Abstract:
A process for extruding a section or the like from a billet, in which a billet is introduced into the bore of a container and, by an extrusion stem, is fed in the direction of extrusion into a shape-forming cross-sectional opening in a die. The billet material is pressed into a central inlet in the die and the resultant ductile mass fed outwards at an angle to the direction of extrusion through a plurality of channels to the shape-forming cross-section. The main load is applied by the extrusion force acting outside the central inlet and the shape-forming region and is preferably diverted outside the shape-forming region to the supporting die parts.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a process for extruding a hollow section or the like from a billet which is introduced into the bore of a container and, by means of an extrusion stem, is fed in the direction of extrusion into a shape-forming cross-sectional opening in a die. Furthermore, the invention also relates to a device which is specially suited for that purpose. 
     2. Discussion of the Prior Art 
     During extrusion, a material which is in a ductile state—in the case of metals this includes materials such as non-ferrous metals, sintered metals or steel but in particular material in the form of an aluminium alloy—viz., a heated cast billet or rolled bar of material, is pressed in the direction of extrusion by an extrusion stem—or in the case of hydrostatic extrusion, by means of a fluid—out of a container through one or more shape-forming openings in a die. In the case of direct or forward extrusion the stem moves in the direction of the die opening, in the same direction as the resultant section. In indirect or backward extrusion the material is moved in the direction counter to that of the stem, through a die which is mounted on the hollow stem. 
     To produce hollow sections, so called hollow dies with a die plate are employed in the extrusion process, an example of this is described in DE 24 46 308 Al. The die plate is integrated in a part of the mandrel to provide the outer contour of the resultant section. In that case, in order to shape the inner contour, a mandrel—in the case of multi-chamber sections a plurality of mandrels—is arranged such that the mandrel projects into the die plate and beyond the shape-forming region. In such a process the ductile material is guided over inlets and into the extrusion tool in such a manner that the strands from the individual inlets flow together again under mandrel support arms—into a welding chamber—where they are welded together again. As the extrusion process proceeds further, the material or the aluminium alloy flows past the mandrel and the die opening, thereby adopting the prescribed hollow section shape. The inlets are always situated outside around the hollow space or spaces in the section; the aluminium alloy is introduced into the shape-forming region of the die from the outside, in particular via a plurality of inlets. If in the case of multi-chamber dies the inner regions of the hollow section can not be adequately supplied with metal from outside, then additional feeding inlets are provided in the inner part of the hollow section. 
     The main supply inlets are always situated around the outer contour of the hollow space in the section. 
     The size of hollow section that can be manufactured i.e. its maximum diameter of circumscribing circle is limited therefore by the diameter of the container and the size of the inlets arranged around the hollow space as well as the strength of the above mentioned mandrel support arms. 
     In general, the maximum section size that can be manufactured on conventional extrusion presses is limited by the size of the extrusion press, the diameter of the container used and the strength of the extrusion die. The above mentioned patent DE 24 46 308 and patent DE 28 12 690 of the applicant are concerned with the dimensioning of the latter for hollow section manufacture using large mandrel surface area. Also, the quality of the extrusion weld is influenced by the outer edge zone of the extrusion billet flowing into the outer inlets in the extrusion die, with the result that it is possibly necessary to machine away the outer skin of the billet before use. Furthermore, the shaping capacity and the service life of the extrusion tool are considerably reduced by the high load on the mandrel surface, by creep resulting from this high load, and by bending. 
     Attention must also be given to the fact that metal billets, especially billets of aluminium alloys, are covered with contaminants—for example residual lubricant—and with an oxide layer. In particular, oxide particles on the end and outer surface of the ingot may be extremely detrimental with respect to the structure of the section; the resultant zone of contaminating inclusions in the section is relatively long—depending on the shape of the section and the extrusion speed. Consequently, with increasing quality requirements, manufacturers are forced to scrap increasingly longer lengths of section. The result is diminished output and lower cost efficiency due to diminishing yield of section length. 
     SUMMARY OF THE INVENTION 
     In view of the above, the object of the present invention is to enable section widths to be manufactured with maximum independence on extrusion press geometry. In addition, contaminated regions which arise during extrusion, in particular extrusion of aluminium alloys, should be prevented. 
     According to the invention the billet material is introduced under pressure into a central inlet in the shape-forming die and the resultant ductile mass fed outwards at an angle to the direction of extrusion through a plurality of channels to the shape-forming section. The extrudate therefore no longer reaches the shape-forming region via inlets arranged around the hollow section, but instead is fed through a central inlet opening in the interior of the space in the hollow section. The extrudate flows according to the invention from this central inlet, out via the radial, outward inclined channels of a large welding chamber into the shape-forming region. 
     The diameter of the circumscribing circle of the section to be manufactured may be significantly larger than the diameter of the container. 
     Also within the scope of the invention is a device for extruding a hollow section or the like from a billet which is introduced into the bore of a container and is fed by means of an extrusion stem in the direction of extrusion to a shape-forming cross-sectional opening in the die, whereby from the inlet side of the die an approximately central inlet is provided within the hollow space of the section. From the wall of that inlet a plurality of arm-like channels branches out at an angle of preferably more than 90° to the die end face; joining up to these is the shape-forming cross-sectional opening which is preceded by a welding chamber. 
     In the case of rotationally symmetrical sections, the central inlet is preferably in the centre of the die. In the case of irregularly shaped sections the centre of gravity of the area of the inlet is situated as close as possible to the centre of gravity of the section or in the middle of the die—or in another suitable region of the hollow space in the section. 
     If hollow sections with large side-length ratios or asymmetric shape have to be produced, then the necessary amount of metal feed is achieved by means of a further feature according to the invention viz., via at least two of the described central inlets which form the respective central inlet element for the channels running at an angle out of them. 
     In the case of certain extrusion cross-sections it may be necessary in special cases to provide, in addition to the central inlet, material feed channels also outside the central inlet or hollow section space, this in order to feed particular parts of the section. In all of these special cases the so-called central inlet also serves as the main inlet; these metal feed channels are simply supplementary. 
     The production of round tubes of different diameter and wall thickness may be performed using basic central inlet dies in which, advantageously, mandrel rings of different outer diameter and die plates of different internal diameter are provided in predetermined cross-sectional regions. 
     One of the advantages achieved by the procedure according to the invention is that the size of the section that can be produced is not limited in its geometry by the size of the extrusion press and diameter of the container. Tubes or hollow sections of large circumscribing circles can also be manufactured using small diameter containers on extrusion presses having relatively small extrusion force as the amounts of extrudate necessary for deformation can be fed to the shape determining zone via central inlets of small cross-section—i.e. openings of small diameter. It is therefore possible to manufacture sections with small cross-sectional area and large diameter of circumscribing circle also using materials that are difficult to shape, and to do so using small containers and high specific pressure; as a result the spectrum of cross-sections that can be produced is greatly increased. 
     Of particular importance is that the material is always fed to the die from the middle of the billet and is not spread out to the shape-forming region of the die until in the die itself. Extrudate from the contaminated outer region of billet can not flow into the die. The material from the contaminated outer edge zone is collected in the ingot butt and sheared off at the end of the extrusion stroke. As a result, using the die according to the invention it is basically no longer necessary to machine away the outer region of the billet—as may be necessary when extruding large cross-sections in old extrusion presses. 
     The load acting on the die is much lower in the region which is important for shaping the section viz., in the mandrel interior; this because the load is applied only over the cross-sectional opening of the central inlet, and not as in the case with conventional dies over the whole cross-sectional surface on the section hollow spaces projected on the die inlet side. 
     The main load applied to the cross-section of the billet to be extruded occurs in the die region outside the central inlet or inlets. This load may be taken up by the outer region of the die, i.e. not the shape-forming region—or by the die support parts. 
     The low load on the die in the process according to the invention results in accurately dimensioned extruded sections over a longer service life of the die, or for the same service life permits the production of lighter section cross-sections or such using materials that are difficult to extrude. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages, features and details of the invention are revealed in the following description of preferred exemplified embodiments and with the aid of the drawing which shows in 
     FIG.  1 : a perspective view of part of an extrusion press with horizontal stem; 
     FIG.  2 : a sectioned view of part of another extrusion press enlarged with a respect to FIG. 1; 
     FIG.  3 : a schematic epresentation of a longitudinal section through a container of the extrusion press with stem followed, in the direction of extrusion, by a die; 
     FIG. 4,  5 ,  6 : the representation shown in FIG. 3 but with container and stem in different positions; 
     FIG. 7,  9 ,  11 ,  13 : schematic end views of various, different extrusion dies; 
     FIG. 8,  10 ,  12 ,  14 : cross-sections through FIG. 7 along line VIII—VIII, through FIG. 9 along X—X, through FIG. 11 along XII—XII and through FIG. 13 along XIV—XIV 
     FIG.  15 : a longitudinal section through a shape-forming die showing the influence of load thereon; and 
     FIG. 16 a perspective view through a partially sectioned die. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An extrusion press  10  for direct extrusion of sections  12  features, as shown in FIG. 1, on a main cylinder  14 , an extrusion stem  16  which lies along the longitudinal axis A of the bore  19  of a recipient or container  18 . The diameter d of a dummy block  17  at the free end face of the stem  16  is slightly smaller than the free bore diameter d 1  with the result that the stem  16  is able to penetrate the container bore  19 . The mentioned free bore diameter d 1  is delimited by the inner surface  20  of a sleeve  21  inserted in the container  18  or its bore  19 . In the following the space inside this sleeve  21  is called the container bore  22 . 
     The maximum distance between the front  23  of the container  18  and the dummy block  17  in the inactive position of the stem  16 —which is not shown here—is such that a billet or ingot  24  of light weight metal, in particular preheated aluminium alloy, can be aligned by means of a loader  26  in front of the container bore  22  and pushed by the stem  16  in the direction of extrusion x into the container bore  22 . 
     Close to a container end face  23   a , remote from the stem  16 , is the shape-forming die  32  resting in a die holder  28  on an extrusion platen  30 . With respect to the direction of extrusion x this is followed by a run-out channel  34  in the platen  30  through which the resulting section  12 —having the shape endowed by the contour of the die  32 —is removed. Above the container  18  is, as shown in FIG. 1, a jacking system  36  for a shearing tool  38  which moves radially to a gap  40  between the container  18  and the die  32 . 
     In the example shown in FIG. 2, a mandrel part  33  is provided between the container  18  and the plate-shaped die  32 , this for the purpose of creating the inner contour of a resultant section  12   a . The die plate lies—in the direction of extrusion x—immediately downstream of a bolster plate  42  in a bolster plate holder  44 . A ring-shaped collar  46  is situated adjacent to the bolster plate  42  followed by a closing ring  48  in the platen  30 . A die container  50  is provided for the die holder  28 , the bolster plate  44  holder and the ring-shaped collar  46 . 
     At the end of the extrusion process a so-called butt  52 , from which the dummy block  17  has already separated, forms on the facing die surface at the end of the container bore  22  away from the stem  16 . As a result of a collar  54  of oversize h on the container sleeve  21 , that tool face remains a distance from the front end  23   a  of the container. Also at the front container end  23  the container bore  22  surrounds a ring-shaped collar  56  which provides a projecting length of the container sleeve  21 . 
     On inserting a new billet  24 , the free end of the butt  52  is e.g. about 80 mm thick. The back end distance e of ingot material amounts to at most 20 mm. 
     The container  18  is then drawn back—e.g. somewhat more than 450 mm—until the butt  52  is standing free (FIG.  5 ). If the billet  24 , as shown in FIG. 6, projects out a collar length t of about 10 mm beyond the collar  54 , then the billet  24  is compressed by the stem  16 ; it should then not be possible for the billet  24  to be displaced by the shearing tool  38  as a result of a subsequent shearing step. Before the shearing process takes place, the container  18  is drawn counter to the direction of extrusion x until the rear face of the shaping tool or die  32  is a distance from the end face  23   a  of the container  18 . The container  18  and the die  32  are temporarily fixed in this position. 
     By lowering a shearing blade of the shearing tool  38 —shown in FIG.  1 —the butt  52  or an end slice  58  of the projecting length t of billet  24  is removed, and with that the end face  60  of the billet  24  facing in the direction of extrusion x. Prior to the mentioned shearing operation an oxide layer forms at the end face  60 , which oxide particles would create undesirable impurities in the resultant section  12 . By removing the end slice  58  along with the end face  60  of the billet a billet end free of the oxide layer is obtained. 
     After the shearing operation the container  18  is again moved towards the die  32  and the extrusion process can begin again from the start. 
     FIGS. 7,  8  show a plate-shaped forming tool or die  32  of diameter n—equal here to approx. 500 mm—comprising two die parts  31 ,  31   a  for the purpose of manufacturing a rotationally symmetrical tube  12  or the like hollow section of circular cross-section of inner diameter q, here 236 mm in magnitude. As viewed in the direction of extrusion x a so called central inlet  64  which is shaped as a blunted-cone, is provided in the mandrel or die part  31  in the end  62  of the die facing the mandrel. The die axis M forms thereby the axis of symmetry; the diameter d 2  of its inlet contour K measures 170 mm. Branching out from the inlet wall  65 , which runs at an angle w—here 65°—from the end face  62  of the die, are arm-like channels  66  the outer channel contour  67  of which in this section runs approximately parallel to the diametrically distant contour of the inlet wall  65  to form an angle w 1  with the other visible neighbouring contour of the inlet wall  65 —here an angle of 50°. These channels  66 —tapering in the plan view shown in FIG. 7 ultimately to dome-like end section  66   e —terminate in the direction of extrusion x in a ring-shaped welding chamber  68  which is followed by a circular shaping cross-section  70  of width z for the corresponding wall thickness of the tube  12   a . The shaping cross-section  70  is limited on the inside by the surface  72 —here ring-shaped—of a mandrel projection  74 . 
     The extrudate is therefore not—as is normally the case—fed to the shaping region through a plurality of inlets situated outside around the hollow section or tube  12 , but instead only via that central inlet  64 . During the subsequent extrusion process the extrudate is fed via the radially inclined channels  66  out of the central inlet  64  outwards to the welding chamber  68  and to the shape-giving cross-section  70 . 
     In the case of irregular shaped sections the areal centre of gravity of the inlet is situated as close as possible to the centre of gravity by mass of the section or in the middle M of the die—or in another suitable region of the section hollow space. 
     As shown in FIGS. 9 and 10 hollow sections  12   p  may also be created with a polygonal or asymmetric cross-section using a central inlet  64   a . The inlet wall  65 , shown in FIG. 10, creates an asymmetric cross-section i.e. the die axis M lies outside the inlet axis M 1 . With such asymmetric section shapes or hollow sections  12   p  or  12   k  with large side length ratios, the necessary amounts of material can be fed via at least two of the described central inlets  64 , as indicated in the die shown in FIGS. 11 and 12. There the central axes M 1  of the central inlets  64  run a radial distance k from the die axis M. 
     The production of round tubes  12  of different diameter q and wall thickness y can be performed using dies  32   a  in which mandrel rings  76  of different outer diameter and die plates  31   a  of different inner diameter are employed in predetermined cross-sectional regions. 
     In FIG. 15 it can be seen that the load P on the die is much lower in that region which is important for creating the section viz., in the interior of the mandrel part  31 , this is because the load is created only over the cross-sectional opening of the central inlet  64  and not—as in conventional dies—over the whole cross-sectional surface of the section hollow space areas projected onto the die inlet side  62 . 
     The main load over the cross-section of the billet to be extruded takes place in the die area outside the central inlet or inlets  64 . This load can, as indicated by the arrows Q, be borne in the outer region of the die  30 —i.e. not in the shaping region—by the die support parts. 
     The perspective view in FIG. 16 of a mandrel part  31  of a die  32  shows clearly its make up with the central inlet  64 , the subsequent channels  66  and a plate-shaped mandrel projection  74  which projects out at the central axis of the die and determines the inner surface of the section and with that also the inner limit  72  of the shape-forming opening  70 .