Patent Application
20150321282
This document relates generally to the resistance spot welding field and, more particularly to an improved electrode for the resistance spot welding of aluminum at high clamping pressures and high welding currents.
The use of aluminum in the construction of automobiles, trucks and other vehicles is steadily increasing. This is because it offers a number of advantages to iron alloys including the fact that it is lower density and corrosion resistant. The use of aluminum allows vehicle manufacturers to maintain safety and strength requirements while the resulting reduction in weight advantageously reduces engine-load which decreases the consumption of fuel and exhaust emissions.
Resistance spot welding is a technique utilized by vehicle manufacturers to join aluminum workpieces. Advantageously, resistance spot welding is relatively low cost, rapid, simple and easy to automate. Recent developments and advancements in mid-frequency power sources, electrode dressing and servo gun equipment further support the increased use of resistance spot welding of aluminum in vehicle manufacturing.
Significantly, high power welding guns are required as aluminum welding currents must be two to three times higher than required for steel yet aluminum welding times are perhaps ¼ to ½ that required for steel. Thus, aluminum welding equipment must be able to deliver high current levels in a time window that is 50-75% shorter than what is commonly employed for steel. These requirements clearly highlight the need to have proper weld pressure and electrode alignment when initiating the welding operation.
Toward this end, U.S. Patent Application Publication No. 2013/0020288 to Moision et al. discloses a system and method for welding aluminum workpieces wherein a predetermined current is applied through electrodes that engage the workpieces. A resistance profile is then generated based upon the predetermined current. A proper weld profile is then selected based upon the resistance profile. The weld profile is then used to execute the workpiece weld.
Welding currents and current profiles are not the only parameters that may be utilized to efficiently provide consistently high quality aluminum welds. In fact changes in the clamping force applied to the workpieces have an effect on (a) the pressure between the welding electrode and the workpieces and (b) the resistance distribution at the electrode-workpiece interfaces. It has recently been determined that spot welding forces of up to 12 kN and welding currents of up to 80 kA may be useful in providing the most effective and high quality welds between aluminum workpieces such as bodies made from aluminum alloy sheet material.
A prior art aluminum spot welding electrode assembly E of three piece construction is illustrated in
The mounting adapter A also includes a bore that receives and holds a tapered portion P of the shank S. The sidewall R of the adapter A engages and reinforces this portion P of the shank S. A socket K at the distal end of the shank S receives the mounting end M of the electrode cap C. The working end or welding portion D of the cap C extends from the shank S.
The welding electrode assembly E is made from copper or copper alloy. The shank S includes a lumen U for the circulation of water or other cooling medium to the cooling passage G in the electrode cap C to reduce electrode heating during the welding process. This lumen U compromises the structural integrity of the shank S to the extent that it is not capable of withstanding spot welding forces up to 12 kN and welding currents of up to 80 kA over an appropriate service life.
This document relates to a novel welding electrode assembly characterized by improved strength and extended service life when subjected to spot welding forces up to 12 kN and welding currents of up to 80 kA. Advantageously the new electrode provides these benefits yet is still made from the same material and is the same overall standard length of the prior art electrode assembly E. Thus, the new electrode may be used with standard welding guns, standard electrode dressing equipment and standard electrode changing equipment already installed and in operation on the production line.
In accordance with the purposes and benefits described herein a new welding electrode assembly is provided. That welding electrode assembly comprises a body and an electrode cap carried on the body. The electrode cap has a mounting end connected to the body and a working end for welding. Further the electrode cap includes a raised rim between the mounting and working ends to protect the body during electrode cap dressing and facilitate electrode cap removal when changing the electrode cap.
The electrode cap further includes a liquid cooling passage. The liquid cooling passage extends through the mounting end and past the rim. In one embodiment the ratio of length of the mounting end to length of the working end is between 1 to 0.6 and 1 to 1.9. In another embodiment the ratio of length of the mounting end to length of the working end is between 1 to 1.5 and 1 to 1.7. In still another embodiment, the ratio of length of the mounting end to length of the working end is about 1 to 1.3.
Still further, in one embodiment the ratio of the length of the liquid cooling passage to length of the electrode cap is between 1 to 1.3 and 1 to 2.0. In yet another embodiment the ratio of the length of the liquid cooling passage to the length of the electrode cap is between 1 to 1.65 and 1 to 1.75.
In one embodiment, the mounting end has a taper angle of about 1°26′+/−0°3′ and a wall thickness of between about 1.98 and 2.71 mm. The liquid cooling passage has a diameter of about 12.7+/−0.3 mm. Taken together the increased wall thickness and larger cross-sectional area of the cooling passage greatly enhance the performance of the electrode cap.
Still further, the working end has a length of 20.5+/−0.3 mm and a diameter of 19.1+/−0.3 mm. The added length of the working end substantially increases the service life of the electrode cap.
In accordance with an additional aspect, in a three-piece welding electrode assembly having an overall length L, the shank has an overall length of between 0.41 and 0.59 L with between 0.29 and 0.60 L of that length being received in the tapered bore or socket and reinforced by the sidewall of the mounting adapter. Further between 0.16 and 0.33 L of the shank length receives the mounting end of the electrode cap and is thereby reinforced by the electrode cap. Accordingly, between 45.3 and 92.9% of the overall length of the shank is structurally reinforced by the mounting end of the electrode cap and the sidewall of the mounting adapter.
In an alternative embodiment the shank is an overall length of between 0.52 and 0.59 L with between 0.29 and 0.40 L of the proximal end of the shank length being received in the socket or tapered bore and reinforced by the mounting adapter. Further between 0.16 and 0.22 L of the shank length receives the mounting end of the electrode cap and is thereby reinforced by the electrode cap. Thus, between 45.3% and 61.1% of the overall length of the shank is structurally reinforced by the mounting end of the end cap and the sidewall of the mounting adapter.
These and other embodiments of the welding electrode assembly will be set forth in part in the description which follows, and in part will become apparent to those of ordinary skill in the art by reference to the following description and drawing figures.
The accompanying drawings incorporated herein and forming a part of the specification, illustrate several aspects of the welding electrode assembly and together with the description serve to explain certain principles thereof. In the drawings:
Reference will now be made in detail to the present preferred embodiments of the welding electrode assembly.
Reference is now made to
As illustrated, the mounting adapter 14 includes a mounting end 20 for engaging a cooperating electrode receiving aperture in a welding gun. The integral hex nut 22 allows one to securely tighten the welding electrode assembly 10 to the welding gun or loosen the same when necessary for maintenance or changing of the welding electrode assembly. The mounting adapter 14 further includes a tapered bore or socket 24 having a sidewall 26 made of relatively heavy gauge material.
The shank 16 includes a proximal or tapered mounting end 28 and a distal end 34. As illustrated in
As illustrated, the electrode cap 18 includes a tapered mounting end 36, that is received and engages the counterbore 32 in the shank 16, and a working end 38 having a face 40 for engaging the aluminum workpiece to be welded. More specifically, the mounting end 36 has a taper angle of about 1°26′+/−0°3′ and a wall thickness of between about 2.16 and 2.56 mm. A raised rim 42 extends concentrically around the electrode cap 18 on the working end 38. In one possible embodiment, that rim 42 is raised between 1.2 mm and 2.4 mm above the outer surface of the end 38 and may be between 21.9 and 22.5 mm wide (diameter). Further, the raised rim 42 may include edging or roughened surface features if desired to aid in gripping or holding the electrode cap 18 when it is inserted into or removed from the shank 16 during electrode cap changing operations.
As further illustrated in
In one possible embodiment, the ratio of the length of the mounting end 36 to the length of the working end 38 is between 1 to 0.6 and 1 to 1.9. In another possible embodiment, that ratio is between 1 to 1.5 and 1 to 1.7. In yet another, that ratio is about 1 to 1.3. In one possible embodiment the working end has a length of 20.5+/−0.3 mm and a diameter of 19.1+/−0.3 mm. Thus the length is greater than the diameter.
In one possible embodiment, the ratio of the length of the liquid cooling passage 46 to the overall length of the electrode cap 18 is between 1 to 1.3 and 1 to 2.0. In yet another embodiment, that ratio is between 1 to 1.65 and 1 to 1.75. When these ratios of the length of the mounting end 36 to the length of the working end 38 and the length of the liquid cooling passage 46 to the overall length of the electrode cap 18 are considered together, it is possible to provide an electrode cap with a longer working end while still providing the desired cooling to support an extended service life.
As indicated previously, the raised rim 42 on the electrode cap 18 may be conveniently utilized when handling the cap during insertion into and removal from the shank 16. The raised rim 42 feature also serves to limit taper engagement and provides an indication of taper wear by viewing the width of the gap 45 between the rim 42 and the end of the shank 16 (see
It should be appreciated that the raised rim 42 is just one of the unique aspects of the welding electrode assembly 10. The following Table 1 compares other significant physical attributes of the new electrode assembly 10 to the prior art electrode assembly E. As should be appreciated, while the taper angle is the same, the wall thickness at the taper of the electrode assembly 10 is about 59-81% thicker than for the electrode assembly E (2.71 vs. 1.70 and 1.98 vs. 1.09). The heavier gauge and larger diameter taper wall positively impacts load bearing capability, current carrying capability, overheating, electrode cap seating and removal. Further, these benefits are all achieved while minimizing taper depth/length of engagement so as to not comprise the access of the electrode assembly 10 to tight work spaces.
At the same time, the cooling passage diameter has been increased from 11.2 mm in the electrode assembly E to 12.7 mm in the electrode assembly 10. This represents about a 13% increase which improves and optimizes heat removal. Generally increases in cooling passage diameter are made at the expense of wall thickness. Significantly, both are increased in the electrode assembly 10 as compared to the prior art electrode assembly E.
As should be further appreciated, the length of the working end 38 of the electrode cap 18 has been increased dramatically by about 111% as compared to the working end of the electrode cap C (20.5 vs. 9.7), although increases of approximately 200% are possible. This potentially more than doubles the service life of the electrode cap 18 between changes thereby significantly improving line productivity. At the same time, the diameter of the working end 38 of the electrode cap 18 has been made consistent with the diameter of the working end of the prior art electrode cap C to allow standard use of electrode dressing and changing tools and weld set up tools (e.g. force gauges).
Significantly, the welding electrode assembly 10 provides a stronger and more durable construction and a larger or greater electrode cap dressing zone or working end 38 for a longer service life between cap changes than prior art electrode assemblies E of the same length L as illustrated in
As should be appreciated from reviewing
In another possible embodiment, the shank 16 has an overall length of between 0.52 and 0.59 L with between 0.29 and 0.40 L of the proximal end 28 of the shank length being received in the bore 24 and reinforced by the sidewall 26 of the mounting adapter 14. Further between 0.16 and 0.22 L of the length of the shank 16 receives the mounting end 36 of the electrode cap and is thereby reinforced by the electrode cap. In this embodiment, between 45.3% and 61.1% of the overall length of the shank 16 is structurally reinforced.
For purposes of comparison to the prior art, reference is now made to
The foregoing has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Obvious modifications and variations are possible in light of the above teachings. For example, the connections between the electrode cap 18 and shank 16 and the shank 16 and the mounting adapter may be threaded. Further, while illustrated in conjunction with a three-piece electrode assembly 10, it should be appreciated that the electrode cap 18 may be used with an electrode of substantially any appropriate construction. All such modifications and variations are within the scope of the appended claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.
