Limitations of Vibratory Stress Relief

Although the composition and chemical properties of metals do not affect their ability to respond to metal stabilizing through vibratory stress relieving, certain metal conditioning practices such as hardening or tempering will resist the vibratory stress procedure and treatment. Often these metal conditioning practices are applied to such metals as high-carbon steels and specific grades of aluminum and very small workpieces.

Borderline candidates for the VSR Process include:

  • Workpieces or components that are too small. Often, small components, eg, 24″ x 24″ x 30″ or smaller, cannot be made to resonate. If workpiece resonance cannot be reached then the induced vibration will only cause mass oscillation which generates minimal flexure. Workpiece flexure is key to generating the internal force levels required to cause metal to undergo plastic flow. However, if a vibrator with sufficient speed can be combined with an effective workpiece fixturing technique, some smaller workpieces can be successfully treated.
  • Components that have had their physical properties extensively altered by cold working or tempering. Metal components fabricated in a cold-forming operation, e.g., cold-rolled steels, and highly tempered aluminum alloys, resist vibratory stress relief.
  • Metals that have been through hardened. If the hardening is mild, however, ie, < 35-40 RC, and if the workpiece geometry lends itself to vibratory rreatment, the VSR process can be utilized. Long dies and some aluminum die casting molds, for example, can be made more dimensionally predictable during final grinding operations.

    NB: The common element of the latter two non-candidates is lack of ductility. If a metal is unable to undergo plastic flow, ie, large scale migration of dislocations, then its ability to respond to vibratory treatment is limited.

  • Multiple workpieces or components, that would need to be table or rack mounted for treatment. Even though each workpiece will receive some vibration, it’s impossible to monitor whether each workpiece achieved resonance (unless a vibration sensor is placed on each), or whether every resonance peak of each workpiece is treated, i.e., caused to undergo the peak growth and/or shifting which is indicative of effective vibratory treatment.

Even within this category of borderline candidates, however, there are exceptions which can make the use of vibratory stress relief a viable alternative to heat treating. In the case of aluminum weldments, for example, even if the weldment’s components are of a highly tempered metal, the weldment remains a candidate for treatment. This is because both the welded areas, and the areas affected by the heat (the Heat-Affected Zone, or HAZ), are no longer in a highly tempered state, ie, welding has softened the metal to a T4 condition, which is highly ductile. These weldments are good candidates for the VSR process, since the HAZ areas, which can carry high residual stresses, can be successfully treated and, it’s important to note, the treatment will have no effect on the physical properties of the highly tempered members.

Mild steel fabrication treated by VSR

50' L X 15' W X 3' H, mild steel fabrication, a 100,000 lb. capacity open railcar platform.

Large metal component stress relieved by VSR