Zbigniew Gronostajski

Laboratory and Performance Studies of Anti-wear Coatings Deposited on Nitrided Surfaces of Tools used in an Industrial Hot Die Forging Process

Abstract The paper presents the results of laboratory studies performed on produced anti-wear coatings as well as the results of performance tests conducted on tools with these coatings in industrial conditions, in the process of hot die forging. Three different coatings were selected: AlCrTiSiN, Cr/CrN and AlCrTiN, deposited by means of the vacuum-arc method on test samples as well as forging tools used in the hot forging process of a lid. The first part of the paper discusses the results of the studies performed in laboratory conditions, which included: surface morphology by means of SEM, hardness and Young modulus measurements, determination of the chemical composition by means of the EDS method, adhesion tests by means of the scratch method and tribological tests by means of the ball-on-disk method. The obtained results were correlated and applied in the analysis of the performance tests on forging punches with these coatings at an early stage of their performance (up to 4000 produced forgings), which were tested on 19 tools, of which 3 representatives were selected for each coating. A thorough analysis was performed of the wear phenomena and mechanisms and the manner of wear of hybrid layers as well as their resistance to the particular destructive mechanisms. Based on the performed laboratory and performance studies as well as their analysis, it was possible to select the optimal hybrid layer, which enables an increase in the durability of forging tools used in industrial hot die forging processes. The preliminary results showed that the best results for the whole working surface of the tool were obtained for the Cr/CrN layer, which characterizes in high adhesion as well as a lower Young modulus and hardness. In the case of high pressures and the correlated friction, better results were obtained for the AlCrTiN coating, which, besides its good adhesion properties, also exhibited the highest frictional resistance.

Application of Physical Similarity Utilizing Soft Modeling Materials and Numerical Simulations to Analyse the Plastic Flow of UC1 Steel and the Evolution of Forces in a Specific Multi-Operational Industrial Precision Forging Process with a Constant-Velocity Joint Housing

This article concerns an application of physical similarity using soft non-metallic materials to compare and identify plastic flow and evolution of forces during a multi-operational precision forging of UC1 steel with a constant-velocity joint housing. Studies were conducted in order to analyze and select the optimal profile of the working impression of the bottom tool used in the second forging operation with the application of two die shapes (arched and conical) as well as the preforms corresponding to them, in the form of cylinders of slightly different geometry but of the same volume. In the first stage of studies, the modeling material was selected on the basis of “Filia” synthetic wax with modifiers, and the group of materials best fitting the actual material, UC1 steel, were selected for tests according to the author’s original condition of plastic similarity. Next, extrusion forging experiments were conducted with both die shapes applied in the industrial process (appropriately adapted) on a specially designed physical modeling station – a horizontal press. Conducted tests demonstrated that a more uniform method of material flow and lower forces on the punch were achieved with the arched profile than with conical dies. The results obtained were additionally confirmed by numerical simulation of the industrial forging process, which also demonstrated that the application of arched dies is more favorable due to strain distribution and forces.