JP5228224B2 - Laser overlaying method - Google Patents

Description

  The present invention relates to a laser build-up method in which a metal powder is supplied to a valve seat of a cylinder head and melted by irradiating the metal powder with a laser to form a build-up layer.

Since the valve seat of the cylinder head for an internal combustion engine is a portion that repeatedly contacts the valve, the valve seat is subjected to processing for improving wear resistance. As this type of processing, there is known laser overlay processing (also referred to as laser cladding) in which the laser irradiation position is moved in an annular shape while the metal powder is melted by irradiating a laser to perform overlay.
It is known that in this laser overlay processing, defects such as unwelded portions and voids (such as blow holes) are likely to occur in an overlap portion formed by overlapping the start and end portions of the overlay. Therefore, conventionally, at the start of the build-up, the supply amount of the metal powder is gradually increased and the output of the laser is increased in accordance with the supply amount of the metal powder, thereby forming a starting end portion having a moderately increased thickness. The technology to do is known. According to this technique, since the thickness of the starting end portion is thinner than other portions, the occurrence of the defect in the overlapping portion between the starting end portion and the terminating end portion can be suppressed (for example, see Patent Document 1). .
JP 2005-299598 A

However, even in the prior art, the above-described defects cannot still be eliminated, and further improvement is required in order to improve the yield of the valve seat.
The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a laser cladding method capable of further suppressing defects generated in the overlay layer when overlaying the valve seat of the cylinder head. .

  In order to achieve the above-described object, the present invention provides a method for forming a built-up layer at a laser irradiation position by irradiating a laser while supplying a metal powder to a valve seat of a cylinder head, and setting the laser irradiation position to the valve seat. In the laser overlaying method in which the metal powder is moved in an annular shape along the line, the laser output is increased according to the supply amount of the metal powder while gradually increasing the supply amount of the metal powder at the start of the buildup. To form a start portion of the build-up, to maintain the supply amount of the metal powder and the output of the laser constant, to form a normal portion of the build-up, and to make the output of the laser constant from the front of the start end portion The supply amount of the metal powder is reduced to a predetermined amount as it is, and a terminal end portion of the build-up is formed and overlapped with the start end portion.

When overlaying by moving the laser irradiation position in an annular shape, if the laser irradiation position comes before the start end, residual powder accumulated upstream of the laser irradiation position during the start end and normal part formation will start. It is pushed by the part and enters the laser irradiation position, and the amount of powder at this laser irradiation position increases.
According to the present invention, since the metal powder supply amount is decreased from the front of the start end to start the formation of the end portion, fluctuations in the amount of powder at the laser irradiation position are suppressed, and defects at the end portion are generated. It can be suppressed.

In the present invention, when the terminal portion is formed, the supply amount of the metal powder may be gradually decreased to the predetermined amount in accordance with the inclination formed at the starting end portion before overlapping with the starting end portion. .
That is, the amount of residual powder that is pushed by the start end and enters the laser irradiation position gradually increases according to the inclination of the start end, and by reducing the supply amount of metal powder along with this increase, Generation | occurrence | production can further be suppressed.

Moreover, in this invention, a groove part may be formed along the seat surface of the said valve seat, and the said build-up layer may be formed in this groove part.
By forming the build-up layer in the groove, the wear resistance of the valve seat can be further improved. Moreover, although metal powder tends to accumulate in the groove portion when building up, as described above, the amount of metal powder supplied is reduced in accordance with the amount of residual powder, thereby suppressing the occurrence of defects. Thereby, the further suppression effect of a defect is acquired with the improvement of abrasion resistance.

Further, in the present invention, when the laser irradiation position is moved in an annular shape around the center of the valve seat, even if the formation of the end portion is started at a timing moved from about 270 degrees to about 315 degrees from the start end portion. good.
In the valve seat build-up processing, the residual powder starts to enter the laser irradiation position at the timing of moving about 270 to 315 degrees from the start end, and from this point on, supply of metal powder as described above By reducing the amount and starting the formation of the terminal portion, it is possible to satisfactorily build up the occurrence of defects.

According to the present invention, since the supply amount of the metal powder is decreased from the front of the start end portion to start the formation of the end portion, even when the residual powder accumulated on the upstream side of the laser irradiation position enters the laser irradiation position. The fluctuation of the amount of powder at the laser irradiation position is suppressed, and the occurrence of defects at the terminal portion is suppressed.
In addition, when forming the terminal portion, the metal powder supply amount is gradually reduced to the predetermined amount in accordance with the inclination formed at the starting end portion before being overlapped with the starting end portion. Accordingly, the supply amount of the metal powder can be decreased in accordance with the residual powder that gradually increases, and the generation of defects can be further suppressed.
Further, by forming a groove portion along the seat surface of the valve seat and forming the build-up layer in the groove portion, the wear resistance of the valve seat can be further improved. Furthermore, since metal powder is reduced so as to suppress fluctuations in the amount of powder at the laser irradiation position, the occurrence of defects is suppressed.
In addition, when the laser irradiation position is moved in an annular shape around the center of the valve seat, the formation of the end portion is started at a timing moved from about 270 degrees to about 315 degrees from the start end portion, so that the occurrence of defects is good. It is possible to build up the valve seat that is kept to a minimum.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a view showing a laser clad apparatus 10 used in the laser cladding method of the valve seat 16 according to the present embodiment, and FIG. 2 is a view showing a cylinder head 12.
The laser cladding apparatus 10 supplies a laser beam of a semiconductor laser while supplying copper alloy powder (metal powder) 18 to a valve seat 16 around a supply / exhaust valve hole 14 (see FIG. 2) in a cylinder head 12 as a workpiece. An apparatus that irradiates light 20 to melt and solidify the copper alloy powder 18 to form a built-up layer at the laser irradiation position P, and build up the material while moving the laser irradiation position P (see FIG. 2) in an annular shape. is there.

  The cylinder head 12 is for a four-cylinder engine, and as shown in FIG. 2, four valve seats 16 are provided for each cylinder. On the seat surface 16 </ b> A of the valve seat 16, a U-shaped groove portion 17 for building up is provided along the periphery. The cylinder head 12 is made of an aluminum alloy and is reduced in weight. Further, the valve seat 16 of the cylinder head 12 repeatedly contacts the valve, the Hertz surface pressure of the seat surface 16A is a high load, and this high load is continuously applied. By increasing the thickness of the sheet surface 16A, the wear resistance and heat resistance are improved. The copper alloy powder 18 is an alloy powder based on copper and nickel, and is an atomized powder.

  The laser cladding apparatus 10 includes a table 22 that moves the cylinder head 12 in the horizontal biaxial direction and positions the cylinder head 12 around a predetermined valve seat 16, a table controller 24 that controls the table 22, and a valve seat. 16 includes a feed mechanism 26 that supplies the copper alloy powder 18 to 16 and a feed controller 28 that controls the feed mechanism 26. The copper alloy powder 18 is put into the storage portion 26 a of the feed mechanism 26, and the copper alloy powder 18 can be supplied to a part of the periphery of the valve seat 16 through the nozzle 29 under the action of the feed controller 28. The supply amount S of the copper alloy powder 18 can be adjusted by a feed controller 28.

  The laser cladding apparatus 10 also includes a laser oscillation mechanism unit 30 that irradiates the laser light 20 of the semiconductor laser onto the valve seat 16, a laser controller 32 that controls the laser oscillation mechanism unit 30, and an enlarged photograph of the valve seat 16. And a monitor 36 that displays an image captured by the camera 34. The camera 34 is, for example, a camera having a CCD type or MOS type imaging unit. Further, the laser cladding apparatus 10 includes a main controller 40 that integrally controls the table controller 24, the feed controller 28, the laser controller 32, and the camera 34.

The laser oscillation mechanism section 30 is a device that has a laser oscillation section of, for example, a modular type, GaaAlbAs type (a and b are solid phase ratios), and generates laser light 20 from a semiconductor PN junction. The wavelength of 20 is set to be a predetermined value in the range of 800 to 950 [nm] depending on the semiconductor component. Further, the laser oscillation mechanism unit 30 can adjust the output W of the laser beam 20 under the action of the laser controller 32. Specifically, the laser oscillation unit 30 can change the control voltage applied to the PN junction by changing the control voltage. The output W is adjusted. The output W of the laser light 20 changes instantaneously by changing the applied voltage, and there is no response delay or overshoot when the output W changes, and the output W has a very high response to the applied voltage. Therefore, the output W of the laser beam 20 can be changed gradually and can be changed stepwise.
Further, in the wavelength range of 800 to 950 [nm] of the laser beam 20, energy is easily absorbed by the copper alloy powder 18 and the semiconductor alloy laser is 1.2 to 2. A low output of about 0 [kW] is sufficient, and the thermal effect on the cylinder head 12 can be reduced. Moreover, the molten pool by the copper alloy powder 18 becomes larger, and it is possible to increase the thickness of the built-up layer. For example, a thickness of 5 [mm] can be formed.

  The laser oscillation mechanism unit 30 can spray an inert gas (such as argon gas) as a shielding gas against the valve seat 16. The laser oscillation mechanism 30 can be adjusted in height with respect to the table 22.

Next, a method for overlaying the valve seat 16 using the laser clad apparatus 10 configured as described above will be described.
First, the cylinder head 12 is mounted on the table 22 according to a predetermined procedure, and horizontal positioning is performed so that a predetermined valve seat 16 is disposed at the rotation center position under the action of the table controller 24.
Next, as shown in FIG. 2, the copper alloy powder 18 is supplied from a nozzle 29 of the feed mechanism 26 to a part of the periphery of the valve seat 16, and the laser light 20 is irradiated from the laser oscillation mechanism unit 30, so that the table 22 Rotate. The table 22, the feed mechanism 26, and the laser oscillation mechanism unit 30 are controlled by the table controller 24, the feed controller 28, and the laser controller 32, and are synchronized with each other under the action of the main controller 40 and simultaneously start operating. Also, the ejection of shield gas starts simultaneously.

  At this time, while the rotation speed of the table 22 is maintained at a constant speed according to the size of the valve seat 16, the supply amount S of the copper alloy powder 18 and the output W of the laser light 20 are as shown in FIG. The valve seat 16 is variably controlled based on the rotation angle [deg] of the valve seat 16 as the table 22 rotates.

  That is, at the start of the build-up, the output W of the laser beam 20 is gradually increased to the optimum value Wa according to the supply amount S of the copper alloy powder 18 while gradually increasing the supply amount S of the copper alloy powder 18 to the optimum value Sa. The build-up start end 50 is formed ((I) start end forming step)). In this way, the build-up is performed while gradually increasing the supply amount S of the copper alloy powder 18, thereby forming the start end portion 50 in which the thickness of the build-up layer gradually increases as shown in FIG. 4. For this reason, when an end portion 52 described later overlaps, the occurrence of defects in the overlap portion 54 is suppressed.

By the way, generally, when the thickness of the diffusion layer of aluminum and copper is 50 [μm] or less, blowholes are generated due to non-welding, and when it is 400 [μm] or more, alloying cracks between aluminum and copper are generated. It is known to be easy to do. In this laser cladding method, since the output W is adjusted in accordance with the supply amount S, the amount of melting of the cylinder head 12 as the base material becomes an appropriate amount, and the thickness of the diffusion layer is 50 to 400 [μm]. It is said. Thereby, alloying cracking and unwelding can be prevented, and as a result, generation of defects can be prevented.
As a method for controlling the output W of the laser beam 20, for example, the supply amount S for each predetermined time may be measured using a timer, and the output W may be controlled according to the supply amount S.

  Next, the normal portion 51 of the build-up is formed while maintaining the supply amount S of the copper alloy powder 18 and the output W of the laser beam 20 at the optimum values Sa and Wa, respectively ((II) normal portion forming step). Thereby, as shown in FIG. 4, the normal part 51 which has the build-up layer of substantially constant thickness is formed. The optimum values Sa and Wa are set to values that allow the amount of melting of the cylinder head 12 to be an appropriate amount when a build-up layer having a normal thickness is formed. Occurrence is also suppressed.

  Thereafter, the terminal portion 52 that merges and overlaps the starting end portion 50 is formed ((III) terminal portion forming step). This end portion forming step is started at a timing before the laser irradiation position P moved in an annular shape reaches the start end portion 50 (before the rotation angle 360 [deg]). Further, in the terminal portion forming step, unlike the normal portion forming step, the supply amount S of the copper alloy powder 18 is decreased to a predetermined amount Sb (<Sa) while the output W of the laser beam 20 is kept constant at the optimum value Wa. Thus, the end portion 42 is formed.

  More specifically, as a result of observing the laser irradiation position P with a high-speed camera, the inventors have observed that the copper alloy powder 18 injected from the nozzle 29 in the laser cladding is a laser as shown in FIG. It was found that the copper alloy powder 18 remaining in the zone K1 on the upstream side of the workpiece rotation direction with respect to the irradiation position P (the molten pool 60) is scattered in the zone K2 on the surface of the starting end portion 50. .

That is, while the starting end portion 50 and the normal portion 51 are formed, residual powder accumulates in the zone K1, but when the laser irradiation position P moves in an annular shape and comes to the front of the initial starting end portion 50, FIG. As shown in (III) terminal portion forming step, residual powder in the zone K1 is pushed by the start end portion 50 and enters the laser irradiation position P.
As a result, at the laser irradiation position P, in addition to the supply amount Sa of the copper alloy powder 18, the amount of residual powder increases, so the balance between the amount of copper alloy powder 18 and the output W of the laser light 20 is lost. For this reason, if no countermeasure is taken, as shown in FIG. 6, the build-up layer applied to the start end 50 from the position before the laser irradiation position P reaches the start end 50 (rotation angle is about −90 [deg]). Defects occur intensively.
In particular, in this laser embedding method, since the laser embedding is performed along the U-shaped groove portion 17 for embedding the valve seat 16, residual powder tends to accumulate in the U-shaped groove portion 17.

  Therefore, in this laser build-up method, the terminal portion forming process is started from the timing when the residual powder in the zone K1 is pushed by the starting end portion 50 and starts to enter the laser irradiation position P. In this terminal portion forming step, the copper alloy powder 18 Is gradually reduced to a predetermined amount Sb. As a result, fluctuations in the amount of the copper alloy powder 18 at the laser irradiation position P are suppressed, so that the balance between the amount of the copper alloy powder 18 and the output W of the laser beam 20 is maintained, and defects in the overlay layer are generated. Will be suppressed.

In this terminal portion forming step, the supply amount S of the copper alloy powder 18 is reduced from the start to a predetermined amount Sb with a reduction rate α corresponding to the inclination formed in the starting end portion 50.
More specifically, since the inclined surface of the start end portion 50 pushes the residual powder in the zone K1 into the laser irradiation position P, the temporal change in the amount of pushing changes according to the slackness of the inclined surface. That is, as the inclined surface of the start end portion 50 becomes gentler, the amount of the residual powder pushed into the laser irradiation position P gradually increases. Thus, by gradually reducing the supply amount S of the copper alloy powder 18 in accordance with the temporal change in the amount of indentation, fluctuations in the amount of the copper alloy powder 18 at the laser irradiation position P are suppressed, and defects are detected. Is further suppressed.

  Further, in this laser overlaying method, the supply amount S of the copper alloy powder 18 in the start end portion forming step is such that the angle θ (see FIG. 5) of the inclined surface of the start end portion 50 is about 30 to 40 degrees. Is set. By forming the inclined surface of this angle at the start end portion 50, when the start end portion 50 pushes the residual powder into the laser irradiation position P, the residual powder that wraps around the inclined surface of the start end portion 50 also increases. Thereby, the temporal change of the residual powder pushed into the laser irradiation position P can be made more gradual with respect to the angle of the inclined surface, and the occurrence of defects at the terminal portion 52 can be suppressed more satisfactorily. Further, since the angle of the inclined surface can be increased to some extent, it is not necessary to minutely change the supply amount S of the copper alloy powder 18 in the starting end forming step, and the starting end 50 can be easily formed.

Here, in the zone K2 (refer to FIG. 5) on the inclined surface of the starting end 50, in addition to the above wraparound of the residual powder, as a result of observation of the laser irradiation position P, knowledge that red hot powder is scattered is obtained. ing. In the terminal portion forming step, the supply of the copper alloy powder 18 from the nozzle 29 is continued even after the laser irradiation position P reaches the starting end portion 50, and the overlap portion 54 is formed on the starting end portion 50. In the zone K2 on the inclined surface of the start end 50, the amount of powder is increased. For this reason, if no countermeasures are taken, a relatively large number of defects occur in the overlap portion 54 as shown in FIG.
Therefore, in this laser build-up method, the overlap portion 54 is formed in a state where the supply amount S of the copper alloy powder 18 is reduced to a predetermined amount Sb even after the laser irradiation position P overlaps the start end portion 50 ( (III-A) Overlap portion forming step). As a result, the fluctuation of the amount of the copper alloy powder 18 in the zone K2 is suppressed, so that the occurrence of defects is satisfactorily suppressed.

  The predetermined value Sb of the supply amount S of the copper alloy powder 18 is determined according to the amount of residual powder deposited in the zone K1, more specifically, the maximum value of residual powder pushed into the laser irradiation position P. Specifically, it has been found that this maximum value is substantially constant in the laser build-up of the valve seat 16, and the predetermined value Sb is about 20-30 with respect to the optimum value Sa of the supply amount S. Defects can be satisfactorily suppressed by reducing the content in the range of%. That is, if the predetermined value Sb is decreased by more than about 30% from the optimum value Sa, the output of the laser beam 20 becomes relatively high and cracks are generated in the built-up layer. If the amount is reduced to less than 20%, the amount of powder at the laser irradiation position P is relatively increased, and a defect is generated in the built-up layer.

  Further, in the laser build-up of the valve seat 16, the residual powder in the zone K <b> 1 reaches the start end portion 50 at a timing when the laser irradiation position P moves approximately 270 to 315 degrees from the start of the formation of the start end portion 50 with the rotation of the valve seat 16. The knowledge that it starts to be pushed is obtained. Therefore, by starting the terminal portion forming process at such timing, the supply amount S of the copper alloy powder 18 can be reduced at an appropriate timing at which the residual powder starts to be pushed in at the laser irradiation position P, thereby suppressing defects. An end portion 52 can be formed.

As shown in FIG. 3, the build-up in the overlap portion forming step is continued to a position where the build-up layer at the start end portion 50 has a predetermined constant thickness. Thereafter, the supply of the copper alloy powder 18 and the laser beam 20 are stopped, and the build-up on the valve seat 16 is finished. At the end, the build-up may be terminated by gradually decreasing the supply amount S and the output W so that the build-up layer in the overlap portion 54 of the end portion 52 becomes gradually thinner.
Thereafter, the same build-up process is sequentially performed on the other valve seats 16 that are not subjected to the build-up process.

  As described above, according to the laser cladding method of the valve seat 16 according to the present embodiment, the terminal portion forming step is started from the front of the starting end portion 50. In this terminal portion forming step, the copper alloy powder 18 The terminal portion 52 is formed by reducing the supply amount S. Thereby, even when the residual powder accumulated in the upstream zone K1 of the laser irradiation position P is pushed by the start end portion 50 and enters the laser irradiation position P, the fluctuation of the powder amount at the laser irradiation position P is suppressed. Therefore, the occurrence of defects in the terminal portion 52 is suppressed. In addition, when the starting end portion 50 pushes in the residual powder, the residual powder wraps around the surface of the starting end portion 50, thereby increasing the amount of powder on the inclined surface of the starting end portion 50, but supplying the copper alloy powder 18. Since the overlap portion 54 with the starting end portion 50 is formed while the amount S is reduced, the occurrence of defects in the overlap portion 54 can be well suppressed.

Further, in the terminal portion forming step, the supply amount S of the copper alloy powder 18 is reduced to a predetermined amount Sb at a reduction rate α corresponding to the inclination formed at the start end portion 50 before the laser irradiation position P overlaps the start end portion 50. It is gradually decreasing.
As a result, the supply amount S of the copper alloy powder 18 is reduced in accordance with the pushing amount of the residual powder that gradually increases at the laser irradiation position P according to the inclination of the starting end portion 50, and the generation of defects is further suppressed. Thus, the end portion 52 can be formed.

  In addition, a U-shaped groove portion 17 is formed along the seat surface 16 </ b> A of the valve seat 16, and a built-up layer is formed in the U-shaped groove portion 17. Thus, by forming a build-up layer in the U-shaped groove part 17, the wear resistance of the valve seat 16 is further improved. Further, although the copper alloy powder 18 is likely to be accumulated in the U-shaped groove portion 17 when building up, as described above, the supply amount S of the copper alloy powder 18 is reduced in accordance with the amount of residual powder as described above. Therefore, the occurrence of defects can be suppressed satisfactorily. As a result, the wear resistance is improved and a good defect suppression effect is obtained.

  In addition, the end portion forming process is started at a timing when the laser irradiation position P is moved from the start end portion 50 in an annular shape by about 270 degrees to about 315 degrees. According to this, in the laser build-up of the valve seat 16, the supply amount S of the copper alloy powder 18 can be reduced at an appropriate timing when the residual powder starts to be pushed in at the laser irradiation position P, and defects are suppressed. A terminal portion 52 can be formed.

  It should be noted that the above-described embodiment is merely an aspect of the present invention and can be arbitrarily modified and applied without departing from the gist of the present invention.

It is a functional block diagram of the laser clad apparatus concerning the embodiment of the present invention. It is a schematic diagram which shows the process of building up, irradiating a valve seat with a semiconductor laser. It is a chart of the output of a semiconductor laser and the supply amount of copper alloy powder. It is a schematic diagram which shows each process of a start part formation process, a normal part formation process, and a termination | terminus part formation process. It is a schematic diagram which expands and shows a laser irradiation position. It is a figure which shows the tendency of the defect distribution which generate | occur | produces in a buildup layer.

DESCRIPTION OF SYMBOLS 10 Laser clad apparatus 12 Cylinder head 14 Supply / exhaust valve hole 16 Valve seat 16A Sheet surface 17 U-shaped groove part 18 Copper alloy powder (metal powder)
20 Laser light 29 Nozzle 50 Start end portion 51 Normal portion 52 End portion 54 Overlap portion 60 Weld pool P Laser irradiation position Sb Predetermined values K1, K2 zones

Claims (4)

By irradiating a laser while supplying metal powder to the valve seat of the cylinder head, a build-up layer is formed at the laser irradiation position, and the laser irradiation position is moved annularly along the valve seat to build up In the laser cladding method,
At the start of the build-up, gradually increasing the supply amount of the metal powder while increasing the laser output according to the supply amount of the metal powder to form the start end of the build-up,
The supply amount of the metal powder and the output of the laser are kept constant to form a normal part of the overlay,
A laser cladding method comprising: forming a terminal end portion of a build-up by overlapping a predetermined amount by reducing the supply amount of the metal powder to a predetermined amount while keeping the output of the laser constant from before the start end portion. .   The supply amount of the metal powder is gradually decreased to the predetermined amount according to the inclination formed at the start end before the end portion is formed, before being overlapped with the start end. The laser cladding method according to 1.   The laser cladding method according to claim 1 or 2, wherein a groove is formed along a seat surface of the valve seat, and the build-up layer is formed in the groove.   When the laser irradiation position is moved in an annular shape around the center of the valve seat, the formation of the end portion is started at a timing moved from the start end portion by about 270 to 315 degrees. 4. The laser cladding method according to any one of 3 above.

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