Local continuous forming method for large-length-diameter-ratio deep blind hole steel member with truncated cone-shaped end

Abstract

The invention discloses a local continuous forming method for a large-length-diameter-ratio deep blind hole steel member with a truncated cone-shaped end, which comprises the following steps of: forming a large-truncated cone-shaped structure by rotary forging: removing a heating coil after heating is completed, fixing a non-heating end of a blank on horizontal forging and pressing equipment through a tool, the axial feeding movement of the blank is controlled through a program of forging and pressing equipment; according to the forging and pressing equipment, three sets of forging hammerheads arranged at intervals are adopted, the three sets of forging hammerheads synchronously move, the radial displacement of the three sets of forging hammerheads is progressive in sequence, and local increment continuous forming of a large-truncated-cone-shaped structure at one end of a blank is achieved through rotation and hammering movement of the three sets of forging hammerheads in cooperation with translational movement in the generatrix direction of the truncated-cone-shaped section of a forge piece. The method has the advantages of high material utilization rate, low manufacturing cost, good mechanical property of the conical part of the obtained component and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of forming of steel members with large length-diameter ratio and deep blind holes, and particularly relates to a local continuous forming method for steel members with large length-diameter ratio and deep blind holes with a truncated conical end at one end. Background Art

[0002] Currently, the following manufacturing method is usually adopted for thin-walled steel members with large length-diameter ratio and deep blind holes with a truncated conical end at one end: The preform with large length-diameter ratio and deep blind holes is formed by punching + stretching method, and then the truncated conical structure at one end is formed by machining. However, the foregoing manufacturing method has the following disadvantages.

[0003] When forming deep blind hole members with an inner hole length-diameter ratio greater than 3, due to the high hot forming temperature and the large load force on the punch, the punch is prone to unstable bending deformation. Therefore, it is required that the inner hole length-diameter ratio of the punched preform is ≤ 3 during design, resulting in a large wall thickness of the formed blank. In order to form a deep blind hole member with a large length-diameter ratio, multiple heating and multiple passes of stretching are required to reduce the wall thickness of the blank and increase the length-diameter ratio. The forming process is complex and the production efficiency is low; moreover, when stretching thin-walled members, the metal at the wall of the blank is also prone to be pulled and broken axially, resulting in low qualification rate and high cost. Repeated heating makes the overall grains of the blank metal grow and coarsen, and the compressive strength and impact toughness decrease significantly. The forming of the truncated conical structure adopts the way of direct subtractive machining, with low material utilization rate and high manufacturing cost for metal members with a high proportion of expensive alloying elements; moreover, the forming streamline of the metal is cut off, the anti-fatigue performance of the member is reduced, the mechanical properties of the conical part are low, and the service performance is difficult to meet the design requirements. Summary of the Invention

[0004] At least for the problems mentioned in the background art, the present invention provides a local continuous forming method for steel members with large length-diameter ratio and deep blind holes with a truncated conical end at one end.

[0005] The present invention adopts the following technical solutions: A local continuous forming method for steel members with large length-diameter ratio and deep blind holes with a truncated conical end at one end, comprising the following steps: Step S1, blanking to obtain a blank: Design the forging structure diagram based on the part drawing, and design the structural dimensions of the blanking part (blank) according to the principle of constant volume of metal plastic forming. Step S2, heating: Heat one end of the blank by using a heating coil. Step S3. Rotary forging to form a large truncated conical structure: After heating is completed, remove the heating coil. Fix the non-heated end of the blank to a horizontal forging equipment through a tooling, and control the axial feeding movement of the blank through the program of the forging equipment. The forging equipment uses three groups of forging hammers arranged at intervals. The three groups of forging hammers move synchronously, and the radial displacements of the three groups of forging hammers increase progressively in sequence. Through the rotary and hammering movements of the three groups of forging hammers, combined with the translational movement along the generatrix direction of the truncated cone section of the forging, realize the local incremental continuous forming of the large truncated conical structure at one end of the blank to obtain a semi-formed part. Step S4. Heating: Use a heating coil to heat one end of the non-truncated conical structure (cylindrical section) of the semi-formed part. Step S5. Hot extrusion to form a blind hole preform: After heating is completed, remove the heating coil from the semi-formed part, and use a hot extrusion forming process to obtain a blind hole preform with an inner hole depth-diameter ratio ≤ 3. Step S6. Radial precision forging: Fix the truncated cone end of the preform on the pusher rod of the radial forging equipment, insert a mandrel into the blind hole of the preform, push the preform to feed axially through the pusher rod, and multiple precision forging hammers of the radial forging equipment perform rotary and hammering movements on the preform. The deformation amount of each precision forging hammer on the preform is the same, and the deformation zone of the preform gradually extends from the opening position to the bottom of the blind hole, realizing the local continuous forming of the preform, reducing the wall thickness and increasing the length of the preform. Step S7. Take out the mandrel, process the flash around the blank to obtain a large aspect ratio deep blind hole steel component.

[0006] In the present invention, during the process of rotary forging to form a large truncated conical structure, the blank between any two groups of hammers undergoes axial upsetting deformation, and the deformation zone repeatedly undergoes a complex thermo-mechanical coupling severe plastic deformation of "drawing - upsetting - drawing - upsetting".

[0007] Preferably, the heating temperature in step S2 is 900 - 950 °C, the heat preservation time is 0.5 - 1 h, the original length of the blank along the axial direction before forging the cone part is N, wherein, L is the projection length of the generatrix of the cone part forging blank along the axial direction, α is the included angle between the generatrix of the cone part and the axis, A is the diameter of the original bar, and S is the diameter of the end face of the cone part.

[0008] Preferably, the three groups of forging hammers in step S3 respectively include two first hammers, two second hammers and two third hammers. The first hammers, second hammers and third hammers are arranged at equal intervals in sequence from the end face close to the frustum to the end face far from the frustum. The axial spacing Δ between adjacent two groups of forging hammers is 10 - 20 mm, the moving speed of the forging hammers is 25 - 50 mm / s, and the radial displacement amounts of the first hammers, second hammers and third hammers are y 1 , y 2 , y 3 , wherein, A is the diameter of the original bar, S is the diameter of the end face of the tapered part, is the angle between the generatrix of the tapered part and the axis, a 1 is the axial distance from the first hammer to the end face of the tapered part, a 2 is the distance from the second hammer to the end face of the tapered part, a 3 is the axial distance from the third hammer to the end face of the tapered part.

[0009] Preferably, the widths of the first hammers, second hammers and third hammers are D, wherein, N is the original axial length of the blank before forging the tapered part, and Δ is the axial spacing between adjacent two groups of forging hammers.

[0010] Preferably, in step S4, the heating temperature is 950 - 1050 °C, the heat preservation time is 1 - 1.5 h, and the height of the blank to be heated is H, wherein, L is the axial projection length of the generatrix of the forging blank of the tapered part, B is the height of the initial round bar, N is the original axial length of the blank before forging the tapered part, and Q is the total height of the tapered part.

[0011] Preferably, the hot extrusion forming speed in step S5 is 20 - 30 mm / s, and the tonnage of the isothermal forging equipment is 6300 t.

[0012] Preferably, the radial precision forging equipment in step S6 uses four precision forging hammers evenly distributed circumferentially. The four precision forging hammers are divided into two groups for forging in the same plane (the same radial area). The movement frequency of the precision forging hammers is 480 times / min - 720 times / min, and the tonnage of the radial forging equipment is 1300 t.

[0013] Preferably, in step S5 and step S6, glass powder or oil-based graphite is used as the lubricant between the blank and the die or between the mandrel and the blank.

[0014] The beneficial effects include: In the present invention, three groups of forging hammers are adopted to form the large truncated conical structure of the blank by rotary forging. The radial displacement amounts of the three groups of forging hammers increase progressively in a stepped manner. Through the radial loading of the three groups of forging hammers, axial elongation occurs in the deformation zone directly acted on by the forging hammers, while upsetting deformation in the axial direction occurs to the blank between any two adjacent groups of forging hammers due to the obstruction of axial flow. The blank deformation zone repeatedly undergoes severe plastic deformation of "elongation - upsetting - elongation - upsetting" of the composite thermo-mechanical coupling, effectively increasing the cumulative deformation amount of the conical part of the blank, refining the microstructure, improving the forming efficiency, enhancing the anti-deformation and anti-destruction capabilities of the conical part. After heat treatment, the impact absorption work of the conical part of the component is ≥80 J, and the grain size is above grade 9, which is suitable for mass production.

[0015] In the present invention, hot extrusion forming of the blind hole preform and radial precision forging forming are completed in one heating process. Since the hitting frequency of the precision forging hammer is high during the radial precision forging process, which can reach three times that of the quick forging, the contact time between the precision forging hammer and the surface of the workpiece to be processed is greatly shortened, and the surface temperature drop is small. After the hot extrusion preform is completed, the blank does not need secondary heating, with high production efficiency and effective control of the grain structure. Moreover, due to the fast hitting speed of the precision forging hammer, the strain rate of the metal is high, and the temperature rise effect of the material reduces the critical deformation amount of the metal, which is beneficial to obtaining a fine-grained structure. After heat treatment, the grain size of the surface layer structure reaches above grade 9.5, and the grain size at half of the wall thickness is not lower than grade 9.

[0016] For the local continuous forming method of the large aspect ratio deep blind hole steel component with one end truncated conically disclosed in the present invention, the forging forming of the truncated conical structure is adopted. Compared with the traditional method of cutting forming, the material utilization rate is higher, the manufacturing cost is lower, and the mechanical properties of the conical part are better. Brief Description of the Drawings

[0017] Figure 1 It is a schematic diagram of the forging structure of the present invention; Figure 2 It is a schematic diagram of the forging forming process of the present invention; Figure 3 It is a schematic diagram of the heating operation of the present invention; Figure 4 It is a schematic diagram of the rotary forging of the present invention; Figure 5 It is a schematic diagram of the radial precision forging of the present invention; Figure 6 It is a schematic diagram of the sampling detection position of the cross-section of the conical part in the embodiment.

[0018] In the figure: heating coil 1, first hammer head 2, second hammer head 3, third hammer head 4, precision forging hammer 5. Detailed Description of the Embodiment

[0019] The following is a further detailed description through specific embodiments: Embodiment

[0020] A local continuous forming method for a steel component with a large aspect ratio deep blind hole having a truncated conical shape at one end includes the following steps: Step S1, blanking to obtain a blank: Based on the part drawing, design the forging structure drawing (as Figure 1 shown). Among them, the inner hole diameter of the forging is Φ215 mm, the total length of the inner hole is 1764.5 mm, the outer diameter is Φ341.5 mm, the total height of the forging is 2041 mm, the angle between the generatrix of the head cone part and the axis is 12.89°, the total height of the cone part is 276.4 mm, and the outer diameter of the end face of the cone part is Φ215 mm; According to the principle of constant volume of metal plastic forming and considering the influence of the oxidation of the inner and outer surfaces of the hot forming blank, design the structural dimensions of the blanking part (blank). The structural dimensions of the original bar designed are Φ535 mm × 588.16 mm.

[0021] Step S2, heating: According to the process flow and the structural dimensions of the forging, calculate the original length N of the blank along the axial direction before forging the cone part, wherein, L is the projection length of the generatrix of the forging blank of the cone part along the axial direction, is the angle between the generatrix of the cone part and the axis, A is the diameter of the original bar, and S is the diameter of the end face of the cone part; Use the heating coil 1 to heat one end of the blank (as Figure 3 shown). Substitute the specific dimension values into formulas (1) and (2) to calculate that the original length (i.e., the height that the blank needs to be heated) N of the blank along the axial direction before forging the cone part is 364.37 mm, accounting for 62% of the total height of the original bar. The heating temperature is 920 - 930 °C, and the holding time is 0.9 - 1 h.

[0022] Step S3, rotary forging to form a large truncated conical structure: After heating is completed, remove the heating coil 1. Fix the non-heated end of the blank on the horizontal forging equipment through a tooling, and control the axial feeding movement of the blank through the program of the forging equipment; the forging equipment uses three groups of forging hammers arranged at intervals. The three groups of forging hammers move synchronously, and the radial displacements of the three groups of forging hammers increase progressively in sequence. Through the rotation and hammering movements of the three groups of forging hammers, and in cooperation with the translational movement along the generatrix direction of the truncated cone section of the forging, realize the local incremental continuous forming of the large truncated conical structure at one end of the blank; As Figure 4As shown, the three groups of forging hammers respectively include two first hammers 2, two second hammers 3 and two third hammers 4. The first hammers 2, the second hammers 3 and the third hammers 4 are arranged at equal intervals in sequence from the end face close to the truncated cone to the end face far from the truncated cone. The axial spacing Δ between adjacent two groups of forging hammers is 15 mm, the moving speed of the forging hammers is 30 mm / s, and the radial displacement amounts of the first hammers 2, the second hammers 3 and the third hammers 4 are y 1 、y 2 、y 3 , Among them, A is the diameter of the original bar, S is the diameter of the end face of the tapered part, is the included angle between the generatrix of the tapered part and the axis, a 1 is the axial distance from the first hammer 2 to the end face of the tapered part, a 2 is the distance from the second hammer 3 to the end face of the tapered part, a 3 is the axial distance from the third hammer 4 to the end face of the tapered part; The widths of the first hammers 2, the second hammers 3 and the third hammers 4 are D, Among them, N is the original axial length of the blank before forging the tapered part, and Δ is the axial spacing between adjacent two groups of forging hammers.

[0023] Step S4, Heating: Use a heating coil to heat one end of the non-truncated conical structure (cylindrical section) of the blank. The heating temperature is 1010 °C, the heat preservation time is 1 - 1.5 h, and the height H that the blank needs to be heated is Among them, L is the axial projection length of the generatrix of the forging blank of the tapered part, B is the height of the initial round bar, N is the original axial length of the blank before forging the tapered part, and Q is the total height of the tapered part; Substitute the specific dimension values into formula (6) to calculate and obtain that the height H that the blank needs to be heated is 647.43 mm.

[0024] Step S5, Hot extrusion forming of the blind hole preform: After the heating is completed, remove the heating coil, and use the hot extrusion forming process to obtain a blind hole preform with an inner hole depth-diameter ratio ≤ 3. The hot extrusion forming speed is 25 mm / s, the tonnage of the isothermal forging equipment is 6300 t, and glass powder or oil-based graphite is used as the lubricant between the blank and the die to ensure the lubrication effect during the long-term contact between the blank and the die.

[0025] Step S6, Radial precision forging: Fix the truncated cone end of the preform on the pusher rod of the radial forging equipment. Insert a mandrel into the blind hole of the preform. Push the preform to feed axially through the pusher rod. The contact surface between the mandrel and the preform is coated with glass powder or oil-based graphite to facilitate the rapid removal of the mandrel after the radial precision forging is completed. As Figure 5 shown, the radial forging equipment uses four precision forging hammers 5 evenly distributed circumferentially to perform rotational and hammering movements on the preform. The four precision forging hammers 5 are divided into two groups for forging in the same plane. The movement frequency of the precision forging hammers 5 is 480 times / min to 720 times / min, and the tonnage of the radial forging equipment is 1300t. The deformation amount of each precision forging hammer 5 on the preform is the same. The deformation zone of the preform gradually extends from the opening position to the bottom of the blind hole, realizing local continuous forming of the preform, reducing the wall thickness and increasing the length of the preform.

[0026] Step S7: Remove the mandrel, process the peripheral flash of the workpiece, and obtain a deep blind hole forging with a large length-diameter ratio.

[0027] In this embodiment, for the obtained deep blind hole steel component with a large length-diameter ratio, 4 specimens are evenly taken at the cross-section of the cone part (the sampling positions are shown as H1~H4 in Figure 6 ) for microstructure and property testing. The impact absorption energy is 83~86J, and the grain size is 9~10 grades. For the same position of the metal in the cylindrical section of the component, 3 specimens are taken respectively. The grains of the surface layer structure reach 9.5~11 grades, and the grain size at 1 / 2 of the wall thickness is 9~10 grades, showing good mechanical properties.

[0028] The present invention uses rotary forging to form a large truncated cone structure. Through radial loading by three groups of spaced forging hammers, axial elongation occurs in the deformation zone directly affected by the forging hammers. The billet between adjacent two groups of forging hammers undergoes axial upsetting deformation due to the obstruction of axial flow. The "elongation-upsetting-elongation-upsetting" complex thermo-mechanical coupling severe plastic deformation repeatedly occurs in the billet deformation zone, effectively increasing the cumulative deformation amount of the cone part of the billet, refining the microstructure, improving the forming efficiency, and effectively improving the anti-deformation and anti-destruction ability of the cone part under the conditions of high temperature, high speed and high impact load. After heat treatment, the impact absorption energy of the cone part of the component is ≥80J, the grain size is above grade 9, and the mechanical properties are excellent.

[0029] The hot extrusion forming of the blind hole preform and the radial precision forging forming are completed in one heating process. During the radial precision forging process, the hitting frequency of the precision forging hammer head is high, which can reach three times that of the quick forging. The contact time between the precision forging hammer head and the surface of the workpiece to be processed is greatly shortened, and the surface temperature drop is small. After the hot extrusion preform is completed, the billet does not need secondary heating, with high production efficiency and effective control of the grain structure. Moreover, due to the fast hitting speed of the precision forging hammer head, the strain rate of the metal is high, and the temperature rise effect of the material reduces the critical deformation amount of the metal, which is beneficial to obtaining a fine grain structure. After heat treatment, the grain size of the surface layer structure reaches above grade 9.5, and the grain size at 1 / 2 of the wall thickness is not lower than grade 9.

Claims

1. A local continuous forming method for a steel member with a large aspect ratio and a deep blind hole with a truncated cone at one end, characterized in that: The following steps are involved: Step S1, cutting to obtain blank; Step S2, heating one end of the blank using a heating coil; Step S3, rotary forging to form a large truncated cone structure: after heating is completed, the heating coil is removed, and then the non-heating end of the blank is fixed to the horizontal forging equipment through a tooling, and the axial feeding movement of the blank is controlled by the program of the forging equipment; the forging equipment adopts three groups of forging hammers arranged at intervals, the three groups of forging hammers move synchronously, and the radial displacements of the three groups of forging hammers are progressive in sequence, and the rotation and hammering movement of the three groups of forging hammers are combined with the translational movement along the generatrix direction of the truncated cone section of the forging to achieve local incremental continuous forming of the large truncated cone structure at one end of the blank to obtain a semi-formed part; Step S4, heating the non-truncated cone structure of the semi-formed part by using a heating coil; Step S5, hot extrusion forming a blind hole preform: after reaching the temperature, remove the heating coil on the semi-formed part, and adopt a hot extrusion forming process to obtain a blind hole preform with an inner hole depth-to-diameter ratio of ≤3; Step S6, radial precision forging: fix the truncated cone end of the preform on the push rod of the radial forging equipment, insert the mandrel into the blind hole of the preform, push the preform axially through the push rod, and the multiple precision forging hammers of the radial forging equipment rotate and hammer the preform. Each precision forging hammer has the same deformation amount on the preform. The deformation zone of the preform gradually extends from the opening position to the bottom of the blind hole, so as to realize local continuous forming of the preform, so that the wall thickness of the preform is reduced and the length is increased; Step S7, taking out the mandrel, processing the flash around the blank, and obtaining a deep blind hole steel component with a large aspect ratio.

2. The method according to claim 1, characterized in that The heating temperature of step S2 is 900-950°C, the holding time is 0.5-1h, and the original length of the blank along the axial direction before the cone forging is N. Where, L is the projection length of the generatrix of the tapered forging blank along the axial direction, is the angle between the generatrix of the cone and the axis, A is the diameter of the original bar, and S is the diameter of the end face of the cone.

3. The method according to claim 2, characterized in that The three groups of forging hammer heads in step S3 respectively include two first hammer heads, two second hammer heads and two third hammer heads, the first hammer heads, the second hammer heads and the third hammer heads are equidistantly arranged from close to the truncated cone end surface to far away from the truncated cone end surface, the axial spacing Δ between two adjacent groups of forging hammer heads is 10-20 mm, the movement speed of the forging hammer heads is 25-50 mm / s, and the radial displacements of the first hammer heads, the second hammer heads and the third hammer heads are y1, y2 and y3 respectively. Among them, A is the diameter of the original rod, S is the diameter of the end face of the cone, is the angle between the generatrix of the cone and the axis, a1 is the axial distance between the first hammer and the end face of the cone, a2 is the distance between the second hammer and the end face of the cone, and a3 is the axial distance between the third hammer and the end face of the cone.

4. The method according to claim 3, characterized in that The width of the first hammer head, the second hammer head and the third hammer head is D, Wherein, N is the original axial length of the blank before the cone forging, and Δ is the axial spacing between two adjacent groups of forging hammers.

5. The method according to claim 4, characterized in that In step S4, the heating temperature is 950-1050°C, the holding time is 1-1.5h, and the height to be heated of the blank is H. Among them, L is the projection length of the generatrix of the tapered forging blank along the axial direction, B is the height of the initial round bar, N is the original length of the blank along the axial direction before the tapered forging, and Q is the total height of the tapered portion.

6. The method according to any one of claims 1 to 5, characterized in that: During the rotary forging process of forming a large truncated cone structure, the blank between any two sets of hammers undergoes axial upsetting deformation, and the deformation zone repeatedly undergoes a composite thermal-mechanical coupling severe plastic deformation of "drawing-upsetting-drawing-upsetting".

7. The method according to claim 6, characterized in that The hot extrusion forming speed of step S5 is 20-30 mm / s, and the tonnage of the isothermal forging equipment is 6300 t.

8. The method according to claim 6, characterized in that The radial precision forging equipment in step S6 uses four precision forging hammers evenly distributed in the circumferential direction. The four precision forging hammers are divided into two groups for forging in the same plane. The movement frequency of the precision forging hammers is 480 times / min to 720 times / min. The tonnage of the radial forging equipment is 1300t.

9. The method according to claim 6, characterized in that In the step S5 and the step S6, glass powder or oil-based graphite is used as a lubricant between the blank and the mold, or between the core rod and the blank.

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