Edge curve fitting and optimization of the wave-type cutting disc for castor

Castor is one of the most important chemical raw materials and strategic plants. High economic benefit can be integrated with the low input cost, because of the low requirement of growing environment and simple planting. However, the low level of mechanization has confined the large-scale production of the castor industry, especially in harvesting. Therefore, there is an urgent need to mechanize castor harvesting. Castor harvesters can be divided mainly into segmented and combined harvesting. Among them, the combine harvester has been widely used in various crop production, due to its efficiency, low loss rate and power consumption. Furthermore, the cutting disc can be selected to realize the combined harvest for castor stalk cutting. The rotary motion, smooth operation, small vibration, and strong cutting are also required for the coarse and hard stalk crops. The blade shape and structural parameters of the cutting disc can dominate the working performance and cutting quality of the castor harvester. Therefore, the edge curve of the cutting disc is generally preferred to design the castor combine harvester. As such, the numerical simulation has been carried out on the maple, castor stalk, mulberry branch, sugarcane, and wild chrysanthemum. The castor stalks cutting with the wave-type cutting disc is characterized by the typical penetration and high-speed collision. However, the accuracy of cutting force can be limited to the finite element (FEM) simulation without considering conservation. This study aims to find a suitable simulation model, according to the physical and mechanical properties of low-castor beans planted in China. The edge parameters of the wave-type cutting disc were fitted and then optimized using preliminary tests and theoretical analysis. B-spline and three-point circular curvature analysis were used to calculate the contour curvature of the cutting disc curve. Then, the parameter range was determined for the edge structure curve of the cutting disc using the least square method (LSM) with geometric constraints. Smoothed particle hydrodynamics (SPH) and FEM were also coupled to simulate the dynamic process of castor stalk cutting by LS-DYNA software. The orthogonal rotation combination test was conducted to simulate the effects of cutting disc thickness, radius of bottom circle, and edge angle on the maximum cutting force and cutting power consumption. The edge parameters of the wave-type cutting disc were optimized to fit the circular arc. The optimal combination of parameters was verified by the response surface method (RSM) and experiment. The results showed that the radius of the bottom circle, the thickness of the cutting disc and the edge angle shared significant effects on the maximum cutting force. The significance of each factor was then ranked in the descending order of the edge angle, the thickness of the cutting disc, and the radius of the bottom circle. Among them, the thickness of the cutting disc and edge angle also shared significant effects on the cutting power consumption. The significance of each factor was ranked in the descending order of the thickness of the cutting disc, edge angle, and radius of the bottom circle. Multi-objective optimization was carried out using Design-Expert 8.0.10 software. The optimal combination of cutting operation parameters was obtained as follows: the thickness of the cutting disc was 3 mm, the radius of the bottom circle was 7 mm, and the edge angle was 19°. The maximum cutting force and cutting power consumption were 109.763 N and 1.43 J, respectively. The verification test showed that the relative error of the SPH-FEM simulation and the bench test was less than 5%. Thus the better cutting performance was achieved in the castor cutting disc. The finding can provide technical support to the castor harvester.