JP6003498B2 - Creating a stress-strain curve for the sizing process - Google Patents

Description

  The present invention relates to a method for creating a stress-strain curve in a sizing process for creating a stress-strain curve for each workpiece density.

2. Description of the Related Art Conventionally, a sizing process is performed on a workpiece constituted by a sintered body by placing the workpiece in a mold including an inner core and a die. Such a mold is re-made many times while fine-tuning the dimensions until the desired dimensions of the workpiece can be achieved.
That is, in the sizing process, it is not possible to create a mold that can achieve the target dimensions at one time.

As a means for creating a mold that can achieve a target dimension at one time, for example, it is conceivable to use a computer aided engineering (CAE) to create a sizing process prediction technique.
In the sizing process prediction technique using CAE, it is necessary to create a stress-strain curve for each work density as information for determining the dimensions of the work after the sizing process.

  The stress-strain curve is generally created based on the measurement result obtained by performing a tensile test on a workpiece (test piece), measuring the load on the workpiece and the elongation of the workpiece (for example, Patent Document 1). reference).

JP 2002-332531 A

Since the sintered body has a non-uniform density distribution, it is necessary to create a stress-strain curve for each different density in the sizing process prediction technique using CAE. Further, when creating a stress-strain curve by a tensile test as described in Patent Document 1, in order to obtain a certain degree of reliability, a tensile test is performed a plurality of times (for example, about three times) for each type of density. There is a need to do.
Therefore, to create a stress-strain curve for the sizing process, that is, a stress-strain curve for each density necessary for the prediction technique of the sizing process using CAE, the density type and the number of tensile tests are integrated. It is necessary to perform a tensile test as many times as necessary.
That is, in the prior art, since it is necessary to perform a very large number of tensile tests, the stress-strain curve of the sizing process cannot be created in a short time.

Further, the tensile test needs to be performed on a sintered body having a uniform density distribution (constant density). On the other hand, it is difficult to obtain a uniform density distribution due to the fact that a sintered compact is formed by baking and compacting a green compact obtained by pressing metal powder or the like.
Therefore, in the tensile test, for example, it is necessary to use a part of a large-shaped sintered body cut out.
That is, in the prior art, since it is necessary to perform a process for obtaining a sintered body having a uniform density, a stress-strain curve of the sizing process cannot be easily created.

  The present invention has been made in view of the above situation, and provides a method for creating a stress-strain curve in a sizing process that can easily create a stress-strain curve for each density in a short time.

In Claim 1, it is a creation method of the stress-strain curve of the sizing process which creates a stress-strain curve for every density of a work, Comprising: Before and after the sizing process of putting the above-mentioned work into a mold and forming it in a predetermined shape, The step of measuring the shape of the workpiece at multiple points, the step of measuring the gap of the mold at the position corresponding to the measurement location of the workpiece, the measurement result of the workpiece before the sizing step, and the measurement result of the gap of the mold The amount of elastic strain at the measurement location of the workpiece is calculated based on the step of calculating the maximum strain amount at the measurement location of the workpiece, the measurement result of the gap of the mold and the measurement result of the workpiece after the sizing step. A step of calculating, a step of measuring a density at a measurement location of the workpiece, a step of measuring a Young's modulus at a measurement location of the workpiece, The first vertex is set on the strain axis of the stress-strain curve of the density corresponding to the density measurement result at the workpiece measurement location based on the calculation result of the maximum strain amount for each measurement location of the workpiece. And a step of setting a second vertex based on the calculation result of the elastic strain amount, and a first extending from the first vertex along the axial direction of the stress for each measurement point of the workpiece. together draw a virtual line, from said second vertex, pull the second virtual line that along the slope out extension corresponding to the measurement result of the Young's modulus with respect to the axial direction of the stress, the respective virtual line And a step of creating a stress-strain curve by connecting the third vertex for each density corresponding to the density measurement result at the measurement location of the workpiece. , That is.

  In the present invention, the Young's modulus at the measurement location of the workpiece is measured based on the measurement result of the density at the measurement location of the workpiece.

  The present invention has an effect that a stress-strain curve for each density can be easily created in a short time.

Explanatory drawing which shows the flow of a sizing process continuously. Explanatory drawing which shows the change of the stress and distortion | strain in a sizing process. Explanatory drawing which shows a mode that a 1st vertex and a 2nd vertex are set on the axis | shaft of the strain of a stress-strain curve. Explanatory drawing which shows a mode that a 1st virtual line and a 2nd virtual line are set on the coordinate of a stress-strain curve. Explanatory drawing which shows a mode that a stress-strain curve is created. The figure which shows the shape of a workpiece | work. (A) The figure which looked at the workpiece | work from the height direction. (B) Perspective view. The figure which shows a mode that the shape of a rib is measured. The figure which looked at the work from the height direction. (B) Perspective view. The figure which shows the result of having measured the shape of the rib before a sizing process. (A) The figure which shows an outer radius. (B) The figure which shows an inner radius. (C) The figure which shows thickness. The figure which shows the result of having measured the shape of the rib after a sizing process. (A) The figure which shows an outer radius. (B) The figure which shows an inner radius. (C) The figure which shows thickness. Explanatory drawing which shows a mode that the shape of a rib is corrected. The figure which shows the result of having calculated the volume of the rib. (A) The figure which shows the volume before a sizing process (b) The figure which shows the volume after a sizing process. Explanatory drawing which shows a mode that the shape of the rib after correction is calculated. The figure which shows the result of having corrected the shape of the rib before a sizing process. (A) The figure which shows an outer radius. (B) The figure which shows an inner radius. The figure which shows the result of having corrected the shape of the rib after a sizing process. (A) The figure which shows an outer radius. (B) The figure which shows an inner radius. The figure which shows a mode that the clearance gap of a type | mold is measured. The figure which shows the state which the inner core shifted | deviated. The figure which shows the result of having estimated the shift | offset | difference of the inner core. (A) The figure which shows the prediction result in the workpiece | work 1. FIG. (B) The figure which shows the prediction result in the workpiece | work 2. FIG. (C) The figure which shows the prediction result in the workpiece | work 3. FIG. The figure which shows the result of having measured the shape of the rib before and behind a sizing process, and the clearance gap of a type | mold. (A) The figure which shows the measurement result in the workpiece | work 1. FIG. (B) The figure which shows the measurement result in the workpiece | work 2. FIG. (C) The figure which shows the measurement result in the workpiece | work 3. FIG. The figure which shows a mode that a true strain is calculated typically. The figure which shows the result of having calculated the maximum strain amount and the elastic strain amount. (A) The figure which shows the calculation result in the workpiece | work 1. FIG. (B) The figure which shows the calculation result in the workpiece | work 2. FIG. (C) The figure which shows the calculation result in the workpiece | work 3. FIG. The figure which shows the result of having measured the density of the rib. The figure which shows a mode that a Young's modulus is calculated from the relationship between a density and a Young's modulus. Explanatory drawing which shows a mode that the 1st vertex is set for every density. Explanatory drawing which shows a mode that a triangle is produced for every density. Explanatory drawing which shows a mode that a stress-strain curve is created for every density.

  Hereinafter, a method for creating a stress-strain curve in the sizing process of the present embodiment (hereinafter referred to as “method for creating a stress-strain curve”) will be described.

  The stress-strain curve creation method creates a stress-strain curve G for each density of the workpiece W based on the result of performing the sizing process on the workpiece W (see FIG. 25).

First, the sizing process will be described with reference to FIGS.
As shown in FIG. 1, the sizing process is for putting the workpiece W into a mold 10 constituted by the inner core 11 and the die 12 and forming the workpiece W into a predetermined shape, thereby increasing the dimensional accuracy of the workpiece W.

  The workpiece W is a sintered body manufactured by baking and compacting a green compact obtained by press-molding a metal powder or the like.

In the sizing process, the workpiece W is set on the mold 10.
In the sizing process, the workpiece W is pressed downward by the upper punch 20 to put the workpiece W into the mold 10 (see the downward arrow shown in FIG. 1). In other words, in the sizing process, the workpiece W is ironed by the upper punch 20.
As a result, in the sizing process, a load is applied to the workpiece W by the mold 10 and the upper punch 20 to crush the workpiece W.

  At this time, as shown in FIG. 2, in the sizing step, a load exceeding the elastic range in the stress-strain curve G of the workpiece W is applied to the workpiece W (see the symbol M · P3 shown in FIG. 2).

Thereafter, as shown in FIG. 1, in the sizing step, the workpiece W is pressed upward by the lower punch 30 and the workpiece W is extracted from the mold 10 (see the upward arrow shown in FIG. 1).
That is, in the sizing process, the workpiece W is extracted from the mold 10 and the load on the workpiece W is unloaded.

At this time, as shown in FIG. 2, the stress generated in the workpiece W falls in parallel to the inclination of the elastic region in the stress-strain curve G of the workpiece W.
Therefore, the work W is elastically recovered by an amount smaller than the strain when it is placed in the mold 10, and a certain amount of strain remains (refer to reference sign P3 · N shown in FIG. 2).

  As a result, as shown in FIGS. 1 and 2, in the sizing process, the workpiece W is elastically recovered and the workpiece W is formed into a predetermined shape (see the left and right arrows shown in the workpiece W in FIGS. 1 and 2). .

  In order to create the mold 10 for performing such a sizing process at one time, it is conceivable to create a prediction technique for the sizing process using, for example, Computer Aided Engineering (CAE).

The density distribution of the workpieces W is not uniform because the workpieces W are molded by pressing the powder. That is, the density of the workpieces W varies depending on the position.
Therefore, in the sizing process prediction technique using CAE, it is necessary to create a stress-strain curve G for each density of the work W as information for determining the dimensions of the work W after the sizing process.

  The stress-strain curve creation method according to the present embodiment creates a stress-strain curve G for each density of the workpiece W within a density range in which a sizing process prediction technique using CAE can be created. is there.

As described above, in the sizing step, the workpiece W is formed, that is, a load exceeding the elastic range in the stress-strain curve is applied to the workpiece W.
That is, in the method of creating the stress-strain curve in the sizing process, the stress-strain curve G of the workpiece W in the strain range required for the sizing process (the range larger than the elastic region and smaller than the breaking point) is obtained. create.

  Below, the procedure of the preparation method of the stress-strain curve of this embodiment is demonstrated.

  In the stress-strain curve creation method, based on the result of the sizing process, points indicating the relationship between stress and strain are interspersed on the coordinates of the stress-strain curve G, and the created points are connected to generate stress- A strain curve G is created (see symbol P3 shown in FIG. 5).

  First, as shown in FIG. 2, in the stress-strain curve creation method, before the sizing process (before the work W is put into the mold 10) and during the sizing process (when the work W is put into the mold 10). The amount of strain M is calculated.

  The workpiece W before the sizing process is in a state without distortion. The workpiece W in the sizing process is in a state where it is crushed by the upper punch 20 and is most distorted.

  Hereinafter, the strain amount M before and during the sizing process will be referred to as “maximum strain amount M”.

As shown in FIG. 3, such a maximum strain amount M is the strain axial direction of the maximum strain amount M from the origin of the stress-strain curve (position of strain 0) on the strain axis of the stress-strain curve. Corresponds to the position moved along.
In the method of creating the stress-strain curve, a position moved along the strain axial direction by the maximum strain amount M from the origin of such a stress-strain curve is set as the first vertex P1.

  After setting the first vertex P1, as shown in FIG. 2, the stress-strain curve creation method calculates the strain amount N between the sizing process and after the sizing process.

  The workpiece W after the sizing process is in a state of being elastically recovered by being extracted from the mold 10.

  Hereinafter, the strain amount N during and after such a sizing process is referred to as “elastic strain amount N”.

As shown in FIG. 3, such an elastic strain amount N is located on the strain axis of the stress-strain curve at a position moved along the strain axial direction by the elastic strain amount N from the first vertex P1. Correspond.
In the method for creating the stress-strain curve, the position moved along the strain axial direction by the elastic strain amount N from the first vertex P1 is set as the second vertex P2.

As described above, when the workpiece W is taken out of the mold 10, the stress falls in parallel to the inclination of the elastic region. Such an inclination of the elastic region is determined by the Young's modulus of the workpiece W.
Therefore, in the method of creating the stress-strain curve, based on the first vertex P1, the second vertex P2, and the Young's modulus, the change in stress when elastically recovered is calculated back to obtain the relationship between stress and strain. Set the point to show.

  Specifically, as shown in FIG. 4, in the stress-strain curve creation method, a first imaginary line L1 that passes through the first vertex P1 and is parallel to the axial direction of the stress is drawn.

  Then, in the stress-strain curve creation method, the Young's modulus of the workpiece W is measured, and the second slope inclined along the slope corresponding to the Young's modulus measured with respect to the axial direction of the stress from the second vertex P2. A virtual line L2 is drawn.

Thus, in the stress-strain curve creation method, a triangle T composed of the virtual lines L1 and L2 and the strain axis is created.
In the method of creating the stress-strain curve, the intersection of the virtual lines L1 and L2, which are points indicating the relationship between stress and strain, is set as the third vertex P3.

  In the sizing process, the maximum strain amount M and the elastic strain amount N have different values depending on the position of the workpiece W due to different loads applied depending on the position of the workpiece W. Therefore, the triangle T differs depending on the position of the workpiece W.

Therefore, as shown in FIG. 5, in the stress-strain curve creation method, the shape of the workpiece W is measured from a plurality of locations (multi-point measurement), and a plurality of triangles T is created. In the stress-strain curve creation method, the third vertex P3 of each triangle T is connected to create the stress-strain curve G.
At this time, in the stress-strain curve creation method, a triangle T is created for each position where the workpiece W is measured on the coordinates of the stress-strain curve having the same density as the density of the location where the workpiece W is measured. A stress-strain curve G is created for each density by connecting the three vertices P3 (see FIG. 25).

  Hereinafter, the procedure for creating the stress-strain curve G will be specifically described on the assumption that the workpiece W is a VVT housing.

As shown in FIG. 6, the workpiece W is formed in a substantially cylindrical shape, and the inner peripheral surface partially protrudes radially inward (in the present embodiment, four protruding portions are formed). The workpiece W extends from one end in the height direction of the workpiece W to the other end in the height direction while maintaining the cross-sectional shape as shown in FIG.
In such a workpiece W, portions formed in a substantially arc shape, that is, portions other than the protruding portions are formed as ribs W1 to W4.

First, as shown in FIG. 7, in the stress-strain curve creation method, a step of measuring the shape of the workpiece W before the sizing step is performed at multiple points (see arrows shown in FIG. 7). At this time, in the stress-strain curve creation method, the workpiece W is measured at multiple points at a measurement pitch that can create the stress-strain curve G for each density.
That is, in the stress-strain curve creation method, the thicknesses of the ribs W1 to W4 are measured for each constant pitch along the circumferential direction of the workpiece W and the height direction of the workpiece W.

  When the workpiece W is a VVT housing as in the present embodiment, the thickness of the ribs W1 to W4 is measured at multiple points in the stress-strain curve creation method.

  In the present embodiment, the thicknesses of the ribs W1 to W4 of the three workpieces W are measured (see the workpieces 1 to 3 shown in FIG. 8).

At this time, as shown in FIG. 8A and FIG. 8B, in the stress-strain curve creation method, for example, the outside of the ribs W1 to W4 is detected by a three-dimensional measuring device (Coordinated Measuring Machine (CMM)). Measure the radius and inner radius.
And as shown in FIG.8 (c), in the preparation method of a stress-strain curve, the measurement result of an inner radius is subtracted from the measurement result of an outer radius, and the thickness of rib W1-W4 is measured.

In FIG. 8, only the measurement results of the ribs W1 to W4 are shown, and the measurement results of the ribs W1 to W4 are connected by a straight line. That is, FIG. 8 does not reflect the shape of the protruding portion of the workpiece W.
Further, in FIG. 8, the horizontal axis is represented in a form corresponding to the angle (phase of the workpiece W) illustrated in FIG. 6A, and only the measurement results of the ribs W1 to W4 at a predetermined height position are illustrated. doing. That is, in the stress-strain curve creation method, the measurement results of the thicknesses of the ribs W1 to W4 as shown in FIG. 8 are actually obtained for each measurement pitch along the height direction.
This also applies to FIGS. 9, 11, 13, 14, 17, 18, and 20.

  After the workpiece W before the sizing process is measured at multiple points, the sizing process is performed on the workpiece W in the stress-strain curve creation method (see FIG. 1).

After performing the sizing process, as shown in FIG. 7 and FIG. 9, in the stress-strain curve creation method, the work W after the sizing process is performed in the same manner as when the work W before the sizing process is measured at multiple points. The step of measuring the shape of the multipoint is performed.
That is, in the stress-strain curve creation method, the thickness of the ribs W1 to W4 after the sizing process is measured by subtracting the measurement result of the inner radius from the measurement result of the outer radii of the ribs W1 to W4 after the sizing process.

Here, as shown in FIG. 10, the workpiece W is formed in a substantially elliptical shape when viewed from the height direction, before and after the sizing process, for convenience of processing accuracy. Therefore, the ribs W1 to W4 have an arc shape corresponding to an approximately ellipse before and after the sizing process.
That is, the outer radius and the inner radius of the ribs W1 to W4 measured before and after the sizing process are increased or decreased depending on the phase of the workpiece W.

Therefore, in the stress-strain curve creation method, the shape of the workpiece W after the sizing process is corrected at multiple points, and then the shape of the workpiece W before and after the sizing process is corrected (see the arrow shown in FIG. 10).
That is, in the stress-strain curve creation method, the shape of the ribs W1 to W4 is corrected so as to have an arc shape corresponding to a perfect circular cylinder for each measurement pitch.

Specifically, as shown in FIG. 11, in the stress-strain curve creation method, the volumes of the ribs W1 to W4 are calculated for each measurement pitch.
Then, as shown in FIG. 12, in the stress-strain curve creation method, the volume-calculated portion is deformed into a circular cylinder divided into each measurement pitch without changing the volume, and the outer radius at the time of deformation is changed. And calculate the inner radius.

At this time, in the method of creating the stress-strain curve, the outer radius and the inner radius are calculated based on the following equations.
x = S * 360 / θ * 1 / π * 1 / 4r * 1 / h
Here, x is the distance along the radial direction from the neutral plane C (the central portion of the thickness of the perfect circular cylinder) to the outer peripheral surface and the inner peripheral surface of the perfect circular cylinder, and S is the measurement pitch of the perfect circular cylinder. The volume of each divided part, θ is the central angle of a perfect circular cylinder divided for each measurement pitch, π is the circumference, r is the radius of the neutral plane C, and h is along the height direction of the measurement pitch. Distance.

As shown in FIGS. 13 and 14, in the stress-strain curve creation method, the outer radius and the inner radius calculated by the above equations are the outer radius and the inner radius of the ribs W1 to W4 before and after the sizing process.
In the method of creating the stress-strain curve, the outer radius and the inner radius of the ribs W1 to W4 before and after the sizing process are corrected in this way.

  In the stress-strain curve creation method, the thickness of the ribs W1 to W4 before and after the sizing process is measured from the outer radius and the inner radius of the ribs W1 to W4 before and after the corrected sizing process (see FIG. 18).

According to this, the stress-strain curve creation method can acquire the accurate outer radius and inner radius of the ribs W1 to W4 before and after the sizing process regardless of the phase of the workpiece W.
That is, since the stress-strain curve creation method can accurately measure the thicknesses of the ribs W1 to W4, the stress-strain curve G can be created with high accuracy.

After correcting the workpiece W before and after the sizing process, as shown in FIG. 15, in the method for creating the stress-strain curve, the gap of the mold 10 used in the sizing process is measured (see the arrow shown in FIG. 15). That is, in the stress-strain curve creation method, the thicknesses of the ribs W1 to W4 during the sizing process are measured.
At this time, in the stress-strain curve creation method, for example, the outer radius of the inner core 11 and the inner radius of the die 12 are measured by CMM, and the outer radius of the inner core 11 is subtracted from the measured inner radius of the die 12. The gap of the mold 10 is calculated.

  In addition, the preparation method of a stress-strain curve should just measure the clearance gap of the type | mold 10 in the position corresponding to the measurement location of the workpiece | work W at least.

  As described above, in the method of creating the stress-strain curve, a step of measuring the gap of the mold 10 at the position corresponding to the measurement location of the workpiece W (ribs W1 to W4) is performed.

Here, as shown in FIG. 16, the inner core 11 is subjected to a partially high load during the sizing process due to the non-uniform density distribution of the workpiece W, and the position of the inner core 11 is the workpiece W. There is a possibility of deviation along the radial direction.
That is, the gap of the mold 10 during the sizing process is not uniform and may vary depending on the phase of the workpiece W.

  Therefore, as shown in FIG. 17, in the stress-strain curve creation method, the deviation amount of the inner core 11 during the sizing process is predicted, and the measurement result of the gap of the mold 10 is corrected based on the prediction result. At this time, in the stress-strain curve creation method, for example, the shift amount of the inner core 11 is predicted using CAE.

Specifically, in the stress-strain curve creation method, a three-dimensional model of the workpiece W is created based on the measurement results of the thicknesses of the ribs W1 to W4 as shown in FIG. A sizing process is virtually performed on the model.
And in the creation method of a stress-strain curve, the result of the sizing process performed virtually becomes the measurement result of the thickness of ribs W1-W4 as shown in FIG. Predict the position (that is, the amount of deviation).

According to this, the stress-strain curve creation method can reflect the deviation of the inner core 11 during the sizing process in the measurement result of the gap of the mold 10.
That is, the stress-strain curve creation method can accurately measure the gap of the mold 10, so that the stress-strain curve G can be created with high accuracy.

  Accordingly, as shown in FIG. 18, in the stress-strain curve creation method, the measurement result of the shape of the workpiece W (the thickness of the ribs W1 to W4 after correction) before and after the sizing process, and the gap (after correction) of the mold 10 The measurement result of the gap of the mold 10 is obtained.

  In the stress-strain curve creation method, the amount of strain (maximum strain amount) when the workpiece W is placed in the mold 10 based on the measurement result of the shape of the workpiece W before and after the sizing process and the measurement result of the gap of the mold 10. M) and a strain amount (elastic strain amount N) when the workpiece W is taken out of the mold 10 are calculated.

  That is, in the method for creating the stress-strain curve, the measurement result of the shape of the workpiece W (the thickness of the ribs W1 to W4 after correction) before the sizing step shown in FIG. A step of calculating the maximum strain amount M is performed based on the measurement result of the (gap).

At this time, in the stress-strain curve creation method, the measurement result of the shape of the workpiece W before the sizing process is denoted by reference symbol L shown in FIG. 19, and the measurement result of the gap of the mold 10 is denoted by reference symbol L0 shown in FIG. By calculating, the maximum strain amount M is calculated.
As shown in FIG. 20, in the stress-strain curve creation method, the true strain is calculated for each measurement location of the ribs W1 to W4, and the maximum strain at the measurement location of the workpiece W (ribs W1 to W4). The amount M is calculated (see squares, rhombuses, and circles shown in white in FIG. 20).

Thereby, in the stress-strain curve creation method, a plurality of pieces of information for setting the first vertex P1 (see FIG. 3) and the first virtual line L1 (see FIG. 4) are acquired (the upper portion shown in FIG. 20). See arrow for direction).
That is, in FIG. 20, the distance from the position of strain 0 to the position of the maximum strain amount M (rectangle, rhombus, and circle shown in white in FIG. 20) is the first from the origin of the stress-strain curve in FIG. Corresponds to the distance to the vertex P1.

  In the stress-strain curve creation method, the measurement result of the gap of the mold 10 (gap of the corrected mold 10) and the measurement result of the workpiece W (the thickness of the ribs W1 to W4 after correction) after the sizing process are used. The step of calculating the elastic strain amount N is performed by calculating the true strain on the basis.

At this time, in the method for creating the stress-strain curve, the true strain is calculated with the measurement result of the gap of the mold 10 as the symbol L shown in FIG. 19 and the measurement result of the workpiece W after the sizing process as the symbol L0 shown in FIG. Thus, the elastic strain amount N is calculated.
As shown in FIG. 20, in the stress-strain curve creation method, the elastic strain amount N is calculated for each measurement location of the ribs W1 to W4, and the measurement location of the workpiece W (ribs W1 to W4) is measured. The elastic strain amount N is calculated (see squares, rhombuses, and circles shown in black in FIG. 20).

Thereby, in the stress-strain curve creation method, a plurality of pieces of information for setting the second vertex P2 (see FIG. 3) is acquired (see the downward arrow shown in FIG. 20).
That is, in FIG. 20, from the position of the maximum strain amount M (rectangle, rhombus, and circle shown in white in FIG. 20) to the position of elastic strain amount N (square, rhombus, and circle shown in black in FIG. 20). Corresponds to the distance from the first vertex P1 to the second vertex P2 in FIG.

In the present embodiment, there are portions where the thicknesses of the ribs W1 to W4 are increased after the sizing process due to the influence of measurement errors caused by the CMM (the portions surrounded by the squares in FIGS. 20 (a) and 20 (b)). reference).
In the method for creating the stress-strain curve, the portion where the ribs W1 to W4 are thick after such a sizing process is determined to be the portion where the measurement error has occurred, and is used in creating the stress-strain curve G. do not do.

After calculating the maximum strain amount M and the elastic strain amount N, in the stress-strain curve creation method, as shown in FIG. 21, a step of measuring the density at the measurement location of the workpiece W (ribs W1 to W4) is performed. .
In the stress-strain curve creation method of the present embodiment, the workpiece W after the sizing process is cut along the height direction to divide the workpiece W into ribs W1 to W4, and the divided ribs W1 to W4 are inserted. The density of the ribs W1 to W4 is measured from the change in water when the water is discharged.

  In FIG. 21, only the result of measuring the density of the ribs W1 to W4 of one workpiece W is shown, but actually the density of the ribs W1 to W4 of the three workpieces W is measured.

  After measuring the density, the stress-strain curve creation method includes a step of measuring the Young's modulus at the measurement location of the workpiece W (ribs W1 to W4).

As shown in FIG. 22, the Young's modulus has a correlation with the density of the ribs W1 to W4.
Therefore, in the stress-strain curve creation method, the correlation between the Young's modulus and the density of the ribs W1 to W4 is acquired in advance. In the stress-strain curve creation method, the Young's modulus at the measurement points of the ribs W1 to W4 is calculated based on the measurement result of the density at the measurement points of the ribs W1 to W4 and the correlation.

  In FIG. 22, only the result of calculating the Young's modulus of the ribs W1 to W4 of one workpiece W is shown, but actually the Young's modulus of the ribs W1 to W4 of the three workpieces W is calculated. Yes.

According to this, the stress-strain curve creation method can measure the Young's modulus at the measurement points of the ribs W1 to W4 only by measuring the density at the measurement points of the ribs W1 to W4. That is, the stress-strain curve creation method can measure the Young's modulus without measuring the Young's modulus at the measurement points of the ribs W1 to W4 separately.
Therefore, the stress-strain curve creation method can easily measure the Young's modulus at the measurement points of the ribs W1 to W4 in a short time. For this reason, the stress-strain curve creation method can easily create the stress-strain curve G in a short time.

  As described above, in the stress-strain curve creation method, the Young's modulus at the measurement location of the workpiece (ribs W1 to W4) is measured based on the measurement result of the density at the measurement location of the workpiece W (ribs W1 to W4).

  Thus, in the stress-strain curve creation method, a plurality of pieces of information for setting the second virtual line L2 (see FIG. 4) are acquired.

After measuring the Young's modulus, in the stress-strain curve creation method, the first vertex P1 is set based on the calculation result of the maximum strain amount M as shown in FIGS.
That is, in the stress-strain curve creation method, a position moved along the strain axial direction by the maximum strain amount M from the origin of the stress-strain curve is set as the first vertex P1.

At this time, in the stress-strain curve creation method, the first vertex P1 is set on the strain axis of the stress-strain curve having a density corresponding to the density of the ribs W1 to W4.
In the stress-strain curve creation method, the first vertex P1 is set for each measurement location of the ribs W1 to W4.

  In FIG. 23, a state in which the first vertex P1 is set based on the measurement result of the density of the ribs W1 to W4 of one workpiece W is described, but actually, the ribs W1 to W3 of the three workpieces W are set. From the measurement result of the density of W4, the first vertex P1 is set.

After setting the first vertex P1, in the stress-strain curve creation method, the second vertex P2 is set based on the calculation result of the elastic strain amount N in the same manner as when the first vertex P1 is set. Set (see FIGS. 3, 20 and 23).
That is, in the method of creating the stress-strain curve, the position moved along the strain axial direction by the elastic strain amount N from the first vertex P1 in the same manner as when the first vertex P1 is set, Set as the second vertex P2.

  As described above, in the method of creating the stress-strain curve, the workpiece W (rib W1) is placed on the strain axis of the stress-strain curve of the density corresponding to the density measurement result at the measurement location of the workpiece W (ribs W1 to W4). The step of setting the first vertex P1 and the second vertex P2 is performed for each measurement location of .about.W4).

  After the second vertex P2 is set, the stress-strain curve creation method extends from the first vertex P1 along the axial direction of the stress in the same manner as when the first vertex P1 is set. The first virtual line L1 is drawn (see FIGS. 4 and 23).

  After drawing the first imaginary line L1, the stress-strain curve creation method is the same as the case where the first vertex P1 is set. A second imaginary line L2 extending along an inclination corresponding to the rate measurement result is drawn (see FIGS. 4 and 23).

Thus, as shown in FIG. 24, in the stress-strain curve creation method, a plurality of triangles T composed of virtual lines L1 and L2 and a strain axis are placed on the coordinates of a plurality of stress-strain curves having different densities. The ribs W1 to W4 are created according to the measurement locations.
In the stress-strain curve creation method, the third vertex P3, which is the intersection of the virtual lines L1 and L2, is dotted on the coordinates of the plurality of stress-strain curves having different densities.

  In FIG. 24, a state in which the third vertex P3 is scattered from the measurement result of the density of the ribs W1 to W4 of one workpiece W is illustrated, but in reality, the ribs W1 of the three workpieces W are illustrated. From the measurement result of the density of ˜W4, the third vertex P3 is scattered.

  As described above, in the stress-strain curve creation method, the first virtual line L1 is drawn and the second virtual line L2 is drawn for each measurement location of the workpiece W (ribs W1 to W4). A step of setting the intersection of L2 as the third vertex P3 is performed.

  After drawing the second virtual line L2, as shown in FIG. 25, in the stress-strain curve creation method, for each density corresponding to the density measurement result at the measurement location of the workpiece W (ribs W1 to W4). The step of creating the stress-strain curve G by connecting the third vertex P3 is performed.

  In FIG. 25, a state in which a stress-strain curve G is created for each density from the measurement results of the density of the ribs W <b> 1 to W <b> 4 of one workpiece W is described. From the measurement results of the density of the ribs W1 to W4, a stress-strain curve G is created for each density.

In the stress-strain curve creation method of the present embodiment, a straight line corresponding to the elastic region is drawn from the origin based on the measurement result of the Young's modulus, and the end of the straight line corresponding to the elastic region on the opposite side from the origin. Are connected to the third vertex P3 having the smallest distortion.
However, in the method for creating the stress-strain curve, it is not always necessary to create a straight line corresponding to such an elastic region.

According to this, the stress-strain curve creation method can create the stress-strain curve G for each density only by performing the sizing process on the workpiece W.
Therefore, the stress-strain curve creation method can create the stress-strain curve G for each density of the workpiece W to such an extent that a sizing process prediction technique using CAE can be created without performing many tensile tests.

If a single stress-strain curve G (with a certain density) is created by a tensile test as in the prior art, a plurality of times (for example, about three times) are required in order to obtain a certain degree of reliability. It is necessary to conduct a tensile test.
That is, when a stress-strain curve G is created for each density by a tensile test as in the prior art, the type of density (number of stress-strain curves G created) and the number of tensile tests (for example, three times) It is necessary to perform a tensile test as many times as the number of times accumulated.

On the other hand, in the method for creating a stress-strain curve of the present embodiment, a plurality of stress-strain curves G having different densities can be created only by performing a sizing process once for each density.
For this reason, the stress-strain curve creation method can create the stress-strain curve G for each density of the workpiece W in a short time.

Further, the stress-strain curve creation method can create the stress-strain curve G for each density of the workpiece W without using a sintered body having a uniform density.
Therefore, the stress-strain curve creation method can create the stress-strain curve G using the workpiece W that can be easily prepared. Therefore, the stress-strain curve G for each density of the workpiece W can be easily created.

That is, the stress-strain curve creation method can easily create the stress-strain curve G required for the sizing process prediction technique in a short time.
For this reason, the method for creating the stress-strain curve can shorten the time required to create the prediction technique for the sizing process, and can easily create information necessary for creating the prediction technique for the sizing process.

If the stress-strain curve G of the workpiece W is created for different powder types, that is, for each of a plurality of powder types, the sizing process is performed on the workpiece W of different powder types in the stress-strain curve creation method. A stress-strain curve G is created for each different powder type and each different density.
In this case, in the method for creating the stress-strain curve, the correlation between the Young's modulus, the powder type, and the density is acquired in advance, and the measurement result of the powder type and density of the workpiece W and the correlation are used to determine the workpiece W. The Young's modulus at the measurement location is calculated.
According to this, in the stress-strain curve creation method, the stress-strain curve G can be created easily for each different powder type and for each different density in a short time. That is, in the stress-strain curve creation method, the stress-strain curve is obtained for each different powder type and for each different density without performing the tensile test as many times as the number of times of the powder type, density type, and tensile test. G can be created.

  In the method of creating the stress-strain curve, it is not always necessary to calculate the maximum strain amount M and the elastic strain amount N by calculating the true strain. That is, the stress-strain curve creation method may calculate the maximum strain amount M and the elastic strain amount N by calculating the nominal strain.

In the method for creating the stress-strain curve of the present embodiment, the workpiece W is cut along the height direction and the density is measured for each of the ribs W1 to W4. However, the method is not limited to this.
That is, the method for creating the stress-strain curve may be to cut the workpiece W at every measurement pitch and measure the density of the cut piece. In addition, the stress-strain curve is created by cutting the workpiece W according to the tendency of the density distribution of the workpiece W (for example, the density is likely to be different between the end portion and the middle portion in the height direction of the workpiece W). It doesn't matter.

The stress-strain curve creation method of the present embodiment calculates the Young's modulus based on the density measurement results, but is not limited to this.
That is, the stress-strain curve creation method may measure the Young's modulus at the measurement location of the workpiece W by irradiating the measurement location of the workpiece W with laser.

10 type G stress-strain curve L1 first virtual line L2 second virtual line M maximum strain amount N elastic strain amount P1 first vertex P2 second vertex P3 third vertex W work

Claims (2)

A method for creating a stress-strain curve in a sizing process for creating a stress-strain curve for each workpiece density,
A step of measuring the shape of the workpiece in multiple points before and after a sizing step of putting the workpiece into a mold and molding the workpiece into a predetermined shape;
Measuring the gap of the mold at a position corresponding to the measurement location of the workpiece;
Based on the measurement result of the workpiece before the sizing step and the measurement result of the gap of the mold, calculating the maximum strain amount at the measurement location of the workpiece;
Based on the measurement result of the mold gap and the measurement result of the workpiece after the sizing step, calculating the amount of elastic strain at the measurement location of the workpiece;
Measuring the density at the measurement location of the workpiece;
Measuring the Young's modulus at the measurement location of the workpiece;
On the strain axis of the stress-strain curve of the density corresponding to the density measurement result at the measurement location of the workpiece, a first vertex is set for each measurement location of the workpiece based on the calculation result of the maximum strain amount. And setting a second vertex based on the calculation result of the elastic strain amount,
For each measurement location of the workpiece, a first imaginary line extending along the stress axial direction is drawn from the first vertex, and from the second vertex to the stress axial direction. a step of pulling the second virtual line that gives extending along a slope, sets the intersection of each of the imaginary line as a third vertex of which corresponds to the measurement result of Young's modulus,
For each density corresponding to the density measurement result at the measurement location of the workpiece, connecting the third vertex and creating a stress-strain curve;
I do,
A method for creating a stress-strain curve in a sizing process. Based on the measurement result of the density at the measurement location of the workpiece, measure the Young's modulus at the measurement location of the workpiece,
A method for creating a stress-strain curve in the sizing process according to claim 1.

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