JP2003062862A - Breaking separation method for molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a breaking separation method capable of rapidly breaking and separating a molded product from a molding-finished article without using an edge tool or laser beam. SOLUTION: In separating (breaking) the molded product by applying ultrasonic vibration to the molded completion article, the intrinsic vibration frequency possessed by the molding-finished article itself is allowed to approach the vibration frequency of an ultrasonic exciter (most preferably allowed to coincide) to intentionally generate resonance to increase not only amplitude but also bending stress to generate breaking.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for separating a molded product of a synthetic resin material or a metal material from a runner.

[0002]

2. Description of the Related Art As a method of molding a molded product, for example, a plastic lens, a plurality of runners are projected from a central sprue portion in a radial direction, and a plastic lens is molded at the tip of this runner through a gate portion. It is known how to do it. In this molding method, after completion of molding, the molded product taken out from the molding die is in a state in which the sprue, runner, gate portion and plastic lens are connected.

Conventionally, in order to separate a plastic lens from this molded product, a gate tool (nipper, rotary blade, etc.) has been used to cut the gate portion of each plastic lens. Recently, as disclosed in Japanese Patent Laid-Open No. 10-123306, a method of gate cutting with a laser beam has been proposed. However, these cutting operations have to be performed for each small plastic lens connected to the gate portion, resulting in extremely poor work efficiency. Further, the cutting work with a blade may require additional deburring work after cutting depending on the lens shape and the cutting blade shape.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a fracture separation method capable of rapidly fracture-separating a molded product from a molded product without using a knife or a laser beam.

[0005]

SUMMARY OF THE INVENTION According to the present invention, when ultrasonic waves are applied to a molded product to separate (break) the molded product, the natural frequency of the molded product itself and the frequency of the ultrasonic vibrator are By intentionally causing resonance by increasing (most preferably matching) and increasing the amplitude,
It was made based on the idea that bending stress is increased and breakage easily occurs.

According to the present invention, a molded product having a molded product connected to the tip of a runner through a gate is subjected to ultrasonic vibration by an ultrasonic vibrator to break and separate the molded product from the gate. And a method of setting a frequency for substantially equalizing the vibration frequency of the ultrasonic vibrator and the natural frequency of the finished product; and the finished product having the natural frequency set in the frequency setting step. In addition, a vibration applying step of applying ultrasonic vibration by an ultrasonic vibrator whose vibration frequency is set in the same frequency setting step;

To make the vibration frequency of the ultrasonic vibration generator substantially equal to the natural frequency (both frequencies) of the finished product means that the vibration frequency (amplitude, velocity, acceleration, etc.) is input, When the vibration actually generated in the finished product is taken as the output vibration value, it means that both frequencies are set to the frequency at which the value of (output value / input value) shows a peak or the frequency in the vicinity thereof. In this way, by setting both frequencies in the frequency setting step and vibrating the finished product at the vibration frequency in the vibration applying step, it is possible to break and separate the molded product from the gate part very efficiently in a short time. You can

In the frequency setting step, the physical quantity such as the shape of the finished product is set so that the natural frequency of the finished product is approximately equal to the vibration frequency of the ultrasonic vibrator. Any one of the modes of setting the physical quantity such as the shape of the ultrasonic vibration horn of the ultrasonic vibration machine is used so that the natural frequency of the ultrasonic vibration machine becomes almost equal to the natural frequency of the finished product. It is preferable.

In the frequency setting step, the natural frequency of the molded product is accompanied by a vibration mode suitable for breaking and separating the molded product from the gate portion from among a plurality of natural frequencies of the molded product. It is preferable to select the natural frequency. That is, it is known that the molded product has a plurality of natural frequencies, and the respective natural frequencies have different vibration modes (different vibration axes and vibration directions). Therefore, in consideration of the shape of the molded product, the natural frequency suitable for breaking and separating the molded product from the gate portion is selected and the vibration is given.

In the frequency applying step, vibrations of two or more natural frequencies of a plurality of natural frequencies of the molded product may be applied simultaneously.

The present invention can be applied regardless of the shape of a molded product or a molded product, but as a specific example, for example, a sprue at the center and a plurality of runners extending in the radial direction from the sprue. Also, the present invention can be applied to a molded product having a molded product molded at the substantially equidistant position from the sprue through the gate portion at the tip of this runner.

The ultrasonic vibrator used for this specific finished product is, for example, a table on which the finished product is placed with its runners in contact; A cylindrical ultrasonic vibration horn having a hole through which the sprue of the molded product is inserted; the ultrasonic vibration horn and the table are relatively moved toward and away from each other, and the annular end surface of the ultrasonic vibration horn and the table It is possible to provide an ultrasonic exciter that includes an advancing / retreating mechanism that sandwiches the plurality of runners between and, and an ultrasonic vibration device that applies ultrasonic vibration to the ultrasonic vibration horn.

The present invention can be applied regardless of the type, shape, material (synthetic resin, metal), etc. of the molded product.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawings show an embodiment in which the present invention is applied to a multi-cavity plastic lens separating device. Multi-cavity plastic lens finished product 10
As shown in FIG. 1, the sprue 1 in the shape of a conical rod at the center is
1, a plurality of runners 12 extending in the radial direction from the sprue 11 in the same plane orthogonal to the axis of the sprue 11, and plastics connected to the tip end of each runner 12 via a gate portion 13. And a lens (hereinafter simply referred to as a lens) 14. Sprue 11
A downward extension sprue 1 extending downward from the runner 12 in FIG.
Has 1U. In the illustrated example, four runners 12 are formed at 90 ° intervals, and two gate portions 13 and two lenses 14 are formed at the tip of each runner 12. Further, all the lenses 14 are formed at positions equidistant from the center of the sprue 11.

The gate portion 13 has a constant width in plan view (FIG. 2), but has a front (side) shape in which the thickness is monotonically reduced from the runner 12 side to the lens 14 side (FIG. 2). ing. That is, the cross-sectional area of the gate portion 13 is 1
It decreases monotonically from the second side to the lens 14 side. Further, the lens 14 in the illustrated example has a plane circular shape, and a circular thin step portion 14a is formed inside the peripheral edge thereof. The circular thin-walled stepped portion 14a has an outer diameter D and a working diameter d of the lens 14.
A cross-sectional area portion having a smaller cross-sectional area than the minimum cross-sectional area portion of the gate portion 13 is formed between the two. A concave portion 14b that forms a minimum cross-sectional area portion in cooperation with the circular thin-walled step portion 14a is formed on the peripheral portion of the lens 14. Straight line 15 shown in FIG.
Is a minimum cross-sectional area portion, and this minimum cross-sectional area portion 15 is located between the outer diameter D of the lens 14 and the used diameter d.

FIG. 6 shows an ultrasonic vibrator (breaking separating device) 2 for breaking and separating the lens 14 from the above finished product 10.
0 shows an example. The ultrasonic vibrator 20 has a fixed table 21 on which the finished product 10 is placed. The fixed table 21 has a mounting plate 22 made of an elastic material such as rubber on the upper end surface thereof.
In No. 1, an escape hole 23 into which the downward extension sprue 11U of the finished product 10 is inserted is formed in the center thereof. Insert the downward extension sprue 11U of the finished product 10 into this escape hole 2
When it is inserted into 3, the runner 12 is placed in contact with the placing plate 22 and the sprue 11 extends in the vertical direction.

An ultrasonic vibrating horn 25 having a bottomed cylindrical shape is located on the fixed table 21. This ultrasonic vibration horn 25 has a sprue 11 of the finished product 10 at the center.
Has a sprue entry hole portion 24 for allowing the entry. The ultrasonic vibrating horn 25 is connected to an elevating mechanism 26 and an ultrasonic vibrating device 27, and ascends and descends on the fixed table 21 by the elevating mechanism 26, and ultrasonic vibration is applied by the ultrasonic vibrating device 27. The ultrasonic vibration control device 28 controls the amplitude and the like of the ultrasonic vibration generated by the ultrasonic vibration device 27. The center of the sprue entry hole portion 24 of the ultrasonic vibration horn 25 and the center of the escape hole 23 of the fixed table 21 coincide with each other. The lower end surface of the ultrasonic vibration horn 25 constitutes an annular contact surface 25t which is a flat surface orthogonal to the axis of the ultrasonic vibration horn 25.

In the ultrasonic vibrating device 20 having the above structure, the lens 14
In order to break and separate the ultrasonic wave by ultrasonic vibration, the finished product 10 is placed on the fixed table 21 in a state where the ultrasonic vibration horn 25 is raised by the elevating mechanism 26. At this time, position the downward extension sprue 11U at the center of the escape hole 23,
The runner 12 is brought into contact with the mounting plate 22. In this set state, the ultrasonic vibration horn 25 is lowered by the lifting mechanism 26, and the runner 12 is sandwiched between the contact surface 25t and the mounting plate 22. Then, the contact surface 25t has the sprue 1
The runners 12 come into contact with each other at positions equidistant from the center of 1.

Next, ultrasonic vibration is applied to the ultrasonic vibration horn 25 through the ultrasonic vibration device 27. Then, the entire molded product 10 in which the runner 12 is in contact with the contact surface 25t vibrates, and the vibration causes the lens 14 to move.
3 is broken and separated.

In this embodiment, focusing on the vibration frequency applied to the ultrasonic vibration horn 25 at this time and the natural frequency of the molded product 10, the ultrasonic vibration generator 20 is set in the frequency setting step.
And the natural frequency of the finished product 10 were made to substantially match, and the finished product whose natural frequency was set in this frequency setting step was set with the vibration frequency in the same frequency setting step. Ultrasonic vibration is applied by an ultrasonic vibrator.

FIG. 7 shows the transfer function of the molded product 10 of this embodiment. Ultrasonic vibrator 20 of this embodiment
The vibration frequency of is 15.15 KHz. Transfer function Z
Is Z at each frequency = output piece amplitude (amplitude of lens 14)
/ Indicates the input one-sided amplitude (one-sided amplitude of the contact surface 25t).
As the vibration output value and the vibration input value, arbitrary values such as amplitude, velocity, acceleration can be used as long as they are values related to vibration. In the example of FIG. 7, the finished product 10 is A, B,
It has four natural frequencies C and D, and its natural frequency D is 25 KH, which is higher than the vibration frequency of 19.15 KHz.
In the vicinity of z and near 19.15 KHz, Z≈1. In this way, even if the vibration frequency is greatly different from the natural frequency of the molded product 10, the lens 14
It is difficult to break and separate from the gate portion 13.

However, the natural frequency D of the molded product 10 is brought close to the vibration frequency of the ultrasonic vibrator 20 (arrow X in FIG. 7), or the vibration frequency of the ultrasonic vibrator 20 is completed. It is possible to approach the natural frequency of the product 10 (arrow Y in FIG. 7), and by bringing both frequencies close (resonating state), the vibration of the ultrasonic vibrating horn 25 is sufficiently passed from the gate portion 13 to the lens 14. And the lens 14 can be efficiently broken from the gate portion 13.

In order to change the natural frequency D of the finished product 10, the physical quantity such as the material and shape of the finished product 10 may be changed. When the molded product is the lens 14, the degree of freedom in selecting the material is low, but the frequency can be set (changed) by setting the shape of the sprue 11, the runner 12, or the gate portion 13. The shape and natural frequency can be calculated.

The vibration frequency of the ultrasonic vibrator 20 can be changed most simply by changing the shape of the ultrasonic vibration horn 25. Of course, the natural frequency of the molded product 10 and the vibration frequency of the ultrasonic vibration machine 20 may be set at the same time so that both frequencies match.

In the illustrated embodiment, the plurality of runners 12 is
Since the lens 14 is in contact with the contact surface 25t at an equal distance from the sprue 11, all of the lenses 14 are separated from the finished product 10 almost at the same time. Ultrasonic vibration device 2
Various conditions of ultrasonic vibration due to No. 7 are set by the ultrasonic vibration control device 28 so as to obtain the above actions.
The vibration by the ultrasonic vibration device 27 is preferably such that a timer gives a vibration characteristic sufficient for the lens 14 to be fractured and separated according to the property of the molded product 10 for a certain period of time. When the separation of the lens 14 from the molded product 10 is completed, the vibration by the ultrasonic vibration device 27 is stopped, and the ultrasonic vibration horn 25 is raised by the elevating mechanism 26 to prepare for the next work.

Next, a plurality of natural frequencies of the finished product 10 and vibration modes of the respective natural frequencies will be described.

Recent plastic lenses are required to have both high optical performance (accuracy) and miniaturization. In order to satisfy high precision, the gate diameter needs to be relatively large compared to the lens size due to the molding conditions (pressure, fluidity of material, etc.). Further, a commercially available ultrasonic vibrator (for example, an ultrasonic welder manufactured by Seiden Co., Ltd.) has an amplitude of about 20 μm. When this ultrasonic vibrator is used as a gate cut for a plastic lens, the above-mentioned one-sided amplitude is simply applied to the molded product 10. The gate portion 13 of the molded product 10 has a cross-sectional area that monotonically decreases toward the lens 14 in order to facilitate breakage separation of the lens 14, and a minimum cross-sectional area portion is formed at the boundary with the lens 14. It is usually provided.

Here, the mass of the plastic lens itself; m (kg) (3.7 × 10 ⁻⁷ kg as a specific example) Excitation frequency; f (KHz) (19.15 KHz) Ultrasonic wave amplitude; a ( m) (20 μm) The distance from the center of the plastic lens to the connection plane with the gate portion; r (mm) (3 mm) Gate cross-sectional shape on the connection plane; b × h (mm ² ) square (1. 5 × 0.8 mm), the maximum stress generated is calculated as follows.

The maximum bending moment M applied to the gate portion and the lens outer peripheral portion is M = rma (2πf) ² (kgfm
m), and the section modulus (= I) of the gate portion is I = bh
Is a ^3/12 (mm ^4). Therefore, the maximum stress (= σma
x) is σmax = (M / I) × (h / 2) (kgf / mm ² ), and is about 2 (kgf / mm ² ) in a specific example.

When an Abel material (manufactured by Mitsui Chemicals, Inc.), which is often used recently as a plastic lens material, is used, the bending strength is 10.2 (kgf / mm ² ), and it does not break under the above stress. However, when a repeated stress due to ultrasonic vibration is applied, a fatigue fracture phenomenon occurs, leading to fracture. Fatigue fracture refers to a phenomenon such as the SN curve illustrated in FIG. 8 that even if the stress is lower than the bending strength, the stress is repeated to cause fracture. As can be seen from FIG. 8, when the stress is low, fracture does not occur unless the number of repetitions is exponentially increased. Since plastic has a very low melting point (about 140 ° C for Abel material), depending on the number of repetitions, melting occurs due to temperature rise before fatigue failure, and the melted part becomes convex and remains. Occurs.

In the example shown in FIG. 7, the molded product 10 is
It has four natural frequencies A, B, C, and D, and its natural frequency D is around 25 KHz, which is higher than the vibration frequency of 19.15 KHz, and Z near 19.15 KHz.
≈1. The bending stress generated as a result of the applied vibration is also much lower than the bending strength of the material. in this way,
If the vibration frequency and the natural frequency of the molded product 10 are significantly different from each other, there is a possibility that the temperature rises due to the vibration and melting (melting) occurs before the breakage occurs. FIG. 4 is a schematic diagram showing a separated shape of the lens 14 from the gate portion 13 when melting occurs. If the melting occurs, the broken portion between the lens 14 and the gate portion 13 projects beyond the outer diameter D of the lens 14 as shown in the figure, which becomes an obstacle when the lens 14 is incorporated into the lens frame.

On the other hand, each natural frequency of the molded product 10 has its own vibration mode. The vibration modes of the four natural frequencies A, B, C, and D of the transfer function shown in FIG. 7 are as follows. Vibration modes A, B, C and D are schematically shown in FIG.

In the example of FIG. 7, the vibration mode D of the natural frequency closest to the vibration frequency of the ultrasonic vibration machine 20 is the runner shaft 1
This is a vertical vibration with 2a as the center of rotation. Therefore, lens 1
A vertical load is generated at the center of gravity of No. 4, a maximum stress is generated on the tangent line between the gate portion 13 and the upper and lower surfaces of the lens 14, and a crack is generated from this maximum stress position. Even if a crack occurs, the maximum stress position is at the connecting plane 14 between the gate portion 13 and the lens 14.
Since it passes through the inside of c, the gate portion 13 does not remain in a convex shape beyond the outer peripheral surface D (see FIG. 3).

The vibration mode A is vibration of the lens 14 in the lateral direction (direction orthogonal to the optical axis), and since the vibration is applied in the vertical direction (optical axis direction), it is inefficient in fracture separation.

In the vibration mode B, the lens 14 and the gate unit 1
3 shows vertical deformation with the tangent line of 3 as a node (fixed point), which is the vibration mode most advantageous for breaking.

In the vibration mode C, the shaft 13a of the gate unit 13 is
Is the torsional vibration of the lens 14 with the center of rotation as. The maximum stress portion generated by this torsional vibration is generated at the four corners of the connecting portion having a rectangular cross section between the gate portion 13 and the lens 14 because stress concentration and the like also affect. Therefore, although cracks at break occur from the points at these four corners, since cracks occur from the points, it is unstable how the crack progresses, and the gate portion 13 is also related to the stress direction and the like. There is a possibility that it will remain convex outside the outer circumference of the lens 14 (FIG. 5).
reference).

As described above, from the gate portion 13 to the lens 1
Vibration mode B is most preferable for breaking and separating No. 4.
However, since the vibration mode B has a low frequency of about 5 (KHz), it is necessary to give a large amplitude. Therefore, when it is difficult to give a large amplitude, the advantage of the vibration mode B is ensured by using it together with another vibration mode, for example, the vibration mode D (vibrating at both frequencies),
The advantage of the vibration mode D can be obtained at the same time. As a specific method of using the two vibration modes together, for example, the ultrasonic vibration horn 25 is vibrated in the first vibration mode (for example, the vibration mode D), and the entire ultrasonic vibrator 20 is set in the second vibration mode (for example, the vibration mode). It is sufficient to vibrate in vibration mode B).

Further, in the example of FIG. 7, the natural frequency D is in a relation of approximately an integer multiple of the natural frequency B. In the illustrated embodiment, the ultrasonic vibration horn 25 is a vibration generated by the ultrasonic vibration device 27. Is resonated by adjusting the length of the ultrasonic vibration horn 25 in the vertical direction, thereby expanding the vibration of the contact surface 25t. In such a relationship, the ultrasonic vibration horn 25
The ultrasonic vibrating device 27 for vibrating is vibrated by a combined signal of both drive pulses of two natural frequencies, or one ultrasonic vibrating horn 25 is vibrated by two ultrasonic vibrating devices of different excitation frequencies. By driving, two vibration modes can be given.

Depending on the value of the transfer function Z, the generated stress may exceed the bending strength. For example, when a crack is suddenly generated from one side and fractured (impact fracture), how the crack progresses to the other side is unstable. In such a case, it is possible to control the traveling direction of the crack by controlling the amplitude of the ultrasonic vibrator. By controlling the amount of amplitude, it is possible to prevent the accuracy from deteriorating due to thermal deformation of the lens due to temperature rise.

The finished product 10 of the above embodiment is an example, and as shown in FIG. 10, the number of the runners 12 extending from the sprue 11 in the radial direction and the molded product 30 formed at the tip of the runner 12 are shown. The number and the shape do not matter. If the molded product has a molded product 14 connected to the tip of the runner 12 via the gate portion 13, the molded product exists at different distances from the center of the sprue 11 (that is, concentric circles with different diameters). The present invention can of course be applied to the above-mentioned modes) and others.

In the above embodiment, the present invention is applied to the molding of the plastic lens 14, but the present invention can also be applied to other resin molded products or metal molded products. Further, the transfer function of FIG. 7 shows an example, and the transfer function itself varies depending on the shape of the finished product.

[0042]

According to the present invention, it is possible to provide vibration conditions suitable for breaking and separating a molded product from a molded product by ultrasonic vibration without using a blade.

[Brief description of drawings]

1A and 1B are a plan view and a right side view of a finished product having a multi-cavity plastic lens, which is illustrated as a finished product.

2A and 2B are an enlarged plan view and a front view of a main part of FIG.

FIG. 3 is a plan view showing a shape example (non-defective product) of a plastic lens after gate cutting.

FIG. 4 is a plan view showing another shape example (defective product) of the plastic lens after gate cutting.

FIG. 5 is a plan view showing another shape example (defective product) of the plastic lens after gate cutting.

6 is a front view, partly in section, showing an example of a device (vibrating device) for separating a plastic lens from the molded product of FIG. 1. FIG.

FIG. 7 is a graph showing a specific example of a transfer function of a molded product.

FIG. 8 is an SN curve diagram showing an example of flexural strength and the number of repeated vibrations leading to breakage.

9 (A), (B), (C) and (D) are shown in FIG.
It is a figure which shows the vibration mode of the shaping | molding completion product shown in FIG.

FIG. 10 is a plan view showing an example of another finished product to which the present invention can be applied.

[Explanation of symbols]

10 Molded products 11 sprues 12 runners 13 Gate 14 Plastic lenses (plastic molded products) 14c Connection plane 20 Ultrasonic shaker 21 fixed table 22 Placement plate 23 escape hole 24 Sprue entry hole 25 ultrasonic vibrating horn 25t contact surface 26 Lifting mechanism 27 Ultrasonic vibration device 28 Ultrasonic vibration control device

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Susumu Takatsuka             2-36 Maeno-cho, Itabashi-ku, Tokyo Asahikou             Gaku Kogyo Co., Ltd. F-term (reference) 4F202 AH74 CA11 CB01 CK03 CK06                       CK11 CK89 CM90 CS10                 4F206 AH74 JA07 JL02 JM06 JN41                       JQ81 JW23 JW50

Claims (7)

[Claims] 1. A method of subjecting a molded product having a molded product connected to the tip of a runner via a gate part to ultrasonically vibrated by an ultrasonic vibrator to separate the molded product from the gate part by fracture. And a frequency setting step for substantially matching the vibration frequency of the ultrasonic vibrator and the natural frequency of the finished product; and the finished product having the natural frequency set in the frequency setting step. And a vibration applying step of applying ultrasonic vibration by an ultrasonic vibration machine whose vibration frequency is set in the same frequency setting step; 2. The fracture separation method for a molded product according to claim 1, wherein in the frequency setting step, the natural frequency of the molded product is substantially equal to the vibration frequency of the ultrasonic vibrator. A method for separating and breaking a molded product by setting a physical quantity such as the shape of the molded product. 3. The fracture separating method for a molded product according to claim 1, wherein in the frequency setting step, the natural frequency of the ultrasonic vibration machine is substantially equal to the natural frequency of the molded product. A method for breaking and separating a molded product, wherein a physical quantity such as a shape of an ultrasonic vibration horn of the ultrasonic vibrator is set. 4. The method for breaking and separating a molded product according to claim 1, wherein in the frequency setting step, the natural frequency of the molded product is a plurality of natural vibrations of the molded product. A method for breaking and separating a molded product, wherein a natural frequency with a vibration mode suitable for breaking and separating the molded product from the gate portion is selected from among the numbers. 5. The method for breaking and separating a molded product according to claim 4, wherein in the frequency applying step, the molded product is provided with a composite vibration of two or more natural frequencies of a plurality of natural frequencies of the molded product. Break separation method. 6. The method for breaking and separating a molded product according to claim 1, wherein the molded product is
A molded product that includes a sprue in the center, a plurality of runners extending in a radial direction from the sprue, and a molded product that is molded at the tip of the runner at positions equidistant from the sprue through gate portions, respectively. Fracture separation method. 7. The fracture separating method for a molded product according to claim 6, wherein the ultrasonic vibration machine places the molded product with the runner in contact therewith; It is possible to move away,
A cylindrical ultrasonic vibrating horn having a hole for allowing the sprue of the above-mentioned molded product to enter at the center; A method for breaking and separating a molded product, comprising: a forward / backward mechanism for sandwiching the plurality of runners between the table and the table; and an ultrasonic vibration device for applying ultrasonic vibration to the ultrasonic vibration horn.