Metallife Application possibilities for compressive stress and die surface treatments

Die Casting Dies - NEW, USED, WELDED, POLISHED

Die casting dies because of temperature gradient thermal shock, develop high levels of tensile stresses in a short amount of use time. Sometimes micro cracking can develop in as little as 10-100 shots. By applying MetaLLife when the tool is NEW, and once again at the existing historical HALF life, a minimum increase of 25% can be observed. It is recommended that, if possible, the tool should be processed before any molten metal has contacted the surface of the die.

Die casting dies that are USED and have developed some thermal heat check cracks may be candidates for MetaLLife depending on the size and depth of the cracks. In these instances it is best to send a recent casting that will provide a fingerprint of the operating condition of the die including any cracks that have developed. Even if the cracks are too large to close, the compression benefit at each end of the crack will slow further propagation. Gross cracking and cavitation breakout cannot be repaired using MetaLLife.

Die casting dies that are welded have an inherent high level of tensile stress. Residual tensile stress from welding is created because the weld consumable is applied in its molten state. This is its hottest, most expanded state. It then bonds to the base material, which is much cooler. The weld cools rapidly and attempts to shrink during the cooling. Because it has already bonded to the cooler and stronger base material, the weld is unable to shrink. The net result is a weld that is, essentially, "stretched" by the base material. Inconsistencies in the weld filler material, metal chemistry, weld geometry, porosity, etc..., act as stress risers. These residual tensile stress conditions start further initiation of premature die fatigue failure. The weld negatively affects the integrity of tooling. Common practice is to perform a subsequent stress temper to remove these stresses.

MetaLLife is beneficial in reversing the residual stress from welding that tends to cause failure. These stresses in the die cast tool's heat affected zone are converted to a beneficial compressive state. The above graph shows the "as welded" condition and then the reduction in tensile stress when only a stress temper is performed and finally the compressive benefits induced after MetaLLife, and a prior stress temper. Tensile stresses generated from welding are additive with applied load stresses. This is why these "as welded" combined stresses accelerate failure at welded locations. Heat stress tempering to reduce the tensile to zero (approximate) then following with MetaLLife, restores the integrity of the weld and its relationship with the base material.

A relatively new procedure to reduce fillet and radii cracking of die casting dies is now known and practiced by a limited number of informed die casters (introduced in 2008). The procedure involves a diamond polish to these specific areas as opposed to finishing them with a 300-400 stone. When MetaLLife is applied before the diamond polishing, the effective fatigue resistance in these areas can be increased 30-40%. Field trials and production usage have shown increases in tool life from 38% to over 100%. There is no concern about reducing the compressive stress benefit since a higher resulting fatigue protection is revealed after polishing due to the knee shape of the compression curve. See resource section of our site for more information.

Drawing, Forming, Blanking Dies

Blanking and piercing dies fatigue at sharp corners. This requires them to be frequently reground to restore the sharpness. By applying MetaLLife, the frequency or need to do this is reduced or eliminated. The process is applied without damaging existing sharpness of the tooling.

Drawing and Forming dies have a tendency to gall and pick up material during use. Coatings and plating make the surface slicker, however, applied lubricants do not adhere very well. With use, the coating can wear and must be reapplied. MetaLLife, before coating, will provide a topography to the surface on a micro level that retains lubricant. When this is combined with the coating or other surface treatments, it enables these dies to perform at maximum efficiency.