International Conference On Industrial Technology And . - Atlantis Press

International Conference on Industrial Technology and Management Science (ITMS 2015)Experimental Study of Laser Assisted Drilling and Parameters AnalysisYingpin WANG*, Gong ZHANG, Lei ZHENG, Yunpeng REN, Olaf Eichstaedt,Xianshuai CHENPrecision Engineering Research Center, Guangzhou Institute of Advanced Technology, Chinese Academy ofSciences, Guangzhou 511458, ChinaABSTRACT: Drilling holes in the key parts of automotive transmissions (e.g. the crank shaft) can be difficultand time consuming. For this reason, laser assisted drilling is proposed to increase processing speed andreduce wear of tools. In this paper, an experimental study is used to investigate optimum processingparameters of laser assisted drilling in different materials relevant for the automotive industry, such as 45steel , 40Cr steel , QT600 steel and stainless steel 430L. The experimental results show that laser assisteddrilling offers process improvements and are provided with a high application value.KEYWORD: Laser assisted drilling; Experimental study; Automotive industry; Power train componentsburnishing experiments with MP35N and AISI 4140,to evaluate the effect of laser power on the polishingprocess. His experiments show that LAB canproduce a much better surface finish, higher surfacehardness then conventional methods and also offersreduced wear on the tools.LEE C.M. [7-9] applyingFEA method to predict the temperature distributionof inclined laser preheating assisted machining andconducted one-axis manipulator with a CNCmachining center. Budong Yang [10] of KansasState University built a laser assisted milling system(LAM) to study the machinability of Si3N4 ceramic.University of Aachen’s Fraunhofer Institute forLaser Technology (ILT) have done a lot ofresearches on laser assisted machining and designedsome LAM equipments[11]. In China, many scholarshave engaged in research about LAM, such as WangHuiyi [12] who uses finite element analysis (FEA) topredict the temperature field of 45 steel during laserassisted milling. Research of Wu Jian [13] focuseson hardening and phase transformation in laserassisted machining, and analyses the influence ofseveral parameters. YAN Cuo [14] established aquasi-steady state heat conduction model for laserassisted machining of hot-sintered Al2O3 ceramicsusing the finite difference method (FDM) tocalculate the temperature distribution in the workpiece.However, not much research are focused on laserassisted drilling (LAD). Only Tien-Chien Jen[15] ofUniversity of Wisconsin-Madison did apply annularlaser spot to improve drilling performance. He alsoused finite element analysis (FEA) to simulate the1 INTRODUCTIONThe key parts of automobile, such as gear shaft,crank shaft, balance shaft etc., usually employ forgedwork-piece or hardened materials, and as aconsequence the high surface hardness makestraditional drilling processes time consuming anddifficult, e.g. the temperature can increase quicklyand the wear of the tools is considerable [1]. This isespecially true for drilling hole which are notperpendicular to the parts surface. When thin toolsare required, it will be difficult to drill at theintended location and the tool may easily break. Toovercome these problems, laser assisted drilling hasbeen proposed. Laser assisted drilling belongs to thegroup of laser assisted machining, which means alaser is used to locally heat the work piece. In thecase of laser assisted drilling, a small area is heatedunder the tip of the drill, the increased temperaturewill soften the work-piece, and reduce cuttingresistance, thus achieving higher material-removalrates, and offering to precisely control the machinedgeometry and increase tool life, thereby significantlyreducing cycle time for both operator and machine.Recently, innovations in laser assisted machininghave been made in laser assisted turning and laserassisted milling. Shin Y.C.[2-5] of PurdueUniversity built a 3D finite element analysis (FEA)model of laser assisted machining, investigated laserand cutting parameters and their influence on workpiece temperature, cutting force and wear of toolswhile turning Si3N4 ceramics. Tian Y.G. [6] appliedlaser assisted burnishing (LAB) instead conventional 2015. The authors - Published by Atlantis Press145

temperature field during laser assisted machining. Inthis paper, we describe a experimental platform toinvestigate LAD, study the parameters which areimportant to laser assisted drilling, and obtainoptimum parameters for different materials toillustrate the effect of laser assisted drilling.I 2r 2 2Pexp 2 2 rb rb (4)Where, P is the power of laser, rb is the radius oflaser spot, r is distance of the spot center to the goalpoint.It can be seen From Fig. 1 that, the laser lightincidence angle is not 0 , so the light beam reflect onthe work-piece surface is elliptical. Its long radius isrb/cosθ and short radius is rb, thus the power densitydistribution I is:2 THEORYLaser assisted drilling is an advance manufacturetechnology, it applies laser to heat and soften thework local. By doing this, the precision andefficiency can be both improved [14]. The workingprinciple shows in Fig.1. n is rev of drilling tool, θ isthe angle of laser light with tool’s center line.I 2r 2 cos 2 Pcos exp 2 rbrb2 (5)In laser assisted drilling experiment, the surfacelayer metal can be heated up and softened rapidlywhich is beneficial to drilling. From above formula,it can be seen that the less incidence angle θ is, thebigger power density I will be.3 EXPERIMENT SETUPFig.2 shows an overview of the experimental setup.The main components of the setup are an ABB sixaxis robot IBR2400-16, a SPI 200W optical fiberlaser, HASS laser head, a bench-type drillingmachine, and an infrared thermo-sensor. Workpieces are plates and tubes of 45# steel, 40Cr,QT600, and stainless steel.430L respectively, Platedimensions are 100 50 20mm, tube dimensions areØ40 5 200mm. To establish similar initialconditions, the work-pieces are polished, to removemicro-cracks at the surface, oxide layers, andscratches. The surface is then cleaned with alcohol toremove oil before the experiment. A 3mm (hardalloy YG3X) drill is used as drilling tool, the angleof incidence for the laser beam is 30 .Fig.1 Schematic diagram of laser assisted drilling zoneThe heat transfer equation could be expressed as: T T T T K T K T K T g (T )CP (T ) x x y y z z t(1)Where, K is heat transfer coefficient of material, ρis material density, Cp is material specific heat, g isinternal heat source of material.To be brief, it is assumed that:1. The material heat parameters (as specific heatCp, heat transfer coefficient K) not change withtemperature; (is this right? Generally not)2. All of materials are isotropic;3. Ignore convection and eradiate heat transfer ofthe surface on heating;4. In the whole process, internal heat source g iszero.From above, the Eq.(1) could be simplified as: 2T 2T 2T TK 2 2 2 CP y z t x(2)In heating process, the heat flow density inducedby laser is q.q A*IFig.2 Experiment device of laser assisted drillingThe work-piece is fixed on the drilling machine’swork platform, and a constant axial load is applied tothe drill. The process is evaluated under differentprocess conditions using two characteristics: (1)drilling holes diameter, and (2) drilling time. Duringdrilling the laser power is kept as 200W and drillingmachine rotate speed is 235r/min. The laser beam(3)Where, A is absorb coefficient of work-piecesurface, I is power density of incidence light.Assuming that laser beam is Gaussiandistribution, then the power density distribution I is :146

diameter, laser heating time, loading force, andmaterials are variables.surrounding temperature still low, so it could coolingdown rapidly, it may be quenched, so the work-pieceis harden [16]. Therefore, heating time is importanceto laser assisted drilling.4 RESULTS AND DISCUSSIONS4.1.2 Effects of laser beam diameter on the drillinghole4.1 Effects of processing parameters on the drillingholes diameter4.1.1 Effects of heating time on the drilling holediameterThe drilling tool apex angle is 118 , so we canmeasure the drill hole’s diameter Ød, and thencalculate the drill deep h. The relation is shown inFig.3 At following research, we abide the rule thatthe bigger diameter is, the deeper hole is, and themore efficiency is.Fig.4 shows the change in drilling hole diameterfor laser heating times between 0 and 20 seconds forstainless steel, a laser power of 200W, a beamdiameter of 3mm, and an angle of incidence 30 ,axial load is 18N. The experiment shows that thedrilling hole diameter increases from about 1mm to2mm while increasing heating time.Fig.5 Relationship between hole diameter and laser spotdiameterAs the laser power is constant, the laser beamdiameter determine the power density of the incidentlight and thus temperature distribution over time.Fig.5 represents the results for stainless steel, a laserpower of 200W, a heating time of 10s, a drillingtime of 10s, and an angle of incidence 30 . From thefig.5 shown that while laser beam is 3mm the holediameter is best. While the laser beam is 2mm, thelaser power density is very high and the temperaturehigher than AC1, and temperature gradient is large,so the work-piece maybe oxidizing or quenching;while the laser beam is 4 or 5mm, the laser powerdensity is low, and the temperature is low thantempering temperature.Fig.3 Drilling tool’s geometry dimension4.1.3 Effects of axial load on the drilling timeFig.4 Hole diameter change with laser heating timeWe test the temperature by infrared thermosensor, but the infrared thermo-sensor is test theaverage temperature of a zone, and the laser beam isabide Gaussian distribution, so we can’t test thetemperature accurately, the tested temperature islower than we expect. However, the temperaturevariation trend may have inference value, thetemperature of heating part is raise quickly at thebeginning, and then increase slowly approximately10 degree centigrade per second. As we all known,the work-piece below Ac1, tempering, the workpiece is soften ; whereas higher than Ac1 , and theFig.6 Relationship between drilling time and applied loadThe drilling time means the time of drillingthrough a 5mm thickness tube, Fig.6 shows theobserved drilling time for different axial loads, usingstainless steel tube, dimensions are Ø40 5 200mm,with laser is a laser power of 200W, a spot diameterof 3mm, and 10s heating time. As expected thedrilling time shortens as the axial load is increased.Using a laser spot to soften the material has a bigger147