Abstract:
Press for producing dimensionally stable pressed parts from powdered material, with a press frame, a die holding plate, at least one upper punch holding plate, at least one lower punch holding plate, adjusting drives for the upper punch and lower punch holding plate and/or die holding plate, a vertical guide in the press frame for at least the upper and lower punch holding plate and a measuring device for measuring the position of the upper punch holding plate, the lower punch holding plate and/or the die holding plate. A single measuring rule is attached in its thermal fixed reference point to a support vertically uncoupled from the press frame, on which measurement slides cooperating with the holding plates are guided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
       [0002]    Not applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    Presses for producing dimensionally stable pressed parts from powdered material essentially comprise a die, at least one upper punch and at least one lower punch which compress the powdered material from opposing sides in the cavity of the die. The upper and lower punches are, for example, connected to the ram and/or the piston rod of a hydraulic cylinder, which are attached to the press frame. The powdered material is introduced into the die bore by a suitable filling device, the position of the lower punch usually predetermining the filling height and/or the filling volume. After the pressing of the material, the pressed part is removed from the die bore. 
         [0004]    Different designs are used with such presses. With so-called single-sided presses, the lower punch and the die are fixed. With double-sided presses, the die is either floatingly or forcibly moved with a fixed or movable lower punch. For removing the pressed part from the mould, either the so-called ejection method or the withdrawal method is used. With the ejection method, the pressed part is moved out of the stationary die by means of the lower punch, whilst with the withdrawal method, the lower punch is stationary and the die is moved. 
         [0005]    The press tools are normally not directly attached to the hydraulic adjusting drives, but via so-called adaptors. Thus, for example, the die is clamped to a die holding plate which—if movable—is connected in turn to an adjusting drive by means of force transmission elements The same applies to upper and lower punches which are attached to corresponding holding plates. As a result, different press tools may be fitted into an existing press. 
         [0006]    In the prior art, a press is designed according to whichever principle is used for removal from the mould. A modification to the respective other principle for removal from the mould is, therefore, not normally considered. 
         [0007]    For controlling and/or regulating a press process, information about at least two parameters is important. Firstly, the press force is measured in order to determine the maximum force with which the powder is compressed. The press force characteristic of the tools over the path and/or over time during the press process is also possibly useful. A further parameter is the position of the upper and lower punch with regard to a reference value, which is generally formed by the upper edge of the die. In the known manner, temperature effects and the press forces lead to alterations in the length of the press frame, the force transmission elements and the tools. By means of suitable measuring systems, the position of the tools may be measured via their adaptors but, without a correction of the respective temperature and press force, the position indications are not sufficiently accurate. In addition, there is the risk that the measuring systems themselves and/or the attachment thereof suffer temperature-related or press force-related deformation and, therefore, bring inaccuracies into the measurement. 
         [0008]    A typical hydraulic press has been made known from DE 102 54 656 B4, the entire contents of which is incorporated herein by reference, in which a die holding plate and a plurality of punch carriers (adaptors) are adjustably mounted in the press frame via hydraulic drives. In the known press, support devices are provided which support the punch carriers in the final position of the press relative to the base body of the press frame. A press for producing stepped, dimensionally stable pressed parts made from ceramic powdered material has been made known from DE 3142126 B1, the entire contents of which is incorporated herein by reference, in which the receiver plates carrying the lower punch may be moved together hydraulically away from a base plate and, in the final position of the press, are positioned as receiving plates against adjustable mechanical stops of the base plate. The receiving plates may be raised together in steps for ejecting the pressed parts after withdrawing the die and releasing the peripheral surface of the pressed part which is in contact with the die, respectively until the next contact surface is released. In the final positions of the press formed by fixed stops, the counter force or supporting force is formed, in both presses, by mechanical stops. 
         [0009]    A press has been made known from DE 103 00 722 B3, the entire contents of which is incorporated herein by reference, in which an upper and a lower slide carriage are vertically guided for attaching an upper and lower punch to a guide post. The guide post is fastened to a frame table to which the die holding plate is also attached. The holding plates are guided in a wear-free manner by attaching the sliding carriage to the hydraulic drive via an angle compensation element and a lateral compensation element. 
         [0010]    The object of the invention is to provide a press for producing dimensionally stable pressed parts from powdered material, which allows a position identification of the tools with as few errors as possible. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    In the press according to the invention, a support for a single measuring rule is uncoupled from the press frame in the vertical direction. Thus a relative movement between the press frame and the support is possible, whereby alterations to the length of the press frame caused by heat and press forces produce no alterations to the length of the support. The measuring rule is, for example, attached to a vertical guide for the holding plates which is uncoupled from the press frame. As the support and/or the vertical guide have, namely, inherent alterations to their length caused by heat, said alterations to the length have to be considered with the measured position values, but alterations to the length of the press frame, in particular also due to press forces, do not have an effect on the measuring rule. The effects of temperature on the spacings between the holding plates are, moreover, also largely of no consequence. 
         [0012]    It is advantageous if, according to one embodiment of the invention, the measuring rule is only fastened at the height of a reference plane for the press tools, for example at the height of a clamping surface for the die on the die holding plate. The thermal fixed reference point is naturally located in the centre of a length measuring system. If a plurality of length measuring systems are provided, it results in a change of direction of the longitudinal expansion, when the measurement slide passes through this fixed reference point. In the invention, only one fixed reference point is provided, namely in the reference plane. As a result, thermal expansion of the vertical guide does not interfere with the measuring rule, so that only the thermal expansion of the measuring rule itself has to be considered. 
         [0013]    The measuring system according to the invention may be used for different operating modes of a press, irrespective of whether the ejection or withdrawal method is used. 
         [0014]    As mentioned above, a specific arrangement of the vertical guide is provided with the invention According to one embodiment of the invention, it is additionally proposed that the vertical guide is formed by a vertical guide post, which is arranged eccentrically in the press frame relative to the main press axis and comprises two parallel vertical guide tracks for holding plates. 
         [0015]    For the arrangement of the guide post, one embodiment of the invention provides that the lower end of the guide post, together with a lower adjusting drive is fastened to the press frame and is secured in all directions and the upper end of the guide post is only secured in the horizontal direction to the press frame, whilst vertical relative movements of the guide post and the press frame are allowed. The guide tracks, according to a further embodiment of the invention, are preferably formed by dovetail-shaped guide rails which are parallel in cross section and which are fastened to the one-piece guide post and guide carriages are guided on the guide rails, to which one respective holding plate is connected. 
         [0016]    As no forces are to be transmitted from the holding plates to the guide post, the alignment of the axes of the guided holding plates is desirable. As a result, one embodiment of the invention provides that the upper adjusting drive is located positively in an upper bearing plate, which in turn is screwed to an upper connecting plate of the press frame. An alignment plate is connected to the upper end of the guide post and the bearing plate and alignment plate have a positive connection such that they may only be secured horizontally to one another. The lower adjusting drive is located positively in a lower bearing plate and the guide post is supported on this bearing plate. If a connection of the alignment plate with the upper bearing plate results by means of the positive connection, an alignment of the axes of the upper and lower bearing plate and thus also of the upper and lower punches is thus automatically provided. The beating plate and alignment plate preferably comprise at least one pair of bores which may be aligned with one another and which respectively receive a locating pin. 
         [0017]    The holding plates, tools, vertical guide and measuring rule are naturally subjected to longitudinal expansion depending on the prevailing temperatures. With an accurate measurement of the position of the lower and upper punch and/or of the die, these alterations to the length as a result of heat, therefore, have to be considered. A direct measurement of the upper end of the lower punch and/or the lower end of the upper punch is naturally excluded. The position thereof may, therefore, be only determined by the position of the holding plates. One embodiment of the invention provides that temperature sensors are associated with the press tools and/or the holding plates and/or the vertical guide and/or the measuring rule and a computer is provided, into which the position signals of the measuring rule and the measuring signals of the temperature sensors are entered and, by considering the coefficients of thermal expansion of the materials for the parts of which the temperature is recorded, the computer corrects lengths and thus the positional values of the press tools according to the temperature values. 
         [0018]    The press tools are also deformed by means of the press force. According to one embodiment of the invention, it is therefore advantageous if, by means of force measuring elements, the forces exerted on the press tools are measured and the measured values are entered into the computer. The computer corrects the positional values measured by the measuring rule, according to the spring characteristics of the press tools. 
     
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0019]    The invention is described in more detail hereinafter with reference to an embodiment, in which: 
           [0020]      FIG. 1  shows a perspective view of the construction of a bearing arrangement of the holding plates for a hydraulic press without a press frame and hydraulic drives according to the invention, 
           [0021]      FIG. 2  shows schematically a section through the construction according to  FIG. 1  with an indication of the press frame and the upper and lower hydraulic drives, 
           [0022]      FIG. 3  shows schematically the plan view of the arrangement according to  FIG. 2 , 
           [0023]      FIG. 4  shows schematically a similar view to  FIG. 2  with a position measuring system, 
           [0024]      FIG. 5  shows the view of the schematic arrangement according to  FIG. 4  in the direction of the arrow  5 , 
           [0025]      FIG. 6  shows schematically the position indication of the press tool according to  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    While this invention may be embodied in many different forms, there are described in detail herein a specific preferred embodiment of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiment illustrated. 
         [0027]    A bearing plate  10  may be seen in  FIG. 1  in which a guide post  12  of substantially rectangular and/or square cross section is supported. The guide post  12  is preferably formed in one piece and may also be configured in one piece with the bearing plate  10 . 
         [0028]    On one side of the guide post  12  are attached two parallel guide rails  14 ,  16 , preferably by means of screwed connections, which in cross section are dovetail-shaped. The vertical parallel guide rails  14 ,  16  support guide carriages  18 ,  20 ,  22 ,  24 ,  26 ,  28  and  30 ,  32  which are attached to horizontal, axially spaced holding plates  34  to  40 . The holding plates are of substantially the same construction and have a T-shape in section. The upper holding plate  34  serves to clamp an upper punch (not shown), the holding plate  36  is a die holding plate and serves to clamp a die and the lower holding plates  38 ,  40  serve to clamp lower punches. The holding plates  34  to  40  may be coupled to an upper and lower hydraulic drive, not shown in  FIG. 1 , for the purpose of vertical adjustment along the guide rails  14 ,  16 . This is described in more detail below. The lower holding plates  38 ,  40  have apertures  42 ,  44  for passing through force transmission elements of a lower hydraulic drive to the respective holding plate located thereabove, i.e. in the present case of the die holding plate  36  and/or the holding plate  38 . 
         [0029]    To the upper end of the guide post  12  a horizontal alignment plate  46  is fastened, which comprises two bores  48  in the vicinity of the free end. 
         [0030]    On the right side of the guide post  12  in  FIG. 1 , a measuring rule  47  is attached on which measurement slides  48 ,  50 ,  52 ,  54  slide. The measurement slides  48  to  54  are respectively coupled to a holding plate  34  to  40 . By means of the measurement slides  48  to  54  and the measuring rule  47 , the position of the holding plates  34  to  40  is detected and thus the position of the press tools, not shown. 
         [0031]    The arrangement of the unit shown in  FIG. 1  in a press frame is indicated in  FIGS. 2 and 3 . 
         [0032]    As emerges from  FIGS. 2 and 3 , a press frame has four vertical frame posts  56  arranged in a square, which in the upper region are connected to one another by an upper connecting plate  58  and in the lower region by a connecting plate  60 . The connecting plates  58 ,  60  which extend horizontally, have circular apertures  62  and/or  64 . 
         [0033]    The lower bearing plate  10  has a circular opening  66  in which a lower hydraulic drive  68  is positively inserted. The bearing plate  10  is screwed in the aperture of the connecting plate  60 . The guide post  12  is supported on a radial shoulder  70  of the bearing plate  10  and is screwed thereto. In  FIGS. 2 and 3 , only one respective holding plate is indicated, for example the holding plate  38  for a lower punch. An upper bearing plate  72  positively receives an upper hydraulic drive  74 . The bearing plate  72  may be screwed in the recess of the upper connecting plate  58 . The bearing plate  72  has two bores of which one is shown at  76 . They may be aligned with the bores  48  of the alignment plate  46 . Through the pair of bores, locating pins may be inserted of which one is shown at  78  in  FIG. 2 . As a result, it is possible to position the bearing plate  72  horizontally relative to the alignment plate  46  and, as a result, also to bring the axis of the upper hydraulic drive  74  into alignment with the axis of the lower hydraulic drive  68 , whereby a common vertical axis  73  is achieved. In the vertical direction, a relative movement may be allowed between the guide post  12  and the frame, shown here by the posts  56  and the connecting plates  60 ,  58 . 
         [0034]    The arrangement according to  FIG. 2  is indicated schematically in  FIGS. 4 and 5 . The same parts in  FIG. 2  are shown in  FIGS. 4 and 5  with the same reference numerals. A die  102  may also be seen on the die holding plate  36 , an upper punch  104  on the upper holding plate  34  and a lower punch  106  on the lower holding plate  38 . The upper and lower punches  104 ,  106  cooperate with the die  102 . 
         [0035]    The press tools are shown in  FIGS. 4 and 5  in a reference position, the upper edge of the die  102  being important for the referencing. By means of the referencing, the tool zero point of the system is determined. Further tools refer to this zero point. The thermal reference plane is the clamping plane of the holding plate  36  for the die  102 , i.e. the upper face of the die holding plate  36  with which the measurement slides  50  cooperate. In this plane at  108 , the measuring rule  47  is fastened to the post  12  and namely only in this plane. 
         [0036]    The measurement of the tool lengths is not directly possible but—as mentioned above—is possible via the holding plates  34  to  38 . Thus the temperature, which is measured when referencing, may be included therewith. A temperature measurement takes place at the points denoted with a “T”, i.e. on the holding plates  34  to  38 , upper punch  104  and lower punch  106  as well as also in the die  102 . When the tool lengths  1  are measured during operation, therefore, the value detected during referencing has to be included in the measured temperature. Moreover, alterations to the length occur with the press forces which are measured by means of force transducers, sensors or the like. These values also have to be considered together for the correction of the respective tool positions. 
         [0037]    In order to be able to carry out the disclosed operations, a computer is required, into which the signal values measured by the measuring rule  47  as well as the temperature values and force values are entered, in order to calculate the current respective lengths  1  for determining the position of the tools. 
         [0038]    Relative to  FIG. 5 , it still remains to be added that on opposing sides support elements  120 ,  122  are provided which are supported on the plate  10  and in turn mechanically support the die holding plate  36 . They are arranged such that they may be rotated about a vertical axis in order to be arranged optionally below the die holding plate  36  or outside thereof. If the die holding plate is stationary for the ejection method, the support elements  120 ,  122  adopt the position shown in  FIG. 5 . With the withdrawal method, however, the die holding plate  36  is movable. 
         [0039]    In  FIG. 6  a control computer  126  is indicated into which the temperature values T from the individual sensors are entered. Moreover, individual press forces P which are measured by press force measuring elements, not shown, are entered into the computer  126 . The measuring signals of the measurement slides  48 ,  50  and  52  on the measuring rule  47  are finally entered into the computer and which, by means of the lengths  1  for the lower and upper punches  104 ,  106  and the die  102 , determines the individual positions of the press tools by considering the temperature values and the press force values by which the length values have to be corrected. After measuring the corrected length values, corresponding position values P OS , P M  and P US  are then recorded for the press tools for the purpose of controlling and/or regulating the hydraulic cylinder for the press tools. In  FIG. 6 , only the outlets for an upper and a lower hydraulic cylinder are indicated by HZ O  and HZ U . 
         [0040]    The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the claims where the term “comprising” means “including, but not limited to”. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims. 
         [0041]    Further, the particular features presented in the dependent claims can be combined with each other in other manners within the scope of the invention such that the invention should be recognized as also specifically directed to other embodiments having any other possible combination of the features of the dependent claims. For instance, for purposes of claim publication, any dependent claim which follows should be taken as alternatively written in a multiple dependent form from all prior claims which possess all antecedents referenced in such dependent claim if such multiple dependent format is an accepted format within the jurisdiction (e.g. each claim depending directly from claim  1  should be alternatively taken as depending from all previous claims). In jurisdictions where multiple dependent claim formats are restricted, the following dependent claims should each be also taken as alternatively written in each singly dependent claim format which creates a dependency from a prior antecedent-possessing claim other than the specific claim listed in such dependent claim below. 
         [0042]    This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.