Songlin Ding

Experimental investigation of end milling of titanium alloys with polycrystalline diamond tools

The low thermal conductivity and high chemical reactivity of titanium alloys result in a short tool life in the milling process. This article investigates the performance of polycrystalline diamond tools in the end milling of titanium alloys (Ti6Al4V) by using small customized cutting tools. The relationship between cutting force and cutting parameters was analysed; tool life, tool wear, and causes that lead to tool failure were discussed. To analyse tool wear and cutting temperatures, residual chemical components on the cutting tool were examined with X-ray diffraction method, while surface integrity of cutting tools was inspected based on the images taken by the scanning electrical microscope. Finite element analysis models were developed to simulate the initiation of cracks under different loading cycles. Through cutting experiments, it was found that brittle chipping and fatigue were the two major modes of failure, and feed rate was the dominant factor that causes large cutting forces.

Electrical Discharge Grinding of Polycrystalline Diamond—Effect of Machining Parameters and Finishing In-Feed

Electrical discharge grinding (EDG) is becoming more prevalent in the manufacturing of polycrystalline diamond (PCD) tools. This paper concerns investigation of the effects of machining parameters, as well as finishing in-feed, to the surface quality obtained when using EDG to erode PCD. With the aid of the morphological findings, different PCD erosion mechanisms are discussed. Experimental results demonstrated that the eroded surface quality of PCD was significantly affected by the selected parameters. High temperature due to the erosion process resulted in the partial conversion of diamond to graphite phase under the surface. Higher finishing in-feed produced better surface quality and caused lower surface graphitization and lower tensile residual stress. A model for the thermal stress prediction was developed and found to have good agreement with the experimental findings.

Electrical discharge grinding of polycrystalline diamond – Effect of wheel rotation

ABSTRACT Electrical Discharge Grinding (EDG) is an advanced machining process that becomes popular in manufacturing of Polycrystalline Diamond (PCD) tools. This research investigated the effects of wheel rotation as well as debris flow direction on the quality of PCD tools based on a series of EDG experiments. Experimental results showed the debris that flowed toward the cutting edge could significantly affect the edge sharpness and symmetry of the tool, which were critical for the smaller edge apex angle. Evidence of spark concentration caused by the debris accumulation phenomenon were found through microscopic analysis on the eroded surfaces. This research also revealed the unexplained phenomenon associated with the undercut that normally formed beneath the PCD cutting edge after erosion. By examining PCD samples using scanning electron microscopy (SEM) and Raman spectroscopy, the formation of the heat-affected layer caused by the high-temperature erosion process in the EDG was analyzed. Results also proved that the surface finish of tungsten carbide (WC) and notch width of the PCD tools, particularly on the tungsten carbide WC/PCD interface, should not be taken as the index to measure PCD tool quality.

The prediction of cutting force in end milling titanium alloy (Ti6Al4V) with polycrystalline diamond tools

Cutting force coefficients were conventionally described as the power function of instantaneous uncut chip thickness. However, it was found that the changes in the three controllable machining parameters (cutting speed, feed and axial cutting depth) could significantly affect the values of cutting coefficients. An improved cutting force model was developed in this article based on the experimental investigation of end milling titanium alloy (Ti6Al4V) with polycrystalline diamond tools. The relationships between machining parameters and cutting force are established based on the introduction of the new cutting coefficients. By integrating the effects of varying cutting parameters in the prediction model, cutting forces and the fluctuation of cutting force in each milling cycle were calculated. Validation experiments show that the predicted peak values of cutting forces highly match the experimental results; the accuracy of the model is up to 90% in predicting instantaneous cutting forces.

Experimental study on quality of PCD tools machined by different electric discharge grinding processes

Abstract Polycrystalline diamond (PCD) is a promising tool material which is utilized to cut difficult-to-machine materials used in aerospace industry. Because of its ultra-hardness, electrical discharge grinding (EDG), a variation of electrical discharge machining, is often adopted to manufacture PCD tools to reduce manufacturing time. This paper investigates the quality of PCD inserts manufactured by two different EDG eroding methods: “2-step machining” and “3-step machining”. Surface roughness and residual stress were investigated after EDG process. An orthogonal cutting experiment was conducted to test the performance of each PCD insert. PCD tools machined with the two methods do not have significant difference in surface roughness. The residual stress status changed from compressive to tensile after EDG process. Also, after being eroded by 3-step EDG process, there was an over 30% declination of residual stress compared with 2-step machining. The results of the orthogonal cutting test showed that the wear amount and the thrust force of PCD inserts machined by 3-step EDG were smaller for the CTB010 insert and the CTX002 insert. In contrast, the CTM302 machined by 3-step EDG did not show obvious improvement in tool wear resistance during the cutting tests.

Model-driven design of a fast material removal electrical discharge machine

Abstract In order to minimize cost of machining, modern aerospace components are highly unitized to utilize functions of multi-axes CNC machining centres. However, PCD tools are preferred for machining of titanium alloys and metal matrix composites but they are hard to grind. A new fast material removal electric discharge machine suitable for small PCD workpiece machining has been developed from an innovative model consisting both high and low frequency response actuators and a dual stage non-linear control algorithm. This innovative approach has been proved successful in the single axis machine prototype and the fast material removal rate has been verified a series of tests and the outcomes were verified.