In my work on sand casting process modernization, I focused on a horizontal molding machine used for clay sand molding. The original machine relied on a single-sided double shooting method, a three-phase asynchronous motor, and independent hydraulic control. These features caused high mechanical energy consumption, low production efficiency, insufficient parting surface compactness, and poor adaptability to different sand mold heights. To solve these problems, I designed and implemented a fully automatic control system for an upper and lower box double-shooting molding machine based on a programmable logic controller. This retrofit was specifically aimed at improving sand casting quality, reducing energy use, and increasing flexibility in sand casting production.
The main objectives of my retrofit were to replace the original shooting method with vertical upward and downward shooting, to replace the asynchronous motor with a servo motor, to develop a new opening and closing device, and to build a servo hydraulic system with an integrated PLC control system. I retained the original machine frame, sand box, and guide rod model hanger. The new system uses a servo motor directly coupled to a hydraulic pump, and the PLC collects displacement and pressure signals to dynamically adjust motor speed and pump displacement. Through a segmented control strategy, I achieved high-precision position control during fast clamping, stable pressure control during compaction and holding, and accurate positioning of the upper and lower frames. The retrofitted machine can adapt its speed according to different sand mold heights, which is a critical requirement in modern sand casting.
1. Process Requirements and Retrofit Scope
The original horizontal molding machine in sand casting had several limitations. The single-sided double shooting method could not uniformly fill deep recesses in the pattern. The three-phase asynchronous motor ran at a constant speed, so the hydraulic pump delivered constant flow regardless of the actual demand in different phases. This led to excessive throttling losses, high energy consumption, and unstable compaction. The parting surface compactness often fell below the required value, especially for complex castings with large concave depths. In sand casting, insufficient compactness can cause mold wall movement, shrinkage defects, and low yield.
My retrofit targeted these issues by introducing vertical shooting from both above and below the pattern. This approach guides sand into the back shadow areas of the pattern more effectively. I also replaced the fixed-speed motor with a servo motor and developed a new hydraulic system that uses proportional and cartridge valves. The control system was designed to manually adjust operating speed through a touch screen and to automatically adjust speed by real-time detection of hydraulic pressure and actuator position. The main technical requirements are summarized in Table 1.
| Requirement | Original state | Retrofitted state |
|---|---|---|
| Shooting method | Single-sided double shooting | Vertical upward and downward shooting |
| Drive motor | Three-phase asynchronous motor | Permanent magnet synchronous servo motor |
| Speed control | Fixed speed, no adaptive adjustment | Manual and automatic speed adjustment |
| Compaction control | Independent multi-valve control | Segmented pressure and position closed-loop control |
| Parting surface compactness | Often below 80 | Measurement value above 80 |
| Energy consumption | High hydraulic throttling loss | Reduced by servo pump control |
| Sand casting yield | Low for complex parts | Improved to 96.5% in tests |
The retrofit work included the design of the opening and closing device, the hydraulic control system, the control system hardware selection, and the control system software design. I kept the original mechanical frame, sand box, and guide rod model hanger. The new opening and closing device consists of an upper fixed assembly and a lower fixed assembly. The upper fixed assembly includes an upper compaction plate connection seat, an upper pressure plate adjustment motor, a lifting nut, an upper fixed seat, an upper box cylinder, an upper closing plate, and an upper sand frame. The lower fixed assembly mainly consists of a lower compaction plate, a lower sand frame, a lower sand frame seat, a lower compaction plate seat, a lower fixed seat, a clamping cylinder, and a lower box cylinder.
2. Composition and Working Principle
The horizontal molding machine for sand casting mainly includes the opening and closing device, the guide rod model hanger, the sand hopper, and the control system. There are two shooting hopper assemblies. The upper shooting hopper is fixed on the upper compaction plate connection seat. The lower shooting hopper is arranged on the frame and fastened by hex bolts at the upper fixed seat and the fixed frame. Each hopper uses a box body and a ventilation device to blow molding sand vertically toward the pattern. The sand then enters the opening and closing device for compaction.
The guide rod model hanger is driven by a cylinder to send the model along a guide slide rail to the position between the upper and lower sand boxes. According to the compaction requirements, the model hanger can move vertically along the slide rail together with the lower sand box. This coordinated motion is essential for producing uniform sand casting molds.
The working process of the horizontal molding machine has two modes: manual control and automatic control. The PLC receives signals from various sensors and commands from the host computer. It then outputs control signals to hydraulic cylinders, pneumatic cylinders, and other actuators. The machine performs sand shooting, sand compaction, mold opening and closing, and sand mold push-out. It can continuously and cyclically perform sand casting molding operations. The opening and closing device has three magnetostrictive displacement sensors to detect the positions of the upper and lower sand frames, the upper and lower compaction plates, and the clamping lower frame. These sensors provide position detection and feedback for mold opening and closing. Pressure sensors are used to detect and feed back the hydraulic cylinder pressure, ensuring that the cylinders run at the required speed and meet the adaptive speed control requirements. This ensures stable and reliable operation and enables automatic and efficient sand casting molding.
The overall working cycle can be expressed as a sequence of stages. I define the cycle time as:
$$ t_{cycle} = t_{clamp} + t_{shoot} + t_{compact} + t_{open} + t_{slide} + t_{push} + t_{return} $$
where each term represents the time for clamping, shooting, compaction, mold opening, slide-out, push-out, and return, respectively. Reducing any of these terms while maintaining sand casting quality improves productivity. The servo hydraulic system allows faster motions during non-critical stages and slower, more controlled motions during compaction and positioning.
3. Hydraulic Control System Design
According to the molding process requirements, the control system automatically calculates the required pump pressure, feed distance, and speed transition points based on the mold information entered by the user. The PLC sends a 0–10 V analog signal to the servo driver. The servo driver controls the hydraulic pump, and the hydraulic oil circuit drives the hydraulic cylinders. With feedback from various sensors, the PLC adjusts the analog output in real time to achieve reasonable pressure and flow values under different working conditions.
In many horizontal molding machines for sand casting, the compaction mechanism occupies the sand addition position at the top of the mold. The upper and lower compaction cylinders are controlled by directional valves that act simultaneously. Due to electrical signal delays, hydraulic pressure changes, and valve response times, the upper and lower compaction cylinders can become unsynchronized. This causes uneven stress in the sand mold, leading to deformation or displacement. The synchronization of compaction determines the uniformity of sand casting compaction. Therefore, I proposed a compaction synchronized electro-hydraulic servo pump control system for the retrofitted machine. This system cancels the additional pressure control adjustment and control valves of the compaction plates. The main compaction force is generated by the clamping cylinder, and a proportional directional valve is used for precise position control. The sand casting molding quality and energy utilization rate are higher than those of the original dual-pump multi-way valve independent control hydraulic system.
The hydraulic system uses a cartridge valve integrated structure. It consists of a servo motor, a hydraulic pump, a hydraulic oil source, cartridge solenoid valves, cartridge check valves, cartridge balance valves, cartridge relief valves, electromagnetic directional valves, proportional directional valves, and hydraulic cylinders. The hydraulic principle includes the following main components: a servo-driven gear pump, a relief valve for system safety, a check valve to prevent reverse flow, a proportional directional valve for position control, and a set of cartridge valves for logic control. The system operates in different modes depending on the stage of the sand casting cycle.
The relationship between pump flow and motor speed is:
$$ Q_p = V_p n_p \eta_v $$
where \(Q_p\) is the pump flow rate, \(V_p\) is the pump displacement, \(n_p\) is the pump speed, and \(\eta_v\) is the volumetric efficiency. The torque required by the pump is:
$$ T_p = \frac{\Delta P V_p}{2\pi \eta_m} $$
where \(\Delta P\) is the pressure difference across the pump, and \(\eta_m\) is the mechanical efficiency. The motor power is:
$$ P_{motor} = \frac{T_p \omega_p}{1000} $$
where \(\omega_p = 2\pi n_p / 60\) is the angular speed. By controlling \(n_p\), the PLC can control both flow and pressure. The cylinder force during compaction is:
$$ F_c = P_c A_c = P_c \frac{\pi D_c^2}{4} $$
where \(P_c\) is the cylinder pressure, \(A_c\) is the effective area, and \(D_c\) is the cylinder bore diameter. The cylinder velocity is:
$$ v_c = \frac{Q_p}{A_c} $$
These equations form the basis for the adaptive speed control. The PLC uses the measured pressure and displacement to calculate the desired pump speed and valve opening. The solenoid action sequence is given in Table 2.
| Action | YD1 | YD2 | YD3 | YD4 | YD6 | YD7 | YD8 | YD9 | YD11 | YD12 | YD13 | YD14 | YD15 | YD16 | YD17 | YD18 | Analog |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Clamping fast down | + | + | – | – | – | – | – | – | – | – | – | – | – | + | – | 0 | 0–10 V |
| Clamping slow down | + | + | – | – | – | – | – | – | – | – | – | – | – | – | – | 0 | 0–10 V |
| Clamping up | + | + | – | + | – | + | – | – | – | – | – | – | – | – | 0 | – | 0–10 V |
| Clamping fast up | + | + | – | + | – | + | – | – | – | – | – | – | – | + | 0 | – | 0–10 V |
| Slow compaction | + | + | – | + | – | – | – | – | – | – | – | + | + | – | 0 | – | 0–10 V |
| Upper frame up | – | – | – | – | – | – | – | – | – | – | + | – | – | – | – | – | – |
| Upper frame down | – | – | – | – | – | – | – | – | – | – | – | + | – | – | – | – | – |
| Lower frame up | – | – | – | – | – | – | + | – | – | – | – | – | – | – | – | – | – |
| Lower frame down | – | – | – | – | – | – | – | + | – | – | – | – | – | – | – | – | – |
| Slide-out | – | – | – | – | – | – | – | – | + | – | – | – | – | – | – | – | – |
| Slide return | – | – | – | – | – | – | – | – | – | + | – | – | – | – | – | – | – |
| Push-out | – | – | – | – | + | – | – | – | – | – | – | – | – | – | – | – | – |
| Push return | – | – | – | – | – | + | – | – | – | – | – | – | – | – | – | – | – |
In Table 2, “+” means the solenoid is energized, and “-” means it is de-energized. The analog column indicates that the servo pump receives a 0–10 V signal for speed control. The PLC coordinates these solenoids and analog signals according to the sand casting cycle.
4. Control System Hardware Design
The control system of the horizontal molding machine mainly consists of a programmable logic controller, a touch screen, limit switches, displacement sensors, pressure sensors, a hydraulic system, and a pneumatic system. The hardware is divided into a signal acquisition module, a logic control module, and an execution module.
4.1 Signal Acquisition Module
Based on the structure and working principle of the opening and closing device, I selected a BTL6-E500-M0550-PF magnetostrictive displacement sensor and an FX3U-4AD analog input module to convert current and voltage signals into digital values. In the hydraulic system, the output terminals of the liquid level and liquid temperature sensors are connected to the AD module to collect oil temperature and oil level information. The pressure sensor and the pressure and flow output terminals of the DA module are connected to the analog input terminals of the servo driver. The RS485 digital signal output bus of the servo driver is connected to the PLC controller to complete the pressure and flow acquisition of the opening and closing device at each moment.
The cylinder and pneumatic cylinder stroke detection uses AG-49DF series magnetic switches. The E2B-M18KS08-WZ-C1 proximity switch is used to transmit the presence and departure position information of objects. When the equipment performs actions such as pushing the middle frame out and sliding the lower frame out, it triggers the proximity switch to send a signal.
4.2 Logic Control Module Selection
According to the requirements of the molding machine control system, I counted the I/O points. There are 43 digital input signals, 7 analog input signals, 50 digital output signals, and 5 analog output signals. The system needs expandable I/O ports and communication module functions. After comparison, I selected a FX5U series PLC as the control core. The specific modules are listed in Table 3.
| Module type | Model | Quantity | Function |
|---|---|---|---|
| Main PLC | FX5U-80MT-ES | 1 | Logic control, high-speed processing |
| Digital I/O expansion | FX5-32ET/ES | 1 | Expand digital inputs and outputs |
| Digital output expansion | FX5-8EYT/ES | 1 | Expand digital outputs |
| Analog input | FX3U-4AD | 2 | Displacement, pressure, temperature, level |
| Analog output | FX3U-4DA | 2 | Servo driver command, proportional valve command |
| Communication adapter | FX-485ADP | 1 | RS-485 communication with servo driver |
| Communication board | FX3-232-BD | 1 | RS-232 communication with host computer |
The main PLC has 80 I/O points, which is not enough for all external inputs and outputs. Therefore, I added one FX5-32ET/ES digital input/output expansion module, one FX5-8EYT/ES digital output module, two FX3U-4AD analog input modules, and two FX3U-4DA analog output modules. The system also uses an FX-485ADP communication adapter module for RS-485 communication with the hydraulic servo driver and temperature detection equipment. An FX3-232-BD communication board provides an RS-232 interface for real-time data exchange with the host computer. The I/O allocation is summarized in Table 4.
| Signal type | Quantity | Allocated module |
|---|---|---|
| Digital input | 43 | FX5U-80MT-ES + FX5-32ET/ES |
| Analog input | 7 | 2 × FX3U-4AD |
| Digital output | 50 | FX5U-80MT-ES + FX5-8EYT/ES |
| Analog output | 5 | 2 × FX3U-4DA |
| Communication | RS-485, RS-232 | FX-485ADP, FX3-232-BD |
4.3 Output Execution Module Selection
According to the working load and speed requirements of the hydraulic cylinders during clamping, compaction, mold opening, slide-out, receiving, and stripping, I calculated the working pressure and rated flow of the hydraulic pump, as well as the rated power of the motor. The main selection parameters are shown in Table 5. Based on the requirements of the hydraulic control system and the calculated motor torque and speed, I selected an internal gear pump with high self-priming capacity and efficient stable output. I also selected an IS580 series servo driver and permanent magnet synchronous servo motors, models ESMG1-25D20CD and ESMG1-75D17CD.
| Component | Specification | Application in sand casting |
|---|---|---|
| Hydraulic pump | Internal gear pump, high pressure | Provides flow for clamping and compaction |
| Servo driver | IS580 series, 0–10 V analog input, RS-485 | Controls pump speed and pressure |
| Servo motor 1 | ESMG1-25D20CD | Main pump drive |
| Servo motor 2 | ESMG1-75D17CD | Auxiliary pump drive |
| Displacement sensor | BTL6-E500-M0550-PF | Measures cylinder position |
| Pressure sensor | Analog output, 0–10 V | Measures hydraulic pressure |
| Proximity switch | E2B-M18KS08-WZ-C1 | Detects slide-out and push-out positions |
| Magnetic switch | AG-49DF | Detects cylinder stroke limits |
4.4 Control System Wiring
After completing the hardware selection, I designed the control cabinet. The hardware components are connected directly through their own terminal blocks. The electrical wiring of each component is connected using different specifications of terminal heads according to current intensity and incoming/outgoing line dimensions. The connection between the control cabinet and the motor uses a terminal block. The PLC terminal wiring includes inputs from sensors and switches, and outputs to relays, solenoid valves, and analog modules. The wiring is designed to minimize electromagnetic interference, especially for the analog signals used in sand casting pressure and position control.
5. Control System Software Design
5.1 Speed Control Program Design
The manual speed control system in the PLC is mainly used for no-load testing and manual control during operation or maintenance. Before work, the operator checks all connections, electrical circuits, and oil inlet and return pipes. After ensuring everything is normal, the power is turned on and the manual mode is started. The operator can input the pressure and flow of the servo pump through the user interface to control the forward and backward movements of the corresponding cylinders.
The automatic speed control system is mainly used for automatic adjustment and control of servo pump pressure and flow. The system automatically adjusts the working intervals between processes according to different mold parameters such as sand mold thickness. It also sets acceleration and deceleration segments in each process to achieve smooth transition, reduce impact, and reduce energy consumption caused by peak power. The speed control flow is as follows: first, the system reads the mold parameters; second, it calculates the target speed profile for each stage; third, it compares the actual position and pressure with the target values; fourth, it adjusts the servo pump speed and proportional valve opening; fifth, it monitors the cycle and repeats for the next mold. This process is repeated continuously for each sand casting cycle.
5.2 Speed Feedback Control Algorithm Design
In the speed control system, the disturbance rejection and speed accuracy of the cylinder directly affect the molding efficiency and sand casting quality. Because the system experiences continuous changes from low pressure to high pressure, and the working pressure and flow are different in each stage, the molding load causes fluctuations in hydraulic cylinder displacement. As a result, the operating speed of the horizontal molding machine is difficult to stabilize at the given speed curve and pressure curve values for each stage. Therefore, open-loop control or a single control method cannot meet the requirements of fast, accurate, and stable control of the sand casting process. For this reason, I adopted pressure feedback closed-loop control in the pressure curve tracking stage and position feedback closed-loop control in the fast forward and return stages. The principle of the operating speed closed-loop control system is shown in the equations below.
The PID control law used for both pressure and position loops is:
$$ u(t) = K_p e(t) + K_i \int_0^t e(\tau)\,d\tau + K_d \frac{de(t)}{dt} $$
For the pressure loop, the error is:
$$ e_p(t) = P_{set}(t) – P_{meas}(t) $$
For the position loop, the error is:
$$ e_x(t) = x_{set}(t) – x_{meas}(t) $$
where \(P_{set}\) and \(x_{set}\) are the target pressure and position, and \(P_{meas}\) and \(x_{meas}\) are the measured values. The output \(u(t)\) is converted by the D/A module and sent to the servo driver or proportional valve amplifier. The control strategy for different stages is summarized in Table 6.
| Stage | Controlled variable | Feedback sensor | Actuator | Control algorithm |
|---|---|---|---|---|
| Clamping fast forward | Position | Displacement sensor | Proportional directional valve | Position PID |
| Clamping slow forward | Position | Displacement sensor | Proportional directional valve | Position PID |
| Pressure holding | Pressure | Pressure sensor | Servo pump | Pressure PID |
| Clamping return | Position | Displacement sensor | Proportional directional valve | Position PID |
| Upper frame positioning | Position | Displacement sensor | Servo pump | Position PID |
| Lower frame positioning | Position | Displacement sensor | Servo pump | Position PID |
For the clamping cylinder pressure holding stage, maintaining stable pressure is the core of the sand casting operation. The opening and closing device applies load to the lower compaction plate and upper closing plate through the hydraulic cylinder. The hydraulic cylinder rod contacts the lower compaction plate seat, and the lower compaction plate contacts the lower sand frame and other frames to drive the upper closing plate. The pressure sensor measures the actual pressure in the hydraulic cylinder and compares it with the target pressure set manually or automatically for sand mold compaction. The deviation is processed by the main controller, and the PLC outputs a signal to the hydraulic servo driver. By changing the hydraulic pump flow, the system controls the speed of the hydraulic cylinder to maintain the sand mold compaction pressure without exceeding a set value.
In the fast forward and return stages of the clamping cylinder, I introduced an electro-hydraulic proportional position PID control algorithm. The input is the error between the target displacement and the actual displacement collected by the sensor. After calculation by the PLC controller, the control signal is amplified by the proportional amplifier and used as the control signal for the proportional directional valve. This controls the hydraulic cylinder displacement to approach the target value.
During the molding process, the position accuracy of the upper and lower frames directly affects the sand mold quality. To ensure accurate sand thickness during the sand filling process and avoid cavity misalignment when joining with the molding line, the hydraulic circuit in this stage uses servo pump displacement adjustment. This achieves stable and uniform driving and precise positioning during cylinder movement. The error between the target displacement and the actual displacement is used as the input for PID calculation. The result is converted by D/A and used as the driver input to drive the hydraulic pump. The segmented control strategy provides high precision, meets high-speed motion requirements, and ensures stable system operation.
5.3 Molding Machine Control System Software Design
The PLC program is written in GX Works3 using logic and sequential control to implement manual and automatic control. The control system flow is as follows. After the system starts, the mold is selected. After confirming the mold parameters, the system calculates the points and performs system initialization. After initialization, the clamping cylinder and the lower frame cylinder act simultaneously. The lower frame cylinder is controlled by a small pump to control the flow and thus the cylinder speed. The clamping cylinder action is completed under the regulation of the speed control system. The lower frame quickly moves to 10 cm directly below the middle frame, decelerates and buffers to fit the middle frame. After completion, it accelerates upward to directly below the upper frame, decelerates, and completes clamping.
After clamping, sand shooting is performed. After gas is exhausted, compaction is performed. The sand is sandwiched between the molds, and the clamping cylinder performs the compaction action. At this point, the upper frame cylinder and the lower frame cylinder are depressurized. The compaction force of the clamping cylinder is detected by the pressure sensor until the required position is reached. Compaction is then complete.
After compaction, the clamping cylinder uses variable speed mold opening to move down to the origin. The lower frame cylinder rises to the lower frame pre-slide-out position. Mold opening is complete. After the lower frame moves to the slide-out position, the middle frame cylinder retracts, and the slide-out cylinder simultaneously slides out. The worker performs sand mold inspection and core setting. When a sand mold is scrapped, the PLC sends a slide-out cylinder return signal, pushes out the sand mold, and selects stop or enters the next cycle according to the mode input. If core setting is confirmed, the PLC performs the subsequent receiving action according to sequential control.
After the slide-out cylinder returns, the clamping cylinder fits the lower frame and upper frame by variable speed. After receiving and clamping, the upper frame cylinder moves up to drive the upper frame. Under the action of the upper compaction plate of the upper fixed seat, the upper frame stripping is completed. The lower frame stripping is completed by the clamping cylinder and the lower frame cylinder moving down to the origin. After stripping, the middle frame and push-out cylinder are pushed out simultaneously. After push-out is completed, the upper frame cylinder and push-out cylinder move to the origin at the same time, waiting for the PLC to issue the next molding command.
5.4 HMI Design
I used EasyBuilder Pro configuration software to write the graphical user interface. The production monitoring interface includes cumulative output, molding time, hydraulic station motor power consumption, and other monitoring parameters. It also includes user login and serial port switching buttons. The function selection interface displays buttons for switching between functions. For example, clicking the “clamping and shooting” button jumps to the parameter setting interface. There, the operator can modify the clamping operation status and related technical parameters. The interface displays the current position of the clamping cylinder, the large pump pressure, flow, and the opening and closing proportional valve flow. It also allows modification of the slow pressure, flow, opening, position of the upper frame, the fast rising pressure of the clamping cylinder, and the delayed clamping parameters. The manual mode interface allows manual adjustment of the large and small pump pressures and flows, enabling the operator to perform jog debugging and later troubleshooting.
6. Experimental Testing and Results
I selected a clutch pressure plate casting process from a foundry for testing. The test used horizontal parting and ordinary clay sand casting. The clutch pressure plate material was QT450-10, with a spheroidization grade of 1–3, pearlite content less than or equal to 35%, and a required sand mold hardness measurement value of 80–95. The casting weight was about 20 kg. The casting structure was complex, with large wall thickness differences and wide distribution, making it prone to shrinkage defects. These defects accounted for 57% of the company’s annual scrap rate. Casting process simulation analysis showed that the thinnest part and the lower part of the casting solidified first, but the mold hardness measurement value did not satisfy 85. This caused mold wall movement during solidification, making it difficult to achieve self-feeding during graphitization expansion.
I conducted a comparative experimental study on the horizontal molding machine control system. I compared the retrofitted shooting and compaction molding system with the original shooting process molding system. The purpose was to determine whether the retrofitted horizontal molding machine could effectively improve sand compaction, solve the “arch effect” in deep concave sand molds, and improve the product quality of the original molding machine. Both tests used molding sand that met the sand supply requirements of the original horizontal molding machine. The sand casting process parameters are listed in Table 7.
| Parameter | Value |
|---|---|
| Moisture content | 3%–4% |
| Permeability | 100–150 |
| Wet compressive strength | 115–165 kPa |
| Mud content | 10%–14% |
| Sand mold hardness requirement | 80–95 |
| Casting material | QT450-10 |
| Casting weight | About 20 kg |
During the test, I recorded the time of one working cycle of the molding machine and the total power of the hydraulic station motor. After molding, I checked whether a sand mold with high compactness and uniform distribution could be obtained. Finally, I counted the qualified rate of the sand mold and the casting yield. The comparison results are shown in Table 8.
| Machine state | Yield (%) | Hydraulic station motor energy consumption (kWh) | Operating efficiency (s/mold) |
|---|---|---|---|
| Original horizontal molding machine | 77.5 | 16.16 | 41 |
| Retrofitted molding machine | 96.5 | 14.18 | 37 |
The yield is calculated as:
$$ \eta_{yield} = \frac{N_{qualified}}{N_{total}} \times 100\% $$
The energy saving is:
$$ \Delta E = \frac{E_{old} – E_{new}}{E_{old}} \times 100\% = \frac{16.16 – 14.18}{16.16} \times 100\% \approx 12.3\% $$
The improvement in operating efficiency is:
$$ \Delta \eta = \frac{\eta_{new} – \eta_{old}}{\eta_{old}} \times 100\% = \frac{37 – 41}{41} \times 100\% \approx 9.8\% $$
The productivity in molds per hour is:
$$ P_{prod} = \frac{3600}{t_{cycle}} $$
For the retrofitted machine, \(P_{prod} = 3600 / 37 \approx 97.3\) molds per hour. For the original machine, \(P_{prod} = 3600 / 41 \approx 87.8\) molds per hour. This confirms the efficiency improvement.
The experimental results show that the retrofitted molding machine runs smoothly. The sand filling effect in all areas of the sand mold meets the process requirements. The parting surface compactness measurement value reaches above 80. The process yield reaches 96.5%. The hydraulic station energy consumption is 12.3% lower than the original machine. The molding speed reaches 37 s per mold. These results demonstrate that the PLC-based control system retrofit is successful for sand casting applications.
7. Discussion
The retrofit demonstrates several advantages for sand casting. First, the vertical upward and downward shooting improves sand filling into deep recesses, reducing the “arch effect” that often causes low compactness and casting defects. Second, the servo hydraulic system allows the pump to deliver only the required flow and pressure at each stage, reducing throttling losses and energy consumption. Third, the segmented closed-loop control provides precise position and pressure control, which is essential for consistent sand casting quality. Fourth, the HMI and PLC software make the system flexible and easy to operate, allowing manual tuning and automatic adaptation to different mold parameters.
In terms of sand casting quality, the improvement in parting surface compactness directly affects mold wall stability during pouring. When the mold hardness is above 80, the mold resists metal static pressure and expansion forces more effectively. This reduces shrinkage defects, especially in complex castings such as the clutch pressure plate. The yield increase from 77.5% to 96.5% is significant for sand casting production economics. The reduction in energy consumption also aligns with sustainable manufacturing goals.
From a control perspective, the use of pressure feedback in the holding stage ensures that the compaction force does not exceed the set value, preventing sand mold damage. The position feedback in fast forward and return stages ensures accurate mold closing and opening, reducing cycle time and mechanical impact. The PLC program is designed with modular functions, making it easy to adjust parameters for different sand casting patterns. The communication between the PLC, servo driver, and HMI is reliable and allows real-time monitoring.
Future improvements could include adaptive tuning of PID parameters based on sand properties, integration with a sand casting simulation database, and predictive maintenance using the collected pressure and displacement data. The system could also be extended to other types of molding machines in sand casting foundries.
8. Conclusion
I designed and implemented a PLC-based control system retrofit for a horizontal sand casting molding machine. The retrofit replaced the original single-sided double shooting with vertical upward and downward shooting, replaced the asynchronous motor with a servo motor, and introduced a servo hydraulic system with segmented pressure and position closed-loop control. The hardware design included a FX5U series PLC, expansion modules, magnetostrictive displacement sensors, pressure sensors, servo drivers, and permanent magnet synchronous motors. The software design included manual and automatic speed control, PID feedback algorithms, PLC sequential control, and an HMI interface.
The experimental results confirmed that the retrofitted machine operates smoothly, achieves parting surface compactness above 80, reaches a process yield of 96.5%, reduces hydraulic station energy consumption by 12.3%, and improves operating efficiency by 9.8%. The molding speed reaches 37 s per mold. These improvements address the original problems of high energy consumption, low efficiency, and insufficient compactness in sand casting. The retrofit provides a feasible technical path for the modernization of traditional sand casting molding machines.
In summary, the integration of PLC control, servo hydraulics, and real-time sensor feedback significantly enhances the performance of horizontal molding machines for sand casting. The system is flexible, energy-efficient, and capable of producing high-quality sand molds for complex castings. This work contributes to the ongoing digital transformation of sand casting foundries and supports the production of reliable castings with reduced environmental impact.