GB2148162A - Apparatus for the explosive deformation of tubular blanks - Google Patents

Abstract

Apparatus for hydroplastic deformation of a tubular blank under the force transmitted through a lubricating coolant by an explosive blast comprises a housing (1) containing front and rear stop members (2) and (3) respectively. The rear stop member houses a working tool (15) and has an explosion chamber (10) positioned behind it. The front stop member (2) houses a travelling cylindrical piston (7) in whose interior a tubular blank (8) is to be disposed. The cylindrical piston is fitted with one end on a fixed ram (6) and has its other end entered by the working tool (15) which is to be driven therethrough by the pressure exerted thereon by fluid when explosion takes place. A recoil chamber (9) at the remote end of the traveling cylindrical piston (7) completes a fluid duct system providing for location of fluid at both ends of the travelling cylindrical piston, that end at the opposite end to the recoil chamber (9) being in a compensating chamber (12) surrounding the working tool (15). All lubricant containing zones intercommunicate through appropriate ducting, including radial ducting (17) from a blind bore (16) in the working tool (15). The working tool carries a sealing member (18) which enters the tubular blank (8) to define a further fluid containing chamber (19) between sealing member and working tool in communication with the other aforesaid fluid-containing chambers. <IMAGE>

Description

SPECIFICATION Apparatus for explosive deformation of tubular blanks This invention relates to an apparatus for the explosive deformation of blanks, in particular tubular blanks which are to be used in engineering industry and more particularly to the use of an explosive charge to achieve hydroplastic deformation thereof.

An apparatus is described in Bulgarian Authors Certificate No.23783 for modifying the external surface shape of cylindrical bodies by plastic deformation. The essential elements of such an apparatus are a housing and a die coupled to a press. A vertically operating power cylinder with a piston is attached to the housing. The die possesses a profiled inner surface and a tubular billet to be machined is disposed therein with both die and billet resting on a dynamic support. A smooth broach with a blind central hole formed with radially extending ducts therein is firmly attached to the piston of the power cylinder. The piston of the power cylinder has a central channel communicating the high pressure side of the power cylinder with the blind central hole of the smooth broach.Ducts exist in the housing through which the high pressure side of the power cylinder is connected to an oil feed system.

When working a tubular billet using such a press ram system, the power cylinder and the working tool (the smooth broach) move along the axis of the tubular billet being processed. This motion produces a counterforce, with high pressure being created in the interior of the power cylinder. As a result of this pressure driven lubrication of the surface being processed and of the tool, plastic deformation of the billet is effected.

Disadvantages of such an apparatatus are as follows: Because the apparatus is attached to a press, the length of the billets to be processed is restricted by the clearance between support surfaces as the piston is displaced. This renders the unit inappropriate for the working of large cylindrical billets.

Moreover, the die wherein the billet is disposed is fixed and this limits metal flow in the direction opposite to that in which deformation stress occurs.

As a result, the apparatus cannot be used for processing billets of a length and at a deformation rate exceeding predetermined limits for the die. Practical limits are placed on the pressures which can be created in the power cylinder, which limits are equal or similar to the resistivity contact pressures between the work tool and the billet being processed. This condition limits the creation of a sufficiently thick lubricating layer guaranteeing the required fluid friction for causing plastic deformation of the billet. Finally as a result of the absence of feed of lubrication fluid under pressure, the tool operates under conditions of dry or threshold friction in the entire billet at the start of processing of the cylindrical billet and also during the whole period of processing in the first deformation element of the tool.

Hydroplastic deformation from the inside of a tubular blank can also take place. An apparatus for this purpose which uses an explosion detonation technique is disclosed in USSR Authors Certificate No.412,724 and comprises a housing to which front and back stop members are attached. An acoustic damper. an explosion chamber and an intermediate stop member are attached to the back stop member. The back stop member accommodates a piston with a blind axial hole in which a working tool is positioned. The blank is placed in the front stop and behind it is fitted a trapping hopper. In use, explosive is loaded into the explosion chamber and after it has been ignited, the working tool is projected freely under the action of the blast and while passing through the blank processes its inner surface by plastic deformation.

Such an apparatus possesses various disadvantages: Thus, surface impulse processing of the inner surface of the blank under dry friction conditions takes place during the free flight of the tool. As a result of this friction and the extremely high speeds reached within longer blanks, high temperatures will develop and this will provoke intensive wear or melting of blank and tool surfaces. Hence, longer blanks cannot be processed because of the possibility of tool seizure in them and of the unit blowing up.

In addition, because the front stop serving as an encompassing rim is fixed, there is no possibility for pre-setting a higher deformation rate and achieving plastic flow of the metal because of the fact that the flow of metal becomes entrapped against the front stop and detaches it from the apparatus.

According to the present invention, there is provided an apparatus for the hydroplastic deformation of tubular blanks, comprising a housing, a front stop member and a back stop member in line within the housing, the back stop member being of hollow construction defining, in turn, towards the open, forward end thereof an explosion chamber, a guiding chamber and a compensating chamber and housing a working tool, said chambers intercommunicating, the guiding chamber providing a rest position for the working tool and the working tool being formed with a forwardly extending blind bore and with at least one radially extending duct connecting the blind bore with its exterior and carrying at its forward end a sealing element; and the front stop member housing a fixed ram and a travelling cylindrical piston in whose central passage a tubular blank is to be positioned, in use, which travelling piston has one end positioned over the fixed ram for sliding travel thereover and to define a recoil chamber therebetween, longitudinally extending duct means in the travelling cylindrical piston communicating the recoil chamber with the compensating chamber. The term tubular is used herein to denote hollow elongate bodies of divers cross-section, including circular and polygonal cross-section.

The apparatus according to the invention is ca pable of wide application in the explosively activated deformation of tubular blanks employing a hydroplastic deformation technique to achieve both smooth and profiling processing of tubular blanks whose lengths may vary considerably. The apparatus of this invention possesses special applicability in the processing of tubular blanks made from metals which are difficult to deform.

The deformation process which takes place when employing the apparatus according to the invention utilises universal uneven compression. The flow of non deformed metal in a direction opposite to the direction of motion of the working tool is assisted by back recoil thrust resulting from fluid pressure acting on the front end of the travelling cylindrical piston which is of larger area than the front end of the working tool. Tubular bodies can be obtained using the apparatus of this invention which possess both mechanical and physical characteristics differing from those of the initial blank as a result of the extremely high pressure to which the blank is subjected and the rate at which the deformation process takes place.It will be readily appreciated from the foregoing that the economic benefits of use of the apparatus of this invention lie in increased productivity rate and the high surface quality of the bodies which are produced.

The apparatus of this invention may be modified when it is desired to work relatively long tubular blanks. In such a case, the blind central bore of the working tool is desirably of stepped design and houses in the rear end thereof a multiplicator. The multiplicator comprises a free travelling piston. A chamber which the piston is able to enter lies behind the blind end of the blind bore which the piston is not able to enter.

The apparatus of this invention can be utilised to work tubular blanks in a number of ways. If the outer surface of the working tool is profiled, then a tubular product having a profiled inner surface will be obtained. If the inner surface of the travelling cylindrical piston is profiled, then a tubular blank will be profiled on its external surface. When both internal and external surfaces of the tubular blank are to be profiled, then use is to be made simultaneously of the working tool with an outer profiled surface and a travelling cylindrical piston having a profiled inner surface.

For a better understanding of this invention and to show how the same can be carried into effect, reference will now be made by way of example only to the accompanying drawings wherein: Figure l is a longitudinal section through apparatus embodying this invention, shown in its reference position before explosion has taken place; Figure 2 is a partial longitudinal through the apparatus of Figure 1, showing the working tool and the travelling cylindrical piston undergoing relative displacement; Figure 3 is a partial longitudinal section through the apparatus of Figure 1, showing knock-out of a blank after processing; Figure 4 is a partial longitudinal section through a variant of the apparatus of Figure 1, modified to include a multiplicator in the work tool;; Figure 5 is a transverse cross-section through a tubular blank processed to give it an inner profiled surface; Figure 6 is a transverse cross-section through a tubular blank processed to give it an outer profiled surface; and Figure 7 is a transverse cross-section through a tubular blank which has been processed to give it inner and outer profiled surfaces.

Referring to the drawings and in particular to Figure 1, the apparatus of this invention comprises a housing 1 to which a front stop member 2 and a back stop member 3 are attached. Behind the front stop member 2 there is mounted a trapping hopper 4. Front stop member 2 is attached to the housing 1 by a detachable joint 5 (for example using wedges). In the front stop member 2 there is mounted a fixed ram 6 in which there is positioned a travelling cylindrical piston 7 with a central passage in which a tubular blank 8 to be processed is positioned. At one end, the travelling cylindrical piston 7 is able to slide on fixed ram 6 with a chamber 9 existing between piston 7 and ram 6 for serving as a recoil chamber.

In the back stop member 3, there are successively formed an explosion chamber 10, a guiding chamber 11 and a compensating chamber 12. The explosion chamber 10 and the compensating chamber 12 are connected through ducts 13 in back stop member 3. The recoil chamber 9 is connected to compensating chamber 12 through longitudinally extending ducts formed in travelling cylindrical piston 7.

In guiding chamber 11 there is shown, at rest, a working tool 15 having a blind central bore 16 and formed with radial ducts 17 which connect the exterior of the working tool 15 with the blind central bore 16. In the front end of working tool 15 there is a sealing member 18 which is positioned in the tubular blank 8. A chamber 19 exists between sealing member 18 and working tool 15. Compensating chamber 12 is equipped with a vent valve 20 and explosion chamber 10 is equipped with a feed valve through which explosive material 22 is loaded. Between the front stop member 2 and back stop member 3 there is a guide 23 for supporting travelling cylindrical piston 7.

When relatively long tubular billets are to be processed, the blind central bore 16 of working tool 15 is of stepped design as shown in Figure 4.

In its free end there is positioned a multiplicator consisting of a freely travelling piston 24. A chamber 25 exists in the working tool 15 behind the blind bore 16 into which the piston 24 is unable to enter. For this version of the apparatus, longitudinally extending ducts 26 in working tool connect an anar space flanking the free travelling piston 24 with chamber 19 formed behind the sealing member 18.

Apparatus of this invention operates in the r jI- lowing manner: Travelling cylindrical piston 7 together with front stop member 2 and guide 23 are displaced in a direction which, in Figure 1, is to the right, until travelling cylindrical piston 7 is completely out of compensating chamber 12. Explosion chamber 10 is now loaded with explosive material 22 and working tool 15 is positioned at rest in guiding chamber 11. Then front stop member 2 with travelling cylindrical piston 7 and guide 23 is returned to the start position so that the travelling cylindrical piston 7 penetrates into compensating chamber 12 up to a predetermined position. In this position, working tool 15 does not touch the face of the tubular blank 8 to be processed, and sealing member 18 has entered the interior of the tubular blank.A coolant fluid, for example oil, is fed through feed valve 21 and by virtue of the system of ducts fills recoil chamber 9, compensating chamber 12, guiding chamber 11 and explosion chamber as well as chamber 19 behind the sealing member 18 and the blind bore 16. In the embodiment of Figure 4, chamber is also filled at this stage. Filling is effected using a pump unit (not shown). The air which is initially present within the apparatus is removed through vent valve 20 which is then shut and the pump unit stopped. The system formed by front stop member 2, travelling cylindrical piston 7 and tubular blank 8 is then forced against working tool 15 against the pressure of the coolant by means of an auxiliary screw mechanism or the like until the inner edge of tubular blank 8 presses against working tool 15. In this way, the chamber 19 becomes a closed chamber.Next explosive material 22 is detonated and, under reaction of the explosive, an almost equal pressure P, is generated in recoil chamber, compensating chamber 12, explosive chamber 10 and guiding chamber 11, this being relieved through the weakest link of the system, in this case working tool 15. The latter is forced through the interior of tubular blank 8 with force P while working it. At the moment working tool 15 passes thrdugh the interior of tubular blank 8 at rate P, (see Figure 2) under the action of explosive pressure P1, this extremely high pressure P, is also acting on a coolant behind working tool 15 and filling blind central bore 16, radial groove 17 and closed spaces a, b and c which result from profiling of the working tool for providing corresponding profiling of the internal surface of the blank.This pressure compresses the lubricating coolant and a fluid layer of a sufficient thickness for achieving hydrodynamic friction is formed in the contact zone between the deforming serrations or profiling of working tool and the surface of tubular blank 8 being processed. In chamber 19, a pressure P2 P1 is generated, pressure P2 resulting from the pressure exerted by sealing member 18 on the coolant behind sealing member 18. This pressure P2 coupled with the pressure of the coolant travelling at rate V1 provides a fluid layer which gives rise to hydrodynamic friction along the front surface of working tool 15. The tubular blank processed is thus subject to universal uneven compression which causes it to undergo deformation as metal of the blank flows in the direction of lowest resistance at rate V2, which direction is opposite the direction of motion of working tool 15.This metal flow is subject to counteraction by the friction of forces created between the outer surface of the tubular blank 8 1 and the inner surface of travelling cylindrical piston 7. As it is only force Q2 that is acting on the travelling cylindrical piston 7, this piston moves in the direction of metal flow and it has an entrapping effect on the flow while simultaneously partially damping the impact of the blast from the explosion and forcing the coolant out of the compensating chamber 12 towards working tool 15. At the end of the travel of the working tool, coolant leaves the area of working tool at a rate lower than its initial flow rate and drops into trapping hopper 4.

In order to remove the deformed tubular blank from the travelling cylindrical piston 7, the arrangement shown in Figure 3 may be adopted.

After pushing the working tool 15 out of the blank, a cap 27 is fitted in the end of the tubular blank 8 with interposition of a sealing ring 28. The travelling cylindrical piston 7 is taken to its rearmost position (to the left) and application of a fluid pressure P applying force Q3 to the cap 27 causes the tubular blank 8 to be knocked out of the travelling cylindrical piston 7. Alternatively a controlled blast from a small amount of explosive in the chamber 10 could be employed for this purpose.

Finally Figures 5, 6 and 7 show typical examples of the form of profiling which may be applied to the internal and/or external surfaces of a tubular blank 8 using the apparatus of this invention.

Claims (8)

1. An apparatus for the hydroplastic deformation of tubular blanks, comprising a housing, a front stop member and a back stop member in line within the housing, the back stop member being of hollow construction defining, in turn, towards the open, forward end thereof an explosion chamber, a guiding chamber and a compensating chamber and housing a working tool, said chambers intercommunicating, the guiding chamber providing a rest position for the working tool and the working tool being formed with a forwardly extending blind bore and with at least one radially extending duct connecting the blind bore with its exterior and carrying at its forward end a sealing element; and the front stop member housing a fixed ram and a travelling cylindrical piston in whose central passage a tubular blank is to be positioned, in use, which travelling piston has one end positioned over the fixed ram for sliding travel thereover and to define a recoil chamber therebetween, longitudinally extending duct means in the travelling cylindrical piston communicating the recoil chamber with the compensating chamber.

2 An apparatus according to claim 1, wherein the blind bore of the working tool is of stepped configuration and houses at its mouth a multiplicator comprising a free travelling piston and a chamber extending in front of it which is of greater cross-section than that of the blind bore at its blind end.

3. An apparatus as claimed in claim 1 or 2, additionally comprising a trapping hopper for lubricating coolant, attached to the forward end of the front stop member.

4. An apparatus as claimed in any one of claims 1 to 3 additionally comprising a feed valve for supply of lubricating coolant to the explosion chamber and a vent valve for removal of air from the apparatus at the compensating chamber.

5. An apparatus as claimed in any one of the preceding claims, wherein the external surface of the working tool is profiled.

6. An apparatus as claimed in any one of claims 1 to 4, wherein the internal surface of the cylindrical piston is profiled.

7. An apparatus as claimed in any one of claims 1 to 4, wherein the external surface of the working tool and the internal surface of the cylindrical piston are both profiled.

8. An apparatus for the explosive deformation of a tubular blank, substantially as hereinbefore described with reference to and as shown in Figure 1 or 3 of the accompanying drawings.