US2030906A - Method and means for spot-welding aluminum and aluminum alloys - Google Patents

Description

4 Sheets-Sheet 1 INVENTOR. 'fi/s-zso/v E/V/ML-Y f m ATTORNEYS Feb. 18, 1936. N. F. MALLEY METHOD AND Ems FOR S'PO'I' WELDING ALUMINUM AND ALUMINUM ALLO Filed Sept. 10, 1935 Feb. 18, 1,936. Nj F.IMAII LEY 2,030,906

METHOD AND MEANS FOR S-POT 'WELDING ALUMINUM AND ALUMINUM ALLOYS Filed Sept. 10, 1935 4 sheetF-sheet 2 '8 5 -65 W I l I I' 67 l 60 n i 6 .2 1 lo I I s- 60:9 :M i 7- 651' l s I s l I 4- I y l 3 225/57 2- CU I 0/4 W: n [A 77015 INVENTOR. A622 s'a/V M6441 1 ATTORNEYS Feb. 1 1936. 1 MA EY 2,030,906

METHOD AND MEANS FOR SPOT WELDING ALUMINUM AND ALUMINUM ALLOYS Filed Sept. 10, 1935 4 Sheets-Sheet 4 108 103 105 I I J h 3: 5 :0 CUE-BENT WI {06 7 E60 E 102 5 O I 9 I I 90 INVENTOR.

BY Manda ATTORNEYS Patented Feb. 18, 1936 PATENT OFFICE METHOD AND MEANS FOR SPOT-WELDING ALUMINUM AND ALUMINUM ALLOYS Nelson F. .Malley, Brooklyn, N. Y., assignor to Aluminum Alloys Welding Corporation, a corporation of New York Application September 10, 1935, Serial No. 39,078 0 8 Claims.

This invention relates to a method and means for spot-welding aluminum and aluminum alloys.

Heretofore aluminum plates and the like were welded by the so-called resistance spot-welding process which consists in placing the plates or articles to be welded between two electrodes and causing an electrical current to circulate between these electrodes. This process is essentially a resistance process, since it relies upon the resistance of elements situated in the path of the electrical current to generate the entire heat necessary for the purpose of obtaining a welded spot. It was suggested to use two steel plates placed between the electrodes and the plates to be welded, for the purpose of generating an amount of heat sufl'lcient to transform the intermediate portions of aluminum into a plastic or plastic and molten state, and thus cause a spotwelding or fusion 01' the aluminum plates.

It is a matter of common knowledge that aluminum is an excellentconductor of electricity, namely, it has the very low electrical resistance 01' 2.828 microhms per cm. cube at a temperature of C.; in the liquid state, at a temperature of 700 C. it has a resistance of only 26.2 mi-' crohms per cm. cube. rapidly from the solid state to a molten liquid state when subjected to the influence of heat and when at a temperature of 658.'7 C. might be in the liquid or in the solid state. Due to these peculiar characteristics of aluminum, it was found impossible in prior art to weld by the above-described method aluminum plates of any substantial thickness. It was found that as soon as attempts were made to spot-weld aluminum plates having a thickness of A; ofan inch each, ,ora greater thickness, the spot-welding usually resulted in a large hole at the spot where the electrodes were applied, while molten aluminum would pour out and be blown out of the hole by. an explosive effect caused by parasitic voltages.

The resistance welding consisting in the application of external heat has the further disadvantage that a large area of the metal is heated around the spot which is to be welded.

A portion of this area is heated to the so-called germinative temperature which results in grain growth in the structure of the metal, causing a weakening thereof.

It is customary to support aluminum plates by the two electrodes which carry out the spotwelding process. If aluminum is permitted to become molten throughout its entire thickness, the electrodes will crush through the molten metal, with the result that large holes are formed Furthermore, it changes instead of the welded spot. A blowing out or an explosive eqect will also occur it the pressure is insufficient or fails to remain sufl'lcient.

All of the "above drawbacks rendered it exceedingly diificult to apply the resistance spotwelding process known in prior art for the purpose of spot-welding aluminum plates having a thickness of more than of an inch.

An object of the present invention is the provision of a new method, through the use of which comparatively thick plates consisting. of aluminum or aluminum alloys can be easily and conveniently welded.

Another object is the provision of a device for spot-welding aluminum plates which may be more than A; of an inch thick, said device being comparatively inexpensive and easy to manufacture and being adapted to spot-weld plates consisting of other materials.

The above and other objects of the present invention may be realized through the provision of a new process for spot-welding aluminum which may be described as a conductivity spotwelding process.

One of the important distinctions between this new process and the process known in prior art consists in that, while in prior art the resistance of certain elements other than the plates to be welded to the passage of the electrical current was utilized for the purpose of generating the major portion of heat for melting the aluminum plates, in accordance with the present process aluminum is made plastic, or plastic and molten not by the heat generated by some other element, but by the actual passage of an electrical current ofhigh amperage through the aluminum.

In accordance with the present process, the electrical current which is caused to flow through the two plates to be welded is sufliciently great to melt the metal between the electrodes. Therefore, in the course of the present process the temperature of the aluminum plates is caused to rise substantially by the electrical current itself, and not by externally developed heat. In order to eliminate parasitic voltages, I have found is advisable to connect each of the electrodes with a separate grounded resistance.

Another important feature of the present invention is the regulation of the amount of pressure which is applied by the electrodes upon the aluminum plates to be welded. It is essential that the pressure be maintained substantially constant is practically unavoidable, in prior art such penetration caused a considerable drop in pressure. In accordance with the present invention, the pressure is regulated so that a penetration of the electrode will cause merely a slight drop in pressure.

The invention will appear more clearly from the following detailed description, when taken in connection with the accompanying drawings, showing by way of example preferred embodiments of the inventive idea.

In the drawings:'

Figure 1 shows a spot-welding machine in side elevation and partly in section;

Figure 2 is a diagrammatic view illustrating the electrical circuit containing the electrodes;

Figure 3 is a front view of the electrodes;

Figures 4 and 5 illustrate diagrammatically the welding process carried out by means of the machine shown in Figure 1;

Figures 6 and '7 are similar to Figs. 4 and 5 and illustrate a somewhat different welding process, wherein two slugs are employed;

Figure 8 is a diagram illustrating the pressure of an electrode upon the aluminum plates and the amount of penetration of the electrode into the aluminum plate in the course of the welding process, as a function of time; 4

Figure 9 shows a portion of a spot-welding mawhich isconnected to the toggle levers l1 and 2|.

The link l8 connects the toggle lever IT to the electrode 20. The toggle lever 2| is connected with a block 22 serving as a support for a coil spring 23 surrounding a rod 24 which is movable along with the block 22 and the toggle lever 2|. A pressure adjusting nut 25' surrounds the free end of the rod 24 and is used for the purpose of adjusting the pressure of the electrode 20 upon the aluminum plates situated underneath the electrode.' The actual amount of pressure exert- A cable 32 connects the opposite end of the sec-,

ondary winding 34 of the transformer 23 with the support 33 which carries the electrode 21.

The primary winding of the transformer is connected to any suitable source of'electrical energy not shown in the drawings.

The electrode 21 may consist of two copper pieces or blocks 31 and 38 which are separate from each other and which are interconnected by a block 33 made of steel or the like, so that an electrical current flowing through the electrode." and the aluminum plates to the copper block 38 is obliged to pass through the steel block 33 having an exceedingly great resistance, before it can reach the copper piece 31 of the electrode 21. The object of the steel block is to increase the stathrough the pipe 42.

Figure 3 illustrates the position of the electrodes, viewed in the direction of the arrow 3 in Figure 2. The electrodes 20 and 21 comprise, in addition to the copper pieces 43 and 38, two copper rods 44 and 45. The rod 44 is carried in a suitable opening provided in the block 43, while the rod 45 is held in an opening formed in the piece 38. It will be noted that the rods 44 and 45 are inclined in relation to the pieces 43 and 38 and that their central lines form an acute angle with each other in the example illustrated.

. One end of a suitable resistance 80 is connected to the electrode 44, while the opposite end of this resistance is grounded.- A similar grounded resistance is connected to the electrode 45. The object of the resistances 30 and 8| is to facilitate the dissipation of parasitic voltages. They may be eliminated if suflicient pressure is maintained at all times.

The process of spot-welding comparatively thick aluminum pieces is shown in'Figures 4 and 5 and illustrated in the diagram shown in Figure 8.

Figures 4 and 5 show two aluminum plates 50 and 5| which overlap each other and which are placed between the rods 44 and 45 in such manner thatthe area 52 to be welded is situated exactly between the two rods. A thin steel plate 53 is placed between the rods 45 and the aluminum plate 5|.

While in prior art the purpose of utilizing steel plates was to generate heat sumcient to melt the two aluminum plates, the steel plate 53 in the process according to the present invention serves the purpose of preventing the penetration of the rod 45 into the aluminum and generates only a small additional supply of heat, the main heat being supplied by the conduction of the electrical current itself.

The electrical current and the voltage to be applied in the spot-welding process vary depending upon the thickness of the plates to be welded and the materials of which they consist. I prefer to use a voltage of six volts and an electrical current which may vary from 35,000 amperes to 100,000' amperes depending upon the thickness of the plates, their composition and the time used for welding. In order to weld two plates of 5|S material, each of which is of an inch thick, I prefer to use an amperage of 40,000 amperes, the welding time being approximately of a second. The actual amount of amperage necessary for plates of each particular thickness and composition can be easily determined by the operator after some tests.

As shown in Figures 4 and 5, the rods 44 and 45 actually grip the two plates 50 and 5| and hold these plates in position, while the-process f spot welding is carried out. ,The pressure which'the rods 44 and 45 exert upon the aluminum plates 50 and has been found to' be a very the aluminum plates should be maintained as constant as possible in the course of the welding operation. This is carried out by suitably-shapineh.lpretertoemployapsessureoiilopounds or lpounds,whilei'orsoitermaterialotthe The electrical current can he-switched on and oil automatically through theprovision of a conwhich is rotatable along with the lathe course of rotation oi the cam i2 it comes in contact with the switch It. switching on the electrical current whichisautomaticallyswitchedoilassoonasthe piecepassesoutoicontactwiththeswitchll.

The which the electrical current maintaineddependsuponthetypeoimaterial plates. In the diagram meraltt. Itwillbenotedthatthecurrentis entinventiomitisementialthatthe penetrationoitherodllin lustrated by the slanting line i oiduraluminum havingathickness inch, thepressurewhichwasoriginal1yl00poimds l5 shouldnotdrophelowwpounds. Inthecaseoi not drop below pounds.

- The electrical current should be preferably switched ofl' before the drop in pressure has occurred. It the current is maintained while.the pressure falls below apredetermined amount, the electrode will sink too deeply into the molten aluminum,withtheresultthatthecmstflmay be broken, the liquidaluminum ti will pour out andblowoutandaholewillbei'ormed. Inthe diagramshowninl'lgure8,thetimeatwhichthe current is switched oil is indicated by the nuswitched oil'bei'ore the drop in pressure begins and before a constant pressureis maintained, said constantpressurebeingindicatedbythelinetl' in Figure 8.

Thedlagramshowninl'lgureBalsoshowsthe movements of the electrode II as a function of time. Priortothebeginningoi'theweldingprocess the aluminum plates II and Ii are placed uponthelowerrodliandtherodllismoved toward the plate I. This movement is indicatedbythelineilinl'igureil. Thentherod' remains stationary, while the welding process is carried out. This is shown by the horizontal line tlinl 'igurel. Whentheunderlyingcrustll formed in the aluminum plate ll becomes soit. the rod it penetrates sllshtly into. the aluminum platell. This is shown by theslantins line 6| inl'igurell. 'lhecurrentisswitchedoiifatthe point 68, before the penetration oi the rod 44 into the plate ll.

'l lienthepressureoitheroduponthealuminum plate is gradually diminished. This is shownbythestraightlinetlinl 'igureil- Finally, the aluminum plates I. and Ii are removed and slight mechanical pressure will suiilce to separate the steel plate '3 from the plate ii. The plates may be quenched alter the completion of the described method;

Practical experience has shown that throughthe use of the. above described process. it is possible to spot-weld plates consisting of very hard aluminum alloys which usually contain from 92% to 95% aluminum such as 17 8, 24 S, and other alloys containing, in addition to aluminum, manganese, magnesium, copper and the like. Plates having a thickness oi V 95 inch. or even thicker plates may be conveniently and safe y POt-welded by the described process.

Figures 6 and "1 illustrate a welding process wherein,.in additionto the steel plate 58, two slugs l0 and ii are employed. The slug I0 is situated between the rod 44 and the plate 50, while the slim Ii is situated between the aluminum plate 5| and'the steel plate It The two .slugsllandliwhichconsistotthesamema-rs terialastheplatesllandllremain-intheweldedaluminum platesatter thespct-weldinghas beencompleted. 'l'heweldingm'oce'ssinthiscase issuhstantiallysimilartothatalreadydescribed 'lheohiect oithesluss lland'lListoincrease thetblcknessoithespottobewelded,thereby thestreugth; 'lheprocessotspot-weldingcarriedoutinacccrdancewiththeprinciplesotthe'presentinflrst increase alongthe line I12, then remain constant when the current is mlline Ill) and then drop slightly as illustrated by the line I".

.Then, due to the provision of the projection I DI the pressure after having remained constant for a while, as shown by the line ill, increases along theline lllandismaintainedonahigherlevel as indicated by the line iI9,-until it is finally reduced, as shown by the line ill.

What is claimed is: a

1. The spot-welding process, which comprises placing at least-two partly overlapping-aluminum containing plates between two electrodes, causing said electrodes to press with a constant pressure against said plates, causing an electrical current a to flow through said electrodes and the underlying portions or said plates, while said constant pressure is being maintained, interrupting the flow oi the electrical current, I said constant pressure until a predetermined lower pressure is attained, and then increasing'said lower pressure while the material is still hot.

2. In a device for spot-welding aluminum-and aluminum'alloys, an electrical circuit comprising a source or electrical energy, apair of electrodes,

means connecting oneoi' said electrodes with said source of electrical energy, a comparatively high connected in series with the other oi! said electrodes, and means connecting said resistance with said source or electrical energy.

, 3. A device for spot-welding aluminum and. aluminum alloys, which comprises an electrical circuit comprising a source of electrical energy, a pair of electrodes, each of said electrodes, 'comprising a rod and a block carrying said rod: means connecting the blocks oi said electrodes with said source ofelecirical en rgy. anda sepacreasedpressureottheelectrodesconstanhand a projecting surface forming a continuation or saidcylindricalsuriacetoiurtherimreasethe pressureottheelectrodeameansconnectedwith oneoisaidelectrodes'andlncontact withsaid camsm'taeestocausesaidclectrodetoexerta pressmeuponplateslnsertedbetween said-electrodes,saidpressm-ebeingnrieddependingupon saidsln-iaces,asourceorelectricalcnergy,aud-

meansrorconnectingsaidsourceodelectricalen- 1 w th said electrodes.

5. In a machine for spot-welding aluminum and uminum alloys, a pair or electrddes situated substantially opposite" each other, a cam having operative surfaces, means connected with one oif said electrodes and in contact with said cani suriaces tocausesaidelectrodetoexertapressure upon plates inserted between said electrodes,

a source of electrical energy, means connecting said source 01' electrical energy with one of said electrodes, a steel block connected with the other of said electrodes, and means connecting said steel block with said source or electrical energy.

6. In a machine for spot-welding aluminum and aluminmn alloys, a pair 01' electrodes situated substantlallyopposite'eachothenacamhaving operative surtaces, means connected with one-o! said electrodes and in contact with said cam surfaces to cause said electrode to exert a pressure upon plates inserted between said electrodes, a

source 01 eiectrlcalenergy, the first-mentioned electrode comprising and and a block carrying said rod; the second-mentioned electrode comprisingarodablockcarryingsaidrod, another blockhavingagmterresistaneethantheseccud-mentioned block and connected in series with the second-mentioned block, and a firmer block connected in series with the third-mentioned block: means 0 the last-mentioned block with said source of electrical energy,

and means connecting the first-mentioned block with said source of electrical energy. 7. 'I'hespot-weldingprocess, which comprises ing said electrodes to press with a constant presplates, and causi g a stabilized electrical current v, mpe age to flow through said electr' es and the underlying porpressln'e f of a substantially constant tions'ot said plates while said constant is maintained to weld said plates.

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