Key Engineering Materials Vols. 315-316

Abstract: The volumetric positioning precision of CNC machine tools is the key factor to get high machining precision, so the analysis, measurement and compensation of the volumetric error is becoming more and more important. In this paper, the modeling results of 3-axes CNC machine tools with four different configurations are given based on rigid body theory and homogeneous coordination transformation matrices. An improved sequential step diagonal measurement method is proposed and analyzed because the current laser measurement methods are complex and time cost. At the final section of the paper, the measurement data was applied into the error compensation and the sequential step diagonal measurement method was validated efficient and convenient.

Abstract: The present study was undertaken to examine the feasibility of circular sawing of granite with a newly shaped diamond saw blade. Three slots were formed on each side of each segment of the saw blade. Side-slotted segments and traditional segments were compared under same operating parameters. Measurements were made of the horizontal and vertical force components and the consumed power in order to obtain the tangential and normal force components. The surfaces of worn blade segments were examined by a scanning electron microscope. The consumed powers, normal and tangential force components for the side-slotted segments were found to be lower than those of the traditional segments. The position of resultant forces for the side-slotted segments is a little further away from the bottom of the cutting zone than the traditional segments. SEM observations indicated that the wear of the side-slotted segments was similar to sawing with traditional segments.

Abstract: As its hardness and wear resistance being approximate to that of natural diamond, polycrystalline diamond (PCD) is a kind of perfect tool material for cutting Si-Al alloy pistons. In the turning process of Si-Al alloy pistons, the normal wear of PCD tools is a continuous and gradual process, which mainly is hard grain wear, as well as adhesion wear, diffusion wear, and chemical wear. The breakages of PCD tools include collapse, crash and flake etc, which occur mainly in discontinuous turning process. Experimental results and production statistic indicate that about 40~55% of PCD tools failure is breakage in discontinuous turning process of Si-Al alloy pistons. Reducing impact load is the main method to avoid tool breakage.

Abstract: This paper presents the experiments of Nd:YAG pulsed laser cutting of GH3536 superalloy sheet and investigates the influences of different cutting parameters on laser cut quality factors including recast layer, kerf width and dross formation. The results show that the recast layer possesses finer granularity and higher hardness than those of the matrix, and the thickness of recast layer increases with increased pulse energy and decreases as the cutting speed and gas pressure increase. Oxygen-assisted cutting comes with thick recast layers and argon-assisted cutting acquires thin layers. The low-strength oxide layer worsens the kerf surfaces in oxygen-assisted cutting while argon-assisted cutting produces unaffected surface quality and is suitable for applications with subsequent welding.

Abstract: An advanced ceramic cutting tool material was developed by means of micro-scale SiC particle cooperating with nano-scale SiC particle dispersion. With the optimal dispersing and fabricating technology, this multi-scale nanocomposite may get both higher flexural strength and fracture toughness than that of the single-scale composite. The improved mechanical properties may be mainly attributed to the inter/intragranular microstructure with a lot of micro-scale SiC particles located on the grain boundary and a few nano-scale SiC particles located in the matrix grain. Because of the thermal expansion mismatch between SiC and Al2O3 resulting in the compressive stress on the SiC/Al2O3 interface, the interface bonding strength between Al2O3 and SiC was reinforced, which can compel the crack propagating into the relatively weak matrix when meeting the SiC particle on the boundary; while the alumina grain boundary is not the same strong as the SiC/Al2O3 interface and the Al2O3 grain, therefore the crack propagates sometimes along the Al2O3 grain boundaries and sometimes through the grains, when reaching to the nano-scale SiC particle inside the matrix, the crack was pinned and then deflected to the sub-grainboundaries. These coexisting transgranular and intergranular fracture mode induced by micro-scale and nano-scale SiC and the fining of matrix grain derived from the nano-scale SiC resulted in the remarkable strengthening and toughening effect.

Abstract: In this paper, a TiB2 composite with nano-scale Al2O3 as dispersion phase was hot-pressed at 1750
. The effect of nano-scale Al2O3 on sinterability and mechanical properties of the TiB2 was investigated. The results show that the relative density of sintered body increases firstly and then decreases with the increasing of the Al2O3 content. When containing 10vol% nano-scale Al2O3, the composite with fine and uniform grains is obtained and the flexural strength reaches maximum. The nano-scale Al2O3 may agglomerate together when the Al2O3 content is up to 20vol%, which is harmful to the densification and mechanical properties of the composite.

Abstract: As a unique machining way, Abrasive Waterjet Machining (AWJ) is one of the fastest developing new non-traditional machining methods and has a wide range of machinable materials. In this paper, the machining mechanism in AWJ is theoretically analyzed by impact dynamic mechanics method. There is stagnancy layer between waterjet and workpiece surface. It is found that the stagnancy layer and low energy abrasive particle are the main factors, which weaken machining capability and effective utilizing ratio of energy of AWJ machining. Ultrasonic Vibration Abrasive Waterjet Machining, a new machining method, is put forward and the influence of ultrasonic vibration on machining mechanism of AWJ machining is discussed.

Abstract: Ultra-precision positioning technique has become one of the important parts in the development of precision machines. Flexure stage driven by piezoelectric actuator (PZT) has been used widely as micro-feed installation because they have many advantages, such as: driving directly, fine displacement resolution, no friction or spacing. This paper designed a micro-feed stage driven by PZT using clinograph mechanism, analyzed the influence of flexure hinges on the static and dynamic performance of micro-feed stage based on finite element analysis. The design procedure was presented by which we can determine the geometrical dimensions of flexure hinge easily and achieve desired performance parameters of the stage, and the effectiveness of the design method was validated by experiment.

Abstract: This paper investigates the influence on finish high-speed Wire-cut Electrical Discharge Machining (WEDM) in atmosphere and emulsion liquid. Experimental results have shown that WEDM in atmosphere offers a series of advantages such as better straightness accuracy and higher removal rate (material removal rate). It was also found that the removal rate increased significantly at a higher wire winding speed, with the straightness got worse at the meanwhile both in atmosphere and emulsion liquid. Considering its better processing quality and higher removal rate, the high-speed WEDM in gas possesses broad prospects for its application.

Abstract: An orthogonal cutting model was presented to simulate high-speed machining (HSM) process based on metal cutting theory and finite element method (FEM). The residual stresses in the machined surface layer were obtained with various cutting speeds using finite element simulation. The variations of residual stresses in the cutting direction and beneath the workpiece surface were studied. It is shown that the thermal load produced at higher cutting speed is the primary factor affecting the residual stress in the machined surface layer.