KR20010064338A - Tube hydroformability tester and test method - Google Patents

Abstract

PURPOSE: An evaluation device for an up/down divisional tube hydroforming performance and a method thereof are provided to precisely measure the hydroforming performance of a tube efficiently by using the up/down divisional testing metal mold and a low capacity press. CONSTITUTION: An evaluation device for an up/down divisional tube hydroforming performance includes a press main body(610) mounted with a main cylinder and a sub cylinder for applying a closing force to metal molds(650) against a separation force of the molds and applying the feeding to the tube in a longitudinal direction, a control part(620) for controlling operation distances of the main and sub cylinders according to a testing condition, controlling a testing pressure by controlling a high pressure generating unit to maintain a required pressure cycle, and monitoring an operation state of the press, a hydraulic unit(630) for supplying an oil pressure for the operation of the press and the high pressure generating part, and the high pressure generating part(640) for converting a low pressure supplied from the hydraulic unit to a high pressure required for the testing.

Description

Top and bottom split tube hydroformability evaluation apparatus and a suitable evaluation method {Tube hydroformability tester and test method}

The present invention relates to a vertical split tube hydroforming property evaluation apparatus which can be widely used in the production of automotive parts and evaluate the suitability of the hydroforming of the tube for tube hydroforming, which is one of the component processing methods.

In general, due to the social demand for lighter body weight of automobiles, the use of new parts processing methods that can maintain the required strength while reducing the weight of the components in the automobile production has emerged.

Among these new processing methods, tube hydroforming technology has many advantages such as reduction in production cost, strength improvement, and weight reduction of parts, and the interest of automobile companies is increasing.

As shown in FIG. 1, the tube hydroforming technique places the tube 101 in the cavity of the upper and lower molds 102 and 103 having a predetermined shape, closes the upper and lower molds 102 and 103, and then closes the tube 101. Both ends are sealed using a punch 104, and a high pressure is applied using a fluid therein to inflate the tube 101 like a balloon to form a product having the same shape as the internal cavity of the upper and lower molds 102 and 103. .

At this time, both ends of the tube 101 are sealed by the punch 104 so that the high pressure works well, and in the longitudinal direction of the tube 101 by the punch 104 according to a change in pressure applied therein. Feeding takes place.

At this time, the pressure and the amount of feeding should be maintained in an appropriate relationship. If the correlation is not appropriate, the tube 101 such as FIG. 2 bursts or a buckling defect such as FIG. It becomes impossible.

In tube hydroforming, it is very important to evaluate the hydroforming formability of the tube because the material is not plated and the plate is piped into the tube. This is because when the plate is tubed, it undergoes work hardening and exhibits molding properties that are completely different from those of the original plate.

In addition, since tube hydroforming is formed by a high-pressure fluid in the tube rather than being formed by a punch during forming, it is impossible to evaluate the hydroforming property of the tube by a method of evaluating the formability of existing plates. Moldability should be evaluated under similar conditions to hydroforming processes.

Tube materials used in hydroforming are mostly high strength and thick, so very high pressures of over 1000 bar are required for molding, and these pressures cannot be obtained using conventional hydraulic pumps, so an appropriate pressure amplification device is required. .

In general, in the tube hydroforming, the mold is formed in a left-right divided manner in which the dividing line 402 of the mold coincides with the length direction of the tube 401 with respect to the shape of the product to be molded. In this case, the force (F) to act on the mold in response to the force that the mold is to be separated by the pressure inside the tube 401 to the pressure (P) and the dividing line 402 acting inside the tube (401). It is represented by Equation 1 by the projection area A of the tube 401.

F = PA

Here, since the pressure required for forming during tube hydroforming is very high pressure, and the projected area also increases as the length of the tube 401 increases, a large-sized press of thousands tons in tube hydroforming is usually used to separate the mold from tube hydroforming. It is used to prevent the separation of the mold by resisting force.

Here, as shown in FIG. 5, when the dividing line 502 of the mold is vertically divided to be perpendicular to the longitudinal direction of the tube 501, the projection area A is determined by the cross-sectional area of the tube 501. It is determined by the length of the tube 501, the force (F) required to support the mold is very small compared to the left and right split type can be molded using a conventional small press.

An object of the present invention is to develop an apparatus capable of evaluating the formability of a tube with respect to a hydroforming tube using a low-capacity press apparatus under similar conditions to an actual hydroforming process.

1 is a schematic of a hydroforming process,

2 is a view showing a failure state that occurred during the hydroforming,

3 is a view showing a bad state caused by buckling occurred during the hydroforming,

4 is a left and right split molding test method for a conventional molded article,

5 is a vertical split molding test method for the molded article of the present invention,

6 is a schematic view of the hydroforming property evaluation apparatus of the present invention,

7 is a circuit diagram of a hydroforming property evaluation apparatus of the present invention,

8 is a vertical split molding test mold for the molded product of the present invention,

9 is a view showing a principle of operating the pressure amplification of the high pressure generating unit used in the present invention.

♠ Explanation of symbols on the main parts of the drawing ♠

101, 401, 501: tube 102, 103: up and down mold

104: punch 402, 502: dividing line

610: press main body 611: main cylinder

612: sub cylinder 620: control unit

630: hydraulic unit 631: hydraulic servo valve

640: high pressure generating unit 650: mold

In order to achieve the above object, the present invention is equipped with a main cylinder and a sub-cylinder for supporting the mold and acting a closing force against the mold against a force to be separated from the test and applying a feeding in the longitudinal direction of the tube during the test. A press main body portion; A control unit for adjusting an operating distance between the main cylinder and the sub cylinder of the press main body part according to test conditions, controlling a high pressure generator to control a test pressure, and monitoring an operating state of the press to maintain a required pressure cycle; A hydraulic unit for supplying hydraulic pressure for the operation of the press and the operation of the high pressure generator; Characterized in that it consists of a high pressure generating unit for converting the pressure of the low pressure supplied from the hydraulic unit to the high pressure required for the test.

In addition, the evaluation method according to the present invention is to mount a tube cut to a predetermined length in the lower part of the test mold, and input the length and thickness of the tube into the computer of the control unit to set the test pressure and the position of the main cylinder and the sub cylinder Steps; Filling the machined oil by operating a feed pump, which is a pressure acting medium for the tube and the high pressure generating portion; After the control unit moves the upper main cylinder to the calculated position and the upper and lower parts of the tube are completely sealed and fixed by the mold, the servo valve of the hydraulic unit is operated to supply the hydraulic pressure of the high pressure generating unit to move the cylinder, and to the opposite side. Applying high pressure to the located machining oil; Continuously controlling the internal pressure of the tube and the displacement of the main and sub cylinders by the control unit; Compensating for the pressure changed by the expansion of the tube by controlling the position of the cylinder of the high pressure generator; A bursting of the tube due to the pressure acting on the inside of the tube after the compensating step, and when the pressure inside the tube drops rapidly, detecting the pressure to stop the servo valve and the high pressure generating unit; After the stop step, move the main cylinder and the sub-cylinder to the initial position, measure the diameter of the largest expansion portion of the tube bursting and compare the diameter with the diameter of the initial tube to calculate the expansion ratio to the hydroforming properties of the tube It is characterized by consisting of the steps shown.

6 shows a schematic view of the hydroforming property evaluation apparatus of the present invention.

The press main body 610 supports the mold 650 for hydroforming property evaluation and supports the mold against a force to separate the mold 650 generated by the high pressure applied to the inside of the tube during the molding test up and down. The operation of the main cylinder 611 and the sub cylinder 612 of the main body 610 is precisely controlled by the control unit 620 and the hydraulic servo valve 631 of the hydraulic unit 630.

At present, the capacity of the press main body 610 is 100 tons, but the present invention is not limited to the press capacity, and any capacity can be used as long as it is commonly used in the art.

The control unit 620 controls the operation of the press body 610 and the operation of the hydraulic unit 630 and controls the discharge pressure of the high-pressure generating unit 640. The control unit 620 is connected to the main cylinder 611 of the press main body 610 installed in the hydraulic unit 630, and the hydraulic servo 631 for controlling the movement of the sub cylinder 612, a given test tube The position of the main cylinder 611 is controlled according to the length of.

In addition, according to the test pressure and the punch displacement cycle determined by the strength of the tube, the control hydraulic servo 632 of the high-pressure generator 640 is controlled to control the test pressure, and the displacement of the sub-cylinder 612 is precisely controlled. The displacement of the punch attached to the tip of the cylinder 612 is controlled.

In addition, the control unit 620 detects the pressure applied to the displacement sensor 621 and the test tube inside the pressure sensor 624 to detect the position of the main cylinder 611 and the sub cylinder 612 while the test is in progress. Check whether it is working correctly with the displacement cycle of, and if the tube bursts during the test to stop the operation of the pressure generating unit 640 to prevent the scattering of the test liquid.

The hydraulic unit 630 supplies hydraulic pressure necessary for the operation of the main cylinder 611, the sub cylinder 612, and the high pressure generator 640 of the press body 610. Hydraulic servo valves 631 and 632 for operating these main cylinders 611, the sub cylinders 612 and the high pressure generator 640 are provided.

The high pressure generating unit 640 is a device for generating a high pressure required to test the hydroformability of the tube, since it is difficult to generate a high pressure of 100 Bar or more when using a conventional hydraulic pump, as shown in FIG. It has the same structure and generates high pressure over 1000 bar using Pascal principle.

In FIG. 7, the relation between the pressure on the input side and the pressure on the output side is expressed by Equation 2 below.

By using Equation 2 as above, when the ratio of the cross-sectional area of the input side to the output side is increased, a high pressure amplification ratio can be obtained.

The vertically divided mold portion 650 for the hydroforming test is configured to minimize the load required for the test by dividing the tube 711 up and down in the longitudinal direction during the test.

In order to prevent the leakage of the high pressure liquid acting inside during the test, the sealing structure is sealed, and the feeding of the tube 711 in the longitudinal direction during the test is performed by the upper punch 712 and the lower punch ( 713).

The method of measuring the hydroformability of a tube using the hydroformability evaluation apparatus of the tube of this invention as mentioned above is demonstrated.

In order to measure the hydroforming property of the tube according to the present invention, the tube is first cut to a predetermined length to completely remove burrs from the cut surface and to remove foreign substances in the tube.

The tube is mounted under the test die, and the length and thickness of the tube are input to a computer of the controller 620 to set the test pressure and the positions of the main cylinder 611 and the sub cylinder 612. Next, by operating the pump for supplying the machine shares, which is a pressure action medium to be used for the test, the machining oil is filled into the tube and the high-pressure generator 640.

Next, according to the experiment start signal of the experimenter, the computer of the controller 620 moves the upper main cylinder 611 to the calculated position so that the upper and lower parts of the tube are completely sealed and fixed by the mold, and then the hydraulic unit 630. By operating the servo valve 632 of the) to supply the hydraulic pressure of the high pressure generating unit 640 to move the cylinder, and to apply high pressure to the machining oil located on the opposite side. At this time, the cylinder of the high pressure generating portion compensates for the pressure changed by the expansion of the tube by controlling the position.

During the test, the control unit 620 continuously detects the internal pressure of the tube and the displacement of the main and sub cylinders 611 and 612.

The pressure inside the tube causes the tube to expand and expand locally, causing the material to burst beyond the forming limits. When the burst occurs, the test machine is leaked into this part, and the internal pressure decreases sharply. When the sudden pressure drop is detected through the pressure sensor 624, the hydraulic unit 630. Stop the operation of the high pressure generating unit 640 so that no further high pressure is applied, and then move the main cylinder 611 and the sub cylinder 612 to the initial position. The test is terminated.

After the end of the test, the diameter of the largest dilated tube of the bursting tube was measured and compared to the diameter of the initial tube to calculate the expansion ratio and expressed as the hydroforming property of the tube.

For example, a 50.8mm diameter, 3.2mm thick tube is cut to 300mm length to remove burrs on the cut surface and to remove the foreign substances generated during the cutting of the tube to prepare a specimen.

The hydroforming property of the tube of the present invention was set to an initial forming pressure of 200 Bar and a final test pressure of 1000 bar, and the pressure was changed linearly with time to measure the hydroforming property of a given tube.

As a result of repeating the test three times on this specimen, the maximum tube diameter of the test tube was 68.2 mm, and the expansion ratio was 138%. The repetition error at this time was within ± 0.005.

As described above, the present invention has the effect of providing a measuring device capable of accurately and efficiently measuring the hydroforming property of the tube by using a vertically divided test die and using a press of a low capacity.

Claims (2)

A press main body mounted on the main cylinder and the sub-cylinder for supporting the mold and acting a closing force on the mold against a force to be separated from the mold during the test and feeding the tube in the longitudinal direction of the tube during the test; A control unit which adjusts an operating distance between the main cylinder and the sub cylinder of the press main body part according to test conditions, controls a high pressure generator to control a test pressure, and monitors an operation state of the press to maintain a required pressure cycle; A hydraulic unit for supplying hydraulic pressure for the operation of the press and the operation of the high pressure generator; Vertically divided tube hydroformability evaluation apparatus comprising a high pressure generating unit for converting the pressure of the low pressure supplied from the hydraulic unit to a high pressure required for the test. Mounting a tube cut to a predetermined length in a lower part of the test mold, and inputting the length and thickness of the tube into a computer of the controller to set a test pressure and positions of the main cylinder and the sub cylinder; Filling the machined oil by operating a feed pump, which is a pressure acting medium for the tube and the high pressure generating unit; After the control unit moves the upper main cylinder to the calculated position and the upper and lower parts of the tube are completely sealed and fixed by the mold, the servo valve of the hydraulic unit is operated to supply the hydraulic pressure of the high pressure generating unit to move the cylinder, and to the opposite side. Applying high pressure to the located machining oil; Continuously controlling the internal pressure of the tube and the displacement of the main and sub cylinders by the control unit; Compensating for the pressure changed by the expansion of the tube by controlling the position of the cylinder of the high pressure generator; A bursting of the tube due to the pressure acting on the inside of the tube after the compensating step, and when the pressure inside the tube drops rapidly, detecting the pressure to stop the servo valve and the high pressure generating unit; After the stop step, move the main cylinder and the sub-cylinder to the initial position, measure the diameter of the largest expansion portion of the tube bursting and compare the diameter with the diameter of the initial tube to calculate the expansion ratio to the hydroforming properties of the tube Hydroforming property evaluation method using a split test mold, characterized in that it comprises the step of indicating.