including in-depth measurements, coating thickness and adhesion parameters determined by the REVETEST method and microanalysis (SEM and EDS), were investigated. Performance tests were made in real working conditions in the UNIOR hot forging industry in Zreče, Slovenia, and included three types of technological processes: (a) form milling of graphite electrodes (to produce dies by the electrical discharge machining process with cemented carbide cutters improved with a BALINIT® Diamond coating); (b) hot forging of steel components (with two step forging dies fixed in a 1650 t eccentrically driven press, improved with the DUPLEX treatment); (c) hole punching in forged parts (with dies made of ASP30 tool steel and improved with a standard PVD TiN coating). The hole punching in forged parts and milling of graphite electrodes were performed successfully in practice for many years. In hot forging, the first positive results were obtained after three experimental studies in the last two years. Optimisation of the parameters of the DUPLEX treatment is still needed before this technology can be introduced into regular manufacturing operations for hot forged steel parts.