Abstract:
Considering the practical fettling operations of large steel castings, such as bolsters and side frames for railway freight cars, this paper introduces a comprehensive intelligent solution. Based on the integration of 3D vision, robotics, safety and environmental protection, system integration, and control technologies, this solution aims to enhance production efficiency, improve operational quality, and reduce manual workload. The paper presents the detailed design of various units, including preparation stations, intelligent cutting units, manual cutting units, intelligent grinding units, manual welding and grinding units, intelligent logistics systems, safety and environmental protection units, and sprue and riser collection systems. Through practical production validation, it is demonstrated that this new scheme significantly enhances operational quality, decreases manual working intensity, and offers an environmentally friendly solution.
1. Introduction
Large steel castings, such as bolsters and side frames for railway freight cars, are typically produced using sand casting processes. After casting, these components undergo a series of operations including sand removal, flashing and sprue/riser cutting, shot blasting, carbon arc gouging, surface grinding, defect welding, and inspection before heat treatment. Traditional production methods involve synchronized cutting, welding, grinding, and inspection tasks, often accompanied by the use of overhead cranes for material handling. This open, multi-disciplinary, and multi-personnel production environment results in multiple pollution sources, complex pollution types (arc light, noise, dust), high pollution concentrations, and intensities, posing significant environmental governance and occupational health challenges.
In response to these issues, CRRC Meishan Co., Ltd. has proposed an intelligent solution for the cleaning of large steel castings for 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 exhibits high system integration, intelligent management, and environmental friendliness, exploring a new path for the production of large steel castings in the railway industry.
2. Overview of the Cleaning Process
Before heat treatment, bolster and side frame steel castings must undergo a series of processes including sand removal, flashing cutting, sprue/riser cutting, shot blasting, carbon arc gouging, surface grinding, internal and external surface inspection, defect welding, and inspection confirmation. Table 1 summarizes the cleaning operations, working hours, and pollution types.
Table 1: Cleaning Operations, Working Hours, and Pollution Types
| No. | Operation Name | Operation Content | Working Hours | Pollution Types |
|---|---|---|---|---|
| 1 | Mechanical Sand Removal | Remove the sand from the outer surface of the casting | 15 min/box | Dust, Noise |
| 2 | Manual Sand Removal | Remove the core sand from the inner cavity of the casting | 90 min/piece | Dust, Noise |
| 3 | Sprue/Riser Cutting | Remove fixed positions such as sprues, risers, and venting pins | 15 min/piece | Fume, Noise |
| 4 | Flashing Cutting | Remove flashing of varying positions and sizes | 12 min/piece | Fume, Noise |
| 5 | Shot Blasting | Remove residual sand and oxide scale from the casting surface | 3-5 min/piece | Dust |
| 6 | Carbon Arc Gouging | Remove high cutting allowances, abnormal protrusions, and prepare welding grooves | 12 min/piece | Fume, Dust, Arc Light, Noise |
| 7 | Surface Grinding | Remove flashing, burrs, smooth key surfaces, and achieve smooth transitions | 60 min/piece | Grinding Dust |
| 8 | Defect Welding | Eliminate shrinkage porosity, porosity, cracks, etc. | 15 min/piece | Fume, Arc Light, Noise |
| 9 | Inspection Confirmation | Check casting quality, identify defects, specify operations, and record | 15 min/piece | – |
| 10 | Workpiece Flipping | Flip the workpiece | 1 min/piece | – |
3. Intelligent Solution Design
3.1. Overall Scheme
The intelligent cutting and grinding production line for bolster and side frame steel castings includes units such as a preparation station, intelligent cutting unit, manual cutting unit, intelligent grinding unit, manual welding and grinding unit, intelligent logistics system, safety and environmental protection unit, and sprue and riser collection system.
3.2. Workstation Design
Based on the current process flow, operation content, working hours, pollution types, and the actual plant layout, logistics, and process plan arrangement, the production line workstations are designed. Due to the large area required for sand removal and its close connection with molding and sand processing, as well as the long operation time, sand removal is not included in the production line. Similarly, shot blasting and carbon arc gouging are not included due to existing equipment.
Robotic cutting of sprues and risers ensures flat cutting surfaces, with subsequent manual fine cutting to eliminate high cutting allowances and local abnormal protrusions. Surface grinding, defect welding, and inspection confirmation are integrated into one workstation due to their synchronization requirements.
3.3. Logistics Design
Logistics design focuses on planning workpiece flow based on workstation design. Bolster and side frame manufacturing specifications require that castings from the same pouring batch undergo heat treatment in the same furnace (typically 12 bolsters or 16 side frames per batch). In practice, castings from the same batch are concentrated, processed individually, and then transported to the heat treatment process.
Table 2: Logistics Operations and Equipment Configuration
| No. | Pick-up Location | Logistics Method | Placement Location |
|---|---|---|---|
| 1 | Shot Blasting | Overhead Crane, Batch Flow | Preparation Station |
| 2 | Preparation Station | Overhead Crane, Single Piece Flow | Loading Cart |
| 3 | Loading Cart | Gantry Robot, Single Piece Flow | Intelligent Cutting Unit |
| 4 | Intelligent Cutting Unit | Gantry Robot, Single Piece Flow | Manual Cutting Unit |
| 5 | Manual Cutting Unit | Gantry Robot, Single Piece Flow | Intelligent Grinding Unit |
| 6 | Intelligent Grinding Unit | Gantry Robot, Single Piece Flow | Receiving Cart |
| 7 | Receiving Cart | Single Beam Crane, Single Piece Flow | Manual Welding and Grinding Unit |
| 8 | Manual Welding and Grinding Unit | Single Beam Crane, Batch Flow | Discharging Cart |
| 9 | Discharging Cart | Overhead Crane, Batch Flow | Logistics Channel Flatcar |
Equipment such as loading carts, gantry robots, receiving carts, single beam cranes, and discharging carts are configured to meet logistics requirements, with operation and control logic consistent with the workstation sequence and adapted to the required pace.
3.4. Equipment Configuration and Requirements
Table 3: Equipment Configuration and Requirements
| Unit | Equipment/Requirements |
|---|---|
| Intelligent Cutting Unit | Variable-position machine, workpiece fixture, vision recognition system, robotic system, cutting torch, cutting gas control system, sprue/riser collection device, turntable |
| Manual Cutting Unit | Turntable, variable-position machine, fixture, automatic igniter, foot controller, dual-hand control console, hand torch, cutting residue conveying device |
| Intelligent Grinding Unit | (Configuration similar to intelligent cutting unit but tailored for grinding tasks) |
| Logistics Unit | Loading cart, gantry robot, receiving cart, single beam crane, discharging cart |
Specific requirements for each component, such as robot arm length, rotation radius, load capacity, positioning accuracy, and operational speed, are detailed in the following sections.
3.5. Detailed Design of Key Units
3.5.1 Intelligent Cutting Unit
The Intelligent Cutting Unit employs programmable robots to drive the cutting torch. Its primary function is to remove fixed elements such as gating systems, risers, and venting pins from the large steel castings of railway freight car bolsters and side frames, and to collect waste materials generated during the cutting process. The design of this unit aims to enhance cutting precision and efficiency while ensuring operational safety.
The configuration of the Intelligent Cutting Unit includes key components such as a positioning machine and workpiece clamping fixture, a visual recognition system, a robotic system, a cutting torch, a gas control system for cutting, and a riser collection device. Below is the detailed design of these components:
Positioning Machine and Workpiece Clamping Fixture: The fixture design incorporates a suitable flexible structure to meet the different clamping requirements of bolsters and side frames and ensures the safe fixation of workpieces in any orientation. The structure between the fixture and the positioning machine is easy to dismantle and provides reliable positioning, facilitating installation, use, and maintenance. The positioning machine can rotate 360° and stop at any angle, with a rotation radius not less than 600mm and a load capacity not less than 1 tonne.
Visual Recognition System: This system identifies fixed cutting elements such as risers on bolsters and side frames and completes tasks such as photographing, cloud image synthesis, cutting element extraction, measurement, and positioning through algorithmic programs. Its comprehensive positioning accuracy should not exceed 0.5mm to ensure cutting accuracy. The visual recognition system is driven by robots and matches the field of view and accuracy of the 3D vision camera, with a robot arm reach of 2600mm.
Robotic System: Based on experimental validation data and operational cycle requirements, the robotic system is configured with two robots, each with a repositioning accuracy not exceeding 0.2mm and an arm reach of 3200mm. These robots can efficiently and accurately complete cutting tasks.
Cutting Torch: A machine-mounted cutting torch is used to ensure stability and efficiency during the cutting process.
Riser Collection Device: This device collects waste materials generated during the cutting process, maintaining cleanliness and safety in the work area.
The workflow of the Intelligent Cutting Unit includes external loading and internal operation stages. External loading primarily involves workpiece positioning and clamping, 3D vision scanning, and data analysis and processing. Internal operations mainly involve data retrieval, workpiece repositioning, and cutting system operation. The key drive system is implemented using a high-precision, fast-feedback system controlled by PLCs, drives, and servo motors to ensure precision and stability during the cutting process.
3.5.2 Manual Cutting Unit
The Manual Cutting Unit is primarily responsible for cleaning up remaining flash and burrs on bolsters and side frames, as well as removing residues generated during the cutting process. The design of this unit aims to assist the Intelligent Cutting Unit in handling detailed areas that are difficult for robots to process.
The configuration of the Manual Cutting Unit includes components such as a turntable, positioning machine and its fixture, automatic igniter, foot pedal controller, dual-hand control console, hand-held cutting torch, and residue conveying device. Below is a detailed description of these components:
Turntable, Positioning Machine, and Fixture: These components are similar to those in the Intelligent Cutting Unit but are designed with greater flexibility to accommodate manual operations.
Automatic Igniter and Hand-held Cutting Torch: The automatic igniter is used in conjunction with the hand-held cutting torch, allowing operators to quickly ignite the torch for cutting operations.
Foot Pedal Controller and Dual-hand Control Console: The foot pedal controller is used to control the rotation of the positioning machine, enabling convenient cutting of workpieces at different angles. The dual-hand control console controls the rotation of the turntable, achieving rapid workpiece repositioning.
Residue Conveying Device: This device, powered by a rodless cylinder, collects residues generated during the cutting process, maintaining cleanliness in the work area.
The operation process of the Manual Cutting Unit is relatively flexible, allowing operators to adjust cutting parameters and workpiece orientations based on actual conditions to ensure cutting quality and efficiency. Additionally, the unit is equipped with necessary safety protective measures such as dust hoods and harmful gas monitoring devices to ensure the safety and health of operators.