The invention relates to a method for shape cutting a pipe end, said method comprising cutting two arc-rimmed pieces from the pipe end by means of a punching tool and a mold, the punching tool having therefore an arc-shaped cutting edge and the mold having a contour arc consistent with the curvature of the cutting edge, and the cutting procedures of the pieces being performed outwardly from within the end of a pipe in two successive cutting phases.

The invention also relates to an apparatus for shape cutting, said apparatus comprising a punching tool provided with a cutting edge consistent with the curvature of a piece to be cut off, and a mold for restraining a pipe to be shaped, the mold having a contour arc consistent with the curvature of the cutting edge.

In the process of making T-junctions for relatively thin-walled flow pipes, the main pipe and a branch pipe are joined to each other by welding. The round tubular shape requires shaping of the pieces to be joined in order to enable the welding.

The most common technique is to conduct welding from outside a pipe on an exterior surface of the pipe. In order to ensure penetration welding, particularly in pipes of considerable thickness, the end of a branch pipe will be cut diagonally in such a way that, when the branch pipe has its end curve in engagement with a surface of the main pipe, the collision point thereof develops an outwardly opening V-groove (chamfer). Such a cutting procedure has been disclosed in Patent publication GB 1,025,685. In welding techniques, in which the pipes to be joined are welded without a filler metal by fusing pieces to be joined from within the pipe, the pieces to be joined require a different type of preliminary preparation. The front sur- face (cut end) of a branch pipe that collides with a main pipe must come together over its entire area in a gapless manner (snugly) with an exterior surface of the main pipe. The cutting area of a contoured branch pipe section is not allowed to have cutting burrs in an internal corner of the pipe. Thus, the cutting must be performed outwardly from within.

Patent publication US 4,986,154 discloses a foregoing type of method and tool, which enables contour cutting to be performed outwardly from within a tube. Between operations of cutting off the pieces, the tube must be re- leased, rotated 180°, positioned and secured. Automation of these procedures is difficult. In addition, the shaping of a punching tool requires a major use of force, nor does it enable the engagement of a branch tube's front surface (cut end) over its entire area in a gapless manner (snugly) with an exterior surface of the main pipe as a chord of the cutting edge matches an in- ternal diameter of the tube to be cut. Hence, a section of the tube end between the cutting arcs is left with uncut surfaces made up by a part of the original tube end surface.

Patent publication DE 1096717 discloses a foregoing type of method and ap- paratus, which enables cutting to be performed outwards from with a pipe with one and the same cutting tool in both directions. In this case, likewise, a section of the pipe end between the cutting arcs is left with uncut surfaces made up by a part of the original pipe end surface. In addition, the cutting tool operating in both directions is difficult to design so as to have a suffi- cient durability.

An objective of the invention is to provide a method and an apparatus, whereby cutting can be performed outwardly from within a pipe in such a way that a chord of the cutting arc substantially exceeds the internal diame- ter of a pipe to be cut or can also exceed the external diameter of a pipe to be cut or, if desired, is substantially consistent with the external diameter of a pipe to be shaped. This objective is attained with a method presented in the appended claim 1 and with an apparatus presented in claim 3. The dependent claims disclose preferred embodiments of the invention.

In addition to a cutting procedure, the shape cutting apparatus must have a capability of using readily replaceable tool arrangements for handling pipe blanks in a given range of sizes and lengths. In addition to this, the apparatus must have a capability of its operation in a working process to be au- tomated in view of handling large volumes. These objectives can also be attained with the invention.

The invention will now be described in more detail with reference to the accompanying drawings, in which:

Fig. 1 shows a shape-cut pipe end in a cutting direction,

Fig. 2 shows a shape-cut pipe end rotated 90° with respect to fig. 1 and additionally a shape-cutting punch with its punching tool in a side view and in a partial section,

Fig. 3 shows a cut pipe placed in a mold 7 and a shape-cutting punch in a plan view, Fig. 4 shows a shape-cutting punch inserted into a pipe end and ready for a first cutting phase, shows a shape-cutting punch inserted into a pipe end and ready for a second cutting phase, and shows schematically a shape-cutting apparatus in a side view with arrows indicating movements of various components, and a turntable 6 for supporting and operating the molds 7. If to the end of a pipe 1 is to be joined another pipe identical or larger in diameter, the pipe 1 must have its end shape-cut for a cutting line 2a which makes an arc in the form of a semicircle or a circular segment as seen in the cutting direction. In the case of pipes identical in diameter, the cutting arc 2a has a radius equal to an external radius of the pipe 1. If the pipe 1 is joined as a branch pipe to a main pipe larger in diameter, the cutting arc 2a must be made respectively with an arc consistent with an external radius of the main pipe. The cutting arc 2a has a chord which is substantially identical to an external diameter of the pipe 1 to be shaped, whereby sharp edges 2.1 developed in junctions of the cutting arcs 2a will be limited to an exterior surface of the pipe.

To the end of a rod 5 co-directional with a center axis C of the pipe 1 is mounted to punching tool 3, 4, which is provided with a sharp-rimmed cutting edge 4 in the shape of a circular arc. The cutting edge has a radius of its arc matching the external radius of a pipe to be joined. This is achieved e.g. by making a flat surface on an otherwise curved surface and obtuse protrusion, whereby the cutting edge 4 is formed by an intersection line of the flat surface and the curved surface. The apparatus comprises two two-part molds 7, which are provided on a parting plane of the molds with a half-groove matching the diameter of a pipe to be joined. The mold 7 has one of its end edges, as seen perpendicularly to the parting plane, provided with contour arcs consistent with the arc to be cut in a central position relative to the groove on the parting plane, whereby the junctions of the contour arcs and the parting plane develop sharp corners on either side of the parting plane. When the molds are opening, the lower groove functions as a receiving space for a pipe to be cut. The upper half mold is lowered on top of the pipe and in a cutting position the half molds are pressed immovably against each other.

The cutting is conducted in two successive sequences. Both cutting sequenc- es are performed with one and the same punching tool 3, 4. In a first phase, the punching tool 3, 4 is inserted into an end of the pipe 1 by displacing the rod 5 in an axial direction of the pipe 1, i.e. co-directionally with a center line C of the pipe, while the cutting edge lies in the vicinity of the pipe center line. Towards the end of insertion, it is advisable that the punching tool be simultaneously displaced also in radial direction as shown in fig. 4 with a dashed line ABi. The punching tool 3, 4 is penetrating into the pipe wall in a plane of the cutting edge 4, since the cutting edge 4 has its chord, with a maximum penetration distance at the end of the pipe 1, corresponding substantially to an external diameter of the pipe 1. When the axial motion of the punching tool 3, 4 has reached its extreme position, the displacement of the rod 5 will occur perpendicularly to the axial direction of the pipe 1. In the illustrated case, this displacement direction Bi is downward in fig. 4 for cutting a first piece 2 matching the punching tool shape off the end of the pipe 1 against a contour arc present on a first side of the parting plane of the mold 7. The cutting edge 4 by-passes the contour arc at a close distance.

For a second cutting phase, the punching tool is withdrawn out of the pipe end by displacing the rod 5 in axial direction away from the pipe 1. This is followed by rotating the rod 180° around its axis, whereby the cutting edge 4 also rotates 180°, after which the rod 5 is displaced in the direction of an arrow A for re-inserting the punching tool 3, 4 into the end of the pipe 1. At this point, the cutting edge 4 lies at an adjusted distance relative to the center line C closer to the first cutting. This is followed by displacing the rod 5 and respectively the punching tool 3, 4 in a direction B ₂ which is perpendicu- lar to the center line C of the pipe 1 and which is opposite to the previous displacement direction Bi, thus enabling a second piece matching the shape of the cutting edge 4 to be cut off the pipe end against a contour arc of the mold. In the illustrated case (fig. 5), the displacement direction B ₂ is upwards.

As depicted in fig. 4, the cutting edge 4 of a punching tool is inserted into an end of the pipe 1 and penetrated into a wall of the pipe in a plane of the cutting edge 4 below the pipe center line C, and the punching tool is pressed downwards for cutting a piece matching the shape of the cutting edge 4 off a bottom edge of the pipe end. Having been withdrawn out and rotated through 180°, the punching tool 3, 4 is re-inserted into the pipe end (fig. 5) so as to place the cutting edge 4 again below the pipe center line C, thus enabling the cutting off of a second piece by lifting the punching tool 3, 4 upward. In the condition shown in fig. 5, the piece 2 cut off a bottom edge of the pipe end provides a space for the punching tool 3, 4. With this arrangement, the punching tool can be designed so as to provide a solid sup- port near the cutting edge 4 on that side of the cutting edge plane which follows behind the cutting edge during the course of a cutting displacement. Thereby, the punching tool is made durable.

Naturally, the first and second cutting phases can also be conducted in oppo- site displacement directions in such a way that the cutting edge 4 is inserted into a pipe end above the pipe center line C and the punching tool is lifted upward for cutting a piece matching the shape of the tool curvature off a top edge of the pipe end. In the second sequence, once the punching tool 3, 4 has been rotated through 180°, the cutting edge 4 is inserted into the pipe again above the center line C and the punching tool is pressed downward for cutting a second piece matching the shape of the cutting edge off a bottom edge of the pipe end. Illustrated in figs. 4 and 5 is an alternative, wherein the cutting is commenced from the bottom edge of a pipe end.

Fig. 6 shows an apparatus providing external support for a pipe 1 to be cut and for a mold 7. Two two-part molds 7 are supported on a turntable 6 which is rotatable around a vertical rotation shaft 10 through 180° for dis- placing the mold 7 from a loading position to a cutting position and for simultaneously displacing the other mold from a cutting position to a loading position. On either side of the rotation shaft 10 is a backstop 11 for the pipe 1 to be shaped, which determines the pipe position and holds the pipe axially sta- tionary while a punching tool 3, 4 is being inserted into the pipe. A retainer 8 presses the half molds together and holds the mold 7 stationary during the shape cutting of a pipe end. On the opposite side of the turntable 6, a lifting grapple 9 raises an upper half of the mold 7 up for replacing the pipe. While cutting a second pipe, one of the molds is relieved of the already cut pipe and the mold is supplied with another pipe to be cut. The retainer 8 is lowered on top of a mold 7 holding the pipe 1 for bracing the mold during a cutting procedure. The retainer 8 is lifted up for as long as it takes to rotate the turntable 6. Even though the preferred embodiment has just one punching tool for both cutting phases, it is possible to employ two jointly or separately movable punching tools with pre-established directions opposite to each other in a manner corresponding to figs. 4 and 5.