JPH0313050B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an injection compression molding apparatus.

In injection molding, molten resin is injected and filled into a cavity that is strictly fixed by the mold structure, and the sprue and runner parts are released from the injection cylinder through an operation called holding pressure until the narrow part of the gate part solidifies. Pressure is applied through the resin to prevent the resin in the cavity from flowing back, and after solidifying the gate, the heat of the resin in the cavity is transferred to the mold and cooled to form a product.

The density of a molten resin is usually lower than that of a solid, and as the molten resin solidifies, its volume decreases, that is, shrinkage occurs. As an example, consider a product with a diameter of 100 mm and a wall thickness of 10 mm. Assuming that the resin density is 1.17 in the molten state and 1.20 in the solid state, when the volume in the molten state is equal to the volume of the cavity (78.54 cc), it solidifies and reaches room temperature. It becomes 76.57cc. If we assume that this reduced volume is caused by contraction only in the thickness direction, the thickness of the finished product will be 9.75 mm, which is 0.25 mm.
The wall thickness is insufficient by mm.

In order to deal with such shrinkage, a method of overpacking the mold until it opens slightly at the parting line has been considered, and a method of controlling the amount of mold opening at that time (Japanese Patent Application Laid-open No. 50-39351) and a method of overpacking the mold until it opens slightly at the parting line have been studied. Use a cavity that makes it easy to
Rolinx method (“New concept in injection”
molding, Rolinx process extended
application of plastics”Plastics, 30, 330,
Apr. (1965)) has been proposed. In addition, a small hydraulic cylinder is buried in the mold so that the cavity core can be moved forward and backward, or an ejector cylinder is used to intentionally enlarge the cavity for injection, and after filling is completed, the hydraulic cylinder is moved forward. It was proposed that the cavity be made smaller by molding to obtain a molded product with a predetermined thickness, and this method is known as the micromolder method (H. Holt: “New
techniques in shrinkage control”SPE J.
P519, Jun (1964)).

Of course, the most basic method is to design the cavity larger in anticipation of this contraction, but
In the case of thick-walled products or products with uneven thickness, such a design is virtually impossible and requires repeated trial and error.

It has been recognized that the above-mentioned overpacking method also has the drawback of requiring high injection pressure, and that when the product has uneven thickness, the shrinkage correction effect is limited in the thin wall portion where shrinkage is small. In the case of the micromolder method, the cylinder drum advances as it contracts, and although the product surface on the moving core side is produced with good precision, the facing precision is not sufficient.

In view of this current situation, ENGEL (LUDWIG ENGEL KG MACHINEN) has developed an injection compression molding method that uses mold clamping force to perform compression operations.
FABRIK, A-4311 SCHWERTBERG
AUSTRIA), this method uses the toggle type mold clamping force as compression pressure, and is an innovative method in which the toggle is held so that it is not fully extended during the injection process, and is fully extended during the compression process. It is something.

However, the toggle compression method has the disadvantage that the compression pressure cannot be controlled. The necessity of controlling the compression pressure indicates the relationship between "pressure applied to the resin - specific volume of the resin - temperature of the resin"
This can be explained using the PVT curve as follows.
The horizontal axis shows the resin temperature T, the vertical axis shows the specific volume V of the resin, and the relationship between V and T of the resin under a constant added pressure P (which can be considered as the pressure of the resin as a reaction) The PVT curve in Figure 1 shows this.

Using the above-mentioned injection compression molding equipment, let's follow this graph to see how resin is injected into the mold cavity, compressed, and taken out. If the end point of the primary injection pressure is indicated by (V→P)A, it is the process A- in which the resin pressure increases while the resin temperature decreases due to injection.
Even if pressure holding is completed, the resin temperature continues to fall, and since there is no external pressure, the volume contracts and becomes the specific volume when the pressure is low, so the process B-C is followed. If the toggle is fully extended and the compression operation is performed while taking into account backflow, the resin pressure will increase while the resin temperature has hardly cooled, resulting in process C-D. If the toggle is fully extended at this time, then the resin temperature will drop and the pressure will decrease, which is the process D-E.
It is. At this time, since the accommodation is reduced, the resin is moved, and pressure is applied to the resin in a state where its fluidity is deteriorated, causing distortion. After this, when the mold is opened after reaching the ejecting temperature, the resin pressure increases in the process of increasing the specific volume because the external pressure decreases E-F
This is followed by process FG in which the resin temperature reaches room temperature under atmospheric pressure, and the molding is completed.

The molding shrinkage rate in this case can be determined from the difference in specific volume between E and G. In the toggle compression method, the arm length is fixed, so the pressure is adjusted by positioning, but the pressure varies depending on the mold temperature, tie bar temperature, and position settings, so the pressure cannot be fixed. Have difficulty. For this reason, it is difficult to control the compression pressure, and on the PVT curve, the end point when the toggle is fully extended is D.
It is unclear whether it is D' and cannot be controlled.

On the other hand, in the compression method using direct pressure hydraulic pressure, the maximum compression pressure can be precisely adjusted, and the
If the compression pressure is controlled to decrease so that the specific volume of the resin remains constant as the resin temperature decreases as shown in the figure, the resin will not deform at all during the solidification process, so distortion may occur. do not have. This shows that if steps A to G in the upper part of FIG. 2 are followed, molding with a constant molding shrinkage rate is possible. In this case, the difference in volume between the cavity and the resin is the difference in the specific volumes of D and G. Since it is possible to control the volume of the cavity to be constant, this allows molding to have a constant molding shrinkage rate from cycle to cycle.

Based on the above considerations, the present invention proposes an injection compression molding device that enables direct pressure compression. (1) How to increase the volume of the cavity and how to control it. (2) The aim is to solve the following problems: (3) how to smoothly open and close the mold to take out the product; and (3) how to obtain a compression process that allows compression to be controlled.

In order to achieve the above object, the present invention has fixed and movable die plates and a tie bar support plate, and at least the tie bar support plate or the movable die plate is provided with a setting rod that adjustably sets the compression margin. In order to increase the cavity volume and take up the compression margin during injection, a removable key is provided that is inserted so as to come into contact with the setting rod and mechanically fixes the distance between the tie bar support plate and the movable die plate. Before injection and filling, the key is inserted to remove the compression margin of the movable die plate, and after filling is completed, the compression operation is performed by high-pressure mold clamping, and the key is removed to enable opening and closing of the mold.

FIG. 3 shows the correlation between the distance between the die plates, the distance between the tie bar support plate and the movable die plate, and the tie bar length in each process in the injection compression molding apparatus of the present invention, and the concept of the present invention will be explained using this. do.

FIG. 3a shows the distance between each plate during low-pressure mold clamping, where the tie bar length is l and the distance l' between the stationary die plate 1 and the movable die plate 2 corresponds to the mold thickness. The distance l'' between the movable die plate 2 and the tie bar support plate 3 can be changed by moving the movable die plate 2 by the clamping cylinder ram.From this state, the clamping cylinder ram is moved by high-pressure hydraulic pressure. The state of the driven high-pressure mold clamp is shown in Fig. 3b.

At this time, when the molds can be sufficiently joined by low-pressure mold clamping, l' hardly changes even with high-pressure mold clamping, but the tie bar length increases by △ and becomes (l + △), and the length of the elongation is approximately l''. Corresponding to the change in distance, the distance of the tie bar support plate 3 becomes (l″+△).

In the injection compression molding apparatus of the present invention, the mold is slightly opened between the parting lines P and L or other mold plates as shown in FIG. 3c, without performing high-pressure mold clamping during injection. The mold thickness is (l′+δ). It says to compress δ. At this time, since high-pressure mold clamping is not performed, the tie bar length remains l, so the compression margin δ changes by l'', and the distance between the tie bar support plate 3 becomes (l'' - δ). . Next, in the compression process after injection, high-pressure mold clamping is performed, so
As shown in Figure 3b, the mold thickness is from (l'+δ)
l', and compression is performed by δ.

When the injection pressure increases during the injection process, (l″−
In a molding device where δ) is fixed, the tie bar length increases slightly to become (l + △'), so
The mold thickness is (l' + δ + △'), and when compressed from that state to l', the actual amount of compression is (δ + △'). Δ' is approximately 0.3 mm or less using a molding device with a mold clamping force of 150 tons.

From the above, the amount by which the mold is opened prior to the injection process, that is, the compression margin δ, is determined experimentally by taking into consideration the shape of the product, the temperature of the resin, the injection pressure, and the like. For this reason, it is important to have a compression margin adjustment means that allows for easy readjustment of δ and that is accurate.

The present invention relates to a means that can maintain (l″−δ) even if the injection pressure changes during injection and filling, and allows the compression operation after injection to be performed by high-pressure mold clamping, as well as for opening the mold to take out the product and The mold can be closed freely for the cycle, and the compression margin can be reduced to microns (μ
This invention relates to an injection compression molding apparatus in which a means for precisely setting in m) units is provided between a movable die plate 2 and a tie bar support plate 3.

An embodiment of the present invention will be described below based on the drawings. FIG. 4 is a model representation of the compression margin setting means in the present invention. A mold is placed between a stationary die plate 1 and a movable die plate 2, and a cavity 7 is constituted by a stationary mounting plate 4, a template 5, and a movable template 6. The movable template 6 has a complicated structure because it incorporates an ejector mechanism, but is omitted for the sake of simplicity. A mold clamping cylinder 9 having a mold clamping cylinder ram 8 connected to the movable die plate 2 is attached, and the tie bar support plate 3 to which the tie bar 16 is fixed is attached to the tie bar 16 by the mold clamping cylinder ram 8 of the mold clamping cylinder 9. A compression margin setting means is provided between the movable die plate 2 and the movable die plate 2 that moves along the movable die plate 2.

In FIG. 4, a key 10 is rotatably provided on a mounting rod 13 fixed to, for example, the movable die plate 2 and supported and guided by the tie bar support board 3. Compression allowance setting rod 1 attached to 3
1 and 12, and when the cylinder ram 8 is retracted, the state shown in the upper part of FIG. 4 is ready for injection, and the state shown in FIG. 3c is reached. In the lower part of Fig. 4, the compression operation is performed, and when the key 10, which transmits the injection pressure through the compression margin, becomes movable, the key 10 is removed from between the compression margin setting rods 11 and 12, and the next product is moved. Prepared for opening the mold for removal. Mounting rod 1
The rod 11 can be omitted if the fixation of the key 10 to the key 3 has sufficient rigidity to resist the force of opening the mold due to the resin pressure within the mold generated by the injection pressure. 14 is a nozzle provided on the stationary die plate 1.

Figures 5a and 5b show examples of the arrangement of the compression range setting rod 12, keys 10, and mounting rods 13 when the number of keys 10 is two;
are arranged vertically, and b are arranged horizontally. For example, a hydraulic or air cylinder is provided on the movable die plate 2 parallel to the die plate surface to drive the key 10 to rotate, or a solenoid is built into the key 10. , rotates the key 10 with respect to the mounting rod 13. Figure 5c shows one key 10 in cylinder ram 8.
For example, a hydraulic or air cylinder is provided on the movable die plate 2 parallel to the die plate surface to rotate the key 10. The number of compression margin setting rods 12 is not limited to two, but can be set in several pieces, and each rod is not independent as shown in Fig. 5, but can be set as shown in Fig. 6b. It can also be configured as an integral part.
Figure 6c shows an example in which a block with four legs on the outer periphery of the cylinder ram 8 and a length longer than the mold opening/closing stroke is used as a compression setting rod, and the key is an integral one as shown in Figure 6a. and key
By rotating it 45 degrees, you can switch between the position where it corresponds to the four legs of the compression allowance setting rod, and the position where it becomes loose and can freely enter the interior. Also, as shown in Fig. 7, the key 1 is integrated.
It is also possible to use a compression margin setting rod 12 that plays the same role as a key by changing its position relative to 0.

Although the keys used in FIGS. 5 and 7 are rotary keys, slide keys driven by air cylinders or hydraulic cylinders are also used. An example is shown in FIG. A ring (not necessarily a ring) 20 corresponding to the compression allowance setting rod 12 is provided on the outer periphery of the mold clamping cylinder ram 8, and a key 21 is driven by a hydraulic cylinder 22 to the guide 2.
3 and reaches the position indicated by the broken line in the figure, the key 21 is fully inserted. When viewed from the side, the configuration in this case is as shown in FIG. 8b, and when the key 21 is lifted up, the mold can be opened freely. The hydraulic cylinder 22 is fixed to the tie bar support plate 3, the movable die plate 2, or the tie bar. Of course, tie bars can be used as guides in this case.

The above is a mechanism that uses a set of mold clamping cylinders to perform injection with a compression margin of a predetermined thickness without high-pressure mold clamping during injection, and later allows the mold to be opened and closed freely for product removal. was explained in detail.

Next, as a method for setting the compression margin δ, (i) Directly change the length of the compression allowance setting rod.

(ii) Change the mounting position of the compression allowance setting rod.

There are two possible methods. In the first method, the length can be adjusted in microns by attaching a micrometer head to the tip of the rod. That is, the lengths of the respective rods may be adjusted using a micrometer head to make them equal. A precision screw can be used as a substitute for the micrometer head. In this case, in order to make settings in micron units, it is difficult to balance the lengths of several rods unless the screw diameter is made large or the angle indexing mechanism is not good.

The second method is to adjust the mounting position of the rod. As a model, as shown in FIG. 9a, the rod length L changes as a result of tightening the threaded portion of the compression allowance setting rod 12.

As an example using this, as shown in FIG. 9b, a position adjustment base 25 having a threaded portion on the outer periphery and connected to the tie bar support plate 3 is attached to a position adjustment plate having a threaded portion on the inner periphery. When installing 26,
Changes in the rod length can be adjusted by changing the distance between the tie bar support plate 3 and the position adjustment plate 26 to obtain △L.
The effective rod length is L. Compression allowance setting rod 1
2, all the lengths are made to be the same, and the mounting method is such that they are pressed against the position adjustment plate 26 with a spring 27. When using this method, the diameter of the position adjustment base 25 can be increased, so that highly accurate adjustment is possible. For example, if the base is φ400mm and the screw pitch is 3mm, it is possible to move forward and backward by 24μm per 10mm distance on the outer periphery, and the change is linear and extremely easy to control.
In the case of the integrated rod shown in FIG. 6, a screw with a large diameter can be used, so it is easier to use a method in which the rod length itself is adjusted.

FIG. 10 shows a structure in which the rod length can be changed using the structure shown in FIG. 6c. In the structure shown in FIG. 6c, the compression allowance setting rod is replaced by a rod portion 32 of which is attached to an adjustment screw plate 31.
When this adjustment screw plate 31 is attached to the rod length adjustment base 30, the length of the compression allowance setting rod 12 shown in FIG. 4 corresponds to the assembled length L of 30, 31, and 32. Only ΔL can be varied depending on the screw fitting part. ΔL is required to be the maximum mold thickness - minimum mold thickness + compression margin δ, and is approximately expressed as maximum mold thickness - minimum mold thickness.

It is easy to infer that the key plays the role of the setting rod as described above. In other words, the aforementioned adjustment rod is set to a fixed length, and a micrometer head is attached so that the length of the key can be adjusted.
A large diameter screw as mentioned above is used.

As described above, the present invention uses an injection molding apparatus to increase the thickness of the cavity in the mold by using a key that keeps the distance between the support plate of the tie bar and the movable die plate constant in order to take up the compression margin during injection. In addition, the compression margin can be maintained by a key without relying on the mold clamping force of the mold clamping cylinder, and after filling the cavity, compression can be performed using the mold clamping force. By doing so, the resin does not deform at all during the solidification process, making it possible to obtain a product with no distortion. Moreover, the mold can be opened and closed freely to take out the product by performing a compression operation using mold clamping force and removing the key when the key is separated from the setting rod.

[Brief explanation of the drawing]

Figure 1 is a so-called PVT curve that shows the change in specific volume with respect to resin temperature, using the pressure applied to the resin as a parameter, and shows the change when injection compression molding is performed using a toggle compression process. ,
Figure 2 shows the ideal process when injection compression molding is performed using the direct pressure compression process using the same PVT curve, and Figure 3 shows the die for each process in the injection compression molding apparatus of the present invention. This is a diagram illustrating the concept of the present invention by showing the correlation function of the inter-plate distance l', the distance l'' between the tie bar support plate and the movable die plate, and the tie bar length l. b shows the state when the mold is clamped under high pressure from this state, c shows the state where the injection compression molding apparatus of the present invention has entered the injection process, and Figure 4 shows the compression molding in the present invention. Figure 5, which is a model representation of the margin setting means, shows examples of the arrangement of compression margin setting rods and key attachment rods for cases where the number of keys is 2 and 1, where a is vertically arranged and b is horizontally arranged. ,
c is a diagram showing one key attached to the cylinder ram, Figure 6 is a diagram showing an example in which the compression margin setting rod and several keys are integrated, and Figure 7 is a diagram using a rotary type key. Figure 8 shows an example using a slide type key, Figure 9 shows how to finely set the compression margin by adjusting the mounting position of the rod, and a indicates the tie bar. Figure 10 shows an example in which a rod with a threaded portion is screwed onto a support plate for adjustment.B shows an example in which a position adjustment base is provided and the rod length is adjusted by changing the distance between it and the tie bar support plate. 6 is a diagram showing an example of changing the rod length using the structure of FIG. 6c; FIG. 1... Fixed side die plate, 2... Movable side die plate, 3... Tie bar support board, 5, 6... Template plate, 7...
Cavity, 8...Mold clamping cylinder ram, 9...Mold clamping cylinder, 10...Key, 11, 12...Compression allowance setting rod, 13...Mounting rod, 25...Position adjustment base, 26...Position adjustment plate, 27...Spring, 30 ...rod length adjustment base, 31...adjustment screw plate.

Claims (1)

[Claims] 1. It has fixed side and movable side die plates and a tie bar support plate, and at least the tie bar support plate or the movable side die plate is provided with a setting rod for setting the compression margin so that the compression margin can be adjusted, and the cavity volume is increased and compression is performed during injection. In order to stop
A removable key is provided to mechanically fix the distance between the tie bar support plate and the movable die plate by being inserted so as to come into contact with the setting rod, and the key is inserted to control the movable die plate before injection and filling. An injection compression molding device that removes the compression margin, performs compression by high-pressure mold clamping after filling is completed, and allows the mold to be opened and closed by removing the key.