US2955638A - Forming and pressure dies for pipe-bending machines - Google Patents

Description

A.- HELLWIG 2,955,638 FORMING AND PRESSURE DIES FOR PIPE-BENDING MACHINES Oct. 11, 1960 Filed Feb. 5, 1958 INVENTOR. AueusT HELLWIG United States Patent "ice FORMING 'AND PRESSURE DIES FOR PIPE-BENDING MACHINES August Hellwig, Chicago, 111.; Frank P. Hellwig,

administrator of said August Hellwig, deceased Filed Feb. '5, 1958, Ser. No. 713,330

2 Claims. (Cl. 153-32) This invention relates to improvements in pipe-bending machines. 'More specifically, it relates to improvements in the forming dies and wiping members or follow bars of such machines.

Existing dies result in two disadvantages. One is the flattening of the bent pipe into elliptical section, a form heretofore referred to as final. Another is the indentation of the pipe, in which the outline of the forming die is impressed into the pipe, particularly at the starting portion of the bend.

It is an object of this invention to provide improved forming dies and follow bars, adapted to form bends of true circular section and free of indentation.

It is another object to provide means whereby the bending force is applied initially at a pre-determined point with respect to the fulcrum of the bend, and thereafter applied at varying points determined independently of the judgement or skill of the operator.

Still another object is to provide dies with novel grooves,

dimensioned in accordance with a newly discovered prin- .ciple herein described.

Other objects and advantages of the invention are explained with reference to the accompanying drawings, of which:

Figure 1 is a fragmentary plan view of a commercial pipe-bending machine.

Figure 2 is a plan view on a larger scale, of the improved fonning die and follow bar, shown in their relative starting positions.

Figure 3 is a sectional view, taken on the line 3-3 of Figure 2.

Figure 4 is a plan view similar to Figure 2, showing the improved forming die and follow bar after advancing operatively.

Figure 5 is a sectional view, taken on the line 5--5 of Figure 4.

Figure 6 is a diagrammatic view, illustrating the dimensioning of the novel grooves.

It should be understood at the outset, that the present invention is concerned solely with the co-operation of the forming dies and follow bars, and that other elements are shown and described only 'as they are incidental. With this in mind, Figure 1 illustrates a commercial pipebending machine such as is used to bend thin-wall electrical conduit. It comprises in part, the body 10 of a hydraulic ram, to which links 11 are att-ached'by studs 12. Apin 13 rotatably supports a roller 14. Bearing against this roller is a follow bar 20' provided with a longitudinally extending groove 21, dimensioned to accommodate a pipe P.

A plunger 15 is pivotally attached by a pin 16 to a .tached'by a pin 18 to the forming-die Patented Oct. 11, 1960 the forming die 30', which carries the pipe around with it, and forms a bend nesting in the arcuate groove 31'. This process is well known to those skilled in the art of bending pipe.

Existing forming dies and mating follow bars are commonly made with a combined depth of grooves which measures less than'the diameter of the pipe, as indicated at 19. This aggravates the inherent tendency of the pipe to flatten. Also, it was heretofore believed essential to restrict minutely, the portion of the pipe being worked, so that drawingof the metal occurred rather than bending. A characteristic result is the indentation of the pipe, particularly at the starting portion of the bend, in which the outline of the forming die is noticeably impressed in the pipe.

The co-action of several improvements serves to overcome these disadvantages. Looking now at Figures 2 and 3, the improved follow bar 20 has a groove 21 bordered by flat portions 22. These serve as rails, on which the die 30 rolls. Starting at the end 23, the rails slope at a small angle to an intermediate point 24. The groove 21 is deepest at the end 23, and decreases gradually in depth to the point 24. For the remaining length of the follow bar 20, the groove 21 is of uniform depth.

At the start of a bending operation, the peripheral edges 32 of the forming die bear against the rails 22 near the deeper portion of the groove .21. The excess depth affords a space as indicated at 25. Obviously there is no force. tending to crush the pipe.

As shown in Fig. 2, the normal 33 passes through the point 26, a few degrees from the start of groove 31. The pipe P is shown at a small angleto the groove 21. This situation occurs when sufiicient force is exerted to flex the pipe longitudinally to its yield point, but without causing permanent bending.

The pipes impingement in groove 31 terminates at point 26. This point is referred to as the momentary fulcrum, against which the pipe is bent. Further bending results in advancing the terminus of the bend, with a corresponding advance of the momentary fulcrum.

Heretofore, the pipe was closely confined by the combined grooves of the forming and pressure dies, and force was exerted by the pressure die at a point substantially coincident with the momentary fulcrum, without first flexing a substantial portion of the pipe. The result is more of a drawing of the metal than one of bending.

In the present invention, as shown in Fig. 2, the pipe is fiexed in a long curve, extending from the starting end of the pressure die to a point 28. A normal through this point intersects the opposite side of the pipe at 27, and defines an angle of 15 with the normal 33 It is apparent that in this situation bending force is applied at a point 28 which is 15 removed from the momentary fulcrum 26. As a result, the pipe is flexed into a long curve, longitudinally equivalent to a 15 are.

As the forming die rolls further along the pressure die, the angle between the momentary fulcrum and the point at which force is applied, gradually decreases. When the forming die has rotated 15, it assumes the position shown in Fig. 4. The normal 55, drawn through the momentary fulcrum, simultaneously passes through the 'point 28 in the forming die, defining the point at which When the plunger 15 is caused to advance, it rotates bending force is exerted. Thereafter, until the completionof the bend, this relationship remains constant.

'The present invention limits the flexing of the pipe to an initial portion of the bending cycle, during which the flexed portion of the pipe decreases in length until the momentary fulcrum is substantially in line with the point at which force is exerted by the pressure die. If the flexing is permitted to extend throughout the bending cycle, or to a portion substantially exceeding at 15 arc, the resultis a wrinkling of the pipe. Limiting the flexing as described is significant, because while some older bending devices are provided with means for adjusting the initial position of the follow bar with respect to the fulcrum, the present invention is the first'to provide for the pre-determined and automatic variation of this relationship.

As an example, for bending thin-wall conduit of 1%" trade size, the added depth of the groove at the end 23 is The length of the inclined portion of the rails, from the end 23 to the point 24 is 3". For pipes of other diameter, material or wall-thickness, the length and rise of the inclined portion of the rails 22 may be determined experimentally.

Older forming dies and follow bars were made-with grooves which, besides being less in depth than the diameter of the pipe, were also greater in width. This was done to accommodate the pipe after it had been permitted to flatten.

Other dies have been dimensioned to form bends which are permanently and substantially flattened in the plane of the bend. While such bends may be adaptable to particular applications, they do not conform to the true roundness which has been the long-sought object of most pipe-bending inventions.

It is well known that a pipe or tube may easily be compressed or flattened. Beyond this bare fact, no data has ever been compiled of the extent to which various sizes of pipes may be laterally compressed without permanent distortion. Neither has lateral compressibility been previously recognized as the determining factor in dimensioning the grooves of forming dies to an optimum value.

I have discovered that there is, for every right section of pipe, a lateral elastic limit which bears a direct relationship to the bending of the pipe, and to the correct dimensioning of the grooves in the forming dies. Moreover, I have discovered a simple method for determining this lateral elastic limit.

If a short piece of pipe is clamped between the jaws of a machinists vise, it may be measured while being subjected to increasingly greater compression. It is a simple matter to determine in this manner, the ultimate compression from which the pipe still resumes its full diameter upon release. Both the minor and major axis are recorded at the ultimate compression.

The minor axis determines the correct width of the groove in the forming die. The major axis determines the correct depth of the combined grooves in the forming die and follow bar. A few thousandths of an inch may be added to both the width and depth, as a safety factor. This dimensioning, as well as a further novelty in the grooves, is illustrated in Figure 6.

The groove 31 is formed with a true semi-circle as the base, with tangent portions T extending therefrom. The diameter of the semi-circle is equal to the minor axis described above. The tangent portions T are so dimensioned that the total depth of the groove 31 is sixtenths of the major axis. Heretofore it has always been customary to make the grooves in the forming die and follow bar of equal depth. The purpose of the additional depth of groove in the novel forming die is to insure that the pipe is confined laterally before it bottoms in the groove, so that it cannot flatten when flexed at the beginning of the bending operation.

The groove 21 is formed as the arc of a circle having the same radius as the groove 31, and having a depth of four-tenths of the major axis. This is substantially equal to an arc of 144 degrees.

The combined grooves 21 and 31 encircle the pipe at whatever point the follow bar 20 bears against the forming die 30. It will be understood that the groove 21 is deepened in the inclined portion of the follow bar as previously explained.

"Bends formed by the co-operation of the improved forming die and follow bar are of true circular section. -If at any portion of a bend, measurements are taken of the diameter in the plane of the bend and lateral thereto, the difference between such measurements will not exceed the accidental variations similarly measured at unbent portions of the pipe.

The invention has been described with reference to an illustrative pipe-bending machine, and with particular means for varying the position of the pressure die with respect to the fulcrum ofthe bend. Obviously the advantages extend to other pipe-bending machines, and to alternative means for varying the relative position of the pressure die.

It is therefor not the intention to limit the invention to the particular embodiment herein described. Rather, the intention is to include all such variations and alternative embodiments and adaptations as fall Within the spirit of the invention, and of the appended claims.

I claim:

1. A pipe-bending machine comprising, in combination, a pressure die having an initial pressure application end, a final pressure end, and sidewalls therebetween defining a groove adapted to partially receive a pipe to be bent, said pressure die groove being of true semi-circular configuration bordered by flat surface portions adapted to serve as rails running thelength of said groove, a forming diehaving a curved surface provided with sidewalls at the periphery thereof defining a groove adapted to cooperate with said pressure die by circumferentially enclosing said pipe while said curved surface bears upon the rails of said pressure die, said forming die groove being of true semicircular configuration terminating in tangential flats at the inner portions of the sidewalls, means pivotally attached to said forming die tangentially holding said pipe in the forming die groove, and means for rotating said forming die whereby said pipe is carried around to form a bend nesting in the curved groove of said forming die, each of said grooves having a width equal to about the minor compressive axis of said pipe, the depth of said forming die groove plus tangential flats being equal to about 0.6 of the major compressive axis of said pipe and the depth of said pressure die groove being equal to about 0.4 of the major compressive axis, said rails sloping at a small angle from said initial pressure end to a point intermediate said initial pressure end and said final pressure end to provide therebetween a groove of depth slightly greater than about 0.4 of the major compressive axis, whereby the initial bending force can be applied to a pipe at a point along its length substantially removed from the point of first impingement on the forming die so that a greater portion of the pipe can be worked initially, while the point at which the pressure die exerts force is being automatically varied to gradually change the bending force to a drawing force.

2. A pipe-bending machine comprising, in combination, a pressure die having an initial pressure application end, a final pressure end, and sidewalls therebetween defining a groove adapted to partially receive a pipe to be bent, said pressure die groove being bordered by flat surface portions adapted to serve as rails running the length of said groove, a forming die having a curved surface provided with sidewalls at the periphery thereof defining a groove adapted to cooperate with said pressure die by circumferentially enclosing said pipe while said curved surface bears upon the rails of said pressure die, said forming die groove terminating in tangential flats at the inner portions of the sidewalls, and means for rotating said forming die whereby said pipe is carried around to form a bend nesting in the curved groove of said forming die, each of said grooves having a Width equal to about the minor compressive axis of said pipe, the depth of said forming die groove plus tangential .flats being equal to about 0.6 ofthe major compressive axis of said pipe and the depth of said pressure die groove being equal to about 0.4 of the major compressive axis, said rails sloping at a small angle from said initial pressure end to a point intermediate said initial pressure end and said final References Cited in the file of this patent UNITED STATES PATENTS Stephens Nov. 28, 1882 Abramson et a] Nov. 21, 1933 FOREIGN PATENTS Canada .u. May 17, 1949 Canada Oct. 1, 1957

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