Patent Publication Number: US-10323309-B2

Title: Method and device for processing extruded profile segments composed of magnesium or magnesium alloys and a lightweight construction element produced therefrom

Description:
The invention relates to a method and to a device for working extruded profile sections made of magnesium or magnesium alloys with respect to the outer contours thereof by way of hot shaping and/or hot stamping and/or cutting operations and/or punching operations for the subsequent joining processes. 
     In particular, the invention relates to extruded hollow chamber profiles, which are subsequently to be joined to form assemblies (lightweight construction element). 
     A method for producing an extruded profile section from a hardenable aluminum alloy is known from DE 10 2008 045 441 B3, in which, after the profile has been pressed and the profile sections have been cut to size, an internal pressure forming step for shaping the outer contour of a profile section is carried out when the profile section is in the solution-annealed state thereof, or in a solution annealed-like state, wherein the internal pressure forming step for shaping the outer contour of the profile section is carried out after the profile section has been cooled to the ambient temperature, before more than 20% of the cold hardening process has been completed. 
     A tool for hot shaping and hot punching workpieces is known from DE 19725300 C2, which allows corresponding workpieces to be shaped and punched quickly and easily. For this purpose, the workpiece is placed onto the receiving tool in correct positional arrangement. For the shaping process, the shaping tool is moved in the direction of the receiving tool and pressed against this, wherein the hot shaping is carried out by the wall parts surrounding the tool on the outside and the part extending between the wall parts. Shaping is not carried out to the finished dimensions, but the corresponding workpieces are subsequently machined and finished to the final dimensions. 
     DE 2 105 537 C3 describes a device for hot shaping rod-shaped goods to be rolled during hot rolling in the production flow of a continuous rolling train, in which a die is disposed downstream of the finishing roll stand, and the rod-shaped goods to be rolled and hot-shaped are pushed through the die by the rolls of the finishing roll stand, wherein the die is designed as a closed ring die, and the ring die, which can be heated to the rolling temperature, is made of a high temperature resistant material, and, upstream of the ring die, a nozzle ring having an opening for adding thermally stable lubricants, such as colloidal graphite, glass having a low melting point, soda, burnt lime or salts is disposed, and, upstream of the nozzle ring, two labyrinth ring chambers are disposed, and the ring die is spring-cushioned axially in both directions. 
     A lightweight construction element and a production method are known from DE 10224198C1, in which the lightweight construction element comprises multiple extruded hollow sections that are joined to each other in a planar arrangement. The associated method comprises the following steps: a) extruding hollow sections having a wall thickness of no more than 0.5% of the diameter of the circumscribed circle of the lightweight construction element produced therefrom; and b) joining multiple hollow sections in a planar arrangement to form a lightweight construction element, which has a circumscribed circle of at least 300 mm. The hollow sections are joined by way of friction welding or adhesive bonding. 
     Extruded profiles, and in particular multi-chamber extruded profiles, become warped upon exiting the die of the extrusion press. This causes problems, especially during a subsequent joining process, in which planar assemblies are to be assembled from the extruded profile sections. 
     One of the greatest challenges today in the construction of vehicles, in particular automobiles, lies in minimizing the weight as one of the most effective options for saving fuel. 
     A cost-benefit comparison of various lightweight metals shows that ever progressing weight savings are driving up manufacturing costs. This means that lightweight construction can only be economically implemented if it is possible to lower the associated manufacturing costs through higher productivity, and especially by using materials sparingly. 
     Compared to steel materials, which are used predominantly today, lightweight metals have the advantage that these have a considerably lower density. The lightest of these metals is magnesium, which is approximately 35% lighter than aluminum. The current new magnesium alloys exhibit very good properties, such as corrosion resistance and good deformation properties, allowing these to be used for extrusion. 
     One drawback with extrusion is that the size of the extruded profiles that can be produced is limited, requiring assemblies to be joined from individual extruded profile sections. 
     It is the object of the invention to provide a method and a device for working extruded profile sections made of magnesium or magnesium alloys which eliminate the above-described drawbacks. 
     A further object is to create a lightweight construction element produced therefrom, which is produced from individual extruded profile sections by way of joining, whereby a practically arbitrarily sized lightweight construction element can be achieved. 
     According to the invention, this object is achieved by using the method to bring the extruded profile sections made of magnesium or magnesium alloys to a dimensional accuracy with respect to the outer contours thereof for the subsequent joining process by way of hot shaping, so as to simplify the joining process. At the same time, it is possible to carry out stamping operations, cutting operations and/or punching operations, together with the hot shaping process. Hot shaping is preferably carried out in the production flow subsequent to the extrusion process. This has the advantage that the profile exiting the die already has a temperature in the range of 250 to 450° C. and does not require additional heating. 
     Compared to shaping according to the internal high pressure forming method, this is considerably more effective and, given the extremely high costs of hydroforming tools, considerably more cost-efficient. 
     The profile sections thus shaped can be joined to form lightweight construction elements without great complexity. In vehicle construction, such lightweight construction elements can be supporting structures in the form of floor pans, for example. 
     The invention will be described in more detail based on one exemplary embodiment. 
    
    
     
       The associated  FIG. 1  shows a device for carrying out the method for hot shaping extruded profile sections. 
     
    
    
     The method according to the invention comprises the following steps:—inserting the profile sections  1  heated to a temperature in the range of 250 to 450° C. into a two-part shaping tool  2  preheated to a temperature in the range of 300 to 600° C.; and—applying pressure to the shaping tool  2  by way of one or more pressing cylinders  3  of a press  4 . In addition, insertion elements may be inserted into the end faces of the profile sections  1  that have been cut to size, if needed. 
     The insertion elements can comprise pin-like projections, the cross-sections of which are adapted to the inner cross-sections of the profile sections  1 . 
     It is advantageous if the method steps for hot shaping take place subsequent to the extrusion process, since heating of the extruded profile section can then be dispensed with. 
       FIG. 1  shows a representative illustration of the device for carrying out the method. The device essentially comprises a press  4  and a shaping tool  2 . The shaping tool  2  has a two-part design and accordingly comprises two tool halves I, II, which can be displaced with respect to each other and between which the profile section  1  is inserted, wherein the tool halves are adapted to the cross-section of the profile to be shaped. 
     By applying pressure to at least one of the two tool halves I, II via a pressing cylinder  3  of the press  4 , the tool halves are displaced toward each other, and the profile section is shaped, which is to say the profile sections are brought to uniform dimensions, while being straightened. 
     The tool halves I, II have boreholes, into which corresponding heating cartridges are inserted to heat the tool halves I, II or maintain these at the temperature. 
     If needed, one or more stamping dies can be disposed in one or both tool halves I, II, with the aid of which surface stamping of the profile sections on one side, or on both sides, can be carried out simultaneously during the shaping process. 
     Another option is to integrate cutting or punching tools into the tool halves I, II so as to simultaneously carry out cutting or punching operations in the profile sections  1  during the shaping process. 
     Subsequent to the hot shaping process, the shaped and/or stamped and/or punched profile sections can be joined to form a lightweight construction element. 
     The lightweight construction element can be designed, for example, as a supporting structure for a land vehicle, an aircraft or a watercraft, and the individual hot-shaped profile sections  1  of which, that form the lightweight construction element, are joined to each other by way of a non-detachable connection. This can preferably take place by way of friction stir welding, whereby shorter welding times and high economic efficiency are achieved during the joining process. 
     LIST OF THE REFERENCE NUMERALS 
     
         
           1  profile sections 
           2  shaping tool 
           3  pressing cylinder 
           4  press 
           5  boreholes 
         I tool half 
         II tool half