JP4389165B2 - Die-casting injection speed setting method - Google Patents

Description

  The present invention relates to a molten metal injection speed setting method in die casting. More specifically, the present invention relates to a method of automatically setting an injection speed pattern in the acceleration region by calculation by setting an acceleration and an arrival speed in the acceleration region of the injection velocity.

  There are two main types of quality defects in die-cast products: poor hot water (insufficient hot water flow) and casting defects. Poor hot water occurs when the pressure during injection filling is insufficient, or when the molten metal temperature is too low. Moreover, there are two types of defects in the cast hole, one caused by air entrained in the molten metal and the other caused by shrinkage shrinkage. The entrainment of air into the molten metal may occur in the sleeve at the initial stage of injection of the molten metal, or it may occur in the cavity of the mold. In particular, the entrainment of air in the sleeve at the initial stage of injection when the molten metal temperature is high. Is a problem. Therefore, when injecting the molten metal from the sleeve, it is important to prevent the molten metal from undulating and entraining air, and many proposals have been made (for example, see Patent Document 1).

FIG. 12 is a schematic view showing an injection speed pattern of conventional die casting. The horizontal axis represents the injection stroke position S of the plunger, and the vertical axis represents the injection speed V (specifically, the speed of the plunger). The cavity is filled with the low speed V1 and the high speed V2.
That is, in the low speed range, the molten metal in the sleeve is filled without undulating, and when the filling rate in the sleeve is increased, the plunger is pushed out at a high speed to push the molten metal into the cavity at once.

In such an injection speed pattern, the speed pattern in the low speed range is important with respect to the air entrainment in the sleeve. In general, when the injection speed is increased to a predetermined speed, the acceleration also increases linearly. FIG. 11 is a conceptual diagram showing a comparison between changes in speed and acceleration. In (a), I is a region where the injection speed is increased, and II is a steady region. In the acceleration region I until the injection speed reaches the predetermined speed V1 as in (a), the acceleration also increases linearly (b). Then, the maximum value αmax is reached immediately before reaching the predetermined speed V1, and at the same time as reaching the predetermined speed V1, there is no time change of the speed, so that the speed drops to zero. That is, in such an injection speed pattern, the maximum acceleration αmax is large and the change is large. For this reason, the risk of a wave (swaying) in the molten metal due to inertial force and entrainment of air increases. On the other hand, if the acceleration is reduced, the rise of the plunger speed is delayed and the filling time of the molten metal is lengthened. As a result, the temperature of the molten metal is lowered, the hot water circulating property is deteriorated, and the quality of the die cast product is deteriorated.
Japanese Patent Laid-Open No. 9-253821

  The present invention has been made in view of the above-described problems, and automatically sets an injection speed pattern capable of maintaining the molten metal temperature without the risk of the air in the injection sleeve being caught in the molten metal in the acceleration region of the plunger. It is an object of the present invention to provide an injection speed setting method.

  The inventors of the present invention have completed the present invention by paying attention to the fact that the air can be prevented from being caught in the molten metal by making the change in acceleration in the acceleration region of the plunger continuous and smooth.

In other words, the injection speed setting method for die casting of the present invention is an injection speed setting method for die casting in which the plunger is operated to fill the mold cavity with the molten metal supplied into the injection sleeve, and the molten metal is fed at a constant speed. A first step of setting a steady speed to be injected, a second step of setting an upper limit value of acceleration in an acceleration region in which the acceleration is increased to the steady speed, and the acceleration region from the steady speed and the upper limit value of the acceleration. A third step of creating a first injection speed pattern by calculation, a fourth step of obtaining an approximate expression approximating the first injection speed pattern by a second-order polynomial, and the increase based on the approximate expression. a fifth step of calculating the maximum value of the acceleration to calculate the change in the acceleration in the speed range, is compared with the maximum value of the upper limit value of the acceleration acceleration, the pressurized speed If the maximum value is greater than the upper limit value of the acceleration is again calculated an approximate expression in polynomial said fourth increased primary the order returns to step, the maximum value of the acceleration is smaller than the upper limit value of the acceleration A sixth step of repeating this operation until a seventh step of setting a second injection speed pattern in the acceleration region based on the approximate expression finally obtained in the sixth step, To do.

In the injection speed setting method in die casting of the present invention, the upper limit value of the acceleration is preferably 0.2 to 0.7 m / s ² .

  According to the injection speed setting method of the present invention, the acceleration in the acceleration speed increase range can be kept low without increasing the acceleration time, and the change in acceleration can be made small and smooth. Therefore, the swell of the molten metal due to the inertial force can be suppressed, the air entrainment generated in the sleeve can be reduced, and the quality of the die cast product can be improved.

  In addition, by incorporating the injection speed setting method of the present invention into the injection speed control device of the die casting apparatus by software, it is possible to arbitrarily and easily set the optimal injection speed pattern according to the type of casting. it can.

  Embodiments of the present invention will be described below with reference to the drawings.

  The setting procedure of the injection speed setting in the present invention is shown in FIG. First, in step S1, a steady speed V1 for injecting molten metal at a constant speed is set. V1 may be appropriately set depending on the material of the molten metal, the shape of the die-cast product, etc., and a normal value can be used.

Next, an upper limit value α1 of acceleration in the acceleration range until the steady speed V1 is reached in step S2 is set. Here, the upper limit α1 of the acceleration can be arbitrarily set within the range of 0.2 to 0.7 m / s ^{2 to be} described later in consideration of the material of the molten metal, the amount of pouring, or the pouring temperature.

  In step S3, the first injection speed pattern in the acceleration region is created by calculating as follows from the steady speed V1 set in step S1 and the acceleration upper limit value α1 set in step S2.

  The first injection speed pattern is schematically shown in FIG. (A) shows the time change of the injection speed, and (b) shows the time change of the acceleration. I is the speed increasing range, and II is the constant speed range. As the injection speed pattern, the horizontal axis may be the movement distance (or position) of the plunger instead of the elapsed time after the start of injection.

The acceleration alpha between the injection start (start of movement of the plunger) arbitrary time t ₁ and t ₂ after, when the velocity at t ₁ v _1, the speed at t ₂ and _{v 2, α = (v 2} - Since v ₁ ) / (t ₂ −t ₁ ), it can be expressed as v ₂ = α (t ₂ −t ₁ ) + v ₁ . When t ₀ = 0 and V ₀ = 0 when the plunger starts moving from the stationary state, and the acceleration α is the acceleration upper limit value α1, v ₁ = α1 (t ₁ −t ₀ ) + v ₀ , t _{Since 0} and V ₀ are both 0, the speed v ₁ after t ₁ after the plunger starts moving can be obtained. Similarly, v ₂ to v _n can be obtained and an injection speed pattern (FIG. 2A) up to the steady speed V1 can be created. However, in the injection speed pattern obtained here, the acceleration α in the acceleration region I is constant at the upper limit value α1, and therefore, as shown in FIG. 2B, the movement of the plunger for pushing out the molten metal B and the steady speed V1. The change in the acceleration α at C immediately after reaching it is large. Therefore, the speed pattern increasing at the constant acceleration is not necessarily sufficient to reduce air entrainment in the sleeve.

  Therefore, in step S4, the first injection speed pattern created in step S3 is approximated by a mathematical formula as in the example described later. Typical approximate expressions include a linear approximate expression, an exponential approximate expression, a logarithmic approximate expression, a polynomial approximate expression, and the like, but it is appropriate to approximate with a second or higher order polynomial.

  Subsequently, in step S5, the time change of the acceleration α in the acceleration region I is calculated based on the approximate expression obtained in step S4 (see, for example, FIG. 6B), and the maximum value of the acceleration α in the acceleration region I is calculated. α2 is calculated. Here, the approximate expression and the change in acceleration based on the approximate expression can be automatically calculated on a program using commercially available software.

In step S6, the maximum acceleration value α2 obtained in step S5 is compared with the acceleration limit value α1 set in step S2, and a predetermined criterion, for example, the maximum acceleration value α2 is within the limit value α1. Determine if there is. If the maximum acceleration value α2 is smaller than the limit value α1, the process proceeds to step S7. If the maximum acceleration value α2 is larger than the limit value α1, the process returns to step S4 and the polynomial whose degree is increased linearly. The approximate expression is obtained again, and this operation is performed until the maximum value α2 of acceleration becomes smaller than the limit value α1, or until the maximum value α2 and the limit value α1 are substantially equal and the time change of the acceleration becomes sufficiently smooth. repeat.

In step S7, the second injection pattern in the acceleration region is obtained based on the approximate expression obtained in step S6, and the setting of the injection speed pattern is completed.

  As described above, in the injection speed setting method of the present invention, first, the first injection speed pattern that is increased to the predetermined steady speed V1 at the constant acceleration α1 is obtained, and then the final injection is based on the approximate expression that approximates it. Set the speed pattern. Therefore, the injection speed can be increased to the steady speed V1 while smoothly changing the acceleration in the acceleration range. In addition, since the second injection speed pattern is obtained by approximating the first pattern, the time for the injection speed to reach the steady speed does not increase. Therefore, it is possible to reduce both the entrainment of the air by suppressing the undulation of the molten metal in the sleeve and to maintain the temperature of the molten metal.

As described above, the acceleration limit value α1 can be arbitrarily set within the range of 0.2 to 0.7 m / s ^{2 for} the following reason.

  If the acceleration in the acceleration range is lowered, air entrainment can be suppressed, but the entire molten metal filling time becomes longer. For this reason, the molten metal temperature is lowered, the hot water circumference (hot water flow) is deteriorated, and finally the quality of the cast member is lowered. On the other hand, if the acceleration in the acceleration region is increased, the molten metal temperature can be maintained, but there is a risk of air entrainment. For this reason, it is desired to fill the molten metal in a short time with low acceleration. FIG. 3 shows the relationship between the acceleration in the speed increasing region and the filling time of the molten metal. The horizontal axis is the acceleration, and the vertical axis is the time for filling the mold cavity with the molten metal. Here, the time is required for the plunger to move 1 m through the sleeve. FIG. 3 is a trial calculation for the case where the steady speed V1 is three levels of 0.3, 0.5, and 0.7 m / s. The filling time is shortened with increasing acceleration. The effect of shortening the filling time is remarkable on the low acceleration side. Of course, the larger the steady speed, the shorter the filling time.

In the case of FIG. 3, in the D region where the acceleration is less than 0.2 m / s ² , the filling time becomes as long as 4 seconds or more, and the temperature drop of the melt becomes a problem. Further, in the region F where the acceleration exceeds 0.7 m / s ² , the undulation of the molten metal becomes large, which is not appropriate. Further, in the region F, the time for the acceleration region of the plunger is shortened, so even if the acceleration is increased, the entire filling time is not significantly shortened. Accordingly, the range of acceleration that can achieve both low acceleration and shortening of the filling time is 0.2 to 0.7 m / s ² indicated by the arrow, and more preferably 0.2 to 0.5 m / s ^{2 corresponding} to the region E. .

  Next, steps S4 to S6 will be described in detail with reference to specific examples shown in FIGS.

FIG. 4A shows a first injection speed pattern created by setting the steady speed V1 = 0.4 m / s and the upper limit value α1 of acceleration = 0.4 m / s ² . The acceleration α1 is constant until the steady speed V1 is reached as shown in FIG. The injection speed pattern shown in FIG. 4A is approximated by various approximation formulas and shown in FIGS. 5-9, each solid line of (a) is an approximate expression, and (b) shows the time change of the acceleration (alpha) obtained by calculating based on the approximate expression.

  FIG. 5 shows a logarithmic approximation. The maximum acceleration value α2 obtained in (b) is larger than the upper limit value α1 of acceleration in FIG. That is, it is understood that logarithmic approximation is not appropriate because α2 <α1 in step 6 is not satisfied.

  FIG. 6 shows approximation by a quadratic equation. The maximum acceleration value α2 obtained in (b) is larger than the upper limit value α1 of acceleration in FIG. That is, since α2 <α1 in step 6 is not satisfied, it can be understood that approximation by the quadratic expression is not appropriate.

  FIG. 7 shows an approximation by a cubic equation. The maximum acceleration value α2 obtained in (b) is larger than the upper limit value α1 of acceleration in FIG. 4B, and the rise is steep. That is, it is understood that the approximation by the cubic equation is not appropriate because α2 <α1 in step 6 is not satisfied.

  FIG. 8 shows approximation by a quartic equation. The maximum acceleration value α2 obtained in (b) is substantially the same as the upper limit value α1 of acceleration in FIG. 4B, but the rise is steep. That is, it is understood that the approximation by the quartic equation is not appropriate because the condition “smooth is α2≈α1” in step 6 is not satisfied.

  FIG. 9 shows approximation by a quintic equation. The maximum acceleration value α2 obtained in (b) is substantially equal to the upper limit value α1 of acceleration in FIG. 4B, and the time change of the acceleration is clearly smooth. The rise is steep. That is, the condition “smooth with α2≈α1” in step 6 is satisfied. Therefore, it can be seen that approximation by a quintic equation is appropriate in order to smooth the acceleration change in the injection speed pattern of FIG.

  As described above, according to the injection speed setting method of the present invention, the acceleration in the acceleration region can be kept low without increasing the acceleration time, and the change in acceleration can be reduced. Therefore, the entrainment of air generated in the sleeve can be reduced and the quality of the die cast product can be improved. Furthermore, by incorporating the injection speed setting method of the present invention into the injection speed control device of the die casting apparatus by software, it is possible to arbitrarily and easily set the optimal injection speed pattern according to the type of casting. it can.

  In order to realize high-accuracy speed control as in the present invention, it is desirable to change the injection speed control of the die casting apparatus from the conventional hydraulic control to the servo control by the servo motor. FIG. 10 shows an example of the configuration of a die casting apparatus having servo control means. The die casting apparatus 10 includes a mold 12 that forms a cavity 11, a sleeve 13 that communicates with the cavity 11, a plunger 14 that is slidably fitted in the sleeve 13, and a drive unit 15 that drives the plunger 14. The control means 16 controls the drive means 15.

  The driving means 15 includes a servo motor 22 having a ball screw 21 and a pedestal 23 that is screwed with a screw portion of the ball screw 21 and is coupled to the plunger 14. The pedestal 23 is slidably supported by a plurality of linear guides 24 parallel to the axis of the plunger 14.

  The control means 16 is a means for controlling the rotation of the servo motor, and controls the rotation of the servo motor 22 based on the position and speed signal of the plunger obtained from various sensors. The control means can incorporate the injection speed pattern set in the present invention in software.

  The servo motor 22 is not particularly limited, and a motor having a servo driver in a broad sense such as a DC servo motor, a brassless servo motor, or an induction servo motor can be used. Further, a stepping motor or the like is preferable because it can perform highly accurate acceleration control.

  The servo motor 22 moves the base 23 via the ball screw 21. Since the plunger 14 is fixed to the pedestal 23, the molten metal M in the sleeve 13 can be injected into the cavity 11 as the pedestal 23 moves. The position and speed when the plunger 14 moves can be measured by a linear scale 26 arranged along the linear guide 24. Although the linear scale 26 is useful for high-precision control, an acceleration sensor 25, a servo motor encoder 27, or the like can be used as a measurement sensor.

  With the injection speed pattern set according to the present invention, the acceleration in the acceleration range is controlled. However, if the acceleration is integrated, the velocity is obtained, and if the velocity is further integrated, it can be converted into a position (displacement). Therefore, the control method can be any control method such as position control, speed control, and acceleration control. An efficient control method may be selected according to the target accuracy.

  The injection speed setting method in the die casting of the present invention can be suitably used for light metal alloy die casting products such as automobile cylinder blocks and transaxle cases.

It is a flowchart explaining the injection speed setting method of this invention. It is a graph which shows the (a) speed pattern and (b) acceleration pattern at the time of making the acceleration of an acceleration area into a uniform acceleration. It is a graph explaining the relationship between acceleration and filling time. It is a graph which shows (a) injection speed pattern and (b) acceleration pattern which were created by setting injection speed V1 = 0.4 and acceleration α1 = 0.4. 5 is a graph showing (a) an injection speed pattern and (b) an acceleration pattern obtained by logarithmically approximating the injection speed pattern of FIG. 4. It is a graph which shows the (a) injection speed pattern and (b) acceleration pattern which approximated the injection speed pattern of FIG. 4 with the quadratic polynomial. 5 is a graph showing (a) an injection speed pattern and (b) an acceleration pattern obtained by approximating the injection speed pattern of FIG. 4 with a cubic polynomial. FIG. 5 is a graph showing (a) an injection speed pattern and (b) an acceleration pattern obtained by approximating the injection speed pattern of FIG. 4 with a quartic polynomial. 5 is a graph showing (a) an injection speed pattern and (b) an acceleration pattern obtained by approximating the injection speed pattern of FIG. 4 with a fifth order polynomial. It is a schematic diagram explaining the structural example of the die-casting apparatus which can perform highly accurate acceleration control. It is a schematic diagram which shows (a) injection speed pattern and (b) acceleration pattern at the time of linearly increasing to a predetermined speed. It is a figure which shows the injection speed pattern of a prior art.

Explanation of symbols

10: Die casting apparatus 11: Cavity 14: Plunger 16: Servo motor controller 21: Ball screw 22: Servo motor 23: Base 24: Linear guide 25: Acceleration sensor 26: Linear scale 27: Encoder

Claims (2)

An injection speed setting method of die casting in which a plunger is operated to fill a mold cavity with a molten metal supplied into an injection sleeve,
A first step of setting a steady speed for injecting the molten metal at a constant speed;
A second step of setting an upper limit value of acceleration in a speed increasing range in which the speed is increased to the steady speed;
A third step of creating a first injection speed pattern in the acceleration region by calculation from the steady speed and the upper limit value of the acceleration;
A fourth step of obtaining an approximate expression approximating the first injection speed pattern by a polynomial of second order or higher;
A fifth step of calculating a change in acceleration in the acceleration region based on the approximate expression and calculating a maximum value of the acceleration;
When the upper limit value of acceleration and the maximum value of acceleration are compared, and the maximum value of acceleration is larger than the upper limit value of acceleration, the process returns to the fourth step and is approximated again by a polynomial whose degree is increased linearly seeking expression, and a sixth step of repeating this operation up to the maximum value of the acceleration is smaller than the upper limit value of the acceleration,
And a seventh step of setting a second injection speed pattern in the speed increasing region based on the approximate expression finally obtained in the sixth step. Upper limit injection speed setting of die casting according to claim 1 which is 0.2~0.7m / s ² of the acceleration.

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