THAI NGUYEN UNIVERSITY THAI NGUYEN UNIVERSITY OF TECHNOLOGY Vu Van Dam DETERMINING PROPER PARAMETERS OF THE CHOPPING PROCESS OF HAVESTED CORN STALKS Specialty: Mechanical Engineering Code: 52 01 03 SUMMARY OF DOCTORAL THESIS IN ENGINEERING Supervisor Assoc Prof Dr Nguyen Quoc Tuan Prof Sc Dr Pham Van Lang THAI NGUYEN – 2020 Introduction Motivation Agricultural residues, including stems, leaves and other components (often thrown away after harvested), have been considered to be rich in organic polymers such as lignin, cellulose, hemiaellulose, protein and lipids [74] In Vietnam, agricultural residues are mainly from rice and corn (maize), often used as direct feed, or silage for livestock feed [2-4, 7, 8, 15, 17] According to statistical calculations [111], the total annual amount of agricultural residues in the world is about 3736 million tons, which can replace 2283 million tons of coal, 1552 million tons of oil or 1847 million cubic meters of gas This output has increased steadily over the years to meet the growing world’s population On average, the annual volume of residues from wheat, rice, maize, and soybean are 763 million tons, 698 million tons, 1730 million tons and 417 million tons, respectively Corn is the third most important food crop after rice and wheat [27], widely grown around the world [45, 97] Corn stalks account for one-third of the annual production compared to other agricultural residues [41] In Vietnam, maize is not only an important cereal and food, but also recently plays a role as a raw material plant for the production of environmentally friendly ethanol - E5 [10] In particular, a new trend is being developed that direct cultivation of biomass maize will also increase the demand for post-harvest processing Chopping of harvested corn stalks is an important preliminary step in the processing of animal feed, biomass pellet production as well as in other processing processes For example, the corn stalk should be chopped into 6.4 mm lengths for gasification [95], mm long for chemical conversion [102], 2-10 mm for composting yeast forage, or 5-6 mm long for briquetting [76] On the industrial scale, chopping can be done by specialized chopping components, which are combined at the rear of harvesters In developing countries such as Vietnam, farmers often burn all kinds of agricultural residues on fields This is not only a waste but also a negative impact on the environment, such as air pollution or causing forest fires One of the reasons is that the cost of chopping is still high Because agricultural residues are often very cheap, depreciation, labor and especially energy consumption will account for a large proportion of the cost of semi-finished products Therefore, finding solutions to reduce the amount of energy consumed when chopping has been carried out by many international studies [24, 34, 37, 43, 78, 87, 107] In Vietnam, scientific publications were found to mainly focus on design techniques based on productivity, durability, etc for harvesting machines combined with chopping of some agricultural products such as maize [ 3, 4, 6, 17], straw after harvesting rice [19] or banana stalks [1], processing pineapples [9], cutting fibers from coconuts [13] These designs focus on solving the chopping function according to the principles of cutting discs, cutting drums, designed to achieve the chopping productivity However, the issue of energy saving has hardly been mentioned by previous studies Many international studies have been done to reduce cutting force and cutting power by improving the tool design and selecting a reasonable cutting mode Reducing shear force is considered as one of the optimal solutions to reduce energy consumption Moreover, reducing the cutting force will also contribute to reducing the size of the machine's parts and thus reducing the size of the machine However, because energy consumption is calculated by the multiple product of the shear force and shear velocity, in several cases if the chopping process has a small shear force with high velocity, it may required a large power consumption In some studies, empirical models using a pendulum have been developed to measure the shear force and shear power required when chopping agricultural residues [32, 39, 66, 71, 85, 100] Factors assessed include the effects of the type of cutting blade, the different cutting angles [24, 27, 44, 96] Several other studies have evaluated the influence of the straight blade sharp angle, the rotation speed of the disc-type knives to the cutting ability of corn stalks [32, 78, 85, 90, 103] A new approach of is applying biomechanics to design and manufacture of knife profiles based on the tooth profile of insects such as mantis, corn-eating worms, grasshoppers, hair trimmers [64] , 65, 71, 72, 100] Finite element method and experimental simulation results show numerous benefits in terms of shear force and power consumption reductions However, this type of blade profile would be difficult in manufacturing, sharpening and thus would be difficult to apply in commercial machines There have been many studies to find solutions to save energy consumption [27, 28, 38, 44, 49, 66, 68, 69] However, the solution to the multi-objective optimization problem for both shear forces and energy consumption, especially for chopping machines using counter edge [24, 34, 37, 43, 78, 87, 107] is still a remained knowledge gap Another research direction to save energy in the process of chopping agricultural residues is to identify proper working parameters [28, 31, 33, 49, 50, 58, 59, 61, 78, 88, 89] To date, the problem of concurrently reducing the force and cutting power directly on chopping machines, using counter edge has not been solved No studies have been found to evaluate the simultaneous effects of working parameters and structural parameters on cutting force and power on such machines For the above reasons, the topic: "The study identifies some reasonable parameters of the process of cutting corn stalks after harvest" with urgency and practical significance Aims, objectives and scopes of the present research 2.1 Research aims The main aims of this study is to determine important structural parameters and proper operational parameters of the chopping process of havested corn stalks in order to concurrently minimize the cutting force and cutting power Research subjects: The study subjects are some main parameters affecting shear force and energy consumption of corn stalk choppers 2.2 Research objectives Objectives of this study are as following: + Designing and manufacturing an experimental device that can control the input parameters, obtain all output parameters of the chopping process, meeting the requirements of the experimental study; + Identify parameters that have strong effects on the force and cutting power when chopping corn stalks after harvesting; + Identify a set of design and operation parameters of chopping machines to minimize cutting force and cutting capacity; + Develop a profile model of chopping blade to ensure design parameters 2.3 Scopes The scope of the study is to conduct experiments of chopping single corn stalks in order to determine the specific cutting force and cutting power, providing a basis for calculating the problem of cutting process Experiments are carried out in laboratories Parameters to be evaluated include: feed angle, approach angle and cutting speed The harvested corn stalks used as experiments were stored under the same conditions It is assumed that mechanical properties and moisture content of experimental samples are the same The research methods used in this study include design of experiments, applied statistical analysis and mathematical regression techniques Application-oriented significances + The results can be applied to design and manufacture of agricultural chopping machines Although only experimented with corn stalks, the significant effects of the feed angle and the approach angle were due to the grain texture of the stem Most other stalks and agricultural residues also have such grain structure Therefore, the trend of influence of the above angles can be applied when chopping other plants + The research results of the thesis can be used in design calculations and selection of working parameters for disk chopping machines, contributing to the exploitation and processing of agricultural residues for production and life, reduce energy costs, thereby contribute to reduce the environmental pollution The new contributions of the study + Studied the cutting force and cutting power in chopping of corn stalks for an intermediate cutting speed (Ranged from to 10 m/s) This is a new contribution to this research trend in the world + Evaluated the simultaneous effects of approach angle, feeding angle and cutting velocity to the cutting force and cutting power in chopping process of corn stalks This is a new contribution compared to previous scientific publications + Carried out a couple of conflict objective functions, including the cutting force and cutting power Thereby, the multi-objective optimization problem for both cutting force and cutting power of corn stalks has been solved Compared to a typical case of practical use of chopping machines, applying the optimal parameters not only reduced the cutting force by 2.3 times, but also dropped down the power consumption by times Identified a set of working parameters, which serves as a basis for designing and manufacturing chopping machines of agricultural residues, applied in production practices + Proposed a blade profile using logarithm spiral and evaluated its advantages compared to blades using straight and curved edges Using the proposed profile allows to keep the approach angle as constant along the blade edge Consequently, the optimum value of the approach angle can be maintained belong the cutting edge of the blade + Developed an algorithm to automatically calculate and draw the blade shape with different sizes The embedded software module in AutoCAD environment allows to create technical drawings and to export the data sets for tool machining on CNC machines Thesis structure Chapter Literature review Chapter Theoretical basis of chopping process of agricultural residues Chapter Design, manufacture and evaluate the experimental system Chapter Experimental study and development of the blade profile CHAPTER LITERATURE REVIEW 1.1 Introduction 1.2 State-of-the-art of corn production in the world and in the country 1.2.1 Corn production in the world 1.2.2 Maize production in the country 1.3 Some characteristics of the maize after harvested 1.3.1 Humidity 1.3.2 Specific gravity 1.3.3 Mechanical properties 1.3.4 Sliding friction between corn stalks and other materials 1.4 Processing agricultural residues 1.4.1 Processing animal feed 1.4.2 Processing commercial products 1.5 Agricultural residues chopping machines 1.5.1 Drum chopper 1.5.2 Disc chopper 1.5.3 Chopping machine using tooth knives 1.6 Experimental studies 1.6.1 Assignments of angle parameters 1.6.2 Pendulum-impact for experimental device 1.6.3 Vertical rotational disk device 1.6.4 Universal testing machine 1.7 Some results in saving energy consumption Chapter conclusions Chapter presented an overview of the issues directly related to the topic of the thesis, specifically as follows: Maize is one of the most important crops in the world and in Vietnam The statistics show that there is an increase in productivity and output Chopping of corn stalks after harvested is a mandatory preliminary step of further processing The specific parameters of corn stalks that affect the chopping process have been confirmed in previous studies Important parameters include: the moisture content, elastic modulus, friction coefficient between corn stalks and some materials Experimental models for harvesting machines would not be fully applied to practical chopping machines, due to the inconvenience to implement fedding angle The experimental model used inconvenient impact pendulum to measure shear force, which is difficult to vary the cutting speed Some other types of experimental devices using univeral testing machines are not convenient to vary the cutting speed and feed angle Therefore, this study uses a real chopping machine with rotational disk to implement experimental study CHAPTER THEORETICAL BASIS OF CHOPPING PROCESS OF AGRICULTURAL RESIDUES 2.1 Introduction 2.2 The chopping principle 2.3 Basis of chopping process dynamics 2.4 Multi-objective optimization Chapter conclusions Chapter presented a summary of the theoretical basis and the cutting principles of the chopping process The contents of this chapter provided a basis for the study of dynamics and energy consumption of corn stalk chopping Some important contents are summarized as follows: There are two basic principles of the process of cutting agricultural stalks, including: 1) impact cutting, the relative movement between the knife and the material tree (cutting motion) performed in the normal direction; 2) shear cutting, cutting motion combines both normal and tangent directions Compared to impact cutting, the shear-cutting process significantly reduces the cutting force In order to keep the stalks in the wedge-shaped clearance of the cutter and the counter edge, the velocity of the slide should be set based on the friction coefficient between the stem and the tool material Cutting force and power consumption are two objective functions that have a conflict of interest Therefore, it is necessary to solve the optimal problem simultaneously for both above mentioned criteria The multi-objective problem identifies each criterion in accordance with cutting technology steps: applying two expected functions (2.8) and (2.9); Implementing experimental study on a real chopping machine (cutting) to concurrently optimize the two objective functions In order to clarify the research question, it is necessary to develop an experimental device similar to commercial chopping machines, having capable of varying the cutting speed and the correlation angles between the knife and the stalks These contents will be presented in the next chapter CHAPTER DESIGN, CREATION AND EVALUATION OF TESTING EQUIPMENT SYSTEM 3.1 Introduction 3.2 Design of experimental system 3.2.1 Experimental model The input and output parameters in this study are shown in Fig 3.1 and Figure 3.2 Fig 3.1 Experimental schema Fig 3.2 Relative position of the stalk in the cutting process: 1) cutting tool, 2) hinge joints, 3) force sensor, 4) maize stalk, 5) counter shear, 6) spring 3.2.2 Structural design Some of the structural design are presented in Fig 3.3 and 3.4 (a) (b) Fig 3.3 Diagram of the drive principle of a chopping machine a) Structure of a commercial machine, b) Proposed structure: 1) electric motor; 2) Belt transmission; 3) drive shaft; 4) flat knife disc; 5) Coupling; 6) Torque sensor; 7) Load cell; 8) counter shear Fig 3.3 A 3D model of the experimental setup 1) belt wheel, 2) spindle shaft, 3) knife, 4) screw, 5) clamp, 6) maize stalk, 7) counter shear Fig 3.4 Relative position of the stalk in the cutting process 3.3 Selecting measuring and data collection equipment 3.3.1 Cutting force sensor The cutting force sensor Kistler 9712A500 (Figure 3.6) was used to measure the impact force 11 3.5.2 Measure cutting force and torque (a) (b) Fig 3.9 Example of experimental cutting force and power consumption signals 3.5.3 Measurement of sliding friction between counter shear and corn stalk Fig 3.10 Friction measurement experiment Bảng 3.1 Experimental results of sliding friction measurement Mass (kg) Normal force (N) Friction force (N) Friction coefficient  2.5 4.5 6.5 8.5 24.525 44.145 63.765 83.385 11.971 21.146 28.147 34.907 0.488 0.479 0.441 0.419 Angle friction (0 ) 26.02 25.59 23.82 22.72 Friction coefficient  was calculated as the ratio of friction force and normal force The friction angle  was then calculated from the coefficient of friction according to the following formula:   arctan    (3.3) 12 3.6 Chapter conclusions In this chapter, input parameters were determined including: feed angle, approach angle, cutting speed and the gap between the cutting edge and the counter edge The experimental device has been developed to allow for infinite control of these parameters, meeting well the data requirements according to theory of design of experiments The system of measuring and data collection equipments allows to measure output parameters simultaneously including cutting force and cutting torque to ensure reliability An experimental model was developed to determine the coefficient of sliding friction between corn stalks and cutter material Experimental studies, carried out on the above mentioned experimental system will be presented in the next chapter CHAPTER EXPERIMENTAL RESULTS AND DEVELOPMENT OF CUTTING NETWORK MODELS 4.1 Introduction 4.2 Experimental description Three sets of experiments were performed including: screening test; optimization of single objective, and multi-objective optimization experiments 4.3 Screening experiment Table 4.1 Experimental Factors in Screening Experiments Approach angle () 60 Level Low (-1) High (+1) Feed angle () Gap (mm) 50 Table 4.2 Results of screening Experiments StdOrder a 60 60 60 60 b 0 50 50 0 50 50 d 1 1 2 2 Fc 305.77 204.49 235.18 164.59 293.50 241.32 373.30 155.38 STT 13 14 15 16 17 18 19 20 a 60 60 60 60 b 0 50 50 0 50 50 d 2 2 1 1 Fc 287.36 225.97 367.16 146.17 296.57 247.46 247.46 155.38 13 StdOrder 10 11 12 a 60 60 b 0 50 50 d 1 1 Fc 311.91 250.53 225.97 161.52 STT 21 22 23 24 a 60 60 b 0 50 50 d 2 2 Fc 284.29 219.84 361.02 152.31 The main effect graph of factors (Figure 4.1) shows that the effect of approach angle is the most significant, and then the following factors: 2nd, the interaction effect between approch angle and the feed angle; 3rd is the interaction effect between approach angle, feed angle and the gap between the cutting edge and the counter edge, 4th is the interaction between feed angle and gap; the fifth is the feed angle, and finally is the gap between the cutting edge and the counter edge Fig 4.1 Pareto Chart Obtained from Screening Experiments 4.4 Experiment to optimize shear force when cutting slowly 4.4.1 Screening experiment Bảng 4.3 Experimental Factors in Screening Experiments Approach angle, a (0) 10 Level Low (-1) High (+1) Feed angle, b (0) 10 Fig 4.4 Design and Results of Screening Experiments StdOr der Approach angle a (0) Feed angle b (0) Cutting force Fc (N) 10 0 10 348.74 189.14 232.11 14 StdOr der 10 11 12 Approach angle a (0) Feed angle b (0) Cutting force Fc (N) 10 10 10 10 10 10 0 10 10 0 10 10 198.35 351.81 201.42 247.46 195.28 370.23 207.56 222.91 210.63 The cutting force was expressed as a function of approach angle, a and feed angle, b as: Fc = 248.0 – 47.6*a – 30.2*b (4 1) 4.4.2 Downhill experiment to find minimum region Fig 4.2 Contour Plot of Initial Experiments Fig 4.3 The Cutting Force at Steepest Descent Steps The model of cutting force as a response function of the two input factors are depicted in Figure 4.2 The results obtained are presented in Figure 4.3 and Table 4.5 As can be seen, the general vicinity of the minimum cutting force would potentially be located around step The final optimum experiments should be implemented nearby this point Table 4.5 Results of Steepest Descent Experiments Symbol Approach angle a (0) Encode Real value Feed angle, b (0) Encode Real value FC (N) Initial 0 348.74 Initial 10 10 195.28 15  +10 0,7 +7 - Start 20 0,00 20 183.1818 + 30 0,7 27 152.5661 + 2 40 1,4 34 139.5095 + 3 50 2,1 41 113.3962 + 4 60 2,8 48 98.33087 + 5 70 3,5 55 78.24374 + 6 80 4,2 62 106.3657 4.4.3 Optimal experiment The optimal experiments were implemented follow Central Composite Design (CCD) plan, as shown in Table 4.6 The results was then analyzed by ANOVA technique Summary of the cutting force model is depicted in Fig 4.4 Table 4.6 Design and Results of CCD Optimal Experiments Std Ord er 10 11 12 13 Approh ch angle a, (0) 37,3 72,7 37,3 72,7 55,0 55,0 55,0 30,0 80,0 55,0 55,0 55,0 55,0 Feed angle, b (0 ) 38,1 38,1 57,9 57,9 48,0 48,0 48,0 48,0 48,0 34,0 62,0 48,0 48,0 Cutting force (N) 107,79 75,58 81,72 84,93 90,93 90,93 90,93 103,20 75,44 87,86 75,58 87,86 87,86 TT 14 15 16 17 18 19 20 21 22 23 24 25 26 Approhc h angle a, (0) 55,0 37,3 72,7 37,3 72,7 55,0 55,0 55,0 30,0 80,0 55,0 55,0 55,0 Feed angle, b (0) 48,0 38,1 38,1 57,9 57,9 48,0 48,0 48,0 48,0 48,0 34,0 62,0 48,0 Cutting force (N) 87,86 109,86 75,58 78,65 87,00 90,93 90,93 90,93 100,13 75,44 90,93 72,51 87,86 16 Fig 4.4 Analysis of Variance for Cutting Force The cutting force was expressed as a function of approach angle, a and feed angle, bas: FC  210,1  3,132 a  0,409b  0,03293b  0,05574 ab (4 2) This function was then used to carry out the optimal set of input factors so as to obtain smallest cutting force A contour plot of the force model is shown in Figure 4.5b From the figure, the smallest cutting force would be obtained as less than 60 N if the approach angle is of 70°-80°, coupled with the feed angle of 35°40° Another set of parameters includes 30°-40° approach angle and around 65° feed angle Compared to a typical case in practice, where commercial choppers use straight knifes with both approach and feed angles are set to be 0°, where the cutting force would be higher than 300 N (Figure 4.2), optimal input parameters were found to reduce the cutting force by around times (a) (b) Fig 4.5 Surface plot and Contour Plot of the Cutting Force 4.5 Multi-objective optimization of experiments 17 4.5.1 Description of the objective function 4.5.2 Optimization experiment Table 4.7 Real values of experimental parameters Cutting velocity, Approach angle, Level (Coded) V a (0) (m/s) Low (-1) 4.40 Middle (0) 5.66 30 High (+1) 6.91 60 Table 4.8 Experimental tests and corresponding results Std Or der V a b F 4.4 0 6.91 0 4.4 P tt V 706.07 82.37 11 5.66 548.56 100.57 12 60 282.26 32.93 13 6.91 60 325.32 59.64 4.4 50 392.18 45.75 6.91 50 344.59 4.4 60 50 312.86 6.91 60 50 4.4 30 25 10 6.91 30 25 a Feed angle, b (0) 25 50 b F P 25 485.1 72.77 5.66 60 25 327.59 49.14 5.66 30 359.39 53.91 14 5.66 30 50 312.86 46.93 15 5.66 30 25 367.25 55.09 63.17 16 5.66 30 25 364.98 54.75 36.50 17 5.66 30 25 293.59 44.04 425.04 77.92 18 5.66 30 25 243.74 36.56 313.99 36.63 19 5.66 30 25 236.94 35.54 210.87 38.66 20 5.66 30 25 230.14 34.52 The Analysis of Variance tables summarise the linear terms, the squared terms, and the interactions of input parameters in the response functions As can be seen from both Fig 4.6 and 4.7, there appeared significant p-values (smaller than the typical significance level of 0.05) for the square terms (p=0.002 in Fig 4.6 and p=0.004 in Fig 4.7), as well as for the 2-way interactions (p=0.003 in Table 4.6 and p=0.013 in Table 4.7) This indicates that there are curvatures in the response surfaces of the cutting force and the power consumption In Fig 4.6, the small p-values for a (p=0.000) and for b (p=0.002) indicate that the effects of those factors on the cutting force are statistically highly significant However, the cutting velocity, V and the approach angle, a, but not b, are the factors having significant effects on the power consumption, as shown in Fig 4.7 The p-values of the term “Lack-of-fit” appeared as high 18 values (greater than 0.05) in both Tables 4.6 and 4.7 indicate that the regression models of the cutting force and of the power consumption fitted the experimental data well Fig 4.6 Analysis of Variance of the Force response Fig 4.7 Analysis of Variance of the Power response (a) (b) Fig 4.8 The cutting force peak and power consumption as functions of cutting velocity: a) when α=0 and β=0; b) when α=30 and β=35 The two functions were considered as conflicting objectives, as illustrated in Fig 4.8 The cutting force appeared to decrease with higher cutting velocity with approach angle a=00 and feed angle b=00 (Fig.4.8(a)), whereas the power consumption increased with increasing velocity The difference between the trend of cutting force and that of the power can also be observed in Fig.4.8(b), where a=300 and b=350 On the one hand, the minimum cutting force is sought so as to strengthen the machine elements On the other hand, saving energy is also an important issue either in designing or 19 operating the machine The response optimisation was needed to identify the combination of input variables that satisfy a set of tradeoff objectives The cutting force and power consumption were then modelled as functions of input parameters by using regression The equations of the response characteristics, i.e the cutting force and the power consumption, as functions of input parameters, are obtained as: F  411  151V - 19.72 a - 12.49b - 19.2V  0.1263 a  0.0695 b  1.196 Va   0.713Vb  0.1080 ab  2 P  -41  44.8V - 2.545 a - 1.595b - 3.62V  0.01955 a  0.01131b  0.1080 Va   0.0555V b  0.01598 ab (4 3) 4.5.3 Determining optimal parameters The optimal solution (Fig 4.9 and 4.10) can provide the minimum cutting force of around 238.8 N combined with the minimum power consumption of 23.7 W The optimal set of input parameters consists of the cutting velocity of 4.4 m/s, approach angle of 41.8 and the feed angle of 30.3 Compared to a typical case in practice, where commercial chopping machines usually use straight knifes with both approach and feed angles are set to be 0, the optimal parameters were found to significantly reduce both cutting force and power consumption The optimal solution can provide a cutting force 233.8 N (around 2.5 times compared to 546.56 N) and power consumption of 23.66 W, as around times smaller than 100.57W Fig 4.9 Response optimisation of P and F 20 Fig 4.10 Optimisation plot of the multi-objective problem 4.6 Compare, choose the blade profile 4.6.1 Straight blade When cutting in the model of a scissor with a straight-edged blade, the feed angle changes continuously along the blade, resulting in a changing shear force, as shown in Table 4.9 Table 4.9 Example of changing approach angle with a radius R1=100 mm L(mm) α () 150 41, 175 34, 200 30, 225 26, 250 23, 58 275 21, 300 19, 47 325 17, 350 16, 375 15, 400 14, 4.6.2 Circular blade Fig 4.11 Varying of the approach angle of a curve knife Fig 4.12 Variation of the appoarch angle of the straight edge α1 and that of the curve edge α2 21 Table 4.10 Statistics of the value of the feed angle at different cutting points L (mm) α straight blade (0) α Circular blade (0) 15 41, 26, 17 34, 26, 20 30, 27, 22 26, 28, 25 23, 30, 27 21, 32, 30 19, 34, 32 17, 36, 35 16, 39, 37 15, 42, 40 14, 46, 4.6.3 Logarithm blade Logarithmic spiral curves always have a constant angle α between the tangent of the curve and the corresponding radius (Figure 4.13) Figure 4.14 depicts an example where the angle is constant α=30at different points along the cutting edge Fig 4.13 A logarithm curve Fig 4.14 Constant tangent angle of the logarithm edge 22 4.7 Automatic design of uniform cutting blades A software module to create the logarithm spiral was implemented in AutoCAD environment The module can automatically build the technical drawing and export data of the points along the cutting edge for manufacturing the cutter on CNC machines 4.8 Design, manufacture and test logarithm blade Fig 4.15 A logarithm cutter Fig 4.16 Drawing of cutter support Fig 4.17 The manufactured logarithm cutter on chopping Fig 4.18 Cutting force at different points along the logarithm edge 4.9 Chapter conclusions This chapter presents experimental results to determine a reasonable set of parameters for cutting havested corn stalks Some important conclusions are summarized as follows: The results of the screening test showed that the gap between the chopping knife and the millet did not significantly affect the shear force compared to the feed angle and approach angle The results of the single objective optimization experiments have found a set of parameters as following: the approach angle is from 23 70° to 80°, the feed angle is from 35° to 40° Accordingly, the cutting force is times lower than that of commercial chopping machines The results of the multi-objective optimization experiments have found the optimal set of parameters, including the cutting speed of 4.4 m/s, the approach angle of 41.8° and the feed angle of 30.3° Accordingly, the cutting force is more than 2.5 times, the power consumption is reduced about times compared to commercial chopping machines From results of analysis, comparison and evaluation of experimental data, a practical cutting blade using logarithm profile was designed and successfully manufactured, which allows to maintain a constant approach angle as given along the cutting edge An AutoLisp software module, applicable to automatically create drawing of the logarithm profile in AutoCAD environment has been made This allows to perform completely automatically the process of calculating the coordinates of the tool contour points, rendering data files for manufacturing the cutter profile on CNC machines CONCLUSIONS Compared to previous studies in the same field, the thesis has achieved the following scientific and practical values: Successfully designed experimental systems, measuring systems and data collection directly on small commercial chopping machines, using two rotation blades This experimental system can provide a similar cutting conditions to the actual environment in terms of cutting speed and tool arrangement, better than the two common models in many other publications using quasi-static and impact cutting processes The knowledge gap in maize cutting studies has been found to be that there are no studies on shear force and consumption power in the chopping form at medium velocity (within the range from to 10 m/s) Therefore, experiments have been carried out in this study to collect and analyze data for a range of cutting speeds from to m/s This result has been internationally reviewed and published in high-ranking scientific journals (ISI Q1) 24 Detected two objective functions that have a conflict of interest, including the cutting force and the cutting power Thereby, the problem of maximizing goals to reduce simultaneously the cutting force and cutting power for each single cut of corn stalks was solved The optimal set of input parameters were found as following: the cutting speed of 4.4 m/s, the approach angle of 41.8 and feed angle of 30.3  This set of parameters allows to obtain a cutting force of 238.8 N, a power consumption of about 23.7 W, as 2.5 times smaller in cutting force and times reduction of the power consumption, compared to a conventional cutter with a feed angle and approach angle of 0 Successfully proposed, designed and fabricated a blade using logarithm profile Compared to flat and curved blades, the logarithm profile provided a constant approach angle at all cutting positions along the blade length Consequently, the study results can be used to improve the efficiency of the chopping process of agricultural residues THE PROPOSAL FOR FUTURE RESEACH Some suggestions for further studies are as follows: Complete the solution of the optimal problem to simultaneously meet many criteria, such as the cutting force, the power consumption, cutting capacity, quality of chopped residues Taking into consideration the influence of many factors: figure parameters study blade, correlation angle between knife and stalks, cutting speed, mechanical properties of different type of residue materials… Develop a dynamical model for a chopping machine using logarithm blades 25 LIST OF PUBLICATIONS RELATED TO THE THESIS Vu Van Dam, Ngo Quoc Huy, Nguyen Thanh Toan, Nguyen Huu Cong, Nguyen Quoc Tuan, Nguyen Van Du (2020).“Multiobjective optimization of cutting force and cutting power in chopping agricultural residues”, Biosystem Engineering (ISI Q1, H=95) Vu Van Dam, Nguyen Huu Cong, Nguyen Quoc Tuan, Ngo Quoc Huy, Nguyen Thanh Toan (2019), “Parameter optimization of cutting force in corn stlk chopping” International Journal of Mechenical and Production Engineering Research and Development, Vol 9, Issue 3, pp.656-663 (SCOPUS) Ngô Quốc Huy, Nguyễn Thanh Toàn Vũ Văn Đam (2019), “Design and realize experimental device for agricultural stalk chopping” Thai Nguyen University Journal of Science and Technology, Vol 200(07), pp.163-168 Vũ Văn Đam, Đỗ Thị Tám, Phạm Văn Lang (2017) “mechanization of food crops production (rice, corn) in the provinces of northern midlands and mountains region - current status and contribution of the agricultural engineering sector” Vietnam Mechanical Engineering Journal, no 3, 2017 ... conflict objective functions, including the cutting force and cutting power Thereby, the multi-objective optimization problem for both cutting force and cutting power of corn stalks has been solved... of cutting agricultural stalks, including: 1) impact cutting, the relative movement between the knife and the material tree (cutting motion) performed in the normal direction; 2) shear cutting,... direction; 2) shear cutting, cutting motion combines both normal and tangent directions Compared to impact cutting, the shear-cutting process significantly reduces the cutting force In order to keep