Method and apparatus for arc welding

Abstract: A method and apparatus for welding include a source of power, a wire feeder and a controller. The controller sends control signals to the wire feeder and the source of power. The controller also has an adjustable arc control input, and the controller controls at least three welding parameters in response to the arc control input, The arc control input may be an arc width input, and the controller may simultaneously control at least three welding parameters to obtain a desired arc width. The at least three welding parameters may include at least three of peak welding current, background welding current, pulse width, and frequency and the arc control input may be a user-selectable input.

Description: FIELD OF THE INVENTION This invention relates generally to the field of electric arc welding, and more particularly to the field of controlling welding parameters in electric arc welding. BACKGROUND OF THE INVENTION Electric arc welding is well known, and is performed with a variety of processes using a variety of types of equipment. One electric arc welding process is a pulse spray process, which is typically performed using a wirefeeder and a power supply. An example of a prior art power supply used in pulse spray welding is a Miller S64M™ wirefeeder. The Miller S64M™ wirefeeder may be used with a Miller XMT304™ power supply. Typically, in pulse spray processes, power is provided from the power supply to the wirefeeder, and the wirefeeder provides the wire and power to the arc. The wirefeeder typically includes a controller, which may be part of or separate from the wirefeeder, and which controls the wire feed speed based on a user-selected input. Additionally, the controller provides a command signal to the power supply which causes the power supply to output a current and voltage at a desired magnitude. The command is produced in response to a user-selected wire feed speed. The power supply provides a specified current by adjusting the output voltage until the desired current is obtained. The current amplitude is often controlled as a function of time, switching between a background current and a peak current, thus creating a pulsed output. The welding process is often controlled by controlling various welding parameters. For example, the pulse spray process is typically controlled by adjusting such welding parameters as A) peak amps, B) background amps, C) pulse width, and D) frequency. The parameters are typically adjusted using a controller which provides control signals to the wire feeder (or power supply). As used herein, welding parameters refer to parameters of the welding power output, such as peak amps, background amps, frequency, and pulse width. Some wirefeeder controllers include factory programs which preset various welding parameters. The values for these parameters are stored by the controller (often in digital or other types of memory). Also, many controllers allow the user to store user-created programs which store user-selected welding parameters. In such a case, the user teaches or sets the desired values for welding parameters, and stores them in the memory. When the user wishes to access either the factory preset or the user-created programs, they are individually selected using some type of digital interface. Then, the controller commands the power supply to provide power at the called for current, peak current, background current, frequency and pulse width, thus providing the desired welding parameters. Different types of welding require different types of arc characteristics (such as the plasma cone angle\width and intensity, hereafter referred to as arc width). For example, flat, horizontal down, welding typically may be performed using a relatively wide arc. Conversely, overhead welding, or welding in other difficult or inconvenient physical positions, often requires a narrow arc. The preset factory programs are typically set to provide for welding with a wide arc, since this is the one most inexperienced welders will use. To access the narrower arc the welder must adjust the welding parameters manually and individually until the desired arc is obtained. It may be necessary to decrease one parameter as another parameter is increased, so that arc characteristics such as arc length do not change. Power and/or deposition rate do not change in alternative embodiments. However, many welders lack the experience to know how to properly adjust the various parameters, and in particular welders do not understand the interaction between adjusting various parameters. For example, to decrease arc width, frequency is decreased. However, increasing frequency also increases arc length. Many welders do not know this, nor do they know how to adjust the other welding parameters to offset the effect of changing frequency on arc length. Some prior art wirefeeders provide for automatic adjustment of two welding parameters. The Miller 60M™ wire feeder includes a trim setting that adjusts up to two parameters (frequency and/or peak amps). Other welding power supplies may also adjust two welding parameters with a single knob. However, these do not properly adjust the arc width to a desired value while maintaining one or more other arc characteristics constant by adjusting welding parameters. Accordingly, it is desirable that a welding power supply and wirefeeder include a controller that allows the user to adjust the arc width using a single knob, such that multiple welding parameters are adjusted to obtain a desired arc width, while maintaining one or more other characteristics of the arc. US-A-5063282 shows a welding power supply having a single input for wire feed speed that also controls a welding parameter such as output frequency and pulse width. This reference does not show an arc control input. US'282 teaches away from controlling an arc because it teaches to control welding parameters (wire feed speed, current magnitude, current frequency, pulse width etc.). Many welders lack the experience and skill to know how to adjust a welding parameter, such as wire feed speed frequency current magnitude or pulse width, to obtain a desired change in an arc characteristic such as arc width. Thus, such an inexperienced welders using this prior art would not be able to control the arc parameter. It is an object of the invention to provide a welding power supply enabling to do so. SUMMARY OF THE PRESENT INVENTION Accordingly, the invention relates first to a welding power supply comprising : a source of power, having at least one power source control input; a wire feeder, connected to the source of power and having at least one wire feeder control input; a controller, having a plurality of control outputs connected to the power source control input and the wire feeder control input; and characterized by a single adjustable arc control input for adjusting an arc parameter connected to the controller, wherein at least three welding parameters are controlled in response to the arc control input, thereby adjusting said arc parameter. The invention also relates to a method of arc welding comprising: providing power to a welding arc; providing wire to the arc; receiving a single adjustable arc control input for adjusting an arc parameter; controlling at least three welding parameters in response to the arc control input, for adjusting said arc parameter. Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a waveform of a typical welding output for a pulsed arc welding process such as that used in the present invention and Figure 2 is a flow chart of a program or a subroutine used to implement the preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention generally includes adjusting welding parameters with a single knob (i.e. a single arc control input) that controls arc width (or a different arc characteristic) without adversely affecting other arc characteristics. For example, in the preferred embodiment a single digital knob (or other input device such as a digital input panel, keyboard, analog knob, sliding switch, etc) on the controller allows the user to select between an arc width adjustment of 0 and 20. An arc width adjustment of 0 is no arc width adjustment, and an arc width adjustment of 20 is the maximum arc width adjustment in the preferred embodiment. No adjustment is having the parameters be as they were in the original program, which is typically best for flat, horizontal down, welding (i.e., using a wide arc). The preferred embodiment uses the Miller S64M™ wire feeder and Miller XMT304™ power supply. The preferred wire feeder includes a digital controller, which includes an Intel80C196™ microprocessor and a 1 Meg EPROM memory. The controller, as described above, sets welding parameters according to factory set, or user-set, programs. Alternative embodiments provide that the controller is part of the power supply, or in a separate housing. The controller also receives as an input the arc width adjustment knob setting in the preferred embodiment. This input is used to scale (i.e. change from the previous setting) the program welding parameter settings, as detailed below, to adjust the arc width from a minimum to a maximum. The knob setting is stored with the other weld parameter settings in any user-created programs in the preferred embodiment. The arc width adjustment is made by adjusting three or four welding parameters simultaneously, such that one or more other characteristics of the arc are minimally affected. Various percentage adjustments of these parameters have been determined which certainly adequately satisfy these objectives given the equipment used in the preferred embodiment, but other adjustments may be made, and the invention is not limited to the specific adjustments detailed below. Referring now to Figure 1 a typical wave form of a pulse spray welding process is shown. The wave form includes a background amperage level B A and peak amperage level of P A . Also shown by the wave form is a pulse width PW and a period 1/f or 1/frequency. The steepness of the transitions and flatness of the peak and background current may vary, and is dependent in part on the speed with which the power supply responds. Also, the range of obtainable frequencies is limited by the power supply, and is 60 Khz or less for the Miller XMT304™. Four welding parameters, peak amps, background amps, pulse width and frequency are adjusted according to the preferred embodiment of the present invention (or at least three of the four are adjusted according to one alternative) such that when the user adjusts the arc width one or more other arc characteristics are not adversely affected. For example, a decrease in arc width is obtained by decreasing frequency. If only the frequency is changed, the arc length will increase. The present invention also adjusts background amps and pulse width (and peak amps at higher wire feed speeds). These changes, if made alone, shorten the arc length. The magnitudes of the changes are selected to offset the increase in arc length caused by the frequency increase, resulting in a no, or little, net change in arc length. Figure 2 is a flow chart showing a routine which implements the preferred embodiment of the present invention. The flow chart is implemented with a computer routine in the controller for the wire feeder. The routine may be accessed on an ongoing basis, or when the welding process is initiated. The user-selected arc control is determined in a box 201. This is the input used to scale the welding parameters to change the arc width, without adversely affecting one or more other arc characteristics. The preferred embodiment uses a scalar value of between 0 and 20, corresponding to the arc width knob setting, for the minimum and maximum adjustments to the arc width. The arc is widest with no adjustment (in the preferred embodiment). The controller determines if the wirefeed speed is more than or less 5,7 m (225 inches) per minute in a bow 202. Which parameters are scaled, as well as the amount of scaling, is dependent on whether the wire feed speed is more or less than a threshold of 5,7 m per minute (225 IPM) in the preferred embodiment. Other embodiments have the scaling vary with wire feed speed to a greater extent (more thresholds e.g.), or based on wire diameter. If the wirefeed speed is more than 5,7 m per minute the peak amperage is scaled in box 204. If the wirefeed is less than or equal to 5,7 m per minute (225 IPM) the peak amps are not scaled. The background amps, frequency, and pulse width are adjusted (for both over and under 5,7 m (225 inches) per minute for wirefeed speed) in boxes 205, 206 and 208. The actual code used to implement the invention will now be described. Of course, one skilled in the art will readily understand that other routines may be used to implement the invention. The first line of the computer code is ScaledArcWidth= ((prog->ArcWidth*100) / ARC_WIDTH_MAX); , where ScaledArcWidth is the variable for determining the scaling of the welding parameter, ArcWidth is the input from the control knob (and has a 1 to 20 value), and ARC_WIDTH_MAX is a scalar. This adjusts the user-selected arc control input to the appropriate scale for the rest of the routine. The next statement is if(prog->ipm[WELD] <= 225; , and is part of an "if/else" statement where the wire feed speed is determined. If the wire feed speed is less than or equal to 5,7 m per minute the background amps, frequency, and pulse width are adjusted. If the wire feed speed is more than 5,7 m per minute then the background amps, frequency, pulse width, and peak amps are adjusted. Each of the parameters are set by a program (a factory program or user-defined program) implemented by the wire feeder microprocessor (or analog control circuitry in an alternative embodiment). The preferred embodiment adjusts those parameters as set forth below. The specific adjustments of the preferred embodiment were determined using empirical data, and may be different in different alternatives. Thus, a more narrow arc may be obtained with an increased frequency, a decreased background amps, and a decreased pulse width. Proper adjustment of these parameters will also result in a relatively unchanged arc length. This is especially useful when welding in physically inconvenient positions. If the wire feed speed is less than or equal to 5,7 m per minute, then the next three lines of code are temp[BACK_A] = (long) (((temp[BACK_A] * ScaledArcWidth * 10) / 10000)); , followed by temp[FREQ] += (long) (((temp[FREQ] * ScaledArcWidth * 66) / 10000)); , and temp[PULSE_W] -= (long) (((temp[ PULSE W] * ScaledArcWidth * 25) / 10000)); . The background amps set point is adjusted in the first line, the frequency set point is adjusted in the second line, and the pulse width set point is adjusted in the third line. The background amps set point is adjusted by 0 if the knob setting is zero, and downward 10% (of the prior set point) if the knob setting is 20, and proportionally between these settings. The frequency set point is adjusted by 0 if the knob setting is zero, and upward by 66% (of the prior set point) if the knob setting is 20, and proportionally between these settings. The pulse width set point is adjusted by 0 if the knob setting is zero, and downward by 25% (of the prior set point) if the knob setting is 20, and proportionally between these settings. If the wire feed speed is more than 5,7 m per minute (225 IPM), then the next four lines of code (the" else part of the "if/else" statement) are temp[BACK_A] -= (long)(((temp[BACK_A] * ScaledArcWidth * 40) / 10000)); , followed by temp[FREQ] += (long)(((temp[FREQ] * ScaledArcWidth * 97) / 10000)); , and followed by temp[PULSE_W] -= (long)(((temp[PULSE_W] * ScaledArcWidth * 33) / 10000)); and finally followed by temp[PEAK_A] -= (long)(((temp[PEAK_A] * ScaledArcWidth * 2) / 10000)); . The background amps set point is adjusted in the first line, the frequency set point is adjusted in the second line, the pulse width set point is adjusted in the third line, and the peak amps set point is adjusted in the fourth line. The background amps set point is adjusted by 0 if the knob setting is zero, and downward 40% (of the prior set point) if the knob setting is 20, and proportionally between these settings. The frequency set point is adjusted by 0 if the knob setting is zero, and upward by 97% (of the prior set point) if the knob setting is 20, and proportionally between these settings. The pulse width set point is adjusted by 0 if the knob setting is zero, and downward by 33% (of the prior set point) if the knob setting is 20, and proportionally between these settings. The peak amps set point is adjusted by 0 if the knob setting is zero, and downward by 2% (of the prior set point) if the knob setting is 20, and proportionally between these settings. Adjusting the peak amps at higher wire feed speeds preferably helps to maintain a constant arc length if the arc width is changed. A final line of code is if( temp[PULSE_W] < (11 * COUNT_CONVERT)), then temp[PULSE_W]= (10 * COUNT_CONVERT); , and provides an error check to make sure the pulse width is not too narrow. One alternative includes a knob or input that controls an arc characteristic other than arc width, and the controller adjusts three of more welding parameters to change that characteristic, while avoiding an adverse change to one or more remaining characteristics (such as arc width). Another alternative includes having the adjustment of each welding parameter be a function of both the knob setting and the wirefeed speed. In other words, the line of codes that adjust the parameters would include a scaled variable based on wire feed speed. Another alternative is always adjusting only three welding parameters, and different sets of three parameters in different alternatives.

Claims: A welding power supply comprising : a source of power, having at least one power source control input; a wire feeder, connected to the source of power and having at least one wire feeder control input; a controller, having a plurality of control outputs connected to the power source control input and the wire feeder control input; and characterized by a single adjustable arc control input for adjusting an arc parameter connected to the controller, wherein at least three welding parameters are controlled in response to the arc control input, thereby adjusting said arc parameter. A welding power supply according to claim 1, wherein the controller has welding parameter outputs and an arc width input, said welding parameters being simultaneously controlled in response to the arc width input such that a desired arc width is obtained. A welding power supply according to claim 1, further comprising : an arc width input means for providing an arc width input, the arc width means being connected to the controller; and wherein the controller means includes means for controlling the arc width in response to the arc width input means. The welding power supply of one of claims 1 to 3 wherein the at least three welding parameters include at least three of peak welding current, background welding current, pulse width, and frequency. The welding power supply of one of claims 1 to 4 wherein the arc control input is a single user-selectable input. The welding power supply of one of claims 1 to 5 wherein the controller includes at least one program to control welding parameters to be set values, and further wherein the controller adjusts the set values in response to the arc control input. The welding power supply of one of claims 1 to 6 wherein the controller includes a wirefeed speed output that is connected to the wire feeder control input. The welding power supply of one of claims 1 to 7 wherein the source of power is a pulsed power source. The welding power supply of one of claims 1 to 8 wherein the controller includes digital means for storing at least one program to control welding parameters to be set values, and further wherein the controller includes means for adjusting the set values in response to the arc control input. The welding supply of one of claims 3 to 9 wherein the controller includes means for controlling at least three of peak welding current, background welding current, pulse width and pulse frequency in response to the arc width input means. A method of arc welding comprising: providing power to a welding arc; providing wire to the arc; characterized by receiving a single adjustable arc control input for adjusting an arc parameter; controlling at least three welding parameters in response to the arc control input, for adjusting said arc parameter. A method of arc welding according to claim 11 wherein an arc width control input is received and the arc width is controlled in response to the arc control input. The method of one of claims. 11 and 12 wherein the step of controlling includes controlling at least three of peak welding current, background welding current, pulse width, and frequency. The method of one of claims 11 to 13 wherein the step of receiving includes receiving a single user-selectable arc control input. The method of one of claims 11 to 13 further including the step of controlling a wirefeed speed. The method of one of claims 11 to 15 further including the step of storing at least one program to control welding parameters to be set values, and further including the step of adjusting the set values in response to the single arc control input. The method of one of claims 11 to 16 wherein the step of providing power includes the step of providing pulsed power.

Inventors: ALMY DAVID G, IHDE JEFFREY, OTT BRIAN L, ALMY, DAVID G., IHDE, JEFFREY, OTT, BRIAN L.
Applicants: ILLINOIS TOOL WORKS, ILLINOIS TOOL WORKS INC.
Application year: 1999
Main classification: B23K9
IPC codes: B23K9