JP5679651B2 - Punching method with reduced noise during breakthrough - Google Patents

Description

  The present invention relates to a punching method that reduces noise generated during breakthrough when punching an austenitic stainless steel sheet.

For example, as shown in FIG. 1, the punching process is performed on the steel sheet by pressing the punch from above in a state where the steel sheet placed on the die is pressed with a plate press, and breaking the material to punch. It is common.
In the press punching process with such a break, a large noise is generated. This noise includes noise generated when the punch collides with a steel plate as a workpiece, and noise generated by vibration of a mold, a press frame, and the like during breakthrough immediately after material separation. Since the noise resulting from the latter is larger, it is necessary to reduce the noise caused by the breakthrough in order to reduce the noise during the punching process.

  Thus, various methods for reducing noise during breakthrough have been proposed. For example, in Patent Document 1, in order to release the elastic energy accumulated in the mechanical system of the punch press, which is a noise generation source at the time of breakthrough, the punch is quickly transferred to the die by the punch driving means until just before the breakthrough. It has been proposed that the punch is moved away from the die once under the control of a control device, and then punched by approaching the die at a speed slower than the approaching speed.

JP 2001-353598 A

However, the punching method proposed in Patent Document 1 basically attempts to control the punch driving by a hydraulic cylinder by a computer, and the apparatus is also large. For this reason, production costs increase.
In addition, once the punch is raised, there is a concern that productivity will decrease and mold wear will increase due to an increase in the sliding distance between the punch and the workpiece.
In addition, when comparing machining immediately before the breakthrough and machining once after raising, the elastic energy accumulated in the punch press mechanical system is different, so the punch core is displaced before and after the punch rises, and machining There is a risk of product quality degradation and uneven wear of the mold.

By the way, recently, a servo press capable of arbitrarily setting a slide motion using a servo motor as a drive source has been used for punching a steel sheet.
By using an arbitrary press motion using a servo press, noise reduction can be expected by slowing the processing speed during breakthrough.

  The present invention has been devised to solve such problems. When punching an austenitic stainless steel sheet, the use of a servo press immediately before the punch punches the processed austenitic stainless steel sheet. It is an object of the present invention to provide a punching method with a reduced processing speed and reduced noise.

The punching method with reduced noise at the time of breakthrough according to the present invention is started when punching is performed by pressing a punch into a workable austenitic stainless steel plate fixed by a die and a plate press to achieve the object. From the time until just before the workable austenitic stainless steel sheet breaks, the work speed is increased to suppress hardening due to work-induced martensitic transformation of the work steel sheet, and then the work speed is decreased.

Specifically, the die and punch material / shape, die clearance, plate pressing and lubrication conditions are the same as the actual punching conditions, and punching is performed at a predetermined processing speed. After measuring the distance from the processing start position that first contacted the stainless steel plate to the breaking position, at the time of actual punching, a predetermined processing is performed up to a distance of 60 to 85% of the distance from the processing start position to the breaking position. It is preferable that the punch is pushed in at a speed, and when the distance of 60 to 85% is passed, the punch pushing speed is reduced to 4 to 10% of the machining speed.
The mold clearance used is preferably 3 to 8%.
Moreover, it is preferable to use the servo press which used the servomotor for the drive source as a press apparatus.
The “processing speed” in the method of the present invention means the punch or die slide speed.

In the punching method of the present invention, when punching a workable austenitic stainless steel sheet, the work speed is increased until immediately before the workable austenitic stainless steel sheet is punched, thereby inducing the processing induction unique to austenitic stainless steel. By suppressing the martensite transformation and reducing the shear load, and reducing the processing speed immediately before breaking, the release speed of the elastic energy accumulated in the press machine and the mold is also reduced, so that almost no noise is generated. It can reduce without reducing productivity.
Moreover, the generated noise can be further reduced by making the clearance of the mold to be used smaller than about 10% which is conventionally employed.

Diagram explaining the punching method Diagram showing the relationship between tensile speed and tensile strength of austenitic and ferritic stainless steels The figure explaining the processing speed switching position in the present invention Diagram explaining the effect of machining speed on the relationship between mold clearance and maximum sound pressure level during stamping of austenitic stainless steel sheet Diagram explaining the relationship between the processing speed during punching with small clearances and the ease with which cracks meet Diagram showing the relationship between punching load and processing distance during punching The figure which shows the measurement result of the processing speed switching position and the maximum sound pressure level in an Example

The present inventors use a servo press capable of arbitrarily setting a slide motion using a servo motor as a driving source as a press device, and can reduce noise generated during breakthrough without substantially reducing productivity. We have been searching for possible punching methods.
In the process, when the material steel plate is an austenitic stainless steel plate, it has been found that it is effective to punch by increasing the processing speed up to just before breaking and slowing down the processing speed just before breaking.
Details will be described below.

The noise generated at the time of breakthrough is a function of the shear load (F) at the time of punching and the load reduction rate (dF / dt) at which the punching load rapidly decreases when the workpiece is broken. Has been. The greater the shear load (F) and the faster the load reduction rate (dF / dt), the greater the noise generated.
Therefore, it can be seen that it is effective to reduce the shear load (F) and reduce the load reduction rate (dF / dt) in order to reduce the noise generated during breakthrough.

By the way, in general, when austenitic stainless steel is strained by processing, the austenite structure is transformed into a hard martensite structure by processing-induced martensite transformation. Known to be less likely to occur. Due to the above characteristics of austenitic stainless steel, the higher the processing speed, the greater the heat generated by the processing, making it difficult for processing-induced martensitic transformation to occur and the tensile strength to decrease. For example, as shown in FIG. Since the shear load is proportional to the tensile strength of the workpiece, the shear load can be reduced by reducing the tensile strength.
Therefore, in the present invention, when punching is performed using an austenitic stainless steel plate as a raw material, the processing speed is increased to reduce the shear load (F) to reduce noise generated during breakthrough.

Further, if the machining is continued at the same speed until the extracted product is separated from the punch in FIG. 1, that is, until the breakthrough, the load reduction speed (dF / dt) is increased and a large noise is generated, which is not preferable. Therefore, in the present invention, the processing speed is reduced immediately before the workpiece is broken, that is, the load reduction speed (dF / dt) is decreased.
The combination of increasing the machining speed immediately before the breakthrough and reducing the machining speed immediately before the breakthrough reduces the noise generated during the breakthrough.

When actually punching a steel sheet, the breakthrough position varies depending on the processing conditions. For example, it varies depending on the material and shape of the die and punch, mold clearance, plate pressing force, lubrication conditions, and the like.
Therefore, in the present invention, when punching an austenitic stainless steel sheet having a specific material and thickness, the above-mentioned conditions are made constant, a preliminary machining test is performed at a predetermined machining speed, and the punch is processed austenitic. The distance from the processing start position where the stainless steel plate is first contacted to the fracture position is measured in advance. After that, at the time of actual punching, the punch is pushed in at the same processing speed as in the preliminary machining test until the punch reaches the distance from the processing start position to the breaking position, and when the distance is exceeded, the punch indentation speed is set to the processing speed. Decided to be slower than the speed.

Details will be given in the examples described later. As shown in FIG. 3, the switching position immediately before reaching the distance from the machining start position to the breaking position is 60 to 85% of the distance from the machining start position to the breaking position. It is preferable that If the processing speed is slowed at such a time point that the position is less than 60%, the productivity is deteriorated and the shear load (F) is increased. However, if an attempt is made to delay at a point of delay exceeding 85%, the response of the machine operation is delayed, which may cause a breakthrough before the machining speed is reduced.
The processing speed after slowing down is preferably 4 to 10% of the previous speed. If the speed is less than 4%, the load required for machining may not be obtained. Conversely, if the speed is faster than 10%, the reduction amount of the load reduction speed is small, so the noise reduction effect is small.

When punching a steel sheet, the mold clearance has a great influence on formability and the like.
Therefore, in implementing the present invention, the effect of the mold clearance on noise generation during breakthrough was examined. Noise was measured by the same method as in the examples described later.
The result is as shown in FIG.
It can be seen that the maximum sound pressure level decreases as the mold clearance decreases.

  In general, it is said that as the mold clearance becomes smaller, as shown in FIG. 5, the meeting state of cracks extending from the corners of the mold changes depending on the processing speed. That is, if the processing speed is high, cracks are likely to associate, but if the processing speed is low, cracks are difficult to associate. For this reason, it is predicted that the load reduction rate (dF / dt) becomes smaller and the generated noise is reduced as the mold clearance becomes smaller.

However, when punching is performed at a constant speed using an austenitic stainless steel sheet as a raw material, the influence of the processing speed on noise generation is not so great, and as shown in FIG. 4, the generated noise is reduced as the mold clearance is smaller. I understand that
Usually, when punching a steel sheet, the mold clearance is about 10%, but in the present invention, the mold clearance is preferably 3 to 8%.
If the mold clearance is so small that it is less than 3%, the load on the mold increases and the wear of the mold becomes severe. On the other hand, if it is increased to exceed 8%, the effect of noise reduction is reduced.

Then, in order to confirm the effect of this invention, the example which investigated the noise level which generate | occur | produces by variously changing the process speed change position at the time of a punching process is introduced.
A servo press machine was used as the punching device. As the austenitic stainless steel plate to be processed, a stainless steel plate of SUS304 having a nominal plate thickness of 6.0 mm having the component composition shown in Table 1 and the mechanical properties shown in Table 2 was used.
Furthermore, the conditions shown in Table 3 were adopted as the punching conditions.
The generated noise was measured with a sound level meter at a position 1 m away from the processed part mold and 1 m away from the ground. As the sound level meter, a normal sound level meter NL-22 manufactured by Rion Co., Ltd. was used, and the frequency characteristics were set to A characteristics.

First, the punch was pushed in at a speed of 50 mm / sec without decelerating during processing.
The maximum sound pressure level in the machining area was set as the noise during breakthrough.
Note that the break position was a point at which the punching load in the punching load-working distance diagram shown in FIG. And the position from a process start position to a fracture | rupture position was measured from the punching load-process distance diagram by making the position where a load begins to increase into a process start position.
In this punching process, the distance from the processing start position to the breaking position was 2.7 mm.

Subsequently, punching was continued under the same processing conditions, but punching was performed while reducing the processing speed to 5% of the previous speed during the processing.
And the noise at the time of breakthrough was measured like the previous preliminary test.
The noise measurement values are shown in Table 4 and FIG.
Incidentally, the maximum sound pressure level at the time of breakthrough was 109.0 dB when punching was performed under the same conditions as in the examples except that the press speed was constant at 2.5 mm / sec (5%).
From this result, it is possible to reduce the level of noise generated when machining is performed at a high speed between 60% and 85% of the distance from the machining start position to the fracture position, and thereafter the machining speed is reduced.

Claims (4)

When punching is performed by pressing a punch into a workable austenitic stainless steel plate fixed by a die and a plate retainer, the work speed is increased from the start of processing until just before the workable austenitic stainless steel plate breaks. A punching method with reduced noise at the time of breakthrough, characterized by suppressing hardening due to processing-induced martensitic transformation of a steel sheet and then slowing the processing speed.   Die and punch material / shape, mold clearance, sheet pressing and lubrication conditions are the same as the actual punching conditions, and punching is performed at a predetermined processing speed. The punch is the first to austenitic stainless steel sheet to be processed. After measuring the distance from the machining start position in contact with the fracture position to the fracture position, during the actual punching process, 60 to 85% of the distance from the machining start position to the fracture position pushes the punch at a predetermined machining speed. The punching method with reduced noise during breakthrough according to claim 1, wherein when the distance of 60 to 85% is passed, the punch pressing speed is slowed to 4 to 10% of the processing speed.   The punching method which reduced the noise at the time of breakthrough of Claim 1 or 2 which makes the clearance of the metal mold | die used 3 to 8%.   The punching method which reduced the noise at the time of the breakthrough in any one of Claims 1-3 which uses a servo press as a press apparatus.

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