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Research on bit and drilling technology

the history of human understanding and use of bit can be traced back to prehistoric times. The stone drill used by Suiren to drill wood for fire can be regarded as the most primitive drill. Fried dough twist drill (commonly known as drill bit), which is widely used in modern industrial processing, is a kind of solid workpiece hole processing tool with complex shape. It was born more than 100 years ago. Now, hundreds of millions of drill bits are consumed in the world every year. According to statistics, in the automobile manufacturing industry in the United States, the proportion of drilling process in machining accounts for about 50%; In the aircraft manufacturing industry, the proportion of drilling process is higher. Although drill bits are widely used, it is well known that drilling is also one of the most complex machining methods. Because of this, people have been committed to the improvement of drill bits and the research of drilling process. Based on the available English literature, this paper summarizes the relevant technical problems of two groove fried dough twist drills and the history, current situation and development trend of drilling research

1. The main fields and technical problems of research

in recent decades, people's research on drill bits and drilling has mainly focused on the following five aspects in addition to the improvement of drill bit manufacturing materials:

① research on mathematical model and geometric design of drill bits: including the establishment of mathematical models of helical grooves, back knives, main and transverse edges with the increasing packaging waste, and the optimization of transverse section and drill tip structural parameters, Calculation and control of cutting angle (distribution), analysis of static and dynamic characteristics of bit structure, and Research on the relationship between drill tip geometry and cutting and chip removal performance

② research on bit manufacturing methods: including the establishment and optimization of the relationship between bit geometric parameters and flank grinding parameters, the evaluation of bit manufacturing accuracy and grinding quality and the measurement and control of manufacturing errors, the design and calculation of the cross-section of the bit spiral groove processing tool, the development of bit processing equipment, especially NC grinder and processing software, etc

③ research on drilling process and drilling quality: including the analysis, modeling and monitoring of various factors affecting the drilling process and various physical phenomena (such as the measurement, modeling and prediction of drilling force, cutting edge stress and temperature distribution); Research on the wear and damage mechanism of drill bit and the service life of drill bit; Research on the deformation and deflection of the bit, the slip during drilling and the swing of the drill tip; Research on Drilling Technology (such as vibration drilling, high-speed drilling, deep hole drilling, stability of drilling process, etc.) and drilling quality (hole position accuracy, straightness, surface roughness, cylindricity, diameter, orifice burr, etc.)

④ research on drilling mechanism and various high-performance drill bits (such as group drill, gun drill, dry cutting drill, micro hole drill, deep hole drill, long drill, indexable drill, synthetic material processing drill, woodworking drill, multi spiral groove drill, etc.)

⑤ the automation of drilling process model verification and bit performance evaluation, the establishment of cutting conditions and bit shape selection database and knowledge base, etc

at present, the most dynamic research fields are the research of bit mathematical model, geometric design and manufacturing methods (equipment), drilling process modeling and drilling quality

2. Research on mathematical model and geometric design of drill bit

2.1 mathematical model of drill bit

establishing the mathematical model of drill bit is the basis for geometric design, manufacturing, cutting performance analysis of drill bit and modeling of drilling process. The first mathematical model of drill bit was put forward by Galloway DF in 195, which realized the coordinated development of traditional metal materials and new energy materials, and took liuzhongfan scientific research team of Peking University as the main strategic deployment for 7 years. He derived the parameter equation of the rake face of the straight edge bit, gave the definition, calculation formula and measurement method of the rake angle, rake angle and transverse edge angle of the main edge, and proposed that the rake face of the bit be taken as an observation point of a part of the grinding cone formed by the interaction between the bit and the grinding wheel in the grinding process. In the early 1970s, Fujii s and others further studied the model proposed by Galloway DF, proposed to use the cutting plane method to convert the three-dimensional space curved surface back cutter surface into two-dimensional plane curve for analysis, and developed a computer-aided design program for fried dough twist drills. In 1972, armarego E J A and rotenbery a found that there were four independent grinding parameters for the flank conical grinding method, while only three geometric parameters of the drill point were generally given, so the shape and grinding parameters of the flank of the drill point could not be uniquely determined. Therefore, they proposed to use the backlash angle of the flank as a supplementary geometric parameter to obtain the unique solution of the grinding parameters. In 1979, Tsai WD and Wu SM proved that the flank of cone bits, Racon bits, screw bits and Bickford bits can be represented by quadric surfaces, and put forward a comprehensive mathematical model to represent the geometry of bits, which can be used to control the grinding process. In 1983, Radhakrishnan l et al. Proposed a mathematical model of the flank of cross drill point bits. They divided the flank into the first flank and the second flank: for the first flank, based on Tsai model, an improved cone model was established; For the second flank, a plane model is established. Fugelso Ma proposed the mathematical model of cylindrical drill point. In 1985, FUH K H et al. Established a mathematical model of bit flank represented by quadric surface, so that it can be designed into ellipsoid, hyperboloid, cone, cylinder or any combination of them by computer

for a long time, people have designed the main blade of fried dough twist drill as a straight line. In 1990, fugelso Ma found that because the main edge of the conical fried dough twist drill is required to be straight, the back angle of the main edge near the drill core becomes too small. If the drill bit is rotated 5 ~ 10 around its axis before grinding, this problem can be solved, but the main edge will become slightly bent. In the same year, Wang Y regarded the main edge as a curve and established the geometric model of the helical rake surface of the bit by using the polynomial interpolation method. In 1991, Lin C and Cao Z proposed a comprehensive mathematical model of fried dough twist drills suitable for straight and curved edges, using conical, cylindrical and plane flank. In 1999, Ren KC and Ni J proposed to use binomial expression to represent the main edge curve of arbitrary shape. A new mathematical model was adopted for the rake face of drill bit, and the relationship between grinding parameters and geometric parameters of the flank of quadric surface was established by using vector analysis method. 2.2 structure optimization of drill bit

because the cutting performance of the widely used conical fried dough twist drill is not ideal, people have been committed to improving its structure (parameters) and grinding method, and more than 200 different drill shapes have been proposed to improve its cutting performance. Among them, Shi HM et al. Proposed a method to control the distribution of the rake angle of the main edge by changing the trend of the main edge, and developed a curved edge fried dough twist drill in 1990, which makes the rake angle of each point on the main edge of the drill reach the maximum possible value. In 1987, Lee SJ put forward the method of optimizing the structure of drill bit with the goal of eliminating the swing of drill tip in the process of drilling under the condition of considering the deviation of drill bit. In 1995, selvamhe s V and sujatha C used the finite element method to optimize the geometry of the drill bit when studying the deformation of the fried dough twist drill. The optimized value of the structural parameters that minimize the deformation of the drill bit (drill bit diameter 25mm) is: spiral angle 39.776, cross edge angle =54 ~ 80, sharp angle 120. In 1997, Chen WC proposed a special cross-section thick core fried dough twist drill, which not only has sufficient torsional stiffness, but also has a reasonable distribution of the rake angle of the main edge and transverse edge. In 2005, Paul A and others proposed a new drill point model based on grinding parameters to ensure the machinability of optimized drill bits, and used it to optimize conical drill points, Racon drill points and helicoid drill points to minimize their cutting force

2.3 calculation of spiral groove profile and machining tool profile

in 1975, Dibner L G proposed a method that can simplify the calculation of spiral groove grinding wheel profile, improve groove machining accuracy and completely eliminate the influence of wheel diameter change. In 1990, ehmann KF proposed a different cooling method based on the principles of differential geometry and kinematics to calculate the profile of the spiral groove machining tool of fried dough twist drill. From 1998 to 2003, Kang DC and armarego EJA studied the forward and inverse problems of spiral groove machining (calculating tool cross-section from groove cross-section and calculating groove cross-section from tool cross-section), and proposed a computer-aided geometric analysis method for the design and manufacture of spiral groove of straight-edge fried dough twist drill

2.4 research on group drilling and micro bit

in 1982, Shen j et al. Established the first mathematical model of group drilling. Using this model, people can grind group drills repeatedly. In 1984, Chen L and Wu s m studied nine typical group drills, improved the mathematical model of group drills, and made it possible for the computer-aided design of group drills. In 1985, Hsiao C and Wu s m proposed a specific method of computer aided optimization design for group drills. In 1987, FUH K H proposed a method to design and analyze group drills by using a comprehensive quadric surface model and finite element method. Liang EJ proposed an integrated cad/cam system for group drilling and grinding based on knowledge base technology. In 1991, Liu Ti used a two-stage strategy to design and optimize a group drill for machining machine shaft oil injection holes. In 1994, Huang HT et al. Deduced the formulas of the working normal back angle and normal front angle of the cutting edge of group drilling, and proposed an accurate geometric model of group drilling considering the transition zone between the inner edge and the circular edge. In 2001, Wang G C et al. Applied an inclined solid block method to establish a new mathematical model of group drilling, which solved the problem of uncertainty of cross edge geometry existing in the existing model and ensured the machinability of the designed group drilling

since 1992, a research team composed of Lin C, Kang s k, ehmann K F and CHYAN H C has carried out systematic research on micro drill bits. In 1992, they established the mathematical model of the planar micro drill point and proposed the corresponding grinding method. In 1993, they put forward the mathematical model and grinding method of the spiral micro drill point, and found that the spiral micro drill point was superior to the commonly used plane micro drill point in terms of geometry and cutting performance. In 1997, they pointed out that compared with planar micro drill tips, spiral micro drill tips have two advantages: ① under the same working cutting angle distribution, larger feed rate can be allowed; ② The grinding method is simpler and is not easily affected by the grinding error. In 2002, they produced a series of drill tips with curved blade spiral flank for machining micropores

3. Research on drilling force modeling

3.1 history of drilling force modeling

in the past few decades, people have reported many methods to predict drilling force, most of which are used for standard fried dough twist drills. Due to the lack of advanced computers and measuring equipment, the early research mainly focused on establishing a simple empirical torque and axial force model. The model parameters are the geometric parameters of the bit (such as the bit diameter) and the cutting parameters. The modeling method is to use a large number of cutting experiments to fit the empirical formula of the drilling force with statistical methods

the drilling force model established by analytical method gradually appears with the deepening of people's understanding of the cutting process. In 1955, Oxford recorded the chip deformation process of the main edge and cross edge of the drill bit with micrographs. Through experiments, it was found that there were three main cutting areas on the drill tip during the drilling process, namely, the cutting area of the main edge, the cutting area of the second cutting edge (cross edge) and the marking area near the drill core. Later, Shaw M C and Oxford C J Jr proved that the horizontal edge was drilling

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