Key Engineering Materials Vols. 407-408

Abstract: The streamline method was used to investigate the plastic strain rate in machining. The streamline function presented in this paper is a general equation with three parameters controlling the complex variation of flow line shape. Velocity and deformation field were obtained by streamline analysis. The validation of this model was conducted by comparing with other experimental results published. It shows that the streamline model presented in the paper can be applied to the evaluation of strain rate in machining.

Abstract: A study measured the drill resistances of larch and Scotch pine by a drill resistance technique and compared the densities of the same specimens measured with a traditional volumetric method. The drill resistance technique was found to be a good measure of the density profile of wood to reflect tree rings and defects (knots, decay and hollows). The drill resistance technique as applied to pines uses a linear relationship between the wood density and the average drill resistance. This technique has the applicability and possibility as a possible method for the density measurement and the defects detection. The technique is rapid, inexpensive, safe, portable and has the potential to be adopted as an on-line density profile method.

Abstract: This paper focuses on the influence of difference of tool materials on generation of wear protective layer when turning gray cast iron containing Al and Mg. In this experiment, the gray cast iron to which small quantities of Al and Mg was added were cut with cermet, P grade carbide (P10), silicon nitride ceramics (Si3N4), titanium nitride (TiN) coated carbide and K grade carbide (K10) at high speed. In turning gray cast iron containing Al and Mg with cermet, the tool wear was significantly reduced compared to that resulting from the cutting of conventional gray cast iron. Further, the protective layer consisting of nonmetallic inclusions in the work material was formed on the tool surface. In addition to cermet, this layer was formed on tool surface of Si3N4 and TiN coated carbide. The elements of Al and Mg added to the work materials were detected in the layers formed on these tool surfaces as well as cermet. The inhibiting effect on tool wear was also caused when turning with P10. However, P10 had much greater wear than cermet. On the other hand, in the case of turning with K10, the effect reducing wear with the addition of Al and Mg was not caused. The wear increased as cutting speed increased regardless of work materials.

Abstract: The metallurgical observations of microstructure characteristics of the adiabatic shear bands(ASB) within the primary shear zones of the serrated chips produced during high speed machining high strength steel have been performed by using optical microscope, SEM and TEM. The observations showed that the microstructure between the matrix and the center of the ASB gradually was changed, the fine equiaxed grains appeared with size of about 0.4～0.6μm in the center of the adiabatic shear band. The serrated chip formation was likely due to material softening that occurred in the primary shear zones. The microstructural development of dynamic recovery and rotational dynamic recrystallization is the dominant metallurgical process leading to material softening in primary shear zone during high speed machining. A model of microstructural development in primary shear zone during serrated chip formation in high speed machining was suggested by analyzing material softening mechanism.

Abstract: Sculpture surface machining is a critical process commonly used in die/mold industries. Since there is a lack of scientific tools in practical process planning stages, feedrates for CNC machining are set individual constant values all along the toolpath. In this paper, an enhanced mathematical cutting force model is presented and is used for selecting varying and ‘appropriate’ feed values along the tool path in order to decrease the cycle time in sculpture surface machining. The model is tested under various machining conditions and proved to be effective.

Abstract: Austenitic stainless steels are extensively used in the areas with high corrosion. The high heat resistance and strength make them difficult-to-cut materials. The tool life in machining austenitic stainless steels is restricted by the high cutting force and temperature which induce the tool wear and edge chipped. To achieve tool edge strength and reduce the edge-related problems, tool edge preparation is applied by introducing the chamfered and honed edges. In the current paper, the effects of the cutting edge preparation in face milling of austenitic stainless steels were studied using statistical method. The output cutting parameters as cutting force, temperature were obtained by finite element analysis. The purpose for this research is to give guidance to the tool edge preparation for machining stainless steels.

Abstract: In order to study fundamental methods for determining modulus of elasticity (MOE) of structural lumber with vibration methods, the theoretical basis of the measurement is introduced and a hanging style testing system, which consists of an impulse hammer, accelerometer, computer, etc., is built up. It is found that transverse vibration method can determine resonant frequencies of structural lumber specimens effectively. On the specimen, the distance between impact point and detection point should be as far as possible, i.e. the two points should be situated near the two ends of the specimen. The test results are not influenced by using different supports ––– springs or soft strings. Compared with modulus of elasticity values derived by traditional bending methods, the modulus of elasticity obtained by the transverse vibration method are larger. Also, the both have a very good correlation. Therefore, the vibration testing method can be used to determine lumber MOE. Finally, in order for research results to be truly applied to practices, a portable lumber MOE testing equipment based on simply supported beam vibration was developed. This equipment is suitable for determining dynamic MOE and, consequently, for stress grading structural lumber.

Abstract: Warpage deformation is an inevitable phenomenon as a cantilever sheet part is machined by combined saw milling tool. This problem affects machining quality obviously. In order to find the formation mechanism and a suitable solution, the paper carried out a qualitative analysis of the warpage causations, clarified the relationships of many factors and carried out quantitative analysis through the combined method of AdvantEdge FEM and Ansys. Furthermore, experiments of residual stress release and warpage solution were carried out in order to verify the correctness of theory analysis results. As is shown by the research results, warpage has already formed during residual stress formation. The causation of warpage is the unreasonable cutting path and the residual stress imbalance of the up and down sheet plane. The solution can control the warpage deformation well. The research results have an explicit guiding function to the actual production.

Abstract: A methodology to determine the flow stress of material was presented and Johnson–Cook (JC) constitutive model of titanium alloy Ti6Al4V was obtained based on cutting experiment and optimization. This JC model was verified by comparison between simulations with different JC models respectively and experiment. It showed that the accuracy of simulation of cutting force has an increase and the new model is more suitable for cutting simulations. This simple method could improve the accuracy and reliability of the cutting simulation, and could be used to establish the constitutive model of workpiece with more accuracy.

Abstract: This study deals with the influence of tool characteristics on the cutting edge temperature in turning case hardened steel. The cutting test is undertaken with the inserts which have different thermal conductivity and coating layer. The tool edge temperature is measured with a two-color pyrometer. The tool edge temperature increases with the increase in cutting speed. The higher thermal conductivity cutting insert causes lower tool edge temperature. The coating hardly affects the tool edge temperature. The white layer thickness increases with increasing cutting speed reaching a maximum at certain cutting speed and decreases with cutting speed.