Hot forming tools for aluminum and magnesium sheets
AssigneeGM Global Technology Operations LLC
InventorMichael D. Hanna
Life of this patent
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Abstract
A ferrous metal tool is provided for the forming of light metal sheet workpieces at elevated temperatures, with the forming surface of the tool prepared to minimize friction and adhesion when engaged in deformation of the hot sheet metal. The forming surface of a steel tool is nitrocarburized to form a compound layer and diffusion layer on the surface. The compound layer initially comprises an outer gamma-phase material and an underlying epsilon phase material. Gamma-phase material is removed to expose underlying epsilon phase material, and low friction particles are embedded in the modified nitrocarburized compound layer of the forming tool.
Claims14
A ferrous metal tool for forming aluminum alloy or other light metal alloy sheet workpieces at forming tool and workpiece temperatures above about 250° C., the tool having a body with a machined portion defining a forming surface for sliding contact engagement with a heated sheet workpiece in deforming the workpiece, the forming surface comprising:
- a nitrocarburized surface layer at a forming surface to be contacted by the workpiece, the nitrocarburized surface layer being coextensive with the forming surface, the nitrocarburized surface layer initially comprising a compound surface layer with an underlying diffusion layer, the compound surface layer comprising an outer gamma-prime phase and underlying epsilon-phase;
- and
- the nitrocarburized epsilon phase material of the compound layer containing embedded particles of low friction material that are infusible at the forming temperature of the forming surface, and at least a majority of the gamma-prime phase layer being removed from the forming surface of the tool prior to embedding of the particles in the epsilon phase material.
A method of making a forming tool for the forming of aluminum alloy sheet metal workpieces, or sheet metal workpieces of other light metal alloys, at a forming temperature of at least 250° C., the method comprising:
- machining a surface on a ferrous metal tool body, the surface being shaped for sliding contact engagement with a sheet metal workpiece to deform a contoured shape in the sheet metal at the forming temperature;
- cleaning the machined surface for nitrocarburization;
- nitrocarburizing the machined surface to form an outer compound layer and an underlying diffusion layer generally coextensive with the intended forming surface, the compound layer comprising an outer gamma-prime phase material and an underlying epsilon phase material;
- removing gamma-prime phase material from the compound layer to expose epsilon phase material;
- and
- embedding low friction particles in the epsilon phase material and coextensive therewith to yield a forming surface on the tool body, the friction particles being substantially non-fusible in the epsilon phase layer at the forming temperature of the tool for the sheet metal workpieces, the forming surface for the sheet metal workpieces thus comprising the low friction particles embedded in the nitrocarburized forming surface.
Dependencies are inferred from the claim text.