Quick-change resistance welding pin

Abstract

A welding electrode for welding an object includes a body that has a cavity and is configured to conduct welding current and facilitate cooling. A replaceable electrode head is removable secured to the body and configured to transmit force and welding current to the object to be welded. The electrode head includes a bore, and a pin is slideably received in the bore. The pin includes an end that has a neck with a neck diameter. A flange that is slideably received in the cavity, and the flange has a periphery and a slot that extends to an opening in the periphery. The slot has a throat with a width less than the neck diameter to provide an interference fit between the end and the flange.

Description

QUICK-CHANGE RESISTANCE WELDING PINTECHNICAL FIELD

[0001] This disclosure relates to a resistance welding electrode for welding fasteners to a metallic object, for example. More particularly, the disclosure relates to quick-change resistance welding pin and reusable flange for the welding electrode.BACKGROUND

[0002] Weld gun assemblies are used to resistance weld fasteners to metallic objects, such as body panels for vehicles. A fastener such as a weld stud or nut is loaded onto one of the electrodes. The electrodes are moved together with an actuator placing the fastener into engagement with the panel under pressure. Very high currents are applied to the electrodes, which welds the fastener to the panel. The use of weld guns is typically an automated process in which the fasteners are loaded into the weld gun assembly.

[0003] A widely used electrode in the industry utilizes a pin that receives a weld nut and precisely aligns it with a clearance hole in the sheet metal component. The pin is biased to an extended position to receive the weld nut and sheet metal component. The pin moves during the welding operation, and its position is precisely monitored to ensure that the nut is loaded properly on the pin. These locating pins require regular replacement because the holes in the sheet metal in which the pins are received during welding wear the pins. Further, heat and debris from the welding process can damage the pins. If the pin tip is subjected to excessive side force it may be bent to an unusable condition or broken.

[0004] In welding electrodes that include an integrated measurement sensor, such as a linear variable displacement transducer, the pin is supported by an axially slidable flange that is operatively secured to the sensor core. A biasing force is applied to the flange via a spring or compressed air to urge the pin to an extended position. The pinand, in turn, the flange moves during the welding process, and that movement is detected by the sensor. The measured pin displacement is used to monitor weld quality, electrode wear, pin travel consistency, and other welding process parameters.

[0005] When the sensor core is permanently assembled to the pin or flange, it increases the pin inventory and replacement cost, as well as the fragility of the pin assembly. Replacement of the pin requires at least partial removal of the pin / flange assembly from the welding electrode. Numerous components must typically be removed and disassembled to complete pin replacement, further increasing the complexity of component design and down time required to complete the process.SUMMARY OF THE INVENTION

[0006] In one exemplary embodiment, a welding electrode for welding an object includes a body that has a cavity and is configured to conduct welding current and facilitate cooling. A replaceable electrode head is removable secured to the body and configured to transmit force and welding current to the object to be welded. The electrode head includes a bore, and a pin is slideably received in the bore. The pin includes an end that has a neck with a neck diameter. A flange that is slideably received in the cavity, and the flange has a periphery and a slot that extends to an opening in the periphery. The slot has a throat with a width less than the neck diameter to provide an interference fit between the end and the flange.

[0007] In a further embodiment of any of the above, the electrode head is secured to the body to enclose the flange within the cavity.

[0008] In a further embodiment of any of the above, the flange includes an annular groove that is arranged in the periphery, and a seal is provided in the annular groove and engagement with the body.

[0009] In a further embodiment of any of the above, a linear variable displacement transducer (LDVT) is arranged in the cavity. The LVDT includes a core that is operatively secured to the flange opposite the pin.

[0010] In a further embodiment of any of the above, the core includes a head captured between the pin and the flange.

[0011] In a further embodiment of any of the above, the flange includes first and second holes that adjoin one another, the second hole has a larger diameter than the first hole, the head is received in the second hole and is in engagement with the end, and the core extends through the first hole and out the flange.

[0012] In a further embodiment of any of the above, the throat is provided by at least one protrusion in the slot.

[0013] In a further embodiment of any of the above, the slot includes an arcuate wall against which the neck is seated in a pin operating position, the arcuate wall has a slot diameter greater than the width.

[0014] In a further embodiment of any of the above, a head is captured between the pin and the flange. The flange includes first and second holes that adjoin one another. The second hole has a larger diameter than the first hole. The head is received in the second hole. The slot diameter is greater than the second diameter.

[0015] In a further embodiment of any of the above, the pin is a ceramic.

[0016] In a further embodiment of any of the above, the flange is a polymer.

[0017] In a further embodiment of any of the above, the polymer is polyoxymethylene.

[0018] In another exemplary embodiment, a method of installing a welding electrode pin for supporting a fastener, the method includes a) sliding an end of a pin through an opening in a periphery of a flange and into a slot, b) pushing the end past a throat on the flange that extends into the slot and that provides an interference fit with the end, and c) seating the end relative to the flange in a pin operating position.

[0019] In a further embodiment of any of the above, the method includes a step of capturing a sensor core between the pin and the flange subsequent to performing step b).

[0020] In a further embodiment of any of the above, the method includes d) inserting the flange into a welding electrode body, and e) passing the pin through a bore in an electrode head, and securing the electrode head to the body.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Other advantages of the example embodiment can be understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

[0022] Figure 1 is a schematic view of an example weld gun assembly.

[0023] Figure 2 is a cross-sectional view of an example electrode having a quick-change pin.

[0024] Figures 3A-3C are respectively perspective, top and side views of a disclosed flange to which the removable, quick-change pin is mounted.

[0025] Figure 4 is a side view of another quick-change pin and flange configuration.

[0026] The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. Like reference numbers and designations in the various drawings indicate like elements.DETAILED DESCRIPTION

[0027] Figure 1 is a highly schematic view of a weld gun assembly 10. The weld gun assembly 10 includes a stationary lower arm 12 supporting a lower electrode 13. A movable electrode holder 14 is connected to an actuator 16. The movable electrode holder 14 supports an upper electrode 15. The actuator 16 moves the moveable electrode holder 14 from an open position (shown) to a closed position in whichthe electrodes 13 and 15 are in engagement with an object 18 to be welded, such as a vehicle body panel, and a fastener. While the arms and electrodes are referred to in terms of “upper” and “lower,” it is to be understood that the weld gun assembly 10 and its components may be oriented in a manner other than described and remain within the scope of the claims.

[0028] A fastener, such as a weld stud or nut, is loaded onto one of the electrodes 13 and 15 and forced into engagement with the object 18. In the example shown in Figure 1 , the lower electrode 13 includes a pin 44 that supports a nut (not shown). The pin 44 is received in a hole in the object 18, and the nut is then loaded onto the pin 44. Locating pins 44 may be made of materials such as nonmagnetic stainless steel, hardened steel, oxide or ceramic coated steel or aluminum, ceramics, or an assembly including such materials. The material selection is influenced by cost, lead time, the design complexity, and the application requirements.

[0029] A position sensor 20 in the electrode 13 can be used to detect the position and orientation of the fastener from underneath the object 18. During the welding operation, the electrodes 13,15 are clamped about the fastener and object 18, and current is applied. The pin 44 is displaced during the welding operation, and this displacement is detected by the sensor 20. The displacement signal from the sensor 20 is sent to a sensor control system 22 that includes an amplifier 24 and a controller 26, for example, which processes the signal into information that may be used to validate the welding process or trigger a fault.

[0030] An example electrode 13 (e.g., the lower electrode) is shown in Figure 2. The electrode 13 includes a body 30 which may have various cooling passages. An outer sleeve 34 is arranged over the body 30 along with seals 36 to enclose the cooling passages. A head 38, which supports the object 18 on a face during welding, is secured to the body 30 at a threaded joint 42. A bore 40 is provided in the head 38 and axially slidingly receives and locates the pin 44. The head 38 can be removed to resurface the face as it becomes worn from use, or to service the components located within the body 30.

[0031] The pin 44 extends through the bore 40 to a tapered tip that supports the fastener. Other tip geometries can be used for different fasteners. An end opposite the tip is supported by a flange 50 that axially slidable within a cavity 32 in the body 30. The flange 50, and in turn the pin 44, is biased outward using a spring or other force, such as compressed air. The flange 50 includes an annular groove its periphery 58 (Figs. 3A- 3C) that receives a seal 52 engaging the body 30 to seal the cavity 32. In the example, the cavity 32 is pressurized using fluid, such as air, from a fluid source 29 regulated by one or more valves 28.

[0032] The sensor 20, which may be a linear variable displacement transducer (LVDT), is operatively secured to the pin 44 via the flange 50 to monitor the pin’s linear movement during the welding process. In the example, the sensor 20 includes a coil assembly 48 arranged in the body 30, and a core 46 is disposed in coil assembly 48 and operatively secured to the flange 50.

[0033] The disclosed pin 44 / flange 50 configuration reduces the cost and complexity of the weld nut locating pin used in resistance welding electrodes. The design also supports standardization and inventory reduction efforts, while reducing the time required to replace weld nut locating pins.

[0034] Referring to Figures 2-4, the flange 50 has a slot 54 that cooperates with a neck 70 of the pin 44 to provide a quick-connect snap-fit configuration. The embodiment in Figure 2 has a removable core 46 retained in the flange, and the embodiment in Figure 4 shows a threaded fastener 78 that may be similarly removably supported. Alternatively, the fastener 78 may be integrated into the flange 50 (i.e. , a unitary structure formed as a single, monolithic piece of the same material that is formed as one structure by machining, molding and / or 3D printing, for example).

[0035] The flange 50 is manufactured from a material having different properties than the locating pin 44. While the flange 50 could be made of a metal, a high- performance engineering thermoplastic polymer such as polyoxymethylene (POM; commonly known by the brand name Delrin) can be used to provide a number of advantages. POM is readily machined into a finished component in a single operation,has exceptional creep resistance, durability, impact resistance, strength, and temperature resistance to improve survivability under the application conditions within the nut welding electrode. POM also has considerable toughness, which enables it to deflect without consequence during the snap-through assembly process. Furthermore, POM is a dielectric material so there is no potential for electrical conduction or galvanic corrosion. Other polymer materials may be used if suitable for the application.

[0036] The end of the pin 44 supported by the flange 50 includes a neck 70 with a neck diameter. Adjoining the neck 70 is a conical portion 68 (e.g., 60Q) that terminates in a cylindrical base 66. A cylindrical body 72 extends from the neck 70 to a tapered end 74 that supports the fastener to be welded. The pin end configuration employs gentle, blended diameter transitions to minimize stress concentrations. The pin end provides a standardized attachment configuration designed to optimizes the available raw material diameter(s). This requires the end to have a smaller diameter than the cylindrical body 72; however, it is desirable to limit the amount of material that needs to be removed from bar stock while still provided a relatively large diameter base 66 for support within the flange 50.

[0037] The flange 50 is machined to permit attachment of the locating pin 44 in a direction perpendicular to its operational loading. Therefore, the direction of force is normal (i.e., perpendicular) to the direction of disassembly. The slot 54 extends to an opening 56 in the periphery 58, and the slot has a throat with a width D less than the neck diameter to provide an interference snap-fit between the neck 70 and the flange 50. The slot 56 incorporates detent features, such as opposing protrusions 62, at the throat to retain the locating pin 44 on center of the flange 50, which also ensures there is minimal binding when stroking within the welding electrode. When the pin 44 is fully seated in the slot 54 in a pin operating position, the neck 70 abuts an arcuate wall 55 adjoining the protrusions 62. The arcuate wall 55 has a slot diameter greater than the width D.

[0038] The flange 50 is machined with a dovetail milling cutter (e.g., 60Q), providing opposing tapered walls 60 (joined by surface 59) that mate with the conical portion 68, providing preloaded angular contact that creates a centering force and an axialpreload force. The preload results from a small amount of mechanical deflection in the flange 50 caused by an intentional interference fit between the two components. The axial preload force ensures the flange 50 remains tight to the locating pin 44.

[0039] The flange 50 has a first and second concentric, adjoining counterbored holes 64, 65 to locate and secure a head 47 of the sensor core 46 (Fig. 2), actuator rod attachment (e.g., threaded fastener), or other accessory. The head 47 sits flush with or slightly proud of the surface 59. The second hole 65 has a larger diameter than the first hole 64. The head 47 is received in the second hole 65 and is in engagement with the end such that the head 47 is captured between the pin 44 and the flange 50 and firmly held by the preload to ensure accurate position sensing. The core 46 (or removable fastener, if used) extends through the first hole 64 and out the flange 50.

[0040] The weld nut locating pin assembly and disassembly can be accomplished by hand without the assistance of tools. The locating pin 44, flange 44, and if used, a sensing core 46 or actuator rod connection are secured in proper relationship by an interference fit that is secured by “snap-through” detent features in the flange 50. Engagement and disengagement require the application of a deliberate radial force so the components will remain securely and properly aligned during shipping, storage, and use. The locating pin 44, most subject to wear and damage in installation can be replaced, and the other components reused.

[0041] The pin 44 is installed by sliding its end through the opening 56 in the periphery 58 and into a slot 54. The end (e.g., neck 70) is pushed past the throat, for example, at least one protrusion 62, which provides an interference fit with the end. The neck 70 is seated relative to the flange 50 (e.g., abutting arcuate wall 55) in the pin operating position. The flange 50 with its pin 44 is then reinserted into the body 30, and the pin 44 is passed through the bore 40 in the head 38 before securing the head 38 to the body 30.

[0042] The disclosed pin 44 / flange 50 configuration provides a quick, effective and reliable way to change pins, particularly, for more fragile, brittle materials like ceramic. The disclosed quick-change pin / flange can reduce the amount of material required tomake most locating pins by providing for the comparatively large-diameter flange to be separate from the perishable locating pin. Weld pin machining effort, time, and complexity can also be reduced. Locating pin can be standardized by relocating special attributes for tooling engagement to a separate component, i.e. , the flange.

[0043] The example embodiment has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the example embodiment are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the example embodiment may be practiced otherwise than as specifically described.

Claims

CLAIMSWhat is claimed is:1 . A welding electrode for welding an object, comprising: a body including a cavity and configured to conduct welding current and facilitate cooling; a replaceable electrode head removable secured to the body and configured to transmit force and welding current to the object to be welded, the electrode head includes a bore; a pin slideably received in the bore, the pin includes an end having a neck with a neck diameter; a flange slideably received in the cavity, the flange has a periphery and a slot extending to an opening in the periphery, wherein the slot has a throat with a width less than the neck diameter to provide an interference fit between the end and the flange.

2. The welding electrode of claim 1 , wherein the electrode head is secured to the body to enclose the flange within the cavity.

3. The welding electrode of claim 1 , wherein the flange includes an annular groove arranged in the periphery, and a seal is provided in the annular groove and engagement with the body.

4. The welding electrode of claim 1 , wherein a linear variable displacement transducer (LDVT) is arranged in the cavity, the LVDT includes a core operatively secured to the flange opposite the pin.

5. The welding electrode of claim 4, wherein the core includes a head captured between the pin and the flange.

6. The welding electrode of claim 5, wherein the flange includes first and second holes adjoining one another, the second hole having a larger diameter than the first hole, the head is received in the second hole and is in engagement with the end, and the core extends through the first hole and out the flange.

7. The welding electrode of claim 1 , wherein the throat is provided by at least one protrusion in the slot.

8. The welding electrode of claim 7, wherein the slot includes an arcuate wall against which the neck is seated in a pin operating position, the arcuate wall having a slot diameter greater than the width.

9. The welding electrode of claim 8, wherein a head is captured between the pin and the flange, the flange includes first and second holes adjoining one another, the second hole having a larger diameter than the first hole, the head is received in the second hole, the slot diameter is greater than the second diameter.

10. The welding electrode of claim 1 , wherein the pin is a ceramic.1 1 . The welding electrode of claim 10, wherein the flange is a polymer.

12. The welding electrode of claim 1 1 , wherein the polymer is polyoxymethylene.

13. A method of installing a welding electrode pin for supporting a fastener, the method comprising: a) sliding an end of a pin through an opening in a periphery of a flange and into a slot; b) pushing the end past a throat on the flange that extends into the slot and that provides an interference fit with the end; and c) seating the end relative to the flange in a pin operating position.

14. The method of claim 13, comprising a step of capturing a sensor core between the pin and the flange subsequent to performing step b).

15. The method of claim 13, comprising: d) inserting the flange into a welding electrode body; and e) passing the pin through a bore in an electrode head, and securing the electrode head to the body.

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