IL182156A - Automated production line for manufacturing wax patterns for the investment casting process - Google Patents

Description

N AUTOMATED PRODUCTION LINE FOR MANUFACTURING WAX PATTERNS FOR THE INVESTMENT CASTING PROCESS An Automated Production line for manufacturing wax patterns for the investment casting process The present invention relates to an automated production line for manufacturing wax patterns for the lost wax or investment casting process used for casting jewelry articles or for casting small non-ferrous metal products.

The invention enables production of wax patterns in an automated production line equipped with a computer or PLC, vacuum wax injectors, a conveyor which is assigned to transfer rubber molds to an injection line, feeders for transferring rubber mold from said conveyer on to an autoclamp, wherein said auto clamp is assigned to provide automatic alignment and adjustment of rubber mold to the nozzle of the injector, further clamping and pushing same against the injector nozzle, further disengaging of rubber mold from injector when injection-molding operation has been performed, and further transferring of filled (injected) rubber mold onto a conveyor for transferring of same from the production injection line onto working table for removal of wax patterns out of rubber mold.

FIELD OF THE INVENTION The present invention is in the field of investment casting. Essentially the process involves few steps. The first is making a wax pattern that is expendable then investing the pattern or groups of patterns in gypsum bonded with crystallite silica, cristobalite and other additives. Next step is burning out the pattern leaving a negative mold inside the investment material, next step is casting by filling the mold with metal and the last step is recovering the casting by destroying the investment mold. The invention relates to the first step i.e. preparing the wax patterns. This operation is labor intensive and the invention is directed to minimize it by forming an automated production line in such a way that will increase productivity immensely.

High efficiency is reached due to the fact that manufacturing of wax patterns is done using an automated production line.

BACKGROUND OF THE INVENTION 1. State of current products and technology Current injection of wax patterns is done either fully by hand or semi by hand using an autoclamp beside the wax injector. There are known wax injectors, controlled by a computer system or a PLC. Such as, for example, wax injectors provided with auto clamp W1500 and W1500D of Schultheiss company (Germany) and computerized vacuum injector 2 500 of Maxmatic company (France). All these products are single standalone stations and require an operator in front of every station. Inserting the rubber mold to the autoclamp is done by hand as well as the removal of the mold from the autoclamp. Identification of the rubber mold is also done manually. 2. Description of wax pattern production A master model of the item that is to be cast is provided. A rubber or silicone rubber mold is being made in order to duplicate the model as many times as required. Wax patterns of the master model are being formed by injecting liquid wax into a rubber mold that is being pressed manually (by hand) against an injector nozzle as many times as required. At the end of the process every single wax pattern will become a cast item.

The injector is a metal container that is heated to a predetermined temperature (65-80*c) and has a pressure regulator for adjusting the injection pressure. More advanced injectors have a vacuum pump for creating vacuum in the rubber mold before the wax injection in order to get a better wax pattern.

More modern injectors have an autoclamp connected. An autoclamp comprises of a mechanical fixture for injection of wax patterns. The fixture is a pneumatic clamp that clamps the rubber mold and presses it against the injector nozzle. The rubber mold is inserted into the fixture manually. Pressing a button begins operating the injection operation and preset values for the injection are set by a PLC controller. After the injection cycle has ended the mold must be removed manually from the autoclamp. The most advanced autoclamp today can inject rubber molds of different sizes, though no matter the size of the rubber mold, it is entered into the autoclamp manually, aligned manually and removed from the autoclamp manually. Opposite each autoclamp/injector station there must be an operator.

The present invention takes care of all the aforementioned manual operations. The transport of the rubber mold to the autoclamp/injector station, the in process recognition of the mold, the feeding of the station, the alignment of the mold in the station, the removal of the rubber mold from the station and the transport of the filled mold to the stripping down table. Using an advanced computer PLC system enables also production management i.e. when the system manufactures the set quantity of wax patterns from a specific rubber mold, the rubber mold is automatically removed from the feeding conveyor to a designated collecting container.

BREIF DESCRIPTION OF THE INVENTION The object of the invention is to achieve a substantial increase of productivity and a decrease in expenditures of labor. These objects are achieved by eliminating all manual operations in the production of multiple wax patterns except the removal of the wax pattern from the rubber mold. Once all necessary production parameters are fed into the system (automated production line) the only manual operation will be stripping down the rubber mold.

The system (automated production line) consists of two conveyors for transporting the rubber molds to the injection stations and back to the stripping down table. A camera or barcode scanner is mounted above the feed conveyor before the first station for recognizing of the rubber mold. On the side of the feed conveyor and in front of each station there are pneumatic cylinders called herein feeders to feed the rubber mold into the appropriate station (autoclamp). On one side of the autoclamp another pneumatic cylinder is installed and has two functions. First it aligns the rubber mold and second is to remove the rubber mold from the autoclamp once the injection and cooling operations are complete onto a slide that sends the rubber mold to the return conveyor and that transport the rubber mold to the stripping table. Once the mold has been stripped of the wax pattern the operator puts the rubber mold back on to the feed conveyor.

All the operations of conveyors, camera/scanner, autoclamp, and injectors are computer/ PLC controlled and synchronized as one system.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example only, with reference to the accompanying drawings wherein: Fig. 1 is a block diagram illustration of the elements of the disclosed production line and their co-relation ; Fig. 2 is a general view of the production line including the conveyors for transferring molds to and from the stripping table, feeders, injecting stations, reader device and injectors; Fig. 3 is a general view of an autoclamp assigned for managing the rubber mold during the injection period; DETAILED DESCRIPTION OF THE INVENTION The current invention provides a production line for manufacturing wax patterns intended for investment casting. The disclosed production line eliminates the shortcomings of conventional devices and is able to achieve high production capacity, decrease in labor and an improvement in the quality of the wax patterns that consequently improves the metal cast products.

Referring to Fig. 1 , a block diagram of a production line for manufacturing wax patterns is shown. The said production line comprises the following units: 1. A frame whereon all the elements of the production line are mounted; 2. Electric motors coupled with gear reducers that are assigned to turn the conveyors; 3. Feed conveyor for transferring rubber molds from the stripping down table to the injection stations; 4. Return conveyor for receiving of filled (injected) rubber molds from the injection stations and returning them to the stripping down table for removing the wax patterns from the rubber molds; . Pneumatic cylinders (feeders) for feeding of rubber injection molds from the feed conveyor into the autoclamp; 6. Autoclamp; 7. Injectors that contain pressurized liquid wax and injecting nozzle; 8. Reading device for rubber mold identification (camera/barcode scanner); 9. Process control station for controlling all operations of the production line. The process controller is also used as a data entry station for data required for line operation (new rubber mold entry, alteration of rubber mold parameters already stored in the controller, etc.) and for order entry.

. A working table for stripping down rubber molds and removing the wax patterns from them.

The frame (1 ) is comprised of two levels. The top level is used to mount all injection related elements and units of the production line and handles the rubber mold from the moment it is laid on the feed conveyor by a person up to the point that it is ejected from the injection station. The bottom level is used for returning the rubber molds to the stripping down table. The bottom level is basically comprised of a conveyor that towards its end is elevated in order to bring the rubber molds back to the top level at the stripping down table. The rubber molds reach the return conveyor by slides once they are ejected from the injection stations or when they reach the end of the feed conveyor. The bottom level also houses the solenoids, valves and electric wiring used to operate the line.

The electric motors coupled with gear reducers (2) and are controlled by controller. They may be chosen in accordance with the desired movement rate of conveyors.

The feed Conveyor (3) is intended for transferring empty rubber molds from the strip down table to the injection stations in the line. The conveyor is divided to cells. The rubber mold is inserted into one of these cells at the strip down table (where the conveyor starts). These cells are used as a reference to the location of a certain rubber mold and as a pre-alignment point of the rubber mold before feeding it into the injection station. In the case that the rubber mold has not been fed to any injection station and has reached the end of the conveyor, there is a slide that receives the rubber mold and guides it onto the return conveyor.

The return conveyor (4) is intended for transferring rubber molds that have been injected from the injection stations and the end of the feed conveyor back to the strip down table where the injected wax patterns are removed from the rubber molds and the now empty rubber molds are again being put on the feed conveyor. The return conveyor is padded in order to soften the fall from the slide onto the conveyor and to enhance the grip of the rubber mold in order to prevent it from sliding backwards once it reaches the inclined part of the conveyor.

The feeders (5) are intended for feeding the rubber mold into the injection station. The mold is situated on the feed conveyor in one of the cells. Once the mold on the feed conveyor is in front of the appropriate injection station for this specific mold planned by control algorithm, the feed conveyor (3) stops, the feeder pushes the rubber mold off the conveyor and into the autoclamp (6) of the said injection station. There is a feeder opposite each injection station and it is comprised of a pneumatic cylinder provided with a plate mounted perpendicularly to the cylinder at the end of the cylinders rod. The cylinder size and length is chosen in such a way that the rubber mold reaches the stopper in the autoclamp before the end of the cylinder stroke but so that it doesn't warp the rubber mold with excessive force.

Fig 2 illustrates the general view of the disclosed production line, wherein bellow is the description of the main parts: 1. Frame; 2. Electric motors; 3. Feed conveyor for transfer of rubber molds; 4. Return conveyor for transfer of injected rubber molds back to table; . Feeders; 6. Autoclamps; 7. Injectors; 8. Reading device for identifying rubber molds; 9. Process control station; . Stripping down table for removing wax pattern from rubber mold; 11. Autoclamp clamping cylinder; 12. Inclined slide for transferring of filled rubber molds onto return conveyor; 13. Cooling air duct for cooling rubber molds on conveyors; 14. Autoclamp gate cylinder and aligning plate; . Cooling plates for cooling rubber molds before strip down; 16. Autoclamp ejector and aligning cylinder; Fig. 3 illustrates the general view of the autoclamp: . Pneumatic cylinder of gate; 1 1. Pneumatic cylinder of clamping plate; 16. Pneumatic cylinder of ejector; 17. Top of clamp; 18. Bottom of clamp; 19. Posts (columns); . Sliding rail bearings and housing; 21. Lead screw; 22. Gate and aligning plate; 23. Ejector and aligning plate; 24. Clamping plate; . Rubber mold; 26. Rubber mold injection opening; The autoclamp (Unit 6 Fig. 1 and 2), is intended for handling the rubber mold during injection procedures from the moment the rubber mold is fed into the autoclamp up to its ejection from the autoclamp. The sequence of the procedures is as follows: 1. Receiving of rubber mold from feed conveyor (3 fig. 2). This is done by the feeder (5 fig. 2). The rubber mold is indexed into the station utilizing the aligning plates (22 and 23 fig. 3). These plates are tapered at the opening of the autoclamp and allow some degree of error during the feed operation. 2. Clamping the rubber mold. After the rubber mold is fed into the autoclamp it is left justified using the ejection and aligning plate being pushed by its' pneumatic cylinder (23 fig. 3) and then clamped to place using the clamp plate (24 fig. 3). 3. Positioning of rubber mold. After the rubber mold is aligned with reference to the autoclamp the autoclamp must be aligned in such a way that the injection opening in the rubber mold is coaxial with the injector nozzle. This is done by positioning motors connected to the lead screws that set the autoclamp to the desired height and width position. This position is determined by the rubber mold characteristics and its parameters are downloaded to the motors from the controller database. 4. Injecting the rubber mold. After the station is positioned the autoclamp presses the rubber mold (25 Fig. 3) against the nozzle of injector (7 Figs. 1 and 2). Wax is injected into the rubber mold and a wax pattern is created. After the injection time has ended (set by the rubber mold parameters) the autoclamp moves back and the rubber mold is released from the injector nozzle.

. Initial cool down and homing. After injection the rubber mold must be allowed to cool down while still clamped. This period is also set by the rubber mold parameters. While cooling down takes place the autoclamp prepares for ejecting the rubber mold. The gate of the autoclamp opens and the autoclamp moves to home position. This position is adjacent to the slide so that the rubber mold is ejected directly on to the slide. 6. Ejection. Once these operations are complete and the cool down time has ended, the clamp is released, the ejector pushes the rubber mold out of the autoclamp and on to the slide where it falls on to the return conveyor. 7. Reset. After the rubber mold is ejected the autoclamp is reset in order to receive the next rubber mold: The ejector returns to its initial position, the gate closes and the autoclamp is positioned in front of the feeder.

The injector (Unit 7 Figs. 1 and 2) is composed of a main tank that can be heated up to 90°C. The tank is filled with wax in liquid state (due to heating) and can be pressurized up to 3.5bars. On the side of the tank an injecting nozzle is fitted. This nozzle can also be connected to a vacuum source in order to create vacuum in the rubber mold cavity prior to injecting wax in to the cavity. Apart from this, the injector is connected to the controller through pressure sensors and temperature sensors. The controller maintains the preset temperature of the injector and regulates the injection pressure for each injecting event as required according to the parameters of the rubber mold being injected at the said event. The reading unit (8 Figs. 1 and 2) is intended for identifying the rubber molds before entering the injection stations. The reading unit can be, for example, a camera or a barcode scanner. It is situated above the feed conveyor between the strip down table and the first injection station. The reading unit reads the identity number that is located on the face of the rubber mold as the rubber mold passes under it. Once identified by the reading unit, the unit sends the identity of the rubber mold to the controller.

The process controller (9 Fig 1 ) is intended to control, manage and synchronize all procedures of the production line. This includes all pneumatic cylinders, regulators, motors, temperature control, sensors, readers and data management. The controller also has an internal database. The database stores all the rubber mold identification numbers and all related parameters for each rubber mold. Such parameters are rubber mold id number, injection time, injection pressure, clamp pressure, cool time, horizontal and vertical position of injection opening (hole) in rubber mold, wax type to be used (the injector to be used by wax type), vacuum value before injection, date of first injection, last date rubber mold was in use, etc. The database is also used for order management and is used for pattern quantity production management. An interface with the controller is provided in order to monitor, enter and alter these parameters.

The stripping down table (10 Fig. 2) is intended for the following tasks: Receiving rubber molds from the return conveyor; a work area for stripping down the rubber molds, removing the wax patterns from them and preparing the rubber molds for their next cycle; provisional space for containers for accumulation of wax patterns prior to transiting them to the next step in the casting process. The table also serves as the base of the feed conveyor where the rubber molds that are ready for their next injection are loaded on to the feed conveyor.

During multiple injections of the rubber mold, the rubber molds accumulate heat. This changes the characteristics of the injection parameters. In order for a smooth and regular operation of the production line, it is necessary to keep the rubber molds at a constant temperature. This is achieved by adding cooling ducts and cooling devices in the production line. Above the conveyors an air duct is installed (13 fig.2). This duct blows cold air on the rubber molds being transferred and on the conveyor surface. Inside the conveyors a cooling element is installed for additional cooling of the conveyors. The slides of the injection stations are also cooled with a cooling element. On the stripping table cooling plates are installed in front of each operator station and at the end of the return conveyor (15 fig.2) in order to cool the rubber molds at all the places it passes before and after injection.

Detailed description of the process Rubber molds usually consist from a top and bottom plate (halves) wherein a hollow cavity is present. This cavity represents a negative shape of the product that we wish to cast. As part of the casting process we must inject wax (designated specifically for the casting process) in to the aforementioned cavity thus creating a replica of the desired part in the form of solid wax. This replica is regarded as the wax pattern and is essentially the duplication method used in casting. The present invention is intended for mass production of wax patterns (duplicates) from each rubber mold used in the production line.

According to the present invention, the production line operates in the following way: The operators sit around the strip down table. Every one of them has access to the start of the feed conveyor (3 fig.2) and to the end of the return conveyor (4 fig. 2). The work cycle starts by placing empty rubber molds on the feed conveyor. The feed conveyor moves automatically towards the injection stations. The rubber molds advance and pass under the reading device. The rubber mold is identified and the identification number is sent to the controller.

The controller assigns the identification number with the location of the rubber mold on the feed conveyor and searches the database to locate all the parameters associated with the specific rubber mold. If the "manage order" function is enabled the controller checks if the required quantity of wax patterns has been produced. If the answer is positive the rubber mold is not fed into any injection station but rather fed to the "order complete" station. This station is essentially a container for accumulating rubber molds that their required quantity of wax patterns has been reached. If the answer is negative or the "manage order" function disabled or the rubber mold doesn't have a specified order, the controller sends the rubber mold to the next injection station that is vacant for injection and has the correct wax type for the specific rubber mold. When a rubber mold is assigned to an injection station the controller downloads all relevant injection parameters of the specific rubber mold to the injection station. This sets the correct injection times and pressures for the specific rubber mold. Once the rubber mold is fed into the injection station the autoclamp begins operation: it clamps the rubber mold, positions the injection opening according to the parameters of the rubber mold, checks that the set pressure values have been reached and when all these are set it injects the rubber mold with wax. Once injection time has been reached the injection is stopped and the set cooling time takes effect. Meanwhile the autoclamp moves to home position and when the cooling time has been reached the rubber mold is ejected from the station onto the slide. When ejected, if the rubber mold appears in the order entry of the database, the "manufactured quantity" is incremented by one. The rubber mold now filled with wax slides on to the return conveyor where it is transferred back to the strip down table. The injection station is reset after the ejection and is ready to be assigned to the next rubber mold on the feed conveyor. When the filled rubber mold reaches the table it is stripped and the wax pattern removed and stored in one of the containers on the table. The feed conveyor is independent of the injection stations and each injection station is independent of the others so that as soon as an injector station is vacant, a rubber mold can be assigned to it. The program in the controller thus optimizes injection procedures utilizing all injecting stations simultaneously. The controller also has the ability to simultaneously handle other tasks not linked directly to the production line operation while still operating the production line (such as updating parameters of a rubber mold).

The number of injectors provided in the assembly line is determined by the time that is necessary for the operating cycle, the number of different wax types used in the production line, the conveyors velocities and the mean quantity of rubber molds to be used at any given time.

Claims (9)

1. automated production line for manufacturing wax patterns of master models comprising two or more injectors arranged in a line on a frame, The purpose of this automatic production line is threefold, first, is to increase productivity, Second is to decrease labor and third is to improve the quality and uniformity of the wax patterns, Said frame is used to mount thereon computerized vacuum wax injectors, conveyors, autoclamps and reader device for injecting rubber molds, The feed conveyor transfers the empty rubber molds to the injecting stations and the return conveyor that transfers the filled rubber molds to the strip down table, The rubber molds are fed into the injecting stations from the feed conveyor automatically, prepared automatically for all injection characteristics required, injected and then after are ejected on to the return conveyor.

2. The production line according to claim 1 where single injection stations are placed in a line and the rubber molds are being transferred to them and back to the strip down table automatically, This transfer operation can be done by two separate conveyors (one for feed and one for return) or by one circular conveyor or by any other means.

3. Method according to claim 1 in which the feed conveyor stops where the rubber mold is in front of the injection station and the feed cylinder pushes the rubber mold from the feed conveyor in to the injection station, This operation can be done also by electric motor or other means.

4. Method according to claim 1 in which the autoclamp now has to enable the rubber mold to be aligned and ejected mechanically, The alignment is done by fixed alignment plates in the station and by left or right justifying against the gate of the rubber mold using the alignment and ejection cylinder, The ejection is done by opening a mechanical gate and pushing the rubber mold through it using the alignment and ejection cylinder, It can be applied in a single station regardless of the production line.

5. Method according to claim 1 in which the autoclamp comprises screw mechanisms capable to transfer said autoclamp on a trajectory perpendicular to the axis of injector nozzle (vertically and horizontally) and adjusting of said injector nozzle to injection opening of rubber mold.

6. Method according to claim 1 in which a reading device is situated above the feed conveyor and before the injection stations, identifies the rubber molds and sends the rubber molds identity to the controller for managing the rubber mold through the process.

7. Method according to claim 1 in which a computer or a controller (PLC) or a chip with appropriate embedded software manages and controls all operations and processes of the automated production line.

8. Method according to claim 1 in which cooling devices are installed throughout the production line, Above the conveyors runs an air duct that channels cool air on to the rubber molds on the conveyor, In the conveyor itself a cooling element is also installed for cooling the conveyor surface as well, In addition the slides are also cooled, On the strip down table a cooling plate is installed next to each operator station.

9. Method according to claim 1 in which order entry and order management is provided, An order is entered into the controller and the controller monitors production of the order, When an order of a specific rubber mold has been completed the controller send a command to the system to eject the rubber mold from the production line and into a container for collecting rubber molds that their order has been completed. Inventors: Mr. Ittai Racine Mr. Michael Racine