CN112680677A - Process for reinforcing assembly hole by adopting slotted core rod cold extrusion - Google Patents
Process for reinforcing assembly hole by adopting slotted core rod cold extrusion Download PDFInfo
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- CN112680677A CN112680677A CN202011447830.0A CN202011447830A CN112680677A CN 112680677 A CN112680677 A CN 112680677A CN 202011447830 A CN202011447830 A CN 202011447830A CN 112680677 A CN112680677 A CN 112680677A
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Abstract
本发明涉及一种采用开缝芯棒冷挤压强化装配孔的工艺，（1）在对被挤压工件装配孔冷挤压强化前，开缝芯棒（4）正面依次穿过辅助板（3）、被挤压工件装配孔；开缝芯棒上对称设有多个狭缝，则开缝芯棒工作环可收缩，不对被挤压工件装配孔进行挤压强化。（2）向开缝芯棒内插入支撑棒，则开缝芯棒工作环位置处不可收缩，其直径大于被挤压工件装配孔孔径，匀速拉出开缝芯棒的过程，开缝芯棒工作环挤压装配孔孔壁，使其发生塑性变形，从而实现强化效果。该发明在孔挤压强化过程中不需要使用衬套，消除了挤压过程中衬套的消耗，从而提高了挤压强化效果。
The invention relates to a process for strengthening the assembly hole by cold extrusion with a slotted mandrel. (1) Before cold extrusion strengthening of the assembly hole of the extruded workpiece, the front face of the slotted mandrel (4) passes through the auxiliary plate ( 3) The assembly hole of the extruded workpiece; the slotted mandrel is symmetrically provided with a plurality of slits, the working ring of the slotted mandrel can be contracted, and the assembly hole of the extruded workpiece is not squeezed and strengthened. (2) Insert the support rod into the slotted mandrel, the position of the working ring of the slotted mandrel cannot be contracted, and its diameter is larger than the diameter of the assembly hole of the extruded workpiece. The working ring squeezes the hole wall of the assembly hole to make it plastically deform, so as to achieve the strengthening effect. The invention does not need to use a bushing in the process of hole extrusion strengthening, which eliminates the consumption of the bushing in the extrusion process, thereby improving the extrusion strengthening effect.
Description
Technical Field
The invention provides a process for reinforcing an assembly hole by adopting slotted core rod cold extrusion, belonging to the technical field of hole cold extrusion reinforced precision machining.
Technical Field
The aluminum alloy and the titanium alloy have the characteristics of small density, high strength, good mechanical property, strong corrosion resistance and the like, and are widely applied to aviation parts. There are tens of thousands of assembly holes in a wide-body passenger aircraft, and fasteners need to be installed in the assembly holes for assembly. Stress concentration is easily formed at the edge of the assembling hole, cracks are easily generated due to the stress concentration, the crack propagation rate is increased, the usability of the assembling hole workpiece is reduced due to the existence of the cracks, and the fatigue life of the assembling hole workpiece is shortened.
Along with the increasing use amount of the aluminum alloy, the titanium alloy and the aviation material with the laminated structure in the aviation parts, the improvement of the fatigue performance and the fatigue resistance of the assembly holes of the aluminum alloy, the titanium alloy and the material with the laminated structure and the prolonging of the service life of the extruded workpiece are very important. The cold extrusion strengthening technology for the assembly hole of the extruded workpiece changes the distribution condition of residual stress on the hole wall of the assembly hole by locally strengthening the assembly hole workpiece, thereby improving the fatigue performance of the assembly hole workpiece and prolonging the service life of the assembly hole workpiece. For example, chinese patent application publication No. CN104626726A provides a method for cold extrusion strengthening of a CFRP composite laminated board assembly hole, the method includes: a. providing a bushing capable of being installed in the assembling hole; b. providing a tapered metal core rod and inserting the core rod into the bushing; c. installing the bushing into the assembly hole; d. applying an axial force to the mandrel through an extrusion device so that the bushing is extruded by the maximum diameter part of the mandrel; e. the core rod is removed and the bushing is retained within the assembly bore. The patent application document aims at the assembly hole of the CFRP composite material laminated plate, and the assembly hole adopts a bushing and is matched with a cold extrusion strengthening process, so that the fatigue life of a part can be effectively prolonged, and the service time of an airplane is prolonged. Because the bushing is fastened in the assembling hole, the wear resistance of the connecting structure is increased, and the disassembly of the assembling fastener and the maintenance of the manufactured piece are facilitated. However, in this patent application, a solid extrusion core rod is used to cold-extrude and strengthen the assembly hole of the extruded workpiece.
At present, a slotted bushing and a solid extrusion core rod are widely applied to cold extrusion reinforcement of a workpiece with a hole. However, the slotted bush is used for cold extrusion strengthening of the workpiece with the hole, the extrusion core rod is not directly contacted with the wall of the assembling hole, so that the extrusion amount cannot be completely acted on the wall of the assembling hole, the extrusion amount is acted on the slotted bush, the plastic deformation of the bush is larger, the slotted bush with large deformation cannot be used for cold extrusion strengthening of the hole again, and the cost of the cold extrusion strengthening process of the hole is seriously increased; the solid extrusion core rod is used for directly carrying out cold extrusion strengthening on the assembly hole, hole extrusion strengthening with larger extrusion amount can not be carried out, and the extrusion strengthening range of the assembly hole is limited.
The invention provides a method for cold extrusion strengthening of an assembly hole by using a slotted core rod, and aims to realize repeated use of the slotted core rod, improve extrusion efficiency and increase hole extrusion amount.
Disclosure of Invention
Aiming at the problem that the slotted bush is used for carrying out cold extrusion strengthening on the assembly hole of the extruded workpiece, the extrusion core rod is not in direct contact with the wall of the assembly hole, so that the extrusion amount cannot be completely acted on the wall of the assembly hole, and the extrusion amount acts on the slotted bush to cause the slotted bush to generate plastic deformation, so that the bush cannot be reused, and the hole cold extrusion strengthening process cost is seriously increased; the invention provides a process for strengthening assembly holes by cold extrusion of a slotted core rod, which solves the problem that the assembly holes of extruded workpieces cannot be extruded in a large extrusion amount by using a solid extrusion core rod. The adopted slotted core rod can contract at the position of the slotted core rod working ring due to the existence of the slot, so that the extrusion with large extrusion amount can be realized. The hardness of the materials of the slotted core rod and the supporting rod is higher than that of the extruded workpiece, and the slotted core rod and the supporting rod have small deformation in the hole cold extrusion strengthening process, so that the slotted core rod and the supporting rod can be repeatedly used, and the cost of the hole cold extrusion strengthening process is reduced.
Technical scheme
A process for reinforcing an assembly hole by adopting slotted core rod cold extrusion comprises the following steps:
(1) before cold extrusion strengthening of the extruded workpiece assembly hole, the front surface of the slotting core rod penetrates through the auxiliary plate and the extruded workpiece assembly hole; the auxiliary plate is placed in front of the extruded workpiece, and the hole diameter of the auxiliary plate is the same as and coaxial with the hole diameter of the assembly hole of the extruded workpiece; the slit core rod is provided with a slit, so that the position of the working ring of the slit core rod can be contracted, and the extrusion strengthening of the assembly hole of the extruded workpiece is not carried out.
(2) The supporting rod is inserted into the slotted core rod, the position of the slotted core rod working ring cannot contract due to the existence of the supporting rod, the diameter of the slotted core rod working ring is larger than the diameter of the assembly hole of the extruded workpiece, and the slotted core rod inserted into the supporting rod extrudes the wall of the assembly hole in the process of pulling out the assembly hole of the extruded workpiece at a constant speed, so that the wall of the assembly hole of the extruded workpiece generates plastic deformation, and the strengthening effect is realized.
On the slotted core rod, the end part provided with the slit is provided with a slotted core rod guide section, the cross section of the slotted core rod guide section is in an isosceles trapezoid shape, and the auxiliary plate and the extruded workpiece are placed at the position of the slotted core rod guide section.
The slotting core rod is of a hollow structure, slits are symmetrically formed in the end portion of the slotting core rod along the length direction, the slits penetrate through the slotting core rod in the radial direction, and the number of the slits is more than one. The non-free end of each slit extends inwardly to provide a pilot hole.
The tail part of the supporting rod is provided with a holding piece which is convenient for taking out the supporting rod. In detail, the holding piece is a screw and is fixed on the tail part of the supporting rod by screw threads.
According to the invention, the slotted core rod is adopted to carry out cold extrusion strengthening on the assembling hole of the extruded workpiece, a bushing is not needed in the hole cold extrusion strengthening process, the extrusion amount is completely acted on the wall of the assembling hole of the extruded workpiece, the consumption of the bushing in the hole extrusion strengthening process is eliminated, and the strengthening efficiency is improved; in the process of hole cold extrusion strengthening, the hardness of the slotted core rod and the support rod material is higher than that of the material of the extruded workpiece, and the deformation is small in the extrusion process, so that the slotted core rod and the support rod can be repeatedly used, and the cost of the hole cold extrusion strengthening process is reduced.
Has the advantages that:
the invention relates to a cold extrusion strengthening process for slotted core rod holes, which has the following advantages:
1. the cold extrusion strengthening assembly hole process does not need to use a bushing, the extrusion amount is completely acted on the hole wall of the assembly hole of the extruded workpiece, the consumption of the bushing in the extrusion process is eliminated, and the hole cold extrusion strengthening efficiency is improved.
2. The hardness of the slotted core rod and the support rod material is higher than that of the extruded workpiece material, the deformation of the slotted core rod and the support rod is smaller in the hole cold extrusion strengthening process, and the slotted core rod and the support rod can be reused.
3. The slotted core rod has a central structure, so that the section of the slotted core rod is annular, and the existence of the radial through slit enables the position of a working ring of the slotted core rod to be contracted, thereby realizing extrusion with large extrusion amount.
4. The slotted core rod is used for carrying out cold extrusion strengthening on the assembly hole of the extruded workpiece, so that the residual stress field of the hole wall of the assembly hole of the extruded workpiece can be increased, the fatigue performance of the extruded workpiece can be improved, and the service life of the extruded workpiece can be prolonged.
Drawings
FIG. 1 is a schematic illustration of the drilling of a slotted core rod hole cold extrusion strengthening process of the present invention;
FIG. 2 is a three-dimensional view of FIG. 1;
FIG. 3 is a two-dimensional view of a slotted core rod;
FIG. 4 is a three-dimensional view of a slotted core rod;
FIG. 5 is a schematic view of a support rod;
FIG. 6 is a cross-sectional view of a support rod
FIG. 7 is a graph of the distance of the extruded end of a TC4 titanium alloy plate assembly hole from the wall of the hole as a function of the tangential residual stress;
FIG. 8 is a variation of tangential residual stress and distance of an intermediate layer of a pilot hole of a TC4 titanium alloy plate from a hole wall;
FIG. 9 is a graph of the distance from the extrusion end of a TC4 titanium alloy plate assembly hole to the hole wall and the change of tangential residual stress.
Wherein, the support rod-1; an extruded workpiece-2; an auxiliary plate-3; slotting mandrel-4; slotting mandrel working ring-5; a slotted core rod guide section-6; a support rod threaded hole-7; a stop hole-8; a slit-9.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
Example 1
Fig. 1 is a schematic view of a process for reinforcing a pilot hole by cold extrusion using a split core rod according to the present invention, and fig. 2 is a perspective view of fig. 1. Referring to fig. 1 and 2: (1) before the assembly hole of the extruded workpiece 2 is subjected to cold extrusion strengthening, the front surface of the slotted core rod 4 penetrates through the auxiliary plate 3 and the assembly hole of the extruded workpiece 2. The auxiliary plate 3 is placed in front of the extruded workpiece 2, and the hole diameter of the auxiliary plate is the same as and coaxial with the assembling hole of the extruded workpiece; the auxiliary plate 3 with the pressed workpiece 2 is placed at the position of the slotted-core-rod guide section 6. Due to the existence of the slit 9 on the slit core rod 4, the position of the slit core rod working ring 5 can be contracted, and the extrusion strengthening of the assembly hole of the extruded workpiece 2 is not carried out.
(2) The supporting rod 1 is inserted into the slotted core rod, the position of the slotted core rod working ring 5 cannot be contracted due to the existence of the supporting rod 1, the diameter of the supporting rod is larger than the diameter of the assembly hole of the extruded workpiece 2, the assembly hole of the extruded workpiece 2 is pulled out at a constant speed along with the slotted core rod 4, and the slotted core rod working ring 5 extrudes the wall of the assembly hole in the process that the slotted core rod 4 inserted into the supporting rod 1 is pulled out of the assembly hole of the extruded workpiece 2, so that the wall of the assembly hole of the extruded workpiece 2 is subjected to plastic deformation, and the strengthening effect is realized.
FIG. 3 is a plan view of a slotted core rod; fig. 4 is a perspective view of the slotted core rod. The adopted core rod is a slotted core rod 4, the end part of the slotted core rod 4 is symmetrically provided with 4 slits along the length direction, the slits are communicated in the radial direction of the slotted core rod, the non-free end of each slit extends towards the inside to be provided with a stop thread hole 8, and the situation that the service life of the core rod is influenced by taking the slotted core rod as a crack is prevented.
On the slotted core rod, the end part provided with the slit is provided with a slotted core rod guide section 6, the cross section of which is isosceles trapezoid, so that a support rod can be conveniently placed into the slotted core rod after being contracted for carrying out extrusion strengthening on the hole. The middle part of the periphery of the slit of the slotting core rod 4 is provided with a working ring 5. After the slit core rod 4 is provided with the slit, the outer diameter of the part of the working ring 5 is larger than the inner diameter of the assembling hole, so the diameter of the part of the working ring 5 needs to be reduced, the core rod can be placed in the hole, the wide slit in the guide section is extruded, the narrow slit of the working ring 5 is closed, and the core rod can be placed in the hole of the extruded workpiece 2.
FIG. 5 is a schematic view of a support rod; fig. 6 is a schematic cross-sectional view of a support rod. Referring to fig. 5 and 6, the tail part of the support rod is provided with a threaded hole 7, and after the slotted core rod is subjected to cold extrusion strengthening, a screw is inserted into the threaded hole 7, so that the support rod can be conveniently taken out.
Example 2
A TC titanium alloy plate with the diameter of a central hole of 12.12mm and the diameter of 60mm multiplied by 10mm is simulated by ABAQUS finite element simulation analysis software by a hole cold extrusion strengthening process with the extrusion amount of 5 percent by using a solid extrusion core rod and a 4 slotted extrusion core rod.
After the cold extrusion strengthening of the assembly hole of the extruded workpiece, residual stress in the radial direction, the tangential direction and the plate thickness direction is generated on the hole wall of the assembly hole, however, the extruded workpiece bears alternating load in the service process, and the tangential residual stress has the largest influence on the service life of the part due to the residual stress in the three directions of the hole wall of the assembly hole. Therefore, in example 2, only the variation of the distance from the wall of the assembled hole to the wall of the hole and the tangential residual stress at different positions after the hole is subjected to extrusion strengthening is analyzed.
Based on the cold extrusion strengthening simulation process of the solid extrusion core rod and the 4-slit extrusion core rod hole, the obtained change of the distance between the extrusion end of the assembly hole of the TC4 titanium alloy plate and the hole wall and the tangential residual stress is shown in FIG. 7; the variation of the distance between the middle layer of the assembly hole and the hole wall and the tangential residual stress is shown in FIG. 8; the variation of the distance of the extrusion end of the assembly hole from the hole wall and the tangential residual stress is shown in fig. 9.
The distance between the three different positions of the TC4 titanium alloy plate assembly hole extrusion end, the middle layer and the extrusion end and the hole wall and the change of the tangential residual stress can be known, along with the gradual increase of the distance from the hole wall, the assembly hole is subjected to cold extrusion strengthening by using a solid extrusion core rod and a 4-slotted extrusion core rod, the tangential residual stress at different positions of the hole wall of the assembly hole presents the same change rule, and the tangential residual stress of the extrusion end is smaller than that of the middle layer and the extrusion end; at the extrusion end of the hole wall of the assembly hole, the maximum residual compressive stress generated on the hole wall after the extrusion strengthening of the solid extrusion core rod is 290MPa, and the depth of a residual compressive stress layer is 4.2 mm. 4, the maximum residual compressive stress generated by the hole wall after extrusion strengthening of the slotted extrusion core rod is 310MPa, the depth of a residual compressive stress layer is 5mm, and the residual stress generated by the hole wall after extrusion strengthening of the slotted extrusion core rod 4 away from the same position of the hole wall is larger than that of a solid extrusion core rod; and at the middle layer and the extrusion end of the hole wall of the assembly hole, the depths of residual compressive stresses generated on the hole wall after the solid extrusion core rod and the 4-slit extrusion core rod are extruded and reinforced are the same, and the residual compressive stresses generated on the hole wall after the 4-slit extrusion core rod is extruded and reinforced are larger than that of the solid extrusion core rod at the same position from the hole wall.
The residual stress field generated by the hole wall after the hole is extruded and reinforced can effectively inhibit the generation of cracks at the hole edge and delay the crack propagation rate, thereby improving the fatigue performance and prolonging the service life of the extruded workpiece. Extruding the TC4 titanium alloy plate by using a solid extrusion core rod and a 4-slotted extrusion core rod, wherein residual compressive stress and residual compressive stress fields generated after cold extrusion strengthening of the 4-slotted extrusion core rod at the extrusion end of the hole wall of the assembly hole are both larger than those of the solid extrusion core rod; the depth of the residual compressive stress layer generated after the extrusion strengthening of the middle layer of the hole wall of the assembly hole, the solid extrusion core rod at the extrusion end and the 4-slit extrusion core rod hole is the same, but the residual compressive stress generated after the extrusion strengthening of the 4-slit extrusion core rod hole at the same position of the hole wall is larger than that of the solid extrusion core rod.
In conclusion, the slotted core rod is used for carrying out cold extrusion strengthening on the assembling hole of the extruded workpiece, so that the residual stress field of the hole wall of the assembling hole of the extruded workpiece can be increased, and the fatigue performance and the service life of the extruded workpiece can be improved.
Claims (7)
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114807548A (en) * | 2022-03-24 | 2022-07-29 | 南京航空航天大学 | A detachable extrusion mandrel ultrasonic vibration hole extrusion strengthening device and its operation process |
| CN115652047A (en) * | 2022-10-08 | 2023-01-31 | 南京航空航天大学 | A slotted mandrel extrusion strengthening process to improve the uniformity of residual stress around the hole |
| CN115652047B (en) * | 2022-10-08 | 2025-04-15 | 南京航空航天大学 | A slotted mandrel extrusion strengthening process for improving the uniformity of residual stress around the hole |
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