Experimental Investigation of Grit Blasting Parameters on Alpha Case Removal of Forged Alloy Part Ti-6Al-4V used in Aviation Industry

Experimental Investigation of Grit Blasting Parameters on Alpha Case Removal of Forged Alloy Part Ti-6Al-4V used in Aviation Industry

Ketan Ghorpade1

1, PG Student,

Department Production Engineering, Veermata Jijabai Technological Institute Mumbai

India 400019

Pramod A. Naik2

3,Ph D Scholar,

Department Production Engineering, Veermata Jijabai Technological Institute Mumbai

India 400019

D. K. Shinde3

3Associate Professor,

Department Production Engineering, Veermata Jijabai Technological Institute Mumbai

India 400019

D. N. Raut4

4Professor,

Department Production Engineering, Veermata Jijabai Technological Institute Mumbai

India 400019

Abstract Titanium and its alloys are attractive engineering materials used in aerospace industry because of their superior mechanical properties such as high specific strength and excellent corrosion resistance. Ti6Al4V alloy commonly used for manufacturing components in jet engines, such as fan blades, disks, wheels and sections of the compressor where the maximum temperature is in the range of 300450 °C. Titanium forged parts are heated above 900°C during forging undergoes reduce roll, blocker, flattener, finisher, trimming etc. processes for producing final forging. During this process when surface of forged part gets contact with oxygen from environment and producing oxide layer. This oxide layer is commonly known as alpha case. The alphacase layer has adverse effect on mechanical properties such as ductility, fracture toughness and especially the fatigue life when an engine component is subjected to dynamic loading. The effect of grit blasting parameters on the alpha case removal and surface roughness of Ti6Al4V alloy was examined using the Taguchi designs of experiments and Grey relational analysis.

KeywordsAlphacase, Taguchi design, Grey relational analysis, Surface Roughness, ANOVA, Grit Blasting Parameters

1. INTRODUCTION

   During titanium forging when heated parts are in contact with atmospheric oxygen forms oxide layer on surface called as alpha case[1]. Failure of titanium forged parts may be causes due to crack propagation on alpha case layer present on the surface. Etching is the process which removes the alpha case layer and avoids formation of cracks on the surface. This process involves use of hazardous chemicals like concentrated hydrofluoric acid (HF) and nitric (HNO3) acid with required proportion, which makes this process dangerous and required proper attention and safety measures to carry out process. Chemical etching also have adverse effect on part surface by introducing pitting and/or intergranular corrosion and thus affects the fatigue strength[2]. Grit blasting can be used as alternate process for

   etching and can be used for removing alpha case layer by applying proper process parameters. Grit blasting process involves various process parameters like grit selection, exposure time, blasting pressure, blasting angle, distance of nozzle from the part surface. Hence it is required to develop scientific method to have both economic and damage free grit blasting surface in case of titanium forged parts.

   Grit Blast cleaning with abrasive media removes old coatings, rust, and other unwanted material from a surface, and creates an anchor pattern to allow new coatings to adhere better. Manufacturers who turn to grit blast cleaning as an environmentally responsible alternative to chemical stripping processes often realize substantial cost savings as well.

2. EXPERTIMENTAL PROCEDURE

   1. Material

      Titanium forged flaptrack Prolongations of material Ti6Al4V is used in experiment. The flaptrack is used in wings of Boeing 737 for aviation purpose. For experimental trails, the extracted prolongations are taken having dimensions height 48mm; width 77mm; length 120mm. The flaptrack material is given in table 1.

      Table 1: Chemical composition of Ti6Al4V flaptrack

      El e m en t	Al	V	Fe	O	C	N	H	Y	Oth er	Ti
      % w ei gh t	6. 75	4 . 5 0	0. 30	0 .2 0	0 . 0 8	0.05 (500 ppm )	0.01 25 (125 ppm )	0.00 5 (50 ppm )	0.5 0	remai ning

   2. Prolongation and Bracket Preparation

      Bracket preparation is carried out for experimental work. Total 8 Prolongation are used to make 16 trials and for that it is required to mask half portion of prolongation. To mask that portion bracket preparation is done having dimensions 200mm×200mm×100mm as shown in figure 1 A). dia. 16mm and dia. 13mm rods are taken out from bracket which will further used for locating of prolongation while experimental trails.

      Figure 1: Shows A) Flaptrack Prolongation; B) Bracket

   3. Trail Setup

      asted s

      asted s

      Fig 2a-e shows the trial setup for the experimentation of grit blasting of the flaptrack prolongation and bracket component. This experiment consists of air receiver tank, air drier unit, hopper, and nozzle (L9 mm). For measuring alpha case hardness Clemex micro-hardness tester is used and Mitutoyo surface roughness tester is used for

      Table 2 Grit blasting parameters and their levels

      Process Parameter	Symbol	Level 1	Level 2	Level 3	Level 4
      Nozzle Distance (mm)	A	300	350	400	450
      Blasting Angle (Degree)	B	30	45	60	75
      Blasting Time (Second)	C	60	90	120	150
      Blasting Pressure (Bar)	D	4.5	5.0	5.5	6

3. DESIGN OF EXPERIMENT AND TAHUCHI METHOD

   The Taguchi method is an optimization technique which is widely used in engineering analysis. This method reduces the no. of experimental runs and cost associates with it. The Taguchi method uses a loss function to calculate the deviation between the experimental values and the desired values. The design of experiment (DOE) was based on Taguchi design considering four factors each at four levels. In the present analysis total number of runs = L16 have been taken. The experimental results for alpha case depth (ACD) and surface roughness (Ra) are depicted in Table 3 for 16 runs. Both alpha case depth is measured on transverse section of mounting and surface roughness were measured at surface of grit blasted prolongation of flaptrack as shown in Fig. 1

   checking surface roughness of grit bl

   1. urface.

   2. B).

   The effective use of Taguchis Orthogonal Array

   a Approach for predicting the effects of individual process parameters on thickness of deposited layer in powder coating process. An orthogonal array approach and the signal to noise ratio have been used to understand the factor effects in powder coating of EN8 Steel Shaft. Experimental results are also provided to confirm the effctiveness of this

   d e approach [4].

   The body component traceability throughout the manufacturing process has the potential to change the way we approach the quality assurance and control issue. Thus, there is huge scope for data collection and analysis. This will assist

   Figure 2. a) Air receiver tank, b) Air Drier, c) Hoper Unit, d) Surface roughness testing and e) Clemex Microhardness tester.

   1. Experimental Parameters and levels

   Grit mix, grit flow rate, intensity, Grit blasting angle, grit velocity, distance between nozzle to work piece, coverage area, grit blasting pressure and exposure time are the input parameters. Since some parameters such as velocity, intensity, and coverage are difficult to control, controllable influential parameters such as grit mix selection, grit blasting angle, grit blasting angle and exposure time factors were considered in the present investigation. Pilot experiments are carried among GH050 and GH025 nominal size are in mm from which GH050 gives promising results to remove maximum material. Other controllable factors levels are determined from literature base. These shot peening parameters along with their levels are shown in Table 2.

   to achieve the extremely ambitious goal of Zero Defect i. e. the title of World Class Manufacturer[5].

   Sr.	Nozzle Distance mm	Blasting Angle Degree	Blasting Time Second	Blasting Pressure Bar	ACR (HV)	Ra (µm)
   1	300	30	60	4.5	1	6.470
   2	300	45	90	5.0	8	8.288
   .3	300	60	120	5.5	6	5.816
   4	300	75	150	6.0	11	6.659
   5	350	30	90	5.5	18	5.505
   6	350	45	60	6.0	4	7.586
   7	350	60	150	4.5	19	5.877
   8	350	75	120	5.0	26	7.654
   9	400	30	120	6.0	24	4.629
   10	400	45	150	5.5	16	6.794
   11	400	60	60	5.0	9	4.536
   12	400	75	90	4.5	19	6.285
   13	450	30	150	5.0	17	3.674
   14	450	45	120	4.5	3	7.245
   15	450	60	90	6.0	18	6.333
   16	450	75	60	5.5	31	7.461

   Sr.	Nozzle Distance mm	Blasting Angle Degree	Blasting Time Second	Blasting Pressure Bar	ACR (HV)	Ra (µm)
   1	300	30	60	4.5	1	6.470
   2	300	45	90	5.0	8	8.288
   .3	300	60	120	5.5	6	5.816
   4	300	75	150	6.0	11	6.659
   5	350	30	90	5.5	18	5.505
   6	350	45	60	6.0	4	7.586
   7	350	60	150	4.5	19	5.877
   8	350	75	120	5.0	26	7.654
   9	400	30	120	6.0	24	4.629
   10	400	45	150	5.5	16	6.794
   11	400	60	60	5.0	9	4.536
   12	400	75	90	4.5	19	6.285
   13	450	30	150	5.0	17	3.674
   14	450	45	120	4.5	3	7.245
   15	450	60	90	6.0	18	6.333
   16	450	75	60	5.5	31	7.461

   Table 3 Taguchi L16 factorial design and Experimental Observation

   1. S/N RAITO ANALYSIS

      The analysis of variance is done to investigate which of the following process parameters has more influence on response value. ANOVA table can be generated from Minitab software or manual calculations. This is accomplished by separating the total variability of the S/N ratios, which is measured by the sum of squared deviations from the total mean of the S/N ratio, into contributions by each of the process parameters and the error [5]. The overall mean of S/N ratios can be calculated using the equations 1-3.

      Lower the best type (LB) (1)

      Higher the better type (HB) (2)

      Nominal the better type (NB) ..(3)

      In the Taguchi method the term signal represents the desirable value (mean) for the output characteristic and the term noise represents the undesirable value (S.D) for the output characteristic. Therefore, the S/N ratio is the ratio of the mean to the standard deviation. Taguchi uses the S/N ratio to measure the quality characteristic deviating from the desired value. Loss function obtained from Taguchi analysis is further converted into a signalnoise (S/N) ratio[3]. Generally, there are three kinds of quality characteristics in the analysis of the S/N ratio, such as the higher the- better, lower-the-better and the nominal-the-best. [6].

      The objective of this project is to reduce alpha case depth and surface roughness. Therefore, smaller the better characteristic is used shown in equation. Table 4 shows the experimental results for alpha case depth and the corresponding S/N Ratios using the equations mentioned above. The response table and S/N response graph for alpha case depth are shown below. Regardless of the lower-the- better or the higher-the-better quality charcteristic, the greater the S/N ratio corresponds to the smaller variance of the output characteristic around the desired value[5].

      The manufacturing, assembly process and powder coating process. There was a problem during assembly of parts of Manual Squeezer. By conducting experiments as per Taguchis Orthogonal array, following results have been obtained after the Statistical analysis using descriptive method. The study showed influencing parameter in powder coating process is the spraying voltage. Because it shows large variation in response value if its level is changed from 1 to 2. One can say that as Voltage increases, the thickness of deposited layer increases. Also its has no effect on outcome even if its level is changed from 1 to 2. The bake time and Curing Medium showed less variation when their levels are changed from 1 to 2. The Amount of layer deposited on smooth part is less in comparison with that of Rough part if all other parameter settings remain unchanged [8].

      The DOE trials conducted using Taguchi OAs L4 (2^3) experimental setup suggests optimum Laser engraving DMC parameters is 8×8 mm2 (DMC Size) and 3 Laser passes. The DMC code engraved by Laser has performed successful scanning within required time constraint in the various manufacturing environment. So, it implements for the mass production applications [9].

      Table 4 Response Table for S/N Ratios

      Level	A, [D(mm)]	B, [A(degree)]	C, [T(sec.)]	D, [P(bar)]
      1	-13.61	-17.20	-13.66	-15.17
      2	-21.25	-15.93	-23.46	-21.01
      3	-21.96	-21.33	-16.62	-22.07
      4	-20.69	-23.05	-23.77	-19.26
      Delta	8.34	7.12	10.11	6.90
      Rank	2	3	1	4

      Fig. 3. Main effects ploy for S/N ratios Table 5 Response Table For Means

      Level	Nozzle distance	Blasting angle	Blasting time	Blasting pressure
      1	6.500	11.250	7.250	10.500
      2	13.500	7.750	15.750	11.750
      3	13.250	13.000	7.750	13.750
      4	13.250	14.500	15.750	10.500
      Delta	7.000	6.750	8.500	3.250
      Rank	2	3	1	4

      Fog. 4. Main Effects plot for Means

   2. ANALYSIS OF VARIANCE

   ANOVA is a statistical method which is used to determine the interaction of individual for all the control factors in the test design. ANOVA is performed by using statistical software MINITAB 14 to determine the significant process parameter. It helps in predicting the best combination of process parameters for optimal performance characteristics.[4] In this study, ANOVA was used to analyze the effects of grit blasting distance, grit blasting time, grit blasting angle and grit blasting pressure on alpha case removal and surface roughness. This analysis was carried out a 5% significance level and a 95% confidence level. The

   significance of control factors in ANOVA is determined by comparing the F value of each control factor.

   The last column of the Table 6 shows the percentage value of each parameter contribution which indicates the degree of influence on the process performance. According to Table 6, the percent contributions of the A, B, C and D factors on the surface roughness were found to be 25.23%, 18.22%, 49.08% and 5.08% respectively. Thus, the most important factor affecting the parameter on alpha case removal was blasting time (Factor C, 49.08%).

   Table 6 Results of ANOVA for alpha case depth

   Process param eter	Degree of free Dom DOF	Sum of squares (SS)	Mean square (MS)	F ratio	Contribution Rate (%)
   ACD
   A	3	140.25	46.750	10.58	25.23
   B	3	101.25	33.750	7.64	18.22
   C	3	272.75	90.917	20.58	49.08
   D	3	28.25	9.417	2.13	5.08
   ERROR	3	13.25	4.417	–	2.39
   TOTAL	15	555.75	–	–	100

4. CONCLUSION

Grit Blast cleaning with abrasive media removes old coatings, rust, and other unwanted material from a surface, and creates an anchor pattern to allow new coatings to adhere better. Manufacturers who turn to grit blast cleaning as an environmentally responsible alternative to chemical stripping processes often realize substantial cost savings as well. Experimental work of removal of alpha case using grit blasting parameters based on Taguchi analysis has shown following important findings.

Taguchis robust orthogonal array design method is suitable to analyze the alpha case depth problem. The parameter design of the Taguchi method provides a simple, systematic, and efficient methodology for the optimization of the cutting parameters. Further S/N ratio analysis for alpha case depth predicts the optimum parameter combination for grit blasting parameters as level 3 for nozzle distance, level 1 of blasting angle, blasting pressure at level 4 and for blasting pressure at level 2 give maximum value of S/N ratio. Thus, ANOVA for

data means of grit blasting with L16 DOE shows that alpha case depth is most significantly affected by the blasting time is the most affecting factor on the alpha case depth with 49.08% followed by nozzle distance, blasting angle and blasting pressure with 25.23%, 18.22% and 5.08%contribution respectively.

ACKNOWLEDGMENT

We thank thanks to Production Engineering Department of VJTI, Mumbai for financial support for this project work and giving us the opportunity to conduct the project in industrial environment. Also, we thank to Mr. S, N. Gawali, Senior Manager Aerospace Department of Bharat Forge Ltd. Pune for giving this opportunity to work in the company and providing me the necessary support.

REFERENCES

1. B. Sefer, Oxidation and AlphaCase Phenomena in Titanium Alloys used in Aerospace Industry: Ti6Al2Sn4Zr2Mo and Ti6Al4V. 2014.

2. B. Sefer, R. Gaddam, J. Josep, A. Mateo, M. Antti, and R. Pederson, Chemical milling effect on the low cycle fatigue properties of cast Ti

   6Al 2Sn 4Zr 2Mo alloy, vol. 92, pp. 193202, 2016.

3. T. Kivak, Optimization of surface roughness and flank wear using the Taguchi method in milling of Hadfield steel with PVD and CVD coated inserts, Meas. J. Int. Meas. Confed., vol. 50, no. 1, pp. 1928, 2014.

4. Sawant, P., & Shinde, D. K. Experimental Study of Process Parameters Influencing Powder Coating of EN8 Steel Shaft used for Manual Squeezer off Toolusing Taguchi Approach, International Journal of Engineering Research & Technology, Vol.9 Issue 11, 2020 page 182-186.

5. Chandak, M., Shinde, P. A. N. D. K., & Raut, D. N. Process Parameter Optimization for Laser 2D Barcode Engraving using Taguchi Design of Experiment Technique, International Journal of Engineering Research & Technology, Vol.9 Issue 11, 2020 page 263-267.

6. L. Singh, R. A. Khan, and M. L. Aggarwal, OPTIMIZATION OF SHOT PEENING PROCESS FOR AISI 304 USING GREY RELATIONAL ANALYSIS WITH TAGUCHI METHOD, vol. 2, no. 5, pp. 4558.

7. N. K. R. C, N. K. V, and S. P. Selvan, Optimization of Machining Parameters and Surface Roughness Measurement using Image Processing, vol. 2, no. 1, pp. 26, 2011.

8. Sawant P. U. (2020) Quality Control Of Gas Control Equipment By Taguchi Method (Master of Technology Theis of VJTI, Mumbai).

9. Chandak M. G. (2017) Process Quality Improvement Using Taguchi DoE Method (Master of Technology Theis of VJTI, Mumbai).