In terms of part machining, the proportion of hole machining is still high, and the development trend of technology for high-efficiency and high-precision hole machining has also attracted a lot of attention. Recently, due to the rapid development of hole machining technology and products, the usage of hole machining tools such as coated hard alloy drilling and reaming tools has increased significantly.

   The cutting edge shape of coated hard alloy drill has been optimized to improve its machining performance. For example, the land of the drill is optimized, the secondary relief of the cross edge is ground, and the straight shank (andThe milling cutter shank (of the same diameter) has also been given a lot of thought.

   The use of cutters for hole finishing, the use of thread end mills for thread hole machining and so on are also developing towards the direction of improving cutting speed and accuracy, making the tool products and machining methods diversified.

   This paper will introduce the new development trend of hole machining technology.

   High-speed, high-precision drilling process

   In the past, drilling was mainly carried out with high-speed steel drill bits, and drilling technology has not changed much.

   However, with the increasing use of coated cemented carbide twist drill, there is a trend towards high-speed and high-precision drilling, and considering the environmental requirements, dry cutting and semi-dry cutting technologies have been introduced. The new development of hole machining is mainly manifested in: ① coated cemented carbide twist drill can be machined at a cutting speed of more than 60 m/min, achieving high-speed drilling that can process a hole in an average of a few seconds; ② twist drill for drilling high hardness steel has been developed, making it possible to drill high hardness steel with a hardness of about 60 HRC; ③ dry and semi-dry drilling can achieve a deep hole of about 20 times the diameter of the drill bit, which has been applied in machining; ④ the R-shaped design of the outer cutting edge of the twist drill can effectively prevent burrs from being generated at the entrance and exit of the hole, and can improve the surface roughness of the inner hole wall.

   The shape of the cutting edge of the drill increases the third back face of the plane shape, making the cross edge part very thin, reducing the axial force during drilling.

   Although the target of reducing the cutting force on the cutting edge part is consistent, the shape of the cutting edge of the drill bit from different manufacturers is characterized by its own features and shows a diversified trend.

   On the other hand, for cases like mold parts where drilling is less involved, the focus is on drilling holes in a reasonable manner. In addition to using drilling tools such as drill bits, vertical milling cutters are also used to mill holes in a spiral or circular manner, which reduces the number of tools required to machine holes of different sizes.

   The technology of micro-hole cutting with increasing attention

   In the fields of electronics (including digital household appliances, digital cameras, and related areas), and medicine, for many products that are expected to be developed on a global scale, it is required to achieve both high precision and high efficiency in the micro-hole processing on their micro-structures. Recently, small high-speed machining centers that can process micro-holes at high speed and high precision have appeared, which continuously strengthens the trend of miniaturization of drill bits.

   On the other hand, the micro-hole machining technology has involved the fields of cutting, discharge, laser, electron beam and stamping, so it is necessary to select the appropriate machining method. Among these machining methods, cutting machining is still the machining method that can be well adapted to the changes of product quantity, hole machining mode, machining accuracy and so on.

   The smaller hole diameter that can be achieved during micro-hole drilling is determined by the diameter of the drill that can be manufactured. According to several companies, the diameter of micro-drills can now reach 10 to 20µm.

   When drilling small diameter holes, the setting of cutting parameters varies depending on the material of the drill bit. Tungsten carbide and coated tungsten carbide drill bits, due to the higher elastic modulus (Young's modulus) of the substrate material, experience minimal vibration at the front end of the cutting edge when rotating at high speeds due to centrifugal force. Therefore, these bits can be used for drilling at high speeds that are standard for the material of the tool. On the other hand, sintered diamond drill bits can be drilled under higher cutting conditions, as they exhibit excellent wear resistance, allowing for high-precision, long-life machining.

   It is also very common to bore hundreds or even thousands of small holes in a single workpiece, in which case factors such as hole diameter expansion, bending, and hole pitch accuracy requirements need to be considered. The use of a guide hole or center hole as shown in Fig. 4 can prevent vibration at the front end of the drill bit. Performing a moderate amount of reverse feed can ensure the discharge of chips and effectively prevent drilling faults.

   On the other hand, the machining center suitable for micro-hole processing has the characteristics of small vibration at high-speed rotation and can achieve high-precision flat and stable positioning, and has good dynamic characteristics.

   In recent years, the workpiece materials that must be processed by micro-drilling have a wide range, from high hardness steel, stainless steel, copper alloys, titanium alloys to ceramics, and the better cutting conditions set also change.

   Coolant is required when drilling. For example, when drilling stainless steel, it is necessary to supply cutting fluid with high lubricity to the cutting edge; while materials like ceramics produce powdery chips that can only be effectively removed with water-soluble cutting fluid. Therefore, the appropriate cutting fluid should be selected for different workpiece materials.

   To enable the micro-diameter drill to cut at a better cutting speed, the spindle of the machining center should have a high-speed rotation function, and the higher spindle speed of the high-speed machining center is about 30,000 to 50,000 rpm.

   The shape of the cutting edge and the vibration of the handle of the micro-drill are effective in improving the accuracy of hole machining and extending the service life of the tool, so high-precision grinding of the cutting edge of the drill bit is indispensable, that is, it is necessary to have a feed mechanism that can achieve a feed amount of 1µm, a high-precision tool grinding machine with a high-precision grinding wheel spindle, and a high-level tool grinding technology and a high-precision inspection system.

   Drill chuck tool system for high-speed, high-precision drilling

   Compared to a three-jaw chuck known as a drill chuck, the more widely used drill chuck tool system is a spring chuck system that offers high rigidity and high trueness accuracy.

   The insert-type spring chuck system has excellent performance such as a wide range of drill bit diameters that can be clamped, good clamping rigidity, and high clamping accuracy. In recent years, in order to improve the clamping speed and accuracy, the thermal insertion type clamping system has been increasingly attracting attention, and it is very suitable for clamping miniature diameter drill bits with a rotation speed of tens of thousands of revolutions.

   High-speed, high-precision finishing of holes and tapping of screw holes

   The finishing tool with more holes is still a counterbore, boring tool, etc., but it is also possible to use a vertical milling cutter for precision milling of holes in a spiral or circular feed mode. Coated hard alloy can be used,CBN and other materials are used to manufacture boring tools with adjustable cutting edge size functions to improve cutting speed and tool life.

   For tapping, since the use of thread end mills and spiral interpolation machining technology, high-speed and high-precision thread cutting is realized. The vertical milling cutter for M3 small diameter thread processing has been launched, and the research on smaller diameter thread processing technology is also ongoing.

   Processing center for high-speed drilling

   High-speed, high-precision hole machining requires the drill bit to achieve high-speed cutting while also shortening the time the drill bit moves, which is an unavoidable issue for hundreds of multiple hole machining.

   The above briefly introduces the development of hole processing technology in recent years. Although the traditional cutting processing method is still adopted, practical progress has been made in all aspects of the processing system, such as cutting tools, clamping system, machine tools, and processing technology.

   In order to reform the manufacturing industry, hole processing is an indispensable processing technology in promoting high added-value production, and it has a great impact on the quality and cost of products. In recent years, with the miniaturization and high performance of products, the demand for micro-shape and micro-diameter processing technology has also increased. On the other hand, the emergence of small-sized CNC processing centers that can use micro-diameter drill bits to process micro-holes, the application of coated hard alloy and other high-performance cutting tool materials, and the emergence of high-rigidity high-speed drilling bits, mark the arrival of the real micro-hole processing era.

   However, in today's rapidly changing technological environment, further development and refinement of databases that cover aspects such as machining centers, cutting tools, clamping systems, machining conditions, etc., the CAM system for generating NC programs, tool management, etc., to construct the entire machining system for achieving stable and reliable hole machining, is an important issue facing production technicians.