JP2009298035A - Method for designing mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of a prediction accuracy which is derived from the fact that since the conventional method of designing a mold for injection molding is with reference to general analysis results about warpages, that a contraction direction is limited to one direction of a centroid direction, and that the resistance value calculated from the contraction not considering a restraint of a mold surface is used. <P>SOLUTION: The method for designing the mold includes the step of carrying out the analyses of filling and pressure keeping in an injection molding simulation sequentially, of asking a demolding resistivity from the fact that the mold contacting a molded product restrains the molded product by carrying out a contraction calculation in consideration of not only the product surface configuration, but also the contact in the mold in the state of defining the mold surface configuration also using the analysis results, of indicating the surface when it does not fit in the range of the demolding resistivity, and of asking proper conditions by sequentially changing molding conditions-gate shapes (gate position and size)-mold surface conditions and inclinations of the mold surface to a demolding direction to the surface. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a mold design method for optimizing molding conditions and mold structure that affect mold release in mold design of injection molded products.

Conventionally, when performing injection molding, a molten resin is injected into a mold and solidified, and the solidified product is pushed out with a release pin to take out the product.
At the time of this molding, the product is thermally contracted as the molten resin is solidified, and friction occurs on the contact surface between the mold and the product. Therefore, the product is taken out by applying a release force by a release pin. However, there are cases in which the molded product causes mold release defects due to mold release resistance.

Therefore, when designing a mold, by calculating the mold release force etc. of the surface where the product and the mold are in contact by simulation, the gradient of the mold gradient surface relative to the mold release direction, the mold surface A design value of a mold in which a state and the like are appropriate is obtained (see Patent Documents 1 to 3). For example, in the mold design method described in Patent Document 1, the mold release resistance force generated between the mold and the mold based on the stress calculated from the deformation amount of the molded product in the injection molding simulation is obtained, and the surface gradient and A method to optimize the surface condition is proposed. The mold design method described in Patent Document 2 pays attention to the dynamic change of the frictional force when the product is ejected from the mold, and uses a unique parameter to improve the prediction accuracy of the mold release resistance value. It is improving. The mold design method described in Patent Document 3 defines the shape of the product and the mold, and then dynamically calculates the deformation that occurs when the product is pulled out and the frictional force with the mold surface to improve accuracy. It is improving.
JP 2001-62872 A JP 2005-46892 A JP 2007-320221 A

  However, since these methods are based on general warpage analysis results, the shrinkage direction is limited to one direction of the center of gravity, and the calculation is based on shrinkage that does not consider the constraint on the mold surface. Since the value was used, there was a problem in prediction accuracy. In particular, the direction of contraction is not actually limited to one direction of the center of gravity, and these methods have a problem that galling and embrace often seen in a cylindrical shape away from the center of gravity cannot be predicted. As for the prediction of warpage (shrinkage), stress is accumulated in the molded product due to the restraint of free thermal deformation of the resin due to the presence of the mold, and the accumulated stress is greatly applied to the mold release. Since the phenomenon such as influence is not taken into consideration at all, it is one of the major factors that deteriorate the prediction accuracy.

  The present invention has been made in view of the above points, and when performing warp analysis (shrinkage calculation), the product and the entire mold shape are defined, and analysis is performed in consideration of the restraint state, thereby achieving high accuracy. It is intended to provide a mold design method capable of performing simple analysis.

  The present inventor sequentially analyzes the filling and holding pressure in the injection molding simulation, and uses the result to calculate not only the product surface shape but also the mold surface shape, and the shrinkage calculation considering the contact in the mold. By determining the mold release resistance based on the fact that the mold in contact with the molded product restrains the molded product, if the mold release resistance does not fall within the range, the surface is displayed and molded. The present inventors have found a mold design method for obtaining appropriate conditions by sequentially changing conditions, gate shape, mold surface state, and the gradient of the mold surface with respect to the mold surface in the mold release direction.

That is, the present invention is a mold design method including the following steps.
First, create an element model of the product used in the injection molding simulation, and input the element model of the movable mold and the fixed mold in such a way that the product fills the mold based on this element model. .
Next, in order to sequentially analyze the filling and holding pressure in the injection molding simulation, the molded product shape data, the molding condition data (each data such as the injection condition, the holding pressure condition, the cooling condition), the data indicating the resin characteristics (viscosity, (PvT data, mechanical characteristics, etc.) and other conditions necessary for analysis are input, temperature changes and pressures of the molding material during the injection molding process are calculated, and each part of the molded product is cooled by the calculation results. The temperature distribution and pressure distribution of the resin at the start of deformation are calculated.
Subsequently, the product element model with the initial values of the temperature and pressure of each element calculated in the injection molding simulation and the element model in which the element model of the movable side mold and the fixed side mold are integrated are input. By giving the same temperature distribution to the whole at the time of actual molding, shrinkage calculation is performed when the resin that has become high temperature and pressure is cooled to a temperature at which it can be released. In this calculation, the shrinkage direction and the shrinkage amount that are not limited to the center of gravity direction are predicted in consideration of the constraint and contact (friction) of the mold surface, and the stress with which the molded product is pressed against the mold is calculated.
Next, the collision calculation when pulling the product element model away from the mold model with the surface condition (adhesion force, frictional force) of each surface of the mold entered based on the stress on the mold obtained by the shrinkage calculation as a reference. By doing so, the reaction force (resisting force) is obtained. At this time, since the frictional force generated between the mold surface and the product surface is taken into consideration, excessive adhesion, galling, and hugging to the mold that occur when the molded product is pressed against the mold surface. Predictable.
This release resistance is judged to be within a certain range. If it does not fit, the surface is displayed and the molding conditions and gate shape (gate position and dimensions) are changed to change the pressure applied to the product. The state resistance such as temperature is changed to adjust the release resistance.
Further, an appropriate state of the mold surface is obtained by sequentially changing the mold surface state and the mold surface gradient.

  According to the mold design method of the present invention, when designing an injection mold, by calculating the mold release force of the surface where the molded product and the mold are in contact, the molding conditions, the gate shape, and the mold surface are calculated. It is possible to obtain a value that is appropriate for the state, and it is easier to find the appropriate molding conditions and mold design than before, without performing actual molding trials, reducing the development period and the number of molding trials. The cost can be reduced.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a part of a flowchart showing a procedure for carrying out a mold designing method according to the present invention, and FIG. 2 is a remaining part of the flowchart shown in FIG. 3 is an example of a three-dimensional model of a molded product to which the present invention is applied, FIG. 4 is an example of a three-dimensional model of a molding die to which the present invention is applied, and FIG. 5 is a sectional view of the molding die.

  Based on the three-dimensional shape model of the molded product shown in FIG. 4, a three-dimensional model of the molding die is created. At this time, the product and the mold surface are not combined, and the product and the mold are separated or rubbed together. Further, the product and the mold surface data are defined using elements that are filled with no space such as an air layer. Furthermore, in order to take into account mold opening and ejection at the time of mold release, the mold is divided and input on the fixed side and movable side with reference to the parting line, and collision calculation is performed for the position where the ejection pin is scheduled. It is necessary to input in such a way that a force can be applied in the direction of projecting the product. (Step S1 in FIG. 1).

  Only the 3D model data of the shape product input in step S1, gate shape, molding condition data (each data such as injection conditions, pressure holding conditions, etc.), data indicating resin characteristics (viscosity, PvT data, mechanical characteristics, etc.), etc. Input the various condition data necessary for the analysis of the mold, sequentially analyze the filling and holding pressure in the injection molding simulation, and the resin temperature and pressure distribution on the surface of the molded product and the internal resin just before the cooling in the mold starts Ask for. (Step S2 in FIG. 1).

  Using the three-dimensional model data of the molded product and product mold input in step S1, the resin temperature distribution and resin pressure distribution of the molded product calculated in step S2 are input as initial values, and the molded product is cooled to the mold. The thermal strain calculation at the time and the stress that the product is pressed against the mold surface when the strain occurs are calculated at the same time. (Step S3 in FIG. 1).

  Using the distortion of the molded product obtained in step S3 and the stress on the mold surface as an initial state, the molded product is calculated by applying a load to the protruding pin portion, and the reaction force generated at each protruding pin portion. Is added to obtain a release resistance value when releasing the molded product (step S4).

  If the mold release resistance value generated for each surface unit of the molded product obtained in step S4 is within a predetermined mold release resistance judgment value, the mold design used at the time of the calculation becomes the design value as it is (step S5).

  In step S5, when the release resistance value obtained in step S4 exceeds a predetermined release resistance determination value, the corresponding position is displayed on the three-dimensional shape model data (step S6). .

  In step S6, the calculation is performed again for the case where the molding condition is changed with respect to the position displayed on the three-dimensional shape model data as the surface exceeding the mold release resistance determination value. The molding conditions used for the change may be obtained from a data file such as a predetermined standard molding condition database or may be given by a person (step S7).

In step S8, when changing the molding conditions, it is checked whether or not the product can be filled.
The judgment criteria are (1) that the molten resin is not filled to the end (short shot), and (2) exceeds the maximum capacity (injection pressure and clamping force) of the molding machine that is planned to be used. (3) The maximum temperature that has been confirmed in advance in the verification experiment is that the resin temperature predicted at the time of the filling analysis is burnt black due to shearing heat generation or the surface property defect called silver caused by thermal decomposition occurs. Do not exceed.

  If it is determined in step S8 that filling is possible, the pressure holding analysis is sequentially performed, and the release force is calculated in the same manner as in steps 2 to 4. On the other hand, if it is determined in step S8 that the filling is impossible, the molding conditions are reviewed, and the measures that can lead to a reduction in the mold release force of the mold under consideration are possible. For example, when there is a problem in the criterion (1), it is conceivable to increase the resin temperature / mold to improve fluidity.

  In step S10, when the release resistance value of the molded product obtained in step S9 exceeds a predetermined release resistance determination value, the corresponding surface of the molded product is displayed on the three-dimensional shape model data. (Step S11).

  In step S12, after confirming the position displayed on the three-dimensional shape model data as the position exceeding the mold release resistance determination value, the gate shape is changed. The gate shape used for the change may be obtained from a data file such as a predetermined standard condition database or may be given by a person (step S12).

In step S13, when changing the gate shape, it is checked whether or not the product can be filled.
The judgment criteria are (1) that the molten resin is not filled to the end (short shot), and (2) exceeds the maximum capacity (injection pressure and clamping force) of the molding machine that is planned to be used. (3) The maximum temperature that has been confirmed in advance in the verification experiment is that the resin temperature predicted at the time of the filling analysis is burnt black due to shearing heat generation or the surface property defect called silver caused by thermal decomposition occurs. Do not exceed.

  If it is determined in step S13 that filling is possible, the pressure holding analysis is sequentially performed, and the release force is calculated in the same manner as in steps 2 to 4. On the other hand, if it is determined in step S13 that filling is impossible, the gate shape (gate position and dimensions) is reviewed, and a measure that is considered to lead to a decrease in the mold release force of the mold being studied under conditions that allow filling. Take. For example, it is conceivable that the pressure can be easily transmitted to the product by increasing the cross-sectional area of the gate portion or increasing the number of gate points.

  In step S15, when a position where the release resistance value generated for each surface unit of the molded product obtained in step S14 exceeds a predetermined release resistance determination value occurs, the corresponding position of the molded product is set to 3 Displayed on the dimensional shape model data (step S16).

  In step S17, the mold surface state is changed with respect to the position of the molded product displayed on the three-dimensional shape model data as a surface exceeding the mold release resistance determination value (step S17). The value of the mold surface state used for the change can be obtained from a data file such as a predetermined standard mold surface state value database or given by a person.

  Similarly, if there is a surface of the molded product displayed on the three-dimensional shape model data as a surface exceeding the mold release resistance determination value in step S18, it occurs for each surface of the molded product for each corresponding surface. It was determined whether the mold release resistance value was within a predetermined mold release resistance judgment value. If it was within the mold release resistance judgment value for all surfaces of the molded product, it was determined that there was no problem with the mold release property. The value of the mold surface state becomes the design value as it is, and the process ends (step S19).

  In step S19, when the obtained release resistance value of the molded product exceeds a predetermined release resistance judgment value, the surface of the corresponding molded product is displayed on the three-dimensional shape model data for design. The return shape is examined (step S20).

  In the above, an example of the procedure for obtaining the optimal molding conditions and the optimal mold structure for the mold release direction has been shown. The calculation order is such as determining the optimal molding conditions after determining the optimal mold structure first. It can be easily imagined that it can be applied even when changes occur.

It is a part of flowchart which shows the procedure of this invention. It is the remainder of the flowchart shown in FIG. It is an example of the three-dimensional model of the molded article to which this invention is applied. It is a perspective view of a shaping die. It is an element model of the said molded article. It is the element model of the said metal mold | die. It is sectional drawing of the said element model. It is an element model figure of a product and a metal mold | die (movable side). It is an element model figure at the time of performing protrusion calculation.

Explanation of symbols

1 Product shape 2 Mold shape (fixed side)
3 Mold shape (movable side)
A Product element model B Mold element model (fixed side)
C Mold element model (movable side)
X Horizontal direction (length direction) when creating an element model
Depth direction (width direction) when creating Y element model
Z element model vertical direction (height direction)

Claims (1)

Analyzes filling and holding pressure in injection molding simulation sequentially,
Using the result, not only the product shape but also the mold shape is defined, and the contact state between the molded product and the mold based on the stress obtained by performing shrinkage calculation considering the contact between the product and the mold Predict
The resistance required in the collision analysis that pulls the product away from the mold is defined as the release resistance.
When the mold release resistance force does not fall within a certain range, the surface is displayed and the molding conditions, gate shape, and mold surface state are sequentially changed to obtain appropriate conditions. Design method.

Images