A precision stamping die for magnesium alloy anastomosis nails and a manufacturing method thereof

Abstract

The application discloses a precision stamping die for magnesium alloy anastomosis nails and a manufacturing method thereof, and belongs to the technical field of precision forming of medical devices. The die comprises an upper die seat, a punch, a stripper plate core, a concave die insert, a lower die seat, a guide column and a guide sleeve, the punch and the concave die insert cooperate to form an anastomosis nail forming cavity, and the cavity inlet is provided with a progressive shape R angle. A Cr base layer, a CrN / CrCN transition support layer and a ta-C functional self-lubricating layer are arranged on the working surface of the die. The manufacturing method comprises vacuum heat treatment, super deep cold treatment, ultra-precision machining, magnetorheological combined ion beam polishing, composite coating deposition and soft abrasive polishing. The application is favorable for reducing stress concentration and adhesion risk of magnesium alloy wire stamping forming.

Description

Technical Field

[0001] This invention belongs to the field of precision forming technology for medical devices, specifically relating to a precision stamping die for magnesium alloy anastomotic staples and its manufacturing method. Background Technology

[0002] In surgical procedures, the reliance on staplers is increasing in surgeries such as digestive tract reconstruction, gastrointestinal and lung resections. Staples are small, typically with wire diameters in the millimeter range, and require high precision in dimensional accuracy, surface integrity, and internal stress control after forming. Traditional staplers usually use stamped titanium alloy or stainless steel staples, but these metal materials are non-biodegradable.

[0003] Replacing traditional titanium alloy or stainless steel materials with medical-grade magnesium alloy wire can make anastomotic staples biodegradable. However, magnesium alloy wire is subjected to significant shear and tensile stress during the stamping process into U-shaped or D-shaped anastomotic staples, posing a risk of microcracks forming on the outer side of the staple legs. Furthermore, magnesium alloys are chemically reactive and are prone to cold welding and adhesion to the mold surface during high-speed stamping, which can affect the micro-geometric stability of the mold and scratch the surface of subsequently formed anastomotic staples.

[0004] Therefore, it is necessary to provide a forming die and its manufacturing method that can improve material flow, reduce local stress concentration and reduce stamping adhesion for the precision stamping process of magnesium alloy staples. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a precision stamping die for magnesium alloy staples and a method for manufacturing the same.

[0006] The precision stamping die provided by the present invention includes an upper die base, a punch, a stripper core, a die insert, a lower die base, a guide post, and a guide sleeve; the die insert is fixed to the lower die base and located between the upper die base and the lower die base; the stripper core is located between the upper die base and the die insert, and is guided by the guide sleeve along the guide post; the punch is fixedly connected to the upper die base and passes downward through the stripper core; the punch and the die insert cooperate to form a matching pin forming cavity, and the cavity entrance is provided with a progressive guide radius.

[0007] Furthermore, the radius of curvature of the progressive guide radius is 0.5 mm at the cavity entrance and 0.15 mm at the cavity bottom; the single-sided punching clearance between the punch and the die insert is 5% to 10% of the diameter of the magnesium alloy staple wire. The punch sidewall has an inwardly inclined taper angle of 1.5° to 2.5°, the cavity depth is 2.0 mm, and the diameter of the magnesium alloy staple wire is 0.25 mm ± 0.05 mm.

[0008] Furthermore, the base material of the punch and die insert is made of powder metallurgy high-speed steel; the composition of the powder metallurgy high-speed steel by mass percentage is: C 1.5%~2.5%, Cr 3.5%~4.5%, V 5%~5.5%, Co 7%~8%, with the balance being Fe and unavoidable impurities.

[0009] Furthermore, at least the working surfaces of the punch and die insert that directly contact the magnesium alloy staples are provided with a composite coating; the composite coating, from the inside out, includes a Cr base bonding layer, a CrN / CrCN transition support layer, and a hydrogen-free tetrahedral amorphous carbon functional self-lubricating layer. The total thickness of the composite coating is 1.35 μm to 3.85 μm; this application describes its surface microhardness as 3500 HV to 4500 HV, its critical bonding load as not less than 50 N, and its surface roughness Ra as not greater than 0.02 μm.

[0010] This invention also provides a method for manufacturing the aforementioned precision stamping die, comprising precision machining of the substrate and multi-stage vacuum heat treatment, ultra-precision machining of the micro-cavity, magnetorheological combined with ion beam polishing, composite coating deposition, soft abrasive polishing of the coating surface, and assembly. The specific process parameters are consistent with those described in the claims and specific embodiments.

[0011] According to the embodiments described in this application, the progressive guide radius (R-angle) allows the magnesium alloy wire to obtain continuous guidance and progressive deformation when entering the cavity, which helps to reduce local stress concentration during the stamping process; the composite coating and sub-nanometer polishing help to reduce the risk of cold welding adhesion and surface scratches on the magnesium alloy. The combination of the progressive guide structure and the composite coating can balance the forming quality of the staples, the die life, and the surface integrity. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the precision stamping die structure for magnesium alloy staples according to an embodiment of the present invention;

[0013] Figure 2 This is an enlarged cross-sectional view of the cavity of a precision stamping die according to an embodiment of the present invention;

[0014] Figure 3 This is an enlarged schematic diagram of the guide radius (R-angle) of the precision stamping die cavity according to an embodiment of the present invention;

[0015] Figure 4 This is a partially enlarged schematic diagram of the precision stamping die insert according to an embodiment of the present invention;

[0016] Figure 5 This is a schematic cross-sectional view of the composite coating of a precision stamping die according to an embodiment of the present invention;

[0017] Figure 6 This is a flowchart of a precision stamping die manufacturing method according to an embodiment of the present invention.

[0018] Among them, the upper die base 1, punch 2, stripper core 3, die insert 4, cavity 41, matching nail wire 5, lower die base 6, guide post 7, guide sleeve 8, bottom bonding layer 9, transition support layer 10, and functional self-lubricating layer 11; area A is the cavity area, area B is the progressive guide R-angle area of ​​the cavity entrance, and area C is the wire fixing area. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described below with reference to the accompanying drawings. The following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0020] Example 1 Reference Figures 1 to 4 This embodiment provides a precision stamping die for magnesium alloy staples. The die includes an upper die base 1, a punch 2, a stripper core 3, a die insert 4, a lower die base 6, a guide post 7, and a guide sleeve 8. The die insert 4 is fixed on the lower die base 6 and located between the upper die base 1 and the lower die base 6; the stripper core 3 is located between the upper die base 1 and the die insert 4, and is guided by the guide sleeve 8 along the guide post 7; the punch 2 is fixedly connected to the upper die base 1 and passes downward through the stripper core 3.

[0021] During the stamping process, the punch 2 descends and cooperates with the die insert 4 to form a matching nail forming cavity 41; the matching nail wire 5 is placed at the entrance of the cavity 41, and the entrance of the cavity 41 is provided with a progressive guide R angle. After the matching nail wire 5 is pressed into the cavity 41 by the punch 2, it is formed into a matching nail; after the stamping is completed, the upper die returns, and the stripper core 3 is stripped under the action of spring force.

[0022] The radius of curvature of the progressive guide radius (R-angle) is 0.5 mm at the cavity entrance and 0.15 mm at the cavity bottom. The single-sided punching clearance between the punch 2 and the die insert 4 is 5% to 10% of the diameter of the matching thread 5, which has a diameter of 0.25 mm ± 0.05 mm. The sidewall of the punch 2 has an inwardly inclined taper angle of 1.5° to 2.5°, and the cavity 41 has a depth of 2.0 mm.

[0023] The base of punch 2 and die insert 4 is made of powder metallurgy high-speed steel. The composition of powder metallurgy high-speed steel by mass percentage is: C 1.5%~2.5%, Cr 3.5%~4.5%, V 5%~5.5%, Co 7%~8%, with the balance being Fe and unavoidable impurities.

[0024] Reference Figure 5At least the working surfaces of the punch 2 and the die insert 4 that are in direct contact with the magnesium alloy staples are provided with a composite coating. The composite coating, from the inside out, includes a base bonding layer 9, a transition support layer 10, and a functional self-lubricating layer 11. The base bonding layer 9 is a high-purity metallic Cr layer with a thickness of 50 nm to 150 nm; the transition support layer 10 is a gradient-distributed CrN / CrCN layer with a thickness of 0.8 μm to 2.5 μm; the functional self-lubricating layer 11 is a hydrogen-free tetrahedral amorphous carbon layer with a thickness of 0.5 μm to 1.2 μm, wherein the proportion of sp³ carbon bonds is 75% to 85%. The total thickness of the composite coating is 1.35 μm to 3.85 μm; according to this application, its surface microhardness is 3500 HV to 4500 HV, the critical load for bonding force is not less than 50 N, and the surface roughness Ra is not greater than 0.02 μm.

[0025] Reference Figure 6 This embodiment also provides a method for manufacturing the above-mentioned precision stamping die, including the following steps.

[0026] (1) Precision machining of the base material and multi-stage vacuum heat treatment: The powder metallurgy high-speed steel blank used to make punch 2 and die insert 4 is mechanically rough machined to form a basic outline and leave a precision machining allowance; the rough machined high-speed steel is placed in a vacuum furnace and preheated twice at 550℃ and 850℃, then heated to the austenitizing temperature of 1180℃ and held for 25 minutes; after quenching, the mold is placed in liquid nitrogen at -196℃ for deep cryogenic holding for 24 hours within 1 hour; then it is tempered at 560℃ three times, each time for 2 hours.

[0027] The above-mentioned vacuum preheating can reduce the temperature difference between the inside and outside of the workpiece and avoid surface oxidation and decarburization; quenching enables the matrix to form a high-hardness martensitic structure; ultra-deep cryogenic treatment promotes the transformation of residual austenite and promotes the precipitation of fine carbides; multi-stage tempering is used to eliminate quenching residual stress and promote secondary hardening.

[0028] (2) Micro-cavity ultra-precision machining: The tempered punch 2 and die insert 4 are precision shaped and ground using CBN grinding wheels, and the dimensional accuracy is controlled within 0.002mm; for extremely fine areas such as the progressive guide R angle, a fine tungsten wire with a wire diameter of 0.05mm is used for micro-electro-electric wire cutting, and the depth of the surface discharge alteration layer is controlled within 3μm.

[0029] (3) Magnetorheological combined with ion beam polishing: a magnetorheological fluid containing 30nm nanodiamond powder was used to perform non-destructive conformal polishing on the cavity of the concave mold insert 4 and the R-angle surface under the action of a magnetic field. The processing time was 45min. Then, the surface was bombarded for 15min in a vacuum chamber with a 500eV high-energy argon ion beam to peel off the surface alteration layer. After treatment, the surface roughness Ra of the substrate was no greater than 0.01μm.

[0030] (4) Multi-arc ion plating and filter cathode vacuum arc deposition composite coating: Argon gas is first introduced and a -600V bias voltage is applied to clean for 20 minutes to activate the substrate; the chromium target is turned on and the bias voltage is adjusted to -150V, and a Cr base bonding layer is obtained after 10 minutes of deposition; nitrogen gas is gradually introduced and a CrN layer is formed after 20 minutes of deposition; then acetylene is gradually introduced and nitrogen gas is reduced, and a CrN / CrCN gradient layer is formed after 30 minutes of deposition.

[0031] A filtered cathode vacuum arc technique was employed, with a high-purity graphite target activated. Large carbon droplets were filtered out using a magnetic filtration system. Deposition was carried out for 50 minutes at a substrate temperature below 150°C and a bias voltage of -100V to obtain a ta-C functional self-lubricating layer. This self-lubricating layer is used to reduce frictional resistance during the pressing process and to reduce the risk of surface scratches and die sticking during the stamping of magnesium alloy wire.

[0032] Soft abrasive polishing of the coating surface and mold assembly: The coated punch 2 and die insert 4 are polished for 2 hours in a three-dimensional vibration grinding machine using a composite soft abrasive of plant shell fragments and polishing wax to achieve a mirror-like self-lubricating state on the working surface of the mold. Then, the punch 2, stripper core 3, and die insert 4 are installed between the upper mold base 1 and the lower mold base 6 through the guide post 7 and guide sleeve 8 to obtain a precision stamping mold.

[0033] The experimental methods for determining each parameter in this embodiment are as follows: Coating thickness measurement: The thickness of each layer was measured by scanning electron microscopy (SEM).

[0034] Determination of sp³ carbon bond ratio: The spectrum was measured using a Raman spectrometer (laser wavelength 532nm). The D peak and G peak were Gaussian fitted, and the sp³ carbon bond ratio was calculated using an empirical formula.

[0035] Microhardness determination: According to ISO 14577-1, a nanoindenter was used for determination, and the maximum indentation depth was controlled to be less than 1 / 10 of the total coating thickness. The hardness was calculated by taking the load-displacement curve.

[0036] Film-substrate adhesion determination: According to ASTM C1624, a diamond indenter was used to conduct a scratch test. The positive load at which the coating showed obvious peeling and was accompanied by a sharp increase in acoustic emission signal was taken as the critical load for adhesion.

[0037] Surface roughness measurement: Ra is measured by scanning the forming working surface using a white light interferometer in accordance with ISO 4287.

[0038] Example 2

[0039] This embodiment provides a manufacturing scheme for a precision stamping die. A powder metallurgy high-speed steel substrate is precision machined, quenched at 1180℃, subjected to 24 hours of ultra-deep cryogenic treatment, and multi-stage vacuum heat treatment. A cavity with a single-sided blanking clearance of 0.02mm and an involute transition angle R of 0.5mm to 0.15mm is prepared. After magnetorheological polishing, a 0.1μm Cr underlay bonding layer, a 1.2μm CrN transition layer, and a 0.8μm functional self-lubricating layer are deposited sequentially, wherein the functional layer has an sp³ carbon bond content of 80%. The rest is the same as in Embodiment 1.

[0040] According to this application, the mold prepared in this embodiment continuously stamped 50,000 U-shaped staples. No microcracks were found in the R-angle during random inspection, and the yield rate was 99.2%. No sticking phenomenon was observed after 50,000 continuous stamping cycles. When the mold life test reached 50,000 cycles, the cutting edge wear was 0.002 mm.

[0041] The method for determining the stamping performance of the die in this embodiment is as follows: Stamping yield and crack determination: Anastomotic staples were formed by continuous stamping using medical magnesium alloy wire with a diameter of 0.25 mm. Random samples were taken and the bending area was observed by scanning electron microscope (SEM). The absence of microcracks was considered as a qualified product.

[0042] Anti-adhesion performance test: The surface of the cavity and punch was scanned by energy dispersive spectroscopy (EDS). No Mg element accumulation was detected, and there were no scratches or tears on the surface.

[0043] Cutting edge wear measurement: The profile of the cutting edge of the punch and die is scanned using an optical coordinate measuring microscope and compared with the initial profile before stamping.

[0044] Comparative Example 1

[0045] The manufacturing process is similar to that of Example 2, but the thickness of the functional self-lubricating layer is 2.2 μm, and the total thickness of the composite coating is 3.5 μm. Due to the thicker coating, the die clearance is reduced, resulting in a stamping yield of approximately 91.5%. This application describes a die with an effective stamping life of over 80,000 cycles. This comparative example illustrates the impact of increased coating thickness on forming clearance and yield; the thickness of the functional layer exceeds the preferred range of this application.

[0046] Comparative Example 2

[0047] The powder metallurgy high-speed steel matrix is ​​precision machined, quenched at 1180℃ and subjected to multi-stage vacuum heat treatment, but the -196℃ ultra-deep cryogenic treatment is omitted and tempering is performed directly. The rest is the same as in Example 1.

[0048] This application describes that the die had a normal yield rate for the first 5000 stampings; however, when continuous high-frequency stamping reached 50,000 cycles, the residual austenite inside the die underwent a phase transformation, resulting in micron-level dimensional changes. This caused the die clearance to narrow, raising the draft force to over 45N, and scratches appeared on the surface of the mating pins. This comparative example is used to illustrate the impact of ultra-deep cryogenic treatment on the dimensional stability of micro-dies.

[0049] Comparative Example 3

[0050] The mold is made of ordinary tungsten steel without any surface composite coating, and uses ordinary electrical discharge machining and manual polishing processes. The single-sided punching clearance is 0.02mm, and the cavity entrance uses a common rounded transition.

[0051] According to this application, the mold only required 500 stamping cycles before magnesium alloy cold welding adhesion occurred, the draft force was 85N, and scratches appeared on the surface of the staples; in the simulated intestinal fluid degradation test, the batch of products experienced pitting and breakage on the 8th day, and the breakage rate of the staple leg R angle was 87%.

[0052] Comparative Example 4

[0053] The high-speed steel mold substrate is made of powder metallurgy, but only a 2.0μm thick single TiN coating is deposited by ordinary PVD process, without setting an underlayer and transition layer.

[0054] According to this application, the coefficient of friction of the TiN coating is about 0.45. After 5000 stamping cycles, the alternating stress causes the hard TiN coating to detach brittlely in some areas. The detached hard particles scratch the surface of the subsequently formed magnesium alloy wire, resulting in the product being scrapped.

[0055] In this document, the directional terms such as front, back, top, and bottom are defined according to the position of the components in the accompanying drawings and the relationships between the components. They are used only to clearly express the technical solution and should not be construed as limiting the scope of protection.

[0056] Where there is no conflict, the embodiments and features described above can be combined with each other. The above descriptions are merely embodiments of the present invention and are not intended to limit the present invention; any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A precision stamping die for magnesium alloy staples, characterized in that, It includes an upper die base, a punch, a stripper core, a die insert, a lower die base, a guide post, and a guide sleeve; the die insert is fixed to the lower die base and located between the upper die base and the lower die base; the stripper core is located between the upper die base and the die insert, and is slidably guided along the guide post by the guide sleeve; the punch is fixedly connected to the upper die base and passes downward through the stripper core; the punch and the die insert cooperate to form a matching pin forming cavity, and the entrance of the cavity is provided with a progressive guide radius.

2. The precision stamping die for magnesium alloy staples according to claim 1, characterized in that, The radius of curvature of the progressive guide R-angle at the cavity entrance is 0.5 mm, and the radius of curvature at the bottom of the cavity is 0.15 mm; the single-sided punching gap between the punch and the die insert is 5% to 10% of the diameter of the magnesium alloy staple wire.

3. The precision stamping die for magnesium alloy staples according to claim 2, characterized in that, The sidewall of the punch has an inwardly inclined tapered angle of 1.5° to 2.5°; the depth of the cavity is 2.0 mm; and the diameter of the magnesium alloy staple wire is 0.25 mm ± 0.05 mm.

4. The precision stamping die for magnesium alloy staples according to claim 1, characterized in that, The base of the punch and the die insert is made of powder metallurgy high-speed steel; the composition of the powder metallurgy high-speed steel by mass percentage is: C 1.5%~2.5%, Cr 3.5%~4.5%, V 5%~5.5%, Co 7%~8%, with the balance being Fe and unavoidable impurities.

5. The precision stamping die for magnesium alloy staples according to any one of claims 1 to 4, characterized in that, At least the working surfaces of the punch and the die insert that are in direct contact with the magnesium alloy staples are provided with a composite coating; the composite coating includes, from the inside out, a base bonding layer, a transition support layer and a functional self-lubricating layer.

6. The precision stamping die for magnesium alloy staples according to claim 5, characterized in that, The base bonding layer is a Cr layer with a thickness of 50nm to 150nm; the transition support layer is a CrN / CrCN gradient layer with a thickness of 0.8μm to 2.5μm; the functional self-lubricating layer is a hydrogen-free tetrahedral amorphous carbon layer with a thickness of 0.5μm to 1.2μm, and the proportion of sp³ carbon bonds in the hydrogen-free tetrahedral amorphous carbon layer is 75% to 85%.

7. A method for manufacturing a precision stamping die for magnesium alloy staples as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Precision machining of the substrate and multi-stage vacuum heat treatment: The powder metallurgy high-speed steel blanks used to make punches and die inserts are subjected to rough machining, followed by vacuum preheating, quenching, ultra-deep cryogenic treatment and multi-stage tempering. (2) Micro-cavity ultra-precision machining: The tempered punch and die insert are precision shaped and ground, and fine tungsten wire micro-wire cutting is used to form a cavity that matches the punch; (3) Magnetorheological combined with ion beam polishing: The cavity is polished non-destructively and conformally using a magnetorheological fluid containing nanodiamond powder, and the modified layer on the surface of the cavity is stripped off using a high-energy argon ion beam. (4) Composite coating deposition: A base bonding layer, a transition support layer and a functional self-lubricating layer are deposited sequentially on the working surface treated in step (3); (5) Soft abrasive polishing and assembly of the coating surface: The punch and die insert after the composite coating is deposited are polished with soft abrasive, and the punch, stripper core and die insert are installed between the upper die holder and the lower die holder through guide pillars and guide sleeves.

8. The manufacturing method according to claim 7, characterized in that, In step (1), the vacuum preheating includes preheating at 550℃ and 850℃ respectively, followed by heating to the austenitizing temperature of 1180℃ and holding for 25 minutes; the ultra-deep cryogenic treatment is to place the mold in liquid nitrogen at -196℃ for 24 hours within 1 hour after quenching; the multi-stage tempering is to perform 3 high-temperature temperings at 560℃, each time holding for 2 hours.

9. The manufacturing method according to claim 8, characterized in that, In step (2), a CBN grinding wheel is used for precision forming grinding, and the dimensional accuracy is controlled within 0.002 mm; the progressive guide R-angle region is cut by micro-electro-electric wire cutting with a fine tungsten wire with a wire diameter of 0.05 mm, and the depth of the surface discharge metamorphic layer is controlled within 3 μm; in step (3), the magnetorheological fluid contains nanodiamond powder with a particle size of 30 nm, and the polishing time is 45 min; the energy of the high-energy argon ion beam is 500 eV, the bombardment time is 15 min, and the surface roughness Ra of the substrate after treatment is not greater than 0.01 μm.

10. The manufacturing method according to claim 9, characterized in that, In step (4), argon gas is first introduced and a bias voltage of -600V is applied for cleaning for 20 minutes; then the chromium target is turned on and the bias voltage is adjusted to -150V, and a Cr base bonding layer is formed after 10 minutes of deposition. Nitrogen gas was introduced and deposited for 20 minutes to form a CrN layer. Then acetylene was introduced and nitrogen gas was reduced, and CrN / CrCN gradient layer was formed after 30 minutes of deposition. Using the filtered cathode vacuum arc technology, a high-purity graphite target was turned on, and hydrogen-free tetrahedral amorphous carbon functional self-lubricating layer was formed after 50 minutes of deposition under the conditions of substrate temperature below 150℃ and bias voltage of -100V. In step (5), plant shell fragments and polishing wax composite soft abrasive were used to polish for 2 hours in a three-dimensional vibration grinding machine.

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