Preparation method for internal thread of MIM metal workpiece
By embedding soluble injection molding materials into MIM metal workpieces to prepare threaded mandrels, and combining ultrasonic cleaning and sintering technologies, the problem of internal thread processing in MIM metal workpieces has been solved, achieving high-precision, smooth-surface internal thread forming and efficient mass production.
Patent Information
- Application Number
- CN202610088743.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-22
- Publication Date
- 2026-04-10
AI Technical Summary
Existing technologies struggle to efficiently process special internal threads on MIM metal workpieces, especially micro-threads, deep-hole threads, thin-walled threads, and threads on extra-hard materials, resulting in problems such as easy tool damage, high processing difficulty, and low precision.
Threaded mandrels are prepared using soluble injection molding materials. They are then formed using MIM molds, dissolved, and combined with degreasing and sintering to produce MIM metal workpieces with internal threads. The process includes ultrasonic cleaning and alternating pulses of pressurized water to remove residues, ensuring thread accuracy and integrity.
It achieves high-precision and smooth surface forming of internal threads in MIM metal workpieces, eliminating the need for subsequent tapping processes, and enabling high-strength, high-precision, and high-efficiency mass production. The thread accuracy can reach IT7 to IT8 level, and the surface roughness Ra < 1.6 micrometers.
Smart Images
Figure CN121820663A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of powder metallurgy technology, and in particular to a method for preparing internal threads on MIM metal workpieces. Background Technology
[0002] Metal powder injection molding (MIM) is widely used because it can efficiently manufacture metal parts with complex three-dimensional shapes.
[0003] Currently, machining special internal threads on many MIM metal workpieces is challenging. For example, machining micro-threads (such as those below M1.4) is extremely difficult due to the tiny thread size, leading to frequent tool breakage and very low yield rates with traditional mechanical tapping. Deep hole thread machining presents difficulties in chip removal and tool breakage. Thin-walled thread machining can result in deformation of the thin-walled portion due to the cutting force required for tapping. Non-axial thread machining presents challenges in tool entry or even complete failure. Furthermore, machining threads in extremely hard materials results in low tool life due to the high hardness of the substrate. Therefore, how to machine special internal threads on MIM metal workpieces is a pressing issue that needs to be addressed. Summary of the Invention
[0004] To address the aforementioned problems, this invention provides a method for preparing internal threads in MIM metal workpieces. This method can produce internal thread structures with precise dimensions and smooth surfaces, eliminates the need for subsequent tapping processes, and enables high-strength, high-precision, and high-efficiency mass production.
[0005] To achieve the above objectives, the technical solution provided by the present invention is as follows: This invention provides a method for preparing internal threads in a MIM metal workpiece, comprising the following steps: S1, injection molding a soluble injection molding material into a threaded mandrel with external threads; S2, using the threaded mandrel obtained in S1 as an insert and fixing it into the MIM mold cavity of the MIM metal workpiece; S3, injecting feed material into the MIM mold cavity and wrapping the threaded mandrel to form a composite green body within the MIM mold cavity; S4, immersing the composite green body obtained in S3 into a dissolving solution to completely dissolve the threaded mandrel and form a MIM semi-finished product; S5, sequentially degreasing and sintering the MIM semi-finished product obtained in S4 to finally prepare a MIM metal workpiece with internal threads.
[0006] Furthermore, in S1, the soluble injection molding material is PA46 resin or PMMA resin.
[0007] Furthermore, in S4, the dissolving solution is a formic acid solution.
[0008] Furthermore, the formic acid solution is used to rinse the threaded mandrel on the composite green blank using alternating ultrasonic cleaning and pressurized water pulses to remove residues in the thread gaps, thereby obtaining clean and complete internal threads.
[0009] Furthermore, in S5, the degreasing includes catalytic degreasing and thermal degreasing.
[0010] Furthermore, during catalytic degreasing, the MIM semi-finished product is placed in a nitric acid atmosphere at 110–120°C to remove the POM-based binder.
[0011] Furthermore, in S2, the two ends of the threaded mandrel are respectively provided with a positioning structure and a support structure to ensure that it does not shift or twist during the high-pressure injection process.
[0012] Furthermore, in S3, the feeding is TC4 feeding.
[0013] The technical solution provided by this invention has the following beneficial effects: This invention involves implanting a soluble threaded mandrel into the cavity of a MIM mold for secondary forming to obtain a composite green blank. The threaded mandrel is then removed by dissolution. Finally, MIM degreasing and sintering are used to prepare a MIM metal workpiece with internal threads. Therefore, this invention can produce MIM metal workpieces with precise dimensions, smooth surfaces, and built-in thread structure in one step during the MIM forming process, and can also eliminate the subsequent tapping process. At the same time, it can achieve high-strength, high-precision, and high-efficiency mass production of MIM metal workpieces. Attached Figure Description
[0014] Figure 1 The diagram shown is a schematic of the threaded mandrel, MIM half-product, and MIM metal workpiece in the embodiment. Figure 2 The diagram shown is a schematic of the composite green body in the embodiment. Detailed Implementation
[0015] To further illustrate the various embodiments, the present invention provides accompanying drawings. These drawings are part of the disclosure of the present invention and are mainly used to illustrate the embodiments, and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these drawings, those skilled in the art should be able to understand other possible implementations and the advantages of the present invention. Components in the drawings are not drawn to scale, and similar component symbols are generally used to represent similar components.
[0016] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments.
[0017] Reference Figure 1 and Figure 2 This embodiment provides a method for preparing internal threads on MIM metal workpieces, applicable to the one-time, high-precision, and mass production of MIM metal workpieces with internal thread structures (such as micro threads, deep hole threads, or irregular position threads), and specifically includes the following steps: Step S1: The soluble injection molding material is injection molded into a threaded mandrel 1 with external threads through a threaded core mold, wherein the soluble injection molding material is PA46 resin material.
[0018] Step S2: The threaded mandrel 1 is used as an insert and fixed inside the MIM mold cavity of the MIM metal workpiece.
[0019] Step S3: TC4 is injected into the MIM mold cavity and wrapped around the threaded mandrel 1 to form a composite green body 2 inside the MIM mold cavity.
[0020] Step S4: Immerse the composite green blank 2 in the dissolving solution to completely dissolve the threaded mandrel 1 and form the MIM semi-finished product 3, wherein the specific dissolving solution is a formic acid solution.
[0021] In step S5, the MIM semi-finished product 3 is subjected to catalytic degreasing, thermal degreasing, and sintering in sequence to finally prepare a MIM metal workpiece 3' with internal threads. During catalytic degreasing, the MIM semi-finished product 3 is placed in a nitric acid atmosphere at 110-120°C to remove the POM-based binder. Naturally, the overall structure of the MIM metal workpiece 3' is similar to the overall structure of the MIM semi-finished product 3.
[0022] In this embodiment, formic acid solution is used to rinse the threaded mandrel 1 on the composite green blank 2 with alternating ultrasonic cleaning and pressurized water pulses to remove residues in the thread gaps or narrow thread grooves, thereby obtaining a clean and complete internal thread and ensuring the assembly performance of the subsequent thread.
[0023] Furthermore, the combined use of the threaded core mold, the MIM mold, and the soluble core structure ensures that the thread structure of the composite green body 2 has extremely high thread accuracy.
[0024] When the MIM semi-finished product 3 is sintered, it can achieve high-precision shrinkage to ensure that the thread structure of the MIM metal workpiece 3' remains intact, and its thread density is accurate, and its mechanical strength is almost close to that of the post-processing method.
[0025] In summary, the preparation method of this embodiment involves implanting a soluble threaded mandrel 1 into the cavity of a MIM mold for secondary molding to obtain a composite green blank 2. The threaded mandrel 1 is then removed by dissolution. Finally, the MIM metal workpiece 3' with internal threads is prepared by MIM degreasing and sintering. Therefore, this invention can produce a MIM metal workpiece 3' with precise dimensions, smooth surface and built-in thread structure in one step during the MIM molding process. It can also eliminate the subsequent tapping process and achieve high-strength, high-precision and high-efficiency mass production of MIM metal workpieces 3'.
[0026] Of course, in other embodiments, the soluble injection molding material may also be a PMMA resin material.
[0027] More preferably, in step S2, the two ends of the threaded mandrel 1 are respectively provided with a positioning structure and a support structure to ensure that it does not shift or twist during the high-pressure injection process.
[0028] In addition, compared with the prior art, the preparation method of this embodiment has the following significant advantages: 1. The preparation method of this embodiment can directly form threads with a dimensional accuracy of IT7 to IT8 and a surface roughness Ra < 1.6 micrometers. Therefore, the thread accuracy of this embodiment far exceeds that of traditional tapping.
[0029] 2. The preparation method of this embodiment breaks through the limitations of traditional machining and can easily produce special threads such as micro threads, deep hole blind threads, and non-axial threads. It can also process internal threads in MIM metal workpieces with extremely high hardness 3' material, thus having the ability to process a variety of thread processing materials.
[0030] 3. The preparation method of this embodiment can eliminate the tapping process and realize the whole process production. Therefore, the MIM metal workpiece 3' or part has good consistency and high production efficiency.
[0031] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.
Claims
1. A method for preparing internal threads on a MIM metal workpiece, characterized in that, Includes the following steps: S1, Injecting soluble injection molding material into a threaded mandrel with external threads; S2, the threaded mandrel obtained in S1 is used as an insert and fixed in the MIM mold cavity of the MIM metal workpiece; S3, the feed material is injected into the MIM mold cavity and wrapped around the threaded mandrel to form a composite green body inside the MIM mold cavity; S4, the composite green blank obtained in S3 is immersed in the dissolving solution to completely dissolve the threaded mandrel and form a MIM semi-finished product; S5, the MIM semi-finished product obtained in S4 is degreased and sintered in sequence to finally prepare a MIM metal workpiece with internal threads.
2. The method for preparing internal threads on a MIM metal workpiece according to claim 1, characterized in that: In S1, the soluble injection molding material is PA46 resin or PMMA resin.
3. The method for preparing internal threads on a MIM metal workpiece according to claim 2, characterized in that: In S4, the dissolving solution is a formic acid solution.
4. The method for preparing internal threads on a MIM metal workpiece according to claim 3, characterized in that: The formic acid solution is used to rinse the threaded mandrel on the composite green blank using alternating ultrasonic cleaning and pressurized water pulses to remove residues in the thread gaps, thereby obtaining clean and complete internal threads.
5. The method for preparing internal threads on a MIM metal workpiece according to claim 1, characterized in that: In S5, the degreasing includes catalytic degreasing and thermal degreasing.
6. The method for preparing internal threads on a MIM metal workpiece according to claim 5, characterized in that: During catalytic degreasing, the MIM semi-finished product is placed in a nitric acid atmosphere at 110–120°C to remove the POM-based binder.
7. The method for preparing internal threads on a MIM metal workpiece according to claim 1, characterized in that: In S2, the two ends of the threaded mandrel are respectively provided with a positioning structure and a support structure to ensure that it does not shift or twist during high-pressure injection.
8. The method for preparing internal threads on a MIM metal workpiece according to claim 1, characterized in that: In S3, the feeding method is TC4 feeding.