CN110883179B - Hydraulic forming part rebound control method and system based on liquid volume loading - Google Patents
Hydraulic forming part rebound control method and system based on liquid volume loading Download PDFInfo
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- CN110883179B CN110883179B CN201911188778.9A CN201911188778A CN110883179B CN 110883179 B CN110883179 B CN 110883179B CN 201911188778 A CN201911188778 A CN 201911188778A CN 110883179 B CN110883179 B CN 110883179B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D26/00—Shaping without cutting otherwise than using rigid devices or tools or yieldable or resilient pads, i.e. applying fluid pressure or magnetic forces
- B21D26/02—Shaping without cutting otherwise than using rigid devices or tools or yieldable or resilient pads, i.e. applying fluid pressure or magnetic forces by applying fluid pressure
- B21D26/033—Deforming tubular bodies
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Abstract
The invention discloses a rebound control method and a system of a hydraulic forming piece based on liquid volume loading, wherein the rebound control method comprises the following steps: determining the bulging amount of the die during forming; determining a target pressure; determining the volume of the inner cavity of the pipe fitting at the end of loading according to the bulging amount of the die during forming; determining the liquid volume compression compensation amount according to the target pressure and the volume of the inner cavity of the pipe fitting at the end of loading; determining the liquid volume increase in the absence of compression; and determining the total liquid volume increment according to the liquid volume increment in the non-compression state and the liquid volume compression compensation amount, and filling liquid into the tube blank according to the total liquid volume increment, so as to realize the rebound control of the hydraulic forming part and obtain the pipe fitting meeting the set size precision requirement. The method for controlling the resilience of the hydraulic forming part, disclosed by the invention, avoids the problems of repeated die repair, long period, high cost and the like of the traditional resilience compensation method and the problems of large size dispersion, poor precision and the like of the forming part caused by pressure fluctuation in the shaping phase of the traditional pressure loading method.
Description
Technical Field
The invention relates to the technical field of pipe hydraulic forming, in particular to a hydraulic forming part rebound control method and system based on liquid volume loading.
Background
Tube hydroforming (internal high pressure forming) is an advanced technology for manufacturing hollow and variable-section thin-wall components, and the formed parts have the advantages of light weight, high structural rigidity and fatigue strength and the like, and are widely applied to the fields of automobiles, aerospace and the like. With the continuous improvement of the requirement of light weight, the internal high-pressure forming technology is applied to manufacturing high-strength steel, aluminum alloy or magnesium alloy pipe fittings, and the double effects of light weight of materials and structures can be realized. However, the pipe will have a certain elastic recovery after the liquid pressure is unloaded during the internal high pressure forming process, which will affect the dimensional accuracy of the final pipe, resulting in large size dispersion, even exceeding the design requirement.
The high-pressure forming in the pipe is generally divided into three stages of filling, forming and shaping, wherein in the filling stage, the pipe blank is filled with liquid, and two ends of the pipe blank are completely sealed by using punches; in the forming stage, the tube blank basically clings to the die, and only the fillet of the transition area is not completely clinging to the die; and in the shaping stage, increasing the internal pressure to enable the fillet area to be completely attached to the die. In the existing internal high-pressure forming, the size precision of a formed part is controlled by controlling the liquid pressure in a tube blank cavity in a shaping stage, and the size precision of a transition fillet radius of a rectangular or special-shaped section is mainly controlled. The pressure in the shaping stage of the internal high-pressure forming process is generally very high (more than 100MPa), and in actual production, in order to ensure the dimensional accuracy and the production efficiency of the internal high-pressure formed part, the internal pressure must be rapidly increased to the shaping pressure, and the shaping pressure in each time should be kept consistent. However, it is difficult to rapidly and precisely control the variable of the internal pressure in a short time, and for example, the internal pressure is increased to 200MPa within 3 to 5 seconds, and the internal pressure value fluctuates. The fluctuation of the internal pressure value in the shaping stage can cause the sizes of the pipe fittings obtained by each internal high-pressure forming to be inconsistent, so that the product has large size dispersion, poor precision and high rejection rate.
In order to solve the problems of poor pipe fitting size precision, large dispersion, high rejection rate and the like of the traditional internal high-pressure forming technology based on pressure control, an applicant proposes a method and a system (an authorization notice number: CN 108687210B) for controlling the fillet size precision of an internal high-pressure forming part. The basic idea is as follows: the size precision of the pipe fitting is controlled by the volume of liquid injected into the pipe blank, and the method specifically comprises the following steps: determining the relation between the total liquid volume increment and the target pipe fitting fillet radius by acquiring the pipe blank inner cavity volume, the target pipe fitting inner cavity volume and the liquid volume compression compensation amount, and utilizing the liquid volume increment delta VLQuantitative relation with fillet radius r only through controlling delta VLAnd the accurate control on the dimensional accuracy of the round corner of the target pipe fitting is realized. In the forming process, a displacement sensor is used for measuring the fillet radius of the pipe fitting in real time so as to feed back through a control system, and further whether to continue to inject a liquid medium or not and the specific volume to be injected are determined. Compared with the traditional control method for controlling the dimensional accuracy of the pipe fitting by taking the internal pressure as a control variable, the method has the advantages that the dimensional accuracy of the internal high-pressure forming part based on volume loadingThe control method can realize real-time accurate control of the pipe fitting fillet size precision and has the advantages of high process stability, low requirement on the die precision and the like. However, the above-mentioned volume loading method needs to utilize displacement sensor to carry out real-time measurement and feedback in fillet department to guarantee the fillet precision, and mould and control are all comparatively complicated, though solved the problem of pipe fitting fillet radius size precision control, when fillet radius size precision satisfies the demands, radial or other direction size precision whether satisfy the demands must be unknown. In addition, the sizes are calculated or measured under the condition of internal pressure loading, and the influence of the rebound generated by the pipe fitting after the internal pressure is unloaded on the final size precision is not considered. For the internal high-pressure forming of a pipe with high strength (high-strength steel) and small elastic modulus (aluminum alloy or magnesium alloy), the pipe fitting can generate obvious springback after internal pressure is unloaded. Therefore, how to control or compensate the springback in the internal high-pressure forming is the key to obtain the high-precision formed pipe. According to the traditional method, the rebound quantity of each part of the pipe fitting can be predicted firstly, and then the die cavity of the internal high-pressure forming die is modified according to the geometric error of the shape of the rebounded pipe fitting and the shape required by the design, so that the rebound control is carried out by die compensation. However, the conventional die compensation method needs to repeatedly modify the die, so that the die machining precision requirement is high, the die manufacturing cost is high, the production period is long, and one set of die cannot be suitable for forming tube blanks with different properties. In summary, a quick and effective method for controlling the rebound of a hydraulic forming member for a pipe has not been developed.
Disclosure of Invention
The invention aims to provide a method and a system for controlling resilience of a hydraulic forming part based on liquid volume loading, which aim to solve the problem that the dimensional accuracy of the forming part is reduced by resilience after pressure relief in the process of high-pressure forming in a pipe, so that the pipe fitting meeting the requirement of set dimensional accuracy can be quickly obtained.
In order to achieve the aim, the invention provides a rebound control method of a hydraulic forming piece based on liquid volume loading, which comprises the following steps:
step S1: determining the bulging amount of the die during forming;
step S2: determining a target pressure;
step S3: determining the volume of the inner cavity of the pipe fitting at the end of loading according to the bulging amount of the die during forming;
step S4: determining the liquid volume compression compensation amount according to the target pressure and the volume of the inner cavity of the pipe fitting at the end of loading;
step S5: determining the liquid volume increase in the absence of compression;
step S6: determining the total liquid volume increment according to the liquid volume increment in the absence of compression and the liquid volume compression compensation amount;
step S7: and filling liquid into the tube blank according to the total liquid volume increment to realize the rebound control of the hydraulic forming piece and obtain the tube fitting meeting the set size precision requirement.
Optionally, the specific formula for determining the die bulging amount during forming is as follows:
wherein, σ'siThe flow stress of the tube blank at the unloading point B, and Delta D' is the bulging amount of the die during forming, D0The diameter of a die cavity of a bulging area, K is the strength coefficient of a pipe blank, n is the strain hardening index of the pipe blank, d0The initial pipe diameter of the pipe blank, and E is the elastic modulus.
Optionally, the determining, according to the amount of bulging of the die during forming, the volume of the inner cavity of the pipe at the end of loading specifically includes:
when the cross section of the pipe fitting is a circular cross section, a specific formula for determining the volume of the inner cavity of the pipe fitting when the loading is finished is as follows:
wherein, Delta D' is the bulging amount of the die during forming, D0The diameter of a die cavity of the die in an expansion area, L is the length of the expansion area, and t is the wall thickness of the pipe fitting;
when the cross section of the pipe fitting is a rectangular cross section, the specific formula for determining the volume of the inner cavity of the pipe fitting when the loading is finished is as follows:
wherein a is the length of the rectangular cross section of the pipe fitting, b is the width of the rectangular cross section of the pipe fitting, and r is the radius of the transition fillet;
and when the cross section of the pipe fitting is a special-shaped cross section, inputting the bulging amount of the die during forming into CAD software to determine the volume of the inner cavity of the pipe fitting after loading.
Optionally, the liquid volume compression compensation amount is determined according to the target pressure and the volume of the inner cavity of the pipe fitting at the end of loading, and the specific formula is as follows:
wherein, is Δ VpIs a liquid volume compression compensation, p'crIs the target pressure, V is the volume of the lumen of the tube at the end of the loading, EVIs the liquid bulk modulus.
Optionally, the determining the volume increase of the liquid without compression specifically includes:
when the cross section of the pipe fitting is a circular cross section, the specific formula for determining the liquid volume increment without compression is as follows:
wherein, is Δ V0The volume increase of liquid when no compression occurs, and delta D' is the bulging amount of the die during forming, D0The diameter of the die cavity in the bulging area, L the length of the bulging area, d0The initial pipe diameter of the pipe blank;
when the cross section of the pipe fitting is a rectangular cross section, the specific formula for determining the liquid volume increment without compression is as follows:
wherein a is the length of the rectangular cross section of the pipe fitting, b is the width of the rectangular cross section of the pipe fitting, and r is the radius of the transition fillet;
when the cross section of the pipe fitting is a special-shaped cross section, the specific formula for determining the liquid volume increment without compression is as follows:
wherein V is the volume of the inner cavity of the pipe fitting at the end of loading, t0The initial wall thickness of the tube blank.
Optionally, the total liquid volume increase is determined according to the liquid volume increase without compression and the liquid volume compression compensation amount, and the specific formula is as follows:
ΔV＝ΔV0+ΔVp；
wherein DeltaV is the target pressure p 'reached by the liquid pressure in the pipe blank'crTotal liquid volume increase, Δ V, required0Volume increase of liquid, Δ V, without compressionpThe liquid volume compression compensation is carried out.
The invention also provides a hydraulic forming rebound control system based on liquid volume loading, which comprises:
the device comprises an upper die, a lower die, a pipe blank, a left punch, a right punch, a supercharger and a control system;
the pipe blank is arranged on the lower die, the left punch is arranged on the left side of the pipe blank, the right punch is arranged on the right side of the pipe blank, after the upper die descends and the lower die is closed, the left punch and the right punch are used for sealing two sides of the pipe blank, and the control system sequentially passes through the supercharger and the channels on the left punch to fill liquid into the pipe blank according to the rebound control method, so that a pipe fitting meeting the requirement of size precision is obtained.
Optionally, the cross section of the pipe fitting is a circular section, a rectangular section or a special-shaped section.
Optionally, the tube blank is a metal tube blank.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention discloses a method and a system for controlling resilience of a hydraulic forming piece based on liquid volume loading, wherein the method comprises the following steps: determining the bulging amount of the die during forming; determining a target pressure; determining the volume of the inner cavity of the pipe fitting at the end of loading according to the bulging amount of the die during forming; determining the liquid volume compression compensation amount according to the target pressure and the volume of the inner cavity of the pipe fitting at the end of loading; determining the liquid volume increase in the absence of compression; and determining the total liquid volume increment according to the liquid volume increment in the non-compression state and the liquid volume compression compensation amount, and filling liquid into the tube blank according to the total liquid volume increment, so as to realize the rebound control of the hydraulic forming part and obtain the pipe fitting meeting the set size precision requirement. The rebound control method for the hydraulic forming part disclosed by the invention avoids the problems of repeated die repair, long period, high cost and the like of the traditional rebound compensation method, can accurately compensate the rebound of the pressure-relieved pipe fitting by controlling the volume of high-pressure liquid to enable the die to generate elastic deformation, and can be suitable for the precise forming of pipe blanks with different performances or wall thicknesses by controlling the bulging amount of the same set of die. In addition, the liquid volume compression is considered, the target pressure is converted into the liquid volume increment, the liquid volume is used as a control variable to control the size precision of the pipe fitting, and the problems of large size dispersion, poor precision and the like caused by pressure fluctuation in the shaping stage of the traditional pressure loading method are solved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a schematic diagram showing the positions of a tube blank and a mold in a closing and filling stage according to an embodiment of the invention;
FIG. 2 is a schematic view of a tube blank completely fitting a mold in a shaping stage according to an embodiment of the invention;
FIG. 3 is a schematic diagram of an equivalent stress-strain curve and elastic recovery of a tube blank according to an embodiment of the present invention;
FIG. 4 is a schematic view showing the positional relationship between the A-A section tube blank and the die after pressurizing and depressurizing the internal pressure in the embodiment of the invention;
FIG. 5 is a schematic diagram showing a positional relationship between the tube blank with the A-A section and the die when the die is expanded in the shaping stage according to the embodiment of the present invention;
FIG. 6 is a schematic diagram showing the relationship between the tube blank and the die after the internal pressure is pressurized and unloaded under the condition that the bulging amount of the die is smaller than the pipe fitting resilience amount according to the embodiment of the invention;
FIG. 7 is a schematic diagram showing the relationship between the tube blank and the die after the internal pressure is pressurized and unloaded under the condition that the bulging amount of the die is equal to the pipe fitting resilience amount in the embodiment of the invention.
FIG. 8 is a schematic diagram showing the relationship between the tube blank and the die after the internal pressure is pressurized and unloaded under the condition that the bulging amount of the die is greater than the pipe fitting resilience amount according to the embodiment of the invention;
FIG. 9 is a graph of pipe diameter versus die swell, pipe spring back, and fluid pressure for an embodiment of the present invention;
FIG. 10 is a schematic view of the non-equal diameter circular cross-section tube blank completely attaching to the die in the shaping stage of the embodiment of the invention;
FIG. 11 is a schematic view of a rectangular cross-section tube blank fully fitted to a mold in a shaping stage according to an embodiment of the present invention;
FIG. 12 is a flow chart of a method for controlling rebound of a hydroforming member based on fluid volume loading according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a method and a system for controlling resilience of a hydraulic forming part based on liquid volume loading, which aim to solve the problem that the dimensional accuracy of the forming part is reduced by resilience after pressure relief in the process of high-pressure forming in a pipe, so that the pipe fitting meeting the requirement of set dimensional accuracy can be quickly obtained.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
As shown in fig. 1, the present invention provides a hydraulic form rebound control system based on liquid volume loading, the system comprising:
the device comprises an upper die 1, a lower die 4, a tube blank 6, a left punch 2, a right punch 5, a supercharger 7 and a control system 8;
the tube blank 6 is arranged on the lower die 4, the left punch 2 is arranged on the left side of the tube blank 6, the right punch 5 is arranged on the right side of the tube blank 6, when the upper die 1 descends and the lower die 4 is closed, the left punch 2 and the right punch 5 are used for sealing two sides of the tube blank 6, and the control system 8 sequentially fills liquid into the tube blank through the supercharger 7 and the channel 3 on the left punch 2;
that is, the control system 8 determines whether the volume of the liquid charged is greater than or equal to the liquid volume increase; if the volume increment of the liquid is larger than or equal to the volume increment of the liquid, the liquid in the pipe fitting is unloaded, the pipe fitting rebounds, and the pipe fitting meeting the set size precision requirement is obtained; if the volume increment of the liquid is less than the volume increment of the liquid, the liquid is continuously filled into the tube blank 6 through the supercharger 7, and the tube fitting meeting the requirement of dimensional accuracy is obtained.
The following embodiments of the present invention take the cross section of the pipe as a circular section for analysis, and assume that the initial pipe diameter of the pipe blank 6 is d0Initial wall thickness t0The length of the bulging area is L, and the volume of the inner cavity of the initial tube blank is
The diameter of the die cavity of the bulging area is D0(D0And also the design value for the target pipe diameter); diameter of the pipe fitting is DTarget expansion ratio of the pipe member of
After filling the tube blank 6 with liquid, the control system continues to fill liquid into the tube blank 6 through the supercharger 7 and the channel 3 on the left punch 2 in sequence, and the volume change of the liquid without compression (the volume increment of the injected liquid required for forming the tube after the initial tube blank is filled with the liquid) is recorded as delta V0The liquid pressure in the tube blank 6 gradually increases with the increase of the volume of the injected liquid, and when the liquid pressure p in the tube blank 6 is equal to pcrWhen in use, the tube blank 6 is just completely attached to the cavity of the mould, and the mould does not elastically deform, wherein p iscrTo shape the pressure. At this time, the pipe diameter is just equal to the die diameter, i.e., D ═ D0The liquid volume increase Δ V required for this process is shown in FIG. 20Comprises the following steps:
however, as can be seen from the equivalent stress-strain curve and the elastic recovery diagram of the tube blank shown in fig. 3, after the tube blank is subjected to a certain amount of plastic deformation, when the external load is removed, the tube blank is subjected to a certain elastic recovery. As shown in FIG. 3, the tube blank was loaded with flow stress σ 'through OAB'siThe unloading is carried out, the tube blank elastically recovers along BC, and the recovery strain is delta epsiloniFrom the blank flowing stress σ 'at the unloading point B'siAnd the modulus of elasticity E, i.e. Δ εi＝σ′siAnd E is used. Therefore, when the liquid pressure in the pipe billet 6 in fig. 2 is relieved, the pipe billet 6 will have a certain elastic recovery, and the positional relationship between the pipe billet and the die after the relief of the internal pressure is as shown in fig. 4. The diameter D of the pipe fitting is smaller than the diameter D of the die0，D＝D0- Δ D, where Δ D is the pipe springback, in which case the pipe size obtained is smaller than the design value.
When the liquid is continuously filled into the tube blank 6 through the channel 3 on the left punch 2 by the pressure booster 7 at the end of the shaping phase shown in FIG. 2, the liquid pressure in the tube blank 6 is continuously increased (p is more than p)cr) At the moment, the die can follow the pipe blank6 are deformed together. As shown in fig. 5, when the amount of elastic deformation (bulging amount) of the die is Δ D' in consideration of the elastic deformation of the die, the liquid volume increase Δ V at that time is0Comprises the following steps:
pressure p of shaping stage during high pressure forming in pipecrGenerally high, the liquid volume compression must be taken into account when the pressure is greater than a certain value (for example 100 MPa). Liquid volume compression compensation amount DeltaVpCan be expressed by equation 3:
thus, considering the liquid volume compression, the total liquid volume increase Δ V when the mold deformation is Δ D' can be expressed by equation 4, where Δ V is the total liquid volume increase, Δ V0Δ V to account for the increase in liquid volume required when compressing the liquid volumepFor taking into account the compensation of the compression of the liquid volume during the compression of the liquid volume, V is the volume of the inner cavity of the tube at the end of the loading, EVThe liquid bulk modulus is, and p is the liquid pressure inside the tube blank at the end of loading.
When the liquid volume increment reaches delta V shown in the formula 4 and the liquid pressure in the pipe blank reaches the pressure shown in the formula 4, the diameter D of the pipe fitting is equal to D0+ Δ D ', the pipe diameter changes to D ═ D' due to elastic recovery of the pipe after unloading the liquid pressure0+ Δ D' - Δ D, wherein Δ D0Δ D' - Δ D is the tube size deviation. Therefore, the dimensional accuracy of the final pipe can be controlled according to the relation between the die bulging amount delta D' and the pipe resilience delta D. When the bulging amount delta D 'of the die is equal to the rebound amount delta D of the pipe fitting, namely delta D', delta D, the size deviation is zero, and the diameter of the pipe fitting is just equal to that of the dieThe diameter (design value) was measured with the highest accuracy, and the liquid pressure in the tube blank 6 was p'crDefined as the target pressure. At a target pressure p'crFor the sake of limitation, the following three cases can be distinguished:
when p iscr＜p＜p′crIf the bulging amount of the die is smaller than the resilience of the pipe fitting, the value is delta D' < delta D, and D < D0I.e. the resulting pipe diameter is smaller than the die diameter (design value), as shown in fig. 6.
When p ═ p'crIf the die bulging amount is equal to the pipe resilience amount, the die bulging amount is Δ D ═ Δ D, and at the moment, D ═ D0I.e. the resulting pipe diameter is exactly equal to the die diameter (design value), the dimensional accuracy is highest, as shown in fig. 7.
When p is > p'crWhen the bulging amount of the die is larger than the resilience of the pipe fitting, the value is more than delta D', and D is more than D0I.e. the resulting pipe diameter size is larger than the die size (design value), as shown in fig. 8.
Fig. 9 shows the relationship between the pipe diameter D and the die deformation amount Δ D', the pipe spring-back amount Δ D, and the internal pressure p.
Therefore, the target pressure p 'required when the die bulging amount is equal to the pipe resilience amount is obtained according to theoretical calculation or experiment'crThe total liquid volume increment Δ V required for forming the pipe with the highest dimensional accuracy can be obtained by substituting the formula 4. When the liquid volume increment reaches delta V during forming, the pipe fitting rebounds after pressure relief, the size of the pipe fitting is just equal to the size (designed value) of the die, and the precision is highest.
As an alternative embodiment, the cross section of the pipe fitting of the present invention is a circular section, a rectangular section or a profiled section. FIG. 10 is a schematic diagram showing that the non-equal-diameter circular-section tube blank is completely attached to the mold in the shaping stage; fig. 11 shows a schematic view of the rectangular section tube blank fully fitting the die during the shaping stage.
As an alternative embodiment, the tube blank 6 of the present invention is a metal tube blank. The tube blank 6 includes, but is not limited to, low carbon steel, high strength steel, aluminum alloy, magnesium alloy tube.
Fig. 12 is a flowchart of a method for controlling rebound of a hydroforming member based on liquid volume loading according to an embodiment of the present invention, as shown in fig. 12, the method for controlling rebound includes:
step S1: determining the bulging amount of the die during forming;
step S2: determining a target pressure;
step S3: determining the volume of the inner cavity of the pipe fitting at the end of loading according to the bulging amount of the die during forming;
step S4: determining the liquid volume compression compensation amount according to the target pressure and the volume of the inner cavity of the pipe fitting at the end of loading;
step S5: determining the liquid volume increase in the absence of compression;
step S6: determining the total liquid volume increment according to the liquid volume increment in the absence of compression and the liquid volume compression compensation amount;
step S7: and filling liquid into the tube blank according to the total liquid volume increment to realize the rebound control of the hydraulic forming piece and obtain the tube fitting meeting the set size precision requirement.
The individual steps are discussed in detail below:
step S1: determining the bulging quantity delta D' of the die during forming, wherein the bulging formula of the die is as follows:
wherein, σ'siThe flow stress of the tube blank at the unloading point B, and Delta D' is the bulging amount of the die during forming, D0The diameter of a die cavity of a bulging area, K is the strength coefficient of a pipe blank, n is the strain hardening index of the pipe blank, d0The initial pipe diameter of the pipe blank, and E is the elastic modulus.
When the die bulging amount Δ D' is determined using equation 5, the following conditions are distinguished:
when the cross section of the pipe fitting is a circular section, the formula of the die cavity diameter of the bulging area is as follows:
D0set value (6)
When the cross section of the pipe fitting is a rectangular cross section, the rectangular cross section is equivalently converted into a circular cross section (the circumferences are equal), and the equivalent bulging area die cavity diameter formula is as follows:
wherein a is the length of the rectangular cross section of the pipe fitting, b is the width of the rectangular cross section of the pipe fitting, the length-width ratio a/b is fixed, and r is the radius of the transition fillet;
when the cross section of the pipe fitting is the special-shaped cross section, the special-shaped cross section is equivalently converted into a circular cross section (the circumferences are equal), and the equivalent formula of the diameter of the die cavity of the bulging area is as follows:
D0＝S/π (8)
wherein S is the perimeter of the special-shaped section.
Step S2: determining the target pressure specifically comprises the following steps:
step S21: determining a target pressure through an experimental method;
step S211: applying different internal pressures p to the tube blank 6, carrying out a plurality of groups of experiments, and measuring the diameter D of the tube after unloading the internal pressure. When the diameter D of the pipe fitting is equal to the diameter D of the die cavity0The corresponding internal pressure is the target pressure p of the tube blankc′r。
Step S212: for non-equal diameter pipe with circular section, the diameter D of the die cavity0Varying along the axial direction of the pipe, with the diameter D of the mould cavity being the highest position of dimensional accuracy requirements (as in section B-B in figure 10)0The corresponding internal pressure is used as the target pressure p 'of the tube blank'cr。
Step S22: determining the target pressure through theoretical calculation, specifically comprising:
step S221: when the cross section of the pipe fitting is a circular cross section, determining a target pressure;
step S2211: determining the flowing stress of a die material according to the bulging amount of the die during forming, wherein the specific formula is as follows:
wherein σseThe flow stress of the die material, Δ D' is the amount of die bulging during forming, D0The diameter of the die cavity in the bulging area, EeIs the modulus of elasticity of the mold;
step S2212: determining initial target pressure required when the die bulging amount is equal to the pipe fitting resilience amount according to an initial target pressure formula;
step S2213: taking the initial target pressure as a target pressure;
the target pressure formula is:
wherein, p'crIs target pressure, σ'siFlow stress after work hardening for pipe bulging, riAnd reRespectively the inner and outer radii of the pipe, sigmaseIs the flow stress of the mold material, RiAnd ReRespectively the radius of a mold cavity and the outer radius;
step S222: when the cross section of the pipe fitting is a rectangular cross section, determining the target pressure, specifically comprising:
step S2221: determining an initial target pressure according to an initial target pressure formula;
step S2222: determining a shaping pressure according to a first shaping pressure formula; the first shaping pressure formula is:
wherein p iscFor the shaping pressure, r is a transition fillet radius, t is the pipe wall thickness sigma'siThe flow stress after the pipe fitting bulging is processed and hardened;
step S2223: determining whether the initial target pressure is greater than or equal to the shaping pressure; if the initial target pressure is greater than or equal to the shaping pressure, then taking the initial target pressure as a target pressure; if the initial target pressure is less than the shaping pressure, then taking the shaping pressure as a target pressure;
step S223: when the cross section of the pipe fitting is a special-shaped cross section, determining the target pressure, specifically comprising:
step S2231: determining an initial target pressure according to an initial target pressure formula;
step S2232: determining a shaping pressure according to a second shaping pressure formula; the second shaping pressure formula is:
wherein p iscTo shape the pressure, rminIs the minimum value of the transition fillet radius, t is the pipe wall thickness, sigma'siThe flow stress after the pipe fitting bulging is processed and hardened;
step S2233: determining whether the initial target pressure is greater than or equal to the shaping pressure; if the initial target pressure is greater than or equal to the shaping pressure, then taking the initial target pressure as a target pressure; and if the initial target pressure is smaller than the shaping pressure, taking the shaping pressure as the target pressure.
Step S3: according to when shaping the pipe fitting inner chamber volume when mould bulging volume confirms the loading and finishes specifically includes:
step S31: when the cross section of the pipe fitting is a circular cross section, a specific formula for determining the volume of the inner cavity of the pipe fitting when the loading is finished is as follows:
wherein, Delta D' is the bulging amount of the die during forming, D0The diameter of a die cavity of the bulging area is L, the length of the bulging area is L, and the wall thickness of the pipe fitting is t.
Step S32: when the cross section of the pipe fitting is a rectangular cross section, the specific formula for determining the volume of the inner cavity of the pipe fitting when the loading is finished is as follows:
wherein a is the length of the rectangular cross section of the pipe fitting, b is the width of the rectangular cross section of the pipe fitting, r is the radius of a transition fillet, delta D' is the bulging amount of the die during forming, and L is the length of a bulging area;
step S33: and when the cross section of the pipe fitting is a special-shaped cross section, inputting the bulging amount of the die during forming into CAD software to determine the volume of the inner cavity of the pipe fitting after loading.
Step S4: determining the liquid volume compression compensation amount according to the target pressure and the volume of the inner cavity of the pipe fitting when the loading is finished, wherein the specific formula is as follows:
wherein, is Δ VpIs a liquid volume compression compensation, p'crIs the target pressure, V is the volume of the lumen of the tube at the end of the loading, EVIs the liquid bulk modulus.
Step S5: determining the liquid volume increment in the absence of compression, which specifically comprises:
step S51: when the cross section of the pipe fitting is a circular cross section, the specific formula for determining the liquid volume increment without compression is as follows:
wherein, is Δ V0The volume increase of liquid when no compression occurs, and delta D' is the bulging amount of the die during forming, D0The diameter of the die cavity in the bulging area, L the length of the bulging area, d0Is the initial pipe diameter of the pipe blank.
Step S52: when the cross section of the pipe fitting is a rectangular cross section, the specific formula for determining the liquid volume increment without compression is as follows:
wherein, a is the length of the rectangular cross section of the pipe fitting, b is the width of the rectangular cross section of the pipe fitting, r is the radius of a transition fillet, Delta D' is the bulging amount of the die during forming, D0The initial pipe diameter of the pipe blank, and L is the length of the bulging area;
step S53: when the cross section of the pipe fitting is a special-shaped cross section, the specific formula for determining the liquid volume increment without compression is as follows:
wherein V is the volume of the inner cavity of the pipe fitting at the end of loading, t0Initial wall thickness of the tube blank, d0Is the initial pipe diameter of the pipe blank, and L is the length of the bulging area.
Step S6: determining the total liquid volume increment according to the liquid volume increment in the absence of compression and the liquid volume compression compensation amount; the concrete formula is as follows:
ΔV＝ΔV0+ΔVp (19)
wherein DeltaV is the target pressure p 'reached by the liquid pressure in the pipe blank'crTotal liquid volume increase, Δ V, required0Volume increase of liquid, Δ V, without compressionpThe liquid volume compression compensation is carried out.
Step S61: when the cross section of the pipe fitting is a circular cross section, a specific formula for determining the volume increment of the total liquid is as follows:
wherein DeltaV is the target pressure p 'reached by the liquid pressure in the pipe blank'crTotal liquid volume increase, Δ V, required0Volume increase of liquid, Δ V, without compressionpThe liquid volume compression compensation amount is obtained, V is the volume of the inner cavity of the pipe fitting at the end of loading, EVThe liquid bulk modulus,. DELTA.D' is the amount of die swell during forming, D0For expanding the mould cavity straight in the areaDiameter, L is the length of the bulging area, t is the wall thickness of the pipe, d0Is the initial pipe diameter of the pipe blank.
Step S62: when the cross section of the pipe fitting is a rectangular cross section, a specific formula for determining the volume increment of the total liquid is as follows:
wherein DeltaV is the target pressure p 'reached by the liquid pressure in the pipe blank'crTotal liquid volume increase, Δ V, required0Δ V to account for the increase in liquid volume required when compressing the liquid volumepThe compensation amount for liquid volume compression, delta D' is the amount of die bulging during forming, D0For the initial pipe diameter of the pipe blank, a is the length of the rectangular cross section of the pipe fitting, b is the width of the rectangular cross section of the pipe fitting, r is the radius of a transition fillet, t is the wall thickness of the pipe fitting, L is the length of the bulging area, EVIs the liquid bulk modulus;
step S63: when the cross section of the pipe fitting is a special-shaped cross section, a specific formula for determining the volume increment of the total liquid is as follows:
wherein DeltaV is the target pressure p 'reached by the liquid pressure in the pipe blank'crTotal liquid volume increase, Δ V, required0Δ V to account for the increase in liquid volume required when compressing the liquid volumepThe liquid volume compression compensation amount is obtained, V is the volume of the inner cavity of the pipe fitting at the end of loading, EVIs the liquid bulk modulus.
Step S7: and filling liquid into the tube blank according to the total liquid volume increment to realize the rebound control of the hydraulic forming piece and obtain the tube fitting meeting the set size precision requirement.
Specific example 1
The method comprises the following steps: taking the example of an internal high pressure forming pipe fitting made of SAPH440 steel, the diameter d of the pipe billet060mm thick t02mm, length of bulging zone 300mm, of pipeThe target expansion ratio was λ 20%. The elastic modulus E of the SAPH440 pipe is 210GPa, and the flow stress strain curve is
The diameter of the die cavity of the bulging area is D0The die is simplified to a thick-walled cylinder with an outer radius R of 72mme180mm, the material of the die adopts Cr12MoV, and the elastic modulus is Ee207GPa, yield strength 650 MPa. According to the known parameters, the bulging quantity delta D' of the die can be determined to be 0.18mm, and the rebound quantity delta D of the pipe fitting is determined to be 0.18 mm. Thus, in combination with the condition of a constant pipe volume, the pipe outer radius reAnd an inner radius riAre respectively re36.09mm and ri34.44mm, and t 1.65 mm. The flow stress σ ' after work hardening of the pipe can be obtained from the die swell amount Δ D ' of 0.18mm 'siAnd die material flow stress σseAre respectively sigma'si524MPa and σse517MPa, the target pressure p 'can be obtained according to the known parameters'cr314.8 MPa. Obtaining that the internal liquid pressure of the tube blank reaches the target pressure p'crThe increase in total liquid volume required, i.e.
Wherein the liquid bulk modulus EV1950 MPa. From the above known parameters, Δ V is 0.595L. That is, after the tube blank was filled with the liquid, the volume increase Δ V of the liquid to be injected into the tube blank for molding was 0.595L.
Step two: and (3) putting the SAPH440 pipe blank into an internal high-pressure forming die, descending an upper die to carry out die assembly, advancing a left punch and a right punch after the die assembly is completely carried out to seal two ends of the pipe blank, and filling liquid into the pipe blank.
Step three: and continuously injecting liquid into the tube blank by using the supercharger, gradually deforming the tube blank, controlling the volume increment of the liquid injected into the tube blank by using the control system, and feeding back by using the control system to stop loading when the volume increment of the injected liquid reaches 0.595L.
Step four: and (3) relieving the pressure of the supercharger, enabling the pipe fitting to rebound, opening the die of the die, and taking out the pipe fitting to obtain the hydroformed pipe fitting with the dimensional precision meeting the design requirement.
The dimensional accuracy of the SAPH440 pipe formed by the embodiment is improved by more than 40% compared with the traditional pressure control method without considering the deformation of the die.
Specific example 2
The method comprises the following steps: taking the example of forming a pipe fitting with a rectangular cross section by SAPH440 steel at internal high pressure, the diameter d of the pipe blank060mm thick t02mm, bulging district length is 300mm for L, and the size of target pipe fitting rectangular cross-section is: the length a is 65mm, the width b is 50mm, and the transition fillet radius r is 6 mm. The equivalent transformation of a rectangular section into a circular section (equal circumference) with an equivalent diameter D069.9 mm. The elastic modulus E of the SAPH440 pipe is 210GPa, and the flow stress strain curve is
The diameter of the die cavity of the bulging area is D069.9mm, the die is simplified into a thick-walled cylinder with an outer radius Re180mm, the material of the die adopts Cr12MoV, and the elastic modulus is Ee207GPa, yield strength 650 MPa. According to the known parameters, the bulging quantity delta D' of the die can be determined to be 0.17mm, and the rebound quantity delta D of the pipe fitting is determined to be 0.17 mm. Therefore, the equivalent outer radius r of the rectangular section pipe is combined with the condition that the volume of the pipe is not changedeAnd an inner radius riAre respectively re35.04mm and ri33.34mm and the tube wall thickness t 1.70 mm. The flow stress σ ' after work hardening of the pipe can be obtained from the die swell amount Δ D ' of 0.17mm 'siAnd die material flow stress σseAre respectively sigma'si511MPa and σse503MPa, the target pressure p 'can be obtained according to the known parameters'cr308.7 MPa. Furthermore, for a rectangular cross section, the shaping pressure determined by the radius of the fillet when the fillet is fully conformed is
Thus, target pressure is selected to be p'cr308.7 MPa. Obtaining the target pressure p 'of the internal liquid pressure of the tube blank according to the known parameters'crWhen the required total liquid volume increment delta V is 0.250L, the liquid volume modulus E is solvedV1950 MPa. Namely, after the pipe blank is filled with the liquid, the liquid volume increment delta V which needs to be injected into the pipe blank for forming the pipe fitting with the rectangular section is 0.250L. Other steps are the same as those in embodiment 1 and will not be discussed one by one.
The dimensional accuracy of the SAPH440 rectangular section pipe formed by the embodiment is improved by more than 20% compared with that of the traditional pressure control method without considering the deformation of the die.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (9)
1. A method for controlling rebound of a hydraulic forming member based on liquid volume loading is characterized by comprising the following steps:
step S1: determining the bulging amount of the die during forming;
step S2: determining a target pressure;
step S3: determining the volume of the inner cavity of the pipe fitting at the end of loading according to the bulging amount of the die during forming;
step S4: determining the liquid volume compression compensation amount according to the target pressure and the volume of the inner cavity of the pipe fitting at the end of loading;
step S5: determining the liquid volume increase in the absence of compression;
step S6: determining the total liquid volume increment according to the liquid volume increment in the absence of compression and the liquid volume compression compensation amount;
step S7: filling liquid into the tube blank according to the total liquid volume increment to realize the rebound control of the hydraulic forming part and obtain the tube fitting meeting the set size precision requirement;
step S2: determining the target pressure specifically comprises the following steps:
step S21: determining the target pressure through an experimental method, which specifically comprises the following steps:
step S211: applying different internal pressures p to the pipe blank, performing a plurality of groups of experiments, and measuring the diameter D of the pipe fitting after the internal pressures are unloaded; when the diameter D of the pipe fitting is equal to the diameter D of the die cavity0In this case, the corresponding internal pressure is the target pressure p 'of the blank tube'cr；
Step S22: determining the target pressure through theoretical calculation, specifically comprising:
step S221: when the cross section of the pipe fitting is a circular cross section, determining a target pressure;
step S2211: determining the flowing stress of a die material according to the bulging amount of the die during forming, wherein the specific formula is as follows:
wherein σseThe flow stress of the die material, Δ D' is the amount of die bulging during forming, D0The diameter of the die cavity in the bulging area, EeIs the modulus of elasticity of the mold;
step S2212: determining initial target pressure required when the die bulging amount is equal to the pipe fitting resilience amount according to a target pressure formula;
step S2213: taking the initial target pressure as a target pressure;
the target pressure formula is:
wherein, p'crIs target pressure, σ'siFlow stress after work hardening for pipe bulging, riAnd reRespectively the inner and outer radii of the pipe, sigmaseIs a dieHaving a material flow stress, RiAnd ReRespectively the radius of a mold cavity and the outer radius;
step S222: when the cross section of the pipe fitting is a rectangular cross section, determining the target pressure, specifically comprising:
step S2221: determining an initial target pressure according to a target pressure formula;
step S2222: determining a shaping pressure according to a first shaping pressure formula; the first shaping pressure formula is:
wherein p iscFor the shaping pressure, r is a transition fillet radius, t is the pipe wall thickness sigma'siThe flow stress after the pipe fitting bulging is processed and hardened;
step S2223: determining whether the initial target pressure is greater than or equal to the shaping pressure; if the initial target pressure is greater than or equal to the shaping pressure, then taking the initial target pressure as a target pressure; if the initial target pressure is less than the shaping pressure, then taking the shaping pressure as a target pressure;
step S223: when the cross section of the pipe fitting is a special-shaped cross section, determining the target pressure, specifically comprising:
step S2231: determining an initial target pressure according to a target pressure formula;
step S2232: determining a shaping pressure according to a second shaping pressure formula; the second shaping pressure formula is:
wherein p iscTo shape the pressure, rminIs the minimum value of the transition fillet radius, t is the pipe wall thickness, sigma'siThe flow stress after the pipe fitting bulging is processed and hardened;
step S2233: determining whether the initial target pressure is greater than or equal to the shaping pressure; if the initial target pressure is greater than or equal to the shaping pressure, then taking the initial target pressure as a target pressure; and if the initial target pressure is smaller than the shaping pressure, taking the shaping pressure as the target pressure.
2. The method for controlling the rebound of a hydroformed member based on liquid volume loading according to claim 1, wherein the amount of die swell during forming is determined according to the following formula:
wherein, σ'siThe flow stress of the tube blank at the unloading point B, and Delta D' is the bulging amount of the die during forming, D0The diameter of a die cavity of a bulging area, K is the strength coefficient of a pipe blank, n is the strain hardening index of the pipe blank, d0The initial pipe diameter of the pipe blank, and E is the elastic modulus.
3. The method for controlling resilience of a hydroforming member based on liquid volume loading according to claim 1, wherein the determining the volume of the inner cavity of the tube at the end of loading according to the amount of bulging of the die during forming comprises:
when the cross section of the pipe fitting is a circular cross section, a specific formula for determining the volume of the inner cavity of the pipe fitting when the loading is finished is as follows:
wherein, Delta D' is the bulging amount of the die during forming, D0The diameter of a die cavity of the die in an expansion area, L is the length of the expansion area, and t is the wall thickness of the pipe fitting;
when the cross section of the pipe fitting is a rectangular cross section, the specific formula for determining the volume of the inner cavity of the pipe fitting when the loading is finished is as follows:
wherein a is the length of the rectangular cross section of the pipe fitting, b is the width of the rectangular cross section of the pipe fitting, and r is the radius of the transition fillet;
and when the cross section of the pipe fitting is a special-shaped cross section, inputting the bulging amount of the die during forming into CAD software to determine the volume of the inner cavity of the pipe fitting after loading.
4. The method for controlling rebound of a hydroformed member according to claim 1, wherein the compensation amount for compression of the liquid volume is determined according to the target pressure and the volume of the inner cavity of the tube at the end of the loading by the following formula:
wherein, is Δ VpIs a liquid volume compression compensation, p'crIs the target pressure, V is the volume of the lumen of the tube at the end of the loading, EVIs the liquid bulk modulus.
5. The method for controlling the rebound of a hydroformed member based on fluid volume loading according to claim 1, wherein the determining the fluid volume increase without compression comprises:
when the cross section of the pipe fitting is a circular cross section, the specific formula for determining the liquid volume increment without compression is as follows:
wherein, is Δ V0The volume increase of liquid when no compression occurs, and delta D' is the bulging amount of the die during forming, D0The diameter of the die cavity in the bulging area, L the length of the bulging area, d0The initial pipe diameter of the pipe blank;
when the cross section of the pipe fitting is a rectangular cross section, the specific formula for determining the liquid volume increment without compression is as follows:
wherein a is the length of the rectangular cross section of the pipe fitting, b is the width of the rectangular cross section of the pipe fitting, and r is the radius of the transition fillet;
when the cross section of the pipe fitting is a special-shaped cross section, the specific formula for determining the liquid volume increment without compression is as follows:
wherein V is the volume of the inner cavity of the pipe fitting at the end of loading, t0The initial wall thickness of the tube blank.
6. The method of claim 1, wherein the total increase in liquid volume is determined from the increase in liquid volume without compression and the compensation for liquid volume compression by the formula:
ΔV＝ΔV0+ΔVp；
wherein DeltaV is the target pressure p 'reached by the liquid pressure in the pipe blank'crTotal liquid volume increase, Δ V, required0Volume increase of liquid, Δ V, without compressionpThe liquid volume compression compensation is carried out.
7. A hydraulic form rebound control system based on liquid volume loading, the system comprising:
the device comprises an upper die, a lower die, a pipe blank, a left punch, a right punch, a supercharger and a control system;
the pipe blank is arranged on the lower die, the left punch is arranged on the left side of the pipe blank, the right punch is arranged on the right side of the pipe blank, after the upper die descends and the lower die is closed, the left punch and the right punch are used for sealing two sides of the pipe blank, and the control system fills liquid into the pipe blank through the passages on the supercharger and the left punch in sequence according to the rebound control method of any one of claims 1 to 6 to obtain a pipe fitting meeting the requirement of size precision.
8. The liquid volume loading based hydroforming member rebound control system according to claim 7, wherein the cross section of the tube is a circular section, a rectangular section or a profiled section.
9. The liquid volume loading based hydroforming member rebound control system according to claim 7, wherein the tube blank is a metal tube blank.
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