The implementation of a modern, fully automated resin sand casting line represents a significant technological leap for producing complex, high-precision castings such as engine blocks. I was involved in a project where such a line was designed, installed, and commissioned to meet the stringent production demands for Euro II emission standard engine blocks. The entire project, from initial feasibility studies and facility construction to equipment customization, installation, debugging, and full-scale production, was completed in under a year. A core philosophy was to utilize reputable domestic equipment manufacturers while standardizing on Siemens automation products for the electrical control systems. This standardization strategy facilitated seamless integration and simplified maintenance and spare part management alongside other existing production equipment. Since its launch, the line has successfully achieved an annual output of 60,000 qualified engine block castings, reliably fulfilling the requirements of the assembly plant.
The entire resin sand casting system is a sophisticated integration of several major subsystems working in concert. For the purpose of this detailed discussion, the focus will be on the core molding and handling systems, while the sand mixing and reclamation systems—though critical—operate as relatively independent modules. The heart of the operation consists of two primary loops: the molding loop and the mold conveyance and cooling loop.
The resin sand casting process for engine blocks follows a meticulously timed sequence. The process begins in the molding loops where cope and drag molds, along with two side core molds, are produced. After molding, these sand cores and molds proceed to a core setting and closing station. The assembled mold is then transported to the pouring station. Critical to quality is the subsequent cooling phase. The sand mold itself requires a surface drying and a cooling period of at least 40 minutes post-pouring. The complete casting within the mold then undergoes a much longer solidification and cooling cycle in dedicated cooling tunnels for a minimum of 5 hours, with 8 hours being the standard for optimal metallurgical properties. Finally, the cooled molds are transported to a shakeout station where the castings are separated from the sand, which is then sent to the reclamation system for processing and reuse in the resin sand casting cycle.
Molding Loop System Architecture
The production line incorporates two identical molding loops, one dedicated to producing the engine block’s cope and drag sections and the other for the two side core molds. Apart from the pattern equipment, these loops are functionally identical. Each loop is a self-contained cell comprising a jolt-squeeze molding table, two transfer cars, a pallet handling/flipping machine, and a rollover drawing machine.
The operational sequence within a resin sand casting molding loop is as follows: Resin-coated sand from the mixer is discharged into the pattern on the jolt table. The sand is compacted through a combination of jolting and vibration. The pattern with the compacted sand is then transferred via a shuttle car to the pallet flipper. A pallet (or carrier plate) is added to support the sand mold. This assembly is then indexed into the rollover drawing machine. Here, the entire unit is inverted 180 degrees. Vibration is applied to facilitate the separation of the cured sand mold from the pattern—a critical step in the resin sand casting process. The completed sand mold, now resting on its pallet, is discharged onto the main conveyor line. Meanwhile, the empty pattern is transferred back to the jolt table via the second shuttle car, ready for the next cycle.
The central piece of equipment in each loop is the Z29 series jolt-squeeze molding table. Its technical specifications for different models are summarized below:
| Machine Model | Max Load (kg) | Vibration Motor Power (kW) | Vibration Frequency (rpm) | Amplitude (mm) | Max Excitation Force (kN) | Air Pressure (MPa) |
|---|---|---|---|---|---|---|
| Z291 | 630 | 0.37 x 2 | 3000 | 0.5 – 1 | 5 x 2 | ≥0.6 |
| Z292 | 1600 | 0.75 x 2 | 3000 | 0.5 – 1 | 8 x 2 | ≥0.6 |
| Z293 | 2500 | 0.75 x 2 | 3000 | 0.5 – 1 | 10 x 2 | ≥0.6 |
| Z294 | 4000 | 1.1 x 2 | 3000 | 0.5 – 1 | 16 x 2 | ≥0.6 |
| Z296 | 6300 | 2.2 x 2 | 3000 | 0.5 – 1 | 32 x 2 | ≥0.6 |
| Z2910 | 10000 | 3.7 x 2 | 3000 | 0.5 – 1 | 50 x 2 | ≥0.6 |
The table operates using air springs for elevation and high-frequency vibration motors for compaction. The standard work cycle, when integrated with roller conveyors, is: 1) The pattern and flask are positioned over the table; 2) Air springs inflate, raising the table to lift the flask off the rollers; 3) Sand is filled and the vibrators are activated for compaction; 4) After vibration, the air springs deflate, lowering the flask back onto the conveyor rollers for transfer out of the station.
Mold Conveyance and Cooling Loop
This extensive network forms the backbone of the resin sand casting line’s material handling. It consists of multiple synchronized zones: two mold drying ovens, three mold cooling tunnels, two core setting conveyor lines, one pallet return line, one pouring line, one jacket return line, five casting cooling tunnels, one bottom plate return line, seven transfer machines, and six shuttle cars.
The workflow progresses as follows: Newly produced sand molds from the molding loops enter a drying oven for surface curing. They then travel through cooling tunnels to stabilize. After cooling, molds move to the core setting station where operators assemble the internal cores into the main mold cavity. The fully assembled mold is transported to the pouring station. The pallet, having served its purpose, is diverted onto a return loop back to the molding cells. After pouring, the filled molds enter the long casting cooling tunnels. Following the mandated cooling time, molds are conveyed to the shakeout station. Here, castings are separated, the sand is reclaimed, and the bottom plates are returned to the molding loop via their dedicated return line.
Two key machines in this loop are the Rollover Drawing Machine and the Pallet Flipper.
Rollover Drawing Machine (Z7118 Type)
This hydraulically operated machine is designed for the precise demolding of resin sand casting molds. Key parameters are listed below:
| Parameter | Value |
|---|---|
| Maximum Load | 2500 kg |
| Theoretical Cycle Time | 120 s |
| Applicable Pallet Size | 1600 x 900 x 800 mm |
| Hydraulic System Pressure | 16 MPa |
| Total Motor Power | 17.5 kW |
Its operational sequence is controlled by a series of proximity and photoelectric sensors: 1) Pallet with pattern enters on motorized rollers and is detected; 2) Rollers stop, clamping cylinders secure the pallet; 3) Lift cylinders raise the assembly; 4) A hydraulic motor rotates the frame 180°; 5) Air springs inflate and vibration motors activate to separate the sand mold from the pattern; 6) Once separation is confirmed by a sensor, a belt conveyor discharges the sand mold; 7) The frame rotates back to 0°, clamps release, and the empty pattern is conveyed out, completing the cycle. The machine’s adjustment is crucial, particularly setting the vibration force via eccentric weights on the motors and regulating the air spring pressure.
Pallet Hydraulic Flipper (2YF Type)
This machine performs the complementary task of placing a pallet onto a completed sand mold. It shares similar load and size specifications with the drawing machine. Its operation involves: 1) An empty pallet is conveyed in and clamped; 2) The machine flips 180°; 3) A sand mold is conveyed into position beneath it; 4) Lift cylinders lower the pallet onto the mold and a final clamping action secures them together; 5) The assembly is released and conveyed out to the main line, and the flipper returns to its start position. Its drive uses a self-locking hydraulic motor with a proportional valve controlled by PLC logic to achieve smooth slow-fast-slow rotation profiles, ensuring precise and stable movement essential for the delicate resin sand casting molds.
Automation and Control System Design
The reliable, automatic operation of the entire resin sand casting line is governed by a hierarchical, distributed control system based on Siemens SIMATIC programmable logic controllers (PLCs). The control architecture is divided into two main segments: the Mold Conveyance Loop and the Molding Loops.
Hardware Configuration
1. Mold Conveyance Loop Control: Given the vast geographical footprint, numerous actuators (over 114 roller motors), and sensors (more than 400 proximity switches), a distributed I/O system was implemented. A SIMATIC S7-400 PLC acts as the central master station on a PROFIBUS-DP network, with five ET200M remote I/O stations acting as slaves. This topology significantly reduces wiring complexity. The master station (CPU 414-2DP) handles central logic and coordination. Each slave station (with IM153-1 interface modules) is equipped with a mix of digital input (DI) and output (DO) modules to interface with local devices like motors, solenoids, and sensors. Five frequency converters for controlling shuttle car speeds are also integrated into the network.
For operator interaction, each major section features a local SIMATIC OP270 HMI (Human-Machine Interface) panel connected via MPI (Multi-Point Interface) protocol. These panels provide local manual control, real-time status displays, and detailed fault diagnostics. Crucially, the MPI connection ensures that a communication fault on an HMI does not disrupt the automatic operation of the PROFIBUS-controlled line. A central supervisory station uses a Siemens PC670 industrial computer running SCADA software for plant-wide monitoring.
The hardware configuration for the conveyance loop is summarized as:
| Station | Core Components | Key I/O Modules |
|---|---|---|
| Master | CPU 414-2DP, PS405 4A | DI16xDC24V, DO16xDC24V |
| Slave #1 | IM153-1 | 4x DI32xDC24V, 4x DO16xAC120/230V |
| Slave #2 | IM153-1 | 4x DI32xDC24V, 4x DO16xAC120/230V |
| Slave #3 | IM153-1 | 3x DI32xDC24V, 4x DO16xAC120/230V |
| Slave #4 | IM153-1 | 4x DI32xDC24V, 4x DO16xAC120/230V |
| Slave #5 | IM153-1 | 1x DI32xDC24V, 2x DO16xAC120/230V |
2. Molding Loop Control: Each molding cell is controlled by a more compact SIMATIC S7-300 PLC system. The main CPU 313C-2DP station manages the core sequence logic. It is connected via PROFIBUS-DP to two satellite stations built with SIMATIC S7-200 PLCs (CPU 224). These satellite stations, using EM277 communication modules and various I/O expansion modules, are strategically placed to handle the I/O points for the hydraulic power unit and other peripheral devices within the cell, keeping wiring local and manageable.
Software and Control Logic
The system software comprises three layers: PLC programming, SCADA visualization, and HMI panel configuration.
1. PLC Programming (STEP7): The control logic for the entire resin sand casting line was developed in Siemens STEP7 V5.2. The program employs a state-based or sequential control strategy for the conveyor loop, ensuring deterministic movement of molds from one station to the next. The cooling tunnel selection logic can operate in automatic mode (based on line congestion) or manual override. Critical manual functions, such as shakeout station operation, are kept independent so that a fault there doesn’t halt the entire upstream process. The molding loops run semi-autonomously, providing a “ready” signal to the main conveyor control. This decoupling allows the conveyor to complete its current cycle even if a molding loop pauses temporarily.
The control logic for motor sequencing often follows pattern-based algorithms. For instance, the activation of a series of rollers ($R_n$) to move a pallet from Sensor $S_a$ to Sensor $S_b$ can be generalized as:
$$ \text{Start Condition: } S_a = \text{ON} \land \text{Downstream\_Space} = \text{TRUE}$$
$$ \text{Sequence: } R_a \rightarrow R_{a+1} \rightarrow … \rightarrow R_{b-1} $$
$$ \text{Stop Condition: } S_b = \text{ON} $$
$$ \text{Deactivation: } R_{b-1} \rightarrow … \rightarrow R_{a+1} \rightarrow R_a $$
2. SCADA System (WinCC): The central PC670 runs Siemens WinCC V5.1, a powerful SCADA package. It provides a plant-wide graphical overview of the resin sand casting line, showing real-time status of every major motor, cylinder, and sensor. Its integrated alarm management system logs and displays faults, helping maintenance personnel quickly identify and locate issues. Historical data archiving allows for production analysis and process optimization.
3. HMI Panel Configuration (ProTool): The local OP270 panels are configured using ProTool software, which integrates seamlessly with STEP7. This allows the use of shared data blocks and symbols from the PLC program as variables in the HMI projects. The panels provide intuitive screens for manual jogging of individual machines, local cycle initiation, and detailed diagnostic messages specific to that section of the resin sand casting line.
System Performance and Reliability
The chosen control architecture for this resin sand casting line has proven highly effective. The use of a robust fieldbus (PROFIBUS-DP) for distributed I/O and a reliable master PLC (S7-400) ensures fast, deterministic control over the extensive conveyor network. The modularity of the design, with separate control systems for the conveyor and the molding cells, provides excellent fault containment; a problem in one molding loop does not necessarily stop the entire line. Standardization on Siemens components across the control system has minimized spare part variety and simplified troubleshooting. The extensive diagnostic capabilities through both central SCADA and local HMIs have resulted in very high operational availability. Since commissioning, the control system has demonstrated exceptional reliability, with minimal downtime attributed to electrical or control failures, a testament to the soundness of both the hardware selection and the software design for this demanding resin sand casting application.