Method for laser cladding

Abstract

To provide a technology of laser cladding that can inhibit a base material from being damaged.SOLUTION: A method for laser cladding includes: a first formation step of forming a first clad layer so as to include part of the surface of a base material of which base material has stiffness that is equal to or lower than a predetermined first threshold; and a second formation step of forming a second clad layer so as to include part of the surface of the first clad layer of which base material has stiffness that is equal to or lower than the first threshold.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a laser cladding method.

Background Art

[0002] In overlay welding by laser cladding technology in which a wear-resistant powder is directly built up with a laser to form a clad layer, a technology for forming the clad layer by stacking is known in order to suppress the variation of beads. Patent Document 1 describes a technology in which overlay welding is performed by laser cladding technology using a material having a higher thermal conductivity than the base material, and overlay welding is performed by laser cladding technology using a material having a fatigue strength comparable to that of the base material thereon.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since the amount of heat input is large at the site where the clad layers are stacked, the thermal shrinkage becomes large. Therefore, cracks may occur in the base material or between the base material and the clad layer due to the stress generated against the thermal shrinkage.

Means for Solving the Problems

[0005] The present disclosure has been made to solve the above-described problems and can be realized in the following forms.

[0006] (1) According to an aspect of the present disclosure, a laser cladding processing method is provided. This laser cladding processing method includes a first forming step of forming a first cladding layer on the surface of a base material so as to include a portion where the rigidity of the base material is equal to or less than a predetermined first threshold value, and a second forming step of forming a second cladding layer on the surface of the first cladding layer so as to include a portion where the rigidity of the base material is equal to or less than the first threshold value. According to the laser cladding processing method of this aspect, since the second cladding layer is formed at a portion where the rigidity of the base material is low, the stress on the second cladding layer due to thermal contraction is smaller than the stress when the second cladding layer is formed at a portion where the rigidity of the base material is high. Therefore, it is possible to suppress the occurrence of cracks in the base material or between the base material and the cladding layer due to the stress generated by thermal contraction. (2) In the second forming step of the laser cladding processing method of the above aspect, the end portion of the second cladding layer may be formed at a position where the rigidity of the base material is equal to or less than the first threshold value. According to the processing method of this aspect, the end portion of the second cladding layer where the tensile stress generated by contraction is large is formed at a position where the rigidity of the base material is equal to or less than the first threshold value. Therefore, it is possible to suppress the occurrence of cracks in the base material or between the base material and the cladding layer due to the stress generated by thermal contraction. (3) In the laser cladding processing method of the above aspect, the starting portion of the first cladding layer may be formed at a position where the rigidity of the base material is equal to or less than a predetermined second threshold value that is greater than the first threshold value. According to the processing method of this aspect, the end portion of the second cladding layer where tensile stress due to thermal contraction first occurs in the first forming step is formed at a position where the rigidity of the base material is equal to or less than the second threshold value. Therefore, it is possible to suppress the occurrence of cracks in the base material or between the base material and the cladding layer due to the stress generated by thermal contraction. (4) In the laser cladding processing method of the above aspect, the portion where the output of the laser in the first forming step is the largest in the first cladding layer may be formed at a position where the rigidity of the base material is equal to or less than a predetermined third threshold value that is greater than the first threshold value. According to the processing method of this form, the portion where the laser output is the largest is formed at a position where the rigidity of the base material is equal to or less than the third threshold value. Therefore, it is possible to suppress the occurrence of cracks in the base material or between the base material and the clad layer due to the stress generated by thermal contraction.

[0007] Note that the present disclosure can be realized in various forms, for example, it can be realized in the form of a method for determining processing conditions of a laser cladding processing apparatus or the like.

Brief Description of Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0009] A. First Embodiment: FIG. 1 is an explanatory diagram showing the configuration of a laser cladding processing apparatus 100 according to the present embodiment. The laser cladding processing apparatus 100 is an apparatus for performing laser cladding processing on an object. In the present embodiment, the laser cladding processing apparatus 100 performs laser cladding processing on a base material 200 to be processed, and forms a clad layer on a valve seat portion 220. The base material 200 is, for example, an aluminum alloy cylinder head. The laser cladding processing apparatus 100 includes a processing unit 10 and a control unit 20.

[0010] The processing unit 10 includes a laser irradiation unit (not shown), a powder supply unit, and an actuator. While supplying metal powder from the powder supply unit to the base material 200, the processing unit 10 irradiates the base material 200 with laser light from the laser irradiation unit to melt the metal powder, thereby forming a clad layer on the object. The metal powder is, for example, powdered steel or a steel alloy. In the present embodiment, the processing unit 10 forms a clad layer along a substantially circular clad groove formed in the valve seat portion 220 of the base material 200 while moving the laser irradiation unit and the powder supply unit by the actuator. This clad layer is also referred to as a bead.

[0011] The control unit 20 is composed of a computer including a central processing unit (CPU), a RAM, and a ROM, and controls the operation of the processing unit 10 by the CPU executing a program pre-installed in a storage area such as the RAM and ROM of the control unit 20. However, part or all of the functions of these respective units may be realized by a hardware circuit. The control unit 20 controls the processing unit 10 according to the set output intensity of the laser and the supply amount of the metal powder.

[0012] The base material 200 has a combustion chamber surface 210 that is a concave surface. The combustion chamber surface 210 constitutes a piston (not shown) and a fuel chamber. The combustion chamber surface 210 has a plurality of valve seat portions 220 that serve as valve seats for an intake valve and an exhaust valve. The valve seat portion 220 serves to seal the intake valve and the exhaust valve from the combustion chamber surface 210 in the combustion chamber. In FIG. 1, a part of the base material 200 is depicted in a state of being cut along the thickness direction of the base material 200, and the overall shape of the base material 200 and the shapes of the combustion chamber surface 210 and the valve seat portion 220 are depicted in a simplified manner.

[0013] FIG. 2 is a flowchart showing an example of a processing procedure. This processing is a procedure in which the laser clad processing apparatus 100 performs laser clad processing on the base material 200.

[0014] In step S100, the control unit 20 operates the processing unit 10 to form a first clad layer at a position on the surface of the base material 200 that includes a portion where the rigidity of the base material 200 is equal to or less than a predetermined first threshold value. More specifically, the control unit 20 operates the processing unit 10 to form a first clad layer at a position that includes a portion where the rigidity in the valve seat portion 220 is equal to or less than the first threshold value. This step is also referred to as the "first formation step". The first threshold value is a rigidity value at which the stress against thermal shrinkage caused by laser cladding processing is smaller than the tensile strength of the clad layer and the base material 200. The greater the rigidity of the base material 200, the greater the stress corresponding to thermal shrinkage. The first threshold value is determined, for example, based on a map or function that defines the relationship between the stress generated experimentally in advance and the rigidity of the base material 200. Also, the rigidity at each position of the base material 200 can be obtained by analysis in advance, for example. The rigidity at a position where the height of the clad groove formed in the valve seat portion 220 is low and the thickness is thin is lower than the rigidity at a position where the height of the clad groove formed in the valve seat portion 220 is high and the thickness is thick.

[0015] In step S110, the control unit 20 operates the processing unit 10 to form a second clad layer CL2 at a position on the surface of the first clad layer CL1 formed in step S100 that includes a portion where the rigidity of the base material 200 is equal to or less than the first threshold value. This step is also referred to as the "second formation step". In the present embodiment, the end portion of the second clad layer CL2 is formed at a position where the rigidity of the base material 200 is equal to or less than the first threshold value.

[0016] FIG. 3 is an explanatory diagram showing an example of the processing in the present embodiment. As shown in FIG. 3, the processing unit 10 forms a cladding layer while moving along a locus A1 represented by a dashed line by an actuator driven by the control unit 20. More specifically, the processing unit 10 performs a one-week processing clockwise from the start position Ps to the start position Ps again to form the first cladding layer. The processing unit 10 further continues the processing clockwise to the end position Pe where the rigidity of the base material 200 on the same circumference is equal to or less than the first threshold value to form the second cladding layer. That is, the second cladding layer is formed by processing the portion 221 from the start position Ps to the end position Pe twice.

[0017] FIG. 4 is a cross-sectional view of the base material 200 at the end position Pe where the processing is completed. The first cladding layer CL1 is formed on the base material 200, and the second cladding layer CL2 is formed on the first cladding layer CL1.

[0018] FIG. 5 is a diagram showing an example of the stress applied to the base material 200 immediately after forming the second cladding layer. In the graph shown in FIG. 5, the vertical axis represents stress, and the horizontal axis represents the distance from the surface of the second cladding layer CL2 in the direction of arrow A2 shown in FIG. 4. A compound layer made of a compound of the metal powder and the base material 200 is formed on the surface of the second cladding layer CL2, and a remelted layer in which the base material 200 is melted is formed between the compound layer and the base material layer. The layer below the remelted layer is the base material layer in which the base material 200 is not melted.

[0019] In FIG. 5, the stress against thermal contraction by laser cladding is shown by a solid line, and the tensile strengths in the compound layer, remelted layer, and base material layer of the base material 200 are shown by a one-dot chain line. The characteristic line gr1 is a characteristic line showing the stress corresponding to the thermal contraction at the end position Pe where the rigidity of the base material 200 is below the first threshold value, and the characteristic line gr2 is a characteristic line showing the stress corresponding to the thermal contraction at a position where the rigidity of the base material 200 is greater than the first threshold value. The limit stress CS1 indicates the limit stress of the compound layer, the limit stress CS2 indicates the limit stress of the remelted layer, and the limit stress CS3 indicates the limit stress of the base material layer. The limit stress CS2 of the remelted layer is greater than the limit stress CS3 of the base material layer. The limit stress CS3 of the base material layer is greater than the limit stress CS1 of the compound layer.

[0020] As described above, the first threshold value is the value of the rigidity at which the stress against the thermal contraction generated by laser cladding becomes smaller than the limit stress CS1, the limit stress CS2, and the limit stress CS3. As shown in FIG. 5, since the stress corresponding to the thermal contraction at a position where the rigidity of the base material 200 is greater than the first threshold value is greater than the limit stress CS1 of the compound layer and the limit stress CS3 of the base material 200, there is a risk of damage to the base material 200 and the like. Since the stress corresponding to the thermal contraction at the end position Pe where the rigidity of the base material 200 is below the first threshold value is smaller than the limit stress CS1, the limit stress CS2, and the limit stress CS3, it is possible to suppress damage to the base material 200.

[0021] According to the laser cladding method of the present embodiment described above, since the second cladding layer CL2 is formed at a portion where the rigidity of the base material 200 is low, the stress against the thermal contraction of the second cladding layer CL2 is smaller than the case where the second cladding layer CL2 is formed at a portion where the rigidity of the base material 200 is high. Therefore, it is possible to suppress the occurrence of cracks between the base material 200 and between the base material 200 and the cladding layer. Therefore, it is possible to suppress damage to the base material 200.

[0022] In the second forming step, the end portion of the second cladding layer CL2 where the tensile stress generated by thermal contraction is large is formed at a position where the rigidity of the base material 200 is equal to or less than the first threshold value. Therefore, it is possible to suppress the occurrence of cracks in the base material 200 or between the base material 200 and the cladding layer due to the stress generated by thermal contraction.

[0023] B. Other embodiments: (B1) In the above-described embodiment, a cladding layer having an annular outer shape is formed. However, the present invention is not limited to this, and for example, a cladding layer having a polygonal frame-shaped outer shape such as a quadrangle may be formed. Further, the second cladding layer CL2 may not be formed on the starting end portion of the first cladding layer CL1.

[0024] (B2) In the second forming step in the above-described embodiment, the end portion of the second cladding layer CL2 is formed at a position where the rigidity of the base material 200 is equal to or less than the first threshold value. However, the present invention is not limited to this, and the second cladding layer CL2 may be formed at a position including a portion where the rigidity of the base material 200 is equal to or less than the first threshold value, and the end portion of the second cladding layer CL2 may be formed at a position where the rigidity of the base material 200 is greater than the first threshold value.

[0025] (B3) In the first forming step in the above-described embodiment, the starting end portion of the first cladding layer CL1 may be formed at a position where the rigidity of the base material 200 is equal to or less than a predetermined second threshold value. That is, the starting position Ps is a position where the rigidity of the base material 200 is equal to or less than the second threshold value. The second threshold value is equal to or less than the first threshold value. The starting end portion of the first cladding layer CL1 is the portion 221 where tensile stress due to thermal contraction first occurs in the processing step. Therefore, the stress generated by thermal contraction is more likely to be applied than to other portions. According to this embodiment, it is possible to suppress the occurrence of cracks in the base material 200 or between the base material 200 and the cladding layer due to the stress generated by thermal contraction.

[0026] (B4) In the first forming step in the above-described embodiment, the portion where the laser output is the largest may be formed at a position where the rigidity of the base material 200 is equal to or less than a predetermined third threshold value. The third threshold value is equal to or less than the first threshold value. In the first forming step, the portion where the laser output is the largest generates a larger amount of heat than other portions. Therefore, the tensile stress generated by thermal contraction becomes large. With this configuration, it is possible to suppress the occurrence of cracks in the base material 200 and between the base material 200 and the clad layer due to the stress generated against thermal contraction.

[0027] (B5) In the above-described embodiment, in the above-described embodiment, the processing unit 10 performs a circumferential machining in a clockwise direction from the start position Ps to the start position Ps again, and further continues the machining in a clockwise direction to the end position Pe on the same circumference. Not limited to this, the processing unit 10 may perform a circumferential machining in a counterclockwise direction from the start position Ps to the start position Ps again, and further continue the machining in a clockwise direction to the end position Pe on the same circumference. Further, the processing unit 10 may perform a circumferential machining in a counterclockwise direction and further continue the machining in a counterclockwise direction to the end position on the same circumference.

[0028] The present disclosure is not limited to the above-described embodiments, and can be realized in various configurations without departing from the gist thereof. For example, the technical features in the embodiments corresponding to the technical features in each form described in the summary of the invention can be appropriately replaced or combined in order to solve the above-described problems or to achieve some or all of the above-described effects. Further, if the technical feature is not described as essential in this specification, it can be appropriately deleted.

Explanation of reference numerals

[0029] 10... Processing unit, 20... Control unit, 100... Laser cladding processing apparatus, 200... Base material, 210... Combustion chamber surface, 220... Valve seat portion, 221... Portion, CL1... First clad layer, CL2... Second clad layer

Claims

1. A laser cladding processing method, comprising: a first forming step of forming a first cladding layer on the surface of a base material so as to include a portion where the rigidity of the base material is equal to or less than a predetermined first threshold value; a second forming step of forming a second cladding layer on the surface of the first cladding layer so as to include a portion where the rigidity of the base material is equal to or less than the first threshold value.

2. The laser cladding processing method according to Claim 1, wherein in the second forming step, the end portion of the second cladding layer is formed at a position where the rigidity of the base material is equal to or less than the first threshold value.

3. The laser cladding processing method according to Claim 1 or Claim 2, wherein the starting portion of the first cladding layer is formed at a position where the rigidity of the base material is equal to or less than a predetermined second threshold value that is greater than the first threshold value.

4. The laser cladding processing method according to Claim 1 or Claim 2, wherein the portion where the output of the laser in the first forming step is the largest in the first cladding layer is formed at a position where the rigidity of the base material is equal to or less than a predetermined third threshold value that is greater than the first threshold value.

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