KR101706533B1 - Method for trimming workpieces made of high strength steel - Google Patents

Abstract

A method of easily trimming a high-strength steel part using electric power firing, comprising steps of: lowering a top shape of a press and pressing the object with a trim cutter; Stopping the motion of the upper mold when the pressing force or shearing force applied to the object by the trim cutter reaches a reference value; Initiating energization of the object; And resuming lowering of the upper mold to complete the trim.

Description

[0001] METHOD FOR TRIMMING WORKPIECES [0002] MADE OF HIGH STRENGTH STEEL [0003]

The present invention particularly relates to a method for cutting high strength steel parts using electroplasticity.

There is a high demand for light weight and high strength of vehicle parts due to fuel efficiency regulations and strengthened safety regulations. As a result, 1 Giga Pascal (GPa) class super high strength steel parts have been commercialized and recently, 2 Giga class steels have been developed.

In general, an increase in the strength of the steel sheet lowers the elongation and lowers the workability. The new technology proposed to solve this problem is hot stamping. The hot stamping is excellent in moldability because it is press-molded and cooled after heating the high-strength steel sheet to about 900 ° C.

However, even if the formability is secured by hot stamping, trimming for finishing the product is also a problem. Normally, trimming using a press is used, but when applied to an ultra-high strength steel, it is not applicable to the mass production due to frequent breakage of the trimming tool. Lasers are currently used for trimming high-strength steels hot-stamped.

Korean Registered Patent No. 1368276 (registered on February 21, 2014)

The present invention is a result of research carried out with the support of the project of "local specialized industry development project" of the Ministry of Commerce, Industry and Energy and the Korea Industrial Technology Development Agency.

The above-mentioned laser cutting is required not only for a long cycle time but also for post-processing due to burr due to working environment. Therefore, a new technique for cold-trimming extra-high strength steels other than laser is required.

Electricity firing is a phenomenon in which, when a current is applied to a metal material, the strength of the material is temporarily reduced and the elongation is changed. Thus, it has recently attracted attention because it has a possibility of being used for processing a metal material. However, the principle has not been clearly defined, and systematic studies on commercialization have not been made.

The present inventors have carried out research on a method for processing ultra-high strength steel using electric firing and one of the results is obtained Korean Patent No. 1368276 on trimming method of ultra high strength steel. The invention introduced in this patent was in the early stages of development and was in fact limited in its application to product production.

In particular, Korean Patent No. 1368276 discloses an electric current supplied to an object for a certain period of time after a top-shaped pad comes into contact with an object and before a top-shaped cutter comes into contact with the object. However, it was not enough to obtain the desired level of strength reduction. In order to commercialize electrification plasticity using press, process improvement was needed.

The present invention has been achieved as a result of research and development for realizing and commercializing the above-mentioned problems and realizing the firing and firing of high strength steel parts, and to provide a new high strength steel part trimming method.

According to an aspect of the present invention, there is provided a method of cutting a high strength steel part, comprising steps of: lowering a top of a press to press a target with a trim cutter; Stopping the motion of the upper mold when the pressing force or shearing force applied to the object by the trim cutter reaches a reference value; Initiating energization of the object; And resuming the descent of the upper mold to complete the trim.
According to an embodiment, a high strength steel part trimming method includes the steps of: a) loading an object onto a lower mold of a press; b) lowering the upper mold of the press and applying a shearing force to the object with a trim cutter provided on the upper mold; c) supplying an electric current to an object through a plurality of electrodes provided on the lower mold; And d) resuming the downward motion of the upper mold to complete the shearing and supplying an electric current to the object through the electrode during the process, and a sensor for measuring shear force may be provided on the trim cutter.
The step (b) may further comprise: (b-1) holding the object by a pad provided on the upper mold before the trim cutter makes contact with the object; And (b-2) stopping the lowering motion of the upper mold when the reference value is reached by shearing force applied to the object, while stopping the lowering motion of the upper mold with the press mold of the object held by the pad.

According to the embodiment, energization during the stop of the upper mold is maintained for 400 to 1,000 ms. Preferably, the lowering of the upper mold is resumed during energization, and the upper mold reaches the lowering point and the trim is completed, and then the energization is terminated. Even if the temperature of the object to be energized rises to 180 ° C or more even before the end of energization, discoloration or the like of the object is a problem.

In addition, according to the embodiment, the energization is performed by using a plurality of power supply devices through a plurality of electrodes provided on the lower mold. Preferably, the electrodes are grouped and arranged in the lower mold, and the power supplies are connected to one of the electrode groups of the grouped electrode groups so as to be able to supply current independently of the other electrode groups.
According to an embodiment of the present invention, each of the power supply devices includes a TC unit for converting an AC external power source into a DC current to supply a current, and a control unit for converting the current supplied from the TC unit provided in the lower unit into a current value required for current- And a TR unit for supplying to one of the electrode groups, wherein the TR unit can be cooled by a cooling line branched from a cooling water line for cooling the lower mold.

As in the above embodiment, supplying current for electric firing and firing independently for each of the parts or sections of the lower mold or the object requires that the thickness and material components of the object are different from other parts or the supply current should be different for other reasons And also enables a stable current supply.

The above-described machining apparatus for high-strength steel parts according to the present invention can be used for trimming high-strength steel parts or for molding and machining high-strength steel parts.

Further, the machining apparatus of the present invention can precisely control or monitor the electrification and firing process, and as a result, a high-quality high-strength steel component can be obtained.

Further, the machining apparatus of the present invention can accurately manage the supply and termination timings of the current supplied to the object, the current amount, the current supply time, etc. to a target numerical value, Commercialization of the processing method can also be verified.

1 is a schematic view of a machining apparatus for a high strength steel part according to an embodiment of the present invention,
2 is a view showing a mold according to an embodiment of the present invention,
3 is a view showing an upper mold according to an embodiment of the present invention,
FIG. 4 is a view showing a pad of the upper mold shown in FIG. 3,
FIG. 5 is a view showing a die among the upper mold shown in FIG. 4,
6 is a view for explaining a mounting structure of a load sensor according to an embodiment of the present invention,
7 is a view showing a lower mold according to an embodiment of the present invention,
FIG. 8 is a view showing a steel assembly among the lower molds of FIG. 7;
Fig. 9 is a view for explaining the conditions of the energization and plastic working according to the embodiment of the present invention, Fig.
Fig. 10 is a view showing a process flow chart of energization and plastic working according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same components or parts are denoted by the same reference numerals as much as possible for convenience of description.

First, an example of a machining apparatus for a high strength steel part for applying the trim method according to an embodiment of the present invention will be described, and then a trim method will be described.

Fig. 1 is a block diagram showing components of a high-strength steel part machining apparatus according to an embodiment, and Fig. 2 shows an example of a mold.

1 and 2, a machining apparatus supplies electric current from a power supply device 40 to an object W through an electrode 30 provided on a metal mold 20 of a press 10 during a process of processing an object W. [ And includes a controller 50 for controlling the power supply unit 40 and a plurality of sensors 60, 70, 80, and 90.

The press 10 needs to be configured so as to be capable of temporarily stopping the slide, that is, the topsheet 100. [ According to an embodiment, the press 10 can be equipped with a servomotor to stop the movement of the topsheet 100 at a desired position, and is configured such that there is no torque change of the press 10 as it is reactivated.

The mold 20 is mounted on the press 10. The mold 20 includes a top mold 100 corresponding to a slider and a bottom mold 200 corresponding to a bolster. The bottom mold 200 includes an electrode (not shown) for supplying a current for electric power plastic working to an object W 30 are installed.

The electrode 30 is disposed in a pair of an anode and a cathode (which need to be understood to be simply referred to as an electrode in the present description including claims), and is installed in the lower mold 200 at least. In the case of the trim device, a plurality of electrodes 30 are required to be installed for each trim position.

The power supply device 40 converts an alternating current supplied from an external power source into a direct current and supplies the direct current to the electrode 30 for machining the object W using electric firing and firing. As an example, the external power source is a 3-phase current of 380 to 440 V, and this current is converted to a low voltage and a high current of 8 V, 40,000 A in the power supply device 40 and supplied to the electrode.

It is necessary to control at least the starting time of energization from the power supply device 40 to the electrode 30 in order to carry out the electric power firing process. In the mold 20, various sensors 60, 70, 80, and 90 are disposed, and the measured values of these sensors are collected by the data logger 51 of the controller 50. The controller 50 uses the measured value received from the load sensor 60 to determine the start time of the energization and sends it to the power supply unit 40.

It is necessary to control the energization time or the energization end point, the amount of current, the interval between the energization start points, and the like in addition to the energization start point. When the controller 50 instructs to start energization, the power supply 40 supplies current to the electrode 30 in accordance with preset values such as the amount of current, energization time, and the like, . ≪ / RTI >

A current sensor 70 is provided between the power supply device 40 and the electrode 30 for measuring the amount of current supplied from the power supply device 40 and the energization time and for sending the measured values to the controller 50. Therefore, the controller 50 can check whether the electrification plasticity is smoothly performed according to the preset values by using the measured values of the current sensor 70. [

When the energization completion signal is transmitted from the power supply device 40 to the controller 50 upon completion of energization, the controller 50 can prepare energization for the next object. The measured value received from the current sensor 70 may be used for determining whether or not the energization has been completed, or for determining or checking the time.

The power supply device 40 and the controller 50 described in the embodiments of the present invention are for electric power processing. The control unit and the power supply unit necessary for the operation of the press 10, such as the lifting and lowering motion of the upper mold 100, are separately provided.

In the press 10, basic sensors such as displacement sensors are also provided. However, as an example, the displacement sensor of the press 10 is inconvenient to be provided at the cam angle and is insufficient to correctly read the motion of the upper die 100. It is preferable that a displacement sensor 70 is separately provided in the mold 20 in order to measure the motion of the upper mold part 100 and send the value to the controller 50. [

On the other hand, the values measured in the sensors installed in the press 10 can be collected by the controller 50. Information about the operation ready state of the press 10, whether or not the object W is loaded, etc. can be obtained from these information, and it is possible to judge whether or not there is an abnormality in the press 10 or the like.

According to the embodiment, the power supply unit 40 may include a time contact (TC) unit and a transformer (TR) unit.

1 and 2, the TC unit 41 is a module for converting an external power source of an AC into a direct current and controlling the amount of current to the electrode 30, the energization time, the repetition period of energization, and the like. The power supply start command from the controller 50 is input to the TC unit 41. The TC unit 41 starts energization in accordance with the command and supplies a current to the electrode 30 in accordance with the preset amount of current and energization time do.

2, the TR unit 42 is a module for changing the current and voltage supplied from the TC unit 41 to the values required for current shaping and supplying the current and voltage to the object W. For example, the TR unit 42 converts the current received from the TC unit 41 into a low voltage and a high current of 8 to 16 V, 1,000 to 40,000 A, and supplies the converted current to the electrode 30.

The TR portion 42 is directly mounted on the lower mold 200. As the distance from the electrode 30 increases, the loss due to the resistance increases. On the other hand, the TR portion 42 and the electrode 30 are connected to a bus-bar protected by an insulating tube.

Two or more such power supply devices 40 may be provided in the processing apparatus. Referring to FIG. 1, the power supply unit 40 may include three power supply units 41a and 42a, 41b and 42b, 42c and 42c. It is configured to be able to supply current for firing and firing independently for each of the three power supply substatements 200 or the object W by region or region.

At least two electrodes 30 to receive a current may be provided in the lower mold 200, and grouping may be made of which one of the power supplies 40 is to be supplied with current. As an example, the electrodes 30 corresponding to the three power supply units 40 may be classified into any one of three groups including one or more electrodes 30.

The use of the plurality of power supply devices 40 as described above is advantageous in that the thickness or the material composition of a specific part of the object W is different from the other parts or the other part is used for a certain amount of current, This is useful when you need to do something different. Moreover, since the power supply device 40 is shared by the plurality of power supply devices 40, stable current supply is possible even when the load is large.

Referring to FIG. 1, sensors 60, 70, 80, and 90 are separately provided in the apparatus for electrification and plastic working, unlike sensors that are basically installed in the press. These sensors 60, 70, 80, and 90 are installed at or around the mold 20 so as to measure a value at an accurate position.

The mold 20 needs to be provided with a load sensor 60, and in addition, a displacement sensor 70 may be provided. It is preferable that the processing apparatus includes both the load sensor 60 and the displacement sensor 70.

On the other hand, a temperature sensor 90 for measuring the temperature of the object W may be installed in the processing apparatus. The temperature sensor 90 sends the measured value to the controller 50. When the temperature of the object at the energized portion rises above a specified value, the controller 50 sends a power supply end signal to the power supply device 40 . Generally, when the temperature rises to 180 DEG C or more, there arises a problem that the object W is discolored.

The high-strength steel part processing apparatus according to the embodiment will be described with reference to FIG. 1 and FIG. 2 to FIG. These illustrated processing devices are trim devices.

Referring to FIG. 2, the mold 20 includes a basic upper mold 100 and a lower mold 200. A TR portion 42 of a power supply device 40 for supplying current to the electrode 30 is mounted on the side of the lower mold 200.

3 to 5, the upper die 100 includes an upper die 120 having a blade part 121 and a pair of upper teeth 120 so that the blade part 121 can hold the object W before it contacts the object W. [ And a pad 110 elastically supported by the die 120. Because it is a trim device, the blade part corresponds to a cutter.

The pad 110 is provided with a surface 101 on which the object W contacts and through holes 102 for allowing the blade 121 to protrude and retract. The upper die 120 is provided with columns 122 having a blade 121 disposed at the tip thereof and members 123 for elastically supporting the pad 110. The blade portions 121 are disposed at positions corresponding to the through holes 102.
The columns 122 are spaced apart from each other on the base surface of the upper die 120. The blade 121, that is, the trim cutter, is provided at the tip of the columns 122.
The pad 110 covers the base surface of the upper die 120 provided with the columns 122. The pad 110 has a contact surface 101 with the object W and the through holes 102 described above are formed around the contact surface 101. [ The pad 110 is brought into close contact with the object W to hold the object W before the blade 121 shears the object W in the trimming process.

6, the load sensor 60 detects the force applied to the object W by the surface 124, that is, the blade 121, parallel to the traveling direction of the blade 121 under the blade 121, (W) is attached to the side surface of the trim cutter (121) in the load direction so as to more accurately measure the force against the external force.

According to the embodiment, the load sensor 60 is a strain gauge. When the blade portion 121 presses the object W, a force against the pressing force is transmitted to the blade portion 121, and a strain of the strain gauge is generated due to the force. The deformation amount of the strain gage can be sent to the controller 50 through the signal line 61 and converted into the load at the controller 50.

It is preferable that at least the surface of the mounting groove 125 is coated with insulation so that noise due to the current supplied to the electrode 30 is not mixed for firing and firing.

Referring to FIG. 7, the lower mold 200 includes a lower die 220 and a steel assembly 210 in contact with the object W. The lower die 220 is provided with a TR portion 42 for supplying an electric current to the electrode 30. In the lower die 220, a cooling water line for cooling the lower mold 200 is formed. The cooling water line is branched to cool the TR unit 42.

Referring to FIG. 8, electrodes 30 are installed in the steel assembly 210. The electrodes 30 are installed in the seating grooves 211 formed in the steel assembly 210 and the insulator 212 having elasticity is interposed between the electrodes 30 and the steel assembly 210.

According to the embodiment, the electrodes 30 are installed in the seating grooves 211 so as to protrude from the contact surface of the object W of the steel assembly 210. Preferably, each electrode is positioned 1-2 mm higher than the contact surface of the object W of the steel assembly 210. The side of the electrode 30 that is in contact with the steel assembly 210 is protected by the insulator 212.

When the pad 110 or the blade 121 of the upper mold 100 presses the object W, the insulator 212 is compressed and contact between the electrode 30 and the object W is smooth.

Hereinafter, a method of cutting a high-strength steel part using electric power firing according to an embodiment of the present invention will be described with reference to FIGS. 9 and 10. FIG.

The optimum trim conditions are shown in Fig. 9, and the trim process is shown in Fig. 10 in order for its implementation. The example of the trim process or the basic process may be applicable to other processing methods. In the description, the reference numerals of the machining apparatus constituent parts described above are used as they are.

9, in order to use the effect of electroplasticity in the processing of a high-strength steel part, the start of energization is performed when the object W is pressed by the blade part 121 of the upper mold 100, It should be selected at a later time. When the object W is pressed and stress is accumulated, energization must be started to sufficiently obtain the effect of the strength reduction.

It is preferable that the energization is started at least at the time when the motion of the press 10, that is, the movement of the blade portion 121 is stopped, or preferably stopped. Accordingly, it is possible to stably supply a current to the electrode and to prevent the occurrence of sparks due to the energizing current during the process.

It is preferable that the energization time is maintained for 400 ms or more on the basis of a hot stamped high strength steel sheet having a thickness in the range of 0.7 to 1.5 mm. When the energization time is less than 400 ms, it is difficult to obtain an appropriate strength reduction effect, and when energizing for more than 1500 ms, color change due to heating of the steel sheet occurs.

It is preferable that the time for stopping the motion of the press 10 and energizing is about 400 to 1,000 ms, and the trimming is resumed while the upper mold 100 is lowered again before the energization is completed, so that the energization is completed after the trim is completed . In other words, it is concluded that it is desirable to stop the motion of the press 10, to energize for a certain period of time, and to continue the energization while continuing the machining.

The trim process according to the embodiment will be described with reference to FIG.

Referring to FIG. 10, the trim process according to the embodiment can be divided into an object loading step S1, a step S2 to S6 for moving the slide to the energization start position, and an energization and trimming step S7 to S10.

In the object loading step S1, the object W is loaded into the steel assembly 210 of the lower mold 200 where the electrode 30 is installed.

In the next step, when the slider of the press 10 starts to descend (S2) and the slide of the upper mold 100 is slid down after the pad 110 of the upper mold 100 is contacted with the object W, (S3). In FIG. 9, the area (1) where the shearing force gradually increases is not a state in which the object W is pressed by the pad 110. The increase of the shearing force is caused by the blade portion 121 pressing the object W.

When the slide is continuously lowered in step S4, the trim cutter 121 comes into contact with the object W and reaches the predetermined load setting value in step S5. In step S6, the controller 50 issues a stop command to the press 10, To temporarily stop the slide. The slide stop time can be set in advance in the control unit of the press 10.

In step S7, the controller 50 sends an energization start command to the power supply 40 to start energizing the electrode 30, and after a predetermined period of time, the control unit 50 of the press 10 or the controller 50 The slide is resumed to descend (S8).

After the trim is completed in step S9, that is, the top mold 100 reaches the bottom dead center, the power source device 40 completes the energization and sends a completion signal to the controller 50 to prepare the next trim.

While the invention has been shown and described with respect to the specific embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims It should be understood that it is obvious to those of ordinary skill in the art.

In addition, the reference numerals in the following claims are provided to facilitate understanding of the configuration of the present invention through the embodiments shown in the drawings, but the present invention is not limited thereto.

10: Press 20: Mold
30: Electrode 40: Power supply
50: Controller 60: Load sensor
70: displacement sensor 80: current sensor
100: image forming die 110: pad
120: upper die 121:
200: Lower mold 210: Steel assembly
220: Lower die 212: Insulator

Claims (6)

a) loading an object into a lower mold of the press;
b) lowering the upper mold of the press and applying a shearing force to the object with a trim cutter provided on the upper mold; Wherein step b)
b-1) holding the object by the pad provided on the upper mold before the trim cutter makes contact with the object; And
b-2) stopping the lowering motion of the upper mold when the reference value is reached by shearing force applied to the object by shearing the object held by the pad with a trim-
c) supplying an electric current to an object through a plurality of electrodes provided on the lower mold; And
d) resuming the falling motion of the upper mold to complete the shearing, and supplying electric current to the object through the electrode in the process,
And a sensor for measuring the shear force is provided on the trim cutter. 2. The method of claim 1, wherein in step c)
And the energization for 400 to 1,000 ms is performed in a state where the movement of the upper mold is stopped. The upper mold of claim 1, wherein the upper mold includes an upper die and the pad elastically supported by the upper die,
The upper die has a plurality of columns spaced apart from each other on a base surface, the trim cutter being provided at the tip of the column,
Wherein the pad covers the base surface of the upper die provided with the columns and has a contact surface with the object, and through holes for allowing the trim cutter to protrude / retract are provided around the contact surface. The method of claim 1, wherein in step d)
Wherein the upper mold reaches the bottom dead point, and after the trim is completed, the energization is terminated. The apparatus of claim 1, wherein the sensor provided on the trim cutter is a strain gauge,
Wherein the strain gauge is provided in a mounting groove formed in a plane parallel to the traveling direction of the trim cutter and the surface of the mounting groove is insulated. The plasma display apparatus according to any one of claims 1 to 5, wherein the electrodes are grouped and arranged in a lower mold, a plurality of power devices for supplying current to the electrodes are provided,
The power supply devices are configured to be connected to any one of the electrode groups of the grouped electrode groups and to supply current independently of the other electrode groups,
The power supply unit includes a TC unit for converting an external AC power source into a DC current and supplying the current to the DC power supply unit, and a controller for converting the current supplied from the TC unit to a current value required for current- And a TR unit supplying the group,
And the TR portion is cooled by the cooling line branched from the cooling water line for cooling the lower mold.

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