ABSRTACT: In the deep hole drilling of oxygen-free copper (TU1) , chip breaking and chip removing are always the difficulties. In order to solve this problem, 18mm deep hole drilling test of oxygen-free copper was carried out by using orthogonal experimental design method to study the influence of chip-breaking slot, spindle speed and coolant flow on chip shape. It is found that the size of the chip-breaking groove is the main factor affecting the chip-breaking, and the spindle speed and coolant flow are relatively small. The optimal drilling parameters for deep hole drilling of oxygen-free copper are the chip-breaking groove r = 0.9 mm and the spindle speed n = 255 R/min, coolant flow Q = 90 L/min.

Keywords: oxygen-free copper; Deep Hole; drilling; chip breaker

1.Introduction

With the development of science and technology, the oxygen-free copper material has excellent electrical properties such as high purity, good conductivity and thermal conductivity, it has been widely used in the fields of aeronautics, astronautics, weapons and atomic energy. At the same time, oxygen free copper has the characteristics of low hardness, large plastic deformation, small elastic modulus, large Coefficient of thermal expansion, etc. , how to solve the problem of chip breaking in oxygen-free Copper machining is the most important task. Compared with other processing methods, deep hole processing of oxygen-free copper is more difficult, mainly because the cutting heat produced in the processing process is not easy to dissipate, easy to cause tool adhesion wear. The most difficult point is that the chip can not be broken effectively, which leads to the breaking and breaking of the deep hole drill, and seriously affects the quality of the inner hole machining. In the commonly used deep hole processing methods, the gun drill pipe has a v-shaped cross-section, the path of chip removal is narrow, and the drill pipe rotates at high speed during the processing. In contrast, the BTA system is used in this experiment because the chip removal space of BTA deep hole drill is larger and the length of hole has less influence on the machining process.

At present, there are many researches on the mechanical processing of oxygen-free copper at home and abroad. X. The results show that the local stress of the rake face deforms and accumulates at the edge of the groove at a higher cutting depth, and the cutting strategy of reducing cross feed is adopted, it can improve the cutting performance of micro-tools, obtain constant cutting force, reduce burr size and improve the surface roughness. Liu Chuang [5] studied the effect of different cutting parameters on the Surface roughness through simulation and test of oxygen free copper micro-machining. The above research on oxygen-free copper is mainly for turning and milling, but the research on deep-hole drilling of oxygen-free copper is less.

In this paper, the influence of chip-breaking groove, spindle speed and coolant flow on chip shape change in the process of Bta deep-hole drilling of oxygen-free copper is studied and analyzed, the optimum technological parameters of deep hole drilling with oxygen-free copper internal chip removal are obtained.

(1)deep-hole drilling test 

1.1 test condition: The workpiece is made of copper-niobium composite rod, the intermediate material is oxygen-free copper (TU1) , the diameter of the workpiece is 52 mm, the length is 1500 mm. Material specific properties are shown in table 1[8-9] .

CW6163 is used to reform the deep hole drilling and boring machine, the length of drill pipe is 2000mm, the maximum drilling depth is 1500mm, the four-jaw Chuck is used to clamp, the cutting fluid is selected emulsion, the test equipment is as shown in Fig. 1. In the process of machining, the workpiece rotation, cutting tool feed drilling method. Test bit selected 18mm single-edge inner chip removal drill Table 1 oxygen-free copper material property diagram 1cw6163 test equipment diagram 218mm single-edge inner chip removal drill

Thermal conductivity/(W (Mk)-1) density/(GCM-3) Modulus of elasticity/GPa value 4018.9110 item Siméon Denis Poisson ratio soft hardness hardness hardness value 0.34 HBS40HBS121191 head, YG8[9] is used as the material of the cutter teeth, and the cutter body is welded. The test bit is shown in figure 2 and the bit geometry is shown in Table 2[10-11] .

1.2 orthogonal experiment 

design was used to study the influence of chip breaking Groove R, spindle speed n and coolant flow rate Q on chip shape during oxygen-free copper processing. As shown in Table 3, the factors are set to different levels according to the properties of the oxygen-free copper material and related studies, and the inner holes of the processed workpiece are shown in figure 3.

2. Test Results and analysis 

table 4 is the table of deep-hole drilling test and chip measurement for oxygen-free copper. 9 groups of deep-hole drilling tests were carried out according to l9(33) orthogonal experimental table, and chip shapes were observed in each test, the change of chip shape during the machining process was compared statistically. In deep hole machining, chip curling shape and chip length and width have direct influence on chip removal. When the cutting volume coefficient R < 50, chip removal can be smooth. A single-edge deep hole drill for chip removal was used in the experiment. The width of chip is determined by the width of chip slot. In order to better chip removal effect, according to the size of the drill bit diameter, the General Grinding 1 ~ 3 chip slot. The length of the chip is usually dependent on the spindle speed and the size of the chip breaker R. The influence of chip-breaking slot, spindle speed and coolant flow rate on the chip removal in oxygen-free copper drilling test is obtained through experiments. 

(1) Chip Breaker R. The effect of chip-breaking groove size on chip-breaking during drilling is obvious. When the chip breaker r = 0.6 mm, the material is more plastic and can not break the chips, which results in the blocking of the drill pipe and the test can not be processed, frequently causes the chip to block, after the chip block causes the tool to withstand the big stress, causes the tool to be damaged, as figure 4(A) , 4(b) shows. When the chip breaker R = 0.9 mm,

The chips obtained are 1 ~ 2 mm and can be discharged smoothly from the drill pipe, meeting the test requirements, as shown in Fig. 4(c) . 

(2) spindle speed. In the drilling process of deep hole processing, with the increase of rotating speed and the increase of cutting temperature, the plasticity of the material increases further, the fracture strain of the material increases, and the chip is more difficult to be broken, if the speed is too fast, the chips will be crushed and piled up in the chip-removing space, which will cause the chips to be blocked. When the chip breaker r = 0.9 mm can break the chip smoothly, when the rotating speed reaches n = 335 R/min, there will appear the extrusion block chip. The appearance of this chip is very likely to cause the chip plugging in the processing, as shown in Fig. 4(d) . 

(3) coolant flow. The role of the coolant is to absorb the heat generated by the cutting and to provide power for the removal of chips. The flow rate of coolant has little effect on chip breaking. The larger flow rate can impact the uncut chip, provide more power for chip removing, and reduce the possibility of chip accumulating in the process of chip removing. However, due to the limited drill pipe space, excessive flow will inevitably put forward higher requirements for the sealing of the processing system.

3. Conclusion the deep-hole drilling experiments of oxygen-free copper (TU1) were carried out by means of orthogonal experimental design, and the influences of chip-breaking Slot R, spindle speed n and coolant flow q on chip morphology were analyzed. The conclusions are as follows: 

(1) the size of chip-breaking Slot r plays an important role in the deep-hole drilling of oxygen-free copper.

 (2) the optimum processing parameters for deep hole drilling of Oxygen Free Copper: Chip Breaker r = 0.9 mm, spindle speed n = 255 R/min, coolant flow Q = 90 L/min. 

ANNEX: (1) through multi-body dynamic analysis and finite element static analysis, the 5 dangerous working positions which appear in one revolution of the crankshaft are found, and the stress analysis value of the crankshaft is obtained to meet the strength check of the crankshaft. 

(2) through the fatigue analysis software, the fatigue life and fatigue damage distribution nephogram of the crankshaft is obtained, and the fatigue minimum cycle number is 1.23 ~ 107. The fatigue position occurs at the fillet of the 2nd Crank Pin root. 

(3) the structural strength and fatigue characteristics of crankshaft are studied by means of dynamic simulation analysis, finite element numerical calculation and fatigue software simulation. This method has the characteristics of strong universality, high efficiency and accurate calculation. 

Source: Chinanews.com, author: Song Ziyang, Li Zhong, Li Wenjie, editor: Wang Zhisheng