PROTECTIVE GAS MOUTHPIECE, CONNECTION DEVICE AND CONNECTION METHOD

Abstract

Protective gas mouthpiece for a connection device, having a base member which has an axial opening and a mouth arranged around the opening and which can be placed on a workpiece on which a connection process is intended to be carried out, wherein the opening adjacent to the mouth defines a cleaning space into which protective gas can be introduced and which, when the connection process is carried out, can be axially delimited by the workpiece which covers the opening. The protective gas is introduced into the cleaning space in such a manner that a main flow direction of the protective gas in a radial centre of the cleaning space is orientated in a substantially radial and unidirectional manner.

Claims

1. A Protective gas mouthpiece for a connection device, the protective gas mouthpiece for supplying a protective gas during a connection process between a connecting element and a workpiece, the protective gas mouthpiece comprising: a base member partially defining an axial opening and a mouth arranged around the opening and which can be placed onto the workpiece, and the opening adjacent to the mouth defines a cleaning space in which the protective gas can be introduced and which, when the connection process is carried out, is axially delimited by the workpiece which covers the opening, and a protective gas supply channel is directed into the cleaning space such that a main flow direction of the protective gas in a radial centre of the cleaning space is orientated in a substantially radial and unidirectional manner.

2. The protective gas mouthpiece according to claim 1, wherein the base member defines a plurality of the protective gas supply channels which are located so as to be distributed over a periphery of the cleaning space.

3. The protective gas mouthpiece according to claim 2, wherein the distribution of the protective gas supply channels over the periphery is non-uniform so that no protective gas supply channel is located in a peripheral portion (γ) which extends over an arc of more than 90°.

4. The protective gas mouthpiece according to claim 3, wherein the plurality of protective gas supply channels is precisely three protective gas supply channels which are defined in the base member, and two of the protective gas channels are diametrically opposed.

5. The protective gas mouthpiece according to claim 2 and further including an annular space located at an axial region which is opposite the axial opening and into which the protective gas can be supplied for distribution to the plurality of protective gas channels, and the annular space is connected to the plurality of protective gas supply channels in the base member.

6. The protective gas mouthpiece according to claim 5, wherein the annular space is connected to at least one of the protective gas supply channels through a flow resistance arrangement.

7. A method for carrying out a welding process using a protective gas to purge ambient air from a welding site between a connecting element and a workpiece, the method comprising the steps of: providing a protective gas mouthpiece for supplying the protective gas during the connection process between the connecting element and the workpiece, the protective gas mouthpiece comprising; a base member which has an axial opening and a mouth which is arranged around the opening and which can be placed on the workpiece, wherein the opening adjacent to the mouth defines a cleaning space into which the protective gas can be introduced and which, when the connection process is carried out, is axially delimited by the workpiece which covers the opening, and the protective gas is introduced into the cleaning space such that a main flow direction of the protective gas in a radial centre of the cleaning space is orientated in a substantially radial and unidirectional manner; axially placing the protective gas mouthpiece onto the workpiece, and wherein inside the protective gas mouthpiece a connection element is arranged axially movable with respect to the protective gas mouthpiece; setting the connection element at a spacing (Si) from the workpiece so that an intermediate space is partially defined between the connection element and the workpiece; and supplying the protective gas to the intermediate space.

8. The method according to claim 7, wherein the step of supplying protective gas to the intermediate space includes supplying the protective gas in an asymmetrically so that the supplied protective gas flows in the intermediate space in a main flow direction orientated in a substantially radial and unidirectional manner in order to displace ambient gas from the intermediate space.

9. The method according to claim 8, further including the steps of: lowering the connection element onto the workpiece and switching on an electric current (I) which flows through the connection element and the workpiece, raising the connection element from the workpiece so that an electric arc is produced between the connection element and the workpiece, and electric arc melts an opposed faces of the connection element and the workpiece; and lowering the connection element onto the workpiece and switching off the electric current (I) so that the connection element is secured to the workpiece.

10. The method according to claim 7, wherein the spacing (Si) is greater than 1 mm.

11. A connection device for performing a connection process between a connecting element and a workpiece, the connection device comprising: a connection element retention device; and a protective gas mouthpiece for supplying a protective gas during the connection process, the protective gas mouthpiece surrounding the connection element retention device and including: a base member which has an axial opening and a mouth arranged around the opening and which can be placed onto the workpiece, and the opening adjacent to the mouth defines a cleaning space in which the protective gas can be introduced and which, when the connection process is carried out, is axially delimited by the workpiece which covers the opening; and a protective gas supply channel directed into the cleaning space such that a main flow direction of the protective gas in a radial centre of the cleaning space is orientated in a substantially radial and unidirectional manner.

12. The connection device according to claim 11, wherein the base member defines a plurality of the protective gas supply channels which are located so as to be distributed over a periphery of the cleaning space.

13. The connection device according to claim 12, wherein the distribution of the protective gas supply channels over the periphery is non-uniform so that no protective gas supply channel is located in a peripheral portion (γ) which extends over an arc of more than 90°.

14. The connection device according to claim 13, wherein the plurality of protective gas supply channels is precisely three protective gas supply channels which are defined in the base member, and two of the protective gas channels are diametrically opposed.

15. The connection device according to claim 12 and further including an annular space located at an axial region which is opposite the axial opening and into which the protective gas can be supplied for distribution to the plurality of protective gas channels, and the annular space is connected to the plurality of protective gas supply channels in the base member.

16. The connection device according to claim 15, wherein the annular space is connected to at least one of the protective gas supply channels through a flow resistance arrangement.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0058] Embodiments of the invention are illustrated in the drawings and are explained in greater detail in the following description. In the drawings:

[0059] FIG. 1 is a schematic longitudinal section of a connection device with an embodiment of a protective gas mouthpiece according to the invention;

[0060] FIG. 2 is a sectioned view along the line II-II of FIG. 1;

[0061] FIG. 3 is a sectioned view along the line III-III of FIG. 1;

[0062] FIG. 4 is a sectioned view along the line IV-IV of FIG. 1;

[0063] FIG. 5 shows the connection device of FIG. 1 during a cleaning step before carrying out a connection process;

[0064] FIG. 6 shows a time graph of the spacing between the workpiece and connection element and electrical connection current over time;

[0065] FIG. 7 is a schematic longitudinal section through another embodiment of a protective gas mouthpiece according to the invention; and

[0066] FIG. 8 is a schematic cross section through another embodiment of a protective gas mouthpiece according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0067] In FIGS. 1 to 4, a connection device is shown in schematic form and generally designated 10.

[0068] The connection device 10 serves to connect a connection element 12 which is constructed in this instance as a stud with a shaft and an enlarged flange to a workpiece 14, more specifically to the workpiece surface 16 thereof.

[0069] The connection device 10 is constructed in particular as an arc stud welding device but may also be constructed as a soldering or adhesive bonding device or the like.

[0070] The connection device 10 has a retention device 20 which is constructed to retain a connection element 12 which is intended to be connected to the workpiece 14. Via the retention device 20, there is optionally also supplied an electrical connection current I which is used for the stud welding operation.

[0071] A conventional stud welding process makes provision for the connection element 12 to first be placed on the surface 16 of the workpiece 14. Subsequently, a reduced electric current I in the form of a pilot current 1.sub.P is switched on. Subsequently, the connection element 12 is raised from the workpiece surface 16 so that an arc is drawn. Subsequently, the electric current I is increased to a welding current I.sub.W which may be greater than 1000 ampere. The mutually opposed faces of the connection element 12 and the workpiece 14 thereby melt. Subsequently, the connection element 12 is lowered onto the workpiece 14, preferably as far as a location below the workpiece surface 16 so that the electric current is short-circuited and switched off. Subsequently, the overall melt hardens so that a materially engaging connection is achieved between the connection element 12 and the workpiece 14.

[0072] In order to carry out this connection process which is generally known, the retention device 20 can be axially moved along a longitudinal axis as shown in FIG. 1 at 22 in order to axially raise and lower the connection element 12 with respect to the workpiece 14.

[0073] To this end, the retention device 20 is connected to a housing portion 24 which may be part of a connection head which is automated or guided by means of a robot but which may also be part of a mobile or portable connection device. The housing portion 24 may, for example, contain an axial drive and may further contain a connection element delivery or receiving member, by means of which connection elements 12 are automatically supplied. A loading pin which is supported so as to be able to be axially moved with respect to the housing portion 24 and with respect to the retention device 20 can load a connection element 12 in the retention device 20.

[0074] All these elements are known in the prior art. In addition, it is also known that connection elements are supplied to the retention device 20 from the front.

[0075] The connection device 10 further contains a protective gas mouthpiece 30 which is supported on the housing portion 24 in such a manner that the retention device 20 can carry out relative movements in relation to the mouthpiece 30.

[0076] The mouthpiece 30 has a base member 32 which has an axial opening 34 inside which the retention device 20 with a connection element 12 retained therein can be received. The axial opening 34 may also be constructed substantially as a through-opening (or bore) 34 so that the housing portion 24 extends into the axial opening 34 from the opposing axial end 52.

[0077] At the portion of the base member 32 facing forwards in the connection direction, the base member has a mouth 36 which can be placed on the workpiece surface 16 in such a manner that the axial opening 34 is covered or can be closed axially by the workpiece 14 and together with the base member 32 or the axial opening 34 thereof defines a cleaning space 38.

[0078] Protective shield gas can be supplied to the cleaning space 38. The protective inerting gas is intended to displace oxidizing ambient gas and moisture, such as air, from the cleaning space 38 in order to improve the above-described stud welding process.

[0079] In the above-described connection process, the connection device 10 is first moved in such a manner that the mouthpiece 30 is placed with the mouth 36 on the workpiece 14. Subsequently, in a first step, the retention device 20 is moved relative to the mouthpiece 30 in order to place the connection element 12 on the workpiece surface 16 and consequently to carry out a type of zero point determination. The mouthpiece 30 consequently also acts as a type of support base.

[0080] Generally, protective gas can be supplied to the cleaning space 38 in different manners. In this instance, a plurality of supply channels 40a, 40b, 40c are constructed in the base member 32, as can be seen in particular in FIG. 2 and FIG. 3. The supply channels 40a, 40b, 40c extend from the axial end 52 of the base member 32 facing away from the workpiece 14 at a supply angle 42 in an inclined manner in the direction towards the cleaning space 38. The supply angle which is shown in FIG. 1 at 42 may be in a range from 5° to 90°. The supply channels 40 may be constructed as linear holes, as illustrated in FIG. 1, which is preferable for reasons of cost. However, they may also be formed from a plurality of channel portions which are formed at an angle relative to each other.

[0081] FIGS. 1, 2 and 4 illustrate that protective gas supply flows 44a, 44b, 44c are introduced into the cleaning space 38 via the supply channels 40a, 40b, 40c in such a manner that a main flow direction 48 of the protective gas in a radial centre of the cleaning space 38 is orientated in a substantially radial and unidirectional manner.

[0082] The excess protective gas from the cleaning space 38, in the same manner as the displaced ambient gas, is discharged or exhausts axially upwards away from the workpiece 14, as schematically indicated in FIG. 1 at 46. The discharge of the protective gas and the ambient gas may be constructed in a similar manner to that described in document DE 20 2004 001 667 U1, the content of which is therefore further incorporated herein by reference in this instance.

[0083] FIG. 2 and FIG. 4 show the radially orientated main flow direction 48. This is produced by the protective gas supply channels being distributed over the periphery in a non-uniform manner so that no protective gas supply channel 40 is arranged in a peripheral portion γ which extends over more than 90°.

[0084] The angle y is in this instance preferably less than or equal to approximately 180°. FIG. 2 illustrates that the angle γ is 180° or slightly less than 180° since the supply channels 40b, 40c are arranged diametrically opposite each other on diametrically opposed sides of the main flow direction 48. The protective gas supply channels 40 are all arranged inside a peripheral portion β, for which: 360°−γ=β.

[0085] A third supply channel 40a is arranged in the peripheral direction between the two supply channels 40b, 40c so as to be spaced apart from both over an angle α which according to FIG. 2 is preferably 90°.

[0086] The main flow direction 48 for the protective gas inside the cleaning space or in the centre of the cleaning space is produced by the protective gas with the flows 44b, 44c which are directed directly towards each other, then being pressed away by means of the third protective gas supply flow 44a in a radial direction in a unidirectional manner and then preferably being directed away primarily inside the peripheral portion y in an upward direction, also partially at a diametrically opposed side, which is, however, not illustrated in FIG. 1.

[0087] The protective gas mouthpiece 30 further has a protective gas distributor device 50 which is arranged at an axially upper end 52 of the base member 32. The protective gas distributor device 50 defines an annular space 54 in which protective gas 44 can be supplied by means of an individual supply connection 56.

[0088] The protective gas supply channels 40a, 40b, 40c each open directly in the annular space 54.

[0089] However, there is preferably arranged between the ends of the supply channels 40a, 40b, 40c and the annular space 54 a flow resistor arrangement 58 which may be constructed as a ring which is placed in the annular space 54. The flow resistance arrangement 58 may, for example, be formed from a sintered metal arrangement with fine holes or fine pores but may also be formed by means of a fine-pored metal foam, a wire mesh or the like.

[0090] As a result of the flow resistance arrangement 58, there is produced inside the annular space 54 a dynamic pressure which ensures that the protective gas supply flows 44a, 44b, 44c are all substantially of the same size. This construction is generally preferred.

[0091] The supply of protective gas to the cleaning space 38 can be carried out according to the invention when the connection process is started, that is to say, after the mouthpiece 30 has been placed on the workpiece 14 and the connection element 12 has also been placed on the workpiece surface 16. In this instance, the supply of protective gas takes place substantially when the connection process is carried out, that is to say, when the arc is drawn.

[0092] FIGS. 5 and 6 show an alternative method indicating how the connection process on the whole can be carried out.

[0093] Thus, FIG. 5 shows that, in a cleaning step which is upstream of the actual connection process, the connection element 12 is raised from the workpiece 14 by a distance S.sub.1. It is thereby possible for the protective gas which flows when introduced in a main flow direction 48, which is orientated in the radial centre of the cleaning space 38 in a substantially radial and unidirectional manner, to be able to flow in particular below the connection element 12, that is to say, in an intermediate space 59 between the mutually opposed connection faces of the connection element 12 and the workpiece 14. It is thereby possible, precisely in this region in which the arc will later be produced, for a significant displacement of ambient gas to be carried out, without occurrences of turbulence or the like.

[0094] In FIG. 6, this is illustrated in a time sequence.

[0095] At S, the spacing (height) between the connection element 12 and the workpiece 14 is illustrated. At I, the electric current is illustrated. The graph 60 shown in FIG. 6 shows these variables over time t.

[0096] Based on an initial state, in which the connection device 10 is moved in the direction towards the workpiece 14, the spacing S is reduced until, at a time to, the connection element 12 has been placed on the workpiece 14. In this state, the mouthpiece 30 is generally also placed on the workpiece 14.

[0097] Subsequently, at time to, the connection element 12 is raised from the workpiece by the spacing S.sub.1 and protective gas is supplied so that a displacement of ambient air can be carried out, as schematically shown in FIG. 5, in a main flow direction 48.

[0098] At the time t.sub.1, with the end of this cleaning step, the connection element 12 is lowered onto the workpiece 14 again. Subsequently, the electric current I is switched on, initially in the form of a pilot current IP. Subsequently, the connection element 12 is raised again from the workpiece 14 by a distance S2 which may be equal to the value of S.sub.1 but which may also be larger or smaller. Shortly after t.sub.1, the electric current I is increased to a weld current I.sub.W.

[0099] As soon as the connection faces have begun to melt, the connection element 12 is lowered onto the workpiece 14, preferably to below the zero point, so that, at the time t.sub.2, the connection element 12 and the workpiece 14 are in contact and an electric short-circuit is produced, as a result of which the electric weld current I is switched off.

[0100] FIG. 7 shows an embodiment of a connection device 10 with a mouthpiece 30 which in terms of structure and operating method generally corresponds to the connection device 10 and the mouthpiece 30 of FIGS. 1 to 5.

[0101] FIG. 7 shows the state in the cleaning step in which, between the time t.sub.0 and t.sub.1, the protective gas is supplied whilst, between the connection element 12 and the workpiece 14, a spacing S.sub.1 is produced. This leads, as shown by the simulated flow with many arrows, to a main flow direction 48 which is orientated in a substantially radial and unidirectional manner. Protective gas is discharged from the cleaning space 38 in an upward direction, in particular at 46 in the region of the peripheral portion γ. A smaller portion of the protective gas (and the air) is also discharged in the other peripheral portions, as shown in FIG. 7 at 46′.

[0102] FIG. 8 shows another embodiment of a protective gas mouthpiece 30′ which has a base member 32′ which is constructed to be elliptical in cross section, with a main axis a and an auxiliary axis b. As a result of an elliptical mouthpiece 30, the connection device can also be used with workpieces which are difficult to access.

[0103] The protective gas supply is in turn carried out via three flows 44a, 44b, 44c, wherein the main flow direction 48 is preferably produced parallel with the main axis a.

[0104] Although exemplary embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.