CN115652047A - A slotted mandrel extrusion strengthening process to improve the uniformity of residual stress around the hole - Google Patents

Abstract

The invention provides a slotting core rod extrusion strengthening process for improving the homogenization degree of residual stress around a hole, (1) a sample with a hole is placed on a guiding section of the slotting core rod; (2) mounting a support rod; (3) Extruding and reinforcing primary holes of the porous sample, and forming convex ridges on the wall of the sample hole after extruding and reinforcing the slotted core rod hole; (4) Turning the sample by 180 degrees, enabling the extrusion end of the first hole extrusion reinforced sample of the slotted core rod to be used as the extrusion end of the second hole extrusion reinforced sample, enabling the extrusion end to be used as the extrusion end of the second hole extrusion reinforced sample, rotating the slotted core rod by 10-30 degrees, and carrying out second extrusion reinforcement on the slotted core rod; and (6) reaming. According to the invention, the slotted core rod twice-hole extrusion strengthening process is adopted to carry out extrusion strengthening on the sample with the holes, after the hole extrusion strengthening, the plastic deformation degree of the extrusion end and the extrusion end of the hole wall of the sample is similar, the residual compressive stress formed on the hole wall is uniform, and the fatigue performance of the sample with the holes is improved.

Description

A slotted mandrel extrusion strengthening process to improve the uniformity of residual stress around the hole

technical field

The invention relates to a hole extrusion strengthening method for uniformizing the residual stress around the hole by twice extrusion strengthening of a slotted mandrel, which belongs to the field of anti-fatigue manufacturing technology of hole extrusion strengthening, and particularly relates to the use of a slotted mandrel to The samples were strengthened by extrusion twice in opposite directions.

Background technique

Connecting holes are more connecting structures on aircraft. Fasteners are installed in connecting holes to connect aircraft structures. Due to the existence of connecting holes, the material is discontinuous, and the sample with holes is subjected to external alternating loads. Fatigue cracks are easy to initiate under the action, which affects the fatigue life of the sample with holes. Hole extrusion strengthening is a simple and effective process in anti-fatigue manufacturing technology, and it is widely used in the aerospace field. However, when the slotted bushing and solid mandrel are used to strengthen the hole by extrusion, the hole wall of the sample will form uneven residual compressive stress after extrusion strengthening, which will affect the fatigue performance of the hole.

The Chinese patent document with the publication number CN111118270B (hereinafter referred to as Document 1) proposes a cold extrusion process and device for uniform residual stress around the hole. The cold extrusion process for uniform residual stress around the hole is suitable for straight through holes. The pressing process includes the first strengthening of the through hole along the first axis through the first mandrel; the second strengthening of the through hole along the second axis through the second mandrel; wherein, the first axis and the second Axially opposite, the maximum diameter of the portion of the first mandrel to be strengthened is less than or equal to the maximum diameter of the portion of the second mandrel to be strengthened. After strengthening by two-step bidirectional cold extrusion, the circumferential residual stress of the through hole is distributed more uniformly along the thickness direction, and no residual tensile stress occurs at the edge of the hole on the two end faces, which is beneficial to improving the fatigue resistance of the strengthened hole. The main differences between this patent document and this application document: (1) The hole extrusion strengthening tools are different. The hole extrusion strengthening tool used in document 1 is a bushing, and the thickness of the bushing used for the two successive hole extrusion strengthening is different, while the hole extrusion strengthening tool used in this application is a slotted mandrel, and the two hole extrusion strengthening The slotted mandrel used for strengthening is the same, which reduces the process cost. (2) Hole extrusion strengthening process. The slotted mandrel mentioned in this application is strengthened by two extrusions, and the slotted mandrel needs to be rotated at a certain angle during the second extrusion strengthening. The ridge formed on the wall of the sample hole, the residual stress uniformity around the hole, and the patent documents of the cold extrusion process and device do not limit the angle of the extrusion mandrel. (3) Reaming processing. This application uses a slotted mandrel for two times of extrusion strengthening, and reaming is required to trim the wall of the sample hole after extrusion strengthening, in order to make the hole diameter of the sample after extrusion strengthening reach the diameter of the final hole. Document 1 There is no mention of the need for reaming after two times of extrusion strengthening. .

The Chinese patent document with the publication number CN114085968A (hereinafter referred to as document 2) proposes a method for strengthening the cold extrusion assembly hole of a slotted bush and a supporting tooling device. The method includes steps S1-S5. The matching tooling includes an extrusion gun, an extrusion mandrel and a bushing top block; a piston chamber is arranged in the outer casing, a telescopic movable mechanism is arranged in the piston chamber, and an extension end is arranged at the front end of the outer casing, and an extension end is provided in the extension end. A telescopic passage connected to the piston cavity, a telescopic rod is arranged in the telescopic passage, and one end of the telescopic rod is connected with the telescopic movable mechanism; the end of the extruding mandrel is provided with an annular first extrusion part, and the first extrusion part is connected to the second A transition section for placing slotted bushes is arranged between the extrusion parts; the bushing top block is a conical tubular structure with a large upper part and a smaller bottom part, and the bushing top block is set on the extrusion mandrel. It proposes a method of secondary extrusion strengthening of the assembly hole by using a slotted bush to achieve the uniformity of the stress value of the entire assembly hole, better ensure the quality and effect of strengthening, and further significantly improve the fatigue resistance. The main differences between this patent document 2 and this application document: (1) extrusion strengthening tool. The hole extrusion strengthening tool used in Document 2 is a slotted bushing, and a slotted bushing needs to be replaced every time extrusion strengthening is performed, but in this application document, the same tool is used in the two extrusion strengthening processes of the sample with holes. Mandrel. (2) The slit position of the extrusion strengthening tool during hole extrusion strengthening. In Document 2, the slit positions of the slotted bushings used in the two extrusion strengthenings are aligned, so that the ridges on the wall of the sample hole still exist after two extrusion strengthenings, while in this application document, the sample with holes When carrying out the second slotted mandrel hole extrusion strengthening, the slotted mandrel is rotated at an angle of 10-30°, which can eliminate the ridge formed on the hole wall of the sample with holes during the first extrusion strengthening of the slotted mandrel. (3) The structure of the extrusion mandrel is different. In Document 2, the mandrel used for the second extrusion strengthening is a solid mandrel, and the solid mandrel contains two extruded parts, the first extruded part and the second extruded part, and the diameter of the first extruded part is larger than The diameter of the second extrusion part, the extrusion mandrel used in this application document is a slotted mandrel, the extrusion strengthening part of the extrusion mandrel is provided with a slit, and the sample with a hole can realize unilateral extrusion strengthening, and the opening The structure of the slotted mandrel is composed of a connecting section, a guide section, a front cone section, a working ring, and a rear cone section, among which the front cone section, the working ring, and the rear cone section are the extrusion strengthening parts of the slotted mandrel, and the slotted mandrel The same slotted mandrel is used for the double extrusion strengthening of the rod. (4) The two extrusion strengthening forms of the sample with holes are different. In document 2, the slotted bush is inserted into the assembly hole from one end of the assembly hole, the extrusion tooling device drives the extrusion mandrel to shrink, and the first extrusion part on the extrusion mandrel shrinks backward to extrude the slotted bush , after the first extruding part pulls out the slotted bushing completely, complete the first extrusion, take out the slotted bushing from the assembly hole, replace a new slotted bushing and fit it on the extruded mandrel, put the new one The slotted bush is inserted into the assembly hole from the other end of the assembly hole, and the slotted position of the new slotted bush is aligned with the slotted position of the slotted bush used for the first extrusion, and the extrusion tooling device drives The extrusion mandrel shrinks, and the first extruding part on the extruding mandrel shrinks backward to extrude the slotted bushing. After the first extruding part is completely drawn out of the slotted bushing, the second extrusion is completed. In this application document, the front of the slotted mandrel passes through the auxiliary plate and the sample with holes, and the slotted mandrel inserted into the support rod is pulled out at a uniform speed to complete the first hole extrusion strengthening of the sample with holes. The sample is turned 180°, and the extrusion end of the first hole of the slotted mandrel to strengthen the wall of the sample hole is used as the extrusion end of the second hole of the slotted mandrel to extrude the wall of the reinforced sample hole, and the slotted core The extrusion end of the hole wall of the rod for the first hole extrusion strengthening sample is used as the extrusion end of the second hole extrusion strengthening sample hole wall of the slotted mandrel, and the slotted mandrel is rotated by 10° to 30°. The force is applied to the extrusion strengthening part of the slotted mandrel, so that the slot of the extrusion strengthening part of the slotted mandrel shrinks, and the slotted mandrel can pass through the auxiliary plate and the first hole extrusion strengthening test of the slotted mandrel. In this way, a support rod is inserted into the slotted mandrel, and the slotted mandrel inserted into the support rod is pulled out at a uniform speed, and the sample with holes completes the second hole extrusion strengthening of the slotted mandrel.

In summary, slotted bushings and solid mandrels are widely used in hole extrusion strengthening technology. However, the wall of slotted bushings is thin, and large plastic deformation is prone to occur in the process of hole extrusion strengthening, resulting in the failure of slotted bushings. Repeated use will seriously affect the cost of the extrusion strengthening process of the slotted mandrel hole, and the diameter of the extrusion strengthening part of the solid mandrel is larger than the diameter of the initial hole of the sample with holes, resulting in limitations in the application range of the extrusion strengthening process of the solid mandrel hole . Combining the slotted bushing and the solid mandrel, the hole extrusion strengthening process of the slotted mandrel can solve the existing problems of the slotted bushing and the solid mandrel. However, the slotted mandrel is used to squeeze and strengthen the sample with a hole once. After the hole is squeezed and strengthened, the extrusion force on the extrusion end, the middle layer, and the extrusion end of the sample hole wall is different, and the sample hole wall occurs. The degree of plastic deformation of the sample with holes is different, resulting in the formation of non-uniform residual compressive stress on the wall of the sample hole after the hole is squeezed and strengthened. For this reason, the present invention proposes a slotted mandrel extrusion strengthening process to improve the uniformity of the residual stress around the hole, aiming at forming a uniform residual pressure on the hole wall of the sample with holes after two times of extrusion strengthening of the slotted mandrel. Stress, improve the fatigue performance of the sample with holes.

Contents of the invention

In view of the above-mentioned process of using the slotted bushing to squeeze the holed sample to strengthen the hole, the extrusion mandrel squeezes the slotted bushing, and the slotted bushing elastically deforms and squeezes the wall of the holed sample. Due to the thin wall of the slotted bushing, the slotted bushing is prone to large plastic deformation during the hole extrusion strengthening process, so that the slotted bushing cannot be strengthened by secondary extrusion, which increases the process cost. If a solid mandrel is used to carry out hole extrusion strengthening on the sample with holes, the diameter of the working ring of the solid mandrel is larger than the diameter of the initial hole of the sample with holes, and the solid mandrel passes through the sample with holes from the extrusion strengthening part of the mandrel, that is, it cannot The realization of unilateral extrusion strengthening of the sample with holes leads to the fact that the solid mandrel cannot be used for extrusion strengthening of large samples with holes, and there are technological limitations.

Based on slotted bushing and solid mandrel, a slotted mandrel hole extrusion strengthening process is proposed. There is a slit in the extrusion strengthening part of the slotted mandrel. Before the hole extrusion strengthening, a force is applied to the extrusion strengthening part of the slotted mandrel. The slot in the extrusion strengthening part of the slotted mandrel shrinks, and the working ring of the slotted mandrel The diameter is smaller than the diameter of the initial hole of the sample, and the slotted mandrel can pass through the sample with a hole from the extrusion strengthening part to realize the unilateral extrusion strengthening of the sample with a hole. During the extrusion strengthening process of the slotted mandrel hole, the extrusion end and extrusion end of the sample hole wall are not constrained to be free ends, the middle layer of the hole wall is constrained by the extrusion end and extrusion end, and the extrusion force borne by the middle layer of the hole wall is The pressure is greater than the extrusion end and the extrusion end, and the slotted mandrel moves axially and reversely along the hole wall of the sample hole, and the material of the hole wall is subjected to the extrusion force to produce metal flow along the axial direction of the sample hole wall , resulting in a small amount of extrusion at the inlet end of the sample hole wall, and a large extrusion amount at the extrusion end of the sample hole wall. Therefore, the plastic deformation degree of the middle layer of the hole wall > the plastic deformation degree of the extrusion end of the hole wall > the plastic deformation degree of the extrusion end of the hole wall, resulting in the residual compressive stress of the middle layer of the hole wall > the residual compressive stress of the hole wall extrusion end > the hole wall Residual compressive stress at the extrusion end. Aiming at the inhomogeneous residual compressive stress formed on the hole wall of the sample with holes after extrusion strengthening of the slotted mandrel hole, the present invention proposes a slotted mandrel extrusion strengthening process to improve the uniformity of the residual stress around the hole. The invention carries out two times of hole extrusion strengthening in opposite directions to the sample with holes, the degree of plastic deformation of the sample hole wall at the extrusion end and the extrusion end is relatively uniform, and the residual compressive stress formed on the hole wall is relatively uniform, so that the test with holes can be improved. Such fatigue performance.

Technical solution: In order to realize the above invention object, the present invention adopts the following technical solutions:

The slotted mandrel extrusion strengthening process to improve the uniformity of the residual stress around the hole includes the following steps:

(1) Install the sample with holes. There is a slit in the extrusion strengthening section of the slotted mandrel, and force is applied to the extrusion strengthening section of the slotted mandrel before the hole extrusion strengthening, the slit of the extrusion strengthening section of the slotted mandrel shrinks, and the diameter of the working ring of the slotted mandrel Smaller than the diameter of the initial hole of the sample with a hole, the slotted mandrel can pass through the auxiliary plate and the sample with a hole in sequence from the extrusion strengthening section, and the auxiliary plate and the sample with a hole are placed in the guide section of the slotted mandrel, and the test piece with a hole During the sample installation process, the slotted mandrel does not squeeze and strengthen the sample hole wall;

(2) Install the support rod. When the slotted mandrel passes through the auxiliary plate and the same side of the sample with holes in turn, a support rod is inserted into the slotted mandrel. With the support function of the support rod, the slotted mandrel extrudes the strengthening section without shrinkage, and the slotted mandrel does not shrink. The diameter of the working ring of the rod is greater than the diameter of the initial hole of the sample with holes;

(3) One-time hole extrusion strengthening of the sample with holes. Pull out the slotted mandrel inserted into the support rod from the sample with holes at a uniform speed, the slotted mandrel is in direct contact with the hole wall of the sample with holes, the slotted mandrel squeezes and strengthens the hole wall of the sample, and the material of the hole wall becomes elastic-plastic Deformation, the hole wall forms beneficial residual compressive stress, and completes the primary extrusion strengthening of the sample with holes;

(4) Slotted mandrel is extruded twice to strengthen. Due to the slits in the extrusion strengthening section of the slotted mandrel, the hole wall of the sample hole after extrusion strengthening of the slotted mandrel forms a ridge, which affects the quality of the sample hole wall, and the root of the ridge is prone to fatigue cracks. Therefore, the slotted mandrel hole needs to be reamed after extrusion strengthening. However, during the extrusion strengthening process of the slotted mandrel hole, the intrusion end and extrusion end of the sample with holes are not constrained to be free ends, the middle layer of the sample hole wall is constrained by the intrusion end and extrusion end, and the middle layer of the sample The extrusion force received is greater than the extrusion end and extrusion end of the hole wall. During the movement of the slotted mandrel along the axial direction of the sample with holes, the metal flow of the hole wall material along the axial direction will cause the actual deformation of the hole wall extrusion end. If the extrusion amount is small and the actual extrusion amount at the extrusion end of the hole wall is large, then the residual compressive stress formed at the extrusion end of the sample hole wall after the extrusion strengthening of the slotted mandrel hole is smaller than the residual compressive stress formed at the extrusion end of the sample hole wall Stress <The residual compressive stress formed by the middle layer of the sample hole wall. Therefore, the perforated sample is extruded twice to strengthen the sample with a slotted mandrel to increase the degree of plastic deformation of the hole wall material of the holed sample and increase the residual compressive stress of the hole wall of the holed sample.

The "twice extrusion strengthening of the slotted mandrel" is one extrusion strengthening of the slotted mandrel + two times of extrusion strengthening of the slotted mandrel rotating at a certain angle in different directions, and the "rotating at a certain angle" is the The sewing mandrel rotates 10°～30°.

The above-mentioned "slotted mandrel double-hole extrusion strengthening process" is preferred:

(1) Scheme:

Scheme 1: Slotted mandrel double extrusion strengthening in the same direction, wherein the direction of the second hole extrusion strengthening is the same as that of the first hole extrusion strengthening.

Scheme 2: The slotted mandrel is strengthened by double extrusion in different directions, wherein the direction of the second hole extrusion strengthening is opposite to that of the first hole extrusion strengthening.

Scheme 3: Slotted mandrel one-time extrusion strengthening + slotted mandrel rotation at a certain angle and two extrusion strengthenings in the same direction, based on scheme 1, the slotted mandrel is slit when the second hole extrusion is strengthened The mandrel rotates at a certain angle.

Scheme 4: Slotted mandrel one-time extrusion strengthening + slotted mandrel rotated at a certain angle and two extrusions in different directions to strengthen, it is based on scheme 3, when the slotted mandrel performs the second hole extrusion strengthening The mandrel rotates at a certain angle.

Among them, the "rotation by a certain angle" in scheme 3 and scheme 4 refers to "rotation of the slotted mandrel by 10° to 30°".

(2) Results and conclusion analysis:

Among them, scheme 1 (slotted mandrel double extrusion strengthening in the same direction) cannot eliminate the ridges formed on the hole wall after one extrusion strengthening, and will increase the height of the ridges formed on the hole wall, because the hole wall has been strengthened twice Extrusion strengthening, the degree of plastic deformation of the hole wall material after extrusion strengthening is greater than that of the slotted mandrel for one-time extrusion strengthening, and the residual compressive stress formed by the hole wall is greater than that of the slotted mandrel for one-time extrusion strengthening.

Scheme 2 (slotted mandrel double extrusion strengthening), the extrusion end (extrusion end) of the hole wall of the first hole extrusion strengthening sample is the extrusion end of the second hole extrusion strengthening sample (extrusion end), this scheme cannot eliminate the ridge formed by one-time extrusion of the slotted mandrel to strengthen the hole wall, and increase the height of the ridge formed by the hole wall. Since the hole wall has been extruded twice, after extrusion The degree of plastic deformation of the hole wall material is greater than that of the slotted mandrel for one-time extrusion strengthening, and the residual compressive stress formed by the hole wall is greater than that of the slotted mandrel for one-time extrusion strengthening. The residual compressive stress formed by the wall is relatively uniform.

Scheme 3 (one-time extrusion strengthening of the slotted mandrel + two times of extrusion strengthening of the slotted mandrel in the same direction at a certain angle), the second hole extrusion strengthening can eliminate the hole wall formed by the first extrusion strengthening of the slotted mandrel The raised ridge increases the degree of plastic deformation of the hole wall material of the sample. The degree of plastic deformation of the hole wall material after the hole extrusion strengthening is greater than that of the open mandrel for one-time extrusion strengthening, and the residual compressive stress formed by the hole wall is greater than that of the slotted mandrel for one-time extrusion. strengthen.

Scheme 4 (one-time extrusion strengthening of the slotted mandrel + two times of extrusion strengthening of the slotted mandrel in different directions at a certain angle), the second hole extrusion strengthening can eliminate the hole wall formed by the first extrusion strengthening of the slotted mandrel The raised ridge increases the degree of plastic deformation of the hole wall material of the sample. The degree of plastic deformation of the hole wall material after the hole extrusion strengthening is greater than that of the open mandrel for one-time extrusion strengthening, and the residual compressive stress formed by the hole wall is greater than that of the slotted mandrel for one-time extrusion. Strengthening, the direction of the two times of extrusion strengthening of the sample with holes is opposite, and the residual stress formed on the wall of the sample hole after hole extrusion strengthening is relatively uniform.

On the whole, plan 3 "slotted mandrel one-time extrusion strengthening + slotted mandrel rotation at a certain angle twice extrusion strengthening in the same direction" and plan 4 "slotted mandrel one-time extrusion strengthening + slotted mandrel rotation certain Double extrusion strengthening with different angles", the hole extrusion strengthening effect of the two processes is significantly better than that of scheme 1 "double extrusion strengthening with slotted mandrel in the same direction" and scheme 2 "double extrusion strengthening with slotted mandrel in different directions" ". Among them, after scheme 4 extrusion strengthening, the residual stress formed by the extrusion end of the sample hole wall and the extrusion end hole wall is relatively uniform, and the hole extrusion strengthening effect is better than that of scheme 3. Because there is a slit in the extrusion strengthening part of the slotted mandrel, the wall of the sample hole forms a ridge after extrusion strengthening of the hole of the slotted mandrel. When performing the second extrusion strengthening on the sample with holes, the slotted mandrel is rotated From 10° to 30°, the second extrusion strengthening of the slotted mandrel can eliminate the ridge formed on the wall of the sample hole after the first extrusion strengthening of the slotted mandrel.

(5) Reaming processing. After the slotted mandrel is strengthened by extrusion twice, it is necessary to ream the sample after extrusion strengthening, so that the diameter of the sample hole reaches the diameter of the final hole.

Beneficial effects The slotted mandrel extrusion strengthening process of the present invention improves the uniformity of the residual stress around the hole, and has the following advantages:

1. The residual stress of the hole wall is uniform. After the first extrusion of the slotted mandrel, the sample is turned over 180°, and the extrusion end (extrusion end) of the sample is strengthened by the first hole extrusion of the slotted mandrel and the second hole extrusion of the open mandrel. The extruded end (intruded end) of the strengthened sample is interchanged, the direction of the two hole extrusion strengthening is opposite, and the residual compressive stress formed on the hole wall is more uniform.

2. Before the second extrusion strengthening of the slotted mandrel, rotate the slotted mandrel (clockwise or counterclockwise) by 10°~30°, the hole extrusion strengthening effect is the best. After the hole is strengthened by extrusion, the degree of plastic deformation of the hole wall of the sample with holes is more uniform at the extrusion end and the extrusion end.

3. Slotted mandrel The same slotted mandrel is used for the two hole extrusion strengthening, and there is no need to replace the extrusion strengthening tool. There is a slit in the slotted mandrel, and the wall of the sample hole forms a convex ridge after extrusion strengthening of the sample hole with a hole; The extrusion force at the exit end position is different, and the hole wall of the sample after hole extrusion strengthening is uneven; there are processing errors in the processing of the slotted mandrel. Three reasons cause the hole diameter of the slotted mandrel hole to be smaller than The final hole diameter of the specimen. The second extrusion strengthening of the perforated sample was carried out using the same slotted mandrel to complete the two extrusion strengthening of the perforated sample. The two-time hole extrusion strengthening of the slotted mandrel does not need to replace or add hole extrusion strengthening tools, so that the cost of the hole extrusion strengthening process of the slotted mandrel can be saved.

Description of drawings

Fig. 1 is the strengthening process of one-time hole extrusion of slotted mandrel. (a) Extrude the extrusion strengthening section of the slotted mandrel so that the diameter of the extrusion strengthening section of the slotted mandrel is smaller than the diameter of the initial hole of the sample with holes; (b) The front of the slotted mandrel passes through the auxiliary plate, belt Hole sample; (c) Insert the support rod into the slotted mandrel; (d) Pull out the slotted mandrel inserted into the support rod at a uniform speed.

Fig. 2 is a schematic diagram of the slotted mandrel double extrusion in the same direction (Scheme 1);

Fig. 3 is a schematic diagram of the slotted mandrel double extrusion strengthening (Scheme 2);

Figure 4 is a schematic diagram of one-time extrusion strengthening of the slotted mandrel + double extrusion strengthening of the slotted mandrel at a certain angle in the same direction (Scheme 3). (a) Slotted mandrel primary extrusion strengthening; (b) Slotted mandrel rotated at a certain angle for the second co-extrusion strengthening.

Figure 5 is a schematic diagram of one-time extrusion strengthening of the slotted mandrel + double extrusion strengthening of the open mandrel rotating at a certain angle in different directions (Scheme 4). (a)-(d) are the one-time extrusion strengthening process of the slotted mandrel; (e) the sample is turned 180° after the first extrusion strengthening of the slotted mandrel; (f) the rotation of the slotted mandrel at a certain angle The second anisotropic extrusion strengthening.

Figure 6 shows the distribution of residual stress at the extrusion end of the hole wall of the slotted mandrel hole extrusion strengthened sample.

Curve 1 is the one-time extrusion strengthening of the slotted mandrel;

Curve 2 is the one-time extrusion strengthening of the slotted mandrel + the double extrusion strengthening of the slotted mandrel rotating at a certain angle in the same direction (Scheme 3);

Curve 3 is the one-time extrusion strengthening of the slotted mandrel + the double-extrusion strengthening of the open mandrel rotating at a certain angle in different directions (Scheme 4).

Figure 7 shows the distribution of residual stress in the middle layer of the hole wall of the slotted mandrel hole extrusion strengthened sample.

Curve 1 is the one-time extrusion strengthening of the slotted mandrel;

Curve 2 is the one-time extrusion strengthening of the slotted mandrel + the double extrusion strengthening of the slotted mandrel rotating at a certain angle in the same direction (Scheme 3);

Curve 3 is the one-time extrusion strengthening of the slotted mandrel + the double-extrusion strengthening of the open mandrel rotating at a certain angle in different directions (Scheme 4).

Figure 8 shows the distribution of residual stress at the extrusion end of the hole wall of the slotted mandrel hole extrusion strengthened sample.

Curve 1 is the one-time extrusion strengthening of the slotted mandrel;

Curve 2 is the one-time extrusion strengthening of the slotted mandrel + the double extrusion strengthening of the slotted mandrel rotating at a certain angle in the same direction (Scheme 3);

Curve 3 is the one-time extrusion strengthening of the slotted mandrel + the double-extrusion strengthening of the open mandrel rotating at a certain angle in different directions (Scheme 4).

Among them, 1-connection section; 2-guiding section; 3-front cone section; 4-working ring; 5-back cone section; 6-auxiliary plate; 7-sample with hole; 8-support rod; 9-slit 1st-extrusion strengthened sample of mandrel; 10-sample strengthened by second extrusion of slotted mandrel in the same direction; 11-sample turned 180° after first extrusion strengthening of slotted mandrel; 12-slotted core 13-The middle layer of the sample hole wall after the first extrusion strengthening of the slotted mandrel; 14-The test piece after the first extrusion strengthening of the slotted mandrel Extrusion end of sample hole wall.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments.

Example 1 Slotted Mandrel Hole Extrusion Strengthening Process

Fig. 1 is the strengthening process of one-time hole extrusion of slotted mandrel. Including the following steps:

(1) Install the sample with holes. Slotted mandrel extrusion strengthening section (including: front cone section 3, working ring 4, rear cone section 5) has a slot, if force is applied to the slotted mandrel extrusion strengthening section before hole extrusion strengthening, the slotting will occur Contraction, the diameter of the working ring 4 is smaller than the diameter of the initial hole of the sample with holes 7, and the slotted mandrel passes through the auxiliary plate 6 and the sample with holes 7 sequentially from the extrusion strengthening section. The auxiliary plate 6 and the sample with holes 7 are placed in the guide section 2 of the slotted mandrel, and the slotted mandrel does not squeeze and strengthen the wall of the sample hole during the installation of the sample with holes 7 .

(2) Install the support rod. Insert the support rod-8 into the slotted mandrel from the end far away from the sample. Under the support of the support rod 8, the extrusion strengthening section of the slotted mandrel does not shrink, and the diameter of the working ring 4 is larger than that of the sample with holes 7. hole diameter.

(3) One-time hole extrusion strengthening of the sample with holes. The slotted mandrel inserted into the support rod 8 is pulled out at a uniform speed from the sample with holes 7, and the slotted mandrel is in direct contact with the hole wall of the sample with holes 7, and the slotted mandrel squeezes and strengthens the hole wall of the sample, and the material of the hole wall Elastic-plastic deformation occurs, and beneficial residual compressive stress is formed on the hole wall, and the primary extrusion strengthening of the sample with holes is completed.

Example 2 Slotted mandrel double-hole extrusion strengthening process

1. Program settings:

Scheme 1: Slotted mandrel double extrusion strengthening in the same direction, wherein the direction of the second hole extrusion strengthening is the same as that of the first hole extrusion strengthening.

Scheme 2: The slotted mandrel is strengthened by double extrusion in different directions, wherein the direction of the second hole extrusion strengthening is opposite to that of the first hole extrusion strengthening.

Scheme 3: Slotted mandrel one-time extrusion strengthening + slotted mandrel rotation at a certain angle and two extrusion strengthenings in the same direction, based on scheme 1, the slotted mandrel is slit when the second hole extrusion is strengthened The mandrel rotates at a certain angle.

Scheme 4: Slotted mandrel one-time extrusion strengthening + slotted mandrel rotated at a certain angle and two extrusions in different directions to strengthen, it is based on scheme 3, when the slotted mandrel performs the second hole extrusion strengthening The mandrel rotates at a certain angle.

Among them, the "rotation by a certain angle" in scheme 3 and scheme 4 refers to "rotation of the slotted mandrel by 10° to 30°".

2. Implementation process:

Fig. 2 is a schematic diagram of double-extrusion strengthening of a slotted mandrel in the same direction. After the first extrusion strengthening of the sample 7 with holes was completed according to Example 1, the same process was repeated once to realize double extrusion strengthening of the slotted mandrel of the sample 7 with holes in the same direction.

Fig. 3 is a schematic diagram of double-extrusion strengthening of a slotted mandrel. After completing the primary extrusion strengthening of the perforated sample 7 according to Example 1, the obtained perforated sample is turned over 180°, and the intruded end of the slotted mandrel for the first time extruded and strengthened sample hole wall is used as the extruded end , take the extrusion end as the extrusion end, repeat the hole extrusion strengthening process of Example 1, and realize the slotted mandrel of sample 7 with holes in different direction twice extrusion strengthening.

Fig. 4 is a schematic diagram of one-time extrusion strengthening of the slotted mandrel + double extrusion strengthening of the slotted mandrel rotating at a certain angle in the same direction. After completing the primary extrusion strengthening of sample 7 with holes according to Example 1, rotate the slotted mandrel at a certain angle, repeat the process of Example 1, and realize the primary extrusion strengthening + slotting of the slotted mandrel of sample 7 with holes The mandrel is rotated at a certain angle and extruded twice in the same direction for strengthening.

Figure 5 shows the one-time extrusion strengthening of the slotted mandrel + the double-extrusion strengthening of the open mandrel rotating at a certain angle in different directions. According to Example 1, after the primary extrusion strengthening of the perforated sample 7 is completed, the obtained perforated sample is turned over 180°, the extrusion end of the sample is used as the extrusion end, and the extrusion end is used as the extrusion end. The mandrel is rotated at a certain angle, and the process of Example 1 is repeated, so that the slotted mandrel of sample 7 with a hole can be strengthened by one extrusion + the open mandrel rotated at a certain angle and twice extruded in different directions.

3. Result description and analysis

Among them, in Scheme 1 and Scheme 2, the second hole extrusion strengthening of the slotted mandrel cannot eliminate the ridge formed on the hole wall during the first hole extrusion strengthening process of the slotted mandrel, and the second hole of the slotted mandrel After the extrusion strengthening, the height of the ridge formed on the hole wall after the first hole extrusion strengthening of the slotted mandrel is increased. Therefore, using the finite element simulation analysis method to compare the hole extrusion strengthening effect of Scheme 3 and Scheme 4, the double hole extrusion strengthening process method of the slotted mandrel with the best hole extrusion strengthening effect is selected.

1. By establishing a three-dimensional finite element simulation analysis model for two-hole extrusion strengthening of the slotted mandrel, extract the tangential residual stress at the extrusion end, middle layer, and extrusion end of the hole wall of the sample with holes. The variation law of the residual stress of the hole wall of the hole-strengthened sample with the slotted mandrel double-hole extrusion is shown in Fig. 6.

The hole wall of the sample is squeezed into the end, and the residual compressive stress formed by the hole wall of scheme 4 is greater than that of scheme 3;

In the middle layer of the sample hole wall, the residual compressive stress formed by schemes 3 and 4 is similar;

At the extrusion end of the sample hole wall, the residual compressive stress formed on the hole wall of Scheme 3 is greater than that of Scheme 4.

The residual compressive stress formed at the extrusion end of the hole wall in scheme 4 is closer to that at the extrusion end.

The residual compressive stress formed by the hole wall of Scheme 3 is greater than that of the slotted mandrel after one extrusion strengthening.

2. Scheme 1 "Slotted mandrel double extrusion strengthening in the same direction", the extrusion strengthening direction of the sample with holes is the same, and the hole wall material flows along the axial direction during the extrusion strengthening process of the slotted mandrel hole, The actual extrusion amount at the extrusion end of the sample hole wall is reduced, and the actual extrusion amount at the extrusion end of the sample hole wall is increased, resulting in residual The compressive stress is greater than that of the extrusion end.

Scheme 2 "Slotted Mandrel Double Extrusion Strengthening", the extrusion strengthening direction of the sample with a hole is opposite, and the metal flow of the hole wall material along the axial direction occurs during the extrusion strengthening process of the slotted mandrel hole. The metal flow of the mandrel’s first hole extrusion strengthening hole wall material flows from the sample hole wall extrusion end to the hole wall extrusion end. The intrusion end of the slotted mandrel for the first extrusion strengthening of the sample hole wall is the extrusion end of the slotted mandrel for the second extrusion strengthening of the sample hole, and the slotted mandrel for the first time extrusion strengthening of the sample hole wall The extrusion end is the extrusion end of the second extrusion of the slotted mandrel to strengthen the hole wall of the sample. The metal flow of the second hole extrusion of the slotted mandrel to strengthen the hole wall material flows from the extrusion end of the sample hole wall to the extrusion end. At the entry end, the degree of plastic deformation at the entry end and the extrusion end of the sample hole wall is relatively uniform after the double hole extrusion strengthening of the slotted mandrel in different directions, and the residual compressive stress formed at the entry end and extrusion end of the hole wall is relatively uniform.

Scheme 3 "Slotted Mandrel Double Extrusion Strengthening in the Same Direction", Scheme 4 "Slotted Mandrel Double Extrusion Strengthening in Different Directions", the slotted mandrel carried out two extrusion strengthening on the sample with holes, and Rotate the slotted mandrel at a certain angle during the second hole extrusion strengthening of the slotted mandrel, eliminating the ridges formed on the hole wall during the first hole extrusion strengthening of the slotted mandrel, and the sample with holes passed through twice The degree of plastic deformation of the hole wall material after extrusion strengthening is greater than that of the slotted mandrel for one-time extrusion strengthening, resulting in the residual compressive stress formed on the hole wall of the sample with holes after two times of extrusion strengthening is greater than that of the slotted mandrel for one-time extrusion strengthening . When the slotted mandrel is subjected to the second extrusion strengthening, the slotted mandrel needs to be rotated by 10° to 30°. Due to the existence of slits in the slotted mandrel, the hole wall of the sample hole forms a convex ridge after the hole extrusion strengthening of the slotted mandrel. The positions and directions of the slotted mandrels are the same, and the ridge formed on the hole wall after the second extrusion strengthening of the slotted mandrel does not disappear, and the height of the ridge is higher than the ridge formed on the sample hole wall after the first hole extrusion strengthening high. Rotate the slotted mandrel 10° to 30° during the second hole extrusion strengthening of the slotted mandrel, the second hole extrusion strengthening of the slotted mandrel can eliminate the holes after the first hole extrusion strengthening of the slotted mandrel The ridge formed by the wall. If the angle of rotation of the slotted mandrel is too small or too large when the slotted mandrel is strengthened by hole extrusion for the second time, the ridges formed on the hole wall after the first hole extrusion strengthening of the slotted mandrel cannot be eliminated.

In summary, scheme 4 has the best hole extrusion strengthening effect, that is, after the first slotted mandrel hole extrusion strengthening of the sample with holes, due to the existence of slots in the slotted mandrel, the hole extrusion of the slotted mandrel After strengthening, the hole wall of the sample forms a ridge. Then the sample is turned 180°, so that the extrusion end of the slotted mandrel for the first hole extrusion strengthening sample is used as the extrusion end of the slotted mandrel for the second hole extrusion strengthening sample, and the slotted mandrel for the second hole extrusion strengthening sample extrusion end. The extrusion end of the first hole extrusion strengthening sample is used as the extrusion end of the second hole extrusion strengthening sample of the slotted mandrel, and the slotted mandrel is rotated by 10° to 30°, and the slotted mandrel is The second extrusion strengthening improves the uniformity of residual stress around the hole.

Claims (6)

1. The slotted core rod extrusion strengthening process for improving the residual stress homogenization degree around the hole is characterized by comprising the following steps of:

(1) And (3) mounting the sample with the hole: the slotting core rod extrusion strengthening section is provided with a slot, force is applied to the slotting core rod extrusion strengthening section before hole extrusion strengthening, the slot of the slotting core rod extrusion strengthening section shrinks, the diameter of a working ring of the slotting core rod is smaller than the diameter of an initial hole of a sample with holes, after the slotting core rod sequentially penetrates through an auxiliary plate and the sample with holes from the extrusion strengthening section, the auxiliary plate and the sample with holes are placed on a slotting core rod guide section, and the slotting core rod does not extrude and strengthen the hole wall of the sample in the installation process of the sample with holes;

(2) Installing a support rod: inserting a supporting rod into the slotted core rod from one end far away from the sample, wherein under the supporting action of the supporting rod, the extrusion strengthening section of the slotted core rod does not shrink, and the diameter of a working ring of the slotted core rod is larger than the diameter of an initial hole of the sample with the hole;

(3) Primary hole extrusion strengthening of a sample with holes: pulling out the slotted core rod inserted into the support rod from the sample with the holes at a constant speed, wherein the slotted core rod is directly contacted with the hole wall of the sample with the holes, the slotted core rod extrudes and reinforces the hole wall of the sample, the hole wall material generates elastic-plastic deformation, and the hole wall forms beneficial residual compressive stress, so that the primary extrusion reinforcement of the sample with the holes is completed;

(4) And (3) carrying out twice extrusion strengthening on the slotted core rod: the two-time extrusion strengthening is selected from any one of the following schemes:

scheme 1: extruding and reinforcing the slotted core rod twice in the same direction, wherein the direction of extruding and reinforcing the second time hole is the same as that of extruding and reinforcing the first time hole;

scheme 2: performing extrusion strengthening on the slotted core rod twice in different directions, wherein the direction of the second hole extrusion strengthening is opposite to that of the first hole extrusion strengthening;

scheme 3: after the slotted core rod is subjected to primary extrusion strengthening, the slotted core rod rotates for a certain angle and is subjected to extrusion strengthening twice in the same direction, and the slotted core rod rotates for a certain angle when the slotted core rod is subjected to secondary hole extrusion strengthening on the basis of the scheme 1;

scheme 4: after the slotted core rod is subjected to primary extrusion strengthening, the slotted core rod rotates by a certain angle and is subjected to anisotropic extrusion strengthening twice, wherein on the basis of the scheme 3, the slotted core rod rotates by a certain angle when the slotted core rod is subjected to secondary hole extrusion strengthening;

(6) Reaming: and reaming the sample after extrusion strengthening to ensure that the aperture of the sample reaches the diameter of a final hole.

2. The extrusion strengthening process of the slotted core rod for improving the uniformity of the residual stress around the hole according to claim 1, wherein the extrusion strengthening process comprises the following steps: the two-time extrusion strengthening adopts a scheme 4, after the once extrusion strengthening of the slotted core rod, the slotted core rod rotates a certain angle to perform the two-time extrusion strengthening in different directions, when the first extrusion strengthening of the sample with holes is performed, the slotted core rod moves along the hole wall of the sample in the axial direction, when the second hole extrusion strengthening of the sample with holes is performed, the sample is turned over by 180 degrees, the extrusion end of the first hole extrusion strengthening sample of the slotted core rod is used as the extrusion end of the second hole extrusion strengthening sample of the slotted core rod, and the slotted core rod moves along the hole wall of the sample in the axial direction;

the perforated sample is extruded and reinforced twice, and the slotting core rod has the same axial movement direction along the perforated sample.

3. The extrusion strengthening process of the slotted core rod for improving the uniformity of the residual stress around the hole according to claim 1, wherein the extrusion strengthening process comprises the following steps: the same slotted core rod is adopted for the twice extrusion strengthening of the slotted core rod.

4. The extrusion strengthening process of the slotted core rod for improving the uniformity of the residual stress around the hole according to claim 1, wherein the extrusion strengthening process comprises the following steps: the diameters of the slotted core rod working rings used in the two-time hole extrusion strengthening are consistent.

5. The slotted core rod extrusion strengthening process for improving the uniformity degree of the residual stress around the hole according to claim 1, is characterized in that: when the slotted core rod is subjected to secondary extrusion strengthening in the schemes 3 and 4, the rotation of the slotted core rod by a certain angle means that the slotted core rod rotates by 10-30 degrees, because the slotted core rod has a slot, the hole wall of the sample after the slotted core rod hole is subjected to extrusion strengthening forms a convex ridge, if the slotted core rod is subjected to secondary hole extrusion strengthening and the position and the direction of the slotted core rod are the same as those of the slotted core rod during the primary hole extrusion strengthening, the convex ridge formed on the hole wall after the slotted core rod is subjected to secondary extrusion strengthening does not disappear, and the height of the convex ridge is greater than that formed on the hole wall of the sample after the primary hole extrusion strengthening;

rotating the slotted core rod by 10-30 degrees during second hole extrusion strengthening, wherein the second hole extrusion strengthening of the slotted core rod can eliminate the convex ridge formed on the hole wall after the first hole extrusion strengthening of the slotted core rod;

if the rotation angle of the slotted core rod is too small or too large when the slotted core rod is subjected to secondary hole extrusion strengthening, the convex ridge formed on the hole wall after the slotted core rod is subjected to primary hole extrusion strengthening cannot be eliminated.

6. The extrusion strengthening process of the slotted core rod for improving the uniformity of the residual stress around the hole according to claim 4, wherein the extrusion strengthening process comprises the following steps: the rotation is either counter-clockwise or clockwise.

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