COLD WORKING TOOL FOR OPENINGS IN METAL PIECES

A segmented mandrel for cold working having two forward segments and two rear segments positioned between the two forward segments, when fitted together have an approximately circular outline. The two forward segments and the two rear segments are movable separately and together.

TECHNICAL FIELD

This invention relates generally to cold working tools and more specifically concerns a mandrel which does not include a sleeve to accomplish cold working.

BACKGROUND OF THE INVENTION

Cold working is widely used in the aircraft industry. Cold working creates compressive stress around the edges of a hole such as in an aircraft structural part, which tends to counteract the stress riser normally produced there, greatly increasing the number of load cycles for the aircraft structural part, which is desirable. Cold working is accomplished by pulling a tapered tool, such as a mandrel, through the hole, with the tool being larger than the hole. As the mandrel is pulled through the hole, it permanently increases the diameter of the hole. When the mandrel has pulled through, material apart from the hole attempts to return to its former position, which results in the material at the edge of the hole being in a high state of compression.

Generally, there are two methods which are currently used to accomplish cold working, one using a split sleeve mandrel the other a split mandrel. In split sleeve cold working, the largest diameter of a tapered mandrel is made slightly smaller than the hole to be cold worked so that it can easily pass through the hole. A thin split sleeve is slipped onto the mandrel before cold working the hole. The sleeve is placed on a smaller diameter of the tapered mandrel so that the wide part of the mandrel and the smaller part of the mandrel with the sleeve can pass through the hole. To expand the hole, the sleeve is held back and the mandrel is pulled back through the hole. The thickness of the sleeve creates the expansion needed to make the hole larger. However, since the sleeve has a split in it, allowing it to spring open and go over the larger diameter of the mandrel, a raised ridge is left inside the hole. Split sleeve also tends to over stress the material in vicinity of the split, which can result in cracks in alloys with lower ductility such as high strength aluminum alloys. Further, the sleeve can only be used once; it is also difficult to install on the mandrel and in some cases can be very difficult to remove from the hole, resulting in the cold working process being slow, expensive and virtually impossible to automate.

In split mandrel cold working, the mandrel has a hole drilled through its center, with four slots, leaving what appears to be a solid mandrel but with four fingers. The large diameter of the mandrel is larger than the hole to be cold worked; however, it is able to pass through the hole easily in one direction because the fingers can flex, which allows the mandrel to collapse and to pass through the hole in the metal member. When the mandrel is all the way through the hole, it springs back open. A pin is then moved into the hole in the center of the mandrel, preventing it from springing back when it is pulled back through the hole. The split mandrel does not require a sleeve, so it eliminates the disadvantages of that arrangement. However, the split mandrel has its own disadvantages by use of a center pin. Since the four fingers of the split mandrel do not contact each other during cold working, there is no “arch effect” between the fingers to react to external pressure, which can lead to very high stresses on the split mandrel parts, resulting in a short life for the split mandrel, and significantly limiting its usage in automatic cold work machines.

The specific structure of the present invention has a primary objective to overcome the disadvantages of the existing cold working tools.

SUMMARY OF THE INVENTION

Accordingly, the cold working tool comprises a segmented mandrel having four segments, two forward segments opposing each other and two rear segments opposing each other positioned between the two forward segments, wherein the two forward segments and the two rear segments when fitted together have an approximately circular outline, wherein each segment of the two forward segments and each segment of the two rear segments have a curved outer surface, a flat inner surface and connecting surfaces between the outer and inner surfaces, wherein the connecting surface of the two forward opposing segments are slightly relieved from a front end a distance toward the rear thereof to permit the two rear segments to press adjacent the two forward segments and permit the two rear segments and the forward two segments to pass through an opening in a metal piece and then to move outwardly so that the circumference of the segmented mandrel is larger than the opening in the metal piece, so that the opening in the metal piece is cold worked as the mandrel is pulled back through the opening.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS.1and2are exploded views of a preferred embodiment of the mandrel of the present invention referred to generally at10.FIG.3is a close-up view of a portion of the mandrel ofFIGS.1and2. The mandrel is referred to herein as a segmented mandrel. The mandrel10includes 4 separate segments14,16,18and20. Each segment is generally triangular in the preferred embodiment. The mandrel has a circular outer surface, with each segment in the preferred embodiment having an arc of approximately 90°. Referring toFIGS.2and3, each segment includes an arcuate outer surface22, shown for clarity on segment14, and an inner surface24, with the inner surface being generally flat, with a relatively small dimension of approximately 0.005″-0.015″, so that the four segments can fit together conveniently, leaving a very small opening between the respective inner surfaces, as shown inFIG.3. The outer surface and the inner surface of each segment are connected by two connecting surfaces26and27, shown inFIG.3for segment16.

For a selected distance rearwardly from a front end30toward the back of each of the forward segments14and16the connecting surfaces are slightly relieved, for example 0.003″-0.050″ for a distance of approximately 0.8 inches. This is an important aspect of the segmented mandrel as it allows the rear segments to move inwardly toward the forward segments, reducing the circumference of the segmented mandrel allowing the combination of the forward and rear segments to pass through an opening in the metal piece to be cold worked.

In operation, the segmented mandrel ofFIGS.1and2is positioned in a delivery assembly, shown in an embodiment inFIG.4as a driver29, with a trigger53for an operator. The driver29generally includes an arrangement capable in operation of moving the two forward mandrel segments and the two rear segments independently, as well as moving the four segments together, with a dual piston arrangement, as shown inFIGS.5and6.

The driver29operates an outer piston31, controlling the forward set of mandrel segments32, with an adaptor35shown inFIG.5, while the rear set of mandrel segments37are controlled by an inner piston38, as shown inFIG.6. The piston31, adaptor35and forward set of mandrel segments32are threaded together so that they move as a single solid piece by piston31. The rear mandrel segments are also threaded together so that they move as a single piece by piston38and plunger36. The forward mandrel segments are moveable independently of the rear mandrel segments, as well as moving together with the rear mandrel segments, to accomplish cold working. The pistons31and38are operated by air pressure and hydraulic pressure from an external source to move the forward mandrel segments through the metal piece by air pressure and then pull the mandrel back through the metal piece by hydraulic pressure.

Independently moving the forward mandrel segments, two in the preferred embodiment, and the rear mandrel segments, two in the preferred embodiment, at selected times is an important structural and functional feature of the segmented mandrel10of the present invention.

FIGS.7-10show the sequence of operations for the segmented mandrel of the present invention in combination with a driver40.FIG.7shows the combination of driver40and forward segments42about to begin the cold working process, with the forward segments42extended in a forward position by air pressure.FIG.8shows the driver40in a further step where the forward segments42of the mandrel have been inserted forwardly through a metal piece44, with operator action alone pushing forward segments through the hole, since air pressure has already extended the forward segments.

FIG.9shows a further step in which the rear mandrel segments46have been moved through the metal piece by air pressure with the operator pulling trigger45and are now positioned in a forward arrangement adjacent to the forward mandrel segments42, shown in combination. Again, as indicated above, the physical arrangement of the forward mandrel segments42with the connecting surfaces being slightly relieved, approximately 0.003″-0.050″, permits the rear mandrel segments46to be moved through the metal piece44by air pressure. When the rear mandrel segments have been moved through the metal piece and now form a complete segmented mandrel as shown inFIG.9, the segmented mandrel is far enough forward so that the rear mandrel segments expand outwardly, such that the complete segmented mandrel has a larger circumference than the opening in the metal piece44. In the next step, as shown inFIG.10, driver40has actuated the forward and rear mandrel segments42,46together, drawing them back though opening45in the metal piece by hydraulic pressure, performing the cold working function. In operation, when the driver40senses that the rear segments46are all the way through the metal piece, it sends a signal to the hydraulic pump to start pumping, 10,000 PSI is one embodiment. When the mandrel is pulled completely back through opening45in the metal piece, the pistons controlling the rear mandrel segments and the forward mandrel segments are activated to return the rear mandrel segments and the forward mandrel segments to their original position, as shown inFIG.7. These actions are controlled by the driver40with air pressure and a hydraulic pump for pulling action via trigger45.

FIGS.11through16show the sequence of operation of a segmented mandrel60in simplified form, for clarity, without the driver assembly/handle, but with individual steps to accomplish cold working of a hole in a metal piece.FIG.11shows the position of the mandrel60with forward segments62,64positioned in an opening66in a metal piece68with rear segments70,72approaching the opening. It should be understood that in the manufacture of aircraft, a very large number of openings in a given metal piece are pre-established, each of which can be cold worked using the cold working process (technique) of the present invention. As shown inFIGS.11and12, in operation, the two rear segments70and72in the segmented mandrel are positioned rearwardly, before entering the metal piece68. The two forward segments62,64can easily pass through opening66in metal piece68.FIG.12shows the forward segments completely through the metal piece, while the rear segments remain outside of the metal piece.

InFIG.13, the rear segments70and72have now been moved through the hole66by air pressure since the forward segments have room to move inwardly because of the relieved portions of the connecting surfaces of the forward segments62,64. Again, the relieved portions of the connecting surfaces of the forward segments permit sufficient space to permit the rear segments to pass through the opening.FIG.14shows the rear segments70,72having been moved through opening66by air pressure.FIG.15shows the rear segments70,72fully through the opening66in the metal piece68and aligned forwardly with the forward segments62,64. In this position, the front end of the segmented mandrel60has a diameter which is greater than the opening of the hole66in the metal piece68. Next, inFIG.16, the segmented mandrel has been pulled back through the opening66by hydraulic pressure, 10,000 PSI in the embodiment shown, creating the desired cold working results. The hole66is expanded without pressing any ridges into the hole, since the present invention does not require a sleeve. This invention thus overcomes the substantial disadvantages of the two presently used cold working systems.

Accordingly, a new cold working tool has been developed which overcomes the disadvantages of prior cold working tools, with a mandrel which is segmented into four parts with two opposing parts having relieved contact surfaces. As shown in the several figures, the movement of the segments of the mandrel is accomplished with piston action, air pressure and a hydraulic pump. Other arrangements can be used to accomplish movement of the forward and rear segments of the mandrel, individually and together.

It should be understood that while the preferred embodiment includes four segments, other numbers of segments can be used, including additional segments. The segments must be configured, however, to permit the rear segments to move inward to permit them to pass through the opening in the metal piece and then expand outwardly after they have moved forward through the opening to cold work the metal piece in combination with the forward segments by hydraulic or other high-pressure action.

Although a preferred embodiment of the invention has been disclosed for purposes of illustration, it should be understood that various changes, modifications and substitutions may be incorporated in the embodiment without departing from the spirit of the invention, which is defined by the claims which follow.