CN118558739A - A three-roller cross-rolling forming method for hollow shafts of equal wall thickness based on mandrel control - Google Patents

Abstract

The invention discloses a three-roller oblique rolling forming method of hollow shaft parts with equal wall thickness based on core rod control, which is characterized in that rollers of a three-roller oblique rolling machine are set to be drum-shaped, and the shapes of the rollers are optimized so that the rollers are in line contact with rolled parts at any time under a rectangular coordinate system of the rollers in the rolling process; the method has the advantages that the shape of the roller is optimally designed, so that the roller and a rolled piece are in line contact at any moment under a rectangular coordinate system of the roller in the rolling process, the finishing times and finishing time of the roller to the surface of a rolled piece forming area in the rolling process are increased, the spiral mark defect on the surface of the rolled piece is effectively reduced, the mechanical property of hollow shaft pieces is ensured, the machining allowance of subsequent machining is reduced, and the waste of materials is reduced.

Description

A three-roller cross-rolling forming method for hollow shafts of equal wall thickness based on mandrel control

Technical Field

The invention relates to the technical field of cross-rolling forming of hollow shafts, and in particular to a three-roll cross-rolling forming method for hollow shafts of equal wall thickness based on mandrel control.

Background Art

Since hollow axles can not only meet the strength requirements of axles, but also greatly reduce the unsprung weight of trains, and improve the stability and safety of EMU operation, hollow axles are generally used in train axles. At present, for the manufacturing and processing of hollow axles, some adopt solid axle billets for rolling and then drill the inner hole. Although this method has a simple process, it wastes a lot of materials and requires a large amount of subsequent cold processing; some directly roll the hollow billets into hollow axles through oblique rolling. Compared with the above methods, this method has significant material and energy saving effects. However, during the oblique rolling process, spiral marks will inevitably appear on the surface of the hollow shaft, which will reduce the mechanical properties of the hollow shaft, and at the same time increase the processing allowance of subsequent machining, wasting materials.

Summary of the invention

The technical problem to be solved by the present invention is to provide a three-roller oblique rolling forming method for equal-wall-thickness hollow shaft-like parts based on mandrel control, which can effectively control the spiral mark defects on the surface of the rolled parts.

The technical solution adopted by the present invention to solve the above technical problems is: a three-roller cross-rolling forming method for hollow shaft parts of equal wall thickness based on mandrel control, comprising the following specific steps:

(1) The rollers of the three-roller cross-rolling mill are drum-shaped, i.e., they include a front cone section, a cylindrical section and a rear cone section arranged in sequence;

(2) The relationship between the working generatrix of the roller is set as:

so that the roller and the workpiece are in line contact at any time in the roller rectangular coordinate system during the rolling process, wherein: R is the roller radius at section II on the roller perpendicular to the workpiece axis and intercepted through the intersection of the workpiece axis and the roller axis, _r0 is the outer radius of the workpiece cross section corresponding to section II, x is the distance from section xx on the roller to section II, section xx is a section on the roller perpendicular to the workpiece axis and parallel to section II, β is the roller deflection angle of the roller axis relative to the workpiece axis, _L1 is the length of the front cone section of the roller, _L2 is the length of the cylindrical section of the roller, _L3 is the length of the rear cone section of the roller, _α1 is the forming angle of the front cone section of the roller, _α3 is the forming angle of the rear cone section of the roller, and y is the roller radius at section xx on the roller;

(3) The tube billet is placed in a three-roller cross-rolling mill. During rolling, the rollers are controlled to rotate around their own axes and move radially toward the tube billet to roll the tube billet in the reduced diameter section. At the same time, the four-claw chuck clamps the tube billet and moves axially at a uniform speed. A mandrel with a conical head is inserted into the tube billet and the mandrel is controlled to move axially. The moving direction of the mandrel is opposite to that of the tube billet, and the gap between the conical surface of the front conical section of the roller and the conical surface of the mandrel remains unchanged during the diameter-reducing rolling process.

(4) After the diameter reduction section is rolled, the rollers are kept stationary in the radial direction, and the four-jaw chuck clamps the tube billet and continues to move at a uniform speed along the same axial direction at the same speed. At the same time, the mandrel is controlled to stop axial movement to roll the tube billet in a straight axial section;

(5) After the straight shaft section is rolled, the four-jaw chuck clamps the tube billet and continues to move at a uniform speed along the same axial direction at the same speed. The roller moves radially away from the tube billet to roll the tube billet in the diameter-increasing section. At the same time, the mandrel is controlled to move axially in the same direction as the tube billet. The gap between the conical surface of the front conical section of the roller and the conical surface of the mandrel remains unchanged during the diameter-increasing rolling process until the diameter-increasing section is rolled to obtain the finished product.

Furthermore, in step (3), the radial moving speed of the roller is set to v _r , the axial moving speed of the mandrel is set to v _x , and V _r =V _x tan α ₁ , so that the gap between the conical surface of the front conical section of the roller and the conical surface of the mandrel remains unchanged during the diameter reducing rolling process.

Furthermore, in the steps (4) and (5), the axial movement speed of the tube billet is equal to the axial movement speed of the tube billet in the step (3); in the step (5), the radial movement speed of the roller is equal to the radial movement speed of the roller in the step (3), which is v _r ; the axial movement speed of the mandrel in the step (5) is equal to the axial movement speed of the mandrel in the step (3), which is v _x , and V _r =V _x tan α ₁ , so that the gap between the conical surface of the front conical section of the roller and the conical surface of the mandrel remains unchanged during the diameter-increasing rolling process.

Furthermore, the cone angle of the mandrel head is less than or equal to the forming angle α ₁ of the front cone section of the roll, and the maximum diameter of the mandrel head is less than the initial inner diameter of the tube blank.

Compared with the prior art, the advantage of the present invention is that the method optimizes the shape of the roller, so that the roller and the workpiece are in line contact at any time in the roller rectangular coordinate system during the rolling process, increasing the number of times and time for the roller to finish the surface of the forming area of the workpiece during the rolling process, effectively reducing the spiral mark defects on the surface of the workpiece, ensuring the mechanical properties of hollow shaft parts, while also reducing the processing allowance of subsequent machining and reducing material waste. In addition, during the diameter reduction and diameter increase rolling process, by controlling the radial movement speed of the roller and the axial movement speed of the mandrel, the gap between the conical surface of the front cone section of the roller and the conical surface of the mandrel remains unchanged, so that the wall thickness of the hollow shaft parts obtained by rolling is uniform and equal, which is conducive to the precise forming of the inner and outer surfaces of hollow shaft parts with equal wall thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the coordination of the rolls, the workpiece, the four-jaw chuck and the mandrel in the rolling process of the present invention;

FIG2 is a schematic structural diagram of a roller according to the present invention;

FIG3 is a schematic structural diagram of a mandrel of the present invention;

FIG4 is a projection comparison diagram of the roll and the workpiece during the rolling process of the present invention;

Fig. 5 is a left side view of the section I-I in Fig. 4;

FIG6 is a schematic diagram of the rolling state of the reduced diameter section of the tube blank rolled piece of the present invention;

FIG7 is a schematic diagram of the rolling state of the straight shaft section of the tube blank rolled piece of the present invention;

FIG8 is a schematic diagram of the rolling state of the pipe blank rolled piece of the present invention at the diameter increasing section;

FIG9 is a right side projection diagram of the contact between the roller and the workpiece at different rolling stages of the present invention;

FIG10 is a diagram showing the effect of a rolled piece obtained by conventional disc roller rolling;

FIG. 11 is a diagram showing the effect of a rolled piece obtained by rolling with the optimized rollers of the present invention.

DETAILED DESCRIPTION

The present invention is further described in detail below with reference to the accompanying drawings.

As shown in the figure, a three-roller cross-rolling forming method for hollow shaft parts of equal wall thickness based on mandrel control includes the following specific steps:

(1) The roller 1 of the three-roller cross-rolling mill is drum-shaped, that is, it includes a front cone section 11, a cylindrical section 12 and a rear cone section 13 arranged in sequence;

(2) The relationship between the working generatrix of roller 1 is set as:

So that during the rolling process, at any time in the rectangular coordinate system of the roll, the roll 1 and the workpiece are in line contact. Specifically, a section II is cut on the roll 1 perpendicular to the axis of the workpiece and through the intersection of the axis of the workpiece and the axis of the roll, and a parallel section xx is cut on the roll 1 at a distance x from section II, as shown in Figure 4. The projections of the intersections of the two sections with the axis of the roll are O _I and O _x respectively in the left view, and the axis center of the workpiece is O. As shown in Figure 5, since the roll deflection angle is generally very small (±10°), the roll cross section can be approximated as a circle in the left view, but due to the existence of the roll deflection angle, the center of section xx moves from point O _I to point O _x in the left view; therefore, in the above relationship, R is the roll radius at section II on the roll, _r0 is the outer radius of the workpiece cross section corresponding to section II, x is the distance from section xx on the roll 1 to section II, β is the roll deflection angle of the roll axis relative to the workpiece axis, and L _L1 is the length of the front cone section 11 of the roller, _L2 is the length of the cylindrical section 12 of the roller, _L3 is the length of the rear cone section 13 of the roller, _α1 is the forming angle of the front cone section 11 of the roller, _α3 is the forming angle of the rear cone section 13 of the roller, and y is the roller radius at the section xx on the roller;

(3) Put the tube blank 2 into the three-roller cross-rolling mill. During rolling, the roller 1 is controlled to rotate around its own axis, and the speed of the roller 1 remains unchanged during the entire rolling process. The roller 1 moves radially at a speed v _r in the direction close to the tube blank 2 to roll the tube blank 2 in the diameter-reducing section. At the same time, the four-jaw chuck 3 clamps the tube blank 2 and moves axially at a uniform speed. The mandrel 4 with a conical head is inserted into the tube blank 2, and the cone angle θ of the head of the mandrel 4 is less than or equal to the forming angle α ₁ of the front cone section 11 of the roller. The maximum diameter d _m of the head of the mandrel 4 is less than the initial inner diameter of the tube blank 2. The mandrel 4 is controlled to move axially at a speed v _x . The moving direction of the mandrel 4 is opposite to that of the tube blank 2, and V _r =V _x tan α ₁ , so that the gap between the cone surface of the front cone section 11 of the roller and the cone surface of the mandrel 4 remains unchanged during the diameter-reducing rolling process, as shown in FIG6 ;

(4) After the rolling of the diameter-reducing section is completed, the roller 1 is kept radially stationary, and the four-jaw chuck 3 clamps the tube billet 2 and continues to move at a uniform speed along the same axial direction, while the mandrel 4 is controlled to stop axial movement, so as to perform straight-axis section rolling on the tube billet 2, as shown in FIG7 ;

(5) After the straight-axis section is rolled, the four-jaw chuck 3 clamps the tube billet and continues to move at a uniform speed along the same axial direction at the same speed. The roller 1 moves radially at a speed v _r in a direction away from the tube billet 2 to roll the tube billet 2 in the diameter-increasing section. At the same time, the mandrel 4 is controlled to move axially at a speed v _x . The moving direction of the mandrel 4 is the same as that of the tube billet 2, and V _r =V _x tan α ₁ , so that the gap between the conical surface of the front conical section 11 of the roller and the conical surface of the mandrel 4 remains unchanged during the diameter-increasing rolling process, as shown in FIG8 , until the diameter-increasing section rolling is completed to obtain a finished rolled product.

The specific derivation process of the relationship formula of the roller working generatrix in the present invention is as follows:

Since the roll surface area of the three-roller oblique rolled hollow axle in contact with the workpiece is different at different rolling stages, the right-view projection diagram of the roll 1 in contact with the workpiece at different rolling stages is shown in Figure 9. In order to reasonably design the roll working generatrix at each stage, the design process of the roll working generatrix at different rolling stages is as follows:

(1) The radius of any point on the roller working generatrix during the rolling of the rolled piece

Along the axis of the workpiece, _a section x1 - x1 perpendicular to the axis of the workpiece is taken at a distance _L1x from the section II on the front cone section ₁₁ of the roll _1. The axis _Ox1 of the roll on the section x1 _- x1 is projected in the right view as shown in (a) of FIG9. From FIG(a), we can get:

(1)

In the formula: O _{x 1} O ₁ is the distance from the axis O _x1 of the roller at section x ₁ - x ₁ to the axis O ₁ of the workpiece; OO _{x 1} is the distance from the axis O _x1 of the roller at section x ₁ - x ₁ to the axis O when the roller is not deflected (i.e., at section II); R _{x 1} is the ideal roller radius at section x ₁ - x ₁ ; r ₁ is the outer radius of the workpiece at section x ₁ - x ₁ ; r ₀ is the radius of the forming area of the workpiece; β is the roller deflection angle of the roller axis relative to the workpiece axis, and α ₁ is the forming angle of the front cone section 11 of the roller.

From formula (1), it can be seen that in order to maintain the linear contact between roller 1 and the workpiece in the roller rectangular coordinate system during roller reducing rolling, the ideal roller radius R _{x 1} at the section x ₁ - x ₁ is:

(2)

Right now: (3)

Where: R is the roller radius at section II.

(2) The radius of any point on the roller working generatrix when rolling the straight shaft section of the rolled piece

Along the axis of the workpiece, _a section x2 - x2 perpendicular to the axis of the workpiece is taken at a distance _L2x from the section _II on the cylindrical section ₁₂ of the roll 1. The axis _Ox2 of the roll on _the section x2 - x2 is projected in the right view as shown in (b) of Figure 9. From Figure (b), we can get:

(4)

In the formula: O _{x 2} O ₁ is the distance from the axis O _x2 of the roller at section x ₂ - x ₂ to the axis O ₁ of the workpiece; OO _{x 2} is the distance from the axis O _x2 of the roller at section x ₂ - x ₂ to the axis O when the roller is not deflected (i.e. at section II); R _{x 2} is the ideal roller radius at section x ₂ - x ₂ .

From formula (4), it can be seen that in order to keep the roller 1 in linear contact with the workpiece in the roller rectangular coordinate system during roller straight axis rolling, the ideal roller radius R _{x 2} at the section x ₂ - x ₂ is:

(5)

Right now: (6)

(3) The radius of any point on the roller working generatrix during the rolling of the workpiece

Along the axis of the workpiece, a section x3 - x3 perpendicular to the axis of the workpiece is taken at a distance _L3x from the section _II on the rear cone section ₁₃ of the roller 1. The axis _Ox3 of the roller on _the section x3 _- x3 is projected in the right view as shown in (c) of Figure 9. From Figure (c), it can be obtained that:

(7)

In the formula: O _{x 3} O ₁ is the distance from the axis O _x3 of the rolling mill at section x ₃ - x ₃ to the axis O ₁ of the workpiece; OO _{x 3} is the distance from the axis O _x3 of the rolling mill at section x ₃ - x ₃ to the axis O when the rolling mill is not deflected (i.e., at section II); R _{x 3} is the ideal roller radius at section x ₃ - x ₃ ; r ₃ is the outer radius of the workpiece at section x ₃ - x ₃ ; L ₂ is the length of the cylindrical section 12 of the rolling mill; α ₃ is the forming angle of the rear cone section of the rolling mill.

From formula (7), it can be seen that in order to keep the roll 1 in linear contact with the workpiece in the roll rectangular coordinate system during the roll diameter increase rolling, the ideal roll radius R _{x 3} at the section x ₃ - x ₃ is:

(8)

Right now: (9)

By combining equations (3), (6) and (9), we can get the following relationship between the roller working generatrix that ensures that the roller 1 and the workpiece are in linear contact at any time in the roller rectangular coordinate system during the entire rolling process:

.

The rolling effect of hollow shaft rolling using the optimized rollers in this method was experimentally verified, specifically:

The optimized drum roll of the present invention and the conventional disc roll are respectively used in a three-roller cross-rolling mill to cross-roll the tube billets of the same specifications, and the same process parameters (i.e., roll speed, tube billet axial movement speed and roll radial movement speed) are used in the rolling process. The surface forming quality comparison of the rolled product is shown in Figures 10 and 11. It can be seen that the surface of the rolled product obtained by the optimized drum roller rolling is obviously smoother than that obtained by the conventional disc roller rolling. Under the same process parameters, the maximum height _Rz of the rolled product surface profile obtained by the optimized drum roller rolling of the present invention is 1.25, while the maximum height _Rz of the rolled product surface profile obtained by the conventional disc roller rolling is 2.97. The maximum height _Rz of the rolled product surface profile is an evaluation index of the spiral mark on the rolled product surface. The deviation between the actual contour line of the rolled product and the theoretical contour line is the contour deviation of the rolled product, which is represented by d . The maximum height _Rz of the rolled product surface profile is: _Rz = _dmax - _dmin , where _dmax is the maximum contour deviation and _dmin is the minimum contour deviation. This shows that the spiral mark defect on the surface of the rolled product can be effectively controlled by rolling hollow shaft parts with the optimized drum roller of the present invention. In addition, the wall thickness of hollow shaft parts can be well made equal by this method.

The protection scope of the present invention includes but is not limited to the above embodiments, and its protection scope is subject to the claims. Any replacement, deformation, and improvement of the technology that can be easily thought of by technicians in this field shall fall within the protection scope of the present invention.

Claims (4)

1. A three-roller oblique rolling forming method of a hollow shaft part with equal wall thickness based on core rod control is characterized by comprising the following specific steps:

(1) The rollers of the three-roller inclined rolling mill are drum-shaped, namely, the rollers comprise a front cone section, a cylindrical section and a rear cone section which are sequentially arranged;

(2) The relation formula of the set roll working bus is as follows:

So that the roller and the rolled piece are in line contact at any moment under the rectangular coordinate system of the roller in the rolling process, wherein: r is the roll radius of a section I-I of a roll, which is perpendicular to the axis of the rolled piece and is cut by the intersection point of the axis of the rolled piece and the axis of the roll, R ₀ is the outer radius of the section of the rolled piece corresponding to the section I-I, x is the distance from the section x-x to the section I-I of the roll, the section x-x is the section of the roll, which is perpendicular to the axis of the rolled piece and is parallel to the section I-I, beta is the roll deflection angle of the roll axis relative to the axis of the rolled piece, L ₁ is the length of a front cone section of the roll, L ₂ is the length of a cylindrical section of the roll, L ₃ is the length of a rear cone section of the roll, alpha ₁ is the forming angle of the front cone section of the roll, alpha ₃ is the forming angle of the rear cone section of the roll, and y is the roll radius of the section x-x on the roll;

(3) When the tube blank rolled piece is rolled, the control roller rotates around the axis of the control roller and moves radially towards the direction close to the tube blank rolled piece to roll the reducing section of the tube blank rolled piece, meanwhile, the four-jaw chuck clamps the tube blank rolled piece to move axially at a constant speed, the mandrel with the conical head is inserted into the tube blank rolled piece and controls the mandrel to move axially, the moving direction of the mandrel is opposite to the moving direction of the tube blank rolled piece, and the gap between the conical surface of the front conical section of the roller and the conical surface of the mandrel is kept unchanged in the reducing rolling process;

(4) After the rolling of the reducing section is finished, the roller is kept to be radial, the four-jaw chuck clamps the tube blank rolled piece to continuously move at a uniform speed along the same axial direction at the same speed, and meanwhile, the mandrel is controlled to stop moving axially so as to roll the tube blank rolled piece in a straight shaft section;

(5) After the straight shaft section rolling is finished, the four-jaw chuck clamps the tube blank rolled piece to continuously move along the same axial direction at a constant speed, the roller moves radially in the direction away from the tube blank rolled piece to roll the tube blank rolled piece in the diameter-increasing section, meanwhile, the axial movement of the core rod is controlled, the moving direction of the core rod is the same as the moving direction of the tube blank rolled piece, and the gap between the conical surface of the front conical section of the roller and the conical surface of the core rod is kept unchanged in the diameter-increasing rolling process until the diameter-increasing section rolling is finished, so that a rolled piece finished product is obtained.

2. The three-roller skew rolling forming method of the hollow shaft type piece with the same wall thickness based on the control of the core rod, which is characterized by comprising the following steps of: in the step (3), the radial moving speed of the roller is set to be V _r, the axial moving speed of the mandrel is set to be V _x and V _r=V_xtanα₁, so that the gap between the conical surface of the front cone section of the roller and the conical surface of the mandrel is kept unchanged in the reducing rolling process.

3. The three-roller skew rolling forming method of the hollow shaft type piece with the same wall thickness based on the control of the core rod as claimed in claim 2, wherein the method comprises the following steps: in the steps (4) and (5), the axial moving speed of the tube blank rolled piece is equal to that of the tube blank rolled piece in the step (3), and in the step (5), the radial moving speed of the roller is equal to that of the roller in the step (3) and is v _r; the axial moving speed of the core rod in the step (5) is equal to that of the core rod in the step (3), V _x and V _r=V_xtanα₁ are adopted, so that the gap between the conical surface of the front cone section of the roller and the conical surface of the core rod is kept unchanged in the diameter-increasing rolling process.

4. The three-roller skew rolling forming method of the hollow shaft type piece with the same wall thickness based on the control of the core rod, which is characterized by comprising the following steps of: the angle of the conical surface of the head part of the core rod is smaller than or equal to the forming angle alpha ₁ of the front conical section of the roller, and the maximum diameter of the head part of the core rod is smaller than the initial inner diameter of the tube blank rolled piece.