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Vibrate Away Weld Stress
Almost anything that is made from metal harbors unseen stress that is either mechanical or thermal in nature. It is invisible until the part fails prematurely, cracks, or distorts.
Mechanical stress is induced when metal is bent, formed, or stamped. More destructive, however, is the thermal stress created when metal is cut, welded, cast, drilled, or quenched as a result of a sharp drop in its temperature. For example, when welding, air quenches the metal as you move away from the line of work. This is known as the heat-affected zone (HAZ). During this sharp temperature drop, both the weld metal and HAZ are affected. This results in potential cracking or distortion over time.
There is a new procedure that helps remove thermal stress created by welding on hard-to-weld items such as engine blocks or transmissions. This device, developed by Bonal Technologies, Inc., works via induced vibrations.
Identified as subharmonic vibrational stress relief, the Meta-Lax process does not require disassembly of equipment or components. The system consists of a control console, a transducer to read the amplitude, and a forced inducer that creates the vibration. The forced inducer and transducer are mounted on the piece to be stressed relieved.
Depending on the metal alloy, weight, and thermal stress, the complete job will take approximately one hour.
Without getting mired in physics, the basis of the process resides in a principle of Young’s Modulus of Elasticity.
Vibration is induced at an increasing rate while amplitude is monitored. At some frequency, amplitude will reach a high point (the harmonic peak), which is the greatest rate of molecular excitement.
An amplitude corresponding to the lower one third of the harmonic peak amplitude is then maintained for up to one hour. During this time, the molecules will properly realign, eliminating thermal stress and restoring strength and dimensional stability.
Unlike heat treating that cannot be done to complete machines, Meta-Lax is the only method that can confirm the elimination of thermal stress. This is done by first identifying the harmonic peak frequency. Then, it periodically monitors the harmonic peak to observe a shift in frequency. When the harmonic peak frequency repeats within 0.8 hertz as read on the console, the process is complete.
An additional feature of Meta-Lax processing is that subharmonic vibrations can be applied while welding. The most desired benefit for farm equipment is longer service life after welding, after all.
Other benefits include less distortion and less welding blow through. Weld metal is more or less pulled into the joint, making the weld easier to start. Thermal stress is removed throughout the welding.
Metallurgically, the weld metal will have significantly higher ductility (up to 400%) and impact values (up to 75%), which are indicative of a crack-resistant weld.
As with any new tool, fixturing the forced inducer and transducer is awkward until you become familiar with it. As stated, the Meta-Lax system is pricey. The base model 2001 starts at $19,000.