Counterbore structure cold extrusion strengthening tool and extrusion method thereof

Abstract

The cold extrusion strengthening tool is composed of a retainer, a cap, an inner ejector sleeve, an outer ejector sleeve and a core rod, one end of the core rod is of a bullet structure, a boss is arranged at the other end of the core rod, the bullet structure end of the core rod sequentially comprises a rear conical section, an extrusion large-diameter section and a front conical section from top to bottom, and a small-diameter section is arranged between the front conical section and the first boss. The diameter of the small-diameter section is smaller than the diameter of the straight hole of the countersunk head structure, the sum of the diameter of the extrusion large-diameter section and the thickness of the lining is larger than the diameter of the straight hole of the countersunk head structure, external threads are arranged on the outer side of the retainer and are in matched threaded connection with internal threads of the cap, and the inner side of the top end of the outer top sleeve is matched with the outer side of the top end of the inner top sleeve. The fatigue life of the hole can be prolonged by 3-10 times, residual compressive stress can prevent fine cracks around the hole from expanding, the weight does not need to be increased or the structure of a rigid body does not need to be changed, single-side operation can be achieved, the extrusion strengthening time is greatly shortened, the failure rate is small, stability and reliability are achieved, the method is suitable for aviation metal of aluminum alloy, titanium alloy and high-strength steel, and economic benefits are good.

Description

Technical Field

[0001] The invention belongs to the technical field of cold extrusion strengthening, and in particular relates to a cold extrusion strengthening tool for a countersunk hole structure and an extrusion method thereof. Background Art

[0002] With the progress of the times, lightweight and long life have become the focus of the aviation field. In the manufacturing process of aircraft, the fatigue strength of aircraft structure cannot be ignored. Through the investigation of the causes of aircraft crashes by relevant departments, it was found that about 80% of aircraft failures are related to fatigue failure. In order to avoid the influence of welding stress on the strength of aircraft during aircraft manufacturing, riveting is generally used to connect parts. This greatly increases the number of aircraft structural holes, and these structural holes are the main parts where stress concentration occurs, which will accelerate the initiation and expansion of fatigue cracks and cause fatigue fracture of the structure. Therefore, improving the fatigue strength of aircraft fastening holes and thus improving the fatigue life of the aircraft as a whole has become a highly concerned issue in the aviation field. In order to solve this problem, fatigue strengthening technology is usually used to solve the fatigue problem caused by hole stress concentration.

[0003] Fatigue strengthening technology is a method to improve fatigue strength without changing the structure and size of the component. At present, the most commonly used cold extrusion fatigue strengthening technology for conventional straight holes is to use flanged slit bushings for strengthening. However, during the strengthening process of countersunk holes, only the straight hole part can be strengthened, and the countersunk part cannot be strengthened. Therefore, ordinary slit bushings and extrusion tools cannot meet the needs of countersunk hole strengthening. Summary of the invention

[0004] The purpose of the present invention is to realize extrusion strengthening of the countersunk hole by using a straight slotted bushing, which can effectively solve the problem that ordinary slotted bushings and tools cannot extrude and strengthen the countersunk hole.

[0005] The technical solution of the present invention is as follows: a cold extrusion strengthening tool with a countersunk hole structure is composed of a retainer, a cap, an inner top sleeve, an outer top sleeve, and a core rod, wherein one end of the core rod is in a bullet structure and the other end is provided with a boss, the inner top sleeve is sleeved on the outside of the middle of the core rod, the outer wall of the inner top sleeve at one end close to the boss protrudes outward to form a circle of convex ring, the outer top sleeve is placed on the outside of the inner top sleeve and a gap is set, the lower end of the inner hole of the outer top sleeve is provided with an inner step surface placed on the upper end surface of the convex ring, the retainer is placed at the lower end of the outer top sleeve, and the outer side of the outer top sleeve is provided with an outer step surface, the inner hole of the cap is stepped and provided with a first step surface and a second step surface, the first step surface matches and matches the outer step surface, the second step surface matches and matches the top end of the retainer, the outer side of the retainer is provided with an external thread that is threadedly connected with the inner thread of the cap, and the inner side of the top end of the outer top sleeve matches and matches the outer side of the top end of the inner top sleeve.

[0006] Furthermore, the core rod bullet structure end includes a rear cone section, an extruded large diameter section and a front cone section from top to bottom, and a small diameter section is between the front cone section and the boss one. The diameter of the small diameter section is smaller than the aperture of the straight hole of the countersunk structure, and the sum of the diameter of the extruded large diameter section and the thickness of the bushing is larger than the aperture of the straight hole of the countersunk structure.

[0007] Furthermore, grooves are uniformly formed along the axial direction at one end of the inner top sleeve away from the convex ring.

[0008] Furthermore, the inner hole diameter of the top end of the outer top sleeve is slightly larger than the maximum outer diameter of the bushing.

[0009] An extrusion method using the above-mentioned cold extrusion strengthening tool with a countersunk hole structure, the method comprising:

[0010] Step S1, drilling an initial hole in a structural part,

[0011] Step S2, reaming the initial hole,

[0012] Step S3, check the initial hole diameter with a comprehensive gauge,

[0013] Step S4, check the mandrel extrusion diameter with a mandrel ring gauge,

[0014] Step S5, connect the mandrel, the inner top sleeve, the outer top sleeve, the retainer, and the cap to the pulling gun in sequence, and install the bushing coated with the anti-friction lubricating coating on the mandrel,

[0015] Step S6, inserting the mandrel of step S5 into the initial hole,

[0016] Step S7, placing the outer top cover and the structural member close to each other,

[0017] Step S8: Press the start button of the pulling gun and release it after the core rod completely passes through the workpiece.

[0018] Step S9, remove the bushing from the initial hole and use a comprehensive gauge to check whether the hole diameter after extrusion is qualified.

[0019] Step S10: If the hole is unqualified, use a reamer to ream it to the required final diameter and check whether the diameter is qualified.

[0020] Step S11, if unqualified, repeat step S10 until qualified.

[0021] Step S12: After passing the test, the parts to be installed can be installed.

[0022] During the extrusion strengthening process, a straight slotted bushing coated with a friction-reducing lubricating coating is used to reduce the friction between the extrusion tool and the bushing. During the extrusion process, the straight hole part and the countersunk hole part are interfered to achieve the strengthening effect. After the extrusion is completed, a reamer is needed to machine the inner diameter of the structure to the required size.

[0023] Beneficial effects of the present invention:

[0024] (1) The fatigue life of the hole can be increased by 3 to 10 times.

[0025] (2) Residual compressive stress can prevent the propagation of small cracks around the hole.

[0026] (3) No need to add weight or change the structure of the rigid body.

[0027] (4) It can be operated on one side, which greatly shortens the extrusion strengthening time, has a low failure rate, and is stable and reliable.

[0028] (5) Commonly used in the field of aviation maintenance, for some holes that have already cracked, residual stress can also make the amplitude of the effective stress intensity factor close to or lower than the value required by the stress intensity factor of the material itself, thereby effectively inhibiting crack initiation, inhibiting fatigue crack propagation, and improving the fatigue life of the hole.

[0029] (6) Suitable for aviation metals such as aluminum alloys, titanium alloys and high-strength steel, with good economic benefits, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings herein are incorporated into and constitute a part of the specification, showing embodiments consistent with the present invention, and together with the specification, are used to explain the principles of the present invention. Obviously, the drawings described below are only some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0031] Figure 1 A schematic diagram of the structure of the cold extrusion strengthening tool for the countersunk hole structure provided by the present invention, which is assembled with a structural part and a bushing;

[0032] Figure 2 A schematic diagram of the inner top sleeve structure provided by the present invention;

[0033] Figure 3 The extrusion strengthening flow chart provided by the present invention;

[0034] In the attached figure: 1-retainer

[0035] 2-cap, 21-first step surface, 22-second step surface

[0036] 3-inner top sleeve, 31-convex ring, 32-groove

[0037] 4-outer top sleeve, 41-inner step surface, 42-outer step surface

[0038] 5-mandrel, 51-boss, 52-rear cone section, 53-extrusion large diameter section, 54-front cone section, 55-small diameter section

[0039] 6-Structural parts, 7-Bushing DETAILED DESCRIPTION

[0040] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that the present invention will be more comprehensive and complete and fully convey the concept of the example embodiments to those skilled in the art.

[0041] See also Figure 1-2 The figure shows a schematic diagram of the structure of the cold extrusion strengthening tool for the countersunk hole structure provided by the present invention, which is assembled with a structural part and a bushing, and is composed of a retainer 1, a cap 2, an inner top sleeve 3, an outer top sleeve 4, and a core rod 5. One end of the core rod 5 is a bullet structure, and the other end is provided with a boss 51. The inner top sleeve 3 is sleeved on the outer side of the middle part of the core rod 5. The outer wall of one end of the inner top sleeve 3 close to the boss 51 protrudes outward to form a circle of convex rings 31. The outer top sleeve 4 is placed on the outer side of the inner top sleeve 3 and a gap is set. The lower end of the inner hole of the outer top sleeve 4 is provided with an inner step surface 4 1 is placed on the upper end surface of the convex ring 31, the retainer 1 is placed at the lower end of the outer top sleeve 4, the outer side of the outer top sleeve 4 is provided with an outer step surface 42, the inner hole of the cap 2 is stepped and provided with a first step surface 21 and a second step surface 22, and a hole is opened at the top end so that the outer top sleeve 4 passes through, the first step surface 21 matches with the outer step surface 42, the second step surface 22 matches with the top end of the retainer 1, the outer side of the retainer 1 is provided with an external thread that is threadedly connected with the internal thread of the cap 2, and the inner side of the top end of the outer top sleeve 4 matches with the outer side of the top end of the inner top sleeve 3.

[0042] The warhead structural end of the mandrel 5 includes a rear cone section 52, an extruded large diameter section 53 and a front cone section 54 from top to bottom. A small diameter section 55 is between the front cone section 54 and the boss 1 51. The diameter of the small diameter section 55 is smaller than the straight hole diameter of the structural member 6. The sum of the diameter of the extruded large diameter section 53 and the thickness of the bushing 7 is larger than the straight hole diameter of the structural member 6. The inner top sleeve 3 is evenly provided with grooves 32 along the axial direction at one end away from the convex ring 31. The inner hole diameter of the top end of the outer top sleeve 4 is slightly larger than the maximum outer diameter of the bushing 7.

[0043] See also Figure 3 , the figure shows the extrusion strengthening flow chart of the cold extrusion strengthening tool using the countersunk hole structure provided by the present invention, including the following steps:

[0044] Step S1, drilling an initial hole in a structural part,

[0045] Step S2, reaming the initial hole,

[0046] Step S3, check the initial hole diameter with a comprehensive gauge,

[0047] Step S4, check the mandrel extrusion diameter with a mandrel ring gauge,

[0048] Step S5, connect the mandrel, the inner top sleeve, the outer top sleeve, the retainer, and the cap to the pulling gun in sequence, and install the bushing coated with the anti-friction lubricating coating on the mandrel,

[0049] Step S6, inserting the mandrel of step S5 into the initial hole,

[0050] Step S7, placing the outer top cover and the structural member close to each other,

[0051] Step S8: Press the start button of the pulling gun and release it after the core rod completely passes through the workpiece.

[0052] Step S9, remove the bushing from the initial hole and use a comprehensive gauge to check whether the hole diameter after extrusion is qualified.

[0053] Step S10: If the hole is unqualified, use a reamer to ream it to the required final diameter and check whether the diameter is qualified.

[0054] Step S11, if unqualified, repeat step S10 until qualified.

[0055] Step S12: After passing the test, the parts to be installed can be installed.

[0056] Because the sum of the diameter of the large diameter section of the mandrel extrusion and the thickness of the bushing is larger than the diameter of the straight hole of the structural component 6, there is a large amount of interference when the large diameter of the mandrel extrusion passes through the straight hole during the extrusion process, thereby ensuring that the extrusion force applied is transmitted to the countersunk part of the hole through the extrusion tool, so the straight hole part and the countersunk hole part are extruded simultaneously during the entire extrusion process.

[0057] Extrusion causes the surface metal of the hole wall to undergo plastic deformation, and the deep metal farther away from the hole wall to undergo elastic deformation. After unloading, the deep metal layer will tend to return to its original state due to the elastic deformation. At this time, the surface metal layer that has undergone plastic deformation will be reversely loaded, thereby forming a residual compressive stress layer within a certain range of the hole wall. It can be used to reduce the average value of the external cyclic fatigue load, greatly reduce the influence of concentrated tensile stress on the hole edge, and achieve the effect of improving fatigue life.

[0058] After extrusion, a ridge along the axial direction will be formed at the opening of the bushing, so reaming is often required after extrusion to eliminate cracks at the root of the ridge and round it to the specified size.

[0059] It is often used in the field of aviation maintenance. For some holes that have already cracked, the residual stress can also make the amplitude of the effective stress intensity factor close to or lower than the value required by the stress intensity factor of the material itself, thereby effectively inhibiting crack initiation, inhibiting fatigue crack propagation, and increasing the fatigue life of the hole. The fatigue life of the hole can be increased by 3 to 10 times. The residual compressive stress can prevent the expansion of small cracks around the hole. There is no need to increase weight or change the structure of the rigid body. It can be operated on one side, which greatly shortens the extrusion strengthening time, has a low failure rate, is stable and reliable, and is suitable for aviation metals such as aluminum alloys, titanium alloys and high-strength steels, with good economic benefits.

[0060] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Any modification or equivalent substitution made to the technical solution of the present invention by ordinary technicians in this field shall be included in the scope of the claims of the present invention as long as it does not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A cold extrusion strengthening tool for a countersunk hole structure, characterized in that: The invention is composed of a retainer (1), a cap (2), an inner top sleeve (3), an outer top sleeve (4), and a core rod (5). One end of the core rod (5) is in a bullet-shaped structure, and the other end is provided with a boss (51). The inner top sleeve (3) is sleeved on the outer side of the middle part of the core rod (5). The outer wall of one end of the inner top sleeve (3) close to the boss (51) protrudes outward to form a circle of convex ring (31). The outer top sleeve (4) is placed on the outer side of the inner top sleeve (3) with a gap. The lower end of the inner hole of the outer top sleeve (4) is provided with an inner step surface (41) placed on the upper end surface of the convex ring (31). The retainer (1) The outer side of the outer top sleeve (4) is provided with an outer step surface (42); the inner hole of the cap (2) is stepped and provided with a first step surface (21) and a second step surface (22); and a hole is opened at the top end so that the outer top sleeve (4) can pass through; the first step surface (21) matches with the outer step surface (42); the second step surface (22) matches with the top end of the retainer (1); the outer side of the retainer (1) is provided with an external thread which is threadedly connected with the internal thread of the cap (2); the inner side of the top end of the outer top sleeve (4) matches with the outer side of the top end of the inner top sleeve (3).

2. The cold extrusion strengthening tool for countersunk hole structure according to claim 1, characterized in that: The warhead structural end of the core rod (5) comprises, from top to bottom, a rear cone section (52), an extruded large diameter section (53) and a front cone section (54); a small diameter section (55) is provided between the front cone section (54) and the boss one (51); the diameter of the small diameter section (55) is smaller than the diameter of the straight hole of the structural component (6); and the sum of the diameter of the extruded large diameter section (53) and the thickness of the bushing (7) is larger than the diameter of the straight hole of the structural component (6).

3. The cold extrusion strengthening tool for countersunk hole structure according to claim 1, characterized in that: The inner top sleeve (3) has grooves (32) uniformly formed along the axial direction at one end away from the convex ring (31).

4. The cold extrusion strengthening tool for countersunk hole structure according to claim 1, characterized in that: The inner hole diameter of the top end of the outer top sleeve (4) is slightly larger than the maximum outer diameter of the bushing (7).

5. An extrusion method using a cold extrusion strengthening tool with a countersunk hole structure as claimed in any one of claims 1 to 4, characterized in that: The method comprises: Step S1, drilling an initial hole in a structural part, Step S2, reaming the initial hole, Step S3, check the initial hole diameter with a comprehensive gauge, Step S4, check the mandrel extrusion diameter with a mandrel ring gauge, Step S5, connect the mandrel, the inner top sleeve, the outer top sleeve, the retainer, and the cap to the pulling gun in sequence, and install the bushing coated with the anti-friction lubricating coating on the mandrel, Step S6, inserting the mandrel of step S5 into the initial hole, Step S7, placing the outer top cover and the structural member close to each other, Step S8: Press the start button of the pulling gun and release it after the core rod completely passes through the workpiece. Step S9, remove the bushing from the initial hole and use a comprehensive gauge to check whether the hole diameter after extrusion is qualified. Step S10: If the hole is unqualified, use a reamer to ream it to the required final diameter and check whether the diameter is qualified. Step S11, if unqualified, repeat step S10 until qualified. Step S12: After passing the test, the parts to be installed can be installed.

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