Abstract:
This paper presents a comprehensive study on the sand casting process design and simulation optimization analysis of a rotary disc, a critical component in drilling machine spindles requiring high precision and hardness. Based on the structural characteristics of the rotary disc, numerical simulation analysis and optimization were conducted to determine the optimal casting position, parting surface, gating system, riser, and chill placement. The results indicate that the designed casting process ensures the quality of the dovetail guide surface and the large plane, significantly reduces post-processing workload, simplifies the molding process, and achieves a high yield rate. This study provides valuable technical references for the production of similar castings.
Keywords: rotary disc, HT250, sand casting, process design, simulation optimization
1. Introduction
Rotary discs, as key components in drilling machines, play a crucial role in ensuring the accuracy and stability of the machining process. These components are typically manufactured using sand casting due to its versatility and cost-effectiveness. However, achieving high-quality castings with minimal defects, especially in complex geometries such as the dovetail guide surface and large plane of rotary discs, poses significant challenges.
This paper focuses on the sand casting process design and simulation optimization of a rotary disc made from HT250 material. HT250 is chosen for its high strength, good wear resistance, excellent damping properties, and favorable casting performance. Through numerical simulation and iterative optimization, an optimal casting process is developed to ensure the quality of the rotary disc and improve production efficiency.
2. Structural Analysis of the Rotary Disc
The rotary disc has a three-dimensional shape with dimensions of 1040 mm × 375 mm × 158 mm. The overall structure is relatively symmetrical, with a multi-ribbed semi-open porous internal structure. The maximum wall thickness is 30 mm, while the minimum is 10 mm, and the smallest hole diameter is 6 mm, classifying it as a thin-walled medium-sized complex casting.
The dovetail guide surface and screw hole surfaces require exceptional quality, with no casting defects allowed. The internal ribbing and multiple hole structures make coremaking a challenging aspect of the casting process.
3. Casting Process Design
3.1 Material and Molding Method Selection
The rotary disc is made from HT250 material, chosen for its favorable casting properties. For the molding material, furan resin self-hardening sand is selected due to its high dimensional accuracy, smooth surface finish, and dense microstructure of the castings. Alcohol-based coatings are used, and manual molding and coremaking methods are employed.
3.2 Determination of Casting Position and Parting Surface
The casting position is chosen with the large plane facing upwards and the dovetail guide surface facing downwards. This configuration ensures that the thin and complex dovetail guide surface is adequately filled and solidified, while the defects such as slag and gas can float to the top, facilitating their removal during post-processing.
The parting surface is located at the large plane of the casting, facilitating mold stripping, simplifying mold structure, and ensuring dimensional accuracy.
3.3 Gating System Design
The gating system is designed to ensure smooth and stable filling of the mold cavity. The inner gates are positioned at the bottom and top surfaces at one end of the casting’s length direction. A step pouring method combined with inclined pouring is adopted, where the mold is tilted slightly to create a pressure gradient within the cavity, maximizing the filling efficiency and reducing porosity.
3.4 Chill and Riser Placement
To ensure the crystallization quality of the thicker sections of the large plane, chills are placed at these locations. The use of tubular core bones within the main core facilitates exhaust and transportation. Three open risers are strategically placed at the highest point of the casting to collect residual gases and slags.
3.5 Second Optimization Numerical Simulation and Analysis
To further enhance the crystallization quality of the machined screw holes in the vicinity of the top hot spots, a secondary optimization was conducted by employing chilled irons. The chilled irons, made of cast iron, were strategically placed. This positioning specifically targets the threaded hole areas, enhancing the strength of the screw holes.
The simulation results, reveal a significant improvement in mitigating hot spots. The casting surface exhibits no notable defects, and the contraction hot spots are successfully diverted to the risers, thereby satisfying the quality requirements of the casting. A quantitative analysis of the casting’s dimensions and masses was also conducted. The casting’s mass was measured to be 174.45 kg, while the gating system and risers weighed 85.25 kg and 9.8 kg, respectively. Using the casting process yield formula:
textCastingProcessYield=fractextCastingMasstextCastingMass+textGatingSystemMass+textRiserMasstimes100
The casting process yield was determined to be 64.73%.
4. Core Design
Given the rectangular shape of the casting, a multi-core embedding approach was adopted to address its internal and external geometries. To ensure precise positioning and fixation of the smaller embedded cores, steel pins and adhesives were utilized for core splicing and prevention of displacement. illustrates the use of small cores for bonding and embedding in shadowed regions. The final assembly of the cores is presented, with the indicated areas showing the embedded small cores. The main core, supplemented by small block cores, was designed to ensure structural integrity. The ends of the cores were extended to facilitate secure fixing within the sand mold, preventing floatation during pouring.
To maintain the cores’ structural integrity throughout manufacturing, transportation, assembly, and pouring, a core bone framework made of welded hollow thin steel tubes in a triangular shape was employed. Multiple holes were drilled into the tubes to serve as core supports, venting channels, and reduce mold weight. The structure of the core bone is depicted. This design minimizes the number of core boxes required, contributing to precision and efficiency.
5. Conclusion
- A comprehensive and reasonable casting process scheme has been developed for the rotary disc produced in small batches using sand casting. The use of resin sand cold box precision core assembly ensures high-precision components. Furthermore, the sand box and core bone design facilitate ease, safety, and security during handling, box assembly, and pouring.
- The inner gates were strategically positioned at the side bottom and top surfaces of one end of the rotary disc’s length direction. The combination of step pouring and inclined pouring ensured smooth filling and reduced overheating in the bottom dovetail guide area. The inclusion of risers at the highest processing surface and the use of chilled irons minimized casting defects, effectively meeting the quality requirements of the dovetail guide surface and the top plane.
- By employing Anycasting simulation software, the filling, solidification, and shrinkage defect processes were analyzed and optimized. This validated the effectiveness and correctness of the design, resulting in a high casting yield, reduced production costs, and improved efficiency.