Abstract:
A method for producing a thin-walled rotationally symmetric component from aluminium or an aluminium alloy in a die-casting process. The die-casting process operates with a double casting cavity, in which the shell of the component is produced without recesses, and the recesses are made in the shell by cutting.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority 35 U.S.C. §119 to German Patent Publication No. DE 102015203033.4 (filed on Feb. 19, 2015), which is hereby incorporated by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    Embodiments relate to a method for producing a thin-walled rotationally symmetric component from aluminium or an aluminium alloy in a die-casting process. In particular, a method for re-machining the cylindrical components. 
       BACKGROUND 
       [0003]    In the automotive sector, steel components are being increasingly replaced by lighter components, whereby, for instance, fuel savings in respect of the running of the motor vehicle can be obtained. However, there are at least the same demands on the components made of lighter materials as on those made of steel, for instance in terms of corrosion resistance, machinability and rigidity. 
         [0004]    As replacement materials, aluminium alloys, in particular, are suitable candidates. Aluminium alloys have a high corrosion resistance combined with, at the same time, good mechanical properties, such as rigidity and machinability, and a reduced weight. Moreover, the properties in aluminium alloys can be influenced by the constituents of these same. 
         [0005]    For cost-effective production, parts are preferably cast from aluminium alloys. In order to ensure good castability of the generally geometrically highly complex castings, the aluminium alloy must also allow the casting of thin-walled parts which nevertheless have the required stability. 
         [0006]    Particular importance is attached to the composition of the alloy here. This firstly determines the properties which are necessary with regard to an end product. Moreover, it also, however, influences the properties which enable and facilitate the processing into the end product. 
         [0007]    Thus, the silicon content of an aluminium alloy, for instance, influences the flowability, and thus the castability, of a molten alloy. In order to be able to ensure good castability of an aluminium alloy, this must consequently contain a silicon component. The silicon content also, however, reduces the breaking elongation and the mechanical strength of the casting. These opposing properties are important, however, particularly in the casting of large, high-strength castings comprising thin-walled sections. 
         [0008]    In the specific application, cylindrical cages comprising a multiplicity of recesses and openings, which further weaken the wall, are to be produced. 
         [0009]    Examples of advantageous alloys are numerously found in the related art, but are not part of the solution in accordance with embodiments. 
         [0010]    Castings exhibit after the casting operation a rough surface having a brittleness and strength which is different from the solid material. In the prior art, such components are remachined. 
         [0011]    In the related art, casting methods and casting devices for the production of thin-walled moulds are disclosed in German Patent Publication No. DE 102012100900 B3. For the formation of the apertures, of ribs and webs, cores which are movable in the casting mould are in this case used. As a result, the moulds become larger than a simple mould without variable cores would be. 
         [0012]    Moreover, the material usage per component is higher for such a casting mould. 
         [0013]    The machining of such a blank is also disclosed in German Patent Publication No. DE 102012100900 B3. In this process, the recesses are made in the wall already in the casting process. 
         [0014]    A process in the related art is represented in the process flow of  FIG. 2 . A first process step or block S 1  includes a casting of an aluminium alloy. The casting mould contains a middle core and an outer mould, the apertures and recesses in the shell of the cylinder being produced by variable cores. A second process block S 2  includes metal cutting. A final or third process block S 3  includes balancing and measurement. 
       SUMMARY 
       [0015]    Embodiments relate to an enhanced process of aluminium die-casting and mechanical machining. 
         [0016]    Embodiments relate to an advantageous production method for producing rotationally symmetric, hollow components from aluminium (alloy), with recesses in the wall of the components. 
     
    
     
       DRAWINGS 
         [0017]    Embodiments will be illustrated by way of example in the drawings and explained in the description below. 
           [0018]      FIGS. 1( a ) and 1( b )  illustrate a cylindrical component. 
           [0019]      FIG. 2  illustrates a method in accordance with the related art. 
           [0020]      FIG. 3  illustrates a method, in accordance with embodiments. 
           [0021]      FIG. 4  illustrates a casting mould, in accordance with embodiments. 
           [0022]      FIG. 5  illustrates a laser cutting cell, in accordance with embodiments. 
       
    
    
     DESCRIPTION 
       [0023]      FIGS. 1( a ) and 1( b )  illustrates an example of a cylindrical component or cylinder  1 , which in this embodiment is open at both end faces  22  and  23 . The cylinder  1  has an outer shell surface  9  and an inner shell surface  10 . 
         [0024]    The cylinder  1  is cast as a casting comprising at least one boss  3  on the lower periphery of the cylinder  1  and/or at least one boss  11  on an upper periphery thereof. The function of the bosses  3 ,  11  is explained hereinbelow. The cylinder  1  includes a section  5  along the rim of the inner shell surface  10 . This section  5  is not intended for the after-treatment of the surfaces. Within the section  5 , bearing surfaces  2  are present. Also on the outer shell  9  is represented, by way of example, a bearing surface  4 . 
         [0025]    As illustrated in  FIG. 3 , in a production process in accordance with embodiments, the cylinder  1  in a first process step or block S 1  is cast from aluminium alloy. In accordance with embodiments, the casting process  51  is simplified. Instead of the mould comprising movable slides and cores, a die-casting tool  15  with double cavity is used, as is represented, by way of example, in  FIG. 4 . In the section through the double tool, two cylindrical components  1 , which are supplied with casting material via a common runner  30 , can be seen. 
         [0026]    The material usage per component is thereby reduced. If, in a single die-casting mould provided with slides, 4.8 kg of material is needed to produce the blank with a weight of 1.4 kg, the double cavity requires 6.8 kg of casting material for two blanks of 1.4 kg each. 
         [0027]    Since specifically the time for the casting of the blanks and their removal from the mould is critical to the following machining process, an advantage is obtained as a result of the doubling of the number of blanks per casting at the start of the production process. 
         [0028]    In accordance with embodiments, a second process block S 4  includes a first machining a first machining involving cutting. Following removal from the mould, the components  1  are fed to a cutting unit  16 . The cutting unit  16  may take automatic delivery of two of the components  1  via a robot, in order that the double capacity is exploited in the cutting unit also. 
         [0029]    An inner clamping tool receives the component in order to machine the component in the laser cutting station  16  and to subsequently turn the outer shell. In order to optimize the process flow, it is sensible to turn the component after the cutting operation first on the inside, with the clamping tool making contact on the outside, and only afterwards to machine the outer side. To this end, the component is clamped on the inside. The clamping concept is described in greater detail in connection with the metal cutting. 
         [0030]    In accordance with embodiments, the cutting unit may be, for example, a laser cutting unit. The components  1  are clamped on the outside and are rotated in the cutting unit  16  radially in cycles, for example, sixteen cycles, and also moved axially along their longitudinal axis L. In this way, the laser cutting heads  17  cut desired recesses  40 , in the case of a uniform movement ellipses or circles, in the cylindrical wall. 
         [0031]    Alternative cutting units are here likewise conceivable, such as a water jet cutting unit. It is equally possible to make the recess  40  in a traditional manner with drill heads, wherein parallel drill heads can be used to produce a plurality of recesses at the same time. 
         [0032]    In a third process block S 2 , a second machining step S 2  includes removing the two components with their recesses from the cutting unit, and feeding them to a metal cutting unit. A final or fourth process block S 3  includes balancing and measurement. 
         [0033]    The cylinder is finish-turned in lathes both on the inner side  10  of its shell and on the outer side  9  of its shell, wherein at least one section  5  of the inner side of the shell remains untreated. In the section  5 , bearing surfaces  2 , 2 ′ are present in unfinished castings, which bearing surfaces are produced directly in the casting process. The bearing surfaces  2 , 2 ′ serve as an abutment for a clamping tool  6  which is introduced into the cylinder and acts with clamping elements  7 ,  8  on the bearing surfaces. The clamping tool is designed such that the cylinder is round-clamped in order to achieve maximum precision. As the bearing surfaces, at least two bearing surfaces  2 ,  2 ′ are present for this purpose. The cylinder which is round-clamped on the inside can thus be turned on its shell outer surface  9 . The small wall thicknesses of the cylinder reduce the inherent stability of the component and make a more complex clamping concept necessary. The clamping concept here anticipates future installation in a sub-assembly in order thus to use the same bearings. Moreover, the centric installation position and the turning behaviour of the cylinder are optimally defined already in the machining situation. 
         [0034]    For the machining of the inner shell surface  10 , the cylinder  1  is round-clamped from the outside, wherein bearing surfaces  4  on the outer shell surface  9  are placed precisely opposite the bearing surfaces  2  disposed in the inner shell surface  10 . The outer bearing surfaces  4  are in this case no longer untreated. 
         [0035]    As a result of the precise positioning of the cylinder  1 , ensured via the bosses  3 ,  11 , on the depositing surfaces during the process, the clamping is achieved at the correct positions. 
         [0036]    A somewhat more specific embodiment uses a method for producing a cylinder, which on the inner side of its shell contains on both rims respectively a section  5  configured as a gear ring. These gear rings serve in a larger sub-assembly to receive further gearwheels, for instance the gearwheels of a gear mechanism. 
         [0037]    In the mechanical production, the unfinished part must with the external boss  11  on the external surface of the teeth  20 . 
         [0038]    For the finish-turning of the outer shell surface  9  of the cylinder  1 , the unfinished part must be taken from the workpiece carrier with the internal handling mechanism of the lathe and turned through 180°. At the next depositing station for the turned-over component, the component must be mounted with the outer or external boss  3  on the external surface of the teeth  21  directly into a further recess of the depositing station. 
         [0039]    A receiving spindle of the lathe for the external finish-turning of the cylinder  1  fetches the component and, following turning, deposits it again precisely with the same rotational orientation on a depositing station. In the external finish-turning of the cylinder, the unfinished part is round-clamped at both teeth  20 ,  21  on a tooth tip, with the clamping tool bearing against the bearing surfaces  2  which optimally reflects the state of installation of the cylinder in the sub-assembly. 
         [0040]    The internal handling mechanism of the lathe turns the semi-finished part back through 180° and deposits it again, precisely with a defined rotational orientation, on a depositing station, wherein this depositing station has pins which engage in the teeth  20  of the semi-finished part. 
         [0041]    For the internal turning of the cylinder  1 , the semi-finished part is once again round-clamped on the outside precisely opposite the internal clamping points of the teeth  20 ,  21  and bears in the axial direction of the cylinder against the end face  23 . 
         [0042]    A receiving spindle for the internal turning of the cylinder  1  fetches the component from the last depositing station and, following turning, deposits it again with the same rotational orientation on a depositing station, this depositing station too possessing pins with which the finish-turned component is fixed in the tooth  20 . 
         [0043]    A robotic gripper of the lathe takes the finish-turned component from the depositing station and deposits it with precisely the same rotational orientation on the workpiece carrier, the workpiece carrier in turn possessing pins with which the finish-turned component is fixed in the tooth  20 . 
         [0044]    For applications of the cylinder as a rapidly rotating component of a sub-assembly, the turned component, which has been provided with recesses and has been prepared in this way, must still be balanced. 
         [0045]    A robot takes the finish-balanced component from the workpiece carrier in rotationally orientated state and inserts this in rotationally orientated state into the clamping device of the brushing unit, the clamping device possessing a specific pin with which the finished part is fixed in the tooth  20 . Following completion of a brushing operation, the clamping device rotates again into the same position as when the component was received, and the robot fetches the brushed component and deposits it in rotationally orientated state on the workpiece carrier of a washing machine. 
         [0046]    Following completion of the washing operation, a robot takes the washed component, rotates it through 180°, and places it in rotationally orientated state onto the clamping device of a measuring machine and enables the component to be measured at a precise position which is given by the position of the teeth  20 ,  21 , which have a different number of teeth. 
         [0047]    The proposed method is represented by way of example and is also executed in steps which may be regarded as equal in value for a person skilled in the art. 
         [0048]    The term “coupled” or “connected” may be used herein to refer to any type of relationship, direct or indirect, between the components in question, and may apply to electrical, mechanical, fluid, optical, electromagnetic, electromechanical or other connections. In addition, the terms “first,” “second, etc. are used herein only to facilitate discussion, and carry no particular temporal or chronological significance unless otherwise indicated. 
         [0049]    This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of embodiments is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. Aspects from the various embodiments described, as well as other known equivalents for each such aspects, may be mixed and matched by one of ordinary skill in the art to construct additional embodiments and techniques in accordance with principles of this application. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
           1  component, cylinder 
           2  bearings 
           3  boss 
           4  bearing surface 
           5  section 
           6  clamping tool 
           7 ,  8  clamping elements 
           9  outer shell 
           10  inner shell 
           11  external boss 
           15  die-casting tool 
           16  laser cutting unit 
           17  laser cutting heads 
           20 ,  21  teeth 
           22 ,  23  end faces 
           30  runner 
           40  recesses