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Abstract Code: OP89
Theme: Product Design
A New Approach for the Machining and Tool Design of Advanced Composite Materials for the Drilling Operation
Sujit Mandaogane, Akash Mohanty*
School of Mechanical and Building Sciences, VIT University, Vellore
*Email id of corresponding author:
ABSTRACT
Delamination and tool wear are the major causes of concern for machining fiber-reinforced polymer based composites. This paper gives the analysis of machining parameters such as feed, depth of cut, tool angle, etc. influencing the resultant force during the machining of fiber-reinforced polymer-based composites for the drilling operation and to study the tool geometry for the arrest of de-lamination to obtain good surface finish. In this study, drilling process is analysed on a thick GFRP laminate and simulation for the tool geometry is performed by using the finite element software ANSYS to obtain necessary solutions.
Key Words: Delamination, Drilling, FRP composites, Tool geometry, Simulation
1. INTRODUCTION
Advanced composite materials are often characterized by remarkably high strength fibers having exceptionally high stiffness, or modulus of elasticity attributes. These fibers have low density while engaging a large fraction of the volume. The Advanced Composite materials have wide and established applications in the field of aerospace, aircraft and sports equipment’s sectors.
Among all the machining operations, drilling is the most commonly used machining operation for the composite materials. However, due to their anisotropic and non-homogeneous properties, they are difficult to machine. Delamination and tool wear are the major causes of concern during their machining [1]. A lot of study has been done related to the process parameters to investigate the cause of tool wear [2-7]. Sakuma and Seto [8] highlight the correlation between the swift advancing of the cutting temperature and the presence of the critical speed causing immediate tool wear.
Measurement of cutting forces is one of the most sought out technique known for the detection of tool wear. However, a difference of opinion still exists as which component of cutting force is more reliable or sensitive. Ertunc and Oysu [9] exercised the transient time method, the phase plane method, the mechanistic approach and the hidden Markov models (HMM) for real-time identification of tool wear status involving cutting force and torque measurements from dynamometer using metal drilling. Oh et al. [10] examined the effect of cutting torque control on drill flank wear.
In this study, drilling process is performed on a thick GFRP laminate to analyse the machining parameters such as feed, depth of cut, speed, etc. influencing the resultant force during the machining and simulation for the tool geometry is performed by using the finite element software ANSYS to obtain necessary solutions.
2. MATERIALS:
Epoxy Resin PC351:
It is a modified liquid epoxy resin, procured from Resinova Chemie Ltd. Kanpur, India.
Hardener PH861:
It is a low viscosity aliphatic polyamine hardener, procured from Resinova Chemie Ltd. Kanpur, India.
The properties and curing characteristics of Epoxy Resin (PC351) and Hardener (PH861) are illustrated in Table I and II respectively [11].
Table I: Properties of Epoxy Resin (PC351) and Hardener (PH861)
Grade / Appearance / Specific Gravity(G/CM3) / Viscosity
(CPS AT 250C) / Ratio of mixing
PC-351 / Pale yellow to amber liquid / 1.15 at 200C / 2000-3500 / 100 parts by weight
PH-861 / Colorless to yellow liquid / 1.00 at 200C / 10-20 / 10 parts by weight
Table II: Curing characteristics of Epoxy Resin (PC351) and Hardener (PH861)
Temp. 0C / POT LIFE (MINUTES)PH-861 / CURING (HOURS)
PH-861
25 / 60 / 14-20
40 / - / 5-7
70 / - / 1-3
3. EXPERIMENTAL SET-UP:
3.1 Specimen
The Glass fibers were cut in similar size (9 cm x 4 cm) and the specimen with 75 layers of glass fiber was prepared using the open cast molding technique. The mold was kept under pressure for 24 hours at room temperature. The specimen was then kept in an oven for 8 h at a temperature of 50 0C for the post curing process. The weight percent of the fiber is 25%.
3.2 Drilling test
The specimen was machined on a conventional drilling machine, using a drill bit of 6mm diameter made of High Speed Steel (HSS). For measuring the forces in x, y and z direction, Kistler-9275B Dynamometer was used, with a capacity of 5 kN.
Four drilling tests were conducted without the use of coolant at spindle speed of 1000 and 1400 rpm with the feed rates as 40 mm/min and 56 mm/min while the depth of cut was kept constant i.e. 20 mm. Figure 1 shows the specimen after the drilling operation.
Figure 1: Specimen after drilling operation
4. FEA ANALYSIS:
The drill bit was modelled in CATIA V5R16 and the FEA Analysis was done in ANSYS Workbench 14.0 to analyze the stress induced on the tool during the machining period. The force generated during the machining of the specimen i.e. 55N (maximum) was utlised during the analysis. The drill bit was modified from the conventional one by providing holes in the middle and near the tip of the drill. The trajectory near the tip of the drill was made similar to a parabolic trajectory and also the pitch of the helix was kept at 80mm.
5. RESULTS AND DISCUSSIONS:
Table III: Forces in x,y and z direction measured from Kistler-9275B Dynamometer
Speed (RPM) / Feed Rate (mm/min) / Fx(N) / Fy(N) / Fz(N)1000 / 40 / 38.94 / 42.00 / 40.28
56 / 47.24 / 45.65 / 48.31
1400 / 40 / 40.41 / 44.19 / 41.02
56 / 36.13 / 46.26 / 46.14
The result of machining shows that at the same speed the force in all the directions increases with increase in the feed rate. Table III interpretes this result. The graphs obtained from the dynamometer are depicted in Figure 2 and Figure 3 respectively. The values of the forces doesnt change very alarmingly when the speed increases.
Figure 2: Graph from dynamometer with speed=1000 rpm and feed rate= 40mm/min
Figure 3: Graph from dynamometer with speed=1400 rpm and feed rate= 56mm/min
Figure 4 shows the directional deformation of the drill bit in y-axis from which it is interpreted that the stress at the tip of the drill bit is maximum compared to the rear end of the drill which is the cause of its high wear. The modification of providing holes to allow coolant flow into the drilled hole may lead to less tool wear and the parabolic trajectory maintained near the tip of the drill may help to reduce the delamination effect. The bending stress for the measured force i.e. 55N was calculated as 987.65 psi and the bending moment was calculated to be 1546.87 lb-ft.
Figure 4: Directional Deformation (Y-axis) of the drill bit in ANSYS 14.0
6. CONCLUSIONS:
This work presented a constructive description of the effect of machining parameters on the resultant force during the drilling of composite materials (GFRP laminate) and provides the FEA analysis of the drill bit. The analytical results are obtained based on the classical elasticity, energy conservation and linear elastic fracture mechanics. The study also suggests the modification in the drill bit to reduce the tool wear as well the delamination effect. The experimental results suggests that the force increases with the increase in feed rates. The FEA analysis shows that the stress values are maximum at the tip of the drill. This approach can be extended to further modify the drill bit to reduce the tool wear and delamination effect.
7. REFERENCES:
[1] Tsao CC, Hocheng H. Effect of tool wear on delamination in drilling composite materials International Journal of Mechanical Sciences 49 (2007) 983–988
[2] Rao SB. Tool wear monitoring through dynamics of stable turning. Transactions of the ASME, Journal of Engineering for Industry 1986;108:183–90.
[3] Danai K, Usloy AG. A dynamic state model for on-line tool wear estimation in turning. Transactions of the ASME, Journal of Engineering for Industry 1987;109:396–9.
[4] Choudhury SK, Ramesh S. On-line tool wear sensing and compensation in turning. Journal of Materials Processing Technology 1995;49(3–4):247–54.
[5] Caprino G, De lorio I, Nele L, Santo L. Effect of tool wear on cutting forces in the orthogonal cutting of unidirectional glass fibre-reinforced plastics. Composites Part A 1996;27(5):409–15.
[6] Kaye JE, Yan DH, Popplewell N, Balakrishnan S. Predicting tool flank wear using spindle speed change. International Journal of Machine Tools and Manufacture 1995;35(9):1309–20.
[7] Akgerman N, Frisch J. The use of cutting force spectrum for tool wear compensation during turning. In: Proceeding of 12th international machine tool design research conference, UMIST, Manchester 1991. pp. 517–26.
[8] Sakuma K, Seto M. Tool wear in cutting glass fiber-reinforced plastics. Bulletin of JSME 1981;24(190):748–55.
[9] Ertunc HM, Oysu C. Drill wear monitoring using cutting force signals. Mechatronics 2004;14(5):533–48.
[10] Oh YT, Kwon WT, Chu CN. Drilling torque control using spindle motor current and its effect on tool wear. International Journal of Advanced Manufacturing Technology 2004;24(5–6):327–34.
[11] Manufacturer data book, Resinova Chemie Ltd. Properties and characteristics of PC-351 and PH-861.
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