Laser welding repair of 1.2738 steel plastic mold and post-weld heat treatment method thereof

Abstract

This invention discloses a laser welding repair method for 1.2738 steel plastic molds and its post-weld heat treatment, belonging to the field of plastic mold repair. The invention first uses welding wire of the same composition as the 1.2738 steel plastic mold to perform laser welding repair on the plastic mold at room temperature, and then performs post-weld heat treatment on the repaired area. During heat treatment, the repaired area and a 10 cm outer edge of the plastic mold are heated by quartz sand for heat transfer and insulation, and a flexible heating blanket is used for post-weld heat treatment. The laser welding repair method for 1.2738 steel plastic molds and its post-weld heat treatment described in this invention not only effectively avoids mold oxidation, significantly saves energy, and improves the uniformity and control accuracy of heat treatment temperature, but also ensures that the maximum difference between the Vickers hardness of the repaired area and the Vickers hardness of the mold body is less than 30 HV.

Description

Technical Field

[0001] This invention relates to a laser welding repair method for plastic molds and a post-weld heat treatment method, particularly to a laser welding repair method for 1.2738 steel plastic molds and a post-weld heat treatment method. Background Technology

[0002] To create specific textures on the surface of injection-molded products, plastic molds typically require surface etching before use. Achieving consistent etching results necessitates a uniform microstructure in the molded plastic. However, in actual production, issues frequently arise, such as machining errors, impacts or wear during transportation or service, leading to dimensional inconsistencies and unusable molds. Since the cost of a medium-sized mold can often reach millions of yuan, repairing unusable plastic molds is essential.

[0003] Laser welding is a welding method that uses a focused laser beam to bombard the workpiece, generating heat for welding. It has advantages such as low heat input and minimal weld deformation, and is currently widely used for the localized repair of plastic molds. However, in the laser welding repair process of plastic molds, due to the large size of the mold, the mold itself acts as an infinitely large cold body during weld cooling, resulting in a very rapid cooling rate of the molten weld metal. This leads to the formation of an ultrafine-grained martensitic structure. This microstructure is significantly different from the original microstructure of the plastic mold, resulting in inconsistent texture patterns during etching, severely affecting the surface quality of the injection molded product. Currently, the problem of the significant difference between the heat-affected zone and the weld microstructure of the laser-welded repair mold and the microstructure of the plastic mold body has not been effectively solved. Summary of the Invention

[0004] The purpose of this invention is to provide a laser welding repair method for 1.2738 steel plastic molds and a post-weld heat treatment method, so that the difference between the microhardness of the repaired area of ​​the plastic mold and the microhardness of the plastic mold body is less than 30HV.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] First, the plastic mold was repaired by laser welding at room temperature using welding wire material with the same composition as the 1.2738 steel plastic mold.

[0007] (1) Then perform post-weld heat treatment on the plastic mold.

[0008] Post-weld heat treatment refers to heating the laser-welded repair area of ​​the plastic mold and its outer 10 cm range to 250℃-700℃ and holding it at that temperature for 1-10 hours.

[0009] The preferred temperature for heating and holding the laser-welded repair area of ​​the plastic mold and its outer 10 cm range is 450℃-650℃, and the preferred holding time is 2-5 hours.

[0010] The laser welding repair area of ​​the plastic mold and its outer 10 cm edge are heated and kept warm. This is achieved by covering the area to be heated and kept warm with 10-12 cm thick quartz sand with an average particle size of less than 0.5 mm. The quartz sand is filled in the laser welding repair area and its outer 10 cm edge, which is surrounded by refractory asbestos, and a flexible heating blanket is placed on the surface of the quartz sand.

[0011] Flexible and deformable heating blankets refer to refractory asbestos inlaid with resistance heating wires.

[0012] A thermocouple is placed in the center of the quartz sand, and the thermocouple is connected to a temperature controller.

[0013] Due to the adoption of the above technical solutions, the laser welding repair method for 1.2738 steel plastic mold and its post-weld heat treatment method provided by the present invention have the following beneficial effects: In the post-weld heat treatment process, the use of quartz sand for heat transfer and heat preservation, and the placement of the temperature measuring thermocouple in the middle of the quartz sand, can significantly improve the temperature control accuracy and the uniformity of heating temperature; the use of a flexible heating blanket for heating can effectively address the problem of heating the curved surface of the mold. Existing research typically involves overall heat treatment of laser-welded molds or localized heat treatment using direct contact heating with an oxy-acetylene flame. Overall heat treatment requires heating the entire mold, while in actual production, only localized heat treatment is often necessary. This significantly increases the cost of heat treatment and can lead to severe oxidation of the entire mold during high-temperature heat treatment. On the other hand, using direct contact heating with an oxy-acetylene flame for localized heat treatment results in poor temperature control accuracy and temperature uniformity in the treated area. Furthermore, excessively high heating temperatures can easily cause significant grain coarsening in the heated area, or even exceed the austenitization requirements of the mold, leading to martensitic transformation and rendering the entire mold unusable. This invention uses quartz sand to uniformly transfer and insulate the mold, and refractory asbestos surrounding the quartz sand provides insulation for both the quartz sand and the mold in the repair area. Temperature is measured by a thermocouple placed in the center of the quartz sand, heated by a heating blanket covering the quartz sand, and controlled by a temperature controller connected to the thermocouple and heating blanket. This allows for high-precision and highly uniform temperature control in the areas of the mold requiring heat treatment, thereby achieving fine control of the microstructure of the mold in the repair area. Furthermore, because heat treatment is performed only on a localized area of ​​the mold (the repair area and its surrounding 10 cm radius), it significantly reduces energy consumption and saves costs compared to overall heat treatment. Attached Figure Description

[0014] Figure 1This is a schematic diagram of laser welding repair and post-weld heat treatment of 1.2738 steel plastic mold in this invention.

[0015] In the diagram, 1-plastic mold; 2-quartz sand; 3-refractory asbestos; 4-resistance heating wire; 5-heating blanket; 6-thermocouple; 7-temperature controller. Detailed Implementation

[0016] The present invention will be further described below with reference to embodiments.

[0017] Example 1

[0018] The following is a detailed explanation, using schematic diagrams of laser welding repair and post-weld heat treatment of 1.2738 steel plastic molds, as shown below. Figure 1 As shown, the plastic mold 1 was repaired by laser welding at room temperature using welding wire material with the same composition as the 1.2738 steel plastic mold 1. Then, the laser-welded repair area and its outer 10 cm radius were heat-treated at 250℃ for 10 hours. During heat treatment, a 12 cm thick layer of quartz sand 2 with an average particle size of less than 0.5 mm was used to cover the area requiring heating and heat preservation. The quartz sand filled the laser-welded repair area and its outer 10 cm radius, which was surrounded by refractory asbestos 3. A refractory asbestos heating blanket 5, embedded with a resistance heating wire 4 and capable of flexible deformation, was placed on the surface of the quartz sand. A thermocouple 6 was placed at the center of the quartz sand, and the thermocouple was connected to a temperature controller 7. The final microhardness difference between the repaired area and the plastic mold body was 28 HV.

[0019] Example 2

[0020] Laser welding repair of the plastic mold was performed at room temperature using welding wire material with the same composition as that used in the 1.2738 steel plastic mold. The repaired area and a 10 cm radius around it were then heat-treated at 700°C for 1 hour. During heat treatment, an 11 cm thick layer of quartz sand with an average particle size of less than 0.5 mm was placed over the area to be heated and maintained. This quartz sand filled the laser-welded repair area and its outer 10 cm radius, which was surrounded by refractory asbestos. A flexible refractory asbestos heating blanket with embedded resistance heating wire was then placed on top of the quartz sand. A thermocouple was placed at the center of the quartz sand and connected to a temperature controller. The final microhardness difference between the repaired area and the mold body was 20 HV.

[0021] Example 3

[0022] Laser welding repair of the plastic mold was performed at room temperature using welding wire material with the same composition as that used in the 1.2738 steel plastic mold. The repaired area and a 10 cm radius around it were then heat-treated at 380°C for 7 hours. During heat treatment, a 10 cm thick layer of quartz sand with an average particle size of less than 0.5 mm was placed over the area to be heated and maintained. This quartz sand filled the laser-welded repair area and its outer 10 cm radius, which was surrounded by refractory asbestos. A flexible refractory asbestos heating blanket with embedded resistance heating wire was then placed on top of the quartz sand. A thermocouple was placed at the center of the quartz sand and connected to a temperature controller. The final microhardness difference between the repaired area and the mold body was 10 HV.

[0023] Example 4

[0024] Laser welding repair of the plastic mold was performed at room temperature using welding wire material with the same composition as that used in the 1.2738 steel plastic mold. The repaired area and a 10 cm radius around it were then heat-treated at 650°C for 3 hours. During heat treatment, a 10 cm thick layer of quartz sand with an average particle size of less than 0.5 mm was placed over the area to be heated and maintained. This quartz sand filled the laser-welded repair area and its outer 10 cm radius, which was surrounded by refractory asbestos. A flexible refractory asbestos heating blanket with embedded resistance heating wire was then placed on top of the quartz sand. A thermocouple was placed at the center of the quartz sand and connected to a temperature controller. The final microhardness difference between the repaired area and the mold body was 15 HV.

[0025] Example 5

[0026] Laser welding repair of the plastic mold was performed at room temperature using welding wire material with the same composition as that used in the 1.2738 steel plastic mold. The repaired area and a 10 cm radius around it were then heat-treated at 550°C for 6 hours. During heat treatment, a 10 cm thick layer of quartz sand with an average particle size of less than 0.5 mm was placed over the area to be heated and maintained. This quartz sand filled the laser-welded repair area and its outer 10 cm radius, which was surrounded by refractory asbestos. A flexible refractory asbestos heating blanket with embedded resistance heating wire was then placed on top of the quartz sand. A thermocouple was placed at the center of the quartz sand and connected to a temperature controller. The final microhardness difference between the repaired area and the mold body was 6 HV.

Claims

1. A method for repairing a laser welding of a plastic mold of 1.2738 steel and post-weld heat treatment, characterized in that: First, the plastic mold is repaired by laser welding at room temperature using welding wire material with the same composition as the 1.2738 steel plastic mold. Then, the plastic mold undergoes post-weld heat treatment. The post-weld heat treatment refers to heating the laser-welded repair area of ​​the plastic mold and its outer 10 cm edge to 250℃-700℃ using a heating device and holding it at that temperature for 1-10 hours. The heating and holding of the laser-welded repair area of ​​the plastic mold and its outer 10 cm edge is achieved by covering the laser-welded repair area of ​​the plastic mold and its outer 10 cm edge with 10-12 cm thick quartz sand with an average particle size of less than 0.5 mm, and covering the surface of the quartz sand with a flexible and deformable heating blanket. The heating device is controlled by a temperature controller. ​ 2. The laser welding repair and post-weld heat treatment method of a 1.2738 steel plastic mold according to claim 1, characterized in that: The temperature for heating and holding the laser-welded repair area of ​​the plastic mold and its outer 10 cm range is 450℃-650℃, and the holding time is 2-5 hours.

3. The laser welding repair and post-weld heat treatment method of a 1.2738 steel plastic mold according to claim 1, characterized in that: The flexible heating blanket is made of refractory asbestos inlaid with resistance heating wires.

4. The laser welding repair and post-weld heat treatment method of a 1.2738 steel plastic mold according to claim 3, characterized in that: A thermocouple is placed at the center of the quartz sand, and the thermocouple is connected to a temperature controller.

5. The laser welding repair and post-weld heat treatment method of a 1.2738 steel plastic mold according to claim 4, characterized in that: The quartz sand is filled in the laser welding repair area surrounded by refractory asbestos and within 10 centimeters of its outer edge.

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