US2983176A - Stripper construction for a perforator - Google Patents

Description

y 1961 P. H. TAYLOR 2,983,176

STRIPPER CONSTRUCTION FOR A PERFORATOR Filed Aug. 21. 1956 H l 82 I 1 INVENTOR. 82a WW RwZ/f. 72 20? 65 69 (21403625. Fiat United States Patent STRIPPER CONSTRUCTION FOR A PERFORATOR Paul H. Taylor, North Tonawanda, N.Y., assignor to Tayco Developments, Inc., North Tonawanda, N.Y., a corporation of New York Filed Aug. 21, 1956, Ser. No. 605,245

1 Claim. (Cl. 83-138) This invention relates to self-contained punch and stripper combinations such as may be used in conventional dies for individual 0 frame self-contained sub press dies for perforating sheet metal or other materials.

Self-contained perforating units have been universally adopted by industry for punching holes in sheet metal or the like, particularly where it is desired to punch a number of holes simultaneously. Individual perforating devices are ordinarily secured to a templet or mounted adjustably on bed rails in a press so that the perforators can be located in a pattern corresponding to the pattern of holes which is to be punched and so that they can be actuated simultaneously by the ram of the press.

Perforating units of the type described ordinarily include both a punch and an aligned die together with work stripping means. Common devices of this type are disclosed in Wales Patent 1,955,866 and Wales Patent 2,364,- 011. In these devices the downward Working stroke of the press actuates a punch and at the same time stores energy in a wound steel Wire spring which in turn actuates a stripper unit to strip the workpiece from the punch when the press ram is raised.

Due to the large force required to Withdraw punch members from thick metal stock, the capacity of perforating units is limited by the capacity of the stripping device. When a large stripping spring is utilized, the overall width of the perforating'unit is increased, which in turn limits the proximity of adjacent holes which can be punched in a single perforating operation. Consequently, such units are frequently utilized with undersized, overloaded stripping springs With the result that early failure occurs. When adequate size coil stripping springs are utilized, they are of such a size that the perforating units cannot be used with standard presses having limited shut heights. Consequently, in order to punch holes in material of more than Me of an inch in thickness, it has been necessary to utilize special types of punch presses, and even with such machines a practical limit of inch work piece thickness is encountered. As a result of these difliculties, two or three operations have been necessary to punch hole patterns with relatively close centers.

To overcome the deficiencies of perforating units utilizing mechanical stripping springs, efiorts have been made to utilize compressible liquid or compressible solid devices to eflect the stripping. Units of this type are disclosed in Taylor Patent 2,732,898 and Taylor Patent 2,740,475. With perforating units of this type utilizing compressible material stripping devices, it is possible to achieve greater stripping forces and to perforate material up to of an inch in thickness with the same hole proximity as achieved with prior mechanical stripping spring devices. However, even these perforating devices have not been practical for most applications because of high cost and because of inherent difficulties encountered by reason of use of conventional piston arrangements in the stripping means.

In addition to the basic difiiculties encountered in prior perforating devices, several more specific difliculties have arisen. Ordinarily self-contained perforators are reciprocably retained in closely fitted vertical apertures in the upper frame members of C frame units in the manner shown in Wales Patent 2,364,011 and Taylor Patent 2,740,475. The perforator holder thickness adds to the overall width of the unit, thereby increasing the distance between hole centers which can be simultaneously punched. Ordinarily the holders are made of cast steel or a similar expensive, high strength material in order that the holder wall surrounding the punch will have the required high strength. Such constructions have precluded the use of thinner, lighter sections and lighter, lower strength materials such as aluminum or fiber glass compositions. Furthermore, the holder aperture construction is not adapted to interchangeability With different punch assemblies so that Where different sized punches are required, diiferent holders must be provided.

Where apertured holders are used with punch assemblies having compressible material stripping devices, another serious difliculty is encountered. In order that the punch be properly aligned 'm'th the die, close tolerance fit within the holder aperture is necessary. Since the casing of a liquid spring or the like ordinarily expands one thousandth of an inch (.001") or more in diameter during a compression stroke, such expansion is sufiicient to cause seizing of the perforator assembly with the '0 frame holder aperture. Consequently, prior compressible ma terial stripper devices have necessarily utilized relatively heavy casing wall thicknesses in order to prevent measurable expansion, thus eliminating the advantageous utilization of wall resiliency to increase the spring efliciency. In addition, an increase in casing wall thickness further increases the distance between hole centers which can be simultaneously punched.

To eliminate the various basic difiiculties in prior perforating devices in which compressible material stripping means are utilized, the present invention provides a punch assembly containing a solid central punch member and a tubular stripper which also acts as a liquid spring piston. A number of advantages flow from this type of construction. Among these advantages are simplification of the construction and operation of the punch assembly, reduction of the cost of manufacture, reduction in the compressive load on the punch shank, provision of additional support for the punch end portion of the punch member, and simplification of the punch member itself.

All of the specific difliculties encountered in utilizing apertured holders are elirninated by the present invention which provides a close tolerance dovetail connection between the punch assembly casing and the upper arm of the '6 frame. Thus, there is no holder thickness to be contended with. Furthermore, the dovetail arrangement permits expansion of the spring chamber wall since it does not surround the Wall but is connected to a relatively small portion of the periphery of the spring chamber. In addition, C frame members of lighter construc tion, formed of less expensive and more easily fabricated materials, can be produced.

Where self-contained perforator units are directly connected with die sets, the present invention provides very much simplified means of connecting the ends of the punch assembly and the die block with mating sockets in the die sets.

It is an important object of the present invention to provide an improved self-contained punch and stripper combination for use in perforating materials.

Another object of the invention is to provide an improved perforating unit embodying a liquid spring stripping means.

A further object of the invention is to provide a perforating unit capable of punching larger holes on closer centers in thicker metal work pieces.

A still further object of the invention is to' provide a perforating unit with a liquid spring stripper in which the stripper also acts as the piston for the liquid spring.

Still another object of the present invention is to provide a liquid spring utilizing a tubular piston acting about a stem member whereby the stem member can be utilized as a perforating punch and the tubular piston can be utilized as a work piece stripper.

An additional object of the invention is to provide improved means for connecting a perforator unit punch assembly to a frame holder, whereby the holder can be at least as narrow as the punch assembly, thus permitting simultaneous formation of larger diameter holes on closer centers.

A related object is to provide improved means for connecting a self-contained punch and liquid spring stripper to a holder whereby expansion of the punch-stripper casing wall does not interfere with reciprocation of the punchstripper relative to the holder.

Another related object is to provide improved means for connecting a self-contained perforator to a holder to permit interchangeability of difierent sizes of perforators.

A kindred object is to provide improved perforator assembly connecting means whereby a single C frame can be utilized with varying perforator sizes to permit punching a variety of hole sizes.

Other objects, features and advantages will be apparent from the following detailed description taken in conjunction with the accompanying drawings, in which.

The drawing is an enlarged fragmentary sectional view, partly in elevation. The invention is designed particularly for heavy duty punching such as a diameter hole through a A thick plate.

The construction as shown in the drawing is particularly well suited for punching and stripping metal thicknesses up to or for large diameter holes. It consists of a punch and die assemblage 80 comprising a punch stripper assembly '81 and a die 82 having pilot pins 81a and 82a, respectively, for engaging templates 84 and which will operatethe stripper piston 90 upon removal of the punch 105' from the die 82. The advantages of a stepped tubular piston in a liquid spring are set forth in my co-pending application Serial No. 481,658, filed January 13, 1955, now Patent No. 2,909,368, dated October 20, 1959.

' One of the problems associated with liquid spring stripper punch combinations is the variation in stripping loads relative to the grind life on the punch. As the punch is 84 of a die set which are held in accurate alignment through the leader pins (not shown) of a die set 85. Cap screws 88 and 89 engage pins 81a and 82a, respectively, to hold the parts on the templates.

The die member 82 has 21 dia aperture 82b and a slug chute 82c. Punch assemblage 81 consists of a casing 86 having stepped bores 87 and 88 for receiving a stepped tubular piston 99 having an internal bore 92 in a stepped tubular section 91. The bore 88 is of smaller diameter and consequently receives the smaller diameter portion of the stepped tubular piston, as shown. A central punch piston closure member 109 has a sturdy punch support body 101 terminating in enlarged heads 102 and 163 at its opposite ends and having the general appearance of a spool used for holding thread. The enlarged head 163 has a bore 194 for receiving a punch insert 195 as will be noted in the drawing, the minimum diameter of the punch insert 105 is less than the minimum diameter of the punch support body 161. A through-bolt 1% provides the pilot pin projection 81a and has a shoulder 167 for sealing the casing 86 at 108. The bolt 106 has a bottom end portion threadedly inserted into and holding a punch tip 1&5 at the lower end of the punch body 161. Thus, the bolt 106 takes the stripping loads on the punch tip 105. A male seal 109 about the head 103 coacts with a male seal 110 about the upper end portion of the tubular stripping piston 90 to seal the inside and outside of the tubular piston. The tubular piston 90 provides a thin annular net piston area equivalent to the annular swept area between the seals but with a thick stepped tubular body of high strength. The effective piston area at the top of the stripper piston 90 is greater than the effective piston area at the bottom of the spool 161 so as to provide a differential pressure in the punch 80 g ground, the spring force must be adjusted to the new length or designed oversize initially to accommodate grind life. I propose to accomplish this without adjusting the spring by providing a A" thick high strength plastic stripping pad 112 formed of nylon or the like, backed by a steel back up member 113 through which the punch tip 105 extends. The nylon pad 112 is a tight fit on the punch 105 and the steel member 113 to exclude dust and dirt, and the construction is such that the end of the punch and the bottom face of the pad 112 are flush when the punch assembly is unactuated as shown. The stripper head assembly, comprising the nylon pad 112 and the back up member 113, may be secured to the lower end of the lower tubular section 91 in any suitable manner such as by being pressed in the annular groove at the end of the piston section 91. .Thus, the inexpensive molded or machined non-working stripper cap 112 can be ground with the punch and at the same time will exclude dirt from the precision bore 92 during grinding operations. When a new punch tip 105 is inserted, a new stripper cap 112 can be inserted using the former steel back up member 113. In some instances, the steel back up member 113 can be dispensed with as the nylon or plastic member 112 will have sufiicient rigidity itself.

The construction of this embodiment operates in the same manner as the previous embodiments. The punch assembly 81 is moved downwardly to engage a flat sheet work piece (not shown) on the end of the die 82 and thereafter as the downward movement of the punch assembly continues, the punch tip 105 perforates the work piece. The downward movement of the stripping piston is halted by the work piece, and as the punch continues downward, the liquid in the chamber 88 is compressed. After the perforating operation has been completed, the punch assembly is moved upwardly to retract From the foregoing discussion it Will be understood that the present invention provides a substantially improved perforator device in which a tubular liquid spring piston also acts as the work stripper for the perforator punch assembly. This construction makes it possible to punch holes at least /1 of an inch in diameterin metal having a thickness of at least of an inch. By combining the stripper and the liquid springpiston into a single member the construction is greatly simplified. At the same time the life of the punch is lengthened because of the reduction in compressive force carried by the punch and because of the support for the punch end portion pro- ,vided by the tubular piston. Where large holes are to be punched in thick metal, the tubular piston-stripper is constructed in stepped form providing a rugged body with any desired spring rate. Precision attachment means are provided which provide for accurate retention of the punch assembly and the mating die and at the same time allow ready interchangeability of various punch sizes. Since the precision attachment means do not encircle the punch or die casings, the perforator sets may be placed closer together to allow simultaneous punching of holes with minimum distances between centers. Furthermore, the substantial freedom of the punch assembly casing from attaching means permits limited casing expansion to provide increased liquid spring efliciency and to elimi- -nate necessity for thick casing walls which would cut down on the proximity of holes which can be simultaneously punched. Simplified punch grinding is Provided for by adding a high strength plastic stripping pad about the punch end so that the punch and the pad can be ground simultaneously while the pad prevents entry of foreign matter into the punch. assembly.

Variations and modifications may be eitected without departing from the scope or" the novel concepts of the present invention.

1 claim:

A pertorator punch assembly adapted for utilizing a compressible liquid Work stripping means comprising a a cylindrical casing open at one end, the other end having a wall with a recessed opening therethrough, an axial cylindrical chamber in said casing, 21 compressible liquid in said chamber, an elongated punch support member coaxially mounted in and radially spaced from the walls of said punch support member, a punch mounted in a the punch support member recess and secured to said through-bolt and extending out of the cylindrical chamber, said punch support member having a spool-shaped configuration, said cylindrical casing having an ofiset inside said casing Wall portion, a tubular stripper disposed in the offset portion and having a portion closely fitted 0 above the free end portion of said punch, the etfective piston area at the top of the stripper being greater than the effective piston area at the bottom of the spool, said stripper including a stepped tubular piston portion extending into and reciprocable in the space between the punch support member and the cylindrical casing, first liquid seal means formed on the outer surface of said tubular stripper in sealing engagement with the opposing wall of said cylinder, second liquid seal means on the portion of the punch support member opposing the inner surface of said tubular stripper and in sealing engagement therewith, the maximum diameter of said spool being less than the minimum diameter of said chamber, whereby upon operation of the punch, the liquid is compressed thereby exerting a force against the etfective piston areas to cause the stripper to operate upon removal of the punch from a die.

References Cited in the file of this patent UNITED STATES PATENTS 928,256 Grissom July 20, 1909 1,822,468 Wales Sept. 8, 1931 2,168,377 Wales Aug. 8, 1939 2,191,826 Bath Feb. 27, 1940 2,432,804 Rieske Dec. 16, 1947 2,674,311 Griswold Apr. 6, 1954 2,716,451 Taylor Aug. 30, 1955 2,867,276 Taylor Jan. 6, 1959

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