Optimization of Machining Parameters for Turning on CNC Machine of Inconel-718 alloy

Optimization of Machining Parameters for Turning on CNC Machine of Inconel-718 alloy

Pooja Petkar 1

1M.Tech ,

Department of Mechanical-Production, KITCOEK, Kolhapur, Maharashtra, India

S.S Karidkar 2

2Assistant Professor, Department of Mechanical Engineering, KITCOEK, Kolhapur, Maharashtra, India

Abstract:- In this study an experimental investigation of cutting parameters (cutting speed, feed rate and depth of cut) in turning operation of Inconel 718 was done and influence of cutting parameters on surface roughness, tool wear, material removal rate was studied. The machining was performed using tool such as carbide coated insert. Taguchi method is used to find optimum result. Orthogonal array, signal to noise ratio and used to study the performance characteristics in turning operation

Key Words: Inconel-718, Cutting Parameters, Taguchi Method, ANOVA, S/N Ratio

1. INTRODUCTION

   Metal cutting or machining is considered as one of the most important and versatile processes for imparting final shape to the preformed blocks and various manufactured products obtained from either casting or forging. Major portion of the components manufactured worldwide necessarily require machining to convert them into finished product. This is the only process in which the final shape of the product is achieved through removal of excess material in the form of chips from the given work material with the help of a cutting tool. Basic chip formation processes include turning, shaping, milling, drilling, etc. [1] The demand for higher strength and heat resistant materials is increasing particularly in aerospace applications. However these materials are often difficult to machine due to their physical and mechanical properties such as high strength and low thermal conductivity, which make the cutting forces and cutting temperature very high and lead to a short tool life [2] High- temperature super alloys are mainly classified into three groups: nickel based, cobalt based, and iron-nickel based alloys. Among the super alloys, the most widely used are nickel-based alloys, which contain at least 50% nickel, Nickel based super alloys display rather difficult machinability characteristics owing to their high temperature strength, work hardening tendency and low thermal diffusivity. Besides, during high machining temperatures, these alloys have affinity to weld with the tool material. The strong tendency to form built up edge (BUE) and the presence of hard intermetallic compounds and abrasive carbides in their microstructure further exacerbate cutting difficulties.[3]

   Almost 70 % of alloys used in the aerospace engine are nickel-based alloys and others are titanium alloys. Super

   alloy Inconel 718 has large number of applications in different fields of manufacturing sector due to its unique properties like high thermal resistance, high creep and corrosion resistance and retains toughness and strength at elevated temperatures. It is very important that Inconel 718 has excellent yield strength (550 MPa) even at elevated temperature (700-800°C). Almost about 70% by weight in the case of aerospace applications and 50% by weight in the case of aero-engines components are made of Inconel 718. Further Inconel 718 applications are not limited to aerospace industry but it includes ship engines, nuclear power plants and petro-chemical plants. The use of Inconel 718 alloy in such destructive environments ensures that it upholds high corrosion resistance, high fatigue resistance, withstand them at high mechanical and thermal shock, creeps, and erosion at elevated temperature. In aero engines, Inconel-718 is normally used for manufacturing of gas turbine blades, which operates at very high temperature and pressure. Inconel 718 retains high toughness and strength over a wide temperature range, striking for high temperature applications where other aluminum and steel alloys would get soften. But on other hand Inconel 718 offers serious challenge as a work material during turning/machining due to their exceptional combined properties such as high temperature strength and toughness, hardness and chemical wear and creep resistance. Although these properties are attractive for design requirements, they creates a bigger challenge to manufacturing engineers due to high temperatures and stresses generation during machining. There are two main problems in machining of super alloy Inconel 718 a. less tool life due to the work hardening and abrasion properties of the Inconel718, b. metallurgical and surface damages to the work piece due to very high cutting pressure and temperature, which also contributes towards work hardening, surface tearing, and deformation.[4]

2. LITERATURE REVIEW

   Halil Caliskan, Bilal Kursuncu [7] investigated effect of Boron Nitride Coating on Wear Behavior of Carbide Cutting Tools in Milling of Inconel 718, Surface roughness and tool wear was recorded in relation with cutting length. Wear mechanisms on the coated carbide tools were determined using scanning electron microscopy in combination with energy dispersive spectroscopy with Cutting speed – 30 m/min, Feed rate – 0.05 mm/tooth, Axial depth of cut – 0.1

   mm & Abrasive and adhesive wear was found as main failure mechanisms on the worn tools. Approximately two times longer tool life was obtained with the BN coated carbide tools.

   A. Altin , M. Nalbant [8] studied the effects of cutting speed on tool wear and tool life when machining Inconel 718 with ceramic tools, A series of tool life experiments has been carried out using silicon nitrite based and whisker reinforced ceramic tools which have two different geometries and three different ISO qualities with 10% water additive cutting fluid. The experiment results show that crater and flank wears are usually dominant wear types in ceramic square type (SNGN) inserts while flank and notch wear are dominant in round type (RNGN) inserts. Minimum flank wear is seen with SNGN tools at low cutting speeds while it is seen with RNGN tools at high cutting speeds.

   H.Z. Li, H. Zeng, and X.Q. Chen [9] did An Experimental Study of Tool Wear and Cutting Force Variation in the End Milling of Inconel 718 with Coated Carbide Inserts, with cutting speed of 600 rpm, 900 rpm & Damage observed on the rake surface, such as crater wear, was quite limited. The development of the flank wear of the coated carbide inserts used for both the down milling and the up milling under the spindle speed of 600 rpm.

   D.M. D'Addonaa, Sunil J Raykarb [10] investigated High speed machining of Inconel 718: tool wear and surface roughness analysis, Turning trials are conducted at various speed ranging from low to high (60 m/min, 90 m/min, 190 m/min, 255 m/min). Tool wear and surface roughness, which are two major aspects of machinability, have been discussed in this investigation, Wear patterns observed at these cutting speeds are uniform along the nose radius along with some traces of peeling coating. Comparatively at high cutting speeds tool gets worn out at very faster rate with major tool failure patterns like heavy notching. Also at high speed because of very high amount of heat is generated in cutting zone while machining Inconel 718 burns marks are visible on the tool.

   Xiaohong Lu, Zhenyuan Jia [11] studied tool wear appearance and failure mechanism of coated carbide tools in micro-milling of Inconel 718 super alloy with the rotational speed 60,000 rpm, depth of cut of 20m, feed per tooth of 0.6 m/flute, cutting parameters were the same and the cutting time were 0.5, 2, 4, 8, 16, 32 minutes. Each group of tests adopted a new cutting tool, and contain Fe), it can be inferred that diffusion wear occurred or that the workpiece material bonded on the surface of the matrix. If Ni did not appear, then Fe probably diffused on the surface of the matrix, indicating diffusion wear. The main wear appearance on the cutting tool are flank wear, micro-crack blade, boundary wear, flaking, rake face of crater wear and plastic deformation.

   Abheek Maiti,Mrinal Raj [12] investigated Machinability studies on INCONEL 718, to determine the influence of controllable parameters on machining characteristics and to achieve the optimum parameters for sustainable and efficient

   turning with PVD Carbide, CBN, Ceramic tools with cutting speeds-60,90,120 mm/min, doc- 0.2,0.4,0.6 mm & feed- 0.1,0.2,0.15mm/ rev. surface roughness on the work specimen machined using carbide tools increases at higher speeds on the other hand carbide tools show relatively high micro hardness with increase in the cutting velocity.

3. EXPERIMENTAL SETUP

   For the present experimental work four process parameters each at three levels have been decided. It is desirable to have minimum three levels of process parameters to reflect the true behavior of output parameters under study. The L9 orthogonal array with all values selected for the experimental run is shown in table. There are 9 parameter combinations that need to be tested. Each parameter combination is tested for replications for effective error reduction and for accurate S/N ratio. The process parameters are renamed as factors and they are given in the adjacent column. The levels of the individual process parameters / factors are given in and shows L9 Orthogonal Array of Process Parameter.

   Table 7.1- parameters and their levels

   Sr. No.	Notation	Name of Parameter	levels
   1	S	Spindle Speed (m/min)	60	50	40
   2	f	Feed rate (mm/min)	0.2	0.15	0.1
   3	D	Depth of cut (mm)	1	0.8	0.6

   Table 3.1- parameters and their levels

   Fig. 3.1 Experimentation Setup

   1. Mechanism and Evaluation of MRR :

      MRR is the rate at which tha material is removed the workpiece.. The MRR is defined as the ratio of the difference in weight of the workpiece before and after machining to the machining time.

      1. Metal removing rate (mm3/sec) :

         Turning is most common process in whole manufacturing, for turning process the CNC machine is selected.

         Material Specification.

         Ø 25mm and length 270mm.

         Depth of cut	2	0.000473	85.88%	0.000473	0.000237	70.40	0.014
         Feed(m m/rev)	2	0.000007	1.25%	0.000007	0.000003	1.02	0.495
         Error	2	0.000007	1.22%	0.000007	0.000003
         Total	8	0.000551	100.00%
         Model Summary
         S 0.0018330 R-sq(adj)- 98.78% R-sq-95.12%

         Depth of cut	2	0.000473	85.88%	0.000473	0.000237	70.40	0.014
         Feed(m m/rev)	2	0.000007	1.25%	0.000007	0.000003	1.02	0.495
         Error	2	0.000007	1.22%	0.000007	0.000003
         Total	8	0.000551	100.00%
         Model Summary
         S 0.0018330 R-sq(adj)- 98.78% R-sq-95.12%

         Currently, the MRR for turning is calculated by the formula:

      2. Removal Rate ( mm. cu./Min) :

         MRR = v f D

         MRR = Material Removal Rate (mm.cu./Min) v = Cutting Speed (SFPM)

         f = Feed (Dist./Rev.) D = Depth of Cut (mm)

         Sample calculation for case 1: N = 40m/min

         Do= 25 mm

         f = 0.1 mm/rev D = 0.6

         Rotational Speed: N (RPMs) N = V/D

         N = Rotational Speed (RPMs) v = Cutting Speed (SFPM) DO = Original Diameter

         Cutting speed , v = Do N = 509.55 SFPM Feed , f = 0.1 mm/rev

         DOC = D= 0.05 mm

         MRR = vfD = 0.1540 mm3/min

         Table 3.2- parameters and their levels

         Sr. No.	Speed	Feed rate	Depth of Cut
         1	60	1.0	0.20
         2	60	0.8	0.15
         3	60	0.6	0.10
         4	50	1.0	0.15
         5	50	0.8	0.10
         6	50	0.6	0.20
         7	40	1.0	0.10
         8	40	0.8	0.20
         9	40	0.6	0.15

         Source	DF	Seq. SS	Contri.	Adj SS	Adj MS	F- Value	P – Value
         Speed(m m/min)	2	0.000064	11.66%	0.000064	0.000032	9.56	0.095

         Source	DF	Seq. SS	Contri.	Adj SS	Adj MS	F- Value	P – Value
         Speed(m m/min)	2	0.000064	11.66%	0.000064	0.000032	9.56	0.095

         Table 3.3- ANOVA table

         The main effect values are plotted in Figure no 3.2 for the cutting speed, depth of cut, and feed rate respectively. The main effects plot shows the influence of each level of factors and the mean with maximum value is taken as the optimum values of material removal rate

         Fig. 3.1 Main effect Plot for Mean for MRR

         The plot shows that as the speed increases material removal rate decreases. Depth of cut increase material removal rate increases.

         Table 3.4- ANOVA table

         Source	DF	Seq SS	Contribut ion	Adj SS	Adj MS	F-Value	P-Value
         Depth of cut	2	0.16889	9.34%	0.16889	0.08444	4	0.2
         Feed	2	1.50222	83.05%	1.50222	0.75111	35.58	0.027
         Speed	2	0.09556	5.28%	0.09556	0.04778	2.26	0.306
         Error	2	0.04222	2.33%	0.04222	0.02111
         Total	8	1.80889	100.00%	Adj SS	Adj MS
         Model Summary
         S 0.145297 R-sq-97.67% R-sq(adj)- 90.66%

         After the experiment we find the speed , feed, depth of cut Create an effect on material removal rate .in this experiment we got that feed which affect significantly on material removal rate followed by depth of cut, speed respectively. Speed is less significant to material removal rate, contribution of feed is 85.88%

         The main effect values are plotted in Figure no 3.1 for the cutting speed, feed and depth of cut respectively. The main effects plot shows the influence of each level of factors and the mean with maximum value is taken as the optimum values of surface roughness.

         Fig. 3.2 Main effect Plot for Mean for SR

         The plot shows that as the speed and depth of cut increases surface roughness increases. feed increase surface roughness decreases.

         Table 5 Rank for Response Variable

         	Responses Variable
         Process Parameter	MRR (mm3/min.)	SR (µm)
         Speed	2	2
         Depth of Cut	1	1
         Feed	3	3

4. CONCLUSIONS

Turning tests were performed on Inconel-718 Alloy work piece using three different parameters. The influences of cutting speed, feed rate, and depth of cut were investigated on the machined surface roughness and Material Removal Rate (MRR). Based on the results obtained, the following conclusions have been drawn:

• The analysis of the experimental observations highlights that MRR in CNC turning process is greatly influenced by cutting speed followed by depth of cut.

• It is observed that the depth of cut is most significantly influences the Surface Roughness (Ra).

• For all response variables depth of cut was found most significant & feed was most insignificant factor.

4. REFERANCES

1. K. Wegener, F. Kuster, S. Weikert, L. Weiss, J. Stirnimann Success Story Cutting, CIRP Conference on High Performance Cutting 46 ( 2016 ) 512 524.

2. S. Sun M.Brandt, M.S.Dargusch, Thermally enhanced machining of hard-to-machine materialsA review, International Journal of Machine Tools & Manufacture 50 (2010) 663680.

3. Eren Kaya and Birol Akyüz, Effects of cutting parameters on machinability characteristics of Ni-based super alloys: a review, Open Eng. 2017; 7:330342

4. M Anthony Xavior Machinability studies on INCONEL 718, IOP Conf. Ser.: Mater. Sci. Eng. 149 01/ 2016

5. ZBALA W, Sodki, STRUZIKI EWICZ G. Productivity and reliability improvement in turning Inconel 718 alloy case study, Maintenance and Reliability 2013; 15 (4): 421426.

6. Machining of nickel alloys, A nickel development institute reference book, series N11008

7. Halil Caliskan, Bilal Kursuncu, Sevki Yilmaz Guven, Abdullah Cahit Karaoglanli, Mustafa Sabri Gok and Akgun Alsaran Effect of Boron Nitride Coating on Wear Behavior of Carbide Cutting Tools in Milling of Inconel 718, Springer Science Business Media Singapore 2016 A. Öchsner and H. Altenbach (eds.), Machining, Joining and Modifications of Advanced Materials, Advanced Structured Materials 61,

8. A. Altin , M. Nalbant , A. Taskesen The effects of cutting speed on tool wear and tool life when machining Inconel 718 with ceramic tools Materials and Design 28 (2007) 25182522

9. H.Z. Li, H. Zeng, and X.Q. Chen An Experimental Study of Tool Wear and Cutting Force Variation in the End Milling of Inconel 718 with Coated Carbide Inserts, Singapore Institute of Manufacturing Technology 71 Nanyang Drive, Singapore 638075.

10. D.M. D'Addonaa, Sunil J Raykarb, M M Narkec High speed machining of Inconel 718: tool wear and surface roughness analysis, 10th CIRP Conference on Intelligent Computation in Manufacturing Engineering CIRP 62 ( 2017 ) 269 274

11. Xiaohong Lu, Zhenyuan Jia, Hua Wang, Likun Si, Yongyun Liu and Wenyi Wu, Tool wear appearance and failure mechanism of coated carbide tools in micro-milling of Inconel 718 super alloy,

    Industrial Lubrication and Tribology, Vol. 68 Iss 2 pp. 267 -277

12. M Anthony Xavior,Mahesh Patil,Abheek Maiti,Mrinal Raj and Nitesh Lohia, Machinability studies on INCONEL 718, IOP Conf. Series: Materials Science and Engineering 149 (2016) 012019