PSI - Issue 14

Rohit K. Mahalle et al. / Procedia Structural Integrity 14 (2019) 945–951 Rohit Kumar Mahalle / Structural Integrity Procedia 00 (2018) 000–000

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Make: Vitech Enviro System). For enhanced safety machining parameters viz. Speed, feed and depth of cuts for the propellant machining were established after taking trials on dummy propellant. It was taken care that during machining of dummy propellant (where mechanical properties were similar as HTPB based propellant), temperature in cutting zone does not exceed 50 o C with vacuum suction. Temperature was measured with IR thermometer. During experiment of machining operation, the ambient conditions of facility along with machining parameters are shown in Table 1 and Table 2. Table 1. Machining Parameters and environmental factors Machining parameters Cutting speed 100 m/min Rotary table feed 0.42 m/min Depth of cut 1-3 mm

Machining environmental factors Machining bay ambient temperature

28-36 o C 75-85%

Relative humidity

Coolant

Dry machining with vacuum suction cooling

Vacuum at cutting edge

500 mm of Hg

Table 2. Mechanical properties of propellant Grain material Tensile Strength 600 KN/m 2 Initial Modulus 4000 KN/m 2 %elongation 30 Density

1.17-1.21x10 3 Kg/m 2

Hardness 60-65 Shore-A Mechanical properties of propellant were determined so as to have an idea about different properties and characteristics of propellant prior to carrying out the machining operation. INSTRON UTM machine (model: 5566-J2936) was used to determine the mechanical properties of propellant grain viz. Tensile strength, initial modulus and %elongation as per IS3400 part-1 standards. Hardness was measured using Shore hardness tester (make: MITUTOYO model: MCR322). Density was evaluated by Psyncometer. For dimensional measurement tubular inside micrometer (make: ETALON model: 072109128) was used to measure the diameter for counter-bore & lever type dial test indicator (make: INTERAPID model: 74.111367) was used to measure the distances from reference surface using CNC machine co-ordinate. Machining operation was conducted on ARTICLE motor Sr. No. 21, 22 & 23 for collecting the data. Each ARTICLE motor comprises of three segments Head, Middle and Nozzle, which are finally assembled together to form a full motor ARTICLE.

Figure 1: (a) Dummy Machining ;( b) Special Purpose VTM; (c) Machined Propellant Chips; (d) HSS Conical Insert ;( e) The Turbine Cutter