KR20170075100A

KR20170075100A - Apparatus and method of press hemming

Info

Publication number: KR20170075100A
Application number: KR1020150183917A
Authority: KR
Inventors: 김우영; 김장수; 최문석; 김응천
Original assignee: 주식회사 엠에스 오토텍
Priority date: 2015-12-22
Filing date: 2015-12-22
Publication date: 2017-07-03

Abstract

A press forming apparatus and a method applicable to a metal plate material having an embossing property are also introduced. The apparatus includes an upper die 100 having a movable pad 110, a main hemming tool 130 having a top electrode at its tip and a preheating actuator 140; A lower die 200 having a lower electrode 201 corresponding to the upper electrode 131; And a pre-hemming machine (300) dispensed to one side of the lower die (200). A direct current for electrification forming is supplied to the hemming portion 11 of the object through the upper and lower electrodes 131 and 201 at the main hemming.

Description

[0001] APPARATUS AND METHOD OF PRESS HEMMING [0002]

The present invention relates to an apparatus and a method for press-hemming a press plate, particularly a plate material having poor moldability.

One of the biggest issues in the vehicle manufacturing industry is light weight. At least, it should be possible to achieve weight reduction while ensuring equal strength and stability with existing ones.

Application of ultrahigh strength steels is expanding to achieve lighter weight. Various reinforcements can be omitted, which helps to reduce weight. However, since steel is used basically, there is a limit in the range of weight reduction.

In addition to steel, attempts to reduce weight through the application of lightweight alloys such as aluminum or magnesium are also active. Among these, magnesium is the lightest metal, which can be lightened by 60% compared to steel and can be recycled, so there are many possibilities as lightweight materials.

However, the magnesium alloy has an HCP structure, so the slip system is limited to the bottom slip, which is poor in moldability at room temperature. Therefore, magnesium alloys are mainly used in casting products and have not yet been applied to plate products such as doors.

The present invention is based on the recognition of the limitations and problems of the prior art described above and aims to provide a press hemming apparatus and method for cold pressing hemming of metal sheet metal.

The present invention relates to the development of manufacturing-based technology for the body parts of ultra-high strength steel Al5000 of 1GPa or more using electrification by the Industrial Technology Innovation Project, funded by the Ministry of Industry and Commerce (MOTIE) and supported by the Korea Industrial Technology Evaluation and Management Service (KEIT) "Task.

The present invention utilizes an electroplastic effect for press hemming on an embossed plate. Electricity firing is a molding method that uses a phenomenon in which the strength of a material is temporarily reduced and elongation is changed when a current is applied to a metal material.

Although the principle of electrification firing has been recently attracted attention in that it can be used for machining of an embossable metallic material such as ultrahigh strength steel, the principle has not been clarified clearly, and systematic research to such a degree of commercialization, There are no empirical studies on the conditions, methods, and characteristics of materials.

In case of magnesium alloy, it is not applied to the parts of flat products such as door due to the molding property. Particularly, when the outer and inner plates of the door are made of magnesium alloy plates, the hemming of the outer plates is a problem.

According to an aspect of the present invention, there is provided a press hemming apparatus including: an upper die having a movable pad, a main hemming tool having an upper electrode at a tip thereof, and an actuator for pre-hemming; A lower die on which a hemming object is loaded and on which a lower electrode corresponding to the upper electrode is provided so as to supply current to a hemming portion of the object; And a pre-hemming machine disposed on one side of the lower die, the pre-hemming machine having a slider capable of moving back and forth by an actuator of the upper die.

According to the embodiment, the movable pad can be raised and lowered independently of the upper die, and the main hemming tool and the actuator are configured to ascend and descend depending on the lift movement of the upper die.

Also according to an embodiment, the pre-hemming machine comprises a body; A slider installed on the body and movable forward and backward; And a link mechanism configured to connect the slider and the body and to support the slider in a horizontal state when the central portion is supported by the lifter and to move the slider backward when the center portion is raised or lowered.

According to another aspect of the present invention, there is provided a hemming method comprising: a first step of loading an object having a 90-degree bend-molded hemming part onto a lower die; A second step of lowering the movable pad provided on the upper die to press the object; A third step of advancing the slider of the pre-hemming unit disposed at one side of the lower die to bend the hemming unit at an acute angle; A fourth step of lowering the upper die and pressing the hemming part with the main hemming tool; A fifth step of stopping the upper die when the angle of the hemming portion pressed by the main hemming tool or the distance from the bottom dead center of the main hemming tool reaches a reference value; A sixth step of supplying a direct current to the hemming part through an electrode provided on the tip of the main hemming tool and an electrode provided on the lower die; And a seventh step of resuming the downward movement of the upper die while maintaining current supply to perform the main hemming.

According to the embodiment, the direct current applied to the hemming portion through the upper and lower electrodes for the main hemming should meet the conditions of the current density of 60 to 140 A / mm 2 and the energization time of 500 to 1,200 ms.

According to the present invention as described above, cold press hemming of an embossable metal sheet can be performed.

According to the present invention, since the preheating and the main hemming are performed using one press hemming device, the production efficiency is improved, and the molding quality is excellent because there is no need to move the hemming object through various devices.

1 is a flow chart of a press-hemming process according to an embodiment of the present invention,
2 is a schematic diagram of a press hemming apparatus according to an embodiment of the present invention,
FIGS. 3 to 5 are diagrams for explaining the pre-hemming process using the apparatus of FIG. 2,
6 is a view for explaining a main hemming process using the apparatus of FIG.

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.

The press-hemming process according to the embodiment will be briefly described with reference to FIG.

As shown in FIG. 1, in the hemming process, the object is loaded on the press hemming device (S1), the wafer is pressurized (S2, S3), and the current is preheated (S4 to S6) And performing the main hemming (S7 to S10) while feeding.

The object to be loaded into the press hemming device has a 90 degree bending shaped hemming part in advance in the previous step. It is to be understood that it does not necessarily mean that the hemming portion of the object is maintained at a 90 degree angle by being bent at 90 degrees.

Pressurization, pre-hemming, and main hemming for the loaded object occur within a single hemming device. The current supplied to the object in the main hemming is not for the generation of the resistance heat but for the current injection, and the current is supplied.

The current supplied to the main hemming process is a short pulse direct current, which requires a current density of 60 to 140 A / mm 2 and an energization time of 500 to 1,200 ms. If the current density is outside the range of 60 to 140 A / mm 2, the effect of the electric firing and firing is lowered. If the current exceeds 1,200 ms, the color of the material may change due to overheating. .

A press hemming apparatus according to an embodiment will be described with reference to FIGS. 2 to 5. FIG.

As shown in FIG. 2, the press hemming apparatus according to the embodiment includes a press mold and pre-hemming machine 300 composed of upper and lower dies 100 and 200.

The upper die 100 includes a movable pad 110 that can be driven independently of the vertical movement of the upper die 100 and a main hemming tool 130 and an actuator 140 that are subjected to a vertical movement of the upper die 100.

The movable pad 110 is for fixing the object 10 during hemming and is installed on the upper die 100 and is moved up and down along with the movement of the upper die 100. The movable pad 110 is supported by a hydraulic cylinder 120 or a pneumatic spring, and is movable independently of the movement of the upper die 100.

The main hemming tool 130 has a top electrode 131 insulated by an insulator 132 at its tip for main hemming which totally bends the pre-hemmed hemming part 11 at an acute angle. The upper hemisphere 11 is moved upward and downward along the upward movement of the upper die 100 to perform the main hemming.

The actuator 140 is disposed at a location spaced from the main hemming tool 130 and has the shape of a column extending downward from the upper die 100. And performs the free hemming while ascending and descending depending on the upward and downward movements of the upper die 100. At the front end of the actuator 140, an elastic body 141 is provided.

The lower die 200 has a loading surface on which the object 10 is loaded and a lower electrode 201 corresponding to the upper electrode 131 is provided at a position where the hemming unit 11 is placed. The lower electrode 201 is insulated from the die 200 and peripheral members by an insulator 202. [

The pre-hemming machine 300 is disposed on one side of the lower die 200 and is configured to perform the pre-hemming operation on the hemming section 11 by switching the upward and downward movements of the actuator 140 to horizontal motion.

The pre-hemming machine 300 includes a body 310 and a slider 340 installed on the body 310 to move the slider 340 in a forward and backward direction and a body 310. The pre-hemming machine 300 has a vertical movement force of the actuator 140 And a lifting link 320 which is switched to a forward / backward movement force in the horizontal direction and transmits the force to the slider 340.

The slider 340 has a free hemming tool 350 at its tip. The free hemming tool 350 is a tool for bending a 90 degree bending-molded hemming portion 11 at an acute angle of about 45 degrees, and is a tool for optimizing the horizontal pressing force to be perfectly transmitted to the hemming portion 11. [ .

The slider 340 is installed on the body 310 so as to be movable back and forth. To this end, a rail (not shown) may be installed on the body 310 to allow the slider 340 to ride on the body 310.

The force by which the slider 340 moves back and forth is transmitted by the lifting link 320 that switches the pressing force from the actuator 140 to a horizontal force. The lifting link 320 has a link 321 in the middle and the intermediate link 321 is supported by the lifter 330 in the upward direction.

The slide link 322 may be provided between the body 310 and the slider 340 in addition to the lift link 320. [ The slide link 322 guides the slider 340, which receives force in the horizontal direction by the lifting link 320, to move forward and backward in the forward direction. In this process, the slide link 322 is pivotally moved, so that a slit or the like structure for allowing the pivotal movement can be provided on the slider 340.

As shown in FIGS. 2 to 5, the lifting link 320 supported by the lifter 330 is located at the highest point of the intermediate link 321 in the initial state. When the lift link 320 receives a pressing force by the actuator 140, the slider 340 advances while the lift link 320 is extended. When the intermediate link 321 further moves downward than the horizontal position, Back again.

2, a sensor for measuring the load applied to the hemming portion 11 by the main hemming tool 130 may be installed on the main hemming tool 130 of the upper die 100. [ And is a sensor for calculating the supply time point of the current for current firing in the main hemming.

According to the embodiment, the distance from the bottom dead center of the main hemming tool 130 can be used instead of or together with the load sensor for control of the current supply time for energization firing. It is convenient to carry out the process control based on the bottom dead center position of the hemming stroke utilizing the current-forming data using the load sensor and the distance data from the bottom dead center position of the hemming stroke.

The press-hemming process according to the embodiment will be described in more detail with reference to FIGS. 1 to 6. FIG.

The object 10 is loaded (S1) onto the lower die 200 for press hemming. The object 10 has a 90 degree bending-shaped hemming portion 11 and the portion 11 is disposed so as to be able to receive an energization firing current through the upper and lower electrodes 131 and 201. [

When the object 10 is loaded, the movable pad 110 is lowered by the hydraulic cylinder 120 so that a portion where the inner plate and the outer plate of the object 10 overlap each other is pressed and fixed (S2). When the pad 110 is lowered, the upper die 100 may also be pivoted to some extent.

The hydraulic cylinder 120 is configured to be manually operated to simply support the pad 110 like a lifter and the pad 110 is moved up and down depending on the movement of the upper die 100 and a force The hydraulic cylinder 120 may be configured to absorb the force. To ensure sufficient hemming strokes and convenient process control, it is desirable to be able to drive the pad 110 independently of the upper die 100.

When the object 10 is stably fixed (S3) by the pad 110, the upper die 100 descends in earnest and pre-hemming is performed (S4 to S6). The pre-hemming is a process in which the hemming portion 11 of the object 10 is bent in an acute angle, for example, 45 占 bending before the main hemming. In this process, the object undergoes deformation, and accordingly, it becomes important to select the point of time when the conductive plasticity is required.

According to the embodiment, when the actuator 140 descends (see FIG. 3) and presses the intermediate link 321 of the lift link 320 (see FIG. 4) as the upper die 100 descends, 320 are spread horizontally to advance the slider 340 and the hemming portion 11 is bent at an acute angle by the force. The upper die 100 may be suspended in the state of FIG. 4 for sufficient free hemming.

When the actuator 140 is further lowered in the state where the lifting link 320 is horizontally extended, the intermediate link 321 moves to the lower position (see FIG. 5), and the slider 340 is then moved backward. The time point at which the slider 340 is retracted again and the time point at which the main hemming tool 130 performs main hemming should be appropriately adjusted.

In the schematic diagram of FIG. 2, the actuator 140 and the lifting link 320 do not have separate connecting means, but the actuator 140 and the lifting link 320 may be connected to each other for a stable pre-hemming stroke.

When the pre-hemming is completed as described above, the main hemming by the main hemming tool 130 is performed.

6, when the upper die 100 is lowered so that the main hemming tool 130 contacts and presses the hemming part 11 (S7) and presses the hemming part 11 by the main hemming tool 130 When the angle of break or the distance H from the bottom dead center of the main hemming tool 130 reaches the reference value, the movement of the upper die 100 is stopped and the hemming portion 11 and the upper and lower electrodes 131, A direct current is supplied (S9) using a circuit.

In step S9, the main hemming tool 130, more specifically, the upper electrode 131 presses the tip of the initial hemming section 11 and presses the entirety from the tip to the bent vertex 12 in the latter half of the main hemming process, .

The current supply timing may be determined based on the load value transmitted to the hemming portion 11 by the main hemming tool 130 but may be determined based on the distance H from the bottom dead center of the main hemming tool 130 It is convenient for mass production control and device configuration.

According to the experimental example, in the case of the magnesium alloy plate (AZ31B) or the steel steel plate, the 45 ° point becomes the critical angle for the current firing. When the hemming portion 11 is pressed more than this angle, a crack easily occurs. The thickness of the metal plate is about 0.8 to 1.5 mm, but the effect of the electric firing is not greatly different from this thickness.

The distance H from the bottom dead center can be calculated by considering the width of the hemming flange with reference to the critical angle of 45 degrees. According to the hemming condition of a typical vehicle component, the main hemming tool 130 must be stopped 20 milliseconds before the bottom dead center and the current for current firing must be supplied.

In particular the hemming portion 11, by the main hemming tool 130 when stopping the main hemming tool 130 at a distance of less than 20 mm from the bottom dead center and feeding the hemming portion 11 with an energizing current, The probability of cracking after hemming is high despite the increase in elongation due to energization.

According to the embodiment, in the case of a magnesium alloy sheet material or a high-strength steel plate material, a direct current having a current density of 60 to 140 A / mm 2 should be supplied to the hemming portion 11 for 500 to 1,200 ms. If this condition is exceeded, the effect of electric power firing may be insignificant, or excessive current may flow, and the plate material may be heated and denatured.

After the start of energization as described above, the main hemming tool 130 which has been stopped while the energization is maintained is lowered to complete the main hemming stroke (S10). It is important that the energization should be maintained during the main stroke.

It is preferable that the time point at which energization is terminated is immediately before or immediately before the hemming is completed. If energization continues even after completion, spark may be generated due to the upward movement of the upper die 100.

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 of the invention as set forth in the following claims.

100: upper mold 110: pad
120: Hydraulic cylinder 130: Main hemming tool
140: actuator 200: lower mold
300: pre-hemming machine 310: body
320: lift link 321: slide link
330 Lifter 340 Slider
350: Free Hemming Tool

Claims

An upper die provided with a movable pad, a main hemming tool provided with an upper electrode at a tip thereof, and an actuator for pre-hemming;
A lower die on which a hemming object is loaded and on which a lower electrode corresponding to the upper electrode is provided so as to supply current to a hemming portion of the object; And
And a pre-hemming machine disposed on one side of the lower die, the pre-hemming machine having a slider capable of moving back and forth by an actuator of an upper die,
Wherein the movable pad is independently liftable with respect to the upper die, and wherein the main hemming tool and the actuator are subjected to a lifting movement of the upper die.

The apparatus of claim 1,
body;
A slider installed on the body and movable forward and backward; And
And a link mechanism that connects the slider and the body and has a central portion supported by the lifter to maximize the slider when the slider is in a horizontal state and to move the slider backward when the central portion is raised or lowered Pressing hemming device.

A first step of loading an object having a 90-degree bend-molded hemming portion onto a lower die;
A second step of lowering the movable pad provided on the upper die to press the object;
A third step of advancing the slider of the pre-hemming unit disposed at one side of the lower die to bend the hemming unit at an acute angle;
A fourth step of lowering the upper die and pressing the hemming part with the main hemming tool;
A fifth step of stopping the upper die when the angle of the hemming portion pressed by the main hemming tool or the distance from the bottom dead center of the main hemming tool reaches a reference value;
A sixth step of supplying a direct current to the hemming part through an electrode provided on the tip of the main hemming tool and an electrode provided on the lower die; And
And a seventh step of resuming the downward movement of the upper die while maintaining current supply to perform the main hemming.

4. The method of claim 3, wherein the pre-
The actuator provided on the upper die is lowered together with the die to advance the slider by activating the link mechanism of the pre-hemming machine,
The pre-
body;
A slider installed on the body and movable forward and backward; And
And a link mechanism that connects the slider and the body and has a central portion supported by the lifter to maximize the slider when the slider is in a horizontal state and to move the slider backward when the central portion is raised or lowered Pressing the hemming method.

4. The method according to claim 3, wherein, in the sixth and seventh steps,
Wherein the current density of the direct current applied to the hemming portion through the upper and lower electrodes is 60 to 140 A / mm 2 and the energizing time is 500 to 1,200 ms.