Electric heating – Metal heating – By arc
Reexamination Certificate
1999-05-24
2001-05-01
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
C219S137610, C219S137700
Reexamination Certificate
active
06225599
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to gas metal arc welding (GMAW), and more particularly to guns used in mig welding.
2. Description of the Prior Art
Mig guns must perform several different functions in order for successful welding to occur. Those functions include directing the weld wire to the workpiece, conducting electric power to the weld wire, and shielding the welding arc from atmospheric air. In addition to the foregoing basic requirements, it is highly desirable that the weld wire be fed to the workpiece at an adjustable rate that suits the particular welding operation at hand. For maximum productivity, it is also necessary that the gun be very comfortable for the operator to maneuver as he directs the weld wire to the workpiece.
To satisfy the foregoing requirements, the gun is connected by a long flexible cable to a wire feeder, which is in close proximity to a welding machine. The welding machine supplies the weld wire, electric power, cooling fluid, and inert shielding gas through the cable to the gun. In some instances, the cable may be as long as 30 feet. Small diameter aluminum weld wire, as is typically used when welding aluminum workpieces, has insufficient column strength to be satisfactorily pushed for such long distances to the gun. Accordingly, it is known to provide mig guns with a feed mechanism that pulls the weld wire at the same time the wire feeder attached to the welding machine is pushing the weld wire.
The gun feed mechanism is contained in a handle that is held by the operator. There is a head tube on the end of the handle opposite the flexible cable. A diffuser is joined to the free end of the head tube. A contact tip is connected to the diffuser. The weld wire is guided by a liner that extends from the handle to the diffuser. From the diffuser, the weld wire passes through the contact tip, from which it emerges under the impetus of the feed mechanism.
An example of a prior mig gun is manufactured by M. K. Products, Inc., of Irvine, Calif., under the trademark Cobra. That gun has a long straight handle that contains a weld wire feed mechanism. The feed mechanism includes a motor having an axial center line inside and parallel to the handle longitudinal axis. The motor drives a feed roller that, in conjunction with an undriven idler roll, pulls the weld wire from the wire feeder of the welding machine. The axes of rotation of the feed rollers are perpendicular to the motor axial center line. The gun feed mechanism is adjustable by a non-graduated knob on a side of the handle. The non-graduated knob enables the operator to control the weld wire feed rate through a range from zero to a maximum over three turns of the knob.
The prior Cobra gun has two disadvantages. First, the straight handle makes the gun rather cumbersome to maneuver by the operator through the multiplicity of spacial positions encountered when welding various workpieces. Second, the weld wire feed control knob is located where it is awkward to adjust by a left-handed operator and, being non-graduated, it is almost impossible to determine the preset position. The operator must either transfer the gun to his right hand to adjust the knob, or he must turn the gun in his left hand so the knob is accessible to his right hand.
An example of another prior mig gun with a weld wire feed mechanism may be seen in U.S. Pat. No. 5,728,995. The gun of that patent is in the general configuration of a pistol. The operator holds an electric motor that is at a right angle to the longitudinal axis of the gun. The motor axial centerline is parallel to the axes of rotation of feed rollers that pull the weld wire. A head tube curves away from the handle at the handle downstream end. The pistol-type gun is also awkward to maneuver into some of the numerous spacial positions encountered in welding operations.
As mentioned, it is vital that the mig gun adequately shield the welding arc from the atmosphere. For that purpose, inert gas is supplied to prior guns from the welding machine through the flexible cable. The inert gas is directed through the gun head tube to the interior of the diffuser. The gas flows from the diffuser to a nozzle that surrounds the contact tip. The gas then flows out the nozzle and surrounds the contact tip and the weld wire emerging from it. The gas thus shields the weld wire and the welding arc from the atmosphere.
Despite the widespread use and general acceptance of the prior designs of diffusers and nozzles, they nevertheless are not completely acceptable. Specifically, a sooty deposit has been noticed from some welding operations on aluminum workpieces that use aluminum weld wire. The soot is carbon residue produced in the welding arc. The source of the carbon is a boundary layer of air that surrounds the weld wire inside the clearance holes in the liner and the contact tip. Although the spaces between the weld wire and the liner and contact tip clearance holes are very small, they nevertheless are sufficient to enable some air to pass inside the inert gas shield from the nozzle and thus be present at the welding arc.
Accordingly, it is desirable that improvements be made to GMAW guns.
SUMMARY OF THE INVENTION
In accordance with the present invention, a mig gun with an offset handle and a gas seal provides superior maneuverability and performance compared with prior guns. This is accomplished by apparatus that includes a motor with an axial centerline that makes an acute angle with the axes of rotation of weld wire feed rollers.
The motor is part of a feed mechanism that pulls a weld wire from a welding machine. The motor is supported in and is parallel to the longitudinal axis of a first section of the gun handle. On the motor armature is a pinion of a non-right angle gear set. The pinion meshes with a gear of the gear set. The gear is connected to a first shaft mounted for rotation in the gun handle. The axis of rotation of the first shaft and of the gear makes the acute angle with the axial centerline of the motor armature. In one embodiment, a first feed roller is fixed to the first shaft. A second feed roller is fixed to a second shaft. Gears on the first and second shafts mesh with each other. Energization of the motor causes the feed rollers to rotate in opposite directions and pull the weld wire.
The gun handle has a second section with a second longitudinal axis that is perpendicular to the axes of rotation of the two feed rollers. The longitudinal axis of the handle second section intersects the longitudinal axis of the handle first section at an angle that is the complement of the angle between the motor axial centerline and the axes of rotation of the feed rollers. For example, if the motor axial centerline intersects the feed rollers axes of rotation at 70 degrees, the longitudinal axes of the handle first and second sections intersect at 20 degrees.
The weld wire is directed in a downstream direction through a flexible cable between the welding machine and the gun. The weld wire passes inside a guide in the handle to the feed rollers. The guide bends at the junction between the handle first and second sections so as to follow the two longitudinal axes of the handle. A curved head tube projects from the handle second section. The weld wire emerges from the head tube to contact the workpiece. The offset handle increases the comfort of the operator's hand and wrist as he maneuvers the gun through a wide range of spacial positions while welding different workpieces.
It is a feature of the present invention that the speed of the motor, and thus the rate of weld wire fed by the feed mechanism rollers, is controlled from a central location on the gun. For that purpose, there is a small thumbwheel on the center of the gun handle near the flexible cable. The thumbwheel rotates about an axis that may be perpendicular to the motor axial centerline. The thumbwheel is connected to a potentiometer that is part of the electric circuit that controls the speed of the motor such that turning the thumbwheel controls the speed of
Croll Mark W.
Illinois Tool Works Inc.
O'Brien John P.
Pilarski John H.
Shaw Clifford C.
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