Abstract:
An assembly method of a piston-cylinder group ( 10 ), where the piston-cylinder group ( 10 ) includes a cylinder ( 20 ) at an end of which a head ( 40 ) is fixable, provided with seal gaskets ( 43 ). The method includes the steps of: mounting the seal gaskets ( 43 ) in appropriate seatings in the head ( 40 ); coupling the head ( 40 ) with the cylinder ( 20 ); and a low-temperature welding of the coupling between the head ( 40 ) and the cylinder ( 20 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an assembly method of a piston-cylinder group and a piston-cylinder group obtained thereby. 
       BACKGROUND 
       [0002]    Piston-cylinder groups are known comprising a cylinder in which a stem is housed. The cylinder is closed at an end thereof by a base to which it is joined by a circumferential weld and has at an opposite end thereof a head to which it is joined by a further circumferential welding. 
         [0003]    In a known assembly method of the piston-cylinder group, the head is welded to an end of the cylinder without seal gaskets by means of a conventional welding process and in a second operation the seal gaskets and the stem are inserted and lastly the base is welded to the other end of the cylinder. 
         [0004]    This process is followed since the high heat levels caused by the welding operation must be dissipated before inserting the seal gasket, which is generally made of a thermoplastic material, with the purpose of preventing damage thereto. 
         [0005]    One of the drawbacks of this known assembly process is that it involves long working times with consequent negative repercussions on production costs. 
         [0006]    An aim of the present invention is to provide an assembly method of a piston-cylinder group which enables rapid execution times, with consequent savings on associated costs. 
         [0007]    This aim is attained by the characteristics of the invention as recited in the independent claim. The dependent claims delineate preferred and/or particularly advantageous aspects of the invention. 
       SUMMARY 
       [0008]    The invention in particular relates to an assembly method of a piston-cylinder group, where the piston-cylinder group comprises a cylinder at an end of which a head is fixable, provided with seal gaskets, where the method comprises steps of: 
         [0009]    mounting the seal gaskets in appropriate seatings in the head; 
         [0010]    coupling the head with the cylinder; and 
         [0011]    a low-temperature welding of the coupling between the head and the cylinder. 
         [0012]    An advantage of this solution is given by the fact that it enables welding the head to the cylinder with the seal gaskets already inserted in position, maintaining sufficiently low temperatures for avoiding damage thereto. 
         [0013]    In an aspect of the invention a low-temperature welding step is included of a base to an end of the cylinder not coupled to the head. 
         [0014]    In an aspect of the invention the low-temperature weld between the cylinder and the head and the low-temperature weld between the cylinder and the base are carried out in parallel. 
         [0015]    An advantage of this solution is that it enables realising the piston-cylinder group with a rapid and economical process. 
         [0016]    The invention further comprises a piston-cylinder group comprising a cylinder at an end of which a head is fixable, provided with seal gaskets, where the head is coupled to the cylinder by means of low-temperature welding. 
         [0017]    In a further embodiment of the invention, the piston-cylinder group comprises a base coupled to the cylinder by means of low-temperature welding. 
         [0018]    Further characteristics of the invention can be derived from the dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Further characteristics and advantages of the invention will emerge from a reading of the following description, provided by way of non-limiting example with the aid of the figures illustrated in the appended tables of drawings, in which: 
           [0020]      FIG. 1  is an axonometric view of a piston-cylinder group according to an embodiment of the invention; 
           [0021]      FIG. 2  is a section view of the piston-cylinder group of  FIG. 1 ; 
           [0022]      FIG. 3  is a partly-sectioned lateral view of the piston-cylinder group of  FIG. 1 ; 
           [0023]      FIG. 4  is a detail in section of the head of the piston-cylinder group of  FIG. 1 ; 
           [0024]      FIG. 5  is a detail in section of the base of the piston-cylinder group of  FIG. 1 ; 
           [0025]      FIG. 6  is a larger-scale detail, in section, of  FIG. 4 , and 
           [0026]      FIG. 7  is a block diagram that illustrates the main steps of the assembly method of the piston-cylinder group according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    With particular reference to  FIG. 1 , reference numeral  10  denotes in its entirety the piston-cylinder group according to an embodiment of the invention, which comprises a cylinder  20  in which a stem  30  is housed, an end of which projects from the cylinder through a hole provided in a head  40 . 
         [0028]    In particular the cylinder  20  is closed at an end thereof by a base  50  to which it is joined by a circumferential weld  55  and has at an opposite end  40  thereof a head to which it is joined by a further circumferential weld  45 . 
         [0029]    A piston  60  is fixed to an end of the stem  30 , which can slide between a proximal position to the base  50  of the cylinder  20  to a position proximal to the head  40  of the cylinder  20 . 
         [0030]    In particular, the piston  60  can slide internally of the cylinder  20 . Further, the piston  60  divides the internal volume of the cylinder into two chambers  70  and  80 , each of which is supplied with fluid, for example oil, through a conduit denoted respectively by  75  and  85  ( FIGS. 2 and 3 ). 
         [0031]    With reference to  FIG. 5 , the piston  60  has on a lateral surface thereof two annular seatings, wherein one of the annular seatings a seal gasket  62  is housed, while a guide ring  64  is housed in the other annular seating. 
         [0032]    With reference to  FIG. 4 , the head  40  has on the internal surface thereof two annular seatings, where a seal gasket  43  is housed in one of the annular seatings, while a scraper ring  47  is housed in the other annular seating. 
         [0033]    Lastly,  FIG. 6  is a larger-scale detail, in section, of  FIG. 4 , where a caulking  49  can be seen. 
         [0034]    In an embodiment of the invention, the circumferential weld  45  which joins the cylinder  20  to the base  40  and/or the circumferential weld  55  joining the cylinder  20  to the head  50  are realised by low-temperature welding, for example by cold metal transfer (CMT). 
         [0035]    The welding process, which is of known type, is defined by the alternation of an “arc” step and a “short-circuit” transfer step. 
         [0036]    During the arc step, the metal wire is neared to the piece to be welded and fused by means of an arc of current. At the moment when the metal wire fuses and the metal begins falling towards the welding puddle, the short-circuit step begins in which the arc of current is reduced and the metal wire is distanced from the workpiece. 
         [0037]    The distancing of the wire from the workpiece facilitates detachment of drops of fused metal from the wire and deposits them in the welding puddle. This method therefore enables obtaining a welding process that is highly controllable, is low-temperature and reduces the energy used during the working process. 
         [0038]      FIG. 7  is a block diagram that illustrates the main steps of the assembly method of the piston-cylinder group  10  according to the present invention. 
         [0039]    In a first assembly step (block  310 ) all the components of the piston-cylinder group are assembled. 
         [0040]    The piston  60  is provided with the seal gasket  62  and the guide ring  64 , while the seal gasket  43  and the scraper  47  are positioned in the appropriate annular seatings of the head  40 . 
         [0041]    The piston  60  is coupled with the stem  30  and inserted internally of he cylinder  20  at the ends of which the head  40  and the base  50  are positioned. 
         [0042]    Once all the components are assembled, the piston-cylinder group  10  is positioned on a welding template and the piston  60  is positioned at the centre of the cylinder  20  (block  320 ) with the aim of distancing the seal gaskets  62  from the weld joints. 
         [0043]    When the piston-cylinder group  10  is positioned on the welding template the low-temperature welding step is begun (block  330 ). 
         [0044]    The welding is performed at the join between the cylinder  20  and the base  50  and the join between the cylinder  20  and the head  40 . 
         [0045]    In a further embodiment of the invention, only the weld  45  between the cylinder  20  and the head  50  is carried out by low-temperature welding, for example by cold metal transfer CMT, while the weld  55  between the cylinder  20  and the base  50  is carried out by means of another known welding method. 
         [0046]    In a further embodiment of the invention, both welds  45  and  55  can be done using CMT. In this particular embodiment the welds can be carried out in succession by use of a single hot wire, or contemporaneously by use of two hot wires which work in parallel on the profiled elements to be welded. 
         [0047]    At the end of the low-temperature welding, the piston-cylinder group  10  can be positioned on a bench where thermocouples are present, usable for controlling the cooling of the piston-cylinder group. 
         [0048]    In an aspect of the invention, the seal gaskets  43  and  62  can be mounted in the destination position thereof, before the welding step, since by using the described method, the welding temperature does not exceed 65° C. and the integrity of the seal gaskets is preserved. 
         [0049]    The present invention is also applicable to piston-cylinder groups having a through-stem where a head  40  provided with seal gaskets  43  is fixed to both ends of the cylinder  20 . In this case the piston is fixed at the halfway line of the stem and both the ends of the stem project from the cylinder through holes afforded in the heads  40 . 
         [0050]    The invention as it is conceived is susceptible to numerous modifications, all falling within the scope of the inventive concept. 
         [0051]    Further, all the details can be replaced with other technically-equivalent elements. 
         [0052]    In practice the materials used, as well as the contingent shapes and dimensions, can be any according to requirements, without forsaking the scope of protection of the following claims.