THE STATE-OF-THE-ART IN COLD-FORGING LUBRICATION

The manufature of components in steel, aluminium and copper alloys by cold forging production has increased ever since the 1950's. Typical p rocesses are forward rod extrusion and backward can extrusion, upsetti ng, ironing, tube extrusion and radial extrusion. The tribological con ditions in cold forging are extremely severe due to large surface expa nsion and normal pressure in the tool/workpiece interface combined wit h elevated tool temperatures. Except for the more simple cold forging operations successful production therefore requires advanced lubricati on systems. The present paper gives a detailed description of the stat e of art for lubricant systems for cold forging of C-steels and low al loy steels as well as aluminium alloys including all the basic operati ons such as cleaning of the slugs, application of eventual conversion coating and lubrication. As regards cold forging of steel the conversi on coatings are based on zinc phosphates but different requirements to the coating properties have to be met in different cold forging opera tions. This is obtained by adopting different oxidants leading to diff erent composition, layer thickness and morphology of the conversion co atings. Concerning aluminium unalloyed and softer alloys like the AA 1 000, 3000 and 6000 series can be cold forged with either grease, oil o r zinc stearate whereas the harder alloys from series AA 2000, 5000 an d 7000 require a conversion coating to carry the lubricant. Three diff erent types of conversion coating are described, i.e. phosphate coatin g, calcium aluminate coating and aluminium fluoride coating. Alternati ve lubricants and their application are also described.