US2898442A

US2898442A - Manufacture of compressor vane assembly

Info

Publication number: US2898442A
Application number: US621945A
Authority: US
Inventors: Charles C Anderson; Virgil K Eder; William P Zimmerman; Thomas A Heath; James F Mclaughlin
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1956-11-13
Filing date: 1956-11-13
Publication date: 1959-08-04
Anticipated expiration: 1976-08-04

Description

Aug. 4, 1959 c. c. ANDERSON ETAL 2,898,442

' MANUFACTURE oF coMPREssoRvANE ASSEMBLY 'Original Filed Deo. 1 1950 4 Sheets-Sheet 1 :inventors das.

lill/Irda IHN f M I l f H a, f mm Aug. 4, 1959 c. c. ANDERSON ET Ax. 2,898,442

MANUFACTURE oF COMPRESSOR vANE ASSEMBLY f original Filed'neo. 1, 195o 4 sheets-Sheet 2 WAugQ 4, 1959 c. c. ANDERSON ET AL 2,898,442

MANUFACTURE OF' COMPRESSOR VANE ASSEMBLY Original Filed Dec. 1, 1950 4 Sheets-#Sheet 3 "l fmlll f /ff il' Aug. 4, 1959 c. c. ANDERSON ET Ax. j 2,898,442

l MANUFACTURE oF COMPRESSOR VANE ASSEMBLY Original Filed Dec. l, 1950 4 Sheets-Sheet' 4 United States Patent() MAlsIUFACTUIIU?.I or comREssoR ASSEMBLY Charles C. Anderson, Virgil-"K. Eder, William P. Zim- Thomas A.` Heath, and-James E. McLaughlin, Indianapolis, Indg., assignors toGeneral Motors Corporation, Detroit, Mich., a corporation of Delaware Continuation of application Serial No. 198,687, Decemheli 1*, 1950. This application November 13, 1956, Serial No. 621,945

4` Claims. (Cl. 21S- 80).

This application is a continuation of application Serial No. 198,687,v tiled December 1, 195,0; (now abandoned). y This invention relates to. the,y manufacture of blade or vane assemblies lfor axial-flow compressors and other similar structures. Such axial-flow machines commonly comprise a cylindrical or conicall stator within which is mounted a rotating drum to provide a ow path of annular cross-section for air or other gas. A number of rows of blades are mounted on the rotor and a number of rows of stationary blades are supported in the stator to guide the air from the outlet of each rotating stage into the inlet Q'f the succeeding rotating stage. Ordinarily, in such machines, the rotor blades are not shrouded and are Supported only at the rotor or inner end. The stator blades, on the other hand, may be mounted between inner and outer rings, the outer ring being supported` in the stator and' the inner ring serving as a shroud and customarily providing' a labryrinth seal with the rotor kto prevent re, verse'ow around the inner ends of thev stator blades'.

Since an axial-how compressor may ordinarily have from `ten to twenty stages and typically about'forty to eighty stator blades per stage, the' large number of blades presents a substantial manufacturing problem. A strong and rigid assembly is required and, particularly in air# craft installations, weight must be minimized. This invention is directed to a process and apparatus by which the fabrication of stator vane assemblies has been greatly facilitated and the quality of the product has been signincantly improved.

In brief, the process consists of Aproducing an arcuate assembly which forms a part, preferably one half, of one stage of stator blading. This assembly comprises an outer arcuate strip, an inner arcuate strip concentric with the outer strip, and vanes or blades radiatingy from the inner strip to the outer strip and xed to bothstrips. The vanes are formed with tongues ork tabs extending from each end which` extend throughholes punched in the strips and are upset or headed by heat and pressure toA lock the entire assembly together. A very strong, light, and reliable vane assembly is thus produced and the processr is quite economical, which is highly signicant injview of the large number of blades in a multistage ax-ial-flow` compressor. The process by which this result is achieved is simple, expeditious, requires little skill, and may beaccomplished with relatively simple and inexpensiveV equipment. l'

The preferred apparatus for accomplishing the process is simple, reliable, and easy to operate. Y

l The principalobjectsof the invention are l to improve the quality andl reduce the costof` compressor ,vane assemblies' and'analogous structures, to provide an improved process for the fabrication of assemblies of this character, and' to provide anr apparatus particularly suitable and e'icient for the production of compressor vane assemblies andy the like. A further Object is tol provideaV process Suitable yfor fabrication of assemblies of staiulesshsteel, @Which is `rmore diicultto handle, insorne respects, than other materials..k More specific objects ofthe invention r*ice 2 are to forml a compressor vane assembly or the likel by upsetting and, more particularly, by upsetting with elec'- trical resistance heating.` The manner in which` these objects of the invention are realized will` be apparent to those skilled in the art from the. description herein? oflthe preferred process andappa-ratus.

Referring to the drawings, Figure l.. is av frontelevation of an upsetting machine with a supporting tix-ture for the vane assembly in` place,` Figure 2 isi an enlarged partial View of the same, principally shown in section on a plane containing the axisi of the heating electrodesgfFigure r3 is an enlarged partial sectional View ofthe fixture taken: on the plane of line 3 3 in Figure l-;.Figure 41 is a partial sectional View taken on the plane ofIV line 4--4 in Figure l and illustrating a detail of the fixture; Figure 5" is an enlarged view of a portion of Figure l; Figure 6-is a broken transverse section of the -xture with the vane assembly therein taken on the plane of line 6-6 in Fig. l; Figure 7 is a partial elevation view ofthe machine as set up forv a vane assembly with long blades; Figure 8 is a sectional' View taken on the plane ofl line 8--8 in Figure 7', illustrating principally the locating and supporting device for the blades; Figure 9 is an elevation vievv-l of the same, projected on the plane of line 9-9 in Figure 8; Figure l0 is a partial perspective view ofthe apparatus illustrated in Figure 7; and Figures ll, l2 and 13 are greatly enlarged partial cross-sectionall views of the' vane ring` assembly illustrating successive stages in an upsetting process.

While itwill be understood that the process and appara'- tu-s of the invention may be employed in the production of various articles, they are particularly adapted'to'the production of a stainless steel stator vane assembly for a compressor or turbine of the axial-How type. Therefore, for the purpose of illustration of the invention, apparatus employed in the production of an assembly disclosed. in the copending application of lohn B. Wheatley, Arthur W. Gaubatz, and Charles C. Anderson, Serial No. 150,954, tiledl March 2l, 119.50, entitled' Turbine Or Cornpressor Stator Ring, (Patent 2,640,679) assigned to the assignee of this application, will be describedf Since the stator ring is fully disclosed in the abovem'entioned application, it will not be. described in detail herein in th interest of conciseness. f

Before proceeding with the detailedv description of the apparatus and process, the nature of the processi Willbe outlined by Way of introduction. The stator ring comprises arcuate inner and outer strips, which are specifically semi-circular, although they might be of any other arcuate extent. The blades are sheet metal strip rolled tov an appropriate airfoil section and cut into sections, eachk section'corresponding to a blade. The bladesar formed with projecting tenons at each end of lessV width than the width of the blade. The arcuate inner andi outer strips are punchedy to receive the tenons. In assembly, the blades are mounted with the tenons projecting through the rings or strips and held temporarilyin a'sesmbled'relation. The tenons at each end of the blade are then `upset by heat and pressure, heat being preferablyprovided by passing current between electrodes engaging the respec`` tive end of the blade and urged together. n When)v the blades are thus upset or headed, a strong, rigid, :unitary structure is formed. l f, l y" v l During the upsetting 'operation,` the -assemblyfis supported in a fixture which is mounted in theupsetting ma. chine sothat the blades maybe readily Operatedupone'in succession. This fixture also servesythfel purppse of holdj ing the arcuate strips concentric andtheblades inlprop'er' radial, .relation and" thus, 'prevents any, defguaetioa .dus fohesl'sfa'race of the @nella in the .str'iiis'ad the force exerted on the blades by the upsetting machine. ,Depende ing upon the size of the blades, the tenons may be of greater or less width and thickness and depending upon the size of the tenons, they may be upset in a single operation or ina series of operations, each operation upsetting `a part of the tenon.

`The blades in the initial stage of a compressor of average size are of considerable length, and the invention provides also for supporting the major part of each blade during the upsetting operation to prevent deformation of the blade by the compressive force thereon. This additional support is not necessary for short blades such as are used in the high pressure stages of compressors of average size.

The apparatus of the invention comprises and electrical upsetting machine and appropriate fixtures for supporting the blade ring assemblies and aligning the blades with the electrodes of the machine. The holding and aligning apparatus is of two general types, depending upon the size of the blades, the type for short blades being illustrated in Figures 1 to 6, and the type for the longer blades in Figures 7 to 10. It will be understood that in general a special xture is required for each size of vane assembly.

Referring now to Figures 1 to 6, illustrating one form of the apparatus of the invention, Figure 1 is a general elevation view of the machine. It comprises a base 10 on which are mounted supports 11 for a lower electrode assembly 12. A support 13 for the blade ring tixture is mounted on the assembly 12. The xture 14 is thus supported above the lower electrode assembly 12 and below an upper electrode assembly 16 mounted on a crosshead 17. The crosshead reciprocates vertically between guides 18 mounted on the base 10 and is coupled to the piston rod 19 of an air cylinder 21 by a link 22. When the cylinder is supplied from any suitable source of air under pressure by a conventional valve (not shown), the crosshead 17 and the electrode assembly 16 are pressed downward to provide the necessary upsetting force. The crosshead is recesses 48 and 49 equals the design radius of the outer strip 36 so that when the strip is abutted against the outer circumference of the recesses and clamped in place it is held to a circular arc of the correct radius. The blades 37 act as converging struts to support the inner strips 38 and 39. LocatingA blocks 50 (Fig. l) iixked to the ring 47 abut the ends of the arcuate strips and locate the assembly correctly in the recess 49. The strip 38 is clamped between the faces of the rings 46 and 47. The rings k46 and 47 may be separated to mount the partially finished assembly in place, and are then clamped together by machine screws 51 threaded into the plate 47 and a machine screw 52 (Fig. 4) which passes through the plates at an angle so as to clear the blades 37. A spacing ring 53 is disposed around the upper machine screw 51, since the blade assembly iills only the lower half of the fixture. As will be apparent, the assembly of the blades and strips may be laid on the ring 47 abutting the locating blocks 50. The ring 46 is then placed on top of the blade assembly and the machine screws 51 and 52 are inserted and tightened. The assembly is thus held ready for the upsetting operation.

Before continuing with the description of further steps of the process, the preferred structure of the upsetting machine, including the arrangement for supporting and locating the xture 14, will be described. The lower electrode assembly 12 (Figs. l and 2) mounted on the supporting blocks 11 comprises a hollow column or pedestal 54 within which a support member 56 is mounted for vertical sliding movement. The support 56 is urged upwardly by a compression spring 57 mounted between the bottom of the support and a flange at the base of the column 54. Upward movement of the support is limited lifted when the pressure is relieved in the cylinder by a counterweight 23 sliding in a vertical tube 24 and coupled to the crosshead by a cable 26 running over a pulley 27. The force for upsetting may be adjusted by a conventional regulating valve (not shown) in the supply line to the cylinder 21.

Current is supplied to the electrodes from any suitable source such as the current supply apparatus of a commercial spot-welding machine (not shown) through leads connected to the electrodes in a conventional manner.

Since current supply devices of this type are well known, f

The vane assembly 35 (Figures l, 2, 4 and 6), which is preferably semi-circular, comprises an outer strip 36, blades 37, and inner strips 38 and 39. While the inner strip may be single it is preferably, in practice, two strips 38 and 39 of channel section to provide additional sealing, as described more fully in the aforementioned Wheatley et al. application. For structural purposes, one ring 38 would suice. The surfaces of the rings may be conical rather than cylindrical (note Fig. 6). The ends of the blades are formed with projecting tenons 41 and 42 which are upset to form heads 43 and 44 locking the assembly together.

The assembly, after the blades have been tted into the strips 36, 38, and 39, is mounted in the fixture 14, which comprises two rings of relatively heavy plate, a front ring 46 and a back ring`47. As will appear most clearly from annular recesses 48 and 49.` The outer radius of the by a dog 58 attached to the pedestal by a machine screw S9. The support 13 xed to the support 56 is slotted, as indicated at 62, to receive the projecting shafts 63 of spool-shaped rollers 64 of insulating material which support the fixture 14 and permit it to be readily rotated about its axis to bring the succsive blades into position for upsetting. Rollers 64 of different sizes may be provided for fixtures 14 of dilerent size. A cylindrical support 66 for the lower electrode is fixed in a block 67 which may be supported from the base 10 in any suitable manner, as by blocks 60 and insulating plates 70. The cylinder 66 is insulated from the

members

54 and 56 by an insulating washer 68 and an insulating sleeve 69, respectively. A plug 71 extending from the upper end of the cylinder 66, which may be brazed or otherwise fixed in place, is tapped to receive the lower electrode 72. The lower end of lthe cylinder 66 is closed by a plug, which is drilled to receive tubes 73 and 74k for circulation of cooling water through the electrode support. The electrode and its support are preferably of copper or other material of high electrical and heat conductivity. The block 67 may be connected in any conventional manner tok one side of the electric current source. A pressure pad 76 of Bakelite or other insulating material may be mounted in the upper end of 1 the sliding support 56. This pressure pad engages the outer ring 36 during the upsetting operation. The pressure pad is closely adjacent the surface of ring 36. When the upper electrode to be described engages the work and urges it downwardly, the supporting arms 13 may tiex slightly to allow the outer edge of the ring 36 to engage the pressure pad 76. 1

The upper electrode assembly 16 is mounted on the crosshead k17. A horizontally slidable post or support 77 is received in a socket 78 in the crosshead and clamped in position by a hand screw 79. A vertical sleeve 81, welded or otherwise xed in a bore in the post 77, is brazed to a tube 82 threaded to receive a nut 83.' yThe upper electrode 84 is threaded into the nut 83. The upper end of the sleeve 81 is threaded'for a nipple 86, to the M upperendofwhich is threaded a cap 87. Water circulat'- ing tubes 88 and 89 are mounted in the cap 87. Water is`thus circulated through the'intcrior o'f the electrod '-5 ysupport to .cool .the electra-de .84s P1191 destro@ ,assembly may .include a y)pressure nad .devise iCQmPFiSi-ES an abutment 90a, a spring 90b, and a pad 90 to Iengage .the lchannels 38 and '39.

The position of the fixture 14 with `respect to the rlower .electrode may be adjusted by screws-91 threaded brackets ,92 adjustably bolted to the supporting brackets 13. These screws may be locked by jam nuts if desired. Insulators 91a on the ends of the screws 91 engage the faces of ,the fixtures 14. The upper electrode'may be adjusted across the width of the vane ring by releasing the hand screw 79 and moving .the post 77 inwardly or outwardly.

l'lfhe vane ring ,is indexed `to insure .proper location .of each blade vin alignment with ,the upsetting electrodes by a springurged indexing finger 93 (Fig. 3) which engages in notches 94 in the face of the front `ring 46. "Ihe indexing finger .may be f .any kSuitable structure .The finger preferably is pvoted in a block 96 adjustably mounted on the forward support 13 lb ,y means of a post '497i .lclarnped in a block 98 of insulating material fixed to the support. An over-center spring -99"connected between l,the block 9 6 and the `finger 93 urges the finger Vinto engage.- ment with the fixture, or may hold it outof ,the way when the fixture is placed in the machine. The .proper alignment 0f the blades with .respelft t9 the' lldexins y.notches 94 is assured by the locating blocks In order to perform .the heading operation, ,electrodes 7 2 and l.8.4 of appropriate V.size and shape are screwed into A the ,electrode holders and the fixture 14 with .the assembly .clamped in .place is lifted onto the support '13, resting on Vthe rollers 64. The `s et screws 91 may be adjusted if necessary -to locate the ,fixture lcorrectly with respect to the lower electrode and .the post 77 may be adjusted to locate the upper electrode 4correctly with respect to rthe vfixture.

The air pressure fed to the cylinder 21 and the intensityand duration of the heating current areset to values found vto give the kdesired results. In .this connection, these values may b e determined .by ,trial A s is well known, the pressure and .the amount of heat should be gauged so as to be suited to the particular operation, .since .otherwise unsatisfactory results will be obtained. In view ofthe great possible variation in the .dimensions of the structures being upset, particularly the dimensions of the tongues 42, and the variations .in materials which may Eb e used, no standard values of .theseconditions can be stated. Suitable values may be readily determined for ,any given operation by those skilled inthe art, and tabulated for ready reference. With the machine thus `set for the particular operation, air is admitted to the 4cylinder 2.1, forcing the .upperelectrode against the upper tongue .42 and forcing the fixture and

Vthe sliding support

13, 56 downward until the lower ltongue .41 ellgags .the llower electrode 72. The electric current is then switched .on andthe heating of the .tongues .is accomplished b y vresistance to flow of current, the resistance being primarily at the Contact between the .electrodes and the tongues. When the heating has progressed sufficiently .t0 ,soften the tongues, the force exerted v.on .the upper electrode upsets .the `tongues and heads them against .the inner and outer ring, ythe support moving downwardly toa .slight extent during the heading operation. The ,pressure .p ads 76 and 9.0, if used, assist in seating the inner and outer strips `firmly against the shoulders on the blades. When Vthe upsetting is completed, the air is released from the ycylin- -der 21 and -the counterweight raises the lcrosshead and the upperelectrode. The ,spring 57 raises the support so that the tongues 41 are clear of the lower electrode and the fixture ,may be rotated `to align the next blade to be headed with the electrode. It 'has been f ound desirable in some cases to skip several blades lbetween heading steps to prevent undue local heating of `the `arcuate strips,

which are of relatively ilight weight. `'-I-'hus,ffor example, the first, fifth, ninth, and soon`,-blades mayfbeupset and .6 then .the second, sixth, tenth, `and so on, until all .have been cmpletedl i Dependingupon the width of the tongues l41 and .42 and the dimensions of the ystructure in general, it may be desirable or necessary to upset each tongue in stages so that less heat and pressure are required. This procedure is illustrated in Figures -1l to 13, inclusive. Figure 1 1 shows a blade 37 with the inner Ytongue 42 inserted through .the innerfstrips 38 .and 39, .to a considerably enlarged scale. 4In Figure 12, the upper ,electrode 184 is illustrated lheading one vhalf of ,the tongue 42. After this operation has been completed for all the blades, .the position Vof the electrodes with respect to the blades ,can be readjusted and then the other half of each tongue may be upset, as illustrated in Figure 13, .to complete .thehead `.44. If the tongue is wide'enough, the operation maybe performed infthree stages, preferably upsetting first one edge, then the other, vthen the central portion; It will be understood that .the principal reasons Vfor thusdividing the operation zare to prevent undue columnar stresses and overrnuch heating of the blades 37 4and Vtoo great heating of the arcuate strips. In some assemblies, dividing the ,upsetting has made successful operation vof the process possible. i

When lthe securing of .all ,the blades has been completed, the fixture 14 is removed from v,the machine and disassembled and the completed blade ring is lifted out. As will .be apparent, the operation is of great simplicity, may be carried .out expeditiously, and 'requires little skill on the part of the machine operator. The operator may be furnished with a tabulation of the appropriate pressures, currents, and heating times for each assembly, and ysuitably shaped electrodes and holding fixtures are provided for each distinct vane assembly.

The apparatus and procedure f or assembling vane rings with long blades, such as those for the entrance stages of compressors, are illustrated in Figures 7 to l0 inclusive, so far as they differ from what has been previously described. The basic machine is the same; the procedure .differs `in lthat the blades are held rigidly against lateral deformation. For lthis purpose, a vise or clamp for the blades vis added to the machine. The vise also serves to locate the blades so that the indexing mechanism of the previous .form is not required. The fixture for holdying; the uncompleted vane assembly is generally similar to that previously ldescribed except for dimensions, but `the front ring is cut away Vto provide for access of the blade clamp to the blades. i

In ,the .general view of Figure 7, the parts of the machine are identified by the same reference characters as in Figure l. T he vane assembly is the same as the vane assmbley 35 previously described, .except for dimensions, the principal differences being the greater radial length, width, and spacing of the blades. The holding fixture 1 14 is, in general, similar tothe fixture 14 previously described, comprising a yfront rring 146 and aback Vring 1,47, the rings being recessed to define an arcuate shoulder Yagainst which the ,outer strip 136 is located. Clamping screws 151 and 1*'52 hold the two sides of the 4ring together after the assembly has been inserted. `Where Vthe spacing of the blades permits, the screw 152 may be parallel to the axis of the fixture, as illustrated in Figure 8, .and may be threaded into a block 152g fixed tothe `ring 146. Locating blocks fixed to one of the

rings

146 and 147 of the fixture bear against the ends ofthe strips 136, 138, and 139, similarly to the blocks 50 of Figure 1 The face of the ring 4114 is cut away toprovide an arcuate slot 201 exposing substantially'all of the length of the blades. i

Pressure pads such as 76 and 9 0 (Fig. 2) are preferably employed.

l'The viseor clamp for locating and supporting the :blades is indicated .generally inFigure 7 by the reference numeral `202. As shown ingreaterpdetailsin Figures 8,29., and flO, thisarrangement comprises sa ibase 103 `:which 4may be fixed to the sliding support 56 in any convenient manner, as by machine screws 204 (Fig. Ways 206 fixed tothe upper surface of the support 203 guide the body 207 of the vise assembly, which is formed with flanges 208 disposed under anges 209 of the guide strips 206. An arm 211, the outer end of which provides one jaw 212 ofthe blade clamp, is fixed to the body 207. The other jaw 213 of the blade clamp is integral with a lever 214 pivotally mounted on the fixed arm 211.

Arms

211 and 214 are preferably of copper. The pivot arrangement comprises a vertical pin 216 passing through the arm 211 and a block 217 extending from the arm 214 through an opening in the arm 211. The jaws are urged toward the open position indicated by broken lines in Figure 8 by a compression spring 218 mounted between the arms. The jaws are closed on the blade 137 by a bar or blade 221 with a handle 222 pivoted on the member 211- by a bolt 223. When the blade 221 is in the position illustrated in Figure 10, the jaws are open. When the blade is moved upwardly to the position indicated in Figures 8 and 9, it wedges between the ends of the

arms

211 and 214 and closes the jaws on the blade. 'Ihe end of the lever 214 is bevelled, as indicated at 224, to admit the wedging blade 221. As will be apparent from Figure 8, the faces of the jaws 212 and 213 are formed to the contourof the blade 137 so that the clamping will not distort the blade. Since the vise assembly can be slid out of the ways 206, individual assemblies may be readily exchanged when the machine is converted from the assembly of one blade form to an assembly with a different blade form. Also the vise may be readily drawn outward, as indicated in Figure lO, to permit rotation of the fixture 114 to bring another blade into position. A pin 226 inserted in the arm 211 abuts the fixture 114 when the vise is in position to grip the blade. The ways 206 are set at an angle to the axis of the fixture 114 commensurate with the angle of the blades. The vise arrangement is so constructed and located that the blade is held in proper position between the electrodes when it is clamped in the vise, and the vise thus serves as an indexing means. The vise is insulated from the support 12, as by forming the support 203 from an insulating material.

The process in which the apparatus of Figures 7 to 10 is utilized is the same as that previously described with the additional feature that the blades are supported against the columnar load imposed by the electrodes, and need not be described.

The adjustment of the fixture transversely of the electrodes may be dispensed with by establishing a fixed path vof movement of the fixture and shaping the electrodes for each assembly so that they engage the tongues, or sections of the tongues as desired.

The apparatus and process of the invention have been employed successfully in the manufacture of blade assemblies of stainless steel, a material difficult to upset. So far as we know, it has not been considered possible hitherto to assemble stainless steel vane assemblies by upsetting.

The advantages of the process for the formation of the blade assemblies shown herein will be obvious to those skilled in the art. It should also be apparent that the process is readily adaptable to other assemblies of an analogous nature by providing a suitable holding fixture arranged for convenient progression of the work to present the successive points to be headed to the electrode and to hold the workfpieces against distortion. The principles of the invention may thus be applied to various assemblies. In this connection it will be apparent that the vane assembly, the fabrication of which has been described herein, is an example of a type of structure comprising more or less parallel side members or strips with cross members extending from one strip to the other-in other words, a'ladderllike structure, and that the invention may be employed in the fabrication of such structures whether the cross members are vanes or blades or are for some other purpose.

The invention, therefore, is not to be construed as limited by the detailed description of the preferred ernbodiment thereof, since many modifications may be made by those skilled in the art within the scope of the invention.

We claim: y

1. An apparatus for assembling structures comprising two strips formed with holes and comprising cross members extending between the strips and provided with tongues extending through the holes in the strips, the apparatus comprising, in combination, a fixture for holding a said structure against distortion, two electrodes relatively movable to engage the tongues, means for forcing the electrodes against the tongues, means for passing a heating current from one electrode to the other through a cross member, and means for indexing the fixture to align the cross members with the electrodes comprising a clamp for the cross member to engage and brace the cross member between the electrodes against lateral distortion and disposed in alignment with the electrodes to locate the cross member in alignment with the electrodes.

2. An apparatus for assembling structures comprising two strips formed with holes and comprising cross members extending between the strips provided with shoulders at the ends of the cross members engaging the strips and with tongues extending through the holes in the strips, the apparatus comprising, in combination, a fixture for holding a said structure against distortion, two electrodes relatively movable to engage the tongues, one electrode being fixed and one being movable, means for forcing the movable electrode against the tongues, means for passing a heating current from one electrode to the other through a cross member, and a support for the fixture freely displaceable lengthwise of the cross member with respect to the fixed electrode to substantially balance the force on the tongues, the support engaging and supporting the fixture with freedom of movement of the fixture to present the cross members successively to the electrodes.

3. An apparatus for assembling an arcuate blading section composed of an outer arcuate strip, an inner arcuate strip, and blades extending from one strip to the other with tongues projecting through holes in the strips, the apparatus comprising, in combination, a ring-shaped fixture for holding the blading section against distortion, two electrodes relatively movable to engage the tongues, means for forcing the electrodes against the tongues, means for passing a heating current from one electrode to the other through a blade, a support for the fixture displaceable with respect to one electrode and mounting the fixture for rotation of the fixture to present the blades successively to the electrodes, and means for indexing the xture to align the blades with the electrodes cornprising a clamp aligned with the electrodes and engageable with the blade between the electrodes to brace the blade against lateral distortion.

4. A machine for assembling structures comprising two strips formed with holes and comprising cross members extending between the strips provided with shoulders at the ends of the cross members engaging the strips and with tongues extending through the holes in the strips, the machine comprising, in combination, means for supporting a said structure in assembled relation, means concurrently engaging opposite ends of a cross member for upsetting the tongues against the strips' to complete the assembly of the structure, means mounting the supporting means for movement thereof with the structure longitudinally of the strips to present the cross members successively to the upsetting means, and means for bracing the cross members against exure due to the load imposedby the upsetting means, the bracing means 9 10 being mounted for movement transversely relative to the References Cited in the file of this patent strips and cross members between an active position in UNITED ST ATES PATENTS which it is disposed to align the cross members with the upsetting means and a retracted position in which it is 11554385 Sull Sept' 22 1925 clear of the structure and supporting means to provide 5 1679988 Rf'bezzana Aug' 7 1928 clearance for moving the structure to present the succes 2,237121 Stm@ et al Apr' 1f 1941 sive cross members to the upsetting meansv