JP2019150846A - Welding method - Google Patents

Abstract

To provide a welding method that can prevent a softened layer from being generated on a surface of a metal mold to suppress abrasion and breakage.SOLUTION: A welding method according to one embodiment comprises: a step of obtaining an actual measured value relating to hardness of a cross section of a welded part and specifying a phase transformation region appearance condition from a relation between exposure time and a temperature at which the actual measured value can be obtained; a step of predicting generation of a softened layer, assuming that the softened layer is generated in a heat-affected part, when the heat-affected part of the welded part is included in a phase transformation region appearance condition; a step of determining whether welding quality is good or not on the basis of a predicted result of the generation of the softened layer; and a step of changing a welding condition on the basis of a determined result of whether the welding quality is good or not.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a welding technique for tool steel.

  Conventionally, various techniques for determining welding quality (for example, mechanical strength, residual stress, welding deformation) have been proposed (for example, Patent Documents 1 to 5). In Patent Document 1, a feature value of the surface temperature distribution of the molten pool / heat-affected zone is extracted from the image data, and the amount of heat input that forms the molten pool is estimated based on the feature value. Estimate temperature change (cooling rate) of weld pool and heat affected zone from heat input and various databases. And based on this temperature change, the material physical property based on the microstructure of a welding part is estimated, and the quality of welding quality is determined from this material physical property and a load stress database.

  In Patent Document 2, a temperature change in the vicinity of a welded portion irradiated with laser light is detected, and whether or not the welded portion is welded is determined based on the temperature change. Moreover, in patent document 3, the range in the average value of the radiant temperature of the to-be-processed part which the quality of a to-be-processed part becomes a good product is memorize | stored, and the average value of the radiated temperature of the to-be-processed part measured by the radiation thermometer is A technique for determining that the quality of a processed part is a non-defective product when it is within the stored range is disclosed.

  Patent Document 4 discloses a welding analysis method in which the temperature of each member when a plurality of members are welded is analyzed by computer simulation. Patent Document 5 discloses a technique for performing a numerical simulation of a structure including a heat affected zone using a finite element analysis model.

JP-A-2006-198805 Japanese Patent Laid-Open No. 05-337662 JP 2017-217675 A JP 2006-247746 A JP 2013-246830 A

  Products used for automobile bodies and the like are produced by pressing a steel plate using a press die. Further, casting products such as engine blocks are produced by casting using a mold. Since various molds such as a press mold and a mold are used continuously for a long time, wear or breakage may occur on the molding surface, particularly on a high load part such as an edge part or a strong pressure part. When wear or breakage occurs on the molding surface of the mold, the surface is scratched and the quality of the product is degraded.

  In order to reduce the cost of such a mold, a technique for repairing and repairing a damaged portion of the mold by welding is known. In the repair of the mold, the welded material is welded and welded to the repaired portion to form a welded portion, and then machined to cut into the original shape. However, welding has a problem that a softened layer is generated in a HAZ (Heat Affected Zone). If a softened layer of the welded portion appears on the surface of the mold after machining, there is a possibility that it becomes a new cause of wear and breakage of the mold after repair. Similarly, when a new mold is created using a welding technique, there is a concern about problems due to the appearance of a softened layer on the mold surface. The same problem may occur when a softened layer is generated in a welded portion of a cutting tool such as a drill or a milling cutter or a hammering tool.

  Therefore, it is required to predict the occurrence of a softened layer in the weld and reflect it in the welding conditions. Since the generation of the softened layer is considered to be caused by the phase transformation occurring in the HAZ, a method of estimating the microstructure by verifying the phase transformation of the welded portion and predicting the generation of the softened layer is conceivable. In patent document 1, in order to estimate the microstructure of a welded part, the cooling rate of the heat affected zone is used. However, the shape and cooling rate of each region must be verified / calculated one by one, and there is a problem that the calculation amount is enormous and takes time.

  The present invention has been made in view of such problems, and an object of the present invention is to predict the occurrence of a softened layer in a heat-affected zone of a welded part in a short time, and to determine and change welding conditions. It is to provide a possible welding method.

  The welding method according to an aspect of the present invention includes a step of acquiring an actual measurement value related to the hardness of a cross section of a welded portion, and specifying a phase transformation region appearance condition from a relationship between exposure time and temperature at which the actual measurement value is obtained; When the heat affected zone of the welded portion is included in the phase transformation region appearance condition, a process of predicting the generation of the softened layer on the assumption that the softened layer is generated in the heat affected zone, and the predicted generation result of the softened layer And determining the quality of the welding quality, and changing the welding conditions based on the quality determination result of the welding quality.

  According to the present invention, it is possible to provide a welding method capable of predicting the occurrence of a softened layer in a heat-affected zone of a welded portion in a short time and determining and changing welding conditions.

It is a flowchart which shows the welding method which concerns on embodiment. It is a figure explaining the method of determining a calculation area | region. It is a figure explaining the method of determining a calculation area | region. It is a figure which shows the relationship between the exposure time of a laser, and the temperature of the cross section of a welding part. It is a continuous cooling transformation diagram of tool steel.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Equivalent components in each drawing are denoted by the same reference numerals, and redundant description is omitted.

  The present invention relates to a welding technique for tool steel used for tools such as cutting tools and impact tools, and various dies. The outline of the welding method according to the embodiment is the initial setting of the welding conditions, the occurrence of a softened layer that reduces the mechanical properties of the welded portion is predicted, and the welding condition is changed to suppress the occurrence of the softened layer. To do.

  For example, when repairing a mold, weld material is welded to a damaged part of the mold that has been worn or damaged to form a welded part, and the welded part is cut and repaired. When repairing a damaged part of a mold by TIG welding, there is a problem that heat affected zone (Heat Affected Zone: HAZ) is softened because TIG welding has a large heat input.

  On the other hand, in laser clad welding, since it is easy to control the total amount of heat and the melting point, it is considered that the generation of the softened layer can be reduced as compared with TIG welding, but it is difficult to eliminate the generation of the softened layer itself. Therefore, in the embodiment, the occurrence of the softened layer in the heat-affected zone of the welded portion is easily predicted in a short time, and the welding conditions are determined and changed.

  FIG. 1 is a flowchart for explaining a welding method according to an embodiment. FIG. 1 shows a method for determining welding conditions. In FIG. 1, for convenience, a method for determining welding conditions is illustrated using a flowchart. However, a process / procedure as a “method” is illustrated, and whether or not a welding apparatus for performing welding is automatically controlled. It is not limited.

  With reference to FIG. 1, the overall flow of a method for determining the welding conditions of a mold will be described. As shown in FIG. 1, first, welding conditions are initially set (S1). In the initial setting of the welding conditions, for example, known or standard welding conditions such as conventional values, experience values, know-how values, experimental values, simulation values, and the like are set. In the case of laser clad welding, laser output, scanning position / pattern, material supply amount / speed, etc. are set.

  Next, a calculation area that is a target for which the occurrence of the softened layer is predicted is determined (S2). Since it takes a very long time to verify / calculate the generation prediction of the softened layer one by one in all regions and feed back to the welding conditions, the embodiment limits the region in which the computation is performed. The calculation region determination step includes determination of a thermal energy stable region (S21) and determination of a curing region (S22). In FIG. 2, it is described that the respective processes are executed in the order of S21 and S22. However, these processes may be performed from either, or may be performed simultaneously.

  First, determination of the thermal energy stable region (S21) will be described with reference to FIG. FIG. 2 shows a cross section at a position where the heat input amount of the welded portion becomes maximum. When welding is performed on the base material 10, the temperature continuously changes from a region heated from the melting boundary toward the base material 10 to a temperature close to the melting point of the material to a region hardly affected by heat. A place where a change occurs in the microstructure in this region is referred to as a heat affected zone 11. The welded portion 13 includes a weld metal (melted region) 12 that has been melted and solidified, and a heat-affected zone 11 in which a structural change has occurred due to the heat of welding. The weld metal 12 has a composition in which the weld material and the base material 10 are mixed.

  As shown in FIG. 2, the base material 10 is formed with a welded portion 13 in which a weld metal 12 is built up. A region in contact with the weld metal 12 of the base material 10 becomes the heat affected zone 11. In laser clad welding, the thermal energy of the laser becomes unstable immediately after the start and immediately before the end of welding. For this reason, in the welded portion 13 formed on the base material 10, the region immediately after the start of welding and the region immediately before the end are set as the excluded region 14 that is excluded from the calculation region for the prediction of occurrence of the softened layer, and the stable region 15 in which the thermal energy is stabilized. The calculation area.

  Next, the determination of the curing region will be described with reference to FIG. In general, the softened layer 11 a is formed on the heat affected zone 11 of the base material 10. Therefore, the melting region made of the weld metal 12 in the welded portion 13 is excluded from the calculation region in which the generation prediction of the softened layer is performed. Further, as shown in FIG. 3, in laser cladding welding or the like, the melting region becomes a high temperature of about 1500 ° C., so that the heat affected zone 11 has a two-layer structure of a softened layer 11a and a hardened region 11b due to a quenching effect. Accordingly, the hardened region 11b of the welded portion 13 is also excluded from the calculation region in which the occurrence of the softened layer is predicted.

  And about the calculation area | region determined by S2, phase transformation is verified, a micro structure is estimated, and generation | occurrence | production of a softening layer is estimated (S3). The generation prediction of the softened layer includes, for example, prediction of the material and generation region of the softened layer. In the embodiment, in order to reduce the calculation amount, the generation of the softened layer is simply predicted using the past actual measurement value without using the cooling rate of the welded portion. The generation prediction of the softened layer will be described in detail later.

  Thereafter, whether the weld quality of the welded portion is good or not is determined based on the predicted generation of the softened layer obtained in S3 (S4). The quality of the weld quality is determined by, for example, the amount and thickness of the softened layer, the expected hardness of the weld based on these, and the like.

  When there is no problem in the welding quality (S4, YES), the welding condition determination method ends, and the initial condition set in S1 becomes a condition for welding performed thereafter. On the other hand, when there is a problem in the welding quality (S4, NO), the initial conditions set in S1 are changed so as to suppress the generation of the softened layer (S5).

Here, the generation | occurrence | production prediction process of the softening layer of S3 is demonstrated in detail.
Before describing the embodiment, a comparative example of a method for predicting the occurrence of a softened layer will be described with reference to FIG. FIG. 5 is a schematic diagram in which the temperature history of the cross section of the welded portion is superimposed on a CCT (Continuous Cooling Transformation) diagram of SKD61, which is an example of tool steel. In FIG. 5, the broken line shows SKD61, and the continuous line has shown the temperature history of the cross section of a welding part. In FIG. 5, the vertical axis represents temperature (° C.), and the horizontal axis represents cooling time (min) from the maximum attained temperature of 1030 ° C. In FIG. 5, B, P, and M are temperature-time regions in which a bainite phase, a pearlite phase, and a martensite phase are generated, respectively.

  It is believed that the softened layer is caused by a phase transformation that occurs in HAZ. For this reason, as shown in FIG. 5, a method of obtaining the “cooling rate” from the CCT diagram, verifying the phase transformation, estimating the microstructure of the weld, and predicting the occurrence of the softened layer is conceivable. However, the shape and cooling rate of each region must be verified / calculated one by one, and the computation takes time.

  Therefore, in the embodiment, the generation of the softened layer is simply predicted using the past actual measurement value without using the cooling rate of the welded portion. FIG. 4 is a diagram showing the relationship between the “exposure time” of the laser and the “temperature” of the cross section of the weld. In FIG. 4, the horizontal axis represents time, and the vertical axis represents temperature.

  For example, in laser welding in which the base material is alloy tool steel SKD, since the heat input energy is large, the softened layer is formed by changing the pearlite phase from a layered structure to a granular structure in the heat-affected zone. Therefore, in laser clad welding in which the base material is alloy tool steel SKD, the appearance of a pearlite phase in the heat-affected zone is considered to generate a softened layer.

  First, an actual measurement value relating to the hardness of the cross section of the welded portion is acquired. Then, the phase transformation region appearance condition is specified from the relationship between the exposure time and the temperature at which the actual measurement value is obtained, and stored in the actual measurement database. For example, in laser clad welding in which the base material is alloy tool steel SKD, the condition that the pearlite phase appears in the heat affected zone can be specified as the temperature of the heat affected zone in the range of 500 to 600 ° C. By satisfying this phase transformation region appearance condition, it is considered that a softened layer having a Vickers hardness of Hv 60 or less is generated.

  In FIG. 4, a region surrounded by an alternate long and short dash line represents a pearlite phase transformation region where a pearlite phase appears. When predicting the occurrence of a softened layer in the heat affected zone, referring to the measured DB, the region of the heat affected zone included in the temperature range of 500 to 600 ° C. specified as the phase transformation region appearance condition is a softened layer It is regarded. In the embodiment, the calculation is not performed for other phase transformation regions such as a ferrite phase and a martensite phase. In this way, by suppressing the amount of calculation, it is possible to predict the occurrence of a softened layer in a short time.

  Note that, in arc welding or the like where the heat input energy is smaller than that of a laser, the influence of the change in the structure of the ferrite in the heat-affected zone may become greater with respect to the generation of the softened layer. In this case, the phase transformation region appearance condition in which the ferrite phase appears can also be stored in the measurement DB based on the correlation between the measured value regarding the hardness of the cross section of the weld, the exposure time, and the temperature.

  If it is determined in S4 that there is a problem in welding quality due to the generation of the softened layer, the welding conditions are changed in S5 so as to suppress the generation of the softened layer. For example, in laser clad welding, in order to suppress the generation of a softened layer, the time and amount that the powder material is in a molten state can be reduced, and the cooling rate of the molten region can be increased. For this purpose, it is possible to change welding conditions such as “narrowing the laser irradiation diameter” and “increasing the scanning speed”.

  As described above, according to the embodiment, it is possible to predict the occurrence of the softened layer directly from the hardness, temperature, and exposure time of the cross section of the weld without using the cooling rate calculation with a large amount of calculation. It is possible to determine the quality of the welding quality and change the welding conditions without requiring much time. Furthermore, by limiting the calculation area in which the generation prediction of the softened layer is limited, the calculation amount of the generation prediction of the softened layer can be reduced, and the time required for verification / calculation can be reduced.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 10 Base material 11 Heat affected zone 12 Weld metal 13 Weld zone 14 Exclusion zone 15 Stable zone 11a Softening layer 11b Hardening zone

Claims (1)

Obtaining a measured value related to the hardness of the cross section of the weld, and identifying a phase transformation region appearance condition from the relationship between the exposure time and temperature at which the measured value is obtained;
When the heat-affected zone of the weld zone is included in the phase transformation region appearance condition, assuming that a softened layer is generated in the heat-affected zone, predicting the occurrence of a softened layer;
A step of determining whether the welding quality is good or not based on the predicted generation result of the softened layer;
Based on the quality determination result of the welding quality, changing the welding conditions;
Having
Welding method.

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