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The Second Engineering Conference for Graduate Research Middle Technical University - Electrical Engineering Technical College Baghdad – Iraq

Effect of Graphite & TiO2 as a Lubricant additive in Single Point Incremental Forming on Titanium G2 Sheets. Islam N. AbdulHasan 1, Nasri S. M. Namer 2 & Sami Ali Na’ama 3 1

MSc Student, Department of Dies&tools Engineering, Engineering Technical College, Middle Technical University, Baghdad, Iraq, Email: [email protected] 2 Professor, Department of Dies&tools Engineering, Engineering Technical College, Middle Technical University, Baghdad, Iraq, Email: [email protected] 3 Assist. Prof, Department of Dies&tools Engineering, Engineering Technical College, Middle Technical University, Baghdad, Iraq, Email: [email protected]

Abstract: This research study investigates the tribological behavior of (Graphite and Titanium dioxide (Ti ) Microparticles as particulate additives in two mineral based (HD50, 144.Mg) oils in Single point incremental forming (SPIF) on final average surface roughness, thickness distribution and average surface hardness at different weight fractions. Using different forming tool tip diameters (8,10,12,14) mm, feed rate (100,200,400,600,800,1000) mm/mim and spindle speed (200,400,640,800,1200) r.p.m to form pure Titanium sheets with thickness (0.6) mm.The optimum conditions were obtained from primary tests its (Tool Tip Diameter 14 mm, Spindle Speed 640 r.p.m, feed Rate 100 mm/min),then All tests were performed with optimum conditions for forming Titanium sheets by the (SPIF) forming. The results show that the final average surface roughness, thickness distribution and surface hardness, were improved after adding the (Graphite & Titanium dioxide (Ti )) in Two mineral based oils, especially in the range (2-4) wt. %. It was found the average surface roughness improvements due to adding particles of (Graphite and Titanium dioxide) to lubricant type (HD50) are (36% and 70%) and lubricant type (144.mg) are (37% and 48%) respectively. In addition, it was also found that the thickness distribution as a function of (distance) can be fitted using Weibull model at fully correlation coefficient 99.9 % and approximately zero standard deviation for forming Titanium sheets. Also, the experimental results of thickness distribution are closed to the theoretical results obtained from the mathematical sine law used to finding the thickness distribution during the Single Point Incremental Forming.

Keywords: - Incremental Sheet Forming, Additive Lubricant, Titanium, Dieless Forming.

1. INTRODUCTION Single Point Incremental Forming (SPIF), likewise, is recognized as a dieless forming which is a promising candidate as an alternative sheet metal forming process. In this process, a simple shaped tool moves along the sheet surface and imposes plastic deformation locally on the sheet according to the desired shape based on layered manufacturing principles, where the model is divided into horizontal slices [1]. It enables three-dimensional shaping without the usage of dedicated dies and even asymmetrical parts can be easily produced [2]. Sheet metal forming is one of the most used manufacturing processes in different sectors of industry. Besides the high economic and technical requirements of metal-forming products, the manufacturers are challenged by increasing globalization, growing competition, shorter product life cycles and the demand for lower prices [3]. The forming of commercially pure Titanium sheet by Incremental Forming was studied by Hussain et al., (2008) [4].They investigated the effects of lubricants on some forming parameters; vertical step (pitch), feed rate and tool tip diameters. The forming process parameters were investigated in present of three lubricants (oil, grease and inorganic oil) and 98.5% pure MoS2 particles mixed with grease as a particulate lubricant. The obtained results summarize that the formability decreased as the increasing in pitch and tool diameter, and decreasing in feed rates. The higher the friction, the poorer the surface quality will be obtained, while better surface quality was obtained with particulate lubricant (MoS2 mixed with grease). The effects of the initial sheet thickness and the use of dummy sheets inserted between the tool and sheet metal on the surface quality and formability in SPIF of Aluminum sheets was studied by Alves et al. (2009) [5],.

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All experiments have been carried out using Aluminum AA1050-HIII with three levels of the initial thickness: (1, 1.5 & 2) mm. The material of dummy sheets is deep drawing steel 0.63 mm thick. The surface quality has been investigated through the measurements of the average roughness (R a), and the average roughness of 5 peak-to-valley points (Rz) of the samples on five points. The experimental study reveals that the use of dummy sheets between the tool and the Aluminum sheet allows giving a surface quality better than the conventional SPIF process. It has been also proved that the initial thickness is a variable that influences the surface quality of the parts improving them for small values. The influences of lubricant types on the surface finish in the single point incremental forming was studied by Azevedo et al., (2015) [6] .Moly Slip, Weicon Al. M and Moly Slip HSB were the three types of grease which will be used with different base content and different viscosity properties of two types of oil; Repsol and Total. They formed two types of sheet metal 1mm AA 1050 and (1mm) thickness high strength steel DP780. The results found that all used lubricants reduced the surface roughness for steel sheets, while the roughness was increased in aluminum sheets. The aim of the current work was study the effects of weight fractions for particulate (Titanium dioxide (TiO2) & Graphite) in two lubricants on commercial Titanium sheets G2 by SPI forming into pyramid cup shape that effects on: Inside surface roughness, Thickness distribution, Maximum forming depth, Hardness of the formed surface, and Achieving dimensions' stability for pyramid shape. Sheet deformation that occurred due to tool imposing through a single point incremental forming is limited to the processing zone only and is combination of stretching and shearing. During SPIF mechanism, sheet thinning occurs as a result of this peculiar deformation. Figure (1) was shown the elements of single point incremental forming to form Pure Titanium and the product after (SPIF).

(A)

(B)

Fig. 1. Single Point Incremental Forming Process and elements (A) Before Single Incremental Forming (B) after Single Point Incremental Forming of Titanium sheet G2

2. EXPERIMENTAL WORK: The purpose of the experimental work is to inspect the effects of weight fractions of particulate additives TiO2 and graphite powders in two lubricants on commercial titanium sheets G2 by SPI forming. The SPIF parameters that measured experimentally at constant maximum forming depth are: inside surface roughness, thickness distributions profile along the forming part, and hardness of the forming part.

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The outline of experimental work in form of flowchart is illustrated in Figure (2)

Fig.2. Flow Chart of Experimental Works. The chosen Titanium (Ti –G2) sheets to be formed in this process are Titanium grade2 had 0.6 mm thickness and (200200) mm dimensions. Important mechanical properties and the main elements of these metal sheets are listed in Tables (1) and (2) which were tested at Central Organization for Standardization and Quality Control, Technical institute of Baghdad and Production & Metallurgy Engineering Department at University of Technology .The measurements have been done according to standard Standards (ASTM E 8 M). The original surface roughness of the used metals sheets was approximately equal to (0.46µm) for Titanium.

Table 1: Mechanical properties of Titanium sheets Measurements by Tech. Institute Ultimate Stress Elongation Metal Sheets (MPa) (%) Pure Titanium 340 18% Ti –G2 Standards (ASTM E 8 M) Pure Titanium 345 20% Ti –G2

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Hardness (Hv) 231-334

140-240

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Table 2: The Main Elements of Titanium Sheets

Cu%

Fe%

Mg%

M%

Ni%

Cr%

Z%

Si%

V%

0.198

Not found

0.0036

0.0224

0.0015

Not found

0.225

0.0082

Pure Titanium Ti –G2

Pure Titanium Ti –G2

Metal Sheets

0.0096

Measurements by Q.C (ASTM E 2371-13)

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0.3

Standards (ASTM) -----------

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Pyramid shape was selected to be the formed shape in this process as shown in Figure (3). The dimensions of the CNC milling machine table and its displacement limit the pyramid dimensions to be 80 mm, 32 mm height at 40-pyramid angle of pure titanium grade II.

Fig.3. Formed pyramid for Titanium Sheets by SPIF Process

The Forming Tool was carbon steel with 300-Hv hardness, 125mm total length. Different tip diameter 8, 10, 12, and 14mm were used in this research work as a main variable parameter. Figure (4) represents the Forming Tools were used.

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Fig.4. Four Tools Used in SPIF Process Experiments were conducted to study the effect of vertical depth on the formability of Titanium sheet materials, which are directly related to the maximum forming angle up to these materials. All experiments took the horizontal step ( fx ) for (Ti-G2) equal to 0.25, 14 mm the diameter of forming tool, feed rate 100 mm /min , and spindle speed 640 rpm and best lubricants (oil-1 HD50) .

Table 3: Explaining the Experiments on Ti –G2 Expt. No.

Incremental depth (fz) (mm)

Forming Angle(Φ)

Max. depth (mm)

Notes

1

0.3

51˚

6.5

Fracture

2

0.25

45˚

12

Fracture

3

0.1

21˚

16

No Fracture

4

0.2

40˚

32

No Fracture

0.125

30˚

20

No Fracture

5

The graphite (C) and Titanium dioxide (TiO2) are two different powders used as lubricant additives have particulate size (