Abstract:
A method and an apparatus are provided for marking a sheet-shaped workpiece using a marking tool. The marking tool is mounted in a punch holder of a punch press and a counter-support is fixed in place on a side opposite of a marking surface of the workpiece to be marked. The surface of the workpiece is marked by displacing the workpiece in its plane while engaging the marking tool with the workpiece. In one form, a support roller provides counter-support. In another form, an elastic element is cooperatively associated with the punch stroke of the punch press to translate an exactly defined contact pressure force between the tool tip and the workpiece to be marked.

Description:
FIELD OF THE INVENTION 
   This application is a continuation of application Ser. No. 09/881,678 filed Jun. 18, 2001 now abandoned which is a continuation-in-part of prior application Ser. No. 09/688,094 filed Oct. 16, 2000 now abandoned. 
   The present invention relates to a method and an apparatus for marking workpieces on a punching press, wherein the marking tool is forced by means of the punching stroke either against the surface of the workpiece or a certain depth into the surface of the workpiece. The workpiece, which is generally a piece of flat sheet metal, is displaced within its plane in order to create a straight or curved marking line. 

   BACKGROUND OF THE INVENTION 
   There is an increasing demand for altering the surface of workpieces, including as one example, providing workpieces with individual identifications. In this connection the use of stamping dies is not always practical because the stamping is often also visible on the back of sheet metal workpiece. Difficulties in connection with stamping dies occur particularly when it is intended to punch parts of different lengths out of a sheet metal workpiece (e.g., in order to minimize waste) and wherein a certain orientation of the marking on the workpiece is desirable. 
   A known method for marking sheet metal consists of embossing dot matrices to produce an alpha-numeric symbol with the aid of a pointed embossing tool. The workpiece must be moved stepwise after each dot has been embossed. This results in a multitude of required stamping stroke cycles, just to represent a single symbol. Besides the large amount of required time and the increased wear of the driving mechanism for the stroke, which is driven in a quasi load-free manner, the loud noise is considered to be a disadvantage. A coarser dot matrix does simplify the marking process, but it also results in a more unsatisfactory matrix. 
   A qualitatively appealing marking can be achieved by inscribing markings into the surface of the workpiece, wherein no waviness or “rear embossing” will occur. Borries Markiersystem GmbH of Pliezhausen, for example, offers a machine, by means of which inscribing the desired identification is possible by displacing a tip forced into the surface of the workpiece in accordance with the contours of the marking. 
   It would seem that in principle one could employ such a known marking device in a punch press. However, if this were done, the space available for the main punching operation would be reduced and the progress of the main punching operation would be made more difficult. Also, this marking device could only operate within a limited portion of the area of the punch press so that movement of the sheet metal workpiece in order to apply markings on different areas thereof would become more difficult. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to create an improved apparatus for altering the surface of a sheet metal workpiece, which apparatus can be integrated into a punching process in a punch press. 
   This object is attained in accordance with the invention by a method and an apparatus wherein a tool is equipped with a tip which, after having been forced against or into the surface of the workpiece, is maintained at a fixed position, at which time the workpiece is displaced in its plane in accordance with the desired result, and thereafter the tip is moved away from the workpiece to its rest position. 
   The principles of the present invention can be utilized to mark workpieces in many different ways. For example, a tool can be forced to a certain depth into the surface of the workpiece for an inscribing action. Or, a tool can be forced against the surface, without going beneath the surface, for the purpose of marking the surface. In another application, if the workpiece has a protective plastic cover over a metal base, such as a sheet metal base, a tool can be utilized to cut the plastic cover, while not altering the underlying metal sheet. These various applications of the present invention will be referred to as marking the workpiece, and the different apparatus and tools will be referred to as marking tools, or marking apparatus. 
   The production of markings of any arbitrary symbol or shape on or in the workpiece surface is made possible by means of the marking tool being placed on the punch press without any additional, space-consuming devices. At the same time a marking method is optimally integrated into the punching process so that, for example with a turret punch press, a sheet metal workpiece is first marked at the desired locations and thereafter is finished by means of the tools seated in other holders of the punch press. The marking tool may be arranged in a punch tool holder so that the marking can be made from above the workpiece. The orientation of the marking can be determined by means of the software which controls the workpiece driving mechanism. 
   It is also advantageous in connection with the operation of the invention that the tool tip need be moved only once into its marking position, so that the number of punch strokes which must be performed by the punch press is considerably reduced. The results are reduced noise generation and reduced wear of the stroke driving mechanism. 
   In one preferred embodiment of the invention, at least a portion of the punch stroke is absorbed by an elastic element which extends between a table for seating the workpiece and the punch tool holder. 
   Since punch presses are designed for very high processing forces, with high precision and almost load-free, it can be very difficult under certain circumstances to move the stroke driving mechanism into a precisely defined position. To compensate for this, it is possible by an elastic element to achieve considerably more precise movement of the tool tip on or into the surface of the workpiece. In the process, the elastic element translates the relatively large punch stroke of the punch press into an exactly defined contact pressure force of the tool tip, which leads to the desired marking position. 
   In a further preferred embodiment of the invention at least one marking is formed as a center mark, wherein, following pressing the tool tip, the workpiece is maintained in its predefined position until the marking tool is retracted. 
   It is desirable for some applications to be able to set a center mark on the workpiece, for example in order to be able to position or center bolts or pins which are to be welded onto the workpiece. The provision of the center mark can be integrated into the marking process and apparatus in accordance with the invention, wherein it might be advantageous if, in connection with a center mark, the tool tip were pressed deeper into the workpiece than the usual inscribing depth. 
   For example, when making a center mark it is possible in a further development of the invention that by different positioning of the tool tip with respect to a counter-support, for example, the spring travel of the tool tip reaches its maximum before it has reached the deepest depth in the workpiece. While making surface marks or inscribing are performed by means of a resilient tool tip, the latter rests against a stop when making a center mark. 
   It has been shown to be practical to guide the workpiece by means of at least one support roller which may be elastically spring-loaded in the area of the workpiece support table since, among other things, the support roller provides the required support for the workpiece while not hampering the displacement of the workpiece. 
   In one preferred embodiment, the present invention comprises at least one marking tool disposed in a punch press where the marking tool includes a tool tip, a guide bush axially supporting a support, and a marking tool elastic element operatively connecting a drive head to the tool tip. At least one counter-support is located opposite the marking tool and fixed in place on a side opposite of a marking surface of a workpiece to be marked. When the apparatus has a workpiece disposed between the marking tool and the counter-support, the marking tool is operable to be pressed onto or into a marking surface of the workpiece against a restoring force of the marking tool elastic element and mark the workpiece when the workpiece is translated in its plane. 
   In another form of the present invention, an apparatus for marking a sheet shaped workpiece comprises at least one marking tool fixed in place in a punch holder of a punch press and at least one counter-support fixed in place on the side of the workpiece located opposite the marking tool such that a workpiece can be disposed between the marking tool and a counter-support. The marking tool has a tool tip which can be pressed into or onto the workpiece against a restoring force of an elastic element. The elastic element is cooperatively associated with a punch stroke of the punch press to provide an exactly defined contact pressure force between the tool tip and a workpiece to be marked. 
   The counter-support preferably comprises at least one rotatable roller. The counter-support roller along with workpiece support table rollers facilitate movement of the workpiece during marking. Moreover the counter-support roller provides mobility without damage to the workpiece surface, and minimizes frictional losses such that they occur only at the contact point between the workpiece and counter-support roller. 
   For an inscribing marking tool, a tool with a cone shaped tip is used. The tip is preferably forced into the workpiece surface, so that an inscribing force is achieved regardless of the direction of movement. Shapes which are not round are also conceivable. Moreover, the inscribing element may cut grooves of different thicknesses into the workpiece surface. 
   In accordance with yet another preferred embodiment, the marking tool has an adjustable support, by means of which the position of the tool tip and/or the prestress of its elastic element can be adjusted. 
   The adjustable support makes possible the individual adaptation of the contact depth, for example in order to improve the clarity of the shapes formed in the workpiece, or to make possible an adaptation to the material of the workpiece. 
   As mentioned above, with the present invention, it is possible to make a marking such as an ink marking or the like on the surface of the sheet metal instead of inscribing the marking into the sheet metal. Making an ink marking would use the same method and apparatus as described above with respect to inscribing except that the method and the equipment would be adjusted such that the marking tools such as a pen or the like would simply be forced with sufficient pressure against the surface of the workpiece, as opposed to entering into the surface of the workpiece. Any suitable pen could be used including for example, a ball-point pen, a roller ball pen, a felt tip pen or a grease pencil. 
   Alternatively, a marking tool made of brass, plastic or any other material which is incapable of cutting the workpiece may be utilized for the purpose of marking a shape in a protective covering placed over the workpiece without damaging the workpiece. 
   Thus, it is an object of the present invention to provide a new and improved method and apparatus for marking a workpiece, wherein the apparatus is incorporated within a punch press. 
   It is another object of the present invention to provide a new and improved method and apparatus for marking a sheet-shaped workpiece in conjunction with a punch press, wherein the marking can be either inscribed into the surface of the workpiece, made as an ink marking on the surface of the workpiece or made as a cut in a protective covering placed over the workpiece. 
   It is a further object of the present invention to provide a new and improved method and apparatus for marking a sheet-shaped workpiece in conjunction with a punch press where an elastic element is associated with the punch stroke of the punch press to translate an exactly defined contact pressure force between a marking tool tip and a workpiece to be marked. 
   These and other objects of the present invention will become more apparent from the detailed description to follow. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in detail with respect to preferred embodiments of the invention wherein: 
       FIG. 1  is a central cross sectional view of a marking tool for insertion into a punch holder of a punching press; and 
       FIG. 2  is an enlarged view of a portion of  FIG. 1 , but showing a modification thereof. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings, like elements are represented by like numerals throughout the several views. 
   Referring to  FIG. 1 , the marking tool has a guide bush  14 , in which a support  16  is axially guided, and a driving head  20 , which are in engagement with each other via a threaded connection  22 . By means of a guide insert  24 , the support  16  holds a marking tool  26 , which is axially movable with respect to the support  16  and has a tool shaft  28  which is guided in an appropriately fitted bore  30  of the guide insert  24 , a pressure plate  32 , formed at the top of the shaft  28 , as well as an inscribing element  34 , seated on the free lower end of the shaft  28 . The tip  34  of the marking tool can be of different constructions, depending on the type of mark to be made. In a first embodiment, the tip  34  may be made of a hard material and shaped as a pointed cone to be used as an inscribing element. As an inscribing element,  34  can be made, for example, of a diamond, boron nitride, a hard metal, or an otherwise suitable material for inscribing the respective workpiece. 
   The axial mobility of the marking tool  26  in relation to the support  16  is limited by a first shoulder  36  of a bore  38  in the support  16 , and by the top  40  of the guide insert  24  inserted into the bore  38 . A compression spring  44 , arranged under prestress between a second shoulder  42  and the pressure plate  32 , urges the pressure plate  32  downwardly against the top  40  of the guide insert  24 . 
   In the exemplary embodiment represented, the workpiece  12  is a sheet metal plate which rests on a counter-support  46  with a rotatably seated ball  48 , wherein the contact point between the workpiece  12  and the ball  48  lies exactly in alignment with the inscribing element  34 . 
   In a preferred form, the workpiece  12  is guided by means of support rollers, such as support rollers  50  mounted in workpiece support table  54 . Rollers  50  are elastically spring-loaded by compression springs  52 . 
   To inscribe a symbol on the workpiece  12 , the workpiece is first appropriately aligned with the marking tool  10 . Thereafter, lowering of the marking tool  26  is started by actuating the stroke driving mechanism of the punch press, which acts on the driving head  20 , wherein the guide bush  14  is urged against the support  16  by means of a shoulder  49 . In the course of the downward movement of the support  16  the marking tool  26  is initially moved along until the element  34  rests on the surface to be cut. The continued downward movement of the support  16  leads to compression of the compression spring  44 , and therefore the pressure exerted on the pressure plate  32  steadily increases. Where the element  34  is a diamond tip, it will actually penetrate the surface of the workpiece as a result of the pressure exerted by the compression spring. Maximum penetration depth is reached at the end of the punch stroke. The compression spring  44  provides for precise movement of the tool tip  34  on or into the surface of workpiece  12 . During marking, the compression spring  44  translates a relatively large punch stroke of the punch press into an exactly defined contact pressure force of the tool tip  34  which leads to a desired marking position. 
   In some applications, it is desirable to use an element  34  which is not capable of penetrating the surface of the workpiece  12 . Here, instead of utilizing a diamond tip, the element  34  is constructed from a material which does not penetrate the workpiece. It is often desirable to protect the workpiece  12  from inadvertent scratches or other blemishes which can occur during processing. For example, if the workpiece is stainless steel and will ultimately be used in the manufacture of an appliance or the like, the workpiece  12  may be covered with a plastic film or other protective covering during the hole punching or cutting operations. In order to create holes in the workpiece  12  in such cases, it is desirable to remove areas of the protective covering where the workpiece  12  will eventually be cut by a punch or a laser. This is necessary because the protective covering may interfere with the accuracy of such cuts in the workpiece  12 . In order to cut holes in the protective covering without damaging the workpiece  12 , a marking element  34  constructed from plastic or brass, or another material which is too soft to penetrate the workpiece may be utilized. Thus, when pressure is exerted by the compression spring  44 , the element  34  will penetrate the surface of the protective covering (not shown), but will not penetrate the surface of the workpiece  12 . 
   An adjustment of the penetration depth of the element  34  (when used as an inscribing element) can be performed by a relative turning of the driving head  20  in relation to the support  16 . This changes the effective total combined length of support  16  and driving head  20 . With this increased length of the support  16  and driving head  20  the element  34  reaches the surface to be cut earlier in the punch stroke and the pressure built up by means of the compression spring  44  becomes correspondingly greater. 
   As an inscribing marking tool, as soon as the element  34  reaches its inscribing position, the stroke driving mechanism of the punch press is blocked. Conversely, if the stroke driving mechanism of the punch press did not permit the marking tool to stop in the inscribing position, a separate detent device must be provided between the support  16  and the guide bush  14 . With the element  34  held down, the workpiece  12  is now displaced in its plane in order to form the contours of the symbol or shape to be inscribed, wherein any arbitrary orientation of the symbol or shape is possible by an appropriate control of the workpiece driving mechanism. When the symbol or shape has been completely inscribed, the stroke driving mechanism is reversed, wherein first the support  16  is moved away from the workpiece  12  because of the diminishing pressure force by the compression spring  44  and, following the contact of the pressure plate  32  with the top  40  of the guide insert  24 , the element  34  is lifted off the workpiece  12 . The workpiece  12  is appropriately horizontally displaced within its plane and the inscribing process is repeated for inscribing additional symbols or shapes. 
   During the horizontal displacement of the workpiece  12 , the roller ball  48  of the counter-support  46  follows this movement, wherein an optimal counter-support directly in alignment with the inscribing element  34  always exists. Because the roller ball  48  turns, sliding movements against the underside of the workpiece  12  are prevented, so that the underside of the workpiece  12  is not detrimentally affected. 
   Where the marking tool of  FIG. 1  is used in a punch press the guide bush  14  is adapted to the tool holder and the driving head  20  is adapted to the stroke driving mechanism of the punch press. 
   The compression spring  44  can be replaced with a pneumatically or hydraulically operating pressure spring. 
     FIG. 2  illustrates a modification of the present invention wherein, instead of an inscribing element, there is provided an ink point  134  for marking the surface of the workpiece  12  without penetrating same. Ink point  134  is shown at the lower end of a shaft  134  mounted in guide insert  24  of  FIG. 1 . All of the above described features of all embodiments of the invention can utilize an ink point  134  to mark the surface of a workpiece in place of the previously described elements for inscribing the workpiece and/or forming a center mark. As would be understood by one of ordinary skill in the art, when using an ink marking point  134 , one would simply adjust movements of all of the other movable parts such that instead of penetrating the workpiece, the apparatus would move the ink point  134  to a position where it exerted sufficient force onto the workpiece to form an ink marking. As with the other embodiments, the workpiece  12  could then be displaced horizontally within its plane so as to form an ink shape or symbol of straight or curved lines. Any type of known ink point could be used such as a ball-point, a roller ball point, a felt tip or a grease pencil. 
   Although the invention has been described in considerable detail with respect to preferred embodiments thereof, it will be apparent that the invention is capable of numerous modifications and variations, apparent to those skilled in the art without departing from the spirit and scope of the invention.