Manufacturing method for fixing internal splints
The method addresses low yield and burr issues in internal fixation device manufacturing by using forward extrusion and die forging with annealing to refine crystal grains, achieving improved yield and equiaxed structure for complex bone-end shapes.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- FUJI OOZX INC
- Filing Date
- 2022-09-07
- Publication Date
- 2026-05-21
AI Technical Summary
Existing methods for manufacturing internal fixation devices with complex bone-end shapes face low yield due to generation of cutting chips and burrs, and difficulty in achieving an equiaxed crystal structure required by ISO 20160 using conventional forging techniques.
A method involving forward extrusion forging to create a billet with integrated large and small diameter portions, followed by die forging and annealing, to refine crystal grains and achieve the equiaxed structure, thereby improving yield and reducing burrs.
The method enhances material yield and achieves the equiaxed structure required by ISO 20160, while minimizing burrs and simplifying the manufacturing process for complex shapes.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a method for manufacturing an internal fixation device (plate) used for fixing a fracture site, and particularly to a method for manufacturing an internal fixation device (plate) having a complex shape adapted to the shape of a bone end.
Background Art
[0002] With the progress of aging faced by many countries around the world including Japan, the demand for internal fixation devices (plates) used for fracture accidents due to falls of the elderly has been increasing. Here, the internal fixation device (plate) used for the bone end part has a complex shape and is thin-walled, so it has been manufactured by cutting from a metal block as a material. At this time, a large amount of cutting chips are generated, and the problem has been that the yield is low.
[0003] Therefore, Non-Patent Document 1 discloses a hot forming processing technology that does not perform cutting in order to suppress the generation of cutting chips and improve the yield of metal materials. This technology heats a round bar as a metal material to a high temperature in a heating furnace and forms the round bar into the shape of an internal fixation device (plate) by two-stage forging of rough forming and finish forming using a mold.
[0004] Although hot forming processing significantly improves the yield compared to cutting, the internal fixation device (plate) used for the bone end part often has a non-uniform width, and a large amount of burrs are generated in the narrow part with a round bar material, resulting in a poor yield. In order to reduce the generation of burrs in the narrow part, it is necessary to change the diameter of the round bar corresponding to the wide part and the narrow part, but for this purpose, cutting of the round bar becomes necessary, and it is difficult to improve the yield.
Prior Art Documents
Non-Patent Documents
[0005]
Non-Patent Document 1
[0006] On the other hand, forward extrusion forging is known as a method for changing the diameter of the round bar in the wide and narrow sections of the fixing internal splice (plate) without machining the round bar. However, forward extrusion forging has the problem that it is difficult to achieve the equiaxed structure required by ISO 20160 because the crystal grains elongate in the extrusion direction.
[0007] Therefore, the present invention proposes a method for manufacturing a fixing splint (plate) that uses forward extrusion forging and can achieve the equiaxed structure required by ISO 20160. [Means for solving the problem]
[0008] According to the present invention, the above problem is solved as follows. (1) The present invention provides a method for manufacturing a fixing internal splint (plate), characterized by heating a round bar metal material, forming a billet consisting of a large diameter head and a small diameter shaft portion integrally formed with the head using a forward extrusion device, heating the billet, and then using die forging with a die to produce a die forged product that is close in shape to the final product, a plate-shaped fixing internal splint (plate), and then annealing the die forged product.
[0009] By using the manufacturing method for the fixing internal splint (plate) according to the present invention, a billet in which crystal grains have been formed by elongation in the extrusion direction using a forward extrusion device is subjected to die forging using a die, resulting in a die-forged product in which the strain of the elongated crystal grains is increased. By annealing this die-forged product, the strain is released and the crystal grains can be refined.
[0010] Generally, annealing can release internal strain and restore coarse grains to a standard structure. However, this invention more effectively refines grains by further increasing the strain generated by stretching the grains through forward extrusion, followed by die forging, and then performing annealing in that state. In this way, the equiaxed structure required by ISO 20160 can be achieved.
[0011] (2) The method described in item (1) above is characterized in that the billet is subjected to die forging using a die one or more times.
[0012] By producing a product with the desired shape in a single die forging process, the manufacturing process can be simplified. Furthermore, by performing die forging in multiple stages, products with complex shapes can be manufactured using die forging.
[0013] (3) In the above item (1) or (2), the head of the billet corresponds to the wide portion of the fixing internal attachment (plate) as a product, and the shaft portion of the billet corresponds to the narrow portion of the fixing internal attachment (plate).
[0014] By matching the shape of the billet to the shape of the internal fixing splice (plate) in the product, the material yield can be improved.
[0015] (4) In item (1) or (2) above, the metal material of the round bar is characterized in that it is pure titanium or a titanium alloy.
[0016] (5) In the above (1) or (2), the metal material of the round bar is characterized in that it is a cobalt-chromium-molybdenum alloy.
[0017] (6) In the above (1) or (2), the metal material of the round bar is characterized in that it is austenitic stainless steel.
Brief Description of Drawings
[0018] [Figure 1] It is a process diagram of a method for manufacturing a fixing inner auxiliary member (plate) of the present invention. [Figure 2] It is a schematic diagram of a forward extrusion device used for forward extrusion in FIG. 1. [Figure 3] It is a front view of a die used for die forging in FIG. 1. [Figure 4A] It is a photograph A1 - A6 of an equiaxed structure required by ISO20160. [Figure 4B] It is a photograph A7 - A12 of an equiaxed structure required by ISO20160. [Figure 5] It is a photograph of the metal structure after forward extrusion, after die forging, and after annealing.
Embodiments for Carrying Out the Invention
[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each figure, the same parts are denoted by the same reference numerals.
[0020] FIG. 1 shows a process diagram of a method for manufacturing a fixing inner auxiliary member (plate) 100 of the present invention. This process consists of process 1: material cleaning, process 2: material heating, process 3: forward extrusion, process 4: billet heating, process 5: die forging, process 6: annealing, process 7: burr removal, and process 8: machining.
[0021] In the manufacturing method of the fixing inner accessory (plate) 100 of the present invention (hereinafter, simply referred to as "plate 100" as appropriate), the material 10 used in step 1 is a metal round bar. Specifically, it is a round bar of Ti-6Al-4V ELI titanium alloy, cobalt-chromium-molybdenum alloy, austenitic stainless steel, etc. In step 1, impurities and oils and fats adhering to the material 10 are removed. Specifically, since mineral oil-based oils and fats are the target, a semi-aqueous cleaning agent of a type that combines a petroleum solvent containing a surfactant and water is generally used.
[0022] Taking the Ti-6Al-4V ELI titanium alloy as an example, the heating in step 2 is to heat the round bar as the material 10 to a temperature below the β transformation point. It is preferable to take sufficient time to achieve a uniform temperature up to the center of the round bar.
[0023] The forward extrusion in step 3 is a process of loading the round bar (material) 10 heated to a temperature below the β transformation point into a cylindrical die 25 (see Fig. 2) using a forward extrusion device 20 and extruding it forward by a punch 21 (see Fig. 2) to manufacture a billet 30 having a shape suitable for open die forging. Step 3 will be further described using Fig. 2.
[0024] Fig. 2(a) shows the round bar as the material 10, Figs. 2(b) and 2(c) show the forward extrusion device 20, and Fig. 2(d) shows the billet 30 manufactured by forward extrusion. The size of the round bar as the material 10 is, for example, an outer diameter of 19.2 mm and a length of 48 mm. The size of the billet 30 manufactured by forward extrusion is, when using the material shown in Fig. 2(a), a head with a large diameter having an outer diameter of 20 mm, a shaft part with a small diameter having an outer diameter of 11.5 mm, and a total length of 110 mm.
[0025] Figure 2(b) is a schematic diagram of the forward extrusion device 20 with material 10 loaded. By applying a forward pushing force to the punch 21 via the shim 24, the loaded material 10 is molded to the shape of the die 25. In this forward extrusion device 20, the punch 21 is held by a punch guide 23 incorporated into the punch case 22. The die 25 is incorporated into the die case 28, and its lower part is blocked by a packing block 29.
[0026] Figure 2(c) shows a forward extrusion apparatus in which the material 10 is pushed forward by the punch 21 to form a billet 30. By employing forward extrusion in this manner, it is possible to form a billet 30 in which a large diameter head 30a and a small diameter shaft portion 30b are integrally formed, thereby reducing material loss due to machining.
[0027] Figure 2(d) shows the billet 30 formed by the forward extrusion device. This billet 30 is heated to a temperature below the β transformation point in step 4 of Figure 1, similar to step 2, and then used in die forging using the die 40 in step 5.
[0028] Figure 3 shows a front view of the die 40 used in die forging in step 5 of Figure 1. The die 40 consists of an upper and lower pair, each mounted on the press machine 50. The billet 30 is placed between the upper and lower pairs of dies, and the pressing force of the press machine 50 deforms the billet 30 into the shape of the die.
[0029] In Figure 3, the upper die set 41 of the die set 40 is attached to the slide 51 of the press machine 50, and the upper die set 41 moves up and down together with the vertical movement of the press machine 50 along with the punch plate 43 and the punch 42. On the other hand, the lower die set 46 of the die set 40 is fixed to the bolster 52 of the press machine 50, and the lower die set 46 receives the pressing force of the press machine 50 via the punch 42 together with the die plate 45 and the die 44.
[0030] Furthermore, the die 40 has a burr relief section 47 formed between the upper and lower pairs of the die 40 to release burrs generated when the billet 30 is deformed. The gap of this burr relief section 47 varies depending on the degree to which the billet 30 is deformed, but is usually adjusted to a range of 1 to 3 mm. As shown in step 5 of Figure 1, the die-forged product 60 formed by die forging has burrs 61 formed all around its circumference.
[0031] In this invention, annealing is performed in step 6 and deburring is performed in step 7. By annealing, in the case of Ti-6Al-4V ELI titanium alloy, the material 10 can be restored to the uniform α-β two-phase metallic structure it had, and the hardness of the metallic structure, which had increased due to die forging, can be reduced. Therefore, tool life can be improved in deburring in step 7, in which unwanted protrusions, or burrs 61, are removed by machining. Annealing is performed at 700-750°C for 1-4 hours. After deburring in step 7, the die-forged product 60 becomes an intermediate product 70 before machining. Alternatively, after deburring in step 6, annealing may be performed in step 7.
[0032] The final step, process 8, is performed on the pre-machining intermediate product 70. The machining process consists of two parts: surface machining and hole machining. Surface machining removes the scale that has formed on the surface of the pre-machining intermediate product 70 due to forward extrusion and die forging, and processes it to the target dimensions of the final product. Hole machining is the process of cutting screw holes for inserting fixing screws that will fasten the final plate 100 to the frame.
[0033] A machining center is used for the cutting process in step 8. A machining center is an NC milling machine equipped with an automatic tool changer. A large number of cutting tools are stored in the tool magazine, and the machine automatically changes tools according to computer numerical control commands, allowing for continuous operation of various processes such as milling, boring, drilling, and tapping. The plate 100 is completed as the final product through this cutting process. Furthermore, surface treatment (sterilization) may be performed after machining.
[0034] The present invention provides a method for manufacturing the internal fixing splint (plate) 100. In the process of manufacturing a billet from a round bar of material 10, forward extrusion forging is employed, which eliminates the need for cutting. By taking advantage of the drawback of forward extrusion forging, which is that the crystal grains elongate in the extrusion direction, the strain generated by forward extrusion forging is increased by die forging after forward extrusion forging. By performing annealing in this state, it is possible to more effectively refine the crystal grains. In this way, by using the method for manufacturing the internal fixing splint (plate) 100 of the present invention, the yield of material 10 can be further improved, and the equiaxed structure required by ISO 20160 can be achieved.
[0035] In the process diagram in Figure 1, die forging in step 5 is performed only once, but die forging may be performed two or more times. In this case, heating in step 4 and die forging in step 5 will be repeated two or more times. It is possible to form the intermediate product, pre-machining intermediate product 70, with a single die forging, but by performing die forging multiple times, products with complex shapes can be manufactured by die forging.
[0036] Figures 4A and 4B show photographs of the microstructure of alpha-beta titanium alloy bars, according to the ISO 20160 international standard for surgical implants - metallic materials. For example, in photograph A2 of Figure 4A, the α+β type bilayer tissue constitutes the equiaxed tissue.
[0037] Figure 5 shows photographs of the microstructure after each step in the manufacturing method of the fixing internal splint (plate) 100 of the present invention. As shown on the left side of Figure 5, this photograph shows the microstructure of the central part of the vertical cross-section in the stretching direction of the material 10. Figure 5(a) shows the metallographic structure after forward extrusion, Figure 5(b) after die forging, and Figure 5(c) after annealing.
[0038] Figure 5(a) shows that the microstructure is stretched in the extrusion direction due to forward extrusion. Note that the photograph on the right in Figure 5(a) is the microstructure at a magnification of 2000x, and the photograph on the left is the microstructure at a magnification of 200x. This 200x magnification is the same as the photographs in the ISO 20160 international standard in Figures 4A and 4B. Figure 5(b) shows that the strain of the microstructure stretched in the extrusion direction is increased by die forging. Figure 5(c) clearly shows that the increased strain of the microstructure disappears after annealing, the crystal grains are refined, and an equiaxed structure is formed. The photograph on the left in Figure 5(c) is equivalent to the equiaxed structure of A1-A2 in Figure 4A.
[0039] In this embodiment, we have mainly described a method for manufacturing a fixing internal splint (plate) 100 using Ti-6Al-4V ELI titanium alloy as the material. However, the method for manufacturing the fixing internal splint (plate) of this application, namely the method of die forging after forward extrusion, can be applied to other materials that can be used as fixing internal splints (plates) other than Ti-6Al-4V ELI titanium alloy. For example, the same manufacturing method can be applied to pure titanium (CP-Ti), titanium alloys such as Ti-6Al-4V, Ti-6Al-2Nb-1Ta, Ti-15Zr-4Nb-4Ta, Ti-6Al-7Nb, Ti-3Al-2.5V, Ti-13Nb-13Zr, cobalt-chromium-molybdenum alloy, cobalt-chromium-tungsten-nickel alloy, austenitic stainless steel, austenitic low-nickel stainless steel, etc. [Explanation of Symbols]
[0040] 10 materials 20 Forward extrusion device 21 Punch 22 Punch Cases 23 Punch Guide 24 Sims 25 Dies 28 Die Cases 29 Backing Blocks 30 Billet 30a head 30b Shaft 40 molds 41 Die Set Upper Type 42 punches 43 Punch Plate 44 Dies 45 Die Plates 46 Die Set Lower Mold 50 Press Machines 51 slides 52 bolster 60 type forgings 61 Bali 70 Intermediate product before cutting 100 Fixing internal splint (plate)
Claims
1. A method for manufacturing a fixing internal splint, characterized by heating a round metal bar, forming a billet consisting of a large-diameter head and a small-diameter shaft integrally formed with the head using a forward extrusion device, heating the billet, and then using die forging with a die to produce a die-forged product that closely resembles the shape of a plate-shaped fixing internal splint (plate) as the final product, and then annealing the die-forged product.
2. The method for manufacturing a fixing internal splint according to claim 1, characterized in that the billet is subjected to die forging using a die one or more times.
3. The method for manufacturing a fixing internal splint according to claim 1 or 2, characterized in that the head portion of the billet corresponds to the wide portion of the fixing internal splint (plate) as the final product, and the shaft portion of the billet corresponds to the narrow portion of the fixing internal splint (plate).
4. The method for manufacturing a fixing splint according to claim 1 or 2, characterized in that the metal material of the round bar is pure titanium or a titanium alloy.
5. The method for manufacturing a fixing splint according to claim 1 or 2, characterized in that the metal material of the round bar is a cobalt-chromium-molybdenum alloy.
6. The method for manufacturing a fixing splint according to claim 1 or 2, characterized in that the metal material of the round bar is austenitic stainless steel.