JPH0732173A - Laser cladding method - Google Patents

Abstract

PURPOSE:To provide the laser cladding method which does not generate defects, such as blowholes, improves the uniformity of structures, does not require an intricate table device and grooving of a coating part and is high in the stability of the device. CONSTITUTION:While the prescribed position on a base material is irradiated with a laser beam R having a doughnut-shaped irradiation mode formed by rotating a spot laser beam 20, alloy powder for cladding is supplied toward the inside of the doughnut-shaped irradiation range of the laser beam 20. On the other hand, the base material and the laser beam having the doughnut- shaped irradiation mode are relatively moved.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to a method of cladding dissimilar materials onto a matrix using a laser beam.

[0002]

2. Description of the Related Art In fields such as the automobile, aircraft and robot industries, there is a strong need for weight reduction, and aluminum alloys having a specific gravity as small as about 1/3 of iron are used for various parts. Since it has extremely low wear resistance, it cannot be used as it is in a place where such mechanical properties are required. Therefore, it is necessary to develop a technology to apply a clad layer having excellent heat resistance and wear resistance to the surface of the aluminum alloy so that the aluminum alloy can be used in places where heat resistance and wear resistance are required. It's coming.

Even if a copper-based alloy having a relatively low melting point (about 1080 ° C. in the case of copper) is used as a cladding layer for an aluminum alloy, compared with the melting point of aluminum alloy (about 660 ° C. in the case of aluminum). It is quite expensive, it is very difficult to clad the aluminum alloy base material without melting it by conventional means, the base material aluminum alloy is greatly melted and diluted in the copper alloy,
The hardness and heat resistance of the copper-based alloy clad layer are reduced,
It also causes cracking.

Therefore, recently, a cladding method using a laser beam as a means for melting only the outermost surface without melting the aluminum alloy base material in a wide range has been attracting attention. 2463
No. 7, in the case of overlaying a copper-based alloy having excellent heat resistance and abrasion resistance on the surface of an aluminum alloy, as shown in FIG. And oscillate the laser beam 3 in the direction perpendicular to the build-up direction (arrow a) and move the aluminum alloy base material 2 (arrow b) to melt the alloy powder and Describes a method of forming the overlay layer 4.

In FIG. 13, a laser beam 3'irradiated from a laser generator (not shown) passes through the convex lens 5, is reflected by the reflection mirror 6 toward the oscillating mirror 7, and reciprocally rotates as shown by an arrow. It is reflected toward the processing surface by the oscillating mirror 7. The irradiation mode of the laser beam on the irradiation surface (hereinafter,
The one-way oscillation mode) is shown in FIG.
As shown in, the width w in the traveling direction of the buildup is equal to the spot diameter of the original laser beam 3, and the width in the direction perpendicular to the traveling direction is widened by the amount of oscillates. The energy density m increases at both ends due to the inertial weight of the oscillating mirror 7.

According to the above publication, when this one-way oscillation mode is applied, a cladding process having a wider width than the original spot diameter of the laser beam can be performed, and the irradiation surface is scanned by the laser beam. It is said that there is an advantage that the base material melts little because of the high speed. However, the laser beam cladding method described in the above publication also has the following problems.

First, the beam width w in the direction of laser processing progress
Is narrow, and the interaction time between the laser beam and the base material in the direction of laser processing is extremely short. In other words, the width of the molten pool formed on the base material in the direction of laser processing is narrow and the duration of the molten pool at a certain point on the base material is extremely short, so there are many defects such as blowholes in the cladding layer. However, the uniformity of the structure also becomes poor. That is, in the former case, the melting point of copper is 40% lower than that of aluminum.
This is because, since the temperature is as high as 0 ° C., the copper alloy that has been cladded first is solidified and then the molten aluminum alloy is solidified at the interface between the copper alloy and the base material, and the gas that cannot escape is trapped there. Regarding the latter, it is considered that the stirring of the molten pool becomes insufficient.

As shown in the one-way oscillation mode of FIG. 13 (b), the energy density at both ends is high, and the penetration of the base material becomes large at this part, and the copper alloy is diluted.
Tissue non-uniformity occurs. It is known that when the aluminum alloy melts in a large amount, a brittle γ'phase is formed at the interface with the copper alloy layer, and cracking easily occurs.

Since the oscillating direction is always perpendicular to the laser processing advancing direction, the laser processing advancing direction is limited. Therefore, for example, the seat surface 1 of the valve seat portion 12 of the engine cylinder head 11 shown in FIG.
In the case of cladding directly on the table 2a, the entire cylinder head 11 has to be rotated around the center line of each valve seat portion 12, and the table device 1 having a very complicated operation is required.
3 is required, which increases the initial investment cost.

Since the beam width w in the direction of progress of laser processing is narrow, it is difficult to adopt a powder feeding method in which powder is introduced into a molten pool in accordance with the progress of laser processing, and the powder is preliminarily deposited on the base material (that is, melted). You must take a method of pollination such as putting it in front of the pond). For this reason, as shown in FIG. 14B, the seat surface 12a of the valve seat portion 12 must be kept horizontal, and in addition to the above, a table device 13 that performs a more complicated operation is required (in the end, the cylinder head). 11 is required to be supported in an inclined state and to be rotated around the center line 14 of the valve seat portion 12). Further, in order to increase the efficiency of powder feeding (the weight of powder that has become an alloy layer / the weight of powder that has been supplied), it is necessary to form a groove in the coating portion in advance, which causes a cost increase in mass production.

Since the oscillating mirror 7 oscillates in one direction at high speed, there is a problem in the stability of the device. Therefore, management items such as a strict check of the device and a check of the finished product are increased.

[0012]

SUMMARY OF THE INVENTION In view of the above problems of the conventional laser cladding method, the present invention has few defects such as blowholes and excellent texture uniformity, and has a complicated groove for a table device or a coating portion. No processing required,
It is an object of the present invention to obtain a laser cladding method with high stability of the device.

[0013]

To achieve the above object, a laser cladding method according to the present invention is a laser having a donut-shaped irradiation mode (hereinafter referred to as a donut mode) formed by rotating a spot-shaped laser beam. While irradiating the beam to a predetermined position on the base material, while supplying the alloy powder for cladding toward the irradiation range of the laser beam in the donut mode, relatively moving the base material and the laser beam having the donut mode Is characterized by.

The present invention will be described in more detail with reference to FIGS. 1 to 5. As for the donut mode laser beam R according to the present invention, a spot-shaped laser beam 20 having a small diameter is rotated at a high speed on an irradiated surface (arrow). The laser beam 20 'emitted from a laser oscillator (not shown) is reflected by the plane mirror 21 and is directed to the axis of the motor 22 as shown in FIG. 1 (a). It has an energy density m distributed in a donut shape, which is formed by reflecting it toward the processing surface by a concave or parabolic mirror 23 that is attached at an angle and rotates.

FIG. 2 shows a donut mode laser beam R.
(A) is a combination of a convex lens 24, a fixed plane mirror 25, and a plane mirror 26 that rotates at an inclination, and
Is formed by a combination of a fixed concave or parabolic mirror 27 and an inclined and rotating flat mirror,
In addition, for example, in the above (a), innumerable variations are conceivable, for example, the convex lens 24 is inclined and rotated, and the plane mirror 26 is used as a fixed mirror instead.
In both cases, the donut mode laser beam R is formed by rotating the small spot-shaped laser beam 20 at high speed.

When using a laser beam having an energy density of several kW or more, it is essential to cool the rotating mirror 23 and the like. This cooling is specifically shown in FIG.
And it can be implemented by circulating cooling water or oil in the mirror 23 by the mechanism shown in FIG. In more detail, the shaft 31 of the motor 30 is connected to the center shaft 33 via the coupling 32, the tip of the center shaft 33 is connected to the turntable 34, and the support ring 35 is connected to the end of the support ring 35. The mirror 23 is supported on the support ring 35 by a mounting shaft 37 while being inclined.

Around the central axis 33, a medium diameter tube 38 having a double tube structure together with the central axis 33 and a large diameter tube 39 having a triple tube structure together with the central axis 33 and the medium diameter tube 38 are fitted. The space defined by the outer periphery of the central shaft 33 and the inner peripheral surface of the medium diameter pipe 38 serves as a cooling water supply path, and the space defined by the outer peripheral surface of the medium diameter pipe 38 and the inner peripheral surface of the large diameter pipe 39. Serves as a cooling water discharge path. In FIG. 4A, the supply passage and the discharge passage of the cooling water of the triple pipe structure portion are indicated by arrows. Needless to say, the end surface 38a of the medium diameter pipe 38 is covered with respect to the outer circumference of the central shaft 33, and the end surface 39a of the large diameter pipe 39 is covered with respect to the outer circumference of the medium diameter pipe 38, so that cooling water does not leak. It is supposed not to happen.

Reference numeral 40 in FIG. 3 denotes a supply seal portion for supplying cooling water to the cooling water supply passage through a cooling water introduction pipe 41. In the supply seal portion 40, a part of the medium diameter pipe 38 is cut off with a certain width (FIG. 4B).
A seal ring 43 having a distribution groove 42 on the inner peripheral surface and an oil seal structure on both sides thereof is fitted so as to cover the cut portion. On the other hand, similarly, in the discharge seal portion 44, a part of the large-diameter pipe 39 is cut off with a certain width, and the seal ring 45 is fitted so as to cover the cut part. Due to the above oil seal structure, the medium diameter pipe 38 and the large diameter pipe 39 are rotatable inside the seal rings 43 and 45, respectively. In addition, the medium diameter pipe 38 and the large diameter pipe 39
Connection pipes 46 and 47 are attached to the tip end portion of, and are connected to a cooling plate 48 (having a cooling water passage inside) that cools the mirror 23 from the back through the rotating plate 34.

In this apparatus, the rotational force of the motor 30 is transmitted to the central shaft 33 via the shaft 31 and the coupling 32, and further the rotary disk 34, the support rod 36, and the support ring 3 are provided.
The mirror 23 is rotated via 5. The cooling water enters the supply seal portion 40 from the cooling water introduction pipe 41, and the medium diameter pipe 3
Cooling board 4 through the supply path in 8 and connecting pipe 46
8, the water is discharged from the cooling water discharge pipe 49 from the connection pipe 47 through the discharge passage in the large-diameter pipe 39 and the discharge seal portion.

In FIG. 5, the cladding layer 5 is formed on the base material 53.
4 schematically shows how the laser beam 20 'emitted from the laser oscillation device is emitted from the donut beam shaping device 55 (which accommodates the mirrors shown in FIG. 1 or 2) in a donut mode. The laser beam R is emitted downward. The periphery of the laser beam R is covered with a shield cylinder 56, and the shield cylinder 56 receives a clad alloy powder from a powder supply device (not shown) and supplies it to the irradiation range of the laser beam R with a powder supply port 57 and argon. Shield gas inlet 58 for supplying shield gas such as
Is attached. Here, the base material 53 is moved (arrow d), but conversely, the side of the donut beam forming device 55 can be moved.

The present invention can be preferably applied to the case where the base material is an aluminum alloy and the clad alloy powder is a copper alloy, but when the base material is cast iron and the clad alloy powder is a copper alloy. It can also be applied to other combinations of materials. When cladding with a donut-mode laser beam, instead of using the powder feeding method in which the alloy powder for cladding is fed into the donut-shaped irradiation range of the laser beam, it is placed in a predetermined position on the base material in advance. The powder method can also be adopted.

[0022]

The operation of the present invention will be specifically described below with reference to FIG. First, since the diameter of the donut-mode laser beam R in the present invention is larger than that of the original spot-shaped laser beam 20 having a small diameter, the interaction with the base material in the laser processing proceeding direction (arrow e in FIG. 1B). Time gets bigger. In other words, the molten pool formed on the surface to be treated has a wide circular shape corresponding to the diameter of the donut, and the duration of the molten pool at a certain point on the surface to be treated also becomes long. Further, the small-diameter laser beam 20 rotating at a high speed (arrow f) causes a flow of molten metal in the molten pool due to the difference in surface tension (at the moment the laser beam 20 is received, the temperature of the portion rises. The surface tension decreases, and the flow of molten metal toward the high surface tension part occurs, and the stirring of the molten pool becomes active. By increasing the interaction time and activating the stirring in a large molten pool in this way, the chances of gas release are increased and there are few defects such as blowholes and the clad layer has a uniform structure. Is what you can get.

Further, since the energy density at the central portion of the donut mode laser beam R is zero or very low, the irradiation central portion is not excessively heated, and for example, the base material of aluminum alloy is used. Even when a cladding layer of a copper alloy is formed on the aluminum alloy, the aluminum alloy does not melt excessively.

This effect can be obtained even when the laser beam R'in the donut mode is directly emitted from the laser oscillator 60 itself as shown in FIG. However, the donut-mode laser beam is emitted by the laser oscillator 6
When oscillating directly from 0, a clean donut mode as shown in FIG. 15 (b) is not always obtained. For example, when dust or the like adheres to the concave mirror 61 inside the oscillator 60, this part generates heat and the mirror There is a possibility that the distortion and the left-right balance of the modes are lost as shown in FIG. 15C, and the penetration of the aluminum alloy base material is locally increased. On the other hand, in the present invention, since the narrowed beam 20 that has been narrowed is mechanically rotated in a circular shape at a constant speed, a very clean donut mode R can be formed, and a device such as when directly oscillating from the laser oscillator 60 can be formed. Very stable laser cladding is possible without any fluctuation. When using the donut mode R ′ emitted from the laser oscillator 60 itself,
There is also a drawback that the stirring action by the laser beam cannot be sufficiently obtained.

Further, in the present invention, since a large circular molten pool corresponding to the donut mode laser beam R is generated and the powder is fed toward the center thereof,
Cladding can be done in all directions on the same plane. From this, for example, the complicated table mechanism described with reference to FIG. 14 is not required, the investment initial cost is reduced, and extremely reliable production is possible. For example, when cladding the valve seat portion 12 of the engine cylinder head shown in FIG. 6 (the same as that shown in FIG. 14), the cylinder head 11 is rotated around the shaft 65 so that the valve seat portion 12 is rotated. Among them, for example, the exhaust valve seat portion (front side in the drawing) is set so as to be horizontally oriented, and the head of the donut beam forming device 55 is moved in a circular shape without moving the cylinder head 11 to enable cladding. Of course,
The table may be moved relatively. Therefore, the table device is simplified and very reliable production is possible.

Further, in the present invention, since a large circular molten pool corresponding to the laser beam R in the donut mode is generated, it is possible to directly drive all the supplied alloy powder into the molten pool, and the above-mentioned machining groove is formed. Even if the seat surface 12a is inclined (θ = 45 °) with respect to the horizontal plane as shown in FIG. 6B, the cladding can be performed.
Therefore, when performing laser cladding on the valve seat portion 12 of the engine cylinder head 11, the seat portion pre-machining groove is not required, and the running cost can be reduced.
On the other hand, in the case of the conventional one-way oscillation mode laser beam, since the molten pool has an elongated linear shape, it is impossible to directly implant all the alloy powder to be powdered into the molten pool.

In addition, in the present invention, the principle is based on the oscillation method such that the high-speed moving part of the device for shaping the donut mode only rotates the concave or parabolic mirror 23 (FIG. 1) by a motor. Since it is simpler than the other devices, the device can be highly reliable and highly stable.

In order to effectively bring out the action of the present invention described above, it is desirable to carry out the cladding under the conditions within the following range. That is, the beam diameter of the spot-shaped laser beam 20 is 1 mm to 10 mmφ, its energy density is 50 W / mm ^{2 to} 10000 W / mm ² , its rotational speed is 3000 rpm or more, and the beam outer diameter of the shaped donut mode laser beam R is 2 to 30 mmφ.
Cladding processing speed 50 mm / min ~ 240
It is 0 mm / min.

The above condition is that the beam diameter is 1 m.
If it is less than mφ, the energy density will be too high and the base material will be melted in a large amount. On the other hand, since a high-power laser having an effective beam diameter of more than 10 mmφ has not been developed at present, the above condition is that the energy density is 50 W / If it is less than mm ² , cladding cannot be performed, and if it exceeds 10,000 W / mm ² , the base material melts in a large amount.
If the beam diameter in the donut mode is less than 2 mmφ, the energy density will be too high and the base material will be melted in a large amount, and the beam diameter will be 30 mmφ. Since a high-power laser that is effective beyond the
The above conditions are selected within the above ranges because the base material melts in a large amount at less than 50 mm / min, and insufficient melting or cracking occurs at more than 2400 mm / min.

[0030]

EXAMPLES Specific examples of the present invention will be described below together with comparative examples.

An AC2B equivalent aluminum alloy (Cu2.0) was formed by using a laser beam in a donut mode (example) and a laser beam in a one-way oscillation mode (comparative example).
~ 1.0%, Si5.0-7.0%, Mg≤0.5%,
Zn ≦ 1.0%, Fe ≦ 1.0%, Mn ≦ 0.5%, N
i ≦ 0.35%, Pb ≦ 0.20%, Sn ≦ 0.10
%, Cr ≦ 0.20%, Ti ≦ 0.20%) on a base material made of copper alloy (Cu-10% Sn-2% Ni-0.5).
% Si-0.3% P-0.3% B) was laser-clad. In the embodiment, a 2 mmφ spot-shaped laser beam is rotated in a circular shape to form a donut mode laser beam having an outer diameter of 6 mmφ and an inner diameter of 2 mmφ, as shown in FIG. The spot-shaped laser beam of 4 mm is oscillated by 4 mm to form a unidirectional oscillation mode laser beam having a width of 2 mm in the laser processing direction (arrow g) and a vertical width of 6 mm as shown in FIG. 7B. did. For other conditions, the laser output is 3000 W and the processing speed is 800 mm / min (=
13.3 mm / s) and the amount of powdered powder was 0.89 gr / s, and the conditions were the same for both the examples and comparative examples.

8 and 9 show cross-sectional structure micrographs of the cladding layers of Examples and Comparative Examples, respectively. Figure 10
The results of examining the maximum blowhole diameter (a) and the average number of cross-sectional blowholes (b) in this clad layer are shown. The maximum blowhole diameter is smaller in the clad layer of the example,
It can be seen that the number of blow holes is also small. FIG. 11 shows the result of examining the variation in hardness of this clad layer, and the variation in hardness is smaller in the clad layer of the example.

Such a result is obtained when the interaction time (beam width (traveling direction) (mm) / laser processing progressing speed (mm / s)) of the embodiment is 0.45 seconds.
The interaction time of the comparative example was 0.15 seconds, which was three times longer, and it is considered that the main reason is that the molten pool was sufficiently stirred. The irradiation area of the donut mode of the example is wider than the irradiation area of the unidirectional oscillation mode of the comparative example (28.26 mm ² :
11.14 mm ² ) On the other hand, since both laser outputs are the same, the energy density on the irradiation surface is low in the embodiment, and excessive melting of the base material is prevented even if the interaction time is long.

In FIG. 12, the same tests as those of the above-mentioned Examples and Comparative Examples were conducted except that the laser output was changed, and a donut mode laser beam (Example) and a unidirectional oscillation mode laser beam (Comparative Example) were used. 2) is the result of determining the allowable range of the interaction time, that is, the range in which cladding can be performed and a large amount of the base material does not melt. As shown here, even with the same energy density, the embodiment has a wider allowable range of the interaction time, and the stirring time can be longer. The reason for such a result is that in the embodiment, since the beam center is extracted in a donut shape, the melt of the base material at the beam center can be suppressed (in the case of an ordinary circular beam, the beam center is generally easy to melt). It is conceivable that the uniformity of the beam is always maintained due to the high speed rotation.

[0035]

According to the present invention, it is possible to obtain a clad layer having few defects such as blowholes and excellent in uniformity of structure. Further, it is easy to feed powder to the laser irradiation area during the cladding, does not require complicated table equipment or groove processing of the clad portion, and the stability of the equipment for performing the cladding is high.

[Brief description of drawings]

FIG. 1 is a diagram (a) illustrating a method for shaping a donut mode laser beam and a diagram (b) illustrating an energy density distribution of the laser beam.

FIG. 2 is a diagram illustrating another method of shaping a donut mode laser beam.

FIG. 3 is a schematic perspective view of a mirror rotation device having a cooling mechanism.

FIG. 4 is a cross-sectional perspective view (a) of a triple tube structure portion of the mirror rotation device and a perspective view illustrating a structure of a supply seal portion.

FIG. 5 is a schematic side view illustrating laser cladding of the present invention.

6A and 6B are a schematic diagram (a) and a cross-sectional view (b) for explaining a state in which the laser cladding of the present invention is applied to a valve seat portion of an engine cylinder head.

FIG. 7 is a diagram showing a laser beam in a donut mode (a) and a unidirectional oscillation mode (b) used in Examples.

FIG. 8 is a cross-sectional micrograph (metal micrograph) of a cladding layer of an example.

FIG. 9 is a cross-sectional micrograph (metal micrograph) of a cladding layer of a comparative example.

FIG. 10 is a diagram showing the examination results of the maximum number of blow holes (a) and the average number of cross-section blow holes (b) in the cladding layer.

FIG. 11 is a result of investigation of variations in hardness of the clad layer.

FIG. 12 is a diagram showing a relationship between energy density of a laser beam and interaction time.

13A is a diagram illustrating a method of shaping a laser beam in a one-way oscillation mode, and FIG. 13B is a diagram illustrating an energy density distribution of the laser beam.

14A and 14B are a schematic view (a) and a cross-sectional view (b) for explaining a state in which laser cladding in a one-way oscillation mode is applied to a valve seat portion of an engine cylinder head.

FIG. 15 is a schematic side view of an oscillator that oscillates a donut-mode laser beam (a), a normal laser beam (b), and an unbalanced laser beam (c).

[Explanation of symbols]

 20 Spot-shaped laser beam with small diameter R Donut-mode laser beam

Claims (4)

[Claims] 1. A doughnut-shaped laser beam irradiation of the alloy powder for cladding while irradiating a predetermined position on the base material with a laser beam having a donut-shaped irradiation mode formed by rotating a spot-shaped laser beam. A laser cladding method, characterized in that the laser beam having the doughnut-shaped irradiation mode is moved relative to the base material while being supplied into the range. 2. The laser cladding method according to claim 1, wherein the base material is an aluminum alloy and the clad alloy powder is a copper alloy. 3. The laser cladding method according to claim 1, wherein the base material is cast iron and the alloy powder for clad is a copper alloy. 4. The laser cladding method according to claim 1, wherein the alloy powder for cladding is placed at a predetermined position on the base material in advance, instead of being supplied into the irradiation range of the laser beam.