JP2010201480A - Laser building-up welding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser building-up welding method, by which defects generated in a built-up weld layer of a valve seat of a cylinder head is further inhibited. <P>SOLUTION: A laser building-up welding method is executed by annularly moving a laser irradiation position P along a valve seat 16, while forming a built-up weld layer on the laser irradiation position P by irradiating the valve seat 16 of a cylinder head 12 with a laser beam 20 while supplying a copper alloy powder 18. Further, the laser building-up welding method is executed as follows: a start end part 50 of building-up welding is formed by increasing an output W of the laser beam 20 according to a supply amount S of the copper alloy powder 18 while gradually increasing the supply amount S of the copper alloy powder 18 at the start of the building-up welding; an ordinary part 51 of building-up welding is formed while keeping constant the supply amount S of the copper alloy powder 18 and the output W of the laser beam 20; a terminal end part 52 of building-up welding is formed by increasing the output W of the laser beam 20 to a predetermined output Wb while keeping constant the supply amount S of the copper alloy powder 18, from the position before the start end part 50; and the terminal end part 52 is overlapped on the start end part 50. <P>COPYRIGHT: (C)2010,JPO&INPIT

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 starting end portion of the buildup, to maintain the supply amount of the metal powder and the output of the laser constant, to form a normal portion of the buildup, and to supply the supply amount of the metal powder from before the start end portion The laser output is increased to a predetermined amount while maintaining a constant value, 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 output of the laser is increased from the front of the start end portion to start the formation of the end portion, the laser output is also increased in accordance with the increase in the amount of powder at the laser irradiation position. The occurrence of defects in the is suppressed.

In the present invention, when the terminal portion is formed, the output of the laser may be gradually increased to the predetermined amount in accordance with the inclination formed at the starting end portion before being overlapped with the starting end portion.
That is, the amount of residual powder that is pushed into the laser irradiation position by being pushed by the start end portion gradually increases with the inclination of the start end portion, so that the generation of defects is increased by increasing the laser output in accordance with this increase. Further suppression can be achieved.

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 generation of defects is suppressed by increasing the laser output in accordance with the amount of residual powder. 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 valve seating processing, residual powder starts to enter the laser irradiation position at the timing of approximately 270 to 315 degrees of movement from the starting end, and the laser output increases from this point as described above. Then, by starting the formation of the terminal portion, it is possible to satisfactorily build up the occurrence of defects.

According to the present invention, by increasing the laser output from the front of the start end and starting the formation of the end portion, the residual powder accumulated on the upstream side of the laser irradiation position enters the laser irradiation position and the amount of powder increases. Even in this case, the occurrence of defects at the terminal portion can be suppressed.
In addition, when the terminal portion is formed, the output of the laser is gradually increased to the predetermined amount according to the inclination formed at the starting end portion before being overlapped with the starting end portion, so that it gradually increases according to the inclination of the starting end portion. The output of the laser is increased in accordance with the amount of powder at the laser irradiation position that 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 the laser output is increased in accordance with the amount of residual powder, 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, whereby 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 Wb are set to values that make the amount of melting of the cylinder head 12 an appropriate amount when forming a build-up layer with a normal thickness. 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]). Also, in the terminal portion forming step, unlike the normal portion forming step, the output W of the laser beam 20 is increased to a predetermined amount Wb (> Wa) while the supply amount S of the copper alloy powder 18 is kept constant at the optimum value Sa. Thus, the end portion 52 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 cladding method, the terminal portion forming process is started from the timing at which the residual powder in the zone K1 starts to enter the laser irradiation position P by being pushed by the starting end portion 50. In this terminal portion forming step, the laser beam 20 The output W is gradually increased to a predetermined amount Wb. As a result, the output W of the laser beam 20 increases with the increase in the amount of the copper alloy powder 18 at the laser irradiation position P, so that the balance between the amount of the copper alloy powder 18 and the output W of the laser beam 20 is maintained. Generation | occurrence | production of the defect of a buildup layer will be suppressed.

In this termination portion forming step, the output W of the laser beam 20 is increased from the start to a predetermined amount Wb at an increase rate α corresponding to the inclination formed at the start 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. And generation | occurrence | production of a defect is further suppressed by the output W of the laser beam 20 being raised gradually according to the temporal change of the pushing amount of the residual powder to the laser irradiation position P.

  In this laser build-up method, the supply amount S of the copper alloy powder 18 in the start end portion forming step is set so that the angle θ (see FIG. 5) of the inclined surface of the start end portion 50 is about 30 to 40 degrees. ing. 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 amount of the copper alloy powder 18 at the laser irradiation position P can be made gentler with respect to the angle of the inclined surface, and the occurrence of defects at the terminal portion 52 can be suppressed more satisfactorily. it can. Further, since the angle of the inclined surface can be increased to some extent, it is not necessary to slightly change the supply amount S of the copper alloy powder 18 in the starting end portion forming step, and the starting end portion 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 overlaying method, the overlap portion 54 is formed with the output W of the laser light 20 increased to a predetermined amount Wb even after the laser irradiation position P overlaps the start end portion 50 ((III- A) Overlap portion forming step). As a result, even if the amount of powder in the zone K2 increases, the output W of the laser light 20 is increased, so that the occurrence of defects is satisfactorily suppressed.

  The predetermined value Wb of the output W is determined in accordance with the accumulated amount of residual powder in the zone K1, more specifically, the maximum value of powder amount at the laser irradiation position P (supply amount Sa + residual powder). Specifically, it has been found that the ratio of the residual powder to the maximum value is substantially constant in the laser build-up of the valve seat 16, and the predetermined value Wb is set to the optimum value Wa of the output W. Thus, the defects are satisfactorily suppressed by increasing the content in the range of about 20 to 30%. That is, if the predetermined value Wb is set to exceed the predetermined value Wb by about 30%, a crack is generated in the built-up layer, and if it is set to be less than about 20% than the predetermined value Wb, a defect is generated in the built-up layer. It becomes.

  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 begins to be pushed is obtained. Therefore, by starting the termination portion forming process at such timing, the output W of the laser beam 20 can be increased at an appropriate timing at which the amount of powder at the laser irradiation position P starts to increase, and the termination portion 52 that suppresses defects. Can be formed.

As shown in FIG. 3, in the overlap portion forming step, the build-up is continued until 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 for the valve seat 16 according to the present embodiment, the termination portion forming process is started from the front of the start end portion 50, and in this termination portion forming step, the output of the laser beam 20 is output. The end portion 52 is formed by increasing W. Thereby, the residual powder accumulated in the zone K1 upstream of the laser irradiation position P is pushed by the start end 50 and enters the laser irradiation position P, and the amount of powder at the laser irradiation position P is the optimum value of the supply amount S. Even in the case of increasing from Sa, the output W of the laser beam 20 is increased in accordance with this increase, and hence the occurrence of defects in the terminal portion 52 can be 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 the output W of the laser beam 20. Since the overlap portion 54 with the starting end portion 50 is formed with the increase in the number of defects, the occurrence of defects in the overlap portion 54 can be suppressed well.

In the terminal portion forming step, the output W of the laser light 20 is gradually increased to a predetermined amount Wb at an increase rate α corresponding to the inclination formed at the start end 50 before the laser irradiation position P overlaps the start end 50. Increasing.
As a result, the output W of the laser light 20 increases in accordance with the amount of residual powder that gradually increases at the laser irradiation position P in accordance with the inclination of the start end portion 50, and further suppresses the occurrence of defects and terminates the termination. The part 52 can be formed.

  Further, 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. In addition, although the copper alloy powder 18 tends to accumulate in the U-shaped groove portion 17 when building up, as described above, the output W of the laser light 20 is increased in accordance with the amount of residual powder in the terminal portion forming step. The occurrence of defects can be satisfactorily suppressed. 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 output W of the laser beam 20 can be increased at an appropriate timing at which the amount of powder at the laser irradiation position P starts to increase, and the terminal portion 52 that suppresses defects can be provided. Can be formed.

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.
For example, in the start end portion forming step and the end portion forming step, the output W of the laser beam 20 has been described as increasing in proportion to the rotation angle as shown in FIG. You may make it make it. By changing the output W stepwise, the laser controller 32 does not need real-time control of the applied voltage, and can perform the overlay process in a simple procedure.

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 Wb 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 built-up by overlapping a supply end of the metal powder from a position before the start end portion to increase a laser output to a predetermined amount and overlapping the start end portion .   The output of the laser is gradually increased to the predetermined amount according to the inclination formed at the start end before the end is formed, before being overlapped with the start end. The laser cladding method described.   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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