METHOD OF AUTOMATICALLY SETTING A WELDING PARAMETER FOR MIG/MAG WELDING AND A CONTROLLER FOR PERFORMING THE METHOD

Abstract

A method of automatically setting a welding parameter for MIG/MAG welding including the following steps:initiating (S1) a parameter setting welding operation;measuring (S12) a welding voltage and retrieving (S13) a parameter representing a wire feed speed during said parameter setting welding operation; andidentifying (S14) a second function mapping said welding current to said welding voltage from said measured welding voltage and said retrieved parameter.

Claims

1. A welding controller for automatically setting a welding parameter for MIG/MAG welding comprising: a first function identification control block arranged to determine a first function from a detected response welding current and a present wire feed speed, said first function defining a relationship between the welding current and the wire feed speed; and a wire feed speed control block arranged to determine a desired wire feed speed from the first function provided from first function identification control block and from a desired welding current.

2. The welding controller according to claim 1, further comprising: an operator interface arranged to receive operator information about an actual thickness of a workpiece; and a desired welding current control block arranged to determine the desired welding current from said actual thickness of the workpiece.

4. The welding controller according to claim 2, wherein the operator interface is further arranged to receive operator information about a wire material used in a welding process.

5. The welding controller according to claim 2, wherein the desired welding current control block utilizes a desired welding current mapping function to map the actual thickness of the workpiece to the desired welding current.

6. The welding controller according to claim 5, wherein the desired welding current mapping function is a linear mapping expressed as I=k.sub.1*T+k.sub.2*T.sup.2, where I represents welding current, T represents thickness of a workpiece, and k.sub.1 and k.sub.2 are parameters dependent on a material of the workpiece.

7. The welding controller according to claim 2, wherein the desired welding current control block uses a look up table to define a relationship between the actual thickness of the workpiece and the desired welding current.

8. The welding controller according to claim 1, wherein the first function of the first function identification control block may be a linear mapping expressed as v=k*I.sup.p, where v represents wire feed speed, I represents current, and p is a value between 1 and 2.

9. The welding controller according to claim 1, wherein the welding controller includes further control blocks that enable the welding controller to: generate, during a parameter setting welding operation, a plurality of data couples, each data couple comprising a welding voltage and a wire feed speed parameter; identify a second function mapping a relationship between the welding voltage and the wire feed speed parameter based on the data couples, wherein the second function is defined outside of real welding operating points; determine a welding wire material category using the second function defined outside of the real welding operating points; and determine a controlling voltage based on wire welding material from said second function.

10. The welding controller according to claim 1, wherein the wire feed speed control block determines the desired wire feed speed by interpolating in a look up table that defines a relationship between welding current and the first function, or by using a third function that defines a relationship between the welding current and the first function.

11. A MIG/MAG welding apparatus including a power source, an electrode feeder adapted to feed an electrode to a welding torch, and a welding controller arranged to control the welding current and voltage supplied by the power source to the welding torch, wherein said welding controller furthermore includes: a welding controller for automatically setting a welding parameter for MIG/MAG welding, the welding controller configured to: generate, during a parameter setting welding operation, a plurality of data couples, each data couple comprising a welding voltage and a wire feed speed parameter; identify a second function mapping a relationship between the welding voltage and the wire feed speed parameter based on the data couples, wherein the second function is defined outside of real welding operating points; determine a welding wire material category using the second function defined outside of the real welding operating points; and perform a continued welding process subsequent to the parameter setting welding operation.

12. The MIG/MAG welding apparatus of claim 11, further comprising: a general controller that is configured to provide a present wire feed speed and a response welding current to the present wire feed speed.

13. The MIG/MAG welding apparatus of claim 12, wherein the welding controller further comprises: a first function identification control block arranged to determine a first function from the response welding current and the present wire feed speed.

14. The MIG/MAG welding apparatus of claim 12, wherein the welding controller further comprises: a first sensor adapted to sense a short circuit between the electrode and the workpiece; and a second sensor adapted to sense an arc between the electrode and the workpiece.

15. The MIG/MAG welding apparatus of claim 14, wherein the welding controller further comprises: short circuit percentage value determination control block that establishes a short-circuiting time with the first sensor and establishes an arc time with the second sensor, the short circuit percentage value determination control block is further configured to determine a short circuit percentage value.

16. The MIG/MAG welding apparatus of claim 15, wherein the welding controller further comprises: a welding voltage reference value determination control block that determines a correctional term for a reference voltage from the short circuit percentage value received from the short circuit percentage value determination control block.

17. The MIG/MAG welding apparatus of claim 16, wherein the general controller receives the reference voltage from the welding voltage reference value determination control block.

18. The MIG/MAG welding apparatus of claim 17, wherein the general controller controls increases voltage supplied to the electrode if a measured short-circuiting time of a period time, where the period time is a sum of the short-circuiting time and the arc time, exceeds a pre-defined value and decreases the voltage supplied to the electrode if the short-circuiting percentage goes below the pre-defined value.

19. The MIG/MAG welding apparatus of claim 11, further comprising: a first sensor configured to detect a present wire feed speed; and a second sensor configured to detect a response welding current to the detected present wire feed speed.

20. The MIG/MAG welding apparatus of claim 14, wherein the welding controller further comprises: a first function identification control block arranged to determine a first function from the detected response welding current and the present wire feed speed.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0052] Embodiments of the invention will be described in further detail below with reference to the appended drawings, where

[0053] FIG. 1 discloses schematically a device for MIG/MAG-welding,

[0054] FIG. 2 discloses how the current and the voltage are changed when a droplet is transferred between the weld electrode and the workpiece during short arc welding,

[0055] FIG. 3 schematically discloses an architecture of a welding controller arranged to perform a method according to the invention,

[0056] FIG. 4 schematically shows a set of different first functions 1, 2, 3, 4 and a set of first datacouples Q1, Q2, Q3.

[0057] FIG. 5 schematically shows a set of second functions CO in a welding voltage/wire feed speed space.

[0058] FIG. 6 shows a block scheme of a embodiments of methods according to the invention.

EMBODIMENTS OF THE INVENTION

[0059] FIG. 1 discloses welding equipment for MIG/MAG welding. The welding equipment disclosed comprises a welding machine 10 having a power source 1 adapted to supply welding energy, or melting power, to the electrode 7. Preferably the power source 1 comprises an inverter power supply. An electrode feeder 2 is provided on the welding machine 10. The electrode feeder 2 is adapted to feed the electrode 7 to a welding torch 3. The welding torch 3 is connected to the electrode feeder 2, the welding machine 10 and a gas container 4 via a welding cable. The welding torch 3 comprises a gas cup 5 and a contact tube 6 through which the electrode 7 is fed to a position in the proximity of the workpiece 8. Welding gas is supplied from the gas container 4 to the space enclosed between the gas cup 5 and the contact tube 6.

[0060] Furthermore, the welding equipment comprises a welding controller 20. The welding controller 20 includes a general controller 21 which is arranged to control the welding current and voltage by setting appropriate static and dynamic characteristics for a workpiece to be welded. The general controller 21 is furthermore arranged to regulate the feeding velocity of the electrode feeder 2. The general controller 21 specifically sets a reference voltage Uref which is used as a reference for an average voltage during the welding process. In addition to the conventional control functions for setting a reference voltage and defining the shapes of the welding current and welding voltage performed by the general controller 21, the welding controller 20 includes a set of control blocks to enable operation of the method of automatically setting a welding parameter for MIG/MAG welding according to the invention.

[0061] FIG. 3 schematically discloses an architecture of a welding controller 20 arranged to perform a method according to the invention. The welding controller 20 includes a first function determination control block 22. In the first function identification control block 22 a first function is identified from a detected response welding current I.sub.detected and a present wire feed speed v. The present wire feed speed may be collected from the general controller 21 via path a) or alternatively be detected by a sensor 23 sensing the wire feed speed. The response welding current I.sub.detected may be provided from the general controller 21, which is provided with a sensor 24 for sensing the welding current.

[0062] The present wire feed speed v and welding current I forms a first data couple or a first set of data couples depending on whether a single or a plurality of samples are made.

[0063] The first data couple defines an operating point in a welding current/wire feed speed space. A set of data couples defines a set of operating points in the welding current/wire feed speed space. Functions defining a relationship between welding current and wire feed speed between wires of different dimensions may be stored in a memory accessible by said first function identification control block. By identification of the operating point in the welding current/wire feed speed space, or by linear regression of the set of operating points, a first function which best represents a current welding operation may be selected.

[0064] Generally the first function forms a linear mapping from the response welding current to the present wire feed speed, that is v=(I).

[0065] Suitably the relationship between the welding current and the wire feed speed may be expressed as v=k*I.sup.p, even though more or less complex functions may be contemplated. Here v is the wire feed speed, I is the welding current and p is a number between 1 and 2. This relationship may hold for a set of welding wires with different dimensions and of different materials. The appropriate first function for a specific material and dimension may depend on the values on k and p. With the detected response welding current and the current wire feed speed, the first parameter values k and p may be determined by a straightforward operation in the welding controller. In the event two parameter values are to be determined, at least two data couples v, I are needed. In a simple model, p may be known for a set of welding conditions that are applicable to the welder. Thus the first function may be identified from a single data couple.

[0066] The determination of the first function may be performed by interpolating in a look up table defining a relationship between the welding current I and the wire feed speed v, by using a function defining a relationship between the welding current I and the wire feed speed v and determining suitable coefficients for describing the function or by any other means for identifying an appropriate first function defining a relationship between the welding current I and the wire feed speed v.

[0067] In FIG. 4 it is schematically shown a set of different first functions 1, 2, 3, 4 and a set of first datacouples Q1, Q2, Q3 in a welding current/wire feed speed space. Data representing the different first functions may be stored in a memory area 25. By collecting the first datacouples identification of which of the first functions best represents the datacouples may be performed in a conventional manner.

[0068] For the purpose of determining the first function , the first function determination control block 22 has access to the memory area 25 where the relationship is stored and to processor means 27 for performing the calculation. In an embodiment, the first function may be identified by establishing parameter values, for example k and p as defined above, describing the first function. The memory and processor means may be shared with other control blocks of the welding controller 20 or be locally arranged in the control block. Since the stored relationship may be described with sufficient accuracy as a simple linear function, a hard wired solution providing a measure of the first function may be used.

[0069] An operator may set an actual thickness of a workpiece to be welded as an input data to the welding controller 20. The actual thickness T can be entered via an operator interface 26 by an operator.

[0070] The welding controller further includes a desired welding current control block 28 that determines a desired welding current from an inputted thickness. This may be performed by a desired welding current mapping function which maps a thickness of the workpiece to a desired welding current. The desired welding current mapping function may be provided in the form of a look up table defining a relationship between the workpiece thickness and the desired welding current, by using a function defining a relationship between the workpiece thickness and the desired welding current or by any other means for defining a relationship between the workpiece thickness and the desired welding current. The look up table and/or the function may be generated by collection of welding data in a conventional manner. A desired welding current is determined in the desired welding current control block 28 from said actual thickness T by use of the desired welding current mapping function.

[0071] Generally the desired welding current mapping function forms a linear mapping from the workpiece thickness to the desired welding current. Suitably the relationship between the workpiece thickness and the desired welding current may be expressed as I=k.sub.1*T+k.sub.2*T2, even though more complex functions may be contemplated. Here I is the welding current and T is the thickness of the working piece.

[0072] For the purpose of determining the desired welding current I.sub.desired, the desired welding current control block 28 has access to a memory area 25 where the desired welding current mapping function is stored and to processor means 27 for performing the calculation. The memory and processor means may be shared with other control blocks of the welding controller 20 or be locally arranged in the control block.

[0073] A wire feed speed control block 30 is provided to determine a desired wire feed speed V.sub.desired from the first function provided from first function determination control block 22 and the desired welding current I.sub.desired provided 30 from the desired welding current control block 28. The determination may be performed by interpolating in a look up table defining a relationship between the welding current and the first function, by using a function defining a relationship between the welding current and the first function or by any other means defining a relationship between the welding current and the first function. In the event the first function is described by a set of parameters, which are determined in the first function identification control block, the desired welding current control block 28 will use the determined parameters to calculate the desired welding current.

[0074] For example, in the first function identification control block, k and p in the expression v=k*I.sup.p may be determined from the response welding current and present wire feed speed. Once k and p are determined the desired wire feed speed for a desired current may be determined.

[0075] For the purpose of determining the desired wire feed speed v.sub.desired, the wire feed speed control block 30 has access to a memory area 25 where the relationship defining the first function is stored and to processor means 27 for performing the calculation. The memory and processor means may be shared with other control blocks of the welding controller 20 or be locally arranged in the control block. Since the stored relationship may be described with sufficient accuracy as a simple linear function, a hard wired solution providing a measure of the first function may be used.

[0076] The desired wire feed speed is forwarded to the general controller 21 via a communication channel c for control of the electrode feeder 2 via a communication channel d.

[0077] The welding controller 20 may optionally comprise a sensor 32, which is adapted to sense a short circuit between the electrode 7 and the workpiece 8, and a sensor 34, which is adapted to sense an arc between the electrode 7 and the workpiece 8. A short circuit percentage value determination control block 36 and the sensor 32 together form means for establishing a short-circuiting time, i.e. the duration of a short circuit. The short circuit percentage value determination control block 36 and the sensor 34 together form means for establishing an arc time, i.e. the duration of an arc. In the short circuit percentage value determination control block 36 a short circuit percentage value short % is determined in a straight forward manner. The short circuit percentage value short % is fed forward to a welding voltage reference value determination control block 38 at which a correctional term for the reference voltage Uref is determined. The correctional term for the reference voltage is fed forward via a communication channel e to the general controller 21 which adapts the reference voltage. The general controller 21 is thus adapted to control the energy supplied to the electrode 7 in such a way that the energy supply is increased if a measured short-circuiting time of a total period time, where the period time is the sum of the short-circuiting time and the arc time, exceeds a defined adjustable set value and decreases if said short-circuiting percentage goes below said set value. Consequently, the general controller 21 will maintain the short-circuiting percentage at a constant, desired set value.

[0078] An embodiment of the invention may be used for maintaining the short-circuiting percentage constant at a desired set value. This is achieved by letting the general controller 21 in a conventional way give the power source appropriate static and dynamic characteristics in order to generate a desired short circuiting percentage.

[0079] The embodiment may, however, as an alternative also be performed in more simple machines such as thyristor-controlled weld current sources without any particular process regulator. In this case the regulator of the embodiment controls directly the ignition angle for the thyristor of the welding machine 1.

[0080] Optionally a welding voltage is measured by a volt meter 40. A parameter representing a wire feed speed is determined either from a sensor 23 or via data retrievable from the general controller 21. A second function determination control block 42 is provided to identify a second function . The second function determination control block 42 use the measured welding voltage and the parameter value representing the wire feed speed to determine the second function mapping a parameter representing a wire feed speed to a welding voltage, that is U=(v).

[0081] As have been previously indicated, the welding voltage and the parameter value representing the wire feed speed form a second data couple defining an operating point in a welding voltage/parameter representing the wire feed speed space. A set of data couples defines a set of operating points in the welding voltage/wire feed speed space. Functions defining a relationship between welding voltage and the parameter representing the wire feed speed between wires of different materials may be stored in a memory accessible by said second function identification control block.

[0082] FIG. 5 schematically shows a set of second functions in a welding voltage/wire feed speed space. The functions results from test performed by welding at different welding speeds with welding wires of different material and diameters. For each welding material a set of functions 11, 12, 13 etc. grouped together typically represent different wire diameters. Different welding materials are represented by different groups of functions 11, 12, 13; 21, 22, 23; 31, 32, 33 etc. Functions in different groups may cross each other in the welding voltage/wire feed speed space. By taking a suitable number of second data couples Q4, Q5, Q6, the second function corresponding to the material used can be identified. Instead of storing representations of the functions, a second function may be identified by adapting parameter values to an expression generally describing the functions. The expression may be a polynomial.

[0083] By identification of the operating point in the welding voltage/wire feed speed space, or by linear regression of the set of operating points, a second function which best represents a current welding operation may be identified. In one embodiment the material used is determined from data representing the welding voltage at zero wire feed speed. It has shown that different welding wire materials and different thicknesses of the welding wires are described with different functions in the welding voltage/parameter representing the wire feed speed space and that these functions are easily separable at zero or approximately zero wire feed speed. Hence, from the identification of a specific second function from the welding voltage and the parameter representing the wire feed speed a welding material can be determined. In any way the information may be used for determining a desired welding voltage for a specific welding wire material using the determined second function U=(v) to determine a suitable reference voltage for a desired wire feed speed.

[0084] With the parameter representing the wire feed speed and the welding voltage, the second function may be determined by a straightforward operation in the second function determination control block 42.

[0085] For the purpose of determining the second function , the second function determination control block 42 has access to a memory area 25 where the relationship is stored and to processor means 27 for performing the calculation. The memory and processor means may be shared with other control blocks of the welding controller 20 or be locally arranged in the control block.

[0086] In one embodiment identification of which welding wire material is currently used may be done together with an automatic setting of the welding voltage by regulating the reference voltage with respect to the short arc percentage value. The combined method enables a welding machine to be operable for a large variety of weld electrode dimensions and materials.

[0087] Optionally the welding controller 20 may include welding wire determination control block 44 which automatically determines which welding wire material and wire dimension are presently used from the second parameter provided from the second function determination control block 42. This may be performed in a look up table which defines a material or a class of materials depending on the identified second function.

[0088] The welding controller may thus automatically determine which welding wire material is presently used from the identified second function in welding wire determination control block. This may be performed as suggested above by retrieving a value of a welding voltage at zero wire feed speed from the second function, by use of a look up table which defines a material or a class of materials depending on the value of the second function or by matching the second data couple or couples to a second function, which itself is representative of a specific material. Instead of actually determining which welding wire material is used, the output from the second function determination control block 42 may be used to generate a desired current correction parameter Icorr, which contains information for correction of the desired current generated in the desired welding current control block 28. Alternatively the output from the second function determination control block 42 may be an input to the desired welding current control block 28. Communication may take place via the communication channel f.

[0089] Furthermore a globular area transition current determination control block 46 may be provided. In the globular area transition current determination control block 46 a globular area transition current may be determined for welding from welding wire material and dimension. Once the welding wire material and welding wire dimension has been determined in the welding wire determination control block 44 from the second parameter a globular area transition current may be collected from a look up table. The globular area transition current is a current representative of a globular area at which the metal transfer mode shifts from short arc to spray arc or vice versa.

[0090] The possibility to control the welding process by controlling the reference voltage in dependence of a short arc percentage value enables stable welding at least partly into the spray area. In the colder part of the spray area, a small percentage of short-circuiting droplet transitions is still present. With an adjustment of 2-5% short-circuiting percentage, a stable control also of this part of the spray area, sometimes mentioned under the concept RapidArc, is obtained. During pure short arc welding, a suitable short-circuiting percentage is, however, 17-25%, and 21% has shown to be the most suitable as a start value. If a colder weld is desired, the percentage is increased and vice versa. An inputting device having this function to adjust the set value for the short-circuiting percentage should be present on the current source, electrode feeder or adjustment box.

[0091] An automatic detection of the welding wire material and welding wire dimension enables automatic determination of the globular area transition current. The proposed embodiment thus enables adjustment of the short-circuiting percentage from a first larger value to a second smaller value when said desired welding current is increased to a value equal or greater than the globular area transition current, and adjustment of the short-circuiting percentage from a second smaller value to a first larger value when the desired welding current is decreased to a value equal or smaller than the globular area transition current. The adjustment of the short-circuiting percentage from a first larger value to a second smaller value when said desired welding current is increased to a value equal or greater than the globular area transition current, and the adjustment of the short-circuiting percentage from a second smaller value to a first larger value when the desired welding current is decreased to a value equal or smaller than the globular area transition current is performed in a short circuit percentage adjustment control block 48, which sets an appropriate short circuiting percentage dependent on whether the welding device operates in the short circuit mode or in a low part of the spray mode. An operator input device 50 may adjust the set values for the short circuiting percentage.

[0092] FIG. 6 shows a block diagram of embodiments of a method of welding including the steps of automatically setting a welding parameter for MIG/MAG welding during a parameter setting welding operation. The steps of automatically setting a welding parameter will be followed by a continued welding process controlled by the welding parameter or welding parameters set during the parameter setting welding operation.

[0093] Optionally, in a first step S0 a parameter setting welding operation comprises establishment of a short arc welding process defined by a short-circuiting time 30 and an arc time. In the event the short arc welding process is in operation a short-circuit percentage value short % is calculated in a subsequent step S10. In a following step S11 the melting efficiency of the electrode is controlled in such a way that the melting efficiency is increased if a measured short-circuiting time of a total period time, where the period time is the sum of the short-circuiting time and the arc time, exceeds a defined adjustable set value and decreased if said short-circuiting percentage goes below said set value. The control may be accomplished by setting an appropriate reference voltage Uref.

[0094] In a step S1 a parameter setting welding operation is initiated. This may be initiated automatically by that an operator performs a welding process or by that the operator indicates via an operator input interface that a parameter setting operation should be initiated. Step S1 may optionally be preceded by step S0 and the automatic parameter setting processes defined by the blocks S2-S7 may run in parallel with the automatic parameter setting processes defined by the blocks S10-S17, possibly with exchange of information between the processes.

[0095] During the parameter setting welding operation a response welding current is detected in step S2. In step S3 a set wire feed speed is retrieved. In step S4 a first function mapping said response welding current to said set wire feed speed is identified. This may be done by identifying appropriate parameter values k and p, alternatively a function in a set of functions stored in a decoded format in a memory may be selected. The selection may be based by calculation a minimum deviation from a set of couples and each of the stored function. In step S5 an actual thickness of a workpiece to be welded is retrieved from an operator interface. The operator may also input the wire material used in the process to the operator interface or automatically derive the wire material and optionally wire dimension from the parallel process of steps S10-S15.

[0096] In step S6 a desired welding current is determined from the set actual thickness of the workpiece. In step S7 a desired wire feed speed is determined from the first function and the desired welding current.

[0097] Optionally the steps S10-S15 are performed in parallel with the process defined by steps S1-S7. The steps S16-S17 may also be performed in parallel with steps S1-S7. In step S12 a welding voltage is measured and in step S13 a parameter value representing the wire feed speed is measured. This parameter value may be the wire feed speed or the welding current. In step S14 a second function mapping said parameter value representing the wire feed speed to said welding voltage is determined from the measured welding voltage and parameter value representing the wire feed speed. In step S15 a welding wire material and optionally a wire dimension are determined from the second function. The information derived in step S15 defining the welding wire material and optionally wire dimension may be fed forward to step S6 for determination of a desired welding current.

[0098] Optionally, the method for automatically setting a welding parameter for MIG/MAG welding includes a step S16 where a globular area transition current is determined from information defining the wire welding material determined in step S15. In a step S17 the short-circuiting percentage is adjusted from a first larger value to a second smaller value when said desired welding current is increased to a value equal or greater than said globular area transition current, and the short-circuiting percentage is adjusted from a second smaller value to a first larger value when said desired welding current is decreased to a value equal or smaller than said globular area transition current.

[0099] Beneficially, during the parameter setting welding operation, the welding voltage, welding current and wire feed speed are recorded as data triplets from which a desired wire feed speed and a desired welding current are determined to be used in the continued welding operation by identification of the first and second functions in a manner as described above.