Development of Dry Drilling Diamond Bit and Drilling System

This paper summarizes the current situation, market demand and existing problems of dry drilling for stone and building materials construction at home and abroad. The use and characteristics of dry drilling, the structural design of dry drilling diamond bit and the selection of matrix formula are introduced. Finally, through the test of drilling reinforced concrete with long dry drilling bits, the related equipment of the complete dry drilling system is introduced in detail.

Lubricant Coatings for Mobile Dry Drilling of Stacked Aluminium Alloys

Aluminium alloy stack materials offer good strength-to-weight ratio and are used for high strength airframe structures. For the panels to be joined, numerous holes have to be drilled and due to structure size mobile drilling heads are used. The drilling process releases lubricant oil which becomes airborne or collects on the shop-floor and presents a health and safety hazard. Avoiding this oil release is therefore a major driver for developing dry drilling processes. However, drilling aluminium alloys in the absence of cutting fluids is a challenging task due to its tendency to adhere to the cutting tool, and the high thermal conductivity of the workpiece. Owing to their low coefficient of friction, carbon-based coatings are an option to improve the machinability of aluminium alloys. This paper presents an industrial collaboration study on the performance of carbon-based coatings in dry drilling aluminium alloy 2024 and 7150 stacks. CVD Diamond, a hard DLC, Doped MoS2 and doped amorphous carbon (Doped a-C) were evaluated in comparison with an uncoated WC drills. Coating performance was assessed in terms of tool wear, hole diameter, and surface roughness. The results revealed that CVD diamond coated drills outperformed other coatings in terms of tool wear and hole quality. The coating enabled lower aluminium pick-up on the drills as well as minimised variations in diameter deviation and hole surface roughness. The work shows the capability for dry drilling of stacked aluminium alloys and hence eliminating the health and safety risk associated with use of oil in mobile drilling heads.

Experimental Investigation of Suitable Cutting Conditions of Dry Drilling into High-Strength Structural Steel

Dry machining is one of the main ways to reduce the environmental burden of the machining process and reduce the negative effect of the cutting fluid and aerosols on operators. In addition, dry machining can reduce overall machining costs and, in the case of large workpieces, reduce the extra work associated with removing residual cutting fluid from the workpiece and adjacent area. For high-strength structural steel products, it is typical to drill holes with larger diameters of around 20 mm. Therefore, this work is devoted to the investigation of the dry drilling process carried out on a workpiece made of S960QL steel with a helical drill with a diameter of 21 mm. The aim was to find suitable cutting conditions for dry drilling with regard to process stability and workpiece quality. An experiment performed with a coolant served as a comparison base. A dry drilling experiment was performed with cutting speeds from 30 to 70 m·min−1 and feeds from 0.1 to 0.3 mm·rev−1, and with the results of this experiment, the same experiment with flood cooling was performed. During the drilling process, spindle torque values were recorded using the indirect spindle current recording method. The macroscopic chip morphology was studied to understand the cutting process. The chip thickness ratio was measured, as well as the maximum diameter of spiral chips. On the final workpiece, the qualitative and dimensional parameters of the holes were evaluated, such as the diameter, cylindricity and surface roughness, depending on the change in the cutting conditions and cutting environment. Evaluation of the obtained data led to the following conclusions. When drilling the S960QL material, there is only a very small increase in the drilling torque during dry drilling compared to drilling with cutting fluid. The increase in friction demonstrated by the chip thickness coefficient is significant. The influence of the environment on the dimensional accuracy showed a tendency for a slight increase in the holes’ diameters during dry machining. In comparison, the cylindricity of the dry-drilled holes shows a lower deviation than the holes drilled with cutting fluid. The surface roughness of the holes after dry drilling is affected by the increased friction of the outgoing chips, despite the resulting parameters being very good due to the drilling technology standards. This work provides a comprehensive view of the dry drilling process under defined conditions, and the results represent suitable cutting conditions to achieve a stable cutting process and a suitable quality of drilled holes.

Analysis of Hole Quality and Chips Formation in the Dry Drilling Process of Al7075-T6

Millions of holes are produced in many industries where efficient drilling is considered the key factor in their success. High-quality holes are possible with the proper selection of drilling process parameters, appropriate tools, and machine setup. This paper deals with the effects of drilling parameters such as spindle speed and feed rate on the chips analysis and the hole quality like surface roughness, hole size, circularity, and burr formation. Al7075-T6 alloy, commonly used in the aerospace industry, was used for the drilling process, and the dry drilling experiments were performed using high-speed steel drill bits. Results have shown that surface roughness decreased with the increase in spindle speed and increased with the increase in the feed rate. The hole size increased with the high spindle speed, whereas the impact of spindle speed on circularity error was found insignificant. Furthermore, short and segmented chips were achieved at a high feed rate and low spindle speed. The percentage contribution of each input parameter on the output drilling parameters was evaluated using analysis of variance (ANOVA).