JPS63104729A - Method for improving deep drawability of plate materials - Google Patents

Abstract

PURPOSE:To improve the forming threshold by deep drawing, drawing depth and the uniformity in the thickness of a deep drawing product by making the wrinkle pressing force in a deep drawing stage at the value just before the rupture of a thin sheet material in case of deep-drawing various kinds of thin sheet materials by a press machine equipped with a punch and wrinkle presser. CONSTITUTION:In case of deep-drawing, the lightweight clad material of a steel plate - polypropylene - steel plate, etc., a very thin steel plate and the thin plate like blank 5 of a plastic plate, etc., with a die 4 and punch 6, the punching force of a punch 6 is measured by a load cell 7 and inputted into a central information processing unit 12 via an amplifier and A/D convertor. This processing unit 12 compares the rupture load P0 with the punching force P and in case of the set value P0'<P being slightly lower than P0 the wrinkle pressing force is loosened by an outer ram 1 via D/A convertor, amplifier and servo valve 13 and in case of P0'>P reversely the wrinkle pressing force is controlled so as to increase it by an outer ram 1, the deep drawing is performed by a constant punching force over the whole working process, the deep drawing threshold is improved, the working yield of the material is improved and the thickness of a work is uniformized as well.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a deep drawing method for sheet materials, and in particular to a deep drawing method suitable for sheet materials of new materials such as lightweight steel plate clad materials, as well as conventional ultrathin steel sheets and plastic sheets. This invention relates to a method for improving drawability.

(Conventional technology and problems to be solved) The deep drawing method, which is one of the processing methods for steel plates, is a method of processing plate materials with a press machine equipped with a punch and a wrinkle presser, but other processing methods In comparison, there is an inherent problem of wrinkles occurring at the flange portion of the plate blank, and various pressing methods have been proposed in the past.

A typical wrinkle holding method is the constant load method.

There are constant surface straightness method, wrinkle press force variable method (number of machines method), etc., and constant load method is a method that is more widely used than before and keeps the wrinkle press force constant during processing. is a method of controlling the wrinkle pressing force so that the surface pressure applied to the flange surface is always constant, and the wrinkle pressing force variable method is a method that controls the wrinkle pressing force to the minimum necessary to prevent wrinkles from growing beyond a certain wrinkle height. This is a method of giving

However, in recent years, there are new materials with new properties that have not been seen before, such as clad steel sheets, which are three-layer rad-faded lightweight steel sheets (steel plate/polypropylene/m-plate), and superplastic metals, which have begun to be widely used for automobiles. New materials have appeared, but these have poor wrinkle resistance and low forming limits, making it difficult to put them into practical use with conventional wrinkle suppressing methods due to complicated procedures. Therefore, it has been desired to develop a method for improving deep drawability using a new presser method.

The present invention was made in view of the situation, and
It is possible to improve the forming limit and drawing depth, and to make the wall thickness uniform by deep drawing of plates made of various materials.The purpose is to provide a deep drawing improvement method that is particularly suitable for processing new materials such as lightweight steel plates. That is.

(Means for solving the problem) In order to achieve the above object, the present inventor first conducted various studies on the conventional wrinkle pressing method, and found that the wrinkle pressing force set for the constant wrinkle pressing method was too high. The punching force reaches the breaking load of the specimen and causes it to break, but if it is too low, wrinkles will occur, so we use a variable wrinkle presser method that changes the wrinkle presser force during deep drawing to ensure that the wrinkles are as large as possible in each process. Considering that there is a limit to the wrinkle pressing force, we investigated the effect of variable wrinkle pressing force on wrinkles and punching force and attempted to improve it. In other words, by applying the maximum wrinkle holding force (maximum wrinkle holding force) that does not cause the material to break in each deep drawing process, it has sufficient ability to suppress and correct wrinkles, even if they are It was discovered that even if wrinkles occur, the wrinkles are corrected in the latter stage of molding, improving the forming limit (limit drawing ratio) and improving the drawing depth, and based on this knowledge, the present invention was made.

In other words, the method for improving the deep drawability of a sheet material according to the present invention constantly monitors the punching force during the deep drawing process so that the punching force always maintains a value just below the breaking load of the sheet material blank over the entire process. It is characterized by continuously controlling the variable wrinkle pressing force so that it is always maintained only in the later stages of the stroke.

The present invention will be explained in detail below based on examples.

(Example) Regarding the wrinkle pressing method, the present invention belongs to the category of the variable wrinkle pressing method, which is one of the conventional wrinkle pressing methods, but the principle is fundamentally different.

In other words, the conventional variable wrinkle pressing method is a method that applies the minimum necessary wrinkle pressing force to prevent wrinkles from occurring during each processing process, whereas the present invention allows a certain amount of wrinkles to occur, but does not cause wrinkles in the final product. Adopts a maximum crease suppression method that prevents residue.

FIG. 1 shows the relationship between processing steps, punching force, and wrinkle pressing force in the present invention. Note that the horizontal axis is the instantaneous drawing ratio (DRY), which is the instantaneous blank radius divided by the die radius, as a quantity representing the deep drawing process.

In the same figure, the punching force (load) P always shows a value slightly lower than the breaking load P0 of the plate blank throughout the entire stroke, and for each drawing ratio, the maximum pressing force ( Maximum wrinkle pressing force) Max,
B HF is given. However, this maximum wrinkle pressing force is
As the wrinkle holding force is increased, the punching force reaches the breaking load of the material and the material breaks, but this is the wrinkle holding force when the wrinkle holding force is loosened just before the material breaks, and this is the wrinkle holding force just before the material breaks. It is defined as the maximum value of If the wrinkle pressing force is continuously applied or loosened to a constant value of 1, which is slightly lower than the breaking load of the material, for example, 90% or more of the breaking load, the wrinkle pressing force at that time will eventually reach the maximum. It acts as a wrinkle holding force. This method can be called a constant punch force method.

Next, the deep drawing method of the present invention using this constant punching force method will be explained with reference to the drawings.

FIG. 2 shows an example of a press for carrying out the method of the present invention, which is a computer-controlled double-acting hydraulic press. The left side of FIG. 1 shows the state before pressing, and the right side shows the state during pressing. This press has outer ram 1 and inner ram 2.
A blank holder (wrinkle presser) 3 is fixed to the outer ram 1, and the blank 5 on the die 4 is held down by the blank holder 3. On the other hand, a punch 6 is connected to the inner ram 2. These outer ram 1 and inner ram 2 are each driven hydraulically. 7 is a load cell fixed to the inner ram 2 with a bolt to measure the punching force, 8 is a magnet scale for measuring the displacement of the inner ram 2, and the outer ram 1 is also used to measure the wrinkle pressing force. A load cell 9 is installed to measure the displacement of the outer ram 1, and a transducer 10 is provided to measure the displacement of the outer ram 1. Note that 11 is a guide for the punch 6.

The press constructed as described above is operated by a control system shown in FIG. In the machining process based on the displacement Q of the inner ram 2, the punch force P is constantly measured by the rotor self, and the punch force P is measured by the central information processing unit (
(CPU) 12. In the central information processing unit 12, the breaking load P0 of a blank (e.g., 3-layer clad structure of steel plate (0.4 mm)/polypropylene (0.2 mm)/steel plate (0.4 m), total plate thickness 1.0 mm) is determined. and punch force P are compared. In reality, a value P0' is set slightly lower than the breaking load P0, and when p,'<p, the wrinkle pressing force is loosened by the outer ram 1 via the D/A converter, amplifier, and servo valve 13. Conversely, when p,'>p, the outer ram 1 is similarly controlled to increase the wrinkle pressing force. As a result, deep drawing is performed with a constant punch force throughout the entire processing process, resulting in the maximum wrinkle holding force being applied.

Note that this method: (1) The wrinkle pressing force changes during processing. ■
The method of applying wrinkle pressing force to the aperture ratio can be determined uniquely.

■This method itself is a processing method that already includes a fracture limit1
For these reasons, in order to find the limiting drawing ratio of the single-piece method, for which the conventional method for determining the limiting drawing ratio cannot be applied, for example, as shown in By taking the height and appropriately setting the allowable wrinkle height to 10 μm, the limit drawing ratio LDR can be found to be about 2.26. Therefore, if the drawing ratio is below this limit drawing ratio LDR, a wrinkle-free product of 10 μm or less can always be obtained. As shown in Fig. 1, even if wrinkles occur during the middle stage of the process where the wrinkle pressing force decreases, a greater wrinkle pressing force is applied in the latter stage.

Wrinkles are corrected and no wrinkles remain on the final product.

Improved forming limit.

Figure 5 shows an example of the wall thickness distribution (indicated by Δ) of the side wall of a molded container obtained by deep drawing at DR2 and 18 using the constant punch force method described above, and shows the wrinkles of the conventional constant punch force method. Compared to the presser method (marked 0), because a large pressing force is always applied, the wall thickness distribution of the molded container is thinner overall, and as a result, the increase in wall thickness at the opening edge is suppressed. , on the other hand, it decreases even more at the location corresponding to the punch shoulder.

Due to the difference in wall thickness distribution as described above, according to the present invention, the deepest container can be obtained from the same blank diameter, and it is also possible to improve the material yield.

On the other hand, when thickening of a molded container is required, in the present invention, the thickening can be easily achieved by slightly modifying the constant punching force method. In other words, as shown in the punch force curve in Figure 6, Method 2 is to cut the maximum wrinkle pressing force in the first half of the processing process.In other words, the wrinkle pressing force in the first half of the process is loosened to suppress the decrease in wall thickness, and in the second half, the maximum wrinkle holding force is reduced. In order to suppress thickening by applying wrinkle pressing force, the punching force is gradually increased in the early stage to approach the breaking load of the material, and the punching force is monitored so as to follow a curve that continues to a constant punching force in the latter stage ( (constant punch force improvement method). According to this improvement method, the wall thickness distribution is increased as shown by the * mark in FIG.

In the above embodiment, a double-acting hydraulic press was used as the press, but it goes without saying that other types of presses can be used, but a computer-controlled press is preferable due to the need to constantly monitor the punching force. . It can also be applied to deep drawing of blanks made of materials other than lightweight steel plates.

(Effects of the Invention) As described in detail above, according to the present invention, the punching force is constantly monitored using the breaking load of the plate material to be deep drawn as a measure, and the wrinkle pressing force can be varied without predicting and calculating the maximum wrinkle pressing force. Therefore, it is possible to improve the molding limit and container depth of any material, and also to make the wall thickness uniform, which is very advantageous in improving the yield of the material. It is particularly suitable for deep drawing of new materials such as lightweight steel plates, as well as conventional ultra-thin steel plates and plastic plates.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a punch force curve of a constant punch force method according to the present invention, and FIG. 2 is a cross-sectional view schematically showing an example of a press used in an embodiment of the present invention. Figure 3 is a block diagram of the control system for the press, Figure 4 is an explanatory diagram showing how to determine the critical drawing ratio in the present invention, and Figure 5 is the wall thickness of the side wall of a deep-drawn molded container. Diagram showing distribution. FIG. 6 is a diagram showing a punch force curve of the constant punch force improvement method according to the present invention. 1... Outer ram, 2... Inner ram, 3...
・Blank holder, 4...Die, 5...Blank (plate material). 6...Punch, 7.9...Load cell, 12...
Central information processing unit, 13...Servo valve 6 Patent applicant Hisashi Nakamura, Patent attorney representing the New Technology Development Corporation Figure 1 T-guchi Figure 3 Figure 4 p'FZ

Claims (2)

[Claims] (1) When deep drawing a plate blank using a press machine equipped with a punch and a wrinkle presser, the punching force is constantly monitored during the deep drawing process, and the punching force is constantly adjusted to a value just below the breaking load of the plate blank throughout the entire process. A method for improving the deep drawability of sheet materials, which is characterized by continuously controlling a variable wrinkle holding force so as to maintain the same level of wrinkle holding force. (2) When deep drawing a plate blank using a press machine equipped with a punch and a wrinkle presser, the punching force is constantly monitored during the deep drawing process, and in the first half of the process, the punching force gradually increases to the breaking load of the plate blank during the process. Deep drawing of a plate material characterized by continuously controlling variable wrinkle holding force so that the punching force approaches the breaking load of the plate blank, and so that the punch force always maintains a constant value just below the breaking load of the plate blank in the latter half of the stroke. Sexual improvement method.