Patent Publication Number: US-7594417-B1

Title: Apparatus for wiper die monitoring

Description:
TECHNICAL FIELD 
     The present invention relates, in general, to dies used in the bending of tubular workpieces. More particularly, the present invention relates to an apparatus, and methodology of use therefor, for monitoring of the location and applied pressure characteristics of a wiper die insert of a rotary tube bender. 
     BACKGROUND OF THE INVENTION 
     The process of hydroforming is a metal forming process whereby specialized dies are used in conjunction with high pressure hydraulic fluid to force room temperature metal into the dies to form parts. An important application of hydroforming as used in the automotive industry is the creation of bent tubular parts. Many automotive bent tubular parts are produced utilizing a rotary tube bender, most commonly in the form of a “horizontal rotary draw bender”. 
       FIGS. 1 through 3  schematically depict a rotary tube bender in the form of a horizontal rotary draw bender  10 , as known in the art, which includes a set of four dies: a bend die  12 , a clamp die  14 , a pressure die  16 , and a wiper die  18 . The bend die  12  is mounted to a stationary base  20 , and is a forming tool designed to produce a particular radius of bend in the tubular workpiece  22  to be bent (compare  FIGS. 1 and 3 ) per a concave radius  12   a . The clamp die  14  is a tool designed to close securely upon the tubular workpiece  22 . The pressure die  16  is used to press the tubular workpiece  22  into the bend die  12  via the wiper die  18 , wherein the wiper die is a tool having a predefined curvilinear edge (see  FIG. 4 ) which is shaped to abut the concave radius  12   a  of the bend die  12 . The pressure die may also have a delayed (to avoid collision with the clamp die) “boost” or axial assist to push the tube forward during bending, which will feed material preventing a failure or rupture of the tube during the bending operation. The wiper die  18  is designed to prevent the formation of wrinkles or ridges in the tubular workpiece  22  during the process of its bending by the horizontal rotary draw bender  10 , wherein an electronically controlled hydraulic rotation apparatus (not shown) is connected with the clamp die  14 . 
     In this regard,  FIG. 3  depicts the operation of the horizontal rotary draw bender  10  with respect to the bending of the tubular workpiece  22 , which is inserted between the pressure die  16  and the wiper die  18  in interfacing relation with the bend die  12 . The clamping pressure and rotation of the clamp die  14 , while the pressure die  16  exerts pressure toward the wiper die  18  and bend die  12  and moves linearly forward toward clamp die  14  to prevent unnecessary elongation or tube failure, as provided by the hydraulic rotary apparatus, results in a bend  22   a  of the tubular workpiece  22  which conforms to the concave radius  12   a  (see  FIG. 2 ) of the bend die  12 . The wiper die  18  plays a significant role in the bending process of the tubular workpiece, whereby the wiper die ensures that no wrinkles will be produced while bending the workpiece, particularly at the inner radius of the bend. 
     As can be seen from  FIGS. 4 through 5B , the wiper die  18  is composed of a wiper die holder  24  and a wiper die insert  26 , which have mutually mating surfaces: a concave holder mating surface  24   a  and a convex insert mating surface  26   a , which mating surfaces are complementing with respect to each other. The holder mating surface  24   a  has a raised boss  28  which is received by a complementary keyway (i.e., slot)  30  formed in the insert mating surface  26   a . The wiper die  18  has a workpiece seating surface  34  having a concave radius for seating the convex outer surface of the tubular workpiece  22 , wherein, in this respect, the wiper die holder has a holder workpiece seating surface  34   a , and the wiper die insert has an insert workpiece seating surface  34   b . The wiper die insert  26  is affixed to the wiper die holder  24  via, for example, a threaded fastener (not shown) threading at a bore  36  in the wiper die holder and the wiper die insert, wherein the bore is threaded at the wiper die insert portion thereof. At the distal end of the insert workpiece seating surface  34   b  is an insert edge  32  of the wiper die insert  26  which is of critical importance in the quality of the bend of the workpiece, via careful adjustment of the interface of the insert edge with respect to each of the bend die and the workpiece. 
     The insert edge  32  is the principal location of wear and its location is critical. In low volume production, a skilled operator can visibly detect when the wiper die insert  26  has become unsuitable to the point of needing replacement or adjustment. In a high volume setting, however, the traditional method of waiting for the workpieces to show evidence of this wear is inadequate. 
     Accordingly, what remains needed in the art is a means to monitor the location of the wiper die in the course of workpiece bending so that once the wiper die insert thereof has become unsuitable for production of bent tubular articles of sufficient quality, the operator will quickly and easily be enabled to detect this condition and render appropriate remedy. 
     SUMMARY OF THE INVENTION 
     The present invention provides sensors for monitoring a plurality of normal and axial pressures of the wiper die insert with respect to the wiper die holder, whereby the operator is enabled to quickly and easily detect when the wiper die insert is no longer able to provide bent tubular articles of sufficient quality. 
     In order for the wiper die to perform its function, it must hold a firm abutting relation simultaneously to both the convex outer surface of the workpiece and concave radius of the bend die, and in so doing maintain an optimum fore-aft location and optimum angular orientation, referred to in the art as the “rake angle”, and in addition, the wiper die must be provided an optimum force (or pressure) distribution from the pressure die. Three location parameters of the wiper die insert with respect to the wiper die holder are important to monitor location/pressure variation of the wiper die insert vis-à-vis whether the wiper die insert is in condition to provide quality bending of tubular workpieces: 1) the normal force distribution of the pressure die as realized between the mating surfaces of the wiper die holder and wiper die insert; 2) the rake angle, which is the angle that the entire wiper die and wiper die holder is offset or pivoted from the center line of the tubular workpiece at the point of contact between the wiper die and the bend die, wherein the rake angle places either more or less of the wiper die surface in contact with the tubular workpiece during bending, which affects the frictional forces acting on the workpiece tube and prevents wrinkling on the compression side of the bend; and 3) the fore aft location as between the wiper die insert and the wiper die holder. The present invention enables the operator to continually monitor these three sources of location/pressure variation of the wiper die insert via a pressure sensing wiper die. 
     The pressure sensing wiper die according to the present invention has a first set of pressure sensors placed on a normally disposed mating surface of either the wiper die insert or the wiper die holder so as to be in pressing normal abutment with the other complementing mating surface of the wiper die. The pressure sensors of the first set of pressure sensors are distributed so as to register pressures at strategic locations of the abutting interface between the wiper die insert and the wiper die holder mating surfaces, whereby the operator is enabled to evaluate the normal forces acting on the wiper die during bending operations. 
     The pressure sensing wiper die according to the present invention further has a second set of pressure sensors placed at an axially disposed mutually abutting surface interface between the wiper die insert and the wiper die holder. The pressure sensors of the second set of pressure sensors are distributed so as to register pressures at strategic locations of the abutting axial interface between the wiper die insert and the wiper die holder axial surfaces, whereby the operator is enabled to evaluate the axial forces acting on the wiper die during bending operations. 
     In operation, the wiper die insert is first affixed to the wiper die holder and the wiper die is located such that the wiper die insert has an optimal rake angle, optimal fore-aft location, and optimal normal pressure distribution when performing a bending operation on a tubular workpiece. Initial, or nominal, signal outputs of the first and second set of sensors during at least one bending operation are then stored. The operator will thereafter monitor the signal outputs of the first and second sets of pressure sensors over the course of future bending cycles for comparative signal outputs drift from the nominal signal outputs (having correlation to location variation of the wiper die insert with respect to the wiper die holder), wherein a signal outputs drift indicative of the need of realignment or replacement of the wiper die inset can be discerned before tubular workpieces being bent can be adversely affected thereby. 
     Accordingly, it is an object of the present invention to provide a means to detect when the wiper die insert is approaching a condition in which it will no longer produce bent tubular workpieces of sufficient quality by monitoring drift of normal and axial pressure distributions of the wiper die insert with respect to the wiper die holder from nominal values. 
     This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top plan view of a portion of a prior art hydraulic rotary draw bender, showing in particular the dies thereof. 
         FIG. 2  is a side view of the prior art hydraulic rotary draw bender of  FIG. 1 . 
         FIG. 3  is a top plan view of a portion of a prior art hydraulic rotary draw bender of  FIG. 1 , showing a tubular workpiece being bent thereby. 
         FIG. 4  is a top plan view of an example of a prior art wiper die as used in the prior art bender of  FIG. 1 . 
         FIG. 5A  is a top plan view of a wiper die holder of the prior art wiper die of  FIG. 4 . 
         FIG. 5B  is a bottom plan view of a wiper die insert of the prior art wiper die of  FIG. 4 . 
         FIG. 6A  is a top perspective view of a wiper die holder having a plurality of pressure sensors, shown by example as strain gauges, in accordance with the present invention. 
         FIG. 6B  is a bottom perspective view of a wiper die insert having a plurality of pressure sensors, shown by example as strain gauges, in accordance with the present invention. 
         FIG. 7A  is an example of a first set of pressure sensors in the form of a first flexible circuit of strain gauges for measuring normal pressure distribution between the wiper die insert and wiper die holder mating surfaces. 
         FIG. 7B  is an example of a second set of pressure sensors in the form of a second flexible circuit of strain gauges for measuring axial pressure distribution between the wiper die insert and wiper die holder. 
         FIG. 8  is a top plan view of a pressure sensing wiper die having pressure sensors in the form of strain gauges according to the present invention. 
         FIG. 9A  is a sectional view along line  9 A- 9 A of  FIG. 8 , showing in particular the second set of pressure sensors disposed at the boss of a wiper die holder in accordance with the present invention. 
         FIG. 9B  is a sectional view along line  9 B- 9 B of  FIG. 8 , showing in particular the second set of pressure sensors disposed at the keyway of a wiper die insert in accordance with the present invention. 
         FIG. 9C  is a sectional view along line  9 C- 9 C of  FIG. 8 , showing in particular the first set of pressure sensors disposed between the mating surfaces of the wiper die holder and wiper die insert in accordance with the present invention. 
         FIG. 10A  is a top perspective view of a wiper die holder having a plurality of pressure sensors, shown by example as tactile pressure sensors, in accordance with the present invention. 
         FIG. 10B  is a bottom perspective view of a wiper die insert having a plurality of pressure sensors, shown by example as tactile pressure sensors, in accordance with the present invention. 
         FIG. 11A  is an example of a first set of pressure sensors in the form of a first flexible circuit of tactile pressure sensors for measuring normal pressure distribution between the wiper die insert and wiper die holder mating surfaces. 
         FIG. 11B  is an example of a second set of pressure sensors in the form of a second flexible circuit of tactile pressure sensors for measuring axial pressure distribution between the wiper die insert and wiper die holder. 
         FIG. 12  is a top plan view of a pressure sensing wiper die having pressure sensors in the form of tactile pressure sensors according to the present invention. 
         FIG. 13A  is a sectional view along line  13 A- 13 A of  FIG. 11 , showing in particular the second set of pressure sensors disposed at the boss of a wiper die holder in accordance with the present invention. 
         FIG. 13B  is a sectional view along line  13 B- 13 B of  FIG. 11 , showing in particular the second set of pressure sensors disposed at the keyway of a wiper die insert in accordance with the present invention. 
         FIG. 13C  is a sectional view along line  13 C- 13 C of  FIG. 11 , showing in particular the first set of pressure sensors disposed between the mating surfaces of the wiper die holder and wiper die insert in accordance with the present invention. 
         FIG. 14  is an example of an electronic components diagram according to the present invention. 
         FIG. 15  is an example of an algorithm for carrying out the methodology of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the Drawing,  FIGS. 6A through 15  depict various aspects of a pressure sensing wiper die insert, and methodology of use therefor, according to the present invention which includes a first set of pressure sensors for indicating normal pressure distribution and a second set of pressure sensors for indicating axial pressure distribution. 
     The pressure sensing the wiper die  100   a ,  100   b ,  100   a ′,  100   b ′ according to the present invention (see  FIGS. 8 and 12 ) is composed of a wiper die holder  106  and a wiper die insert  108 , which have mutually mating surfaces, a concave holder mating surface  106   a  (see  FIGS. 6A and 10A ) and a convex insert mating surface  108   a  (see  FIG. 6B  and  FIG. 10B ), which mating surfaces are complementing with respect to each other, and wherein one or the other mating surface has disposed thereat a first set of pressure sensors  102 , as will be discussed in detail hereinbelow. Further, at an axial abutment  118 ,  118 ′ as between the wiper die holder  106  and the wiper die insert  108  is disposed a second set of pressure sensors  104 , as will also be discussed in detail hereinbelow. 
     The holder mating surface  106   a  has a raised boss  110  which is received by a complementary keyway (i.e., slot)  112  formed in the insert mating surface  108   a . The pressure sensing wiper die  100   a ,  100   b ,  100   a ′,  100   b ′ has a workpiece seating surface  114  having a concave radius for seating the convex outer surface of a tubular workpiece (as for example workpiece  22 ), wherein, in this respect, the wiper die holder  106  has a holder workpiece seating surface  114   a , and the wiper die insert  108  has an insert workpiece seating surface  114   b . At the distal end of the insert workpiece seating surface  114   b  is an insert edge  116  which, as mentioned hereinabove, is of critical importance in the quality of the bend of the workpiece, via careful adjustment of the interface of the insert edge  116  with respect to each of the bend die (see  12  in  FIGS. 1 through 3 ) and the workpiece. By way of example, the wiper die insert  108  is affixed to the wiper die holder  106  via, for example, a threaded fastener (not shown) threading at a bore  126  in the wiper die holder and the wiper die insert, wherein the bore is threaded at the wiper die insert portion thereof, however, the affixment may be by another mechanically suitable means. 
     It is to be understood that the pressure sensors used for the first and second sets of pressure sensors  102 ,  104  may be any suitable form of pressure sensors, wherein merely by way of example  FIGS. 6A through 9B  depict the first and second sets of pressure sensors in the form of a plurality of strain gauges  124 , and wherein merely by way of example  FIGS. 10A through 13B  depict the first and second sets of pressure sensors in the form of a plurality of tactile pressure sensors  124 ′, wherein the tactile pressure sensors are most preferred. Further, the first set of pressure sensors  102  is normally disposed and the second set of pressure sensors  104  is axially disposed, wherein by “axially disposed” is meant disposed at a surface in which abutment is along axis A (see  FIGS. 9 and 12 ), and by “normally disposed” is meant at a surface in which abutment is normal to the axis A. 
     As shown at  FIG. 6A , the embodiment of the pressure sensing wiper die  100   a  (of  FIG. 8 ) has the holder mating surface  106   a  of the wiper die holder  106  including a normally disposed first set of pressure sensors  120   a  and an axially disposed second set of pressure sensors  122   a . Each of the pressure sensors is a strain gauge  124 , which is commercially available, for example through Omega Engineering, Inc. of Stamford, Conn. 06907. 
     At  FIG. 6A , the first set of pressure sensors  120   a  is placed on the holder mating surface  106   a  of the wiper die holder  106  so as to be in pressing abutment with the complementing insert mating surface  108   a  of the wiper die insert  108  (see  FIG. 9C ). The strain gauges  124  of the first set of pressure sensors  120   a  are distributed so as to register pressures at strategic locations of the normally abutting interface between the wiper die insert and the wiper die holder mating surfaces, whereby the operator is enabled to evaluate the normal forces acting on the wiper die insert and rake angle of the wiper die insert during bending operations. By way of example, a flexible circuit of strain gauges  128   a , as shown at  FIG. 7A , may be affixed, such as by an adhesive, to the holder mating surface for this purpose, wherein the flexible circuit is formed, for example, according to techniques well known in the art, wherein for example Omega Engineering, Inc. makes a product by etching constatan foil, which is then completely sealed in a carrier medium composed of polyimide film. Electrical leads (not shown for clarity) are attached to each strain gauge  124  and connect with an external electrical circuit (i.e., CPU  146  of  FIG. 14 ). 
     Further at  FIG. 6A , the second set of pressure sensors  122   a  is placed at an axially disposed abutment surface, preferably the abutment surface  110   a  of the boss  110 , such that the abutment surface is at the axial abutment  118  between the wiper die insert and the wiper die holder (see  FIG. 9B ). The strain gauges  124  of the second set of pressure sensors  122   a  are distributed so as to register pressures at strategic locations of the axially abutting interface between the wiper die insert and the wiper die holder axial surfaces, whereby the operator is enabled to evaluate the axial forces acting on the wiper die insert and the fore-aft location of the wiper die insert during bending operations. By way of example, a flexible circuit of strain gauges  130   a , as shown at  FIG. 7B , may be affixed, such as by adhesive, to the boss for this purpose, wherein the flexible circuit is formed, for example, according to techniques well known in the art. Electrical leads (not shown for clarity) are attached to each strain gauge  124  and connect with an external electrical circuit (i.e., CPU  146  of  FIG. 14 ). 
     As shown at  FIG. 6B , the embodiment of the pressure sensing wiper die  100   b  (see again  FIG. 8 ) has the insert mating surface  108   a  of the wiper die insert  108  including a normally disposed first set of pressure sensors  120   b  and an axially disposed second set of pressure sensors  122   b . Each of the pressure sensors is a strain gauge  124 , being commercially available as described above. 
     At  FIG. 6B , the first set of pressure sensors  120   b  is placed on the insert mating surface  108   a  of the wiper die insert  108  so as to be in pressing abutment with the complementing holder mating surface  106   a  of the wiper die holder  106  (see  FIG. 9C ). The strain gauges  124  of the first set of pressure sensors  120   b  are distributed so as to register pressures at strategic locations of the normally abutting interface between the wiper die insert and the wiper die holder mating surfaces, whereby the operator is enabled to evaluate the normal forces acting on the wiper die insert and the rake angle of the wiper die insert during bending operations. By way of example, a flexible circuit of strain gauges  128   b , as shown at  FIG. 7A , may be affixed, such as by an adhesive, to the insert mating surface for this purpose, as discussed above. Electrical leads (not shown for clarity) are attached to each strain gauge  124  and connect with an external electrical circuit (i.e., CPU  146  of  FIG. 14 ). 
     Further at  FIG. 6B , the second set of pressure sensors  122   b  is placed at an axially disposed abutment surface, preferably being the abutment surface  112   a  of the keyway  112 , such that the abutment surface is at the axial abutment  118 ′ between the wiper die insert and the wiper die holder (see  FIG. 9A ). The strain gauges  124  of the second set of pressure sensors  122   b  are distributed so as to register pressures at strategic locations of the abutting interface between the wiper die insert and the wiper die holder axial surfaces, whereby the operator is enabled to evaluate the axial forces acting on the wiper die insert and the fore-aft location of the wiper die insert during bending operations. By way of example, a flexible circuit of strain gauge sensors  130   b , as shown at  FIG. 7B , may be affixed, such as by an adhesive, to the keyway for this purpose, as discussed above. Electrical leads (not shown for clarity) are attached to each strain gauge  124  and connect with an external electrical circuit (i.e., CPU  146  of  FIG. 14 ). 
     As shown at  FIG. 10A , the embodiment of the pressure sensing wiper die  100   a ′ (of  FIG. 12 ) has the holder mating surface  106   a  of the wiper die holder  106  including a normally disposed first set of pressure sensors  120   a ′ and an axially disposed second set of pressure sensors  122   a ′. Each of the pressure sensors is a tactile pressure sensor  124 ′, which is commercially available, and example being the Tactilus® matrix-based tactile surface sensor and force indicating washer products of Sensor Products, Inc. of Madison, N.J. 07940, which are essentially an “electronic skin” that records and interprets pressure distribution and magnitude between any two contacting or mating surfaces and assimilates that data collected into a powerful Windows® based tool kit (for example being resident at Block  146  of  FIG. 14 ), and the Tactilus® force indicating washer measures and assesses bolted joint tension, which, unlike traditional strain gauged load cells and force washers, the Tactilus® force sensor is extremely thin, wherein the Tactilus® force indicating washer reveals precisely how much force (tensile load) is being applied at the interface of the bolt and flange surface and how this force is circumferentially distributed. 
     At  FIG. 10A , the first set of pressure sensors  120   a ′ is placed on the holder mating surface  106   a  of the wiper die holder  106  so as to be in pressing abutment with the complementing insert mating surface  108   a  of the wiper die insert  108  (see  FIG. 13C ). The tactile pressure sensors  124 ′ of the first set of pressure sensors  120   a ′ are distributed so as to register pressures at strategic locations of the normally abutting interface between the wiper die insert and the wiper die holder mating surfaces, whereby the operator is enabled to evaluate the normal forces acting on the wiper die insert and the rake angle of the wiper die insert during bending operations. By way of example, a matrix of tactile pressure sensors  128   a ′, as for example having hundreds or thousands of tactile pressure sensors, as shown at  FIG. 11A , may be affixed, such as by an adhesive, to the holder mating surface for this purpose, wherein the matrix is formed, for example, according to techniques well known in the art, and electrically connect with an external electrical circuit (i.e., CPU  146  of  FIG. 14 ). 
     Further at  FIG. 10A , the second set of pressure sensors  122   a ′ is placed at an axially disposed abutment surface, preferably the abutment surface  110   a  of the boss  110 , such that the abutment surface is at the axial abutment  118  between the wiper die insert and the wiper die holder (see  FIG. 13B ). The tactile pressure sensors  124 ′ of the second set of pressure sensors  122   a ′ are distributed so as to register pressures at strategic locations of the axially abutting interface between the wiper die insert and the wiper die holder axial surfaces, whereby the operator is enabled to evaluate the axial forces acting on the wiper die insert and the fore-aft location of the wiper die insert during bending operations. By way of example, a matrix of tactile pressure sensors  130   a ′, as shown at  FIG. 11B , may be affixed, such as by adhesive, to the boss for this purpose, wherein the matrix is formed, for example, according to techniques well known in the art. Electrical leads connect with an external electrical circuit (i.e., CPU  146  of  FIG. 14 ). 
     As shown at  FIG. 10B , the embodiment of the pressure sensing wiper die  100   b ′ (see again  FIG. 12 ) has the insert mating surface  108   a  of the wiper die insert  108  including a normally disposed first set of pressure sensors  120   b ′ and an axially disposed second set of pressure sensors  122   b ′. Each of the pressure sensors is a tactile pressure sensor  124 ′, being commercially available as described above. 
     At  FIG. 10B , the first set of pressure sensors  120   b ′ is placed on the insert mating surface  108   a  of the wiper die insert  108  so as to be in pressing abutment with the complementing holder mating surface  106   a  of the wiper die holder  106  (see  FIG. 13C ). The tactile pressure sensors  124 ′ of the first set of pressure sensors  120   b ′ are distributed so as to register pressures at strategic locations of the normally abutting interface between the wiper die insert and the wiper die holder mating surfaces, whereby the operator is enabled to evaluate the normal forces acting on the wiper die insert and the rake angle of the wiper die insert during bending operations. By way of example, a matrix of tactile pressure sensors  128   b ′, as shown at  FIG. 11A , may be affixed, such as by an adhesive, to the insert mating surface for this purpose, as discussed above. Electrical leads connect with an external electrical circuit (i.e., CPU  146  of  FIG. 14 ). 
     Further at  FIG. 10B , the second set of pressure sensors  122   b ′ is placed at an axially disposed abutment surface, preferably the abutment surface  112   a  of the keyway  112 , such that the abutment surface is at the axial abutment  118 ′ between the wiper die insert and the wiper die holder (see  FIG. 13A ). The tactile pressure sensors  124 ′ of the second set of pressure sensors  122   b ′ are distributed so as to register pressures at strategic locations of the abutting interface between the wiper die insert and the wiper die holder axial surfaces, whereby the operator is enabled to evaluate the axial forces acting on the wiper die insert and the fore-aft location of the wiper die insert during bending operations. By way of example, a matrix of tactile pressure sensors  130   b ′, as shown at  FIG. 11B , may be affixed, such as by an adhesive, to the keyway for this purpose, as discussed above. Electrical leads connect with an external electrical circuit (i.e., CPU  146  of  FIG. 14 ). 
     An advantage of placing the first and second sets of pressure sensors on the wiper die holder is that this is a component not subject to the wear out replacement rate of the wiper die, whereby the costs associated with replacement of the pressure sensors is minimized. On the other hand, while the placement of the first and second sets of pressure sensors on the wiper die insert may be more costly due to a more rapid replacement, the sensors may detect stresses and strains in the wiper die insert which, for example under empirical or other analytical evaluation, may yield information of the operative characteristics of the wiper die insert vis-à-vis its ability to produce bent tubular workpieces of desired quality. 
     Referring now additionally to  FIGS. 14 and 15  the wiper die insert monitoring apparatus and methodology according to the present invention will be further detailed. 
     As shown at  FIG. 14 , an electrical circuit  140  includes the first set of pressure sensors  102 ,  120   a ,  120   b ,  120   a ′,  120   b ′ and the second set of pressure sensors  104 ,  122   a ,  122   b ,  122   a ′,  122   b ′, which are electrically connected with an electronic central processing unit (CPU)  146 , having an internal signal output storage capability and internal programming to process signal output data of the pressure sensors. It is understood that the various pressure sensors (be they tactile pressure sensors  124 ′, strain gauges  124  or of another type) of the first and second sets of pressure sensors would be, respectively, mutually electrically connected  142 ,  144  in a conventional manner to the CPU, as for example via wiring passing through a passageway  106   p  (shown in phantom at  FIGS. 9C and 13C ) through the wiper die holder. The electrical connection between the pressure sensors and the CPU may be wired or wireless. The CPU  146  has a data line  148  to a display device  150 , as for example an electronically driven LCD screen, wherein stored output signals and current output signals are provided to the display for comparative viewing as selectively formatted by the CPU  146 . 
     Turning attention next to  FIG. 15 , an algorithm  160  for carrying out the monitoring methodology according to the present invention is depicted by way of exemplification. At Block  162 , the algorithm is initialized and moves to Block  164 , whereat the wiper die insert  108  is affixed to the wiper die holder and the wiper die is located so that the wiper die insert has an optimized rake angle and for-aft location, as well as optimized normal pressure distribution when performing a bending operation on a tubular workpiece. Traditional execution of Block  164  involves a manual alignment procedure for optimal location of the wiper die insert utilizing a tube the same or similar to the tubular workpiece to be bent. The tube is inserted into the horizontal rotary draw bender and then clamped by the clamp and pressure dies and any adjustment is manually made by a trained operator. Once the location adjustments to the wiper die have been made, a tubular workpiece is bent to verify that the set-up is correct. This may require iteration of trial-and-error episodes, as well as removal and replacement of the wiper die insert should this become damaged during the manual location set-up, wherein the algorithm then moves on to Block  166 . 
     At Block  166 , nominal signal outputs for each of the first and second sets of pressure sensors are provided by test bending operations, which signal outputs are stored in the CPU. A tubular workpiece is bent and the normal and axial pressures (strains) exerted on the wiper die are recorded at the CPU  146 , and the quality of the bent tube is observed and recorded. This process repeats itself several times and each time with different values for any of the wiper die insert rake angle, fore/aft location and/or the normal pressure distribution. Following this iterative process for multiple tooling configurations, an operating window is established wherein average nominal output signal values are provided and stored in the CPU. Multiple operating windows may also be established based on tube material properties, lubrication, tube coatings, tube thickness, tube diameter, clamp die configuration, bend die diameter, etc, each being recorded in the CPU as a nominal profile which can be called-up by the operator. Once an operating window has been established, the nominal output signal values are used to correctly set-up the dies in order to make a good quality bend by using the strain profiles, knowledge and experience. This operating window should yield a set-up sweet spot which will provide for the longest tool life, best quality and reduce equipment stress for an overall gain in productivity at reduced downtime and cost. This information can now be incorporated into the bender controller and used as a wiper die monitor for production purposes (i.e., provide a set of nominal output signal values for monitoring). Indeed, a step function can be developed that will allow incremental adjustments to the dies during production runs that will allow for the maximum wiper die life, improved bend quality and increased productivity. 
     Thereafter, at Block  168 , in the course of operation of the horizontal rotary draw bender, the signal outputs from the first and second sets of pressure sensors are compared to the stored nominal signal outputs, as for example by an operator observing the display device  150 . Next, at Decision Block  170 , inquiry is made as to whether the current output signals are within a predetermined amount of acceptable drift with respect to nominal output signals via the operator making a comparative viewing or by an electronic data analysis subroutine of the CPU. If the answer to the inquiry is yes, the algorithm loops back to Block  168 , whereat monitoring of bending operations continues. However, if the answer to the inquiry is no, then the algorithm advances to Block  172 , whereat the wiper die insert is considered to be in a condition of unacceptability to make quality bent tubular articles in the horizontal rotary draw bender, whereby corrective action is taken by the operator, as for example by realignment or replacement of the wiper die insert. Thereafter, the algorithm returns to Block  162 . 
     A further exemplification of the execution of Blocks  168  through  172  is as follows. If during a bending operation, the first set of pressure sensors nearest or farthest from the insert edge have an output signal change (drift) from the nominal output signals (above a predetermined acceptable range), then the operator is enabled to evaluate whether the insert edge is improperly mating to the concave radius of the bend die due to an improper rake angle, requiring correction. If during a bending operation, the first set of pressure sensors have an output signal change (drift) from the nominal output signals (above a predetermined acceptable range), then the operator is enabled to evaluate whether the wiper die insert has an improper normal force acting upon it, requiring correction. If during a bending operation, the second set of pressure sensors have an output signal change (drift) from the nominal output signals (above a predetermined acceptable range), then the operator is enabled to evaluate whether the wiper die insert fore-aft location may be improper, requiring correction. If during a bending operation, the first and/or second set of pressure sensors have an output signal change (drift) from the nominal output signals (above a predetermined acceptable range), then the operator is enabled to evaluate whether the wipe friction of the workpiece relative to the insert workpiece seating surface has become too low or too high, requiring correction. 
     To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.