Original Date: 02/10/2003
Revision Date: 01/18/2007
Best Practice : Residual Stress Project
Bender Shipbuilding and Repair Company, Inc. has produced better control of thermal (laser) cutting operations for steel plates through correlation of known plate stresses and monitored plate movement to produce more accurately cut parts. Tool-cut paths can be compensated based on the correlation of plate stresses and plate movements to eliminate the need for micro-tabs on the material to be cut away.
When steel plates cool after the manufacturing process at the steel mill, thermal stresses are retained as residual stress. This inherent stress causes the plate to move during the thermal (laser) cutting process, which misaligns the plate from the numerically controlled tool-cut path. Bender Shipbuilding and Repair Company, Inc. had been using external mechanical restraints and varying cut path sequences for controlling the movement of plates during the cutting operation. However, neither of these methods proved to be consistently successful.
Bender was innovative in developing a new process for controlling residual stress movement by placing micro-tabs, thin sections of uncut material that arrest movement, in discrete locations, along cut paths. The micro-tabs placement process has reduced monitored plate movements that occur during cutting operations. As a result, micro- tabs are also used to retain plate cut-outs through the panel line to the assembly stage. Residual stress maps in each plate can be determined by a laser interferometer (an advanced portable instrument that works on a proprietary technology).
An advanced process under development by Bender attempts to couple known thermal manufacturing parameters with measured residual stress characteristics in each plate and correlate them to monitored plate movements. This correlation during cutting will determine the appropriate compensation for tool-cut paths. Further benefits will be evident through the correlation of coupled plate stress characteristics and compensated tool-cut paths for plate responses during thermal (laser) cutting. More accurate part dimensions will result from improved control of cutting operations. As a result, micro-tabs are also used to retain plate cut-outs through the panel line to the assembly stage.
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