Abstract:
A novel back stop gauge for determining accurate and safe positioning of work piece material in a machine tool, such as a press brake, wherein a linear stop has an axially stiff, but transversely flexible coil spring intermediate end portions, one end portion being engaged by work piece material and the opposite end portion being anchored to a cooperating support. Misplacement of work material either over or beneath the stop, while normally destructive of the work piece upon closure of the press brake, does not result in damage to the machine tool or the press because of the flexible nature of the back stop, which permits movement of the stop out of the path of the machine tool.

Description:
This invention relates to a novel gauge system for insuring an accurate, safe and effective precise location of work material, include sheet metal or plate, in a machine tool, such as a press brake. 
     BACKGROUND OF THE INVENTION 
     It is currently common practice to use rigid screw type back stops in machine tools, dies, jigs and fixtures for the purpose of providing repeatable, accurate positioning of work pieces in a press while allowing stop adjustment to insure accurate positioning of the work pieces in the tool or fixture. In some instances, however, the required stop gauge position in the particular tool is such as to produce interference with mating parts of the machine tool during normal operation. In such cases the machine tool is usually modified to provide clearance for the stop gauge. In some cases there may be multiple locations of the stop gauge in order to accommodate different parts to be made or formed in the same machine tool. To that end multiple clearance slots may be required in the machine tool. This procedure is not only expensive, but materially reduces tool life. Such slots even can be dangerous if during the set up of the machine tool great care is not taken by the set up person to insure proper alignment of the stop gauges and mating tool clearance slots. If misalignment does take place in a press set up, for instance, more than likely there will be considerable damage to the accompanying tooling and possibly to the press, to say nothing of possible danger to the press operator or set up person. 
     There are many instances where even if there is not interference between the stop gauges and the production tooling, there is still the opportunity for operator error, particularly in piece work situations. For example, the operator may inadvertently place the work piece on top of or underneath the stop gauge. In that event, serious damage to the conventional rigid stop gauge and work piece is inevitable once the press or machine is actuated. Furthermore, risk of injury to the operator or damage to the machine tool is present. Accidents of the type briefly described above are costly, not only in down time and repairs, but in the risk of human lives and limbs. 
     It is a primary object of this invention to provide a simple, inexpensive, but highly effective stop gauge for machine tools that eliminates much of the cost and dangers associated with the commonly used standard screw type gauge system. 
     It is a further object of this invention to provide a stop gauge as set out in the immediate preceding object which embodies a basic concept readily useful in precision automated gauging systems with no loss of accuracy. 
     It is another important object of this invention to provide an improved back stop for machine tools which prevents extensive damage to an associated machine tool. 
     BRIEF SUMMARY OF THE INVENTION 
     This invention is embodied in a back stop gauge, particularly useful with press brakes and similar machine tools for forming, shaping and operating on sheet material or metal plate, for instance, wherein precise location of the work pieces is requisite to uniform product; the stop gauge hereof comprising a simple linear assembly of a work piece engagable cap member and a mounting stem at opposite ends of a resilient member, such as a flexible spring having a normal linear axial configuration, but capable of linear deflection under linear load; the stop gauge being axially rigid and incompressible under axial load. 
     Having described this invention the above and other objects, features and advantages there will be recognized by those skilled in the art from the following description of a preferred embodiment thereof illustrated in the accompanying drawings. 
    
    
     IN THE DRAWINGS 
     FIG. 1 is an end elevation of standard press brake tooling with a typical standard screw type stop gauge showing a typical work piece in place abutting the stop gauge prior to bending operation of the press; 
     FIG. 2 is an end elevation of the tooling shown in FIG. 1 with the tools shown closed and the work piece properly formed; 
     FIG. 3 is an end elevation similar to FIG. 1 but showing the work piece improperly placed on top of the stop gauge prior to press operation; 
     FIG. 4 is still another end elevation of the press brake tooling seen in FIGS. 1-3 showing the work piece erroneously placed under the stop gauge prior to press operation; 
     FIG. 5 is a side elevation of a stop gauge according to this invention; 
     FIG. 6 is a right hand end elevation of the stop gauge shown in FIG. 5; 
     FIG. 7 is a full cross sectional view of the stop gauge shown in FIG. 5, taken substantially along vantage line  7 — 7  of FIG. 6, and looking in the direction of the arrows; 
     FIG. 8 is a side elevation of the individual parts of the gauge shown in FIG. 5 with such parts axially separated; 
     FIG. 9 is a end elevation of press brake punch and die tooling in an open position with a work piece abutted against one end of a back stop gauge according to this invention; and 
     FIG. 10 is another end elevation similar to FIG. 9, showing the punch and die tooling in a closed position and the work piece formed after press operation. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the embodiment of this invention set forth in the drawings, particular attention is initially directed to FIGS. 1-4, as illustrative of the difficulties and problems encountered in the prior art. 
     In FIG. 1 a typical screw-type adjustable back stop gauge  15  is shown as it is normally mounted in a press brake forming application. As illustrated, material  16  to be formed is precisely located by abutting the screw back-stop gauge  15  associated with forming tools mounted in the press brake. In this instance, the forming tools comprise a forming punch  17  and a forming die  18  located on opposite sides of the work piece material  16 . These tools are secured and aligned in the press by means of standard press holders and clamps (not illustrated) which assures consistent alignment of the tools during each press operation. 
     The standard screw gauge  15  is positioned by means of mating threads in a gauge holder  19  associated with the forming die  18 . Gauge  15  is threadingly advanced and retracted by threaded movement within a threaded opening in holder  19  until the desired position of its outer end  20  is achieved; the gauge  15  thereupon locked in placed by means of a locking nut  21  according to known practice. 
     As seen in FIG. 2 of the drawings the forming punch  17  and the forming die  18  are shown in a closed position with the work material  16  therebetween after a bending closure of the press tools is complete. During the bending operation the material  16  forms freely and moves away from the screw back stop gauge  15  without any particular interfering incident under normal operating conditions. 
     It will be recognized that when properly used as shown in FIGS. 1 and 2, the screw type adjustable back stop system for locating work material in a forming tool is generally safe, dependable and operationally accurate. However, in the world of high production and repetitive piece work, operational mistakes frequently happen which can be and often are hazardous to the machine operator, the tooling and the machine itself. 
     With reference now to FIG. 3 it will be recognized that the same tools illustrated in FIGS. 1 and 2 are shown with the material or work piece  16  to be formed accidentally positioned or placed over the top of the locating back-stop gauge  15 . If the press brake is cycled while material  16  is in this position, serious and usually costly damage will result to the screw gauge  15  per se, the holder  19  and the work material  16  with possible damage to the forming tools  17  and  18 , as well as the press and operator. 
     In FIG. 4 the same tools of FIGS. 1-3 are shown again and this time the material  16  is placed accidentally beneath or under the locating screw  15 . If the press brake is cycled while the work piece  16  is in this position, serious and very costly damage will follow to the back stop gauge  15 , the gauge holder  19  and the work material  16 , including likely damage to the forming tools, the press and possible injury to the operator. 
     From the foregoing situation, illustrated in FIGS. 1-4 of the drawings, it will be readily understood that misplacing the work material against the back stop gauge, particularly when a rigid screw type of stop gauge is utilized, is not only a costly mistake, but can be seriously dangerous and damaging to equipment and personnel. 
     In FIGS. 5-8 of the drawings, the features of a stop gauge in accordance with the present invention are set forth; the illustrated embodiment presently being the best mode presently contemplated for practicing this invention. specifically, the stop gauge  25  shown in FIGS. 5-8, is a three piece construction including a cylindrical end cap  26 , a resilient mid section  28  and body portion  29 . The three elemental portions of gauge  25  are coaxially aligned and interfitted, as will appear presently, to present a axially rigid structure capable of transverse flexing. It is to be noted that body portion  29  is provided with a standard wrench receptive socket  30  at its outer end (see FIG. 6) whereby its externally threaded body may be adjustably advanced and retracted with respect to the internally threaded gauge holder  19  or other equivalent gauge holding structure. 
     FIG. 7 is a full cross sectional view of the assembled gauge  25 , taken substantially along vantage line  7 — 7  of FIG.  6  and from which view the manner of assembling the three parts or portions of the gauge is clearly apparent. It is to be regarded, in particular, that cap  26  and one end of the threaded body member  29  are each suitably shouldered as at  31  and  32 , respectively, to form opposing cylindrical portions  33  and  34  (see FIG. 8) of reduced diameter having external threads  35  and  36 , respectively, whereby cap  26  and the threaded body portion  29  are able to closely mate with the inside bore and pitch of the coils in spring  28 . The size of the threaded ends  33  and  34  and the threads  35  and  36  thereon, respectively, are such as to provide a threaded resistance fit with the spring member  28 . 
     The midsection  28  is a heavy expansion type coil spring with a selected number of coils wound in such a manner as to insure that there is little or no axial space between adjacent coils. This tight wrapping of the spring insures that the dimensions from the outer end of cap  26  to the adjustably positioned threaded body portion  29  is held at a constant fixed dimension even when the spring is subjected to an axial compression forces (indicated by arrow  37  in FIG. 7) as would be exerted on cap  26  by material  16  positioned against the back stop gauge of this invention. 
     FIG. 8 shows the individual portions or pieces of the gauge  25  prior to assembly. As there indicated, cap  26  and the threaded body portion  29  are coaxially arranged with the intervening spring  28  in assembly. It further is to be recognized that while a coil spring  28  is herein illustrated, other forms of flexible connective devices between the cap and body portion  29  are available so long as they provide a rigid, substantially non-compressible axial formation capable of transverse flexing under laterally imposed loads, as shown in FIGS. 3 and 4, for instance. 
     As shown in FIG. 9, a typical use for the new back-stop gauge of this invention is illustrated. The threaded portion  29  of the gauge is located in holder  19  and threadingly adjusted to precisely position the end cap  26 , so that material  16  to be formed is located at exactly the correct dimension or position to provide the desired product part. The material to be formed is held in position by applying force to the back gauge in the direction of the arrow  37 . In certain instances the cap  26  can be magnetized to hold the material to be formed in place during the folding or bending operation provided, of course, that the work material is magnetic. There also can be any number of gauges used at one time determined by the number of parts or bends being made at any one time and the available space in the tooling. In the tools, as shown in FIGS. 9 and 10, the die section  18  can be of any length, while the heel pieces  38  are made in shorter sections and mounted to the die section  18  in a manner to provide spaces between adjacent heel sections, receptive of the midsection spring  28  of the back stop gauge assembly  25 . In this manner the various stop gauges can be mounted without interfering with the die section. 
     In the illustrated example, the upper forming tool  39  is the same overall length of the holder section  17 . With the particular illustrated tool design shown, interference with the back stop gauge  25  is unavoidable, as indicated in FIG.  10 . At present, if confronted with a situation such as that illustrated in FIGS. 9 and 10, the only known way to solve the problem of interference with the back gauge or gauges is to machine clearance pockets in the upper forming tool  39 . These pockets materially shorten the life and performance of the tool in a very negative way. In this situation utilizing the improved back stop gauge  25  as shown in FIG.  10  and placing a work piece or material to be formed accidentally over the top of a solid back stop gauge as in FIG. 3 above would usually result in damage to the tooling of FIGS. 9 and 10. However, as shown, by using the back stop gauge  25  hereof, its capability to transversely flex and deform, provided by the central spring  28 , avoids the tool damage as would normally occur with a solid fixed back stop gauge  15  (FIGS.  1 - 4 ). 
     The advantages of the herein disclosed flexible safety back stop gauge  25  are readily apparent from FIG.  10 . Rather than cutting many expensive clearance safety pockets in the upper tooling  39 , for example, the upper tooling is kept as is and when the flexible back stop gauge hereof is hit by the upper forming tool  39  at the bottom of each press stroke, no damage occurs to either the gauge or the forming tool, because of the flexible movement of the gauge spring  28 . The flexible spring of the gauge combination will withstand thousands of hits without any damage or sacrifice to accuracy. Even if the material to be formed is placed over the top of the flexible back stop gauge  15  there will be no permanent damage to the tools, the gauges, the press or the operator. 
     It is further to be noted that although the example of the back stop gauge  25 , above described, is shown with threaded stem portion  29  as the most common standard mounting form, it is not the only possible form or manner of mounting the stop gauge. In a similar vein cap  26  which can be made with many shapes or forms may be used in conjunction with expensive automated back gauging systems or other devices, which may or may not require the use of a threaded stem portion  29 . 
     From the foregoing it is believed that those skilled in the art will readily recognize and appreciate the advanced novelty of the current invention and will readily understand that while the same has herein been described in conjunction with a preferred embodiment thereof illustrated in the accompanying drawings, the same nevertheless may be subject to change, modification or substitution of equivalents without departing from the spirit and scope of the invention which is intended to be unlimited by the foregoing except as may appear in the following appended claims.