CA1180056A - Electrical control circuits for flash welders - Google Patents

Abstract

ELECTRICAL CONTROL CIRCUITS
FOR FLASH WELDERS

ABSTRACT OF THE DISCLOSURE
An electrical control circuit which provides means of initiating the start of upset of a flash welding machine at an operator selectable value of flashing electrical energy. The energy signal for this circuit is taken from an energy monitor, such as the output of the circuit shown in U. S. patent No.
4,084,075. The control circuit, by means of a single adjustment of electrical switch means, may include a few additional elec-trical components to enable initiation of the start of upset, or termination of upset, as a function of platen position rather than as a function of flashing energy. Further, by simple adjust-ment of additional electrical switch means, further electrical components may be included to control the distance the movable platen moves during the upset portion of the welding cycle. Also, a meter may be included in the circuit to display either upset distance or upset initiation.

Description

1 ~ Ba~6 ~I,ECTRIC~L CONTROL CIRCUITS
FOR FLASH WELDERS
.. . . _ ... _ .
BACKGROUND A~D SU~ARY
Generally a flash welder comprises a sturdy metal ~ase S on which are mounted a stationary platen and a moveable platen (as suggested in Fig~ 1) the moveable platen being guided for sliding ~ovement toward and away from the stationary platen.
Each platen has a cla~p thereon in which work pieces ,Wl and W2 are respectfully clamped. The usual flash welder also includes a welding transformer having a primary P and a secondary ~S. The primary is conn~cted to a power controller C which in ,turn is connected to a source of electrical energy. Opposite ends of the secondary are electrically connectea to respective clamps.
The workpieces to be welded together are loaded into respective clamps so that adjoining ends are slightly spaced and ithe clamps are firmly engaged on the workpieces. The moveable ,Iplaten is thereafter driven by a hydraulic cylinder ~ in a direc-ltion toward the moveable platon while transformer secondary current J
is qaused to flow between the workpieces to cause an arcing or flashing between the workpleces. The arcing or flashing removes any irregularities between adjoining encls o~ the workpieces and ~au~ a heatlng and oo~tenincJ of 9uch encls.
A~t~r a prade~erminad amount of ~lashing, ~he ~orward 25 mov~m~t o~ the moveabl~ platen 19 ln~reascd materially ~in ~ome c,~ses ~iva to t~n tlr~s the speed o~ ~lashing motionJ. ~his is t~rmad th~ upse~ motlon oE the moveable pla~en and causes the .- ' '~

heated workpiece surfaces to ~e forced together, thereby lowering electrical resistance between tne workpieces and simultaneously ~ncreasing current flow (upset current) therebetween. This abrupt increase ln motion may be effected by the flow of high pressure hydraulic fluid through larger conduits Co and to cylinder }I. A solenoid controlle~ valve ~ ~ay be interposed in the larger conduits to permit or prevent ~low of upset fluid the~ebetween. ~urrent to the coil of the solenoid of the valve is controlled by switch contacts Sw which are controlled in a manner to be described in connection with the descrip'ion of the preferred embodiment of any invention.
My invention provides an electrical circuit which will initiate the ~tart of upset of a ~la~h welding machine at an operator-selectable value of flashing energy. This electrical circuit, by means of a simple adjustment of electrical switch means, may include a few additional electrical components to en~ble initiation of the start of upset, or termination of upset, as a ~unction o~ platen position rather than as a function oE
flashing energy, thus providing the machine operator a choice o~ upset control.
Further, by simple adjustment Oe acldition~l electrical ~wi~ah mQallS, ~u~he~ ~lectrlcal components may be included l:o control thQ dlstcln~e the movcabl~ platen moves durin~ the upset portion o~ ~he weldirlg cycl¢ in~epend~nt o~ platen position at the ~5 ~tart oE up~et. Al50, a meter may be included in the circuit to dl5play eith~r ups¢t dista~ce or upset initiation position clepend-ing upon the ~etting o~ an electrical switcll.

ESCRIPTION OF THE ~RAWINGS
In the drawings accompanying this specification and forming a part of this application, there i5 shown, for purpose of illustrati.on, an emoodiment which my invention may assume, and in thes~ drawings:
Fig~ 1 is a diagram schematically illustrating certain components of a flash welder and an electrical circuit for control of certain functions of the flash welding cycle, Figs. la and lb disclose electrical compone~ts which may be selectively added to the circuit shown in Fig. 1, Fig. 2 is a further control circuit ~7hich may be added to that shown in Fig. 1, Fig. 2a discloses a slightly different circuit arrange-ment between parts of Fig. 2, and ~ig. 3 discloses the oircuit of Fig. 2 with further electrical components added.

DE~CRIP~IOrl OF TM~ PR ~,RRF~ ~MEODIME~I~
Our lnv~ntion utilizcs a potentiom~ter as part o~ the con~ .
trol to initlclte th~ ~tart of upset o a flash welding machine at an operator selcctablc value of Pla~hing electrical energy.
~ig. 1 il.lustrates the use of a linoar potentiometer 2 with one oP its relatively moveable parts, such a~ its slider 3, connected to move in unison with the moveable platen, although any more or le~s sophisticated means may be used to produc~ an electrical signal proportional to platen ~otion, such as a rotary potentio-meter or a linear differential transformer.
At the present ~ime, it is pre~erred to ~se a film-type potentiom~ter, and these are com~ercially availahle from many sources. The length o the potentiometer 2 in the illustrated embodiment is six inches (about 15 ce~timeters) and this length is usually ample since in most cases the full length of platen ~avel does not exaeed six inches.
Source voltages are applied to the potentiometer and, in the em~odiment disclosed, the algebraic sunl of these voltages is equal in volt~ to the potentiometer's length in inches. The ~oxes electrically connected to respective ends of the resistor o~ the potentiometer are common plus and minus voltage supplies (such as Cale~c Model 22-10~) which are in turn regulated by precision adjustable voltage regulators (no~ shown). The regulator for source "Sl" may be a Mational semiconductor Model LM 304 and for source "S2" may be a NS Moclel LM 305. The voltage imprc9~d on tho ~orward or "d1e c,1050d" cncl o~ the potentiometer ~the rlqh~hand cnd o~ Fi~. 1) i.~ made negative, and the retractecl r ~0 or "dias open" end o thc pot~ntiome~er 2 (th~ left-hand end in Fig. 1) is madc: po61tive.
In thc lllustratecl ~n~odiment the alqebraic difference of th¢ voltagQB from sources "Sl" and "S2" i5 six volts so that one volt eq~als one inch of length on the six-inch potentiometer.

_5_ The magnitude of the negative voltage is chosen so that the slider voltage is zero before the "dies closed" position is r~ached. This is done so that the mechanlcal motion limit o~
the potentiometer slide~ 3 does ~ot ha~e to coincide with the ~dies closad" position of the platen. This problem does not exist in the aase of the "dies open" position since the potentio-meter trav~l is ohosen to be of greater length than the maximum platen motion. In the embodiment herein disclosed, source "Sl"
applies -0.50 volts to the right end of the pote~tiometer, and source "S2" applies +5.50 volts to the left end of the pote~ti~-meter, so tha~ the algebraic dif~e~ence is six volts. It will be noted that the 00.00 point on the potentiometer 2 (represent-~ ing the "dies closed" position) is located one-half inch (12.70 ; millimeters) inward of the right-hand end of the potentiometer.
Signal 1 from the potentiometer slider 3 is ~ed to the nor~inverting input of an operational amplifi~r 33. The output ; signal 32 of amplifi~r 33 is connected to the input of a digital direct aurrant volt meter 31. Since signal 1 has a sc~le of one volt per inch of platen movement and signal 32 is equal to sisnal 1, the mater in~ication is a measure of the pl~ten position at any ~ima relatlve to th~ pla~en "die~ ~losed" position. 'rhe m~qx xanLJe is ~ol~tecl so that i~ can indicat~ thq vol~age corr~porldlng to the pla~en maxim-lm ''dles opqn" position as the slid~r 3 move~ toward potentiom~ r end A. ~ha nu~ar of m~tar di~it~ is solected to ~ivc the required resolu~lon, and in the illustrated embodiment the meter has a range of 19.99 volts and, therefore, a measurement range of 19.99 inches and a resolution of 0.01 volts or 0.01 inches. The meter 31 may be a Weston ModeI
1230 and maY be provided with a three-digit BCD (binary coded decimal) output and a "print command" signal. The BCD output and "print command" signal are not shown in Fig. 1 since they are not needed bUt they will be referred to in a later portion of this dlsclosure. In Flg. 1 the meter is shown as grounded.
~he output 4 of an energy monitor (not shown) such as desc~ihed i~ U. S. patent 4,Q84,075, issued to James F. Deffen-~ugh ~one of the inventors herein) on April ll, 1978, and assigned to the same assignee as the presPnt invention, is fed to the invertin~ input o~ an operational amplifier 8 which i5 electrically conneated as a voltage comparator. The output 4 i3 lS a dlrect current voltage wi~h a magnitude proportional to the electrical energy input to the welding machine, as described in said patent. In the embodiment disclosed herein the polarity of output 4 is negatlve and increases from zero as the flashing portion of the machine cycle progresses.
~ Potentiomcter 5 shown ln Fi~. 1 is a precision type with ~ digit~l s~ttlng and r~adout arrangem~nt. In the dlsclosed embodlment ~h~ ran~e o~ potentiometer 5 i~ 9.99 volts with a ~e~olut.lon oE O.Ol volts or 0.~1 lnch~s. Tho end "A" of poten-tiometer 5 is connect~d to a negativc 10-volt ~ource 3nd end "~"

.

ls connected to ground. Signal 7, therefore, is a rlegative voltage whose magnitude is proportional to the position of the s}ider 6 with respect to end "~." With a setting o~ 4.00, for lexample, signal 7 has a value of negative 4.00 volts and is fed Ito the noninverting input of comparator amplifier 8.
Si~co the energy monitor output 4 starts at a value of æero, output 50 of comparator amplifier 8 is negative and ~he dioae 9 is reversed biased and keeps relay 11 deenergi~ed.
~As the flashi~g signal pro~resses, the energy signal 4 increases ,in a negative direction until it just exceeds the value of ,signal 7,-whereupon the output 50 of the comparator amplifier 8 ,switches to positive and ~orward biases diode 9 to cause energi-zation of relay 11.
D~lring the flashing portion of the machine cycle, 15, slider 3 oi the potentiol~eter 2 is mo~ing toward end "Bl' which is ~he ~dies closed" position of the moveable platen. Signals I and ~2 are therefar~ decreasing toward zero from the more positive ~alue they had at the beginning of the ~lashing cycle. As seen ln Pig. 1 ~ignal 32 is connccted to contacts 15 and 16 o~ rel,ay 11.
~`he noninvcrting input 17.1 o~ comparator ampliPier 17 is at ~round potqntial, and i~s invertincJ inpu~ 32 is a~ some positiv~
~ot~rl~ial abov~ ground un~il relay 11 i~ energiæed.
In thls condition, tha~ is prior ~o ~ncrgization Oe th~
~clay 11, th~ output 51 of comparator amplL~i~r 17 is n~qativc to thus rev~rse bias diode 19 through resistor 1~. T~le resistor 18 ls used to reduce the leakage gate current of SCR 29 from maintaining relay ? energi~ed when a contact of a relay to be described is opened later in the machine sequence.
Wnten the relay 11 is energized, as above described, S norntally-closed contact 15 is opened and re~roves signal 32 from the inverting input of comparator amplifier 17, and contact 16 is closed to connect a negative 10-volt source to the inverting input. When the relay contacts 15 and 16 are thus operated, the negative 10-volt sostrce that is now fed to the inverting input o~ comparator amplifier 17 causes the output 51 to c~tange to positive to forward bias diode 19 and fire SCR 29, thus initiat-ing upset motion at a selected value of ~lashing energy.
The condition path of SCR 29 is from a positive source of 24 volts through closed contact 57 of a relay 46, to relay 20 and then to ground. SCR 29 is used as a clamped source for relay 20 since SCR 29 cannot be deenergiæed unless contact 57 is opened. Therefore, a momentary loss of signal from co~tparator 17 due to n~ise will not open relay 20. Energiæation o~ relay 20 lniticttes the upset mectns~ such as the solenoid herotoore ~0 clo~cribecl to close swi tch contacts 9~ artd ~hus increctYc the velocity o~ motion o~ thc ~tovqabl~ platf3n toward the "dies alosed"
position.
I~ it is desired to initiate up~et motion as a ~unction o~ platen position, thc components shown in Figs~ la and lb are added to the circuit shown ,in Fig. 1. The addition of t'he 3~

components in Fiy, la will result in inserting ~ switch 54 in the line 17.1. In the "1" position of the switch, the line 17.1 will be connected to ground, as it i~ in Fig. 1. In the "2"
position of switch 5q the line is connectecl to the output 13 of a slider 12 of a potentiometer 14, the latter having its end "A"
connected to a positive 10-volt source. The addition of the com-ponents in Fig. lb will result in inserting a switch 82 in.the line lV, between the dicde 9 and relay 11. In the "1" position of the switch 82, the signal in line lO goes through relay 11 to ground, as in Fig. 1. In the "2" position of switch 82, the relay is removed from the circuit and line 10 is connected directly to ground.
To initiate upset motion as a Eunction of platen posi-~ tion, the above-noted switches 82 and 54 are both set to their "2" positions. In such position switch 82 deactivates relay 11 and switch 54 energizes the comparator amplifier from the slid#r 12 of potentiometer 14.
When sign~l 32 ~Fig. 1) Erom the ampliE.icr 33, and in turn connectecl to the invertlng input o~ cumparator 17, becomes slightly less than si~n~l 13 Erom slider 12 which is conncct~d to the nonlnv~rting input o~ comparator 17, the output oE th~
latt~r becomes positive and forward biasos diodo l.9 and i~ turn ~ir~ SCR 29, thercby initiati.n~ up~et motion. The initiat.ion position is determincd by the setting of the slider 12 of poten-tiometer 1~. For examplo, i~ thc sctting o~ slider 12 were 4.00, 3~ r,~

,-10-upset would be initiated when the plat~n was at a position 4.00 inches from the "dies closed" position.
The systems just,described may be combined with furthe~
electrical components to control the distance of upset, and S attentiOrl i9 directed to Fig. 2 which discloses such further component~.
As before referred to, the meter 31 may be provided with a three-digit BCD (binary coded decimal) output identified by the reference numeral 52 in Fig. 2, and also may have a "print command" signal 36. The signal 32, heretofore referred tr is connected to the input of meter 31. The meter 31 may be an A-D converter but the particular type of meter disclosed is preferred because it has a readout to show the state of the digital output at the er.d of each conversion, and thus shows the position of the moveable platen at any time.
Since the input~of meter 31 is signal 32, and since contact 35 of relay 11 was closed prior to the energization of relay 11 and the start oE upset, the "print slgnal" 36 Erom thc m~ter 31 maintaln~ ~onversion opcration o~ a di.gital to analog ~onvex~or DAC - VR 30. This converter has a self-contained storagc re~is~er and ~ threc-digit ~CD ~binary coded decimal~ and may be a Datel Modcl DAC-VR.
With the output 52 of rneter 31 connected to the BCD
input, oE convertcx 30 and contact 35 closed, the analog output o~ the converter 30 is fed to a summing junction 28 o~ a unity gain inverting summing,amplifier 37.
A potentiometer 21, which is identical to potentiometer 5, is connected to a negative 10-volt source. The signal 23 from slider 22 is connected to the summing junction 28 of operational amplifier 37.
The purpose o potentiometer 21 is to provide an ad~ust-able signal 23 that can be used to control the distance that the moveable platen moves during the upset movement of the welding machine cycle. Mention is made of the fact that the upset motion of the moveable platen may be terminated at a selectable position relati~e to the "dies closed" position by means of a potentio-me~er 24. This i5 the normal operating mode if the start of upset motion is initiated as a function o the flashing energy signal from the enerqy monitor. ~owever, it will be ~vident that,termination of the upset motion at a fixed position wi:Ll result in the changes ~n the total upset motion if the energy level signal reaches the set operating point of amplifier 8 ~shown in Fig. 1) at diEferent positions of the moveable plat~n durinq the fla5hinq cycle.
In th~ operation o th~ circuit to control ups~t dls-~
tancc, th~ output 59 Erorn the summin~ junctiorl 28 is Eed to the invcrting input o~ the operational ampli~ier 37, and this output $9 is equal to tho algebralc sum o~ the signals 29 and 23.
~5 Signal 23 is d~pendcn~ upon the posltlon of th~ slider 22 relative to the ends "~" and "B" o the potentiometer 21. As an example, it may be assumed that the settiny of the slider 22 is 0.50. This will produce a negative 0.50 volt signal in line 2 and would be equal to à platen motion distance oE 0.50 i~che~.
Signal 1 (oP the circoit shown in Fig. 1) is numeri-cally equal to the position of the platen relative to the "dies closed" position, and since signal 29 trac~s signal 1, the output of summing junction 28 is a positive signal equal to whatever the value of signal 1 or 29 would be if the position of the platen were 0.50 inches closer to the "dies closèd" position than it actual1y is. When relay 11 is energized to initiate upset motion, contact 35 o~ relay 11 is opened. This prevents further conversion of converter 30 and clamps signal 29 at the value it had at the start of upset mot1on. Output 29 of the summinrg junction 28 is tunder the assumed set of circumstances) now O.SO volts less than signals 1 or 29 were at the start of upset motion. Ii it is assu~ed that the start of upset motion occurred at a platen position o~ 1.50 inches from the "die~ closed"
position, si~nal 29 would have a valu~ oP 1.50 volts positive and the uutput 59 o~ summlny junction 2~ would bc 1.50 p.SO or 1.00 volts pos~tiv~
Signal 59 which (under the ~oregoincJ assumed Pac~s) has a valu~ o~ 1.00 volt posltive is fed to the inverting input o~
invorting unity gain summing amplificr 37, and the output 63 of the latter has an equal but inverted ~alue. Sign~l 63 is fed to the inverting input of unity gain inverting amplifier 90 to bring its output signal 91 back to the same polarity and value as signal 5g. Since switch 64 is in its "1" position, signal 91 i~ ed to the noninvertin~ input of comparator ampliier 39.
Signal 32, whi$h at this tim~ has the assumed value of ~.50 volts positive, is connected to t~e inverting input of amplifier 39.
Since signal 32 is greate~ than signal 91 the output 78 of amplifier 39 is negative, diode 40 is revarse-biased and relay 46 is deenergized.
As upset motion progresses, the slider 3 (see Fig. 1) moves toward the end "B" of potentiometer 2, and signals 1 and 32 therefore decrease. When the value of signal 32 becomes slightly less than signal 91 from amplifier90 (or 1.00 volt lS in the assumed example) output 78 of amplifier 39 becomes positlve to thus forward bias diode 40 and energize relay 46. When relay 46 i9 encrgized, its contact 57 (see Fig. 1) opens to thereby deenergize SCR 29 and r~lay 20t Deenergization o~ relay 20 operates w~ known loqic oircuit~ ~f a ~lash waldlng machinq to ~erminate up~et motion.
Oukput 42 of ampliier 39 is also connected to the noninvarting input o~ follower amplifier 43. When tha signal 42 from amplifie 39 becomes positiva at the end of ups~t mOtiQn, output 79 of followar amplifier ~3 also become~ positive and thereby forward biases the diode 45 and energizes relay 47. Energization of , .
.

~elay 47 switches oth@r well-known logic circuits Q~ the welding machine to assist in the termination of upset motion. Thus, in the assumed example, upset motion of the welding machine was stopped after the moveable p~aten traveled a dista~ce equal to 0.50 inches, as commanded by the setting of the potentiometer 21.
The ~oregoing circuitry may also be adapted, by addition of further components, to provide a digital readout in inches (or millimeters if the proper scaling is used~ of either the platen position at which upset motion was started, or the magnitude of upset motion. Attention is directed to Fig. 3 wherein such additional circuit components are located in the rectangular box B shown in dot-dash lines, in combination with the circuit shown in Fig. 2 which, it should be remembered, is combined with the circuit shown in Fig. l.
In operation the signal 29 from the output of DAV-VR 30, with coneact 35 closed, is a positive voltage which is numerically ec3ual, either in inches or millime-ters depending on the scaling used, to the distance of the moveable platen relativ~ to the "di~ closed" posit10n. A~ seen in Fiq. 3, signal 29 is ~ed to one input o~ a ~umming ~unction 70.
~igna~ 32 ~rom the oporational amplifiex 33 ~Fig. l) in addition to bcing ecl to the me~er 31, is ~lso fed to the inverting input of unity gain inverting amplifier 69 and the negative inverted output 67 of the latter is connetted to the other inpu~ of LAe ~umming junction 70. Since signal 67 from amplifier 69 is egual to signal 29, but of opposite polari~y, ~outtput 80 of the sumrning ]unction 70 is zero. With swi~ch 76 at the "1" position, input to meter 77 is also zero. The meter 77 may be the same as meter 31 (Fig. 2) except that no BCD output is required; the "print command" signal is not used; and the polarity sign is blanked. Signal 80 from the summing junction 70 remains at zero as the moveabl~ platen moves toward its "dies ~closed" position.
When contact 35 of relay 11 (Figs. 1 and 2) is opened at the start of upset ~otion, the output signal 29 from DAC-VR 30 ls clamped at the value it had at that instant. As the moveable platen moves through the upset distance negative signal 67 ~the output from amplifier 69~ decreases and the output 80 of the surnrning junction 70 beco~es positlve with a value equal to the algebraic ~um o~ signals 29 and 67. Signal 80 is fed to t:he inverting input o~ unity cJain inverting summing amplifi~r 96.
~his condition continue~ as thc platen mov~s toward "dies closed"
po~i~ion, with the output oE ampliier 96 becoming larger until the upse~ motion is terrninated by operation o relays ~6 and 47 in a manner hereinbe~ore described. Signal 32 and output 67 ~re no longor changing and output signal 99 from amplifier 96 is now numerically etlual to the distance the platen moved during upsct.

~ ~3;~

With switch 76 set to its "1" position, signal 99 is fed to meter 77 and the latter displays a digital number equal to the dimension o~ the upset movement. Contact 81 of relay 46 closes with energization of the latter and clamps meter 77 so S that it retains its display until the start of the next welding cycle. If it is desired to display the position at which upset motion is initiated, switch 76 is set to its "2" position. This connects signal 29 to the input of the metar 77 and, since signal 29 is clamped at upset initiation, the meter will display the position of the platen at which upset motion was initiated.
If it is desired to contrGl upset distance, regardless of platen position, when upset motion has ~een initiated by platen position (switch 54 set at 2 and switch 82 set at 2), switch 83 is set to position 2. Energization o relay 20 at upset initiation opens contact 84 and activates the clamping system of DAC-VR 30 exactly as previously descri~ed, resulting in an upset distance equal to the setting of the slider 22 of potentiometer 21. The display of meter 77 will also indicate olth~r upset distance or upset initiatlon position, depen~ing on

2~ the settln~ o~ switch 76.
I~ it is desired to terminate the upse~ motion ~s a iullction oE platen position, switch 6~ is set to its "2"
position. This ~cds signal 26 from slider 25 o~ po~entio~eter 24 ko the noninvexting input o~ comparator 39 whose action is -~.7-exactly the same as previously described for signal 91 input to amplifier 39. Since the operation of potentiometer 24 is exactly the same as potentiometer 14, the setting of potentiometer 24 is numerically equal ta platen position.
With switch 64 set in its position "2", switch 83 may be set at either position "1" or '2". At position "1" the meter 77 may be set to read platen position by setting switch 76 to its "2" position. With switch 83 set to its "2" position, the meter may be set to read either upset dista~ce or position of upset initiation by means of switch 76, as previously aescribed for flashing energy initiation of upset.
Fig. 2a illustrates a slightly different circuit -rrangement between the meter 31 and the converter, wherein the contact 35 is omitted. If this is done, the description shculd be Lead to specify contact 84 for contact 35 and relay 20 for relay 11.

Claims (20)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a flash welder having relatively moveable platens which carry the workpieces to be welded, said platens moving relatively through flashing and upset operations toward closed position, the improved method of initiating the start of upset operation of said platens at an operator-selectable value of flashing electrical energy, comprising, adjusting the magnitude of a voltage from a voltage source to an operator-selectable value to block operation of a switch-controlling device until an energy signal representing electrical energy input to said welder, said energy signal derived from voltage and current input to said welder, during flash-ing operation has reached a value to counteract said adjusted voltage and effect operation of said switch-controlling device, and utilizing the operation of said switch-controlling device to energize a circuit which includes means for initiating the start of upset operation of said platens.

2. In a flash welder having relatively moveable platens which carry the workpieces to be welded, said platens moving relatively through flashing and upset operations toward closed position, the improved method of initiating the start of upset operation of said platens at an operator-selectable value of flashing electrical energy, comprising, feeding an energy signal to one input of an operational amplifier, said energy signal derived from voltage and current input to said welder during flashing operation and progressively changing as said platens move toward closed position, feeding a voltage to the other input of said operational amplifier, feeding the output signal of said operational amplifier to a diode which controls energization of a relay having contacts, adjusting said voltage to an operator-selectable value to bias said diode to a condition to prevent energization of said relay until said energy signal reaches a value to counteract said adjusted voltage and bias said diode to a condition to energize said relay and operate relay contacts, and utilizing operation of said relay contacts to energize an electrical circuit which includes means for initiating the start of upset operation of said platens.

3. In a flash welder having relatively moveable platens which carry the workpieces to be welded, said platens moving relatively through flashing and upset operations toward closed position, the improved method of initiating the start of upset operation of said platens at an operator-selectable value of flashing electrical energy, comprising, feeding an energy signal of negative polarity to the inverting input of a first operational amplifier, said energy signal derived from voltage and current input to said welder during flashing operation and progressively increasing as said platens move toward closed position, feeding a voltage of negative polarity to the non-inverting input of said first operational amplifier, feeding the output signal from said first operational amplified to a diode which controls energization of a relay having contacts, adjusting said voltage to an operator-selectable value to reverse bias said diode and prevent energization of said relay until said energy signal increases to exceed the value of the adjusted voltage and thereby forward bias said diode and energize said relay and operate the contacts of the latter, feeding a signal of positive polarity to the inverting input of a second operational amplifier, the output of the latter being connected to a second diode which is reverse biased by this signal, and utilizing the operation of said relay contacts to remove the positive polarity signal from said inverting input of said second operational amplifier and replace it with a signal of negative polarity to thereby forward bias said second diode and energize a circuit which includes means for initiating the start of upset operation of said platens.

4. In a flash welder having relatively moveable platens which carry the workpieces to be welded, said platens moving relatively through flashing and upset operations toward closed position, the improved method of initiating the start of upset operation of said platens at an operator-selectable value of flashing electrical energy, comprising, applying a first signal to an operational amplifier, said first signal derived from voltage and current input to said welder, changing the magnitude of said first signal in accordance with the increasing voltage and current input to said welder during flashing operation, applying a second signal to said operational amplifier, said second signal being operator-adjustable to a magnitude corresponding to the magnitude of said first signal at any selected point in the movement of said platens toward closed position, said first and second signals being of the same kind and when the magnitude of said first signal exceeds that of said second signal, said operational amplifier provides for energization of an electrical circuit including components for initiating the start of upset motion of said platens.

5. The method according to claim 4 wherein said first signal is negative and is applied to the inverting input of said operational amplifier and wherein said first signal increases in a negative direction as flashing progresses, and wherein said second signal is derived from a negative source and is applied to the noninverting input of said operational amplifier, and further including the step of applying the output of said operational amplifier to a diode which controls energization of a relay having contacts, wherein while said second signal exceeds the magnitude of said first signal, the output of said operational amplifier is negative to reverse bias said diode and prevent energi-zation of said relay, and wherein when said first signal exceeds the magnitude of said second signal, the output of said operational amplifier is positive to forward bias said diode and effect energi-zation of said relay and activation of said relay contacts and utilizing the actuation of said relay contacts to energize said electrical circuit.

6. The method according to claim 4 wherein said opera-tional amplifier provides for energization of a relay and conse-quent actuation of the contacts of said relay, and wherein said electrical circuit includes a second operational amplifier, and further including the step of applying a third voltage to said second operational amplifier, said third voltage being effective to block initiation of the start of upset motion, and utilizing the actuation of said relay contacts to replace said third voltage with a fourth voltage applied to said second operational amplifier, said fourth voltage being effective to provide for initiation of the start of upset motion.

7. In a flash welder having relatively movable platens which carry the work pieces to be welded, said platens moving relatively through flashing and upset operations toward closed position, the improved method of initiating the start of upset operation of said platens at an operator-selectable value of flash ing electrical energy, comprising, applying a first voltage of negative polarity to the inverting input of an operational amplifier and increasing said first voltage in a negative direction as flashing progresses, applying a second voltage derived from a negative source to the noninverting input of said operational amplifier, said second voltage being operator-adjustable to a magnitude corresponding to the magnitude of said first voltage at any selected point in the movement of said platens toward closed position, applying the output of said operational amplifier to a diode which controls energization of a relay having contacts, wherein when said second voltage exceeds the magnitude of said first voltage, the output of said operational amplifier is of negative polarity to reverse bias said diode and prevent energization of said relay, and when said first voltage exceeds the magnitude of said second voltage, the output of said operational amplifier is of a positive polarity to forward bias said diode and effect energization of said relay and actuation of said relay contacts, applying a third voltage to the inverting input of a second operational amplifier, applying the output of said second operational amplifier to a second diode which is adapted to control conduction of a silicon-controlled rectifier, the latter controlling initiation of the start of upset motion, said third voltage being of positive polarity so that the output of said second operational amplifier reverse biases said second diode and prevents conduction of said silicon-controlled rectifier, and utilizing the actuation of said relay contacts to replace said third voltage with a fourth voltage applied from a source of negative polarity to said inverting input of said second operational amplifier whereby the output of said second operational amplifier forward biases said second diode to trigger said silicon-controlled rectifier into conduction and effect initiation of the start of upset motion of said platens.

8. The method according to claim 7 wherein said third voltage is applied across the resistance of a potentiometer and including the step of moving the slider of said potentiometer in unison with the relative movement of said platens and in a manner so that the voltage on said slider varies in decreasing manner as said platens move toward closed position, applying the variable third voltage on said slider to the inverting input of said second operational amplifier and connecting the noninverting input of said second operational amplifier to ground, the further improvement wherein, by operator choice, circuit subcomponents may be switched into the circuit at the option of the operator to remove said relay from operation and to selectively switch the noninverting input of said second operational amplifier from ground to the slider of a second potentiometer, and apply-ing a fifth voltage from a source of positive polarity across the resist-ance of said second potentiometer whereby a fifth voltage of a selected magnitude may be applied to said noninverting input and effect conduction of said second diode when the magnitude of said fifth voltage exceeds the magnitude of said third voltage, and thereby initiate the start of upset motion of said platens as a function of platen position.

9. In a flash welder having relatively moveable platens which carry the workpieces to be welded, said platens moving relatively through flashing and upset operations toward closed position, an improved control circuit for initiating the start of upset operation of said platens at an operator-selectable value of flashing electrical energy, comprising, an energy monitor connected to said flashwelder and providing an output signal which is derived from voltage and current input to said welder, an operational amplifier, having one input connected to said energy monitor output signal, a source of voltage independent of the voltage of said energy monitor, a potentiometer connected to said source so that the voltage therefrom is applied across the resistance of the potentiometer, the slider of the potentiometer being moveable along said resistance to vary the voltage of said source to a magnitude selected by said operator, the variable voltage from said slider being connected to the other input of said operational amplifier, and means effected by the output of said operational ampli-fier to control initiation of the start of upset operation.

10. The control circuit according to claim 9, and further including a diode electrically connected to the output of said operational amplifier, conduction of said diode being controlled by the relative values of said energy monitor signal and the operator-selected voltage from said separate source, a relay energized by conduction of said diode to effect operation of the contents of said relay, and a circuit energized by operation of said relay contacts to initiate the start of upset operation of said platens.

11. The control circuit according to claim 10 wherein said last-named circuit includes a second operational amplifier, a further source of voltage connected to an input of said second operational amplifier when said relay contacts are operated by energization of said relay, a second diode electrically connected to the output of said second operational amplifier and conducting when said further source of voltage is connected to the input of said second operational amplifier, and a silicon-controlled rectifier triggered into conduction by conduction of said second diode to effect initiation of the start of upset motion of said platen.

12. The control circuit according to claim 11 and further including a second potentiometer with another source of voltage applied across its resistance, the slider of said second poten-tiometer being connected to a moveable one of said platens to provide a voltage which decreases in value as the platens move toward closed potision, the voltage from slider being connected to said input of said second operational amplifier to block con-duction of said second diode, the other input of said second operational amplifier being connected to ground, first switch means operable to electrically remove said relay and electrically connect the first-named diode to ground, and second switch means operable to remove said other input of said second operational amplifier from ground and electrically connect such input to the slider of a third potentiometer adapted to apply a voltage of a magnitude selected by said operator to said other input of said second operational amplifier to thereby provide for initiation of the start of upset motion of said platens as a function of platen position.

13. In a flash welder having fixed and moveable platens which carry the workpieces to be welded, said moveable platen being moveable toward closed position with respect to said fixed platen through flashing and upset operations, the improved method of controlling the amount of upset motion of said moveable platen to a machine operator selectable amount, comprising, applying a voltage from a first source across the res-istance of a first potentiometer, moving the slider of said first potentiometer in unison with movement of said moveable platen so that the voltage on said slider varies in decreasing manner as the moveable platen moves toward closed position, feeding the variable voltage on said slider to a sample-hold conversion unit and feeding the output of said unit to one terminal of a summing junction, applying a voltage from a second source across the res-istance of a second potentiometer, the slider of which is moveable by the machine operator so that voltage on said slider has an adjusted value in selected proportion to the amount of desired platen movement, feeding the adjusted voltage on said slider of said second potentiometer to the other terminal of said summing junc-tion so that the output of the latter is the algebraic sum of said variable voltage and said adjusted voltage, interrupting conversion of said sample-hold unit at the time of initiation of upset motion of said moveable platen to fix the voltage at the output of said conversion unit to the value at the initiation of upset motion, feeding the voltage so fixed to one input of an opera-tional amplifier, also feeding said variable voltage on the slider of said first potentiometer to the other input of said operational amplifier, the latter comparing the two voltages fed to its two inputs and causing its output to actuate controls for interruption of upset motion of said moveable platen when said two voltages reach a predetermined relative value.

14. In a flash welder having fixed and moveable platens which carry the workpieces to be welded, said moveable platen being moveable toward closed position with respect to said fixed platen through flashing and upset operations, the improved method of controlling the amount of upset motion of said moveable platen to a machine operator selectable amount, comprising, applying a voltage of positive polarity across the resistance of a first potentiometer, moving the slider of said first potentiometer in unison with movement of said moveable platen so that the voltage on said slider varies in positive polarity in a decreasing manner at the moveable platen moves toward closed position, feeding the variable voltage on said slider to a sample-hold conversion unit and feeding the output of said unit to one terminal of a summing junction, applying a voltage of negative polarity across the resistance of a second potentiometer, the slider of which is moveable by the machine operator so that the negative voltage on said slider has an adjusted numerical value in proportion to the amount of desired platen movement, feeding the adjusted voltage on said slider of said second potentiometer to the other terminal of said summing junction so that the output of the latter is the algebraic sum of the output of said conversion unit and said adjusted voltage, interrupting conversion of said sample-hold unit at the time of initiation of upset movement of said moveable platen to fix the output of said unit to said summing junction to the value established at the initiation of upset motion, and thereby fix the algebraic sum of the output of said conversion unit and the machine-operator-adjusted voltage from said second potentiometer to a predetermined value, feeding the algebraic sum so fixed to the noninverting input of an operational amplifier, also feeding said variable positive voltage on said slider of said first potentiometer to the inverting input of said amplifier, feeding the output of said amplifier to the input of a diode which is adapted to energize a relay when said diode is forward biased, said diode remaining reverse biased until said variable voltage applied to the inverting input of said amplifier becomes less than said fixed algebraic sum, whereupon said diode is forward biased to energize said relay and effect operation of a circuit to interrupt upset motion of said moveable platen.

15. The method according to claim 14 and further including switching means selectively operable by the machine operator to either one of two positions, in one position the circuit operating as specified, and in another position disconnect-ing said fixed algebraic sum from the noninverting input of said operational amplifier and in place connecting voltage on a slider of a third potentiometer, the resistance of the latter having voltage of positive polarity applied thereacross, said slider of said third potentiometer being adjusted by said machine operator to a value which will forward bias said diode when the value of said variable voltage applied to the inverting input of said amplifier becomes less than said adjusted value, to thereby energize said relay and interrupt upset motion of said moveable platen.

16. In a flash welder having fixed and moveable platens which carry the workpieces to be welded, said moveable platen being moveable toward closed position with respect to said fixed platen through flashing and upset operations, an improved circuit for controlling the amount of upset motion of said moveable platen to a machine operator selectable amount, comprising, a first potentiometer having a voltage of positive polarity applied across its resistance, said potentiometer having a slider which is moveable in unison with movement of said moveable platen to vary said voltage in a progressively decreasing positive polarity as said moveable platen moves toward closed position, a meter having a binary coded decimal output and a print command signal, said output and said signal being electrically connected to the input of a digital to analog converter, the input of said meter being connected to receive the variable voltage sig-nal from the slider of said first potentiometer, and the analog output of said converter tracking said variable signal, a summing function having one of its inputs connected to said analog converter to receive its analog output, a second potentiometer having a voltage of negative polarity applied across its resistance, and having a slider con-nected to the other input of said summing function, said slider being adjustable by the operator of the welding machine to a selected position along the resistance of said second potentiometer to provide a variable voltage signal, said summing junction having an output representing the algebraic difference between said analog output and the variable voltage signal from the slider of said second potentio-meter, an operational amplifier, having a noninverting input receiving the output of said summing junction and an inverting input receiving the variable voltage signal from the slider of said first potentiometer, said amplifier also having an output, a diode having its input connected to receive the output of said amplifier, and having an output, a relay coil connected to the output of said diode and energized when said diode is forward biased, and a switch adapted to be operated at the time of initiation of the start of upset motion of said moveable platen to prevent further conversion of said digital analog converter and to clamp the output thereof at the value it had at the start of upset motion, whereby when the voltage on the slider of said first potentio-meter decreases to a value less than the output of said summing junction, the output of said operational amplifier will forward bias said diode and energize said relay coil, and contacts affected by energization of said relay coil to halt movement of said moveable platen toward closed position, thereby to control upset movement of said moveable platen in accordance with the setting of the slider of said second potentiometer.

17. The control circuit according to claim 16 and fur-ther including switching means selectively operable by the mach-ine operator to either one of two positions, in one position the circuit operating as specified and in the other position dis-connecting the output of said summing junction from the non-inverting input of said operational amplifier and in place con-necting voltage on a slider of a third potentiometer, the resis-tance of the latter having a voltage of positive polarity applied thereacross, said slider of said third potentiometer being adjusted by said machine operator to a value which will forward bias said diode when the value of the voltage applied to the inverting input of said amplifier becomes less than the voltage from the slider of said third potentiometer, to thereby energize coil and effect operation of said contacts to control final position of said moveable platen.

18. In a flash welder having fixed and moveable platens which carry the workpieces to be welded, said moveable platen being moveable toward closed position with respect to said fixed platen through flashing and upset operations, the improved method of providing a reading of the magnitude of upset motion, comprising applying a voltage across the resistance of a poten-tiometer, moving the slider of said potentiometer in unison with movement of said moveable platen so that voltage on said slider varies in a progressive manner as the moveable platen moves toward closed position, feeding the variable voltage on said slider to the input of a sample-hold conversion unit and also to the inverting input of an operational amplifier, feeding the output of said conversion unit to one ter-minal of a summing junction, feeding the output of said amplifier to the other input of said summing junction, the output of said summing junction representing the algebraic difference between the output of said conversion unit and the voltage signal from the slider of said potentiometer, feeding the output of said summing junction to a voltage meter having a digital readout, the voltage signal from said conversion unit tracking and being equal to and of the same polarity with respect to the voltage signal from the slider of said first potentiometer during conversion operation of said sample-hold unit, whereby the output of said summing junction and the input to said meter are zero, interrupting conversion of said conversion unit at the time of initiation of upset movement of said moveable platen to clamp the output of said unit and to said summing junction to a value established at the initiation of upset motion, while the voltage signal from the slider of said potentiometer continued to progressively vary so that the output of said summing junction represents a progressively varying algebraic difference between the clamped output and the progressively varying voltage to effect progressive readout on said meter, and interrupting upset movement of said moveable platen at a predetermined time to thereby clamp the voltage from the slider of said potentiometer and halt further input to said meter.

19. The method according to claim 18 and further inclu-ding switching means selectively operable by the machine operator to one of two positions, in one position the circuit operating as specified, and in the other position disconnecting the output of said summing junction from said digital meter and instead con-necting the output of said conversion unit to said meter, whereby the readout of said meter will display the position of the moveable platen at the time the output of said conversion unit is clamped.

20. In a flash welder having fixed and moveable platens which carry the workpieces to be welded, said moveable platen being moveable toward closed position with respect to said fixed platen through flashing and upset operations, the improvement for providing a readout of the magnitude of upset motion of said movable platen, comprising, a potentiometer having a voltage applied across its re-sistance, the slider of said potentiometer being moveable in unison with movement of said moveable platen to vary voltage on the slider in a progressive manner as said moveable platen moves toward closed position, a sample-hold conversion unit and an operational ampli-fier, and means connecting the voltage from said slider to the input of said sample-hold unit and to the inverting input of said amplifier a summing junction, and means connecting the output of said sample-hold unit to one terminal of said summing junction and the output of said amplifier to the other terminal of said summing junction, the latter having an output representing the algebraic difference between the output of said sample-hold unit and the voltage from the slider of said potentiometer, a voltage meter having a digital readout, and means feeding said output of said summing junction to said meter, the output voltage of said sample-hold unit tracking but being of opposite polarity than the voltage from said slider of said potentiometer, whereby the output of said summing junction and the input to said meter are zero, means interupting conversion of said sample hold unit at the time of initiation of upset movement of said movable platen to clamp the output of said unit and to said summing junction at a value established at the initiation of upset motion, while the voltage from the slider of said potentiometer varies, so that the output of said summing junction progressively varies to effect a progressively varying reading on said meter, and means interrupting upset movement of said movable platen at a predetermined time to thereby clamp the voltage from said slider of said potentiometer and thereby halt further input to said meter.