The present disclosure relates to a press-forming apparatus.
When a metal material is bent or drawn, for example, through press forming, production is generally performed after processing conditions are determined in advance for each material or in accordance with environmental changes.
For example, PTL 1 discloses a pressing-condition setting apparatus that sets processing conditions to obtain predetermined press quality for even a material varying in quality, plate thickness, or the like.
PTL 1: Unexamined Japanese Patent Publication No. H07-266100
A press-forming apparatus according to an aspect of the present disclosure processes a plate-shaped workpiece, the press-forming apparatus including: a punch that moves in a pressing direction; a die that has a hollow part into which the punch is inserted and has an inclined surface inclined toward the hollow part; a die plate that holds the die; a blank holder that is disposed between the punch and the die and has a holding surface facing the inclined surface of the die; a die load sensor that detects a load generated on the inclined surface of the die as a load divided into loads in three directions including a pressing direction, a first direction perpendicular to the pressing direction, and a second direction perpendicular to the pressing direction and the first direction; a controller that calculates normal force of the die based on the loads in the three directions which are detected by the die load sensor, and calculates the amount of correction of clearance between the die and the blank holder based on the normal force of the die; a first driver that moves the die in the pressing direction based on the amount of correction of clearance; and a second driver that drives the punch in the pressing direction.
(Background to the Present Disclosure)
When bending, drawing, or the like is performed using a press-forming apparatus, processing conditions are determined in advance in consideration of influence of material factors such as a material or a plate thickness of metal material to be processed or environmental factors caused by the press-forming apparatus. The processing conditions can be determined through experience or experiment, or by using simulation, for example. Prediction about the influence of material factors or environmental factors is often difficult, and thus various studies have been made as a method for controlling processing conditions in consideration of these influences.
For example, PTL 1 discloses a method in which a relationship between a physical quantity such as a shape of a press material (metal material) and an appropriate load for a blank holder (appropriate pressing conditions) is obtained in advance, and an appropriate amount of pushing with the blank holder is obtained from the relationship in accordance with an actual physical quantity.
The pressing-condition setting apparatus disclosed in PTL 1 still has a room for improvement in terms of stability of processing. Specifically, the pressing-condition setting apparatus disclosed in PTL 1 has a problem that a clearance between the blank holder and the die cannot be appropriately maintained due to a variation factor difficult in prediction, and thus stable processing cannot be performed. The variation factor difficult in prediction indicates a variation due to characteristics of a material of an object to be processed or an environmental change due to temperature. The variation factor difficult in prediction also indicates environmental changes such as due to forming speed, bottom dead center accuracy, processing dimensional accuracy of a die, force caused by a blank holder, clearance between the blank holder and the die, surface roughness of the die, lubricity between the object to be processed and the die, and the like regarding the press-forming apparatus and the die. Environmental changes as described above are difficult in prediction, and thus causing problems that acquiring an appropriate load of the blank holder in advance is difficult, and maintaining clearance between the blank holder and the die at an appropriate value is difficult.
For this reason, the present inventors have studied a press-forming apparatus capable of correcting clearance and performing stable processing to result in achieving the following disclosure. The present disclosure provides a press-forming apparatus capable of correcting clearance of a die and performing stable processing.
A press-forming apparatus according to a first aspect of the present disclosure processes a plate-shaped workpiece, the press-forming apparatus including: a punch that moves in a pressing direction; a die that has a hollow part into which the punch is inserted and has an inclined surface inclined toward the hollow part; a die plate that holds the die; a blank holder that is disposed between the punch and the die and has a holding surface facing the inclined surface of the die; a die load sensor that detects a load generated on the inclined surface of the die as a load divided into loads in three directions including a pressing direction, a first direction perpendicular to the pressing direction, and a second direction perpendicular to the pressing direction and the first direction; a controller that calculates normal force of the die based on the loads in the three directions which are detected by the die load sensor, and calculates the amount of correction of clearance between the die and the blank holder based on the normal force of the die; a first driver that moves the die in the pressing direction based on the amount of correction of clearance; and a second driver that drives the punch in the pressing direction.
This kind of configuration causes the amount of correction of clearance between the blank holder and the die to be calculated based on normal force of the die, so that a press-forming apparatus capable of performing stable processing while appropriately maintaining the clearance can be provided.
A press-forming apparatus according to a second aspect of the present disclosure may be configured such that the amount of correction of clearance is calculated based on a difference between an impulse calculated from normal force of the die at an appropriate clearance and processing time, and an impulse calculated from normal force of the die during processing and processing time.
This kind of configuration enables the amount of correction of clearance to be calculated more accurately.
A press-forming apparatus according to a third aspect of the present disclosure may further include a punch load sensor that detects a load of the punch applied in the pressing direction, in which the controller may calculate the amount of correction of pushing of the punch based on the load of the punch detected by the punch load sensor, and the second driver may drive the punch based on the amount of correction of pushing of the punch.
This kind of configuration enables performing more stable processing by correcting the amount of pushing of the punch.
A press-forming apparatus according to a fourth aspect of the present disclosure may be configured such that the amount of correction of pushing of the punch is calculated based on a difference between an impulse calculated from a load of the punch with an appropriate amount of pushing and processing time, and an impulse calculated from a load of the punch during processing and processing time.
This kind of configuration enables the amount of correction of pushing of the punch to be calculated more accurately.
A press-forming apparatus according to a fifth aspect of the present disclosure may further include a first gap sensor that detects that the punch is at a bottom dead center.
This kind of configuration enables determining whether an upper die including the punch is displaced from a lower die including the die of the press-forming apparatus.
A press-forming apparatus according to a sixth aspect of the present disclosure may further include a second gap sensor that detects contact between the blank holder and the die plate.
This kind of configuration enables determining whether a relative position of the blank holder with respect to the die plate is appropriate.
A press-forming apparatus according to a seventh aspect of the present disclosure may be configured such that the die includes multiple die pieces, and the die load sensor is disposed on each of the multiple die pieces.
This kind of configuration enables performing more stable processing by accurately calculating the amount of correction of clearance even in processing of a complicated shape.
Hereinafter, exemplary embodiments will be described with reference to the drawings.
As illustrated in
Press-forming apparatus 100 corrects clearance between die 2 and blank holder 3 based on loads applied to die 2 and punch 1 detected by die load sensor 14 and punch load sensor 13, respectively. Correcting the clearance based on the loads applied during processing enables performing stable processing.
Punch 1 is a tool for pressing against workpiece 5 for processing and is attached to slide 7.
As illustrated in
As illustrated in
Die 2 including multiple die pieces 2c to 2f enables reduction in influence that may be caused by processing accuracy, surface roughness, a wear state of punch 1, or the like by adjusting a position of each of die pieces 2c to 2f, so that stable processing can be performed.
Blank holder 3 is attached to slide 7 together with punch 1, and presses workpiece 5 against inclined surface 2a of die 2 during pressing. Blank holder 3 includes holding surface 3a facing inclined surface 2a of die 2 (see
Die plate 4 is a member that holds die 2.
Slide 7 is connected to servomotor 11 via ball screw 12. Servomotor 11 rotates ball screw 12 to drive slide 7 in a pressing direction (Z-direction) at a predetermined speed. Slide 7 is guided by shaft 10 to be vertically driven in the Z-direction with respect to bolster 8. When slide 7 is vertically driven with respect to bolster 8, punch 1 is moved toward die 2 to enable workpiece 5 placed on die 2 to be bent and drawn. The servomotor 11 corresponds to the second driver of the present exemplary embodiment.
Punch 1, die 2, blank holder 3, die plate 4, ejector 6, slide 7, bolster 8, and shaft 10 are attached to forming apparatus body 9.
Die 2 is moved in the pressing direction (Z-direction) by actuator 18 based on the amount of correction of clearance described later. Actuator 18 corresponds to the first driver of the present exemplary embodiment.
Die load sensor 14 detects a load applied to die 2 during processing. The die load sensor is a triaxial load sensor that detects a load applied to die 2 as load components in three directions. In the present exemplary embodiment, die load sensor 14 detects a load applied to die 2 as load components in the pressing direction (Z-direction), a first direction (X-direction) perpendicular to the Z-direction, and a second direction (Y-direction) perpendicular to the pressing direction and the first direction.
In the present exemplary embodiment, die load sensor 14 includes four die load sensors 14c to 14f disposed one by one on die pieces 2c to 2f, respectively, as illustrated in
Punch load sensor 13 detects a load applied to punch 1 during processing. Punch load sensor 13 is a uniaxial load sensor that detects load Pz (see
Controller 30 calculates normal force of die 2 based on the load detected by die load sensor 14 to calculate the amount of correction of clearance between die 2 and blank holder 3 based on the normal force of die 2. Details of controller 30 will be described later.
First gap sensor 15 detects that punch 1 is at a bottom dead center, or punch 1 is at the lowest possible position. For example, first gap sensor 15 is attached to an appropriate position on a lower die of press-forming apparatus 100 including die 2, die plate 4, ejector 6, and bolster 8, and detects contact between an upper die including punch 1, blank holder 3, and slide 7, and the lower die to determine that punch 1 is at the bottom dead center. For example, disposing first gap sensors 15 at respective four corners of the lower die enables determination whether the upper die and the lower die are parallel.
Second gap sensors 16 are disposed at respective four corners of die plate 4 and detect contact between blank holder 3 and die plate 4. In the present exemplary embodiment, second gap sensors 16a to 16d are disposed at the respective four corners of die plate 4 as illustrated in
Controller 30 includes first drive controller 19, second drive controller 20, sensor controller 21, arithmetic unit 22, and determination unit 23. Controller 30 includes a digital circuit such as a microcomputer, a CPU, an MPU, a GPU, a DSP, an FPGA, or an ASIC, for example.
First drive controller 19 causes servomotor 11 to be driven to rotate ball screw 12, thereby vertically driving slide 7 in the pressing direction (Z-direction) at a predetermined speed.
Second drive controller 20 causes actuator 18 to be driven based on the amount of correction of clearance described later to move die 2 in the pressing direction (Z-direction).
Sensor controller 21 is electrically connected to die load sensor 14, punch load sensor 13, first gap sensor 15, and second gap sensor 16, and outputs detection values of the respective sensors to arithmetic unit 22 or determination unit 23.
Arithmetic unit 22 calculates normal force and a difference in impulse based on the detection value from die load sensor 14 or punch load sensor 13. Details will be described later.
Determination unit 23 determines whether to perform clearance correction based on the calculation result of arithmetic unit 22.
Press-forming apparatus 100 causes workpiece 5 to be placed on upper surface 2b of die 2 when punch 1 is at the top dead center as illustrated in
As punch 1 is lowered, blank holder 3 attached to slide 7 is also lowered. As a result, forming processing with punch 1 is performed while workpiece 5 is sandwiched and pressed between holding surface 3a of blank holder 3 and inclined surface 2a of die 2 as illustrated in
As punch 1 is lowered, a leading end of punch 1 comes into contact with workpiece 5 to form workpiece 5. When blank holder 3 and die plate 4 come into contact with each other (see
In the present exemplary embodiment, a position of die 2 in the pressing direction or the amount of pushing of punch 1 is adjusted based on loads detected by die load sensor 14 and punch load sensor 13 so that clearance CL has an appropriate value.
Die load sensor 14 detects a load applied to die 2 from when punch 1 starts to be lowered to when punch 1 reaches the bottom dead center. Specifically, the load applied to die 2 is detected as load components in three directions including load Fz in the pressing direction (Z-direction), load Fx in the first direction (X-direction), and load Fy in the second direction (Y-direction), as illustrated in
Punch load sensor 13 detects a load applied to punch 1 in the pressing direction.
With reference to
Clearance CL between holding surface 3a of blank holder 3 and inclined surface 2a of die 2 is adjusted to an appropriate value in advance, and then forming is started (step S1). Next, die load sensor 14 detects a load applied to die 2 (step S2). Load F (Fx, Fy, Fz) detected by die load sensor 14 is output to arithmetic unit 22 via sensor controller 21. At the same time when die load sensor 14 detects the load, punch load sensor 13 detects a load applied to punch 1 (step S3). Load Pz (see
Normal force N of die 2 is calculated based on load F (Fx, Fy, Fz) of die 2 using Expression (1). In Expression (1), θ1 is an angle at which inclined surface 2a is inclined with respect to upper surface 2b of die 2 (see
[Expression 1]
N=Fx×sin θ1+Fz×cos θ1 (1).
When normal force N is calculated, arithmetic unit 22 calculates a difference in impulse with respect to normal force N of die 2 (step S6).
When the magnitude of clearance CL is an appropriate value or a reference clearance, the waveform data on normal force N is a waveform indicated by a solid line in
As illustrated in
An impulse of normal force N is acquired by multiplying normal force N by time, and is calculated by acquiring an area of the waveform data in
For example, when the magnitude of clearance CL is larger than the reference clearance, the difference in impulse is calculated by acquiring an area of region 70 in
Determination unit 23 determines whether to correct the clearance based on the difference in impulse of normal force N of die 2 (step S7). For example, an upper limit value and a lower limit value of the difference in impulse are set in advance, and then it can be determined that the clearance correction is performed when a value of the difference in impulse exceeds the upper limit value or falls below the lower limit value.
For example, when the difference in impulse exceeds ±10% of the impulse in the case of the reference clearance, or when a difference in area from an area of a waveform in the case of the reference clearance exceeds ±10%, it is determined to correct the clearance (Yes in step S7). That is, when the difference in impulse exceeds ±10% of the impulse in the case of the reference clearance, it is determined to correct the clearance. When the difference in impulse is included within ±10% of the reference clearance, it is determined that the difference in impulse is within a reference and the clearance is not corrected (No in step S7).
When it is determined to correct the clearance (Yes in step S7), arithmetic unit 28 calculates the amount of correction (step S8). The amount of correction is a value indicating an increase or a decrease in magnitude of clearance CL.
According to the graphs of
The amounts of correction based on experimental results are as illustrated in the graph of
[Expression 2]
ΔCL=a×D1 (2).
Here, coefficient a changes depending on a wear state of punch 1 or the like. Thus, when coefficient a is changed by acquiring experimental results as illustrated in the graph of
Next, arithmetic unit 22 calculates the amount of movement of die 2 (step S9). The amount of movement of die 2 indicates the amount of movement of die 2 in the pressing direction.
Here, when the amount of movement is indicated as ΔH and magnitude of the reference clearance is indicated as CL1, the relationship of Expression (3) is established between the amount of movement ΔH and reference clearance CL1.
The amount of movement ΔH with a positive number means that die 2 is moved in the −Z-direction, and when the amount of movement ΔH with a negative number means that die 2 is moved in the +Z-direction.
Next, actuator 18 is driven to move die 2 based on the amount of movement ΔH calculated, thereby correcting the magnitude of clearance CL (step S10), and then processing proceeds to step S11.
Returning to step S7, when it is determined that the clearance is not corrected based on the difference in impulse of die 2 (No in step S7), arithmetic unit 22 calculates a difference in impulse of load Pz applied to punch 1 (step S12).
When the amount of pushing of punch 1 has magnitude with an appropriate value, or is a reference amount of pushing, waveform data on load Pz is a waveform indicated by a solid line in
An impulse of load Pz is acquired by multiplying load Pz by time, and is calculated by acquiring an area of the waveform data in
For example, when the magnitude of the amount of pushing is larger than the reference amount of pushing, the difference in impulse is calculated by acquiring an area of region 120 in
Determination unit 23 determines whether to correct the amount of pushing based on the difference in impulse of load Pz (step S13). For example, an upper limit value and a lower limit value of the difference in impulse are set in advance, and then it can be determined that the amount of pushing is corrected when a value of the difference in impulse exceeds the upper limit value or falls below the lower limit value.
For example, when the difference in impulse exceeds ±10% of the impulse in the case of the reference amount of pushing, it is determined to correct the amount of pushing (Yes in step S13). That is, when the difference in impulse exceeds ±10% of the reference amount of pushing, it is determined to correct the amount of pushing. When the difference in impulse is included within ±10% of the reference amount of pushing, it is determined that the difference in impulse is within a reference and the amount of pushing is not corrected (No in step S13).
When it is determined to correct the amount of pushing (Yes in step S13), arithmetic unit 28 calculates the amount of correction (step S14). The amount of correction is a value indicating a position when the punch 1 is at the bottom dead center and a movement distance of punch 1 in the pressing direction (Z-direction).
According to
The amounts of correction based on experimental results are as illustrated in the graph of
[Expression 4]
ΔPR=−b×D2 (4).
Here, coefficient b changes depending on a wear state of punch 1 or the like. Thus, when coefficient b is changed by acquiring experimental results as illustrated in the graph of
Next, the amount of pushing of punch 1 is corrected based on the calculated amount of correction ΔPR by controlling servo motor 11 (step S15).
When die 2 is moved (step S10) or the amount of pushing of punch 1 is corrected (step S15), the processing ends.
[Effects]The present disclosure enables providing a press-forming apparatus capable of correcting the clearance and performing stable processing. Specifically, the exemplary embodiments described above cause the amount of correction of clearance between the blank holder and the die to be calculated based on normal force of the die, so that a press-forming apparatus capable of performing stable processing while appropriately maintaining the clearance can be provided.
Although the exemplary embodiments described above each show an example in which press-forming apparatus 100 includes punch load sensor 13 and corrects the amount of pushing of punch 1 based on load Pz applied to punch 1, punch load sensor 13 is not an essential component.
Then, although the exemplary embodiments described above each show an example in which die 2 includes four die pieces 2c to 2f, the present disclosure is not limited thereto. Die 2 may include one die piece, or may include two or more die pieces. In this case, die load sensor 14 is preferably disposed on each die piece.
Additionally, although the exemplary embodiments described above each show an example in which press-forming apparatus 100 includes first gap sensor 15 and second gap sensor 16, first gap sensor 15 and second gap sensor 16 are not essential components.
The press-forming apparatus of the present disclosure can be applied to a case where bending or drawing is performed on a workpiece, such as a part of a home electric appliance or medical equipment, the workpiece being thin in thickness and being less likely to stretch due to high hardness.
Number | Date | Country | Kind |
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2021-105877 | Jun 2021 | JP | national |