JP2009045639A - Method and apparatus for laser cladding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser cladding method which can form a clad layer having no pore and no crack. <P>SOLUTION: The laser cladding method comprises a casting step for forming a cylinder head 1 having valve seat portions 2, a groove machining step for forming concave grooves on the valve seat portions 2, a melting layer forming step for forming a melting layer 21 by melting a base material by irradiating the groove portions with a laser beam hv, and a laser cladding step for forming a clad layer 20 by the building-up operation by radiating the laser beam while relatively moving the base material and the laser beam while supplying metallic powder on the melting layer 21. In this case, the radiating energy of the laser beam in the melting layer forming step is set to be larger than the radiating energy of the laser beam in the laser cladding step. By this method, the clad layer 20 having no pore and no crack can be formed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laser clad processing method and a laser clad apparatus, and to a technique for forming a clad layer free of voids and cracks.

  For example, in an automobile engine, instead of a conventional method of driving a seat ring as a valve seat, a method of directly depositing a valve seat alloy on a cylinder head has been adopted.

  As described above, if the valve seat alloy is directly built on the cylinder head, the thermal conductivity can be greatly improved as compared with the seat ring driving method, and the cooling performance can be improved.

  This build-up method irradiates a laser from a laser oscillator while supplying metal powder from a nozzle of a powder supply device to a portion (valve seat portion) where a valve seat is formed, and relatively rotates the valve seat portion and the laser. Thus, a ring-shaped build-up layer (valve seat) is formed.

In this build-up method, a concave groove is formed with a cutting tool on the part where the valve seat is to be formed on the metal base material manufactured by casting as a pre-process for laser cladding, and the groove is irradiated with laser. Then, after forming a molten layer by melting a base material, a valve seat is formed by irradiating a laser while supplying metal powder onto the molten layer (see, for example, Patent Document 1).
JP 2002-239711 A

  However, in the molten layer forming step for forming the molten layer, casting gas remains in the molten layer due to insufficient melting (time), and the casting gas moves into the cladding layer during the cladding processing step. Holes may be generated on the valve seat surface.

  Further, due to variations in the width and depth of the molten layer in the molten layer forming step, a portion where the casting gas in the groove portion is not removed occurs, and when the unremoved portion is clad, the casting gas is contained in the cladding layer. Remains.

  Moreover, when the thickness of a molten layer is less than 0.2 mm, the site | part from which the casting gas in the said groove part is not removed arises.

  Furthermore, a groove (hereinafter referred to as an unmelted groove) that is not melted due to insufficient melting occurs in the molten layer forming process, and the edge portion of the unmelted groove is easily melted into the cladding material during cladding processing, and cracking due to dilution occurs. Sometimes.

  Therefore, the present invention provides a laser clad processing method and a laser clad apparatus capable of forming a clad layer having no holes or cracks.

  The laser clad processing method of the present invention includes a casting process for forming a base material having a processed part that is a part to be overlaid, a groove processing process for forming a concave groove in the processed part, and the groove part A molten layer forming step of forming a molten layer by irradiating a laser to the base material, and irradiating and overlaying the laser while moving the base material and the laser relatively while supplying metal powder onto the molten layer And a laser cladding processing step of forming a cladding layer. In the method of the present invention, the laser irradiation energy in the molten layer forming step is set larger than the laser irradiation energy in the laser cladding processing step.

  The laser cladding apparatus of the present invention includes a laser irradiation apparatus for irradiating a workpiece with a laser and a powder supply device for supplying metal powder to the workpiece, and is formed on the workpiece of a cast base material. After forming a molten layer by irradiating the concave groove with a laser to melt the base material, supplying the metal powder onto the molten layer and irradiating the laser while moving the base material and the laser relatively, Thus, an apparatus for forming a clad layer. The apparatus according to the present invention includes control means for making the irradiation energy of the laser when forming the molten layer larger than the irradiation energy of the laser when forming the cladding layer.

  According to the laser cladding processing method of the present invention, casting gas does not remain in the molten layer, and voids and cracks on the surface of the cladding layer can be eliminated.

  According to the laser cladding apparatus of the present invention, it is possible to form a cladding layer having no voids and cracks on the surface of the cladding layer.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings.

"Configuration of laser cladding equipment"
First, the configuration of the laser cladding apparatus will be described. FIG. 1 is a perspective view showing a laser clad apparatus, and FIG. 2 is a view showing a state in which metal powder is supplied from a nozzle tip of a powder supply apparatus to a workpiece.

  As shown in FIG. 1, the laser cladding apparatus includes a laser irradiation apparatus 3 that irradiates a valve seat 2 that is a processed part of a cylinder head 1 such as an automobile engine, and a metal powder on the valve seat 2. 4 and a powder supply device 5 for supplying 4.

  The laser irradiation device 3 includes a laser oscillator 6, a laser oscillator control unit 7 that is a control means for controlling the intensity of the laser oscillated by the laser oscillator 6, an NC control device 8, It consists of the condensing head 9 which irradiates the valve seat part 2. The laser hv oscillated by the laser oscillator 6 is controlled by the laser oscillator control unit 7 and supplied to the condensing head 9. The condensing head 9 squeezes and irradiates the valve seat unit 2.

  The powder supply device 5 includes a nozzle 10 (not shown in FIG. 1 and shown in FIG. 2) for supplying the metal powder 4 to the valve seat portion 2, a hopper 11 in which the metal powder 4 is placed and placed, A load meter 12 for measuring the amount, a feeder 13 for feeding the metal powder 4 from the hopper 11 to the nozzle 10, and a powder control unit 14 for controlling them. From the tip of the nozzle 10, the metal powder 4 accommodated in the hopper 11 is sent to the valve seat portion 2 by being fed by the feeder 13. For example, a copper alloy is used as the metal powder 4.

  In this laser cladding apparatus, the laser oscillator 6, the laser oscillator controller 7, the NC controller 8, and the powder supply controller 14 are controlled by a computer 15. Then, the clad layer (valve sheet) 16 is formed by irradiating the laser while supplying the metal powder 4 to the valve seat portion 2 by the laser clad apparatus configured as described above, thereby forming a clad layer (valve sheet) 16. As shown in FIG. 2, laser cladding is performed while rotating the cylinder head 1 as indicated by an arrow A.

"Laser cladding processing method"
Next, a laser cladding processing method for forming a valve seat will be described. 3 to 9 are diagrams showing a laser cladding processing step.

  First, the cylinder head (base material) 1 shown in FIG. 3A is formed by casting (casting process). In order to form the cylinder head 1, a casting mold is prepared, and a molten aluminum alloy is poured into the casting mold. As shown in FIG. 3B, the cast cylinder head 1 is formed with a valve seat part (processed part) 2 which is a part to be built up in a subsequent process.

  Next, a concave groove is formed in the valve seat portion 2 (groove processing step). In the grooving step, as shown in FIG. 3C, the cutting tool 17 is pressed against the valve seat portion 2 while rotating, and the valve seat portion 2 is cut to form a concave groove on the surface thereof.

  Next, as shown in FIG. 4A, the groove 18 formed in the groove processing step is irradiated with a laser hv to melt the base material to form a molten layer (molten layer forming step).

  Next, as shown in FIG. 4B, while supplying the metal powder 4 onto the molten layer, the cylinder head 1 and the laser hv are relatively rotated and irradiated with the laser hv to form a cladding layer. (Laser cladding processing step).

  Finally, as shown in FIG. 4C, the finishing cutting tool 19 is pressed against the cladding layer 20 while rotating to polish the surface of the cladding layer 20 (polishing process).

  In the molten layer forming step, when melting (time) shortage occurs, a casting gas 22 is generated in the molten layer 21 as shown in FIG. Then, when overlaying is performed in the next step, the laser cladding process, as shown in FIG. 6, the casting gas 22 moves into the cladding layer 20, and in the subsequent polishing process, the cladding layer (valve sheet) 20. Holes are generated on the surface of.

  In the melt layer formation step, if the melt width and melt depth of the melt layer 21 vary, or if the thickness T of the melt layer 21 is less than 0.2 mm, for example, the casting gas 22 in the groove 18 is not removed. And a casting gas 22 remains in the cladding layer 20 when laser cladding is performed. The thickness 0.2 mm (threshold value) of the molten layer 21 is not a constant value, but varies depending on the type of material, casting conditions, and the like.

  In addition, due to insufficient melting in the melt layer forming step, a groove (unmelted groove) 23 that is not melt-partitioned is generated as shown in FIG. 7A, and the edge portion 24 of the unmelted groove 23 is formed in FIG. As shown to (B), it becomes easy to melt | dissolve with the cladding material (cladding layer 20), and the crack (crack) 25 by dilution generate | occur | produces.

  In order to avoid such a problem, in this embodiment, the irradiation energy of the laser hv in the molten layer forming process is set larger than the irradiation energy of the laser hv in the laser cladding processing process. In order to change the irradiation energy of the laser hv, the laser oscillator controller 7 controls the intensity of the laser hv.

  For example, when the laser output during the laser cladding processing step is 1.7 kW, the laser output during the molten layer forming step is 2.2 kW, which is higher than that. However, the wavelength of the laser hv is 0.8 to 0.9 μm.

  Thus, by making the irradiation energy of the laser hv in the molten layer forming process larger than the irradiation energy of the laser hv in the laser cladding processing process, the melting shortage is eliminated and the melting width and the melting depth of the molten layer are eliminated. The variation in thickness is reduced, and the casting gas 22 remains in the molten layer 21, moves to the cladding layer 20, and the unmelted groove 23 is not generated.

  Therefore, as shown in FIG. 8, there can be formed a clad layer (valve seat) 20 in which no voids are present in the clad layer 20 that is cooled and becomes a valve seat, and cracks due to dilution do not occur.

  Furthermore, by improving the laser output, a sufficient melting time can be obtained without using an expensive high-power laser oscillator.

  In addition, the same effect can be obtained by making the moving speed of the laser hv during the molten layer forming process slower than the moving speed of the laser hv during the laser cladding processing process.

  When the moving speed of the laser hv at the time of laser clad processing is, for example, 1.2 m / min, the moving speed of the laser hv at the melt layer forming step is set to 0.6 m / min, which is slower than that. In the present embodiment, the moving speed of the laser hv during the molten layer forming step is set to half the moving speed of the laser hv during laser cladding.

  Thus, by making the moving speed of the laser hv during the molten layer forming process slower than the moving speed of the laser hv during the laser cladding processing process, the shortage of melting is eliminated and the molten layer is eliminated. The dispersion of the melt width and the melt depth is reduced, and the residual casting gas 22 in the melt layer 21, the movement to the clad layer 20, and the occurrence of the unmelted groove 23 are eliminated. Therefore, it becomes possible to form the clad layer 20 in which no voids are present in the clad layer 20 and cracks due to dilution do not occur.

  In addition, the same effect can be obtained by making the spot length in the moving direction of the laser hv in the molten layer forming step larger than the spot length in the moving direction of the laser hv in the laser cladding processing step. be able to.

  As shown in FIG. 9, the spot length L1 in the moving direction of the laser hv in the molten layer forming step is made longer than the spot length L2 of the laser hv in the laser cladding processing step. In FIG. 9, in order to compare the spot lengths L1 and L2 of the laser hv at each step, the laser hv at the laser clad processing step is superimposed on the laser hv at the melt layer forming step.

  Thus, by making the spot length L1 in the moving direction of the laser hv in the molten layer forming step larger than the spot length L2 in the moving direction of the laser hv in the laser cladding processing step, the laser hv Irradiation time is increased, melting shortage is eliminated, and variations in the melt width and melt depth of the melt layer are reduced. Residual casting gas 22 in the melt layer 21 and movement to the clad layer 20, unmelted grooves 23 No longer occurs.

  In addition, the same effect can be obtained even when the thickness of the molten layer 21 is 0.2 mm or more during the molten layer forming step. In order to set the thickness of the molten layer 21 to 0.2 mm or more, the output of the laser hv is increased or the moving speed (workpiece rotation speed) of the laser hv is decreased.

  If the thickness T of the molten layer 21 is less than 0.2 mm, the casting gas is not removed. However, if the thickness T of the molten layer 21 is 0.2 mm or more, the casting gas 22 may remain in the cladding layer 20. In addition, no voids or cracks occur on the surface of the cladding layer 20 after the polishing process. Therefore, a highly reliable valve seat can be manufactured.

  In the other embodiments described above, any of them may be combined with the first embodiment, or all the embodiments may be combined.

FIG. 1 is a perspective view showing a laser cladding apparatus. FIG. 2 is a diagram showing a state in which metal powder is being supplied to the workpiece from the nozzle tip of the powder supply device. FIG. 3 is a process diagram showing a casting process and a grooving process in the laser cladding process. FIG. 4 is a process diagram showing a melt layer forming process, a laser cladding process, and a polishing process in the laser cladding process. FIG. 5 is a diagram showing that casting gas remains in the molten layer during the molten layer forming step. FIG. 6 is a diagram showing that the casting gas moves into the cladding layer during the laser cladding processing step. FIG. 7 is a diagram showing that unmelted grooves are formed due to insufficient melting during the melt layer forming process and cracks are generated in the clad layer during the laser cladding processing process. FIG. 8 is a diagram showing that no holes and cracks are generated in the cladding layer. FIG. 9 is a diagram showing that the spot length in the laser moving direction in the molten layer forming step is made larger than the spot length in the laser moving direction in the laser cladding processing step.

Explanation of symbols

1 ... Cylinder head 2 ... Valve seat (worked part)
DESCRIPTION OF SYMBOLS 3 ... Laser irradiation apparatus 4 ... Metal powder 5 ... Powder supply apparatus 6 ... Laser oscillator 9 ... Condensing head 10 ... Nozzle 16 ... Jet port 18 ... Groove part 20 ... Cladding layer 21 ... Molten layer 22 ... Casting gas

Claims (6)

A casting process for forming a base material having a workpiece that is a part to be built up;
A groove processing step of forming a concave groove in the processed portion;
A molten layer forming step of irradiating the groove with a laser to melt a base material to form a molten layer;
A laser clad processing step of forming a clad layer by irradiating a laser while moving a base material and a laser relatively while supplying metal powder onto the molten layer,
A laser cladding processing method, wherein the laser irradiation energy in the molten layer forming step is larger than the laser irradiation energy in the laser cladding processing step. The laser cladding processing method according to claim 1,
A laser cladding processing method, wherein a laser moving speed in the molten layer forming step is made slower than a laser moving speed in the laser cladding processing step. The laser cladding processing method according to claim 1 or 2,
A laser cladding processing method, wherein a spot length in a laser moving direction in the molten layer forming step is made larger than a spot length in a laser moving direction in the laser cladding processing step. The laser cladding processing method according to any one of claims 1 to 3,
A laser cladding processing method, wherein the melt layer is processed so that the thickness of the melt layer is 0.2 mm or more during the melt layer forming step. The laser cladding processing method according to any one of claims 1 to 4,
The base material is a cylinder head, and the processed part is a valve seat part. It has a laser irradiation device that irradiates a laser beam to the workpiece and a powder supply device that supplies metal powder to the workpiece, and applies laser to the concave groove formed in the workpiece of the cast base material. A laser that forms a cladding layer by irradiating and forming a molten layer by irradiating and forming a molten layer, then supplying a metal powder onto the molten layer and moving the base material and the laser relatively while irradiating the laser A cladding device,
A laser clad apparatus characterized by comprising control means for making the laser irradiation energy at the time of forming the molten layer larger than the laser irradiation energy at the time of forming the clad layer.

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