The invention relates to metal cold-forming and, in particular, machine arrangements and methods for achieving a high reduction in area of a workpiece.
Cold-forming machines are typically used to mass produce shaped parts starting with a cutoff of round metal wire. Blanks or workpieces are sheared from a length of wire after straightening from a coil, positioned in successive stationary dies, and struck by reciprocating tools to change their shape into intermediate and, eventually, finished products. These forming operations can include upsetting where the diameter of the wire blank is increased or extrusion where the diameter is reduced or both upsetting and extrusion. Usually, extrusions are accomplished in a stationary die rather than a reciprocating tool. This technique can be problematic where the workpiece is long, i.e. being several times its diameter in length. In these circumstances, the workpiece can tend to stick in the die. The knockout pin used to eject the workpiece from the die, as a result of the area reduction, is relatively small in cross-section. The greater the length of the workpiece compared to its cross-section, the more acute is the problem of ejecting the workpiece from the die. The knockout pin besides being reduced in diameter must be increased in length in relation to the workpiece length and becomes prone to breakage.
Among the challenges to be met has been the economical, high volume production of pointed parts, especially long pointed parts, where the reduction in area approaches at least 95% and where secondary operations off the cold former are to be avoided.
The invention involves cold-forming methods and machinery for the economical production of metal parts characterized by a high reduction in area and long length or other substantial change in form while avoiding secondary machining operations. The invention is disclosed in the context of a multi-die progressive former, generally known in the art, and a unique arrangement of dies and tools and related instrumentalities. In preferred embodiments, a long, high carbon steel part is pointed with a reduction in area of about 95% in a net shape or near net shape process. At an intermediate station in the disclosed embodiments, the tooling is arranged to perform a novel closed cavity consequent hydrostatic extrusion process. The tooling and method achieves, in high carbon steels for example, area reductions to levels previously generally considered impractical or unobtainable. Use of the hydrostatic extrusion station can be followed by successive forming stations that together can approach or reach a total of 95% reduction in area. This degree of area reduction effectively results in a pointed workpiece. Alternatively, a workpiece can be pointed following the hydrostatic extrusion stage by pulling the workpiece to neck down the area to be pointed and thereafter further extruding it to a final point. Still another pointing method that can follow the unique hydrostatic extrusion step is a pinch pointing process. In this method, once the workpiece is preliminarily reduced in area by the hydrostatic extrusion, it is pinch formed with a flash that can be sheared off or can be broached off by further disclosed techniques.
Referring to
Ahead of the cutoff station 13 is an auxiliary wire drawer, through which a straightened wire from a coil is fed and drawn to a precise diameter for feeding into the forming machine 10. A phosphate and bonderlube coating is drawn into the outside surface of the wire during the drawing process. At a plane indicated at 14, the cutoff station 13 shears a precise length and, therefore, volume of drawn wire for forming a part or workpiece 15. The sheared end surfaces of the workpiece 15 will be irregular and without the coating due to the shearing operation. Before the slide 12 completes a forming blow, each workpiece 15 has been transferred to the next succeeding workstation. Forward motion of the slide causes a tool at a workstation to insert the workpiece into a die.
In the first workstation WS1, the workpiece 15 is inserted into a die 18 and pressed on both ends by a die kickout pin 19 and tool pin 20. The terms die and tool as used herein will often mean an assembly of a case and an insert in the case. The die and tool cases and inserts are typically cylindrical. Die and tool cavities and kickout pins are, likewise, typically cylindrical or, at least, round in cross-section. The ends of the die and tool pins 19, 20 that contact the workpiece 15 may be flat but preferably have a 3° point to displace material from the center of the workpiece ends to remove the surface variations developed at the sheared faces.
At the second workstation WS2, the forming blow forms a radius on the circumference of the end of the workpiece 15 which end, ultimately, will be greatly reduced in area. This radius squeezes the raw uncoated end of the blank or workpiece 15 so that a round and coated surface will be provided for first contact with an extrusion tool in the subsequent workstation WS3. A small corner radius is formed on the same workpiece end to remove any sharp edges or flash burrs. The operation at this second workstation WS2 is a form of trapped extrusion where the workpiece 15 is totally enclosed in the die 21 before the workpiece is deformed in the work stroke.
In the disclosed embodiments of the invention, the point end of the workpiece 15 is formed in the tool; this technique of “reverse forming” is typically not done in cold-forming processes. Pointing the workpiece 15 while it is partially in the tool and partially in the die requires precise alignment and control between the tool and die. Any significant misalignment would result in non-uniformity of the workpiece, with scraping or metal shaving as it enters a misaligned tool.
The reverse forming process begins with insertion of the workpiece 15 into the die 21, stopping on a kickout pin 22 that is held stationary during the forming workstroke. As the heading slide 12 advances, a tool 23 contacts the die 21 to create a closed cavity. The die 21 is arranged to slide in a die holder 24. In one example, a cluster of five nitrogen gas springs 26 (one of which is shown in
At the third workstation WS3, a reverse forming process, again, begins with a tool 33 inserting the workpiece 15 into a die 31, the workpiece stopping on a kickout pin 32 that is held stationary during the forming workstroke. As the heading slide 12 further advances, the tool 33 contacts the die 31 to create a closed cavity for forming the part. The die 31 slides in a holder 34, being spring biased towards the heading slide 12 and pushed back with the advance of the tool 33 as the material is forced into the tool cavity to trap extrude the required shape defined by the tool. A tangential slot 35 on the die, working with a pin 43 serves to limit axial motion of the die 31 on the die breast to the short distance required for the trap extrusion at this station. By way of example, C1055 steel has been successfully extruded to an 80% reduction in area in this single workstation WS3. Normally, reverse forming by extruding into a tool has previously been limited to approximately 55% reduction in area. Extrusions greater than 55% reduction in area typically result in a workpiece beginning to upset into flash between the tool and die.
The disclosed reverse forming process allows parts with long shank lengths (e.g. lengths of about 3 or more diameters) and smaller point diameters to be successfully formed. The majority of the blank or workpiece 15 remains inside the die 31 with only a short length of the workpiece inside the tool 33. This allows ejection of the workpiece 15 from the die 31 to be proportionately robust, with a full workpiece diameter kickout pin 32. A small diameter tool kickout pin 37 in the tool 33 requires very little force and short kickout distance to eject the workpiece from the tool. The longer length of the workpiece 15 that is inside the die 31 will tend to make the workpiece stay in the die and, therefore, avoid the need for high kickout forces from the tool pin 37. By comparison, conventional trap extrusion forming inside the die would require a proportionately small diameter kickout pin equal to the extruded reduced diameter, with a kickout stroke longer than the overall part length. Such kickout pins are subject to high breakage rates due to length to diameter ratio, and the larger workpiece diameter being kicked out by a small diameter kickout pin.
The process performed at the third workstation WS3, in accordance with the invention, involves an adaptation of hydrostatic extrusion. To accomplish this “consequent hydrostatic extrusion” process, the interface between the die 31 and tool 33 is maintained at a contact pressure adequate to contain the hydrostatic medium which in this case, is liquid cold-forming extrusion/cooling oil. This can be achieved by arranging a tool insert 36 to protrude 0.05 mm to concentrate the closing force on the small diameter face of the insert against the opposing face of a die insert 38. The diameter of the tool and die insert end faces are substantially less than the diameters of the end profiles of the tool and die cases. The workpiece 15 is coated by flooding with the extrusion oil from a dispenser nozzle 41 (
It has been found that the tail portion of the workpiece 15 also swells up tight to the die bore to restrict oil loss. When the oil seal is properly maintained, the workpieces 15 extrudes to the required shape without swelling up to the tool and die insert diameters, except for the tail portion of the workpiece near the kickout pin 32. When workpieces are hydrostatically extruding properly as a consequence of the extrusion/cooling oil being confined in the cavity mutually formed in the die insert 38 and tool insert 36, the end of the workpiece remains slightly rounded from underfill, without flashing around the die kickout pin 32. Additionally, the part of the workpiece 15 received in the tool 33 remains about 0.04 mm smaller than the tool and die diameter due to the enclosed hydrostatic oil pressure (with the workpiece having its major diameter nominally about 3.12 mm along its major length). The oil cushion trapped around the workpiece 15 keeps the majority of its body from contacting the cavity surfaces of the tool and die inserts 36, 38, thereby reducing the friction between these forming inserts and the workpiece. It has been found that the workpieces will not extrude properly if the oil application is insufficient or if the tool or die faces, indicated at 39 and 40, are marred so as to prevent a tight oil seal at their interface. These imperfect conditions result in the blank not extruding, but swelling up tight against the tool and die insert surfaces, and flashing around the die kickout pin 32. The added forming pressure may also cause failure of the die kickout pin 32.
The extrusion lengths of the workpieces 15 at the third workstation WS3 are held consistent by stopping the extrusion against the tool knockout pin 37. The end shape of the parts extruded with the disclosed process are unique with a uniform dome shaped end surface. Traditional high reduction trap extrusions have an irregular hollow or cupped end surface.
At the subsequent workstation WS4, a second extrusion is performed to further reduce the end diameter formed in the preceding die 31. At this fourth station WS4, a 35% reduction in area open extrusion of the workpiece 15 into a tool 56 is accomplished. Generally, an open extrusion involves a lighter forming load whereby the body of the workpiece 15 may be unsupported in the open space between a tool 56 and an opposing die 57 without upsetting.
The workpiece 15 is transferred to the fifth workstation WS5 for finish forming. A tool 61 forms an upset head on the workpiece 15 while further reducing the point end diameter. The point end area at this station is reduced by approximately 45%. The 45% reduction is the normal maximum for point forming while upsetting. The die 62 is of the sliding type biased forwardly by a high pressure lever 46 like that shown in
Referring now to
The first three workstations are arranged essentially the same as those described above in connection with the cold-forming machine 10 shown in previous
At the fourth workstation WS4, the end of the stem 71 is upset into a bulb-shape 78 for gripping in the subsequent pulling station WS5. The forming operation at the fourth station WS4 uses a sliding tool 73 with tool segments or inserts 74 for forming a small bulb-shaped upset on the reduced stem 71. The tool segments 74 can be four in number and are disposed at the front of a tool case 76. The segments 74 are allowed to move within the tool case 76 to close together during the upsetting motion and to open to allow clearance for the upset bulb 78 to be ejected from the tool cavity mutually formed by the segments. A plurality of nitrogen gas springs 77 (one such spring is shown in
At the fifth workstation WS5, the upset bulb 78 is pulled apart from the remainder of the workpiece to thereby reduce or neck down the area of the stem beneath the bulb 78. At this workstation WS5, a front pusher sleeve 81 (
At the sixth workstation WS6, a tool 87 forms an upset head on the workpiece 72 while further reducing the point end diameter.
Referring now to
The plane of the drawings at the fifth workstation WS5 in
The process depicted in
While the invention has been shown and described with respect to particular embodiments thereof, this is for the purpose of illustration rather than limitation, and other variations and modifications of the specific embodiments herein shown and described will be apparent to those skilled in the art all within the intended spirit and scope of the invention. Accordingly, the patent is not to be limited in scope and effect to the specific embodiments herein shown and described nor in any other way that is inconsistent with the extent to which the progress in the art has been advanced by the invention.