GB2174318A - Manufacturing branched metal pipes - Google Patents

Abstract

A branched seamless metal pipe or a seamless metal header is made by preforming a flattened seamless tube stock (51') to form a bulging portion by setting a tool, which has an extruding punch (55) attached temporarily at a right angle to a supporting mandrel (56), in the tube stock with the punch directed in the longer diametrical direction of the tube stock to face the inner face at the required bulging portion, by setting the tube stock and the tool between a pair of dies (52, 53) having a die hole (57) such that its longer diameter is directed to extend on the die hole axis, and by pressing the tube stock inward in that direction to extrude the punch into the tube inner face to form the bulging portion (58). The extruding punch and mandrel are removed from the trunk pipe portion and the bulging portion by removing the mandrel, drilling a branch hole and knocking out the punch. The trunk pipe and branch are machined and finished, optionally by drawing out the branch by an internal drawing punch. The pre-formed trunk pipe portion may be pressed to correct its circularity. <IMAGE>

Description

SPECIFICATION Process for Manufacturing Branched Metal Pipes The present invention relates to a process for manufacturing a branched seamless metal pipe of mono-block construction having no weld line and, more particularly, to a process for manufacturing a branched seamless metal pipe such as a T-branched pipe (which will be shortly referred to as a "T-joint"), which is used for branching or shunting a pipeline and in which a trunk and at least one branch have their axes intersecting at a right angle.

Before entering into detailed description of the present invention, cursory review will be made on the background of the invention with reference to the accompanying drawings. Referring firstly to Figure 1, the T-joint indicated generally at numeral 20 is constructed of a trunk pipe 21 and at least one branch pipe 22. The T-joint 20 has its shape characterized bythetwo ratios: (1)the ratio D2/D, of the external diameter D2 of the branch pipe 22 to the external diameter1 of the trunk pipe 21; and (2) the ratio H/D2 of the height of protrusion H to the external diameter D2 of the branch pipe 22.

Reference letters T1, L, and d2 appearing in Figure 1 indicate the thickness and length of the trunk pipe 21, and the internal diameter of the branch pipe 22, respectively. Reference numeral 23 indicates a crotch at which the branch pipe 22 is branched from the trunk pipe 21.

It is well known that the inner face of the crotch 23 and the metal flows mare importantfeaturesfor evaluating the performance of the T-joint 20. A crotch 23 may be classified into one or two types as to its sectional face shape, as shown in Figures 2(A) and (B). The crotch 23 of the type shown in Figure 2(A) will be called the "smooth crotch", whereas the crotch of the other type shown in Figure 2(B) will be called the "sharp crotch". The former smooth crotch has a large radius of curvature R so that it produced smooth shunting of a fluid. The latter sharp crotch has a small radius of curvature R but a large thickness Tc so that it possesses a high strength.

As to the metal flows, on the other hand, it can be said that the metal flows are desired to have continuous lines running from the trunk pipe 21 through the crotch 23 to the branch pipe 22 in case the T-joint 20 is used in a remarkably corrosive circumstance. In other words, corrosion is liable to develop if the metal flow lines run through the branch pipe 22. In the manufacture of the T-joint of the prior art, more specifically, the following relationships are present between the inner face of the crotch 23 and the metal flows m, as shown in Figures 2(A) and (B). The metal flows m are continuous in the case of the smooth crotch 23 of Figure 2(A) but are discontinuous in the case of the sharp crotch 23 of Figure 2(B).In short, it has been very difficult in the prior are to manufacture the T-joint 20 which has both the sharp crotch 23 and the continuous metal flows m, as shown in Figure 2(C). Therefore, it is an object of the present invention to provide a process for manufacturing the T-joint 20 of Figure 2(C) while overcoming the above difficulty.

One of the simplest processes for manufacturing aT-joint is a direct drawing process, which will be described below with reference to Figures 3(A)(a), 3(A)(b), 3(B)(a) and 3(B)(b). First of all, there is prepared a circular, straight tube stock 24 which has substantially the same external diameter D1, length L, and thickness T, as those of the trunk pipe 21 of the target product or T-joint 20 of Figure 1. Then, the tube stock 24 is punched or machined to form a hole 25 at a portion where the branch pipe 22 is to be formed. The punched tube stock 24 is set, after it has been heated either around the hole 25 or in its entirety, on a drawing die 26.This die 26 is formed with a hole 27 which has a shape generally profiling the contour of the branch pipe 22 of the target product 20 and substantially the same internal diameter as the external diameter D2 of the branch pipe 22. After this setting, a drawing rod 28 is inserted from the die hole 27 through the hole 25 into the inside of the tube stock 24. To the extending head of the drawing rod 28, there is connected and fixed a drawing punch 28 which is smoothly rounded to its squared end having an external diameter dp smaller by a finishing allowance than the internal diameter d2 of the branch pipe 22 of the product.Then, the drawing rod 28 is pulled down, as shown in Figures 3(B)(a) and 3(B)(b), to carry the drawing punch 29 downward thereby to widen the hole 25 and to bend and draw the metal around the hole 25 into the diehole 27, thus forming a directly drawn branch pipe portion 22'.

The direct drawing process described above forms the smooth crotch and the continuous metal flows of Figure 2(A) because the crotch itself is formed by the bending work. It is possible to form a sharp corner 45' (Figure 4) by making the thickness To of the tube stock 24 considerably larger than the thickness T, of the trunk pipe 21 of the targetT-joint 20 and by working the trunk pipe 21, as shown in Figure 4, to machine the hatched region 46' of the inner face of the trunk pipe 21. For the direct drawing process, however, it is quite difficult to draw the branched pipe 22 from the thick tube stock 24. A first difficulty arises from the fact that the force required for the drawing work is increased to make the drawing rod 28 liable to rupture.Another difficulty of the direct drawing process in relation to the tube stock thickness To is that the excessive thickness will make it difficult to form the branch pipe portion 22' itself. More specifically, it has been found that if the stock thickness To falls within a range of To /D2 > 0.8 (where D2 designates the diameter of the branch pipe 22), the stock portion around the hole 25 becomes difficult to bend so that the widening deformation of the hole 25 is dominantly caused by the punch drawing work, as shown by arrows in Figure 5. As a result, that stock portion is reluctant to be bent and drawn so that the branch pipe portion 22' formed becomes remarkably low.

The direct drawing process has an intrinsic limitation to the height H' of the branch pipe portion 22' formed, because for this formation the only material used is the material occupying the cylindrical region which is indicated as cross hatched at A in Figures 3(A)(a) and 3(A)(b), which region has an external diameter dp (equal to the external diameter of the drawing punch 29), an internal diameter do (equal to the diameter of the hole 25), and a height To (equal to the thickness of the tube stock 24). Even in the case of the smooth crotch, the height H' of the branch pipe 22 is at the most about 0.3 times as large as the external diameter D2 of the same. In the case of the sharp crotch, however, the height H' of the branch pipe 22 is further reduced to about 0.2 times as large as the external diameter D2.In the T-joint 20 or the like, generally speaking, the height or protrusion H of the branch pipe 22 is desired to be as large as possible from the standpoints of both the work of welding a connection pipe to the branch pipe 22 and the necessity for placing the crotch or branch root as far from the branch pipe end to be welded as possible for the sake of strength. With this in mind, therefore, the low or short branch pipe portion 22' raises a serious defect.

A second process for manufacturing the T-joint by using a straight tube as the tube stock is a reducingdrawing process. This reducing-drawing process is one for compressing a tube stock in the peripheral direction to form a bulging portion for the branch pipe and is executed by a hot working principle.

There is usually prepared a circular tube stock which has an external diameter 1.2 to 1.4 times as large as the external diameter D, of the trunk pipe of the target product and substantially the same thickness To and length L1, as those of that trunk pipe. The tube stock is first flattened to form a flattened tube 41 (Figure 6(A)) which has a shorter external diameter substantially equal to the external diameter D, of the trunk pipe. This flattened tube 41 is heated and then set in a pair of upper and lower dies 42 and 42' which define an internal shape larger than the contour of the target T-joint, by an amount to allow for thermal expansion as shown in Figure 6(A). By means of a press (not illustrated), the flattened tube 41 is pressed in the direction of its longer diameter so that it is compressed in the peripheral direction.As a result, the metal material of the tube stock 41 is partially extruded into a die hole 43, which is formed in the lower die 42' at the branch forming side, around the inlet shoulder 43, of the die hole 43 to make an intermediate product 20' which comprises, as shown in Figure 6(B), a trunk pipe portion 21' having a generally circular cross-section and a bulging portion 22" for the branch pipe 22. Then, the head of the bulging portion 22" is punched or machined at its centre to form a hole 44 so that the branch pipe portion 22' is formed by the direct drawing process which has been described with reference to Figures 3(A) and 3(B).Turning to Figure 6(C), more specifically, the drawing rod 28 is inserted into the interior of the trunk pipe portion 21' from the die hole 43 and through the hole 44, and is connected and fixed to the drawing punch 29 which has the external diameter dp, smaller by the finishing allowance than the internal diameter2 of the branch pipe 22 of the target product, as shown in Figure 1.With at least the bulging portion 22" being in a hot state, the drawing rod 28 is pulled downward to widen the punched hole 44 with the drawing punch 29 and to bend outward the bulging portion 22" around the hole 44, thus forming the branch pipe portion 22', as shown in Figure 6(D).

In the reducing-drawing process, as has been described above, the bulging portion 22" is formed in the die hole 43 at the reducing step so that the reducing-drawing process can achieve a larger branch height than the direct drawing process. At the reducing steps shown in Figures 6(A) and (B), however, the deformation of the material at the inlet shoulder 43, when it intrudes into the die hole 43 is caused by the bending (deformation) work so that the crotch has to be smoothed. In orderto manufacture aT-joint having a sharp crotch by the reducing-drawing process, the sharp crotch corner 45 has to be formed by making the thickness To of the tube stock considerably larger than the thickness T, of the target T-joint and by machining the hatched region 46, as shown in Figure 7.If the diameter ratio D2 /D, is small, however, the extrusion of the material into the die hole 43 becomes more difficult for the larger thickness To during the reducing steps. This is because, during the reducing steps from the stage shown in Figure 6(A) to the stage shown in Figure 6(B), the metal material becomes more reluctant to intrude into the die hole 43 with the decrease in the diameter ratio D2 /D, and with the increase in the ratio To ID2. It has been found that the application of this reducingdrawing process is limited substantially to the ranges of D2 /D, > 0.3 and To /D2 < 0.3.

A third process for manufacturing the T-joint is a forging-machining process. This forging-machining process manufactures aT-joint by machining either a forged solid block shown in Figure 8(A) or a forged tubular block shown in Figure 8(B). According to the forging-machining process, therefore, it is relatively easy to manufacture the T-joint having a sharp crotch. However, because the inner and outer faces of the branch pipe are machined, the metal flows have to become discontinuous, as shown in Figure 2(B). Furthermore, the forging-machining process has a disadvantage in that the forging degree of the branch pipe is lower than that of the foregoing forming processes, in which the rolled tube stock is used as the material, so that the resultant quality is inferior.

As has been described hereinbefore, in any of the direct drawing process, the reducing-drawing process and the forging-machining process it has been found remarkably difficult to make a sharp crotch and continuous metal flows compatible, as shown in Figure 2(C).

It is an object of the present invention to provide a novel process for manufacturing a branched seamless metal pipe or T-joint of monoblock construction having no weld line.

Another object of the present invention is to provide a novel process for manufacturing aT-joint which comprises a relatively thin branch pipe and a relatively thick trunk pipe.

Still another object of the present invention is to provide a novel process for manufacturing a Tjoint which is formed with a branch pipe having a relatively large height or protrusion.

A further object of the present invention is to provide a novel process for manufacturing a T-joint having a relatively slim and high branch pipe with a sharp crotch by using a relatively thick rolled tube stock, such as couid not be made by the directdrawing, bulging and reducing-drawing processes of the prior art.

A further object of the present invention is to provide a novel process for manufacturing a T-joint having a branch pipe with continuous metal flows along its wall.

A further object of the present invention is to provide a novel process for manufacturing a T-joint whose diameter ratio D,/D, is smallerthan 0.3.

A further object of the present invention is to provide a novel process for manufacturing a T-joint having a high innerface quality by using a forged rolled tube stock and by subjecting the tube stock to machining.

A further object of the present invention is to provide a novel process for manufacturing aT-joint of a relatively thick rolled tube stock by using an easily removable punch of simple construction as a tool and by utilizing the external pressure of a press as a direct working force.

A further object of the present invention is to provide a novel process for manufacturing a header having a relatively thick trunk pipe and a plurality of relatively thin and high branch pipes.

In the process of the present invention a portion of the tube stock to be branched may be bulged or raised in advance by extruding that portion by means of a punch applied to the inner face of the portion. The concept per se of extruding that portion from the inner face of the tube stock is known in the prior art. However, the extruding step of these prior art processes, as is disclosed in Japanese Patent Laid-Open Nos. 52-139664 and 57-142725, for example, is performed exclusively by driving a tool in the axial direction of the tube stock into engagement with a punch through wedges or the like to extrude a stock portion to be bulged through the punch in the radial direction (i.e., in the direction of thickness).These techniques of the prior art have had to use the complicated tool and have found its practical application difficult to a thick tu be stock requiring a high working force from the standpoint of the strength of the tool used.

The pre-formation of the bulging portion is intended to bulge and retain such a portion of the material in advance from the outer face of the tube stock as is necessary to form the target branch so that the material may be effectively used for the branch formation (at a subsequent drawing step and) at a final machining step.

According to the present invention, there is provided a process for manufacturing a branched seamless metal pipe comprising a trunk pipe and at least one branch pipe, comprising preforming a flattened seamless tube stock to form a bulging portion, which comprises setting a tool, which has an extruding punch attached substantially at a right angle to a supporting mandrel, in said tube stock such that said extruding punch is directed in the direction of the longest transverse axis of said tube stock to face the inner face of such a side portion of said tube stock as to be formed with said bulging portion, setting said tube stock together with said tool between a pair of dies, one of which has a die hole, such that the longest transverse axis of said tube stock extends in the direction of the axis of said die hole, pressing said tube stock inward in the direction of the largest transverse axis thereof through said dies to extrude said extruding punch relatively in the thickness direction of said tube stock into the inner face of said tube stock through said supporting mandrel, thereby to form an intermediate product having a generally circular trunk pipe portion with said bulging portion, removing said extruding punch and said supporting mandrel from said trunk pipe portion and said bulging portion and machining and finishing said trunk pipe portion and said bulging portion to the sizes of the trunk pipe and the branch pipe of said branched metal pipe.

According to another feature of the present invention, there is provided a process for manufacturing a seamless metal header comprising a trunk pipe and a plurality of branch pipes, comprising preforming a flattened seamless tube stock to form a plurality of bulging portions, which comprises setting a tool, which has the corresponding number of extruding punches attached substantially at a right angle to supporting mandrel, in said tube stock such that said extruding punches are directed in the direction of the longest transverse axis of said tube stock to face the inner faces of the corresponding number of such side portions of said tube stock as to be formed with said bulging portions, setting said tube stock together with said tool between a pair of dies, one of which has the corresponding number of die holes, such that the longest transverse axis of said tube stock extends in the direction of the axes of said die holes, pressing said tube stock inward in the direction of the longest transverse axis thereof through said dies to extrude said extruding punches relatively in the thickness direction of said tube stock into the inner faces of said tube stock through said supporting mandrel thereby to form an intermediate product having a generally circular trunk pipe portion with said bulging portions, removing said extruding punches and said supporting mandrel from said trunk pipe portion any'said bulging portions and machining and finishing said trunk pipe portion and said bulging portions to the sizes of the trunk pipe and the branch pipes of said metal header.

By way of example only, specific embodiments of the invention will now be described, with reference to the accompanying drawings, in which: Figure 1 is a perspective view showing the overall shape of a T-joint; Figures 2(A), 2(B) and 2(C) are cross-sectional side elevations showing three types of crotches of the T-joint of Figure 1; Figures 3(A)(a) to 3(B)(b) are partially crosssectional side and end elevations showing stepwise the direct drawing process of the prior art; Figure 4 is a cross-sectional side elevation for explaining the manufacture of aT-joint having a sharp crotch by machining the inner face of a trunk pipe, in accordance with the prior art;; Figure 5 is a schematic side elevation, partly in cross-section, for explaining the drawn phenomenon of a portion of the relatively thick tube stock around a die hole for use when the tube stock is subjected to the direct drawing process of Figures 3(A)(a) to 3(B)(b); Figures 6(A) to 6(D) are partially cross-sectional side and end elevations for explaining stepwise the reducing-forming process of the prior art; Figure 7 is a sectional side elevation for explaining the manufacture of a T-joint having a sharp crotch, by the reducing-forming process of the prior art; Figures 8(A) and 8(B) are partially cross-sectional side elevations showing two kinds of material blocks, i.e., a solid block and a hollow block, respectively, before forging processes for explaining the forging-machining process of the prior art;; Figures 9(A)(a) and (b) are perspective views showing a tube stock before and after a flattening step, respectively; Figures 9(A)(c) and (d) are cross-sectional end elevations for explaining the flattening step of the tube stock shown in Figures 9(A)(a) and (b); Figures 9(B)(a) and (b) are partially cross-sectional side and end elevations respectively for explaining a preforming step of the flattened tube stock shown in Figures 9(A)(a) to (d); Figures 9(C-l)(a) and (b) are partially crosssectional side and end elevations respectively showing the intermediate product of the preforming step of Figures 9(B)(a) and (b) when intermediate product has a generally circular trunk pipe portion with a bulging portion;; Figures 9(C-ll)(a) and (b) are similar views to Figures 9(C-l)(a) and (b), when the intermediate product is overpressed to have a flattened trunk pipe portion with a bulging portion; Figures 9(D)(a) and (b) are partially cross-sectional end elevations for explaining a correcting step of the intermediate product shown in Figures 9(Gll)(a) and (b); Figures 9(E)(a) to (d) are partially cross-sectional side and end elevations for explaining a punch removing step of the preformed intermediate product shown in Figures 9(C-l)(a) and (b) or the corrected intermediate product shown in Figures 9(D)(a) and (b); Figure 9(F) is a partially cross-sectional side elevation for explaining a machining-finishing step of the intermediate product cleared of its extruding punch at the punch removing step of Figures 9(E)(a) to (d);; Figures 9(G)(a) to (c) are partially cross-sectional side and end elevations for explaining a drawing step of the punchless intermediate product of Figures 9(E)(a) to (d) before the machining-finishing step of Figure 9(F); Figure 10 is a schematic side elevation for explaining the metal flows of the metal material of the tube stock when the tube stock is partially extruded at the preforming step of Figures 9(B)(a) and (b) into a die hole so that it is sheared and deformed to form the bulging portion; Figure 11 is a schematic cross-sectional side elevation for explaining an extrusion reaction force to be exerted upon the extruding punch at the pre-forming step of Figures 9(B)(a) and (b);; Figure 12(A) is a schematic cross-sectional side elevation for explaining the relationship between the ratio of the diameter dp of the extruding punch to the diameter D2 of the die hole at the preforming step of Figures 9(B)(a) and (b) and an extrusion efficiency expressed by the ratio of the volume V2 of the bulging portion prepared at the preforming step and the displacement volume V1 of the tube material to be displaced by the extruding punch; Figure 12(B) is a graph plotting the experimental values of the extrusion efficiency expressed by V2 N1 xl 00 (%) against the diameter ratio dp ID2 for explaining the shape change of the tube stock at the preforming step of Figures 9(B)(a) and (b); and Figure 13 is a perspective view showing the contours of a pair of correcting dies to be used at the correcting step shown in Figures 9(D)(a) and (b).

The process according to the present invention will be described in detail in the following in the order of steps inclusive.

(1) A circular, straight tube stock 51 is prepared, as shown in Figure 9(A)(a), and is then flattened to form a primaryflattube 51', as shown in Figure 9(A)(b). As shown, the circular tube stock 51 has an external diameter D,, a thickness To and a length L0, whereastheflattube5l' has a shorter external diameter (minor axis) D2 and longer and shorter internal diameters (major axis and minor axis respectively) Ii and 12. Turning to Figure 9(A)(c), more specifically, the circular tube stock 51 is set between a pair of upper and lower flattening dies 52 and 53 which are formed with grooves 54 having an arcuate section of a radius of curvature R0 larger than the external diameter (i.e., 1/2 Do) of the tube stock 51.By the action of a not-shown ram (not illustrated), the upper die 52 is forced downward to press the tube stock 51 between the two dies 52 and 53 to form the flattened tube 51', as shown in Figure 9(A)(d). The extent of this flattening work should fall within such a range that a later-described punch and mandrel can be set inside the flat tube 51'. The shorter external diameter D1 should be made substantially equal to the external diameter D1 of the trunk pipe 21 of the T-joint 20 shown in Figure 1 in the case when the flat tube 51' is pressed at a subsequent pre-forming step to have a generally circulartrunk pipe with a bulging portion.In the case when the flat tube 51' is once overpressed at the preforming step to pre-form a flattened tube, which has to be pressed again so that it may be corrected to have the generally circular trunk pipe with the bulging portion, it is desired in view of both the reduction in the peripheral length by the flattening work and the effect of the correction of circularity by the subsequent correcting work that the shorter external diameter D1 be 1.02 to 1.05 times as large as the external diameter D1 of the trunk pipe 21 of Figure 1. On the other hand, the length L0 of the tube stock 51 may be slightly larger than the length L1 of the target trunk pipe 21 in order to take a small finish allowance into account.The selection of the thickness To of the tube stock 51 has an especially important meaning in the process of the present invention, and the tube thickness To is determined from both the thickness T1 of the trunk pipe 21 of the target product and the volume of the branch pipe 22 of the product, as will be described in detail.

The flattening step described above may be executed in either a cold or a hot state, and may be omitted if the flat tube 51' is prepared in advance as a rolled tube stock by a rolling work.

(2) At the subsequent preforming step, the primary flat tube 51' is formed on its outer face with a bulging portionforthe branch pipe 22 of Figure 1.

Referring to Figures 9(B)(a) and (b), the flat tube 51' is turned by 90 degrees from the previous position of the flattening work of Figure 9(A)(d) to have its longer diameter (major axis) oriented in a vertical direction (i.e., the die facing direction), and a tool, which is prepared by attaching an extruding punch 55 art a right angle to a supporting mandrel 56 longer than the flat tube 51', is then inserted and set in the flat tube 51'.More specifically, this flat tube 51' is so set that its portion to be branched faces a die hole 57 which is formed in the lower die 53, as shown, to have a diameter D2 substantially equal to the external diameter D2 of the branch pipe 22 of the target product, and the tool is positioned such that its punch 55 is oriented in the direction of the longer diameter of the flat tube 51' to face the die hole 57 through the inner face of the portion of the flat tube 51' to be branched. The attachment of the punch 55 to the mandrel 56 of the tool is effected by means of a thin bolt or a spot welding work (not illustrated) so that they can be detached easily without any difficulty.

The mandrel 56 has a width dm substantially equal to the diameter dp of the punch 55, which will be discussed later. It is recommended that the upper face 56, (or the back) of the mandrel 56 opposite to the lower face having the punch 55 attached thereto be rounded to have such an arcuate section, in order to prevent the inner face 51 of the flat tube 51', which will be brought into contact with the back 56 of the mandrel in a subsequent extruding procedure, from being deformed.As can be appreciated, the longer internal diameter Ii of the flat tube 51' shown in Figure 9(A)(b) has to be larger than the sum of a mandrel thickness hm and a punch thickness hp, and the shorter internal diameter 12 has to be larger than the larger of the punch diameter dp and the mandrel diameter drn.

With the settings described above, the upper die 52 is moved downward by the action of the ram (not illustrated) to press the primary flat tube 51' in the direction of the longer diameter. As a result of this pressing work, the flat tube 51' is gradually pressed until its inner face 51 comes into contact with the back face 561 of the mandrel 56. Then, that inner face 51 pushes the mandrel 56 downward to force the punch 55 in the direction of thickness into the inner face of the flat tube 51 '. By forcing the punch 55, the metal material is extruded into the die hole 57 to form a bulging portion 58 bulging from the outer face of the tube portion to be branched.As shown in Figures 9(C-l)(a) and (b), more specifically, the flat tube 51' can be pressed to form directly the trunk pipe 21 having a circular cross-section. The deformation of the flat tube stock 51 ' by this pressing work is caused by the shearing phenomenon between a punch shoulder 55, and an inlet shoulder 57, of the die hole 57, as better seen from Figure 10, so that continuous metal flows 59 are established in both the trunk pipe portion 21' and the bulging portion 58 for the branch pipe.On the other hand, the extrusion reaction force F to be exerted upon the punch 55 is applied in a diverged form, as indicated by arrows fin Figure 11, to the inner tube face 51 contacting with the back face 56 of the mandrel 56 so that the deformation of the inner tube face 511' is slight enough to raise no serious problem.

The radius of curvature R0 of the die is set to be larger than the external radius 1/2 Do of the tube stock 51, and then the once-flattened tube 51' of Figure 9(A)(d) is overpressed and flattened to form a flat tube 61 having its longer and shorter diameters reversed from those of the flat tube 51', as shown in Figures 9(C-ll)(a) and (b) so that the flat tube 61 has to be corrected at a subsequent correcting step.

Turning nowto Figures 12(A) and 12(B), the volume V2 of the bulging portion 58 has to be sufficient for supplying the volume of the branch pipe 22 of the target product. With closer reference to Figure 12(A), more specifically, it is apparent that the cross-hatched volume V2 of the bulging portion 58 prepared by the pre-forming work is increased with the cross-hatched volume V1 (which will be called the "displacement volume") of the tube material to be displaced by the pressure of the punch 55. The percentage ratio V2 N1 x100 (%) (i.e, the extrusion (or bulging) efficiency) of those volumes V2 and V1 depends upon the ratio dp /D2 of the punch diameter d and the die hole diameter D2.

Figure 12(B) plots the relationship between the ratios V2 N1 and dp /D2 on the basis of our experimental results. As seen from Figure 12(B), the extrusion efficiency V2 N1 x 100 (%) is increased in linear relationship with the value dp ID2. In other words, for the same displacement volume V1, the larger the bulge volume V2 is obtained with a larger value dp ID2. The experiments have also revealed that the same bulge volume V2 as the displacement volume V1, i.e, the extrusion efficiency of 100% is achieved by setting dp /D2=1.1.

At the preforming step, therefore, the punch diameter dp, the depth h of extrusion of the punch and the thickness To of the flat tube are determined, as follows, when the process of the present invention is to be practised. Firstly, the punch diameter dp may be determined to satisfy the above equation dp /D2=1.1 so as to attain the extrusion efficiency of 100%. Next, the extrusion depth h of the punch is determined as another practical condition by deriving from the volume of the branch pipe of the target product the bulge volume V2 sufficient for supplying the former volume and by calculating such a value of the extrusion depth as corresponds to the necessary displacement volume V1 (=V2).Finally, the tube thickness To is determined by adding the calculated value h to the thickness of the trunk tube of the target product and by taking a small machining allowance into account.

In the case of the trunk pipe portion 21 ' of Figures 9(C-l)(a) and (b), on the other hand, the punch thickness h should naturally be largerthan the extrusion depth h, and the mandrel thickness hm is automatically determined if the punch thickness hp is determined, because it is expressed by the equation hm=h+d1hp, where the letters d1, designate the internal diameter of the trunk pipe portion 21'. Here, the internal trunk diameter d; can be approximated by the equation d1, =D; -2(h+T1), where letters1 designate the thickness of the trunk pipe 21.Moreover, the external diameter Do of the tube stock 51 of Figure 9(A)(a) can be determined to satisfy the condition that the flattened tube 51' of Figure 9(A)(b) should have the necessary thickness To and the internal space capable of receiving the tool constructed of the punch 55 and the mandrel 56.

(3) For a twice-flattened tube i.e., when a secondary flat tube 61 is preformed as shown in Figures 9(C-ll)(a) and (b), the tube has to be corrected in a hot state, as shown in Figures 9(D)(a) and (b), by means of a pair of upper and lower dies 62 and 62'. As shown in an enlarged scale in Figure 13, these upper and lower dies 62 and 62' are formed with two pairs of grooves 63 and 64 which define the contours of the trunk pipe portion 21' and the bulging portion 58 of the secondary flat pipe 61 and which are generally shaped to profile the contour of the target product. With the aforementioned tool (having the punch 55 and the mandrel 56) being left, the secondary flat tube 61 is set to have its longer diameter oriented in the die facing direction (i.e., in the vertical direction).By the action of a ram (not illustrated) the upper die 62 is moved downward in the longer diameter axis to press and correct the secondary flat tube 61 until the trunk pipe portion 21' restores its circular shape. By this pressing work, a high correcting effect can be achieved if the external diameter Do of the tube stock is set at 1.02 to 1.05 D1 (where D1 designates the external diameter of the trunk pipe of the target product), as has been described beforehand.

(4) After this correcting step, the punch 55 and the mandrel 56 are removed from the trunk pipe portion 21' of Figure 9(D)(b), as shown in Figures 9(E)(a) to (d). Without the correcting step, the trunk pipe 21 preformed, as shown in Figures 9(C-l)(a) and (b) is likewise cleared of the punch 55 and the mandrel 56.

Since the punch 55 is attached, so to speak, temporarily to the mandrel 56, as has been described hereinbefore, the mandrel 56 is pushed in the longitudinal direction, as shown by an arrow in Figures 9(E)(a) and (b), by means of a ram (not illustrated) to shear the bolted or spot-welded portion so that it is removed, while leaving the punch 55 as it is in the bulging portion 58. For removal of the remaining punch 55, the extruded bulging portion 58 is drilled longitudinally at its centre to form a punching hole 66, as shown in Figure 9(E)(c). Then, a push rod 67 is driven into the punching hole 66 to punch off the punch 55 into the inside of the trunk pipe portion 21', as shown in Figure 9(E)(d). This punching-off work can be conducted surprisingly easily if a small draft is formed in advance on the circumferential side of the punch 55.

(5) The intermediate product 20' having the punch 55 and the mandrel 56 removed is then subjected to a machining finish, in which its portions 21' and 22', corresponding to the trunk pipe 21 and the branch pipe 22 of the target product respectively, are cut and finished to have the sizes of the target product 20, as shown in Figure 9(F), if the branch pipe portion 22' is high enough for providing the branch pipe 22. With reference to Figure 9(F), more specifically, the trunk pipe portion 21' is machined to remove its inner face 211, as cross-hatched, so that it may be cleared of the marks of the punch intrusion to attain the thickness of the trunk pipe 21 of the product, whereas the branch pipe portion 22' is machined and finished to have the size of the branch pipe 22 of the product.Thus, the final product of the T-joint 20 having a sharp crotch is produced.

On the other hand, if the intermediate product 20' fails to have the sufficient height for the branch pipe 22, it is drawn by means of a punch, as will be described in the following.

(6) After removal of the punch 55 and the mandrel 56, the pre-formed (and corrected, if necessary) intermediate product or tube stock 20" has its bulging portion 58 drawn to form the branch pipe portion 22', as shown in Figure 9(G)(a) to (c). This drawing step is essentially similar to the directdrawing process of the prior art shown in Figure 3.

The preformed tube stock 20" is set, as shown in Figures 9(G)(a) and (b), in a drawing die 68, which is formed with a die hole 69 having the same diameter as the external diameter D2 of the branch pipe 22 of the target product, such that its bulging portion 58 is fitted in the die hole 69. At the same time, a drawing punch 71 is also set by attaching it to the leading end of a drawing rod 72 which is inserted into the inside of the tube stock 20" through the punching hole 66 formed in the bulging portion 58. The drawing punch 71 to be used has the external diameter dp which is smaller by the finishing allowance than the internal diameter d2 of the branch pipe 22 of the target product shown in Figure 1. After these settings, the drawing rod 72 is pulled downward to draw the drawing punch 71 into the punching hole 66. Then, the punching hole 66 is widened to have its internal diameter enlarged to the punch external diameterdp, and the bulging portion 58 has its outer face drawn into the clearance between the outer surface of the drawing punch 71 and the inner wall of the die hole 69 to form the branch pipe portion 22', thus preparing the intermediate product 20', as shown in Figure 9(G)(c). Since this drawing work is executed while completely constraining the outer circumference of the bulging portion 58 in the inner wall of the die hole 69, the metal material to be excluded at the drawing step in accordance with the advance of the drawing punch 71 is wholly extruded to increase the height of the branch pipe portion 22'. In other words, all the material forming the bulging portion 58 is used completely to form the branch pipe portion 22'.In short, the preformation of the bulging portion 58 is to bulge and retain such a portion of the material in advance from the outer face of the tube stock 20" as is necessary to form the branch pipe portion 22', so that the material may be effectively used for the branch formation at this drawing step and at the final machining step.

The process of the present invention thus far described makes it possible to manufacture a T-joint which requires a stock tube having a small diameter ratio D2 /D1 ( < 0.3) and a large thickness To (To / D2 > 0.3) such as has been difficult to realize by the reducing-drawing process of the prior art.

According to the process of the present invention, as has been described hereinbefore, the extruding punch is moved relatively to intrude in the thickness direction into the tube stock by pressing and flattening the tube stock itself. The tool to be used may be simply prepared by attaching the extruding punch to the supporting mandrel. Since the external pressing force is used directly as the working force, moreover, the process of the present invention can be applied to a tube stock having a wide range of thickness.

Incidentally, the foregoing description has been limited to the process for manufacturing aT-joint.

However, it should be understood that the process of the present invention can be widely applied not only to the manufacture of aT-joint but also to a branched pipe such as a header having a plurality of branch pipes. In order to manufacture a header, the tool to be used at the preforming step (and at the subsequent correcting step, if necessary) may be prepared by attaching a desired number of extruding punches to the supporting mandrel.The resultant bulging portions may then be subjected, respectively, to the punch removing step and the subsequent machining step (and the drawing step, if necessary).

As is apparent from the description thus far made, the process of the present invention makes it possible to manufacture a branched pipe or T-joint of a tube stock such as has been impossible in the reducing-drawing process of the prior art.

Moreover, the process of the present invention does not have the disadvantage of the product obtained from the forging process of the prior art. Therefore, the practical value ofthe present invention should be highly appreciated.

Claims (12)

1. A process for manufacturing a branched seamless metal pipe comprising a trunk pipe and at least one branch pipe, comprising pre-forming a flattened seamless tube stock to form a bulging portion, which comprises setting a tool, which has an extruding punch attached substantially at a right angle to a supporting mandrel, in said tube stock such that said extruding punch is directed in the direction of the longest transverse axis of said tube stock to face the inner face of such a side portion of said tube stock as to. be formed with said bulging portion, setting said tube stock together with said tool between a pair of dies, one of which has a die hole, such that the longest transverse axis of said tube stock extends in the direction of the said die hole, pressing said tube stock inward in the direction of the longest transverse axis thereof through said dies to extrude said extruding punch relatively in the thickness direction of said tube stock into the inner face of said tube stock through said supporting mandrel, thereby to form an intermediate product having a generally circular trunk pipe portion with said bulging portion, removing said extruding punch and said supporting mandrel from said trunk pipe portion and said bulging portion and machining and finishing said trunk pipe portion and said bulging portion to the sizes of the trunk pipe and the branch pipe of said branched metal pipe.

2. A process as claimed in Claim 1, comprising flattening a seamless tube stock which comprises of setting said seamless tube stock between a pair of dies and pressing said seamless tube stock inward through said dies to form said flattened seamless tube stock.

3. A process as claimed in Claim 1 or Claim 2, comprising correcting the circularity of said preformed trunk pipe portion, which comprises setting said intermediate product together with said tool between a pair of dies grooved to define the contours of said trunk pipe portion and said bulging portion such that the longer diameter of said trunk pipe portion is oriented in a die facing direction and pressing said trunk pipe portion inward through said dies to correct the same into a generally circular shape.

4. A process as claimed in any of Claims 1 to 3, comprising drawing said bulging portion which comprises setting said intermediate product in a drawing die having a die hole such that said bulging portion is fitted in said die hole, drilling said bulging portion longitudinallytoform a punching hole, inserting a drawing rod into the inside of said trunk pipe portion through said punching hole, attaching a drawing punch to the loading end of said drawing rod, and pulling said drawing rod to draw said drawing punch into said punching or machining hole thereby to widen said punching or machining hole and to increase the height of said bulging portion.

5. A process as claimed in any of Claims 1 to 4, wherein said removing step comprises pushing out said extruding mandrel in the longitudinal direction of said trunk pipe portion to remove the same while leaving said extruding punch in said bulging portion, drilling said bulging portion longitudinally at the centre thereof to form a punching hole and punching off said extruding punch into the inside of said trunk pipe portion to remove the same.

6. A process for manufacturing a seamless metal header comprising a trunk pipe and a plurality of branch pipes, comprising pre-forming a flattened seamless tube stock to form a plurality of bulging portions, which comprises setting a tool, which has the corresponding number of extruding punches attached substantially at a right angle to a supporting mandrel, in said tube stock such that said extruding punches are directed in the direction of the longest transverse axis of said tube stock to face the inner faces of the corresponding number of such side portions of said tube stock as to be formed with said bulging portions, setting said tube stock together with said tool between a pair of dies, one of which has the corresponding number of die holes, such thatthe longest transverse axis of said tube stock extends in the direction of the axes of said die holes, pressing said tube stock inward in the direction of the longest transverse axis thereof through said dies to extrude said extruding punches relatively in the thickness direction of said tube stock into the inner faces of said tube stock through said supporting mandrel thereby to form an intermediate product having a generally circular trunk pipe portion with said bulging portions, removing said extruding punches and said supporting mandrel from said trunk pipe portion and said bulging portions and machining and finishing said trunk pipe portion and said bulging portions to the sizes of the trunk pipe and the branch pipes of said metal header.

7. A process as claimed in Claim 6, comprising flattening a seamless tube stock, which comprises setting said seamless tube stock between a pair of dies and pressing said seamless tube stock inward through said dies to form said flattened seamless tube stock.

8. A process as claimed in Claim 6, comprising correcting the circularity of said preformed trunk pipe portion, which comprises setting said intermediate product together with said tool between a pair of dies grooved to define the contours of said trunk pipe portion and said bulging portions such that the longer diameter of said trunk pipe portion is oriented in a die facing direction and pressing said trunk pipe portion inward through said dies to correct the same into a generally circular shape.

9. A process as claimed in Claim 6, comprising drawing said bulging portions, which comprises of setting said intermediate product in a drawing die having die holes such that said bulging portions are fitted in said die holes, drilling axially saidbulging portions to form the corresponding number of punching holes, inserting the corresponding number of drawing rods into the inside of said trunk pipe portion through said punching holes, attaching the corresponding number of drawing punches to the leading ends of said drawing rods and pulling said drawing rods to draw punches into said punching holes thereby to widen said punching holes and to increase the heights of said bulging portions.

10. A process as claimed in Claim 6, wherein said removing step comprises pushing out said extruding mandrel in the longitudinal direction of said trunk pipe portion to remove the same while leaving said extruding punches in said bulging portions, respectively, drilling said bulging portions longitudinally at the centres thereof to form the corresponding number of punching holes and punching off said extruding punches into the inside of said trunk pipe portion to remove the same.

11. A process for manufacturing a branched seamless metal pipe comprising a trunk pipe and at least one branch pipe, substantially as herein described, with reference to Figures 9 to 12 of the accompanying drawings.

12. A process for manufacturing a seamless metal header comprising a trunk pipe and a plurality of branch pipes, substantially as herein described, with reference to the accompanying drawings.