The Investigation of Hole Delamination in Drilling Kevlar Composite Panel Using HSS Drill Tool

The drilling process has been mostly used in composite panel machining to be a final product. It becomes a critical process when the composite product requires a high hole precision for the purpose of assembly and quality standard. Machining Kevlar composite is a difficult task due its hardness, fiber layer bounding and fiber orientation. The cutting condition needs to be controlled carefully to minimize the vibration, cutting temperature and hole delamination. This paper discusses the investigation of hole delamination in drilling Kevlar composite panel. The twist drill type of High-Speed Steel (HSS) drilling tool with 12 mm diameter was used to drill a 4 mm thick Kevlar composite panel. Three levels of spindle speed (1000 rpm, 1400 rpm and 2000 rpm) and three levels of feed rate (130 mm/min, 160 mm/min and 180 mm/min) were selected as the configuration of cutting condition. The hole diameter was measured and was compared to the drill tool diameter. The result of the experiment shows that the cutting condition gave significant effect to the drill hole delamination factor. The highest delamination factor was 1.36 and achieved by drilling condition with spindle speed of 1000 rpm and feed rate of 160 mm/min. The lowest delamination factor was 1.161 and achieved by drilling condition with spindle speed of 2000 rpm and feed rate of 130 mm/min.

WEDM microdrilling of 316 L stainless steel orthopedic implant

The development in manufacturing has insisted upon the fabrication of microdrilled holes on orthopedic implants, with finished side wall (devoid of cracks and burr), thin recast layer, low taper, and improved circularity at entry and exit of the hole. In this study, therefore, a multiobjective optimization of wire electric discharge machining microdrilling response characteristics is addressed in order to improve the hole quality characteristics and viability of implants. To improve the quality characteristics of the hole, a hybrid statistical analysis is developed based on grey relational analysis and coefficient of variation. It identifies the key process parameters that are responsible for improving the quality of the hole. The parametric study also reveals that wire feed rate and servo feed rate have a striking effect on the quality of the hole. An important implication of this study is that a thin recast layer, improved entry and exit circularity, adequate taper were observed under optimum drilling condition.

Modelling of Time-Dependent Wellbore Collapse in Hard Brittle Shale Formation under Underbalanced Drilling Condition

In recent years, the lithologic traps in a mid-depth formation are the focus of oil or gas exploration and development for eastern oilfields in China. The Shahejie Formation develops thick hard brittle shale, and the wellbore instability problem is prominent due to obvious hydration effect for long immersion time during drilling. Through the analysis of laboratory tests and field test results of physical and chemical properties and microstructure and mechanical properties of hard brittle shale, the instability mechanism is discussed for the wellbore in the shale formation. To simulate the whole process of progressive collapse of a wellbore in a hard brittle shale formation, a coupled hydraulic-mechanical-chemical (HMC) model is developed and this model is compiled with ABAQUS software as the solver. Then the coupled HMC model is applied to simulate the progressive evolution process of wellbore collapse in a hard brittle shale formation, and the influence of different parameters on the progressive failure of the wellbore is analysed. The results show that the wellbore enlargement rate increases with the drilling fluid immersion time and the influence of different parameters on the wellbore enlargement rate is different. The water absorption diffusion coefficient and the activity of the drilling fluid have the most obvious influence on the expansion of the wellbore, and the sensitivity is strong. The permeability of shale has little effect on the wellbore enlargement rate. The calculated progressive failure process of the wellbore is basically consistent with that of the actual drilling.