Determination of critical depth forces of cutting soils and energy consumption of chain scraper trench excavators

The presented results of scientific research are aimed at solving the problem, which is associated with an increase in the productivity of the development of trenches for laying engineering communications due to the use of new less energy-intensive soil development processes with the working equipment of chain trench excavators. The aim of the work is to establish the regularities of the interaction of the working equipment of the chain scraper excavator with the soil, in which the cutters work in the critical cutting depth mode. Among the tasks that are directed to achieve the goal, it was necessary to establish the influence of soil development processes in these conditions on the technical parameters of the machine. The methodology for solving the problem is based on the idea of the theory of soil mechanics and the provisions on the critical depth of soil cutting.Applying this knowledge to the operation of the cutters of the chain excavator for cutters guarantees the consumption of the minimum specific energy and obtaining the maximum performance of the machine. Existing studies do not give a complete picture for calculating the parameters of trench excavators in which the cutters of the working body operate in the mode of critical cutting of the soil, which in turn does not allow carrying out a comprehensive calculation of the chain trench excavator and assessing the energy efficiency of its operation. The result of the research is the obtaining of theoretical dependencies for determining the cutting forces of the soil by the working body of the excavator under the conditions of the critical depth of the work of its cutters, as well as dependencies for calculating the energy indicators of the machine. The originality of the solution to the problem lies in an integrated approach, namely, it took into account not only the influence of the work of the cutters in conditions of a critical depth of cut on the technical parameters of the machine, but also the properties of the soils that are being developed. The practical significance of the results of the research is to obtain dependencies that can be used as the basis for the engineering methodology for the integrated calculation of chain-type trench eesquators in which the cutters operate in the critical blocked and half blocked cutting mode of the soil.

Analysis of the effect of tool posture on stability considering the nonlinear dynamic cutting force coefficient

In aviation and navigation, complicated parts are milled with high-speed low-feed-per-tooth milling to decrease tool vibration for high quality. Because the nonlinearity of the cutting force coefficient (CFC) is more evident with the relatively smaller instantaneous uncut chip thickness, the stable critical cutting depth and its distribution against different tool postures are affected. Considering the nonlinearity, a nonlinear dynamic CFC model that reveals the effect of the dynamic instantaneous uncut chip thickness on the dynamic cutting force is derived based on the Taylor expansion. A five-axis bull-nose end milling dynamics model is established with the nonlinear dynamic CFC model. The stable critical cutting depth distribution with respect to tool posture is analyzed. The stability results predicted with the dynamic CFC model are compared with those from the static CFC model and the constant CFC model. The effects of tool posture and feed per tooth on stable critical cutting depth were also analyzed, and the proposed model was validated by cutting experiments. The maximal stable critical cutting depths that can be achieved under different tool postures by feed per tooth adjustment were calculated, and corresponding distribution diagrams are proposed for milling parameter optimization.

Effect of the Anisotropy Mechanical Properties on LN Crystals Fixed-Abrasive Lapping

The anisotropy of lithium niobate (LN) single crystals in mechanical properties affects its material removal uniformity during lapping. The nano-indentation hardness (HI) and elastic modulus(E) of Z-cut wafer and X-cut wafer were measured by a nano-indentation tester. The nano-scratching tests were adopted to evaluate its critical cutting depth (dc) of brittle ductile transition along crucial orientations of Z-cut and X-cut, respectively. A series of fixed-abrasive lapping tests were carried out to explore the effect of anisotropy on the lapping process. The results indicated that the HI of Z-cut was slightly higher than that of X-cut, while the E of Z-cut was about 1.1 times of the latter. The dc value of each orientation varies greatly. The lapping tests showed that the material removal rate (MRR) of Z-cut was lower than that of X-cut, for its high HI and E. Meanwhile, the surface quality of Z-cut was better than that of X-cut, for the larger dc of Z-cut. The research of mechanical properties of LN has guiding significance for its lapping process.

Prediction of Regeneration Chatter Stability of Composite Boring Bar

The deep holes cutting process by metal boring bar is usually limited due to the development of chatter vibration. This is because metal boring bar has not only low bending stiffness but also low structural damping. A chatter stability prediction of composite boring bar under regenerative cutting force is presented. Based on the theory of Euler-Bernoulli beam, the regenerative chatter dynamic model of composite boring bar is proposed, and the solution formula of the limited cutting depth and corresponding spindle speed is given. The dynamic stability lobes of the composite boring bar are obtained by numerical calculation. The results indicate that composite boring bar exhibits efficient chatter stability than metal boring bar. Chatter stability is closely related to fiber ply angle. It is demonstrated that when ply angle is 0o, carbon/ epoxy reaches its critical cutting depth, and for graphite/ epoxy boring bar about 25o of ply angle gives its critical cutting depth, It is also demonstrated that stability boundary decreases as the ratio length and diameter increases. Finally, the prediction results of stability are compared with those from the dynamic stiffness and time-domain response, agreement is found.

Analytical Prediction of Subsurface Damages and Surface Quality in Vibration-Assisted Polishing Process of Silicon Carbide Ceramics

Subsurface damages and surface roughness are two significant parameters which determine the performance of silicon carbide (SiC) ceramics. Subsurface damages (SSD) induced by conventional polishing could seriously affect the service life of the workpiece. To address this problem, vibration-assisted polishing (VAP) was developed to machine hard and brittle materials, because the vibration-assisted machine (VAM) can increase the critical cutting depth to improve the surface integrity of materials. In this paper, a two-dimensional (2D) VAM system is used to polish SiC ceramics. Moreover, a theoretical SSD model is constructed to predict the SSD. Furthermore, finite element simulation (FEM) is adopted to analyze the effects of different VAP parameters on SSD. Finally, a series of scratches and VAP experiments are conducted on the independent precision polishing machine to investigate the effects of polishing parameters on brittle–ductile transition and SSD.

The Research of Impact Ball End Mills Geometric Parameters on Processing Stable Region

In this paper, modal analysis of ball end mills is modeled by finite element to work out natural frequency and chatter model in tooling system and to calculate the limit curve of stability in single degree freedom system. The effect of cutter flute length and cutter tooth number on maching stability area is also discussed. The results of research show that steady critical cutting depth of milling system declines while the cutter flute length increases, but the trend is not linear, which shows increase partly. An engineering optimization design is made on milling cutter geometrical parameters based on this conclusion.