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EP-4741089-A1 - SHORT ARC JOINING METHOD AND JOINING DEVICE

EP4741089A1EP 4741089 A1EP4741089 A1EP 4741089A1EP-4741089-A1

Abstract

To provide a robust method for carrying out a short-arc welding process with arc phases (LP) and short-circuit phases (KP), reliably reducing weld spatter and avoiding expensive measurement technology, in a first sub-phase (KP-1) of the short-circuit phases (KP), a short-circuit current (IK) is increased from an initial current (IK 1 ) present at the beginning of the first sub-phase (KP-1) to a predetermined melting current (IK m ). In a second sub-phase (KP-2) of the short-circuit phases (KP) following the first sub-phase (KP-1), the short-circuit current (IK) is reduced according to a predetermined target short-circuit current profile (I target ). Finally, an actual droplet value (T is ), which describes an actual value of a droplet parameter (RT) of the weld droplet (T), is determined and used to correct the target short-circuit current profile (I target ) depending on the actual droplet value (T is ).

Inventors

  • SÖLLINGER, Dominik

Assignees

  • FRONIUS INTERNATIONAL GmbH

Dates

Publication Date
20260513
Application Date
20241108

Claims (15)

  1. A short-arc joining method for producing a weld seam (10) on a workpiece (6), comprising arc phases (LP) in which an arc (11) burns between a consumable joining electrode (7) and a workpiece (6), which melts the joining electrode (7) in an end region of the joining electrode (7) facing the workpiece (6) to form a weld droplet, and in which short-circuit phases (KP) alternate cyclically with the arc phases (LP), in which the joining electrode (7) touches the workpiece (6) and a short-circuit current (lK) flows through the weld droplet (T) into the workpiece (6) to melt the weld droplet (T), characterized in that the following are provided in each of the short-circuit phases (KP): - a first partial phase (KP-1), in which the short-circuit current (IK) is increased from an initial current (IK1) present at the beginning of the first partial phase (KP-1) to a predetermined melting current (IK m ), - one of the first sub-phases (KP-1) followed by a second sub-phase (KP-2), in which or short-circuit current (IK) is reduced according to a specified short-circuit current target curve (I target ), and o a droplet actual value (T is ) of a droplet parameter (RT) of the welding droplet (T) is determined and is used to correct the short-circuit current target curve (I target ).
  2. Short-arc joining method according to claim 1, characterized in that the drop actual value (T is ) is compared with a predetermined drop setpoint (T should ) , preferably to determine a drop comparison result (e τ ) , and that the short-circuit current setpoint (I should ) is corrected to reduce a deviation between the drop actual value (T is ) and the predetermined drop setpoint (T should ) , preferably depending on the drop comparison result (e τ ).
  3. Short-circuit arc joining method according to claim 1 or 2, characterized in that the short-circuit current target profile (I target ) is determined empirically or from a database or by means of a numerical simulation of the short-circuit arc joining method.
  4. Short-arc joining method according to one of the preceding claims, characterized in that in the second sub-phases (KP-2) a first sub-phase (KP-21) is performed. and a second sub-phase (KP-22) following the first sub-phase (KP-21) is provided, wherein no correction of the short-circuit current target curve (I target ) is provided in the first sub-phase (KP-21), and only in the second sub-phase (KP-22) is a correction of the short-circuit current target curve (I target ).
  5. Short-arc joining method according to one of the preceding claims, characterized in that an actual electrical voltage (U), which drops at least partially across the weld droplet (T), is determined as the actual droplet value (T is ) and that an electrical target voltage is specified as the target droplet value (T should ).
  6. Short-arc welding method according to one of claims 1 to 4, characterized in that an actual electrical voltage (U), which drops at least partially across the weld droplet (T), is determined, that an actual electrical resistance (RT) is determined as the actual droplet value (T is ) from the actual electrical voltage (U) and the short-circuit current (IK), and that a target electrical resistance is specified as the target droplet value (T should ).
  7. Short-arc joining method according to one of the preceding claims, characterized in that in the case of an actual drop value (T <sub>is</sub> ) which is above the predetermined target drop value (T <sub>should</sub> ) by more than a predetermined deviation threshold, the target short-circuit current profile (I <sub>should</sub> ) is reduced or increased, and in the case of an actual drop value (T<sub> is</sub> ) which is below the predetermined target drop value (T<sub>should</sub>) by more than a predetermined short-circuit current (I<sub>K</sub>), the target short-circuit current profile (I <sub> should </sub>) is increased or decreased.
  8. Short-arc joining method according to one of the preceding claims, characterized in that in the first partial phase (KP-1), preferably in a constant current phase or in a constant voltage phase of the first partial phase (KP-1), in which the short-circuit current (IK) corresponds to the melting current (IK m ), a first drop actual value (T is ) is determined and the first drop actual value (T is ) is taken into account in the second partial phase (KP-2) when determining the drop target value (T should ).
  9. Short-arc joining method according to one of the preceding claims, characterized in that the melting current (IK m ) is more than 0.5 times higher than the initial current (IK 1 ), or preferably more than 1 time higher, more than 5 times higher, or more than 10 times higher than the initial current (IK 1 ).
  10. Short-arc joining method according to one of the preceding claims, characterized in that the joining electrode (7) is exposed during the short-circuit phase KP of the workpiece (6) is moved away in order to further support the resolution of a short circuit by moving the joining electrode (7).
  11. Short-arc joining method according to one of the preceding claims, characterized in that the sum of the time length of a first sub-phase (KP-1) provided in a short-circuit phase (KP) and the time length of a second sub-phase (KP-2) provided in the same short-circuit phase (KP) corresponds to the time length of the short-circuit phase (KP).
  12. Short-arc joining method according to one of the preceding claims, characterized in that a ratio of a time length of a first sub-phase (KP-1) provided in a short-circuit phase (KP) to the time length of a second sub-phase (KP-2) provided in the short-circuit phase (KP) corresponds to a predetermined factor kt, wherein the factor kt preferably corresponds to a value greater than 0.3 and less than 1.7, or preferably corresponds to a value greater than 0.5 and less than 1.5, or preferably corresponds to a value greater than 0.75 and less than 1.25, or preferably corresponds to a value greater than 0.85 and less than 1.15.
  13. Short-arc joining method according to one of the preceding claims characterized in that the short-arc joining method is a short-arc welding method or a short-arc brazing method.
  14. Short-arc joining method according to one of the preceding claims, characterized in that a control law is specified, preferably a PID control law or a sliding-mode control law or an MPC control law or a backstepping control law or a flatness-based control law, with which a correction of the short-circuit current target curve (I target ) is determined as a function of a deviation of the drop actual value (T is ) from the drop target value (T target ), preferably as a function of the drop comparison result (e τ ).
  15. Joining device (1) for carrying out a short-arc joining process, comprising a torch (4), a feed unit (12) for supplying a consumable joining electrode (7) through the torch, a power source (2) for supplying electrical power to the joining electrode (7), and a control unit (14) for controlling the joining device (1), comprising arc phases (LP) in which an arc (11) burns between the consumable joining electrode (7) and a workpiece (6), which melts the joining electrode (7) in an end region of the joining electrode (7) facing the workpiece (6), forming a weld droplet, and short-circuit phases (KP) that alternate cyclically with the arc phases (LP), in which the The joining electrode (7) touches the workpiece (6) and a short-circuit current (IK) flows from the power source (2) through the weld droplet (T) into the workpiece (6) to melt the weld droplet (T), characterized in that the control unit (14) is designed to provide the following in each of the short-circuit phases (KP): - a first sub-phase (KP-1), in which the short-circuit current (IK) is increased from an initial current (IK 1 ) present at the beginning of the first sub-phase (KP-1) to a predetermined melting current (IK m ), - one of the first sub-phases (KP-1) followed by a second sub-phase (KP-2), in which or short-circuit current (IK) is reduced according to a specified short-circuit current target curve (I target ), and o a droplet actual value (T is ) of a droplet parameter (RT) of the welding droplet (T) is determined and used to correct the short-circuit current target curve (I target ).

Description

The present invention relates to a short-arc joining method for producing a weld seam on a workpiece, comprising arc phases in which an arc burns between a consumable joining electrode and a workpiece, which melts the joining electrode in an end region of the joining electrode facing the workpiece, forming a weld droplet, and short-circuit phases that alternate cyclically with the arc phases, in which the joining electrode touches the workpiece and a short-circuit current flows through the weld droplet into the workpiece to melt the weld droplet. The invention further relates to a joining device for carrying out a short-arc joining process, the joining device comprising a burner, a feed unit for supplying a melting joining electrode, a power source for supplying the joining electrode electrically and a control unit for controlling the joining device. Interval arc welding and interval arc brazing are versatile joining processes, particularly suitable for regulating temperature distributions in joined workpieces or for controlling the heat input during arc welding or brazing. The following discussion focuses on the use of short arcs in these joining processes, with the generic term "short arc joining" encompassing both short arc (interval) welding and short arc (interval) brazing. Arc welding processes based on short circuits have two fundamental phases: arc phases and short-circuit phases. These phases alternate cyclically. An arc phase typically follows immediately after a short-circuit phase, and vice versa. In arc welding processes with a consumable wire electrode, the wire electrode melts during an arc phase, forming a weld droplet that grows as it melts. The weld droplet is fed to the workpiece by a continuous wire feed. At the end of an arc phase, the weld droplet touches the workpiece, causing the arc to extinguish (or "break") and initiating a short-circuit phase. As a result of the weld droplet contacting the workpiece, a short circuit forms between the wire electrode and the workpiece (a "short-circuit bridge"). A short-circuit current then flows through the weld droplet, further heating both the wire electrode and the weld droplet. The continuous heating causes the weld droplet to constrict, particularly in the liquid-solid transition zone of the wire electrode. This results in a progressive narrowing of the weld droplet. If the cross-section of the weld droplet becomes so small at least at one point that it can no longer be held to the wire electrode, the weld droplet detaches from the electrode and enters the weld pool on the workpiece, where a weld seam subsequently forms. This detachment process is also known as "breaking the short circuit" or "breaking the short-circuit bridge." In short-circuit welding, the droplet transfer associated with breaking the short circuit occurs exclusively during short-circuit phases. With other arc welding processes, droplet transfer is also possible outside of short-circuit phases, i.e., partially even during arc phases. Breaking the short circuit results in the loss of the low-resistance short-circuit bridge to the workpiece that formed across the weld droplet, and the short-circuit phase ends. The detachment of the weld droplet creates a gap between the wire electrode and the workpiece, in which the arc reignites in the next process step. This reignition of the arc marks both the end of the short-circuit phases and the beginning of the arc phases. As is known from the state of the art, e.g. from EP 1 949 997 A1 During the breakdown of a short circuit, i.e., at the end of the short circuit, unwanted weld spatter can occur. One reason for this is that a potentially high short-circuit current towards the end of the short-circuit phase must flow through a much smaller cross-section, requiring the transfer of a high amount of (electrical) energy through a very small volume. This small volume is heated intensely and can consequently detach uncontrollably from the unmelted part of the wire electrode, as well as from the rest of the weld droplet. Another cause of weld spatter during short-arc welding can be that part of the weld droplet bursts open due to excessive energy and lands as weld spatter next to the weld pool. Welding spatter occurs particularly when, as is often the case in practice, the short-circuit current is continuously increased during the short-circuit phases, e.g., linearly, exponentially, quadratically, or even stepwise, to ensure rapid heating and detachment of weld droplets. A significant disadvantage of this method is that the short-circuit current is usually very high when the short circuit breaks (arc reignition), which can result in significant welding spatter. Furthermore, this can lead to considerable fluctuations in current intensity and thus unpredictable behavior of the joining parameters. To address this problem, various approaches have been developed. One widely used method for short-circuit treatment involves monitoring the time-depe