STUDY ON THE FORMING MECHANISM OF BOUNDARY NOTCH OF CEMENTED CARBIDE CUTTING TOOL*
Wang Guicheng Zhang Chunye Jiangsu University, Xuefu Road 301 Zhenjiang , Jiangsu ,212013 China
In this paper, the forming mechanism of boundary notch of cemented carbide cutting tool is studied and related theories is analyzed, give a definition of the boundary notch size, point out main factors to influences boundary notch of tool. And forming process and change lay of the boundary notch of tool are found out, a certain number of measures to decrease and control the boundary notch of tool have advanced. Key Words: Cemented Carbide Cutting Tool, Boundary Notch, Burr, Corner Radius, Tool Cutting Edge Angle
INTRODUCTION The wear and boundary notch of cemented carbide cutting tools often are found in the machining. They directly influence machining quality of the machined workpiece and the cutting performance and life of the cutter. Especially, in the precision machining, flexible manufacturing system (FMS) and other automation manufacture, wear and boundary notch behaviors of cemented carbide tools are even more important. Metal cutting experiences have expounded that wear and boundary notch of the cemented carbide cutting tools are more serious in the machining of the workpiece in which the strain hardening is high and
the remaining is not even. It badly influences the machining quality of the machined piece and the cutting performance and life of the cutter. Heretofore, the research on the boundary notch mechanism of cemented carbide cutting cutter is not much, and the technical measures to reduce boundary notch of cemented carbide cutting tools are fewer. So, based on the machining experiments of friction welded joint, this research has discussed the forming processes and main rules of the boundary notch, developed several measures to resist or lessen boundary notch, which found a theoretic and experimental base to ensure cutting performances of cutters and machining quality. THE FORMING PROCESS AND MAIN SIZE OF BOUNDARY NOTCH The boundary notch of cemented carbide cutting tools is a wear area, which is relatively large, resulted from friction between main cutting edge and the surface of the workpiece as the following Fig.1. Fig.1 (a) shows a traditional wearing type of the flank. The rake face A? and flank face Aa are also shown. Fig.1 (b) shows the main dimension of boundary notch of the lathe tool, in which VN represented the
This project is supported by the NSF of China (? 59775071, 50275066)
height of boundary notch and C refers to the width. It is apparent that the greater the dimensions of VN and C are, the greater it destroys the performance of tools and influences the machining quality. By experiment, the forming process of the boundary notch can be summed up the following three steps: firstly, several micro cracks are produced at main cutting edge. Secondly, the mesh fractures are found in the boundary areas and they will spread. Finally, the material of pieces will be denuded and the boundary notch is formed. In the subsequent cutting process, the dimension of the boundary becomes bigger and bigger.
Fig. 2 (a)
Micro-tipping of the Cutter
Fig.2 (b) Mesh Fracture Expanding
Typical Wear of Lathe Cutter
Fig. 2 (c) Boundary Notch Forming
Fig.1 (b) Boundary Notch Size of Lathe Cutter
Figure 2 shows the forming process of boundary notch of the cemented carbide cutting tools. Main factors to influence boundary notch are mechanical performance of the piece material, the cutter material, and geometry parameter of the cutter. The following experiments are carried out in order to expound the forming mechanism 164
and evolution rules of the boundary notch.
Tab.3 CUTTING PARAMETRES Value 75m/min 5.5mm 0.3mm/r 100 80 450 ; 750 ; 900 -50 0.1; 0.2; 0.3 (mm) 0.2; 0.4; 0.8 (mm)
EXPERIMENT CONDICTIONS AND TESTING MEASURES The lathe C630 and reversible cutting tool are used in the experiment. Five cutter materials are employed. Main mechanical parameters of cutter material are shown in following Tab.1. The machining piece is the friction-welded line of the single hydraulic pillar. The width of the welded line is 15mm and the machining allowance is 5.5mm. Besides, the above pillar is welded with 270SiMn and 45# steel. The relatively mechanical performances of the welded line are shown as Tab.2.
Item Cutting Velocity (V) Cutting Depth (a p) Feed Rate (f) Rake Angle (? 0) Clearance Angle (a 0) Cutting Edge Angle (Kr) Edge Inclination (? s) Negative chamfer (ba 1) Cutter corner Radius (re )
Mechanical performance HRA s
12.4~12.8 11.5~12.1 11.8~12.5 12.7~13.3 12.8~13.2 North tools North tools ZiGong Zhuzhou Zhuzhou
(kg/mm2) YD10 YD15 707 YW2 YTS25 = 92
= 90.5 = 92 = 91 = 91 = 130 = 125 = 145 = 150 = 200
Based on manufacturing experience and relative information in china and other countries about similar machining process, the chosen machining and tool geometry parameters are shown as Tab.3. The boundary notch dimensions of the cemented carbide cutting tools (boundary notch height VN and width C are directly attained by tool microscope. In order to ensure reliability of the results, repeated experiments are carried out. The recurrent performance is good. EXPERIMENT RESULTS AND ANALYSIS Cutter materials For different cutter materials, as shown in Fig.3, the machining performance and the ability to resist boundary notch are distinctly different.
C t i ng Ti m t =15m n ut e i
MECHANICAL Boundary Notch VN,C (mm)
PERFORMANCES OF CUTTERS
Tensile Elongation Rate Shrinkage Rate Impact Toughness
3 2 1 YW2 YTS25 YD10 YD15 707 0 VN C
d (%) 12 16
T (%) 40 40
? k (kg/cm2) 5 5
C t i ng M er i al ut at line Fig. 3 Different Boundary Notch
Results To Different Cutter Material
Boundary Notch VN,C(mm)
C t er M er i al : YTS25 ut at C t i ng Ti m t =15m n ut e: i 2 Boundary notch VN,C(mm) 1. 5 1 0. 5 0 45 75 90 C t i ng Edge Angl e Kr ut Fig. 4 Influences of Cutting Edge Angle Kr C VN
2. 5 2 1. 5 1 0. 5 0 0. 2 0. 4 0. 8 C t er C ner R us R ut or adi VN C
Influence of Cutter Corner Radius R
From Fig.3, we can find the boundary notch dimensions are relatively large when YD10, YD15 and YW are used. Whereas the boundary notch dimension is smallest when YTS25 is used. Because of the asymmetry allowances some impacts and vibrations will take place. YTS25 cutter has better performance resisting impacts and boundary notch dimension is less. Therefore, YTS25 cutter material is selected to do the following experiments. Influences of cutting edge angle The results of the variety boundary notch are shown as Figure 4 when the cutting edge angle is changed. From Figure 4 we can find that, with the lessening of the cutting edge angle Kr , the dimensions of the boundary notch decrease. The reason is that with the lessening of the cutting edge angle Kr , the length of the cutting edge that acts on cutting becomes larger and the average loads on the cutting edge become lesser. Influences of cutter corner radius re The results of the variety boundary notch with the cutter corner changing are shown as Fig.5.
The boundary notch dimension decreases with the cutter corner radius re becoming lesser. The reason is that with the increasing of the cutter corner radius, the performance resisting impact increases and the volume of the cutter that endures heat becomes larger. Therefore, under the same cutting conditions, boundary notch dimensions (VN , C) decrease when the cutter corner radius becomes lesser. Influences of negative chamfer ba 1 The experiment results of the variety boundary notch are shown as figure 6 when the width of the negative chamfer is changed. The dimension of the boundary notch will decreases when the width of the
C t er M er i al : YTS25 ut at C t i ng Ti m t =30m n ut e: i Boundary Notch VN,C(mm) 3 2. 5 2 1. 5 1 0. 5 0 0. 1 0. 2 0. 3 N egat i ve C f er W dt h ham i (m) m VN C
Influences of Negative Chamfer Width
negative chamfer ba 1 decreases. Therefore, in order to resist or decrease the cutter boundary notch, the lesser negative chamfer ba 1 should be chosen. Deburring machining process Burrs have some influences on cutter boundary notch in metal machining process. A deburring cutter is chosen to decrease the adverse influence on cutter. A different result between deburring machining process and common machining process is shown as Fig.7. It can be seen that about 75% of the boundary notch is decreased. So, burr is a main factor to produce and increase the boundary notch of the cutter.
notch of cemented carbide cutter are piece material, cutter material and cutter geometry parameters. (4)Deburring machining process and adjusting cutter geometry parameters (to reduce edge angle Kr and width of negative chamfer b a 1, to increase cutter corner radius re ) can be chosen to decrease effectively boundary notch, which ensures the quality of workpieces and cutting performances of cutting tool.
REFERENCES  Wang Guicheng. STUDY ON DESREPAIRINMG OF CEMENTED CARBIDE CUTTING TOOL” (in Chinese). Cemented Carbide.1994, ? .1, 169~172.  Wang Guicheng. STUDY ON CRACK OF CEMENTED CARBIDE CUTTING TOOL (in Chinese). Cemented Carbide. 1993? 1, 69~75.  Zhou Zehua. PRINCIPLE OF METAL CUTTING. Shanghai: Shanghai Science and Technology Publishing Company. 1985.  Zhang Youzhen. THERIORY IN METAL CUTTING. Beijing: Aviation Industry Publishing Company.1988.  Wang Guicheng. STUDY ON THE FORMING MECHANISM OF THE FEED DIRECTION BURR AND ITS RESISTING TECHNOLOGY IN METAL CUTTING PROCESS. Zhejiang University. 1993.
C t er M er r i al : YTS25 ut at C t i ng Ti m t =30m n ut e: i Boundary Notch VN,C (mm) 2 1. 5 1 0. 5 0 a b VN C
Deburring Machining Process And Common Machining Process
CONCLUSIONS From above experiment research and theoretical analysis the following conclusions are attained: (1) Boundary notch of the cutter can be expressed by boundary notch height VN and boundary notch width C. (2)The forming processes of boundary notch can be divided into three steps: micro- tipping appears firstly; Then, mesh fractures expand; Finally, boundary notch comes to being. (3)Main factors that influence boundary 167