Abstract
A novel tribologic system was developed in which volatile lubricants (carbon dioxide—CO2 or nitrogen—N2) were used as a substitute for mineral oil-based lubricants in deep drawing processes. This process allows an intermediate medium to be introduced into the tool contact surfaces under high pressure by flow-optimized, laser-drilled microholes. This eliminates the need for subsequent cost-intensive cleaning processes as volatile lubricants evaporate while expanding to ambient pressure without leaving any residue. This article gives an overview of the current findings to enable and characterize the novel tribologic system. The areas of microhole laser drilling by ultrashort pulsed laser radiation, characterization of the novel tribologic system and realization of the system using a prototype tool will be described.
Highlights
Mineral oil or wax-based lubricants are commonly used in deep drawing processes
A novel tribologic system was developed in which volatile lubricants were used as a substitute for mineral oil-based lubricants in deep drawing processes
This eliminates the need for subsequent cost-intensive cleaning processes as volatile lubricants evaporate while expanding to ambient pressure without leaving any residue
Summary
Mineral oil or wax-based lubricants are commonly used in deep drawing processes. To prepare the formed parts for subsequent process steps, timeconsuming and cost-intensive cleaning steps are required, where the lubricants used may contain toxic additives that pollute the environment.[1]. During deep drawing of the sheet metal parts, liquid CO2 or gaseous N2 is fed into the friction zone between the forming tool and the sheet metal under high pressure by diffuser-shaped, laser-drilled microholes Both media serve as volatile lubricants and evaporate free of residues after the drawing process. Laser pulse energy per unit area, on the inner surface of the cone-shaped microholes was assumed in this model When this fluence reaches threshold fluence for ablation of the sample material, the drilling progress becomes significantly decelerated and discontinuous. To create a conical microhole with a required ablation radius of r2 = 300 lm and the required drilling depth of 5 mm, the necessary pulse energy amounts to approximately 4.4 mJ For this example, a threshold fluence for steel of 0.09 J/cm[2], at a wavelength of 800 nm and a. The Gaussian function for the fluence at the position z in the direction of beam propagation is given by
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