Design of a Rotary Threshing Mechanism for a Combine Harvester

Project Overview Our company engineered a rotary threshing mechanism for a combine harvester for leading European OEM, optimized for wheat harvesting with a throughput of 10 tons per hour. The project spanned the entire design lifecycle, from concept design and calculations to finite element analysis (FEA), geometric dimensioning and tolerancing (GD&T), and manufacturing drawings creation. The mechanism, featuring an axial-flow rotor and adjustable concave, was designed to minimize grain damage (<1%) and ensure durability under diverse field conditions, meeting stringent performance requirements. Concept Design The design process began with defining requirements for harvesting, considering stem strength, grain size, and field conditions (e.g., moisture content). Key performance targets included: • Throughput: 10 tons/hour. • Grain Damage: Less than 1% broken grains. • Adaptability: Handling variable crop conditions. An axial-flow rotary design was chosen for its efficiency and gentle grain handling, featuring a rotor with rasp bars and a concave with adjustable grates. The design was modelled using SolidWorks, enabling precise visualization and iteration. Relevant Calculations Calculations ensured the mechanism met performance goals: • Power Requirement: Based on a wheat-specific energy of 0.75 kJ/kg and a throughput of 2.78 kg/s (10 tons/hour),] 3 kW hydraulic motor was selected to account for inefficiencies. • Rotor Speed: Set at 500–700 rpm to balance threshing efficiency and grain protection, adjustable via a variable-speed drive. • Concave Clearance: Designed to taper from 10 mm at the inlet to 5 mm at the outlet, optimizing grain separation while retaining debris. These calculations guided component sizing and system integration. Finite Element Analysis (FEA) FEA, conducted using ANSYS, validated the mechanism’s structural integrity: • Static Analysis: The rotor, constructed from high-strength steel, experienced centrifugal forces up to 10,000 N and crop impact loads. Maximum stress was 250 MPa, below the 400 MPa yield strength, ensuring safety. • Modal Analysis: The rotor’s first natural frequency (120 Hz) was well above the operating range (8.3–11.7 Hz), preventing resonance. • Fatigue Analysis: Designed for over 1 million cycles, ensuring long-term reliability under repetitive loading. FEA results prompted reinforcements at the rotor hub and optimized concave grate spacing for uniform load distribution. Critical Geometric Dimensioning and Tolerancing (GD&T) GD&T ensured manufacturing precision, adhering to ASME Y14.5 standards: • Positional Tolerances: ±0.1 mm for rasp bar alignment to maintain consistent threshing performance. • Flatness: ±0.05 mm for concave mounting surfaces to ensure uniform clearance. • Profile Tolerances: ±0.2 mm for the rotor’s cylindrical surface to guarantee smooth rotation. These tolerances were critical for assembly accuracy and were integrated into the manufacturing drawings. Manufacturing Drawings Creation Detailed drawings were produced in SolidWorks, specifying: • Rotor Assembly: High-strength steel shaft, rasp bars, and bearings, with tungsten carbide coating for wear resistance. • Concave Sections: Modular, wear-resistant steel grates with adjustable mechanisms. • Drive System: Hydraulic motor and mounting details for reliable power transmission. Drawings included material specifications, surface finishes, and assembly instructions, streamlining fabrication and ensuring cost-effective production. Key Technical Challenges The project faced several challenges: • Grain Damage: High rotor speeds risked grain breakage. This was mitigated by optimizing rasp bar patterns and allowing adjustable speeds (500–700 rpm). • Wear Resistance: Abrasive wheat straw caused component wear. Tungsten carbide coatings on the rotor and concave extended service life. • Variable Conditions: Differing moisture levels and crop densities required adaptability. Adjustable concave clearance and rotor speed enabled operator control. • Structural Integrity: High centrifugal and impact loads were addressed through FEA-driven reinforcements, ensuring durability. Our Company’s Contribution Our team delivered significant value: • Innovative Design: Developed a high-efficiency axial-flow mechanism with adjustable features, reducing grain damage and enhancing adaptability. • Advanced Analysis: Utilized FEA and simulation tools to validate and optimize the design for real-world conditions. • Collaborative Execution: Partnered with manufacturers to ensure producibility, balancing precision with cost. • Field Validation: Conducted field tests to confirm performance, achieving <1% grain damage and 10 tons/hour throughput. Additional Considerations • Operator Safety: The mechanism included guards around moving parts and emergency stop features, complying with ISO 4254-7 standards for agricultural machinery safety. • Sustainability: The design minimized energy consumption through efficient power use and reduced grain loss, supporting sustainable farming practices. Conclusion This project underscores our expertise in designing a robust rotary threshing mechanism for combine harvesters. By addressing concept design, calculations, FEA, GD&T, and manufacturing drawings, we delivered a solution that enhances harvesting efficiency, reduces grain damage, and ensures durability. Our innovative approach and rigorous engineering processes position us as leaders in agricultural machinery design.