Abstract:
Methods and apparatus are provided for determining the duty cycle, average amperage, and/or the number of arc starts during a welding operation. The apparatus comprises first and second circuits, the first circuit being a CPU control circuit, and the second circuit being an arc time sensor circuit which is programmed to measure amperage, welding wire feed speed and preferably gas flow rates while welding. A ratio of the cumulative welding time during the audit to the total on-time provides a measurement of the efficiency of the welding arc. The welding deposition efficiency may then be calculated using the average amperage and welding duty cycle as measured and calculated by the apparatus. The number of arc starts where the arc on-time is in excess of one second may also provide a useable measurement in giving secondary information on the overall efficiency of the welding operation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the field of welding. More specifically, the present invention relates to methods and apparatus designed to increase welding productivity of a manufacturing shop. 
     2. Related Art 
     The metal fabrication industry has been around for many years. After the first World War, the shielded metal arc process became very popular through the use of extrusion technology. For continuous operations, such a process was not useful. As a result, semiautomatic welding processes using continuous wire were developed in the 1960s to improve productivity. In the early 1970s, arc welding was a hot and dirty operation, using principally large diameter continuous consumable wires. As the technology to draw continuous consumable wire to smaller diameter became available in the early 1980s, the arc welding industry started using continuous consumable wire diameters as small as 0.030 inch for continuous welding. Today, both cored arc welding wires and solid arc welding wires are available in a range of diameter starting at 0.025 all the way to 0.25 inch for continuous welding. With the advent of robotic technology, the continuous consumable wires can be supplied in bulk packs with torsionless delivery, with individual weights of 1,000 pounds. 
     In spite of this evolution in the supply of continuous consumable wire, the average welding amperages used in the arc welding industry have substantially dropped due to availability of lower diameter continuous consumable wire sizes. Welding deposition rates are related to the welding amperage used. As a result of the decreased amperage, the welding deposition rates have also substantially reduced. 
     In order to increase the arc welding productivity of a manufacturing shop, it is often desirable to measure two (2) key parameters. First, it is desirable to establish the average amperages used during arc welding, which relate to the pounds deposited per hour at 100% arc efficiency. Second, it would be desirable to measure the efficiency of the welding arc at the point of use. The arc welding efficiency, in other words, could be described as the ratio of the time the welder spends actually arc welding divided by the welder&#39;s total time performing arc welding and related processes during the welder&#39;s work day (the sum of &#34;time performing arc welding` and &#34;time for related processes&#34; is referred to as &#34;total elapsed time&#34; for simplicity herein). These related processes typically include setting the welding machine and accessories correctly, positioning himself so that he can appropriately weld in the most comfortable position, time spend changing electrodes, wires, taps, gas bottles, and other activities such as placing the grounds, waiting for cranes or cleaning. Time spent for coffee, lunch and other qualified absences are deducted and not included in total elapsed time. 
     Most arc welding management systems do not objectively measure the duty cycle experienced by the overall welding operation at the manufacturing plant. This is due to the unavailability of a suitable device and method that can be used without interrupting the manufacturing cycle, which would measure effectively the average amperage and the welding efficiency at the selected work station. Further, such a device should be affordable so that a number of such devices can be deployed in a manufacturing plant to generate meaningful evaluation of the overall arc welding productivity over a 24-hour period or more. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, methods and apparatus are presented which overcome many, if not all, problems of previous methods and apparatus. 
     In one aspect, the invention comprises a performance arc time measurement apparatus comprising: 
     a) a first control circuit comprising a central processing unit, at least one RAM, an EPROM, and ACIA, an RS232 serial data port, and a clock; and 
     b) a second control circuit connected to the first circuit, the second circuit comprising an analog digital converter, one or more control buttons, a power switch, a human-readable display (preferably an LCD digital alpha/numeric display), battery charger circuit, and a sensor input circuit. 
     Preferred embodiments of the apparatus of the invention are those wherein the first control circuit and the second control circuit are both contained in a single metal box; apparatus further comprising a DC shunt; a jack for calibration of the first and second control circuits; a welding machine connection diagram inside the metal box; a Hall effect sensor; a and battery charger circuit. Other preferred embodiments include those wherein the second control circuit is programmed to measure a feature selected from the group consisting of amperage during arc welding, welding wire feed speed, shielding gas flow rate while welding, or a combination of one or more of these features. 
     A second aspect of the invention is a method of performance arc time measurement comprising: 
     a) installing a performance arc time measurement apparatus of the invention on each of one or more arc welding power sources; 
     b) measuring the average amperages using the performance arc time measurement apparatus. 
     Preferred methods of the invention include one or more of the following steps: 
     c) calculating the average duty cycle using the performance arc time measurement apparatus; 
     d) measuring welding wire feed speeds using the performance arc time measurement apparatus; 
     e) calculating welding efficiency of a welder using the power source; 
     f) calculating welding deposition rates of a welder using the power source; 
     g) based on data gathered and using a software program (preferably that known under the trade designation BlueShield Consultant, by Air Liquide America), calculating welding cost per linear foot for a single pass weld for the manufacturing operation or determining welding cost per piece manufactured; 
     h) annualizing calculated savings for the manufacturing facility; and 
     i) benchmarking productivity and developing an improvement strategy based on welding management principles and the data gathered in steps b) through h). 
     Other preferred methods of the invention include the steps of recording the duty cycle, average and number of arc starts of the welding machine, and welder efficiency, defined as above. 
     The various performance arc time measurement apparatus embodiments of the invention have been designed to be used in conjunction with a comprehensive welding service designed to provide customers with specialized expertise to streamline operations, maximize welding efficiency and reduce costs. The inventive apparatus is preferably self-contained, and preferably independently powered. The inventive apparatus is preferably capable of gathering information over a period of time (from a few hours to 999 hours) to determine the actual shop arc welding duty cycle by providing the following key data for a welding station: 
     amperage time--to determine average amperage and amperage-time histogram; 
     cumulative arc welding time during the audit/total arc time; 
     number of arc starts; 
     total on time (defined as the total cumulative time the arc is ignited). 
     The ratio of the cumulative arc welding time during the audit to the total elapsed time provides a measure of the efficiency of the welding arc. The arc welding deposition efficiency is then calculated using the average amperage and deposition rate for the wire type and diameter being used. 
     The number of arc starts, where the arc on time is in excess of one (1) second, also provides a useful measurement, which gives secondary information on the overall efficiency of the welding operation. 
    
    
     The present invention will be further understood with reference to the following detailed description and drawings, which are merely representative and not intended to limit the invention. 
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic illustration of an arc welding station, illustrating an arc welding power source having attached thereto a performance arc time measurement apparatus in accordance with the present invention; 
     FIG. 2 is a schematic block diagram of the electrical circuitry of a performance arc time measurement apparatus in accordance with the present invention, including a first and second control circuit, an arc time sensor circuit and associated peripheral equipment. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 illustrates schematically an arc welding station 10, the illustration being helpful to an understanding of the various aspects of the invention. An arc welder 12, here illustrated as human, although robotic welding machines are considered within the invention, holds an arc welding device 14 to which is attached tubing 16 which routes shielding gas from a cylinder or other source 18. Also illustrated schematically connected to the arc welding device 14 is a cable or electrical wire 20 which carries sufficient amperage from a power source 24 to effect the arc welding operation. The human or robot welder is illustrated in position to arc weld pieces 26 and 28 together, typically in a fillet weld, the pieces 26 and 28 being supported in FIG. 1 by fictitious supports 30 and 32, respectively. A performance arc time measurement apparatus of the invention is depicted at 34 and is attached via an electrically conducting wire or cable 36 to cable 20 which connects power source 24 to arc welding device 14. It will be understood that other connection schemes are possible and quite likely will be envisioned by the skilled welder, and those alternative connecting schemes are considered within the present invention. 
     Referring now to FIG. 2, electrical circuitry of a preferred performance arc time measurement apparatus of the invention is illustrated in block diagram format. This embodiment comprises two circuits. The first is a central processor unit (CPU) control circuit 100 and the second is an arc time sensor circuit 200, both preferably contained in the same suitable sheet metal box (not shown), preferably with a locking cover (not shown) for tamper resistance. Also illustrated in FIG. 2 is a DC shunt 300, which will include ajack for calibration, (the jack is not depicted in FIG. 2 for clarity). A Hall effect sensor can also be used instead of shunt 300. A welding machine connection diagram is preferably adhered on the inside of the metal box, preferably on the inside of the locking cover. 
     The CPU control circuit preferably contains a CPU (102), 64K RAM (104), 16K protected RAM (106), an EPROM (108), an ACIA (110), an RS232 serial data port (112) and a clock 114 all positioned on a circuit board (not shown). It interconnects with the arc time sensor circuit via electrical conductor 116. Parallel port 118 provides diagnostics function (typically lights) on the circuit board to help determine a problem with the circuit board. 
     The arc time sensor circuit 200 preferably comprises an analog to digital converter 202, a power switch 204, an LCD digital alpha/numeric display 206, a battery and battery charger circuit 208, and a sensor input circuit 210. The arc time sensor circuit may also have a buzzer 212 and external parallel port 214, the latter functioning to bring in data from the analog to digital converter 202, and from an optional continuous consumable wire speed reader. 
     Arc time sensor circuit 200 is preferably programmed to measure amperage, continuous consumable wire feed speed, and shield gas flow rates while arc welding. The performance arc time measurement apparatus of the invention is applied when an accurate reading of welding efficiency, average amperage and number of arc starts are desired. The information is preferably stored in a non-volatile memory semiconductor chip. This information is then converted with an analog to digital converter, with an adequate accuracy. The inventive apparatus accuracy is due to the crystal controlled accumulation clock, and the added ability to calibrate the unit using a programmable calibration circuit. All amperage readings are taken from a shunt or a Hall effect sensor. The inventive apparatus can be used for DC operations and the circuit is designed to store data in a temporary memory, should the power supply battery get discharged. 
     The arc time sensor circuit also has the ability to measure welding wire feed speeds on a continuous basis during an audit of an arc welding shop. 
     A preferred audit process comprises various steps to gather the relevant data with respect to the welding efficiency. A preferred audit would include the following steps, depending of course on the type of information desired. 
     Step 1 Install a performance arc time measurement apparatus on the welding power sources as required by the audit plan, one apparatus per power source. 
     Step 2 Measure the average amperages using the performance arc time measurement apparatus. 
     Step 3 Calculate the average duty cycle using the performance arc time measurement apparatus. 
     Step 4 Measure welding wire feed speeds using the performance arc time measurement apparatus. 
     Step 5 Calculate welding efficiency at the various stations. 
     Step 6 Calculate welding deposition rates at the various stations. 
     Step 7 Based on the data gathered and using a software program (preferably that known under the trade designation BlueShield Consultant, owned by Air Liquide), calculate welding cost per linear foot for a single pass weld for the manufacturing operation, or determine the welding cost per piece manufactured. 
     Step 8 Annualize calculated savings for the manufacturing facility. 
     Step 9 Benchmark productivity and develop an improvement strategy based on welding management principles. 
     The invention will be further described with reference to the following example which is intended to further illustrate the invention but not limit the scope of the claims to the particular aspects of the example. 
     Evaluation of Productivity 
     Ten (10) monitors were installed in the shop at various stations. The location of the monitors in the different segments of work areas is identified in Table C-1. 
     Production Welding Parameters 
     In tables C-2 and C-3, actual production welding parameters have been recorded. Table C-2, which sampled small assemblies and cabs welding areas, showed welding wire feed speeds between 555 to 599 inches per minute with an average of 577 inches per minute. The amperages varied between 210 to 230 amps and an average voltage was recorded at 29.3 volts. The average wire feed speed for 0.035&#34; inch diameter wire as recorded at 577 IPM appeared substantially higher than the maximum of 450 IPM stipulated on the welding procedure sheets. The welding voltage was also found to be far higher at 29.3 volts to the 25 volts recommended on the welding data sheets. 
     Actual Welding Parameters 
     Table C-3 captures actual welding parameters as observed while using 0.045&#34; inch diameter wire. The wire feed speed varied between 396 IPM to a maximum of 475 IPM with an average of 425 IPM. An average welding amperage was found to be at 296 amps The welding voltage measure varied between 28.8 volts to a maximum of 31.4 volts with an average of 29.9 volts. 
     The maximum wire feed speed per welding data sheets in the spray transfer was 410 IPM and in the short circuit transfer at 425 IPM. These values, again, are slightly lower than the actual wire feed speed values observed in production. The welding voltages as recorded on the data sheets were lower than the voltages observed during this testing with the exception of data sheet where wire feed speed maximum is at 410 IPM with a welding voltage of 30 to 32 volts. 
     Productivity Measurements Using 0.035&#34; Diameter Wires (See Table 4) 
     Productivity for the small assemblies and the cabs areas was measured at an average of 17.2%. 
     It should be recognized that the numbers for welding productivity are uniquely for the welding component of the total assembly. Since this manufacturer employs welder fitters, a large proportion of the work done at the stations may be a fit-up operation as opposed to uniquely welding. However, since this manufacturer produces products on a repetitive basis, the productivity measurements are very significant to be competitive. The 17.2% productivity in the welding operations means that for every 100 minutes of the welders time at the work station, he actually welds for 17.2 minutes. 
     The arc starts varied between 765 and 1,321 per normalized 8-hour shifts. This indicates a significant fit-up and tack activity. 
     Productivity Measurements Using 0.045&#34; Diameter Wires (See Table 5) 
     Table 5 records the productivity measurement numbers as obtained in the various areas using 0.045&#34; diameter wire. An average duty cycle of 19.8% was observed in these areas with an average arc start at 548 per 8-hour shift. The deposition rate varied between 1.78 lbs/hour to a maximum of 3.14 lbs/hour with an average of 2.16 lbs/hour. The weighted averages are also indicated in Table 5 for the various areas. 
     Potential Cost Savings Due to Improved Duty Cycle 
     It is assumed that the duty cycle measured at 19.8% is generalized for the entire shop. In order to improve the duty cycle further, it would be essential to look at workflow and in process working inventory. The benchmark duty cycles for operations where a fixed quota has to be manufactured per day, is in the neighborhood of 28 to 35%. This would be the case for shops where work comes to the welding stations on conveyors and welders keep on completing the tasks with minimal worker interruptions. 
     In the opinion of the auditors, either this manufacturer has to regroup low performing operations and force them into better productivity by managing the workflow or go into some type of integrated robotic operations to improve the duty cycle. For heavily automated plants, where hard automation is used instead of robotics, it is common to encounter productivity numbers as high as 50 to 60%. A robotic cell must operate at 75 to 90% welding efficiency to make robotization really worthwhile. 
     Calculation of phase 2 in this analysis only indicates the magnitude of savings, should this manufacturer decide to streamline their welding operations. If the duty cycles were to be pegged at 25%, this manufacturer would be able to gain $285,507.00 per year in annual productivity gain. In other words, if the shop rearrangement including conveyors and handling devices cost the company. $500,000.00, this entire expenditure can be paid for within 2 years. 
     The software known under the trade designation BlueShield Consultant can be used to analyze potential cost savings, should this manufacturer decide to peg the productivity number at 30%, for example. Such an analysis can be done at a later date to come up with the proper ROI numbers for justifying capital expenditures in terms of shop layout or robotic investments if required. 
     
                       TABLE 1______________________________________DESCRIPTION OF WORK STATIONS  UNDER MONITORING        Arc      Type  Monitor Welding of Wire Gas  No. Process Wire Diameter Type______________________________________1        GMAW     ER70S-6    .045   Ar/CO.sub.2   Semi-auto   90/10  2 GMAW ER70S-6 .035 Ar/CO.sub.2   Semi-auto   90/10  3 GMAW ER70S-6 .045 Ar/CO.sub.2   Semi-auto   90/10  4 GMAW ER70S-6 .045 Ar/CO.sub.2   Semi-auto   90/10  5 GMAW ER70S-6 .035 Ar/CO.sub.2   Semi-auto   90/10  6 GMAW ER70S-6 .045 Ar/CO.sub.2   Semi-auto   90/10  7 GMAW ER70S-6 .045 Ar/CO.sub.2   Semi-auto   90/10  8 GMAW ER70S-6 .045 Ar/CO.sub.2   Semi-auto   90/10  9 GMAW ER70S-6 .045 Ar/CO.sub.2   Semi-auto   90/10  10 GMAW ER70S-6 .045 Ar/CO.sub.2   Semi-auto   90/10  11 GMAW ER70S-6 .045 Ar/CO.sub.2   Semi-auto   90/10______________________________________ 
    
     
                                           TABLE 2__________________________________________________________________________PRODUCTION WELDING PARAMETERS        Wire metal type: Er70S-6  .035 in. diameter                Wire                    Protection Gas: Ar/CO.sub.2 90/10Process: GMAW        Feed     Final   TravelDate    Source        Monitor speed                    Amperage                         Length                             Voltage                                 Speed  D/M/Y Team No. No. Position (IPM) (Amps) (Inches) (Volts) (IPM)__________________________________________________________________________20/05/97Night   LW-009        2   2F  599 230      29,8  20/05/97 Night LW-006B 9 2F 555 210  28,8  Average     577 220  29,3__________________________________________________________________________ 
    
     
                       TABLE 3______________________________________PRODUCTION WELDING PARAMTERS  CLIENT:              Wire metal                      Protection gas: Ar/CO.sub.2   type: Er70S- 90/10      .035 in.  Wire  Process: GMAW diameter 6 FeedDate           Monitor   speed   Amperage                                   Voltage  D/M/Y Team No. (IPM) (Amps) (Volts)______________________________________20/05/97  Night   1         399     275    30,0  20/05/97 Night 3 449 310 28,9  20/05/97 Night 4 441 340 29,8  20/05/97 Night 6 401 285 29,9  20/05/97 Night 7 434 400 29,9  20/05/97 Night 8 475 275 31,0  20/05/97 Night 9 414 290 31,4  20/05/97 Night 10  450 285 29,8  20/05/97 Night -- 421 280 30,2  20/05/97 Night -- 396 270 29,0  20/05/97 Night -- 399 250 28,8  Average   425 296 29,9______________________________________ 
    
     
                       TABLE 4______________________________________PRODUCTIVITY MEASURES - RESULTS  Client:       Process: GMAW (Semi-auto)  Wire metal type: ER70S-6 .035 in. diameter  Protection gas: Ar/CO.sub.2 90/10                                Wire  Deposi-Arc Perform- feed tion  Date   starts ance speed rate  D/M/Y Team Station # % in/min lbs/h______________________________________20/05/97  Night  2        956(765)                         17,2   599   1.60  20/05/97 Night 9 1087(870) 19,8 555 1.70  21/05/97 Day 2 1021(817) 17,4 --  21/05/97 Day 9  986 19,7 --  21/05/97 Night 2 1651(1321) 18,0 --  21/05/97 Night 9 1180(944) 13,3 --  Average    951 17,2 577 1,54______________________________________ 
    
     
                       TABLE 5______________________________________PRODUCTIVITY MEASURES - RESULTS  Client:       Process: GMAW (Semi-auto)  Wire metal type: ER70S-6 .035 in. diameter  Protection gas: Ar/Co.sub.2 90/10                                Wire  Deposi-Arc Perfor- feed tion  Date   starts mance speed rate  D/M/Y Team Station # % in/min lbs/h______________________________________20/05/97  Night  1        477(382)                         25,6   399   2,62  20/05/97 Night 3 1087(870 24,0 449 2,76  20/05/97 Night 4  697(558) 19,1 441 2,16  20/05/97 Night 6 1350(1080) 30,5 401 3,14  20/05/97 Night 7  702(562) 17,4 434 1,94  20/05/97 Night 8  516(413) 14,6 475 1,78  20/05/97 Night 9  621(497) 19,3 414 2,05  20/05/97 Night 10   711(569) 18,2 450 2,10  20/05/97 Night -- -- -- 421 --  20/05/97 Night -- -- -- 396 --  20/05/97 Night -- -- -- 399 --  21/05/97 Day 1  291 25,2 -- --  21/05/97 Day 3  424 14,9 -- --  21/05/97 Day 4  259  8,8 -- --  21/05/97 Day 6  652 23,4 -- --  21/05/97 Day 7  653 23,6 -- --  21/05/97 Day 8  591 20,0 -- --  21/05/97 Day 9  657 22,0 -- --  21/05/97 Day 10   262  4,1 -- --  21/05/97 Day 1  510(408) 23,3 -- --  21/05/97 Day 3 1166(777) 20,2 -- --  21/05/97 Day 4  684(456) 20,6 -- --  21/05/97 Day 6  354(472) 31,3 -- --  21/05/97 Day 7  995(663) 22,1 -- --  21/05/97 Day 8  685(457)  8,6 -- --  21/05/97 Day 9  936(624) 25,1 -- --  21/05/97 Day 10   366(576) 10,0 -- --  Average    548 19,8 425 2,16______________________________________