A cast defect repairing process and its application in nodular cast iron part repairing

Abstract

A kind of as-cast defect repair process, difference is established according to standard casting model and defect casting model to establish molding repair area model, difference is sought between molding repair area model and the repair bottom block series model established by system in advance and the final repair bottom block number used is screened out, and then corresponding prefabricated repair bottom block is selected, 3D printing is carried out on the repair bottom block, and molding repair block is obtained, and the molding repair block is metallurgical sintered to casting body using sintering aid. By adopting conventional processes such as casting, forging, etc. to prefabricate repair bottom block and carry out 3D printing on the basis of repair bottom block, printing time can be greatly reduced and a large amount of customized material powder can be saved. By first making molding repair block and then repairing casting body by metallurgical connection method, the problem that 3D printing equipment cannot perform repair operation at specific parts of casting can be overcome, which is especially suitable for multi-site, batch repair of casting defects of larger specification nodular cast iron parts in industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of casting repair process, in particular to a foundry defect repair process and its application in nodular cast iron casting repair. BACKGROUND

[0002] Nodular cast iron casting is a kind of cast iron material casting with the second largest industrial production scale after gray cast iron, which is widely used. Various power machinery crankshafts, camshafts, connecting shafts, connecting rods, gears, clutch plates, hydraulic cylinder bodies and other components used in industry are mostly nodular cast iron castings, and nodular cast iron pipe fittings play a crucial role in water supply, gas transmission and other applications in municipal and industrial enterprises. The casting defects of nodular cast iron castings include subsurface porosity, cracks, shrinkage holes and porosity, internal non-metallic inclusions, sand holes, slag inclusions and cold shut, etc. Simple superficial defects can be repaired by simple grinding and repair welding, while deep and large area defects can easily lead to casting scrap, and many nodular cast iron castings are complex large parts with high scrap cost.

[0003] With the progress of three-dimensional modeling technology, material technology and laser processing technology, three-dimensional repair is playing an increasingly important role in various industries, and has also gradually begun to be applied in the repair of casting defects. The general procedure of three-dimensional repair can be found in the Chinese invention patent with publication number CN105598450A, which proposes a laser three-dimensional profiling repair method for damaged parts. The method first performs three-dimensional scanning on the appearance of the standard part corresponding to the damaged part, establishes a standard structure model of the part before damage, then performs three-dimensional scanning on the appearance of the damaged part to obtain an actual structure model of the damaged part, compares and processes the obtained standard structure model and actual structure model to obtain a repair area structure model corresponding to the damage area of the damaged part, processes all damage types into concave damage, and then controls the laser three-dimensional profiling equipment to repair the damage area of the damaged part according to the repair area structure model.

[0004] Applying the general 3D repair techniques described above to the repair of as-cast defects in ductile iron castings, laser 3D printing equipment is used to perform laser 3D repair on the damaged areas of milled castings. The repaired area has strong adhesion to the base material, resulting in good repair effects. However, in large-scale repair operations, the following problems remain difficult to solve: 1. Due to angle and space limitations (such as narrow inner cavity surfaces or large-angle inclined surfaces), some extended parts of casting defects are not suitable for direct printing repair on the casting substrate using laser 3D printing equipment; 2. Laser 3D printing uses layer-by-layer printing, resulting in slow execution speed, and the higher the printing accuracy, the lower the efficiency. The repair powder material is a customized material, requiring a large quantity and incurring high costs. Moreover, when the entire repair substrate is printed, the repeated high temperatures of laser melting cause significant burn-off of some functional elements in the powder, such as spheroidizing elements. Summary of the Invention

[0005] To address the problems mentioned in the background section, this invention proposes a process for repairing casting defects. By employing conventional processes such as casting and forging to prefabricate repair base blocks and establishing a database of repair base block models, the process only requires identifying and selecting suitable repair base blocks and then 3D printing them. This significantly reduces printing time and saves a large amount of custom material powder. By first creating the shaped repair block and then repairing the casting body through metallurgical connection, the problem that 3D printing equipment cannot perform repair operations on specific parts of the casting can be overcome.

[0006] The objective of this invention is achieved through the following technical solutions.

[0007] A process for repairing casting defects, wherein the casting defects include one or more of the following defects located under the surface of the casting: porosity, cracks, shrinkage cavities, non-metallic inclusions, sand holes, slag inclusions, and cold shuts. The repair process involves removing the defects present at the defective part of the casting, then using 3D printing to prepare a shaped repair block and metallurgically connecting the shaped repair block to the defective part of the casting. At least one shaped repair block includes a part made by a non-3D printing process.

[0008] The as-cast defect repair process described above includes the following steps:

[0009] S1. Perform a 3D scan on a standard casting with a complete appearance to create a standard casting model;

[0010] S2. Based on the flaw detection results, the defective parts of the casting with casting defects are ground or milled to remove the defects on the surface and below the surface, and the casting defective parts are processed into an inner concave structure that needs to be reshaped and repaired.

[0011] S3. Perform a three-dimensional scan on the casting obtained in step S2 to establish a model of the defective casting.

[0012] S4, performing a contrast difference operation on the standard casting model established in step S1 and the defect casting model established in step S3 to establish a molding repair area model corresponding to the defect removal area;

[0013] S5, performing a contrast difference operation on the molding repair area model established in step S4 and a repair base block series model pre-established by the system, and screening a final repair base block number to be used according to the contrast difference operation result;

[0014] The repair base block is a series of prefabricated blocks of the same material or adaptive material as the casting to be repaired, which are prepared in a non-3D printing manner.

[0015] The repair base block series model pre-established by the system is a series of models established by three-dimensional scanning on the series of prefabricated blocks of different sizes and / or shapes.

[0016] S6, selecting a prefabricated repair base block corresponding to the repair base block number obtained in step S5;

[0017] S7, installing the repair base block selected in step S6 on the substrate of the 3D printing device, and performing 3D printing on the repair base block after layering and slicing the model according to the result obtained by the contrast difference operation between the molding repair area model and the repair base block model, to obtain a molding repair block corresponding to the inner recess structure in step S2.

[0018] S8, coating a sintering aid on the surface of the inner recess structure and / or the surface of the molding repair block, assembling the molding repair block into the inner recess structure, and sintering the assembly part to metallurgically bond the molding repair block into the inner recess structure.

[0019] S9, performing mechanical processing and / or surface treatment on the repaired area in step S8 to obtain a repaired casting.

[0020] The casting defect repair process as described above, wherein the repair base block models of the same shape and different specifications in the repair base block series model form a model group, and a plurality of model groups are pre-established in the database, and the repair base blocks in different model groups have different shapes.

[0021] The casting defect repair process as described above, wherein the repair base block number screened according to the contrast difference operation result is a repair base block that can adapt to the inner recess structure and has the smallest printing workload when a molding repair block is obtained by 3D printing on the repair base block.

[0022] The casting defect repair process as described above, wherein the non-3D printing manner is a casting manner or a forging manner.

[0023] As the as-cast defect repairing process described above, in step S7, the surface of the repairing base block is treated before the repairing base block is installed on the substrate of the 3D printing device.

[0024] As the as-cast defect repairing process described above, in step S8, the inner recess structure is surface treated before the molding repairing block is assembled into the inner recess structure.

[0025] As the as-cast defect repairing process described above, in step S8, the sintering of the assembling part is implemented under the condition of avoiding sintering the entire casting.

[0026] The application of the as-cast defect repairing process in the repairing of nodular cast iron castings, wherein the as-cast defect repairing process is the as-cast defect repairing process described above.

[0027] As the application described above, the defect part to be repaired of the nodular cast iron casting is located in an inner cavity or a slope of the nodular cast iron casting, the inner cavity is an inner cavity that the 3D printing deposition head cannot extend into, and the slope is a slope that exceeds the effective working angle of the 3D printing deposition head.

[0028] The beneficial effects of the present application are as follows:

[0029] The as-cast defect repairing process provided by the present application comprises the following steps: establishing a molding repairing area model by subtracting a standard casting model from a defect casting model; subtracting the molding repairing area model from a series of repairing base block models previously established by the system and screening out a final repairing base block number for use; selecting a corresponding prefabricated repairing base block; performing 3D printing on the repairing base block to obtain a molding repairing block; and metallurgically sintering the molding repairing block to the casting body by using a sintering aid. In this process, the repairing base block is prefabricated by using conventional processes such as casting and forging, and a series of repairing base block model databases are established. When the three-dimensional repairing program is executed, only the appropriate repairing base block needs to be identified and screened, and 3D printing is performed on the basis of the repairing base block. Therefore, the printing time can be greatly reduced, and a large amount of customized material powder can be saved. Through the optimized design of the shape and specifications of the repairing base block, the rapid prefabrication of the repairing base block can be achieved on one hand, and the process optimization when printing the entire molding repairing block based on the repairing base block can be achieved on the other hand. The problem that the 3D printing device cannot perform repairing operations on specific parts of the casting body can be overcome by first manufacturing the molding repairing block and then repairing the casting body by using a metallurgical connection method.

[0030] The as-cast defect repairing process provided by the present application is particularly suitable for the repairing of casting defects of large-specification nodular cast iron castings in industrial production, and is suitable for multi-site and batch repairing. The nodular cast iron castings can be saved from being scrapped due to deep casting defects. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1The series model of the repair base block established in the as-cast defect repair process provided by the embodiment of the present application.

[0032] Figure 2 A schematic diagram of the as-cast defect inside the skin of the casting targeted by the as-cast defect repair process provided by the embodiment of the present application.

[0033] Figure 3 The as-cast defect part shown in FIG. Figure 2 A processing range schematic diagram for milling and grinding processing of the as-cast defect part shown in FIG.

[0034] Figure 4 A schematic diagram of screening the repair base block compatible with the concave structure in the as-cast defect repair process provided by the embodiment of the present application.

[0035] Figure 5 A schematic diagram of printing the complete modeling repair block on the repair base block in the as-cast defect repair process provided by the embodiment of the present application.

[0036] Figure 6 A schematic diagram of metallurgical bonding the modeling repair block to the casting body in the as-cast defect repair process provided by the embodiment of the present application.

[0037] Components represented by reference numerals in the figure:

[0038] 1, repair base block; 2, concave structure; 3, modeling repair block; 4, sintering aid flux. DETAILED DESCRIPTION

[0039] Exemplary embodiments of the present disclosure will be described in greater detail below with reference to the accompanying drawings. It should be noted that these embodiments are provided so that the present disclosure can be more thoroughly understood, and the scope of the present disclosure can be completely conveyed to those skilled in the art, and the present disclosure can be implemented in various forms, and should not be limited by the embodiments set forth herein.

[0040] Embodiment

[0041] The present embodiment provides an as-cast defect repair process for repairing large-area or deep-layer as-cast defects such as pores, cracks, shrinkage porosity, non-metallic inclusions, sand holes, slag inclusions, cold shut, etc. in castings, especially as-cast defects hidden under the surface of complex shapes.

[0042] The as-cast defect repair process provided by the present embodiment is based on three-dimensional stereoscopic repair technology and is improved according to the repaired casting products and production needs. Specifically, it includes the following steps:

[0043] S1, three-dimensional scanning is performed on the standard castings with complete appearance to establish a standard casting model. The three-dimensional scanning step adopts a portable three-dimensional scanner, point cloud data is collected and calculated based on the castings to be repaired (although they are repair castings, but have complete appearance) or other castings without defects, feature parameters are obtained and stored in a computer.

[0044] S2, according to the flaw detection results in quality inspection, the defect sites of the castings with as-cast defects are polished or milled to remove the surface layer and the defects existing below the surface layer, and the as-cast defect sites are processed into concave structures that need to be remodeled and repaired.

[0045] Referring to the Figure 2 and Figure 3 , wherein, Figure 2 is a schematic diagram of an as-cast defect inside the skin of a casting to which the as-cast defect repair process provided by the embodiments of the present application is directed. The defect is found in the flaw detection process in quality inspection. Figure 3 is a machining range schematic diagram for milling and grinding the as-cast defect site shown in Figure 2 . According to the flaw detection results, the as-cast defect site may contain one or more than one of the as-cast defects such as pores, cracks, shrinkage holes and porosities, non-metallic inclusions, sand holes, slag inclusions, cold shut, etc. After polishing or milling the as-cast defect site, a concave structure that needs to be remodeled and repaired will be formed on the surface of the casting. The concave structure should cover all the as-cast defects of the polishing or milling site, or in other words, the volume of the concave structure is greater than the volume of all the as-cast defects of the polishing or milling site.

[0046] S3, three-dimensional scanning is performed on the casting obtained in step S2 to establish a defect casting model. In this step, when the three-dimensional scanning is performed to establish the defect casting model, the scanning area selected should be consistent with the scanning area in step S1, and the entire casting area is generally not selected.

[0047] S4, the standard casting model established in step S1 and the defect casting model established in step S3 are compared and subtracted to establish a modeling repair area model corresponding to the defect removal area.

[0048] In the relatively simple three-dimensional repair operation in the prior art, after the modeling repair area model corresponding to the defect removal area is established, the workpiece to be repaired can be placed on the 3D printing workbench, and the 3D printing device is used to perform layer slicing on the modeling repair area model and perform printing repair on the workpiece to be repaired. The present application is directed to repairing as-cast defects under the complex shape surface of large-scale castings, which is not convenient for the above-mentioned 3D printing operation. Therefore, the following improved modeling method is used for repair:

[0049] S5, compare the modeling repair area model established in step S4 with the repair base block 1 series model pre-established by the system to perform difference operation, and select the final repair base block 1 number according to the comparison difference operation result.

[0050] Figure 1 The repair base block series model established in the as-cast defect repair process provided by the embodiment of the application. According to the means, the repair base block 1 is a series of precast blocks of different sizes and shapes of the same material (which can also be similar or other suitable materials) as the repaired casting, which is prepared in advance by casting or forging such non-3D printing methods. The repair base block 1 series model pre-established by the system is a series of models established by three-dimensional scanning on the above series of precast blocks of different sizes and shapes.

[0051] Preferably as Figure 1 shown, in the repair base block 1 series model, the repair base block 1 models of the same shape and different specifications form a model group, and a plurality of model groups are pre-established in the database. The repair base blocks 1 in different model groups have different shapes. Specifically, a plurality of groups of repair base blocks 1 are produced at one time by using a multi-cavity casting mold in production. The structure of the repair base block 1 is a stepped structure with a circular cross section. According to the aspect ratio, different model groups are divided, for example, the repair base blocks 1 in the same model group have the same aspect ratio but different maximum diameters and heights, and the repair base blocks 1 in different model groups have different aspect ratios. Each repair base block 1 in the database has a corresponding actual spare part number.

[0052] Figure 4 The schematic diagram for screening the repair base block adapted to the concave structure in the as-cast defect repair process provided by the embodiment of the application. The first condition for selecting the final repair base block 1 number according to the comparison difference operation result in step S5 is to select the repair base block 1 that can adapt to the concave structure 2 and has the smallest printing workload when the modeling repair block 3 is obtained by 3D printing on the repair base block 1. Other conditions such as support conditions in the printing process or operation conditions in the process of connecting the modeling repair block 3 to the casting body thereafter can also be combined.

[0053] S6, select the pre-prepared repair base block 1 according to the repair base block 1 number obtained in step S5. If the repair base block corresponding to the selected number is missing in the offline spare parts warehouse, a replacement base block can be selected in the computer.

[0054] S7, install the repair base block 1 selected in step S6 to the substrate of the 3D printing device. The result obtained by comparing the modeling repair area model with the repair base block 1 model is the basis for 3D printing. After layering and slicing the model, 3D printing is performed on the repair base block 1 to obtain the modeling repair block 3 corresponding to the concave structure 2 in step S2.

[0055] Figure 5 The schematic diagram of printing the complete modeling repair block on the repair base block in the as-cast defect repair process provided by the embodiment of the present application. The 3D printing device used here is a synchronous powder feeding laser three-dimensional printing device, and other three-dimensional printing devices can also be used. Before the repair base block 1 is installed on the substrate of the 3D printing device, the repair base block 1 is subjected to surface grinding or chemical cleaning treatment to remove the oxide layer and expose the bright surface. Since the raw material iron powder for repairing nodular cast iron parts is mixed with spheroidizing inoculation powder containing magnesium and other elements, when the remaining part of the complete modeling repair block is printed on the repair base block, the repair base block itself plays a role of cooling and heat dissipation, and also reduces the burning loss of low-melting-point functional elements caused by repeated high temperature of laser melting, so that the modeling repair block has higher mechanical properties.

[0056] S8, coating the sintering aid 4 on the surface of the inner recess structure 2 and / or the surface of the modeling repair block 3, assembling the modeling repair block 3 into the inner recess structure 2, and sintering the assembly part to make the modeling repair block 3 metallurgically combined into the inner recess structure 2.

[0057] Figure 6 The schematic diagram of metallurgically combining the modeling repair block into the cast body in the as-cast defect repair process provided by the embodiment of the present application. The sintering aid 4 is preferably selected to be the same material as the base metal of the cast body, and the alloy composition can be redesigned to adjust the melting point or mechanical properties. For example, when the cast body is nodular cast iron, the sintering aid 4 is also selected to be an iron alloy powder or iron-based mixed powder containing C and Si elements, and metal elements or even non-metallic materials that can play a spheroidizing role or grain refining role can also be added. Of course, according to different technical requirements of the castings, the sintering aid 4 can also be selected to be a material different from the base metal of the cast body, for example, a base metal or alloy with a lower melting point is selected for easier sintering, which is selected according to whether the repaired castings meet all the technical requirements of the customers.

[0058] In this step, if the inner recess structure 2 has been exposed to air for a long time before the modeling repair block 3 is assembled into the inner recess structure 2, the inner recess structure 2 is also preferably subjected to surface grinding treatment to expose the bright surface again.

[0059] Although for small castings, after assembling the molding repair block 3 into the inner recess structure 2, the entire casting can also be heated in a heating furnace to sinter the assembly position, but this is not the preferred method, and the application preferably sinters the assembly position under the condition of avoiding sintering the entire casting. In operation, a local heating device can be manufactured to perform the above-mentioned sintering process outside the furnace, and in the sintering process, the sintering is performed by covering the sintering position with heat preservation material and anti-oxidation material (anti-oxidation raw material components can also be mixed into the sintering aid 4), and inert gas can also be blown to further prevent oxidation. For tubular or long strip-shaped castings, an open-tube furnace can also be used for local heating, which is easier to control the heating temperature and conditions.

[0060] S9, the repaired area in step S8 is machined and / or surface treated to obtain a repaired casting. During the sintering process of the assembly position in step S8, a counterweight is preferably used to apply a certain pressure to the molding repair block 3 to promote the diffusion of the sintering aid 4 with the molding repair block 3 and the body of the casting, and to make the sintering aid 4 dense, so that the repaired surface after sintering is flat, and for the case that the repaired surface is greatly out of tolerance, mechanical processing can be used for flattening treatment. In addition, if the casting has been subjected to surface treatment as required by the technical requirements when repairing the casting, the repaired surface and the surrounding area can also be subjected to appropriate surface treatment to ensure the consistency and integrity of the surface properties.

[0061] Application example

[0062] The cast defect repair process provided by the embodiments of the application can be applied in nodular cast iron repair, especially when the defect part to be repaired of the nodular cast iron is located in the inner cavity that cannot be inserted into by the 3D printing deposition head or the inclined surface that exceeds the effective working angle of the 3D printing deposition head.

[0063] The above description is only a preferred embodiment of the application, and the protection scope of the application should be subject to the protection scope of the claims.

Claims

1. A process for repairing as-cast defects in a ductile cast iron piece, characterized in that, The as-cast defects include one or more of the following: gas holes, cracks, shrinkage porosity, non-metallic inclusions, sand holes, slag inclusions, and cold shut defects located under the surface layer of the casting, and the defect site to be repaired is located in the inner cavity or inclined surface of the ductile iron casting. After removing the defects existing in the defect site of the casting, the repair process uses a 3D printing process to prepare a molding repair block (3) and metallurgically connects the molding repair block (3) to the defect site of the casting. At least one molding repair block (3) includes a portion made by a non-3D printing process, and specifically includes the following steps: S1. Three-dimensional scanning of a standard casting with an intact appearance to establish a standard casting model; S2. According to the flaw detection results, polishing or milling treatment is performed on the defect site of the casting with as-cast defects, the surface layer and the defects existing under the surface layer are removed, and the as-cast defect site is processed into a concave structure (2) that needs to be remodeled and repaired; S3. Three-dimensional scanning of the casting obtained in step S2 to establish a defect casting model; S4. Comparative difference operation of the standard casting model established in step S1 and the defect casting model established in step S3 to establish a molding repair area model corresponding to the defect removal area; S5. Comparative difference operation of the molding repair area model established in step S4 and the system-previously-established repair base block (1) series model to select the final repair base block (1) number according to the comparative difference operation results; The repair base block (1) is a series of pre-prepared blocks of different sizes and / or shapes of the same material or compatible material as the casting to be repaired, prepared by a non-3D printing method; The system-previously-established repair base block (1) series model is a series of models established by three-dimensional scanning of the above-mentioned series of pre-prepared blocks of different sizes and / or shapes; S6. Selection of the corresponding pre-prepared repair base block (1) according to the repair base block (1) number obtained in step S5; S7. Installation of the repair base block (1) selected in step S6 on the substrate of a 3D printing device, and layering and slicing processing of the model according to the results of the comparative difference operation of the molding repair area model and the model of the repair base block (1) for 3D printing, to obtain a molding repair block (3) corresponding to the concave structure (2) in step S2, wherein the 3D printing device is a synchronous powder feeding laser three-dimensional printing device; S8. Coating of a sintering aid (4) on the surface of the concave structure (2) and / or the surface of the molding repair block (3), assembling the molding repair block (3) into the concave structure (2), and sintering the assembly site to metallurgically bond the molding repair block (3) to the concave structure (2); S9. Mechanical processing and / or surface treatment of the repaired area in step S8 to obtain a repaired casting; In step S5, the same shape and different specifications of the repair base block (1) model in the repair base block (1) series model form a model group, and multiple model groups are pre-established in the database, and the repair base blocks (1) in different model groups have different shapes. The final repair base block (1) number screened according to the contrast difference operation result is the repair base block (1) which can adapt to the inner recess structure (2) and has the smallest printing workload when the modeling repair block (3) is obtained by 3D printing on the repair base block (1).

2. The process for repairing as-cast defects of a ductile cast iron piece according to claim 1, characterized in that, The non-3D printing mode is a casting mode or a forging mode.

3. The process for repairing as-cast defects of a ductile cast iron piece according to claim 1, characterized in that, In step S7, the repair base block (1) is surface treated before being installed on the substrate of the 3D printing equipment.

4. The process for repairing as-cast defects of a ductile cast iron piece according to claim 1, characterized in that, In step S8, the inner recess structure (2) is surface treated before the modeling repair block (3) is assembled into the inner recess structure (2).

5. The process for repairing as-cast defects of a ductile iron piece according to claim 1, characterized in that, In step S8, the sintering of the assembly part is implemented under the condition of avoiding sintering of the whole casting.

6. The application of the as-cast defect repair process in the repair of nodular cast iron parts, characterized in that, The casting defect repair process is the casting defect repair process of the nodular cast iron piece according to any one of claims 1-5.

7. Use according to claim 6, characterized in that, The defect part to be repaired of the nodular cast iron piece is located in an inner cavity or an inclined surface of the nodular cast iron piece, the inner cavity is an inner cavity which cannot be extended into by a 3D printing deposition head, and the inclined surface is an inclined surface which exceeds the effective working angle of the 3D printing deposition head.

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