Metal fusion bonding – Including means to provide heat by friction between...
Reexamination Certificate
2002-03-19
2004-05-04
Edmondson, L. (Department: 1725)
Metal fusion bonding
Including means to provide heat by friction between...
C228S112100
Reexamination Certificate
active
06729526
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a novel friction stir welding apparatus and method and a novel processing apparatus and method, both of which keep constant a relative distance between a tool, cutter or grindstone and a work to be welded or processed during friction stir welding, cutting or grinding.
The friction stir welding is a method that can join members of a work of such materials as aluminum and aluminum alloys (simply referred to as aluminum hereinafter), magnesium and magnesium alloys (simply referred to as magnesium hereinafter), copper and copper alloys (simply referred to as copper hereinafter), titanium and titanium alloys (simply referred to as titanium hereinafter), and iron or steel (simply referred to as iron hereinafter) in solid phase at temperatures below their melting points. More specifically, this is the method of inserting a tool, essentially harder than the work to be welded, into the work while rotating the tool, and moving the rotating tool relative to the work to utilize frictional heat generated between the tool and the work as well as a resulting plastic flow and join members of the work together. This method has been known by JP-07-505090A. That is, the method takes advantage of a plastic flow caused by frictional heat between the tool and the work and, unlike conventional welding such as arc welding and electron beam welding, does not melt the work during the process of welding.
Further, unlike the conventional friction welding method in which members to be processed are rotated against each other and joined together by frictional heat produced by the relative rotation, the friction stir welding method can continuously join the members of the work along a joint line longitudinally at a temperature below the melting point of the material. The joint line may be not only a straight line but also a curve or a three-dimensional curve.
FIG. 2
is a sectional view schematically showing a joining state in the friction stir welding. A hard tool
10
comprising a shoulder
11
and a pin
12
is rotated by a spindle motor not shown. A revolution speed, which depends on the material and shape of the work to be joined, is set at around 1,000 rpm. The tool
10
is then inserted into the work a predetermined depth from the surface
13
of the work and is moved relative to the work in a direction of joint
14
. A speed of movement, which also depends on the material of the work to be joined, is about 500 mm/min. It is noted here that the tool
10
is tilted at a predetermined angle &thgr; to the work toward the rear side with respect to the direction of movement. In the friction stir welding, the quality of joint is affected by the shape of the tool, the revolution speed, the speed of tool movement, and others. It is current practice that these factors are optimized based on user's knowhow. The most important one among the factors to be optimized is a distance or depth by which the tool
10
is inserted into the work.
FIG. 3
is a sectional view schematically showing a joining state in the friction stir welding when the distance for which the tool
10
is inserted into the work is set slightly deeper as compared with that of FIG.
2
. The insertion depth of the tool
10
in the range between those of FIG.
2
and
FIG. 3
results in a satisfactory joint quality. When the depth of insertion of the tool
10
into the work is set larger than that of
FIG. 3
, the shoulder
11
on the moving direction
14
side of the tool
10
sinks into the surface
13
of the work, thereby cutting the work with the side surface of the tool
10
. In this case, the surface
13
of that portion of the work which has undergone the joining operation is recessed significantly from the remaining portion, and the material excessively cut off is discharged outside as burrs. Conversely, when the depth of insertion of the tool
10
into the work is set smaller than that of
FIG. 2
, the shoulder
11
on the side opposite the moving direction
14
of the tool
10
parts from the surface
13
of the work, reducing the effect of holding down the material stirred by the pin
12
, with the result that the work is cut by the pin
12
. The material of the work thus cut is discharged outside as burrs.
Hence, keeping the tool insertion depth into the work at an appropriate amount during the joining operation leads to an improvement of the quality of the joint. The insertion depth of the tool
10
into the work depends on a variety of factors, for example, a machining precision of the work, a method of holding the work and a precision of the joining apparatus itself. Establishing these factors within a precision of about 0.05 mm is very difficult to achieve with the current level of technology. Although a desired machining precision may be realized by investing a sufficient time and cost, this leads to an increase in the overall manufacturing cost and is practically difficult to realize.
To deal with such a problem, JP-11-226768A, for instance, shows a method of controlling the insertion depth of the tool
10
into the work to be joined, which uses a laser displacement meter.
FIG. 4
is a sectional view showing an example construction of the joining apparatus. In this apparatus a table
27
is moved in the direction of X by a drive motor
21
. On the table
27
, a work
26
to be joined is securely held by a jig not shown. A machine head
25
is moved in the direction of Z by a head drive motor
22
. The machine head
25
is supported by a ball thread
29
and a guide not shown. The machine head
25
has mounted thereon a tool
24
and a spindle motor
23
that drives the tool
24
. The distance between the machine head
25
and the surface
30
of the work to be joined is measured by the laser displacement meter
28
mounted on the machine head
25
. The distance measured is fed back and the head drive motor
22
is controlled to adjust the position of the machine head
25
so that the distance between the machine head
25
and the surface
30
of the work is kept at a predetermined value at all times.
The position control using such a laser displacement meter is a common measure also in the conventional arc welding and laser welding. It is common to perform the distance measurement by the laser displacement meter at a position offset to and slightly ahead of the tool. Thus, the distance between the machine head and the tool at the measuring position of the laser displacement meter may slightly differ from that measured near the tool. In the case of the friction stir welding, the work to be joined is acted upon by a force of about 1000 kgf from the tool. A problem therefore arises, for example, when a part of the work is slightly floated from the table. The laser displacement meter beforehand reads this flowing and controls the machine head to raise it upward according to the measurement. When the tool passes the floating position, the work is moved down by the force of the tool, increasing the distance between the tool and the work to slightly more than an appropriate distance. Further, it should be noted that the laser displacement meter is designed to detect the state of the surface (surface position). The meter thus tends to be subject to influences from, for instance, a change in radiation factor caused by smear of the surface of the work or by oxidation of the work due to frictional heat.
JP-06-143015A teaches, in a cutting machine that performs cutting while rotating a cutting tool by a main motor, adjusting a feed speed of the cutting tool to keep an electric current of the main motor at a predetermined value. But this reference does not show any particular relationship of the feed speed with the friction stir welding.
JP-11-188517A discloses that, in a cutting machine that performs cutting by rotating a cutting tool by a main motor, means is provided for stopping feed means according to an amount of load detected by the feed means. However, this reference is silent about any particular relationship of the feed means in the friction stir welding.
BRIEF SUM
Doi Masayuki
Hirano Satoshi
Inagaki Masahisa
Odakura Tomio
Okamoto Kazutaka
Antonelli Terry Stout & Kraus LLP
Edmondson L.
Hitachi , Ltd.
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