Friction stir welding spindle downforce and other control techniques, systems and methods

A method of performing friction stirred welding comprising:

• (a) inserting a laser sensor into a friction stirred welding spindle;
• (b) using the laser sensor to map the axial distance the friction stirred welding spindle is disposed from a backing surface;
• and
• (c) removing said laser sensor from said spindle and inserting a tool in its place;
• (d) rotating said tool;
• (e) moving said rotating tool into contact with a workpiece placed on said backing surface;
• and
• (f) using said map to control an electrically controlled actuator to correct axial tool position relative to said workpiece,
• wherein said rotating tool in contact with said workpiece plasticizes portions of said workpiece while keeping said workpiece in the solid state, thereby welding said workpiece.

A friction stirred welding method comprising:

• inserting a laser sensor into a spindle;
• controllably positioning the spindle while using the laser sensor to map the axial distance between the spindle and a backing;
• removing the laser sensor from the spindle and inserting a rotatable tool in place of the laser sensor;
• controlling the spindle to rotate the tool;
• controlling the position of the spindle in six degrees of freedom to move the tool into contact with a workpiece to heat and weld the workpiece in solid state without causing the workpiece to melt;
• measuring the downforce the rotating tool applies to said workpiece;
• controlling the axial position of said tool in six degrees of at least in part in response to said measured downforce to thereby maintain the downforce within desired limits;
• avoiding oscillations by applying proportional integral derivative control to maintain the downforce constant or substantially constant during welding;
• and
• generating an alarm if the axial distance between the tool and the backing is less than a predetermined threshold distance determined based at least in part on the map.