JPH07110513B2 - Method and apparatus for controlling holding pressure of multi-cavity mold in injection molding - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for controlling a holding pressure of a multi-cavity mold in injection molding, and particularly, in a multi-cavity mold, it is caused by a change in temperature conditions such as mold temperature and injection resin temperature. The present invention relates to a new improvement for eliminating variations in molded product quality among mold cavities.

[0002]

2. Description of the Related Art In general, most of injection-molded products are manufactured by a multi-cavity mold that can obtain a plurality of molded products in one molding cycle, without mentioning any literature. Therefore, it is necessary to make the resin filling amount uniform in each mold cavity, and in achieving this, the mold design including the runner and the gate plays an important role.

[0003]

However, even after the runners and gates are designed to be uniformly filled in each mold cavity, in the actual injection molding production, the filling amount between the mold cavities is increased. Imbalance may occur. This is mainly due to variations in temperature conditions such as mold temperature and injection resin temperature. Therefore, due to changes in temperature conditions, a short shot may occur in one mold cavity and an overpack may occur in another mold cavity. Further, in one mold cavity, the size of the molded product becomes larger than the standard, and in another mold cavity, the size becomes smaller than the standard. However, no method has been developed to solve the imbalance between the mold cavities such as the weight and size of the molded product due to the change in the temperature conditions.

The present invention has been made to solve the above problems, and in particular, a safety setting value that minimizes the difference in resin density between mold cavities regardless of changes in temperature conditions. By controlling the holding pressure set value, it is an object of the present invention to provide a holding pressure control method and device for a multi-cavity mold in injection molding in which the resin density of each mold cavity is made uniform. To do.

[0005]

According to the method for controlling the holding pressure of a multi-cavity mold in injection molding according to the present invention, the molten resin accumulated in the front part of the screw is moved forward by the screw so that the resin flow path in the nozzle part and the resin in the mold are The screw is pressed to compensate for the filling step of injecting into each mold cavity of the multi-cavity mold through the flow path and contraction of the molten resin as it cools and solidifies in each mold cavity. In order to minimize a sum of squares of deviations between a product density of each mold cavity and a target product density preset for each cavity in an injection pressure holding step including a pressure holding step of replenishing the molten resin. In this method, the holding pressure set value is obtained by calculation and is controlled to the holding pressure set value.

More specifically, the density of the material in each mold cavity ρ _K (K is the mold cavity number, K = 1
... N, N is the number of cavities expressed by a relational expression with pressure P _K , temperature T _K and density ρ _K, and pressure P _K in the mold cavity is expressed as pressure P _K , holding pressure P _L and It is represented by a relational expression between the mold temperature T _WK and the injection resin temperature T _RK measured at the start of filling, and the resin temperature T _K in the multi-cavity mold at the pressure holding stage is estimated in advance at the filling stage to obtain the resin. From the temperature T _K , the target value ρ _K * of the molded product density set for each mold cavity, and the relational expression of the pressure, temperature and density of the material in the mold cavity, The pressure target value P _K1 * in the mold that achieves the target value ρ _K * of the density is calculated, and the holding pressure P _LK * that achieves the pressure target value P _K1 * is set at the mold temperature T.
_WK , injection resin temperature T _RK , mold pressure P _K and holding pressure P
_The holding pressure P _L * that is calculated from the relational expression with _LK and further minimizes the sum of squares of the deviation between the density ρ _K of each mold cavity and the target value ρ _K * from the holding pressure P _LK *. The holding pressure P
Calculated by the _LK * based on a method to control the holding pressure P _L *.

More specifically, the relationship between the resin temperature T _K , the resin pressure P _K, and the resin density ρ _K in each mold cavity is expressed by the following Spencer-Gillmore equation of state (shown by one equation). This is the method.

More specifically, a method of expressing the relationship among the resin pressure P _{K of} the mold cavity, the mold temperature T _WK , the injection resin temperature T _RK and the holding pressure P _{L by} the formula (2).

More specifically, in estimating the resin temperature T _K in each of the mold cavities in the pressure-holding step in advance in the filling step, the temperature at a fixed time in the pressure-holding step is used. , Mold temperature T _WSK and injection resin temperature T _{RSK based on the} fixed time
At the time tg at which the resin temperature T _K in each mold cavity at the pressure holding stage reaches the flow stop temperature Tg determined by the molding material, the time at which the resin temperature T _K in each mold cavity is estimated. and the mold temperature T _WK used for the calculation is obtained by measuring the mold temperature.
The injection resin temperature T _RK used in the calculation is obtained by measuring the resin temperature of any of the resin flow paths, and the preset mold temperature T _WSK , injection resin temperature T _RSK , and the temperature Tg are used to calculate the time. In this method, the resin temperature T _K (tg) in each of the mold cavities at tg is determined by the equations (3), (4) and (5).

More specifically, when the mold temperature T _WK used for the calculation is obtained by measuring the mold temperature T _WK , the temperature measurement value T _WFK on the fixed mold side and the temperature measurement on the movable mold side are measured. This is a method of _obtaining from the value T _WMK by any one of formulas (6), (7), and (8).

More specifically, when the injection resin temperature T _RK used in the calculation is obtained by measuring the resin temperature in any of the resin flow paths, the measured values at the start and end of filling, or the start of filling It is a method that uses the average value or the maximum value of the measured values from the end to the end.

More specifically, as the holding pressure set value,
It is a method of using a set value for a setter, a hydraulic ram pressure, a nozzle portion resin pressure, or a pressure in each mold.

More specifically, the sum of squares of deviations from the target density ρ _K * set for each mold cavity is calculated.
The density ρ _K of the material in the mold cavity is expressed by (1)
The resin pressure P _K in the mold cavity is expressed by the formula (2), and the resin temperature T _K (tg) in the mold cavity is expressed by the formula (3), (4), (5).
Respectively expressed by formula, holding pressure set value P _L that minimizes G in formula (9)
This is a method of controlling by obtaining * by Eqs. (10), (11), (12), and (13).

More specifically, the mold temperature sensor provided in the multi-cavity mold, the resin temperature sensor provided in any of the resin flow paths in the multi-cavity mold and the nozzle, and the resin temperature sensor Mold temperature,
An amplifier for inputting and amplifying the measured value of the injection resin temperature, an A / D converter for A / D converting the measured value, the measured value and each mold cavity of the multi-cavity mold are set. An arithmetic processing unit that calculates a holding pressure set value that minimizes the sum of squares of deviations of product densities and product density target values for each cavity using at least the molded product weight target value, and the holding pressure set value as a voltage signal. And a holding pressure control section for outputting to a servo valve amplifier for controlling the servo valve.

[0015]

In the method and apparatus for controlling the holding pressure of the multi-cavity mold in the injection molding according to the present invention, the molded product density target value ρ _K *, the reference mold temperature T _WSK , and the injection resin are preset for each mold cavity. Temperature T _RSK , flow stop temperature Tg, material constants R ₁ , ρ ₀ , π _i , coefficients a _1K , a _2K ,
b _1K , b _2K , c _1K and d 1 _K are set in advance. Next, in the actual filling and holding pressure stage, first, the mold temperature T _WK and the injection resin temperature T _Rk are obtained by measurement in the filling stage. Next, immediately before the pressure-holding stage after the filling stage is completed, (3), (4), (5)
The resin temperature T _K (tg) in the mold is calculated using the formula, and the resin pressure target value P _K * of the mold cavity K is calculated from the resin temperature T _K (tg) and the formula (2). . In addition, this resin temperature T _K (t
g) and the resin pressure target value P _K * and the equation (11), the weighting factor L _{K of the} mold cavity K (K is the number of cavities)
Then, the holding pressure P _LK * for achieving the molded product density ρ _K * of each mold cavity K is calculated using the above-mentioned T _Wk , T _RK , P _K * and the equation (13). Finally, from L _K , P _LK * and the equation (10) obtained as described above, the target value ρ _K *
The holding pressure P _L * that minimizes the equation (9), which is the sum of squared deviations from, is calculated. Therefore, the holding pressure P _L obtained as described above
* Is the holding pressure set value, converted into a voltage signal and output to the servo valve amplifier to control to this holding pressure set value.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a pressure holding control method for a multi-cavity mold in injection molding according to the present invention will be described in detail below with reference to the drawings.

The reference numeral 1 in the drawing is a cylinder having a screw 1A, and this screw 1A is
With the motor 2 and the cylinder chamber 3 at the rear of the cylinder 1,
It is installed so that it can rotate and move back and forth. The cylinder 1
A nozzle 4 having a nozzle portion resin flow path 4a is provided in the front portion of the cylinder 1, and a screw front portion 1a is formed in the front portion 1B of the cylinder 1.

The nozzle 4 is connected to a mold 5 composed of a fixed mold 5A and a movable mold 5B, and the fixed mold 5A is provided with an in-mold resin flow path 5a and each of the molds. Between the molds 5A and 5B (assuming that there are K mold cavities, where K is the number of mold cavities), the first resin flow path 5a is communicated with the first mold cavities 5b and the second mold cavities 5b.
Mold cavity 5c, first cavity runner portion 5d, second cavity runner portion 5e, first cavity gate portion 5
f is not formed with the second cavity gate portion 5g.

The fixed mold 5A is provided with a first mold temperature sensor 6a and a second mold temperature sensor 6b, and the movable mold 5B is provided with a third mold temperature sensor 6c and a fourth mold. The temperature sensor 6d, the first runner portion resin temperature sensor 6e, and the second runner portion resin temperature sensor 6f are connected.

The measured values of the respective sensors 6a to 6f are the amplifiers 8a to 8f of the control device 7 and the A / D converters 9a.
9f are input to the arithmetic processing unit 10, and the holding pressure P _L * from the arithmetic processing unit 10 is applied to the holding pressure control unit 11
Has been entered in.

The arithmetic processing unit 10 and the holding pressure control unit 11
Is the injection start signal 12a from the sequence control unit 12.
And the pressure-holding start signal 12b are input to the arithmetic processing unit 10. The coefficients R ₁ , ρ ₀ , π _i , a _1K , a _2K ,
The setting device 13 for inputting the set value 13a consisting of b _1K , b _2K , c _1K , d _1K , T _WSK , T _RSK , T _g , and ρ _K * is connected, and the above-mentioned control device 7 is Each amplifier 8a-8
f, A / D converters 9a to 9f, an arithmetic processing unit 10, a pressure holding control unit 11, and a setting unit 13.

Voltage signal 11a from the holding pressure control section 11
Is input to a servo valve amplifier 15 connected to the servo valve 14, and an operating voltage 15a of the servo valve amplifier 15 is input to the servo valve 14. A pipe line 14a of the servo valve 14 is connected to the cylinder chamber 3, a hydraulic pressure sensor 16 connected to the cylinder chamber 3 is connected to the servo valve amplifier 15, and an oil source 17 is connected to the servo valve 14. Has been done.

Next, a description will be given of the case where the holding pressure control of the multi-cavity mold in the injection molding according to the present invention is performed in the above-mentioned structure. First, the outline will be described. First, when the sequence controller 12 outputs the injection start signal 12a to the controller 7 (first step: 20),
The screw 1A starts moving forward. At the same time, the arithmetic processing unit 10 measures the fixed mold side mold temperature T _WFK and the movable mold side mold temperature T _WMK corresponding to the mold cavities 5b and 5c (second step: 21). Then, the mold temperature T _WK of each mold cavity 5b, 5c used for the calculation is obtained by the following formula. T _WK = (T _WFK + T _WMK ) / 2 ··· Equation (6)

Also, the pressure holding start signal 12b is input after the injection start signal 12a is input (fourth step:
During the filling stage up to 23), the resin temperature of the runner parts 5d and 5e is measured, and any of the maximum value at the resin stage, the time average value, the sample value at the time of injection start, or the sample value at the time of switching the holding pressure is measured. Method of each mold cavity 5b, 5c
The injection resin temperature T _{RK of the above} is determined (third step: 22).

Next, the arithmetic processing unit 10 uses the equations (3), (4) and (5) to calculate the resin temperature in the mold when the mold temperature is T _WSK and the injection resin temperature is T _RSK. The resin temperature T _K (tg) in the mold at the mold temperature T _WK and the injection resin temperature T _RK at the time tg when the temperature reaches the flow stop temperature Tg is obtained (fifth step: 2).
4). Pressure holding start signal 12 from the sequence controller 12
When b is output, the arithmetic processing unit 10 outputs (10), (15), (1
The holding pressure P _L * is calculated using the equations (6) and (17) (sixth step: 25) and output to the holding pressure control unit 11.

In response to this, the holding pressure control section 11 outputs the voltage signal 11a corresponding to the holding pressure P _L * to the servo valve amplifier 1.
5 (seventh step: 26). In response to this, the servo valve amplifier 15 sets the servo valve 14 so that the oil pressure corresponding to the holding pressure P _L * becomes the pressure in the cylinder chamber 3.
The operating voltage 15a is output to. Therefore, when the pressure holding start signal 12b from the sequence controller 12 is cut off (eighth
Step: 26), arithmetic processing unit 10 and holding pressure control unit 1
1 stops the output of the holding pressure P _L * and the corresponding voltage signal 11a, and ends the holding pressure control.

More specifically, the molded product density target value ρ _K *, for each of the mold cavities 5b and 5c, will be described in advance.
Reference mold temperature T _WSK , injection resin temperature T _RSK , flow stop temperature Tg, material constants R ₁ , ρ ₀ , π _i , coefficient a _1K ,
a _2K , b _1K , b _2K , c _1K , and d _1K are set in advance.

Next, in the actual filling and holding pressure stage, first, in the filling stage, the mold temperature T _WK and the injection resin temperature T _RK are obtained by measurement. Immediately before ending the filling stage and entering the pressure-holding stage, the resin temperature T _K (tg) in the mold 5 is calculated using the equations (3), (4) and (5). And this resin temperature T _K (tg)
And the equation (12), the resin pressure target value P _K * of the mold cavities 5b and 5c is calculated.

Further, the weight coefficient L _K of the mold cavity is calculated using the resin temperature T _K (tg), the resin pressure in the mold P _K * and the equation (11), and the mold temperature T _WK and the injection are calculated. Using the resin temperature T _RK , the resin pressure in the mold P _K and the formula (13), the holding pressure P _LK * for achieving the molded product density target value ρ _K * of each mold cavity 5b, 5c is calculated. To do. Finally, from the above-mentioned L _K , P _LK * and the equation (10) thus obtained, the holding pressure P that minimizes the equation (9), which is the sum of squared deviations from the molded product density target value ρ _K *, is obtained. Calculate _L *. The holding pressure P _L * obtained above is used as a holding pressure set value, converted into a voltage signal 11 a and output to the servo valve amplifier 15.

More specifically, the molded product density target value ρ _K * for each mold cavity is set in advance, and the square sum of the deviations of the actual molded product density ρ _K of each cavity from the target value is set.
It is expressed by equation (9). Here, it is assumed that minimizing the deviation of the resin filling amount between the mold cavities 5b and 5c is minimizing G in the equation (9). Each mold cavity 5
If the product shapes of b and 5c are the same, the molded product density target value ρ _K * is a constant value regardless of the value of K, but if the product shapes of the mold cavities 5b and 5c are different, It is considered that the value of ρ _K * takes different values depending on _K , in consideration of quality of marks, sink marks and voids. It is assumed that the relationship between the resin pressure P _K , the density ρ _K , and the temperature T _K of each of the mold cavities 5b and 5c is represented by, for example, the Spencer-Gillmore equation of state of equation (1). Each mold cavity 5b, 5
It is assumed that the resin pressure P _{K of} c has the relation of the mold temperature T _WK , the injection resin temperature T _RK , and the holding pressure P _{L according} to the equation (2).
From the above equations (9), (1), and (2), the holding pressure P _L * that minimizes G in the equation (9) is calculated by the following (10), (11), (12), ( It is expressed by equation (13).

The resin pressures P _K , P _K * and the resin temperature T _K in the mold 5 are fixed at a certain time t in the pressure holding stage.
g, and the fixed time tg is calculated as follows. Pre-set reference dies and T
_WSK, the injected resin temperature T _RSK, the mold cavity 5
b, the resin temperature T _K in 5c is, with the time when it comes to the flow stop temperature Tg which is determined by the molding material, the time tg to estimate the resin temperature T _K of the mold 5. Next, the mold temperature T _WK and the injection resin temperature T _RK are obtained by measurement, and the resin temperature T _K (tg) in the mold 5 at the time tg is calculated using the preset T _WS , T _RS , and Tg. Is calculated by Eqs. (3), (4), and (5). Therefore, the resin temperature T _K (t of the mold cavity K (5b, 5c))
g) is obtained from the equation (3), and the holding pressure P _L * is (10), (11), (1
2), (13) determined in equation and sets, the holding pressure P _L
It is controlled to be *.

[0032]

Since the method and apparatus for controlling the holding pressure of the multi-cavity mold in the injection molding according to the present invention is configured as described above, the density of the molded product caused by the fluctuation of the temperature condition is different between the mold cavities. Can be prevented. Therefore, in the multi-cavity mold, a molded product having a uniform shape and size can be obtained in any cavity, so that it is possible to reduce the defective rate and improve the productivity.

[Brief description of drawings]

FIG. 1 is a block diagram showing a holding pressure control device for a multi-cavity mold in injection molding according to the present invention.

FIG. 2 is a block diagram showing a part of FIG.

FIG. 3 is an enlarged cross-sectional view of a main part of FIG.

FIG. 4 is a flowchart showing a holding pressure control method.

FIG. 5 is a flowchart following FIG.

[Explanation of symbols]

 1A screw 1a screw front part 4a nozzle part resin flow path 5 multi-cavity mold 5a resin flow path inside mold 5b mold cavity 5c mold cavity 5A fixed mold 5B movable mold 6a to 6b mold temperature sensor 6e, 6f Resin temperature sensor 7 Control device 8a to 8f Amplifier 9a to 9f A / D converter 10 Arithmetic processing unit 11a Voltage signal 14 Servo valve 15 Servo valve amplifier

Claims (10)

[Claims] 1. The nozzle resin flow path (4) is formed by advancing the screw (1A) by transferring the molten resin accumulated in the screw front part (1a).
a) and a filling step of injecting into each mold cavity (5b, 5c) of the multi-cavity mold (5) through the resin flow path (5a, 5d, 5e, 5f, 5g) in the mold, and the molten resin In order to compensate for shrinkage of the mold cavity (5b, 5c) as it is cooled and solidified in the mold cavity (5b, 5c), an injection pressure-holding step comprising a pressure-holding step of pressing the screw (1A) to replenish the molten resin. In, the calculation of the holding pressure set value for minimizing the sum of squares of the deviation between the product density of each mold cavity (5b, 5c) and the target product density set in advance for each cavity is calculated. A holding pressure control method for a multi-cavity mold in injection molding, characterized by controlling the holding pressure set value. 2. The density ρ _K of the material in each mold cavity (5b, 5c) (K is the mold cavity number, K = 1 ...
N, N is the number of cavities) is expressed by a relational expression of pressure P _K , temperature T _K and density ρ _K, and the mold cavities (5b, 5c)
The internal pressure P _K is represented by a relational expression of the pressure P _K , the holding pressure P _L, and the mold temperature T _WK and the injection resin temperature T _RK measured at the start of filling, and the above-mentioned holding pressure of the holding pressure stage is previously set in the filling stage. Estimating the resin temperature T _K in the multi-cavity mold, and the resin temperature T _K and each mold cavity (5b, 5c)
Based on the target value ρ _K * of the molded product density set for each and the relational expressions of the pressure, temperature and density of the material in the mold cavity (5b, 5c), the mold cavity (5b, 5c) The pressure target value P _K1 * in the mold that achieves the target value ρ _K * of each density is calculated, and the holding pressure P _LK * that achieves the pressure target value P _K1 * is set to the mold temperature T _WK , It is calculated from a relational expression of the injection resin temperature T _RK , the pressure P _K in the mold, and the holding pressure P _LK, and the holding pressure P _LK * is further used to calculate the mold cavities (5b, 5b).
c) The holding pressure P _L * that minimizes the sum of squares of the deviation between the density ρ _K and the target value ρ _K * is calculated based on the holding pressure P _LK *, and the holding pressure P _L * is calculated. The method for controlling the holding pressure of a multi-cavity mold in injection molding according to claim 1, wherein the method is controlled. 3. The relationship between the resin temperature T _K , the resin pressure P _K, and the resin density ρ _K in each mold cavity (5b, 5c),
The following Spencer-Gillmore equation of state [Equation 1] The holding pressure control method for a multi-cavity mold in injection molding according to claim 2, wherein 4. The resin pressure P _K , the mold temperature T _WK , the injection resin temperature T _RK, and the holding pressure P _{L of the} mold cavity (5b, 5c).
The relation of The method for controlling the holding pressure of a multi-cavity mold in injection molding according to claim 2, which is represented by the formula (2). 5. When the resin temperature T _K in each of the mold cavities in the pressure-holding step is estimated in advance in the filling step, the temperature at a certain fixed time in the pressure-holding step is used and the fixing is performed. With a mold temperature T _WSK and an injection resin temperature T _RSK that are based on time, there is a time tg at which the resin temperature T _K in each mold cavity in the pressure holding stage reaches a flow stop temperature Tg determined by the molding material. , The resin temperature T _K in each mold cavity
Is estimated at time tg, and by measuring the mold temperature,
The mold temperature T _WK used for the calculation is obtained, and the injection resin temperature T _RK used for the calculation is calculated by measuring the resin temperature of any of the resin flow paths (4a, 5a, 5d, 5e ...). Using the preset mold temperature T _WSK , injection resin temperature T _RSK , and temperature Tg, the resin temperature T _K (tg) in each mold cavity at the time tg is calculated as follows: 3. The method according to claim 2, which is obtained by the equations (3), (4) and (5).
A method for controlling the holding pressure of a multi-cavity mold in the injection molding described. By 6. Measurement of the mold temperature T _WK, upon finding the mold temperature T _WK used for the calculation, stationary mold
From the temperature measurement value T _WFK on the (5A) side and the temperature measurement value T _WMK on the movable mold (5B) side, 6. The holding pressure control method for a multi-cavity mold in injection molding according to claim 5, wherein the method is obtained by any one of formulas (6), (7) and (8). 7. The injection resin temperature T _RK used in the calculation is obtained by measuring the resin temperature of any of the resin flow paths (4a, 5a, 5d, 5e ...) At the start of filling and The method for holding pressure control of a multi-cavity mold in injection molding according to claim 5, wherein a measured value at the end of filling, or an average value or a maximum value of measured values from the start to the end of filling is used. 8. The set pressure (13a) for the setter (13), hydraulic ram pressure, nozzle resin pressure or pressure in each mold cavity is used as the holding pressure set value. A method for controlling holding pressure described in multi-cavity in the injection molding described. 9. The sum of squares of deviations from the target density ρ _K * set for each mold cavity is expressed by the following equation: It is expressed by the equation (9), the density ρ _K of the material in the mold cavity (5b, 5c) is expressed by the equation (1), and the resin pressure P _k in the mold cavity (5b, 5c) is expressed by the equation (2). Representation, the resin temperature T _K (tg) in the mold cavity (5b, 5c) is represented by equations (3), (4) and (5), respectively, and the holding pressure set value that minimizes G in equation (9). Let P _L * be the following The method for controlling the holding pressure of a multi-cavity mold in injection molding according to claim 2, characterized in that the pressure is controlled by the expressions (10), (11), (12) and (13). 10. A mold temperature sensor (6a to 6d) provided in a multi-cavity mold (5), and resin flow paths (4a, 5a, 5d) in the multi-cavity mold (5) and a nozzle (4). , 5e ...
・ A resin temperature sensor (6e, 6f) provided on either
Amplifiers (8a to 8f) for inputting and amplifying the measured values of the mold temperature and the injection resin temperature from the resin temperature sensors (6e, 6f), and an A / D converter (A / D converter for converting the measured values into A / D ( 9a to 9f) and the measured value and the product density and product density of each cavity using at least the molded product weight target value set for each mold cavity (5b, 5c) of the multi-cavity mold (5). An arithmetic processing unit (10) for calculating a holding pressure set value that minimizes the sum of squares of deviations of target values, and a voltage signal (11a) for the holding pressure set value.
The holding pressure control section (11) that outputs to the servo valve amplifier (15) that controls the servo valve (14), the target weight value of molded product W _K *, the control constants a _1K , a _2k , b _1K , b _2K , d _1K , c _1K , state equation constants R ₁ , ρ ₀ , π _i , flow stop temperature Tg, reference temperatures T _WSK , T _{RSK, and the} like, and a setter (13), which is characterized in that the injection molding is performed. Pressure control device for multi-cavity mold in.