DESCRIPTION
Title of Invention: Friction Welding Method
5 Technical Field
[OOOl] The present invention relates to a friction
welding method suitable for joining metal members with
each other.
10
Background Art
[0002] As one of the methods for joining metal members
with each other, friction welding has been proposed.
15 "Friction welding" is the method of bringing the joining
surfaces of the metal members to be joined into contact
with each other and applying pressure to the joining
surfaces while mechanically making them move relative to
each other to generate heat of friction and using this as
2 0 the heat source for pressure welding. The relative motion
of the members includes, for example, rotational motion
about the axis vertical to the contacting surfaces, back
and forth motion in a direction parallel to the
contacting surfaces, etc. Friction welding does not
2 5 utilize ohmic heating, so large power facilities are not
required and relatively simple facilities can be used to
obtain products with a high dimensional precision. Due to
this, the method is applied for joining parts which have
been subjected to finishing processes. Further, unlike
3 0 general welding, different types of metal materials can
also be joined, so the fields of application are broad.
For this reason, this is being applied to valves for
automobiles and other numerous precision machine parts
etc.
3 5 [0003] Friction welding requires heating up to close
to the melting point of the metal members and bonding by
plastic flow near the joining surfaces. For this reason,
deformation easily occurs near the joining surfaces.
Further, the heat affected zone of the metal members
becomes wider. That has a detrimental effect in terms of
the stcength and material characteristics. For this
5 reason, various methods have been proposed as methods for
controlling the heat affect of the metal members.
[0004] PLT 1 discloses a method of joining metal
members with different heat capacities by friction
welding during which inserting an insert material as a
19 rotating member between the metal members, individually
controlling the two members in temperature, and making
the insert material rotate for frictional joining. In the
friction welding method of PLT 1, the pair of metal
members can be joined through the insert member.
15 [0005] PLT 2 proposes to lower the joining temperature
by joining an amorphous alloy foil (solder material. for
soldering) used for liquid phase diffusion bonding to a
metal member in advance by the friction welding met.hod.
That is, the primary joining of the friction welding can
2 0 be performed at a temperature of the melting point of the
soldering material (amorphous metal foil) or less and the
secondary joining of the liquid phase diffusion bonding
(soldering) can be performed at a temperature of the
extent of the melting point of the soldering material
2 5 (amorphous metal foil). For this reason, compared with
the usual friction welding, the temperature can be
lowered, so there is little deformation and the heat
affected zone of the metal members can be made smaller.
However, the method of PLT 2 basically joins metal
30 members by liquid phase diffusion bonding, not friction
welding.
Citations List
Patent Literature
35
[0006] PLT 1. Japanese Patent Publication No. 2009-
101374A
PLT 2. Japanese Patent Publication No. 2006-159212A
Non-patent Literature
5 [0007] NPLT 1. Shinya Kyuso, Research Concerning
Friction Welding of Carbon Steel, April 1, 1976, Papers
of the Japan Society of Mechanical Engineers (C Edition),
pp. 1406 to 1414
10 Summary of Invention
Technical Problem
[OOOE] At the joining surfaces of the metal members tc
be joined, there are oxides (including natural oxide
15 films - metal oxides due to the base material, below,
simply called "oxides"). At the time of solid phase
joining such as friction welding, it is important to
remove the oxides from the joining surfaces. This is
because if oxides remain at the joint interface, that
2 0 part will form a defect and the joint strength will fall.
Furthermore, this is because the oxides will become
sources of formation of cracks. The oxides are also
liable to cause remarkable degradation of the fracture
toughness.
2 5 [0009] In normal friction welding, the vicinities of
the joining surfaces soften because they become high in
temperature. For this reason, at the time of pressure
welding, the softened parts plastically flow. The parts
are pushed out to the outside of the members together
3 0 with the oxides. This forms burrs. Due to this plastic
flow, the oxides are removed and clean metal surfaces
closely bond to each other resulting in a defect-free
joined member.
[OOlO] However, to push out the oxides, a sufficient
3 5 amount of plastic flow has to be caused. For this reason,
it is necessary to increase the amount of input heat and
make the temperature as high as possible. The larger the
metal members are made in size, the more the amounts
which plastically flow increase, so the greater the
amount of input heat becomes.
[OOll] For example, in the case of steel, to secure a
5 sufficient amount of plastic flow and raise the joint
strength, the highest temperature becomes 1300 to 1400°C
(NPLT 1). The melting point of general low carbon steel
is 1400°C to 1500°C or so, therefore this is learned to be
extremely high. If heating to a high temperature in this
10 way, it takes time to generate sufficient heat of
friction and it is difficult to shorten the joining time.
[0012] Further, since the heating time becomes longer,
heat conduction causes the heat affected zone of the
metal members to become wider. The material
15 characteristics of the heat affected zone change. For
this reason, it becomes impossible to secure the designed
strength and functions and other problems arise.
[0013] Eor.example, when joining steel materials by
friction welding, the vicinity of the joint rises in
2 0 temperature over a broad range and a heat affected zone
(below referred to as an "HAZ") is formed. The joint
interface is heated once to the austenite region and
after that it is rapidly cooled, so it forms a martensite
structure and sometimes gives rise to remarkable HAZ
2 5 hardening. In the case of hardened steel and other
martensite steel, the steel is tempered in the region
where the HAZ part is only heated to a temperature of
less than the Acl point and so-called "HA2 softening"
occurs. For this reason, in the case of hardened steel, a
30 drop in strength occurs at part of the HAZ and the joined
material as a whole is liable to fall in strength.
[0014] Furthermore, the region softened by high
temperature is discharged to the outside because upset
pressurization (pressing force) causes plastic flow.,.
3 5 This forms burrs. In the case of a metal material, if the
heating temperature of the joint is high, the softened
region also becomes broader, so a broad range near the
joint plastically flows. Not only does the amount of
deformation become large, but also the amount of the
burrs becomes greater. For this reason, the final product
deteriorates in precision, deburring and other processing
5 (cutting etc.) become necessary, and extra trouble and
cost become required. This phenomenon is not limited to
steel. In aluminum, titanium, copper, and other metal
materials as well, a similar thing happens.
[0015] The present invention was made to solve such a
19 problem. It has as its object to eliminate the adverse
effects due to high temperature heating like in the past
in friction welding of metal members while obtaining
sufficient joint strength in a short time.
1 5 Solution to Problem
[0016] The present inventors engaged in intensive
research and as a result obtained the following
discoveries:
2 0 (a) They discovered that, in the friction welding method
of metal members, when inserting an insert material with
a lower melting point than the metal members between the
metal members and then performing friction welding, it is
possible to remove the oxides (oxide film) at the joining
25 surfaces along with the flow of the melted insert
material. Due to this, if the insert material melts, it
is possible to remove the oxides (including oxide film)
present at the joining surfaces of the metal members
without heating the metal members more than necessary.
30 [0017] (b) They discovered that if just inserting,
heating, and pressing an insert material, the oxides on
the joining surfaces cannot be completely removed. That
is, due to the relative motion of the joining surfaces
(for example, rotational motion etc.), the oxides on the
3 5 joining surfaces are peeled off or the oxides become more
easy to peel off. In addition to this, due to the flow of
the melted insert material, the peeling off oxides are
scraped away and pushed out. Due to this, it is possible
to remarkably raise the cleanliness of the joining
surfaces and obtain a defect-free joint interface.
[OOlS] ( c ) They discovered that to obtain the above
5 effects to the maximum extent, it is preferable to make
the melting point of the insert material lower than the
heating temperature required for joining (pressure
welding temperature) by about 50°C. If the melting point
of the insert material is unnecessarily low, before the
1 .O oxides proceed to peel off much, the insert material ends
up being pushed out to the outside.
[0019] By doing this, while the temperature is lower
than with conventional friction welding, it is possible
to press-weld clean joining surfaces from which the
15 oxides have been removed, secure bondability of the metal
members, and obtain a high joint strength. Furthermore,
the heating temperature is low, so the joining time is
shortened.
[0020] Further, metal materials fluctuate in melting
2 0 point depending on their quality, so the inventors
discovered that it is possible to approximately express
the melting point of an insert material by the melting
point of the metal members (centigrade temperature). That
is, they discovered that the melting point of the insert
2 5 material should be selected so as to become a temperature
(centigrade temperature) of 60% to 80% of the melting
point of the metal members.
[0021] The present invention was made based on these
discoveries. It has as its gist the following:
3 0 ( 1 ) A friction welding method of a pair of metal members
comprising the following steps;
starting the friction welding in a state inserting an
insert material between surfaces of the metal members
facing each other, wherein the insert material consists
3 5 of a metal having a melting point (centigrade
temperature) of 60 to 80% of the melting point
(centigrade temperature) of the metal members, melting
the insert material, and pushing the melted insert
material out from between the pair of metal members.
(2) The friction welding method of metal members
according to (1) wherein the insert material has a
5 thickness of 10 to 500 pm.
(3) The friction welding method of metal members
according to (1) or (2) wherein the insert material
covers at least one of the joining surfaces.
(4) The friction welding method of metal members
10 according to any one of (1) to (3) wherein the
temperature at the time of pressure welding is higher
than a melting point (centigrade) of the insert material
by 50°C or more.
(5) The friction welding method of metal members
15 according to any one of (1) to (4) wherein the insert
material does not remain between the metal members after
friction welding.
(6) The friction welding method of metal members
according to any one of (1) to (5) wherein the metal
2 0 members are steel.
Advantageous Effects of Invention
[0022] According to the present invention, in friction
welding of metal members, the adverse effects caused by
high temperature heating like in the past is elj.minated,
2 5 joining is possible in a short time, and a joint strength
equal to or greater than the past is obtained.
Brief Description of Drawings
3 0 COO231 FIGS. 1 (a) to 1 (c) are views for explaining a
friction welding method according to an embodiment of the
present invention.
Description of Embodiments
35
[0024] Below, a friction welding method according to
the present invention will be explained. The friction
welding method according to the present invention is a
method of performing friction welding in the state
inserting an insert material between a pair of metal
members. Here, the surfaces of the pair of metal members
5 which face each other and are joined will be called the
"joining surfaces". Further, the pair of the metal
members joined together will be called the "joined
member". Further, the vicinity of the joint interface of
the joined member will be called the "joint".
1 .0 Furthermore, in the present invention, a parameter
related to temperature (for example, melting point etc.)
shows the centigrade temperature (OC) unless otherwise
indicated.
[002S] FIGS. l(a) to l(c) are views for explaining a
15 friction welding method according to an embodiment of the
present invention. Note that, in FIGS. l(a) to l(c), the
case of joining columnar shaped metal members 1 and 2 is
shown, but the, friction welding method according to the
present invention is not particularly limited to that
2 0 shape. The method can also be applied to joining steel
materials of other shapes (for example, cylindrical
shapes and polygonal prism shapes).
100261 As shown in FIG. l(a), the metal members 1 and
2 are made to abut against each other in the state
2 5 sandwiching between them a disk shaped insert material 3.
The insert material 3 is comprised of a metal with a
melting point of a centigrade temperature of 60% to 80%
of the metal members 1 and 2. For example, when the metal
members 1 and 2 are steel, it need only be a metal which
30 has a melting point of about 900°C to 1200°C with respect
to the melting point of steel (about 1500°C). As the
material of the insert material 3, a Cu, Fe, Ni, or Aubased
alloy etc. may be mentioned. The thickness of the
insert material 3 is, for example, preferably 10 to 500
35 p. The insert material preferably covers the joining
surface of at least one of the metal members.
[0027] In the present embodiment, the metal member 1
is held at a rotary holding part (not shown) of a
friction welding apparatus (not shown), while the metal
member 2 is fastened to a fastening part (not shown) of
5 the friction welding apparatus (not shown). The metal
member 1 is lightly pushed through the insert material 3
against the metal member 2 to establish a state where the
insert material 3 is clamped between the metal members 1
and 2. At this time, from the viewpoint of the
19 workability, the insert material 3 may also be attached
to the joining surface of the fixed metal member 2 by an
adhesive etc. In this state, the friction welding is
started.
[0028] Note that, the friction welding method of the
15 present invention can be worked using a known friction
welding apparatus or an apparatus comprised of a known
friction welding apparatus with some simple design
changes, so a detailed explanation of the friction
welding apparatus will be omitted.
2 0 [0029] Next, as shown in FIG. l(b), in the present
embodiment, the metal member 1 is made to rotate at a
high speed while making it move in thc axial direction to
thereby press it against the steel material 2 through the
insert material 3. The insert material 3 is held by
2 5 receiving pressure from the metal members 1 and 2 while
rotating relative to the two members. Due to this, heat
of friction is generated at both the contact parts of the
steel material 1 and insert material 3 and the contact
parts of the steel material 2 and insert material 3. Due
3 0 to this heat of friction, the insert material 3 is heated
and melted. Note that, the speed and pressing force of
the metal member 1 are determined based on the dimensions
and materials of the steel materials 1 and 2 and insert
material 3, the type of the friction welding apparatus,
35 etc. For example, when the metal members are steel, these
should be suitably set in the ranges of a rotational
speed of 1000 to 4000 rpm and a pressing force of 30 to
300 MPa. Further, the present embodiment makes only the
metal member 1 rotate, but the two members may also be
made to rotate. In this case, making the metal members 1
and 2 rotate oppositely is preferable to increase the
5 relative speed. Of course, the relative motion is not
limited to rotation. Straight back and forth motion etc.
are also possible. The mode of motion is not limited so
long as a type of motion at which heat of friction is
generated.
1 ,0 [0030] Next, as shown in FIG. l(c), the metal members
1 and 2 are further pressed together, whereby the melted
insert material 3 is pushed out from between the metal
members 1 and 2 and the metal member 1 and the metal
member 2 are made to directly contact each other to join
1 5 them. At this time, the oxides at the joining surfaces of
the metal members 1 and 2 peel off and are discharged to
the outside along with the melted insert material.
[0031] Normally, there are oxides at the joining
surfaces of the metal members. For example, when the
2 0 metal members are steel, Fe203 and oxides of Si and Mn in
the steel constituted by SiOz and MnO are present on the
joining surfaces. When the metal members are aluminum,
there is A1203 (so-called "alumina") present on the
joining surfaces. These oxides peel off from the metal
2 5 members due to the high temperature and rotational force
(force due to relative motion) or become easy to peel
off. There, the melted insert material flows so as to be
pushed out to the outside by the pressing action, so the
oxides on the joining surfaces are also pushed out to the
3 0 outside as if being flushed away.
[0032] In this way, the insert material and the
joining surfaces high in cleanliness with no impurities
such as oxides contact each other, so a good joined
member high in joint strength can be obtained. The
35 temperature of the joint at this time is higher than the
melting point of the insert material by about 50°C, so the
temperature is lower than the temperature in conventional
friction welding, but the temperature is a temperature
sufficient for obtaining bondabil-ity. After that, the
insert material 3 discharged from the joining surfaces is
removed and the joined member comprised of the metal
5 members 1 and 2 is completed. While the temperature is
lower than that of conventional friction welding, it is
possible to obtain a joined member with no defects and
with a high joint strength.
100331 In the prior art, the plastic flow of the metal
10 members themselves was used to discharge the oxides to
the outside, but plastic flow of a considerable amount of
the metal members was necessary. However, in the present
invention, the discharge of the oxides is left to the
melted insert material, so there is no flow of the metal
15 members themselves or even if there is, is relatively
small in amount. For this reason, it is possible to
suppress deformation of the metal members and raise the
precision of finish of the obtained joined member.
[0034] Further, due to this, it is possible to prevent
2 0 broad ranges of the metal members 1 and 2 from becoming
high in temperature, so the HAZ can be kept from forming
over a broad range around the joint. As a result, the HAZ
softened region is also reduced and a drop in strength of
the joined member can be suppressed.
2 5 [0035] Insert Material
The insert material according to the present invention
will be explained with reference to the case where the
metal members are steel.
Melting Point of Melting Insert Material
3 0 In the case of steel, at a joining surface temperature of
about 1000°C, it is known that the bonding becomes easier
and the bonding strength (joint strength) is improved
(NPLT 1). The temperature required for this pressure
welding is referred to here as the "pressure welding
35 temperature". It is learned that the pressure welding
temperature is correlated with the melting point. In
research of the inventors, it was confirmed that with
S15C steel (melting point: about 1500°C), sufficient
joining is possible at an insert material melting point
of 900°C and pressure welding temperature of 950°C. That
is, the melting point of the insert material is 60% of
5 the melting point of steel and the pressure welding
temperature is 63%. Note that, the pressure welding
temperature was measured by burying a thermocouple near
the joint interface at the center part of the joint at
the fixed chuck side. On the other hand, in conventional
10 friction welding, the heating temperature of the joining
faces reaches 1300 to 1400°C (NPLT 1). That is, about 90%
of the melting point of steel is reached. In the
conventional method, it is learned how high the
temperature was.
15 100361 As in the problem of the present invention, if
the heating temperature becomes too high at the time of
friction welding, the HAZ becomes broader and a drop in
strength and other adverse effects arise. Therefore, the
heating temperature at the joining surfaces has to be
2 0 made lower than the conventional heating temperature, so
the temperature is preferably made less than 1300°C. By
doing this, the heating time can be shortened, the HAZ
width can be kept down, and the adverse effects due to
the higher temperature can be eliminated.
2 5 [0037] As a result of research of the inventors, it
was discovered that the melting point of the insert
material is preferably 900°C to 120O0C and the heating
temperature of the joining surfaces (pressure welding
temperature) should be made higher than the melting point
3 0 of the insert material by about 50°C.
100381 In general, steel and other metals change in
melting point depending on the compositions of
components. If the melting point becomes lower, the
pressure welding temperature also becomes lower and the
3 5 highest heating temperature of the joining surfaces also
has to be made lower. As explained above, the pressure
welding temperature is correlated with the melting point
to a certain extent. This is deemed approximately as a
proportional relationship. Therefore, in the present
invention, the melting point of the insert material is
shown by a ratio with respect to the melting point of the
metal member. In the case of the above S15C steel, the
melting point is about 1500°C. The melting point of the
insert material should be set to 60% to 80% of the
melting point of the metal members becoming the base
materials. Further, the joining surface temperature
(pressure welding temperature) at the time 01 Lhe
pressure welding operation should be set so as to become
higher than the melting point of the insert material by
about 50°C. If ordinary steel, good pressure welding is
possible if in this range.
[0039] Further, for example, in the case of high
carbon steel (C: 2%), the melting point becomes 1150°C or
so. By ...t he..meltingp oint being made lower in temperature,
the pressure welding temperature also becomes lower in
temperature. In this case as wel~l, it is possible to use
an insert material having a melting point of 700°C
corresponding to 60% of the melting point of the steel
forming the base material and join by friction welding at
a pressure welding temperature of 750°C.
[0040] If considering that the joinability is improved
if the joining temperature is a high temperature, the
pressure welding temperature is preferably more than 70°C
of the melting point of the insert material, more
preferably more than 80°C. The upper limit of the pressure
welding temperature is not particularly set, but even at
the highest, is about 90% of the melting point of the
metal members in the same way as the past.
[0041] The material of the insert material is not
particularly limited, but can be obtained from a Cu-,
Fe-, Ni-, Au-based alloy etc. by adjusting the melting
point. For example, a soldering material etc. can be
used. For example, a Ni-3.5%Si-8%B-ll%V alloy (melting
point: 1073OC), Fe-2.5%Si-12%B-8%V alloy (melting point:
1122"C), and Ni-0.8%Si-15%P-7%V alloy (melting point:
94Z°C) are known (all PLT 2) .
5 100421 Thickness of Insert Material
The insert material also softens and plastically flows by
being pressed if heated to its melting point or so.
Therefore, if the insert material becomes too thin in
thickness, the joining surfaces of the metal members may
1 0 end up contacting each other and the insert material may
disappear bctween the joining surfaces before reaching
the meltiny point of the insert material. this
reason, the thickness of the insert material should be
made 10 pm or more. From the viewpoint of handling
15 ability, manufacturability, etc., it is preferably 25 pm
or more, more preferably 50 pm or more.
100431 On the other hand, if the insert material
becomes too th;ck, the heating time of the insert
material becomes longer and further the time period
2 0 required for discharge of the insert material between the
joining surfaces increases. Due to this, the amount of
heat conducted to the metal members may increase and as a
result the HAZ may become wider. For this reason, the
thickness of the insert material should be made 500 pm or
2 5 less. The effect of reducing the thickness on shortening
of the heating time is large, so the thickness is
preferably 300 pm or less, more preferably 150 pm or
less.
[0044] Shape of Insert Material
3 0 The shape of the insert material is not particularly
limited. There is no problem so long as when the insert
material melts and is pushed out from the joining
surfaces, it passes over the entire joining surfaces.
This is because if there is even a part where the insert
35 material does not pass, the oxides at that part are
liable not to be removed. For this reason, from the
viewpoint of raising the effect of discharge of oxides on
the joining surfaces of the metal members, it is
preferably made a size able to cover at least one of the
joining surfaces. This is because due to this, it is'
possible for the insert material to fill the space
between the joining surfaces as a whole and possible for
the oxides on the joining surfaces to be reliably
discharged. The above findings can also be applied to
metals other than steel. It was confirmed that if based
on the melting point, the numerical ranges become
generally the same. As metals other than steel, alloys of
mainly Al, Ti, Cu, etc. may be mentioned.
Examples
100451 In experiments, a steel material was used as
the metal member. The steel material and insert material
used in the experiments were as follows.
Steel material: Fe-0.45%C-0.2%Si-0.7%Mn
Melting point: about 1440°C
Diameter 20 mmxlength 100 mm columnar shape
The two end faces are finished to flat surfaces by
machining
Insert material: Cu-35%Zn alloy
Melting point: 930°C
Diameter 22 mmxthickness 100 pm (0.1 mm) disk shape
[0046] Two of the steel materials were prepared. One
was set coaxially at the fixed chuck, while the other was
set to the rotating chuck. The chucks were moved in the
axial direction and the insert material was set to be
clamped by the two steel materials (see FIG. l(a)). After
that, the rotating chuck was rotated and the chucks were
made to move so that the two steel materials were pressed
(see FIG. l(b)). The rotational speed at that time was
made a constant 1800 rpm, the friction pressure was 200
MPa, the friction time was 3s ("s" indicates seconds.
same below), the upset pressure was 300 MPa, and the
upset time period was 3s for the joining method.
[0047] The joining operation as evaluated by using the
joined member (steel material comprised of two steel
5 materials joined together to form single member) to
conduct a tensile test and using the ratio of fracture
strength (fracture strength/strength of base material)
and the fracture site. Further, in the comparative
examples, the same steel materials were used and
10. conventional frictional pressure welding was performed
without inserting an insert material. In Comparative
Example 1, the friction time was made 2s, while in
Comparative Example 2, the friction time was made 3s. The
rest of the conditions were made the same conditions as
15 the case of inserting the insert material. The test
results are shown in Table 1.
[0048] Table 1
100491 The invention example and Comparative Example 1
2 0 fracture at other than the joint interfaces, so the
joints themselves appear to be good.
[0050] Further, the hardness profiles of the joints
were measured. As a result, in the invention example, the
distance from the joint interface to the softest part of
2 5 the HAZ was about 1.5 mm, while in Comparative Example 1,
it was about 3 mm. That is, it could be confirmed that
the HAZ width in the invention example became narrower.
[0051] Considered from the fracture strength ratios of
the invention example and Comparative Example 1, the
Fractured part
Base material
HAZ part
(about 3 mm from
joint interface)
Joint interface
Example
Comp.
Ex. 1
Comp.
Ex. 2
Presence
of insert
material
Yes
No
No
Joining time
(pressure
welding
temperature)
3s (990°C)
3s (1300°C)
2s (9OO0C)
Fracture
strength
ratio
1.01
0.95
0.85
fracture strength ratio of Comparative Example 1 is 0.95.
Again it appears that high temperature heating has an
effect, though slight. From, this, it could be confirmed
that the joined member obtained by friction welding
according to the present invention has a joint strength
equal to that of the past regardless of the joining being
performed at a relatively low temperature and that the
HAZ width becomes narrower.
[0052] Comparative Example 2 fractured at the joint
interface, so it seems the joint itself was not
sufficient. As the reasons, it may be considered that the
joining Lime was short and the temperature low, so the
plastic flow was not sufficient and oxides remained at
the joining surfaces or the bondability was poor and the
joint was cooled while the solid phase joining was still
insufficient. The outer circumference of the joined
member was heated to 1000°C or more, but the center part
did not receive peripheral speed and heat of friction was
not generated, so had to be heated by conduction of heat
from the surroundings. That is, if the joining time is
too short, the center part is not sufficiently joined, so
it is believed that the joint strength falls. On the
other hand, in the invention example, the insert material
started to be discharged from a joining time of about 2s.
This means that the joint interface as a whole reached
the melting point of the insert material or more. That
is, by clamping the insert material, it is believed that
the temperature of the joint interface easily rose at the
center part compared with the previous methods.
[0053] From the above, it could be confirmed that by
the friction welding according to the present invention,
a quality of joining equal to or better than the past is
obtained even at a temperature lower than the
conventional method. Note that, needless to say, the
embodiments of the friction welding method according to
the present invention are not limited to the abovementioned
mode.
Industrial Applicability
COO541 According to the present invention, even when
5 joining together steel and other metal members, they can
be joined at a low temperature and a quality of joining
equal to or better than the past can be obtained. For
this reason, the present invention can be utilized in the
manufacture of precision machine parts etc.
10
Reference Signs List
[0055] 1 and 2. metal member
3. insert material

CLAIMS
Claim 1.
A friction welding method of a pair of metal members
comprising the following steps;
5 starting said friction welding in a state
inserting an insert material. between surfaces of said
metal members facing each other,
wherein said insert material consists of a
metal having a melting point (centigrade temperature) of
10 60 to 80% of the melting point (centigrade temperature)
of said metal members,
melting said insert material, and
pushing the melted insert material out from
between the pair of metal members.
15 Claim 2.The friction welding method of metal members according to claim 1 wherein said insert material has a thiclrness of 10 to 500 pn.
Claim 3. The friction welding method of metal members according to claim 1 or 2 wherein said insert material covers at least one of said joining surfaces.
Claim 4. The friction welding method of metal members according to any one of claims 1 to 3 wherein the temperature at the time of pressure welding is higher than a me1 1 lng pint (centigrade temperature) uC sald
insert material by 50°C or more.
Claim 5. 30 The friction welding method of metal members according to any one of claims 1 to 4 wherein said insert material does not remain between said metal. members after friction welding.
Claim 6. 35 The friction welding method of metal members according to any one of claims 1 to 5 wherein said metal members are steel.