Punch assembly with quick attach punch point and stripper plate removably secure thereon

A punch assembly for a turret punch press having a two piece reciprocally movable punch member that has a punch point insert removably attached to a punch driver that allows replacement of the punch point insert without the need to extract the punch member from its punch guide. A locking assembly having four vertical guideways containing slider strips for coupling the punch point insert to the punch driver ensures precision registration of the punch point insert with its driver.

BACKGROUND OF THE INVENTION

I. Field of the Invention

This invention relates generally to high speed metal punching equipment suited for installation in a turret-style punch press and more particularly to the design of a punch assembly used in such equipment that allows for quick removal of a worn punch insert from the punch guide for refurbishment and return or replacement.

II. Discussion of the Prior Art

To provide increased mean-time-to-repair of punch assemblies used in high-speed CNC controlled turret punch presses, it has proved expedient to employ a high-grade high speed steel insert such as American National Standards Institute M2 steel punch point insert affixed to the end of a lower cost steel punch driver to reduce cost of the punch press assembly. Notwithstanding the use of such a high-grade and relatively expensive punch point insert, after a period of use in punching holes through sheet steel and other metals, it becomes necessary to replace the punch point insert with a new or resharpened one. To reduce the downtime of the turret punch press for such punch point insert replacement, it is desirable that an operator be able to perform this task in a minimum amount of time and most preferably without the need for special hand tools.

In prior art punch assemblies having a two-piece driver/insert combination, it has generally been necessary to first remove the punch driver and insert from the upper end of the punch guide and subsequently remove the punch insert from the punch driver so that the punch point insert can be replaced with a new or refurbished unit. The present invention makes possible reduced manufacturing costs, such as machining expenses e.g. through the use of stamped components while at the same time simplifying punch point replacement by providing a way to releasably clamp the stripper member to the end of the punch guide and the punch point insert to the punch driver. The clamping mechanism employed is most preferably actuated by hand and in most cases without the need for any special tools or without the need to remove the punch driver and insert from the punch guide.

SUMMARY OF THE INVENTION

The present invention provides a punch assembly for a turret punch press comprising an outer, generally cylindrical punch guide having a cylindrical bore extending longitudinally therethrough from an upper end to a lower end. Contained within the bore of the guide or housing is a punch driver that is reciprocally movable within the bore. Releasably affixed to the lower end of the punch driver, preferably by one or more flexible stamping elements, is a punch insert having a punch point of a predetermined shape at a lower end thereof.

Affixed to the upper end of the punch driver is a canister assembly which includes a cylindrical, tubular housing containing a compression spring for normally biasing the punch driver to a retracted disposition within the bore.

Formed inward from a peripheral surface of the generally cylindrical punch driver and extending longitudinally are a plurality of guideways in which are fitted a corresponding plurality of locking sliders which can be stampings shaped to engage the punch insert and lock same to the punch driver when the locking sliders are in a first disposition within the guideways and to disengage from the punch insert when in a second disposition within the guideways. Cooperating with the plurality of locking sliders is a lock collar that is concentrically disposed on the punch driver and rotatable through a predetermined arc between a locked disposition and an unlocked disposition relative to the locking sliders.

The stripper member for the punch assembly, which itself can be a metal stamping of substantially uniform thickness throughout, is releasably clamped to the punch guide at a lower end thereof most preferably by leaf spring elements, and it includes an aperture conforming in shape to the punch point of the punch insert allowing the punch point to extend through the aperture in the stripper member upon application of a force to the canister assembly that exceeds the return force offered by the compression spring. The clamping structure holding the stripper member to the bottom of the punch press guide is also manually actuatable without the need for any special tools to unclamp and reclamp the stripper member from and onto the punch guide.

DESCRIPTION OF THE PREFERRED EMBODIMENT

This description of the preferred embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. In the description, relative terms such as “lower”, “upper”, “horizontal”, “vertical”, “above”, “below”, “up”, “down”, “top” and “bottom” as well as derivatives thereof (e.g., “horizontally”, “downwardly”, “upwardly”, etc.) should be construed to refer to the orientation as then described or as shown in the drawings under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. Terms such as “connected”, “connecting”, “attached”, “attaching”, “join” and “joining” are used interchangeably and refer to one structure or surface being secured to another structure or surface or integrally fabricated in one piece, unless expressively described otherwise.

As shown inFIG. 1, the punch assembly is indicated generally by numeral10. It comprises an outer, generally cylindrical punch guide12which, as shown in the cross-sectional views ofFIGS. 8-10, includes a cylindrical bore14that extends longitudinally therethrough from the guide's upper end16toward, but short of its lower end18. A counter bore19of a slightly greater diameter than that of bore14extends inward from the lower end18as can be seen inFIG. 9.

Releasably secured to the lower end18of the punch guide12is a stripper member20in the form of a generally circular plate which can be a metal stamping of substantially uniform thickness throughout that requires minimal machining and has a central aperture22conforming in shape to that of a punch point24, as can be best seen in the enlarged cross-sectional view ofFIG. 10.

As seen inFIG. 2, the stripper member20has an annular sidewall provided with a plurality of regularly spaced upwardly extending tabs26formed around the periphery thereof that are adapted to fit into a corresponding pattern of recesses formed in the bottom end18of the guide12and to be engaged by a pair of leaf spring retainer clips28which can be metal stampings that fit into recesses30that are machined into the sidewall of the guide12. Only one such recess is visible in the view ofFIG. 1, the other being on a diametrically opposed location as depicted in the cross-sectional view ofFIG. 8. The configuration of the leaf spring retainer clip is such that depression of a pad portion thereof, identified by numeral32inFIG. 1, further into the recess30will cause the lower end thereof that engages the tabs26to deflect radially outward so as to no longer engage the tabs and allows the stripper member20to be removed from the bottom end18of the punch guide12.

Referring again to the cross-sectional views ofFIGS. 8-10, there is disposed within the longitudinal bore14and counter bore19of the punch guide a two-piece, reciprocally movable combination of a punch driver34in its cooperative relationship with the punch point insert24. The punch driver34is preferably formed from relatively low-cost steel while the punch point insert24, preferably fabricated from high grade steel such as powdered metal or tungsten carbide that is pressed, formed or machined into a desired shape. While a tungsten carbide insert increases the cost, because it is approximately three times stiffer than steel and is much denser than steel or titanium, it makes for a longer wearing tool that is highly abrasion resistant and capable of withstanding higher temperatures than standard high speed steel tools. It is also well recognized that tungsten carbide is capable of maintaining a sharp cutting edge in a way that is superior to other tools.

The shape configuration of the punch point insert can be discerned from the views ofFIGS. 7A-7D. Here, the punch point insert is illustrated as a rectangular edge and will produce a rectangular slug upon being made to descend through a sheet metal workpiece. Of course, other shapes are achievable by modifying the shape of the downwardly depending portion38of the punch point insert24.

InFIGS. 7B and 7C, the punch point insert is shown to have a generally rectangular head portion40, but with radiused corners, and projecting upwardly therefrom is a somewhat diamond-shaped protuberance42that is designed to fit within a recess44formed in the bottom surface of the punch driver as best seen in the enlarged cross-sectional view ofFIG. 10. If desired, the protuberance can be on the punch driver and the recess in the insert. To maintain a desired angular orientation between the punch point insert24and the punch driver34, a longitudinally extending groove46is formed inward from the peripheral surface of the punch driver as seen inFIG. 3, and fitted into this groove is a leaf spring alignment strap48having a notch50that is arranged to straddle the tapered protuberance42(FIG. 7C) and apply a centrally directed bending force for yieldably engaging punch point ramp surfaces42aand42bwhich are slanted relative to one another so as to maintain the desired exact rotative registration of the insert about a vertical axis with no clearance unlike an ordinary pin or key which require clearance.

With continued reference to the exploded view ofFIG. 3, the punch driver34has opposed flat abutment surfaces52and54machined therein on which a canister assembly, indicated generally by numeral56, is adapted to be secured. With reference toFIGS. 2-4, the canister assembly is seen to comprise a cylindrical, tubular housing58having an inside diameter that is sized to fit over the outer diameter of a relatively stiff compression spring60. Fitted atop the cylindrical housing58is a punch head62that has a pair of spaced-apart, downwardly depending legs64,66where the legs terminate in transversely extending feet68as shown. The canister assembly further includes a spring retainer plate70consisting of a circular plate having a central aperture72. Fitted through the aperture72is a pair of couplers74and76that are generally U-shaped, with the legs of the “U” extending upwardly as seen inFIG. 4and also having feet that are designed to engage the feet68on the legs64and66that are integrally formed with and project downward from the punch head62. The spring retainer plate70is designed to rest upon the upper end of the punch guide12, as seen inFIG. 1. Couplers74and76slide in and out radially in retainer plate70aperture to allow for assembly with punch head62. When so positioned, the flattened portions52and54of the punch driver34above the shoulder78fit between the couplers74and76thereby locking them radially outward to maintain engagement with punch head62feet68. A flathead cap screw80fits through an aperture in the punch head62and is screwed into a threaded bore82formed inward from the top surface of the punch driver34.

From what is described, it can be recognized that a mechanical or electro mechanical ram forming part of the turret punch imparts a downward force on the punch head62, it will drive the punch driver34downward through the aperture in the spring retainer plate70of the canister by a distance, D, shown inFIG. 4and which is sufficient to penetrate through a sheet metal workpiece positioned adjacent the stripper member20. When this driving force is removed, the return spring60acting between the spring retainer plate70and the punch head62will function to move the punch driver34in the upwards direction such that the punch point insert will no longer extend through the aperture22in the stripper member20.

Without limitation, the return spring60follows Hook's Law for springs.

Next to be described is the structure for releasably securing the punch point insert24to the punch point driver34and, in this regard, reference will be made primarily toFIGS. 5,6and8-10of the drawings.

Referring now to the enlarged partial view ofFIG. 5and cross-sectional view ofFIG. 5A, there are formed inward from the cylindrical surface of the punch driver34four guideways, as at84, milled or ground at 90° radial spacings thereabout. These four grooved guideways are adapted to receive four vertical slider strips which can be metal stampings that require little machining, two of which are visible in the view ofFIG. 6and are identified by numerals86. The exposed surface thereof as seen inFIG. 6is slightly rounded so as to conform to the cylindrical profile of the punch driver34and includes a flat facing zone88that extends about half of the distance across the width dimension of the vertical slider strip and a raised zone90extending across the remaining half of the strip's width dimension. Formed in the raised zone90is a notched-out portion92.FIG. 6Ais a rear perspective view of the vertical slider strip86and it is configured to exhibit a notched-out region94adapted to fit about the head portion40of the punch point insert24in the manner shown inFIG. 6.

Each of the slider strips86has associated with it a cylindrical pin as at96. The inner ends of these pins are adapted to contact either the flat portion88of the slider strip or the notched-out portion92thereof. As seen inFIGS. 5 and 5A, the pins96fit into apertures formed radially through a toroidal lock collar98that is supported by an annular, C-shaped retaining ring100designed to reside in the annular groove102formed in the punch driver34as seen inFIG. 6. The retaining ring100prevents the lock collar98from moving longitudinally downward along the punch driver.

From the drawings ofFIGS. 5,5A and6, it can be appreciated that when the locking collar is rotated about a vertical axis, the pins96may be repositioned so as to either reside on the flat surface88or have its end disposed in the notched-out portion92of the vertical slider strip. With the pins96residing on the flat portion88, as the punch point insert24is manually pulled downward, the vertical slide strip is able to move with it to the point where the notched-out region94on the back surface of the strip86no longer locks to the insert and it can be pulled free of the punch point driver34. However, when the locking collar is rotated manually, e.g. through a port99in the guide12(FIG. 1) so as to reside in the notched-out portion92, the vertical slider strip is unable to be displaced within its slot84and the notched-out portion94continues to lock the punch point insert24to the bottom surface of the driver34.

Hidden from view inFIG. 5by a centering collar104, but visible in the partial view ofFIG. 11, is a cone collar106that is shown by itself inFIG. 12. As seen inFIGS. 11 and 12, the cone collar106is machined so as to have an upper ring portion108with four downwardly projecting and inwardly tapered teeth110and when assembled onto the punch driver34in surrounding relationship with respect to the four slider strips86, the teeth are seen to fall between adjacent ones of the strips86and rest upon the inside conical surface of the centering collar104. The cone collar106and the centering collar104work together to create a high precision centering feature. The centering collar104has a precision cylindrical fit with respect to the cone collar106and the cone collar itself has a precision cylindrical fit with the punch driver34which, in turn, has a precision cylindrical fit with the ID of the bore14of the punch guide12. In addition, the slide strips86are forced outward on the bottom end due to the ramping action caused by the sliders86notched-out portion94against angled ramps #95(FIG. 10) on insert24as collar98is rotated such that pins96enter area92against ramping edge #97(FIG. 6) on sliders86to securely hold punch insert and sliders in the up position. To provide extremely precise centering, the outward force of the ramps is further advantaged, by pressing outwardly against the centering collar104. The circular area on the perimeter of the centering collar not being pushed against by the sliders then react equally and opposite thus sway inwardly against the cone collar. This provides a precise centering mechanism not achievable with normal bore and shaft connections.

In that the stripper20is stamped with curled-up fingers26for positioning into the punch guide, it is designed such that the operator can remove the stripper before the punch insert is removed, thus obviating the need for the operator to pull the canister assembly56off the punch guide as required by known prior art designs just to change the punch insert.