Anti-deformation processing method for precise thin-walled open piece and transition structure thereof

Abstract

The application provides a precision thin-wall open piece anti-deformation processing method and a transition structure, and relates to the technical field of precision metal piece processing. The basic flow of the processing method is rough processing, setting a removable process structure, carburizing treatment and removing the process table. The designed removable process structure disperses the stress at the opening root generated in the heat treatment process and ensures uniform structure. The corresponding transition structure comprises a part body and an integrally formed removable process structure. The process structure is removed after heat treatment and does not affect the function of the part. The application can significantly reduce the risk of deformation and cracking of the part opening, does not require additional special anti-deformation tooling, has strong universality, and improves the processing precision, reliability and production efficiency of the part.

Description

Technical Field

[0001] This invention relates to the field of precision metal parts machining technology, and in particular to a machining method for preventing deformation and root cracks in precision open parts during carburizing and heat treatment, as well as a removable transition structure used in this method. In this transition structure, the process table completely closes the original open opening of the part, forming a temporary closed-loop structure. Background Technology

[0002] Precision opening components (such as various snap-fit ​​components and flexible connectors) are widely used in aerospace, precision instruments, and other fields. The dimensional accuracy and root strength of these openings directly affect assembly accuracy and service life. These parts typically require carburizing and heat treatment processes. Carburizing improves the surface hardness of the parts, while heat treatment ensures their overall mechanical properties. However, due to the unique structure of the openings, significant stress concentration and inconsistent microstructure transformation occur at the root of the opening during carburizing and heat treatment. This can easily lead to dimensional deviations, bending deformation, and microcracks at the root, resulting in a high scrap rate and severely impacting product performance and production efficiency.

[0003] In existing technologies, such as the gear carburizing and quenching anti-deformation separation tooling disclosed in CN219730984U, an anti-deformation collar is used to mate with the gear. After heat treatment, the two are separated by a separation component. However, this method has drawbacks such as poor versatility, complex separation process, and increased tooling costs. Another example is the method and mold for preventing deformation of ultra-thin spring sheets during heat treatment disclosed in CN103757193B. This solution uses a special mold to apply preload to the spring sheet and corrects the deformation through tempering. However, this method is only suitable for thin plate parts such as spring sheets, the mold structure is complex, and it cannot solve the fundamental problem of stress concentration at the root of open parts. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of excessive deformation and root cracks in precision open parts caused by stress concentration and inconsistent microstructure transformation during carburizing and heat treatment. At the same time, it overcomes the shortcomings of existing technologies such as strong tooling dependence, poor versatility and complex processes, and provides a precision thin-walled open part anti-deformation processing method and its transition structure.

[0005] The inventive concept of this invention:

[0006] For parts with openings, those skilled in the art generally follow the conventional process path of machining the opening first and then heat treating it; that is, machining the opening to its final shape before heat treatment. This path is the most direct and economical. However, the inventors of this application have found through extensive practical verification that the thermal and structural stresses generated by heat treatment can cause severe stress concentrations at geometric discontinuities such as the ends and roots of the opening, leading to uncontrollable plastic deformation or even cracking at the opening, which cannot be corrected later, and in severe cases, directly causing the part to be scrapped. This is usually attributed to improper control of heat treatment parameters in the art, and attempts have been made to mitigate the opening deformation and cracking problems by optimizing the heat treatment process, but a fundamental solution has not been found.

[0007] In contrast to the conventional processing path described above, this invention proposes a preventative processing approach. Before heat treatment, the part is intentionally not machined into a final open opening. Instead, a removable process structure is added to temporarily close the opening to be formed. This removable process structure effectively connects the two sides of the opening, allowing stress generated during heat treatment to be dissipated and preventing stress concentration at the root. It also constrains the geometry of the open opening. After heat treatment, this process structure is removed through precision machining, ultimately forming an open opening that meets the design requirements.

[0008] Those skilled in the art would generally believe that since an opening is ultimately required, it should be processed as thoroughly as possible before heat treatment. However, this invention proactively adds a step, which would be redundant in conventional logic. But it is precisely this extra step that, through the synergistic effect of stress guidance and form and position constraints of the formed closed structure, fundamentally solves the problem of excessive deformation and cracking during heat treatment of open openings, achieving the technical effect of significantly reducing deformation and reducing the crack rate to zero.

[0009] To achieve the above objectives, the technical solution provided by this invention is:

[0010] A method for preventing deformation of precision thin-walled open parts includes the following steps:

[0011] Step 1: Before heat treatment, a removable process structure is machined at the open opening to be formed on the thin-walled part blank. The removable process structure temporarily closes and connects the solid parts on both sides of the open opening into one piece in the non-functional area of ​​the open opening; the removable process structure is integrally formed with the main body of the thin-walled part blank.

[0012] Non-functional areas refer to the regions of the final thin-walled open component that are not subject to external forces and do not participate in assembly during use;

[0013] Step 2: Heat treat the thin-walled part blank with removable process structure;

[0014] Step 3: The removable process structure is removed by cutting to form the final open opening, resulting in a thin-walled open part.

[0015] Furthermore, in step 1, the removable process structure extends outward along the axis of the main body of the part at the open opening, with an extension length of 4 to 6 mm and a wall thickness equal to the wall thickness of the main body of the part.

[0016] Furthermore, the heat treatment includes, in sequence: copper plating on the non-carburized surface, carburizing the carburized surface, copper removal on the non-carburized surface, and quenching and low-temperature tempering of the entire part.

[0017] Furthermore, the thin-walled part blank has a rotating structure; step 3 includes the following sub-steps:

[0018] Step 3.1: Perform semi-finish grinding on the outer circle of the thin-walled part blank with a removable process structure;

[0019] Step 3.2: Using the semi-finished outer circle as a reference, perform semi-finishing on the inner hole of the thin-walled part blank.

[0020] Step 3.3: Using the semi-finished outer circle as a reference, the removable process structure is removed in one go by wire cutting.

[0021] Step 3.4: Finish machining to the required dimensions for the thin-walled open part.

[0022] Furthermore, in step 3.4, the finishing process includes coordinate grinding, which grinds and cuts the inner hole, outer circle, and side of the open opening of the part in one clamping, ensuring that the symmetry of the open opening to the outer circle is ≤0.01mm, the coaxiality of the inner hole and the outer circle is ≤0.02mm, and the surface roughness Ra is ≤0.1μm.

[0023] Furthermore, a surface treatment step is included after step 4.

[0024] The present invention also provides an anti-deformation transition structure for the above-mentioned anti-deformation processing method for a precision thin-walled open part, the anti-deformation transition structure comprising a part body and a removable process structure; the part body has an open opening to be formed;

[0025] The removable process structure is set in the non-functional area of ​​the open opening to be formed. It is an integral structure with the main body of the part and connects the solid parts on both sides of the opening in the non-functional area into one piece, so that the open opening is closed before heat treatment. The non-functional area refers to the area of ​​the thin-walled open part that is not subject to external force and does not participate in assembly during use. The removable process structure is designed to: relieve the heat treatment stress on the open opening during heat treatment and constrain the geometry of the open opening, and remove it by wire cutting after heat treatment to form the final open opening.

[0026] Furthermore, the removable process structure is an annular process stage integrally formed with the main body of the part. The port of the annular process stage has a 60° chamfer as a center hole, which is used to position the part through the center during the processing.

[0027] The advantages of this invention are:

[0028] 1. This invention relates to a removable process structure integrally machined with the non-functional area of ​​an open opening to be formed on a thin-walled part blank. This removable process structure is integrally formed with the part body and removed after heat treatment. During heat treatment, the removable process structure temporarily closes the open opening, improving the distribution of thermal stress, the uniformity of quenching cooling, and the consistency of microstructure transformation during heat treatment processes such as carburizing and quenching. This reduces the problem of deformation exceeding tolerances due to stress concentration during carburizing and heat treatment of the open part, avoids the generation of cracks at the root of the opening, improves the strength and reliability of the part, and reduces the scrap rate. Experiments show that, under the same conditions, the flatness deformation of the open opening after treatment using the invention method is reduced from 0.3 mm to less than 0.1 mm, and the deformation of the outer diameter of the part is reduced from 0.5 mm to less than 0.1 mm.

[0029] 2. The removable process table designed in this invention is integrally formed with the main body of the part, eliminating the need for additional special anti-deformation tooling. The method is simple and universal, reducing the processing cost and cycle time of thin-walled open parts.

[0030] 3. The method of the present invention is not limited by the shape of the part and is applicable to various opening forms such as rotating bodies, rectangles, U-shapes, and irregular shapes, and has strong versatility. Attached Figure Description

[0031] Figure 1 This is a process flow diagram of the method of the present invention;

[0032] Figure 2 This is a three-dimensional structural view of the final part that needs to be processed and formed in the embodiment of the present invention;

[0033] Figure 3These are multiple views of the final part that needs to be processed and formed in the embodiments of the present invention, wherein (a) is the main view and (b) is the sectional view;

[0034] Figure 4 This is a perspective view of a transition structure with a process table designed in an embodiment of the present invention. The process table can be removed to completely close the opening slot, forming a temporary closed-loop structure.

[0035] Figure 5 These are multiple views of the transition structure with a process station in an embodiment of the present invention; wherein (a) is the main view and (b) is a sectional view.

[0036] In the diagram: 1 - main body of the part, 2 - removable process structure, 3 - open opening, 4 - top hole. Detailed Implementation

[0037] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0038] This invention completely seals the opening by adding a removable process structure and achieves stress dispersion during the heat treatment process of the opening through an optimized processing flow. The deformation-resistant transition structure for carburizing and heat treatment of precision thin-walled opening parts provided in this embodiment includes a main body 1 and a removable process structure 2. This removable process structure is located at the end of the open opening 3 to be formed on the main body of the part, and is situated in its non-functional area. The removable process structure extends outward along the axial direction of the main body of the part at the opening end. The non-functional area referred to here is the region of the final thin-walled opening part that is not subject to external force, does not participate in assembly, or is not used during use; its location includes the outer end face of the opening, the outer wall of the opening edge, etc. This removable process structure is integrally formed with the main body of the part and closes the open opening to be formed, creating a temporary closed-loop structure, allowing the part to temporarily become a complete ring-shaped or frame-shaped part during heat treatment.

[0039] The designed removable process structure is adapted to the open opening to be formed, which includes, but is not limited to, rectangular, U-shaped, or irregular cross-sections. The axial dimension of the designed removable process structure is 4-6 mm, and the wall thickness can be designed to be equal to the wall thickness of the main body of the part, or the wall thickness can be increased according to the allowance of the inner and outer diameter dimensions of the main body of the part.

[0040] Reference Figure 1This embodiment describes the machining of a regular rotating thin-walled open part as an example. The rotating thin-walled open part is made of 12CrNi4A material, with an outer diameter of 19mm and an inner diameter of 12.5mm. The width of the open opening 3 is 9.5mm and its length is 16mm. The wall thickness of the part body is 3mm. The symmetry of the open opening with respect to the outer circle of the part body is required to be less than or equal to 0.01mm, the roughness of the inner surface of the open opening is required to be less than or equal to Ra0.1μm, and the coaxiality of the inner hole and outer circle of the part body is required to be less than or equal to 0.02mm. A bar stock with a blank diameter of 22mm is selected as the part blank for machining. The precision thin-walled open part anti-deformation machining method described in this embodiment includes the following steps:

[0041] Step 1: 3D modeling and process table design.

[0042] Based on the opening shape and dimensions of the thin-walled open part of the rotating body, a three-dimensional digital model of the part is drawn in three-dimensional software. A ring-shaped process stage extending axially along the main body of the part is added to the non-functional area of ​​the opening, serving as a removable process structure in this embodiment. This ring-shaped process stage will be used in this embodiment. The wide, open opening is completely closed. In this embodiment, the wall thickness of the annular process stage is designed to be 3.25 mm, and the axial dimension is 4 mm.

[0043] Step 2: Determine the machining process route based on the part shape and actual machining requirements. In this embodiment, the determined machining route includes rough machining, heat treatment, finishing the center hole in the annular process table, semi-finish grinding the part reference, cutting the annular process table, and finish grinding.

[0044] Step 3: Select the blank. In this embodiment, for rotating parts, bar stock is preferred as the blank; for other shaped parts, profiles or forgings can be selected.

[0045] Step 4: First, use turning to roughly machine a semi-finished part with a process table (structure as follows). Figure 4 and Figure 5 As shown in the figure, a 0.4mm allowance is left for the outer diameter and inner hole during machining. The axial length of the annular process table is machined to 4mm, and a 60° internal tapered chamfer is made at the opening of the annular process table as the center hole 4, which is used to position the part using the center during subsequent machining. To ensure convenient machining and minimize the amount of material removed later, the annular process table is made into a hollow structure that matches the size requirement of the inner hole of the main body of the part, and a grinding allowance of about 0.4mm is reserved.

[0046] Then, a closed rectangular opening groove is formed on the semi-finished part by CNC machining. A grinding allowance of 0.15mm is reserved on one side of the closed rectangular opening groove, and the burrs on the closed rectangular opening groove are removed.

[0047] Finally, the part is positioned by machining the center hole 4, and the inner hole and outer circle of the part are ground as a reference for semi-finish grinding and fine grinding of the part after heat treatment.

[0048] Step 5: Perform heat treatment on the part formed in Step 4, including copper plating on the non-carburized surface, carburizing the carburized surface, copper removal on the non-carburized surface, and quenching and low-temperature tempering of the entire part. In this embodiment, the carburized surface is the sidewall of the closed rectangular opening groove processed in Step 4. Wherein:

[0049] Carburizing treatment: The carburizing temperature can be 880-930℃, the time is 5 hours, the carburized layer thickness is 0.8mm to 1.0mm, and the thickness of the carburized layer after grinding is about 0.6-0.8mm. In this embodiment, the carburizing temperature is selected as 900℃, the carburizing time is 5 hours, and the carburized layer depth is 0.9mm.

[0050] Quenching treatment: The carburized parts are immersed in quenching oil at 820±20℃, and then cooled by ice refrigeration for 2-3 hours. In this embodiment, quenching oil at 810℃ is used for quenching treatment, and ice refrigeration is performed at -70℃ for 3 hours. After quenching, the hardness of the carburized surface is HRC60 to HRC65, and the hardness of the remaining non-carburized parts is HRC32 to HRC38.

[0051] Low-temperature tempering treatment: The quenched parts are tempered at 150°C for 2-4 hours, and then cooled by air cooling. In this embodiment, the tempering temperature is 150°C and the time is 3 hours.

[0052] Step 6: Grind the center hole and semi-finish grind the outer diameter and inner hole of the main body of the part.

[0053] Use the double center holes to position and grind the outer diameter of the main body of the part, leaving a fine grinding allowance of 0.05mm on one side; use the outer diameter as a reference to grind the inner hole of the main body of the part, ensuring that the inner and outer diameters are coaxial.

[0054] Step 7: Wire EDM process table.

[0055] Using the outer diameter of the part as a reference, the added annular process stage is removed in one pass using wire cutting. The shape of the part after cutting is as follows: Figure 2 and Figure 3 As shown.

[0056] Step 8: Perform precision grinding on the cut parts, including blade grinding and coordinate grinding. Among these:

[0057] The sharpening process is as follows: using the outer circular surface of the main body of the part as a reference, sharpen the side wall of the opening groove, leaving a 0.03mm allowance on each side.

[0058] Coordinate grinding: Using the outer cylindrical surface of the part body as a reference, coordinate grinding is employed in a single setup to grind the inner hole, outer diameter, and the side surfaces of open openings, ensuring that the dimensions, geometric tolerances, and surface roughness of the open openings meet the machining design requirements. In this embodiment, the symmetry of the open opening to the outer diameter is ≤0.01mm, the coaxiality between the inner hole and the outer diameter is ≤0.02mm, and the surface roughness is ≤Ra0.1μm. The coordinate grinding method described refers to grinding performed on a high-precision coordinate grinding machine using the coordinate positioning principle; it is a mature technology in the machining field.

[0059] Step 9: Perform surface treatment.

[0060] The appropriate surface treatment is performed according to the part design requirements. This surface treatment includes, but is not limited to, rust prevention, surface strengthening, or plating. Rust prevention treatments include, for example, applying rust-preventive oil, phosphating, or bluing; surface strengthening treatments include, for example, spraying; and plating treatments include, for example, zinc plating or chrome plating. In this embodiment, the surface treatment performed is bluing.

[0061] To demonstrate the reliability of the method of this invention, this embodiment inspected the finished rotating open part obtained based on this method. Upon inspection, the designed inner diameter of the part was found to be... mm, the measured value is 12.508 mm; the design value for the opening groove width is... The measured value is 9.506 mm; the designed outer diameter is... The measured value is 18.99 mm; the design value for the symmetry of the opening groove to the outer circle is 0.01 mm, and the measured value is 0.005 mm; the design value for the coaxiality of the inner and outer circles is 0.02 mm, and the measured value is 0.01 mm. All the above parameters meet the product design requirements, and no cracks were found at the root of the opening after magnetic particle inspection.

[0062] Extensive processing practice has verified that thin-walled open parts processed using the method of this invention exhibit significantly enhanced strength, with opening deformation of only 0.06–0.08 mm, fully meeting design requirements and preventing the formation of cracks at the opening root.

[0063] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A method for preventing deformation in precision thin-walled open parts, characterized in that, Includes the following steps: Step 1: Before heat treatment, a removable process structure is machined at the open opening to be formed on the thin-walled part blank. The removable process structure temporarily closes and connects the solid parts on both sides of the open opening into one piece within the non-functional area of ​​the open opening; the removable process structure is integrally formed with the main body of the thin-walled part blank. The non-functional area refers to the area of ​​the final thin-walled open component that is not subject to external forces and does not participate in assembly during use. Step 2: Heat treat the thin-walled part blank with removable process structure; Step 3: The removable process structure is removed by cutting to form the final open opening, thus obtaining the thin-walled open part.

2. The method for preventing deformation of a precision thin-walled open component according to claim 1, characterized in that, In step 1, the removable process structure extends outward along the axis of the main body of the part at the open opening, with an extension length of 4 to 6 mm and a wall thickness equal to the wall thickness of the main body of the part.

3. The method for preventing deformation of a precision thin-walled open component according to claim 1, characterized in that, The heat treatment process includes, in sequence: copper plating on the non-carburized surface, carburizing the carburized surface, copper removal on the non-carburized surface, and quenching and low-temperature tempering of the entire part.

4. The method for preventing deformation of a precision thin-walled open component according to claim 1, characterized in that, The thin-walled part blank has a rotating structure; step 3 includes the following sub-steps: Step 3.1: Perform semi-finish grinding on the outer circle of the thin-walled part blank with a removable process structure; Step 3.2: Using the semi-finished outer circle as a reference, perform semi-finishing on the inner hole of the thin-walled part blank. Step 3.3: Using the semi-finished outer circle as a reference, the removable process structure is removed in one go using wire cutting. Step 3.4: Finish machining to the required dimensions for the thin-walled open part.

5. The method for preventing deformation of a precision thin-walled open component according to claim 4, characterized in that, In step 3.4, the finishing process includes coordinate grinding, which grinds and cuts the inner hole, outer circle, and side of the open opening of the part in one clamping, ensuring that the symmetry of the open opening to the outer circle is ≤0.01mm, the coaxiality of the inner hole and the outer circle is ≤0.02mm, and the surface roughness Ra is ≤0.1μm.

6. The method for preventing deformation of a precision thin-walled open component according to claim 1, characterized in that, A surface treatment step is included after step 4.

7. A deformation-resistant transition structure for use in the deformation-resistant machining method for a precision thin-walled open part as described in any one of claims 1-6, characterized in that, The anti-deformation transition structure includes a main part body and a removable process structure; the main part body has an open opening to be formed. The removable process structure is set in the non-functional area of ​​the open opening to be formed, and is an integral structure with the main body of the part. It connects the solid parts on both sides of the opening in the non-functional area into one piece, so that the open opening is closed before heat treatment. The non-functional area refers to the area of ​​the thin-walled open part that is not subject to external force and does not participate in assembly during use. The removable process structure is configured to: relieve the heat treatment stress on the open opening during the heat treatment process and constrain the geometry of the open opening, and remove it by wire cutting after the heat treatment is completed to form the final open opening.

8. The anti-deformation transition structure according to claim 7, characterized in that, The removable process structure is an annular process table integrally formed with the main body of the part. The port of the annular process table has a 60° chamfer as a center hole, which is used to position the part through the center during the processing.

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