Sand casting is a fundamental process in manufacturing, widely used for producing complex components due to its versatility and cost-effectiveness. As a primary method for fabricating intricate parts, the technical challenges, auxiliary equipment configuration, and process integration in sand casting are closely tied to the design of the molding line. In modern industrial applications, the demand for higher efficiency, reduced labor intensity, and improved product quality has driven the development of automated systems. We have designed a fully automatic horizontal parting molding line to address common issues in traditional sand casting production, such as unstable sand mold transportation, low recycling rates of auxiliary equipment, low production efficiency, and redundant human resources. This article details the design, key mechanisms, control systems, and practical applications of this innovative sand casting line, emphasizing the integration of automation to enhance overall performance.
The design of the sand casting line focuses on achieving a seamless workflow from molding to cooling and shakeout, leveraging programmable logic controllers (PLCs) for precise coordination. Key components include the overall layout,底板夹持机构 (referred to as the bottom plate clamping mechanism),套箱压铁转换装置 (box and weight conversion device),底板转换装置 (bottom plate conversion device),砂型推出装置 (mold ejection device), and sand trough belt conveyor. By incorporating these elements, we aim to optimize space utilization, increase production throughput, and minimize human intervention in the sand casting process. The following sections elaborate on the design objectives, layout, operational workflow, structural details of critical mechanisms, control system implementation, and real-world performance analysis, supported by tables and mathematical formulations to summarize key aspects.
Design Objectives and Performance Metrics
In developing the fully automatic horizontal parting molding line for sand casting, we established specific design tasks based on the production requirements of a typical foundry. The facility spans an area of 140 m by 24 m and specializes in manufacturing automotive components such as wheel hubs and clutches, both made from HT250 cast iron. The sand molds used have dimensions of 610 mm × 610 mm × 280–400 mm and 570 mm × 670 mm × 360–560 mm, with average weights of approximately 20 kg and 40 kg, respectively. Operating on a two-shift system of 8 hours each for 300 days per year, the line targets an annual output of 12,000 tons, equivalent to 440,000 molds. Key performance indicators include a defect rate of less than 10%, adjustable mold height to accommodate various sand box thicknesses, and a significant boost in production capacity. The design prioritizes optimal resource utilization, minimal environmental impact, and enhanced automation to address the limitations of conventional sand casting methods.
| Metric | Target Value | Description |
|---|---|---|
| Annual Production | 12,000 tons | Total output of sand casting products |
| Mold Output | 440,000 molds/year | Based on two 8-hour shifts for 300 days |
| Defect Rate | < 10% | Ensuring high-quality sand casting outcomes |
| Mold Height Adjustability | 280–560 mm | Compatible with different sand box sizes |
| Labor Reduction | Approximately 87.5% | Compared to manual sand casting processes |
To achieve these goals, we conducted a comprehensive analysis of the production flow, considering factors such as material handling, energy consumption, and cycle times. The design incorporates modular components that allow for flexibility in sand casting operations, ensuring that the line can adapt to varying product specifications. The use of mathematical models helps in optimizing parameters; for instance, the production rate can be expressed as:
$$ P = \frac{N \times T}{C} $$
where \( P \) is the production rate in molds per hour, \( N \) is the number of operational shifts, \( T \) is the time per shift in hours, and \( C \) is the cycle time per mold in hours. For our sand casting line, with \( N = 2 \), \( T = 8 \), and \( C \) optimized to 0.036 hours per mold, we achieve \( P \approx 444 \) molds per hour, surpassing the annual target. This equation underscores the importance of minimizing cycle times through automation in sand casting.
Overall Layout of the Molding Line
The layout of the fully automatic horizontal parting molding line for sand casting is strategically designed to maximize efficiency and minimize bottlenecks. The production area is divided into four main conveyor lines: the pouring conveyor (Line 1), the mold ejection transition conveyor (Line 2), and two cooling conveyors (Lines 3 and 4). This arrangement facilitates a linear flow from molding to shakeout, reducing unnecessary movements and enhancing the smoothness of the sand casting process. The core equipment includes two identical horizontal parting molding machines, which are equipped with adjustable mechanisms for varying mold thicknesses and are integrated with sand storage and conveyor systems for automated control.
Sand handling is a critical aspect of the sand casting line. Loose and raw sand are transported via belt conveyors and bucket elevators to a sand processing line, where they are stored in sand silos awaiting molding instructions. The molding system, upon completing the molding process, ejects the sand molds onto Line 1 using a push-out mechanism. Subsequently, the bottom plate clamping mechanism, box and weight conversion device, and bottom plate conversion device work in tandem to apply boxes and weights to the molds before they proceed to the pouring station. An automatic pouring machine handles the molten metal injection, after which the molds move to the cooling conveyors. After cooling, the boxes and weights are removed and recycled via the conversion device, and the molds are directed to a shakeout station for sand separation. A sand recovery system, located in pits beneath key areas like the shakeout drums and molding systems, collects and recycles used sand, promoting sustainability in the sand casting operation.
The integration of these components ensures a closed-loop system for sand casting, where resources are efficiently utilized. The belt conveyor above the molding system connects the sand silos to each molding machine’s sand cylinder, enabling synchronized sand supply. Additionally, the sand recovery line links the pits to the sand processing elevator, facilitating the reuse of sand and reducing waste. This layout not only improves production efficiency but also creates a cleaner and safer working environment, aligning with modern standards for sand casting facilities.
Operational Workflow
The workflow of the fully automatic horizontal parting molding line for sand casting is meticulously planned to ensure seamless operation from start to finish. It begins with the initiation of the molding system, which sends a signal for sand supply. The horizontal parting mechanism then distributes the sand, and molding occurs. After molding, the bottom plate is clamped and positioned, and the sand mold is ejected onto Line 1. The clamping mechanism secures the mold in place, and the box and weight conversion device transfers the boxes and weights from Line 2 to Line 1, placing them onto the mold for stability during pouring. The mold is then moved to the pouring platform via the bottom plate conversion device, where automatic pouring takes place. Following pouring, the mold undergoes cooling on Lines 3 and 4, after which the boxes and weights are removed and recycled. Finally, the mold is pushed into a vibratory conveyor for shakeout, where the sand is separated, and the castings are output for further processing.
| Step | Action | Key Components Involved |
|---|---|---|
| 1 | Molding system starts and signals for sand | Molding machines, sand silos |
| 2 | Sand distribution and molding | Horizontal parting mechanisms |
| 3 | Bottom plate clamping and positioning | Clamping mechanism |
| 4 | Mold ejection to Line 1 | Ejection device |
| 5 | Box and weight application | Conversion device |
| 6 | Transport to pouring platform | Bottom plate conversion device |
| 7 | Automatic pouring | Pouring machine |
| 8 | Cooling on Lines 3 and 4 | Cooling conveyors |
| 9 | Box and weight removal and recycling | Conversion device |
| 10 | Shakeout and casting output | Vibratory conveyor, shakeout machine |
This workflow is cyclic, allowing for continuous production in the sand casting line. Each step is interlocked with the next through sensor-based feedback, ensuring that operations proceed only when previous steps are completed successfully. For example, the ejection of the mold triggers a signal to the bottom plate conversion device, which then times the transportation of the bottom plate to the next station. Displacement sensors detect the position of the bottom plate, activating clamping mechanisms as needed. This level of automation reduces the risk of errors, such as misalignment or sand mold damage, which are common in manual sand casting processes. The efficiency of the workflow can be modeled using queuing theory, where the average waiting time \( W \) for a mold in the system is given by:
$$ W = \frac{\lambda}{\mu(\mu – \lambda)} $$
where \( \lambda \) is the arrival rate of molds and \( \mu \) is the service rate. By optimizing \( \mu \) through faster cycle times, we minimize \( W \), leading to higher throughput in sand casting.
Structural Design of Key Mechanisms
The fully automatic horizontal parting molding line for sand casting incorporates several critical mechanisms to ensure stability, precision, and efficiency. Each mechanism is designed to address specific challenges in the sand casting process, such as mold transportation, positioning, and recycling of components.
Molding System Structure
The molding system is the heart of the sand casting line, responsible for forming the sand molds using compressed air to inject sand into the boxes, followed by compaction. It consists of upper and lower molding modules, pushing mechanisms, and sand cylinders. The system allows for manual adjustments via configuration software to accommodate different mold designs and sand thicknesses, essential for versatile sand casting operations. It includes five hydraulic cylinders, three pneumatic cylinders, and multiple solenoid valves to control the sequence of operations, such as mold closing, sand shooting, and exhaust. The hydraulic system comprises six circuits for upper and lower frame lifting, sand box sliding, mold ejection, touch mechanism, and mold closing, each independently controlled by directional valves. The use of servo motors driving gear pumps ensures precise movements; for instance, the ejection force \( F_e \) can be calculated as:
$$ F_e = P \times A $$
where \( P \) is the hydraulic pressure and \( A \) is the effective area of the cylinder. This ensures adequate force for ejecting sand molds without damage in the sand casting process.
Box and Weight Conversion Device
This device is crucial for applying and removing boxes and weights during sand casting, enabling their reuse and reducing material waste. It features two lifting cylinders, two brakes, and a roller chain driven by a servo motor. When activated, the cylinders extend to lower the clamping mechanisms onto the boxes and weights on Line 2. The brakes engage to grip them, and the cylinders retract, lifting the assemblies. The servo motor then drives the roller chain to transport them to Line 1, where they are placed onto the sand molds. Positioning columns and displacement sensors ensure accurate alignment, minimizing the risk of misalignment in sand casting. The device’s efficiency can be expressed in terms of cycle time \( t_c \):
$$ t_c = t_{lift} + t_{transport} + t_{place} $$
where \( t_{lift} \), \( t_{transport} \), and \( t_{place} \) are the times for lifting, transporting, and placing, respectively. By minimizing \( t_c \), we enhance the overall productivity of the sand casting line.
Bottom Plate Clamping and Positioning Mechanism
This mechanism ensures stable transportation of sand molds by clamping the bottom plates during critical operations. It employs a gear-driven system with active and passive shafts connected by gears. A driving cylinder, linked to the active shaft via a crank-slider mechanism, rotates the shafts to open or close the clamping arms. Displacement sensors detect the presence of a sand mold, triggering the clamping action. The clamping force \( F_c \) can be adjusted by varying the cylinder stroke, allowing it to adapt to different bottom plate dimensions in sand casting. The relationship is given by:
$$ F_c = k \times \Delta x $$
where \( k \) is the spring constant and \( \Delta x \) is the stroke variation. This design prevents mold shifting, a common issue in sand casting, thereby improving product quality.
Automatic Conveyance Units
The automatic conveyance units include four welded steel rail tracks, bottom plate carts, bottom plate conversion devices, and mold ejection devices. The rails guide the bottom plates, which are pushed by the conversion devices and secured by clamping mechanisms at key points like ejection, pouring, and box-weight conversion. The bottom plate conversion device uses cylinders and servo motors to transfer plates between tracks, with limit switches, dampers, and buffers ensuring precise positioning. For example, the transportation speed \( v \) of the bottom plate can be controlled to avoid jerks:
$$ v = \frac{d}{t} $$
where \( d \) is the distance and \( t \) is the time. The mold ejection device employs chain drives and photoelectric switches to push cooled molds onto vibratory conveyors for shakeout. The vibratory conveyor, with inclined grid plates and rubber springs, is driven by dual motors to separate sand from castings efficiently in the sand casting process.
| Mechanism | Function | Key Components |
|---|---|---|
| Molding System | Forms sand molds using compressed air | Hydraulic cylinders, sand cylinders |
| Box and Weight Conversion | Applies and removes boxes/weights for reuse | Lifting cylinders, roller chain, sensors |
| Bottom Plate Clamping | Secures bottom plates during transport | Gears, clamping arms, displacement sensors |
| Automatic Conveyance | Transports molds between stations | Rails, conversion devices, ejection devices |
Control System Design
The control system for the fully automatic horizontal parting molding line in sand casting is centered on a PLC-based architecture to coordinate all operations. We use a Mitsubishi FX5U series CPU as the central processor, integrated with a Weintek touchscreen for human-machine interface. Communication is established via an N:N network configuration using RS-485 bus, with one master station and one slave station for the molding system. Remote I/O devices are connected through CCLINK, employing modules like AJ65SBTB1-16D for inputs and AJ65SBTB2N-16R for outputs. Input devices include control buttons, touchscreens, and sensors, while output devices drive servo motors, heaters, hydraulic coolers, and solenoid valves. Data exchange with higher-level systems is enabled through Ethernet and industrial internet technologies, facilitating real-time monitoring and management of the sand casting process.
The control logic ensures interlocking between工序; for instance, after the molding system completes a cycle, it sends a signal to initiate ejection. The hydraulic and pneumatic systems are meticulously controlled: the hydraulic system has six circuits for various functions, driven by two servo motors with rated speeds of 2,400 rpm, powering gear pumps with displacements of 32 mL/r and 114 mL/r. The pneumatic system includes three cylinders, two sand shooting pipes, and one mold spraying cylinder, regulated by quick exhaust valves, throttle valves, solenoid valves, and pressure regulators. Each operation, such as sand shooting or core setting, is time-controlled, while others like mold pushing and mold closing are limit-switch controlled. Displacement sensors compare actual frame positions with set values to ensure precise movements in sand casting.
| Input Address | Function | Output Address | Function |
|---|---|---|---|
| X0 | Manual/Auto Mode | Y10 | Mold Ejection Forward |
| X3 | Single/Joint Operation | Y20 | Box/Weight Advance |
| X4 | Emergency Stop | Y24 | Box/Weight Brake |
| X11 | Sand Drop Belt Monitoring | Y30 | First Bottom Plate Conversion Push |
| X21 | Box/Weight Device Fault | Y37 | Sand Drop Belt 1 |
| X26 | Mold Ejection Monitoring | Y42 | Second Bottom Plate Conversion Push |
| X36 | Sand Recovery Operation | Y46 | Sand Drop Belt 2 |
| X40 | Inhibit Mold Line Push | Y54 | Molding 1 Ejection Permit |
| X41 | Sand Drop Belt Overload | Y56 | Auto Operation Indicator |
| X42 | Pouring Emergency Stop | Y57 | Molten Metal Wait |
| X44 | Molding Emergency Stop | Y62 | Mold Line Pushing Active |
| X51 | Molding System Ejection End | Y67 | Sand Return System Start |
The control flow begins with the clamping mechanism gripping the bottom plate upon receiving a signal. After molding, the sand mold is ejected to Line 1, and the bottom plate conversion device moves it to the box-weight conversion station. Sensors detect the mold’s position, activating clamping and conversion processes. The pouring platform then performs automatic pouring, and after cooling, the molds are transported to the shakeout station. The entire sequence is iterative, ensuring continuous operation in sand casting. The reliability of the control system can be analyzed using failure rate models; for example, the mean time between failures (MTBF) for the PLC system is critical for maintaining uptime in sand casting production.
Performance Analysis and Real-World Application
In practical applications, the fully automatic horizontal parting molding line for sand casting has demonstrated significant improvements in efficiency and quality. We tested the line with automotive wheel hubs and clutches, operating it automatically for 16 hours daily with only four workers per shift, compared to 32 workers in traditional manual sand casting processes. The results showed a daily output of 640 wheel hubs and 1,040 clutches, with a defect rate of approximately 0.6%, well below the 10% target. This translates to an annual capacity of 12,000 tons, achieving the design goals. The production area usage was reduced by 22.1%, and the working environment became cleaner due to integrated sand recovery and dust extraction systems.
| Aspect | Manual Sand Casting | Automated Molding Line |
|---|---|---|
| Workers Required | 32 | 4 |
| Production Area Usage | 87.3% | 65.2% |
| Daily Output (Approx.) | 28.8 tons | 46.4 tons |
| Defect Rate | ~10% | ~0.6% |
The performance gain can be quantified using productivity indices. For instance, the overall equipment effectiveness (OEE) in sand casting is calculated as:
$$ OEE = Availability \times Performance \times Quality $$
With availability near 95% due to reduced downtime, performance at 110% of baseline, and quality at 99.4%, the OEE exceeds 100%, indicating superior efficiency. The sand casting line’s ability to recycle boxes and weights reduces material costs, while the automated control minimizes human error. Additionally, the sand recovery system ensures that over 90% of sand is reused, lowering environmental impact. These outcomes highlight the transformative potential of automation in sand casting, making it a viable solution for small and medium-sized enterprises seeking to enhance competitiveness.
Conclusion
The design and implementation of the fully automatic horizontal parting molding line for sand casting represent a significant advancement in foundry technology. By addressing common issues such as unstable transport, low recycling rates, and high labor dependency, this system achieves higher production efficiency, improved product quality, and a more sustainable operation. The integration of key mechanisms like the molding system, box-weight conversion device, and clamping mechanisms, coupled with a robust PLC-based control system, ensures precise coordination and reliability in the sand casting process. Practical applications confirm that the line not only meets but exceeds performance targets, reducing workforce requirements by over 85% and optimizing space utilization. This approach serves as a model for modernizing traditional sand casting practices, offering economic and environmental benefits. Future work could focus on incorporating IoT for predictive maintenance and further optimizing energy consumption, paving the way for smarter sand casting solutions in the industry.