Research Review and Development Trend of Deep hole Machining Technology

Deep hole machining technology was firstly applied in the field of military production, mainly used to process the inner bore of gun barrels and gun tubes. With the development of the national economy and scientific and technological innovation to promote the application of the technology is more and more extensive, almost involving all the machinery manufacturing industry, focusing on the application of high-tech industries, especially in the aerospace manufacturing industry. The field involves more and more deep hole processing content, the technical difficulty is more and more high, such as missile wing mold temperature measurement holes, all kinds of aircraft on the inner hole of the actuator cylinder and so on. This has formed a multi-industry modern deep hole machining process and its key technology urgent needs of the situation, for this reason, in-depth development of new deep hole machining technology and its device research and innovation, the development of the national economy and national defense construction will certainly have a significant impact.

In mechanical manufacturing, hole machining can be divided into two categories of shallow hole machining and deep hole machining, the general length-to-diameter ratio L/D <5 (L is the depth of the hole, D is the diameter of the hole) of the hole is known as shallow holes, L/D>50 holes is known as deep holes, L/D>100 holes is known as ultra-deep holes. As we all know, deep hole machining is an important branch in the field of machining, and at the same time, the dynamic theory of deep hole machining is also an important topic in the research of machining, which has been deeply studied by scholars in many countries.

This paper summarizes the development status of deep hole machining technology from the mechanical behavior of the drill pipe, deep hole machining process, deep hole drilling monitoring, and thus introduces the development status of deep hole machining machine tools, points out the technical problems that exist in them, and looks forward to the future development trend.

Development status of deep hole machining technology

The earliest deep hole machining technology appeared in the military industry in the processing of gun barrels and gun barrels, and then with the progress of science and technology and the development of society, has appeared a variety of new deep hole machining technology. They are gun drilling (Figure 1(a)), BTA drilling (Figure 1(b)), spray suction drilling (Figure 1(c)) and DF drilling system (Figure 1(d)).

The gun drilling system is mainly used for the processing of small-diameter (φ2~ф30 mm) holes, which is the most common deep-hole drilling processing method, suitable for small and medium-sized mass production.

BTA drilling system is mainly used for deep hole drilling of diameter ф>12 mm, which is the first choice for large quantity and high load continuous deep hole machining.

The suction drilling system is a highly efficient method of deep hole machining, but the diameter of the holes machined cannot be less than 18 mm.

The DF drilling system combines the advantages of the BTA drilling system and the suction drilling system, resulting in a wider range of drilling diameters (down to φ6 mm) and improved machining accuracy and efficiency.

1. Mechanical Behavior of Drill Pipe

Prof. Jihua Qin of National Chiao Tung University, Taiwan, used Hamilton’s principle to derive the equations of motion of deep hole drilling rods based on the Timoshenko and Euler-Bernoulli beam models by taking into account the effects of cutting fluid and axial pressure in the fluid, and added random excitation in two different ways with rotating and non-rotating drilling rods to study the dynamic behavior of the rods, which is one of the world’s leading research on the dynamics of the drilling rods. The dynamic characteristics of the drill pipe were investigated by adding random excitation in different ways of rotating and non-rotating drill pipes, which is a leading position in the research of drill pipe dynamics.

FUJJ and EMA etc. observed the vortex behavior of the drill pipe system during deep hole drilling and pointed out that this vortex behavior is a kind of self-excited vibration caused by cutting force and friction.

BAYLY et al. IV compared the theoretical analysis with the experimental results to analyze the torsional vibration of the drill pipe system, examined in detail the distribution range of the tool vibration frequency as well as the stability criterion, and pointed out that there are obvious nonlinear characteristics of the drill pipe system during deep hole machining.

The nonlinear dynamic model of the deep hole machining drilling system was established by KOVAC-IC for the first time, and the tool chatter was analyzed theoretically by using different tool front angles, shear angles and feeds.

2. Research on deep hole machining process

In terms of deep hole machining process, Jun Wang of North Central University invented SIED (Single-tube Inner Chip-removal Ejector Drilling) technology in the 1980s, which solves the problem that internal chip-removal deep hole drilling cannot drill small diameter deep holes, and improves the design of chip container for DF drilling. The design of the chip container of DF drilling is improved, and the cutting part of the drill does not have a chipbreaker, which makes the tool resharpening convenient and the machining performance good.

Peng Hai and Zhang Min of Xi’an Petroleum University, Shi Zhihui of Dalian Jiaotong University, and BTASDELENB2, Arup Kuar NANDI, R HEINEMANN9 of foreign countries have discussed the green processing technology (dry or quasi-dry deep-hole machining) of hole processing.

With the popularization and application of various deep hole drills in various industries, Japan, Germany, Sweden, the United States and other countries are at the forefront of deep hole machining technology.

The United States ATI Stellram Cutting Tool Company specializes in the development of difficult-to-machine materials cutting tools, the development of cutting tool materials in the field of international difficult-to-machine materials at the forefront.

Sweden’s Sandvik-Cotomant company to the diameter of more than 3mm BTA deep hole drilling comprehensive series, and its vibration damping tool is also in the world’s leading level.

Germany BOTEK company’s gun drill specifications have been standardized to φ0.9 ~ φ50 mm.

3. Deep hole drilling monitoring research

Due to the large aspect ratio of deep hole machining and the closed and semi-closed state of machining, it is decided that the change of tool state in the process of deep hole machining can not be directly observed, so the monitoring of the deep hole machining process through various means has become a research direction of deep hole machining.

Some domestic institutions and research organizations such as Harbin Institute of Technology, Xi’an University of Technology, North Central University, Beijing Institute of Technology, Jilin University and University of Science and Technology Beijing have conducted some research on this.

Among them, Zhang Chao and Li Yan of Xi’an University of Technology four used orthogonal wavelet transform to decompose and reconstruct the vibration signals of different tool states, and obtained the reconstructed components of vibration signals in different frequency bands.

Issam ABU-MAHFOUZ et al. in the United States – by obtaining the vibration signals of the machining process, and utilizing a multi-layer feed-forward neural network trained by a backward algorithm, successfully identified five different wear states of the drill bit.

At present, in the deep hole drilling force measurement technology is in the international leading position of Germany Dortmund University research workers WEBBER, THEIS and RAABE, etc. is committed to the development of the measurement of the force element with the measurement of the drill bit, with which the cutting component can be measured directly, but this method is still in the laboratory test stage, and expensive, design and manufacture of the cycle is long.

The fully automatic drilling machine “Micro-ole” produced by Machida Iron Works in Japan is equipped with “torque detector” and “drill wear monitoring system”, once the torque applied to the drill exceeds the pre-selected torque value, the drill will be fed into the drill. Once the torque applied to the drill bit exceeds a pre-selected torque value, the feed system stops the feed, returns the drill bit to the turning position, and then resumes drilling until the entire micro-hole is machined.

In summary, although the deep hole machining technology has experienced more than a century of development, from the processing method has become increasingly mature, but for the processing of micro-fine ultra-long deep holes, in theory and practice has not yet formed a set of complete and mature system, especially for the drilling of the diameter of lmm within the L/D ratio of more than 200 of the micro-fine ultra-long deep holes, is still a problem to be solved.

CNC deep hole machining process technology features

Deep hole parts processing is different from general hole processing, general hole processing often use the workpiece is not fixed, the tool for the feed and rotary movement of the way processing; deep hole parts are often used to rotate the workpiece tool feed for the molding movement. However, due to the shape of the workpiece: material properties, process constraints and needs, etc., the form of deep hole drilling movement has been opened up, generally the following kinds:.

(1) the workpiece rotates, the tool for the feed movement.
(2) The workpiece is fixed, the tool rotates and makes a feeding movement.
(3) the workpiece and tool relative rotation, the tool for the feed movement.
(4) the workpiece for the rotation and feed movement, the tool does not move.

Deep hole machining technology after a long period of development, in the solid drilling gradually formed and perfected five kinds of machining system:.

1) gun drill external chip removal machining system.
2) BTA internal chip removal machining system.
3) Suction drilling machining system; 4) DF machining system; and
4) DF machining system; 5) SIED machining system.
5) SIED machining system.

These five deep hole machining technology in the machine structure, tools, oil supply, chip removal, etc. have their own characteristics, processing the applicable hole diameter, machining accuracy and surface quality are also different.

But its common disadvantage is: in the processing of high precision requirements, such as aircraft on the inner hole of the actuator cylinder, these deep holes after drilling, but also need the corresponding finishing process (such as these holes for grinding), so that the manufacturing cost increases.

Factors affecting the deep hole machining process

1. The material of the processed parts and its uniformity

In the deep hole machining process, due to the material of the machined parts, properties and organization is not uniform and other reasons, often lead to the generation of impact force, shock vibration and other unexpected problems, resulting in tool damage, the production process is forced to stop, and in serious cases, the parts will be scrapped, resulting in the production process is not stable, discontinuous.

2. Tool quality problems

In the process of deep hole machining, due to the quality of the tool, will also produce cutting vibration and other unexpected problems, so that the above phenomenon occurs again.

3. Positioning and clamping devices

Inaccurate positioning and guiding will cause the straightness of the machined hole to be super poor and the position of the hole to be offset. The workpiece clamping is unstable and incorrect, which will also cause sudden problems in the machining process, such as tool damage, poor machining accuracy.

4. Oil supply and vibration damping effect of oil supply device

Deep hole machining process of some of the impact force, shock vibration, etc., will cause inaccurate positioning of the workpiece, hit the knife and the machining process is not stable, seriously affecting the quality of machining and productivity. At present, the oil supply device and its technology, although there is a certain damping and vibration damping effect on the toolbar, but its main function is still mainly to supply oil, vibration damping effect is not obvious.

5. The effect of negative pressure chip extraction device

Poor chip removal has been the main problem affecting the quality of deep hole machining and production efficiency, serious cases of chip blocking, tool breakage and termination of the production process, etc., is the key issue of deep hole machining technology, which is also the focus of attention of many scientific research institutes and universities and colleges in the development of deep hole machining technology. In order to solve the problem, there are a lot of improvements and independent innovation of negative pressure chip extraction device, in order to improve the effect of chip removal.

Deep hole machining machine tool development status

Most companies can not afford the expensive price of deep hole machining equipment and high cost of use, there is no specialized deep hole machining equipment production system, only through the transformation of ordinary lathes, boring machines to meet the basic needs of production.

Manufacturing developed countries, not only three-coordinate (three CNC axis) deep hole drilling machine, and the emergence of four-axis, five-axis, or even six-axis fully automated CNC gun drilling machining centers or CNC drilling and milling centers (Figure 3), and there are automatic tool changer.

In order to expand the scope of processing, some deep hole drilling machine in addition to the gun drilling method of drilling, milling, rigid tapping and other functions, but also has the internal chip drilling method (BTA method) drilling function. Although there are some similar products in China, there is still a big gap between the precision degree and variety of specifications and foreign countries.

Although now there are many types of deep hole machining machine tools, but do not have the generality, in order to solve the machine tool function a few surplus as well as the function of the conversion cost is high. American scholars first proposed reconfigurable manufacturing systems and reconfigurable machine tool concept.

In 1996, the United States, the University of Michigan in the National Science Foundation and industry 25 companies funded, the first to start the reconfigurable manufacturing system research”. Various developed countries have also carried out research on reconfigurable machine tools.

For example, researchers at the University of Stuttgart in Germany have theorized the reconfiguration of manufacturing systems, the interfacing of machine modules, and motion function modules.

In the design and improvement of machine tools, the dynamic and static optimization of the structure of key machine tool components and lightweight design is one of the main ways to achieve machine tool machining performance and machining accuracy.

Development trend of deep hole machining technology

Although since the emergence of the BTA machining method, deep hole technology has not undergone much change. But the optimization of some machining processes, such as the development of new tools, the optimization of the arrangement of the guide block, the application of negative pressure chip removal devices, etc., is still an important means to improve the level of deep hole machining at this stage.

The quasi-dry and dry deep hole machining technology established on the green machining technology will receive more and more attention due to the increasing awareness of environmental protection.

Modern deep hole machining machine tools and other machine tools, like the rapid development, is toward the direction of high efficiency, precision, high reliability, intelligence, modular development. In particular, modular reconfigurable machine tools have done a lot of research in recent years.

However, just like the deep hole machining process, more advanced machining equipment has not appeared internationally in the field of traditional deep hole machining in recent years.

Due to the traditional deep hole machining technology can not avoid the use of cutting force to remove the material of the consistent practice and cutting force on the interference of the process system, is not able to well complete the difficult to machine materials, special complex surfaces, extra small extra deep holes and other processing.

Special processing technology (laser, water jet, EDM and electrolytic deep hole processing, etc.) also opened up a new field of development for deep hole processing technology.