Method for bonding sintered metal pieces

The invention relates to a method for bonding pieces of iron group sintered metals, and more particularly to a method for producing a sintered part having a complicated configuration by bonding more than 2 iron group sintered metal pieces to each other at the flat faces thereof according to this method, through holes are provided in predetermined locations of each of the metal pieces except the one constituting the lowermost layer, and if necessary, a concave groove having a depth of 0.03-1 mm is provided on the metal face to be bonded in each layer. The metal pieces are then superposed with said through holes coinciding with each other, with a brazing alloy being inserted into each of the through holes; heating the whole assembly so as to help said brazing alloy infiltrate into each of the interfaces, thereby bonding more than 2 pieces of iron group sintered metals to each other at a low cost.

The invention relates to a method for bonding iron group sintered metal 
pieces, and more particularly to a method for producing a sintered part of 
a complicated configuration by bonding more than 2 pieces of iron group 
sintered metal produced by powder metallurgy at the flat faces of said 
pieces. The invention is characterized in that a through hole is provided 
at a predeterminedlocation of each metal piece, except the one 
constituting the lowermost layer, and in addition, if necessary, a concave 
groove 0.03-1 mm in depths is provided on the face to be bonded of each of 
the metal pieces, said metal pieces being superposed with said through 
holes coinciding with each other so as to facilitate the infiltration of 
the brazing alloy. The whole assembly is then heated to braze the alloy 
inserted into the through hole to permit it to infiltrate into each of the 
faces of the metal pieces to be bonded to each other. 
In recent years, iron group sintered metal parts have been put into 
practical use in motorcars, household electric appliances, office 
machines, etc. with the scope of application expanding steadily. Such 
metal parts are now supplied in a wide variety of configurations, and 
there is a demand for a still higher quality. 
U.S. Pat. No. 2,652,520, U.S. Pat. No. 2,913,819, BP No. 628,679, DP No. 
749345, etc. disclose conventional powder pressing method according to 
ordinary powder metallurgy techniques. These methods, however, are no 
longer suitable for the bonding of iron group sintered metal pieces. Even 
when a metal mold of complicated configuration is devised and produced, it 
will involve many difficulties, for example, high production cost, lack of 
strength due to density distribution, etc. 
In view of the aforedescribed conventional difficulties, the applicant has 
invented a method for bonding two sintered compacts to each other, wherein 
more than one recess is formed on at least one of the combination 
comprising more than two pieces of iron group sintered metals, said recess 
being filled with a brazing alloy. The whole assembly is then heated so as 
to facilitate the infiltration of the brazing alloy into the interfaces to 
be bonded together, thereby enabling one to bond at least 2 sintered 
compacts to each other. 
When the area to be bonded is large, it is necessary that the amount of the 
brazing alloy be increased. According to the abovedescribed method, 
however, the recess containing the brazing alloy can not be enlarged under 
the restriction of the configuration of the product. Thus satisfactory 
bonding is unobtainable in some cases. 
In order to overcome this difficulty, the applicant has invented another 
method wherein, when the bonding area is large, a third iron group 
sintered metal is inserted into one of the two kinds of iron group 
sintered metals to be bonded together, wherein a brazing alloy is placed 
thereon, with the whole assembly being heated above the melting point to 
bond the two faces together. 
This method, however, has a disadvantage in that it involves a high cost, 
since the extra cost of material and processing is inevitable due to the 
use of a third iron group sintered metal. In addition, insertion of the 
third iron group metal is impossible in some cases due to the 
configuration of the assembly. 
It is an object of the present invention to provide a method for perfectly 
bonding more than two faces of iron group sintered metals without using a 
third iron group sintered metal therebetween, even when the bonding areas 
are large. The invention has for another object to provide a method for 
producing economically, and in large amounts such parts having very 
complicated configurations as are not producible by a single operation 
with a metal mold, for example, a part having a hollow portion or parts 
having steps on the outside and constricted in the middle of the body 
thereof, etc. 
The invention will hereinunder be described in detail in reference to the 
accompanying drawings.

In FIG. 2 the metal piece 1 of the uppermost layer is formed with through 
holes 4 and 5, with no through holes being provided on the metal piece 3 
constituting the lowermost layer. Brazing alloy 6 and 7 are inserted into 
the through holes 4 and 5. The metal pieces 1, 2 and 3 are superposed so 
that the through holes 5 and 5' will coincide with each other. When the 
whole is heated at a temperature at which the brazing alloy melts, the 
melted brazing alloy 6 infiltrates into the interface 8 between the metal 
pieces 1 and 2 while the brazing alloy 7 fully infiltrates into the 
interface 9 between the metal pieces 2 and 3, thereby permitting one to 
produce a part of a complicated configuration having steps on its outside 
in which the metal pieces 1, 2 and 3 have been perfectly and integrally 
bonded together. 
The brazing alloy may be an alloy piece or a tablet obtained by pressing a 
powdered brazing alloy. 
The metal piece may be a pressed compact obtained by pressing a iron group 
metal powder or a sintered compact thereof. In the case of a pressed 
compact, sintering and bonding may be effected synchronously. 
Although an example of 3 metal pieces has been described above, it is to be 
understood, however, that bonding is similarly feasible in the case of 
combining more than 3 metal pieces. 
The through holes can be formed in a predetermined position with precision 
be pressing a metal piece with a preliminarily prepared metal mold. For 
the accurate superposition of the metal pieces, such notch or the like is 
provided so as not to impair the properties of the finished product by 
pressing the process in a suitable location. Such notch is helpful to hold 
the metal pieces in place during the sintering (stage). 
Bonding of 2 iron group sintered metal pieces at the interface thereof will 
now be described below in detail in reference to FIG. 4. 
According to FIG. 4-(B), the weight of the brazing alloy can be varied by 
providing a through hole 24 for receiving the brazing alloy 26 on at least 
one of the iron group sintered metal pieces 21 and 23 to be bonded 
together at the interface thereof. By providing such through holes in 
multiplicity, the length of penetration of the molten alloy can be 
shortened, thereby making it possible to produce a satisfactorily bonded 
interface. In many cases, however, it is impossible to form a multiplicity 
of through holes due to the particular make up of the configuration. Thus, 
the time of penetration of the molten alloy is lengthened. Particularly 
when the interface is smooth, satisfactory bonding cannot be obtained, 
since the two faces are brought into closer contact with each other. 
When the brazing alloy is heated above its melting point, it infiltrates 
into the interface by capillary force. The applicant, therefore, attempted 
to obtain satisfactorily bonded interface by controlling the space between 
the two faces so as to permit the capillary action to work effectively. 
A uniform space and a satisfactorily bonded interface can be provided by 
forming a concave groove 20 on at least one of the two faces to be bonded 
together as shown in FIG. 4(B). Since the iron group sintered metal is 
pressed by a metal mold, the concave groove 20 can be formed in any 
optional size and configuration. Moreover, the depth of the groove has 
high precision thereby providing a highly uniform space between the two 
faces to be bonded together. The depth of the groove is preferably 0.03-1 
mm. 
FIG. 4(B), FIG. 4(D) and FIG. 4(E) each show an example in which a concave 
groove 20 is formed on at least one of the two faces of the iron group 
sintered metal pieces. It is needless to say that the provision of a 
concave groove is not limited to the bonding between the two faces, but to 
bonding of more than two faces. The concave groove can be replaced by a 
projection with the same effect. 
The invention will now be described in more detail in reference to the 
following examples. 
EXAMPLE 1 
Pressed compacts 10, 13 and 15 in the shape of (A),(B),(C) of FIG. 3 were 
produced from a powder mixture of iron group sintered metals composing 2 
weight % Cu and 0.8 weight % C with the residual part consisting of Fe. 
The green density was 6.5 g/cm.sup.3 for (A), and 6.8 g/cm.sup.3 for (B) 
and (C). 
Through holes 11 and 11', 12 and 12', 14 and 14' for receiving brazing 
alloys were formed on the pressed compacts 10 and 13 at the time of 
pressing. Said pressed compacts were superposed as shown in FIG. 3 (D), 
and a pressed compact 18 of the brazing alloy as shown in FIG. 3(E) 
composing 40% Ni and 40% Cu with the residual part consisting of Mn was 
inserted into each of the through holes 11,11', 12 and 12' of the 
uppermost layer. The whole was sintered in an atmosphere of an endothermic 
gas (derived from butane) at 1150.degree. C. for 1 hour. The sintered 
part, thus-obtained, was an integrated part as shown by the perspective 
view of FIG. 3(D). The brazing alloy had fully infiltrated into each of 
the interfaces thereby rigidly bonding the pressed compacts 10, 13 and 15 
to each other. 
In this example, the pressed compacts, FIGS. 3(A), 3(B) and 3(C), were 
combined as shown in FIG. 3(D) before sintering. Alternatively, however, 
the pressed compacts FIGS. 3(A), 3(B) and 3(C) may be preliminarily 
sintered before they are combined and heated. In this case, the 
temperature can be lower and heating time can be reduced to 15 minutes. 
EXAMPLE 2 
There was produced a pressed compact comprising an iron group sintered 
metal designated at 21 in FIG. 4(B), of a composition of Fe-2%Cu-0.8%C, 
with a green density 6.5 g/cm.sup.3, and another iron group sintered 
metal, designated at 23 in FIG. 4(B), of the composition of Fe-2%Cu-0.8%C, 
with a green density of 6.5 g/cm.sup.3. A pressed compact of a brazing 
alloy 26 of the composition of Mn-40%N-40%Cu was placed in a through hole 
24 provided on the sintered metal 21 in FIG. 4(B). The two pressed 
compacts of sintered metal 21 and 23 were combined face to face each 
other. They were bonded to each other by sintering them in an atmosphere 
of an endothermic gas (derived from butane) at a temperature of 
1150.degree. C. 
When the interface was smooth, defective compacts were produced up to 50%. 
However, when a concave groove 20, of 0.1 mm in depth and 1 mm in width, 
was provided on the sintered metal 23, the bonded compacts were 100% 
satisfactorily. It was found that the provision of a concave groove on at 
least one of the faces to be bonded was highly effective. 
The amount of the molten alloy having a composition of Mn-40%Ni-40%Cu 
varies in accordance with the sintering temperature. Even when a brazing 
alloy of the same weight is used, the molten alloy fails to reach the 
outer periphery or overflows it. Even when the sintering temperature is 
fixed, the temperature distribution in the sintering furnace makes it very 
difficult to hold the temperature uniform. In this connection, it was 
found that satisfactory bonding can be accomplished by imparting the 
concave groove with a depth of 0.6-1 mm. 
EXAMPLE 3 
Iron group sintered metal pieces 21 and 23 of a composition of Fe-2% 
Cu-0.8% C and a green density of 6.6 g/cm.sup.3 ; the same as in Example 1 
were used. A pressed compact of a brazing alloy 26 composing 
Mn-40%Ni-40%Cu was placed in a through hole 24 providedon one of the 
sintered metal 21 in FIG. 4(B). On the other pressed compact of sintered 
metal 23 there was preliminarily formed a concave groove 20 of 1 mm in 
depth as shown in FIG. 4(D) and FIG. 4(E). The two pressed compacts were 
combined face to face and bonded to each other by sintering them in an 
atmosphere of an endothermic gas (derived from butane) at 1150.degree. C. 
for 30 minutes. 
As a result, the ratio of defective products was reduced to 2% from 25% 
when a concave groove 20 is provided therein. This shows that the molten 
alloy in a suitable amount has infiltrated into the interface without 
overflowing the outer periphery with its excess being collected in the 
recess. 
When the concave groove 5 provided on one of the pressed compacts of iron 
group sintered metal has a depth below 0.03 mm, the molten alloy does not 
easily infiltrate if the face is smooth. When said concave groove has a 
depth in excess of 1 mm, a large amount of brazing alloy is required, 
while its penetrating length into the interface to be bonded is shortened. 
The results of tests have made it clear that a depth resulting from 0.03 
to 1 mm is most suitable. 
As described hereinbefore, the invention makes it possible to produce 
economically sintered parts having complicated configurations which have 
heretofore been impossible to produce by the pressing process by use of 
conventional metal molds. 
Furthermore, the sintered parts according to the invention can be applied 
to various uses which the conventional products could not cover, such as 
compressor parts, side plates for power steering, etc. This is because the 
tightness against high pressure liquids and gases has been improved as a 
result of full infiltration of the brazing alloy into the faces to be 
bonded together. 
A concave groove of predetermined dimensions can be formed by a 
preliminarily prepared metal mold, while through holes for receiving the 
brazing alloy can also be formed by a metal mold. Thus, the invention 
makes it possible to produce sintered parts having complicated 
configurations in large amounts at a low cost.