WO2008151393A1

WO2008151393A1 - Apparatus and method for monitoring welding

Info

Publication number: WO2008151393A1
Application number: PCT/AU2008/000868
Authority: WO
Inventors: John Norrish; Dominic Cuiuri; Alexander Nicholson
Original assignee: University of Wollongong; BOC Ltd Australia
Current assignee: University of Wollongong; BOC Ltd Australia
Priority date: 2007-06-15
Filing date: 2008-06-16
Publication date: 2008-12-18
Anticipated expiration: 2009-12-15

Abstract

The present invention relates to apparatus and a method for displaying at least one welding condition. The apparatus comprises: a monitoring unit for monitoring at least one welding parameter, a processor for determining at least one welding condition in real-time in response to said monitored parameter(s), and a display operatively associated with said processor for displaying the so-determined welding condition in real-time. The present invention also relates to a method for automatically controlling low fume and/or minimised arc length welding conditions during welding, and a method for automatically controlling welding to avoid globular mode of metal transfer.

Description

APPARATUS AND METHOD FOR MONITORING WELDING

FIELD OF THE INVENTION

The present invention relates to welding and in particular to apparatus for monitoring welding and displaying a welding condition. However, it will be appreciated that the invention is not limited to this particular field of use.

BACKGROUND OF THE INVENTION The following discussion of the prior art is provided to place the invention in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of common general knowledge in the field. There have been numerous attempts in the prior art to control the welding process. These attempts have been driven inter alia by the need to provide consistent welds having reproducible properties such as mechanical and metallurgical properties. Many of these attempts introduce automatic controls of the welding process. For example, weld programmer instruments have been used in the past as a means for duplicating conditions during successive weldments. These programmers have provided a means for storing weld parameters in the form of a welding schedule for later repeated use. The programmed welding schedule is affected by one or more signals which vary in time and act as commands to various equipment which produce the required welding conditions. The controlled equipment would typically include welding power sources, and position mechanisms to move the welding heat source/electrode relative to the work material being welded. However, these weld programmer instruments are typically complex and expensive to operate. Various advances in the art have been proposed, for example U.S. Patent No. 4,390,954, which modifies a pre-programmed weld parameter schedule during real-time welding. However, the welding control is still relatively inflexible.

Other applications have sought to control arc length by various means, e.g. a motorised servo system such that arc length is proportional to arc voltage. However, this methodology is problematic since voltage characteristics for a constant arc length during a changing current is a non-linear function. Therefore, in a motorised system the desired arc length is not maintained during arc current variations.

Various advances in the prior art have been proposed. For example U.S. Patent No. 5,245,546 discloses a welding arc length control system having a power source for providing a welding current, a power amplification system, a motorised welding torch assembly connected to the power amplification system, a computer and a current pick up means. The computer is connected to the power amplification system for sorting and processing arc weld current power source and to the welding torch assembly for providing weld current data to the computer. Therefore, the system maintains the desired arc length as the welding current is varied during operation, which maintains consistent weld penetration.

Other applications which provide sophisticated control and display of the welding process are disclosed in U.S. Patent No.'s 5,571,431 and 6,002,104. However, the control systems provided in these applications are relatively complex, and the welding process display in U.S. Patent No. 5,571,431 simply comprises a display of the welding process demand values (i.e. set-points) compared to the actual real-time values. It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the abovementioned prior art, or to provide a useful alternative.

DISCLOSURE OF THE INVENTION

According to a first aspect the present invention provides apparatus for displaying at least one welding condition, comprising: a monitoring unit for monitoring at least one welding parameter, a processor for determining at least one welding condition in real-time in response to said monitored parameter(s), said processor operatively associated with said monitoring unit, and a display operatively associated with said processor for displaying the so-determined welding condition in real-time.

In preferred embodiments the welding condition is the mode of metal transfer. The processor is preferably adapted to determine the frequency of short circuits, and programmable so as to ascertain the mode of metal transfer from the frequency of short circuits. The processor is also preferably adapted to determine the frequency of transient events, and programmable to instruct the display to give a warning signal if the frequency of transient events is less than a predetermined minimum. The processor is further preferably adapted to determine the stability index when the mode of metal transfer is dip transfer, and programmable to instruct the display to give a warning signal if the stability index is below a certain threshold that indicates instability and potentially higher fume production rate. Preferably the monitoring unit is adapted to monitor the welding voltage and/or welding current.

In one embodiment, the processor acquires at least one welding parameter via the monitoring unit, and then the processor determines the frequency of short circuits, the frequency of transient events, and the stability index, and then the processor calculates/determines the welding conditions (mode of metal transfer, inferred fume production rate, weld stability, inferred arc length). The processor then communicates that data to the display on a continuous basis. In one embodiment the display is operatively associated with the processor, which in turn is operatively associated with the monitoring unit. In other embodiments each of the display, the processor and the monitoring unit are operatively associated with each other.

According to a second aspect the present invention provides a method for displaying a welding condition, comprising the steps of: monitoring at least one welding parameter, determining at least one welding condition in real-time in response to said monitored parameter(s) and displaying said welding condition in real time during a welding operation.

The monitoring unit is adapted to monitor a plurality of welding parameters, such as the welding voltage and current. However, other welding parameters may be monitored as will be apparent to those skilled in the art and discussed below. A welding condition is then determined in response to said monitored parameter(s) and such condition displayed, preferably directly to the welding operator e.g. inside a welding helmet. In other embodiments the welding condition is displayed on a computer screen, or simultaneously on a computer screen and to the welding operator. In further embodiments the welding condition is displayed in the vicinity of the welding operator for others to view. In one embodiment the monitoring unit is a separate unit to the welding power supply. However, in alternative embodiments the monitoring unit is integrated into the welding power supply.

Preferably a plurality of welding conditions may be displayed in real-time, thereby allowing the welding operator to continuously monitor the welding conditions and adjust or adapt their welding technique in real-time to suit the particular shape of the metals being joined and/or the type of metals and/or to suit the particular type of joint (butt joint, lap joint, T-joint, corner joint, edge joint etc) and/or for the particular welding consumables (such as type of welding electrode and shielding gas). The welding conditions determined and displayed include the mode of metal transfer and/or an inferred fume production rate and/or the weld stability and/or an inferred arc length. To explain, the mode of metal transfer of a weld may be dip transfer, globular transfer or spray transfer. The inferred fume production rate may be a low or a high condition. However, in other embodiments the inferred fume production rate may additionally include a medium condition. The weld stability condition may be either stable or unstable, and the arc length may be short/minimised or excessive/high.

By determining and displaying such welding conditions in real time, it allows an operator better understanding and therefore control of the welding process. As will be apparent to those skilled in the art, the GMAW operation for instance, is preferably conducted in dip or spray transfer mode. However, there may be circumstances whereby the welding operator may need to weld in a globular mode. The present invention affords the welding operator such a capability since the welding operator is continuously apprised of the welding conditions in real-time (or at least inferred welding conditions). Further, the present invention allows the welding operator to tailor the weld when using different consumables, such as the welding electrode and the shielding gas. The improved control available due to the increase in information available to the welding operator allows significantly improved precision in welding quality and design. This improved welding provided by enabling the operator to adhere to a welding schedule which specifies a welding mode, and, enabling the operator to achieve improved welding consistency..

Further still, the time required to train a welding operator may be reduced since, for the first time, the welding operator is informed of the actual welding conditions in real-time, whereas in the past significant operator experience was required to understand how to keep the welding process in a particular condition, e.g. to achieve a particular mode of metal transfer, or to maintain the process in a low fume production rate condition.

As discussed above, information on the (inferred) rate of fume production is also available to the welding operator in real-time. This is clearly a major safety advantage for the welding operator since they can now manipulate the welding operation such that it remains in a low fume condition, or, if the particular welding process called for produces a relative high rate of fume, then the welding operator can arrange for appropriate extraction of the welding fume in the vicinity of the weld. The present invention avoids simply measuring certain welding parameters e.g. voltage, current, etc, and relaying them to a welding operator (e.g. as disclosed in US Patent No. 6,242,711). Whilst such parameters are certainly useful information, they are less useful to the welding operator compared to an indication of the actual (or at least inferred) welding conditions such as transfer mode. Rather, the monitored parameters are used to determine the welding condition in real time.

Further, displaying the actual welding conditions to the welding operator teaches away from the complex and sometimes inaccurate control systems of prior art devices. The present applicants have found that since the welding operator is now apprised of the welding conditions in real-time, the manual control which the welding operator can deliver is at least as good as that of such prior art automated control systems. By continuously monitoring and analysing welding signals, and determining and reporting the welding conditions to the welding operator, the operator can tailor the process accordingly. The display preferably includes a plurality of indicators, wherein each indicator is adapted to display at least one welding condition. In one embodiment, the display includes four colour-coded indicators which correspond to dip transfer, globular transfer, low-fume spray transfer and high-fume spray transfer welding modes. The indicators may also flash to indicate the weld stability or an inferred fume production rate. The display can be disposed within the welder's helmet or mask for example, as discussed below giving instantaneous reliable line of sight information to the welder on the welding condition. However, as will be appreciated, any configuration of indicators may be used to display the welding conditions.

In other embodiments, the display is a computer screen which also displays four colour-coded regions corresponding to dip transfer, globular transfer, low-fume spray transfer and high-fume spray transfer welding modes. As above, the regions may also flash to indicate the weld stability or an inferred fume production rate.

In a particular embodiment of the present invention a method for minimising fume concentration is provided, comprising: determining and displaying a rate of fume production on a display in real-time during a welding operation thereby to permit a welding operator responsive to said displayed fume production rate to adapt their welding technique for maintaining a reduced rate of fume production during said welding operation. In one embodiment the rate of fume production is an inferred rate of fume production. In one aspect the present invention provides a method for optimising welding conditions, comprising: determining and displaying a mode of metal transfer on a display in real-time during a welding operation thereby to permit a welding operator responsive to said displayed mode of metal transfer to adapt their welding technique for maintaining the mode of metal transfer in a preferred or pre-determined mode during said welding operation. In one embodiment the mode of metal transfer is an inferred mode of metal transfer. In a related aspect the present invention provides a method for optimising welding conditions wherein the welding condition is arc length.

An important aspect of the present invention is the calculation of the welding conditions from the monitored welding parameters. This may be achieved in a variety of ways as will be apparent to the person skilled in the relevant art, however the following process is a preferred process. The monitoring unit firstly acquires a welding parameter(s) e.g. voltage and/or current signals which are optionally conditioned (filtered). Preferably the voltage/current signals are typically analysed every 0.5 seconds. The sampling period may be varied, for example, between 0.1 to 10 seconds, however, it will be appreciated that the longer the sampling period the greater the delay in relaying the actual real-time welding conditions to the welding operator. The processor may be used to continuously determine the following characteristics of the welding parameters in real time: a. Short circuit frequency - used to determine mode of metal transfer. b. "Transient Event" frequency - used to infer rate of fume production. c. "Stability Index" - only calculated when the mode of metal transfer is dip transfer since the calculation is based on the mean and standard deviation of the short circuit frequency. The stability index is therefore inappropriate in spray since as there are relatively very few (if any) short circuits.

As a result of monitoring one or more of the aforementioned welding characteristics, the processor is able to determine, according to the following logic, the welding condition, comprising: the inferred mode of metal transfer, inferred arc length and/or inferred rate of fume production. Preferably the welding conditions are determined over 4 periods of 0.5 seconds (i.e. 2 seconds), however it will be appreciated that fewer than, or more than 4 periods may be used, and the periods may be shorter or longer than 0.5 seconds in duration. The welding condition is determined according to the following logic:- 1.) Identifying the mode of metal transfer - If the short circuit frequency is greater than, say, 50 Hz then the inferred mode of metal transfer is dip transfer; if the short circuit frequency is between, say, 50 Hz and 9 Hz the inferred mode of metal transfer is globular transfer; and if the short circuit frequency is less than, say, 9 Hz the inferred mode of metal transfer is spray transfer. The average current is also employed to infer the mode of metal transfer, i.e. if the average current is greater than the threshold current then the inferred mode is spray transfer, else the mode is not spray transfer. The 'threshold current' is taken as the well documented spray transition current for the specific consumables being used (see also page 10), as the person skilled in the art would be aware. In general the average welding current must exceed a value of around 200 amps for spray transfer to occur. 2.) Determining arc length and rate of fume production - The following applies if the process is above the spray transition current. If the transient event frequency is greater than or equal to, say, 0.5 Hz, then the inferred fume production rate is low and the inferred arc length is low or minimised; and if the transient event frequency is zero in the last sample period then the inferred fume level is high and the inferred arc length is high or excessive.

It will be appreciated that the thresholds used to determine the mode of metal transfer (for example, 9 and 50 Hz) have been chosen from experience and measurement to be typical or characteristic of the transitions between modes. Similar comments apply for the transient event frequency (viz transient event frequency = 0.5 Hz). The reader is referred to Figures 4 and 5 and the Preferred Embodiment for further details which describe the correlation of electrical signals to the various welding conditions. The transient event frequency could be chosen from a range of values, such as: 0.3, 0.32, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56, 0.58, 0.6, 0.62, 0.64, 0.66, 0.68, and 0.7 Hz. The transient event frequency could also be chosen from the following range of values, such as: 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, and 10. The present applicants have investigated and analysed the welding parameters from a typical GMAW process and discovered that the "transient events" may be used in conjunction with the short circuits to determine the welding conditions. Further, the present applicants make use of hitherto unknown discovery, namely, that in spray transfer welding the rate of welding fume evolution has an inverse relationship to the number of "transient events" per unit time. Up to now, there has been little or no recognition that the number of "transient events" per unit time is a significant parameter. Transient events may be differentiated from short circuits in that transient events have a relatively very short duration (observed to be as low as 0.1 milliseconds), whereas short circuits have a much longer duration (about 2 to 5 milliseconds, i.e. about 20 to 50 times longer). They are further differentiable in that transient events have relatively low amplitudes (in the order of 3 to 10 Volts) whereas for short circuits the amplitude can be as much as the machine voltage setting, for example 22 Volts, since in a true short circuit the voltage drops to zero or thereabouts. The present Applicants consider that transient events are further differentiable from short circuits since they rarely drop below the mean voltage, say, about 10 Volts. Further still, the transient events occur in either direction of the mean voltage - i.e. "up" spikes and "down" spikes. However, short circuits always produce "down" spikes towards zero volts.

The monitoring unit may include a digitally encoded algorithm for determining the aforementioned welding conditions from the welding parameters in real-time, and the display is operable in response to the monitoring for immediately indicating the calculated welding condition. The display may be operatively associated with the monitoring unit and/or the processor. In one embodiment, if the mode of metal transfer is spray and the inferred fume level is low, a first indicator on said display is activated. If the mode of metal transfer is spray and the inferred fume production rate is high a second indicator on said display is activated. If the mode of metal transfer is globular a third indicator on said display may be activated to inform the welding operator to avoid this welding mode (or welding in this welding mode). If the mode of metal transfer is dip transfer a fourth indicator on said display may be activated. The fourth indicator may be configured to flash if the stability index is less than 0.60, for example, to indicate that the process is unstable. The reader is referred to the Definitions section for further details on the calculation of the stability index.

In order to minimise cabling to and from the monitor unit, the apparatus may also include a radio -frequency signal transmitter operatively associated with the monitoring unit for transmitting a signal corresponding to the welding condition to a radio- frequency signal receiver operatively associated with the display. As discussed previously, at least one welding condition is preferably displayed directly to the welding operator, and in preferred embodiments the display is integrated into the welding operator's helmet or mask such that the display is within the peripheral vision of the welding operator when the helmet or mask is being worn.

The monitoring unit may also be programmable with additional welding apparatus/process information for use as input data for the digitally encoded algorithm. Such information may be chosen from the group consisting of welding electrode diameter, welding electrode material, wire feed rate and shielding gas. However other equipment data may also be entered as would be apparent to those skilled in the art. In one embodiment, the welding operator may input the information directly into a suitable interface engaged with the monitoring unit. However, in other embodiments a barcode scanner may be provided with the monitoring unit for scanning barcodes on the welding electrode and/or the shielding gas bottle such that the information is automatically communicated and programmed into the monitoring unit. In further embodiments, readable cards may be provided on the welding electrode and the shielding gas bottle. These cards can then be engaged with a suitable card reader incorporated into the monitoring unit such that the information is automatically programmed into the monitoring unit.

In further embodiments the monitoring unit is connectable to a personal computer for recording and storing one or more of the welding signals and the welding conditions. As would be apparent to those skilled in the art, this may be useful for quality control purposes, or even for training purposes.

According to a further aspect the present invention provides a display apparatus for a welding operator's helmet or mask, comprising: a display for displaying a welding condition in real-time, the display being operatively associated with a processor and a monitoring unit for continuously monitoring at least one welding parameter and determining said welding condition in real-time in response to said monitored welding parameter(s).

Preferably the display apparatus is integrated into the welding operator's helmet or mask such that the display is within the peripheral vision of the welding operator when the helmet or mask is being worn. In a related aspect, the present invention provides a welding operator's helmet or mask incorporating a display according to the first aspect.

In other aspects, the monitoring unit and/or processor may include a programmable controller for automatically controlling the welding condition to a predetermined condition. For example, the control may be based on the transient event firequency and the short circuit frequency and, in one embodiment, could function according to the following logic.

1.) If the average current is greater than the "spray transition current" then the inferred mode of metal transfer is spray transfer and control is enabled. The spray transition current is the current at which the mode of metal transfer changes from globular to spray and is obtained from a lookup table of values, which are based on inputs such as electrode size and material and shielding gas. Additionally, if the short circuit frequency is less than, say, 9Hz then the inferred mode of metal transfer is spray transfer and control is enabled. 2.) If a transient event has been detected, then the process voltage is increased by typically between about 0.2 to 0.5 Volts. Since the incidence of transient events indicates a shortening of the arc and is a precursor to short circuiting, increasing the arc voltage increases arc length and avoids the potential risk of short circuiting and excessive spatter. Alternatively, if no transient event has been detected in the welding signal sampling period the voltage is decreased by typically 0.1 to 0.2 Volts.

This maintains the shortest arc length consistent with stable transfer whilst minimising fume. The Applicants have found that excessive arc length/voltage is associated with increased fume (see also Figure 4).

3.) The foregoing logic is repeated at regular intervals (0.1 to 10 seconds, say) to implement a system that continually adjusts the welding voltage towards a condition that minimises arc length while avoiding severe short-circuiting, excessive spatter and associated instability.

Thus, when in spray transfer mode the voltage is regulated such that transient events are present at greater than, say, 0.5 Hz. In other words, the control system is preferably designed to 'bounce' the process off the floor condition with a relatively low amplitude which is where the lowest fume production rate condition is observed. In alternative embodiments the wire feed rate could be regulated such that transient events are present.

It will be appreciated by those skilled in the art that the consequences of reducing arc length is an increase in spatter, and increasing the arc length is an increase in fume production rate. Therefore, in practice, ideally a balance should be struck between the amount of spatter and the fume production rate. To affect this balance an adjustable control may be provided on the monitoring unit, or in the case where the monitoring unit is integrated into the power supply, the control is provided on the power supply itself. An alternative method of affecting this balance is to change the threshold at which a valid transient event is detected. Reducing the threshold makes the control system more sensitive, and effectively raises the floor condition of lowest fume production. As a consequence, the arc length is increased and tendency to produce spatter is decreased. Increasing the threshold lowers the floor condition, driving the process to a shorter arc length and lower fume formation but with increased spatter.

According to a further aspect the present invention provides a method for automatically controlling low fume and/or minimised arc length welding conditions during welding, said method comprising: monitoring welding voltage, determining a transient event frequency during spray transfer welding as a function of said monitored voltage, and automatically adjusting a welding voltage set point such that said transient event frequency falls within a range of pre-determined values corresponding to low fume and/or minimised are length.

Preferably the pre-determined transient event frequency range is between 0.25 to 10 Hz. However, the pre-determined transient event frequency range may be between about 0.125 to 100 Hz. It will be appreciated that these values have been chosen from experience and other ranges would also be viable. For example the pre-determined transient event frequency range could also be between a range of A to B Hz, wherein A may be chosen from the following values: 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, 1, 1.125, 1.25, 1.375, 1.5, 1.625, 1.75, 1.875, 2, 2.125, 2.25, 2.375, 2.5, 2.625, 2.75, 2.875, 3, 3.125, 3.25, 3.375, 3.5, 3.625, 3.75, 3.875, 4, 4.125, 4.25, 4.375, 4.5, 4.625, 4.75, 4.875, and 5 Hz, and B may be chosen from the following values: 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, and 100 Hz.

According to a related aspect the present invention provides a method for automatically controlling welding to avoid globular mode of metal transfer comprising: monitoring welding voltage, determining the number of short circuits per time period, and automatically adjusting a welding voltage set point such that the number of short circuits per time period falls outside a range of about 9 to 50 Hz. It will be appreciated that these values have been chosen from experience and other ranges would also be viable. For example the number of short circuits per time period could also be chosen to fall outside a range of X to Y Hz, wherein X may be chosen from the following values: 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, and 15 Hz, and Y may be chosen from the following values 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, and 60 Hz.

The control strategy described above is implemented by sending a control reference signal from the analysis software to the welding power source. The power source used would normally have facilities for remote control of output voltage via an electronic signal. Typically this would be an electronically regulated power source and the interface may be achieved via a digital or analogue interface. In the event that remote voltage control is not available (e.g. with switched output power supplies) similar results may be achieved by remote control of wire feed speed (decreasing wire feed speed to increase voltage or increasing wire feed speed to reduce voltage).

As discussed in the foregoing, a welding condition determined and displayed includes the mode of metal transfer, which may be dip transfer, globular transfer or spray transfer. The inferred fume production rate may be a low or a high condition. Typical values for low or high conditions are variable, as the skilled person would appreciate. However, typical values for low fume production rate with a 1.2 mm diameter solid mild steel electrode operating at 8 m/min feed rate and 260 Amperes in spray transfer would be 0.4 to 0.8 g/rnin, and a high fume production rate would be 1.0 g/min and higher. The arc length may be short/minimised or excessive/high. In a typical GMAW spray transfer welding process, a short or minimised arc length is typically below 5 mm, and an excessive or high arc length is typically above 5 mm. In the case of dip transfer, the stability condition may be either stable or unstable. As the person skilled in the art would be aware, a stable condition may be characterised by calculation of the stability index, as described later in this text. A stable condition is characterised by a stability index greater than 0.60, and an unstable condition is characterised by a stability index below 0.60. It will be appreciated that there is a complex interplay between these parameters during a welding process and that these figures are only an approximate guide. Further, it will be appreciated that a range of values may be chosen for the stability index, for example the stability index may be selected from the group consisting of 0.5, 0.525, 0.55, 0.575, 0.6, 0.625, 0.65, 0.675, 0.7, 0.725, 0.75, 0.775, and 0.8.

Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to". DEFINITIONS

In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention only and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one having ordinary skill in the art to which the invention pertains.

For the purposes herein the term "parameters" comprises primarily the welding voltage and current and other data which can be calculated therefrom or monitored directly e.g. the transient event frequency, the short circuit frequency and the stability index. The "welding conditions" (inferred from the welding parameters) comprise the mode of metal transfer (spray, dip or globular), the arc length (short/minimised, or excessive/high) and the inferred fume production rate (low or high).

The dip transfer mode of metal transfer will characteristically show a relatively high short circuit frequency (say, above 50 Hz). Globular transfer will also show short circuits but fewer than dip (say, between about 10-50 Hz). However, short circuits are characteristically almost absent from the spray transfer process (say, below about 9 Hz).

For the purposes herein a "transient event" may be differentiated from a short circuit in that transient events have a very short duration (observed to be as low as 0.1 milliseconds), whereas short circuits have a much longer duration (about 2 to 5 milliseconds, i.e. about 20 to 50 times longer). They are further differentiable in that transient events have relatively low amplitudes (in the order of 3 to 10 Volts) whereas for dip transfer the amplitude can be as much as the machine voltage setting since in a true short circuit the voltage drops to zero or thereabouts, for example 22 Volts. The present Applicants consider that transient events are differentiable from short circuits since they rarely drop below the mean voltage, say, about 10 Volts. Further still, the transient events occur in either direction of the mean voltage - i.e. up spikes, and down spikes. However, short circuits are always towards zero volts. These transient events correlate with the audible "pops" or "crackles" heard during the welding process when in spray transfer mode and are audibly different from the sounds made by short circuits. These transient events are absent from dip or globular modes of metal transfer.

For the purposes of the present application, the "stability index" is calculated as follows: Stability Index = 1 μ where σ is the standard deviation of the weld cycle duration, and μ is the mean value of weld cycle duration. This calculation is typically used for dip transfer. The duration of one weld cycle is the time between the start of a short-circuiting event and the start of the subsequent short-circuiting event. However, as those skilled in the art would be aware, there are a number of alternative definitions of stability index, as described in Table 10.5 (page 197) of "Advanced Welding Processes", J. Norrish, Woodland Publishing (2006), which is incorporated herein by reference.

The recitation of a numerical range using endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a photograph of a front perspective view of a typical welding helmet and a perspective view of a monitoring unit according to the present invention;

Figure 2 provides a rear view of the welding helmet as shown in Figure 1 and an exploded view of one embodiment of a display according to the present invention; Figure 3 provides a computer screen-shot of a display according to another embodiment of the present invention;

Figure 4 is a typical graph of fume production rate (g/min) versus voltage for a particular wire feed rate and consumable combination (material, shielding gas, wire diameter, etc) in a GMAW welding process;

Figure 5 A shows a typical graph of voltage versus time for low fume conditions and minimised arc length (31 Volts average and an average of 2 Hz transient event frequency - i.e. between 2 and 4 seconds on the graph there are approx. 8 to 9 events making an average of 4 Hz in this time period, and between 10 to 12 seconds there are approx. 1 to 2 events making an average of 0.5 Hz in this time period);

Figure 5B shows a typical graph of voltage versus time for medium fume conditions and non-optimal arc length (33 Volts average and 0 Hz transient event frequency);

Figure 5C shows a typical graph of voltage versus time for high fume conditions and excessive arc length (36 Volts average and 0 Hz transient event frequency); Figure 6A is a schematic representation of a welding apparatus for displaying at least one welding condition; and

Figures 6B and 6C are schematic representations of embodiments for controlling the welding condition to a predetermined welding condition.

PREFERRED EMBODIMENT OF THE INVENTION

Referring to the drawings, the present invention provides a method and apparatus for displaying a welding condition, comprising a monitoring unit 1 for monitoring at least one welding parameter and determining at least one welding condition in real-time in response to said monitored parameter(s). The monitoring unit may be integrated with the welding power supply (not shown) or may be a separate unit operable with the welding power supply, as shown in Figure 1. The monitoring unit 1 is preferably adapted to monitor a plurality of welding parameters e.g. the welding voltage and current, and a display 2 is operatively associated with the monitoring unit 1 and adapted to display the welding condition in real-time during a welding operation. Preferably a plurality of welding conditions are displayed, such as the mode of metal transfer, an inferred fume production rate, the weld stability and an inferred arc length. As discussed above, the inferred mode of metal transfer may be dip transfer, globular transfer or spray transfer, and the inferred fume production rate may be a low or a high condition. The weld stability condition may be either stable or unstable, and the arc length may be short/minimised or excessive/high.

The welding conditions are preferably displayed directly to the welding operator in real-time, thereby allowing the welding operator to continuously monitor the welding conditions and adjust or adapt their welding technique in real-time to suit the particular shape of the metals being joined and/or the type of metals and/or to suit the particular type of joint and/or for the particular welding consumables (such as type of welding electrode and shielding gas). For example, in particular embodiments of the invention methods for minimising fume concentration, and for optimising welding conditions are provided. In the former method an inferred rate of fume production is determined and displayed on the display 2 in real-time during a welding operation to permit a welding operator to adapt their welding technique for maintaining a reduced rate of fume production. In the latter method, the inferred mode of metal transfer is determined and displayed in real-time during a welding operation to permit a welding operator to maintaining the mode of metal transfer in a preferred or pre-determined mode during the welding operation.

Preferably the display means includes four colour-coded indicators 3 corresponding to dip transfer, globular transfer, low-fume spray transfer and high-fume spray transfer welding modes. Several of the indicators 3 flash to indicate the weld instability or an excessive fume production rate. For example see Table 1 for a preferred configuration of indicators 3.

Table 1 - Indicator Configuration

As can be seen in Figure 2, the display 2 may be integrated into the welding operator's helmet or mask 4 such that the display 2 is within the line of sight or peripheral vision of the welding operator when the helmet or mask 4 is being worn. However, the display 2 embodiment as shown in Figure 3 is a computer screen 5 such that others can view the welding conditions.

For the embodiment as shown in Figure 2, in order to minimise cabling to and from the monitor unit 1 the apparatus also includes a radio -frequency signal transmitter (not shown) operatively associated with the monitoring unit 1 for transmitting a signal corresponding to the welding condition to a radio -frequency signal receiver 6 operatively associated with the display 2. The radio-frequency signal receiver 6 is similarly integrated into the welding operator's helmet or mask 4.

In one embodiment, the welding conditions are calculated from the welding parameters in real-time by way of a digitally encoded algorithm. This is accomplished by calculating the welding conditions from the welding parameters by firstly sampling welding voltage and current signals every 0.5 seconds. The welding parameters (voltage and current) are then analysed every 0.5 seconds to determine the following information in approximately real time: a.) Short circuit frequency - used to determine mode of metal transfer. If the short circuit frequency is greater than 50 Hz then the mode of metal transfer is dip transfer; if the short circuit frequency is between 50 Hz and 9 Hz the mode of metal transfer is globular transfer; and if the short circuit frequency is less than 9 Hz the mode of metal transfer is spray transfer. b.) "Transient Event" frequency - used to infer rate of fume production and inferred arc length. If the transient event frequency is greater than or equal to 1, then the inferred fume production rate is low and the arc length is low or minimised; and if the transient event frequency is zero in the last 2 seconds then the inferred fume level is high and the arc length is high or excessive, c.) "Stability Index" - only calculated when the mode of metal transfer is dip transfer. It would be understood by persons skilled in the art that the welding parameters of short circuit frequency, transient event frequency and stability index may be calculated from the voltage and current or may be monitored directly with appropriate software in the monitoring unit.

Figure 4 shows a typical fume production rate versus mean voltage trace for a particular welding process, and Figures 5 A to C show voltage versus time graphs for the data points illustrated on Figure 4. The thresholds used to determine the mode of metal transfer (viz 9 and 50 Hz) have been selected from these measurements since they are characteristic of the transitions between welding modes. Analysis of these graphs also provides an estimate of the threshold transient event frequency (transient event frequency = 0.5 Hz) which can be used to differentiate low and high fume conditions, and low or excessive arc lengths. It will be appreciated that the short-circuit frequency for Figures 5 A to C is effectively zero since the mode of metal transfer is spray. The monitoring unit may also be programmable with additional welding information for use as input data for the digitally encoded algorithm. Such information may include welding electrode diameter, welding electrode material, wire feed rate and shielding gas.

In other aspects, the monitoring unit may include a programmable controller for automatically controlling the welding condition to a pre-determined condition. For example, the control may be based on the transient event frequency and the short circuit frequency and functions according to the following logic. When the mode of metal transfer is spray transfer control is enabled, and if a transient event has been detected, then the process voltage set point is increased. The increment is typically 0.5 Volts. Alternatively, if no transient event has been detected in the packet of sampled welding signals the voltage set point is decreased. The decrement is typically 0.2 Volts. This control loop provides control of the welding voltage such that transient events are present at greater than about 0.5 Hz. In other words, the control system is preferably designed to minimise the arc length to where the lowest fume production rate condition is observed. It will be appreciated by those skilled in the art that the consequences of reducing arc length is an increase in spatter, and increasing the arc length is an increase in fume production rate. Therefore, in practice, ideally a balance should be struck between the amount of spatter and the fume production rate. To affect this balance an adjustable control may be provided on the monitoring unit, or in the case where the monitoring unit is integrated into the power supply, the control is provided on the power supply itself.

In other aspects a method for automatically controlling a welding condition during welding is provided. In this method the welding voltage is monitored and the transient event frequency is determined during spray transfer welding. The voltage is then automatically adjusted such that the transient event frequency falls within a range of about 0.5 to 10 Hz thereby maintaining the welding conditions of low fume and minimised arc length. In a related aspect the present invention may provide a method for automatically avoiding a globular mode of metal transfer during welding. Again, the welding voltage is monitored and the number of short circuits per time period is determined. When the number of short circuits per time period is between a range of, say, 9 to 50 Hz the welding voltage set point is automatically adjusted such that the number of short circuits per time period falls outside the range of, say, 9 to 50 Hz thereby avoiding a globular transfer mode.

Figure 6A schematically illustrates an apparatus for monitoring welding, in the form of monitoring unit 101. In the context of Figure 6A, a welding power supply 102 is connected to a welding electrode 103 and parent metal (the "workpiece") 104 by power lines 105 and 106 respectively. An arc is generated by the application of a welding voltage by the power supply between the welding electrode and parent metal to facilitate arc welding. The power supply additionally provides a welding current flowing through powerlines 105 and 106 between positive and negative terminals 107 and 108 of power supply 102.

In the present embodiment, monitoring unit 101 is coupled to power lines 105 and 106 for monitoring the welding voltage and welding current. As illustrated, the monitoring unit includes a voltmeter 110 connected across power lines 105 and 106 for measuring the welding voltage, and an ammeter 111 on power line 105 for measuring the welding current.

In the present context, the terms "voltmeter" and "ammeter" are used to generically describe components for measuring voltages and currents respectively. That is, the terms should not be read as limiting the present disclosure to any particular physical components, and only to the general functionalities of voltage and current measurement. Various components and methodologies for measuring the welding voltage and welding current are used in alternate embodiments, and those skilled in the art will recognise such components and methodologies. Furthermore, in some embodiments only one of the welding voltage and the welding current is monitored.

Voltmeter 110 and ammeter 111 provide respective data indicative of welding voltage and welding current substantially in real time to a processor 112. Processor 112 is coupled to a memory module 113 that maintains software instructions 114. These software instructions include computer readable code that is executable on processor 112 to allow monitoring unit 101 to perform various methods discussed herein. Examples of such methods include methods for displaying welding conditions. For instance, on the basis of software instructions 114, processor 112 is responsive to data indicative of welding voltage and/or welding current (optionally in combination with stored data indicative of previous welding voltage and/or welding current) for determining in real time a welding condition, such as a mode of metal transfer. For example, this is achieved by analysis of transient events, as discussed further above. Processor 112 provides a signal indicative of this welding condition via an output 115.

In the present embodiment, output 115 is coupled, by way of a cable 116, to a display unit 117. A signal indicative of a welding condition is received by display unit 117 which, in response to the receipt of such a signal, displays a human perceptible representation of that welding condition. In one embodiment, the signal is indicative of a command to actuate one of a plurality of coloured lights, these lights being visually associable by a user with respective welding conditions, as discussed above. In another embodiment the signal is indicative of a command to render and display on a screen, such as an LCD screen, a graphical representation of a particular welding condition. In further embodiments the display includes an on-board microprocessor, and the signal is indicative of instructions for the microprocessor, or alternately indicative of data to which the microprocessor is responsive for displaying a human perceptible representation of the welding condition.

Figure 6B schematically illustrates a further apparatus for monitoring welding, in the form of monitoring unit 121. Monitoring unit 121 is similar to monitoring unit 101 however, whereas unit 101 is essentially configured for simply monitoring welding conditions, unit 121 is additionally configured for affecting welding conditions, for example to achieve or maintain a predetermined welding condition.

It will be appreciated that there are a number of possible techniques for affecting welding conditions, and a range of these are used in various embodiments. For the sake of example, in the case of unit 121, processor 112 is coupled to a variable control circuit 122, this circuit being connected to power line 105 intermediate terminal 107 and voltmeter 110, and to power line 106. In the present example, the voltage across terminals 107 and 108 of power supply 102 remains substantially constant. It will be appreciated that it is voltage between electrode 103 and parent metal 104 that affects welding conditions. Control circuit 122 is variable to adjust the voltage between electrode 103 and parent metal 104, as measurable by voltmeter 110. For example, circuit 122 includes variable resistances/impedances that are selectively applied to affect voltage conditions. In one example, a resistance is provided for increasing the voltage drop across circuit 122, and thereby decrease the voltage between electrode 103 and parent metal 104. Additionally, in the present example circuit 122 is configured for ensuring the welding current remains substantially constant in spite of the controlled voltage variation operation, or alternately for varying this current.

In overview, on the basis of software instructions 114, processor 112 assesses the welding current and welding voltage to predict a welding condition. In the event that this welding condition does not satisfy predetermined criteria, processor 112 identifies a parametric change (in terms of welding voltage and/or welding current) that should be applied such that the welding condition is altered so as to satisfy predetermined criteria. This parametric change is implemented by way of control circuit 122. The voltmeter and ammeter continue to monitor welding currents and voltages, and processor 112 in turn continues to monitor welding conditions. It will be appreciated that this essentially provides a feedback loop whereby welding voltage and/or welding current is varied on a continuing basis such that a predefined welding condition is achieved or maintained, as discussed in the foregoing.

Alternate components replace variable control circuit 122 in other embodiments, including components connected across power lines 105 and 106 and/or in parallel/series with either/both of power lines 105 and 106.

Figure 6C illustrates a further embodiment, in the form of monitoring unit 131. Monitoring unit 131 is similar to monitoring unit 121, however, rather than implementing a variable control circuit, unit 131 provides voltage/current control instructions to power supply 102. Specifically, processor 112 is coupled to an output 132 for providing voltage/current variation instructions to power supply 102. A cable 133 connects output 132 to a corresponding control input on power supply 102.

In a further embodiment, voltage/current monitoring components, and optionally voltage/current variation components, are internalised in the power supply so there are no additional external components to the power supply. Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims

CLAIMS:-

1. Apparatus for displaying at least one welding condition, comprising: a monitoring unit for monitoring at least one welding parameter, a processor for determining at least one welding condition in real-time in response to said monitored parameter(s), said processor operatively associated with said monitoring unit, and a display operatively associated with said processor for displaying the so-determined welding condition in real-time.

2. Apparatus according to claim 1 wherein the welding parameters are chosen from the group consisting of welding voltage and current.

3. Apparatus according to claim 1 or claim 2 wherein the welding condition is selected from the group consisting of the inferred mode of metal transfer, inferred fume production rate, weld stability, and inferred arc length.

4. Apparatus according to claim 3 wherein said inferred mode of metal transfer is selected from the group consisting of dip transfer, globular transfer and spray transfer.

5. Apparatus according to claim 3 or claim 4 wherein said inferred fume production rate is either a low or a high condition.

6. Apparatus according to any one of claims 3 to 5 wherein said weld stability condition is either stable or unstable.

7. Apparatus according to any one of claims 3 to 6 wherein said inferred arc length is short/minimised or excessive/high.

8. Apparatus according to any one of claims 3 to 7 wherein said processor is adapted to determine the frequency of short circuits, and programmable so as to ascertain an inferred mode of metal transfer from the frequency of said short circuits.

9. Apparatus according to claim 8 wherein said inferred mode of metal transfer is dip transfer if said short circuit frequency is greater than 50 Hz and if the average current is less than the threshold current.

10. Apparatus according to claim 8 or claim 9 wherein said inferred mode of metal transfer is globular transfer if said short circuit frequency is between 9 Hz and 50

Hz and if the average current is less than the threshold current.

11. Apparatus according to any one of claims 8 to 10 wherein said inferred mode of metal transfer is spray transfer if said short circuit frequency is less than 9 Hz and if the average current is greater than the threshold current.

12. Apparatus according to any one of claims 8 to 11 wherein the threshold current is the spray transition current for the specific welding consumables being used.

13. Apparatus according to any one of claims 3 to 12 wherein said processor is adapted to determine the frequency of transient events, and programmable to instruct said display to give a warning signal if said frequency of said transient events is less than a predetermined minimum.

14. Apparatus according to claim 13 wherein said predetermined minimum is 0.5 Hz.

15. Apparatus according to claim 14 wherein said inferred fume production rate is low and said inferred arc length is short/minimised if said transient event frequency is greater than or equal to 0.5 Hz.

16. Apparatus according to claim 14 or claim 15 wherein said inferred fume production rate is high and said inferred arc length is excessive/high if said transient event frequency is between 0 and 0.5 Hz.

17. Apparatus according to any one of claims 3 to 16 wherein said processor is adapted to determine the stability index when the mode of metal transfer is dip transfer, and programmable to instruct said display to display a warning signal if the stability index is below a threshold.

18. Apparatus according to claim 17 wherein said stability index threshold is 0.60.

19. Apparatus according to any one of the preceding claims wherein said welding condition is displayed to the welding operator.

20. Apparatus according to claim 19 wherein said welding condition is displayed to the welding operator inside a welding helmet.

21. Apparatus according to claim 19 or claim 20 wherein said welding condition is displayed on a computer screen.

22. Apparatus according to any one of the preceding claims wherein said display includes a plurality of indicators, wherein each indicator is adapted to display at least one welding condition.

23. Apparatus according to claim 22 wherein said display includes four colour-coded indicators which correspond to dip transfer, globular transfer, low-fume spray transfer and high- fume spray transfer welding modes respectively.

24. Apparatus according to claim 22 or claim 23 wherein said indicators are also adapted to indicate the weld stability or an inferred fume production rate.

25. A method for displaying a welding condition, comprising the steps of: monitoring at least one welding parameter, determining at least one welding condition in real-time in response to said monitored parameter(s) and displaying said welding condition in real time during a welding operation.

26. A display apparatus for a welding operator's helmet or mask, comprising: a display for displaying a welding condition in real-time, the display being operatively associated with a processor and a monitoring unit for continuously monitoring at least one welding parameter and determining said welding condition in real-time in response to said monitored welding parameter (s).

27. A display according to claim 26 wherein said display apparatus is integrated into the welding operator's helmet or mask such that the display is within the peripheral vision of the welding operator when the helmet or mask is being worn.

28. A method for automatically controlling low fume and/or minimised arc length welding conditions during welding, said method comprising: monitoring welding voltage, determining a transient event frequency during spray transfer welding as a function of said mom^'tored voltage, and automatically adjusting a welding voltage set point such that said transient event frequency falls within a range of pre-determined values corresponding to low fume and/or minimised arc length.

29. A method according to claim 28 wherein the pre-determined transient event frequency range is between 0.125 to 100 Hz.

30. A method according to claim 29 wherein the pre-determined transient event frequency range is between 0.25 to 10 Hz.

31. A method for automatically controlling welding to avoid globular mode of metal transfer comprising: monitoring welding voltage, determining the number of short circuits per time period, and automatically adjusting a welding voltage set point such that the number of short circuits per time period falls outside a range ofabout 9 to 50 Hz.