Patent Publication Number: US-2015076128-A1

Title: Weld monitoring apparatus

Description:
TECHNICAL FIELD 
     The present disclosure relates to a welding apparatus, and more particularly towards a system and method for real time thermal monitoring of a weld portion during a welding operation. 
     BACKGROUND 
     Thermal joining processes in modern manufacturing technology, for example, autogenous fusion welding, Gas Tungsten Arc Welding (GTAW), Plasma Arc (PAW), Laser Beam (LBW) and Electron Beam Welding (EBW) are prevalent in the production industry. These modern methods, combined with automated mechanized and robotic torch motion systems, enable closer control of the weld bead geometry, the material structure and properties, and the thermal stress or distortion effects of the weld, thus contributing to an enhanced joint quality and productivity of welding operations. 
     In the mentioned processes, torch power and torch motion primarily govern the desired characteristics of the final weld. To handle the welding transients such as, the material and torch parameter uncertainty, and process disturbances, sophisticated in-process control systems have been proposed which employ measurement and feedback of some weld variables in order to modulate the torch intensity and speed in real-time. However, such implementations may be expensive, difficult to install, and have limited flexibility in the welding process. 
     Further, during direct metal additive manufacturing, welding material is used to build up an object in a process such as cold metal transfer (CMT) additive manufacturing. However, overheating of the weld material during the welding process may lead to buildup collapse, which in turn may alter the final geometry of the part. Some welding systems make pauses between successive passes of the welding process to control the build up. 
     U.S. Pat. No. 5,506,386 describes simultaneous temperature measurements on laser welded seams with at least two pyrometers in relation to monitoring process parameters and weld quality. In laser butt welding of metal sheets, in particular sheets of unequal thicknesses, the temperature is measured at two points behind the liquid-solid interface. From combination of the two readings obtained a series of process data can be derived whereby the welding process can be monitored. 
     SUMMARY OF THE DISCLOSURE 
     In one aspect of the present disclosure, a welding apparatus for applying consecutive welding beads during a welding operation is described. The welding apparatus includes a welding unit including a torch head and a power circuit. The welding apparatus further includes a first pyrometer and a second pyrometer positioned respectively at a first and second pre-determined distance from a tip portion of the torch head, the first and second pyrometers are configured to respectively generate a first temperature signal and a second temperature signal indicative of temperatures of a portion of successive welds. The welding apparatus further includes a controller configured to receive the first temperature signal and the second temperature signal, determine a difference between the first and second temperature signals, set a predetermined threshold based, at least in part, on the determined difference, and adjust a welding parameter of the power circuit, wherein the adjusted welding parameter is lesser than the predetermined threshold. 
     Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a welding apparatus, according to one embodiment of the present disclosure; 
         FIG. 2  is a schematic view of a welding operation conducted by the welding apparatus of  FIG. 1 , according to one embodiment of the present disclosure; and 
         FIG. 3  is a schematic view of another welding operation conducted by the welding apparatus of  FIG. 1 , according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to specific embodiments or features, examples of which are illustrated in the accompanying drawings. Wherever possible, corresponding or similar reference numbers will be used throughout the drawings to refer to the same or corresponding parts. 
     Turning now to the figures, a welding apparatus  100  constructed according to the principles of the present disclosure is schematically illustrated in  FIG. 1 . Specifically, a controller  110 , such as a computer, controls a welding unit  120  and an X-Y-Z table  150 . The controller  110  may be a proportional-integral (PI) controller or an operational amplifier (OP-AMP) controller. The welding unit  120  includes a torch head  122  for welding a weld part or work piece consisting of a plurality of metal components  160 . The welding unit  120  also includes a power circuit  121  (see  FIG. 2 ) in communication with the controller  110 . The power circuit  121  has conventional circuitry associated therewith, comprising of amperage and voltage components. The power circuit  121  is configured to be controlled by the controller  110  to control and adjust one or more welding parameters associated with the welding unit  120 . The welding unit  120  includes an automated robotic assembly. During a welding operation, the torch head  122  is scanned across the metal components  160  by the coordinated movement of the welding unit  120  and the X-Y-Z table  150 , as dictated by the controller  110 . The controller  110  simultaneously modulates power to the torch head  122  via the power circuit  121 . 
     The torch head  122  is any non-consumable type electrode, for example, a gas tungsten arc welding (GTAW) head, a plasma arc welding (PAW) head, or a gas metal arc welding (GMAW) head. Alternatively, the welding unit  120  and the torch head  122  may be replaced with a laser beam (LBW) or electron beam welder (EBW). In these welding devices, scanning may be accomplished by deflecting the laser or electron beams, which may serve as the torch head  122 , rather than physically scanning an electrode over the surface of the metal components  160 . 
     The X-Y-Z table  150  is capable of translating the metal components  160  along the X, Y, and Z axes to facilitate the scanning the torch head  122  across the metal components  160 . The X-Y-Z table  150  comprises an X actuator stage  152 , a Y actuator stage  154 , and a Z actuator stage  155  controlled by the controller  110 . The metal components  160  are restricted from lateral movement by one or more fixtures  156  that clamp the metal components  160  onto the table base  158 . The metal components  160  are secured from longitudinal movement by an end dummy component  162  placed at either end of the metal components  160 . Alternatively, the torch head  122  may be stationary and the scanning may be accomplished by the movement of the metal components  160  by the table  150 . In one embodiment, the metal components  160  may be stationary and the torch head  122  may be moved relative to the metal components  160  by the welding unit  120 . As mentioned earlier, movement of the torch head  122  across the metal components  160  is dictated by the controller  110  in respect of welding speed, positioning, orientation etc. 
     The welding apparatus  100  further includes a first pyrometer  130  and a second pyrometer  132  disposed on the welding unit  120 . The first pyrometer  130  is positioned at a predetermined distance D 1  from a tip portion  123  of the torch head  122 . Similarly, the second pyrometer  132  is positioned at a predetermined distance D 2  from the tip portion  123  of the torch head  122 . The first pyrometer  130  and the second pyrometer  132  are in communication with the controller  110 . The first pyrometer  130  and the second pyrometer  132  may be statically disposed about the torch head  122  using support structures  124 . In one embodiment, the first pyrometer  130  and the second pyrometer  132  may be dynamically disposed about the torch head  122  using a mechanical gear like arrangement controlled by a servo motor. The servo motor may also be in communication with the controller  110 . 
     The first pyrometer  130  and the second pyrometer  132  may be distanced from the torch head  122  either manually or automatically. The spacing and positioning between the first and second pyrometers  130 ,  132  may be based on a size of a molten pool created during the welding operation while deposition of a weld bead on the metal components  160 . The positioning of the first and second pyrometers  130 ,  132 , in terms of distance and orientation or angular positioning may be adjusted based on the geometry of the surface of the metal components  160 , in order to protect the first and second pyrometers  130 ,  132  from excessive heat, radiation, reflection of scattered light etc. during the welding operation. 
     The first pyrometer  130  and the second pyrometer  132  are embodied as infrared pyrometry camera or any other thermal sensing device known in the art directed at the metal components  160  to detect infrared electromagnetic radiation generated as the metal components  160  is heated by the torch head  122 . In an example, the first pyrometer  130  and the second pyrometer  132  may be ratio, or dual colored, or two colored pyrometers configured to monitor intensity of radiation emitted at individual wavelengths. The first pyrometer  130  and the second pyrometer  132  enables non-contact temperature measurements on the external weld surface. Although not specifically shown, the first pyrometer  130  and the second pyrometer  132  may include a scanning and detecting device sensitive to predefined wavelengths appropriate for temperatures achieved in metal welding. 
       FIG. 2  illustrates a first weld pass of the welding operation performed by the welding apparatus  100 , i.e. deposition of a welding material on the metal components  160  during the welding operation. The welding apparatus  100  is used for forming a first weld bead (WB 1 ) of the welding material for joining the metal components  160 . The welding material may include metal electrodes, wireline depositions, plastics, alloys, powder metals or the like materials and may depend on the type of welding operation performed. Further, characteristics related to feeding of the welding material, for example, supply speed; positioning etc. may also be governed by the controller  110 . The welding material is fed through the torch head  122  during the welding operation. Alternatively, the welding material may be supplied during the welding operation via an external mechanism (not shown) separate from the welding apparatus. As explained earlier, the torch head  122 , the first pyrometer  130 , and the second pyrometer  132  are positioned with respect to the metal components  160  to achieve an optimum welding operation. In an embodiment, joining of the metal components  160  may require consecutive weld passes. 
     During the first weld pass, the controller  110  of the welding apparatus  100  is configured to modulate a three-dimensional heat input distribution across a surface of the metal components  160  over time to create a time dependent temperature field distribution throughout a weld region (WR) on the metal component  160  across which the welding operation is to be or has been performed. 
     The desired temperature field distribution may be selected based on the required weld bead (WB) geometry, material structure and properties, and the thermal stress/strain specifications. The desired field distribution can be designated through an off-line numerical simulation model or can be measured directly by the first pyrometer  130  and the second pyrometer  132  on a joint surface, or the desired field distribution can be evaluated by the controller  110  during a real-time welding operation 
     In context of the present disclosure, the desired field distribution is evaluated by the controller  110  during welding of the metal components  160  on receiving inputs from the first pyrometer  130  and the second pyrometer  132  during the first weld pass. The desired field distribution will serve as a predetermined threshold for one or more welding parameters as evaluated by the controller  110 . The welding parameters may include amperage and voltage values related to torch intensity required for an optimal welding process, the welding speed of the torch head  122 , the speed and quantity of the welding material supplied during the welding operation etc. The controller  110  is configured to adjust and control one or more welding parameters associated with the welding operation based on a comparison with respect to the predetermined threshold. The desired temperature field distribution in most applications will be the distribution that yields the simultaneous weld bead formation along the entire length of the weld in gradual cross-sectional increments. 
     As shown in  FIG. 2 , the first pyrometer  130  and the second pyrometer  132  are positioned at respective predetermined distances D 1  and D 2  from the tip portion  123  of the torch head  122 . The first pyrometer  130  and the second pyrometer  132  are configured to monitor formation of the first weld bead (WB 1 ) during the first weld pass of welding operation of the metal components  160 . In operation, the first pyrometer  130  monitors temperature of at least a portion of the first weld bead (WB 1 ) during the first weld pass. Alternatively, the first pyrometer may monitor the temperature of at least a portion of the prior weld bead during a previous weld before the welding operation. The first pyrometer  130  further generates a first temperature signal T1 indicative of temperature distribution of the first weld bead (WB 1 ). The first temperature signal T1 is received by the controller  110  for further processing. The predetermined distance D 1  of the first pyrometer  130  from the tip portion  123  is decided such that the positioning of the first pyrometer  130  is optimum for sensing the temperature of the first weld bead (WB 1 ) 
     Referring to  FIG. 3 , the second pyrometer  132  monitors temperature of another weld bead or a second weld bead (WB 2 ) of the welding material during a current weld that follows the previous weld of  FIG. 2 . Alternatively, the second pyrometer  132  monitors temperature of a portion of the first weld bead (WB 1 ) after the welding operation of  FIG. 2 . The predetermined distance D 2  of the second pyrometer  132  from the tip portion  123  is decided such that the positioning of the second pyrometer  132  is optimum for generating a second temperature signal T2 indicative of temperature distribution of a second weld bead (WB 2 ) during the current weld. The second temperature T2 signal is received by the controller  110  for further processing. 
     As shown in  FIGS. 2 and 3 , the controller  110  is in communication with the power circuit  121 , the first pyrometer  130 , and the second pyrometer  132 . The controller  110  receives the first temperature signal T1 and the second temperature signal T2 from the first pyrometer  130  and the second pyrometer  132  respectively. The controller  110  includes differential operational amplifier (OP-AMP) circuit or a proportional-integral (PI) controller. On receiving the first temperature signal T1 and the second temperature signal T2, the controller  110  generates a first reference value R1 corresponding to the first temperature signal T1 and a second reference value R2 corresponding to the second temperature signal T2. 
     The controller  110  further determines a difference between the first reference value R1 and the second reference value R2 represented as differential maximum value ΔR (ΔR=R2−R1) or a target temperature differential. The differential maximum value ΔR is indicative of a temperature differential corresponding to the first temperature signal T1 and the second temperature signal T2, and is further indicative of the desired time dependent temperature field distribution of the weld region (WR). The controller  110  further sets a threshold for one or more welding parameters, i.e. the amperage and voltage, the welding speed of the torch head  122  etc. corresponding to the differential maximum value ΔR. In context of welding of the metal components  160  in three-dimensional space defined by orthogonal axes X, Y, Z, the controller  110  modulates the time dependent three-dimensional heat input distribution across the weld region (WR) surface of the metal components  160  so that the desired time dependent temperature field distribution is not disturbed. 
     In other words, as explained earlier, the differential maximum value ΔR indicative of the desired time dependent temperature field distribution as evaluated by the controller  110  serves as the predetermined threshold for achieving an optimal welding procedure. The welding parameters, i.e. the amperage and voltage of the power circuit  121 , the welding speed of the torch head  122  etc. during the welding operation are constantly modulated by the controller  110  such that the differential maximum value ΔR is not exceeded in the current weld, i.e. the threshold for one or more welding parameters as set by the controller  110  based on the previous weld is not exceeded in the current weld. For example, the controller  110  is configured to adjust the weld temperature of the current weld such that the differential maximum value ΔR is not exceeded. The one or more welding parameters (amperage and voltage) associated with the power circuit  121  further modulates power of the torch head  122  to achieve an optimal torch intensity for the welding procedure. Such a process will ensure an optimal, stable, and defect free geometry for the weld beads deposited over the metal components  160  over multiple welds. 
     Although the controller  110  is illustrated in the context of discrete blocks within an overall structure, its most likely implementation is as a software algorithm executed by a computer. Ideally, the controller  110  software would be interfaced directly to a computer-aided design (CAD) package used for the welded parts by sharing the same geometric modelling description of objects and motions and thus, serve as a thermal computer-aided manufacturing (CAM) postprocessor for scan welding. The combination of product and process design procedures in an integrated environment will contribute to the optimization of the welding performance in industrial applications. 
     The controller  110  modulates the power to the torch head  122  according to the deviation from the differential maximum value ΔR. The controller  110  evaluates the differential maximum value ΔR according to the thermal control or performance specifications and dynamic welding process parameters, such as, the arc efficiency. These process parameters are variable in space and time during the operation because of heat transfer nonlinearities, thermal drift of the arc and material properties, and disturbances of the torch characteristics and the weld geometry configuration. Thus, to ensure the maximal closed-loop performance, these parameters must be a function of real-time temperature measurements. 
     It may be contemplated that the welding apparatus  100  may include multiple thermal sensing devices (pyrometers) disposed on the torch head  122 . In an embodiment, the multiple thermal sensing devices may be in communication with a plurality of controllers  110 . Alternatively, a separate controller  110  may be provided for each thermal sensing device. Further, the orientation and dimensions of the thermal sensing devices are not limited to that described herein. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure relates to the welding apparatus  100  configured to conduct a welding operation on the metal components  160 . The welding apparatus  100  includes the controller  110  in communication with the power circuit  121 , the torch head  122 , the first pyrometer  130 , and the second pyrometer  132 . As explained earlier, the first pyrometer  130  and the second pyrometer  132  are disposed around the torch head  122  and are configured to monitor a plurality of weld regions on the component. The first pyrometer  130  and the second pyrometer  132  are further configured to generate signals indicative of temperature distribution around the plurality of weld regions. The signals are received by the controller  110 , and the controller  110  evaluates a temperature differential from the signals. The controller  110  further modulates welding parameters of the power circuit  121 , such that the temperature differential with respect to the previous weld is not exceeded during the current weld and thereby preventing overheating of the weld region (WR). Such a process ensures an optimal welding process where improved weld bead geometry with lesser or no defects is attained. Further, as the temperature distribution of the weld region (WR) between consecutive welds is controlled within limits, welding material build up collapse is also countered effectively. 
     The components described with respect to the welding apparatus  100  are highly flexible and are easily configurable with conventional joining processes known in the modern manufacturing technology. These conventional processes employed a single, localized, sequentially moving torch or weld head which leads to steep temperature distribution on a weld region causing structural defects and residual stresses in the component. The welding apparatus  100  overcomes all such defects in a flexible and cost effective manner. 
     While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.