Abstract:
A machine for forming and fitting core support pins into wax ( 70 ) surrounding a core ( 68 ) prior to covering the wax ( 70 ) with a frit ( 76 ), includes one or more punch devices ( 30 ), ( 82 ) within its structure, so as to enable the forming of one or more indentations in each pin, intermediate its ends, thereby providing a designed weakness in the pin to cause it to more reliably follow slight relative movement which occurs between the pins and the part being cast, thus reducing stresses in the surface of the part.

Description:
This application is a divisional application of Ser. No. 09/978,028 (filed Oct. 17, 2001), now abandoned. 
    
    
     FIELD OF THE INVENTION 
     It is well known in the field of foundry work, to form hollow articles of intricate shape, by first forming a dissolvable core, forming a wax mould thereabout, and then inserting pins in the wax, so that their inner ends abut the core, and their outer ends protrude from the wax. A damp ceramic frit is then applied to the wax, thus covering the outer ends of the pins. The frit is dried so as to solidify it, and provide it with sufficient strength to hold the pins firmly. The wax is then melted and allowed to run from between the core and the frit, and molten metal is poured into the resulting space. 
     BACKGROUND OF THE INVENTION 
     A machine which cuts the pins to a required length, and places them into wax covering a core, is described, illustrated and claimed in European patent 0072088, owned by the applicant for a patent for the present invention, as disclosed and claimed in this specification. 
     Experience gained during use of the machine, the subject of European Patent 0072088 in the production of hollow turbine blades, showed that the machine functioned perfectly, but the pins produced thereby generated unacceptable local stress loads into the surface of the casting. During solidifying of the metal, small, unavoidable relative movement occurs between the casting and the hardened frit, at a time insufficient for the pins to have been melted and absorbed by the cast metal. Stress in the form of tension was thus created in the blade surface at each place of contact with a pin, which required a dressing operation to remove it, some blades being scrapped as a result. 
     SUMMARY OF THE INVENTION 
     A first aspect of the present invention seeks to provide an improved core locating pin. Accordingly, a core locating pin which in operation spaces a core from a surrounding ceramic frit, by having one end buried in said frit, and the other end abutting said core, comprises a rod which includes an indentation intermediate its ends, said indentation being so positioned therein as to lie entirely within said frit, with one edge coinciding with the interior face thereof. 
     A further aspect of the present invention seeks to provide an improved core locating pin forming and fitting machine. Accordingly, a core locating pin forming and fitting machine comprises a cylindrical body containing a pressure actuated piston and rod, said rod having a first bore diametrically therethrough at a position adjacent its free end, which bore, in one position of said rod, and via a bore in the cylinder wall, receives pin wire from an external source, said rod having a second bore normal thereto and connecting said first bore with a space between the rod end and the end wall of the cylindrical body, which space contains a punch device which in operation passes through said second bore, and punches an indentation in pin wire when it is loaded into said first bore, prior to said pin wire, when in said first bore, being cut to form a pin of a desired length by movement of said piston and rod relative to said cylindrical body, to a position wherein said first bore is aligned with a further, pin ejection bore in the wall of the cylindrical body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example and with reference to the accompanying drawings, in which: 
     FIG.  1 . is a diagrammatic, axial cross sectional view through a core locating pin forming and fitting machine, in accordance with the present invention. 
     FIG.  2 . is a cross sectional part view of the machine of FIG.  1 . but including an alternative forming arrangement. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG.  1 . cylindrical body  10  contains a piston  12  and an associated rod  14 , which extends to the right of piston  12 , as viewed in the drawing. In a “ready to operate” situation, the end extremity of rod  14  abuts a stop  16 , so that a bore  18  which is provided diametrically through rod  14  at a position near its free end, is aligned with a bore  20  through the wall of cylindrical body  10 . By this means, pin wire  22  can be pulled from an external supply (not shown) by pinch rollers  24 ,  26 , and passed through bores  18  and  20 , until its end abuts a stop  28  in the wall of the cylindrical body  10 . 
     The right-hand end extremity of cylindrical body  10  as viewed in the drawing, supports a solenoid actuated punch  30 , the operative part of which lies within a space  32  defined by the end  21  of rod  14 , and the inner end portion of cylindrical body  10 . When a microprocessor (not shown) is switched on, stop  16 , which rod  14  abuts, sends an electronic signal via said microprocessor (not shown) to the pinch drums  24  and  26 , causing them to rotate and push pin wire  22 ,via bores  20  and  18 , onto stop  28 . A signal is generated by stop  28 , which via the microprocessor (not shown), cancels the wire pushing signal, but actuates the solenoid and thus causes the punch  30  to thrust through a bore  34  in the end extremity of rod  14 , (and, in the present example, co-axial with rod  14 .) and strike the side of the pin wire so as to create an indentation therein. The depth of the indentation will be decided by design, and the length of the punch  30  accordingly proportioned. Thus, when the striking end of punch  30  is just touching the pin wire  22 , the space  36  between the outer end face of cylindrical body  10  and a stop collar  38  fixed to the outer end of punch  30 , will correspond to the required depth of the indentation. 
     Conduits  40  and  42  are connected to the cylindrical body  10 , so as to straddle piston  12 , and enable pressurized air from a source (not shown) to be supplied as required, to either side of piston  12 . Thus, loading and punching of the pin wire having been achieved as described in the immediately preceding paragraph, punch  30  is withdrawn from the pin wire, in the present example by the action of a diaphragm spring  44 , air is pumped via valve  46  to the right-hand side of piston  12 , to move it and its rod  14  to the left as viewed in the drawing, until an extension  48  of rod  14  abuts a stop  50 , which causes a signal to pass via the microprocessor (not shown) to close valve  46 . 
     Movement of rod  14  as described hereinbefore, shears a pin from pin wire  22  and carries it to a point where rod extension  48  contacts the stop  50 , which ensures that bore  18  is in axial alignment with a bore  52  in a further cylindrical body  54 , which is integral with, and axially normal to, cylindrical body  10 . A further piston  56  and associated rod  58  lie within body  54  and, in a “ready to operate” position as shown in the drawing,  56  lies midway between two stops  60  and  62 , thus holding the lower end extremity of rod  58 , which lies in bore  52 , in spaced relationship with rod  14 . However, contact of rod extension  48  with stop  50 , signals via the microprocessor (not shown) the opening of a valve  64 , which passes pressurized air to piston  56  to move it and thus cause associated piston  58  to push the pin out of bore  18  and through the lower part  29  of bore  52 , and into and partly through a collet device  66 ,  50  as to protrude therefrom. The correct length of stroke of piston  56  is determined by the stop  62 , which piston  56  abuts when the desired pin protrusion has been achieved. 
     Abutment of piston  56  on stop  62  causes output of a signal from the microprocessor (not shown) which drives the machine along slides (not shown) towards a wax covered core  68 , which is located in a jig  72 , so as to push the pin through the wax  70 , until it abuts the core  68 . The abutting action outputs a further signal from the microprocessor, which opens a valve  74 , to allow pressurized air to a piston  76  within body to move its associated rod  58  into the interior of the collet device  66  and force it open, against the collet closing pressure exerted by a bellville washer  80 , so as to release the pin. The opening action of collet device  66  causes output of another signal from the microprocessor (not shown) which brings about withdrawal of the machine, to the position in which the process is re-started. 
     It is preferred that the indentation is positioned in the pin wire, such that when the completed pin is positioned in the wax as described hereinbefore, the indentation is entirely outside the wax, so that the frit, when applied, covers it. However, it is also preferred that one edge of the indentation should be against the outer surface of the wax. This means that the thickness of the wax through which the pin is to penetrate, must decide the position of punch  30  in body  10 , relative to the end of the pin wire that abuts stop  28 , and in use, abuts core  68 . It follows, that if a pin is required, in which the indentation is offset from the mid point of the overall length thereof, the punch must be correspondingly offset from the axis of rod  14 . 
     Referring now to FIG. 2, rod  14  is made in two parts,  14   a  and  14   b . Part  14   b  is bored out to a depth equi-distant from bore  18  as is the end extremity of rod  14 , and bore  34  is extended thereto. A second solenoid operated punch mechanism  82  is provided in the bore in rod part  14   b  in opposition to punch mechanism  30 , so as to enable simultaneous punching of opposing sides of the pin wire  22 , should this be desirable. After fitting the second punch mechanism  82 , parts  14   a  and  14   b  of rod  14  can be joined by appropriate male and female screw threads  86 . 
     On movement of rod  14  to achieve shearing of a pin, the solenoid circuit of punch  82  will be broken. Therefore sliding contacts  84  are provided so as to enable disconnection and reconnection of the circuit, as rod  14  is reciprocated. The solenoid actuation may be substituted by pneumatic or other suitable punch actuating means.