Abstract:
A front end assembly for a plasma torch and methods for assembling and disassembling a torch wherein a plurality of front end parts form a unit that is removable from, and installable in, the torch in a single operation without a special fixture. The front end assembly includes a nozzle retaining cup body connectable to a body of the torch, and a forward end connectable to a shield retainer. A nozzle retaining cup insert fits into the nozzle retaining cup body. The shield retainer has an inner surface for retaining the shield. A nozzle is received within the nozzle retaining cup insert. A stop on the nozzle engages the nozzle retaining cup insert when the front end assembly is removed from the torch so the nozzle does not remain in the torch. The shield engages an insulator, which engages the nozzle, to limit forward axial movement of the nozzle.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     Embodiments of the invention generally relate to plasma arc torches, and in particular relate to a plasma arc torch that is easy to assemble and disassemble. 
     Discussion of Related Art 
     Plasma arc torches generally include a torch body assembly that supports an electrode for emitting an electrical arc that attaches to a workpiece to be operated upon, and a nozzle for directing a flow of a plasma gas toward the workpiece such that the plasma gas stream surrounds the arc. The electrode and nozzle generally are regarded as “consumables” that are subject to deterioration during operation of the torch and that must be replaced periodically in order to restore the torch to a proper condition for satisfactory operation. 
     Typically a plasma arc torch includes a number of parts that must be removed in order to gain access to the consumables for replacement. In many plasma arc torches, these parts must be removed one at a time, and then reinstalled one at a time after replacement of the consumables. As can be appreciated this process is inefficient and cumbersome. Thus, there is a need for an improved plasma arc torch that includes features that make replacement of the consumable portions easier and faster than current arrangements. 
     SUMMARY OF THE INVENTION 
     A front end assembly is disclosed for a plasma arc torch. The front end assembly can include a nozzle retaining cup body having a rearward end removably connectable to a body of the plasma arc torch and a forward end removably connectable to a shield retainer. A nozzle retaining cup insert can be receivable in an interior space formed by the nozzle retaining cup body, the nozzle retaining cup insert having a forward portion extending forwardly beyond a forward end of the nozzle retaining cup body. The shield retainer may have a surface for engaging a shield. A nozzle may be receivable within an interior space formed by the nozzle retaining cup insert. A first central portion of the nozzle may have a first diameter. The first central portion may be positioned in close confronting relation with the forward portion of the nozzle retaining cup insert. The nozzle may further include a stop that is engageable with a nose portion of the nozzle retaining cup insert to prevent axial movement towards the rear of the nozzle retaining cup insert once the stop and the nose portion are engaged. An insulator may be disposed between the shield and the nozzle, where engagement of the shield with the insulator and engagement of the insulator with a forward facing surface of the nozzle limits forward axial movement of the nozzle. 
     A method is disclosed for assembling a front end unit for a plasma arc torch. The method may include inserting a rear portion of a nozzle through an ID of a nozzle retaining cup insert until a stop portion of the nozzle contacts a nose portion of the nozzle retaining cup insert, thereby engaging a seal between the nozzle and the nozzle retaining cup insert; inserting the nozzle retaining cup insert and nozzle into an ID of a nozzle retaining cup body so that a rearward surface the nozzle retaining cup insert engages a forward surface of the nozzle retaining cup body; mounting a gas diffuser on the nose portion of the nozzle; centering a shield on the nozzle using the gas diffuser; engaging the shield against the nose portion of the nozzle retaining cup insert; and screwing a shield retainer onto the nozzle retaining cup body so that the shield and the gas diffuser are locked thereto. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate preferred embodiments of the disclosed method so far devised for the practical application of the principles thereof, and in which: 
         FIG. 1  is a cross-section view of an exemplary plasma torch; 
         FIG. 2  is an enlarged cross-section view of a front-end portion of the plasma torch of  FIG. 1 , rotated 90-degrees; 
         FIG. 3  is a detail view of a portion of the plasma torch of  FIG. 1 ; 
         FIG. 4  is an exploded isometric view of a portion of the plasma torch of  FIG. 1 ; 
         FIG. 5  is another exploded isometric view of a portion of the plasma torch of  FIG. 1 ; 
         FIGS. 6A and 6B  are cross-section, side and isometric views of a nozzle portion of the plasma torch of  FIG. 1 ; 
         FIG. 7  is a cross-section view of an alternative embodiment of an exemplary front end portion of the plasma torch of  FIG. 1 ; 
         FIG. 8  is a detail view of a portion of the front end portion of  FIG. 7 ; 
         FIGS. 9A, 9B and 9C  are top, side and cross-section views, respectively, of an exemplary gas diffuser of the front end portion of  FIG. 7 ; 
         FIG. 10  is an isometric view of a nozzle and gas diffuser of the front end portion of  FIG. 7 ; and 
         FIG. 11  is a detail view of a portion of  FIG. 7   
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The disclosed plasma arc torch will be described more fully hereinafter with reference to the accompanying drawings in which some but not all embodiments of the inventions are shown. Indeed, the disclosed torch and its features may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, the explicitly disclosed embodiments are provided so that this disclosure will satisfy applicable legal requirements. 
     With reference to  FIGS. 1 and 2 , a plasma arc torch  10  is shown. The torch can be a gas shielded plasma arc torch which provides, in addition to the plasma gas flowing through the nozzle orifice, a curtain or jet of shielding or secondary gas surrounding an electric arc during a working mode of operation of the torch. Usually a swirl is imparted to the shield gas. The torch  10  includes a main torch body  12 , a nozzle  14  and an electrode assembly  16 . The electrode assembly  16  may comprise several pieces including an electrode holder  18  at a first end of the electrode assembly, and an electrode  20  at a second end of the electrode assembly. The electrode holder  18  can be coupled to a piston  22  within the main torch body  12 . 
     The piston  22  is situated in a piston cavity  24  within the main torch body  12  of the plasma torch  10 . The piston cavity  24  is in communication with a first fluid passage  26  ( FIG. 2 ) and a second fluid passage  28  ( FIG. 1 ). In particular, the piston  22  may be arranged in the piston cavity  24  such that the first fluid passage  26  communicates with a first region  30  of the piston cavity  24  on a first side  32  of the piston  22  and the second fluid passage  28  communicates with a second region  34  of the piston cavity  24  on a second side  36  of the piston. A connecting pathway  38  conducts fluid between the first and second regions  30 ,  34  of the piston cavity  24 . Thus, fluid may travel in through one of the first and second fluid passages  26 ,  28 , into one of the first or second regions  30 ,  34  of the piston cavity  24 , though the connecting pathway  38 , into the other of the first and second regions of the piston cavity, and out through the other of the first and second fluid passages. 
     The first fluid and second fluid passages  26 ,  28  may connect to respective external lines (not shown) for supplying and returning fluid to the plasma torch  10 . Thus, the fluid may travel in a closed-loop. In such embodiments the plasma torch  10  may further include a fluid heat exchanger (not shown), which cools the fluid. Use of a heat exchanger to cool the fluid may be advantageous because the fluid may be a coolant, such as water, which cools the plasma torch  10 . The water may be mixed with ethylene glycol or propylene glycol to form coolant which resists freezing. Additionally or alternatively, the water may be mixed with additives configured to prevent corrosion, growth of algae, and/or growth of bacteria. 
     Two portions of the plasma torch  10  in particular which may benefit from cooling are the electrode  20  and the nozzle  14 . Thus, in one embodiment, at least part of the connecting pathway  38  may be defined by an electrode fluid passage  46  within the electrode holder  18 . By flowing fluid such that it contacts the electrode  20 , the fluid can cool the electrode. For example, fluid may enter through one or more apertures  48  in the electrode holder  18  and travel through the electrode fluid passage  46 , which can be defined in part by a coolant tube  19  coaxially displaced within the tubular electrode holder  18 . In other embodiments, the connecting pathway  38  can additionally or alternatively be defined at least in part by the nozzle  14 . For example, the connecting pathway  38  can comprise a circumferential channel  50  defined on one side by an outer surface  52  of the nozzle  14 . Thus, by contacting the electrode  20  and/or the nozzle  14 , the fluid can cool the plasma torch  10  during operation. 
     In the above-described closed-loop embodiments, the fluid is heated as it travels through the plasma torch  10  and thus as described above and a heat exchanger cools the fluid before it is returned to the plasma torch. In alternate embodiments, an open-loop may be formed in which fluid is directed through one of the first or second passages  26 ,  28  and out the other of the first or second passages without being recycled. Such embodiments may forego a heat exchanger because the warmed fluid exiting the plasma torch  10  is not returned into the plasma torch. Regardless of whether a closed-loop or open-loop fluid path is used, the fluid may be used for purposes other than just cooling the plasma torch  10 . One such purpose is controlling the positioning of the electrode assembly  16  in order to start and operate the plasma torch  10 . In this regard, the relative direction of travel of the fluid into or out of the first fluid passage  26  and the second fluid passage  28  may be used to control the positioning of the electrode assembly  16 . For example, the electrode assembly  16  can be moved to a starting position in which the electrode  20  contacts the nozzle  14  by directing fluid through the first passage  26  to bias the piston  22  such that the electrode contacts the nozzle. When it is desired that the electrode assembly  16  be refracted to an operating position wherein the electrode  20  does not contact the nozzle  14 , the fluid is directed to flow in an opposite direction, through the second fluid passage  28  into the second region  34  of the piston cavity  24 , then through the connecting pathway  38  into the first region  30  of the piston cavity, and then out through the first fluid passage  26 . This fluid flow in this opposite direction biases the piston  22  such that the electrode assembly  16  retracts to a position whereby the electrode  20  does not contact the nozzle  14 . 
     In general, during starting of the torch  10 , a difference in electrical voltage potential is established between the electrode  20  and the nozzle  14  so that an electric arc forms across the gap therebetween. Plasma gas is then flowed and the electric arc is blown outward from the nozzle orifice  15  until it attaches to a workpiece (not shown), at which point the nozzle  14  is disconnected from the electric source so that the arc exists between the electrode  20  and the workpiece. The plasma torch  10  is then in a working mode of operation. Further details regarding the function and operation of the disclosed plasma torch  10  may can be found in U.S. Pat. No. 8,258,423 to Severance, Jr. et al, and assigned to The ESAB Group, Inc., the entirety of which patent is incorporated by reference herein. It will be appreciated that although the disclosed arrangement is described in relation to a retract start torch, it is equally applicable to conventional high-frequency starting torches such as those described in U.S. Pat. No. 7,081,597 to Severance, Jr. et al, and assigned to The ESAB Group, Inc., the entirety of which patent is incorporated by reference herein. 
     As will be appreciated, certain of the front end components of the plasma torch  10  are subjected to a harsh (e.g., high temperature) environment during operation. The electrode and nozzle generally are regarded as “consumables” that are subject to deterioration during operation. As such, these components must be replaced periodically in order to restore the torch to a proper condition for satisfactory operation. The disclosed plasma torch  10  includes features that enable quick and easy replacement of these front end “consumables.” In some embodiments, various of the front end components can be coupled together in a manner that enables them to be simply and easily removed and replaced as a single assembly. 
     In general, the front end components of the plasma torch  10  can include the nozzle  14 , the electrode  20 , a shield  54  that surrounds a front portion of the nozzle, a shield retainer  56  that retains the shield, a nozzle-retaining cup insert  58  that engages both the nozzle and the shield, and a nozzle-retaining cup body  60  that retains the nozzle-retaining cup insert. A generally cylindrical gas diffuser  62  may be disposed between the nozzle  14  and the shield  54 . In alternative constructions the diffuser may replaced with an insulator which lacks features to direct the flow of shield gas. Such features may alternatively be integrally formed in another torch part such as the nozzle or shield. A front body insert cap  64  and a front body insert base  66  may retain the nozzle  14  with respect to a front insulator body  68  which extends forward from the main torch body  12  to enclose a forward portion of the electrode holder  18 . A gas baffle  70  may surround a portion of the electrode holder  18 . A rear portion  72  of the gas baffle  70  may be engaged with the front insulator body  68  and a forward portion  74  of the gas baffle may be engaged with the nozzle  14 . 
     Although the illustrated embodiment shows the front body insert cap  64  and front body insert base  66  as being separate pieces, they could instead be combined to form a unitary front body insert. In addition, although the illustrated embodiment shows the gas baffle  70  as simply fit between the front insulator body  68  and the nozzle  14 , the gas baffle  70  could have features that enable it to be part of the “front end” assembly. For example, the gas baffle  70  could be threaded into the nozzle  14 . The threads could be positioned below the holes for swirling the gas or they could be above them. In the latter case, gas passages could be provided in the gas baffle by forming slots deeper than the threads in either the gas baffle or the nozzle, or the threads could be loose enough that gas could flow through the gaps in the threads. The gas baffle  70  could alternatively be plastic, and could be secured to the nozzle by snapping it into or onto the nozzle or by a press fit. Alternatively, the gas baffle  70  could be a ceramic material secured to the nozzle by an o-ring, a snap ring, or a spacer made of a resilient material. In addition or alternatively, the gas baffle can be adhered to the nozzle  14  to form the two pieces into a permanent assembly. In any of these cases, of course, the electrode holder  18  and gas baffle  70  would be configured so that the electrode holder doesn&#39;t secure the gas baffle within the torch. As such, the gas baffle  70  would be removed when the “front end” assembly is removed from the plasma torch. 
     It will be appreciated that although these elements are described as separate pieces, it is not critical that they be provided as such. As previously noted, for example, in some embodiments the gas diffuser  62  may be formed as an integral part of the nozzle  14 . In addition or alternatively, the shield  54  and shield retainer  56  could be formed as a single piece, and/or the nozzle retaining cup insert  58  could be permanently attached to the nozzle retaining cup body  60  to constitute a nozzle-retaining cup. Other similar combinations and arrangements are also contemplated. 
     As will be described in greater detail later, it may be desirable to replace the electrode  20 , nozzle  14  and the shield  54  at the same time, as they are most subject to damage or wearing during operation. With the disclosed arrangement, the front end interconnected parts (e.g., nozzle  14 , gas diffuser  62 , shield  54 , shield retainer  56 , nozzle retaining cup  58  insert and nozzle-retaining cup body  60 ) can be removed from the plasma torch  10  as a single unit. The electrode  20  may be separately removed once the aforementioned pieces are removed. The user may have a pre-assembled set of front end interconnected parts ready to join to the plasma torch  10  as a single unit. It will be appreciated that the advantage of the disclosed arrangement is that it does not require a specialized fixture or tools to assemble the front end replacement components, and users can assemble and disassemble the front end components with their hands. 
     The arrangement and inter-relation of the individual front-end components of the plasma torch  10  will now be described in greater detail. As shown in  FIGS. 1 and 2 , The nozzle retaining cup body  60  is a generally cylindrical sleeve that is engaged with the lower end of a torch outer housing  76  which surrounds the main torch body  12 . Specifically, the nozzle retaining cup body  60  comprises a rearwardly positioned internally threaded portion  60   a  that engages corresponding external threads  76   a  formed on the torch outer housing  76 . The nozzle retaining cup body  60  further comprises a forwardly positioned externally threaded portion  60   b  that engages corresponding internal threads  56   a  formed on a rearward cylindrical portion  78  of the shield retainer  56 . 
     The shield retainer  56  has a forward portion  80  of generally frustoconical form. The forward end  82  of the forward portion  80  includes an internal circumferential lip  84  that engages an external circumferential shoulder  86  of the shield  54 . While this is one exemplary way for the shield retainer to secure the shield, other arrangements such as threads can also be used. The shield  54  also has a generally frustoconical shape that includes an internal circumferential recess  88 , positioned forward of the external circumferential shoulder  86 . The internal circumferential recess  88  is shaped to engage a forward face  90  and an outer face  92  of the gas diffuser  62 , thus capturing and centering the gas diffuser therein. 
     The nozzle  14  is received within, and engages, several pieces of the plasma torch  10 . A rearward facing surface  94  of the nozzle  14  engages a forward face  96  of the gas baffle  70 . A rearward outer surface  98  of the nozzle  14  engages an inner surface  100  of the front body insert cap  64 , while an intermediate outer surface  102  of the nozzle  14  engages an inner surface  104  of a forward portion  106  of the nozzle retaining cup insert  58 . A forward portion  108  of the nozzle  14  has a general frustoconical shape that somewhat matches the shape of the shield  54 . The nozzle  14  also has an internal cavity  110  that surrounds the electrode  20  as well as a portion of the electrode holder  18  in non-contact relation therein. The nozzle  14  further has a shoulder  154  ( FIG. 6B ) for engaging the nozzle-retaining cup insert  58  to prevent the nozzle  14  from moving axially rearward once installed. It will be appreciated that the shoulder  154  acts as a stop against rearward movement of the nozzle with respect to the nozzle-retaining cup insert once the shoulder  154  engages the nozzle retaining cup insert. Other examples of appropriate stops include a snap ring, a pressed on ring, such as an insulator or diffuser, a screwed on bushing, or other substitute for a shoulder which may occur to one skilled in the art so long as it can be assembled to the nozzle prior to the nozzle being placed into the nozzle retaining cup insert. 
     The nozzle retaining cup insert  58  includes a cylindrical rearward portion  112 , while the forward portion  106  has a frustoconical shape that generally matches the shape of the forward portion  80  of the shield retainer  56 . The rearward portion  112  of the nozzle retaining cup insert  58  has an inner surface  114  that is sized to be received by a corresponding cylindrical outer surface  116  of the front insulator body  68 . The outer surface  116  of the front insulator body  68  may include a recess  118  configured to receive a sealing element  120  for sealing the front insulator body to the nozzle retaining cup insert  58 . The nozzle retaining cup insert  58  may also include a shoulder  59  ( FIG. 2 ) having a rearward surface  61  configured to engage a forward surface  63  of the nozzle retaining cup body  60  to prevent the nozzle retaining cup insert from moving axially rearward after the two pieces have been coupled. 
     The gas baffle  70  may be a generally cylindrical member received within a circumferential recess  122  in the front insulator body  68 . As previously noted, the gas baffle  70  has a forward face  96  that engages a rearward facing surface  94  of the nozzle  14 . A rear face  124  of the gas baffle engages a forward facing surface  126  of the circumferential recess. Thus, when the front end components are engaged with the remainder of the plasma torch  10 , the gas baffle  70  is locked in the circumferential recess  122 . 
     As can be seen in  FIG. 3 , the front body insert base  66  surrounds the baffle  70  in non-contact relation. The front body insert base  66  is received within a second circumferential recess  128  in the front insulator body  68 . A forward lip  130  of the front body insert base  66  is fit between an inner surface  132  of the front insulator body  68  within the second circumferential recess  128  and a rearward outer surface  134  of the front body insert cap  64 , which fixes the front body insert base  66  within the second circumferential recess. 
     The front body insert cap  64  is also disposed within the second circumferential recess  128  in the front insulator body  68 , and is positioned forward of the front body insert base  66 . As noted, a rearward outer surface  134  of the front body insert cap  64  presses the forward lip  130  of the front body insert base  66  against the inner surface  132  of the front insulator body  68 . A forward outer surface  136  of the front body insert cap  64  engages the inner surface  132  of the front insulator body  68  in a press-fit manner. The front body insert cap  64  includes a circumferential recess  138  between the rearward and forward outer surfaces  134 ,  136 . This recess  138  is configured to receive a sealing element  140  to seal the front body insert cap  64  to the front insulator body  68 . In one embodiment, the sealing element  140  is an elastomeric O-ring. 
       FIGS. 4 and 5  show the inter-relation of the front end components in an exploded isometric view (i.e., the unassembled state).  FIG. 4  shows the shield retainer  56 , shield  54 , gas diffuser  62 , nozzle  14 , nozzle retaining cup insert  58  and nozzle retaining cup body  60  in coaxial alignment.  FIG. 5  shows the front end components in a partially assembled state, with the nozzle inserted in the nozzle retaining cup insert  58 , and nozzle retaining cup engaged with the nozzle retaining cup body  60 . The shield retainer  56 , shield  54  and gas diffuser  62  are aligned with, but positioned away from, the nozzle retaining cup insert  58  and nozzle  14 . 
     Referring again to  FIGS. 6A and 6B , the nozzle  14  will be described in greater detail. As can be seen, the nozzle  14  has a forward portion  108  of generally frustoconical shape and a central body portion  142  that has a generally cylindrical shape. The central body portion  142  itself includes first, second and third portions  144 ,  146 ,  148 . The first portion  144  is adjacent to the forward portion  108  and includes a first shoulder  154 . The first shoulder has a forward face  156  that engages a rear face  160  ( FIG. 2 ) of the gas diffuser  62  to lock the gas diffuser between the nozzle  14  and the shield  54  when the components are assembled. The first shoulder  154  also has a rearward face  157  for engaging a nose portion  57  of the nozzle retaining cup insert  58  to prevent the nozzle from moving axially rearward once installed. As will be explained in greater detail later, the engagement between the first shoulder  154  and the nose portion  57  advantageously facilitates front loading of the nozzle  14  into the nozzle retaining cup insert  58 , and the bottoming of the nozzle within the nozzle retaining cup insert. 
     As can be seen, the first portion  144  has a cylindrical portion  145  positioned forward first shoulder  154 . This cylindrical portion  145  can be sized to receive an inner surface  93  ( FIG. 2 ) of the gas diffuser  62  in a press-fit relation so that the gas diffuser is retained on the nozzle. 
     The first portion  144  also has a first recess  150  for receiving a first sealing element  152  ( FIG. 1 ), which in the illustrated embodiment is an O-ring. The first portion has a first outer diameter D 1  sized to provide close conformity between the first portion  144  and an inner surface  104  ( FIG. 2 ) of the nozzle retaining cup insert  58 . When installed, the first sealing element  152  seals the first portion  144  to the nozzle retaining cup insert  58 . 
     The second portion  146  of the central body portion  142  has a second recess  162  for receiving a second sealing element  164  ( FIG. 2 ), which in the illustrated embodiment is an O-ring. The second portion has a second diameter D 2  sized to provide close conformity between the rearward outer surface  98  of the nozzle  14  and the inner surface  100  of the front body insert cap  64 . When installed, the second sealing element  164  seals the second portion  146  to the front body insert cap  64 . As can be seen, the second diameter D 2  is smaller than the first diameter D 1 . As will be described in greater detail later this difference in diameters facilitates the installation/removal of the nozzle  14  from the front body insert cap  64  and the nozzle retaining cup insert  58  during assembly/disassembly. 
     The third portion  148  of the central body portion  142  includes an internal circumferential shoulder  166  disposed adjacent to the internal cavity  110 . This internal circumferential shoulder seats against the forward portion  72  of the gas baffle  70  when the nozzle is installed. The circumferential shoulder  166  forms rearward facing surface  94  which, upon installation of the nozzle  14  in the plasma torch  10 , abuts the forward portion  72  of the gas baffle  70 , locking the gas baffle  70  between the nozzle and the front insulator body  68  as well as locking the nozzle in a desired axial position within the plasma torch  10 . 
     As noted, the dimensions of the nozzle  14  are selected to facilitate installation and removal of the nozzle with respect to the remaining elements of the plasma torch  10 . Specifically, the second diameter D 2  of the second portion  146  is smaller than the first diameter D 1  of the first portion  144 . And as can be seen in  FIGS. 1 and 2 , the diameter D 3  of the opening in the nozzle retaining cup insert  58  is larger than the diameter D 4  of the opening in the front body insert cap  64 . During installation and removal, this arrangement allows the second and third portions  146 ,  148  of the nozzle  14 , along with second sealing element  164 , to slide past inner surface  104  of the nozzle retaining cup insert  58  without interference from the nozzle retaining cup so that a smooth insertion can be achieved without damaging the second sealing element  164 . Only when the first portion  144  of the nozzle  14  engages the inner surface  104  of the nozzle retaining cup insert  58  is a seal formed between the nozzle and the nozzle retaining cup insert owing to the first sealing element  152 . The seal at  164  with the front body insert cap is made when the front end “unit” is assembled onto the rest of the plasma torch. 
     Selected non-limiting exemplary dimensions of the nozzle retaining cup insert  58 , the nozzle  14 , the front body insert cap  64 , seal  164 , and clearances therebetween are illustrated in Table 1, below. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Piece/Dimension 
                 Example 1 
                 Example 2 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Nozzle Retaining Cup Insert ID @ 102 ± .001 
                 .965″ 
                 .994″ 
               
               
                 Nozzle OD @ 102 D1 ± .001 
                 .962″ 
                 .989″ 
               
               
                 Nozzle OD @ 98 D2 ± .001 
                 .927″ 
                 .975″ 
               
               
                 Front Body Insert Cap ID @ 100 ± .001 
                 .931″ 
                 .979″ 
               
               
                 Nozzle OD @ seal 164 ± .001 
                 .812″ 
                 .860″ 
               
               
                 O-ring wall &amp; compression @ 164 (nominal) 
                 .070″ 
                 .070″ 
               
               
                   
                 &amp; 15% 
                 &amp; 15% 
               
               
                 Min Clearance D1 to Retaining Cup Insert @ 102 
                 .001″ 
                 .003″ 
               
               
                 Min Clearance D2 to Retaining Cup Insert @ 102 
                 .036″ 
                 .017″ 
               
               
                 Nominal Clearance 164 Seal to Nozzle Retaining 
                 .013″ 
                 −.006″ 
               
               
                 Cup Insert @ 102 
               
               
                 Min Clearance D2 to Front Body Insert Cap 
                 .002″ 
                 .002″ 
               
               
                 ID @ 100 
               
               
                   
               
             
          
         
       
     
     Assembly of the front end “unit” can proceed as follows. The third portion  148  ( FIG. 6B ) of the nozzle  14  may be pushed through the ID (D 3 ) of the nozzle retaining cup insert  58  until it bottoms (i.e., ribs  154  ( FIG. 4 ) contact a nose portion  57  of the nozzle retaining cup insert of  58 ), “making” the seal  152 , and sealing the nozzle  14  to the nozzle retaining cup insert  58 . The nozzle retaining cup insert  58  may then be placed into an ID of the nozzle retaining cup body  60  so that the rearward surface  61  of the nozzle retaining cup insert engages a forward surface  63  of the nozzle retaining cup body  60 . For embodiments in which the gas diffuser  62  is not a permanent part of the nozzle  14  or shield, the gas diffuser  62  may then be mounted on the nozzle. The shield  54  may be positioned so that it is centered to the nozzle  14  by the diffuser  62  and rests against the nose portion  57  of the nozzle retaining cup insert  58 . The shield retainer  56  may then be screwed onto the nozzle retaining cup body  60  so that the shield  14  and the gas diffuser  62  are locked down. In this state, the nozzle  14  will be free to move a small amount axially. The front end unit is thereby assembled. 
     Next, assuming that the gas baffle  70 , electrode holder  18 , and electrode  20  are assembled in the torch, the front end unit can be installed by screwing the front end unit onto the threads  76   a  of the torch outer housing  76 . The front end unit will bottom out on the gas baffle when a rearward facing surface  94  of the nozzle  14  engages a forward face  96  of the gas baffle  70 . 
     A reversal of these steps can be employed to remove the front end unit from the remainder of the plasma torch  10 . 
     As will be appreciated, providing the nozzle  14  with a hard stop against the nozzle retaining cup insert  58  enables the elements of the front end unit to be loaded from the front. This is in contrast to prior designs, such as those disclosed in U.S. Pat. No. 7,256,366 to Severance, Jr., which require loading of the elements of the front end unit from the back. 
     Moreover, with prior arrangements (such as those described in U.S. Pat. No. 7,256,366), the nozzle must be loaded onto a fixture that has threads for the nozzle retaining cup and a seat for the nozzle that simulates the gas swirl baffle. With the presently disclosed arrangement, the nozzle  14  loads into the front of the nozzle retaining cup insert  58  without the need for any sort of fixture. In addition, with prior arrangements, it is necessary to screw the cup onto the fixture so as to put the seal between the nozzle&#39;s shoulder and the lip in the nozzle retaining cup insert into compression. With the presently disclosed arrangement, this step is omitted. The nozzle retaining cup insert  58  is simply placed into the nozzle retaining cup body  60 . 
     Further, with prior arrangements a nut must be screwed onto the nozzle to maintain compression of the seal between the nozzle&#39;s shoulder and the lip of the nozzle retaining cup insert. Alternatively, a clip is slipped into a groove in the nozzle to maintain compression of the seal. In either case, a fastener bears against the end of the nozzle retaining cup insert to keep compression on the seal. With the present design, a special fastener is not required to secure the nozzle or to maintain compression on a face seal, as the face seal has been eliminated. Finally, with prior designs the nozzle retaining cup/nozzle assembly must be removed from the special fixture, and the diffuser and shield must be secured in place using the shield retainer by screwing it onto the nozzle retaining cup body. Again, with the presently disclosed design no fixture is required to achieve this engagement. 
     As will be appreciated, the presently disclosed design provides the benefit of enabling the front end parts to be preassembled without the need for a special fixture, or for additional fasteners and tools for installing and removing the fasteners. The presently disclosed design makes assembly/disassembly more efficient. 
     As previously noted, the unique dimensional configuration of the individual pieces of the front unit allows a user to replace the consumable pieces of the torch without the need for a special fixture. It also ensures that the individual front end components are locked in desired axial and concentric position with respect to each other upon final tightening of the nozzle retaining cup body  60  on the torch outer housing  76 . 
     Referring now to  FIGS. 7-11 , an alternative front end arrangement for use with the disclosed plasma torch  10  is disclosed. Similar to the arrangement described in relation to  FIGS. 1-6B , the front end unit of  FIGS. 7-11  includes a shield  54 , shield retainer  56 , nozzle retaining cup body  60 , nozzle  170  and gas diffuser  172 . The shield, shield retainer and nozzle retaining cup body may be substantially the same as the those described in relation to  FIGS. 1-6B . The nozzle  170  and gas diffuser  172  may also be similar to those described in relation to  FIGS. 1-6B , with differences that will now be described. 
     Referring to  FIG. 8 , the nozzle  170  may include all of the features described in relation to the nozzle  14  with the exception that it may have one or more features configured to allow snap-fit engagement with the gas diffuser  172 . In some embodiments, the gas diffuser  172  may be formed from a polymer. In one non-limiting exemplary embodiment the gas diffuser  172  is a glass-reinforced polyetherimide. Other exemplary materials include glass-filled expoxies such as G-10, unreinforced polyimides like Vespel, Meldin 7000, or Tecasint 2011, Torlon, glass-filled PEEK, or unreinforced polyetherimides. In addition, a ceramic material could be used, and it could be cemented in place, or material from the nozzle could be rolled over it to secure it. Thus, any of a variety of materials can be used as long as they function as an electrical insulator and are reasonably resistant to temperature. In some embodiments the gas diffuser  172  may comprise anodized aluminum. The gas diffuser  172  may be formed by an injection molding process or other suitable process. As such, the gas diffuser  172  may have sufficient elastic properties to allow it to snap onto the nozzle  170  during installation. The nozzle  170  may include a forward portion  174  of a general frustoconical shape that matches the shape of the shield  54 . A central body portion  176  has a generally cylindrical shape, and may be divided into first, second and third portions  178 ,  180  and  182 . The first portion  178  is adjacent to the forward portion  174  and includes a first shoulder  184 . The first shoulder has a forward face  186  that engages a rear face  188  ( FIG. 9C ) of the gas diffuser  172  to lock the gas diffuser between the nozzle  170  and the shield  54  when the components are assembled. The first portion  178  has a cylindrical portion  190  positioned forward first shoulder  184 . This cylindrical portion  190  is sized to receive an inner surface  192  ( FIG. 9C ) of the gas diffuser  172 . A second shoulder  194  is disposed at the forward end of the cylindrical portion  190  directly adjacent to the frustoconical forward portion  174 . This second shoulder  194  may have a shoulder diameter D 5  that is slightly larger than the outer diameter D 6  of the cylindrical portion  190 . The shoulder diameter D 5  may also be slightly larger than the inner diameter D 7  ( FIG. 9C ) of the gas diffuser  172 . In some embodiments, the clearance between D 6  D 7  may be from 0-inches to about 0.003-inches, while D 5  may be at least 0.004-inches greater than D 7 . It will be appreciated that these dimensions are not limiting, and that other clearances can be used as desired. 
     As will be appreciated, this slight difference in diameters between the nozzle  170  and the gas diffuser  172  enables the gas diffuser to be snapped onto the cylindrical portion  190  of the nozzle during installation. The gas diffuser  172  is then retained on the nozzle  170  by the second shoulder  194 .  FIG. 10  shows the gas diffuser  172  installed on the nozzle  170 .  FIG. 11  shows the relative arrangement of the gas diffuser  172 , the nozzle  170 , the shield  54 , the shield retainer  56  and the nozzle retaining cup insert  58 . As can be seen, the inner surface  192  of the gas diffuser  172  is received within the trough of the cylindrical portion  190  of the nozzle  170 , and is retained by the second shoulder  194 . 
     The embodiment of  FIGS. 8-11  enables the use of a relatively inexpensive injection molded gas diffuser that can be permanently pressed or snapped onto the nozzle. The diffuser then serves as the feature that the nozzle retaining cup insert  58  bears against to pull the nozzle out of the torch when the front end parts are removed. A side benefit is that nozzle/shield concentricity may be improved. 
     Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. While the present invention has been disclosed with reference to certain embodiments, numerous modifications, alterations and changes to the described embodiments are possible without departing from the spirit and scope of the invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof.