A New Mechanical Cold Trimming Process Assisted by Dashed Lined Infrared Heat Treatment of Martensitic Steel Considering Energy Efficiency

Ultra-high strength steels (UHSSs) cause heavy loading conditions on the trimming tools, which is an obstacle to applying mechanical trimming to UHSSs. This paper presents a new mechanical cold trimming process assisted by dashed lined infrared (IR) heat treatment for martensitic (MS) steel to reduce the trimming load. The newly proposed dashed lined heat treatment (DLH) does not heat the entire trimming line, but heats it in partial broken lines (like dashed lines), in order to increase the energy efficiency while reducing the trimming load. The main idea is that a paper with dashed holes can be easily cut by hand. In addition, the heat treatment (heating followed by cooling) is completed before the material is delivered to the trimming steps to avoid decreasing in productivity due to the heating process time. The experiments of the DLH cold trimming confirm that this process can reduce the trimming load and improve energy efficiency. Moreover, electrical–thermal–mechanical simulations show that the DLH results in longer-lasting plastic deformations closer to shear deformation mode before fracture occurs at the trimmed section, which enables a smoother trimming process. Finally, an application of the DLH cold trimming for a door impact beam is presented with a numerical simulation. The results of this paper show that this method has a sufficient potential to apply the mechanical trimming method to MS steels in manufacturing of the automotive part.