JPH0416259B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention is a precision method for manufacturing small precision cast products such as dental dentures, restorations, and decorative items by melting various alloys using heating means such as high-frequency induction heating and electric resistance heating. This article relates to a casting method and its equipment.

Precision casting methods can be roughly classified by function: (a) a method of heating and melting the casting material, (b) a method of determining the timing of pouring molten metal (hereinafter referred to as casting timing), and (c) a method of applying casting pressure. Methods (a) and (c) above are conventionally generally stable and have no problems, but method (b) has quite a few problems, and is also an important element in the casting process that influences the quality of the product. In other words, the appropriate temperature for casting molten metal (hereinafter referred to as casting temperature)
is generally a temperature slightly higher than the melting point of the material, and overheating beyond this will not only cause the crystal grains to coarsen and impurities to enter the grain boundaries, worsening mechanical properties, but also cause bubbles and bubbles in the cast product. This results in defective products such as rough skin. On the other hand, if the temperature is lower than the appropriate temperature, there will be insufficient melting, resulting in name lare (insufficient pouring) and the largest defect in the cast product. Conventionally, it is common for an expert to visually judge whether or not the casting temperature and casting timing are appropriate, but it is extremely difficult to determine the appropriate timing due to slight changes in color tone and shape during melting, and requires a high level of skill. In addition to requiring skill, even those skilled in the art may make mistakes in judgment, which is a great loss in dental applications where product yields are low and expensive materials are used. Therefore, one of the methods that have been tried in the past to improve the yield of this visual method is to measure the temperature of molten metal using a radiation thermometer, or to set the above casting temperature as a target value, and to set this as the target value and to combine this with radiation temperature. This method compares the detected value with the meter and automatically controls the heating source according to the deviation. However, since the above-mentioned radiation thermometer measures the surface temperature of the material by the amount of infrared rays emitted when the material melts, it is not only troublesome to determine the emissivity of various materials at different temperatures, but also the melting chamber Clouding of the glass in the viewing window causes measurement errors, and if there is little casting material, the image will not be focused on the entire surface of the radiation thermometer's heat receiving plate, making it impossible to measure temperature accurately. It has the disadvantage that temperature measurement is difficult and therefore the casting timing is out of order. Another method is to control melting time to manage casting timing. However, in this method, it is necessary to always maintain a constant melting strength, or in other words, a constant output of heating energy per hour, and furthermore, everything such as the casting amount and the position of the material within the crucible must also be constant. Moreover, this method ignores the melting process, so it has the disadvantage that its range of applications is limited.

As mentioned above, the authors devised this method in the current situation where it is practically difficult to optimize the casting timing.
The patent application for ``Precision Casting Apparatus'' filed on April 25, 1980 is intended to accurately determine casting timing without measuring temperature at all. In other words, based on the metallurgical theorem that metallic materials always undergo shape changes when melted, and that spots (sunspots) and skin tears occur on their surfaces, we use recently developed CCD image sensors to detect the above shape changes. The present invention is configured to detect the contour image signal as a contour image signal and appropriately determine the casting timing, which almost eliminates the current problems and drawbacks in precision casting. However, the above device has the disadvantage that it cannot determine the proper casting timing only in the following cases. In other words, when the casting material is cylindrical and is housed in a concentric crucible, if the outer diameter of the material approximates the inner diameter of the crucible,
The problem is that no change in the contour image captured by the CCD can be detected when the material melts.

This invention was made in view of the above-mentioned current situation, and it eliminates the drawbacks of the "precision casting device" that the authors previously applied for, and confirms the optimal casting timing regardless of the shape of the casting material. It was designed to be poured with hot water. In other words, when heating a casting material in a crucible, it is not possible to uniformly heat the entire material using any heating means currently in use, and therefore, as the material heats up, the material A temperature distribution occurs within itself, and the brightness emitted from each part is measured using a CCD image.
By detecting it with a sensor, the temperature distribution of the material being heated is displayed moment by moment as a brightness distribution image on the display, and the optimal casting timing is determined based on the point when the top of the brightness distribution image forms a straight line. The present invention aims to provide a method for casting high-quality cast products with a high yield by determining the molten metal and pouring it into a mold, and a compact, inexpensive device with a simple construction and high efficiency using this method. .

Embodiments of a casting apparatus using the precision casting method of the present invention will be described below with reference to the drawings. Fig. 1 is an external perspective view of a high-frequency melting and pressure precision casting machine as an example. The bottom outer surface part 3 of the heating chamber (shown in Figure 2) 2 shown in Figure 2 and the lower chamber part 5 consisting of a vertically movable casing are exposed to the outside, and other mechanical parts are exposed to the outside.
This is a partially modified device in which the lower housings 6 and 7 are also enclosed. In other words, the observation window for observing the heating chamber viewing window (9 shown in FIG. 2) from the outside, which was provided on the operation panel 8 on the front side of the upper case 6, has been eliminated, and an image display, which is one of the main parts of the present invention, has been implemented. 10 was established. Therefore, the manual operation button group 11 on the operation panel 8 and the indicator light group 12 interlocked with them
The device is still the same as described above, and the order of manual operations is the same, but the operator does not have to visually observe the melting situation inside the heating chamber through the observation window, but instead displays the image on the video display 10 on the operation panel, that is, the inside of the crucible. The casting timing was decided based on the brightness distribution image of the material. Turning to FIG. 2, a sectional view shows the heating chamber 2 and the convex mold 14 in the upper housing 6, and the mold holder 15 that presses the mold 14 against the bottom outer surface 3 of the heating chamber. Explain and also describe the casting material M in the crucible 17.
The configuration of the main part of the present invention, which images the melting state of the liquid on the display 10, will be explained. The convex mold 14 has a crucible 17 in its upper protrusion, a precision mold cavity 18 formed by the lost wax method, and a runner 19, which are molded into one body. 2, and the convex mold lower base 21 is supported on the mold holder 15 via an asbestos ring 22. This pedestal 15 is pushed up from below with a predetermined pressure by a pneumatic cylinder piston 23 or a compression spring (not shown) on the central axis of the lower chamber 5 shown in FIG. It is pressed into contact with the bottom outer surface portion 3 of the heating chamber via a packing 24. A high frequency induction heating coil 25 is installed around the fireproof cylindrical body 20.
is wound around the heating chamber 2, and is further provided with a viewing window 9 made of a transparent refractory material to seal the upper end of the heating chamber 2, an exhaust pipe 27 for reducing the pressure inside the heating chamber ² , and a An argon gas introduction pipe 28 is provided. The above configuration is that of a conventional device, and the essential part of the present invention is a configuration for displaying the luminance distribution of the casting material M in the crucible 17 as an image. For example, a condenser lens 30 with a magnification of 10 times and a filter 31 are provided at a predetermined position, for example, above the above-mentioned viewing window 9. The condenser lens 30 is not limited to a single convex lens, but may be a compound lens. In this way, the heating of the material M progresses, and the emitted radiation L is emitted from a one-dimensional lens placed at the imaging position of the lens 30.
The light is incident on the photosensitive section 33 of the CCD image sensor 32. This photosensitive section 33 has a width of about 30 μm, for example.
Approximately 2,600 photosensitive pixels are arranged in a row within a length of approximately 30 mm, and the signal charges that are photoelectrically converted and accumulated are converted here.
It is transferred using an analog shift register within the CCD and outputs a time-series analog voltage signal _D1 . This signal D ₁ indicates the luminance distribution on the center line of the material M, and this is converted into a luminance distribution video signal D ₂ by the video signal generation circuit 34, and the video display 10
is input. The image display 10 has a horizontal axis as the center line of the material M, and a vertical axis as a planar image of brightness per unit area, that is, luminance distribution images I and B at each position on the center line. Needless to say, this brightness distribution image changes from moment to moment as the heating of the material M progresses. This will be explained with reference to FIGS. 3 and 4. The figures show changes in the actual brightness distribution image when a casting material is melted using the apparatus described in this example. Each figure A shows the shape of the material obtained by visual observation, and the distribution diagram in figure B shows the change in the actual luminance distribution image. This is an additional note because it is intended for use in the following, and is not an image on the display 10. The horizontal axis P in Figure B is the position (distance (mm) from one end of the crucible inner wall) of the material M in the crucible in the X direction (see Figure A), for example.
, d corresponds to the inner diameter of the crucible 17, and the vertical axis B indicates the brightness (ead/m ² ) of the material. However, as described below, the distribution images I and B of ~ are sequentially imaged in time series, and Figure B shows them all together. After starting heating in Figure 3B
At 60 seconds, the distribution becomes as shown in Figure A, where the brightness at the outer periphery is higher than that at the inside. (High-brightness areas are indicated by diagonal lines) When the high-brightness areas increase several seconds later, the distribution rises in a similar manner as shown below. Heating progresses further,
When , the outer shape changes to a circular shape, but the brightness at the center is still low. When the heating time reaches 70 seconds, only a spot-like low-intensity part remains in the center, and the distribution image becomes almost flat. When the entire surface becomes the same brightness at 72 seconds, a straight line with no unevenness is formed like a distribution image. Since this point indicates that the material M has reached the casting temperature, the appropriate value for the casting timing is 72+2=
It is 74 seconds. The point at which the top of the distribution image becomes straight in this way is determined depending on the material. However, if the delay time beyond this point is long, unevenness will occur again in the distribution image, resulting in the above-mentioned overheating. Next, move to FIG. 4A and B. In this case, since the alloy material has a shot shape as shown in Figure A, many irregular peaks occur on the distribution line during melting, and the shape is irregular, but it is on the verge of complete melting. It can be seen in the distribution image that the crucible had a circular inner diameter, just like the shape. As the heating progresses further, the top of the distribution image forms a straight line, as in the case of FIG. This point indicates that the temperature of the material has reached the casting temperature. By determining the casting timing based on this point, there will be no insufficient melting, and by setting the delay time arbitrarily, there will be no overheating. Optimal casting timing can be established. The above CCD image sensor has excellent sensitivity over wavelengths from 400nm to 1000nm.
Even if the glass of the heating chamber viewing window 9 becomes cloudy due to metal vapor or gas generated during melting, any spectrum of the infrared range emitted from the material M will pass through it, and the brightness distribution will be accurately imaged. Therefore, the above-mentioned casting timing will not be disrupted.

Next, according to FIG. 5, the self-scanning image detector 3
One example device in which 2 is a two-dimensional detector 40 will be described. Figure 5A shows material M, for example,
The hexagonal ingot shown in the figure is taken as a two-dimensional ingot.
When capturing an image with the CCD image sensor 40,
The two-dimensional sensor 40 normally includes self-scanning circuits in the horizontal (X-axis) direction and the vertical (Y-axis) direction, but this figure shows a state in which the vertical scanning circuit is replaced with an output averaging circuit 41. By this, among the outputs of, for example, Y ₁ , Y ₂ , Yn in the Y direction, the luminance signals above a certain level are averaged and output as the luminance signal Dx ₁ , and the outputs of Y ₁₁ to _{Yn 1} are also averaged. Among them, those above a certain level are averaged,
Output as Dx ₂ . In this way, the change up to Dxn can be imaged on the display as a luminance distribution image on the X-axis of the material M, as shown in FIG. 3B, as shown in FIG. Although this two-dimensional sensor 40 is more expensive than the one-dimensional sensor 32, it is not necessary to align the direction of the material and the sensor during the melting process of irregularly shaped materials such as the shot shape explained in FIG. Good work efficiency. However, at the time of complete melting, that is, when the top of the distribution image forms a straight line, there is no particular difference from the one-dimensional sensor.

Although the embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to the illustrations and descriptions. For example, this invention is not limited to high-frequency melting and pressure casting, but can be applied to any method or device that can image the melting state of the material in the crucible using a CCD image sensor, such as an electric resistance type or a heating element crucible heating type. can also be applied. Further, the mounting position of the CCD image sensor 32 is not limited to the radiation optical axis of the material, but may be mounted at any arbitrary position using a reflecting mirror or the like. The video display is usually a CRT for display.
However, it may be an oscilloscope or other display, and it does not necessarily have to be incorporated into the operation panel of the casting machine. Furthermore, the method using the two-dimensional CCD is not limited to the above method, and there are various other methods that can be considered.

Since this invention is constructed as described above, it becomes the decisive factor in determining the optimal casting timing, which was a major concern in conventional precision casting, dramatically improves the yield of cast products, and improves the invention previously filed by the authors. This eliminates the drawbacks of the device. In other words, instead of using a radiation thermometer that is expensive, requires calibration and correction, and is difficult to measure temperature accurately, it is small and inexpensive, and is less affected by gases and metal vapors in the melting chamber, and can be used to measure the melting state of the material. The optimal casting timing for each type of casting material can be easily and accurately determined using a CCD that accurately captures a luminance distribution image and a video display that displays the distribution image, resulting in high-quality castings. The present invention has provided a precision casting method that allows for efficient production of metals, as well as a convenient device that has a simple structure, is compact, and is inexpensive.

[Brief explanation of drawings]

FIG. 1 is an external perspective view of a high-frequency melting and pressure precision casting apparatus as an embodiment of the present invention, FIG. 2 is a cross-sectional view of the melting chamber and a block diagram of the brightness distribution imaging section of the above-mentioned apparatus, and FIG. 3A is a block diagram of the above-mentioned apparatus. Fig. 4A shows the shape and brightness change of the ingot material in the melting process using the above device, Figure B is a change diagram of the brightness distribution image of the ingot material on the display screen, and Figure 4A shows the shape and brightness of the shot material in the melting process using the above device. Figure B is a transition diagram of the luminance distribution image of the above-mentioned shot material on the display screen, and Figure 5A is a diagram illustrating the use of a two-dimensional self-scanning image detector as another embodiment of the present invention. The principle diagram, Figure B, is a brightness distribution diagram based on Figure A above. 2... Melting chamber, 8... Casting operation panel, 10... Video display, 11... Manual operation button group, 12...
Casting process display lamp group, 14... Mold, M... Casting material, 17... Crucible, 18... Precision mold cavity, 19... Runway, 25... High frequency induction coil as heating means, 30... Condenser lens, 32,4
0... Self-scanning image detector (32 is one-dimensional, 4
0 is a two-dimensional detector), _D1 ...Brightness signal, _D2 ...Brightness distribution video signal, I/B...Brightness distribution image.

Claims (1)

[Scope of Claims] 1. A small amount of casting material contained in a crucible is melted by heating means, and the progress of melting is detected as a brightness signal by a self-scanning image detector through a lens, and the A precision casting method characterized in that the brightness distribution of the material is displayed on a display, and when the top of this distribution image forms a straight line, the timing of pouring the metal into the mold is determined based on this as a reference. 2. heating means for melting the casting material in the crucible;
a condensing lens that forms an image of the emitted light of the material; a self-scanning image detector that is provided at the imaging position of the lens and converts the incident light image into a brightness signal and outputs the image; and an output signal of the detector; A precision casting device characterized by being equipped with a video display device that displays an image as a luminance distribution image. 3. The precision casting apparatus according to claim 2, wherein the heating means is a high frequency induction heating device. 4. The precision casting apparatus according to claim 2 or 3, wherein the self-scanning image detector is a one-dimensional detector. 5. The precision casting apparatus according to claim 2 or 3, wherein the self-scanning image detector is a two-dimensional detector.