Molding and Gauging System

This invention relates to a molding and gauging system that is adapted to sense misalignment and warping of die elements, failure of die elements to close properly, and other irregularities in operation, and, more particularly, to a molding and gauging system for die casting and plastic molding operations where extreme forces are exerted on molding dies to close the dies and maintain them closed as they are filled with molten aluminum, zinc or other such metals or plastics under extremely high pressures.

In recent years, the use of die casting and plastic molding has been extended to the manufacture of larger and larger articles and has been extended to the manufacture of articles with closer and closer tolerances.

Such large automotive parts as internal combustion engine blocks and the housings of automatic transmissions are now commonly manufactured with die casting as the first step in formation of the part. Such parts have extensive and complex surfaces with close tolerances; and die casting now permits their formation, eliminating costly machining operations and saving metal. Die casting of such large parts as engine blocks and transmission housings requires massive dies. Extreme pressures are exerted on the liquid metal during the die casting operation, and large amounts of heat are extracted from the molten metals as they change state. The maintenance of dimensional tolerances within limits making such operations economically attractive and the strength to withstand the stresses resulting from high pressures and forces require massive dies. The molds for die casting such large automotive parts as automatic transmission housings, for example, are frequently seven to eight feet (2.1-2.5 meters) tall, seven to eight feet (2.1-2.5 meters) wide, and six to seven feet (1.8-2.1 meters) thick when closed and must be manufactured from high-grade, high-tensile strength steel.

Such molds frequently include one stationary element, one movable element operated by the die-casting machine to close the mold, and several slideable elements, referred to as "slides", that move transversely of the direction of movement of the die-casting machine to provide the mold cavity with intricate and re-entrant surface configurations. The mold slides which slide transversely of the direction of movement of the die-casting machine are generally moved by hydraulic cylinders to their proper position. As the mold is closed by the die-casting machine, surfaces on the slides are engaged by the other mold elements or parts in such a manner that when the mold is closed, interengaging surfaces, such as ramps, on the slides and the other mold parts are clamped and held together by the die-casting machine to prevent the high pressure of the injected, molded metal from moving the sliding mold elements or parts.

A large die-cast part, such as an aluminum housing for an automatic transmission, can be fifteen to twenty inches (0.38-0.5 meters) in diameter and have a length of up to two feet (0.6 meters); and the surface area of the mold cavity exposed to the pressure imposed on the liquid molten metal by the die-casting system can equal several hundred square inches (or over one thousand square centimeters).

In die-casting operations, high pressure is needed to fill quickly the intricate cavities of die-casting molds and avoid solidification of the molten metal as it is cooled by the die. High pressure is also needed to prevent the formation of voids in thick walls formed in the molded part. When the cross section of a mold cavity is designed to provide a relatively thick section of, for example, three-eights of an inch (about one centimeter) or thicker, the molten metal at the surface of the mold cools significantly before the interior and, because of metal shrinkage on cooling, can leave voids within a thick cross section. Thus, in large parts, pressures up to 20,000 psi. (1406 kg/cm.sup.2) are exerted on the molten metal to fill the die quickly and prevent the formation of voids within the thick sections, and the pressure of the molten metal can exert millions of pounds (millions of kilograms) of force on the surfaces of the mold cavity. To prevent the millions of pounds (millions of kilograms) of force exerted by the molten metal against the die surfaces from moving the die surfaces outwardly from their intended position, the die-casting machine is operated to preload the mold prior to the shot of molten metal; that is, by the use of ramp-engaging surfaces on the movable mold parts, the die-casting machine locks the movable parts of the die-casting mold together with the imposition of millions of pounds (millions of kilograms) of force on the ramp-engaging surfaces to hold the movable die-casting elements fixed in their designed, closed position. The force imposed, for example, by a 350-ton (317,000 kilogram), die-casting machine, which is not among the largest of such machines, can reach seven million pounds (3,170,000 kilograms) and this force in larger machines, such as 3,500-ton machines can reach 70,000,000 pounds (31,700,000 kilograms). Such high forces, if imposed on misaligned or jammed partially closed dies, can deform and break mold surfaces and the mold-operating surfaces of the die-casting machine.

Die-casting molds for such large parts must, therefore, be designed to withstand such extreme forces and to use the extreme forces imposed by the die-casting machine to prevent movement of the mold slides outwardly as the molten, die-casting metal is injected into the mold under pressures of several tons per square inch (several hundred kilograms per square centimeter).

Die-casting has become desirable as a manufacturing method for parts such as automobile engine blocks and transmission housings because it can produce intricately shaped parts to close tolerances. Thus, die casting can provide such parts with operating strength and intricately shaped surfaces without extensive and expensive machining operations. Such parts are, however, long and have wall thicknesses designed to take advantage of the economy of die-casting operations. Misalignment of the mold parts, due, for example, to warping of the mold, misalignment of the mold on the molding machine, or non-parallelism in the molding machine platen surfaces or their direction of the movement, can reduce wall thicknesses and distort part surface dimensions to unacceptable limits and result in a substantial waste of die-cast parts. Extensive time is required to inspect such complexly shaped parts completely, and failure to detect poorly cast parts before machining can result in further waste.

Furthermore, as indicated above, if the movable mold parts, including the transversely moving mold slides, are not properly aligned as the mold elements are closed to form the cavity, and if the die-casting machine imposes its millions of pounds (millions of kilograms) of force on misaligned mold parts, the force imposed by the die-casting machine may break the mold or parts of the molding machine which operate the mold. Such misalignments can result from undetected trapped flash or dies that become worn through use or operation under high temperatures and stresses. Aluminum has a high latent heat of fusion, reported to be 76.8 gram calories per gram; and a fifty-six pound (over 25-kilogram) aluminum casting, which is typical of aluminum engine blocks and automatic transmission housings, requires the dissipation in the mold of over 7,700 btus (about 2000 kilogram-calories) every minute or two. Although such large die-casting molds are generally cooled by water forced through cooling passages drilled within the mold elements, the large die-casting molds frequently rise in temperature to 300.degree. to 600.degree. F. (150.degree. to 315.degree. C.) and operate at such elevated temperatures. Such high temperatures, of course, prevent human operators from working too close to the mold surfaces because of the danger of burns and other injuries.

Misalignment of die-casting mold elements, failure of the die-casting machine to provide parallel platen surfaces and movement perpendicular to the platen surfaces, and wear of the die elements all cause similar problems in conducting plastic molding and die-casting operations to manufacture smaller, high-precision parts, notwithstanding the substantially reduced forces presented by such operations. Where plastic molding and die-casting operations are used to manufacture small precision parts having intricate surfaces with close tolerances, misalignment of the mold surfaces and failure of the mold surfaces to close correctly will result in parts that fall outside the close dimensional design tolerances and must be rejected.

This invention is a molding and gauging system that is adapted to sense misalignment and warping of die elements, failure of the die elements to close properly, and other such irregularities in operation before forces are imposed upon the molds by the molding machine and before molding materials are injected into the mold cavity, thus protecting molds and molding machine parts from destructively high forces and the manufacture of reject parts. In addition, the invention is adapted to sense movement of die elements resulting from filling the cavity, distortion from unequal heating of the die elements, the failure of the die elements to open properly, and other such departures from intended operation. In a preferred embodiment, the system of this invention, can provide an alarm to the operator in the event of such malfunctions, automatically interrupt operations to prevent machine breakage and manufacture of rejects, and provide a continuous record of molding operations to permit the verification of correctly manufactured parts and the identification of parts that may be incorrectly manufactured.

This invention includes a molding system, including a mold and a molding machine, that has been adapted to monitor the position of first and second mold surfaces that move with respect to each other and form a mold cavity. The invention is preferably incorporated into the mold although it may be incorporated into the molding machine. The system includes a source of gas, preferably air, under pressure, means on a first molding system surface to direct a flow of pressurized gas from the first molding system surface, and a monitoring means to monitor the flowing gas remote from the first molding system surface to indicate the spacing between the first molding system surface and a second molding system surface as the first and second molding system surfaces move with respect to each other or when there is no relative motion. The monitoring means can indicate the spacing between the first and second molding system surfaces directly and in more sophisticated embodiments can provide one or more outputs useful to automatically signal when the first and second molding system surfaces are not properly spaced and to control operations to prevent the mold from being damaged or reject parts from being formed.

A mold using this invention includes at least a pair of elements or parts with surfaces that move with respect to each other in forming a mold cavity. The first element of such a mold has a first surface with a cavity-forming portion and a portion adapted to adjoin the second mold element. The second element of such a mold has a second surface with a cavity-forming portion and a portion adapted to adjoin the first mold element. The first and second elements are adapted to be moved together to define a closed mold cavity. In the invention, means, located at the first mold element surface portion adapted to adjoin the second mold element, directs a flow of gas at the adjacent portion of the second mold element. Such means preferably comprises an orifice of known area and a passageway leading from such orifice and adapted to be connected to a source of gas under pressure. In practical and preferred systems, the passageway is preferably provided in the first mold element; and the passageway leads from a separate orifice-forming element to a mold element surface conveniently located for connection to other parts of the system, although the orifice-forming element or other air-directing means may be located separately on the platens of the die-casting machine or other such surfaces that move the same distance as the die-casting mold surfaces being monitored. In preferred systems, the monitoring means includes a second orifice in the passageway leading to the first orifice, and a pressure-sensitive output device connected to sense the pressure in the passageway between the first and second orifices. Such pressure-sensitive devices can be a direct reading pressure gauge or a transducer to convert pressure in the passageway between the first and second orifices into an electrical signal as set forth below.

Preferred systems of the invention further include means connected with the transducer to interpret the electrical signal and produce outputs indicative of the spacing between the first and second molding system surfaces. Such means preferably comprises a microprocessor, connected with the transducer, including a central processing unit and a random access memory, and means to relate the output of the transducer to the spacing between the first and second molding system surfaces and to store indicia of the spacing in the random access memory of the microprocessor. The microprocessor in such systems has an operating program to compare the transducer output with the stored indicia in its random access memory and calculate the spacing between the first and second molding system surfaces and produce an output indicative of the spacing. A digital computer can be used to calibrate the system and relate the output of the transducer to the spacing between the first and second molding system surfaces. Such a digital computer can be provided with a calibration program to sample the output of the transducer a specified number of times in the specified time space and to generate an indicia of the spacing between the first and second molding system surfaces based upon the calculated mean of the transducer output and to store the indicia in the random access memory of the microprocessor for use in the operating system.

In more extensive systems of the invention, a die-casting system, for example, can include molds having a stationary member or element, and movable mold members or elements, including a plurality of movable die elements or "slides" that are adapted to move transversely of the direction of the movement of the movable die member by the die-casting machine. Such systems can be provided with a plurality of air-directing outlets. The air-directing outlets can be located at a stationary surface of the stationary die member or at adjoining surfaces of movable mold elements or slides, and the air-directing outlets can determine the spacings and positions of the surfaces of the plurality of die elements with respect to one another.

Such more extensive systems can include a plurality of air-directing outlets directed to indicate, for example, the spacing between one die element and a plurality of positions on another movable die element and detect a lack of parallelism between the two adjacent die elements. In such systems, a source of gas under pressure, preferably "factory air" after filtering and drying, is connected to a manifold; the manifold is connected to the plurality of air-directing outlets; and the pressure of the air from the manifold is controlled by air-pressure-regulating means. In such systems, a plurality of monitoring means, one for each of the air-directing outlets, monitors the pressure of the air to each of the air-directing outlets and provides a signal indicative of the spacing between the mold elements for use in the system. In such more extensive systems, each of the transducers may be connected to the microprocessor which can compare the output of each of the transducers with the information stored in its random access memory, calculate the spacing between the surface at each of the air-directing outlets and the adjacent die elements throughout the cycle of operation of the molding system, and compare the spacings of the die elements with proper spacings and with each other to determine misalignment and failure of the die elements to properly close and other such irregularities and departures from intended operation, thereby avoiding damage to the die elements and the die-casting machine and preventing the manufacture of parts that do not meet the tolerances that have been designed into the molding system.

Other features and advantages will be apparent from the drawings and detailed descriptions that follow.

FIG. 1 is a cross section of a typical horizontal die-casting machine;

FIG. 2A is a side view of a typical mold for the housing of an automatic transmission of an automobile in the open position;

FIG. 2B is a cross-sectional view taken on line 2B--2B of the mold of FIG. 2A, showing the movable carrier of the mold and the plurality of transversely moving mold slides to form the interior of the transmission housing, its upper most surface (by the carrier) and its outer and end portions;

FIG. 3 shows the mold of FIG. 2B in schematic form indicating the position of the slides in phantom lines with the mold open, the position of the slides in solid lines with the mold closed, and arrows indicative of the motion of the slides as the molds are closed;

FIG. 4A is a side view of the mold of FIGS. 2A and 2B in the closed position;

FIG. 4B is a cross-sectional view taken on line 4B--4B of the mold system of FIG. 4A showing the position of the slides with the mold closed and indicating a cross section of the cavity formed by the mold;

FIG. 5 is a graph showing the relative pressure applied to the charge, the velocity of the charge, and the position of the charge piston during the first one and one-half seconds of a typical die-filling portion of a die-casting cycle;

FIG. 6 is a simplified diagram illustrating elements of a preferred system of this invention (omitting an interconnecting portion of passage-forming means 54d);

FIG. 7 is a graph showing an example of system air pressure vs gap spacing for several ratios of system orifice diameters;

FIG. 8 is a block diagram of a more extensive system of this invention adapted to indicate the spacings at a plurality of locations in the molding system;

FIG. 9 is a diagrammatic view of an air-gap measuring system of this invention for purposes of illustration of the physics of the system;

FIG. 10 is a typical calibration curve for the air gap-measuring system of FIG. 9;

FIG. 11 is a side view of the upper slide of the molding system of FIG. 13 indicating by arrow heads the location of air flows directed from the movable carrier to detect improper alignment and movement of the vertical slide and the location of air-directing outlets to detect improper closure of the slide;

FIG. 12 is an end view of the vertical slide of FIG. 11 further showing, by arrow heads, the location of directed air flows in the system of the invention to determine the improper movement and alignment of the vertical slide and the location of air-directing outlets to detect improper closure of the slide; and

FIG. 13 is a cross-sectional view of the molding system of FIGS. 2A and 2B (corresponding to FIG. 3), illustrating by stars the portions of the movable carriage of the mold system whose spacings can be detected by directed air flows from a plurality of sites on the stationary mold element to detect the failure of the system to fully close or to close in such a manner that the mold has a partially open portion.

FIG. 1 is a cross-sectional and diagrammatic view of a typical, horizontal, die-casting machine 10. The die-casting machine is designed to open and close a die-casting mold 11, frequently referred to as a die, including a movable element 11a and a stationary element 11b The die-casting machine includes a base 12 adapted to support a stationary platen 13 and a movable platen 14. Stationary platen 13 and movable platen 14 are supported by the base in such a manner that their vertical surfaces 13a and 14a, respectively, are parallel. The parallel nature of vertical surfaces 13a and 14a of the platens of the die-casting machine is important to ensure that parallel surfaces provided on movable portion 11a and stationary portion 11b of mold 11 remain parallel when the die is installed in the machine and properly closed as moving platen 14 is moved by the die-casting machine toward stationary platen 13. As shown in FIG. 1, the die-casting machine also includes a link housing 15 carried by base 12, and a hydraulic cylinder 16 carried by the link housing 15 with its piston moving horizontally. A piston 16a of hydraulic cylinder 16 is connected to a toggle link assembly 17. Toggle link 17 provides a large mechanical advantage, multiplying the force imposed by piston 16 a of hydraulic cylinder 16 many times to move moving platen 14 toward stationary platen 13 and, upon engagement of the interfacing surfaces of movable die element 11a and stationary die element 11b, to apply extremely high forces to press movable die element 11a against stationary die element 11b to resist the separating forces imposed upon die elements 11a and 11b by the liquid metal charge forced into a cavity 11c formed in die 11.

As shown in FIG. 1, molten metal is forced in cavity 11c by a movable plunger or piston 20. The piston is moved forward by a shot cylinder 21; and upon completion of the forward stroke of piston 20, the plunger is exposed to an extremely high intensification pressure, frequently in the range of 5,500 to 20,000 psi. (350 to 1400 kg./cm.sup.2). The intensifier includes an isolating hydraulic piston assembly 22 and high pressure gas container 23 connected with isolating piston 22 in such a manner that as piston 20 has filled cavity 11c with molten metal, the high pressure of high pressure container 23 is applied to isolating piston assembly 22 and through the hydraulic fluid to piston 20 to exert pressures such as 5,500 to 20,000 psi. (350 to 1400 kg/cm.sup.2) on the molten metal within cavity 11c. To prevent the extreme high pressures of the molten metal from forcing die elements 11a and 11b apart, die-casting machine 10 through toggle link 17 can apply forces of several million pounds, and up to 70,000,000 pounds (31,710,000 kilograms), to moving platen 14.

As shown in FIG. 1, moving platen 14 and movable die 11a are supported by rails 18 on the base; and both movable platen 14 and movable die member 11a are carried and guided by tie bars 19 extending between stationary platen 13 and link housing 15 supported by base 12. Tie bars 19 must carry the force imposed by piston 16a and toggle link 17 and imposed, through moving platen 14 and mold 11, on stationary platen 13. Stationary platen 13 and link housing 17 are held together by tie bars 19 to permit the extreme forces to be imposed upon die elements 11a and 11b by toggle link 17 of the die-casting machine. Tie bars 19 are broken away in FIG. 1 so that they will not restrict the view of toggle link 17 and die elements 11a and 11b (which are shown in cross section).

As shown further in FIG. 1, if the interfacing surfaces of die elements 11a and 11b are prevented by an incompressible material, such as flash, from mating and are held spaced apart, the designed preloading force to be applied by the die-casting machine through toggle link 17 can be many times greater than anticipated and can reach levels sufficient to break the toggle link assembly or tie bars of the die-casting machine. As noted above, the forces imposed by the die-casting machine are frequently in the range from 7,000,000 to 70,000,000 pounds (3,171,000 to 31,710,000 kilograms).

FIGS. 2-4 illustrate a mold to form from aluminum, for example, the housing for an automatic transmission for an automobile.

FIG. 2A is a diagrammatic side view of a molding system 30 with the mold in the open position. As shown in FIG. 2A, the mold includes a movable mold element, or carrier, 31 mounted on the face of a movable platen 32 of a molding machine and carrying a plurality of transversely sliding mold elements, namely, a top slide 33 including a surface portion 33a shaped to form the interior surface of the automatic transmission housing, a side slide 34 having an interior surface shaped to form a portion of the outer surface of the automatic transmission housing (not shown), and a bottom slide 35 shaped to form the end of the automatic transmission housing. Another side slide 41 is carried by mold element 31 as shown in FIG. 2B. The mold system also includes a stationary die element 36 including interior portions (not shown) which cooperate with the cavity-forming surfaces of movable die element 31 and sliding die elements 33, 34, 35, and 41 (shown in FIG. 2B) to complete the formation of an internal cavity when movable element 31 is closed by movable platen 32 of the die-casting machine to force the interfacing and mating surfaces 31a and 36a of die element 31 and die element 36 into engagement. Prior to the movement of movable die element 31 into engagement with stationary die element 36, sliding die elements 33, 34, 35, and 41 (shown in FIGS. 2B, 3, and 4B) are moved transversely and preferably perpendicularly to the direction of motion imposed on movable die element 31 by movable platen 32 of the die-casting machine. Slides 33, 34, 35, and 41 (FIG. 2B) are moved by separate hydraulically driven pistons mounted on die element 31 and fastened one to each of slides 33, 34, 35, and 41 (FIG. 2B) to move the slides as shown in FIG. 3. The mounting and operation of such hydraulic piston-cylinders to drive the slides of a die-cast mold are well known in the art, and the hydraulic piston-cylinder drives are omitted from FIGS. 2-4 for clarity.

As shown in FIG. 2A, top slide 33 includes ramp-like surfaces 33b; and the bottom slide includes a ramp-like surface 35b. In the sequence of operation of molding system 30, the hydraulic drives for slides 33, 34, 35, and 41 drive the slides inwardly into their cavity-forming position. As the die-casting machine, through movable platen 32, moves movable die element 31 to the right, as shown in FIG. 2A, cooperating ramp-like surfaces (not shown) formed on the interior surfaces of stationary die element 36 engage ramp-like surfaces 33b and 35b and engage ramp-like surfaces on the other slides 34 and 41 of the die (not shown in FIG. 2A). The application of the extreme force by the die-casting machine imposes these extreme forces on ramp-like surfaces 33b and 35b to hold top slide 33 and bottom slide 35 in their correct cavity-forming position. Die elements 31 and 36 are carried on rails 38 and are guided by tie rods 39 and 40 of the die-casting machine.

FIG. 2B is a view of the carrier and slides of mold system 30 taken along section 2B--2B of FIG. 2A. FIG. 2B shows the arrangement of slides 33, 34, and 35, and the other side slide 41, which was opposite side slide 34 and not visible in FIG. 2A. As shown in FIG. 2B, movable die element 31 which serves as a carrier for the slides includes an interior portion 31a including surfaces designed to cooperate with the cavity-forming surfaces of die elements 33, 34, 35, 36, and 41 to form the automatic transmission housing. Interior surfaces 34a of slide element 34, 35a of slide element 35, and 41a of slide element 41, as well as a more complete view of the exterior of cavity-forming surface 33a of top slide element 33 are shown in FIG. 2B. Also visible in FIG. 2B are ramp-like surfaces 33b of slide element 33, 34b of slide element 34, 35b of slide element 35, and 41b of slide element 41. The ramp-like surfaces of the slides are omitted from FIGS. 3 and 4.

Each of slides 33, 34, 35, and 41 also includes a "stop", that is, a surface which abuts a corresponding "stop" on carrier element 31 to position the slide transversely of the axis of movement of carrier 31. As shown in FIG. 2B, slide element 33 includes stops 33c which abut coacting stops 31b of carrier 31 when the mold is closed; slide 34 includes stops 34c which abut coacting stops 31c of carrier 31 when the mold is closed; slide 35 includes stops 35c which abut coacting stops 31d of carrier 31 when the mold is closed; and slide 41 includes stops 41c which abut coacting stops 31e of carrier 31 when the mold is closed. As known in the art, the ramp-like surfaces and stops of the mold are preferably formed as separate, hardened, steel elements that are bolted to the mold elements. After the mold is closed and the slide stops are abutting the carrier stops, the application of further force by the die-casting machine to the carrier "preloads" the slides (i.e., applies forces to the slides to force their stops against the coacting stops of the carrier) to prevent movement of the slides as the mold cavity is filled with liquid metal at high pressure. The location of the stops on the mold elements is an important part of the set up of the die since the stops determine the position of the slides when the mold is closed. In setting up a die, the separate stop elements are frequently "shimmed" with thin pieces of metal to adjust the location of slides when the mold is closed.

FIG. 3 corresponds to FIG. 2B and shows the mold system with the slides closed in solid lines and indicates the molding system with the slides open in phantom line. FIG. 3 includes arrows showing the transverse motion of slides 33, 34, 35, and 41 as they are moved with respect to the die element or carrier 31 by their respectively independent hydraulic drive systems.

FIGS. 4A and 4B correspond, respectively, to FIGS. 2A and 2B and show mold system 30 in the closed position. FIG. 4B is a cross section of FIG. 4A taken along the lines 4B--4B of FIG. 4A. Section 4B--4B is taken along the parting line (that is the interface between mold elements 31 and 36) but offset through the center line of the mold cavity to more clearly show the manner in which the mold elements define the housing of an automatic transmission. In the position shown in FIG. 4A, the die-casting machine through movable platen 32 applies forces reaching millions of pounds to molding system 30 to clamp and wedge molding system 30 in the closed position and to prevent molding elements 31 and 36 from being forced apart, that is, so no spacing occurs between die elements 31 and 36, when exposed to the pressure imposed on the liquid metal as it is forced into the mold cavity. Through the high forces imposed on movable die element 31 by movable platen 32 of the die-casting machine and its transfer via ramp-like surfaces 33b of top slide 33, 34b of side slide 34, and 41b of side slide 41, and 35b of bottom slide 35 (FIG. 2B), slides 33, 34, 41, and 35, respectively, are intended to be held in the proper closed position defined by the adjoining slide and carrier stops as shown in FIG. 4B. In a large part such as a housing for an automatic transmission which requires a slide element such as a top slide element 33 shown in FIGS. 2-4 to form its long interior cavity, even a small, angular displacement from its intended central axis can displace its remote end surface (see 33c in FIGS. 2B and 4B) by many thousands of an inch and result in the manufacture of a housing with a wall thickness too thin to provide reliable operation and service.

As shown in FIG. 4B, the imposition of pressure on the molten metal injected into the cavity develops forces on slides 33, 34, 41, and 35, forcing the slides outwardly away from the cavity unless they are firmly held in their intended closed position.

FIG. 5 is an indication of the flow rate and pressure on the liquid metal during the cavity-filling portion of a die-casting cycle as a result of the motion of the die-casting machine charge piston and the pressure intensifier. As shown in FIG. 5, during the initial one-half second of charging, the charge velocity and pressure are low as the piston begins its motion. From about 0.4 second to about 0.7 second after the beginning of charging, the piston moves more rapidly; and the charge velocity substantially increases as the cavity is filled. As shown in FIG. 5, the charge pressure remains low until the cavity is filled. As the cavity is filled, however, the continued movement of the piston raises the pressure on the liquid metal within the cavity to the hydraulic line pressure applied to the piston which, in the example shown in FIG. 5, is about 2,000 psi. (140 kg/cm.sup.2). At this point in the cycle, about 0.7 second after charging has commenced, the very high pressure of the intensifier is applied to the piston and the pressure on the liquid metal increases over the next second to pressures in the range from about 5,500 psi. to 20,000 psi. (380 to 1,400 kg/cm.sup.2).

For large castings, such as the aluminum casting for an automatic transmission housing, a complete cycle, including closing the mold, charging the mold, cooling the charge, and opening and clearing the mold requires from about two minutes to about two and one-half minutes.

A typical housing for an automatic transmission may be eighteen to twenty inches (45 to 50 cm.) in diameter and twenty to twenty-four inches (50 to 60 cm.) long. Referring to FIG. 4B, if the molten metal, shown in black in FIG. 4B, exerts a pressure of 5,500 psi. to 20,000 psi. (380-1400 kg/cm.sup.2) on the surrounding surfaces of molding system 30, the forces tending to move mold slide elements 33, 34, 41, and 35 outwardly away from the cavity may reach several million pounds (several million kilograms) acting on each of the slide elements 33, 34, 35, and 41.

Referring now to FIG. 4A, the imposition of pressure such as 5,500 psi. to 20,000 psi. (380 to 1400 kg/cm.sup.2) on the liquid metal within the cavity also imposes forces on the order of millions of pounds (millions of kilograms) acting to force mold elements 31 and 36 apart. The die-casting machine, through the imposition of the forces of 350 to 3,500 tons (317,000 to 3,171,000 kilograms) or more, must hold the die elements 31 and 36 closed and hold slide elements 33, 34, 35, and 41 in their designed closed position, notwithstanding the high pressures imposed on the liquid metal charge.

Mold systems, such as mold system 30 shown in FIGS. 2-4, must operate in the presence of the temperatures of molten aluminum and zinc, for example, temperatures in excess of 1200.degree. F. (650.degree. C.), and their engaging surfaces and moving parts must withstand forces of millions of pounds (millions of kilograms) without yielding under stress, fracturing or otherwise failing. Furthermore, during operation, die surfaces have temperatures reaching 600.degree. F. (315.degree. C.); and for even large parts, the dies open only to eighteen to twenty inches (46 to 50 cm.), thus making visual inspection very difficult because of the heat and because of the water, steam, and other vapors present when the mold is open. Of course, any effort to work on the mold surfaces manually during operation while the die is hot is virtually impossible because of the risk of burns to the operator. Die-casting operations necessarily present a hostile environment to human operators.

The invention, however, provides a method and apparatus for safely, reliably, and economically verifying the proper movement and alignment of movable die members prior to the imposition of the extreme high forces of the die-casting machine, the proper position of the movable die members after the molding system is closed and prior to the introduction of molten metal, the extent and location of any misaligned surfaces of a molding die member (i.e., unparallelism or unacceptable departure from the proper axis of a die member and its respective cavity-forming surface, or a spatial displacement of a die member from its designed location of the cavity-forming mold surface), the unintended movement of die members during cavity-charging, and other such departures from normal operation which may lead to damage to the molding system or to the die-casting machine or to the manufacture of die-cast parts with unacceptable departures from their dimensional tolerance limits.

FIG. 6 shows the relatively simple manner in which the invention can be incorporated into the elements of a molding system. As shown in FIG. 6, a molding system 50 of the invention includes at least a pair of mold elements 51 and 52 that move together to form a mold cavity 53. First mold element 51 has a first surface with a cavity-forming portion 51a and a portion 51b adjoining the second mold element 52 when the cavity is closed. The second mold element 52 has a second surface with a cavity-forming portion 52a and a portion 52b adjoining the first mold element when the cavity is closed. The first and second mold elements 51 and 52 are adapted to be moved together to define a closed mold cavity 53. In the invention, means 54 located at the element adjoining portion 51b of the first mold element 51 is adapted to direct the flow of gas at the adjacent interfacing portion 52b of the second mold element 52. As shown in FIG. 6, directing means 54 includes an orifice 54a, preferably formed by a separate orifice-forming member 54b inserted into the element abutting portion 51b of the first mold element, and a passageway 54c through the first mold element 51 adapted to be connected to a source of gas, preferably compressed air. Preferably, passageway 54c is formed by flexible, temperature-resistant tubing, like Teflon tubing 54d, inserted into a passage drilled into the first mold element. Such Teflon tubing can provide a continuous passageway 54c and thermal isolation of the gas from the hot surface of the mold element. The separate, orifice-forming member 54b forms an orifice 54a having a cross-sectional area smaller than that of passageway 54c. Air-directing means 54 is adapted so that orifice 54a is located closely adjacent and preferably directly at the element adjoining surface 51b of first mold element 51. If the structure and operation of mold system 50 permits, air-directing means 54 may be a separate element bolted or otherwise fastened to first mold element 51 so that air-directing means 54 is located closely adjacent or at another surface that abuts or adjoins the second mold element when the mold is closed.

FIG. 6 shows a molding system 60 of the invention including, in addition to mold 50 and air-directing means 54, means 61 for monitoring the flowing air remote from first molding surface 51b. Monitoring means 61 includes a second orifice 62 in passageway 54c leading to first orifice 54a of the air-directing means 54. A transducer 64 is connected with first passageway 54c by a second passageway 63 to monitor the air flowing from air-directing means 54. Preferably, transducer 64 is a pressure-sensitive output device connected to sense the pressure in passageway 54c between first orifice 54c and second orifice 62 of the system. In a simple system of the invention, a pressure-sensitive output device or transducer 64 can be a direct reading pressure gauge calibrated to indicate the spacing between the first and second molding system surfaces. In more complex systems, pressure-sensitive output device 64 may be a pressure transducer of the type sold by Omega Engineering, Inc., of Stanford, Conn., under the designation PX 236. Such pressure transducers can convert the pressure in passageway 54c between the first and second orifices into an electrical voltage that is proportional to pressure.

As shown in FIG. 6, the system can further include means 65 connected with a transducer 64 to interpret the electrical signal and produce an output indicative of the spacing between first and second molding system surfaces 51b and 52b, respectively. Means 65 can include a microprocessor 66 connected with transducer 64 through an analog to digital converter. One such satisfactory microprocessor controller is sold by Cincinnati Milacron as its APC-500 Programmable Controller. As is known, such microprocessors include a central processing unit and random access memory. Means 65 can also include a calibration means 67 connected with transducer 64 to relate the output of transducer 64 to the spacing between first and second molding system surfaces 51b and 52b and to store an indicia of the spacing in the random access memory of microprocessor 66. Also stored in microprocessor 66 is an operating program to compare transducer output 64a with the indicia of spacing stored in the random access memory of microprocessor 66 and to calculate the spacing between first and second molding system surfaces 51b, 52b and produce an output 68 indicative of the spacing. Output 68 of microprocessor 66 may be used to automatically stop operations, to operate an alarm, to provide go/no-go information to the operator, and/or to drive a printer recording the spacing between surfaces 51b and 52b as a function of time or its specified times during the cycle of operation of the molding system.

System calibration means 67 may be a digital computer having the capacity of no more than, for example, an IBM PC personal computer, including a central processing unit, random access memory, and input/output devices. Such a digital computer can be provided with a calibration program for the system. Such a calibration program can sample an output 64a of the transducer a specified number of times in the specified time span and generate indicia of the spacing between the first and second molding system surfaces 51b and 52b based upon a calculated mean of transducer output 64a and store such indicia in the random access memory of the microprocessor for use in the operating program of the microprocessor.

As shown in FIG. 6, a source of air under pressure 70 to provide gas to a system 60 can be factory air 71 connected with means 72 to filter and dry the air and means 73 to regulate the pressure of the air applied to the system.

In one simple embodiment of the invention, for example, means 54 is a separate, hard, mold insert 54b with a diameter of about 0.5 inch (1.27 cm.) forming an orifice 54a by a fustroconical wall 54e at an angle of 45.degree. with respect to the central axis of the insert. Orifice 54a is located at a selected surface of one mold element and has a circular cross section with a diameter of 0.147 inch (0.373 cm.) at the termination of a passageway 54c having a diameter of 0.375 inch (0.95 cm.) Mold insert 54b may be any durable metal. The remainder of a simple system can be contained within a metal box about eighteen inches high, eighteen inches wide, and twelve inches deep. Second orifice 62 is formed by a separate durable element with a circular cross section and a diameter of 0.082 inch (0.21 cm.) in a passageway with a diameter of 0.375 inch (0.95 cm.). The monitoring means connected with the passageway 54c is a direct reading bourdon tube static pressure gauge manufactured by the Excel company. Flexible, high-temperature-resistant Teflon tubing 54d interconnects the two orifices 54a and 62. Where mold element 51 is hot, tubing 54d isolates the air in passageway 54c from hot mold element 51. The system can include a Model R216-02F air pressure regulator manufactured by Watts Fluid Air, Inc., of Kitlarg, Me., so that factory air of up to 80 psi. (5.6 kg/cm.sup.2) can be regulated to provide a known pressure in the range of 0 psi. to 15 psi. (0 to 1 kg/cm.sup.2) for application to second orifice 62. The system also includes a compressed air filter/drier which can be any such device of a reliable manufacturer. The face of the static pressure gauge may be calibrated to indicate the spacing in thousandths of an inch (or cm.).

Although FIG. 6 shows the system of the invention as monitoring the position of first and second mold surfaces 51b and 52b at a single site adjacent air-directing means 54 and including a system calibration means 67, the system of the invention can be adapted to monitor the spacing of the first and second mold elements at a plurality of sites or can be modified to monitor a plurality of mold elements, each at a plurality of points.

Such a modified system 100 is shown in FIG. 8. In such a system, factory air from a source 101 is filtered and dried by a filter dryer 102 and delivered to a manifold 103 provided with a plurality of outputs 103a, 103b, 103c, . . . 103n. Each of the outputs of manifold 103a-103n delivers a flow of air to an air-directing means 54.sub.1 -54n (not shown in FIG. 8) at a different mold point as indicated in FIG. 8. The molding system, as shown in FIG. 8, includes a plurality of pressure regulators 104a-104n, each of said pressure regulators being connected between a manifold outlet 103a-103n and one of the air-directing means 54a-54n at a mold point. For example, pressure regulator 104a regulates the pressure from manifold 103 and manifold outlet 103a to the air-directing means 54.sub.1 at mold point 1. In some systems, it may be preferable to use, instead of the plurality of pressure regulators, a single pressure regulator that is connected in the system between filter dryer 102 and manifold 103.

The system further includes a plurality of monitoring means 105a-105n. As in the system shown in FIG. 6, each of the monitoring means 105a-105n includes an orifice/passageway assembly 106a-106n and a transducer 107a-107n. The plurality of orifice/passageway members 106a-106n is connected with the plurality of air-directing means at the plurality of mold points 1-n being monitored. Each of the plurality of transducers 107a-107n monitors the flowing air at its associated one of a plurality of orifice passageway members 106a-106n and provides an output indicating the spacing between each of the mold points 1 though n and surfaces of other elements of the molding system that adjoin each of the mold points 1-n. In this system, each of the transducers 107a-107n is adapted to provide an electrical signal 108a-108n; and each of the electrical signals 108a-108n from the plurality of transducers is connected to a microprocessor 109.

In the invention, the microprocessor can be provided with an E-prom containing an operating program and calibration data, permitting microprocessor 109 to calculate the spacing between each of the mold points 1-n and the adjacent surfaces of the molding system. Microprocessor 109 can compare spacing data from the mold points 1-n to determine if the die-casting system is operating properly. The microprocessor can then provide a plurality of outputs to provide useful signals or information to the operator. For example, as shown in FIG. 8, one output 110 can be used to drive a recorder 112 to provide a permanent record of the operation of the molding system and the spacing of the mold elements of the molding system at specified times during each cycle of operation. Such permanent records can be used to provide a permanent record of the quality of the parts manufactured in the die-casting operation and can be used to identify reject parts and provide information useful in improvement of the operation. Microprocessor 109 can also provide an output 113 to operate an alarm 114 for the operator in the event of misalignment of the die elements or other malfunction determined by the microprocessor to require operator attention. Furthermore, the microprocessor can provide an output 115 to operate a controller 116 for a die-casting machine and bring the system to a stop in the event of impending damage to the molding system or the manufacture of reject parts. In addition, the controller can indicate the nature and location of the danger in the operating system.

As noted above, mold points 1-n of the system of FIG. 8 can be located on a single mold element to indicate its axial and spatial alignment during operation with its designed and correct axial and spatial alignment; and mold points 1-n can be located in the molding system to monitor the spacing and alignment of a number of movable mold elements.

FIG. 9 shows a gap-measuring system 200 in its broader aspects and the fluid conditions, generally air pressure, and flows used in the system of this invention to calculate the spacing between two surfaces. As shown in FIG. 9, in its broader aspect, the invention comprises a fluid gauge sensor system to monitor the spacing X between a first surface 201 and a second surface 202. As indicated above, surfaces 201 and 202 can be part of a die-cast molding system; but in their broader view can be the surfaces of die-casting or plastic molding machine, or can be the surfaces of any other machine where it is important to monitor the spacing between two moving surfaces to determine the reliable operation of the machine or to indicate impending or actual machine malfunction. In such applications, surfaces 201 and 202 may be relatively movable toward and away from one another or may move, or slide, on the planes in which they extend or may become spaced due to wear or distortion in operation.

As indicated in FIG. 9, the system includes a pressurized fluid source 203, providing fluid at a known pressure P.sub.s and a fluid outlet 204 at first surface 201. This system also includes a fluid line 205 forming a passageway 205a and coupling pressurized fluid source 203 to fluid outlet 204 for directing the fluid through outlet 204 from first surface 201. The system further includes means 208 for monitoring the fluid in fluid line 205 for a change in fluid conditions, indicating the spacing between first and second surfaces 201 and 202, respectively. Monitoring means 208 includes a second orifice means 206 forming an orifice 206a and a pressure-sensitive output device 207 communicating with the fluid line 205 to check the pressure P.sub.c in a fluid line 205.

The system of this invention, as indicated by FIG. 9, relies on the physical phenomena that when an air jet from a nozzle 204 impinges on a surface 202 close to a nozzle exit 204c, the pressure P.sub.c on the upstream side of nozzle 204 depends on the distance x between the nozzle exit and the neighboring surface 202. The ratio of the diameter d.sub.N of nozzle orifice 204c to the diameter d.sub.s of second orifice 206a is important because larger ratios dn/ds provide a greater variation in pressure P.sub.c in passageway 205a with gap spacing x, as shown in FIG. 7. Pressure P.sub.c is sensed by a pressure output device or transducer 207 and used to provide a useful output for a gap-measuring system 200. It is important, however, to keep the sizes of orifices 204c and 206a small to conserve the fluid used in operation of the system.

This system has been found to be particularly advantageous in the determining of clearances between surfaces which are so configured, or which are in such an environment, that direct measurement by standard means is either inconvenient, impossible, or dangerous. In such applications, a nozzle can be installed in one of the surfaces and supplied with fluid from an external source without interfering with the relative motion of the surfaces. The pressure then can be measured at a convenient remote point in the fluid line upstream of the nozzle. As set forth below, this measured pressure can be converted to a measurement of the gap x.

In practical applications of the invention, air, at a known regulated supply pressure P.sub.s, is directed through orifice 206a having a diameter d.sub.s at a flow rate of Q.sub.s. The air passes through a fluid line 205, which, in practice, is a tube of diameter D, to a nozzle 204, the exit plane of which is flush with one of surfaces 201. Nozzle exit orifice 204c has a diameter d.sub.N. The air Q.sub.N exiting from nozzle 204 in a jet which impinges on second surface 202 and then expands through the gap x between the surfaces to atmospheric pressure P.sub.A. The distance between the surfaces is called the air gap and is denoted by x. The pressure in chamber or passageway 205a formed by fluid line 205 between orifice 206a and nozzle orifice 204c is assumed to be uniform and have the value P.sub.c. A pressure-sensitive output device, or transducer 207, is installed to sense the pressure in a line 205 between a orifice 206 and nozzle 204 and indicates a pressure P. Under transient conditions, there may be a flow Q.sub.c between chamber 205a and transducer 207; but such transient flow may be neglected in many operations of the system.

For steady flow, the flow rate Q.sub.c to transducer 207 is zero and the pressure at transducer 207 is the same as that in chamber 205a between orifice 206a and nozzle 204; the flow rate through orifice 206 is the same as the flow rate through nozzle 204.

Conventional orifice equations can be used to express the relation between the flow rate through a restriction and the pressure drop across the restriction for both orifice 206a and nozzle orifice 204c.

In these equations Y.sub.s and Y.sub.N represent the density of the air at orifice 206a and at nozzle orifice 204c. The air density at orifice 206a may be different from the density at nozzle orifice 204c due to a temperature difference between these locations. In the invention, line 205 can desirably isolate the air in passageway 205a from any high temperature surfaces of element-forming surface 201. A.sub.s and A.sub.N are characteristic areas at orifice 206a and nozzle orifice 204c and are taken to be:

The parameters C.sub.s and C.sub.N, called flow coefficients, account generally for the geometry of the restriction, the roughness of the flow passage in the restriction, and the flow rate and fluid properties. The geometry is often integrated into the flow coefficient through the nondimensional obstruction parameter

The roughness .epsilon. is also normally incorporated in nondimensional form through the parameter

The effect of flow rate and the fluid properties can be described through the nondimensional parameter

where .sigma. is the kinematic viscosity. Re is called the Reynolds number. While all three of these nondimensional parameters are temperature dependent through changes due to thermal expansion, the Reynolds number is much more sensitive to temperature changes because of the temperature dependence of viscosity.

Substituting Eqn (2) into the second of Eqn (1) and dividing by 2.sup.1/2, we have:

The equation can be converted to gauge pressures by letting:

Next, divide both sides of Eqn (5) by P.sub.s to obtain:

For convenience, two nondimensional parameters can be defined:

Then, Eqn (6) can be written as:

But, from Eqn (3):

Note that z is a nondimensional air gap. Now Eqn (8) takes the form:

Eqn (10), Eqns (7) and (9) express the basic physics of the system of this invention in nondimensional terms. The advantage of this approach is that the phenomena which are ultimately determined empirically are isolated in the factor L. Moreover, the quantities by which these phenomena are expressed are grouped in a small number of nondimensional parameters, Y.sub.s /Y.sub.N, .beta., .epsilon./d and Re.

In the calibration procedure of this invention, the characteristic geometrical parameters, d.sub.s and d.sub.N, are known and fixed. The parameter .alpha. can them be calculated from Eqn (9). Similarly, the supply pressure P.sub.s is known and regulated. The calibration will provide an empirical relation between the parameter L and the nondimensional chamber pressure y. Then for a given (measured) value of the chamber pressure P, the air gap x can be calculated as follows:

1. Calculate y=P/P.sub.s.

2. Evaluate L for this value of y from the empirical relation.

3. Calculate z from Eqn (10), i.e., z={[(1-y)/y].sup.(1/2) }/(.alpha..multidot.L).

4. Finally, calculate the air gap from Eqn (9), i.e., x=z.multidot.d.sub.N.

In order to determine the empirical relation between L and y, both the air gap x and the chamber pressure pressure P are accurately measured for a number of conditions encompassing the normal range of operation for the system. In practice, only six or seven calibration points in the range from fully closed (x=0) to some large value of the air gap (x=X.sub.max) may be necessary. The actual value of X.sub.max used in the calibration depends on the values of d.sub.s, d.sub.N and P.sub.s.

In calibrating the system of this invention, pressure transducer output P and air gap x are measured at the plurality of system spacings (e.g., six to seven spacings); and the results are stored in the random access memory of a system calibrating means, such as a digital computer, set forth below:

The digital computer is provided with a system calibration program to calculate from the values of P and x in this table and the known geometrical parameters and supply pressure, the nondimensional parameters y, .alpha., z, and the L from Eqns (7), (9), and (10), i.e., Y=P/P.sub.s ; z=x/d.sub.N ; and L=[[(1-y)/y].sup.1/2 ]/(.alpha..multidot.z).

The raw data in the previous table is thus converted by the system calibration means to:

FIG. 10 shows a typical calibration curve 300 for a system of this invention. Solid circles 301-307 represent measured calibration points corresponding to L.sub.1 -L.sub.n and Y.sub.1 -Y.sub.n of the table above. The open circle 310 represents an evaluation of the nondimensional flow parameter L for a given measured value of the nondimensional chamber pressure Y for a spacing x (FIG. 9) between two surfaces 201 and 202 (FIG. 9).

The calibration program generates, for storage in a microprocessor (like 66 of FIG. 6) by an interpolation procedure such as the cubic splines procedure, a large table of pressure transducer outputs P.sub.1-M, including interpolated values between the measured values, for air gaps x throughout the range x.sub.max to zero. The operating program of a microprocessor uses this calibration table giving the relation between the (dimensional) pressure transducer output P and the (dimensional) air gap x for the known geometrical parameters and supply pressure. If the number M of subdivisions of P is large enough (e.g., M =100), linear interpolation in the stored table is satisfactory. If, however, the number M of subdivisions of P is on the order of ten or less, interpolation requires calculation and storage of the dimensionless parameters y, z, and L, as set forth above, and interpolation in the stored dimensionless parameter data using an interpolation procedure like the cubic splines procedure. The decision of using a calibration program to provide a large table if P v x data in the system microprocessor, or providing the system microprocessor with an interpolation program depends upon the microprocessor storage capacity and operating speed.

In the dynamic operation of a die-casting system with a plurality of fluid outlets 204c, variations in the length of passageways 205a can cause delays in the pressure changes in the passageways 205a and in the outputs of their respective pressure-sensitive output devices 207. Such variations can provide errors in an immediate comparison of the outputs of the plurality of fluid outlets where the surfaces being monitored move rapidly. Compensation for such variations in length can be made by measurement and calibration if necessary.

FIGS. 11-13 demonstrate how the system of the invention can be incorporated into a molding system including a movable die member having a plurality of movable surface portions and a stationary die member having a plurality of stationary surface portions aligned with the plurality of movable surface portions of the movable die member. For convenience, FIGS. 11-13 illustrates the molding system discussed and illustrated above in FIGS. 2-4. The mold element numbers included in FIG. 13 correspond to the molding die elements of FIGS. 2-4, specifically as shown in FIG. 3. FIG. 13, however, illustrates by a plurality of stars 351, 352, 353, and 354 sites for the location of the fluid-gauging system of this invention. With the fluid-gauging system directing flows of air from air-directing means located in die element 36 (FIG. 2A) and monitoring the conditions of the air flows to determine the spacing of the sites 351, 352, 353, and 354 on die element 31 from corresponding sites on the mold-closing surface of die element 36, information on spacings between the surface of die element 31 and the corresponding mold-closing surface of die element 36 at each of the sites 351, 352, 353, and 354 can be obtained. This spacing data can verify that the surfaces of die elements 31 and 36 are parallel prior to their closing and the imposition of the high forces by the die-casting machine. The continuous monitoring by the fluid-gauging system at sites 351, 352, 353, and 354 can also detect if the imposition of high liquid metal pressure in the mold cavity results in moving the mold-closing surfaces of die elements 31 and 36 apart. Continuous recordation of data on spacing at sites 351-354 can also provide an assurance of the quality of the parts manufactured by die-casting mold system 30 while providing a record that molding system 30 was properly closed throughout its operation.

FIGS. 11 and 12 are a side view and end view, respectively, of top slide 33 of the molding system of FIGS. 2-4 and 13. FIGS. 11 and 12 show by arrows 361-364 sites or locations of the imposition of air from air-directing means located in carrier die element 31 against sliding surfaces of the vertical slide 33 to monitor verticality of movement and position of vertical slide 33 throughout the die-casting cycle. Vertical slide 33 can also be provided with air-directing means 366 and 367 in stops 33c on each side of the vertical slide. As noted above and as shown in FIG. 4B, stops 33c of vertical slide 33 are pressed against stops 31b of carrier 31 when mold 30 is closed. Air-directing means 366 and 367 can thus assure that slide 33 is properly closed by the mold system and maintained in proper position throughout the die-casting cycle. As apparent from examination of FIGS. 2A, 2B, 11, and 12, if vertical slide 33 is or becomes misaligned or moves in an unintended manner, such misalignment can be determined from a variation in the spacings determined by the fluid-gauging means monitoring sites 361-364 and from fluid-gauging means including air-directing means 366 and 367.

Each die system with its movable parts and slides presents different opportunities for malfunction and misalignment of the die elements during installation and operation and because of wear over a period of time. Experienced designers of die-casting molds can, through their experience, determine where to locate the fluid-gauging systems of this invention in the molding system to best monitor the proper operation of the molding system and prevent its damage in use. The air-directing means of the system are, of course, generally located at adjoining interfacing surfaces of cavity-forming die elements that establish the position of the die elements. Such adjoining interfacing surfaces are frequently in the stop-forming surfaces of the die elements, including the slides. The stop-forming surfaces may be separate, hard steel die inserts, as described above, which carry the air-directing means. The air-directing means may also be located in surfaces of die elements surrounding the cavity-forming surfaces of the die elements. In addition, the air-directing means may be located at adjoining sliding surfaces of the die where wear is anticipated to monitor the wear as the die is used. Although it is not necessary for operation of the system, it is preferred that the lengths and diameters of the passageways between the air-directing means of a mold or die and the monitoring means or pressure output devices be substantially equal to provide substantially equal transient responses to spacing or gap changes sensed by each of the air-directing means and to avoid compensation for any differing transient responses.

Thus, in the operation of the system of this invention, gas, preferably air, at a known and regulated pressure is directed from a fluid outlet at a first surface and generally toward an adjoining interfacing second surface which is movable with respect to the first surface. The conditions of flowing gas upstream of the fluid outlet are monitored to indicate the spacing between the first and second surfaces, and changes in conditions in the flowing air are used to generate outputs or signals when the fluid conditions indicate an undesirable spacing or change of spacing between the first and second surfaces or to provide an output or record of the spacing between the first and second surfaces. In die-casting operations in which mold elements are moved to form a mold cavity, the invention provides an improvement in directing a flow of air from a surface of one of the mold elements at an adjoining interfacing surface of second adjacent mold element and monitoring the pressure of the air in a passageway leading to the air-directing means of the first mold element by a pressure-sensitive transducer to produce an electrical signal output, indicating the spacing between the adjoining interfacing surfaces of the mold elements.

Although preferred embodiments have been described above, it should be recognized that the invention may take other specific forms. Because the invention can take other forms, the invention is limited only insofar as is required by the scope of the following claims.