Anti-deformation jig for metal injection molding rack

Abstract

The utility model discloses a metal injection molding rack anti-deformation jig which comprises a mullite plate body, the upper surface of the mullite plate body is provided with a limiting area and a positioning area, the limiting area comprises a plurality of V-shaped grooves, and the V-shaped grooves are matched with the tooth shape of a rack; the positioning area is arranged on one side of the V-shaped groove, and a plurality of positioning concave strips are arranged on the positioning area; the two side edges of the V-shaped groove form an angle of 90 degrees.

Description

Technical Field

[0001] This utility model relates to a metal injection molded rack anti-deformation fixture. Background Technology

[0002] The deformation of metal injection molded (MIM) toothed racks during sintering is mainly due to their process characteristics and material behavior: the sintering stage requires high temperature (e.g., 1300℃) to achieve densification of metal particles, but the anisotropic shrinkage of the material (axial shrinkage rate is usually higher than radial shrinkage), the vaporization of degreasing residues, and the uneven temperature field (temperature difference in the furnace > 20℃) lead to deformation; the fine tooth structure of the rack is prone to local stress concentration due to abrupt changes in cross-section, which exacerbates the difference in shrinkage between the tooth tip and the tooth root.

[0003] The multi-dimensional problems with existing fixtures are key contributing factors to rack sintering deformation. First, regarding surface quality, the working surface of the fixture exhibits varying degrees of unevenness or wear, resulting in surface flatness that fails to meet process requirements. This surface defect directly affects the uniform distribution of pressure and heat during sintering—when the rack is placed in the fixture, locally concave areas cannot provide effective support, causing excessive pressure concentration on the convex parts, which easily leads to warping deformation under high temperature and pressure.

[0004] Secondly, the demolding process of the green blank also has a potential impact on product quality. Because the green blank retains internal stress when it is ejected from the mold, and the existing fixtures cannot achieve uniform distribution of pressure and heat due to structural defects, the risk of deformation during the stress release process is further aggravated, ultimately leading to shape deviations of the rack during the sintering stage.

[0005] Furthermore, the compatibility of the fixture material is also a crucial factor that cannot be ignored. Taking the widely used alumina fixture as an example, if there is a significant difference in the coefficient of thermal expansion between it and the rack material, additional thermal stress will be generated during the high-temperature sintering process due to the inconsistent degree of expansion. The accumulation and release of this thermal stress can also cause irreversible deformation of the rack. The combined effect of these multiple factors seriously affects the sintering quality and yield of the rack. Utility Model Content

[0006] Since the existing fixtures have the above-mentioned technical solutions, this utility model proposes a metal injection molded rack anti-deformation fixture, the purpose of which is to solve the problem of rack deformation caused by the existing fixtures.

[0007] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0008] A metal injection-molded rack anti-deformation fixture includes: a mullite plate, with a limiting area and a positioning area set on the upper surface of the mullite plate; the limiting area includes a plurality of V-shaped grooves, the V-shaped grooves being adapted to the tooth profile of the rack; the positioning area is located on one side of the V-shaped grooves, and the positioning area is provided with a plurality of positioning recesses; the two sides of the V-shaped grooves are at 90°.

[0009] Preferably, one side of the V-shaped groove is inclined at 30° to the vertical direction.

[0010] Preferably, the positioning area is flush with the bottom of the V-shaped groove.

[0011] Due to the adoption of the above technical solution, the fixture of this utility model uses mullite, which has a high melting point and a smooth surface, and good stability; the positioning area and the limiting area work together to restrict the displacement of the rack in all directions, ensuring the consistency of sintering dimensional accuracy, and effectively solving the problem of rack deformation. Attached Figure Description

[0012] Figure 1 This is a structural schematic diagram of the present invention.

[0013] Figure 2 for Figure 1 Side view;

[0014] Figure 3 for Figure 2 Enlarged view of a specific area. Detailed Implementation

[0015] The technical solution of this utility model will be further described in detail below through embodiments and in conjunction with the accompanying drawings.

[0016] Combination Figures 1 to 3As shown, the metal injection-molded rack anti-deformation fixture in this embodiment includes a mullite plate 1. A limiting area 2 and a positioning area 3 are provided on the upper surface of the mullite plate 1. The limiting area 2 includes several V-shaped grooves 21, which are adapted to the rack tooth profile. The positioning area 3 is located on one side of the V-shaped groove 21, and multiple positioning recesses 31 are provided on the positioning area 3. One side of the V-shaped groove 21 is inclined at 30° to the vertical direction, and both sides of the V-shaped groove 21 are at 90°. The positioning area 3 is flush with the bottom of the V-shaped groove 21. The combined design of the 30° inclined side and the 90° right-angle side of the V-shaped groove in this embodiment has multiple advantages: the 30° inclined surface provides a natural assembly guide for the rack, reducing the difficulty of manual adjustment, and simultaneously disperses the effects of stress and thermal expansion differences through inclined contact; while the 90° right-angle side ensures precise positioning and rigid support of the rack, resulting in uniform pressure distribution and stable tooth profile. The synergistic effect of the two achieves a dynamic balance of "flexible guidance + rigid fixation"—the 30° slope relieves assembly stress and allows for fine adjustment of thermal expansion, while the 90° right angle resists sintering pressure and maintains positioning accuracy. This design not only improves the fixture's resistance to deformation during the metal injection molding sintering process, but also ensures the dimensional consistency of the rack forming. It is particularly suitable for mass production scenarios that require a balance between assembly efficiency, positioning accuracy, and high-temperature stability.

[0017] In the metal injection molding (MIM) process for fabricating gear racks, the sintering stage is arguably the core node determining product precision and quality. However, during high-temperature sintering of the green blank, factors such as stress release and uneven heat transfer can easily cause gear rack deformation, which traditional fixtures often struggle to address effectively. Mullite, as a high-performance engineering material, with its high melting point, low coefficient of expansion, excellent thermal shock resistance, and chemical stability, is an ideal choice for solving this problem. It not only provides stable support for the gear rack and reduces the risk of deformation but also ensures the long-term reliable use of the fixture under complex working conditions.

[0018] The mullite V-groove fixture, through innovative design and deep integration of material properties, has successfully overcome the challenge of sintering deformation. Its unique V-groove structure optimizes the heat flow path, promoting uniform heat conduction on the rack surface and within the rack itself, significantly reducing thermal stress accumulation caused by localized temperature differences. Simultaneously, precise positioning and limiting devices effectively constrain the rack's freedom of movement, maintaining its stable shape during thermal contraction or expansion. Furthermore, by constructing a closed or semi-closed microenvironment, combined with the stable chemical properties of mullite, the fixture achieves precise control of the sintering atmosphere, ensuring uniform flow of protective gas and preventing surface variations caused by oxidation, decarburization, and other reactions. The synergistic effect of multiple technologies eliminates the root cause of deformation hazards due to uneven temperature and surface condition changes, significantly improving the dimensional accuracy and quality consistency of the sintered rack, providing a reliable guarantee for the application of MIM technology in precision rack manufacturing.

[0019] This utility model has advantages in both materials and structural design:

[0020] 1. Mullite has a high melting point and remains solid at sintering temperatures of 1000℃-1400℃, providing stable support for the rack and preventing deformation due to fixture softening. 2. Adaptable to thermal expansion: Its low coefficient of thermal expansion minimizes the difference in thermal expansion between the fixture and the rack, reducing additional stress and lowering the risk of deformation. 3. Long service life: Excellent thermal shock resistance and chemical stability ensure that the fixture can withstand drastic temperature changes without reacting with the sintering atmosphere, allowing for long-term stable use.

[0021] 2. Precise Constraint Positioning: The V-groove is adapted to the rack tooth profile, with multiple points of close contact to disperse stress. Combined with positioning and limiting structures, it restricts rack displacement in all directions, ensuring sintering dimensional accuracy and consistency. Optimized Sintering Environment: Moderate thermal conductivity optimizes heat flow and avoids uneven heating of the rack; the V-groove creates a microenvironment to prevent atmospheric erosion from causing differences in rack surface condition and reduce deformation problems.

[0022] The embodiments described above are for illustrative purposes only and are not intended to limit the scope of this utility model. All equivalent changes and modifications made to this utility model by those skilled in the art should fall within the scope of the appended claims.

Claims

1. A metal injection molding rack anti-deformation jig, characterized in that, include: A mullite slab has a limiting area and a positioning area on its upper surface. The limiting area includes several V-shaped grooves that are adapted to the tooth shape of the rack. The positioning area is located on one side of the V-shaped groove and has multiple positioning recesses. The two sides of the V-shaped groove are at 90°.

2. The metal injection molding rack anti-deformation jig according to claim 1, characterized in that, One side of the V-shaped groove is inclined at 30° to the vertical direction.

3. The metal injection molding rack anti-deformation jig according to claim 1, characterized in that, The positioning area is flush with the bottom of the V-shaped groove.

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