Dimension control method for titanium alloy injection molding part with high aspect ratio structure

Abstract

The invention discloses a size control method for a titanium alloy injection molding part with a high aspect ratio structure, the titanium alloy injection molding part is prepared through the processes of internal mixing, granulation, injection molding, catalytic degreasing and sintering, and sintering comprises the following steps: (1) a three-section gradient heating stage; (2) controlling the vacuum degree and preserving heat at constant temperature; and (3) a step-by-step speed control cooling stage. By means of a multi-stage temperature control mode, a three-stage gradient heating strategy is adopted to promote internal stress release to achieve powder densification, then high-vacuum constant-temperature sintering is adopted to reduce shrinkage anisotropy, and then step-by-step speed control cooling is adopted to inhibit thermal stress and phase change stress concentration; the whole size side length deviation of the titanium alloy injection molding part with the high aspect ratio structure is controlled, local warping is avoided, the size precision and batch stability of the titanium alloy injection molding part are improved, and the method is suitable for the fields of consumer electronics, medical implants, miniature aerospace sensors and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal injection molding, and particularly relates to a size control method for a titanium alloy injection molded part with a high aspect ratio structure. BACKGROUND

[0002] Metal injection molding (MIM) of titanium alloy is highly concerned in the fields of aerospace, medical devices, consumer electronics, etc. due to its ability to mass-produce high-complexity and precision parts. Compared with traditional processing techniques, MIM technology is particularly suitable for manufacturing titanium alloy parts with complex geometric structures (such as thin-walled, cantilevered, etc.), and has high material utilization and controllable cost.

[0003] With the increasing demand for miniaturization and lightweight, the market demand for titanium alloy MIM parts has significantly increased, especially in the fields of medical implants such as anchoring teeth / spinal processes in spinal fusion devices, healing abutments for dental implants, etc., and micro-aerospace sensors, etc. such as deep-cavity thin-walled shells with multiple precision internal partitions, gyroscope frames, and gimbal rings, etc. These parts usually have a high aspect ratio structure, i.e. one dimension is much larger than the other two dimensions, such as a long rod structure, or one dimension is much smaller than the other two dimensions, such as a thin-walled structure. During sintering, high aspect ratio structures are prone to deformation and size control problems, resulting in a significant reduction in yield and a significant increase in cost, which makes titanium alloy products prepared by injection molding lose the advantages of low cost and batch production.

[0004] To address the above problems, the current industry generally adopts the strategy of pre-setting support structures, by adding temporary support frames before sintering or optimizing the placement angle of the blank, to offset the effects of gravity and enhance structural stability. For example, auxiliary support points are designed at the ends of long rods, or the arrangement of the parts in the sintering furnace is optimized through thermodynamic simulation. However, such methods have obvious limitations: first, the design of support structures relies on experience and lacks precise modeling of multi-field coupling (temperature field, stress field, flow field), resulting in biased deformation prediction; second, the contact area between the support and the part is prone to interfacial stress due to shrinkage differences, causing new local deformation; third, traditional sintering processes are difficult to suppress the non-synchronous densification of thin-walled structures, ultimately resulting in insufficient overall dimensional accuracy. Even if the support body is made of the same material as the sintered sample, it is difficult to avoid uneven deformation such as warping of the part. These problems indicate that simple reliance on geometric compensation means cannot achieve high-precision sintering.

[0005] Therefore, it is necessary to develop a size control method for titanium alloy MIM parts with high aspect ratio structure to effectively suppress deformation and improve size consistency. The breakthrough of such technology will directly improve product qualification rate, reduce single piece cost, and expand the application boundary of titanium alloy MIM technology in the field of micro precision device manufacturing, meet the urgent needs of high-end market for high-performance complex parts, and provide reliable technical support for frontier fields such as aerospace precision components and personalized medical implants. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a size control method for titanium alloy injection molded parts with high aspect ratio structure to solve the problems of the prior art. To solve the above technical problems, the technical scheme adopted by the present application is as follows: a size control method for titanium alloy injection molded parts with high aspect ratio structure, characterized in that the method is prepared by mixing, granulating, injection molding, catalytic debinding and sintering process, wherein the sintering process includes the following stages: (1) Three-stage gradient heating stage First stage: from room temperature to 400 DEG C, the heating rate is 8 DEG C / min~12 DEG C / min; Second stage, i.e. hot debinding and forming sintering neck stage: from 400 DEG C to 950 DEG C, the heating rate is 3 DEG C / min~5 DEG C / min, and after reaching 950 DEG C, it is kept for 20 min~30 min; Third stage, i.e. sintering neck growth stage: from 950 DEG C to 1000 DEG C~1200 DEG C sintering temperature, the heating rate is 1 DEG C / min~2 DEG C / min; (2) Constant temperature sintering stage, i.e. densification stage Control the vacuum degree not more than 8*10-3Pa, keep at 1000 DEG C~1200 DEG C sintering temperature for 2h~6h; (3) Stepwise speed control cooling stage When the sintering temperature is higher than 1000 DEG C, the sintering temperature is reduced to 1000 DEG C, and the cooling rate is 3 DEG C / min~5 DEG C / min; From 1000 DEG C to 750 DEG C, the cooling rate is 2 DEG C / min~4 DEG C / min, and then the furnace is cooled.

[0007] Generally, the titanium alloy powder is mixed with a binder in proportion, and after granulation, the titanium alloy powder is injection molded into a green body, and then the organic components are removed by catalytic debinding, and then sintering is performed to prepare a titanium alloy injection molded part.

[0008] The traditional sintering process adopts a single rate of temperature rise and fall, which leads to a large thermal stress gradient in the titanium alloy, a prominent anisotropy of shrinkage, and easy warping deformation of a high aspect ratio structure. In view of this technical problem, the present application divides the sintering process into three stages, namely, a three-stage gradient heating stage, a constant temperature sintering stage, and a stepwise controlled rate cooling stage. In the three-stage gradient heating stage, the temperature is rapidly raised at a rate of 8 ℃ / min to 12 ℃ / min below 400 ℃ to reduce the residence time in the low temperature zone, the rate is reduced to 3 ℃ / min to 5 ℃ / min when the temperature rises from 400 ℃ to 950 ℃, and the temperature is maintained for 20 min to 30 min after reaching the temperature to promote the decomposition of the organic binder and the release of internal stress, and the temperature is slowly raised at a rate of 1 ℃ / min to 2 ℃ / min when the temperature rises from 950 ℃ to 1000 ℃ to 1200 ℃, which is close to the sintering temperature, so that the powder particles are uniformly dispersed and recombined, the density difference is reduced, and the titanium alloy powder is uniformly densified; in the constant temperature sintering stage, sintering is performed under low vacuum, and the anisotropy of shrinkage is reduced through the grain boundary diffusion mechanism; in the stepwise controlled rate cooling stage, the temperature is raised at a rate of 3 ℃ / min to 5 ℃ / min when the sintering temperature reaches 1000 ℃, and then the temperature is raised at a rate of 2 ℃ / min to 4 ℃ / min when the temperature is from 1000 ℃ to 750 ℃, and the temperature is slowly cooled near the beta phase transition point, which effectively suppresses the warping deformation caused by the concentration of thermal stress and phase transformation stress, and finally significantly reduces the overall size length deviation of the titanium alloy injection molded part with a high aspect ratio structure, avoiding local warping.

[0009] The size control method of the titanium alloy injection molded part with a high aspect ratio structure, wherein the loading amount of the titanium alloy powder is 61% to 63% by volume percentage during the mixing process, the adhesive used is a polyformaldehyde-based multi-component binder, the mixing temperature is 170 ℃ to 200 ℃, and the mixing time is 1.5 h to 2.5 h.

[0010] The size control method of the titanium alloy injection molded part with a high aspect ratio structure, wherein the catalytic debinding is performed in oxalic acid, the catalytic debinding temperature is 110 ℃ to 130 ℃, and the time is 8 h to 12 h.

[0011] The size control method of the titanium alloy injection molded part with a high aspect ratio structure, wherein the total slow cooling time in the interval from 1000 ℃ to 750 ℃ in the stepwise controlled rate cooling stage is more than 1 h. By limiting the total slow cooling time, the residual strain caused by the phase transformation stress is avoided.

[0012] The aforementioned method for controlling the dimensions of titanium alloy injection-molded parts with a high aspect ratio is characterized in that the sintering process utilizes zirconia ceramic sheets or alumina sheets coated with yttrium oxide throughout. By optimizing the materials of the sintering structure, interfacial reactions between conventional alumina materials and the titanium alloy parts are avoided, thus preventing the introduction of impurities.

[0013] The above-mentioned method for controlling the dimensions of a titanium alloy injection-molded part with a high aspect ratio is characterized in that the titanium alloy injection-molded part has a high aspect ratio, a warpage of no more than 0.5%, a dimensional tolerance of no more than ±0.3%, and a density of 98% or more, wherein the warpage is equal to the maximum warpage height / the length of the plane diagonal or the height of the long column × 100%.

[0014] Compared with the prior art, the present invention has the following advantages: 1. To address the issue that traditional sintering processes employ a single-rate heating and cooling method, resulting in a large thermal stress gradient and causing warping deformation in high aspect ratio structures, this invention utilizes multi-stage temperature control. It employs a three-stage gradient heating strategy: first, rapid heating followed by deceleration heating, and then slow heating again. This promotes the full decomposition of the organic binder and the release of internal stress, leading to uniform densification of the titanium alloy powder. Then, high vacuum is maintained for isothermal sintering to reduce shrinkage anisotropy. Finally, step-by-step controlled cooling near the β-phase transformation point suppresses thermal stress and phase transformation stress concentration, significantly reducing the overall dimensional deviation of titanium alloy injection-molded parts with high aspect ratio structures and preventing localized warping.

[0015] 2. To address the issue that existing sintering processes suffer from poor dimensional control due to excessively rapid heating and cooling rates, resulting in binder pyrolysis residues, increased porosity, and stress concentration at grain boundaries, this invention employs a medium-speed heating rate from 400℃ to 950℃, coupled with a 20-30 minute holding period. This extends the organic matter decomposition time, reducing residual carbon and oxygen impurities. Simultaneously, during isothermal sintering, a high-vacuum environment (≤8×10⁻3Pa) is used to prevent oxidation, increasing the green compact density to over 98%. This ensures stable and controllable shrinkage, significantly improving the dimensional accuracy of titanium alloy injection-molded parts.

[0016] 3. To address the issue that traditional sintering processes rely on empirical parameter adjustments and are susceptible to batch instability due to fluctuations in equipment temperature fields, this invention quantifies temperature control thresholds at each stage (such as the low-speed heating start point and slow cooling range), combined with multi-stage heat preservation and variable-speed cooling designs, to create a precisely reproducible process window. In particular, during the cooling process, multiple cooling stages with different cooling rates fully release the latent heat of phase transformation, significantly reducing thermal stress and avoiding microstructural mutations caused by rapid cooling in traditional processes. This improves the batch stability of titanium alloy injection-molded parts. At the same time, this process has a high fault tolerance and high yield, meeting the stringent requirements of the aerospace industry for high-consistency titanium alloy precision parts.

[0017] 4. This invention, through multi-stage temperature control, controls the warpage of titanium alloy injection-molded parts with high aspect ratio structures to within 0.5%, the dimensional tolerance to within ±0.3%, and the density to above 98%, effectively solving the problem of dimensional deviations caused by thermal stress concentration and uneven shrinkage in traditional sintering processes.

[0018] The technical solution of the present invention will be further described in detail below through embodiments. Detailed Implementation

[0019] Example 1 This embodiment prepares titanium alloy injection-molded sheets through a process of mixing, granulation, injection molding, catalytic debinding, and sintering. The designed dimensions (length × width × thickness) of the titanium alloy injection-molded sheet are 20mm × 20mm × 1mm, and the process includes the following steps: Step 1, Intensive Mixing: Mix TC4 titanium alloy powder with a particle size D90≤25μm with polyoxymethylene-based multi-component binder and intensively mix. The loading of TC4 titanium alloy powder is 61% by volume percentage. The intensive mixing temperature is 180℃ and the mixing time is 1.5h to obtain the feed. Step 2, Granulation: Granulate the feed from Step 1 to obtain feed pellets with a particle size of 2mm~3mm; Step 3, Injection Molding: The feed pellets from Step 2 are injection molded to obtain green sheet; Step 4, Catalytic Degreasing: The green sheet from Step 3 is subjected to catalytic degreasing in an oxalic acid atmosphere at a temperature of 120°C for 8 hours to obtain a degreased green sheet with a residual binder content of no more than 0.5%. Step 5, Sintering: The degreased blank from Step 4 is sintered. The entire sintering process uses zirconia ceramic sheets as the firing support, and includes the following stages: (1) Three-stage gradient heating stage First stage: heating from room temperature to 400℃ at a rate of 8℃ / min; The second stage is the hot degreasing and sintering neck formation stage: the temperature is raised from 400℃ to 950℃ at a rate of 3℃ / min, and then held at 950℃ for 20min. The third stage is the sintering neck growth stage: the sintering temperature is increased from 950℃ to 1000℃ at a rate of 1℃ / min. (2) The isothermal sintering stage, i.e. the densification stage The vacuum degree is controlled to not exceed 8×10⁻³Pa, and the sintering temperature is maintained at 1100℃ for 3 hours. (3) Step-by-step controlled cooling stage The sintering temperature was reduced from 1100℃ to 1000℃ at a rate of 4℃ / min. The temperature was reduced from 1000℃ to 750℃ at a rate of 2℃ / min, and then cooled in the furnace. The furnace was then opened and the titanium alloy injection-formed sheet was obtained.

[0020] Upon testing, the dimensions (length × width × thickness) of the titanium alloy injection-molded sheet prepared in this embodiment are 19.94mm × 19.94mm × 1mm. The warping is not obvious, the maximum warping height is 0.14mm, the warping amount is 0.5%, the dimensional tolerance is -0.3%, and the density is 98.5%. Among them, the warping amount = maximum warping height / plane diagonal length × 100%.

[0021] Example 2 This embodiment prepares titanium alloy injection-molded sheets through a process of mixing, granulation, injection molding, catalytic debinding, and sintering. The designed dimensions (length × width × thickness) of the titanium alloy injection-molded sheet are 20mm × 20mm × 1mm, and the process includes the following steps: Step 1, Intensive Mixing: Mix TC4 titanium alloy powder with a particle size D90≤25μm with polyoxymethylene-based multi-component binder and intensively mix. The loading of TC4 titanium alloy powder is 62% by volume percentage. The intensive mixing temperature is 170℃ and the mixing time is 2h to obtain the feed. Step 2, Granulation: Granulate the feed from Step 1 to obtain feed pellets with a particle size of 2mm~3mm; Step 3, Injection Molding: The feed pellets from Step 2 are injection molded to obtain green sheet; Step 4, Catalytic Degreasing: The green sheet from Step 3 is subjected to catalytic degreasing in an oxalic acid atmosphere at a temperature of 130℃ for 8 hours to obtain a degreased green sheet with a residual binder content of no more than 0.5% by mass. Step 5, Sintering: The degreased blank from Step 4 is sintered. The entire sintering process uses zirconia ceramic sheets as the firing support, and includes the following stages: (1) Three-stage gradient heating stage First stage: heating from room temperature to 400℃ at a rate of 10℃ / min; The second stage is the hot degreasing and sintering neck formation stage: the temperature is raised from 400℃ to 950℃ at a rate of 4℃ / min, and then held at 950℃ for 30min. The third stage is the sintering neck growth stage: the sintering temperature is increased from 950℃ to 1000℃ at a rate of 2℃ / min. (2) The isothermal sintering stage, i.e. the densification stage The vacuum degree is controlled to not exceed 8×10⁻³Pa, and the sintering temperature is maintained at 1000℃ for 6 hours. (3) Step-by-step controlled cooling stage The temperature was reduced from 1000℃ to 750℃ at a rate of 3℃ / min, and then cooled in the furnace. The furnace was then opened and the titanium alloy injection-formed sheet was obtained.

[0022] Upon testing, the dimensions (length × width × thickness) of the titanium alloy injection-molded sheet prepared in this embodiment are 19.96mm × 19.97mm × 1mm. The warping is not obvious, the maximum warping height is 0.11mm, the warping amount is 0.4%, the dimensional tolerance is -0.2%, and the density is 98.7%. The warping amount is calculated as: maximum warping height / diagonal length of the plane × 100%.

[0023] Example 3 This embodiment prepares titanium alloy injection-molded sheets through a process of mixing, granulation, injection molding, catalytic debinding, and sintering. The designed dimensions (length × width × thickness) of the titanium alloy injection-molded sheet are 20mm × 20mm × 1mm, and the process includes the following steps: Step 1, Intensive Mixing: Mix TC4 titanium alloy powder with a particle size D90≤25μm with polyoxymethylene-based multi-component binder and intensively mix. The loading of TC4 titanium alloy powder is 63% by volume percentage. The intensive mixing temperature is 160℃ and the mixing time is 2.5h to obtain the feed. Step 2, Granulation: Granulate the feed from Step 1 to obtain feed pellets with a particle size of 2mm~3mm; Step 3, Injection Molding: The feed pellets from Step 2 are injection molded to obtain green sheet; Step 4, Catalytic Degreasing: The green sheet from Step 3 is subjected to catalytic degreasing in an oxalic acid atmosphere at a temperature of 110℃ for 12 hours to obtain a degreased green sheet with a residual binder content of no more than 0.5% by mass. Step 5, Sintering: The degreased blank from Step 4 is sintered. The entire sintering process uses alumina sheets coated with yttrium oxide as the firing support, including the following stages: (1) Three-stage gradient heating stage First stage: heating from room temperature to 400℃ at a rate of 12℃ / min; The second stage is the hot degreasing and sintering neck formation stage: the temperature is raised from 400℃ to 950℃ at a rate of 5℃ / min, and then held at 950℃ for 30min. The third stage is the sintering neck growth stage: the sintering temperature is increased from 950℃ to 1200℃, and the heating rate is 2℃ / min. (2) The isothermal sintering stage, i.e. the densification stage The vacuum degree is controlled to not exceed 8×10⁻³Pa, and the sintering temperature is maintained at 1200℃ for 2 hours. (3) Step-by-step controlled cooling stage The sintering temperature was reduced from 1200℃ to 1000℃ at a rate of 5℃ / min. The temperature was reduced from 1000℃ to 750℃ at a rate of 4℃ / min, and then cooled in the furnace. The furnace was then opened and the titanium alloy injection-formed sheet was obtained.

[0024] Upon testing, the dimensions (length × width × thickness) of the titanium alloy injection-molded sheet prepared in this embodiment are 20.02mm × 20.01mm × 1mm. The warping is not obvious, the maximum warping height is 0.07mm, the warping amount is 0.2%, the dimensional tolerance is 0.1%, and the density is 98.9%. The warping amount is calculated as: maximum warping height / diagonal length of the plane × 100%.

[0025] Example 4 This embodiment prepares a titanium alloy injection-molded long rod through a process of mixing, granulation, injection molding, catalytic degreasing, and sintering. The designed dimensions (diameter × length) of the titanium alloy injection-molded long rod are φ4mm × 20mm, and the process includes the following steps: Step 1, Intensive Mixing: Mix TC4 titanium alloy powder with a particle size D90≤25μm with polyoxymethylene-based multi-component binder and intensively mix. The loading of TC4 titanium alloy powder is 61% by volume percentage. The intensive mixing temperature is 180℃ and the mixing time is 1.5h to obtain the feed. Step 2, Granulation: Granulate the feed from Step 1 to obtain feed pellets with a particle size of 2mm~3mm; Step 3, Injection Molding: The feed pellets from Step 2 are injection molded to obtain a green body; Step 4, Catalytic Degreasing: The green body from Step 3 is subjected to catalytic degreasing in an oxalic acid atmosphere at a temperature of 120°C for 8 hours to obtain a degreased green body with a residual binder content of no more than 0.5%. Step 5, Sintering: The degreased blank from Step 4 is sintered. The entire sintering process uses zirconia ceramic sheets as the firing support, and includes the following stages: (1) Three-stage gradient heating stage First stage: heating from room temperature to 400℃ at a rate of 12℃ / min; The second stage is the hot degreasing and sintering neck formation stage: the temperature is raised from 400℃ to 950℃ at a rate of 5℃ / min, and then held at 950℃ for 30min. The third stage is the sintering neck growth stage: the sintering temperature is increased from 950℃ to 1100℃, and the heating rate is 2℃ / min. (2) The isothermal sintering stage, i.e. the densification stage The vacuum degree is controlled to not exceed 8×10⁻³Pa, and the sintering temperature is maintained at 1100℃ for 3 hours. (3) Step-by-step controlled cooling stage The sintering temperature was reduced from 1100℃ to 1000℃ at a rate of 5℃ / min. The temperature was reduced from 1000℃ to 750℃ at a rate of 4℃ / min, and then cooled in the furnace. The furnace was then opened and the long rod was removed to obtain a titanium alloy injection-formed rod.

[0026] Upon testing, the dimensions (diameter × length) of the titanium alloy injection-molded long rod prepared in this embodiment are φ3.99mm × 20.06mm. No obvious warping was observed. The maximum warping height is 0.1mm, the warping amount is 0.5%, the dimensional tolerance is 0.3%, and the density is 98.7%. The warping amount is calculated as: maximum warping height / long rod height × 100%.

[0027] Comparative Example 1 This comparative example prepares titanium alloy injection-molded sheets through a process of mixing, granulation, injection molding, catalytic debinding, and sintering. The designed dimensions (length × width × thickness) of the titanium alloy injection-molded sheets are 20mm × 20mm × 1mm, and the process includes the following steps: Step 1, Intensive Mixing: Mix TC4 titanium alloy powder with a particle size D90≤25μm with polyoxymethylene-based multi-component binder and intensively mix. The loading of TC4 titanium alloy powder is 61% by volume percentage. The intensive mixing temperature is 180℃ and the mixing time is 1.5h to obtain the feed. Step 2, Granulation: Granulate the feed from Step 1 to obtain feed pellets with a particle size of 2mm~3mm; Step 3, Injection Molding: The feed pellets from Step 2 are injection molded to obtain green sheet; Step 4, Catalytic Degreasing: The green sheet from Step 3 is subjected to catalytic degreasing in an oxalic acid atmosphere at a temperature of 120°C for 8 hours to obtain a degreased green sheet with a residual binder content of no more than 0.5%. Step 5, Sintering: The degreased blank from Step 4 is subjected to conventional sintering. The entire sintering process uses zirconia ceramic sheets as the firing support, including the following stages: (1) Heat defatting stage First stage: heating from room temperature to 400℃ at a rate of 10℃ / min; Second stage: Raise the temperature from 400℃ to 650℃ at a rate of 5℃ / min, and hold at 650℃ for 60min after reaching the temperature. (2) The isothermal sintering stage, i.e. the densification stage The sintering temperature was increased from 650℃ to 1100℃ at a rate of 5℃ / min, and then the vacuum degree was controlled to not exceed 8×10⁻3Pa. The temperature was then maintained at 1100℃ for 3 hours. (3) Cooling stage The titanium alloy injection-molded sheet was obtained after the furnace was opened and cooled.

[0028] Upon testing, the dimensions (length × width × thickness) of the titanium alloy injection-molded sheet prepared in this comparative example were 19.80mm × 19.82mm × 1mm, with obvious warping. The maximum warping height was 1.03mm, the warping amount was 3.6%, the dimensional tolerance was -1.0%, and the density was 98.5%. The warping amount was calculated as: maximum warping height / diagonal length of the plane × 100%.

[0029] Comparative Example 2 This comparative example demonstrates the preparation of a titanium alloy injection-molded long rod via a process of mixing, granulation, injection molding, catalytic debinding, and sintering. The designed dimensions (diameter × length) of the titanium alloy injection-molded long rod are φ4mm × 20mm, and the process includes the following steps: Step 1, Intensive Mixing: Mix TC4 titanium alloy powder with a particle size D90≤25μm with polyoxymethylene-based multi-component binder and intensively mix. The loading of TC4 titanium alloy powder is 61% by volume percentage. The intensive mixing temperature is 180℃ and the mixing time is 1.5h to obtain the feed. Step 2, Granulation: Granulate the feed from Step 1 to obtain feed pellets with a particle size of 2mm~3mm; Step 3, Injection Molding: The feed pellets from Step 2 are injection molded to obtain a green body; Step 4, Catalytic Degreasing: The green body from Step 3 is subjected to catalytic degreasing in an oxalic acid atmosphere at a temperature of 120°C for 8 hours to obtain a degreased green body with a residual binder content of no more than 0.5%. Step 5, Sintering: The degreased blank from Step 4 is sintered. The entire sintering process uses zirconia ceramic sheets as the firing support, and includes the following stages: (1) Heat defatting stage First stage: heating from room temperature to 400℃ at a rate of 10℃ / min; Second stage: Raise the temperature from 400℃ to 650℃ at a rate of 5℃ / min, and hold at 650℃ for 60min after reaching the temperature. (2) The isothermal sintering stage, i.e. the densification stage The sintering temperature was increased from 650℃ to 1100℃ at a rate of 5℃ / min, and then the vacuum degree was controlled to not exceed 8×10⁻3Pa. The temperature was then maintained at 1100℃ for 3 hours. (3) Cooling stage After cooling in the furnace, the rod is removed from the furnace to obtain a titanium alloy injection-formed long rod.

[0030] Upon testing, the dimensions (diameter × length) of the titanium alloy injection-molded long rod prepared in this comparative example are φ4.02mm × 19.84mm. It exhibits obvious warping with a maximum warping height of 1.98mm, a warping amount of 10%, a dimensional tolerance of -0.8%, and a density of 98.5%. The warping amount is calculated as: maximum warping height / long rod height × 100%.

[0031] The sintering temperature, density, maximum warpage height, warpage amount, and dimensional tolerance of the titanium alloy injection molded parts prepared in Examples 1-4 and Comparative Examples 1-2 of this invention are shown in Table 1 below.

[0032] Table 1

[0033] As can be seen from Table 1, when comparing Comparative Example 1 with Examples 1-3 and Comparative Example 2 with Example 4, the titanium alloy injection-molded parts prepared in Examples 1-4 avoid local warping, with the warping amount controlled within 0.5%, the dimensional tolerance within ±0.3%, and the density above 98%. This indicates that the multi-stage temperature control method of the present invention achieves effective control over the overall dimensional side length deviation of titanium alloy injection-molded parts with high aspect ratio structures. The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A dimensional control method for a titanium alloy injection molded part having a high aspect ratio structure, characterized by, The method prepares a titanium alloy injection molding part through a closed mixing, granulation, injection molding, catalytic debinding and sintering process, wherein the sintering process comprises the following stages: (1) Three-stage gradient heating stage First stage: from room temperature to 400 DEG C, the heating rate is 8 DEG C / min~12 DEG C / min; Second stage, namely the hot debinding and sintering neck forming stage: from 400 DEG C to 950 DEG C, the heating rate is 3 DEG C / min~5 DEG C / min, after reaching 950 DEG C, the temperature is kept for 20 min~30 min; Third stage, namely the sintering neck growing stage: from 950 DEG C to 1000 DEG C~1200 DEG C sintering temperature, the heating rate is 1 DEG C / min~2 DEG C / min; (2) Constant temperature sintering stage, namely the densification stage Control the vacuum degree not more than 8×10⁻ 3 Pa, sintering at 1000℃~1200℃ for 2h~6h; (3) Stepwise controlled cooling stage When the sintering temperature is higher than 1000 DEG C, from the sintering temperature to 1000 DEG C, the cooling rate is 3 DEG C / min~5 DEG C / min; From 1000 DEG C to 750 DEG C, the cooling rate is 2 DEG C / min~4 DEG C / min, and then the furnace is cooled.

2. The dimensional control method of a titanium alloy injection molded part having a high aspect ratio structure according to claim 1, characterized by, In the closed mixing process, the loading amount of titanium alloy powder is 61%~63% by volume percentage, the binder used is a polyformaldehyde-based multi-component binder, the mixing temperature is 170 DEG C~200 DEG C, and the mixing time is 1.5 h~2.5 h.

3. The dimensional control method of a titanium alloy injection molded part having a high aspect ratio structure according to claim 1, characterized in that, The catalytic debinding is carried out in oxalic acid, the catalytic debinding temperature is 110 DEG C~130 DEG C, and the time is 8 h~12 h.

4. The dimensional control method of a titanium alloy injection molded part having a high aspect ratio structure according to claim 1, characterized by, In the stepwise controlled cooling stage, the total slow cooling time in the interval from 1000 DEG C to 750 DEG C is more than 1 h.

5. The method of dimensional control of a titanium alloy injection molded part having a high aspect ratio structure according to claim 1, wherein Zirconia ceramic sheets or yttria-sprayed alumina sheets are used for sintering throughout the sintering process.

6. The method of dimensional control of a titanium alloy injection molded part having a high aspect ratio feature according to claim 1, wherein, The titanium alloy injection molding part has a high aspect ratio structure, the warpage is not more than 0.5%, the dimensional tolerance is not more than ±0.3%, and the density is more than 98%, wherein the warpage = maximum warpage height / plane diagonal length or long column height x 100%.

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