Methods and apparatus for welding performance measurement

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.

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's total time performing arc welding and related 
processes during the welder's work day (the sum of "time performing arc 
welding` and "time for related processes" is referred to as "total elapsed 
time" 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.

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" 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" 
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" 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" Diameter Wires (See Table 5) 
Table 5 records the productivity measurement numbers as obtained in the 
various areas using 0.045" 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 AMETERS 
Wire metal type: Er70S-6 
.035 in. diameter 
Wire 
Protection Gas: Ar/CO.sub.2 90/10 
Process: GMAW Feed Final Travel 
Date Source 
Monitor speed 
Amperage 
Length 
Voltage 
Speed 
D/M/Y Team No. No. Position (IPM) (Amps) (Inches) (Volts) (IPM) 
__________________________________________________________________________ 
20/05/97 
Night 
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 AMTERS 
CLIENT: 
Wire metal 
Protection gas: Ar/CO.sub.2 
type: Er70S- 90/10 
.035 in. Wire 
Process: GMAW diameter 6 Feed 
Date 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 
______________________________________