Titanium alloy earphone shell and production method thereof

Abstract

The invention relates to the technical field of medical instrument electronic product manufacturing, and particularly provides a titanium alloy earphone shell and a production method thereof.The method comprises the steps that S1, TC4 titanium alloy powder serves as a raw material, die-casting forming is conducted through metal injection molding, a green body is obtained, and the green body is sintered under high-purity helium protection to obtain a sintered blank; s2, performing numerical control milling on the sintered blank to obtain an earphone shell precursor with the required shape and size; s3, performing cleaning and surface activation pretreatment on the earphone shell precursor, performing vacuum coating on the pretreated earphone shell precursor, and obtaining an earphone shell middle body after a plurality of different types of coating layers are formed on the earphone shell precursor; s4, removing the coating layer in the local area of the middle body of the earphone shell by adopting laser etching to obtain the earphone shell with recovered conductivity; wherein the local area of the earphone shell middle body is an interface area with an electrical connection requirement between the earphone shell middle body and the outside.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of medical instrument class electronic product manufacturing, and particularly relates to a high-end titanium alloy hearing aid earphone shell (hereinafter referred to as an earphone shell) and a production method thereof. BACKGROUND

[0002] Titanium alloy is not only applied in aerospace, automobiles and high-end industrial equipment, but also widely used in medical instruments, such as artificial joints and hearing aids, due to its lightweight, high strength, corrosion resistance and biocompatibility. Among them, titanium alloy TC4 (Ti-6Al-4V) is one of the most common titanium alloys, containing 90% titanium, 6% aluminum and 4% vanadium, and has high strength, low density, high temperature resistance, corrosion resistance and good biocompatibility. However, when the above titanium alloy TC4 (Ti-6Al-4V) is applied to the production of hearing aid earphone shells, the traditional cutting manufacturing method has problems such as low material utilization rate, high cost and limited structure design, which need to be solved. SUMMARY

[0003] In order to solve the above problems, the embodiments of the present application provide a titanium alloy earphone shell and a production method thereof. The method integrates powder metallurgy, precision machining and surface treatment processes to produce a titanium alloy earphone shell with excellent surface quality, reducing material waste and production cost.

[0004] Therefore, the embodiments of the present application adopt the following technical solutions:

[0005] In a first aspect, the present application provides a production method of a titanium alloy earphone shell, comprising the following steps:

[0006] S1, using TC4 titanium alloy powder as raw material, pressure casting forming by metal injection molding to obtain a green body, and sintering the green body under high-purity helium protection to obtain a sintered body;

[0007] S2, numerically controlled milling processing the sintered body to obtain an earphone shell precursor with the required shape and size; wherein the surface roughness Ra of the earphone shell precursor is less than or equal to 0.2 microns;

[0008] S3, cleaning and surface activation pretreatment of the earphone shell precursor, and vacuum plating of the pretreated earphone shell precursor, after forming a plurality of different types of plating layers on the earphone shell precursor, obtaining an earphone shell middle body;

[0009] S4, removing the plating layer of the local area of the earphone shell middle body by laser engraving to obtain an earphone shell with restored electrical conductivity; wherein the local area of the earphone shell middle body is an interface area of the earphone shell middle body and the outside with electrical connection requirement.

[0010] In this embodiment, the technical solution solves the multi-dimensional technical contradictions in the manufacturing of titanium alloy earphone housings through the integration of the process chain. Specifically: step S1 uses metal injection molding combined with helium gas protection sintering to realize complex structure integrated molding through powder metallurgy process, which significantly improves material utilization compared to traditional cutting process, and helium gas as an inert protective medium can inhibit titanium alloy high-temperature oxidation to ensure the density of the sintered body; step S2 limits the surface roughness Ra≤0.2μm after numerical control milling to create a super-smooth surface for subsequent vacuum coating, and this roughness threshold can not only eliminate surface micro-defects of the sintered body, but also retain appropriate surface energy to promote coating adhesion; step S3 uses cleaning activation and multi-layer coating in combination, where the cleaning process removes processing residues, the activation process reconstructs the surface microstructure, and the multi-layer coating design meets the functional coating and decorative requirements simultaneously by stacking different functional layers (such as chromium layer to enhance adhesion, aluminum nitride layer to achieve insulation, and titanium oxynitride layer to control appearance); step S4 uses laser engraving to selectively remove the coating, which realizes micron-level coating removal without damaging the titanium substrate by precise matching of energy density and action time, and solves the contradictory requirements of insulating coating and electrical connection points. The parameter coupling between steps (such as the correlation between sintering temperature and density, the matching between surface roughness and coating adhesion, and the correspondence between coating composition and laser parameters) forms a technical closed loop, and finally realizes the synergistic optimization of structural strength, surface function and appearance quality.

[0011] As an implementable embodiment, the particle size distribution of the TC4 titanium alloy powder is D50=36.6μm.

[0012] In this embodiment, by precisely controlling the median particle size of the TC4 titanium alloy powder to 36.6μm, the technical solution optimizes the powder flowability and filling performance of the metal injection molding process. The selection of a specific particle size distribution effectively balances the void ratio between powder particles, promoting closer metallurgical bonding between particles during sintering, thereby reducing the formation of internal pores in the sintered body. This particle size control ensures that the material after sintering achieves a higher density, laying the foundation for obtaining a super-smooth surface with Ra≤0.2μm for subsequent numerical control machining. At the same time, uniform particle size distribution helps to eliminate local stress concentration caused by particle size differences and avoid the problem of reduced coating adhesion caused by uneven surface microstructure of the substrate during coating. The setting of this particle size parameter directly solves the negative impact of surface micro-pore defects of the sintered part on coating adhesion mentioned in the background technology, and is a key control point to ensure the basic performance of the material in the entire process chain.

[0013] As one feasible implementation, in S1, the sintering process specifically includes: under a helium protective atmosphere, a heating rate of 6-8℃ / min, controlling the sintering temperature at 1280℃±5℃, and controlling the holding time at 1-4h, to obtain a sintered green body with a density higher than 99%.

[0014] In this embodiment, the technical solution achieves optimized control of the microstructure of titanium alloys through a combination of sintering process parameters. The use of a helium protective atmosphere effectively isolates oxygen contamination, while the high thermal conductivity of helium contributes to temperature uniformity during sintering. Limiting the heating rate to 6-8℃ / min avoids thermal stress cracking caused by rapid heating, while preventing energy waste and abnormal grain growth due to excessively slow heating. Precisely controlling the sintering temperature within the range of 1280℃±5℃, this temperature window is determined based on the phase transformation point and densification kinetics of titanium alloys, promoting sufficient diffusion and bonding of powder particles while avoiding grain coarsening caused by over-firing. The 1-4h holding time design ensures sufficient atomic diffusion while preventing material performance degradation caused by prolonged high-temperature treatment. The resulting sintered green body has a density exceeding 99%, a dense and uniform microstructure, and regular surface grain boundary morphology, providing an ideal substrate material for subsequent precision machining and coating processes.

[0015] As one feasible implementation, in S2, the process parameters for CNC milling are as follows: diamond cutting tool is used, spindle speed is 18000-22000 rpm, feed per tooth is 0.005-0.01 mm / tooth, and feed rate is 180-400 mm / min.

[0016] In this embodiment, the technical solution systematically solves the problem of coordinated control of precision machining of titanium alloys and coating substrate quality through the design of specific process parameters. Diamond tools are used due to their ultra-high hardness and wear resistance, which effectively resist the high strength characteristics of TC4 titanium alloys and prevent tool wear from causing surface quality degradation. The spindle speed is limited to the range of 18000-22000 rpm, ensuring that the cutting speed is within the optimal machining range for titanium alloys while avoiding excessive speed that could lead to heat accumulation and surface phase transformation or micro-damage. A micro-cutting parameter of 0.005-0.01 mm / tooth, combined with a feed rate of 180-400 mm / min, forms a precise chip control mechanism. This mechanism reduces cutting force through small cutting amounts, thus suppressing workpiece deformation, while maintaining machining efficiency through a reasonable feed rate, ultimately achieving a mirror-like surface finish with a surface roughness Ra≤0.2μm. The synergistic effect of the above parameters breaks through the technical bottleneck of the traditional TC4 processing, which makes it difficult to balance surface quality and processing efficiency, and provides a defect-free and highly consistent surface morphology basis for subsequent coating processes.

[0017] As one feasible implementation, in step S3, cleaning the earphone shell front body includes: ultrasonically cleaning the earphone shell front body with acetone, ethanol, and deionized water, followed by plasma cleaning.

[0018] In this embodiment, the technical solution systematically solves the problems of residual contaminants and insufficient activation on the surface of titanium alloy substrates through a combination of innovative multi-stage cleaning processes. First, a gradient ultrasonic cleaning process using acetone, ethanol, and deionized water is employed. The alternating action of organic and polar solvents removes grease-like contaminants and polar residues, respectively, and the cleaning effect is enhanced by ultrasonic cavitation. Subsequently, plasma cleaning is performed, achieving atomic-level cleaning through high-energy particle bombardment, while simultaneously creating dangling bonds on the surface to enhance chemical activity. This combined process overcomes the limitations of traditional single-cleaning methods. Acetone cleaning targets organic substances such as release agents remaining after sintering, ethanol cleaning removes polar contaminants, deionized water cleaning eliminates ionic residues, and plasma cleaning, through the dual effects of physical bombardment and chemical activation, provides a substrate with high surface energy and active sites for subsequent coating, thereby significantly improving the adhesion of the coating.

[0019] As one feasible implementation, the plasma cleaning includes: turning on the radio frequency (RF) bias power supply at an argon gas pressure of 1.0 Pa and setting it to -400V, and performing plasma bombardment cleaning on the front body of the earphone shell for 5-10 minutes.

[0020] In this embodiment, the technical solution achieves deep cleaning and activation of the titanium alloy substrate surface through a plasma cleaning process with specific parameters. Under an argon gas pressure of 1.0 Pa, the plasma formed by argon gas has a moderate ionization density and particle kinetic energy, effectively bombarding the surface without damaging the substrate. The radio frequency bias power supply is set to -400V, and high-energy argon ions bombard the substrate surface, physically stripping adsorbed organic contaminants and oxide layers, while simultaneously eliminating stress concentration areas at the edges of surface micropores through ion sputtering. A 5-10 minute time window ensures a balance between thorough cleaning and production efficiency: less than 5 minutes may result in residual contaminants, while more than 10 minutes may cause excessive etching of the substrate surface. This combination of parameters is specifically designed for the unique surface morphology (such as micropores and grain boundary structures) of metal injection molded sintered parts. The nanoscale surface roughening generated by ion bombardment significantly increases the mechanical interlocking area between the coating layer and the substrate, providing a highly active interface environment for subsequent vacuum coating.

[0021] As one feasible implementation, the surface activation pretreatment specifically includes: starting the titanium target power supply at a working gas pressure of 0.4 Pa, setting the power to 3.5 kW, and performing pre-sputtering for 5 minutes; wherein the gas ratio in the working gas pressure is set to Ar:200 sccm / N2:40 sccm.

[0022] In this embodiment, the technical solution achieves surface activation of the titanium alloy substrate through a pre-sputtering process with specific parameters. A suitable plasma density environment is formed at a working gas pressure of 0.4 Pa, ensuring sufficient particle kinetic energy without excessive bombardment damaging the surface. A titanium target power supply is set to 3.5 kW to generate a high-energy titanium ion stream that physically bombards the substrate surface, removing residual contaminants and forming a transition layer on the substrate surface through titanium atom implantation. A pre-sputtering time of 5 minutes ensures that the surface activation depth matches the thickness of the subsequent coating layer. Ar and N2 are mixed at a ratio of 200:40 sccm (Standard Cubic Centimeter per Minute, cm). 3 The gas mixture is prepared at a ratio of ( / min), with argon as the main sputtering gas to maintain stable discharge. The incorporation of nitrogen forms a trace titanium nitride transition layer on the titanium alloy surface, enhancing the chemical bonding between the subsequent coating layer and the TC4 substrate. This combination of parameters effectively solves the problem of insufficient coating adhesion caused by the porous structure of the sintered titanium alloy surface, providing an active interface for multilayer coatings.

[0023] As one feasible implementation, the multilayer coating layers of different types include a high-purity chromium layer, an aluminum nitride layer, and a titanium oxynitride layer. The specific process parameters of the vacuum coating include: using a zeroed quartz crystal film thickness gauge, applying a DC bias voltage of -70V to the front body of the earphone shell at a working pressure of 0.4Pa to obtain the earphone shell body with the required coating thickness and number of layers; wherein, the deposition temperature is 250℃, and the target power is 3.5kW; the high-purity chromium layer as the underlayer uses a chromium target, and the reaction gas is argon; the aluminum nitride layer as the insulating layer uses an aluminum target, and the reaction gases are argon and nitrogen, with the gas ratio set to Ar:200sccm / N2:40sccm; the titanium oxynitride layer as the color layer uses a titanium target, and the reaction gases are argon, nitrogen, and oxygen, with the gas ratio set to Ar:200sccm / N2:40sccm / O2:(40-100)sccm.

[0024] In this embodiment, the problems of coating adhesion, insulation, and appearance consistency are systematically solved by combining a multilayer film structure design with specific process parameters. A high-purity chromium layer serves as the underlayer, utilizing the high affinity between chromium and the titanium alloy substrate. A dense layer is formed by sputtering a chromium target in an argon atmosphere, enhancing the adhesion between subsequent film layers and the substrate. An aluminum nitride layer serves as the insulating layer, generated using an aluminum target in a mixed atmosphere of argon and nitrogen. The stoichiometry of aluminum nitride is controlled by maintaining a fixed Ar / N2 ratio (200:40 sccm), ensuring stable insulation performance and a dense film. A titanium oxynitride layer serves as the color layer, deposited using a titanium target in a mixed reaction gas of argon, nitrogen, and oxygen. The chemical composition of titanium oxynitride is precisely controlled by adjusting the O2 flow rate (40-100 sccm), achieving adjustable color and wear resistance. In terms of process, a zeroed quartz crystal film thickness gauge is used to monitor the thickness in real time. Combined with a working gas pressure of 0.4 Pa and a DC bias of -70 V, this promotes uniform film deposition and improves the film-substrate bonding strength. A deposition temperature of 250℃ avoids thermal deformation of the substrate, while a target power of 3.5kW balances the deposition rate and film quality. The synergistic effect of gas ratios in each layer, target material selection, and parameters ensures that the coating simultaneously meets the requirements for adhesion, insulation, appearance, and subsequent laser engraving conductivity.

[0025] As one feasible implementation, in step S4, the laser engraving process parameters include: an engraving speed of 0.06 m / s, a power of 60%, and a pulse frequency of 50 kHz.

[0026] In this embodiment, the technical solution achieves high-precision selective removal of the coating layer through a combination of specific laser parameters. The laser engraving speed is set to 0.06 m / s, ensuring sufficient time for the laser beam to act on a unit area to peel off multiple layers of coating while avoiding excessively long thermal action time that could lead to oxidation or phase transformation of the titanium alloy substrate. The power is set to 60%, ensuring effective ablation of the coating layer (including the high-hardness aluminum nitride layer) while controlling the energy density to prevent melting damage to the TC4 substrate after penetrating the coating layer. The high-frequency pulse mode of 50 kHz ensures that the interval between each laser pulse matches the material's thermal diffusion rate, maintaining continuous processing efficiency while reducing the heat accumulation effect through discrete energy input. This results in a clean-edged conductive area during coating layer removal, meeting the stringent requirements of medical-grade hearing aids for the conductive stability and dimensional accuracy of the interface area.

[0027] Secondly, this application provides a titanium alloy earphone shell, which is prepared using the above-described production method.

[0028] The titanium alloy earphone shell achieves synergistic optimization of function and performance through integrated manufacturing processes. Metal injection molding combined with helium-protected sintering, under controlled TC4 powder particle size and sintering temperature profiles, yields a high-density matrix, providing a uniform microstructure for subsequent processing. CNC milling, using diamond tools and specific machining parameters, controls the surface roughness to below 0.2μm, forming a precision substrate conducive to coating adhesion. Cleaning and activation pretreatment combined with a multi-layer coating design, using a chromium layer to enhance adhesion, an aluminum nitride layer for insulation, and a titanium oxynitride layer to regulate appearance, creates a functional composite surface. Laser engraving selectively removes the coating in the interface area, establishing local conductive pathways while maintaining overall insulation. The synergistic use of parameters in each process step (such as matching sintering temperature and density, adapting milling roughness to coating thickness, and matching coating materials to laser parameters) collectively solves the technical challenges of coating peeling, insulation failure, and appearance defects coexisting in traditional processes.

[0029] In summary, the above-mentioned technical solution of the present invention has the following beneficial technical effects:

[0030] (1) Material and structural advantages: Powder die casting process realizes the one-piece molding of complex structures, increases the material utilization rate to more than 95%, and significantly reduces the weight of components (the weight of a single earphone is less than 4g).

[0031] (2) Excellent adhesion: Through exclusive pretreatment and matching of coating parameters, the coating of the final product passes the ASTM D3359 Grade 0 standard in cross-cut adhesion test without any peeling;

[0032] (3) Functionalized surface: The vacuum-coated layer provides extremely high surface insulation resistance (>10). 13 (Ω·cm), and the subsequent laser engraving process precisely achieved local conductivity, meeting the electrical connection requirements of the headphones;

[0033] (4) Top-notch texture and consistency: The synergistic effect of the entire process chain ensures that the product has a metallic matte texture, consistent color and impeccable appearance.

[0034] As can be seen from the above, the titanium alloy earphone shell and its manufacturing method provided in this application achieve integrated molding of complex structures, improved coating adhesion and functional surface treatment through the integrated process of metal injection molding, CNC machining, vacuum coating and laser engraving. It has the advantages of improving material utilization, enhancing coating adhesion, achieving precise control of insulation and conductive areas and improving product appearance consistency. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of a manufacturing process for a titanium alloy earphone shell provided in an embodiment of this application;

[0037] Figure 2 This is a schematic diagram of another method for producing a titanium alloy earphone shell provided in this application embodiment;

[0038] Figure 3 This paper illustrates the relationship between sintering temperature and density of TC4 (Ti-6Al-4V) metal powder provided in an embodiment of this application.

[0039] Figure 4 A schematic diagram of the sintering curve of TC4 (Ti-6Al-4V) metal powder provided in the embodiments of this application using the metal injection molding (MIM) process is shown.

[0040] Figure 5 A schematic diagram of the process for cleaning, surface activation pretreatment, and vacuum coating of the earphone shell precursor is shown.

[0041] Figure 6 A schematic diagram of the laser engraving process for the inner body of the earphone shell is shown;

[0042] Figure 7 A schematic diagram of the appearance of the titanium alloy earphone shell prepared in Example 1 is shown;

[0043] Figure 8 A schematic diagram of the appearance of the titanium alloy earphone shell produced in Comparative Example 1 is shown. Detailed Implementation

[0044] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0045] It should be understood that the scope of protection of this application is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of this application is for describing specific embodiments and not for limiting the scope of protection of this application; in the specification and claims of this application, unless otherwise expressly stated in the text, the singular forms "a", "an" and "this" include the plural forms.

[0046] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this application, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description in this application, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this application may be used to implement this application.

[0047] It should be specifically noted that, unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art to which this application pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are all conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained through commercial purchase or by existing methods; unless otherwise specified, the amounts of experimental reagents used are the amounts used in conventional experimental operations; unless otherwise specified, the experimental methods are all conventional methods.

[0048] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0049] Unless otherwise stated, the terms used in the specification and claims shall have the following meanings.

[0050] The term "room temperature" as used in this application has a meaning known in the art and generally refers to 24-28°C.

[0051] Titanium alloy TC4 (Ti-6Al-4V) is an ideal material for manufacturing high-end medical hearing aid earphone shells due to its high specific strength, excellent corrosion resistance, and good biocompatibility. However, traditional machining methods suffer from low material utilization, high costs, and limitations in structural design. Furthermore, achieving high-quality vacuum coating on titanium alloy shells presents significant challenges.

[0052] 1. Adhesion problem: The sintered TC4 surface has micropores and specific grain boundary morphology. Traditional pretreatment is difficult to ensure the long-lasting adhesion of the coating, and the cross-cut adhesion test cannot reach level 0.

[0053] 2. Insulation requirements: The earphone shell needs to have good electromagnetic insulation, while conventional vacuum coating (such as chrome plating) is conductive.

[0054] 3. Appearance consistency: From powder metallurgy parts to CNC (Computer Numerical Control) precision machining, and then to coating, any mismatch in any link of the process will lead to defects in the final product.

[0055] In summary, surface properties are particularly important for electronic components such as headphone housings, as they affect both aesthetics and functionality. Conventional vacuum coating processes for titanium alloy surfaces typically face challenges such as poor adhesion, insufficient insulation, and inconsistent appearance. Furthermore, when specific areas of a coated component require electrical connections, the coating must be selectively removed without compromising the overall integrity of the component.

[0056] Therefore, the manufacturing of titanium alloy headphone shells presents multiple technical challenges throughout the entire production chain, from initial molding to final surface treatment and electrical connection establishment. These challenges include achieving high material utilization, ensuring sufficient density and surface quality after sintering, establishing strong coating adhesion, providing necessary electrical insulation while maintaining selective conductivity, and ensuring consistent appearance throughout the entire production process. Current technologies lack a complete process chain that can systematically solve these problems.

[0057] To address the aforementioned issues, this application provides a titanium alloy earphone shell and its manufacturing method. Firstly, to address the low material utilization rate, powder metallurgy is employed to achieve near-net-shape forming. Next, to address poor coating adhesion, surface roughness control and activation treatment are used to reconstruct the substrate surface state. To meet insulation requirements, a multi-layer composite coating structure is designed, achieving comprehensive performance through functional layer stacking. Finally, to address electrical connection requirements, a selective coating removal technology is developed to restore localized conductivity while maintaining the integrity of the substrate.

[0058] This application provides a titanium alloy headphone shell and its manufacturing method, solving the problems of low material utilization, poor coating adhesion, insufficient insulation performance, and poor appearance consistency in traditional manufacturing processes for titanium alloy headphone shells. It also addresses the technical challenge of precisely controlling locally conductive areas. In other words, the purpose of this application is not only to provide a titanium alloy headphone shell, but also to provide a complete integrated manufacturing solution that achieves ultra-high yield, superior performance (insulation, high adhesion), and a top-notch appearance.

[0059] Figure 1This is a schematic diagram of a manufacturing process for a titanium alloy earphone shell provided in an embodiment of this application. Figure 2 This is a schematic diagram of a production method for another titanium alloy earphone shell provided in this application embodiment. (See also...) Figure 1 You can refer to this at the same time Figure 2 According to an embodiment of this application, a method for producing a titanium alloy earphone shell is provided, such as... Figure 1 As shown, the specific steps include:

[0060] S1. Using TC4 titanium alloy powder as raw material, a green blank is obtained by die casting through metal injection molding, and the green blank is sintered under high-purity helium protection to obtain a sintered blank.

[0061] In this step, Metal Injection Molding (MIM) is one of the manufacturing technologies for complex-shaped titanium alloy parts. This process involves mixing metal powder with a binder, injection molding it into the desired shape, and then sintering it to obtain the final product. For example, titanium alloy metal powder is mixed with a polymeric binder (such as polypropylene, polyethylene, etc.) in a certain proportion to form a "feedstock" with good flowability. Specifically, through processes such as kneading, the titanium alloy powder and binder are uniformly mixed to form a feedstock with good rheological properties, providing suitable raw materials for injection molding. The metal powder particle size can be 5-40 micrometers to ensure feedstock uniformity and molding accuracy. Then, the feedstock is injected into a mold using an injection molding machine, and after cooling, a "green blank" with the same shape as the final product is obtained. Most of the binder in the green blank is removed by methods such as solvent dissolution, thermal decomposition, or catalytic decomposition to form a "semi-sintered blank" with a certain strength. Optionally, the debinding process can be: catalytic debinding (rapidly removing most of the binder) + thermal debinding (thoroughly removing residual binder). A catalytic debinding process is employed, where the binder in the green billet undergoes decomposition and other reactions under a specific catalytic environment (such as an acidic gas atmosphere), removing most of the binder and preparing it for subsequent sintering. This also reduces the risk of deformation during the subsequent sintering process. High-temperature sintering (60%-90% of the metal's melting point) is then performed in an inert atmosphere (such as argon or nitrogen) or a vacuum furnace. The metal powder particles diffuse and bond, causing the billet to shrink and densify (reaching 95%-99% of the theoretical density), resulting in mechanical properties close to forged metal. Specifically, the debinded green billet can be placed in a sintering furnace protected by high-purity helium and sintered according to a sintering curve (e.g., heating to 1280±5℃ and holding for 2 hours). At high temperatures, metallurgical reactions such as diffusion and fusion occur between the titanium alloy powder particles, gradually densifying the green billet and ultimately obtaining a near-net-shape MIM sintered billet with a density exceeding 99%.

[0062] Figure 3A schematic diagram illustrating the relationship between sintering temperature and density of TC4 (Ti-6Al-4V) metal powder provided in an embodiment of this application is shown. Figure 3 As shown, verification revealed that the density of TC4 titanium alloy exhibited a significant upward trend as the sintering temperature gradually increased from 1260℃. For example, during the temperature increase from 1260℃ to 1280℃, the density continuously rose from approximately 96%, reaching a relatively high level (close to 99.5%) at 1280℃. This is because, with increasing temperature, atomic diffusion between titanium alloy powder particles intensifies, the bonding between particles becomes more complete, and porosity continuously decreases, thereby increasing density.

[0063] When the sintering temperature exceeds 1280℃, the density begins to show a decreasing trend. For example, when the temperature rises from 1280℃ to 1300℃, the density gradually decreases. This may be because excessively high temperatures cause excessive grain growth and localized overheating in the titanium alloy, which in turn affects the material's compactness, causing the density to no longer increase with increasing temperature, and even decrease.

[0064] Overall, the curve shows that there is a relatively good sintering temperature range (approximately between 1270-1290℃, especially around 1280℃) for TC4 titanium alloys under the MIM process and holding temperature for 2 hours, which can enable TC4 titanium alloys to obtain high density.

[0065] More specifically, in one embodiment, the particle size distribution of the TC4 titanium alloy powder is D50 = 36.6 μm. The sintering process specifically includes: under a helium protective atmosphere, a heating rate of 6-8 °C / min, controlling the sintering temperature at 1280 °C ± 5 °C, and a holding time of 1-4 h, for example 1 h, 2 h, 3 h, or 4 h, to obtain a sintered green body with a density higher than 99%.

[0066] Figure 4 This diagram illustrates the sintering curve of the TC4 (Ti-6Al-4V) metal powder provided in this embodiment using a metal injection molding (MIM) process. Figure 4As shown in a specific embodiment, in the initial stage (approximately 0-1 hour) of the sintering curve of TC4 (Ti-6Al-4V) metal powder, the temperature remains at a relatively low level, representing preparation before heating or the initial stage of slow heating. Subsequently (approximately 1-2 hours), the temperature rapidly rises to 450°C at a rate of 7.5°C / min and is held briefly for 1 hour, serving as a transition to higher sintering temperatures and ensuring more uniform heating of the material. Then (approximately 3-4 hours), the temperature further rapidly rises to an even higher temperature of 800°C at a rate of 6.7°C / min and is held for 1 hour, continuously providing heat to the material and promoting internal changes. Afterwards (approximately 5-6 hours), the temperature continues to rise rapidly, reaching the target sintering temperature of 1280±5°C at a rate of 8°C / min, and is then held within this temperature range (approximately 6-7 hours) for 1 hour. This stage is a crucial sintering holding process, allowing the TC4 material to undergo sufficient metallurgical bonding, grain growth, and other changes at high temperatures to obtain the desired properties. Finally (after 7 hours), the temperature drops rapidly, returning to the initial low temperature level within 1 hour, completing the entire sintering process. Figure 3 The overall curve shown illustrates the temperature change over time during the sintering process of a TC4 metal injection molded part in a specific embodiment. Through such temperature control, the performance of the TC4 sintered part can be regulated.

[0067] S2. Perform CNC milling on the sintered blank to obtain the earphone shell precursor with the required shape and size. The surface roughness Ra of the earphone shell precursor is ≤0.2μm. The CNC milling process parameters include: using diamond tools, spindle speed of 18000-22000rpm, feed per tooth of 0.005-0.01mm / tooth, and feed rate of 180-400mm / min.

[0068] In one embodiment, the machining parameters for the five-axis machine tool sidewall finishing process are shown in Table 1:

[0069] Table 1. Machining parameters for the sidewall finishing process of a five-axis machine tool.

[0070]

[0071]

[0072] See Figure 2 Meanwhile, in conjunction with Table 1, in this embodiment, the five-axis machine tool clamping is performed by clamping the MIM sintered blank onto a five-axis machine tool. The five-axis machine tool has the advantage of multi-axis linkage, which can better adapt to the complex spatial curved surface processing of the headphone shell, and ensure the stability and positioning accuracy of the clamping.

[0073] Roughing: Using suitable cutting tools (such as carbide end mills), excess material on the surface of the sintered blank is quickly removed to initially form the approximate shape of the earphone shell, reserving machining allowance for subsequent semi-finishing and finishing. In one specific implementation, a 3mm diameter carbide double-flute end mill ("Φ3mm" indicates a tool diameter of 3 millimeters) is selected. The double-flute design ensures sufficient chip removal space while being suitable for high-precision contour machining, especially for sidewall cutting of thin-walled, complex curved surfaces such as earphone shells. Carbide tools (usually cemented carbide) have high hardness and good wear resistance, capable of handling the high strength and high toughness of titanium alloys (TC4), reducing tool wear. The tool surface is coated with a diamond coating, utilizing the ultra-high hardness (Mohs hardness 10) and low coefficient of friction of diamond to significantly improve tool wear resistance and anti-sticking properties. Titanium alloys are prone to "sticking" during machining (plastic deformation of the material at high temperatures causes it to adhere to the tool surface). The diamond coating can reduce cutting resistance and heat accumulation, ensuring a smooth surface finish. Tool holder type: High-precision heat-shrink tool holder (TIR) ​​<0.002mm. Heat-shrink tool holders: Expanded by heating, they fit over the tool and clamp tightly after cooling, providing uniform clamping force and high rigidity, suitable for high-speed rotation applications. TIR (Total Indicator Reading) <0.002mm: Indicates that the concentricity error between the tool holder and the tool is less than 0.002mm, minimizing vibration during high-speed rotation, preventing surface chatter marks, and ensuring dimensional accuracy.

[0074] Semi-finishing: Further optimize the shape and size of the earphone shell, reduce machining marks left by rough machining, make the part size closer to the final requirements, and at the same time improve the surface quality foundation for finishing.

[0075] Precision machining: High-precision machining parameters (such as using diamond-coated tools, spindle speed of 18000-22000rpm, feed per tooth of 0.005-0.01mm / tooth, etc.) are used to perform fine machining on the earphone shell, so that the surface roughness of the part reaches Ra≤0.2μm, which meets the requirements of subsequent vacuum coating for the surface quality of the substrate.

[0076] More specifically, spindle speed (S): 18000-22000 rpm: A high-speed spindle of 18000-22000 rpm is used because titanium alloy has poor thermal conductivity. High-speed cutting can shorten the contact time between the tool and the material, reduce the heat transfer to the workpiece (avoiding workpiece deformation) and the tool (avoiding overheating and wear); at the same time, high-speed cutting can reduce the cutting force, which is suitable for the precision machining of thin-walled headphone shells.

[0077] Feed per tooth (fz): 0.005-0.01 mm / tooth: This refers to the distance the tool travels in the feed direction for each tooth rotation, which is 0.005-0.01 mm. This parameter directly affects surface roughness and tool load: a small feed rate ensures a smoother machined surface (ultimately requiring Ra≤0.2μm), meeting the requirements of subsequent vacuum coating on the substrate; titanium alloys have high strength, and a small feed rate reduces the cutting force on a single tooth of the tool, preventing chipping.

[0078] Feed rate (F): 180-400 mm / min: This refers to the distance the tool moves per minute along the feed direction, calculated from the spindle speed, feed per tooth, and number of cutting edges (F = spindle speed × feed per tooth × number of cutting edges). This range balances machining efficiency and surface quality: too low a speed will increase machining time and frictional heat between the tool and the workpiece; too high a speed may lead to vibration or a decrease in surface quality.

[0079] Axial depth of cut (ap): Total depth of cut in one pass ≤ 0.5mm, layered, with each layer having a depth of cut of 0.03mm. Axial depth of cut refers to the cutting depth of the tool along the spindle direction (perpendicular to the machined surface). Titanium alloys have high toughness; excessive cutting depth in one pass will generate enormous cutting forces, leading to workpiece deformation or tool bending ("tool deflection"). Therefore, "layered cutting" is adopted: the total depth does not exceed 0.5mm, with each pass cutting only 0.03mm, completing the machining through multiple passes to ensure dimensional accuracy and surface flatness.

[0080] Radial Depth of Cut (ae): The radial depth of cut is equal to the tool diameter. Climb milling is used, with the tool centerline always aligned with the wall center. Radial depth of cut equal to tool diameter: This means the cutting width along the radial direction (parallel to the machined surface) is 3mm (the same as the tool diameter), meaning the tool completely penetrates the material. This is suitable for machining the full width of sidewalls. Climb milling: The tool cuts from the lower part of the workpiece to the upper part (climb milling). Compared to downhill milling (conventional milling), this reduces tool wear and workpiece vibration, making it especially suitable for preventing deformation of thin-walled parts. Tool centerline aligned with the wall center: This ensures that the cutting force is evenly distributed on both sides of the tool, avoiding tool deflection ("tool slippage") caused by unilateral force, and ensuring the perpendicularity and dimensional accuracy of the sidewall.

[0081] Cooling method: High-pressure internal cooling (≥70 bar) + high-quality oil-based cutting fluid. It should be noted that high-pressure internal cooling (≥70 bar): The cutting fluid is directly sprayed at a high pressure of ≥70 bar onto the cutting area (the contact point between the tool edge and the workpiece) through the internal channels of the tool holder, efficiently removing cutting heat (titanium alloys have poor thermal conductivity and are prone to localized overheating), while simultaneously flushing away chips to avoid "secondary cutting" (residual chips causing repeated cutting and surface scratches). Oil-based cutting fluid: Compared to water-based cutting fluid, it has better lubrication, reducing friction between the tool and the workpiece, further reducing surface roughness and tool wear.

[0082] Thus, when machining high-strength, low-thermal-conductivity titanium alloy (TC4), high speed, small feed, and layered cutting are used to reduce cutting force and heat; a high-precision tool system (tool holder, coating) ensures stability; and efficient cooling controls the temperature, ultimately achieving high precision (dimensional tolerance), high surface quality (Ra≤0.2μm), and low deformation of the headphone shell sidewall, providing a qualified substrate for subsequent vacuum coating.

[0083] S3. The earphone shell front body is cleaned and surface activated pre-treatment is performed, and vacuum coating is performed on the pre-treated earphone shell front body to form multiple layers of different types of coating layers on the earphone shell front body to obtain the earphone shell middle body.

[0084] In this step, cleaning the earphone shell precursor includes: ultrasonic cleaning of the earphone shell precursor with acetone, ethanol, and deionized water, followed by plasma cleaning. Plasma cleaning includes: under argon pressure of 1.0 Pa, turning on the radio frequency (RF) bias power supply and setting it to -400V, performing plasma bombardment cleaning on the earphone shell precursor for 5-10 minutes. Surface activation pretreatment specifically includes: under working gas pressure of 0.4 Pa, starting the titanium target power supply and setting the power to 3.5kW, performing pre-sputtering for 5 minutes; wherein the gas ratio in the working gas pressure is set to Ar:200 sccm / N2:40 sccm. The multilayer coating layers of different types include a high-purity chromium layer, an aluminum nitride layer, and a titanium oxynitride layer. The specific process parameters for vacuum coating include: using a zeroed quartz crystal film thickness gauge, applying a DC bias voltage of -70V to the front body of the earphone shell at a working gas pressure of 0.4Pa to obtain the earphone shell body with the required coating thickness and number of layers; wherein, the deposition temperature is 250℃, and the target power is 3.5kW; the high-purity chromium layer as the base layer uses a chromium target, and the reaction gas is argon; the aluminum nitride layer as the insulating layer uses an aluminum target, and the reaction gases are argon and nitrogen, with the gas ratio set to Ar:200sccm / N2:40sccm; the titanium oxynitride layer as the color layer uses a titanium target, and the reaction gases are argon, nitrogen, and oxygen, with the gas ratio set to Ar:200sccm / N2:40sccm / O2:(40-100)sccm.

[0085] Figure 5 A schematic diagram illustrating the process of cleaning, surface activation pretreatment, and vacuum coating of the earphone shell pre-body is shown. Figure 5 As shown, step S3 may further include the following sub-steps:

[0086] S31, the earphone shell front body (the figure shows the TC4 titanium alloy substrate (after precision CNC machining)). After precision CNC machining (such as the five-axis machine tool milling mentioned above, with a surface roughness Ra≤0.2μm), the titanium alloy substrate has the required shape, size and surface precision, providing a high-quality substrate for subsequent coating.

[0087] S32. Pretreatment: Obtain an ultra-clean surface. The substrate is ultrasonically cleaned with acetone, ethanol, and deionized water, and then dried.

[0088] This step is to thoroughly remove oil, impurities, and oxide layers from the substrate surface to ensure the adhesion between the coating and the substrate.

[0089] Among them, ultrasonic cleaning (organic solvent): using organic solvents such as acetone and ethanol, ultrasonic vibration is used to dissolve and remove organic contaminants such as grease and fingerprints from the surface.

[0090] For example, plasma cleaning (argon + oxygen): In a plasma environment, argon (Ar) and oxygen (O2) are ionized into active particles, which remove micron- or even nano-sized residual impurities through physical bombardment (argon ions) and chemical oxidation (oxygen ions), while activating the surface (increasing surface energy) to prepare for the subsequent coating adhesion.

[0091] Ultrasonic rinsing with deionized water: Use high-purity deionized water for ultrasonic cleaning again to remove residual solvents or reaction products from the first two steps, and avoid impurities affecting the coating quality.

[0092] Vacuum drying: Drying in a vacuum environment prevents dust in the air from contaminating the surface again, and avoids moisture residue that could cause bubbles or defects during the coating process.

[0093] S33. Clamping and Furnace Loading: Load the substrate into the fixture and send it into the vacuum chamber. Securely mount the substrate onto the workpiece tray, ensuring good electrical contact.

[0094] The cleaned titanium alloy substrate is fixed onto a special fixture to ensure its stable position within the vacuum chamber and uniform coating on all parts. The fixture is then fed into the chamber of the vacuum coating equipment.

[0095] S34. High Vacuum: Evacuate to 10°C. -5 ~10 -6 mbar. Start the mechanical pump and molecular pump to evacuate the chamber to a background vacuum of ≤5.0 × 10⁻⁶ mbar. -4 Pa.

[0096] By combining mechanical and molecular pumps, the gas pressure in the vacuum chamber is evacuated to an extremely low level (high vacuum environment). The purpose of high vacuum is to: reduce residual gases (such as oxygen and nitrogen) in the chamber, preventing them from reacting with the coating material and ensuring the purity of the film; and reduce the scattering of coating particles by gas molecules, allowing the coating particles to be deposited more directly and uniformly on the substrate surface.

[0097] S35, Etching: Ar is introduced and bombarded with high bias voltage to remove nanoscale contaminants and activate the surface.

[0098] In this step, high-purity argon gas is introduced into the chamber to a pressure of 1.0 Pa. The radio frequency (RF) bias power supply is then turned on and set to -400V, and the substrate is subjected to ion bombardment cleaning for 5-10 minutes. This step thoroughly removes microscopic contaminants and oxide layers from the surface, greatly enhancing the adhesion between the film and the substrate.

[0099] Specifically, this is a "secondary activation" step, which further cleans and activates the surface:

[0100] Argon gas (Ar) is introduced into the chamber, and a high DC bias voltage (usually several hundred volts) is applied to ionize the argon gas into high-energy Ar. + ion.

[0101] Ar + Ions bombard the surface of titanium alloy at high speed under bias voltage, removing residual nanoscale contaminants (such as extremely thin oxide layers and adsorbed gas molecules) through physical sputtering effect. At the same time, they "activate" the surface atoms (increase atomic kinetic energy and further enhance surface energy), greatly enhancing the adhesion between the subsequent film layer and the substrate.

[0102] Then pre-splashing is performed:

[0103] 1. Adjust the gas pressure to the working point of 0.4 Pa, and set the gas ratio to Ar:200 sccm / N2:40 sccm.

[0104] 2. Close the baffle, turn on the titanium target power supply, set the power to 3.5kW, and perform 5 minutes of pre-sputtering.

[0105] 3. Purpose: To clean the target surface, stabilize the plasma state, and ensure that the process is stable before formal deposition.

[0106] S36, Multilayer film deposition (core coating process).

[0107] Table 2 Specific parameter settings for formal deposition

[0108] Parameter Category Specific Parameter Setting Target Power (Power) Direct Current (DC) 3.5 kW Operating Pressure (Pressure) 0.4 Pa (about 3.0 x 10"3Torr) Gas Flow Ar (argon): 200 seem N2 (nitrogen): 40 seem Substrate Bias (Bias) -70 V DC Deposition Temperature ～250℃ End Point Control Set end point thickness: 50.0 nm

[0109] As shown in Table 1, the target power (DC) of 3.5kW refers to the DC power applied to the coating target (such as an aluminum target or a chromium target) being 3.5 kilowatts. Power is the core energy source driving sputtering: a high-voltage DC voltage creates an electric field between the target and the chamber, causing argon gas (Ar) to ionize into Ar. + Ions, high-energy Ar +Ions bombard the target surface, causing target atoms to be "sputtered" (detached from the target surface) and deposited onto a substrate (such as a titanium alloy earphone shell) to form a film. In this embodiment, 3.5kW falls within the medium-to-high power range: excessive power can lead to target overheating and excessive sputtered particle energy (potentially causing internal stress or defects in the film); insufficient power results in a slow deposition rate and low efficiency. This power setting balances deposition efficiency and film quality, suitable for the coating requirements of titanium alloy substrates.

[0110] Working air pressure: 0.4 Pa (approximately 3.0 × 10⁻⁶) -3 Torr refers to a total gas pressure of 0.4 Pascals (approximately 3.0 × 10⁻³ Torr in vacuum units), which falls within the low vacuum range. Gas pressure directly affects the trajectory of sputtered particles: when the gas pressure is too low (vacuum too high), Ar… + Low ion count results in low sputtering efficiency; excessively high pressure leads to frequent collisions between Ar atoms and sputtered target atoms, causing a decrease in the energy of the target atoms reaching the substrate and a path deviation, potentially resulting in a porous film and reduced density. A setting of 0.4 Pa ensures sufficient Ar... + The ions bombard the target material with a sufficient concentration (to maintain stable sputtering) while reducing collisions between target atoms and gas molecules, resulting in a denser and more uniform film deposition, which is especially suitable for the density requirements of insulating layers (such as AlN) and underlayers (such as Cr).

[0111] Gas Flow: Ar (Ar): 200 sccm; N2 (Nitrogen): 40 sccm refers to an argon (Ar) flow rate of 200 standard cubic centimeters per minute (sccm) and a nitrogen (N2) flow rate of 40 sccm. It's important to understand that "standard cubic centimeters per minute" is a unit of gas flow rate, referring to the volume of gas flowing per minute under standard conditions (0°C, 1 atm). Argon (Ar): As the "sputtering gas," it is the core medium for generating plasma and bombarding the target material; its flow rate determines the plasma density and sputtering intensity. A flow rate of 200 sccm provides stable sputtering power for the target material. Nitrogen (N2): As the "reactant gas," it reacts with target atoms to form compound films (e.g., aluminum target + N2 to form AlN, titanium target + N2 to form TiN). A flow rate of 40 sccm is used to form a specific ratio of Ar gas (Ar:N2 = 5:1) to ensure a complete reaction and stable film composition (e.g., an AlN stoichiometric ratio close to 1:1 ensures insulation performance). The flow rate ratio is crucial: an imbalance will cause the film composition to deviate from the design (e.g., insufficient N2 may lead to the formation of aluminum-rich AlN). x (Insulation performance deteriorates).

[0112] Substrate bias: -70V DC refers to applying a -70V DC negative bias voltage to the substrate (titanium alloy earphone shell) to be coated. This negative bias voltage attracts positive ions (such as Ar) within the cavity. + Ion ions (target ions) move towards the substrate, bombarding the surface of the depositing film with a certain energy. This process serves several purposes: compacting the film: ion bombardment eliminates porosity in the film, increasing density (especially for the insulating AlN layer, where density directly affects insulation resistance); cleaning the surface: the bombardment process removes adsorbed impurity atoms from the substrate surface, reducing film defects; and promoting diffusion: it enhances the diffusion ability of deposited atoms on the substrate surface, making the film grains more uniform and reducing stress concentration. Understandably, -70V is a low to medium bias voltage: too high a bias voltage leads to over-bombardment (sputtering and stripping of the film), while too low a voltage fails to effectively compact the film. This value strikes a balance between film density and structural stability.

[0113] Deposition temperature: ~250℃ refers to maintaining the substrate temperature at approximately 250℃ during the coating process ("~" indicates an approximate value). Appropriate heating of the substrate can improve the diffusion ability of deposited atoms, promote more complete grain growth in the film, reduce grain boundary defects, and enhance the adhesion between the film and the substrate (especially for Cr underlayers, where temperature can promote interfacial diffusion between Cr and the Ti matrix). The low temperature setting of 250℃ avoids deformation of the titanium alloy substrate due to high temperatures (earphone shells are thin-walled components, prone to warping at high temperatures), while also preventing structural changes in existing films (such as the underlayer) due to overheating, thus balancing film quality and substrate stability.

[0114] Endpoint Control: The set endpoint thickness is 50.0 nm. The film thickness is monitored in real-time using equipment such as a quartz crystal thickness gauge. When the preset thickness of 50 nanometers (0.05 micrometers) is reached, deposition of that layer automatically stops. Precise control of film thickness: 50 nm falls into the category of ultrathin films, and thickness deviations directly affect performance (e.g., an AlN insulating layer that is too thin may have insufficient insulation, while one that is too thick may generate internal stress leading to cracking; the thickness of the Cr underlayer needs to be just right to ensure adhesion, as excessive thickness increases cost). Ensuring batch consistency: Automated endpoint control ensures that the film thickness of each batch of products is the same, avoiding human error and meeting the mass production requirements of precision parts such as headphone shells.

[0115] These parameters are an optimized combination for a specific functional film layer (such as an aluminum nitride insulating layer) on a titanium alloy substrate (earphone shell). The core objective is to deposit a film layer with precise thickness (50nm), dense structure, and stable performance, while ensuring that the substrate does not deform, through stable sputtering energy (3.5kW), a reasonable gas atmosphere (0.4Pa, Ar:N2=5:1), moderate ion bombardment (-70V bias voltage), and temperature assistance (250℃). This lays the foundation for subsequent processes (such as color layer deposition) and the final product performance (insulation, adhesion).

[0116] Based on Table 2, the formal deposition process is as follows:

[0117] 1. Turn on the quartz crystal film thickness gauge and zero it.

[0118] 2. Open the baffle and begin the formal sedimentation process.

[0119] 3. Simultaneously apply a DC bias voltage of -70V to the workpiece.

[0120] 4. Closely monitor whether the power, air pressure, and flow rate readings are stable.

[0121] Step 5: Process Monitoring and End Point

[0122] 1. The thickness reading on the film thickness gauge screen will increase in real time.

[0123] 2. When the reading reaches 50.0 nm, the film thickness gauge will automatically send a signal to cut off the target power supply and close the baffle.

[0124] 3. Record the actual total time of this process (e.g., t = 14 minutes and 30 seconds). This time is for reference only for subsequent production; the next production will still be based on the film thickness.

[0125] Thus, by using techniques such as magnetron sputtering, three layers with different functions are deposited sequentially to achieve comprehensive performance in terms of "adhesion, insulation, and appearance":

[0126] Table 3 Composite Membrane System Process

[0127]

[0128]

[0129] As shown in Table 3, the base layer is made of high-purity Cr (to enhance adhesion and corrosion resistance), which ensures the stability and safety of the foundation.

[0130] High-purity chromium (Cr) sputtering is performed using a sputtering target under an argon (Ar) atmosphere. The chromium layer has good lattice matching with the titanium alloy substrate, forming a strong metallurgical bond; at the same time, chromium itself is corrosion-resistant and can act as a "protective layer" to prevent the substrate from being corroded.

[0131] Functional layer: Aluminum nitride (AlN, providing core insulation properties).

[0132] Using an aluminum (Al) target, argon (Ar) and nitrogen (N2) gases are introduced to generate aluminum nitride (AlN) through reactive sputtering. AlN is an excellent insulating material (with extremely high resistivity), which can provide electromagnetic insulation for the hearing aid shell and prevent short circuits in internal electronic components.

[0133] Color layer: Titanium oxynitride (TiN) x Oγ By precisely controlling the oxygen content (to achieve the gunmetal gray color), the titanium oxynitride layer provides additional protection while giving the product a high-end, understated gunmetal gray appearance through precise stoichiometric control.

[0134] Using a titanium (Ti) target, argon (Ar), nitrogen (N2), and oxygen (O2) are introduced. By adjusting the flow rate ratio of these three gases, the nitrogen (N) and oxygen (O) content in the film (i.e., the "stoichiometry") is controlled, thereby precisely adjusting the film color to "gunmetal gray." Simultaneously, TiN... x O γ It has high hardness and wear resistance, which can protect the outer shell surface from scratches.

[0135] The entire production process is completed under ultra-high vacuum and fully automated control, ensuring the consistency and reliability of the film performance and fully meeting the stringent requirements of medical-grade hearing aids. The coating process is performed within a specific parameter window to ensure optimal bonding between the film and the TC4 substrate.

[0136] S37. Remove from the furnace after cooling.

[0137] After coating is completed, the film is slowly cooled under vacuum or inert gas protection to prevent internal stress or cracking caused by sudden temperature changes, thus ensuring the stability of the film structure. In this embodiment, the workpiece is removed after cooling to below 80°C under argon protection and the vacuum is broken.

[0138] S38. Final Inspection: Medical-grade QA / QC. Specifically, an ellipsometry or profilometer can be used to randomly check the film thickness and verify the accuracy of the film thickness gauge. A cross-cut adhesion tester is used to test the bonding strength.

[0139] The finished product undergoes multi-dimensional testing in accordance with the quality assurance (QA) and quality control (QC) standards for medical-grade products.

[0140] Membrane adhesion: Ensure no membrane peeling by passing a cross-cut adhesion test (e.g., ASTM D3359) (must meet grade 0 standard).

[0141] Insulation performance: Measure the surface insulation resistance (must be >10). 13 The insulation effect of the AlN layer was verified by measuring Ω·cm.

[0142] Appearance and Dimensions: Check color uniformity (consistency of gunmetal gray), surface flatness, and whether the overall dimensions meet the design requirements.

[0143] S39, Finished product: Insulating / gunmetal gray / medical grade hearing aid shell.

[0144] The final product has the following characteristics:

[0145] Insulation: The AlN layer provides reliable electromagnetic insulation, meeting the protection requirements of electronic components;

[0146] Appearance: TiN x O γ The layer presents a uniform gunmetal gray color, giving it a high-end feel;

[0147] Medical grade: Meets medical product standards such as biocompatibility and corrosion resistance, and can be safely used in devices that come into contact with the human body, such as hearing aids.

[0148] This sub-process, through a synergistic design of "ultra-clean pretreatment → high vacuum environment → multi-layer functional film system," solves three key problems in titanium alloy coating: poor adhesion (pretreatment + Cr underlayer), insufficient insulation (AlN functional layer), and poor appearance consistency (TiN). x O γ (Precise control of the color layer) ultimately achieved high performance and high quality for medical-grade hearing aid shells.

[0149] S4. The coating layer in a local area of ​​the headphone shell is removed by laser engraving to obtain a headphone shell that restores conductivity; wherein, the local area of ​​the headphone shell is the interface area where the headphone shell needs to be electrically connected to the outside.

[0150] Figure 6 A schematic diagram illustrating the laser engraving process for the inner body of the earphone shell is shown. Figure 6 As shown, laser engraving is used to locally remove coatings and restore the conductivity of the substrate. For example, laser engraving equipment can be used to precisely process specific interface areas on the earphone shell to remove the insulating coating in that area and restore conductivity.

[0151] S41, Laser engraving process

[0152] For example, in this embodiment, an ultraviolet laser beam is used to precisely remove the coating layer in a specific area, exposing the underlying TC4 titanium alloy substrate and forming a "conductive area":

[0153] S411, Ultraviolet Laser Beam. Principle: Ultraviolet laser energy is concentrated and has a short wavelength, enabling it to coat the TiN coating layer through "photochemical action" (rather than simple thermal melting). x O γ AlN and Cr undergo layer-by-layer vaporization (decomposing into gases sequentially from the surface to the bottom layer), avoiding film carbonization or substrate deformation caused by thermal effects.

[0154] S412, Layer-by-layer vaporization removal. Process: The laser scans along a preset path, sequentially removing TiN... x O γThe color layer, AlN insulating layer, and Cr base layer are "peeled off" until the underlying TC4 titanium alloy substrate is exposed. Because of the "layer-by-layer vaporization," the precision and cleanliness of the removal boundaries are guaranteed, leaving no residual film.

[0155] S413. Blowing away residue. Function: During laser engraving, tiny vaporized particles are generated. These residual particles are blown away by blowing air (usually an inert gas such as argon) to prevent contamination of the insulating film layer.

[0156] S42. Final structure: Insulating region + Conductive region, with clear and steep boundaries.

[0157] After coating and laser engraving, the earphone shell forms a composite structure with "functional partitions":

[0158] S421, Insulating Area (Intact Coating). Area: The area not laser-etched, retaining the complete "Cr layer + AlN layer + TiN". x O γ layer".

[0159] Performance: Possesses high insulation (due to the AlN layer), good adhesion (due to the Cr layer), and gunmetal gray appearance (TiN). x O γ (Layer function) to meet the main protection and aesthetic requirements of the headphone shell.

[0160] S422, Conductive Area (Exposed TC4 Base). Area: The area where the coating has been removed by laser engraving, exposing the TC4 titanium alloy substrate.

[0161] Performance: Restores the conductivity of TC4 for use in electrical connection interfaces of headphones (such as contact areas with circuit boards and sensors).

[0162] S423, Laser Engraving Interface: Clear and steep boundary. Features: The high precision of laser engraving results in a clear and steep boundary between the insulating and conductive areas, with no transition zone or film residue, ensuring the reliability of the electrical connection (stable contact resistance in the conductive area) and the exquisite appearance.

[0163] Thus, by combining the processes of "vacuum coating to build the overall functional layer and laser engraving to precisely remove local film layers", the coating achieves both insulation and a high-end appearance for the earphone shell, while the local laser engraving preserves the conductivity of the titanium alloy substrate. This results in a composite structure of "insulating body and conductive interface", perfectly meeting the requirements of "functional integration and high-end appearance" for medical-grade hearing aid earphone shells.

[0164] It is worth mentioning that the laser parameters (such as wavelength, power, and pulse frequency) are precisely controlled to ensure that only the coating is removed without damaging the TC4 substrate, and to form a clear, sharp boundary. For example, laser engraving technology is used to remove a localized coating at medium-high speed and medium power, with two scans and two fills. The laser engraving process parameters include: an engraving speed of 0.06 m / s, a power of 60%, and a pulse frequency of 50 kHz.

[0165] The laser engraving speed refers to the linear velocity of the laser beam moving across the processing surface. This can be achieved using a servo motor-driven galvanometer system. This speed range ensures that the laser energy has sufficient time to ablate multiple layers of coating per unit area without causing thermal damage to the titanium alloy substrate. The power percentage refers to the proportion of the laser's output power to its maximum rated power. This can be achieved using the power modulation module of a fiber laser. This power level effectively ablates the aluminum nitride insulation layer while preventing penetration into the TC4 substrate. The pulse frequency refers to the number of laser pulse repetitions. This can be achieved by adjusting the Q-switching frequency. High-frequency pulse modes discretize the thermal effect, thereby suppressing heat-affected zone diffusion.

[0166] Specifically, when the laser beam scans at a uniform speed of 0.06 meters per second, the exposure time of each spot is controlled on the order of microseconds. Combined with 60% power output, this allows for selective vaporization and stripping of the coating material, while the substrate temperature remains consistently below the critical phase transformation point of the titanium alloy. A pulse frequency of 50 kHz matches the interval between adjacent pulses to the material's thermal diffusion time, resulting in a uniform energy distribution during continuous processing. This ensures complete removal of the coating layer while maintaining the steepness of the processed area's edges. This parameter combination, through precise control of heat input, achieves layer-by-layer stripping in a multi-layer composite coating system, ultimately forming a functional region on the titanium alloy surface with restored conductivity and excellent interfacial bonding.

[0167] In some specific implementations, a 1064 nm Nd:YAG laser, combined with a beam shaping system, can be used to control the spot diameter to the 30 micrometer level, and a constant energy density on the processed surface can be maintained through three-dimensional dynamic focusing technology. A spiral progressive trajectory is used in the processing path planning to avoid repeated irradiation of local areas. This achieves high-precision selective removal of the coating layer, forming a conductive interface conforming to IEC 60601-1 standards on the medical-grade hearing aid shell, while maintaining the integrity and appearance consistency of the coating in non-processed areas. The edge roughness of the processed conductive area is controlled within 5 micrometers, meeting the assembly accuracy requirements of micro-connectors, and no coating peeling or poor contact was observed after 1000 mating cycles.

[0168] Example

[0169] Example 1

[0170] The manufacturing of the titanium alloy earphone shell in this embodiment begins with TC4 titanium alloy powder with a particle size distribution of D50 = 36.6 μm. This raw material is die-cast into a green blank via metal injection molding, and then sintered under a high-purity helium atmosphere. The sintering process is carried out under a helium (99.999% purity) protective atmosphere, with a heating rate of 6-8℃ / min, a controlled temperature of 1280℃±5℃, and a holding time of 1-2 hours, resulting in a sintered green blank with a density exceeding 99%. Specifically, the manufacturing process is as follows: Figure 4 The sintering curve shown is used for firing.

[0171] The sintered blank was then CNC milled to obtain the earphone shell precursor of the desired shape and size. The milling process used diamond tools, a spindle speed of 20,000 rpm, a feed per tooth of 0.007 mm / tooth, and a feed rate of 290 mm / min. The resulting earphone shell precursor had a surface roughness Ra ≤ 0.2 μm.

[0172] The earphone shell pre-body undergoes cleaning and surface activation pretreatment before vacuum coating. The cleaning process includes ultrasonic cleaning with acetone, ethanol, and deionized water, followed by plasma cleaning. Plasma cleaning is performed at 1.0 Pa argon pressure with an RF bias power supply set to -400 V for 7 minutes. Surface activation pretreatment is performed at 0.4 Pa working pressure using a titanium target power supply (3.5 kW) for 5 minutes of pre-sputtering with a gas ratio of Ar:200 sccm / N2:40 sccm.

[0173] Multiple layers of different types of coatings are applied to the front body of the earphone shell using vacuum deposition, including a high-purity chromium layer as the base layer, an aluminum nitride layer as the insulating layer, and a titanium oxynitride layer as the color layer. The coating process parameters include: applying a -70V DC bias voltage to the front body of the earphone shell at a working gas pressure of 0.4Pa, a deposition temperature of 250℃, and a target power of 3.5kW.

[0174] Finally, the coating layer in a localized area of ​​the headphone shell is removed by laser engraving to restore conductivity to the area connecting to the external electrical interface. The laser engraving speed is 0.06 m / s, power is 60%, and pulse frequency is 50 kHz.

[0175] Figure 7 A schematic diagram of the appearance of the titanium alloy earphone shell prepared in Example 1 is shown. Figure 7 As shown, the titanium alloy earphone shell obtained in Example 1 possesses excellent mechanical properties, aesthetic appearance, and functional performance. It exhibits appropriate conductivity in the desired areas while maintaining insulation in other areas. Testing of the sample thus prepared yielded the following results: adhesion grade 0, insulation resistance >10 ohms. ^14 Ω·cm, with an appearance yield rate of 95%.

[0176] Comparative Example

[0177] Comparative Example 1: Using traditional processes (e.g., directly performing standard vacuum plating on TC4 milled parts). Figure 8 A schematic diagram of the appearance of the titanium alloy earphone shell produced in Comparative Example 1 is shown, such as... Figure 8 As shown, the test results of titanium alloy headphone shells produced by traditional processes show problems such as plating blistering and large-area peeling during the cross-cut adhesion test.

[0178] In summary, this application proposes a titanium alloy earphone shell, which is manufactured through an integrated process including metal injection molding, CNC milling, multi-layer vacuum coating, and laser engraving. The manufacturing process includes: using TC4 titanium alloy powder as raw material, die-casting and helium-protected sintering to form a high-density matrix; precision machining of the sintered body to control the surface roughness within a predetermined range; constructing a functional composite surface through cleaning, activation, and multi-layer coating; and selectively removing localized coatings using laser technology to restore conductive areas.

[0179] Among these processes, metal injection molding and sintering refer to the process of mixing titanium alloy powder with a binder, injection molding, and then debinding and sintering. Specifically, a helium protective atmosphere and a stepped temperature rise curve can be used to achieve densification. This step forms a uniform microstructure to support subsequent processing. CNC milling refers to precision shaping using superhard tools and high-speed cutting parameters. Specifically, diamond tools and optimized feed parameters can be used. This step ensures the substrate surface quality meets the requirements for coating adhesion. Multilayer vacuum coating refers to the sequential deposition of metal and compound layers with different functions. Specifically, a composite structure can be used, employing a chromium layer as a base layer, aluminum nitride as an insulating layer, and titanium oxynitride as a color layer. This step achieves synergy between insulation protection and appearance control through material combination. Laser engraving refers to the selective removal of coatings from designated areas using a high-energy beam. Specifically, a scanning strategy matching pulse frequency and power can be used. This step establishes precise conductive paths while maintaining overall insulation.

[0180] Specifically, this technical solution achieves synergistic performance optimization through the organic integration of the process chain. Metal injection molding ensures efficient forming of complex structures, while helium sintering controls grain growth and eliminates internal defects. Precision machining creates an ultra-smooth surface, providing an ideal substrate for coating, and a specific roughness range balances mechanical strength and coating adhesion. The composite coating design, based on the chromium layer enhancing adhesion, uses aluminum nitride to achieve an electrical insulation barrier, while the titanium oxynitride layer serves both protective and decorative functions. The matching design of laser parameters and coating materials ensures precise removal of the specified film layer without damaging the substrate. The synergistic effect of parameters in each step effectively solves the problems of coating peeling, insulation failure, and appearance defects coexisting in traditional processes.

[0181] Compared to existing technologies, traditional titanium alloy shell manufacturing relies on a single process, leading to performance limitations. Conventional machining results in high material loss and difficulty in forming complex structures, while direct coating suffers from insufficient adhesion and limited functionality. The lack of a systematic approach to the overall process leads to low yield rates. This solution improves material utilization by integrating powder metallurgy and precision machining, and achieves functional regional design by combining multi-layer coating and laser processing. The matching relationship between process parameters overcomes the limitations of single-technology improvements.

[0182] Thus, this application achieves efficient material utilization and functional integration in the manufacturing of titanium alloy shells. This solution solves the problem of peeling caused by insufficient bonding strength between the coating and the substrate, overcomes the technical obstacle of incompatibility between insulation performance and conductivity requirements, eliminates surface defects caused by poor connection between multiple processes, and simultaneously meets the requirements for complex structure forming, electromagnetic shielding protection, and appearance quality control.

[0183] In various embodiments of this application, the titanium alloy headphone shell can be applied to headphone devices composed of microelectronic components, such as integrated circuits, transistors, and electron tubes. For example, a headphone device can refer to a device that utilizes electronic technology (including software). For instance, the headphone device to which the titanium alloy headphone shell can be applied can be an over-ear headphone, an in-ear headphone, a headphone with ear hooks, a neckband headphone, or a clip-on headphone. Furthermore, the types of headphone devices mentioned above can include high-end wireless Bluetooth headphones (True Wireless Stereo, TWS), high-end wired headphones (in-ear / headband), medical-grade hearing aids, bone conduction headphones (medical auxiliary), aerospace communication headphones, industrial noise-canceling headphones (protective), underwater communication headphones (diving / scientific research), military tactical headphones, and optical conduction headphones. That is, the application scenarios of the titanium alloy headphone shell in this application are not limited to common consumer headphones, but can also extend to professional fields such as medical, aerospace, and industrial applications due to its comprehensive performance, and even meet the equipment requirements in extreme environments through customized design. Its core value lies in achieving multi-dimensional optimization of "function + performance + appearance" through material properties and process innovation (such as powder metallurgy, multi-layer coating, and laser engraving).

[0184] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application. Those skilled in the art should understand that although this application has been described in detail with reference to the foregoing embodiments, modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to depart from the spirit and scope of the technical solutions in the embodiments of this application.

Claims

1. A method for producing a titanium alloy earphone shell, characterized in that, Includes the following steps: S1. Using TC4 titanium alloy powder as raw material, the green blank is formed by metal injection molding and then sintered under high-purity helium protection to obtain a sintered blank. S2. Perform CNC milling on the sintered blank to obtain a headphone shell precursor of the required shape and size; wherein, the surface roughness Ra of the headphone shell precursor is ≤0.2μm; S3. The earphone shell front body is cleaned and surface activated pre-treatment is performed, and vacuum coating is performed on the pre-treated earphone shell front body. After forming multiple layers of different types of coating layers on the earphone shell front body, the earphone shell middle body is obtained. S4. The coating layer in a local area of ​​the headphone shell is removed by laser engraving to obtain a headphone shell with restored conductivity; wherein, the local area of ​​the headphone shell is the interface area where the headphone shell has electrical connection requirements with the outside.

2. The method according to claim 1, characterized in that, The particle size distribution of the TC4 titanium alloy powder is D50 = 36.6 μm.

3. The method according to claim 1, characterized in that, In S1, the sintering process specifically includes: under a helium protective atmosphere, a heating rate of 6-8℃ / min, a sintering temperature controlled at 1280℃±5℃, and a holding time controlled at 1-4h, to obtain a sintered green body with a density higher than 99%.

4. The method according to any one of claims 1-3, characterized in that, In S2, the process parameters for CNC milling are as follows: diamond cutting tool is used, spindle speed is 18000-22000 rpm, feed per tooth is 0.005-0.01 mm / tooth, and feed rate is 180-400 mm / min.

5. The method according to any one of claims 1-3, characterized in that, In step S3, cleaning the earphone shell front body includes: ultrasonic cleaning of the earphone shell front body with acetone, ethanol, and deionized water, followed by plasma cleaning.

6. The method according to claim 5, characterized in that, The plasma cleaning process includes: under an argon gas pressure of 1.0 Pa, turning on the radio frequency (RF) bias power supply and setting it to -400V, and performing plasma bombardment cleaning on the front body of the earphone shell for 5-10 minutes.

7. The method according to claim 5, characterized in that, The surface activation pretreatment specifically includes: starting the titanium target power supply at a working gas pressure of 0.4 Pa, setting the power to 3.5 kW, and performing pre-sputtering for 5 minutes; wherein the gas ratio in the working gas pressure is set to Ar:200 sccm / N2:40 sccm.

8. The method according to claim 5, characterized in that, The multilayer coatings of different types include a high-purity chromium layer, an aluminum nitride layer, and a titanium oxynitride layer. The specific process parameters for vacuum coating include: using a zeroed quartz crystal film thickness gauge, applying a DC bias of -70V to the front body of the earphone shell at a working pressure of 0.4Pa to obtain the earphone shell body with the required coating thickness and number of layers; wherein the deposition temperature is 250℃, and the target power is 3.5kW; the high-purity chromium layer, as the underlayer, uses a chromium target, and the reacting gas is argon; the aluminum nitride layer, as the insulating layer, uses an aluminum target, and the reacting gases are argon and nitrogen, with a gas ratio of Ar:200sccm / N2:40sccm; the titanium oxynitride layer, as the color layer, uses a titanium target, and the reacting gases are argon, nitrogen, and oxygen, with a gas ratio of Ar:200sccm / N2:40sccm / O2:(40-100)sccm.

9. The method according to any one of claims 1-3, characterized in that, In step S4, the laser engraving process parameters include: engraving speed of 0.06 m / s, power of 60%, and pulse frequency of 50 kHz.

10. A titanium alloy earphone shell, characterized in that, It is prepared by the manufacturing method of titanium alloy earphone shell as described in any one of claims 1-9.

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