The Impact of Tube Diameter and Thickness on Laser Tube Bending Process

Transcription

1 The Impact of Tube Diameter and Thickness on Laser Tube Bending Process Khalil Ibraheem Imhan *, 1, 2, B.T.H.T. Baharudin 1, Azmi Zakaria 3, Mohd Idris Shah b. Ismail 1, Nasser Mahdi Hadi Alsabti 2, Ahmad Kamal Ahmad 4 1 Department of Mechanical and Manufacturing Engineering, Faculty of Engineering, Putra Malaysia, UPM Serdang-Selangor Darul Ehsan-MalaysiaUniversity 2 Laser research center, Ministry of science and Technology, Baghdad, Iraq 3 Faculty of Science, University Putra Malaysia, UPM Serdang-Selangor Darul Ehsan-Malaysia, 4 Faculty of Science, Al-Nahrain University, Baghdad, Iraq Abstract theeqar@live.com Laser forming has offered a high promised potential for fabrication, particular laser tube bending because of its important in a different artificial application such as heat exchangers, aerospace, automotive, and aircondition. A high power pulsed Nd-Yag laser JK300HPS of Maximum Average Power Laser 300 (W) emitting at 1064 nm and fiber coupled has been used to irradiate stainless steel 304 (SS304) tubes of diameters (12.7 x 0.6 mm, 12.7 x 0.7 mm, 15.9 x 0.6 mm thickness) and 60 mm in length. In this paper, the effect of tube diameter and thickness have been carried out analytically and validated by experiment. The analytical model utilized in this approach is relatively in the same trend of experiment results and become close in small diameter. The bending angle increases as the diameter and thickness decreasing; the thickness is an effect on the thermal part only, meanwhile the diameter is more effective due to the obvious impact on thermal and mechanical aspects of the process. Keywords: Laser tube bending, bending angle, tube diameter, tube thickness. 1. Introduction Laser forming is a new flexible forming technique without springback and non-contact tools to bend plates, sheets, and tubes. The laser tube bending is distinguished among others laser forming by the complexity forming process due to the geometry conditions. Thus, the thickness and diameter of the tube is guiding the trend of forming process and suggest the effective mechanism. Hence, the tube surface irradiated by a defocused laser beam using buckling mechanism (BM), where the laser beam diameter is much bigger the tube thickness. On other words, the upper tube thickness is thin and can be treated as a thin sheet. After the laser cutoff and cooling stage starts, the upper portion suffers shrinkage and shortening which forced the lower portion of the tube to follow the difference of stresses and bend to the laser forward [1]. Since laser tube bending has basically made possible through the axial thermoplastic shortening at the upper surface of the tube, the tensile deformation at the lower surface is much less than that in mechanical bending. By appropriately modifying process parameters, the wall thinning at the lower surface can be significantly reduced or about avoided. This is one of the main advantages of the laser tube bending process. On another hand, the ovalization in mechanical bending is caused by the external force being made by the bending mold at the inner side 2016(3): eissn

2 as well as the significant tensile stress at the outer side. however, the ovalization in laser bending is smaller than in the mechanical bending because no mold is used and tensile stress at the outer side is greatly reduced [2]. Moreover, tubes with cross-section above 2 inches and thin wall cannot simply bend by mechanical techniques. Laser tube bending is the procedure that can overcome this issue and bend tubes with a 6 inches diameter in light of the fact that there is no outside force utilized [3]. Within this trend, the understanding of the laser tube bending process is focusing on the behavior of the affecting parameters. Thus, formulas were proposed to determine the bending angle based on the thermal plastic deformation and usually validated by experiments. It can be seen that the bending angle is as a result of tube dimension, material properties, laser scanning speed, and laser power [4]. In this paper, an analytical analysis was carried out to assess the tube diameter and thickness impact on laser tube bending and validated experimentally. 2. Analytical model In laser bending of tubes, the proportion between the laser beam diameter and wall thickness of the tube is relatively high, and the angular scanning speed low keeping in mind the end goal to get close homogenous temperature appropriation through the wall thickness through laser heating. In this manner, the temperature rise, ΔT, on the external and internal tube surfaces of the examined area can be considered as an identical. Moreover, as the stream stress in the scanned area is extraordinarily brought down by the temperature rise, and the ambient unheated material extremely compels the expansion, the thermal expansion can be thought to be changed over into compressive plastic distortion totally[5]. Consequently, the heating produces plastic compressive strain, ε hp, can be composed as ε hp =-αδt where α is the thermal expansion coefficient. Figure 1 The Simplified model for laser tube bending As said some time recently, amid the cooling the scanned material suffers of shrinkable as a result of temperature diminishing. And this shrinkage still limited by the unheated material. So the unheated material exerts tensile force, F, to the heated material and the heated material exerts force to unheated material inversely, as shown in Fig. 2. If this force is high enough, the tube can be bent. Assuming the laser scanning region is only the top half of the tube circumference, the average strain of the scanning upper portion of the tube in the axial direction at the centroid O s can be written as εs =- α ΔT + F/SE (1) For unscanned area is ε us =- - F/SE (2) 2016(3): eissn

3 Where S is the area of half tube section, E the Young s modulus of the specimen. S = πdt/2 (3) The equation that can determine the total bending angle is θ = (π l/4d)[ Tα-2( 2-1) σ y /E] (4) Where σy is the yield stress, the bending process is a thermo-mechanical process and the above equation shows the impact of the tube diameter D in the mechanical part, such the flow stress as well as the effective moments. T is represented to the thermal part effect and can be clarified as T= 2Pηv/ωDltρc (5) Where P is the laser power, η the absorption coefficient of the laser, v the ratio of the heating power to input power, w the angular scanning speed of the laser beam, l the laser beam diameter, ρ the material density and c the material specific heat. Substitute (5) in (4) can get θ = (π l/2d)[( Pηυα/ωDltρc)-( 2-1) σy/e] (6) Equation (6) shows the effect of the tube diameter D and the thickness t in the thermal part of the laser tube bending. 3. Experiment setup A high power pulsed Nd-Yag laser JK300HPS of Maximum Average Power Laser 300 (W) emitting at 1064 nm and fiber coupled has been used to irradiate stainless steel 304 (SS304) tubes of diameter (12.7 x 0.6 mm, 12.7 x 0.7 mm, 15.9 x 0.6 mm thickness) and 60 mm in length. Moreover, computerized RSA Series Motorized Rotation Stage with its controller (from Zolix Company) is used for holds and rotates the tube as illustrated in Fig. 1. Hence, the tube is irradiated with different average laser power range is 200 W of the laser beam diameter 7.5 mm; the angular scanning speed is 30 deg/sec and rotated angle 180. The deviation of the tube around the x-axis is measured by dial gauge to determine the bending angle θ. Furthermore, the following specification of the SS404 has used, the yield stress of 205 MPa, density 7930 kg/m 3, Young s modulus of 193 GPa, the coefficient of thermal expansion of 17.5x10-6 /K, the specific heat of 500 J/Kg.K, the absorption coefficient η supposed to be 0.6 [6]. On the other hand, the ratio of heating power to input power υ depends on many conditions such as the heat losses due to convection and radiation which is a function of the material, scanning speed and geometry specification. In this study υ is set 0.8. Extreme care is paid to avoid surface melting of the SS 304 during the bending processes. 2016(3): eissn

4 Bendinn angle deg. Buletin Optik eissn no: Figure 2 Experiment setup 4. Results and discussion The relationship between the tube diameter and the bending angle is illustrated in Fig. 3 for both instances of analytical and experiment investigation. The analytical and the experimental results demonstrate the same pattern consequently the bending angle decreasing as the tube diameter increases Diameter mm analytical experimental Figure 3 The relationship between the tube diameter and the bending angle analytically and experimentally for the SS304 when the average laser power is 200 W, w = 30 de. /sec and l = 7.5mm 2016(3): eissn

5 bending angle deg. Buletin Optik eissn no: As it realized that the laser tube bending is utilized and dynamic to bend large tube diameters, hence identifying with the above diagram the laser power ought to be increased multi times. The experimental results become closer to the analytical results when the tube diameter tend to be smaller. The coefficient of absorption is increased with the temperature increases of the specimen therefore the amount of energy penetrated inside the material will rise the thermal stresses [7]. Hence, the bending angle reaches to the maximum value when the tube diameter is 12.7 mm and 0.6 mm in thickness for either analytical or experimental results. In addition, the tube thickness is proportional inversely to the bending angle as shown in Fig. 4 and the experiment results in the same trend of analytical results in spite of the shift in a direction between the diagrams when the thickness is 0.7 mm. The increasing of tube thickness prompts to raise the material stiffness, hence the laser energy have to increase to achieve the thermal stresses [8] Analytical Experimental Thickness (mm) Figure 4 The relationship between tube thickness and bending angle analytically and experimentally for the SS304 when average laser power is 200 W, w = 30 deg. /sec and l = 5 mm 5. Conclusions The investigations were carried out to analysis the impact of tube diameter and thickness on laser tube bending process. The analytical results have been verified experimentally and it was showing the same trend. The brief notes of the conclusions can be listed as below: 1- The smaller diameter and thickness of tube; the larger bending angle. 2- An analytical and experiment results are in the same trend for both diameter and thickness of the tubes. 3- The difference between the analytical and experimental results becomes smaller when the diameter and thickness are reduced. 4- The impact of the tube thickness is evident in the thermal part of the process. 5- The impact of tube diameter is clear on thermal and mechanical parts hence the effect of the tube is more effectively. 2016(3): eissn

6 6. References [1] M. H. Gollo, S. Mahdavian, and H. M. Naeini. Statistical analysis of parameter effects on bending angle in laser forming process by pulsed Nd: YAG laser. Optics & Laser Technology, 2011(43), pp , [2] W. Li and Y. L. Yao. Laser bending of tubes: mechanism, analysis, and prediction. Journal of manufacturing science and engineering, 2001(123), pp , [3] W. Zhang, M. Jones, M. Graham, B. Farrell, M. Azer, J. Zhang, et al. Large diameter and thin wall laser tube bending. 24th International Congress on Applications of Lasers and Electro-Optics, ICALEO, 2005, pp [4] N. Hao. On the process parameter of laser tube bending. Mechanic Automation and Control Engineering (MACE), 2010 International Conference on, 2010, pp [5] N. Hao and L. Li. An analytical model for laser tube bending. Applied surface science,2003(208), pp , [6] J. R. Davis. Stainless steels. ASM international, [7] H. Pantsar and V. Kujanpää. Effect of oxide layer growth on diode laser beam transformation hardening of steels. Surface and Coatings Technology, 2006(200), pp ,. [8] E. Kannatey-Asibu Jr. Principles of laser materials processing vol. 4: John Wiley & Sons, (3): eissn