Papers by Author: Jian Feng Li

Abstract: Investigation of forming forces in incremental sheet forming (ISF) is of great importance since it provides understanding of the deformation mechanics, monitoring of the forming process, failure prediction, and future means of on-line control and optimization. This paper provides a review of studies on the contact conditions and the effects of the process parameters on forming forces in ISF, followed by the current status on forming force prediction and its potential role in the improvement of ISF technology.

Abstract: The existing end mill is hard to balance the tool rigidity, heat dissipation and chip evacuation. In this study, the geometries of groove and micro-blade of the end mill machining titanium are optimized, through imitating the corn leaf’s tooth based on bionics. The peripheral cutting edge is composed of linear first rake, parabolic second rake and rear face. The chip-hold groove is composed of parabolic main groove and cubic curve vice groove. The cutting process of straight tooth and designed composite tooth are simulated by constructing the two-dimensional orthogonal cutting model using ABAQUS. The results show that: compared to the straight tooth, the designed composite tooth inhibits the generation of serrated chip, and the fluctuations of cutting force are smaller, the squeezing effect on the machined surface is weaker.

Abstract: Biomass cushioning packaging material has been gaining attention in the properties of the materials because of biodegradable and green environmental protection, and the starch plastics play an important role. Urea, formamide, glycerol, ethylene glycol four material compounded with starch respectively, for the purpose to forming hydrogen bonds by the test in this paper, the ability to hydrogen bond with the starch has been observed by infrared spectrum analysis. The results showed that urea, formamide as strong electronegative group stronger binding, glycerol and ethylene glycol are more preferably to form hydrogen bonds with the starch because of more hydroxyl group content.

Abstract: Green and biodegradable may degrade to the direction of the main purposes for cushion packaging material. This paper the bubble growth mechanism of the material in the molding process, the microstructure of four kinds different foaming agent content of biodegradable materials have been studied by using a scanning electron microscope micro-chemical analysis for plant fibers, starch-based materials, through the foam forming process biomass biodegradable materials research object. The results showed that the biomass material in the biodegradable plant fibers are mutually connected to form a three-dimensional network structure of the cross; foaming agent content of 1.0%, the raw material biodegradable material having a structure with a closed air pockets distributed more evenly, which kind of uniform material structure ensures good impact resistance, rebound and thermal insulation.

Abstract: To study the erosion behaviors and mechanism of impeller material FV520B in centrifugal compressor, the erosion experiments with polygonal alumina particles were carried out on the high-speed erosion testing system. Microstructure of the erosion zone was analyzed by SEM to reveal the erosion mechanism. An erosion model to calculate the erosion rate of FV520B was developed. The results showed that, FV520B exhibited the erosion characteristics of typical plastic materials, the highest erosion rate occurred at the impact angle of 24°, the lowest erosion rate occurred at normal impact angle. The velocity index at the impact angle 24° and 90° were 3.37 and 3.68, it grew as the impact angle increased. The erosion mechanism of FV520B was micro-cutting and deformation wear, at low impact angles, the erosion was dominated by micro-cutting wear, while at high impact angle greater than 60 °, the erosion was dominated by deformation wear. Also the predictions of the erosion model were in good agreement with the results of experiments, indicating that this model can be used to estimate the erosion rate of compressor impeller under different working conditions.

Abstract: In this paper, the finite element analysis is made to the modal analysis of the impeller, a finite element model of a impeller with cracks was established. This paper presents results of the modal of the compressor blade subjected to centrifugal force and aerodynamic equilibrium pressure. In this analysis, the numerical models without defects and also with cracks were defined. The simulation results showed that the centrifugal force due to rotational speed can greatly influence the frequency of the impeller. The distribution of two cracked blades effect the natural frequence of the impeller. When two cracked blades locate in the interval position, the increasing value of frequence is maximum. When the two cracked blades interval 150°, the increasing value of frequence is minimum. It provides a basis for modal calculation of the impeller.

Abstract: A purely analytical method, based on the meshing theory, is presented to establish the exact helical groove and circumferential cutting edge model of end mills, for the solution of its low design precision and efficiency problems. Firstly, a coordinate system to represent the relative space position relations between grinding wheels and end mills is built and the mathematical model of the helical groove is precisely calculated with a given wheel profile and relative movements between the wheel and the workpiece. Then, the rake angle, inner radius and wheel positions of machining the clearance faces is computed. Finally, a 3D model of the end mill is generated by using OpenGL.

Abstract: In the present research, an attempt has been made to experimentally investigate the cutting forces in hard milling of H13 steel with coated carbide tools under dry, MQL (minimum quantity lubrication) and MQCL (minimum quantity cooling lubrication) cutting conditions. Based on Taguchis method, four-factor (cutting speed, feed per tooth, radial depth of cut, and axial depth of cut) four-level orthogonal experiments were employed. It is found that the periodical fluctuation of the cutting forces caused by the variation of the undeformed chip thickness with the entry/exit of the cutting edge is an essential feature of the hard milling process. The empirical models for cutting forces are established, and ANOVA (analysis of variance) indicates that the quadratic models can well express the relationship between cutting forces and cutting parameters.

Abstract: The rheological behavior of slurry of foam cushion packaging based on fiber and starch was analyzed using digital viscosity meter. Meanwhile the response relationship of viscosity to time, shear rate to shear stress, and viscosity to temperature were also measured. The results showed that the slurry is a kind of non-newtonian fluid with the character of shear thinning. With the increasing of shear rate, apparent viscosity of system keeps in decreasing till the steady state finally. With temperature rising, plastic viscosity and yield strength of slurry will be smaller susceptibly. At last, Casson-Model was chose for the matching of plastic viscosity and yield strength.

Abstract: In order to study the recrystallization of the thermoplastic starch, this paper obtained the IR spectra of starch respectively plasticized by urea, glycerin and glycol. By analytical solutions spectra of vibration frequency of molecular groups, the paper studied the destructive effect of starch crystal structure, and plasticizer to form new hydrogen bonds with starch by hydroxyl group bonded. Excessive plasticizer was not suggested. When the ratio of starch and urea was 102, the thermoplastic starch was excellent in thermoplasticity and hot-workability.