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10DEVELOPMENT OF A PRINTHEAD ADJUSTMENT DEVICE FOR ROBOTIC SYSTEMS FOR LAYER-BY-LAYER PRINTING
OF FOUNDRY MOLDS
Fedor A. Pleshakov
Far Eastern Federal University (FEFU), Department of Computer-Integrated Manufacturing
Systems, Russian Federation, Vladivostok Email: fedya040298@mail.ru ORCID: 0009-0007-5122-1611
Nina T. Morozova
Far Eastern Federal University (FEFU), Department of Computer-Integrated Manufacturing
Systems, Russian Federation, Vladivostok Corresponding Author: Email: moronin56@mail.ru ORCID: 0000-0002-7520-1304
Cold-curing mixtures molds have been given a new boost in additive manufacturing due to their high curing rate at room temperature. These molds are made by applying a layer of a mixture, usually consisting of silica sand and a catalyst, to the work surface. Inkjet printing then uses a 3D printer to apply a binder to the layer, forming a solid pattern on the layer. Since inkjet printing technology for casting molds is widely used, many companies are developing more efficient binders. Changing the binder composition requires readjustment and calibration of the print heads. It is not feasible to carry out various studies directly on the equipment for direct digital production of foundry molds, so there is a need for specialized installations. This article describes the development of an installation for adjustment, calibration and test printing of print heads, which performs two basic functions: viewing and analysis of falling drops and test printing. The design solutions of the unit are discussed in detail, the important components of which are the observation station, the control system of the unit, and the cleaning station. A high-speed camera will be used for viewing and analyzing droplets. With the help of the developed setup it is possible to carry out adjustment of print heads of robotic 3D printing systems.
Keywords: Additive technologies, casting mold, 3D-printing, test printing, printing head.
Financial Support: The work was carried out with the financial support of the Ministry of Science and Education of the Russian Federation [state contract No. 075-11-2021-054].
РАЗРАБОТКА УСТРОЙСТВА НАСТРОЙКИ ПЕЧАТАЮЩИХ ГОЛОВОК ДЛЯ РОБОТИЗИРОВАННЫХ СИСТЕМ ПОСЛОЙНОЙ ПЕЧАТИ ЛИТЕЙНЫХ ФОРМ
Плешаков Федор Александрович
Дальневосточный федеральный университет (ДВФУ), РФ, г. Владивосток, аспирант департамента Компьютерно-интегрированных производственных систем
Морозова Нина Тихоновна Дальневосточный федеральный университет (ДВФУ), РФ, г. Владивосток, к.т.н., доцент департамента Компьютерно-интегрированных производственных
систем
e-mail: moronin56@mail.ru
Литейные формы из холоднотвердеющих смесей получили новый толчок в развитии в рамках аддитивного производства благодаря высокой скорости отвердевания при комнатной температуре. Такие формы изготавливаются нанесением слоя смеси, обычно состоящей из кварцевого песка и катализатора, на рабочую поверхность. Далее струйной печатью с помощью 3D-принтера на слой наносится связующее, образуя на слое твердый рисунок. Так как технология струйной печати литейных форм широко применяется, то многие компании ведут разработки в области создания более эффективных связующих. При изменении состава связующего требуется перенастройка и калибровка печатающих головок. Проводить различные исследования непосредственно на оборудовании по прямому цифровому изготовлению литейных форм нецелесообразно, поэтому имеется необходимость в применении специализированных установок. В статье описана разработка установки для настройки, калибровки и тестовой печати печатающих головок, которая выполняет две основные функции: просмотра и анализа падающих капель и тестовой печати. Подробно рассмотрены конструктивные решения установки, важными составляющими которой являются станция наблюдения, система управления установкой, станция очистки. Для просмотра и анализа капель будет применяться высокоскоростная камера. С помощью разработанной установки возможно проводить настройку печатающих головок роботизированных систем 3D печати.
Ключевые слова: аддитивные технологии, литейная форма, 3D-печать, тестовая печать, специализированная установка, печатающая головка.
Финансирование: Работа выполнена при финансовой поддержке Министерства Науки и Образования Российской Федерации [госконтракт № 075-11-2021-054].
1 INTRODUCTION
University research team is working on a comprehensive project to create a large-format robotic technological complex (RTC) three-dimensional jet printing of casting molds for high-tech production of metal castings and increasing the productivity of automated foundry lines of the enterprise. Production of sand molds for automated metal casting is performed by Binder Jetting Sand Printing technology (binder jetting on activated sand) by layer-by-layer construction of a sand mold on sand/catalyst (hardener) mixture. This technology makes it possible to produce casting molds of any configuration at high speed in compliance with specified accuracy parameters and all requirements for casting molds [1,3,7,9]. A lot of work was carried out on the development of RTC, structural, technological and technical solutions were selected, reliability requirements for the complex under development were taken into account [2,5,10,11]. In order to select the final solutions for each module of RTC, experimental studies were conducted, for this purpose several experimental units were developed [4, 6, 8]. It is not practical to conduct various studies directly on the equipment for direct digital mold making, as there is always a probability of breaking the expensive equipment. Therefore, there is a need to use specialized units.
The main equipment of RTC is a jet printing unit designed for dosing micro volumes of liquid substance to bind the molding sand in the desired sequence according to the commands of the control system (CS). An important component of the printing unit is the printhead, which contains the many holes and piezo elements necessary to provide a high level of dpi (resolution) (Fig. 1).
Figure 1 - Printhead
The task was set to develop a printhead setting device for robotic layer-by-layer printing systems. Such a setup is necessary when changing the composition of the binder, when the printheads need to be readjusted and calibrated [1,3]. The adjustment is carried out according to the drops released from the nozzles, using a high-speed camera to track small drops (20-30 microns) at high speeds (7 m/s).
2 MATERIAL AND METHODS
The purpose of this paper is to conduct research and develop a specialized installation for setting, calibration and test printing of print heads. The setup performs two main functions:
1. The function of viewing and analyzing the falling drops.
2. Test print function.
Both functions require the following components:
1. Hydraulic and vacuum system of the print head.
It is designed to supply the head with binder. Since the printhead uses piezoelements and open holes, an effective way to keep the liquid inside the head is to create a vacuum in the hydraulic system.
The principle of operation of the vacuum system, shown in Figure 2, is to draw air from the receiver PV, by means of pump P. The feedback is accomplished by measuring the pressure of the vacuum. The feedback is realized by measuring the pressure with a vacuum gauge MN, which signals the vacuum control board, which closes the valves V if necessary.
HC - Choke, F - Filter, V - valve, MN - Vacuometer, R - Relay, PV - Pressure vessel, P -
Pump
Figure 2 - Vacuum system The principle of operation of the hydraulic system, shown in Figure 3, is to move the binder from the tank to the transition tank (the tank is shown in Figure 4) by means of pumps P and valves V. Control is carried out by the hydraulic control board, which has as feedback level sensors LS and
LV (Figure 4). The binder also requires heating, for which purpose a heater H is connected to the tank.
V
Figure 3 - Hydraulic system The principle of operation of the printhead in the system, shown in Figure 4, is to circulate the binder between the transition tanks TK, by creating a vacuum in these tanks. Filters F are used to ensure the operation of the printheads PH. Valves V are turned off to stop the operation of the heads. Valves T are used to pre-equalize the level in the tank. There are auxiliary tanks in the system if the transition tank is full of binder.
TK - Tank, LV - Level sensor, V - Valve, PH - Print head, T - Tap, H - Heater
Figure 4 - Print head system
2. Printhead control system.
It is used to control the piezo elements of the printheads. Signals from the print head controller go to the print head driver, which is different for each head. The control system allows you to control the amount of binder composition fed. The speed of movement of the device can be controlled by the integrated control system, which will allow to achieve the required speed of the layer of the workpiece.
3. Printing head cleaning system.
Designed to remove excess print and binder material during operation, and to protect the printheads from drying out during downtime. Since the printhead works with furan resins, it is necessary to maintain conditions such that the resin cannot harden during operation of the printhead or during extended downtime. This requires periodically cutting off the resin layer from the head itself, and cleaning the head completely during downtime. The problem with furan resin is polymerization. after which the resins become resistant to chemical reactions []. If the resin hardens in the head itself, it will be impossible to clean it. The working area must be kept clean at all times. All spilled liquids, including sand, must be wiped up immediately in the service area using special devices. The printhead surface must be kept wet.
For the droplet viewing and analysis function, the following components are required:
1. High-speed camera.
The FastCam AX200 is used to capture the printing process, allowing the required number of frames per second. The camera is synchronized with the printhead, via a computer.
2. Image analysis software.
MATLAB environment is used for droplet analysis, with the help of prngram analyzes the speed of the droplets and their size.
3. Binder dampener.
Adjustment of the head on the limiting modes of work is carried out. This allows you to get a clearer droplet, but also more velocity. That is why it is necessary to dampen it in order to avoid its getting on other devices and mechanisms. The damper is a triangular prism that reflects the droplets in the desired direction.
The following components are required for the test print function:
1. Linear actuators.
Linear actuators are represented by a helical gear driven by a servo motor. For high speed printing test, a 20 mm pitch helical pair is used.
2. Drive control system.
Represented by two servodrivers and a controller separate from all other systems. Communication between the drives and the printhead controller is provided by one of the servo drivers through a special adapter.
3 RESULTS AND DICCUSSION
The electronic model of the designed unit is shown in Fig. 5. It represents a framework consisting of an aluminum structural profile, on which two linear drives of axes 1 and 2 are mounted, designed for displacement of a test bench, and displacement of a printhead 3 between the observation station 4, cleaning station 7 and the test bench. To ensure operation of the printhead and linear drives, two electric boards 6 are assembled, which contain the plant power supply system, drive drivers, pumps and other auxiliary electrical equipment. For adjustment of printing heads and analysis of
obtained videos the computer is used, for which there is a separate workplace 5 with CNC controller and emergency button.
1 - X-axis drive, 2 - Y-axis drive, 3 - Printhead carriage, 4 - Observation station, 5 - Workplace, 6 - Installation control system, 7 - Cleaning station Figure 5 - Electronic Model of Setting Up the Printheads
4 CONCLUSION
As a result of work on the basis of research, adopted technical solutions in accordance with the electronic model, developed and assembled a device for adjusting print heads for robotic systems of
layer-by-layer printing of casting molds, which is shown in Figure 6. The operability of the unit has been tested and the first experiments have been carried out.
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Figure 6 - Print heads tuning device
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