Device and method for indirect heat conduction bending of diamagnetic material core rod

Abstract

The present invention discloses an indirect heat conduction bending device and method for a core rod of a diamagnetic material, and relates to the technical field of pipe bending equipment, including a bending die for bending a formed pipe, a spherical bearing for driving the bending die to move on an XY plane under the control of an X-axis and Y-axis servo motor, a guide mechanism for pressing and guiding the formed pipe, and a propulsion mechanism for pushing the formed pipe to move along the guide mechanism. The input end of the propulsion mechanism is connected to a Z-axis motor for providing power therefor. The present invention uses electromagnetic induction to heat the core rod to its Curie temperature. During the bending process, the core rod of the universal ball joint contacts the inner wall of the pipe to realize heat conduction heating of the pipe by the core rod. Hot forming of difficult-to-deform materials can reduce the forming difficulty of the pipe during the cold forming process, and the deformation resistance of the pipe can be reduced by the action of thermal stress. While improving the forming limit of the pipe, it effectively solves the defects of thickening and instability of the inner wall of the pipe, and improves the forming quality.

Description

Technical Field

[0001] The invention relates to the technical field of pipe bending equipment, in particular to a device and method for indirect heat conduction bending of a core rod made of a diamagnetic material. Background Art

[0002] As a flexible forming system with few constraints and multiple degrees of freedom, the three-dimensional free bending forming device can realize one-time overall precise forming of complex curved components, and is an important technological innovation in the field of plastic forming. For easy-to-form components such as stainless steel and aluminum alloy, the three-dimensional free bending three-axis machine can achieve forming defect and precision control through process parameter matching and built-in filling. For difficult-to-form metals such as titanium alloys and high-strength steel, cold forming bending is prone to defects such as instability and excessive thinning and thickening. At present, auxiliary hot forming methods such as resistance heating or electromagnetic induction heating can be used to reduce the forming resistance and achieve defect control.

[0003] However, for anti-magnetic and difficult-to-deform materials such as hard aluminum, copper, and austenitic stainless steel, the free bending hot forming by resistance heating has the defects of low heating efficiency and fast heat dissipation speed, and cannot effectively realize the hot forming of pipes. The electromagnetic induction heating free bending forming technology has the advantages of fast heating speed and adjustable heating position, but for anti-magnetic materials, the magneto-thermal conversion efficiency of electromagnetic induction heating is extremely poor, and induction heating is more difficult.

[0004] In the process of bending and forming of difficult-to-deform materials, it is generally necessary to control the excessive thinning and wrinkling of the cross-section during the bending process through the built-in mandrel. The commonly used cast iron universal ball joint mandrel is an induction-heatable material, and its temperature can be stabilized near its own Curie temperature (795°C) by induction heating. In the process of pipe bending, due to the existence of the gap between the mandrel and the pipe, the universal mandrel will completely fit the outer side of the pipe bending to provide support, while the mandrel inside the pipe only provides partial support. In the traditional hot bending process, there are characteristics of outer wall thinning and outer wall thickening. Through the mandrel indirect heat conduction heating process, the mandrel is in full contact with the outer side of the inner wall of the pipe bending and partially in contact with the inner side of the bending. Therefore, the heating efficiency of the outer side of the pipe bending is significantly greater than that of the inner side of the bending. This forming method can reduce the thinning of the outer wall of the pipe during the hot bending process while reducing the thickening of the inner side of the pipe bending. The present invention provides an indirect heat conduction flexible bending device and method for anti-magnetic difficult-to-deform materials, through which electromagnetic induction heating of the mandrel can be realized, and the mandrel heat is conducted to the hot forming process of the anti-magnetic difficult-to-deform materials. Since the core rod will not heat up further after being heated to the Curie temperature, the length of the heating zone is fixed if the core rod parameters remain unchanged. The heating time can be controlled by adjusting the tube feed speed. By constructing a target forming temperature-feeding speed theoretical model, the tube forming temperature can be accurately controlled. Summary of the invention

[0005] The object of the present invention is to provide a device and method for indirect heat conduction bending of a core rod made of diamagnetic material to solve the problems in the background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The indirect heat conduction bending device of the anti-magnetic material core rod comprises a bending die for bending the formed tube, a spherical bearing for driving the bending die to move on the XY plane under the control of the X-axis and Y-axis servo motors, a guide mechanism for pressing and guiding the formed tube, and a propulsion mechanism for pushing the formed tube to move along the guide mechanism, wherein the input end of the propulsion mechanism is connected to a Z-axis motor for providing power thereto;

[0008] An induction heating coil for heating is arranged outside the guide mechanism, and the power supply end of the induction heating coil is connected to a transformer, and the input current is controlled by the transformer. A universal ball joint mandrel is built in the fillet from the front end of the guide mechanism to the bending die, and a connecting rod at the rear end thereof passes through the propulsion mechanism to fix the universal ball joint mandrel in the plastic deformation zone of the pipe;

[0009] The guide mechanism is made of heat-insulating ceramic zirconium dioxide, which can prevent the generation of induced current and play a role in heat preservation at the same time;

[0010] A cooling ring connected to external cooling water is provided at the rounded corner of the bending die and at the rear end of the guide mechanism, which plays a role in controlling the length of the high-temperature zone.

[0011] On the basis of the above technical solution, the present invention also provides the following optional technical solution:

[0012] In the optional scheme: the universal joint mandrel is heated by the electromagnetic induction coil for a period of time to reach its own Curie temperature of 700°C, and is kept constant at this temperature. When the bending forming begins, the tube is fed along the Z axis at a speed v under the push of the propulsion mechanism, and the bending die generates a bending offset U driven by the spherical bearing. During the bending process, the mandrel always fits the outer side of the bent tube and the inner side of the bent tube. Through the contact part, the mandrel continuously conducts heat to the inner wall of the tube to realize hot forming.

[0013] In the optional scheme: the universal ball joint core rod is composed of a ball handle and several core balls. Different core balls are directly hinged through a connecting shaft. The core balls can rotate around the connecting shaft, and play a supporting role for the inner wall of the pipe during the bending process. After the core rod is heated by electromagnetic induction through the connecting shaft, the temperature distribution of each area of ​​the core rod is uniform.

[0014] In the optional scheme: the number of core balls of the universal ball joint core rod corresponds to the plastic forming length of the tube, and the plastic deformation zone of the three-dimensional free bending forming device is from the guide mechanism to the rounded corner of the bending die. Therefore, for the same set of bending dies, the length of the heating zone is fixed. By controlling the feed speed of the propulsion mechanism, the heating time can be regulated. Under the condition of a certain external temperature, the forming temperature can be accurately regulated according to the heat conduction equation.

[0015] The bending method of the diamagnetic material core rod indirect heat conduction bending device comprises the following steps:

[0016] Step 1: The effective contact length of the core ball segment is known to be L, the temperature of the core rod under electromagnetic induction heating is stable at the Curie temperature T0, and the contact heat transfer area between the core rod and the tube is A; for the same tube, its thermal conductivity λ, wall thickness δ, specific heat capacity c, and density ρ are all constants, from which the axial feed speed v at the target tube forming temperature T1 can be derived

[0017] Step 2: The initial temperature of the tube is room temperature, the target forming temperature is T1, and the heat Q0 that the tube with an axial length of dx needs to absorb is taken:

[0018] Q0=cm(T1-25)

[0019] m=ρV=ρπδ 2 dx

[0020] Q0=cm(T1-25)=cρπδ 2 dx(T1-25);

[0021] Step 3: According to the heat conduction equation, the heat Q absorbed during the heating time t can be obtained 入 :

[0022]

[0023] A=πR 2 dx;

[0024]

[0025]

[0026] Step 4: Combine the heat required to heat to the target temperature and the heat absorbed during heating to get the target propulsion speed:

[0027] Q0=Q 入 ;

[0028]

[0029]

[0030] Step 5: The advancing speed calculated by the theoretical model of the forming parameters of the advancing speed and the heating temperature can realize the precise control of the tube forming temperature; the parameters include: the effective contact length L of the core ball segment, the stable temperature T0 of the core rod, the contact heat transfer area A between the core rod and the tube; the thermal conductivity λ of the needle tube, the wall thickness δ, the specific heat capacity c, the density ρ, the target forming temperature T1; the heating time t, and the axial feed speed v.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The present invention uses electromagnetic induction to heat the mandrel to its Curie temperature. During the bending process, the universal joint mandrel contacts the inner wall of the tube to achieve heat conduction heating of the tube by the mandrel. Hot forming of difficult-to-deform materials can reduce the difficulty of forming the tube during cold forming. The deformation resistance of the tube can be reduced through the action of thermal stress. While improving the forming limit of the tube, it effectively solves the defects of thickening and instability of the inner wall of the tube and improves the forming quality.

[0033] 2. Compared with the prior art, the present invention can effectively solve the problems of low heating efficiency, high heating power consumption, and long heating time of resistance heating and direct electromagnetic induction heating for anti-magnetic and difficult-to-deform materials such as hard aluminum, copper, and austenitic stainless steel. And because the mandrel is in full contact with the outer side of the inner wall of the tube and partially in contact with the inner side of the tube during the bending process, the heating efficiency of the outer side of the tube is significantly greater than that of the inner side of the tube. This forming method can reduce the thinning of the outer wall of the tube during the hot bending process while reducing the thickening of the inner side of the tube.

[0034] 3. The advancing speed calculated by the forming parameter theoretical model of the advancing speed and the heating temperature provided by the present invention can realize the precise control of the forming temperature of the pipe in the forming area. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of the structure of the mandrel induction heating indirect heat conduction flexible bending device;

[0036] Figure 2 It is a cross-sectional view of a structural forming component of a mandrel induction heating indirect heat conduction flexible bending device;

[0037] Figure 3 A schematic diagram of a bending example. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0039] In one embodiment, Figure 1-Figure 3As shown, the indirect heat conduction bending device of the diamagnetic material core rod comprises a bending die 3 for bending the formed tube 7, a spherical bearing 4 for driving the bending die 3 to move on the XY plane under the control of the X-axis and Y-axis servo motors, a guide mechanism 6 for pressing and guiding the formed tube 7, and a propulsion mechanism 9 for pushing the formed tube 7 to move along the guide mechanism 6, and the input end of the propulsion mechanism 9 is connected to the Z-axis motor 10 for providing power therefor; an induction heating coil 2 for heating is arranged on the outside of the guide mechanism 6, and the power supply end of the induction heating coil 2 is connected to the transformer 1, and the input current is controlled by the transformer 1, and a universal ball joint core rod 5 is built in the fillet from the front end of the guide mechanism 6 to the bending die 3, and the rear end connecting rod thereof passes through the propulsion mechanism 9 so that the universal ball joint core rod 5 is fixed in the plastic deformation zone of the tube; the guide mechanism 6 is made of heat-insulating ceramic zirconium dioxide, which can play a role of heat preservation while preventing the generation of induced current; a cooling ring 11 connected to external cooling water is arranged at the fillet of the bending die 3 and the rear end of the guide mechanism 6, which plays a role of controlling the length of the high-temperature zone;

[0040] An indirect heat conduction flexible bending device and method for a brass pipe with an outer diameter of 30 mm and a wall thickness of 1.2 mm and a single bend r=100 mm, comprising the following steps:

[0041] Step 1: Determine the number of core balls of the mandrel according to the mold parameters, and thus obtain the length of the heating zone. According to the heat conduction parameters of the tube and mandrel related materials, the advancement speed is calculated through the forming parameter theoretical model of advancement speed and heating temperature;

[0042] The parameters include: effective contact length of the core baseball segment L = 80mm, core rod stable temperature T0 = T Curie temperature = 800℃; pipe thermal conductivity λ = 108.9W / (m*K), pipe outer diameter R = 30mm, wall thickness δ = 10mm, specific heat capacity c = 0.39e3 J / (kg*K), density ρ = 8.5e3 kg / m3, target forming temperature T1 = 300℃; heating time t, axial feed speed v

[0043] Step 2: According to the theoretical model of forming parameters of advancing speed and heating temperature, the required tube advancing speed to be heated to the target forming temperature can be calculated as:

[0044]

[0045] Step 3: Analyze the three-dimensional free bending forming process for the target sample shape and obtain the eccentricity U = 12 mm at the target bending radius r = 100 mm;

[0046] Step 4: Feed the brass thick-walled tube into the three-dimensional free induction hot bending equipment, start the clamping mechanism, adjust the mandrel position so that the ball segment is located between the front end of the guide mechanism and the corner of the bending die, input the relevant parameters of the bending analysis program, and set the axial feed speed to the advancement speed obtained by analysis. A cooling ring connected to the external cooling water is set at the corner of the starting bending die and the rear end of the guide mechanism to control the length of the high-temperature zone;

[0047] Step 5: Start the induction heating power supply, select the input power of 5kw, and start the bending process when the temperature of the core rod is stable at its own Curie temperature through the temperature measuring equipment. During the bending process, the temperature distribution of each area of ​​the core rod is uniform. During the bending process, the core rod always fits the outer side of the bend of the bent pipe, and the inner side of the bend fits. Through the contact part, the core rod continuously conducts heat to the inner wall of the pipe to achieve hot forming.

[0048] Compared with the prior art, the present invention can effectively solve the problems of low heating efficiency, high heating power consumption, and long heating time of resistance heating and direct electromagnetic induction heating methods for anti-magnetic and difficult-to-deform materials such as hard aluminum, copper, and austenitic stainless steel. In addition, due to the different contact modes between the mandrel and the inner wall of the tube during the bending process, this forming method can reduce the thinning of the outer wall of the tube during the hot bending process while reducing the thickening of the inner side of the tube. The advancing speed calculated by the forming parameter theoretical model of the advancing speed and heating temperature provided by the present invention can realize the precise control of the forming temperature of the tube in the forming area.

[0049] The above is only a specific implementation of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any person skilled in the art who is familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present disclosure, which should be included in the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be based on the protection scope of the claims.

Claims

1. An indirect heat conduction bending device for a diamagnetic material core rod, comprising a bending die (3) for bending a formed tube (7), a spherical bearing (4) for driving the bending die (3) to move on an XY plane under the control of an X-axis and a Y-axis servo motor, a guide mechanism (6) for pressing and guiding the formed tube (7), and a propulsion mechanism (9) for pushing the formed tube (7) to move along the guide mechanism (6), wherein the input end of the propulsion mechanism (9) is connected to a Z-axis motor (10) for providing power thereto; It is characterized in that An induction heating coil (2) for heating is arranged outside the guide mechanism (6), the power supply end of the induction heating coil (2) is connected to a transformer (1), and the input current is controlled by the transformer (1). A universal ball joint mandrel (5) is built into the fillet between the front end of the guide mechanism (6) and the bending die (3), and a connecting rod at the rear end thereof passes through a propulsion mechanism (9) so that the universal ball joint mandrel (5) is fixed in the plastic deformation zone of the pipe; The guide mechanism (6) is made of heat-insulating ceramic zirconium dioxide, which can prevent the generation of induced current and also play a role in heat preservation; A cooling ring (11) connected to external cooling water is provided at the rounded corner of the bending die (3) and at the rear end of the guide mechanism (6), which plays a role in controlling the length of the high-temperature zone; The universal joint core rod (5) is heated by the induction heating coil (2) for a period of time to reach its own Curie temperature of 700°C and is kept constant at this temperature. When the bending forming begins, the tube is fed along the Z axis at a speed v under the push of the propulsion mechanism (9). The bending die (3) generates a bending offset U under the drive of the spherical bearing (4). During the bending process, the core rod always fits the outer side of the bent tube and the inner side of the bent tube. Through the contact part, the core rod continuously conducts heat to the inner wall of the tube to achieve hot forming.

2. The indirect heat conduction bending device of the diamagnetic material core rod according to claim 1 is characterized in that: The universal ball joint core rod (5) is composed of a ball handle and a plurality of core balls. Different core balls are directly hinged by connecting the rotating shaft. The core balls can rotate around the connecting shaft to support the inner wall of the pipe during the bending process. After the core rod is heated by electromagnetic induction through the connecting shaft, the temperature of each area of ​​the core rod is evenly distributed.

3. The indirect heat conduction bending device of the anti-magnetic material core rod according to claim 2 is characterized in that: The number of core balls of the universal ball joint core rod (5) corresponds to the plastic forming length of the tube (7). The plastic deformation zone of the three-dimensional free bending forming device is from the guide mechanism (6) to the fillet of the bending die (3). Therefore, for the same set of bending dies, the length of the heating zone is fixed. By controlling the feed speed of the propulsion mechanism (9), the heating time can be regulated. Under the condition of a certain external temperature, the forming temperature can be accurately regulated according to the heat conduction equation.

4. A bending method of the diamagnetic material core rod indirect heat conduction bending device according to claim 3, characterized in that: The following steps are involved: Step 1: The first step: The effective contact length of the core ball segment is known to be L, the temperature of the core rod under electromagnetic induction heating is stable at the Curie temperature T0, and the contact heat transfer area between the core rod and the tube is A; for the same tube, its thermal conductivity λ, wall thickness δ, specific heat capacity c, and density ρ are all constant values, from which the axial feed speed v when the target tube forming temperature T1 can be derived; Step 2: The initial temperature of the tube is room temperature, the target forming temperature is T1, and the heat Q0 that the tube with an axial length of dx needs to absorb is taken: Q0=cm(T1-25) m=ρV=ρπδ 2 dx Q0=cm(T1-25)=cρπδ 2 dx(T1-25); Step 3: According to the heat conduction equation, the heat Q absorbed during the heating time t can be obtained 入 : A=πR 2 dx; Step 4: Combine the heat required to heat to the target temperature and the heat absorbed during heating to get the target propulsion speed: Q0=Q 入 ; Step 5: The advancing speed calculated by the forming parameter theoretical model of the advancing speed and the heating temperature can realize the precise control of the tube forming temperature; the parameters include: the effective contact length L of the core ball segment, the core rod stable temperature T0, and the contact heat transfer area A between the core rod and the tube; Needle tube thermal conductivity λ, wall thickness δ, specific heat c, density ρ, target forming temperature T1; heating time t, axial feed speed v.

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