| The metal forming process, such as forging, is one of the manufacturing processes where metal is pressed, pounded or squeezed under great pressure into high strength parts. Before the process, lubricant is applied to dies to promote the flow of metal, to reduce friction and wear, and to aid in the release of the finished part. The most commonly used lubricant is liquid based lubricant, such as water-based graphite, synthetic oils, liquid soap, and etc. Under high pressures and reductions the lubricant film often breaks down and causing poor metal flow and wears.;This study explores the possibility of using Laser texturing on the tool and its relevance to micro-lubrication in bulk forming. High interface friction is a primary cause for adhesive pickup in cold forging and extrusion of alloys. This study investigates reduction of interface friction through laser texturing of die surfaces, with the hypothesis that textures entrap lubricants hence improving boundary lubrication. Coarse and fine microgrooves were created using pulsed laser on hardened H-13 dies, and tests with axis symmetric aluminum alloy rings and plane strain rectangle coupons carried out with different lubricants. Both ring test and plain stain stamping test have several limitations including low interface pressures and low surface expansions. However, they have many advantages including ease of experimentation, ease of texturing (flat surfaces), ease of measurement (flat surfaces) and reasonable sensitivity to frictional changes. Cold upsetting was selected as the evaluative technique as it avoids the close coupling presented between friction and heat transfer in hot or warm upsetting. Aluminum alloy 5150 rings and AISI 1040 steel rectangle coupons were used as the workpiece materials. Besides their high tendency for surface adhesion, both materials have proper yield stresses which can be handled by lab equipment. The workpieces were upset to different height reductions using oil lubricants with varying viscosities to explore both advantages and limits of texture/lubricant combination. These tests show textures indeed decrease interface friction with coarse ones being more robust and fine ones being lower friction.;In addition to experimental evaluation, theoretical analysis was done based on the Reynolds's equation, slab method of deformation analysis and the link between the design of grooves and friction factors investigated. The theoretical analysis is included in Appendix and the results of this analysis are needed to interpret the results of experimental investigation. |
