US2413518A - Metal forming machine - Google Patents

Description

1946- e. D. RECHTON ETAL 2,413,518

I METAL FORMING MACHINE Filed June 18, 1945 2 Sheets-Sheet l 680 296 Rec/ 0 Jack Wat/0n ATTORNEV 1, 1945- G. DfREcHToN E'I ALY 2,413,518

METAL FORMING MACHINE Filed June 18, 1943 2 Sheets-Sheet 2 Geo/ye 0 Rec/van m UN Mm m H K C w A7 TORNEY Patented Dec. 31 1946 George D. Rechton and Angeles, Calif., assignors to Company, Inc., Santa Monica,

Jack H. Watson, Los Douglas Aircraft Calif.

Application June 18, 1943, Serial No. 491,410

14 Claims. 1

This invention relates to a metal forming machine of the type in which two vertically moving cooperating axially alined dies are brought into simultaneous contact with a work article disposed between them and particularly to a machine of this character for changing the shape of an article, such as a dimpling machine for annularly flanging a sheeted article around a perforation for receiving a rivet or other fastener having a conical manufactured head. The invention as to some of its features is applicable to any machine for forming a work article between two reciprocatively movable dies arranged to formingly Contact opposite sides of the work article.

In dimpling and similar forming operations upon a, work article, particularly operations involving bending, a sheet of an aluminum or magnesium alloy such as is used in aircraft manufacture, where a lightweight material is desired, experience shows that if the forming is efiected by a single pressural contact, whether of a squeeze or percussion character, of sufficient force to secure the desired result, fracture weakness develops in the bend portion of the work article, and that if the same forming is eiiected by a number of light blows, no fracture weakness results. This may probably be explained in part by the fact that in the interval between two light blows the metal molecules move into new relative positions in which they are partially relieved of the strain put upon them by the earlier blow, whereas if the complete forming is eifected by one pressure action of the dies, and particularly if that one action is a percussive one, because of the resulting molecular movement along the initial slip planes which have no opportunity for equalizing, the stress is so great as to produce a movement within these planes of such magnitude that a stressed molecular condition within the slip planes is created in which the ultimate stress point of the metal. is exceeded. It is also believed that each light blow work-hardens the material, which is another way of saying that each light blow raises the ultimate stress point of the material, With the result that when the final blow is delivered, forming to the desired extent has been accomplished without the metal passing the ultimate stress point, beyond which point fracture soon occurs. It is a familiar fact that ii a stress be suddenly applied. to object,'as for instance a tensile stress of great magnitude for a small fractional part of a second to a rod of metal, the rod may be permanently elongated to a given length and then at that length be pulled apart. application of a lesser stress over several seconds or repeated separate applications of a lesser stress, will permanently elongate the rod to the same length without rupturing it. lhe particles of metal in the latter case creep slowly into their new positions without breakage of their cohesive bond. The same principle applies to compressive and bending stresses. Especially is this true of repeated separate applications or a lighter stress, if the applications are of relatively long time duration, such as result from percussion blows by one die upon a work article supported by a cushioned bucking die.

It is accordingly an object of this invention to provide a forming machine (and especially a machine for forming metal sheets such as a dimpling machine) of improved characteristics, in which the forming operation is effected by a succession of automatically repeated, relatively light percussive pressures, or shots of the forming dies.

It, is another object of the invention to provide in such a machine means for automatically determining the number of the relatively light percussive shots.

It is another object of the invention to provide in such a machine means for automatically timing the period for effecting the succession of shots.

It is another object of the invention to provide a stationary gun for delivering the succession of shots, having the structural advantages of its stationary character, and a movable lower die, and especially a pneumatically movable lower die, for effecting the initial pressural engagement of the dies and for initiating the automatic cycle of shots of the stationary gun.

It is another object of the invention to reduce the tendency of the sheet to warp during the dimpling operation by so'constructing the machine that the sheet to be dimpled is at the same level at the end as at the beginning of the dimpling operation and remains virtually stationary during the operation.

It is another object to provide pneumatic means for elevating the lower die into initial pressure contact with the upper die of a stationary gun and for providing a cushioned support for the lower die when subjected to the forming shots of the upper die.

It is another object of the invention to provide a forming machine of the percussion type, either single or multiple shot, in which the forming shot is delivered against an air cushioned bucking die so as to lengthen the duration of On the other hand, a sustained 3' i azure period of the shot and inhibit the c pment of fracture weakness in the formed t is another object of the invention to pro vide a multiple shot machine of the character described having pneumatically moved dies in which electrical means are used to manually initiate the pneumatic movement of the lower die, to automatically initiate the actuation of the gun upon pressural engagement of the dies, and to automatically terminate the actuation of the gun.

It is another object to provide a machine to accomplish the last mentioned purposes excepting for an automatic instead of manual initiation of the pneumatic movement of the lower die, this automatic initiation being responsive to placement of the metal sheet to be dimpled in position upon the lower die.

It is another object of the invention to provide a machine of the character described having pneumatically moved dies in which electrical means are used to manually initiate the pneumatic movement of the lower die in which the pneumatic pressure thus developed is used to initiate actuation of the gun and electrical means are used to automatically terminate actuation of the gun.

In the drawings, which are for illustrative purposes only,

Figure 1 is a perspective view of a dimplin machine embodying the invention.

Figure 2 is an elevational view, partly in section, of a portion of the machine showing the upper and lower dies and the mounting means of the lower die.

Figures 3 to 6 inclusive are diagrammatic views showing the upper and lower dies and a metal sheet to be dimpled in several relative positions at progressive stages of the dimpling operation Figure '7 is a schematic View and wiring diagram of the machine.

Figure 8 is a schematic view and wiring diagram of a machine embodying the invention in another form.

7 The machine shown in Figure 1 has a frame comprising a base ill, a pedestal l2, an upper arm !4 and a lower arm it, these arms defining a work receiving throat 53. At the outer end of the arm i4 is a gun housing 29 and at the outer end of the arm I is a lower die support 22. A female die 24, mounted for limited vertical reciprocative travel in the lower end of a pneumatic percussive gun 38 mounted in the housing 2Q cooperates with a male die 28 mounted on the lower die support 22 to dimple a sheet of metal placed horizontally between them and extending into the throat I 8.

The pneumatic percussion gun 30 is stationarily mounted within the housing 20. The reciprocating percussive piston of this gun strikes the upper die 24 at the lower end of its stroke, imparting a percussive blow thereto. The die 24 is spring held in an uppermost normal position as shown in Figure 1. The die is shown in this same normal position in the other views of the drawings. The only movement of this die relative to the machine occurs when it moves downward a short distance against its spring support in the gun 36 under a blow of the gun piston and is immediately thereafter returned to its normal position in a manner presently to be explained.

The lower die support 22 is shown in Figure 2. It comprises a cylinder 32, in which is reciprocatively'r'nounted a piston 34, faced at its upper end 1 matically elevated, bringing the with a cap 36, the piston and cap serving as a holder for the die 28. A flexible cup 38 secured to the lower end of the piston 34 forms an air seal against the inner wall of the cylinder 32 whereby compressed air admitted through port 49 in the Wall 42 of the arm [6 into the cylinder chamber 44, may elevate the piston 34. Upon venting the air from the chamber 44, a coiled spring 46 returns the piston to its lowermostposition in which a stop 49 carried by the piston bottoms on Wall 42. This spring is seated between a ring 48 secured to the lower horizontal face of the piston 34 and the head of a bolt 59 which is mounted on the wall 42 and projects upwardly into a recess 52 in the piston 34.

When the piston is in this position, a sheet of metal 54 to be dimpled is placed with a previously drilled perforation fitting over a central prong 56 of the die 28. The piston 34 is then pneusheet 54 into contact with the annular nether surface 58 of the die 24. Air pressure then builds up in the chamber 44 to a value sufficient to initiate actuation of the gun 34 through a pneumatic connection to be later described. The gun is of the wellknown automatically repeating type and its piston is caused to deliver a succession of blows to the upper die 24. In a manner to be hereinafter explained, the gun ceases operation at the end of a predetermined time interval. Air pressure is then automatically lowered in the cylinder chamber 44, permitting the die 28 to drop to its normal position, whereupon the sheet 54 with the completed dimple formed therein is lifted from the prong 56 and removed horizontally from the throat of the machine.

The operative movements of this cycle have some novel characteristics. The gun is stationary. The die 24 moves downward with each blow bending the sheet somewhat and is then retracted by the pressure of the lower die to its initial position preparatory to receiving the neXt blow. After each blow of the gun piston, the compressed air in the chamber 44 causes the lower die to move upward with the upper die to the extent permitted by the partially formed dimple, the lower die thus moving upward by increments from its initial metal sheet clamping position shown in Figure 3 to its final dimple forming position shown in Figure 6, after which it falls back to the position shown in Figure 2.

In the dimpllng machines as heretofore constructed the sheet to be dimpled initially rests on the top of the cone of the lower die and during the dimpling operation moves downwardly from this initial upper level a distance equal to the entire depth of the dimple to be formed. This repeated substantial movement of the metal sheet with successive dimpling operations results in setting up stresses in the sheet which under some conditions cause warping.

In a machine of this invention the metal sheet to be dimpled, after it has been elevated into initial contact with the upper die, is relatively stationary, its only movement being a slight up and down movement with each blow of the gun which is but a small fractional part of the depth of the dimple to be formed. Thus the tendency of the sheet to warp is decreased.

The die 28 is supported on an air cushion which allows the die to momentarily drop under the impact of each blow. The time of transfer of the energy of the blow to the sheet metal is thereby lengthened, giving the slip planes of the metal time to creep to their new positions with less breakage of the molecular cohesive bond.

Figures 3 to 6 show how the flange of the dimple is formed with a three shot machine, illustrating the difierent shapes assumed by, the metal. Fracture at the annular bend 60 (Figure 6) is less apt to develop when the flange is thus formed by a succession of bending blows delivered against a cushioned bucking die instead of by one bending blow delivered against a rigidly supported die, for the reason stated in the introductory paragraphs hereof. In practice more. than three shots will be found productive of better results. The machine may be adjusted to secure any desired number of shots for each dimpling operation.

To reduce the time of the complete cycle and thereby better the efficiency of the machine, the travel of the die holder piston 34 from its inactive position of Figure 2 to the position in which as shown in Figure 3 the die 23 is held in pressural engagement with the upper die through the work sheet 54 should be short. The die stem 52, h W ever, must be long in order to firmly hold the die during the operation of the machine. According- 1y, a removable skirted cap 35 fits over the die holder piston 34, and the stem 02 fits snugly both within a cylindrical opening 54 in the cap 36 and a cylindrical pocket 68 in the upper end of the piston 34. The length of the stem 52 being greater than the travel of the die 23, if the 33 and piston 34 were one integral piece, it would be impossible to remove the die from the die holder. But since the cap 38 is removable and the depth of the cap 36 is such that the portion of the stem 2 62 in the pocket 06 is shorter than the travel of the die 28, the die may be removed by lifting the cap and die until the stem 62 clears the upper horizontal face of the piston 34 by then moving the assembled cap and die laterally clear of the piston, after which the die may be removed from the cap and replaced by another die, which may be installed in the holder by reversing the steps of removal.

Figure '7 shows schematically the control sys tern by which the machine is operated. The piston 34 is elevated by compressed air conducted thereto in a conduit til which i supplied from a suitable source through a conduit ":2 having a normally closed, solenoid opened valve I2; The conduit 68 is vented to lower the piston 34 through an exhaust conduit I4 controlled by a normally open, solenoid closed valve I8.

The solenoid of valve E0 is energized by an electric circuit comprising conductors 84 and 85, switch 88 (which is normally spring biased to contact the terminal of conductor 92), conductor as to the solenoid, conductor 32 from the solenoid and conductor 94. Conductors 84 and 94 are connected to power leads I8 by a line switch 82. The solenoid of valve I2 is energized by an electric circuit comprising conductor 84, conductor 85, switch 88 when moved by solenoid 80 to the right to contact the terminal of conductor 06, conductor 86 to the solenoid of valve I2, conductor 98 from this solenoid, and conductor 94.

The solenoid 80 is energized by a circuit comprising conductor 84, conductor I58, normally open foot switch I 84 when the latter is held down in closed position by the foot of the operator, conductor H0 to the solenoid 80, conductor IE2 from solenoid 88 and conductor 94.

W en the foot switch 194 is closed, ener'gizing solenoid 84, va ve it closes and valve #2 opens, admitting compressed air into chamber 44 to elevate the die 28 to raise the metal sheet into contact with die 24. Air pressure then builds up in the chamber 44 and conduit 68 to a value sufficient to close a normally open, pressure operated electric switch I20. When this switch closes, current flows through a circuit energizing the solehold of a normally spring-closed, solenoid-opened air valve I36 in an air pressure line 538 leading to the gun 30, causing the gun to apply a succession of automatically repeated percussive blows to the upper die 24. This circuit comprises conductor I22, conductor I25, switch 620, conductor I28, conductor I30 to the solenoid of air valve I36 conductor I34 leading from the solenoid, normaliy spring closed switch I32, and conductor I24.

The gun continues to operate until a solenoid I52 opens the switch I32. The solenoid I52 is energized by an electric circuit comprising conductor I22, conductor I26, pressure switch I20, conductor I28, conductor I44 to the anodes of a rectifier tube I42, thence to the cathodes of the tube I42 to an electronic timing circuit as shown. to conductor I24. The particular arrangement of the electronic timing circuit of an electronic timer MI is no part of this invention. Suffice it to say that current flows through conductor I46, solenoid I52 to the anode plate of the trigger tube I50 and thence to the cathode of this tube and conductor I24, after a lapse of time in which the voltage inthe grid of the trigger tube I50 is built up over conductor I 41 and the variable resistance I48. This resistance is regulated by a knob I54 (see Fig. l) to Vary the time interval which elapses between the opening and closing of air valve I30. The heating elements of the rectifier tube I42 are energized at all times when the line switch 82 is closed through a circuit comprising conductor I22, conductor I40 and conductor I24. The solenoid I55 of a normally closed "clean-up switch I5'I holds the switch I5'I open when the pressure switch I20 is closed, allowing the timer to function. When switch I20 opens in response to a reversal of valves I2 and I3 efiected by opening foot switch I04, then switch I5'I closes and the voltage of the grid of trigger tube I50 drops to zero. The machine is now reconditioned for the next dimpling operation.

An alternative embodiment of the machine is schematically shown in Figure 8. In this embodiment, the gun and cylinder chamber 44 are subject to the same degree of air pressure. When the lower die is raised into pressural contact with the upper die through the work article and the air pressure thereafter rises to a predetermined value, the gun is actuated to deliver a succession of blows. The air pressure is brought to bear on both cylinder chamber and gun by closing the foot switch and is cut off by the electronic timer. In this view the designating numbers are the same as those of Figure 7 on those parts which are common to the two machines, additional numbers being used to designate parts of the modified machine which are not present in the machine of Figure 7.

A branch air line I58 is Td into air line I38. Line I58 leads to the cylinder chamber 44. The solenoid of air valve I36 is closed by a circuit comprising conductor 84, conductor 85. switch 88 (when moved to the right by solenoid in contact with the terminal of conductor I58), conductor I14 to the solenoid of air valve I36, conductor I34 from this solenoid, switch I32, conductor I30 and cond v 84. Solenoid 80 pulls switch 88 to the right rpm dead contact I66 to the terminal of Contact I58 when energized by 7 an electric circuit comprising conductor 94, conductor IIZ tosolenoid 80, conductor I52 from solenoid 89, foot switch I 04, conductor I64 and conductor 84.

Solenoid I52 is energized to break the circuit operating the solenoid of air valve I36 by an electric circuit comprising conductor I44 leading from conductor I58 to rectifier tube I42 and the other elements of the electronic timer MI and conductors its and 94 leading from the timer. The heating elements of the rectifier tube are energized by connections to conductors I I and I12 as shown. 1

In the operation of the machine, shown in Figure 7, the line switch 82 is closed, and the sheet 54 to be dimpled placed in position on the lower die. Valve I2 is opened and valve 16 closed by closing the foot switch IM, causing the lower die 28 to be elevated until the sheet 56 is pressurally held between the dies. Pressure is built up to operate valve I20 to apply air pressure to the gun 33 which then delivers percussive blows to the upper die until cut off by the electronic timer. The foot switch I04 is then opened.

The time interval of the cycle of each single shot is constant at any given line pressure. Consequently, regulation of the resistance I48 determines both the duration of the time period of actuation of the gun and the number of shots. The line pressure is indicated on the pressure gauge I 56 (Figure 1).

In the machine of Figure 8, closing the foot switch Hit operates the air valve I36 to first elevate the lower die and then actuate the gun, the gun ceasing operation when the air valve I33 is closed by the electronic timer.

What is claimed is:

1. In a metal forming machine, the combination of an upper automatic-cycle pneumatically operated hammer gun having a stationary cylinder and a piston hammer slidably engageable therewith and arranged to deliver percussive blows; a limitedly vertically reciprocatable first die arranged to receive the blows of said hammer and to have contact engagement with a work piece when in its uppermost position; a stationary lower die support; a die holder reciprocatively movable on said support; a second die on said die holder; means for elevating said die holder relative to said support to a position such as to press a work piece between said dies; means responsive. upon said elevation, to the pressure between the dies for initiating the automatic cycle of the hammer gun to cause the gun hammer to strike the first die.

2. In a metal forming machine, the combination of an upper automatic-cycle pneumatically operated hammer gun having a stationary cylinder and a piston hammer slidably engageable therewith and arranged to deliver percussive blows; a limitedly vertically reciprocatable first die arranged to receive the blows of said hammer and to have contact engagement with a work piece when in its uppermost position; a lower stationary pneumatic cylinder; a piston for said cylinder; a second die on said piston; means for admitting compressed air to said cylinder to elevats said piston to a position. such as to press a work piece between said dies; and means responsive to a predetermined air pressure in said cylinder for initiating theautomatic cycle of the gun, causing the gun hammer to strike the first die.

3. The combination defined in claim 2 and in addition thereto; means for venting said cylinder;

8 and a spring arranged to lower said piston upon the venting of said cylinder.

4. In a metal forming machine, the combination of: first and second, axially aligned, axially relatively movable die holders; means limiting retractive axial movement of the die holders relative to each other in excess of a predetermined spacing; first and second dies forv said first and second die holders respectively, said second die having a mounting shank and said second die holder being recessed to receive said shank; and a facing block on the die receiving end of said second:die holder, said block being held in axial alignment with said second die holder and having a through opening to receive said shank, said shank being longer than said predetermined spacing and the linear difierence between the length of said shank and the thickness of said block being shorter than said predetermined spacing.

5. In a forming machine, the combination of upper and lower cooperating forming dies, said dies being mounted for relative movement on said machine; means for bringing the dies into simultaneous pressural contact with a work article to be formedymeans responsive to a predetermined pressural contact for applying a succession of automatically repeated relatively light percussion blows to the upper die during said pressural contact; means for bucking the lower die during said application; and means made operative simultaneously with said pressure-responsive means for automatically terminating said succession of blows at the completion of a predetermined num ber thereof.

6. In a forming machine, the combination of: upper and lower cooperating forming dies, said dies being mounted for relative movement on said machine; means for bringing the dies into simultaneous pressural contact with a work article tobe formed; means responsive to a predetermined pressural contact for applying a succession of automatically repeated relatively light percussion blows to the upper die during said 45 pressural contact; means for bucking the lower die during said application; and time controlled means made operative simultaneously with said pressure-responsive means for terminating said succession of blows after a predetermined elapsed 50 period of time. 7. The combination defined in claim 5 in Which said means for applying contact consists of means for applying fluid pressure of progressively increasing value as a bucking support to said sec- 55 end die and the operation of said means for applying a succession of automatically repeated blows is automatically initiated by said fluid pressure upon said fluid pressure reaching a predetermined value. 1

8. Ina forming machine, the combination of upper and lower cooperating forming dies; a stationary pneumatic gun for the upper die constructed to deliver asuccession of automatically repeated relatively light percussion blows to the 65 upper die; a pneumatic cylinder-piston means movably supportin the lower die; means for supplying air under pressure to said cylinder-piston means; venting means for said cylinder-piston means; means for alternatively connecting 70 said air supplying and venting means to the cylinder-piston means; a valved conduit for supply ing air under pressure to the gun; an electric circuit for opening'said valve, energized-in response to a predetermined pressure in said cylinder pis- 75 ton means; and a simultaneously energized electronic timer for de-energizing said circuit to close said valve.

9. The combination defined in claim 8 in which said means for alternatively connecting said air supplying and venting means to the cylinder piston means comprises an electrically opened, normally closed inlet valve; an electrically opened, normally closed exhaust valve; a switch, spring biased to close an electric circuit to open the exhaust valve and electromagnetically operated to close an electric circuit to open the inlet valve; and a manually closed circuit to energize said electromagnet.

10. In a forming machine, the combination of:

upper and lower cooperating forming dies; a stationary pneumatic gun for the upper die constructed to deliver a succession of automatically repeated relatively light percussion blows to the upper die; a pneumatic cylinder-piston means movably supporting the lower die; a common conduit system co-mmunicatively connecting said gun and cylinder piston means to each other; a normally closed valved conduit connecting said conduit system with a source of air pressure; a solenoid for opening the valve of said valved conduit; a manually operated switch for energizing the circuit of said solenoid; an electronic timer simultaneously energized by said manually operated switch; a normally closed switch in said solenoid energizing circuit; and a solenoid controlled by said timer for opening said last mentioned switch, said gun being actuated by a higher pneumatic pressure than that required to cause said cylinder piston to move said lower die.

11. In a metal forming machine, the combination of: an upper automatic-cycle pneumatically operated hammer gun having a stationary cylinder and a piston hammer slidably engageable therewith and arranged to deliver percussive blows; a limited vertically reciprocatable first die arranged to receive the blows of said hammer and resiliently held to a lowermost position and to have contact engagement with a work piece When in any position of said first die; a stationary lower die support; a die holder reciprocatively movable on said support; a second die on said die holder; means for elevating said die holder relative to said support to a position such as to press a work piece between said dies; and means responsive, upon said elevation, to the pressure between the dies for initiating the automatic cycle of the hammer gun to cause the gun hammer to strike the first die.

12. In a metal forming machine, the combination of: an upper automatic-cycle pneumatically operated hammer gun having a stationary cylinder and a piston hammer slidably engageable therewith and arranged to deliver percussive blows; a limited vertically reciprocatable first dimpling die arranged to receive the blows of said hammer and resiliently held to a lowermost position and to have contact engagement with a work piece when in any position of said first dimpling die; a stationary lower die support; a die holder reciprocatively movable on said support; a second dimpling die cooperatively shaped and related to said first dimpling die and mounted on said die holder; means for elevating said die holder relative to said support to a position such as to press a work piece between said dies; and means responsive, upon said elevation, to the pressure between the dies for initiating the automatic cycle of the hammer gun to cause the gun hammer to strike the first dimpling die.

13. In a dimpling machine the combination of 2 an upper dimpling die; a lower dimpling die; means limiting the upward movement of the upper dimpling die; means for pressurally urging the lower die against the work sheet and the work sheet against the upper die and the upper die against said limiting means; and means for applying a succession of relatively light percussive blows to the upper die against the action of said pressural urging means of such a force relative to said pressural action that only a fractional portion of the dimple is formed with each blow, the upper die and work sheet at each blow moving first downwardly a fraction only of the depth of the dimple cone of the upper die and then upwardly to said limiting means under the pressural action of the urging means againstthe lower die, said urging means moving said lower die upwardly to a new position after each blow applied to said upper die to hold the work piece against the upper die during the dimpling operation.

14. In a dimpling machine, the combination of: first and second cooperating dies; means including means for applying fiuid pressure of progressively increasing value against said second die to move the same toward said first die and bringing the dies into simultaneous pressural contact with a sheet of metal to be dimp-led; and means made operative by said fluid pressure upon said fluid pressure reaching a predetermined value for applying a succession of automatically repeated relatively light percussion blows to said first die during said pressural contact, the fluid pressure applying means bucking the second die during the application of said blows.

GEO. D. RECI-ITON. JACK H. WATSON.

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