WELDING CONDITION DERIVATION DEVICE

Abstract

A welding parameter derivation device of a welding machine having a torch and a weaving mechanism derives welding parameters in accordance with the cross-sectional shape of a weld portion of a new base metal. A database stores welding parameter data, and a welding parameter computation unit computes welding parameters for the shape of a groove or joint of a new base metal. Based on past welding parameter data for a shape similar to that of a groove or joint of a new base metal, and input data pertaining to the specifications of the welding machine, the computation unit derives welding parameter data for the new base metal, taking into account a parameter of the cross-sectional area of the weld portion formed on the new base metal, the bead height of the weld portion, the quantity of heat inputted to the new base metal, and a torch weaving parameter.

Claims

1. A welding condition derivation device provided to a welding machine that automatically executes arc welding by using a torch having a weaving mechanism, and configured to automatically derive a welding condition corresponding to a cross-sectional shape of a deposition part of a new base metal to be welded, comprising: a database that stores welding condition data; and a welding condition computation unit that computes a welding condition in accordance with a shape of a groove of the new base metal or a shape of a joint, wherein the welding condition computation unit, on the basis of welding condition data of a past base metal similar to the shape of the groove of the new base metal or the shape of the joint, and input data relating to specifications of the welding machine, derives welding condition data of the new base metal by taking into account a parameter of a cross-sectional area of the deposition part formed at the new base metal, and at least one of parameters including a bead height of the deposition part formed at the new base metal, an input heat quantity to the new base metal, and a weaving condition of the torch.

2. The welding condition derivation device according to claim 1, wherein the welding condition computation unit sets the bead height of the new base metal within a range between a predetermined upper limit value and a predetermined lower limit value.

3. The welding condition derivation device according to claim 1, wherein the welding condition computation unit sets the input heat quantity to the new base metal within a range between a predetermined upper limit value and a predetermined lower limit value.

4. The welding condition derivation device according to claim 1, wherein the welding condition computation unit sets a weaving amplitude for the new base metal and a weaving pitch being a wavelength of a weaving wave, each serving as the weaving condition, to be respectively within ranges between predetermined upper limit values and predetermined lower limit values.

5. The welding condition derivation device according to claim 3, wherein the welding condition computation unit sets a weaving amplitude for the new base metal and a weaving pitch being a wavelength of a weaving wave, each serving as the weaving condition, to be respectively within ranges between predetermined upper limit values and predetermined lower limit values.

6. The welding condition derivation device according to claim 1, wherein the welding condition computation unit extracts a bead height of the past base metal from the welding condition data of the past base metal, sets the extracted bead height of the past base metal as a bead height of the new base metal, then computes a cross-sectional area of a deposition part of the past base metal, and derives a welding speed serving as one piece of the welding condition data of the new base metal by using the computed cross-sectional area of the deposition part of the past base metal.

7. The welding condition derivation device according to claim 6, wherein the welding condition computation unit computes an input heat quantity to the new base metal by using the derived welding speed, and derives a welding current serving as one piece of the welding condition data of the new base metal by using the computed input heat quantity to the past base metal.

8. The welding condition derivation device according to claim 1, wherein the welding condition computation unit extracts a weaving amplitude for the past base metal and a bead width at the past base metal from the welding condition data of the past base metal, and adds a difference between the bead width at the past base metal and a bead width at the new base metal to the weaving amplitude for the past base metal and sets the result as a weaving amplitude serving as one piece of the welding condition data of the new base metal.

9. The welding condition derivation device according to claim 4, wherein the welding condition computation unit extracts a weaving amplitude for the past base metal and a bead width at the past base metal from the welding condition data of the past base metal, and adds a difference between the bead width at the past base metal and a bead width at the new base metal to the weaving amplitude for the past base metal and sets the result as a weaving amplitude serving as one piece of the welding condition data of the new base metal.

10. The welding condition derivation device according to claim 6, wherein the welding condition computation unit derives a weaving pitch serving as one piece of the welding condition data of the new base metal by adjusting a weaving frequency to fall within a range between a predetermined upper limit value and a predetermined lower limit value of the weaving pitch on the basis of the computed welding speed.

11. The welding condition derivation device according to claim 1, wherein the welding condition computation unit re-calculates the upper limit value and the lower limit value of each piece of the set welding condition data of the new base metal by using the input data relating to the specifications of the welding machine.

12. The welding condition derivation device according to claim 3, wherein the welding condition computation unit re-calculates the upper limit value and the lower limit value of each piece of the set welding condition data of the new base metal by using the input data relating to the specifications of the welding machine.

13. The welding condition derivation device according to claim 4, wherein the welding condition computation unit re-calculates the upper limit value and the lower limit value of each piece of the set welding condition data of the new base metal by using the input data relating to the specifications of the welding machine.

14. The welding condition derivation device according to claim 6, wherein the welding condition computation unit re-calculates the upper limit value and the lower limit value of each piece of the set welding condition data of the new base metal by using the input data relating to the specifications of the welding machine.

15. The welding condition derivation device according to claim 2, wherein the welding condition computation unit sets the input heat quantity to the new base metal within a range between a predetermined upper limit value and a predetermined lower limit value.

16. The welding condition derivation device according to claim 2, wherein the welding condition computation unit sets a weaving amplitude for the new base metal and a weaving pitch being a wavelength of a weaving wave, each serving as the weaving condition, to be respectively within ranges between predetermined upper limit values and predetermined lower limit values.

17. The welding condition derivation device according to claim 2, wherein the welding condition computation unit extracts a bead height of the past base metal from the welding condition data of the past base metal, sets the extracted bead height of the past base metal as a bead height of the new base metal, then computes a cross-sectional area of a deposition part of the past base metal, and derives a welding speed serving as one piece of the welding condition data of the new base metal by using the computed cross-sectional area of the deposition part of the past base metal.

18. The welding condition derivation device according to claim 2, wherein the welding condition computation unit re-calculates the upper limit value and the lower limit value of each piece of the set welding condition data of the new base metal by using the input data relating to the specifications of the welding machine.

19. The welding condition derivation device according to claim 5, wherein the welding condition computation unit re-calculates the upper limit value and the lower limit value of each piece of the set welding condition data of the new base metal by using the input data relating to the specifications of the welding machine.

20. The welding condition derivation device according to claim 7, wherein the welding condition computation unit re-calculates the upper limit value and the lower limit value of each piece of the set welding condition data of the new base metal by using the input data relating to the specifications of the welding machine.

21. The welding condition derivation device according to claim 8, wherein the welding condition computation unit re-calculates the upper limit value and the lower limit value of each piece of the set welding condition data of the new base metal by using the input data relating to the specifications of the welding machine.

22. The welding condition derivation device according to claim 9, wherein the welding condition computation unit re-calculates the upper limit value and the lower limit value of each piece of the set welding condition data of the new base metal by using the input data relating to the specifications of the welding machine.

23. The welding condition derivation device according to claim 10, wherein the welding condition computation unit re-calculates the upper limit value and the lower limit value of each piece of the set welding condition data of the new base metal by using the input data relating to the specifications of the welding machine.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0061] FIG. 1A is a general configuration diagram showing a welding robot system provided with a welding condition derivation device of the present invention.

[0062] FIG. 1B is an explanatory view schematically showing an operation of a weaving mechanism provided at a torch.

[0063] FIG. 2 is a block diagram showing a configuration of the welding condition derivation device of the present invention.

[0064] FIG. 3A is a cross-sectional view schematically showing a groove of a past base metal.

[0065] FIG. 3B is a cross-sectional view schematically showing a groove of a new base metal.

[0066] FIG. 4A is an explanatory view showing a method of computing a cross-sectional area of a deposition part formed at the groove of the past base metal.

[0067] FIG. 4B is an explanatory view showing a method of computing a cross-sectional area of a deposition part formed at the groove of the new base metal.

DESCRIPTION OF EMBODIMENTS

[0068] A welding condition derivation device according to the present invention is described below in detail with reference to the drawings. In the following description, the same reference sign is applied to the same components. The names and functions of the components are also the same. Hence, the detailed description on these components are not repeated. First, before a welding condition derivation device 1 of the present invention is described, an overview of a vertical articulated welding robot system 4 provided with the welding condition derivation device 1 is described with reference to FIGS. 1A and 1B.

[0069] FIG. 1A is a general configuration diagram showing the welding robot system 4 provided with the welding condition derivation device 1 of the present invention. FIG. 1B is an explanatory view schematically showing an operation of a weaving mechanism provided at a welding torch 7.

[0070] As shown in FIG. 1A, this welding robot system 4 includes a welding robot 5, a control device 8 including a teaching pendant 9, and a personal computer 10.

[0071] In addition, the welding robot system 4 in this embodiment is provided with the welding condition derivation device 1 (the details will be described later).

[0072] The welding robot 5 is a vertical articulated industrial robot having a plurality of axes (for example, six axes). A welding tool configured of a welding head 6 provided with the welding torch 7 (hereinafter, occasionally merely referred to as torch), and so forth, is provided at the tip end of the welding robot 5. In addition, although not shown, the welding robot 5 includes a welding power source device that supplies power, and a wire feed device that feeds a welding wire 11 (welding electrode) to the torch 7. It is to be noted that this welding robot 5 may be mounted on a slider (not shown) that moves the welding robot 5.

[0073] As shown in FIG. 1B, this welding robot 5 includes a weaving mechanism that operates the tip end (nozzle) of the torch 7 at a constant welding speed along a welding direction, and swings the torch 7 substantially perpendicularly to the welding direction.

[0074] For the shape of a groove of a base metal Wa or the shape of a joint in this embodiment, various shapes are expected. In this case, as exemplarily shown in FIGS. 3A and 3B, a groove Za of left-right symmetrical V-type (left and right facing surfaces are inclined at the same angle) is described as an example.

[0075] The shapes of grooves Za of base metals Wa include, for example, a left-right asymmetrical single bevel-type (one of facing surfaces is an inclined surface and the other is a vertical surface: single bevel groove), a left-right asymmetrical J-type (one of facing surfaces is a curved surface and the other is a vertical surface), a left-right symmetrical I-type (facing left and right surfaces are both vertical surfaces), a left-right symmetrical U-type (facing left and right surfaces are both curved surfaces), and a T-type (fillet weld welding) in which two or more base metals Wa are perpendicularly joined. This embodiment may be applied to any type of groove Za.

[0076] When arc welding is executed on a base metal (object workpiece) by using the torch 7 with the weaving motion, the control device 8 controls the welding robot 5 according to a welding condition (program), which are taught in advance, such as the adjusted position of the torch 7 (hereinafter, referred to as target position of the torch 7) and groove shapes Za and Zb of base metals Wa and Wb.

[0077] The welding condition may be set, for example, by using the teaching pendant 9 connected with the control device 8 or by using the personal computer 10. In any case, this welding condition is set in advance before arc welding is actually executed.

[0078] The welding condition set as described above is passed to the control device 8 via a storage medium etc., or transferred to the control device 8 by data communication.

[0079] Meanwhile, a command of automatic welding is given to a new base metal Wa to be newly welded on the basis of the welding condition; however, if the groove shape Za of this new base metal Wa is the same as the groove shape Zb of a past base metal Wb having a welded record in the past, the same welding condition may be extracted from data of the welding condition stored in advance in a database 2 or the like provided to the welding robot system 4, and the command of automatic welding based on the same welding condition may be given.

[0080] However, in actual welding, the groove shape Za of the base metal Wa to be newly welded by arc welding may not be the similar groove shape Zb of the past base metal Wb having a welded record in the past (including the material of the past base metal Wb).

[0081] When arc welding is executed on the new base metal Wa having the groove shape Za without a record in the past, the welding condition of the new base metal Wa is required to be calculated and derived on the basis of the extracted welding condition of the past base metal Wb similar to the groove shape Za of the new base metal Wa.

[0082] Hence, the inventors of this application have developed the welding condition derivation device 1 of the welding robot system 4 that can automatically derive the welding condition of the new base metal Wa by taking into account information relating to the deposition part formed at the new base metal Wa and information relating to the torch 7 in addition to the welding condition of the past base metal Wb similar to the groove shape Za of the new base metal Wa and information relating to the groove shape Za of the new base metal Wa. The welding condition derivation device 1 is provided to the above-described welding robot system 4, and automatically derives the welding condition corresponding to the cross-sectional shape of the new base metal Wa to be welded.

[0083] FIG. 2 is a block diagram showing a configuration of the welding condition derivation device 1 of the present invention. As shown in FIG. 2, the welding condition derivation device 1 includes the database 2 storing welding condition data, and a welding condition computation unit 3 that computes a welding condition for the new base metal Wa.

[0084] The welding condition data stored in the database 2 includes a welding condition of a past base metal Wb with a welded record in the past (welding condition of past base metal Wb), a welding condition obtained from a physical model created on the basis of the past base metal Wb, and a welding condition having a derived record in the past (a welding condition actually employed, a welding condition suitable but not employed for certain reasons).

[0085] The welding condition computation unit 3 being a feature of the present invention derives welding condition data of the new base metal Wa by taking into account the cross-sectional area S of the deposition part formed at the new base metal Wa, and further by taking into account at least one of the bead height d of the deposition part formed at the new base metal Wa, the input heat quantity Q to the new base metal Wa, and the weaving condition of the torch 7, on the basis of welding condition data of the past base metal Wb similar to the new base metal Wa extracted from the database 2 and input data relating to the specifications of the welding robot 5.

[0086] The welding condition computation unit 3 in this embodiment derives welding condition data of the new base metal Wa by taking into account a parameter of a cross-sectional area S.sub.pn of the deposition part to the new base metal Wa, and a bead height d.sub.pn of the deposition part formed at the new base metal Wa, and then by taking into account an input heat quantity Q.sub.pn to the new base metal Wa, and the weaving condition of the torch 7, on the basis of the welding condition data of the past base metal Wb similar to the new base metal Wa extracted from the database 2, and the input data relating to the specifications of the welding robot 5.

[0087] The input data is data set on the basis of the specifications of the welding robot 5, and is, for example, a welding voltage E, a welding current I, a feed speed V.sub.W(I) of the welding wire 11, a radius R of the welding wire 11, and a weaving frequency F.

[0088] More specifically, to take into account the bead height d.sub.pn of the new base metal Wa, the welding condition computation unit 3 extracts a bead height d.sub.n of the past base metal Wb from the welding condition data of the past base metal Wb, and sets the extracted bead height d.sub.n of the past base metal Wb as the bead height d.sub.pn of the new base metal Wa. Then, the welding condition computation unit 3 computes a cross-sectional area (groove cross-sectional area) S.sub.n of the deposition part of the past base metal Wb, and derives a welding speed v.sub.p1 being one piece of the welding condition data of the new base metal Wa by using the computed cross-sectional area S.sub.n of the deposition part of the past base metal Wb.

[0089] Also, to take into account an input heat quantity Q.sub.p1 to the new base metal Wa, the welding condition computation unit 3 computes the input heat quantity Q.sub.p1 to the new base metal Wa by using the derived welding speed v.sub.p1. Then, the welding condition computation unit 3 derives a welding current I.sub.p1 being one piece of the welding condition data of the new base metal Wa by using a computed input heat quantity Q.sub.1 to the past base metal Wb.

[0090] Further, to take into account a weaving amplitude W.sub.p1 for the new base metal Wa, the welding condition computation unit 3 extracts a weaving amplitude W.sub.1 for the past base metal Wb and a bead width (leg length) A.sub.1 at the past base metal Wb from the welding condition data of the past base metal Wb. Then, the welding condition computation unit 3 adds a difference (an increment of a bead width A.sub.p1) W between the bead width A.sub.1 at the past base metal Wb and the bead width A.sub.p1 of the new base metal Wa to a weaving amplitude W.sub.1 for the past base metal Wb, and sets the result as the weaving amplitude W.sub.p1 being one piece of the welding condition data of the new base metal Wa (W.sub.p1=W.sub.1+W).

[0091] Also, to take into account a weaving pitch (=distance between weaving end points) dL.sub.p1 for the new base metal Wa, the welding condition computation unit 3 adjusts a weaving frequency F.sub.p1 to fall within a range between an upper limit value and a lower limit value of the weaving pitch dL.sub.p1[P.sub.nP(n=1)], on the basis of the computed welding speed v.sub.p1, and derives the weaving pitch dL.sub.p1 being one piece of the welding condition data of the new base metal Wa.

[0092] In short, the welding condition computation unit 3 computes the cross-sectional area S.sub.pn of the deposition part from the welding speed v and the wire feed speed V of the input conditions, and computes the bead height d.sub.pn and the input heat quantity Q.sub.pn by using the computed cross-sectional area S.sub.pn.

[0093] Then, the welding condition computation unit 3 adjusts the bead height d.sub.pn to fall within a range of (d.sub.nd) and adjusts the input heat quantity Q.sub.pn to fall within a range of (Q.sub.nQ), so that the computed bead height d.sub.pn and input heat quantity Q.sub.pn for each pass are not largely changed from the bead height d.sub.n and input heat quantity Q.sub.n of the welding conditions of the past base metal Wb).

[0094] Then, the welding condition computation unit 3 derives a new welding speed v.sub.pn by using the adjusted bead height d.sub.pn, and derives a new wire feed speed V.sub.pn (=welding current I.sub.pn) by using the adjusted input heat quantity Q.sub.pn.

[0095] The above-described welding condition computation unit 3 may be configured to re-calculate the upper and lower limit values of each set welding condition data of the new base metal Wa by using the input data relating to the specifications of the welding robot 5.

[0096] Next, a method of deriving a welding condition of the new base metal Wa, that is, an operation of the welding condition computation unit 3 being the feature of the present invention (a derivation process of the welding condition) using the welding condition derivation device 1 of the present invention is described in detail with reference to multi-layer overlay welding of a V-type groove Za as an example.

[0097] FIG. 3A is a cross-sectional view schematically showing the groove Zb of the past base metal Wb. FIG. 3B is a cross-sectional view schematically showing the groove Za of the new base metal Wa. Also, FIG. 4A is an explanatory view showing a method of computing the cross-sectional area of a deposition part formed at the groove Zb of the past base metal Wb. FIG. 4B is an explanatory view showing a method of computing the cross-sectional area of a deposition part formed at the groove Za of the new base metal Wa.

[0098] As shown in FIGS. 3A and 3B, in this embodiment, it is assumed that an object to be newly welded by arc welding is the new base metal Wa having the V-type groove Za. Also, it is assumed that the past base metal Wb has a groove angle , and a gap width g. In contrast, it is assumed that the new base metal Wa has a groove angle .sub.p, and a gap width g.sub.p. It is to be noted that the groove angle satisfies (>.sub.p) and the gap width satisfies (g>g.sub.p). That is, the gap angle .sub.p and the gap width g.sub.p of the new base metal Wa are smaller than those (, g) of the past base metal Wb.

[0099] Also, as shown in FIGS. 3A and 3B, in multi-layer overlay welding in this embodiment, the number of passes in arc welding is five passes and the number of layers is four layers.

[0100] First, it is assumed that, in the welding condition derivation device 1 (the welding robot 5) in this embodiment, the following welding conditions are stored as teach data in the database 2. [0101] 1) Number of passes: n (n=1, 2, . . . ) [0102] 2) For each pass, [0103] Welding current I and welding voltage E as output commands to welding robot 5 [0104] Target position P, target angle and advance angle, and speed v in welding of tip end of torch 7 [0105] Parameters of weaving motion (sinusoidal wave): weaving amplitude W and weaving frequency F

[0106] Also, in the welding condition derivation device 1 in this embodiment, it is assumed that a welding condition recognized as providing good welding quality in an actual welding test executed in advance (the welding condition of the past base metal Wb) is stored in advance in the database 2. Table 1 shows an example of welding conditions of the past base metal Wb.

TABLE-US-00001 TABLE 1 [Welding condition data of past base metal] Groove type: V-type groove Groove angle: [RAD] Bottom surface gap width: g [mm] Groove depth: L [mm] Number of layers: 4 Number of passes: 5 Conditions for each pass n: Welding current I.sub.n Welding voltage E.sub.n Welding speed v.sub.n Target position P.sub.n Weaving amplitude W.sub.n Frequency F.sub.n [Hz]

[0107] Also, as shown in Table 2, in the welding condition derivation device 1, the welding power source used in this embodiment, type of the welding wire 11 (for example, radius R), and characteristics determined by the performance limit of the welding robot 5 (for example, a feed speed V.sub.W(I) of the welding wire 11, a standard voltage value E.sub.S(I), a weaving frequency F, etc.) are stored in the database 2.

TABLE-US-00002 TABLE 2 [Input Conditions (specifications of welding machine)] Radius of welding wire R [mm] Upper and lower limit values for welding current I I.sub.min, I.sub.max [A] Wire feed speed corresponding to welding current I Vw(I) [mm/s] Standard voltage value corresponding to welding E.sub.s(I) [V] current I Upper limit value of weaving frequency corresponding F.sub.max(W) [mm] to weaving amplitude W

[0108] Also, as shown in Table 3, as limit values for welding conditions for ensuring the welding quality in this embodiment, in the welding condition derivation device 1, the input heat quantity Q.sub.n, the bead height d.sub.n, the weaving conditions of the torch 7 (for example, a weaving amplitude W.sub.n, a weaving pitch dL.sub.n) of the past base metal Wb are also stored in the database 2.

TABLE-US-00003 TABLE 3 [Limit values for welding conditions] Input heat quantity Q.sub.n Lower limit value Q.sub.min [J/mm], upper limit value Q.sub.max [J/mm] Allowable change threshold Q [J/mm] at adjustment Bead height (thickness) d.sub.n Lower limit value d.sub.min [mm], upper limit value d.sub.max [mm] Allowable change threshold d [mm] at adjustment Weaving amplitude W.sub.n Lower limit value W.sub.min [mm], upper limit value W.sub.max [mm] Weaving pitch dL Lower limit value dL.sub.min [mm], upper limit value dL.sub.max [mm] Allowable change threshold dL [mm] at adjustment

[0109] The above-described limit values of the welding conditions each are set within a range between a predetermined upper limit value and a predetermined lower limit value. For example, in the welding condition computation unit 3, when the input heat quantity Q.sub.pn to the new base metal Wa is taken into account, the input heat quantity Q.sub.pn to the new base metal Wa is set within a range between a predetermined upper limit value Q.sub.max and a predetermined lower limit value Q.sub.min on the basis of the input heat quantity Q.sub.n to the past base metal Wb.

[0110] Also, in the welding condition computation unit 3, when the bead height d.sub.pn of the deposition part formed at the new base metal Wa is taken into account, the bead height d.sub.pn of the new base metal Wa is set within a range between a predetermined upper limit value d.sub.max and a predetermined lower limit value d.sub.min on the basis of the bead height d.sub.n of the past base metal Wb.

[0111] Further, in the welding condition computation unit 3, when a weaving amplitude W.sub.pn for the new base metal Wa, serving as the weaving condition, is taken into account, the weaving amplitude W.sub.pn for the new base metal Wa is set within a range between a predetermined upper limit value W.sub.max and a predetermined lower limit value W.sub.min on the basis of the weaving amplitude W.sub.n for the past base metal Wb. Also, when a weaving pitch (=wavelength of weaving wave) dL.sub.pn is taken into account, the weaving pitch dL.sub.pn is set within a range between a predetermined upper limit value dL.sub.max and a predetermined lower limit value dL.sub.min on the basis of the weaving pitch dL.sub.n for the past base metal Wb.

[0112] In this embodiment, the setting of various data, storage of teach data, and setting of welding conditions of the new base metal Wa (the details will be described later) are executed on the database 2 by using the teaching pendant 9 provided to the welding robot 5.

[0113] Then, as shown in FIG. 3B, the operator inputs parameters (groove angles .sub.p, gap width g.sub.p) of the groove shape Za of the new base metal Wa (new joint) to be welded this time, and activates the welding condition computation unit 3 (automatic computation function for welding conditions).

[0114] The welding condition computation unit 3 executes processing steps (Step 1, Step 2) by a welding robot control CPU.

[0115] First, in Step 1, the bead shape and the input heat quantity are obtained from the welding conditions of the past base metal Wb.

[0116] To be specific, the cross-sectional shape parameter of the deposition part of each pass in a build-up diagram (see FIG. 4A) of beads formed under the welding conditions of the past base metal Wb, and the input heat quantity Q.sub.n to the deposition part of each pass are computed from [welding condition data of past base metal Wb] shown in Table 1 and [input conditions (specifications of welding robot 5)] shown in Table 2.

[0117] In this embodiment, the bead cross section of each pass has a trapezoid shape, and it is assumed that a bead width in an n-th pass (n=1, 2, . . . ) is A.sub.n, a cross-sectional area of a bead (groove Zb) is S.sub.n, a bead height is d.sub.n, and an input heat quantity is Q.sub.n.

[0118] As shown in FIG. 4A, the cross-sectional area S.sub.n [mm.sup.2], the bead width A.sub.n [mm] of the deposition part, the bead height d.sub.n [mm], and the input heat quantity Q.sub.n [J/mm] of the n-th pass are computed on the basis of the conditions of the n-th pass (in this embodiment, n=1 to 5) of the welding conditions of the past base metal Wb, that is, on the basis of a welding voltage E.sub.n [V], a welding current I.sub.n [A], a speed v.sub.n [mm/s], a target position P.sub.n of the torch 7, a weaving amplitude W.sub.n [mm], a weaving frequency F.sub.n [Hz], and so forth.

[0119] First, the welding conditions (n=1 to 3) of the past base metal Wb from first to third passes (n=1 to 3) are derived. The cross-sectional area (bead cross-sectional area) S.sub.n [mm.sup.2] of each of the deposition parts of the first to third passes is computed using Expression (2) as follows on the basis of the weld amount of the welding wire 11.

[00002]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.2\right]& \\ S_n=V_W\left(I\right).Math.\frac{.Math..Math.R^2}{v_n}& \left(2\right)\end{array}$

[0120] In this expression, n=1 to 3.

[0121] Then, the bead height d.sub.n in each of the first to third passes is computed by converting Expression (3) into Expression (4).

[00003]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.3\right]& \\ S_n=\left[A_{n-1}+d_n.Math.\tan \left(\frac{}{2}\right)\right].Math.d_n& \left(3\right)\end{array}$

[0122] In this expression, n=1 to 3.

[00004]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.4\right]& \\ d_n=\frac{-A_{n-1}+\sqrt{A_{n-1}^2+4.Math.S_n.Math.\tan \left(\frac{}{2}\right)}}{2.Math.\tan \left(\frac{}{2}\right)}& \left(4\right)\end{array}$

[0123] In this expression, A.sub.0=g (bottom surface length of first layer=gap length g [min]), and n=1 to 3.

[0124] Further, the bead widths A.sub.n [mm] in each of the first to third passes is computed by Expression (5) as follows.

[00005]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.5\right]& \\ A_n=A_{n-1}+2.Math.d_n.Math.\tan \left(\frac{}{2}\right)& \left(5\right)\end{array}$

[0125] In this expression, n=1 to 3.

[0126] Then, the input heat quantities Q.sub.n [J/mm] in each of the first to third passes is computed by Expression (6) as follows.

[00006]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.6\right]& \\ Q_n=\frac{I_n.Math.E_n}{v_n}& \left(6\right)\end{array}$

[0127] In this expression, n=1 to 3.

[0128] Next, the welding conditions of the past base metal Wb in fourth and fifth passes (n=4 to 5) are derived. The bead cross-sectional area S.sub.n in each of the fourth and fifth passes is computed by Expression (7) as follows.

[00007]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.7\right]& \\ S_n=V_W\left(I\right).Math.\frac{.Math..Math.R^2}{v_n}& \left(7\right)\end{array}$

[0129] In this expression, n=4, 5.

[0130] Then, the bead height d.sub.n in each of the fourth and fifth passes is computed by converting Expression (8) into Expression (9).

[00008]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.8\right]& \\ S_n\left[A_3+\frac{d_n.Math.\tan \left(\frac{}{2}\right)}{2}\right].Math.d_n& \left(8\right)\end{array}$

[0131] In this expression, n=4, 5.

[00009]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.9\right]& \\ d_n=\frac{-A_3+\sqrt{A_3^2+2.Math.S_n.Math.\tan \left(\frac{}{2}\right)}}{\tan \left(\frac{}{2}\right)}& \left(9\right)\end{array}$

[0132] In this expression, n=4, 5.

[0133] Further, the bead width A.sub.n [mm] in each of the fourth and fifth passes is computed by Expression (10) as follows.

[00010]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.10\right]& \\ A_n=\frac{A_3}{2}+d_n.Math.\tan \left(\frac{}{2}\right)& \left(10\right)\end{array}$

[0134] In this expression, n=4, 5.

[0135] Then, the input heat quantities Q.sub.n [J/mm] in each of the fourth and fifth passes is computed by Expression (11) as follows.

[00011]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.11\right]& \\ Q_n=\frac{I_n.Math.E_n}{v_n}& \left(11\right)\end{array}$

[0136] In this expression, n=4, 5.

[0137] In this embodiment, the bead cross-sectional area S.sub.n, bead width A.sub.n, bead height d.sub.n, and input heat quantity Q.sub.n of the past base metal Wb are computed by calculation; however, the bead shape, actual current and voltage, etc., may be measured for each pass during actual welding test, and the measurement results may be stored as actual data of arc welding in the database 2.

[0138] Next, in Step 2, a parameter, such as the bead shape (cross-sectional area S.sub.pn, the bead height d.sub.pn, etc.) of the new base metal Wa (new weld joint), and the input heat quantity Q.sub.pn to the new base metal Wa are computed from the welding conditions of the past base metal Wb, and the welding conditions of the new base metal Wa are derived on the basis of the computed parameter of the bead shape and input heat quantity Q.sub.pn of the new base metal Wa.

[0139] As shown in FIGS. 4A and 4B, it is assumed that the groove angle of the new base metal Wa is .sub.p, the gap width of the new base metal Wa is g.sub.p, the groove angle of the past base metal Wb is , and the gap width of the past base metal Wb is g. Also, the groove angle satisfies (>.sub.p) and the gap width g satisfies (g>g.sub.p).

[0140] First, welding conditions for arc welding of a first layer (first pass) to the new base metal Wa are derived.

[0141] In this embodiment, the welding conditions of the new base metal Wa are derived so that the bead height (thickness) d.sub.pn is not changed from the welding condition of the past base metal Wb as possible, that is, the bead height is substantially similar to the welding condition of the past base metal Wb. This is because the inventors of this application figured out that the bead height d.sub.pn largely affects the welding quality as described in detail in Technical Problem.

[0142] To be specific, a welding speed v.sub.p1 is adjusted so that a bead height d.sub.p1 of the first pass is aligned with a bead height d.sub.1 of the first pass in the welding conditions of the past base metal Wb (d.sub.p1=d.sub.1). First, a bead cross-sectional area S.sub.p1 [mm.sup.2] of the first pass is computed by Expression (12) as follows.

[00012]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.12\right]& \\ S_{p.Math..Math.1}=d_{p.Math..Math.1}^2.Math.\tan \left(\frac{{}_p}{2}\right)+d_{p.Math..Math.1}.Math.g_p& \left(12\right)\end{array}$

[0143] Then, the new welding speed v.sub.p1 is computed by Expression (13) as follows.

[00013]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.13\right]& \\ v_{p.Math..Math.1}=V_W\left(I\right).Math.\frac{.Math..Math.R^2}{S_{p.Math..Math.1}}& \left(13\right)\end{array}$

[0144] In this embodiment, since the groove shape Za of the new base metal Wa is narrower than the groove shape Zb of the past base metal Wb, the welding speed v.sub.p1 of the new base metal Wa is lower than a welding speed v.sub.1 of the past base metal Wb (v.sub.p1<v.sub.1). Also, an input heat quantity Q.sub.p1 to the new base metal Wa is increased as compared with an input heat quantity Q.sub.1 to the past base metal Wb (Q.sub.p1>Q.sub.1).

[0145] When the input heat quantity Q.sub.p1 to the new base metal Wa is computed, the computed input heat quantity Q.sub.p1 to the new base metal Wa is adjusted to fall within a predetermined range.

[0146] Respective thresholds used at this time use [limit values of welding conditions] shown in Table 3. [0147] Input heat quantity Q [0148] Lower limit value Q.sub.min [J/mm], upper limit value Q.sub.max [J/mm] [0149] Allowable change threshold Q [J/mm] at adjustment [0150] Bead height d [0151] Lower limit value d.sub.min [mm], upper limit value d.sub.max [mm] [0152] Allowable change threshold d [mm] at adjustment
It is to be noted that these upper and lower limit values are design values obtained in advance or computed as know-how in welding procedure.

[0153] If the input heat quantity Q.sub.p1 to the new base metal Wa exceeds the upper limit Q.sub.max (Q.sub.p1>Q.sub.max), or the difference between the input heat quantity Q.sub.p1 to the new base metal Wa and the input heat quantity Q.sub.1 to the past base metal Wb exceeds the allowable change threshold Q at adjustment (Q.sub.p1Q.sub.1>Q), the input heat quantity Q.sub.p1 to the new base metal Wa is computed so that the input heat quantity Q.sub.p1 to the new base metal Wa becomes the upper limit value Q.sub.max or the input heat quantity Q.sub.p1 to the new base metal Wa becomes a value in which the allowable change threshold Q at adjustment is added to the input heat quantity Q.sub.1 to the past base metal Wb (Q.sub.1+Q) by Expression (14) as follows, and a welding current I.sub.p1 is computed by Expression (15) as follows.

[00014]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.14\right]& \\ Q_{p.Math..Math.1}=\frac{\left(I_1.Math.E_1\right)}{v_{p.Math..Math.1}}& \left(14\right)\\ \left[\mathrm{Math}.Math..Math.15\right]& \\ I_{p.Math..Math.1}=\frac{Q_{\max }.Math.v_{p.Math..Math.1}}{E_n}& \left(15\right)\end{array}$

[0154] The welding current I.sub.p1 is adjusted on the basis of the computed input heat quantity Q.sub.p1 to the new base metal Wa (in this embodiment, the welding current I.sub.p1 is decreased). As the result, the deposition quantity to the new base metal Wa is changed, and hence the bead height d.sub.p1 of the new base metal Wa is changed.

[0155] The bead height d.sub.p1 of the new base metal Wa is computed by Expression (16) and Expression (17) as follows.

[00015]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.16\right]& \\ S_{p.Math..Math.1}=V_W\left(I\right).Math.\frac{.Math..Math.R^2}{v_{p.Math..Math.1}}& \left(16\right)\\ \left[\mathrm{Math}.Math..Math.17\right]& \\ d_{p.Math..Math.1}=\frac{-A_{p.Math..Math.0}+\sqrt{A_{p.Math..Math.0}^2+4.Math.S_{p.Math..Math.1}.Math.\tan \left(\frac{{}_p}{2}\right)}}{2.Math.\tan \left(\frac{}{2}\right)}& \left(17\right)\end{array}$

[0156] In this embodiment, it is checked whether or not the absolute value of the difference between the computed bead height d.sub.p1 of the new base metal Wa and the bead height d.sub.1 of the welding condition of the past base metal Wb is the allowable change threshold d at adjustment or smaller, that is, satisfies Expression (18) as follows.

[Math 18]

|d.sub.1d.sub.p1|d(18)

[0157] For example, as shown in Expression (19), if the absolute value of the difference between the computed bead height d.sub.p1 of the new base metal Wa and the bead height d.sub.1 in the welding conditions of the past base metal Wb is the allowable change threshold d at adjustment or larger, that is, does not satisfy Expression (18), it means that the bead height d.sub.p1 is largely changed. In this way, if the bead height d.sub.p1 is largely changed (becomes the threshold or larger), the situation may be notified to the operator through the teaching pendant 9.

[Math 19]

|d.sub.p1d.sub.p1|>d(19)

[0158] A bead width A.sub.p1 of the first layer is computed by Expression (20) as follows by using the welding current I.sub.p1 computed as described above.

[00016]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.20\right]& \\ A_{p.Math..Math.1}=A_{p.Math..Math.0}+2.Math.d_{p.Math..Math.0}.Math.\tan \left(\frac{{}_p}{2}\right)& \left(20\right)\end{array}$

[0159] The computed bead width A.sub.p1 of the first layer is used for deriving the welding conditions of the second pass (second layer).

[0160] Thereafter, the above-described derivation of the welding condition of the new base metal Wa is executed repeatedly to the last layer (fifth pass in the fourth layer).

[0161] In particular, at the fourth pass and fifth pass in the fourth layer, a bead height d.sub.p4 (=d.sub.p5) is set by Expression (21) as follows, so that the final bead fills the entire region of the groove Za.

[Math 21]

d.sub.p4=L(d.sub.p1+d.sub.p2+d.sub.p3)(21)

[0162] A bead cross-sectional area S.sub.p4 is calculated by Expression (22) as follows.

[00017]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.22\right]& \\ S_{p.Math..Math.4=}\left(A_{p.Math..Math.3}+\frac{d_{p.Math..Math.4}.Math.\tan \left(\frac{{}_p}{2}\right)}{2}\right).Math.d_{p.Math..Math.4}& \left(22\right)\end{array}$

[0163] Then, a welding speed V.sub.p4 is computed by Expression (23) using the computed bead cross-sectional area S.sub.p4. Then, a welding current I.sub.p4 is calculated by Expression (24) using the computed welding speed v.sub.p4.

[00018]$\begin{array}{cc}\left[\mathrm{Math}.Math..Math.23\right]& \\ v_{p.Math..Math.4}=V_W\left(I\right).Math.\frac{.Math..Math.R^2}{S_{p.Math..Math.4}}& \left(23\right)\\ \left[\mathrm{Math}.Math..Math.24\right]& \\ I_{p.Math..Math.4}=\frac{Q_{\max }.Math.v_{p.Math..Math.4}}{E_4}& \left(24\right)\end{array}$

[0164] The operator references the welding conditions of the new base metal Wa, which are derived by the welding condition derivation device 1 of the present invention as described above and displayed on the teaching pendant 9, and sets the welding conditions of the new base metal Wa.

[0165] As described above, the welding conditions of the new base metal Wa without a welded record in the past can be derived with sufficiently satisfied information relating to arc welding, by taking into account the cross-sectional area S.sub.pn of the deposition part formed at the new base metal Wa, and by taking into account at least one of the bead height d.sub.pn of the deposition part formed at the new base metal Wa, the input heat quantity Q.sub.pn to the new base metal Wa, and the weaving condition of the torch 7 (the weaving amplitude W.sub.pn, weaving pitch dL.sub.pn, etc.), on the basis of the welding condition data of the past base metal Wb similar to the new base metal Wa and the input data relating to the specifications of the welding robot 5. Also, the welding condition derivation device 1 of the present invention automatically adjusts the welding conditions of the new base metal Wa to make the change in the input heat quantity Q.sub.n with respect to the welding condition having a welded record in the past fall within a proper range with the highest priority, and hence can prevent a welding defect, such as incomplete fusion, degradation in mechanical characteristics, etc., due to insufficiency or excess of the input heat quantity Q.sub.pn.

[0166] Also, the welding condition derivation device 1 of the present invention can prevent insufficiency in penetration by using the above-described derivation process of the welding conditions of the new base metal Wa, in particular, by making the bead height d.sub.pn fall within the predetermined range (d.sub.max to d.sub.min), or by not changing the bead height d.sub.pn form d.sub.n as possible.

[0167] Also, the welding condition derivation device 1 of the present invention can widen the adjustable range when the welding conditions of the new base metal Wa are derived, and can handle new base metals Wa of various groove shapes Za and Zb by adding the feed speed V.sub.W(I) of the welding wire 11 (=welding current I) as the object to be adjusted in addition to the welding speed v.sub.p.

[0168] Also, as described above, since the adjustable range when the welding conditions of the new base metal Wa are derived is a wide range, the welding conditions of the past base metal Wb required to be stored in the database 2 in advance can be minimized. Therefore, the number of times of the actual welding test that derives the welding conditions of the past base metal Wb to be stored in the database 2 in advance can be decreased.

[0169] Also, since the welding conditions of the new base metal Wa are derived by taking into account not only limit values in welding procedure of the characteristic and performance limit (the input heat quantity Q.sub.p, the bead height d.sub.p) of the welding robot 5 used for arc welding, but also limit values of the welding robot 5 (the upper limit value of the wire feed speed V.sub.W(I), the limit of the welding speed v of the welding robot 5, the upper limit value of the weaving amplitude W for each weaving frequency F), and hence the computed welding conditions of the new base metal can be reliably executed in the welding robot 5. Therefore, a preparatory check operation of the welding robot 5 is not required after the welding conditions are changed.

[0170] The embodiment disclosed at this time is merely an example in all points of view, and is not limited thereto.

[0171] For example, described in this embodiment is that the operator executes the setting operation for the welding conditions of the new base metal Wa by using the teaching pendant 9 on the basis of the welding conditions of the new base metal Wa derived by the welding condition derivation device 1. However, it is not limited thereto. The welding conditions of the new base metal Wa derived by the welding condition derivation device 1 may be displayed on a display unit (monitor) such as the personal computer 10, and the welding conditions of the new base metal Wa may be set by using an input device, such as a keyboard or a mouse.

[0172] Also, in this embodiment, the articulated welding robot 5 that causes the torch 7 to make the weaving motion is described as an example of a welding machine that automatically executes arc welding. However, this articulated welding robot 5 is merely an example, and the welding machine is not particularly limited as long as the welding machine can make the weaving motion capable of automatic welding. For example, a simple automatic welding machine of linear movement type having a weaving function may be employed. Also, in this embodiment, the multi-layer overlay welding in which the plurality of welding beads are overlaid at the object joint is described as an example of a method of arc welding. However, the present invention may be applied to one-layer one-pass welding. Also, the present invention may be applied to fillet weld joint welding.

[0173] In particular, in the embodiment disclosed at this time, matters not explicitly disclosed, for example, a running condition, an operating condition, various parameters, dimensions, weights, volumes, etc., of components, and so force employ values that are within a range generally employed by those skilled in the art and that can be easily expected by those skilled in the art.

[0174] This application is based on Japanese Patent Application (Japanese Patent Application No. 2014-115700) filed Jun. 4, 2014, which is hereby incorporated by reference herein in its entirety.

REFERENCE SIGNS LIST

[0175] 1 welding condition derivation device [0176] 2 database [0177] 3 welding condition computation unit [0178] 7 torch [0179] 11 welding wire (welding electrode) [0180] Wa new base metal (object workpiece) [0181] Wb past base metal [0182] Za groove of new base metal (groove shape) [0183] Zb groove of past base metal (groove shape)