Abstract
Stamping of sheet metal components without lubrication or using minimum amount of hazard free lubricant is a possible solution to diminish health hazards to personnel and environmental impact and to reduce production costs. This paper studies the application of diamond-like coating (DLC) under severe lubrication conditions by adopting strip reduction testing to replicate industrial ironing production of deep drawn, stainless steel cans. Three DLC coatings are investigated; multi-layer, double layer and single layer. Experiments revealed that the double layer coating worked successful, i.e. with no sign of galling using no lubrication even at elevated tool temperature, while the other two coatings peeled off and resulted in severe galling unless lubrication was applied.
Highlights
In tribologically severe stamping operations e.g. ironing and punching of stainless steel the phenomenon of galling, i.e. breakdown of the lubricant film followed by pick-up of workpiece material on the tool surface and scoring of subsequent workpiece surfaces may appear if lubrication is inadequate
The tool surfaces were scanned in a light optical microscope (LOM) and the workpiece surface roughness was measured across the strip for every 30 mm drawing length by a tactile roughness profilometer, Taylor Hobson Form TalySurf
A repetitive experimental test series was performed on the Diamond-like Coatings (DLC) coating type B under dry friction conditions with 15% reduction and a tool temperature of 110°C
Summary
In tribologically severe stamping operations e.g. ironing and punching of stainless steel the phenomenon of galling, i.e. breakdown of the lubricant film followed by pick-up of workpiece material on the tool surface and scoring of subsequent workpiece surfaces may appear if lubrication is inadequate. Mineral oils containing EP additives are commonly applied to avoid galling in sheet stamping production Application of these lubricants requires additional costs for pre-cleaning, lubrication as well as post-cleaning after stamping. A promising way to eliminate these hazardous lubrication issues is to perform the sheet stamping under dry friction condition by applying hard coatings to the tools, which impedes pick-up. A few promising tool coatings have been reported to work in sheet stamping under dry friction conditions or with minimum lubrication of aluminium, stainless steel and titanium. They include Diamond-like Coatings (DLC) [1], [2] and pure diamond coating [3]. The tool surfaces were scanned in a light optical microscope (LOM) and the workpiece surface roughness was measured across the strip for every 30 mm drawing length by a tactile roughness profilometer, Taylor Hobson Form TalySurf
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