METHOD AND APPARATUS FOR HOLE COLDWORKING

Abstract: A method and apparatus for coldworking of holes using a split mandrel. The apparatus uses a mandrel having radially directed slots to permit contraction of its outer diameter as it is fitted within a hole. The mandrel contains a pilot inside the mandrel. After placing the mandrel and pilot within a hole to be coldworked, the pilot is pushed into the mandrel expanding the mandrel. The pilot and mandrel are then withdrawn through the hole, thereby coldworking the hole.

Description: The invention relates to an apparatus for coldworking holes. This process is especially necessary in the manufacture of airplane wings and body structures. In the coldworking process, a mandrel of a diameter larger than a hole is pulled or pushed through the hole to expand the hole radially, displacing the material immediately surrounding the hole beyond the elastic limit of the material. Parts having holes in them which are processed in this manner will exhibit improved fatigue life. SU-A-192 159 shows and describes an apparatus for expanding tubes comprising housing means housing a mandrel capable of extending through an opening in a nose piece and having a tapered portion with a portion of larger diameter for effecting the tube expansion. The mandrel has four radially directed slots in the tapered portion defining segments of the mandrel to permit changing of the outer diameter of the mandrel, and an axially directed slot through said mandrel in which a pilot is at least partly disposed. To the pilot pushing means are connected for pushing the pilot in the mandrel in the direction to the tapered portion to a position in which an end of the pilot is expanding engagement in the mandrel for effecting the tube expansion. To the mandrel retracting means are connected for pulling the mandrel with the pilot in the expanding engagement therein, in axial direction inwardly relative to the housing means, to an end position in which the portion of larger diameter is fully withdrawn through an opening in a nose piece of the housing means. The end portion of the pilot is tapered, so that the pushing means can push the pilot in the mandrel for expanding same, while the portion of larger diameter of the mandrel is engaged in a tube. According to the invention an apparatus of this kind is provided having a split mandrel which can be expanded by a pilot, for coldworking holes in workpieces. The apparatus according to the invention is defined in claim 1. In this apparatus the loads on the mandrel during the coldworking process are such that a long tool life results. Because the pilot has a constant cross-section in the direction of length, the diameter of the expanded working portion of the mandrel is independent of the axial position of the pilot, so that in each action the outside diameter of the expanded split mandrel, can be maintained with the accuracy required for coldworking holes with high quality. US-A-2 446 713 shows an apparatus having a split mandrel with a larger diameter portion which can be expanded by a pilot having a constant cross-section. This apparatus however is a hand riveter in which the larger diameter portion of the mandrel cannot be withdrawn into the nose piece, and therefore cannot be withdrawn through a hole in a workpiece for coldworking same. Further advantageous embodiments of the present invention appear from the subclaims. Further objects and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings. In the drawings: Figs. 1 - 4 show sectional views depicting the relative positions of the tool during coldworking operations. Fig. 5 shows an alternative nose cap on the tool for use with countersunk holes. Figure 6 shows an alternative embodiment of the invention in cross section. Figure 7 is an enlarged view of the split mandrel nose, showing the offset split embodiment. Figure 8 is a sectional view of the offset split mandrel viewed from the left through line 8-8 of Figure 7. Figure 9 is a schematic of the circuit used to control the apparatus during operation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Figure 1, a split mandrel home expanding tool assembly generally designated as 10 is shown. A workpiece 12 having a hole 14 to be coldworked is shown to the left of the assembly 10. Hole 14 is of such a diameter that pulling the split mandrel assembly through it will cause coldworking. The tool assembly 10 contains a trigger handle, a puller gun assembly, a pilot assembly, and a split mandrel assembly, generally designated as 16, 18, 20, and 22, respectively. The trigger handle 16 consists of handle 24 and trigger button 26. The puller gun assembly 18 consists of housing 28, piston 30, piston rod 31, end cap 32, and nose cap 34. Piston 30 is disposed in cavity 36 of housing 28. A small cavity 33 communicates directly with the end of piston 30 closer to the workpiece during operation. Cavity 33 contains a hydraulic fluid. Piston rod 31 is connected to piston 30. End cap 32 is threaded over the end of housing 28. Nose cap 34 is similarly threaded over the other end of housing 28, closer to the workpiece 12. Figure 5 shows a special nose cap 34 with a tapered portion 35 to fit a countersunk hole. For normal holes, however, the tapered portion 35 would be omitted. Split mandrel assembly 22 consists of coupling 38 and split mandrel 40. Split mandrel 40 has a barrel portion 42 and a tip portion 44. The tip portion 44 if viewed in cross section contains radial slots defining segments of mandrel 40. The splitting of mandrel 40 into segments allows contraction of its outside diameter to occur when the mandrel 40 is placed in hole 14 to be coldworked as shown in Figure 2. Split mandrel 40 also has an axial slot 46 throughout its length. Mandrel 40 is threaded to coupling 38 which in turn is threaded to piston rod 31 of puller gun assembly 18. Pilot assembly 20 contains a pilot 48, a piston rod 50 and piston 52. The pilot 48 is threaded into piston rod 50 which is connected to piston 52. Pilot 48 is disposed in slot 46 of split mandrel 40, and piston rod 50 is contained within piston 30 and cavity 36 of housing 28. Piston 52 fits within cavity 53 located within end cap 32 when the tool is at rest. The end of pilot 48 is capable of fully engaging within the tip portion 44 of mandrel 40 when piston 52 is moved fully toward the workpiece 12. Referring now to Figures 7 and 8, an embodiment of split mandrel assembly 22 is shown wherein mandrel 40 has four segments designated as segments 54, 56, 58 and 60 with an offset split 62 between each segment. Figure shows the offset 64 of offset split 62. The offset split 62 is accomplished by sweeping a split cut through an angle 65 (Figure 8) about the longitudinal axis of mandrel 40. It should be noted that offset 64 of offset split 62 is located in a recessed diameter portion 66 of mandrel 40. Recessed diameter portion 66 of mandrel 40 is located between coldworking diameter portions 68 and 70 of mandrel 40. Locating offset 64 of offset split 62 in recessed diameter portion 66 of mandrel 40 between coldworking diameter portions 68 and 70 provides a means of pulling two coldworking diameter portions through one hole in succession with each portion having a different radial location for its split. The result of this configuration will be that the cold worked hole 14 will have a clean bore with no ridges or extraneous marks from offset 64 or offset split 62. The present invention may also be practiced without an offset split 62. The mandrel 40, in this case, would still be divided preferably into four segments similar to segments 54, 56, 58 and 60 in Figure 7, but it would have no offset. As this type of mandrel is retracted through hole 14 in workpiece 12, small ridges would occur at four radial locations. These ridges could be reamed after coldworking. Also, it should be noted that the mandrel 40 can have as few as three segments and still work. Four segments would be used in a preferred embodiment. The tool assembly 10 is powered by the system shown schematically in Figure 9. Referring to Figure 9, a source of air pressure 72 is connected to cavity 36 resulting in its pressurization at all times. Typically, cavity 36 would be pressurized at 100 p.s.i. The source of air pressure 72 is also connected to cavity 53 through air logic valve 74. When the tool is at rest, air logic valve 74 to cavity 53 is closed, resulting in cavity 53 being exhausted. Due to the pressure on the end of piston 52 communicating with cavity 36, piston 52 remains in cavity 53 when the tool is at rest. The source of air pressure 72 is further connected to a hydraulic power supply generally designated as 76. A separate air valve 78 is connected to the air pressure source 72 which in turn is connected to an air motor 80 for driving a hydraulic pump 82 connected to a source or tank of hydraulic fluid (not shown). The pump 82 is connected through a hydraulic valve 84 to cavity 33 which would contain hydraulic fluid. The source of air pressure 72, therefore, if activated, is capable of opening the air valve 78 which then starts air motor 80 of hydraulic pump 82. Air pressure source 72 can also open hydraulic valve 84 which now will result in pressurization of the fluid in cavity 33 and movement of piston 30 during operation of the tool. A relief valve 88 is provided to prevent overpressurization of the hydraulic fluid. To provide a time delay between the opening of air valve 74 and air valve 78 a timer 86 is connected to air pressure source 72 and valves 74 and 78. The timer 86 merely prevents full flow of air in one direction through valve 87 toward the hydraulic valve 84 and power supply 76 when trigger 26 is depressed. The air must flow through valve 89 of timer 86 and the air pressure to valve 78 and valve 84 takes some time to increase and activate these valves. When trigger 26 is released air is exhausted through valve 87 at full flow with no delay. A time delay between the opening of valves 74 and 78 will insure that piston 52 has come to rest before piston 30 begins to travel. Initiation of the tool assembly's operation is caused by depressing trigger 26 which is connected to the air pressure source 72. To operate the tool, an operator would insert mandrel 40 into hole 14 of workpiece 12 until the nose cap 34 touches the workpiece 12 as shown in Figures 2 and 3. Trigger 26 would then be depressed, thereby opening valve 74 and causing air pressure of approximately 100 p.s.i. to fill cavity 53. Piston 52 will begin to move toward the workpiece 12 until it contacts piston 30 of puller gun assembly 18. This operational position is shown in Figure 3. To avoid clearance problems, pilot 48 would not protrude from the tip portion 44 of mandrel 40. Depressing trigger button 26 simultaneously activates air pressure from source 72 toward the hydraulic power supply 76. This air pressure will cause the air valve 78 that starts the air motor 80 to open, energizing the hydraulic pump 82 and shifting the hydraulic valve 84 open allowing high pressure hydraulic fluid to pressurize cavity 33 causing piston 30 with the mandrel 40 slightly expanded by pilot 48 to move in unison (see Figure 4) until the mandrel is fully retracted from the hole 14, leaving the hole coldworked. As shown in Figure 4, pilot 48 and mandrel 40 will retract through hole 14 together, being maintained in axial tension and effect coldworking of hole 14. This pulling places pilot 48 and mandrel 40 in tension in such a way that each are under less stress with respect to prior art concepts and tool longevity is assured. As mentioned previously, one of the prior art concepts pulled the pilot which pushed the mandrel through the hole and caused tool failure problems. A time delay between the engagement of the pilot 48 and retraction of the pilot 48 and mandrel 40 is preferable to obviate the problem of mandrel 40 retracting prior to the full engagement of the pilot 48. Release of trigger button 26 will: a) close valve 74 thereby exhausting cavity 53; b) shift the air supply valve 78 of the motor 80 to a shut off position; and c) shift the hydraulic valve 84 to an exhaust position. The piston 30 and mandrel 40 now return to the position shown in Figure 1, retaining the pilot assembly 22 in place due to the pressurization of cavity 36 from air pressure source 72. ALTERNATIVE EMBODIMENT Referring to Figure 6, an alternative embodiment of the present invention is shown. Figure 6 shows a coldworking tool assembly generally designated as 90 having a mandrel 92 and a pilot 94 contained in an axial slot 96 within the mandrel 92 similar to the pilot and mandrel of Figure 2. The mandrel 92 is a split mandrel and is threaded to a coupling 98. A nose cap 100 is threaded to coupling 98. Coupling 98 is also threaded to receive a piston rod 102 on the side opposite mandrel 92. A slot 104 is drilled in the piston rod 102 to accept a spring 106. Spring 106 contacts at one end the pilot 94. The coupling 98 is slotted in the axial direction to allow pin 108 to move freely. Pin 108 is connected to pilot 94. A slide 110 is provided which surrounds coupling 98 and accepts pin 108. Slide 110, therefore, can be moved manually over the coupling 98. The piston rod 102 is connected to a standard puller gun (not shown). A housing 112 fits around a tube 114 which receives coupling 98. In operation, the tool shown in Figure 6 works as follows. In the rest position spring 106 retains the end of the pilot 94 within the tip of the mandrel 92. Prior to the insertion of the mandrel into the hole to be coldworked, slide 108 is pulled away from the hole, thereby compressing the spring 106 and removing the end of the pilot 94 from the tip of mandrel 92. The mandrel 92 is then inserted in the hole to be coldworked and the slide 110 released. The force of spring 106 will cause the end of the pilot 94 to once again engage in the tip of mandrel 92. The mandrel 92 containing the pilot 94 can then be retracted by the puller gun (not shown), causing the hole to be coldworked. It should be noted that pilot 94 can also be moved automatically instead of manually by extending the pilot 94 through the housing 112 to an air logic controlled "piggy back" cylinder (not shown).

Claims: Workpiece hole, coldworking apparatus (10) comprising housing means (28), having a nose piece (34) capable of being placed in contact with a work piece having a hole to be coldworked, said housing means (28) housing a mandrel (40) capable of extending through an opening in said nose piece (34) and having a straight (42) portion and a tapered portion (44), said tapered portion extending from said straight portion and having a portion of larger diameter than said straight portion for effecting the coldworking, said mandrel having at least three radially directed slots in the tapered portion, defining segments of the mandrel to permit changing of the outer diameter of the mandrel, and an axially directed slot (46) through said mandrel (40), a pilot (48) having a constant cross-section in its direction of length, and being at least partly disposed within the axially directed slot of said mandrel, pushing means (50,52) connected to said pilot (48) for pushing said pilot in said mandrel (40) in the direction from said straight portion to said tapered portion from a first position wherein said pilot is not in expanding engagement with said tapered portion to a second position in which an end of the pilot extends fully through the larger diameter portion of the tapered portion of the mandrel, in fully expanding engagement therewith for effecting the coldworking and retracting means (30) connected to said mandrel for pulling said mandrel (40) with said pilot (48) in said second position, in axial direction inwardly relative to the housing means, to an end position in which the portion of larger diameter is fully withdrawn through said opening in said nose piece. The apparatus of claim 1, whereby the pushing means includes: a) a first piston disposed within said housing means and connected to said pilot; b) a source of air pressure located outside of said hosuing means and capable of communicating with one end of said first piston; and c) activating means for allowing commincation between said air pressure source and said first piston causing said first pistion to move within said housing means toward the tip of the mandrel and engage the end of said pilot fully in the tip of the mandrel. The apparatus of claim 1, whereby said retracting means includes: a) a second pistion disposed in said housing means and connected to said mandrel. b) hydraulic fluid disposed in said housing means and communicating with one end of said second pistion; c) a source of hydraulic pressure located outside of said housing means and capable of pressurizing said hydraulic fluid; and d) activating means for initiating pressurization of said hydraulic fluid causing said second piston to move and thereby pull said mandrel containing said pilot inwardly relative to the housing means. The apparatus of claim 1 whereby said pushing means and said retracting means comprises: a) a first piston disposed within said housing means and connected to said pilot; b) a cavity within said housing means for receiving said first piston when the apparatus is at rest; c) a source of air pressure located outside of said housing means and communicating with the end of said first piston closer to said mandrel causing said first piston to remain in said cavity when the apparatus is at rest, said source of air pressure capable of communicating with the end of said first piston farther away from said mandrel; d) a second piston disposed in said housing means and connected to said mandrel; e) hydraulic fluid disposed in said housing means and communicating with the end of said second piston closer to the tip of said mandrel; f) a hydraulic pump located outside of said housing means and capable of pressuring said hydraulic fluid, said hydraulic pump connected to and activated by said source of air pressure; g) activation means connected to said source of air pressure for allowing communication between said air pressure source and the end of said first piston farther away from said mandrel, causing said first piston to move within said housing means and engage the end of said pilot in the tip of said mandrel, said activation means further initiating pressurization of said hydraulic fluid by said hydraulic pump causing said second piston to move and thereby pull said mandrel containing said pilot inwardly relative to the housing means. The apparatus of claim 4, whereby said activation means includes: a) a first valve located between said source of air pressure and the end of said first piston farther away from said mandrel; opening of said first valve initiating movement of said first piston within said housing means; b) a second valve located between said hydraulic pump and the end of said second piston closer to the tip of said mandrel; the opening of said second valve required to initiate movement of siad second piston within said housing means; and c) delay means connected to said first and second valves for producing a discreet time interval between the opening of said first valve and said second valve. The apparatus of claim 5, whereby it further comprises. a) a third valve located between said source of air pressure and said hydraulic pump, said third valve initiating said hydraulic pump when open; b) delay means connected to said first, second and third valves for producing a discreet interval between the opening of said first valve and said second and third valves; and c) trigger means located within said housing means, said trigger means when depressed activating the opening of said first, second and third valves and said delay means and when release activating the closing of said first, second and third valves. The apparatus according to one of claims 1-6, whereby stopping means are disposed within said housing means for preventing said pilot from protruding from said mandrel. The apparatus of claim 7, whereby said stopping means consists of said second piston. The apparatus according to one of the preceding claims whereby: a) spring means are disposed in said housing and connected to saidpilot for maintaining the end of said pilot in the tip of said mandrel, while the apparatus is at rest and b) slide means are attached to said pilot and said housing whereby the end of said pilot may be withdrawn manually from the tip of said spring means. The apparatus according to one of claims 1-9, whereby said mandrel contains four radially directed slots defining four segments of the mandrel. The apparatus according to one of claims 1-10, whereby said mandrel contains a recess portion with an offset split.

Inventors: HOGENHOUT, FRANCISCUS
Applicants: WEST COAST INDUSTRIES
Application year: 1984
Main classification: B23P9
IPC codes: B23P9