Abstract:
Considering the practical fettling operations of large steel castings, such as bolsters and side frames for railway freight cars, this paper proposes an intelligent and generalized solution. Based on the integration of 3D vision, robotics, safety and environmental protection, system integration, and control, this solution aims to enhance production efficiency, reduce manual labor intensity, and ensure a favorable working environment. The solution includes various units, forming an intelligent cleaning and grinding production line for bolster and side frame steel castings. Practical production has proven the effectiveness of this scheme.
Keywords: freight car; bolster; side frame; fettling; intelligence; production line; steel casting
1. Introduction
Large steel castings for railway freight cars, such as bolsters and side frames, are typically produced using the sand casting process. After casting, these rough castings undergo a series of processes including sand removal, cutting off flash and runner/riser, shot blasting, carbon arc gouging, surface grinding, defect welding and repairing, and inspection before heat treatment. These processes involve multiple operations conducted simultaneously by various workers in the same space and time, leading to multiple pollution sources, complex pollution types (arc light, noise, dust), high pollution concentrations, and intensities. Consequently, environmental governance and occupational health protection become significant challenges.
To address these issues, CRRC Meishan Co., Ltd. has developed an intelligent solution for cleaning large steel castings of railway freight cars, implemented through an intelligent cutting and grinding production line for bolster and side frame steel castings. This solution integrates advanced technologies such as logistics, environmental protection, safety monitoring, digital 3D inspection, robotics, digital programming, and intelligent control. It is characterized by high system integration, smart management and control, and environmental friendliness, exploring a new path for the production of large steel castings in the railway industry.
Table 1: Overview of Cleaning Processes and Pollutants
| Sequence | Process Name | Operation Content | Operation Time per Piece | Pollution Types |
|---|---|---|---|---|
| 1 | Mechanical Sand Removal | Remove the outer surface sand of the casting | 15min/box | Dust, Noise |
| 2 | Manual Sand Cleaning | Remove the core sand in the inner cavity of the casting | 90min/piece | Dust, Noise |
| 3 | Runner/Riser Cutting | Remove fixed runner, riser, and venting pins | 15min/piece | Smoke, Noise |
| 4 | Flash Cutting | Remove flash of varying positions and sizes | 12min/piece | Smoke, Noise |
| 5 | Shot Blasting | Remove residual sand and oxide scale on the casting surface | 3-5min/piece | Dust |
| 6 | Carbon Arc Gouging | Remove high cutting allowances, abnormal protrusions, and prepare welding grooves | 12min/piece | Smoke, Dust, Arc Light, Noise |
| 7 | Surface Grinding | Remove flash, burrs, polish critical surfaces, and ensure smooth transitions | 60min/piece | Grinding Dust |
| 8 | Defect Welding and Repairing | Eliminate shrinkage pores, porosity, blowholes, cracks, etc. | 15min/piece | Smoke, Arc Light, Noise |
| 9 | Inspection and Confirmation | Inspect casting quality, identify defects, specify operations, and record | 15min/piece | – |
| 10 | Workpiece Turning | Turn the workpiece | 1min/piece | – |
2. Overview of Cleaning Processes
Before heat treatment, bolster and side frame steel castings must undergo processes such as sand removal, flash cutting, runner/riser cutting, shot blasting, carbon arc gouging, surface grinding, internal and external surface inspection, defect welding and repairing, and inspection confirmation. Each process is detailed in Table 1, and after completion, the castings are sent to the heat treatment process in batches by furnace.
2.1 Sand Removal
Sand removal typically involves the use of sand-removing machines to remove the outer surface sand of the casting, and manual air shovel methods to remove the core sand in the inner cavity. This process involves operations such as whole-box handling, box separation, mechanically assisted sand removal, workpiece transfer, manual cleaning, and used sand recycling. For enterprises using the ester-hardened water glass sand process and producing in a two-piece per box manner, the sand-removing machine and manual cleaning operation times are approximately 15min/box and 1.5h/piece, respectively. Due to difficulties in matching their work rhythms, manual cleaning is generally performed in a multi-station, large-area manner. Currently, it is difficult to fully replace manual cleaning with mechanical methods. To improve the environmental treatment effect of manual cleaning workplaces, many enterprises are equipped with atomizing dust suppression devices.
2.2 Runner/Riser and Flash Removal
To ensure casting quality, casting processes include setting gates, risers, and venting pins at fixed positions on the workpiece, with large cross-sections where the risers connect to the casting body. These runner/risers and venting pins are removed after sand removal using flame cutting methods. Manually using hand torches to cut off the runner/risers of bolsters and side frames takes approximately 15min/piece.
Casting flash is a type of defect caused by the gap between the mold and core, resulting in excess metal on the casting. This defect has uncertain positions and sizes and is also removed using flame cutting methods. Manually using hand torches to cut off the flash of bolsters and side frames takes approximately 10min/piece. Due to the large cross-sections of runner/risers and the long residence time of high-temperature molten steel during pouring, residual sand often exists at the runner/risers. The poor thermal conductivity of the surface residual sand increases the difficulty of cutting preheating operations, and in severe cases, may prevent cutting from being achieved. Generally, this is addressed by manually further removing the residual sand, extending the preheating time, and adjusting the preheating position. Using the manual flame method to remove runner/risers and flash typically leaves cutting allowances of 3-5mm. Further reducing the cutting allowance to 1-2mm is possible with manual precision cutting by skilled operators.
2.3 Shot Blasting
Shot blasting further removes residual sand and oxide scale on the casting surface, creating good surface conditions for subsequent operations such as surface inspection. Using a step-through suspension chain-type eight-blasting-head shot blasting machine, the typical set shot blasting time is 3-5min/piece.
2.4 Carbon Arc Gouging
Carbon arc gouging is a commonly used and efficient cleaning method, primarily used to remove larger flash or protrusions on the casting surface (such as removing excessively high cutting stubs, removing large areas of abnormal protrusions on the casting surface, etc.), and to prepare for surface finishing. For deeper casting defects, carbon arc gouging is also often used for elimination. However, carbon arc gouging operations are noisy, produce large amounts of smoke and dust, and emit intense arc light, increasing the difficulty of environmental protection and occupational health protection. Currently, the time for gouging bolsters and side frames is approximately 12min/piece.
2.5 Surface Grinding
Surface grinding is performed to remove small flash and burrs on the casting surface; to trim holes or edges to ensure smooth transitions, reducing stress concentrations during workpiece use; to remove welding protrusions and polish critical surfaces, creating necessary surface conditions for subsequent visual or non-destructive testing. Currently, handheld pneumatic grinding wheels are commonly used, which produce loud noise and dust. The current grinding time for bolsters and side frames is approximately 60min/piece.
2.6 Defect Welding and Repairing
Defect welding and repairing is one of the main tasks in casting cleaning, primarily to eliminate discontinuous defects on the casting body, such as shrinkage pores, porosity, and cracks. It is generally performed using a DC welding machine with a handheld welding electrode. The process produces large amounts of welding smoke and intense arc light. Currently, the welding and repairing time for bolsters and side frame castings is approximately 15min/piece.
During grinding and welding and repairing operations, inspectors identify defects found through visual inspection to determine whether they should be eliminated by grinding or welding and repairing, and supervise and record the welding and repairing process. Due to the long length and heavy weight of the workpieces, they are usually flipped using overhead cranes to implement relevant operations on each side.
3. Overall Solution
The technical solution for the intelligent cutting and grinding production line for bolster and side frame steel castings, represents a comprehensive approach to streamlining and enhancing the production process. This solution encompasses multiple units, each designed to play a crucial role in achieving the overall objectives of improved efficiency, quality, and environmental compliance.
Key Components of the Solution:
- Preparation Station:
- This station serves as the initial setup point for the castings. It involves preparing the castings for subsequent processes by ensuring they are properly positioned and secured.
- It may include activities such as removing any remaining sand from the castings after the initial shot blasting process and preparing them for the cutting and grinding operations.
- Intelligent Cutting Unit:
- Utilizing programmable robots equipped with cutting torches, this unit automatically cuts off the fixed positions of gates, risers, and venting pins from the bolster and side frame steel castings.
- The unit is equipped with a vision recognition system to accurately locate and identify the cutting targets, ensuring precise and efficient cutting.
- Waste materials from the cutting process are collected and disposed of properly.
- Manual Cutting Unit:
- This unit handles the removal of any remaining flash, burrs, and cutting residue from the castings that could not be addressed by the intelligent cutting unit.
- It includes equipment such as turning tables, positioners, and handheld cutting torches, allowing operators to manually fine-tune the cutting process.
- Intelligent Grinding Unit:
- Similar in structure to the intelligent cutting unit, this unit uses high-precision servo motor-driven sanding machines to grind and finish the surfaces of the castings.
- The grinding process ensures that the surfaces are smooth and free of defects, meeting the required standards for subsequent operations.
- Manual Welding and Grinding Unit:
- This unit focuses on welding and grinding operations to address any casting defects such as pores, undercuts, or cracks.
- Operators use welding equipment and hand-held grinding tools to perform these tasks, ensuring that the castings are free of defects and ready for further processing.
- Intelligent Logistics System:
- The logistics system facilitates the smooth flow of materials between the different units of the production line.
- It includes equipment such as overhead cranes, feed cars, gantry robots, and conveyors, ensuring that the castings are transported efficiently and accurately from one unit to another.
- Safety and Environmental Protection Unit:
- This unit is responsible for ensuring the safety of the operators and the environmental compliance of the production line.
- It includes safety enclosures, dust collectors, ventilation systems, noise reduction measures, and monitoring devices to detect harmful gases and dust levels.
- Runner/Riser Collection System:
- This system collects and processes the waste materials generated during the cutting process, such as runners and risers.
- The collected materials can be recycled or disposed of in an environmentally friendly manner.
Conclusion:
By integrating these units into a cohesive production line, the technical solution for the intelligent cutting and grinding production line for bolster and side frame steel castings achieves significant improvements in efficiency, quality, and environmental compliance. The use of intelligent and automated equipment reduces the workload on operators, enhances safety, and ensures consistent product quality. Overall, this solution represents a significant step forward in the production of large steel castings for railway freight cars.