Grinding machine for welding electrodes

Details Grinding machine for welding electrodes Grinding machine for welding electrodes

2001-10-13

2004-01-06

Nguyen, Dung Van (Department: 3724)

Abrading

Precision device or process - or with condition responsive...

With feeding of tool or work holder

C451S048000

Reexamination Certificate

active

06672942

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improvements in a grinding machine to grind to a specific shape the end portion of welding electrodes of tungsten, molybdenum, chromium and the like for use in such welding techniques as TIG welding and plasma arc welding.
2. Description of the Prior Art
The shape of the end portion of a welding electrode for use in TIG welding is dependent on factors such as electric current density, current distribution and cooling effects etc. in the welding area and affects the efficiency of welding work and the welding quality. Therefore, the end portion of the welding electrode is finished to a proper shape, for example, a sharp cone or two-step cut formed of a tapered area and a flat area (a so-called “truncated conic shape”) depending, on the material and thickness of the base metal, welding conditions and other factors. The external surface of the tip of the welding electrode finished to a specific form is polished to a high degree of smoothness. Tungsten electrode A for TIG welding as shown in
FIG. 12
, for example, has a diameter D of 0.5 to 2.0 mm and tapers to a hemispherical tip A
0
with a radius (R) of 0.08 to 0.1 mm. It is desirable that the external surface of the hemispherical tip A
0
is more smoothly ground than the tapered section A
1
of the electrode. If the external surface of the hemispherical tip A
0
is finished to a mirror surface or a specular surface, the directivity and stability of the arc will be substantially improved.
To this end the end portion of the electrode A is usually ground by a special electrode grinding machine. Such as the machine shown in FIG.
13
and disclosed in unexamined Japanese utility model application No. 4-60386 and unexamined Japanese patent application No. 7-276211. The following two methods are widely adopted. In a first method (hereinafter referred to as “the first method”), a grinding disk B
1
which has a relatively large grain size (#
170
, for example) is fixed on motor drive shaft M
1
is used to grind the end portion of electrode A to a specific form. Then, the grinding disk B
1
is replaced with a grinding disk B
2
which has a finer grain size (#
500
, for example). By use of the grinding disk B
2
, the tip of the electrode is finely ground. In a second method (hereinafter referred to as “the second method”), two grinding machines are used. One is equipped with grinding disk B
1
which has a large grain size and another with grinding disk B
2
which has a fine grain size. The end portion of the electrode is shaped to a specific form with the grinding disk B
1
, and is then finely ground or polished with the grinding disk B
2
.
In
FIG. 13
, the letter C indicates a housing, the letter M a grinder motor, the letter D a grinding disk clamping screw, the letter E a dust cover, and the letter F an electrode guide.
However, the problem with the first method is that two grinding disks B
1
, B
2
have to be changed for each stage of the grinding work and therefore the grinding process is inefficient and slow.
The second method requires two electrode grinding machines, which represents poor economy and results in increased maintenance costs.
Furthermore, the axial position of electrode A is often dislocated when grinding disk B
1
with a large grain size is replaced with grinding disk B
2
with a fine grain size. Accordingly it is difficult to maintain the concentricity of electrode A. As a result, it takes a substantial period of time to grind and polish the tip to a mirror surface and furthermore, the form of the tip itself can change in an unintended way.
PROBLEM THAT THE INVENTION IS TO SOLVE
In view of the problems encountered in grinding the end portion of a welding electrode by grinding machines disclosed in the prior art which are; (1) when working with a grinding machine using a grinding disk with a large grain size and another with a fine grain size, it is troublesome to replace one grinding disk with another each time, and it is difficult to maintain the concentricity of the electrode when the grinding disks are changed, and (2) the use of two grinding machines is expensive and it is difficult to maintain the concentricity of the electrode; it is a general object of the present invention to provide a grinding machine for welding electrodes by which the end portion of even a very short electrode can be ground to a specific shape efficiently by a simple procedure and only the tip is finished to a mirror surface, i.e. all the grinding work can be done by this machine alone, and not using two grinding machines.
SUMMARY OF THE INVENTION
To solve the above-mentioned problems, a particular object of the present invention is to provide a grinding machine for welding electrodes the grinding machine comprising a box-like housing
1
, a grinder motor
2
fixed within the housing
1
, a disk-like grinding disk
3
fixed on a motor drive shaft
2
a
of a grinder motor
2
and provided with a grinding area
3
A, a swing plate
4
provided on the housing
1
above the grinding disk
3
and supported movably in the direction of the axis &phgr; of a motor drive shaft
2
a
, a cylindrical holder guide
6
tumably supported on the swing plate
4
in a vertical orientation with a downward portion protruding above the grinding disk
3
in the housing
1
, an electrode holder
7
removably fitted into holder guide
6
and removably clamping an electrode A with its tip in contact with the grinding area
3
A of the grinding disk
3
, an electrode turning motor
8
fixed within the housing
1
to turn the holder guide
6
with the electrode holder
7
held therein, and a swing plate moving mechanism
9
for moving the swing plate
4
by a specific distance
1
along the axis &phgr; of the motor drive shaft
2
a.
A further object of the invention is to provide a grinding machine as described above wherein the grinding area
3
A of the grinding disk
3
is formed of a first grinding part
3
a
made of coarse grains and a second grinding part
3
b
made of fine grains.
According to the invention, the grinding disk exhibits several novel features. The grinding area
3
A of the grinding disk
3
is formed of—on a front side of the disk—a first grinding part
3
a
for grinding an end portion of the electrode A to form a cone and—on an outer circumferential side of the disk—a second grinding part
3
b
provided with a V-shaped grinding groove
3
b
′ for grinding a tip A
0
of the electrode to a mirror surface.
The grinding area
3
A of the grinding disk
3
is so constituted that the first grinding part
3
a
for forming the end portion of the electrode A in the form of a cone and the second grinding part
3
b
for polishing the tip A
0
of the conically formed end portion of the electrode to a mirror surface are provided on the front side of the disk. The first grinding part
3
a
is on an inner portion of the disk in the radial direction and on the front side thereof in the thickness direction and the second grinding part
3
b
is provided on an outer portion of the disk in the radial direction and on said front side thereof but recessed in the thickness direction. The inclination angle &agr;
1
of a longitudinally inclined surface
3
a
1
defining the first grinding part
3
a
is the same as that of a longitudinally inclined surface
3
b
1
, defining the second grinding part
3
b
, wherein the inclination angle &agr;
2
of a transversely inclined surface
3
a
2
defining the first grinding part
3
a
is the same as that of a transversely inclined surface
3
b
2
defining the second grinding part
3
b
, and the radius R of an arc-like joint between the longitudinally inclined surface
3
a
1
and the transversely inclined surface
3
a
2
of the first grinding part
3
a
is identical to that of an arc-like joint between a longitudinally inclined surface
3
b
1
and a transversely inclined surface
3
b
2
of the second grinding part
3
b
. The grinding area
3
A of the grinding disk
3
is integrally formed of grains with a medium grain size.
The grind

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