CHAPTER 3 EXPERIMENTAL PROCEDURE

Transcription

1 60 CHAPTER 3 EXPERIMENTAL PROCEDURE The objective of this study is to evaluate the performance of cermet tools which is subjected to either plain, coated, cryogenically treated. In order to evaluate these following experimental procedures followed. 3.1 CUTTING TOOL INSERTS Machining tests were carried out using different cermet cutting tools on a precision lathe (Venus, Model-SU4) having 18 spindle speeds and 18 table feeds with a maximum speed of 2500 rpm whose specification is listed in Table 3.1. Cermet cutting tools were used for this study which is subjected to various conditions and their notations used as described below: 1) Plain cermet without Ti-Al-N coating (UC) and without Cryogenic treatment (UT) (UC&UT) 2) Cryogenically treated (T) and uncoated tool (UC) (UC&T) 3) Ti-Al-N coated cermet (C) without cryogenic treatment (UT) (UT&C) 4) Cryogenically treated and subsequently Ti-Al-N coated (T&C) and 5) Ti-Al-N coated and subsequently cryogenically treated cermet (C&T).

2 61 Element composition details of cermet cutting tool using XRF is shown in Figure 3.1. The element composition details and specifications of the cutting tool inserts are presented in Tables 3.2 and 3.3 respectively. TiC based cermet (TTI15 grade) cutting tool inserts from WIDIA Inc.with ISO P-10 grade cermet rhombic flat inserts of ISO specification CNMG are used for this study. The Machining was performed using WIDAX tool holder with ISO specification PCLNR 1616 K 12 fitted with one insert. The image and specification of the cermet insert and tool holder assembly are shown in Figures 3.2 to 3.4 respectively. Table 3.1 Lathe specifications Specifications Dimensions Model Venus (SU4) Bed Length 5+1/4 and 6 Bed Width 11" Center Height 9" Spindle bore Horse power of the motor Number of speeds Number of feeds 54 mm 3 HP 18 (45Rpm Rpm) 18 (0.025 mm/rev 0.99 mm/rev)

3 62 Figure 3.1 Element composition details of cermet cutting tool using XRF Table 3.2 Element composition details of cermet cutting tool Elem. Line Mass[%] 2sigma[%] Intensity[cps/mA] 22 Ti K V K Co K Ni K Table 3.3 Details of cutting tool inserts specifications Cutting tools rake angle clearance angle inclination angle plan approach angle Included angle nose radius ( ) ( ) ( ) ( ) (e r ) (r e ) Parameter mm

4 63 Figure 3.2 Photo image of the cutting insert used Figure 3.3 Cermet insert specification details Figure 3.4 Image of the cutting tool holder assembly

5 CRYOGENIC TREATMENT The cermet tools are subjected to cryogenic treatment either in plain condition or with or without Ti-Al-N coating for this study. The cryogenic treatment cycle is given in Figure 3.5, which consists of following stages: (i) (ii) a gradual lowering of temperature to -195 C holding for 18 h, and (iii) then subsequently raising temperature temperature. back to room The cryogenic treatment was carried out by Cryoking processor, CRYOKING Inc. Whose specification is given in Table 3.4. Table 3.4 Specifications of cryogenic processor Specifications Details Model Cryogenic temperature range Maximum Weight of Materials can be treated Controlling Method (Temperature Control ) Cryoking up to -250º C 500 Kg PLC based

6 65 Cryogenic Treatment Schedule Time (Hours) Descend Soak Ascend Figure 3.5 Cryogenic treatment cycle 3.3 Ti-Al-N COATING Tool wear is inherent in machining. There are many steps and measures taken to reduce the level of tool wear on cutting tools. One of the steps is applying surface treatment on the base cutting tool material. A popular method is applying coating onto the base cutting tool material by the use of PVD method. The TiAlN coating provided on the cermet cutting tools by Overlooks Balzers Coating India Ltd with the commercial name of BALINIT FUTURA NANO using INNOVA, a new-generation coating system. In arc evaporation (Figure 3.6) an arc is struck between the backing plate (anode) and the coating material (cathode). The arc moves over the coating material and evaporates it. Due to the high currents and power densities employed, the evaporated material is ionised to a high degree

7 66 reactive gas and metal ions hit the component surface and are deposited there as the coating material. (Courtesy, Oerlikon Balzers Inc.) Figure 3.6 Arc evaporation process 1. Argon 2. Reactive gas 3. Arc Sources (coating material and backing plate) 4. Components 5. Vacuum pump Tools are placed in a processing chamber, which is pumped down to produce a vacuum. The cermet tools are coated with Ti-Al-N whose specification of the coating is listed in Table 3.5.

8 67 Table 3.5 Properties of BALINIT FUTURA NANO coating Coating material Properties Units BALINIT FUTURA NANO Ti-Al-N Micro hardness (HV 0.05) 3300 Coefficient of friction against steel (dry) Coating thickness m) 4 Residual compressive stress (GPa) -2.0 Maximum service temperature ( C) 900 Coating temperature ( C) < 500 Coating colour Coating structure violet-grey Nano - structured 3.4 WORK MATERIALS The work materials used in these machining studies were AISI 4340 steel (also known as EN 24 steel) and AISI D2 steel (also known as Die steel) which were hardened to a hardness value of HRC 45 and HRC 50 respectively. The work piece materials used for the machining studies and their hardness after heat treatment are given in Table 3.6. As per ISO 3685 (1993) the work pieces selected in the present study has the dimensions of 50 mm diameter and 375 mm length, so that L/D ratio should not exceed 10,in order to assure the necessary stiffness of the elastic fixed system chuck/piece/cutting tool.

9 68 Table 3.6 Work piece materials and their hardness after heat treatment Sl. No Work piece Material Hardness after heat treatment 1 AISI 4340 steel HRC 45 2 AISI D2 steel HRC AISI 4340 Steel AISI 4340 steel is Nickel-Chromium-Molybdenum high tensile steel. It has good wear resistance and shock resistance and it is characterised by high strength and toughness. The hardened and tempered AISI 4340 steel can be further surface hardened by flame or induction hardening and followed by Nitriding. It is mostly used in industrial sectors for applications requiring high tensile/yield strength. The typical applications are heavy duty shafts, gears, axles, spindles, couplings etc. The AISI 4340 steel hardened by heat treatment of quenching followed by tempering at 845 C and 440 C. AISI 4340 steel is regarded as readily machinable, and operations such as turning, milling and drilling etc. can be carried out satisfactorily. Some of the related specifications of AISI 4340 steel are EN 24, BS M40, SAE 4340, 40NiCrMo6 etc. The chemical composition of AISI 4340 steel is given in Table 3.7. The microstructure and EDAX analysis of AISI 4340 steel (HRC 45) are presented in Figure 3.7 and 3.8 respectively. Figure 3.7 reveals the presence of carbide particles in the Fe matrix.

10 69 Table 3.7 Composition of AISI 4340 steel by weight percentage Composition C Si Mn Cr Mo Ni (Wt %) Figure 3.7 Optical micrograph showing the microstructure of hardened AISI 4340 steel (HRC 45) Figure 3.8 Electron dispersive X- Ray analysis (EDAX) of AISI 4340 steel

11 AISI D2 Steel AISI D2 is a high-carbon, high-chromium tool steel alloyed with Molybdenum and Vanadium characterized by high wear resistance, high compressive strength, good through-hardening properties, high stability in hardening, and good resistance to tempering reported by Arsecularatne et al (2006). AISI D2 steel is one of the most widely used steel in the industry. The chemical composition and EDAX analysis of AISI 4340 steel is given in Table 3.8 and Figure 3.9 respectively. AISI D2 steel is recommended for tools requiring very high wear resistance, combined with moderate toughness (shock-resistance). The AISI D2 steel hardened by heat treatment of quenching followed by tempering at 1050 C and 530 C respectively. Table 3.8 Composition of AISI D2 steel by weight percentage Composition C Fe Mn Si Cr Mo V (Wt %) rem a Figure 3.9 Electron dispersive X- Ray analysis (EDAX) of AISI D2 steel

12 EXPERIMENTAL CONDITIONS Machining studies were conducted on hardened AISI 4340 steel and AISI D2 steel using the above mentioned cermet cutting tools at different cutting conditions. Experimental conditions are shown in Table 3.9 and For AISI D2 steel machining, the lower and higher cutting conditions are considered, because the middle cutting condition may not be significantly varied. The comparison was carried out in terms of the performance of the different processed cermet tools while machining AISI 4340 steel and AISI D2 steel respectively. Table 3.9 Experimental conditions for AISI 4340 steel Cutting speed m/min 115, 140, 180 Feed rate mm/rev 0.06,0.08,0.12 Depth of cut mm 0.1,0.15,0.2 Environment Dry Table 3.10 Experimental conditions for AISI D2 steel Cutting speed m/min 75, 92, 118 Feed rate mm/rev 0.06,0.12 Depth of cut mm 0.1,0.2 Environment Dry

13 OBSERVATIONS The main objective of the present study is to evaluate the performance of different cermet cutting tools on machining AISI 4340 steel (HRC 45) and AISI D2 steel (HRC 50). The performance of the cermet cutting tools was evaluated by i) Measurement of flank wear ii) Measurement of surface roughness on work materials iii) measurement of cutting forces iv) Microscopic studies on worn out tools and chips of the work materials. The wear measurements were taken using a Tool Makers Microscope (Metzer-model METZ 1395) with 30X magnification factor. The machining time was accurately measured with a stopwatch. The machining was stopped periodically to measure tool wear and surface roughness of the work materials. The surface roughness (R a) values were obtained by moving the stylus of the surface roughness measuring instrument (TR 200) on the work material. The specification of surface roughness measuring instrument is given in Table The cutting force components were measured during turning using strain gauge type dynamometer with a sensitivity of 1 Newton. The metallographic microstructure of cutting tool was obtained according to ASTM B (2000). Scanning Electron Microscope (FEI ESEM Quanta 200) was used to study the wear of worn and microstructure of the tool materials. The electrical resistivity of the cryogenically treated and untreated types of cutting tool inserts used in this study was measured with a standard four probe set-up (Four probes Resistivity Instrument, Concord, India) and the average values of electrical resistivity were evaluated.

14 73 Table 3.11 The specification of surface roughness measuring instrument Specifications of TR200 Surface Roughness Tester Model Name Roughness Parameters Profiles Measured TR200 Surface Roughness Tester TIME make Ra, Rz, Ry, Rq, Rt, Rp, Rmax, Rm, R3z, S, Sm, Sk, tp Primary profile (P), Roughness Profile (R) tp curve (Mr) Measurement Accuracy < ±10% Max Tracing Length Detector Power Battery Capacity Charger Working Temperature Dimensions 17.5mm Standard model TS100, inductive, Diamond tip radius 5microns Li-Ion Battery Rechargeable 1000mAh (>3000measurements) 220V/110V, 50Hz 5 to 40 degree C 141mmx56mmx48mm