Finite element analysis and optimization design of artificial grass tufting machine link based on ANSYS workbench

Shi-hao WU，Hui-liang DAI，Jia-ling SONG

College of Mechanical Engineering，Donghua University，Shanghai201620，China

Finite element analysis and optimization design of artificial grass tufting machine link based on ANSYS workbench

Shi-hao WU?，Hui-liang DAI，Jia-ling SONG

College of Mechanical Engineering，Donghua University，Shanghai201620，China

Link of artificial grass tufting machine is the important linking part which can help cluster needles，circle hooks and cutting knives finishing reciprocating motion．In this paper，the finite element model of artificial grass tufting machine link is established by taking advantage o f the finite element analysis software of ANSYS Workbench．According to the constraints and loads in actual condition，the static analysis is performed．Considering the influence of the vibration on link when operating，the modal analysis is taken．The topology optimization design of the link is performed according to the result of static analysis，which provides the theoretical basis and implementation method for the further optimization of the link and other components of the artificial grass tufting machine．

ANSYS Workbench，Link，Static analysis，Modal analysis，Optimization design

1．Introduction

In recent years，production of artificial grass has become a rapidly growing industry.The so-called artificial grass refers to using non-life plastic chemical fiber as its raw material.This kind of man-made simulation grass was born in 1960s in America［1］. With the improvement of the quality of grass fiber，this product is more and more widely used in the entertainment and sports place.The market demand of artificial grass is growing in China.Chinese market needs those products which are moderate cost and high quality.However，currently in about20 internal artificial grass producers，the manufacturers who have the real strength are only a few.From the index of size，equipment，technology，quality and sales ability，domestic enterprises lag behind foreign enterprises in all aspects.Some producers in the stage of small factory and non-professional production，furthermore，most of them are lack of brand perception，marketing control ability，professional management team and professional technicians.

At present，mainstream enterprises of artificial grass tufting machine in the world are Cobble company of British，Tuftco company of America，CMC company of America，Yamaguchi Industrial Co.Ltd. of Japan and CTS company of Australia［2］.Among them，artificial grass produced by Cobble company of British and Tuftco company of America has already had the huge market share in the world.The development direction and trend of their tufting machines are high speed，automaton and agile.

In this paper，finite element model is established by using the link of artificial grass tufting machine.According to the constraints and loads in actual condition，the static analysis is finished.Considering the influence of the vibration on link when operating，the modal analysis is taken.The topology optimization design of the link is performed according to the result of static analysis.

2．Finite element model of artificial grass tufting machine link

2．1．Mechanism of artificial grass tufting machine spindle box

Mechanical movement of artificial grass tufting machine is to rely on the eccentric mechanism to achieve.The eccentric motion mechanisms of the cluster needle，the hook and the knife are non-interference.Among which，the mechanical structure of hook’s transmission mechanism is similar to that of knife’s transmission mechanism.In actual production，the weaving height of artificial grass can be adjusted by adjusting the initial phase of the cluster needle，the hook and the knife.The spindle box mechanism is shown in Figure 1.

Figure 1.Mechanism of artificial grass tufting machine spindle box

2．2．Digital modeling and force analysis of the link

By using the 3D modeling module of ANSYS Workbench，the 3D model of the link is made.Considering saving the computational time of the meshing and analysis，the link model is simplified.Chamfers and small oil holes which affect the stress a little are omitted.Force analysis of the link，as shown in Figure 2（b），is also given in order to make the following analysis better.

Figure 2.Model and force analysis of the link

The processing method of the link is precision casting.The material of it is HT 250 and the tensile strength ofwhich is250 MPa.Among them，the density of the material is7.2E-3 g／mm3，Young＇s modulus is 1.1E+5 MPa，and Poisson’s ratio is 0.28. Leading the material properties into ANSYS Workbench，the characteristics of the parts are known. Quality is 7 342 g and volume is 1.0E+6 mm3.

3．Static analysis of artificial grass tufting machine link

3．1．Meshing of the link model

Meshing is the key point of finite element analysis.The meshing quality has a direct influence on the accuracy and efficiency of the finite element analysis［3-4］.The surfaces of the two inner holes of the link are directly loading contact with the upper shaft and eccentric wheel，therefore mesh refinement must be carried on it in order to ensure the accuracy of the calculation result.In considering the factors above，the number of the nodes of the finite element mesh is 62549，and the number of the elements is 35539.

3．2．Boundary condition of the link model

The most important thing is to determine the boundary conditions when using the finite element method to analyze the characteristics of static and dynamic［5］.Axial displacement of the link and inner hole’s axis does not exist，so support in this direction is displacement support.The instantaneous forcing situation of the link in the movement of the artificial grass tufting machine can be equivalent to one end fixed support，the other end resultant force.Figure 3 shows the boundary condition of the link.

Figure 3.Boundary condition of the link

3．3．Calculation and analysis of statics

The statics analysis to the link which using ANSYS Workbench is elastic statics analysis.Mechanism’s elastic statics analysis does not consider thoseconditions of inertia and damping，only calculates the constant load effecting on the mechanism［6］.This link mechanism bears the alternating force of pulling and pressure in eccentric motion，so the applied load’s condition of it should be divided into two types.When the link bears pulling force，force effects on the underside semi-circle’s surface of the big circle and the direction is downward.Meanwhile，when it bears pressure，force effects on the upside semi-circle’s surface of the big circle and the direction is upward.The loading situations of the link are shown in Figure 4 and Figure 5.

Figure 5.Figure of the link under pressure

Figure 4.Figure of the link when pulled

Based on the measured data，it is known that the maximum pulling force，which the link bears，is 358 N，meanwhile the maximum pressure is 878 N. The pictures of total deformation are shown in Figure 6 and Figure 7 which are analyzed by ANSYS Workbench.Maximum displacement is 0.008 mm when pulled and maximum displacement is 0.003 mm under pressure.It can be seen that maximum displacement is located in the bottom of the big circle in all situations.

Figure 6.Total deformation of link when pulled

The pictures of equivalent stress are shown in Figure 8 and Figure 9 which are analyzed by ANSYS Workbench.Maximum stress is 1.722 MPa when pulled and maximum stress is0.848 MPa under pressure.It is known that maximum stress is located in both sides of the big circle when pulled，meanwhile maximum stress is located in the connection of the big circle and reinforcing plate under pressure.Particular attention should be paid to the strength checking and quality monitoring in the product’s design and processing according to these areas.

Figure 7.Total deformation of link under pressure

Figure 8.Equivalent stress of link when pulled

Figure 9.Equivalent stress of link under pressure

4．M odal analysis of artificial grass tufting machine link

Modal analysis is an essential step of dynamic analysis，which is mainly used to determine the mechanical structure and components of the natural frequency and vibration mode.And it is the starting point of the harmonic response analysis，transient analysis and spectrum analysis［7］.The pre-treatment of the link’s modal analysis is the same as that of the static analysis，and there is no load applied.First to sixth order’s natural frequency of the link is shownas Table 1 and the vibration modes are shown in Figure 10.

Table 1．Natural frequency of the link

Figure 10.Modal shapes of the link

First to sixth order’smodal shapes are all distorted of the big circle.And with the rise of the order，twist deformation is also gradually increasing. Maximum speed of the artificial grass tuftingmachine spindle is 600 r／min，then the excitation frequency range is from 0 to 120 Hz.So the natural frequencies are far away from the excitation frequency range.

5．Optimization design of artificial grass tufting machine link

The purpose of optimization design is that the certain plan can meet all the design requirements and costing at least.The plan of optimization design should be most efficient and most optimum.In this case，the maximum displacement of the link is larger when pulled，so this situation is chosen to analyze.In topology optimization，the target of material reduction rate is set to 30%.The output results are shown as Figure 11 which indicate that the material of the surrounding section of small circle and kidney hole can be properly and reasonably removed.Characteristic analysis should be done again after the model modified，so as to meet the design requirement of the part.

Figure 11.Optimization design of the link

6．Conclusion

In this paper，the finite element model of artificial grass tufting machine link is established.Static analysis is done which gives the answer to the situation of link’s deformation and stress when working. First to sixth order’s natural frequency of the link is known by modal analysis.The topology optimization design of the link is performed at last，which puts forward a kind of solution of optimization design.A series of analyses above provide the theoretical basis and implementation method for the further optimization of the link and other components of the artificial grass tufting machine.

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10.3969／j.issn.1001-3881.2014.18.013

2014-04-21

?Shi-hao WU，E-mail：wushihao0401＠163.com