Perforated knee joint, hole forming method and forming die

Abstract

The present invention relates to a perforated knee joint, a hole forming method and a forming die. In order to ensure the tight combination of the knee joint implant and the original bone tissue, the present invention adds a threaded hole design to the posterior condylar surface of the knee joint, replacing the conventional rectangular counterbore design. Since the shape of the knee joint metal part is complex and the threaded hole is arranged on the inner wall of the posterior condylar surface, it is easily interfered by the larger anterior condylar surface during machining, which increases the difficulty of processing and manufacturing. The present invention adopts the investment casting method to produce the knee joint metal part.

Description

Technical Field

[0001] The present invention relates to the technical field of part casting, in particular to a knee joint with holes, a hole forming method and a forming die therefor. Background Art

[0002] The advantages of investment casting technology in forming high-precision complex structural parts have become increasingly obvious, especially in artificial joint implants. Since artificial joint implants require high wear resistance and strength, cobalt-chromium-molybdenum alloys with good biocompatibility are often selected.

[0003] Due to its high strength, good toughness, and a large number of second-phase carbide precipitates dispersed in the matrix, cobalt-chromium-molybdenum alloy is extremely difficult to machine. Especially in recent years, with the increasing in-depth research on artificial joint implants, especially knee joints, various novel structural designs have emerged in artificial joint implants, bringing new challenges to the manufacturing of artificial joint implants.

[0004] Currently, the more commonly used knee joint installation method in the industry is bone cement bonding. In artificial knee joint replacement surgery, the last two steps are: making the cut bone block into a bone plug and inserting it into the femoral and tibial drill holes, adjusting the bone cement and then implanting the prosthesis; fixing the patella with a patella compressor, removing the excess bone cement after the bone cement solidifies, flushing the wound surface, removing the excess bone cement and broken bones; and draining and suturing.

[0005] The surgical reliability of bone cement bonding depends on the bonding strength of the bone cement. Since the bone cement is only surface-contact bonding, it cannot fully guarantee that the service life of the artificial knee joint will not be shortened under severe impact. Summary of the Invention

[0006] The applicant of the present invention aims at the above-mentioned disadvantages in the existing production technology, and provides a knee joint with holes, a hole forming method and a forming die therefor. A threaded counterbore is formed on the posterior condyle surface of the artificial knee joint, and a threaded core with specific dimensional requirements can be designed according to the accuracy requirements of the thread. The threaded core is positioned with the die to ensure perpendicularity. After the casting product is demolded, a threaded hole meeting the accuracy requirements can be manufactured, eliminating the subsequent machining steps and greatly reducing the machining cost.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A knee joint with holes, including an anterior condyle surface and a posterior condyle surface, wherein a threaded counterbore is formed on the posterior condyle surface, and the central axis of the threaded counterbore is perpendicular to the posterior condyle surface.

[0009] A hole forming method for a knee joint with holes, comprising the following steps:

[0010] Core design stage:

[0011] Convert the internal thread of the casting product into the external thread of the core, which serves as the threaded section of the core. One end of the threaded section is connected to a core head, and the core head is used to be installed on the corresponding wax mold die.

[0012] Determine the internal thread size, accuracy requirements, and the width of the middle diameter tolerance zone of the internal thread of the casting product; select the casting metal material, determine the axial and radial solidification shrinkage rates of this material, determine the axial and radial sintering shrinkage rates of the ceramic core material, and reserve shrinkage amounts according to the above shrinkage rates; and correct the thread teeth of the core thread to obtain the core size parameters.

[0013] Core mold design stage:

[0014] Adopt upper and lower molds symmetrical to the cavity thread, and form threads in the cavity through electrical discharge machining; on one side of the mold, there is a measuring electrode for measuring the depth of electrical discharge etching. Determine the depth of electrical discharge etching for synchronous etching by the penetration depth of the measuring electrode.

[0015] As a further improvement of the above technical solution:

[0016] Obtain the maximum value of the core head, with the maximum value being 9.09 mm; set positioning holes on the mold, with the diameter of the positioning holes being larger than the maximum value of the core head; set fixing holes in the vertical direction of the positioning holes to position the core from three directions of x, y, and z.

[0017] Casting and correction stage:

[0018] After the casting sandblasting process is completed, manually correct and clean the mold sand with a tap to obtain a finished product screw hole.

[0019] The core parameters are as follows:

[0020] The diameter of the core head ranges from 8 to 10 mm, and the outer diameter of the external thread of the threaded section is 5 to 7 mm;

[0021] The outer circular surface of the core head is concave, and the diameter of the concave groove formed ranges from 6 to 9 mm, and the height ranges from 3 to 5 mm;

[0022] Both ends of the core head are provided with shoulders, the diameter of the shoulders ranges from 8 to 10 mm, and the height ranges from 1 to 3 mm; the bottom of the core head is concave, and the depth range of the concave formed is 1 to 3 mm, and the direction of the concave depth is perpendicular to the axis of the core head.

[0023] The internal thread of the casting product is M6, the accuracy requirement is 6G, and the width of the middle diameter size tolerance zone of the internal thread of the casting product is 0.072 mm;

[0024] The casting material is selected as cobalt-chromium-molybdenum alloy, the solidification shrinkage rate in the height direction is 1.8%, and the solidification shrinkage in the radial direction is 1.9%;

[0025] The core material is selected as ceramic, with a sintering shrinkage rate of 1.0% in the height direction and 1.3% in the radial direction.

[0026] The shrinkage allowance reserved for the casting product is the sum of the solidification shrinkage rate and the sintering shrinkage rate.

[0027] The specific parameters for modifying the thread are: modifying the thread teeth of the thread section to translate 0.024 mm in the direction away from the axis.

[0028] The axial height of the measuring electrode is taken as 4 - 6 mm.

[0029] A core used in a hole forming method for a knee joint with holes, including a core head and a thread section located on the core head; shoulders are provided at both ends of the core head, and the two shoulders form a groove on the outer circular surface of the core head.

[0030] An installation part used in cooperation with the above core, including an installation block body, on which a positioning hole and a fixing hole are provided perpendicular to each other, and the core is embedded in the positioning hole; the installation block body is embedded in the casting mold for use.

[0031] A casting mold for casting a knee joint with holes, in which the above installation part is installed in the casting mold cavity.

[0032] The beneficial effects of the present invention are as follows:

[0033] The structure of the present invention is compact and reasonable, and the operation is convenient. In order to ensure the tight combination of the knee joint implant and the original bone tissue, a threaded hole design is added to the posterior condylar surface of the knee joint, replacing the conventional rectangular counterbore design.

[0034] Due to the complex shape of the knee joint metal part and the threaded hole being arranged on the inner wall of the posterior condylar surface, it is prone to interference from the larger anterior condylar surface during machining, increasing the difficulty of processing and manufacturing. The present invention adopts the investment casting method to produce the knee joint metal part.

[0035] Based on investment casting, the present invention designs a corresponding core for forming the threaded counterbore, and the core of the present invention can be disassembled, and is detachably arranged with the installation block body and the casting mold, facilitating the replacement of the core, making the mold size adjustable, and the produced knee joints being applicable to patients of multiple age groups and various body types.

[0036] In the present invention, electrical discharge machining is used for etching, combined with a measuring electrode, which can accurately control the product size.

[0037] The main object of the present invention is to improve the existing screw hole forming method and apply it to medical devices with higher precision requirements. Conventional screw hole forming methods include milling, extrusion forming, or turning machining, etc. However, these methods all require a very spacious operating space and are inconvenient to use on semi-finished knee joints. In the present invention, a method of preliminary forming and secondary fine repair is adopted to directly cast threads within the allowable deviation range, and then manual fine repair and fine adjustment are carried out to achieve the purpose of forming high-precision screw holes on multi-curved complex parts and very small working surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 FIG. is a cross-sectional view of a knee joint with a threaded hole according to the present invention.

[0039] Figure 2 FIG. is a schematic structural view of the core of the present invention.

[0040] Figure 3 FIG. is a schematic view of the state during the processing of the core and the measuring electrode of the present invention.

[0041] Figure 4 FIG. is a schematic structural view of the core of the present invention installed on the mounting block.

[0042] Figure 5 FIG. is a cross-sectional view of the core of the present invention installed on the mounting block.

[0043] Figure 6 FIG. is a cross-sectional view of the core of the present invention installed on the mounting block from another perspective.

[0044] Wherein: 1, anterior condylar surface; 2, posterior condylar surface; 3, threaded counterbore; 4, core head; 5, shoulder; 6, threaded section; 7, groove; 8, positioning hole; 9, fixing hole; 10, mounting block; 11, measuring electrode. DETAILED DESCRIPTION OF THE INVENTION

[0045] The following will describe the detailed implementation manners of the present invention with reference to the accompanying drawings.

[0046] As Figures 1-6 shown, the knee joint with a hole in this embodiment includes an anterior condylar surface 1 and a posterior condylar surface 2, and a threaded counterbore 3 is formed on the posterior condylar surface 2, and the central axis of the threaded counterbore 3 is perpendicular to the posterior condylar surface 2.

[0047] The hole forming method of the knee joint with a hole in this embodiment includes the following steps:

[0048] Core design stage:

[0049] Convert the internal thread of the casting product into the external thread of the core as the threaded section 6 of the core. One end of the threaded section 6 is connected with a core head 4, and the core head 4 is used to be installed on the corresponding wax mold.

[0050] Determine the internal thread size, precision requirements, and the width of the tolerance zone of the pitch diameter of the casting product; select the casting metal material, determine the axial and radial solidification shrinkage rates of this material, determine the axial and radial sintering shrinkage rates of the ceramic core material, and reserve the shrinkage amount according to the above shrinkage rates; and correct the thread teeth of the core thread to obtain the core size parameters.

[0051] Core mold design stage:

[0052] Use upper and lower molds symmetrical to the cavity thread, and form threads in the cavity by electrical discharge machining; on one side of the mold, there is a measuring electrode 11 for measuring the depth of electrical discharge etching. Determine the depth of electrical discharge etching of synchronous etching by the penetration depth of the measuring electrode 11.

[0053] Obtain the maximum value of the core head 4, which is 9.09 mm; set positioning holes 8 on the mold, and the diameter of the positioning holes 8 is larger than the maximum value of the core head 4; set fixing holes 9 in the vertical direction of the positioning holes 8 to position the core in three directions of xyz.

[0054] Casting and correction stage:

[0055] After the casting sandblasting process is completed, manually correct and clean the molding sand with a tap to obtain the finished product screw hole.

[0056] The core parameters are as follows:

[0057] The diameter value range of the core head 4 is 8 - 10 mm, and the outer diameter of the external thread of the thread section 6 is 5 - 7 mm;

[0058] The outer circular surface of the core head 4 is concave, and the diameter value range of the groove 7 formed by the concave is 6 - 9 mm, and the height value range is 3 - 5 mm;

[0059] Both ends of the core head 4 are provided with shoulders 5, the diameter value range of the shoulders 5 is 8 - 10 mm, and the height value range is 1 - 3 mm; the bottom of the core head 4 is concave, and the range of the concave depth formed is 1 - 3 mm, and the concave depth direction is perpendicular to the axis of the core head 4.

[0060] The internal thread of the casting product is M6, the precision requirement is 6G, and the width of the tolerance zone of the pitch diameter of the internal thread of the casting product is 0.072 mm;

[0061] The casting material is selected as cobalt-chromium-molybdenum alloy, the solidification shrinkage rate in the height direction is 1.8%, and the solidification shrinkage in the radial direction is 1.9%;

[0062] The core material is selected as ceramic, the sintering shrinkage rate in the height direction is 1.0%, and the sintering shrinkage in the radial direction is 1.3%.

[0063] The shrinkage amount reserved for the casting product is the sum of the solidification shrinkage rate and the sintering shrinkage rate.

[0064] The specific parameters of the modified thread are as follows: the thread teeth of the thread section 6 are modified to be translated 0.024 mm in the direction away from the axis.

[0065] The axial height of the measuring electrode 11 is taken as 4 - 6 mm.

[0066] The core used in the hole forming method of the perforated knee joint in this embodiment includes a core head 4 and a thread section 6 located on the core head 4; shoulders 5 are provided at both ends of the core head 4, and the two shoulders 5 form a groove 7 on the outer circular surface of the core head 4.

[0067] The mounting part used in conjunction with the core in this embodiment includes a mounting block 10. Perpendicular positioning holes 8 and fixing holes 9 are provided on the mounting block 10, and the core is embedded in the positioning hole 8; the mounting block 10 is embedded for use in the casting mold.

[0068] In the casting mold for casting the perforated knee joint in this embodiment, a mounting part is installed in the casting mold cavity.

[0069] The specific structure and working process of this embodiment are as follows:

[0070] (1) Core design:

[0071] a) Convert the internal thread of the casting product into the external thread of the core, design the core head. The diameter of the core head is 9 mm, the outer diameter of the external thread of the core is 6 mm. The core head adopts a groove design, the groove diameter is 7 mm, the height is 4 mm, and protrusions are formed at the upper and lower ends to form shoulders. The shoulder diameter is 9 mm and the height is 2 mm; the shoulders contact the mold to determine the center of the core. A groove is provided at the bottom of the core, and the depression depth is 2 mm, which is used to position the height direction of the core.

[0072] b) According to the drawing requirements, the internal thread of the casting product is M6, and the precision requirement is 6G, that is, the tolerance zone width of the pitch diameter dimension of the internal thread is 0.072 mm; the solidification shrinkage rate of the cobalt-chromium-molybdenum alloy in the casting factory in the height direction is 1.8%, and the solidification shrinkage in the radial direction is 1.9%.

[0073] The sintering shrinkage rate of the core material in the core factory in the height direction is 1.0%, and the sintering shrinkage in the radial direction is 1.3%.

[0074] A shrinkage rate of 2.8% is placed in the height direction of the core thread, and a shrinkage rate of 3.2% is placed in the radial direction.

[0075] The thread teeth of the core thread section are modified to be translated 0.024 mm outward, and the dimensional requirements of the core mold can be obtained through the above adjustments.

[0076] (2) Core mold design:

[0077] The core mold has an upper and lower split mold, and the thread teeth are formed by electrical discharge machining.

[0078] In order to monitor the depth of the electrode insertion, a measuring electrode with a diameter of 2 mm is designed beside the core electrode;

[0079] The axis of the core electrode is perpendicular to the axis of the measuring electrode. The height of the measuring electrode is 5 mm. By determining the depth of the measuring electrode inserted into the core mold, the depth of the core electrode insertion is judged to ensure that the roundness of the produced core meets the expected standard.

[0080] (3) Positioning of the core in the wax injection mold:

[0081] Measure the core head diameter dimensions of 32 cores obtained from the core supplier. Calculate the upper control limit of the core head diameter to be 9.09 mm. Design a core positioning hole with a diameter of 9.12 mm on the product wax mold, and design a shoulder on the mold that matches the bottom groove of the core for positioning in the height direction of the core.

[0082] (4) Thread treatment after the casting process:

[0083] After the wax mold with the core undergoes the processes of shell making, melting, and core removal, the product undergoes the final sandblasting process. After sandblasting, a M6-6G YAMAWA tap is manually inserted and rotated to correct the thread teeth and clean the remaining grit.

[0084] The core, the processing method of the core mold, the positioning of the core in the finished mold, and the treatment of the later stage of thread casting designed by the present invention can produce internal thread precision that meets the requirements of the customer's drawing, avoid forming by machining in the later stage, and greatly reduce the cost and time cycle of the later processing. It provides the possibility for designing a new type of artificial joint implant that is more suitable for patients for the customer.

[0085] The above description is an explanation of the present invention, not a limitation of the invention. The scope defined by the present invention is referred to the claims, and any form of modification can be made within the protection scope of the present invention.

Claims

1. A method for forming holes in a perforated knee joint, characterized in that, the applicable perforated knee joint structure includes a front condylar surface (1) and a rear condylar surface (2), and is characterized in that: a threaded counterbore (3) is formed on the rear condylar surface (2), and the central axis of the threaded counterbore (3) is perpendicular to the rear condylar surface (2), the hole forming method includes the following steps: Core design stage: Convert the internal thread of the casting product into the external thread of the core as the threaded section (6) of the core. One end of the threaded section (6) is connected with a core head (4), and the core head (4) is used for installation on the corresponding wax mold die; Determine the internal thread size, precision requirements and the width of the middle diameter tolerance zone of the internal thread of the casting product; select the casting metal material, determine the axial and radial solidification shrinkage rates of this material, determine the axial and radial sintering shrinkage rates of the ceramic core material, and reserve shrinkage according to the above shrinkage rates; and correct the thread teeth of the core thread to obtain the core size parameters; The casting material is selected as cobalt-chromium-molybdenum alloy, the solidification shrinkage rate in the height direction is 1.8%, and the solidification shrinkage in the radial direction is 1.9%; The core material is selected as ceramic, the sintering shrinkage rate in the height direction is 1.0%, and the sintering shrinkage in the radial direction is 1.3%; Core die design stage: Use upper and lower dies with symmetrical cavity threads, and form threads in the cavity by electrical discharge machining; on one side of the die, a measuring electrode (11) for measuring the depth of electrical discharge etching is provided, and the depth of electrical discharge etching of synchronous etching is determined by the penetration depth of the measuring electrode (11); Core positioning stage: According to the existing core specifications and dimensions, obtain the maximum value of the diameter of the core head (4) of the core, set a positioning hole (8) on the die, and the diameter of the positioning hole (8) is greater than the maximum value of the core head (4); set a fixing hole (9) in the vertical direction of the positioning hole (8) to position the core from three directions of xyz; Casting and correction stage: After the casting sandblasting process is completed, use a tap to manually correct and clean the molding sand to obtain a finished screw hole.

2. The method for forming holes in a perforated knee joint according to claim 1, characterized in that: The core parameters are as follows: The diameter of the core head (4) ranges from 8 to 10 mm, and the outer diameter of the external thread of the threaded section (6) is 5 to 7 mm; The outer circumferential surface of the core head (4) is recessed inward, and the diameter of the recessed groove (7) formed ranges from 6 to 9 mm, and the height ranges from 3 to 5 mm; Both ends of the core head (4) are provided with shoulders (5), the diameter of the shoulders (5) ranges from 8 to 10 mm, and the height ranges from 1 to 3 mm; the bottom of the core head (4) is recessed inward, and the depth of the recessed depression ranges from 1 to 3 mm, and the depth direction of the recess is perpendicular to the axis of the core head (4).

3. The method for forming holes in a perforated knee joint according to claim 1, characterized in that: The internal thread of the casting product is M6, the precision requirement is 6G, and the width of the middle diameter size tolerance zone of the internal thread of the casting product is 0.072 mm; The casting material is selected as cobalt-chromium-molybdenum alloy, the solidification shrinkage rate in the height direction is 1.8%, and the solidification shrinkage in the radial direction is 1.9%; The core material is selected as ceramic, the sintering shrinkage rate in the height direction is 1.0%, and the sintering shrinkage in the radial direction is 1.3%.

4. The hole forming method of the perforated knee joint according to claim 2, characterized in that: the shrinkage allowance reserved for the casting product is the sum of the solidification shrinkage rate of the metal and the sintering shrinkage rate of the ceramic core.

5. The hole forming method of the perforated knee joint according to claim 2, characterized in that: the specific parameters for modifying the thread are: modifying the thread teeth of the thread section (6) to be translated 0.024 mm in the direction away from the axis.

6. The hole forming method of the perforated knee joint according to claim 1, characterized in that: the axial height of the measuring electrode (11) is 4-6 mm.

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