Introduction to Welding Automation

Transcription

1 Introduction to Welding Automation This document summaries the Adaptive Control Methods By: Abdullah Alhuzaim 7/20/2011

2 Adaptive Control Methods: Touch Sensing Through-the-Arc Seam Tracking (TAST) -Single Pass - Root Pass Memorization (RPM) Laser Based Seam Tracking Touch Sensing Overview: Allows robot to change a weld path automatically Consists of o Moving the TCP toward an object using a predefined Motion Speed Direction o Using an input signal that the robot has come into contact with the object o Store offset information in position register (PR) o Use data in PR to shift the weld o Set-up Required for Tough Sensing Good TCP I/O assigned Touch frames Touch Frames: o Determines the of the motion in reference to the TCP o Defined by the three points 1 st point is origin 2 nd point is the + X Direction 3 rd point is the + Y Direction o Can have up to 32 touch frames o Taught or Direct Enter Search Pattern

3 o Sets the for each \stores information in position registers o 4 types of patterns o Simple Requires 2-D Surfaces must be perpendicular to each other Stores the found position into the PR Typically used to find the starting position of a weld path Fillet/Lap o 1-D,2-D, or 3-D shift o Used to find position offset information o Stores the position offset a position register o Can be used to rotate the part V-Groove o 1-D Touch o Stores the positional offset in a position register o Can be applied to one or more positions in a path OD/ID o 2-D touch to find the center o Stores the positional offset of the center in a position register o Can be applied to one or more position in a path

4 Touch Schedules o Set up conditions that define the motions including: Position register Touch frame Search pattern to use Robot speed Motion type Incremental o Access from the data screen Touch sensing hardware o Low voltage applied to the weld wire or gas nozzle o When contact is made signal is sent to controller and the location of the TCP is recorded o Never enable the circuit during welding Mastering Defining taught positions in a program as the expected locations of position o When the robot follows the taught path then the offset is zero o Remastering is required when the start position must be retaught o Offset is the between the location of the part and the stored location o Mastering is needed for patterns that generate offset data. (fillet/lab, V- groove and OD/ID) o A simple does not require mastering since it produces an actual location stored in the PR

5 Through the Arc Seam Tracking (TAST) Search pattern 1_D 2_D Simple Not valid Required 2 Fillet/Lab Requires 1 Minimum 1 per Requires 2 X and Y, X and Z. Y and Z minimum 1 per Introduction o Many application are not repeatable to +/- ½ weld wire diameter o Reasons: Forgings Stampings Castings Tolerance stack Fixturing o Sensors can be used to adapt the path of the robot to the weld seam to ensure weld quality TAST can be used to correct weld path since changes in the CTWD change the current TAST can be used for vertical and lateral tracking o Vertical- no weave required o Lateral- requires sine weave TAST can be used on any ferrous metal welding where current feedback is stable o TAST will not function properly if a weld parameter is ramped during operation o Establish good parameters before trying TAST Tool frame must be used with TAST o GMAW 3_D 1_D and Rotation 2_D and Rotation 3_D and Rotation Not valid Not valid Not valid Not valid Requires 3 X, Y, and Z minimum 1 per Requires 1 Minimum 2 per Requires 2 Minimum 2 per Requires 3 in one (usually Z) 2 in each of the remaining V-Groove Requires 1 Not valid Not valid Not valid Not valid Not valid Minimum 1 per OD/ID Not valid Requires 3 in For ex: +X,-X,+Y not X,Y,Z Not valid Not valid Not valid Not valid

6 All transfer Modes Shielding Gasses AR Ar+CO2 or O2 CO2 Weave Plane Lateral Tracking o Current varies as the torch moves back and forth across the seam o The side walls have a higher current that the center o The offset is based on the average current in the center of the weld o The average current can be determined by tacking a sample of the current or entering a value for current Vertical Plane Tracking o Vertical TAST compares the welding current to a reference current The reference current can be determined by taking a sample of the current or entering a value for the current. Weave is not required with vertical TAST. When weaving is used, the current at the weave center is compared to the reference current o If the weld seam is offset downward (away from the weld torch) the sampled current decreases due to increased electrical stick-out and the weld path will be offset closer to the seam. Factors that can affect tracking: o Changes in welding wire type o Changes in weld wire diameter o Extreme change in weld size o Changes in welding arc location in respect to the weld puddle o Transfer mode changes o Changes in weave parameters (Amplitude, Frequency, Dwell) Note: if system has more than 2 motion groups, adjust the delay time to 0.14 seconds TAST Application Guidelines o Material thickness greater than 3 mm (1/8 ) o Groove should have a consistent angle of 90 or less

7 o Fillet welds should have a max included angle of 90 or less and must have at least a 5 mm leg o Tack weld - ½ of the weld size and concave o Weld seam should deviate less than 15 rotation o Torch should be positioned in the center of the weld at the arc start (touch sense) o Outside corner and lap joints must use a weave width 2mm less than material thickness o Base metal must be ferrous o Must use sine weave o Use diameter wire for best results o Weave parameters: Amplitude 1.8mm Frequency 4 Hz Dwell time 0.05 second