Internal hexahedron crack prevention manufacturing method based on punching process

Abstract

The anti-cracking manufacturing method of the hexahedron based on the punching process has been deeply studied in view of the punching deformation, precision tolerance and a large number of hexahedron cracks that occur in actual production. The method of increasing the diameter of the prefabricated bottom hole is used to reduce the back cutting amount, which can greatly reduce the cutting force, thereby solving the problems of punching deformation and precision tolerance; increasing the prefabricated bottom hole can reduce the cutting force and ensure the use requirements and its own strength, while dispersing the circumferential prestress during punching, and at the same time controlling the heat treatment hardness of the parts and using a dehydrogenation process, eliminating the cracking problem caused by the superposition of stress corrosion and hydrogen embrittlement.

Description

Technical Field

[0001] The invention relates to the technical field of internal hexahedron manufacturing, and in particular to a method for preventing cracking of an internal hexahedron based on a punching process. Background Art

[0002] The mass production of hexagonal inner bodies of standard fasteners is mostly carried out by upsetting. For small-volume trial production or special-shaped non-standard parts that are not suitable for upsetting due to process limitations, punching is generally used. Punching requires prefabricated bottom holes, and the punching process is arranged after the completion of the previous machining process. This will bring a greater impact to the matrix of the semi-finished parts, causing the matrix to deform. Especially for slender rods, excessive punching force will cause the loss of the previous machining accuracy. The diameter of the traditional prefabricated bottom hole is smaller than the opposite side size of the hexagonal inner body. Under the action of cutting force, a closed strain zone will be formed along the circumference of the polyhedron after punching. After machining, non-stainless steel parts are generally treated with surface corrosion protection. The commonly used electroplating process is accompanied by the precipitation of cathode hydrogen ions. Hydrogen atoms are the smallest atoms in nature and are easily absorbed by metal materials into the metal lattice. Stress concentration sites have an inductive effect on the diffusion of hydrogen atoms. When hydrogen atoms diffuse to the grain boundaries or material defects, they aggregate to form hydrogen molecules. These molecules gradually accumulate and produce strong expansion pressure. When the expansion pressure and the effect of prestress are greater than the critical stress of the material, the parts eventually crack. Due to the influence of hydrogen embrittlement and stress corrosion cracking, metal damage is quite frequent, especially for high-voltage components, which can lead to dangerous failures and property losses, and the circumferentially closed cold punching prestress will aggravate the cracking effect of hydrogen embrittlement. The delayed cracking of hydrogen embrittlement makes the occurrence of accidents unpredictable and always hides potential risks. For parts with high bearing strength requirements, high-hardness heat treatments are performed after machining, such as carburizing, carbonitriding, and soft nitriding. During these heat treatments, hydrogen will also appear, and hydrogen will easily enter the metal under high temperature conditions. The deeper the carburized layer and the longer the time, the more hydrogen will enter, and it is difficult for the subsequent quenching and tempering processes to completely overflow. As the hardness and strength of the material increase, it becomes more sensitive to stress corrosion cracking and hydrogen embrittlement. Summary of the invention

[0003] The technical problem solved by the present invention is to provide a method for manufacturing an inner hexahedron to prevent cracking based on a punching process, which solves the cracking problem while reducing the cutting force.

[0004] The technical problem solved by the present invention is achieved by adopting the following technical solutions:

[0005] The method for manufacturing an inner hexahedron to prevent cracking based on a punching process includes processing a prefabricated bottom hole on a substrate, the rotation center line of the punch coincides with the rotation center line of the prefabricated bottom hole, and the punch punches the substrate under the drive of a power device to form an inner hexahedron. The method is characterized in that the diameter of the prefabricated bottom hole is larger than the opposite side size of the inner hexahedron. The specific steps are as follows:

[0006] 1. Process the prefabricated bottom hole and make the diameter of the prefabricated bottom hole larger than the opposite side size of the inner hexahedron

[0007] According to the technical scheme of increasing the prefabricated bottom hole, a model is established to control the back cutting amount. The plane coordinate system is established with the center of the prefabricated bottom hole as the origin. The center of the inner hexahedron is located at the origin of the coordinate system, and one set of opposite sides is parallel to the x-axis. As the diameter of the bottom hole increases, the circle of the bottom hole intersects with the edge of the inner hexahedron. The point of intersection is selected as the point closer to the vertex. The distance between the vertex and the intersection is half of the back cutting amount. The coordinates of the intersection are solved, that is,

[0008]

[0009] The coordinates of the intersection point can be obtained by solving equation (1): And the vertex coordinates are converted to The equation for the amount of cutting depth is obtained by calculating the coordinates of the vertex and the intersection point:

[0010]

[0011] According to formula (2), the bottom hole diameter equation is obtained:

[0012]

[0013] Taking the opposite side size as an undetermined constant, the bottom hole diameter in equation (2) is derived to obtain the equation for the rate of change of the cutting depth with the bottom hole diameter:

[0014]

[0015] Taking the opposite side size as an undetermined constant, the equation of the rate of change of the bottom hole diameter with the less cutting back cutting amount is derived by derivation of the less cutting back cutting amount in equation (3):

[0016]

[0017] In formulas (1) to (5): x A is the x-axis coordinate of the vertex;

[0018] x B is the x-axis coordinate of the intersection point, y B is the y-axis coordinate of the intersection point;

[0019] s is the size of the opposite side of the inner hexahedron;

[0020] d is the bottom hole diameter, and the theoretical constraint is

[0021] a′ pi In order to reduce the cutting depth, the theoretical constraint is

[0022] 2. Based on the prefabricated bottom hole, the base of the prefabricated bottom hole is punched by a power device to obtain an inner hexahedron.

[0023] After the base body is prefabricated with the bottom hole, the inner hexahedron is punched out under the action of the power device. During the punching process of the inner hexahedron, the punch only performs the main cutting movement, there is no feed amount, the feed force is zero, and the cutting force is the resultant force of the main cutting force and the back force.

[0024] During punching, the back force comes from the six cutting surfaces of the hexahedron. The diameter of the prefabricated bottom hole in the traditional hexahedron punching process is smaller than the opposite side size of the hexahedron. The back force is the resultant force of the back forces of each surface of the hexahedron. The resultant force vector equation is:

[0025]

[0026] The back forces from each face of the inner hexahedron are equal in magnitude and opposite in direction. According to equation (6), the back force is zero. The main cutting force also comes from the six cutting faces of the inner hexahedron. The main cutting force is the resultant force of the main cutting forces from each face of the inner hexahedron. The resultant force vector equation is:

[0027]

[0028] The main cutting force from each face of the inner hexahedron is equal in magnitude and consistent in direction. According to formula (7), the main cutting force is the sum of the various forces. The entire back cutting depth is the sum of the single-side back cutting depth.

[0029] Although the back force is zero, the resistance generated by the back force will still do work in the direction of the cutting motion, and will thus cause extrusion deformation of the substrate. Since there is no feed in the cutting process, the exponential formulas for the main cutting force and the back force are:

[0030]

[0031]

[0032] In formulas (6) to (9), F c Main cutting force; F p is the back force; F ci Main cutting force; F pi is the back force; C Fc , C Fp is the influence coefficient of workpiece material and cutting conditions on the main cutting force and back force; ap V is the amount of back cutting; c is the cutting speed; K Fc , K Fp is the product of the correction coefficients of various factors affecting the three components; x Fc 、x Fp The back cutting amount a p Influence index on main cutting force and back force; n Fc 、n Fp is the cutting speed V c Influence index on main cutting force and back force.

[0033] From formula (8) and formula (9), we can see that after other factors are determined, the influence index x Fc If 1 is taken, the main cutting force changes linearly with the depth of cutting; the influence index x Fp If 0.9 is taken, the back force changes exponentially with the back cutting depth; thus, it can be seen that reducing the back cutting depth is the dominant way to reduce the main cutting force.

[0034] 3. Heat treatment of the parts after punching the inner hexahedron

[0035] For heat treatment processes such as carburizing, carbonitriding, and soft nitriding, the depth of the diffusion layer shall not exceed 0.5mm. Excessive hardness and diffusion layer depth will increase the risk of hydrogen embrittlement. The hardness is divided into two categories and given different treatment methods. One is the hardness not higher than HR15N80.3, and the other is the hardness higher than HR15N80.3.

[0036] 4. Pre-treatment of heat-treated parts before surface treatment

[0037] For parts with hardness not higher than HR15N80.3, low-temperature tempering treatment can be performed on the parts before surface treatment. For parts with hardness higher than HR15N80.3, local annealing treatment is required for the inner hexahedron part.

[0038] 5. Carry out surface corrosion protection treatment on parts

[0039] For non-stainless steel materials, the parts that have completed step 4) are subjected to surface corrosion protection treatment, including but not limited to oxidation, electroplating, etc.

[0040] 6. Dehydrogenation of surface corrosion protection parts

[0041] For the surface corrosion protection parts that may cause hydrogen embrittlement, dehydrogenation shall be carried out. The constant temperature of dehydrogenation shall be set not less than 120℃ and the insulation time shall be not less than 2 hours. The time interval between the dehydrogenation process and the previous surface corrosion protection process shall not exceed 6 hours.

[0042] In the present invention, the remaining prefabricated bottom holes of the internal hexahedron obtained by the above manufacturing method are divided into multiple parts after the planes are punched, and the separated surfaces on the same side are in the same molding surface.

[0043] Beneficial effects: In the present invention, the diameter of the prefabricated bottom hole is increased so that the diameter of the prefabricated bottom hole is larger than the opposite side size of the inner hexahedron, which reduces the back cutting amount during punching, thereby reducing the cutting force; while increasing the prefabricated bottom hole reduces the cutting force and ensures the use requirements and its own strength, the circumferential prestress during punching is dispersed, and at the same time, the heat treatment hardness of the parts is controlled and a dehydrogenation process is used, eliminating the cracking problem caused by the superposition of stress corrosion and hydrogen embrittlement. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of an enlarged prefabricated bottom hole model in a preferred embodiment of the present invention.

[0045] Figure 2 It is a schematic diagram of punching in a preferred embodiment of the present invention.

[0046] Figure 3 It is a schematic diagram of the punched finished product in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0047] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below with reference to specific diagrams.

[0048] like Figure 1 to Figure 3 As shown, a method for manufacturing an inner hexahedron to prevent cracking based on a punching process includes processing a prefabricated bottom hole 3 on a substrate 2, the rotation center line of the punch 1 coincides with the rotation center line of the prefabricated bottom hole 3, and driven by a power device, the punch 1 punches the substrate 2 to form an inner hexahedron 4, characterized in that the diameter of the prefabricated bottom hole 3 is greater than the opposite side dimension s of the inner hexahedron, and the specific steps are as follows:

[0049] 1. Increase the diameter of the prefabricated bottom 3 during machining before punching, so that the diameter of the prefabricated bottom hole 3 is larger than the opposite side size of the inner hexahedron 4.

[0050] According to the technical solution of increasing the prefabricated bottom hole 3, a model is established, and a plane coordinate system is established with the center of the bottom hole as the origin O. The center of the inner hexahedron 4 is located at the origin O of the coordinate system, and one set of opposite sides is parallel to the x-axis. As the diameter d of the bottom hole increases, the circle of the bottom hole and the edge of the inner hexahedron 4 intersect, and the intersection point closer to the vertex A is selected as B, then the distance between point A and point B is less than half of the cutting depth a′ pi / 2, solve the coordinates of point B (x B ,y B ),Right now

[0051]

[0052] The coordinates of point B are obtained by solving equation (1): After conversion, the coordinates of point A are The equation for the amount of cutting depth is obtained by calculating the coordinates of point A and point B:

[0053]

[0054] According to formula (2), the bottom hole diameter equation is obtained:

[0055]

[0056] Taking the opposite side dimension s as an undetermined constant, the derivative of d in equation (2) is obtained to obtain the less cutting depth a′ pi The equation for the rate of change with the bottom hole diameter d is:

[0057]

[0058] Taking the opposite side size s as an undetermined constant, a′ in equation (3) pi The bottom hole diameter d is derived as a′ pi The rate of change equation is:

[0059]

[0060] In formulas (1) to (5): s is the size of the opposite side of the inner hexahedron;

[0061] d is the bottom hole diameter, and the theoretical constraint is

[0062] a′ pi In order to reduce the cutting depth, the theoretical constraint is

[0063] 2. Use a power device to punch and process the base of the prefabricated bottom hole 3 to obtain the inner hexahedron 4

[0064] After the prefabricated bottom hole 3 of the base 2 is processed, the inner hexahedron 4 is punched out under the action of the power device. During the punching process of the inner hexahedron 4, the punch 1 only performs the main cutting movement, with no feed amount f and feed force F. f is zero, and the cutting force F is the main cutting force F c and the back force F p The combined force.

[0065] During punching, the back force F p The six cutting faces of the inner hexahedron 4 are the result of the conventional inner hexahedron punching process. The prefabricated bottom hole diameter is smaller than the opposite side size of the inner hexahedron. The back force F p is the back force F of each face of the inner hexahedron 4pi The resultant force vector equation is:

[0066]

[0067] The back force F from each of the four faces of the inner hexahedron pi The magnitude is equal and the direction is opposite. From formula (6), we can get the back force F p Zero. Main cutting force F c Also from the six cutting faces of the inner hexahedron 4, the main cutting force F c is the main cutting force F of each surface of the inner hexahedron 4 ci The resultant force vector equation is:

[0068]

[0069] The main cutting force F from each surface of the inner hexahedron 4 ci The magnitudes are equal and the directions are consistent. The main cutting force F is obtained from formula (7): p For each component force F ci The total back cutting amount a p The single-side back cutting depth a pi sum.

[0070] Although the back force F p is zero, but the back force F pi The resistance generated will still do work in the direction of cutting motion, and will thus cause extrusion deformation of the matrix. Since there is no feed f during the cutting process, the main cutting force F c and the back force F p The exponential formulas are:

[0071]

[0072]

[0073] In formulas (6) to (9), F c Main cutting force, N; F p is the back force, N; F ci Main cutting force, N; F pi is the back force, N; C Fc , C Fp is the influence coefficient of workpiece material and cutting conditions on the main cutting force and back force; a p V is the back cutting depth, mm; c is the cutting speed, m / s; K Fc , K Fp is the product of the correction coefficients of various factors affecting the three components; x Fc 、x Fp The back cutting amount a pInfluence index on main cutting force and back force; n Fc 、n Fp is the cutting speed V c Influence index on main cutting force and back force.

[0074] From formula (8) and formula (9), we can see that after other factors are determined, the influence index x Fc Take 1, then the main cutting force F c Amount of knife eaten with back p Changes linearly; influence index x Fp Take 0.9, then the back force F p Amount of knife eaten with back p It changes exponentially; thus, it can be seen that reducing the back cutting amount a p To reduce the main cutting force F c dominant mode.

[0075] 3. Heat treatment of the parts after punching the inner hexahedron

[0076] For heat treatment processes such as carburizing, carbonitriding, and soft nitriding, the depth of the diffusion layer shall not exceed 0.5mm. Excessive hardness and diffusion layer depth will increase the risk of hydrogen embrittlement. The hardness is divided into two categories and given different treatment methods. One is the hardness not higher than HR15N80.3, and the other is the hardness higher than HR15N80.3.

[0077] 4. Pre-treatment of heat-treated parts before surface treatment

[0078] For parts with hardness not higher than HR15N80.3, low-temperature tempering treatment can be performed on the parts before surface treatment. For parts with hardness higher than HR15N80.3, local annealing treatment is required for the inner hexahedron part.

[0079] 5. Carry out surface corrosion protection treatment on parts

[0080] For non-stainless steel materials, after completing step 4), surface anti-corrosion treatment is performed, including but not limited to oxidation, electroplating, etc.

[0081] 6. Dehydrogenation of surface corrosion protection parts

[0082] For the surface corrosion protection parts that may cause hydrogen embrittlement, dehydrogenation shall be carried out. The constant temperature of dehydrogenation shall be set not less than 120℃ and the insulation time shall be not less than 2 hours. The time interval between the dehydrogenation process and the previous surface corrosion protection process shall not exceed 6 hours.

[0083] According to the above-mentioned embodiment, the remaining part of the prefabricated bottom hole 5 after punching each plane of the internal hexahedron is divided into multiple parts, and the separated surfaces 6 on the same side are in the same molding surface.

Claims

1. A method for manufacturing an inner hexahedron to prevent cracking based on a punching process, which includes processing a prefabricated bottom hole on a substrate, coinciding the rotation center line of the punch with the rotation center line of the prefabricated bottom hole, and driving the punch to punch the substrate to form an inner hexahedron under the drive of a power device, characterized in that The diameter of the prefabricated bottom hole is larger than the opposite side size of the inner hexahedron. The specific steps are as follows: 1) Process the prefabricated bottom hole so that the diameter of the prefabricated bottom hole is larger than the size of the opposite side of the inner hexahedron, and establish a model for controlling the back cutting amount when the diameter of the prefabricated bottom hole is larger than the size of the opposite side of the inner hexahedron. The specific method is as follows: A plane coordinate system is established with the center of the prefabricated bottom hole as the origin. The center of the inner hexahedron is located at the origin of the coordinate system, and one set of opposite sides is parallel to the x-axis. As the diameter of the bottom hole increases, the circle of the bottom hole intersects with the edge of the inner hexahedron. A point closer to the vertex is selected as the intersection point. The distance between the vertex and the intersection point is half of the cutting depth. Solve for the coordinates of the intersection point, that is, The coordinates of the intersection point can be obtained by solving equation (1): And the vertex coordinates are converted to s / 2), the equation for the amount of cutting depth is obtained by calculating the coordinates of the vertex and the intersection point: According to formula (2), the bottom hole diameter equation is obtained: Taking the opposite side size as an undetermined constant, the bottom hole diameter in equation (2) is derived to obtain the equation for the rate of change of the cutting depth with the bottom hole diameter: Taking the opposite side size as an undetermined constant, the equation of the rate of change of the bottom hole diameter with the less cutting back cutting amount is derived by derivation of the less cutting back cutting amount in equation (3): In formulas (1) to (5): x A is the x-axis coordinate of the vertex; x B is the x-axis coordinate of the intersection point, y B is the y-axis coordinate of the intersection point; s is the size of the opposite side of the inner hexahedron; d is the bottom hole diameter, and the theoretical constraint is a′ pi In order to reduce the cutting depth, the theoretical constraint is 2) Based on the prefabricated bottom hole, a power device is used to drive the punch to punch the inner hexahedron; 3) Heat treatment of the parts after punching of the inner hexahedron; 4) Pre-treatment of heat-treated parts before surface treatment; 5) Carry out surface corrosion protection treatment on parts; 6) Remove hydrogen from the surface anti-corrosion treated parts.

2. The method for manufacturing an inner hexahedron to prevent cracking based on a punching process according to claim 1, characterized in that: The partial prefabricated bottom holes retained after punching of each plane of the inner hexahedron obtained by the manufacturing method are divided into multiple parts, and the separated surfaces on the same side are in the same molding surface.

3. The method for manufacturing an inner hexahedron to prevent cracking based on a punching process according to claim 1, characterized in that: The heat treatment in step 3) includes carburizing, carbonitriding and nitrocarburizing.

4. The method for manufacturing an inner hexahedron to prevent cracking based on punching process according to claim 1 or 3, characterized in that: The hardness of the heat treatment is divided into two categories, one is not higher than HR15N80.3, and the other is higher than HR15N80.

3.

5. The method for manufacturing an inner hexahedron to prevent cracking based on punching process according to claim 1 or 3, characterized in that: The depth of the heat-treated infiltration layer is no more than 0.5 mm.

6. The method for manufacturing an inner hexahedron to prevent cracking based on punching process according to claim 1, characterized in that: The pretreatment in step 4) is as follows: for parts with a hardness not higher than HR15N80.3, low-temperature tempering treatment is performed on the parts before surface treatment; for parts with a hardness higher than HR15N80.3, local annealing treatment is performed on the inner hexahedron part.

7. The method for manufacturing an inner hexahedron to prevent cracking based on punching process according to claim 1, characterized in that: The dehydrogenation time in step 6) is not less than 2 hours, and the constant temperature set for dehydrogenation is not less than 120°C.

8. The method for manufacturing an inner hexahedron to prevent cracking based on punching process according to claim 1, characterized in that: The time interval between the dehydrogenation in step 6) and the surface corrosion protection treatment in step 5) is no more than 6 hours.

9. The method for manufacturing an inner hexahedron to prevent cracking based on punching process according to claim 1, characterized in that: The surface anti-corrosion treatment in step 5) includes oxidation and electroplating.

Images