Step 5 of 5
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Lubrication application: spray, swab, roller, drip, and why coverage beats volume
Set up a spray bar so coverage is uniform and dwell matches the cycle, tell a wet die from a lubricated die, and read the four classic application failures off the die face.
Step 5 of 5Four application failures, read off the die face
Most application failures show up as a wear pattern that points back to the spray map. Reading the pattern is faster than instrumenting the spray bar.
Dry spots in deep cavities, with galling or pickup. Gall or smeared material in a localized zone, usually a back corner, a deep boss, or a feature shadowed by another feature. Cause: the spray pattern does not reach the zone, either because no nozzle is aimed at it, the nozzle is partially blocked, or the geometry shadows the fan. Fix: add or re-aim a nozzle, fit a supplemental drip line into the feature, or swab the feature manually on each cycle if the geometry truly cannot be sprayed. Adding volume to the existing pattern is the wrong fix.
Puddling in the flash land, with washed-out flash gutters. A matte black graphite crust building up in the flash land, often with adjacent flash-gutter erosion from carrier runoff. Cause: too much lube delivered to a low-flow zone, the carrier carrying excess graphite into adjacent areas as it runs off. The flash land sees less contact stress than the impression and does not need as heavy a film. Fix: reduce volume to the nozzles covering the flash land, narrow the fans on those nozzles, or move the spray pattern slightly so the heavier coverage lands on the working impression rather than the flash. Buildup also changes the dimensional contact on the flash land, which can drift the part's flash thickness over a run.
Overspray cooling networks, seeded as heat check on the open face. A network of fine cracks developing earlier than expected on the open face of the die, often outside the impression itself, in a pattern that matches the spray bar's coverage footprint rather than the impression's thermal map. Cause: the spray bar is delivering coolant to the open face on every cycle, and the open face is not seeing the billet heat the impression sees. The thermal gradient on the open face is being driven harder than the impression, and the surface fatigues earlier. Fix: shield the open face from the spray pattern, narrow the fans on the end nozzles, or reposition the spray bar so the pattern stays within the impression footprint. Heat checking outside the working impression is a spray problem, not a thermal-cycling problem.
Symmetric pattern drifted off-center, with wear concentrated on one side of the impression. Wear, gall, or washout building faster on one side of an otherwise symmetric impression. Cause: the spray bar has shifted relative to the die centerline, often a few millimeters from a maintenance event or a press alignment that nobody flagged. Fix: re-measure the bar position against the original spec, re-shoot a witness card, and reset to centerline. The drift can be subtle (5-15 mm shifts the coverage map noticeably) and is the easiest of the four to miss because the lube system looks like it is working.
The diagnostic discipline is: when the die shows a wear pattern, ask whether the pattern matches the impression's working stress map or the spray bar's coverage map. If it matches the spray, the lube application is the root cause. If it matches the impression, the lube application is not where to start looking.