JPH0321245B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a pressing method, and more particularly to a pressing method that takes into account the amount of elastic recovery of a workpiece after drawing.

[Prior Art] When drawing an automobile panel or the like, the product recovers elastically after pressing, resulting in a product with a shape that differs from the press mold by that amount.
In order to obtain pressed products with high shape accuracy, this amount of elastic recovery must be accounted for in advance in the press mold, but conventionally, in press molds for large products such as automobile panels, it is usually It is not manufactured with the expectation of elastic recovery.

[Problems to be Solved by the Invention] Therefore, when using the conventional press method, the accuracy of the entire product was not necessarily good.

An object of the present invention is to provide a pressing method that takes into account the amount of elastic recovery for the entire mold surface in advance, thereby improving the overall shape accuracy of pressed products.

[Means for Solving the Problem] In order to achieve this object, in the pressing method of the present invention, where the elastic recovery amount δ is the Young's modulus of the workpiece and the yield point load is Y, δ=Y/ When approximated by E and the final pressed product shape desired to be formed on the workpiece is P (x, y, z), the press die surface shape is three-dimensional while pressing the workpiece. x ₁ = (1+δ)x, y ₁ (1+δ)y, z ₁ = (1+
It is formed into a shape of P ₁ (x ₁ , y ₁ , z ₁ ) having coordinate values of δ)z.

Then, a workpiece is press-molded using this press die, and then the workpiece is removed from the press die and elastically recovered to approximate the shape of P(x, y, z).

[Operation] Since the coordinates of such a mold surface shape are specified, even a complicated shape can be accurately machined by using an NC machine tool or the like. A workpiece pressed with a press die having this die surface is formed into the shape of the die surface during pressing, but when removed from the press die, it elastically recovers and deforms. However, in order to form the workpiece by an amount approximating this amount of deformation, press molds have a mold surface that is shaped in advance.
Since it is formed in the shape of P ₁ (x ₁ , y ₁ , z ₁ ),
The final pressed product after being removed from the mold and subjected to elastic recovery deformation is as close to the initial shape of P (x, y, z) as desired, and has a three-dimensional shape compared to conventional products. Its accuracy will be significantly improved.

[Examples] Below, preferred embodiments of the press mold of the present invention will be described with reference to the drawings.

FIG. 1 shows a state in which a workpiece is being formed using a drawing press die. In the figure, reference numeral 1 denotes a press die, which consists of an upper die 2 and a lower die 3. 4 is a workpiece, such as an automobile panel, which is in the process of being pressed. Second
The figure shows the pressed product 5 in its final state after being removed from the press mold. The pressed product 5 in the final state and the workpiece 4 in the press are deformed by the amount of elastic recovery. 6 is a reference point for the final pressed product 5, which is preferably set at a position 7 exactly in the center of the press mold 1 during pressing. The shape of the final pressed product 5 is determined from the desired shape of an automobile panel, etc., and the x-coordinate is
It is expressed as P(x, y, z) as a locus plane of points having coordinate values of x, y, and z in y and z coordinates, respectively. Further, the workpiece 4 being pressed has an x coordinate, a y coordinate, and a position 7 corresponding to the reference point 6 as the origin.
It is expressed as P ₁ (x ₁ , y ₁ , z ₁ ) as a locus plane of points having coordinate values of x ₁ , y ₁ , and z ₁ in coordinate and z coordinates, respectively. In this case, P ₁ (x ₁ , y ₁ , z ₁ ) and P (x, y,
z) has a value that differs overall by the amount of elastic recovery. If P ₁ (x ₁ , y ₁ , z ₁ ) is specified from P (x, y, z), the shapes of the upper die 2 and the lower die 3 are determined by 1 of the thickness of the workpiece 4. It will be specified by adding or subtracting a value that takes /2 minutes into consideration.

FIG. 3 shows the relationship between stress and strain in pressing a workpiece, with strain ε on the horizontal axis and stress δ on the vertical axis. When the upper mold 2 is lowered and the workpiece 4 is clamped between it and the lower mold 3, the workpiece 4 initially deforms elastically and rises at the gradient of the Young's modulus E of the workpiece 4, and reaches a certain point. Yields from Q and enters the plastic region, deformation point R
It is molded until. After the molding is completed, the upper mold 2
It is considered that when the stress rises from the lower die 3, the workpiece 4 recovers elastically and is elastically deformed again from point R, descending parallel to OQ and returning to point S where the stress is zero. If the intersection of the perpendicular line drawn down from point R and the horizontal axis is T, then
ST becomes the elastic recovery rate δ. Point R corresponds to the strained state of the workpiece 4 during pressing, and point S corresponds to the strained state of the pressed product 5. Yield point Q of stress strain characteristics
If we approximate that plastic deformation progresses with the yield point load Y from the point Q onward, the line from point Q onwards will be parallel to the horizontal axis.
When approximated in this way, the elastic recovery rate δ will be approximately specified by Y/E. Since this elastic recovery occurs three-dimensionally, the target final product 5
When the shape of is specified by P (x, y, z), the shape P ₁ (x ₁ , y ₁ , z ₁ ) of the workpiece being pressed has its coordinate values x ₁ , y ₁ , z ₁ as follows. Identified by value. That is, x ₁ = (1 + Y / E) x = (1 + δ) x y ₁ = (1 + Y / E) y = (1 + δ) y z ₁ = (1 + Y / E) z = (1 + δ) z Once the shape of 4 is specified, the mold surfaces of the upper mold 2 and lower mold 3 will have an amount equal to 1/2 of the thickness of the workpiece 4 relative to P ₁ (x ₁ , y ₁ , z ₁ ). It is specified by the adjusted value, processed by using an NC machine tool, and actually press mold 1 of the example device.
is made of materials that have been processed in this way.

When press forming is performed using the above-mentioned apparatus, the workpiece 4 is formed into the shape of P ₁ (x ₁ , y ₁ , z ₁ ) during pressing. Then, when the workpiece 4 is taken out from the press mold 1, it immediately recovers elastically and becomes the final shape of the product 5, which has a shape of P ₁ (x ₁ , y ₁ , z ₁ )
, the x, y, and z coordinates are deformed by −δx, −δy, and −δz, respectively, resulting in a shape of P(x, y, z). This shape is extremely close to the desired shape.

[Effects of the Invention] According to the press die of the present invention, the final shape of the pressed product can be brought close to the desired shape with high accuracy, and the shape accuracy of the product can be achieved throughout the entire pressed product. is obtained.

[Brief explanation of the drawing]

FIG. 1 is an overall cross-sectional view of a press mold in which the pressing method of the present invention is carried out, and FIG. 2 is a perspective view of a pressed product press-formed by the press mold of FIG. 1.
FIG. 3 is a stress-strain diagram showing the deformation relationship between the pressed workpiece and the pressed product. 1...Press mold, 2...Upper die, 3...Lower die, 4
...Workpiece, 5...Pressed product, 6...Reference point, 7...Point corresponding to the reference point.

Claims (1)

[Claims] 1. Young's modulus of the workpiece is E, yield point load is Y,
The final product shape is the x coordinate, y coordinate, and z relative to the reference point.
P(x,
y, z), the workpiece being pressed is x ₁ = (1 + Y/E)x, y ₁ = (1 + Y /E) y, z ₁ = (1+Y/E) A workpiece is formed using a press mold with a mold surface that is formed into the shape of P ₁ (x ₁ , y ₁ , z ₁ ) with the value of z. A pressing method characterized by press forming, and then removing the workpiece from the press die to allow elastic recovery to approximate the shape of P(x, y, z).