Accurate springback compensation method for hydroforming component based on liquid volume control

Abstract

An accurate springback compensation method for sheet hydroforming component based on liquid volume control is related to a springback compensation method for curved surface part hydroformed with liquid as a punch during deep drawing process. According to the difference between a theoretical volume and a post-springback volume of a target part, an elastic deformation of the die is induced by liquid pressure, the die deformation amount is controlled to be equal to the springback amount. The accurate springback compensation control of a curved surface part is realized to overcome the problems of thickness or mechanical properties variations for different batches of sheets, and the manufacture error of the mould is considered to meet the design requirements. The liquid volume compensation is on-line and in-situ performed without mould re-machining. The advantages is good precision, simple process, high efficiency, short cycle and low cost.

Claims

1. An accurate springback compensation method for hydroforming component based on liquid volume control, comprising the steps of, (a) inducing an elastic deformation of a die by regulating a volume of injected liquid based on a volume difference between a theoretical volume of a target part and a volume of the part after springback, and (b) controlling a die deformation amount equal to a springback amount and realizing an accurate springback compensation control of a curved panel member, wherein said method further comprises the steps of: step 1: calculating a theoretical volume V.sub.0 corresponding to the curved panel member according to a designed profile of the curved panel member; step 2: placing a plate blank on the die and filling the die with high pressure liquid through an external pressurization system so that said plate blank begins deep drawing with liquid as a punch under an action of liquid pressure for shape forming; step 3: recording a change of liquid flow inside the die by using a flowmeter, stopping liquid filling through a control system when a liquid volume being filled inside the die reaches V.sub.0 and unloading; step 4: measuring a distance between a profile of an unloaded part and a corresponding die profile in situ and online by a displacement sensor, and calculating an actual volume V of the unloaded part, then calculating to obtain a volume difference ΔV of V.sub.0 and V; step 5: filling the die with high pressure liquid again, continuing to fill the die with high pressure liquid when a liquid volume being filled inside the die reaches V.sub.0 until the die is elastically deformed, recording a change of liquid flow inside the die by using the flowmeter, stopping liquid filling through the control system when a liquid volume being filled inside the die reaches V.sub.0+ΔV, then unloading to obtain the curved panel member; step 6: proceeding batch forming of subsequent target parts using a loaded volume of V.sub.0+ΔV.

2. The accurate springback compensation method for hydroforming component based on liquid volume control according to claim 1, characterized in that, in the step (2), the plate blank is a sheet metal.

3. The accurate springback compensation method for hydroforming component based on liquid volume control according to claim 2, characterized in that, the sheet metal includes but not limited to aluminum alloy, low carbon steel, and high strength steel.

4. An accurate springback compensation method for hydroforming component based on liquid volume control, comprising the steps of: (a) inducing an elastic deformation of a die by regulating a volume of injected liquid based on a volume difference between a theoretical volume of a target part and a volume of the part after springback, and (b) controlling a die deformation amount equal to a springback amount and realizing an accurate springback compensation control of a curved panel member, wherein said method further comprises the steps of: step 1: calculating a theoretical volume V.sub.0 corresponding to the curved panel member according to a designed profile of the curved panel member; step 2: placing a plate blank on the die and filling the die with high pressure liquid through an external pressurization system so that said plate blank begins deep drawing with liquid as a punch under an action of liquid pressure for shape forming; step 3: recording a change of liquid flow inside the die by using a flowmeter, stopping liquid filling through a control system when a liquid volume being filled inside the die reaches V.sub.0 and unloading; step 4: measuring a distance between a profile of an unloaded part and a corresponding die profile in situ and online by a displacement sensor, and calculating an actual volume V of the unloaded part, then calculating to obtain a volume difference ΔV of V.sub.0 and V; step 5: filling the die with high pressure liquid again, continuing to fill the die with high pressure liquid when a liquid volume being filled inside the die reaches V.sub.0 until the die is elastically deformed, recording a change of liquid flow inside the die by using the flowmeter, stopping liquid filling through the control system when a liquid volume being filled inside the die reaches V.sub.0+ΔV, then unloading to obtain the curved panel member; step 6: calculating the liquid volume compression amount ΔVp=β.Math.p.Math.(V0+ΔV) when the liquid volume being filled inside the die is (V.sub.0+ΔV) based on the relationship between the liquid volume compression amount ΔVp and the liquid pressure p: ΔVp=β.Math.p.Math.V, where β is a compression coefficient of the liquid medium; step 7: filling the die with liquid and pressurizing again for elastic deformation of the die, recording a change of liquid flow inside the die by using the flowmeter, stopping liquid filling through the control system when a liquid volume being filled inside the die reaches V.sub.0+ΔV+ΔVp, then unloading to obtain the curved panel member; step 8: proceeding batch forming of subsequent target parts using a loaded volume of V.sub.0+ΔV+ΔVp.

5. The accurate springback compensation method for hydroforming component based on liquid volume control according to claim 4, characterized in that, in the step (2), the plate blank is a sheet metal.

6. The accurate springback compensation method for hydroforming component based on liquid volume control according to claim 5, characterized in that, the sheet metal includes but not limited to aluminum alloy, low carbon steel, and high strength steel.

7. An accurate springback compensation method for hydroforming component based on liquid volume control, comprising the steps of: (a) inducing an elastic deformation of a die by regulating a volume of injected liquid based on a volume difference between a theoretical volume of a target part and a volume of the part after springback, and controlling a die deformation amount equal to a springback amount and realizing an accurate springback compensation control of a curved panel member, wherein said method further comprises the steps of: step 1: calculating a theoretical volume V.sub.0 and a die cavity volume V.sub.1 according to a designed profile of the curved panel member and a measured profile of the die cavity correspondingly, then calculating to obtain a volume difference ΔV.sub.1 of V.sub.0 and V.sub.1 equal to V.sub.0−V.sub.1 (i.e. ΔV.sub.1=V.sub.0−V.sub.1); step 2: placing a plate blank on the dice and filling the die with high pressure liquid through an external pressurization system so that said plate blank begins deep drawing with liquid as a punch under an action of liquid pressure for shape forming; step 3: recording a change of liquid flow inside the die by using a flowmeter, continuing to fill the die with high pressure liquid through an external pressurization system when a liquid volume being filled inside the die reaches V.sub.1 so that the die is elastically deformed, recording a change of liquid flow inside the die by using the flowmeter, stopping liquid filling through the control system when a liquid volume being filled inside the die reaches V.sub.1+ΔV.sub.1=V.sub.0 and unloading; step 4: measuring a distance between a profile of the unloaded part and a corresponding die profile in situ and online by a displacement sensor, and calculating an actual volume V of the unloaded part, then calculating a volume difference ΔV of V.sub.0 and V equal to V.sub.0−V (i.e. ΔV=V.sub.0−V); step 5: filling the die with high pressure liquid again so that the die is elastically deformed, recording a change of liquid flow inside the die by using the flowmeter, stopping liquid filling through the control system when a liquid volume being filled inside the die reaches V.sub.0+ΔV, then unloading to obtain the curved panel member; step 6: proceeding batch forming of subsequent target parts using a loaded volume of V.sub.0+ΔV.

8. The accurate springback compensation method for hydroforming component based on liquid volume control according to claim 7, characterized in that, in the step (2), the plate blank is a sheet metal.

9. The accurate springback compensation method for hydroforming component based on liquid volume control according to claim 8, characterized in that, the sheet metal includes but not limited to aluminum alloy, low carbon steel, and high strength steel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a hemispherical curved member having a design radius r.sub.0,

(2) FIG. 2 illustrates an initial state of the forming process of the hemispherical curved member,

(3) FIG. 3 illustrates an intermediate state of the forming process of the hemispherical curved member,

(4) FIG. 4 illustrates a final state of the forming process of the hemispherical curved member (moulding state formed of the hemispherical curved member),

(5) FIG. 5 illustrates a springback state occurred after unloading of the hemispherical curved member,

(6) FIG. 6 illustrates a springback compensation state of the hemispherical curved member,

(7) FIG. 7 illustrates an initial state of the curved member forming when the die has machining error,

(8) FIG. 8 illustrates a die forming state of the curved member forming when the die has machining error,

(9) FIG. 9 illustrates a die profile compensation state when the die has manufacture error,

(10) FIG. 10 illustrates a springback state of the curved member after unloading when the die has manufacture error,

(11) FIG. 11 illustrates a springback compensation process of the curved member when the die has manufacture error,

(12) FIG. 12 illustrates a semi-ellipsoidal curved member with radii of long axis and short axis of a and b respectively,

(13) FIG. 13 illustrates a springback compensation process of the semi-ellipsoidal curved member,

(14) FIG. 14 illustrates a complex curved member with irregular shape,

(15) FIG. 15 illustrates a springback compensation process of the complex curved member with irregular shape.

(16) FIG. 16 illustrates a flow chart of an accurate springback compensation method for hydroforming component based on liquid volume control according to Embodiment 1 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiment 1

(17) The present embodiment is implemented by the following steps:

(18) Step 1: According to a designed profile of the curved panel member, calculating the corresponding theoretical volume V.sub.0;

(19) Step 2: Placing a plate blank on a die for moulding and filling the die with high pressure liquid through an external pressurization system so that the plate blank begins deep drawing with liquid as a punch under an action of liquid pressure for shape forming;

(20) Step 3: Using a flowmeter to record a change of liquid flow inside the die, when a liquid volume being filled inside the die reaches V.sub.0, stopping liquid filling through a control system and unloading;

(21) Step 4: Using a displacement sensor to online and on-site measuring a distance between a profile of the unloaded part and a profile of its corresponding die, calculating an actual volume V of the unloaded part, then calculating to obtain a volume difference ΔV of V.sub.0 and V;

(22) Step 5: Filling the die with high pressure liquid again, when a liquid volume being filled inside the die reaches V.sub.0, continuing to fill the die with high pressure liquid until elastic deformation of the die occurs, using a flowmeter to record a change of liquid flow inside the die, when a liquid volume being filled inside the die reaches V.sub.0+ΔV, stopping liquid filling through the control system, then unloading to obtain a curved panel member;

(23) Step 6: For batch forming of subsequent parts, using a loaded volume of V.sub.0+ΔV.

Embodiment 2

(24) In consideration of the ultra-high pressure in the entire process, in order to avoid the error caused by the volume compression of the liquid under the ultra-high pressure which may affect the precise control of the liquid volume, on the basis of the step 1 to step 5 of embodiment, this embodiment further comprises the following steps:

(25) Step 6: based on the relationship between the liquid volume compression amount ΔV.sub.p and the liquid pressure p, that is: ΔV.sub.p=β.Math.p.Math.V, calculating the liquid volume compression amount V.sub.p=β.Math.p.Math.(V0+ΔV) when the liquid volume being filled inside the die is (V.sub.0+ΔV), where β is a compression coefficient of the liquid medium;

(26) Step 7: Filling the die with liquid and pressurizing again until elastic deformation of the die occurs, recording a change of liquid flow inside the die by using a flowmeter, when a liquid volume being filled inside the die reaches V.sub.0+ΔV+ΔV.sub.p, stopping liquid filling through the control system then unloading to obtain a curved panel member.

(27) Step 8: Proceeding batch forming of subsequent parts using a loaded volume of V.sub.0+ΔV+ΔVp.

Embodiment 3

(28) In consideration of the machining error of die profile, when the actual size of the die cavity is smaller than the lower tolerance of the part size, the present invention can be used to realize a high-precision forming process of the curved panel member without modifying the die. This embodiment includes the following steps:

(29) Step 1: According to a designed profile of the curved panel member and a measured profile of the die cavity, calculating the corresponding theoretical volume V.sub.0 and the die cavity volume V.sub.1, and calculating to obtain a volume difference ΔV.sub.1 of V.sub.0 and V.sub.1 according to ΔV.sub.1=V.sub.0−V.sub.1;

(30) Step 2: Placing a plate blank on a die for moulding and filling the die with high pressure liquid through an external pressurization system so that the plate blank begins deep drawing with liquid as a punch under an action of liquid pressure for shape forming;

(31) Step 3: Recording a change of liquid flow inside the die by using a flowmeter, when a liquid volume being filled inside the die reaches V.sub.1, continuing to fill the die with high pressure liquid through an external pressurization system so that the die is elastically deformed, recording a change of liquid flow inside the die by using a flowmeter, when a liquid volume being filled inside the die reaches V.sub.1+ΔV.sub.1=V.sub.0, stopping liquid filling through the control system and unloading;

(32) Step 4: using a displacement sensor to online and on-site measuring a distance between a part profile after unloading and a profile of the corresponding die, calculating an actual volume V of the unloaded part, and calculating a volume difference ΔV of V.sub.0 and V according to ΔV=V.sub.0−V;

(33) Step 5: Filling the die with high pressure liquid again so that the die is elastically deformed, recording a change of liquid flow inside the die by using a flowmeter, stopping liquid filling through the control system when a liquid volume being filled inside the die reaches V.sub.0+ΔV, then unloading to obtain a curved panel member.

(34) Step 6: Proceeding batch forming of subsequent parts using a loaded volume of V.sub.0+ΔV.

EXEMPLARY EMBODIMENTS

Exemplary Embodiment 1

(35) Taking 2219 aluminum alloy hemispherical head parts as an example, where: r.sub.0 is the design radius of the head part, and r is the radius of the head part after unloading and being springback. The implementation process of the present invention is described with reference to FIG. 1 to FIG. 6:

(36) Step 1: based on the design radius of the hemispherical head part r.sub.0, calculating the corresponding theoretical volume V.sub.0=2πr.sub.0.sup.3/3;

(37) Step 2: Placing a round plate blank to a die with a cavity radius r.sub.0 for moulding, filling the die with water and increasing pressure through an external pressurization system so that the plate blank begins deep drawing with liquid as a punch under an action of water pressure;

(38) Step 3: Using a flowmeter to record a change of water flow inside the die, when a liquid volume being filled inside the die reaches V.sub.0, stopping water filling through a control system and unloading;

(39) Step 4: Using a displacement sensor to measure a distance between the part and a profile of the die, calculating a measured radius of the part after unloading r, calculating an actual volume V of the part according to V=2πr.sup.3/3, and calculating to obtain a volume difference ΔV of V.sub.0 and V according to ΔV=V.sub.0−V=2π(r.sub.0.sup.3−r.sup.3)/3;

(40) Step 5: Filling the die with water and pressurizing again, when a water volume being filled inside the die reaches V.sub.0, continuing to fill the die with water and pressurizing so that the die is elastically deformed, using a flowmeter to record a change of water flow inside the die, when a liquid volume being filled inside the die reaches V.sub.0+ΔV=2π(2r.sub.0.sup.3−r.sup.3)/3, stopping water filling through the control system, and then unloading to obtain a head part.

(41) Step 6: For subsequent batch forming of head parts, loading liquid according to 2π(2r.sub.0.sup.3−r.sup.3)/3.

Exemplary Embodiment 2

(42) Taking 2219 aluminum alloy hemispherical head parts as an example, where: r.sub.0 is the design radius of the head part, and r is the radius of the head part after unloading and after springback. In order to avoid the error caused by the volume compression of the liquid under the ultra-high pressure, this exemplary embodiment includes the step 1 to step 5 which are the same as that of exemplary embodiment 1 and further includes the following steps:

(43) Step 6: recording the liquid pressure p when the liquid volume being filled inside the die is (V.sub.0+ΔV), according to the formula of the liquid volume compression amount ΔV.sub.p=β.Math.p.Math.(V0+ΔV), calculating the liquid volume compression amount of the liquid filled in the die according to ΔV.sub.p=β.Math.p.Math.2π(2r.sub.0.sup.3−r.sup.3)/3, where where β is a compression coefficient of the liquid medium;

(44) Step 7: Filling the die with liquid and pressurizing again until elastic deformation of the die occurs, recording a change of water flow inside the die by using a flowmeter, when a liquid volume being filled inside the die reaches V.sub.0+ΔV+ΔV.sub.p=(β.Math.p+1)×[2π(2r.sub.0.sup.3−r.sup.3)/3], stopping liquid filling, and unloading to obtain a head part.

(45) Step 8: For subsequent batch forming of head parts, loading liquid according to (β.Math.p+1)×[2π(2r.sub.0.sup.3−r.sup.3)/3].

Exemplary Embodiment 3

(46) Taking 2219 aluminum alloy hemispherical head parts as an example, wherein: r.sub.0 is the design radius of the head part, because of the machining error, the actual measured radius of the die cavity is r.sub.1=r.sub.0−δ (δ is the design tolerance), and r is the radius of the head part after unloading and after springback. The present invention can be used to realize a first-time high-precision forming process of the curved panel member without modifying the die. The implementation process of the present invention is described with reference to FIG. 7 to FIG. 11:

(47) Step 1: based on the design radius of the hemispherical head part r.sub.0 and the actual measured radius of the die cavity r.sub.1, calculating the corresponding theoretical volume V.sub.0=2πr.sub.0.sup.3/3 and the die cavity volume V.sub.1=2πr.sub.1.sup.3/3, then calculating to obtain a volume difference ΔV.sub.1 of V.sub.0 and V.sub.1 according to ΔV.sub.1=V.sub.0−V.sub.1=2π(r.sub.0.sup.3−r.sub.1.sup.3)/3;

(48) Step 2: Placing a round plate blank to a die with a cavity radius r.sub.1 for moulding, filling the die with water and increasing pressure through an external pressurization system so that the plate blank begins deep drawing with liquid as a punch under an action of water pressure;

(49) Step 3: Using a flowmeter to record a change of water flow inside the die, when a liquid volume being filled inside the die reaches V.sub.1, continuing to fill the die with water and pressurizing so that the die is elastically deformed, using a flowmeter to record a change of water flow inside the die, when a liquid volume being filled inside the die reaches V.sub.1−ΔV.sub.1=V.sub.0=2πr.sub.0.sup.3/3, stopping water filling through the control system, and then unloading;

(50) Step 4: Using a displacement sensor to measure a distance between the part and a profile of the die, calculating a measured radius of the part after unloading r, calculating an actual measured volume V of the part according to V=2πr.sup.3/3, and calculating to obtain a volume difference ΔV of V.sub.0 and V according to ΔV=V.sub.0−V=2π(r.sub.0.sup.3−r.sup.3)/3;

(51) Step 5: Filling the die with water and pressurizing again so that the die is elastically deformed, using a flowmeter to record a change of water flow inside the die, when a liquid volume being filled inside the die reaches V.sub.0+ΔV=2π(2r.sub.0.sup.3−r.sup.3)/3, stopping water filling through the control system, and then unloading to obtain a head part.

(52) Step 6: For subsequent batch forming of head parts, loading liquid according to 2π(2r.sub.0.sup.3−r.sup.3)/3.

Embodiment 4

(53) Taking 2219 aluminum alloy semi-ellipsoidal head parts as an example, where: co is the long axis radius of the head part, b.sub.0 is the short axis radius of the head part. The implementation process of the present invention is described with reference to FIG. 12 to FIG. 13:

(54) Step 1: based on the long and short radii of the semi-ellipsoidal head part, calculating the corresponding theoretical volume V.sub.0=2πa.sub.0.sup.2b.sub.0/3;

(55) Step 2: Placing a round plate blank to a die with a cavity long and short radii of a.sub.0 and b.sub.0 for moulding, filling the die with water and increasing pressure through an external pressurization system so that the plate blank begins deep drawing with liquid as a punch under an action of water pressure;

(56) Step 3: Using a flowmeter to record a change of water flow inside the die, when a liquid volume being filled inside the die reaches V.sub.0, stopping water filling through a control system and unloading;

(57) Step 4: Using a displacement sensor to measure a distance between the part and a profile of the die, calculating a measured long and short radii of the part after unloading, calculating an actual measured volume V of the part according to V=2a.sup.2b/3, and calculating to obtain a volume difference ΔV of V.sub.0 and V according to ΔV=V.sub.0−V=2π(a.sub.0.sup.2b.sub.0−a.sup.2b)/3;

(58) Step 5: Filling the die with water and pressurizing again, when a water volume being filled inside the die reaches V.sub.0, continuing to fill the die with water and pressurizing so that the die is elastically deformed, using a flowmeter to record a change of water flow inside the die, when a liquid volume being filled inside the die reaches V.sub.0+ΔV=2π(2a.sub.0.sup.2b.sub.0−a.sup.2b)/3, stopping water filling through the control system, and then unloading to obtain a semi-ellipsoidal head part.

(59) Step 6: For subsequent batch forming of head parts, loading liquid according to 2π(2a.sub.0.sup.2b.sub.0−a.sup.2b)/3.

Embodiment 5

(60) Taking 5A06 aluminum alloy irregular-shape complex curved surface parts as an example, where: h.sub.1, h.sub.2, h.sub.3 are the corresponding step plane height of the complex curved-surface part, r.sub.1 and r.sub.2 are radius of two curved surface respectively. The implementation process of the present invention is described with reference to FIG. 14 to FIG. 15:

(61) Step 1: based on the designed profile of the complex curved-surface part, calculating the corresponding theoretical volume V.sub.0;

(62) Step 2: Placing a plate blank on a die for moulding, filling the die with water and increasing pressure through an external pressurization system so that the plate blank begins deep drawing with liquid as a punch under an action of water pressure;

(63) Step 3: Using a flowmeter to record a change of water flow inside the die, when a liquid volume being filled inside the die reaches V.sub.0, stopping water filling through a control system and unloading;

(64) Step 4: Using a displacement sensor to measure a distance between the part and a profile of the die, calculating an actual measured volume V of the part, and calculating to obtain a volume difference ΔV of V.sub.0 and V;

(65) Step 5: Filling the die with water and pressurizing again, when a water volume being filled inside the die reaches V.sub.0, continuing to fill the die with water and pressurizing so that the die is elastically deformed, using a flowmeter to record a change of water flow inside the die, when a liquid volume being filled inside the die reaches V.sub.0+ΔV, stopping water filling through the control system, and then unloading to obtain a complex curved-surface part.

(66) Step 6: For subsequent batch forming of head parts, loading liquid according to V.sub.0+ΔV.

(67) Under the same testing conditions, compared with the existing method of controlling the liquid pressure to control the springback, the method of the present invention improves the part profile accuracy by at least 20%, the yield rate by at least 10%, and the work efficiency by at least 70%.