Electric heating – Metal heating – By arc
Reexamination Certificate
1999-07-16
2001-02-20
Ryan, Patrick (Department: 1725)
Electric heating
Metal heating
By arc
C219S121610, C219S086220, C219S079000, C219S531000, C219S388000
Reexamination Certificate
active
06191383
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a device for mutually connecting by welding of sheet-metal objects, for instance flat plates. The use of laser welding for this purpose is known. The use of a laser is necessary herefor. Suitable lasers capable of generating infrared radiation of the desired wavelength range are for instance YAG lasers or CO
2
lasers. By means of optical means, for instance lenses, mirrors or the like, a very intense beam of infrared radiation is directed at the weld location. The beam is of the convergent type and the weld location will generally be situated roughly in the focal spot of the optical system.
A laser is a very expensive apparatus. In the mutual connection of for instance stainless steel plates by laser welding the drawback is encountered that, even with automatic control, it is not possible to avoid the laser being cut of use for a time, for instance during transport for feed and outfeed of assemblies of objects to be joined together. In view of the relatively very high price of the laser, it is desirable to increase the time for which the laser is effectively in use.
SUMMARY OF THE INVENTION
With a view to this objective, the invention provides a device for mutually connecting by laser welding of sheet-metal objects laid flat against each other at least in determined zones, for instance two or more flat or previously profiled plates, for instance stainless steel or other objects for mutual connection by laser welding, which device comprises:
a welding station comprising a laser and an optical device for performing a laser welding operation using a laser beam via a preselected path consisting for instance of a plurality of sub-paths;
clamping means, for instance a lower clamping plate and an upper clamping beam, for clamping against each other at least said regions of the objects at the location of the welding station;
transporting means for supplying and carrying successive assemblies of objects laid on top of each other according to a chosen displacement pattern along the welding station, which transporting means comprise two separate conveyors, wherein the welding station is a collective one for both conveyors and respective individual clamping means are added to each conveyor; and
a central control unit for controlling the transporting means and the welding station in mutual coordination such that the conveyors operate for transport at least partially in mutual alternation such that the welding station can operate in the region of the one conveyor while the other conveyor operates for transport.
The objects must be mutually connected for instance in a regular pattern of annular weld zones and linear weld zones, for instance to manufacture per se known heat exchangers. In order to obtain a great freedom of welding patterns it is necessary that the laser beam can operate at all relevant locations of the surfaces for processing. An annular weld zone can be made for instance by causing the welding station to make the associated movement.
In this respect the device preferably has the feature that the laser beam is displaceable in transverse direction of each conveyor.
The device can also have the feature that the laser beam is displaceable in longitudinal direction of each conveyor.
The combination of the two above stated features produces a considerable freedom of movement of the laser station.
The transporting means can however also be used to produce a welding path in longitudinal direction of the conveyors. In this respect the invention provides a variant in which each conveyor is also controllable together with the clamping means on the basis of a chosen path. It will be apparent that this variant can also be combined with the freedom of movement of the welding station.
An accurate positioning can be ensured with an embodiment in which at least one lateral guide, for instance guide rollers, is added to each conveyor.
In order to make the non-operational time of the laser as short as possible during displacement from this one conveyor to the other conveyor, the invention provides a variant in which the conveyors are mutually parallel and extend adjacently of each other.
The depth of the weld zone need only be so great that the objects are welded to each other effectively and reliably at that location. In order to obtain an effective heat discharge and to avoid the weld zone acquiring too great a depth and the weld zone extending to the bottom surface of the assembly, it may be favourable for the device to be provided with a cooled support plate present in the region of the welding station and forming part of the clamping means. Such a support plate can be provided with cooling ducts through which flows heat transfer medium.
An effective strengthening of the clamping force and a very positive positioning of an assembly is obtained with an embodiment in which the support plate takes an electromagnetic form. During operation of the or each electromagnet the assembly is positioned non-movably relative to the support plate. If the support plate is fixedly disposed, a chosen welding path can only be realized with the associated freedom of movement of the welding station.
Since a laser is a vulnerable and comparatively heavy instrument, it can be recommended in some conditions for the laser to be disposed fixedly. With known means the infrared beam generated by the laser can be guided via an optical device to the chosen welding location. The optical system required for this purpose can be controlled accordingly by means of an adapted control by the central control unit. Use can for instance be made of fast stepping motors. Not only can such a “flying optical device” respond very rapidly because it is so light, but it also requires relatively little displacement energy due to the low inertia.
The clamping means, which may comprise for instance a lower clamping plate and upper clamping beams, must leave clear the chosen welding zones. After the forming of a weld zone in the assembly on the one conveyor, the optical device must be displaced as rapidly as possible to the other conveyor in order to process an assembly already present there. The clamping beams are necessarily of heavy construction, this requiring considerable dimensions. Insofar as the focal distance of the optical device allows, vertical displacement of the optical device is avoided. If desired, a vertical displaceability can also be realized to avoid the danger of collision with the clamping beams.
The device according to the invention lends itself to improving the effective efficiency of the laser. It is essential for this purpose to embody the software of the central control unit such that the laser co-acts in alternating manner with the one conveyor and with the other conveyor, whereby its non-operational periods can be considerably shorter than in the case of a welding device added to only one conveyor.
REFERENCES:
patent: 4650954 (1987-03-01), Frings et al.
patent: 4654505 (1987-03-01), Sciaky et al.
patent: 5023427 (1991-06-01), Neilheisel et al.
patent: 5674420 (1997-10-01), Broderick et al.
patent: 5902497 (1999-05-01), Alber et al.
patent: 0136190 (1985-04-01), None
patent: 0189806 (1986-08-01), None
patent: 0452137 (1991-10-01), None
patent: 0743129 (1996-11-01), None
patent: 2549759 (1983-07-01), None
Cooke Colleen
Omega Laser Systems B.V.
Ryan Patrick
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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