Improvement of Tribology in Sheet Metal Forming of High-Strength Steel Sheets by PVD-Coated Dies

• Published in: Materials performance and characterization 2018-10, Vol.7 (3), p.320-329
• Main Authors: Sivarajan, S., Padmanabhan, R.
• Format: Article
• Language: English
• ISSN: 2379-1365; 2165-3992
• DOI: 10.1520/MPC20170035

During sheet metal formation, the high strength of sheet material leads to high contact stress between the die and blank material, which results in increased die wear. Moreover, the reduction in the use of lubricants because of environmental concerns has led to greater wear of sheet metal–forming dies. It is important to understand the tribological behavior of the blank die contact so that steps can be taken to reduce the die wear to an acceptable level. Die wear reduction is possible by using alternative die materials, modifying die geometry, or by creating a wear-resistant surface on sheet metal–forming dies using Physical Vapor Deposition (PVD) coatings. PVD coatings have a thickness in the micro range and greatly improve the tribological properties of the die material. In this work, three pins made of AISI D2 steel were coated with Titanium Nitride, Titanium Aluminum Nitride (TiAlN), and Aluminum Chromium Nitride using the PVD process. Friction and wear tests were conducted on the pin-on-disk testing machine as per ASTM G99, Standard Test Method for Wear Testing with a Pin-on-Disk Apparatus. The pins had diameters measuring 10 mm and lengths measuring 35 mm. They were heat treated until they reached 55 HRC and ground to a Ra value of 0.1 µm. A 5-mm-radius tip was provided on one end of the pin. D3 steel was used as counter material (disk). The normal load was 30 N, and the sliding speed was 0.3 m/s. The experiments were conducted in dry contact conditions. Based on the results, it was concluded that TiAlN coatings are an excellent choice to modify friction behavior and improve wear resistance of die material.