The modeling method of the machine tool spindle system is mostly beam and pipe element modeling. The system joint surface has two parts: The spindle and the tool holder, and the tool holder and the tool. These joint surfaces are mostly simulated by rigid connection or custom stiffness matrix. The system can also be modeled in the form of solid elements, while establishing contact pairs at the contact locations. In this paper, beam elements and solid elements were used to model the spindle system of a vertical machining center. Through the calculation results, the effects on modeling in different element types on the natural frequency of the system and the frequency response function of the tool nose point were compared and analyzed. The results show that the natural frequency value of solid element modeling is larger than that of beam element modeling, and the mode shapes are more abundant. With the increase of the excitation frequency, the amplitude?frequency response curve in the solid element modeling mode oscillates more violently, indicating that more excitation frequency values can be captured in this mode. The research results can provide theoretical reference for the dynamic characteristics of the spindle system for scientific research.

Screw geometry has an important influence on the mixing characteristics of single screw extruder. Three kinds of six rhombic thread elements, four rhombic thread elements and tooth thread elements with special configuration were selected to design three new combined screws of single screw extruder for different processing requirements, and the flow and mixing characteristics of polylactic acid in the three combined screws were studied. The results show that there is a large pressure gradient at the pressure junction of the combined screw, the diamond thread element can provide high tensile action for the material, the residence time of the fluid in its channel is short, and the mixing performance is relatively poor; the toothed screw element can not only provide high shear effect but also high tensile effect for materials, with long residence time and good mixing effect.

Based on the limitation of the eccentric twin screw extruder's own structure, a new type of eccentric three screw extruder was designed. Polyflow software was used to analyze the pressure field, shree velocity field, velocity vector field, mixing index, separation scale, average mixing efficiency, logarithmic stretching and other parameters. The flow and mixing mechanism of the eccentric tri?screw extruder were studied and compared with that of the eccentric twin?screw extruder. The results show that under the same conditions, the stretching and folding effect of the eccentric three?screw extruder is better, and the mixing efficiency is higher than that of the eccentric twin?screw extruder, which provides a theoretical basis for further exploring the chaotic mixing mechanism and optimizing the eccentric multi?screw extruder.

Based on the discrete element method, this paper uses modeling software Solidworks and discrete element simulation software EDEM to simulate the transport movement of solid particles in a single?screw extruder. The research includes the influence of material parameters such as the shape and size of the particles, the screw speed, and structural parameters such as the number of screw edges and the inclination angle of the screw edges on the solid transport capacity, as well as the movement and filling of the particles inside the barrel. The results show that the single screw?barrel model has the best particle size and the best particle shape; the smaller the particle size, the better the filling effect; the maximum particle transport capacity is when the spiral angle is 105°.

The 4WS rotor is a new type of internal mixer rotor, and the ratio of long and short edge length is one of the important geometrical structure design parameters. The flow fields in 4WS rotor internal mixer with ratio of long and short edge length, 2∶1, 3∶1 and 4∶1, were simulated by using the software POLYFLOW. Through particle tracing technology, the macroscopic mixing state of the three internal mixers was visualized and tracked.Using the flow field data, the typical evaluation parameters of dispersive mixing and distributed mixing were calculated, and the mixing efficiency of the fluids in three different rotor internal mixers was compared and analyzed, and the effect of ratio of long and short edge length on mixing characteristics of 4WS rotor mixer was explored. The results show that, compared with the 4WS rotor internal mixer with a length ratio of 3∶1 and 2∶1, the dispersing and distributed mixing ability of 4∶1 type rotor have been greatly improved.

The structure model of the conical twin screw extruder is very different from other ordinary screw extruders and has a unique structure.In recent years, it has played a great role in the processing industry. Three conical twin?screw extruders with the ratio of the groove depth to the screw radius of 1∶2, 2∶5, and 1∶3 were designed.The process of extruding LDPE and HDPE particles from the conical twin?screw extruder was simulated by the discrete element method, and the particle velocity change in the groove of the conical twin?screw extruder was analyzed. At the same time,the conveying efficiency of the three types of conical twin screw extruders were compared under different parameters. The discrete element analysis of LDPE and HDPE particles was carried out using EDEM software, and the mixing situation of the two kinds of particles in the three conical twin?screw extruders at different times was obtained.The results show that the mixing efficiency of the conical twin?screw extruder with the ratio of screw groove depth to screw radius of 1∶2 is better than that of the conical twin?screw extruder with the ratio of the groove depth to the screw radius of 2∶5 and 1∶3.

The Finite Element Method was used to study the flow field of different screw combination sections of single?screw extruder. The Polyflow software was used to calculate the pressure field, shear rate field, velocity vector, mixing index and other parameters of the flow field of ordinary screw, ordinary screw and pineapple head combined screw, ordinary screw and pin combined screw. The post?processing results were compared and analysed.The results show that the ordinary threaded screw can provide a greater axial velocity for the fluid; although the pineapple head screw has greater resistance, the more oblique section design can provide better axial and circumferential velocity for the fluid; the barrier effect of the screw causes a part of the fluid to flow back. The three new types of screws can effectively stretch and shear the fluid while providing a good linear velocity for the fluid to make its dispersion and mixing more uniform. According to the analysis of the curve results, the mixing effect of pin?screw is the best.

Based on the discrete element method, the transport and internal force problem of the double screw conveyor was studied by using the discrete element analysis EDEM software. According to the Hertz contact theory, the contact models of material particles and devices were established, and the influence of the double screw conveyor on the transportation characteristics of the material particles under different physical and geometric parameters was analyzed.The results show that the movement of particles in the conveyor is mainly in a straight line, with the circumferential movement as the auxiliary； the change of the wheelbase has a great influence on the material conveying characteristics of the conveyor. With the increase of the wheelbase, the mass flow rate increases gradually, and the particle force in the central area decreases gradually.