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Laser transmission welding of PMMA using IR semiconductor laser complemented by the Taguchi method and grey relational analysis
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Laser transmission welding of PMMA using IR semiconductor laser complemented by the Taguchi method and grey relational analysis Kadhim A. Hubeatir Laser and Optoelectronics Engineering Department, University of Technology, Baghdad, Iraq
a r t i c l e
i n f o
Article history: Received 8 July 2019 Received in revised form 8 September 2019 Accepted 29 September 2019 Available online xxxx Keywords: Semiconductor laser Laser transmission welding Polymer Taguchi method Grey relational analysis
a b s t r a c t Laser transmission welding involves localized heating and non-contact techniques at the interface of two polymer pieces to be joined. The welding quality is very sensitive to speed welding, thickness and welding line width and depth. This work presents the laser transmission welding of Poly(Methyl Meta acrylate) PMMA polymer transparent and oblique slabs. A semiconductor laser with 808 nm wavelength, 2 W output power and a 2 mm beam diameter was used. Three different transparent slabs with dimensions 40 60 mm and thickness (2.6, 3.7, 4.3 mm) were fixed tightly onto oblique slab (dark color). Three different selected speeds (44, 113, 150 mm/min) of the welding process were applied to the prepared samples. Results indicate the welding line width and depth were inversely proportional to the welding speed while the transparent slab thickness have little effect. Nine experiments were performed for the three different thickness at different speeds. Taguchi method and grey relational analysis were used to determine the optimum values for welding speed, width, depth and thickness during these nine experiments. The results exhibit good agreement with those of the Taguchi method and grey relational analysis. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Materials Engineering & Science.
1. Introduction Laser transmission welding (LTW) technology has attracted considerable interest in recent years. It is typically used to join similar thermoplastic materials at high speed and precision without the use of adhesives. A moving laser source penetrates the upper transparent material and then absorbed by the oblique surface of the lower material. Therefore, the entire or a considerable proportion of the laser beam’s thermal energy is absorbed by the opaque material thereby producing the required heat at the interface between the two materials [1]. Bappa Acherjee, Arunanshu S. Kumar [2] studied (LTW) of polycarbonate to ABS, the effect of laser power, welding speed, stand off distance and clamp pressure on weld strength and track width is investigated. The weld strength is significantly depend on these above factors. Xiao Wang et al. [3] studied laser transmission spot welding with poly(methyl methacrylate) (PMMA) by using the pulsed Nd: YAG laser. The influence of the peak voltage, defocusing distance and welding type, on welding quality have been investigated. L.
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S. Mayboudi et al. [4] examined the thermal modeling aspects of LTW of thermoplastics for joining plastic parts. Lab joint geometry was modelled for semi crystalline (polyamide-PA6) and amorphous (polycarbonate PC) materials. Experimental and theoretical studies have been conducted to estimate the optical properties of materials, such as the absorption coefficient of laser, the absorbing part and light scattering by the laser transmitting part. Annamaria Visco and Cristina Scolaro [5] used a diode laser source with awavelength of 970 nm (Lambda Scientific Systems) and small amounts of carbon nano particles. A morphological study of the welded area was performed. The laser energy produced a thermal effect on the heat-affected zone. Thereby smoothing the surface at a depth of approximately 1.5 mm. Moreover, surface roughness decreased and the permeability of the joint to biological fluids was enhanced. Adhish Majumdar et al. [6] presented thermal analysis of the LTW process for thermoplastics using the finite element method in addition to heat transfer equations, An original approach was used to calculate phase transformation phenomena, such as melting, evaporation or decompostion and solidification, of a polymer. MD shakibul, Mohd. Anecs Siddiqui [7] investigated welding processes, such as hot gas welding, fraction welding and hot plate
https://doi.org/10.1016/j.matpr.2019.09.167 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Materials Engineering & Science.
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welding. Various important polyvinyl chloride welding parameters, such as temperature, speed and equipment requirements, were discussed. important developments in the field of plastic welding to assist in the future improvement of plastic welding, Plastic manufacturing parts are regularly used in many industries. Parts made of polymeric materials and composites can satisfy today’s highly demanding requirements. Plastics exhibit good corrosion resistance, excellent strength-to-weight ratio and the ability to achieve good finish. Plastics can be categorised into thermosets and thermoplastics. Amongst the two, only thermoplastics are weldable. Annalisa Volpe et al. [8] succeeded in microwelding transparent PMMA layers using femtosecond laser pulses at 1030 nm in the megahertz region. They intended to utilise localized heat accumulation to weld layers without preprocessing the sample and any intermediate absorbing media by focusing femtosecond (fs) laser pulses on the interface. The fs laser welding of PMMA samples was successfully demonstrated, and the samples were tested via leakage tests for application to the direct laser assembly of microfluidic devices. The laser welding of transparent materials with micrometre precision is attracting the interest in various applications, particularly in the assembly of biomedical devices. The effect of laser beam on plastic adhesion was investigated to determine the optimum condition for plastic adhesion. CO2 and Nd:YAG lasers have been used experimentally by Sung Jin Park et al. [9]. Their experimental results showed that Nd:YAG laser is the most suitable for plastic adhesion. Three adhesion parameters, namely input power, working time of the laser beam and pulse per second, were systematically adjusted for suitable adhesion. The relationships between adhesion surface of the laser beam and the three aforementioned parameters have been determined. Bappa Acharjee et al. [10] reviewed an experimental investigation of the diode laser transmission welding of dissimilar thermoplastics namely PMMA and Bacrylonitrile butadiene styrene (ABS). The effects of laser welding parameters, such as laser power, welding speed, standoff distance and clamp pressure, on weld strength and weld width were investigated using response surface methodology. A mathematical model established the correlation between the process parameters and the responses. The adequacy of the developed models was tested using the sequential F-test, lack-offit test and ANOVA. All three techniques were used to find the optimum solutions accordance with the desired optimization criteria. In the this study, a semiconductor laser with a wavelength of 808 nm, an output power of 2 W and a laser spot size of 2 mm is used in the LTW of a transparent PMMA piece with different thicknesses and an oblique PMMA piece. The semiconductor laser is considerd an appropriate choice for performing PMMA welding compared with other lasers. The effects of welding speed on weld width and depth at different thicknesses are determined to be inversely proportional. The Taguchi method was used to the find solutions in accordance with the desired optimization criteria. In addition, grey relational analysis is implemented to identify the region in the graphics where the optimal condition is found. 1.1. Laser transmission welding (LTW) background Since the 1980s, LTW of plastic parts has played an increasingly role in industrial mass production due to advancements in processes and machine technologies. Therefore, LTW is an established process for thermoplastics [11]. In LTW the heating of two plastic parts and the joining operation of the two parts occur in a single step. Consequently LTW requires joining parts with different optical properties. One part should exhibit high transmittance for laser radiation, whereas the other part should exhibit high absorbance at the wavelength of the laser [11–14].
Laser plastic welding is a method of bonding two or more thermoplastic components. Although, a method for joining thermoplastic is available, laser plastic welding exhibits several apparent advantages, such as higher joining quality, minimal resulting flash or particulates, higher-quality controls and less stress to components; moreover, components can be welded into complex and intricate shapes [15]. Laser transmission welding is a new technology used in industry. It enables the fast and efficient joining of plastics utilising the merits of laser technology [16]. M. Ilie et al. [17] studied the laser beam weldabillity of ABS plastic by combining experimental and theoretical aspects. An optical model was used to determine the attenuated laser beam by the first material in oreder to obtain the laser beam profile at the interface. The authors have used this information as input data for a thermal model based on the first principles of heat transfer and utilises the temperature variation laws of material properties. The evolution of the temperature field within the two components can be estimated. In LTW, a material that is transparent to the laser wavelength lies on top of an absorbent material. The laser beam penetrates through the transparent component with minimal energy loss and melts the surface of the absorbent material. Heat is transferred under such condition to plasticise the adjacent surface of the transparent material [18]. An ideal transparent polymer for LTW have a low laser absorbance to avoid energy loss, a low scattering level to provide a maximum energy flux at the weld interface and a high resistance to thermal degradation. Laser welding of polymers is successfully used in numerous applications, in the automotive, electronics and telecommications industries, medical devices technology, human care and household devices. The advantages of laser as a tool for joining plastics are as follows: - Laser-welded joints can resist high mechanical loads. - Welding can be precisely localised due to the high density of energy within a small spot. - Minimal thermal and mechanical stresses are applied. - Optional online process monitoring is available. - Weld seams with high visual quality are produced. - Particle-free welding is possible. - No surface damage is produced. - Meanwhile, economic advantages include the following: - Faster product development. - Higher flexibility. - Shorter cycle times and simple product solutions. However, the complexity and poorly understood interaction between laser and transparent materials are amongst the major limitions of this technique [13,19].
2. Materials and methods Three samples of PMMA with different thicknesses for the transparent and absorbent layers with high purity bought from scientific burea having the following specifications: thermal conductivity(0.19–0.24 w/m.k), melting point (130 °C), density 1.15–1.19 g/cm3 , optical absorption 7–20% from UV-Mid IR and refractive index (1.49). Samples were prepared with dimensions of 40*60 mm and thicknesses of 2.6, 3.7 and 4.3 mm using a diamond saw. The two pieces to be welded together were placed in the required configuration. They were fixed using a clamping system to hold them in place during welding and ensure good conduction of heat between the parts. Consequently, uniform adherence was achieved between two pieces over the irradiated area. The first piece was made of PMMA material that was transparent to a
Please cite this article as: K. A. Hubeatir, Laser transmission welding of PMMA using IR semiconductor laser complemented by the Taguchi method and grey relational analysis, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.167
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semiconductor laser at 808 nm and 2 Watt output power. By contrast, the second piece was absorbent. The incident laser radiation on the top surface was partialy reflected and partialy absorbed in transparent part. The remaining energy was transmitted down to the absorbent part. The laser radiation absorbed in the absorbent part produced heat. This heat was conducted to the transparent part, and a welding line was formed at the interface between them, where temperature exceeded the melting temperature of PMMA. A controllable one dimensions (1D) stage was designed using a programmable Arduino microcontroller connected with a blank CDROM driver. The speed of the movable stage could be varied using software with PC or manually using variable resistance. the experiment setup includes the semiconductor laser (808 nm, 2 W o/p) with a beam diameter of 2 mm. The laser was fixed with a perpendicular holder onto a movable stage. Three different speeds, 44, 113 and 150 mm/min, were applied to each sample with varying thicknesses. Good welding was achieved between the two pieces in all samples. The welding width and depth were measured with an optical microscope model Olympus BX51M-Japan and an optical scanner. the Arduino microcontroller with driver designed to control the movement of the one-axis stage with desirable speed. Nine experiments were performed for three different thicknesses of transparent PMMA at different selected speeds (44, 113 and 150 mm/min). The Taguchi method and grey relational analysis were used to determine the optimum values for welding speed, width, depth and thickness at this laser power and wavelength during the nine experiments. Different process parameters considerably influenced the quality of the weld formed. The most important parameters used were laser power, welding speed, beam diameter or spot size, transparent piece thickness and laser wavelength. the transmittance and absorbance of the material used (PMMA) have been measured using UV–Visible spectrophotometer (modelMetertech SP 8001). Particularly the laser absorption characteristics of the bottom pieces and the high transmittance of the transparent the top pieces measured at the operating wavelength. Therefore, to be joined successfully two polymers from the same plastic family (i.e. similar resin properties and melting temperature) is used. Otherwise, one part may melt or burn, whereas the other is unaffected.
The results of the calculations are presented in Table 1: 4. Multi- objective optimization using grey relational analysis In grey relational analysis, experimental data that measure the features of the quality characteristics of a product are firstly normalized from zero to one. This process is known as grey relational generation. Subsequently, grey relational coefficients are calculated based on normalised experimental data to represent the correlation between the desired and actual experimental data. Then, the overall grey relational grade is determined by averaging the grey relational coefficient that corresponds to selected responses. The overall performance characteristic of the multiple- response process depends on the calculated grey relational grade. This approach converts a multiple-response optimization problem into a single-response optimization situation, where the objective function is the overall grey relational grade. The optimal parametric combination is then evaluated by maximizing the overall grey relational grade [25]. 4.1. Normalization of the experimental response results Data preprocessing involves transferring the original sequence to a comparable sequence. For this purpose, the experimental results are normalized within the range from zero to one. Normalization can be implemented using three different approaches. If the expectancy is the smaller the original sequence should be normalized as follow:
vi ðkÞ ¼
The experiment design used was based on the Taguchi method using an L9 orthogonal array. The effects of two parameters, thickness and welding speed, on the welding process were considered in this study. For each parameter, three levels were selected to perform the nine experiments. The responses of the considered were welding width and depth. The signal-to-noise ratio (S/N) of welding depth was considered ‘‘the smaller, the better” and calculated using the following equation:
"
S 1 ¼ 10log10 N n
n X
# y2i
ð1Þ
i¼1
Similarly, the S/N of welding width was considered ‘‘the larger, the better” and calculated using the following equation:
" # n S 1X 1 ¼ 10log10 N n i¼1 y2i
ð2Þ
where n is the number of experiments, and y is the experiment value [20–24].
ð3Þ
where vi is the value after grey relational generation (data preprocessing), max v0i is the largest value of v0i (k), and min v0i is the smallest value of v0i (k) [25]. 4.2. Grey relational coefficient and grey relational grade From the pre-processed data, the grey relational coefficient is calculated to express the relationship between the ideal and actual normalized experimental results. The grey relational coefficient can be expressed as follows:
ni ðkÞ ¼ 3. Taguchi optimization methodology
maxv0i ðkÞ v0i ðkÞ maxv0i ðkÞ minv0i ðkÞ
Dmin þ f:Dmax D0i ðkÞ þ f:Dmax
ð4Þ
where ,ni (k) is a grey relational coefficient, and D0i (k) is the deviation sequence of the reference sequence v0*(k) and Dmax ¼ highest v alue of D0i ðkÞ, Dmin ¼ smallest v alue of D0i ðkÞ, f is the distinguishing or identification coefficient: fe(0, 1), and 0.5 is generally used. After obtaining the grey relational coefficient, we typically regard the average of the grey relational coefficient as the grey relational grade. The grey relational grade is defined as follows:
ci ¼
g 1X
g
ni ðkÞ
ð5Þ
k¼1
where, ci is the Grey relational grade for a particular experiment number, k is the number of responses and ni(k) is the Grey relational coefficient for a particular experiment number and number of responses [24–26]. 5. Results and discussion The effects of welding speed on weld width and depth were determined using a semiconductor laser with a wavelength of
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Table 1 L9 Taguchi design of experiment. No. Exp.
1
2
3
4
5
6
7
8
9
Thickness mm Welding speed mm/min
2.6 44
2.6 113
2.6 150
3.7 44
3.7 113
3.7 150
4.3 44
4.3 113
4.3 150
808 nm and an output power of 2 W. The results were classified into three groups according to thickness. Group 1 includes the samples with a thickness of 2.6 mm applied at three different speeds 44, 113 and 150 mm/min on the surface of the transparent PMMA. The welding width measured in this experiment is shown in Fig. 1, where the sample number 1, 2 and 3 refer to applied three welding speeds. This figure shows that welding width is inversely proportional to the welding speed Moreover, welding depth exerts the same effect (i.e. inversely proportional)., as shown in Fig. 2 Group 2 includes samples with a thickness of 3.7 mm, when the same incident laser power (2 W) and the three different welding speeds mentioned earlier (numbered 4, 5 and 6) were applied. The measured welding width and depth are shown in Figs. 3 and 4, respectively. Finally, Group 3 includes samples with a thickness of 4.3 mm when the same three different welding speeds are applied. Fig. 5 shows the weld width for samples 7, 8 and 9. The weld depth for this experiment is shown in Fig. 6. The weld diameter: depth ratio considerably affected joint quality, such that welding performance was improved. The relation between welding speed and weld width for all three samples at different thicknesses is shown in Fig. 7. This figure indicates that weld width is inversely proportional to welding speed for all three samples. Therefore, weld width, as a function of the applied welding speed at a constant laser power on the top transparent PMMA pieces, slightly depends on its thickness, the transmittance of the transparent pieces with different thicknesses (2.6, 3.7 and 4.3 mm) at this wavelength change from (86–92%) respectively measured by (UV–Visible) spectrophotometer .The reduction in the transmission percentage as a function of wavelength changed less slightly [26]. Due to laser energy melting a thin layer of plastic in both parts. When welding speed is low, molecular diffusion will have plenty of time to occur with high width and depth to form a solid joint as the melt layer solidifies [2–4]. In LTW, the danger of overheating increases due to the laser transmitting surface of the joint, which limit the thickness of the transparent pieces. The welding width to depth ratio considerably affects the quality of the joint, such that welding performance is improved and weld strength is increased as compared with Wang et al. [3]. This relationship between weld strength and width can be achieved using different parameters, such as laser power and speed. Therefore, weld width is more efficient on the tensile strength of the samples, which increases welding quality as compared with Azhikannickal et al. [13]. Table 2 summarises the results of all the experiments for different thicknesses and welding speeds,
thereby providing the values of weld width and depth for all the cases at the same laser power of 2 W and the same wavelength with a laser spot diameter of 2 mm. 5.1. First point. Taguchi optimization The results of the calculations are presented in Table 3. - Effects of parameters on weld depth The S/N and mean plot for weld depth with respect to plate thickness and welding speed are presented in Figs. 8 and 9. As shown in these figures, the best value for S/N is occurred at a thickness of (3.7 mm). This thickness is resulted in the best interaction between the laser beam and black plate. In addition, the minimum weld depth, imposed the least plate damage. The figure also shows that the weld depth decreased with increasing welding speed because the interaction time between the laser and plate became shorter. 5.2. Second point. Effects of parameters on weld width The S/N and mean plot for weld width versus plate thickness and welding speed are illustrated in Figs. 10 and 11. As indicated in these figures, the minimum welding width occurred at a thickness of (2.6 mm and 4.3 mm). At a thickness of 2.6 mm, the transmission of the laser beam was high, and thus, the heat applied by the laser beam was rapidly absorbed by the black plate, thereby producing low weld width and high depth. By contrast when the thickness was 4.3 mm, the transmission was less than that at 2.6 mm, such that the interaction between the laser beam and black plate was reduced. Thus this is leading to a smaller weld width. When the thickness was 3.7 mm, weld depth became smaller and weld width was wider compared to those in the other cases.This caused minimal sample damage, and therefore, could be used to achieve high-quality welding. The figures clearly indicate that the weld width decreases with increasing welding speed. On the basis of the Taguchi method, we determine that the best welding was obtained at a thickness of 3.7 mm, as shown in the aforementioned figures. 5.3. Third point. Grey relational analysis The normalized values are listed in Table 4: The grey relational coefficient and grey relational grade results are presented in Table 5:
Fig. 1. group 1 weld width of transparent thickness 2.6 mm with welding speed 44,113,150 mm/min respectively.
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Fig. 2. Welding depth when the transparent thickness 2.6 mm as a function of three different welding speed 44,113,150 mm/min respectively. 5X.
Fig. 3. group 2 weld width of transparent thickness 3.7 mm with welding speed 44,113,150 mm/min respectively.
Fig. 4. Welding depth when the transparent thickness 3.7 mm at welding speed 44,113,150 mm/min respectively . 5X.
Fig. 5. Group 3 weld width of transparent thickness 4.3 mm with welding speed 44,113,150 mm/min respectively.
Fig. 6. Welding depth when the transparent thickness 4.3 mm as a function of three different welding speed 44,113,150 mm/min respectively. 5X.
On the basis of the experimental performance, Table 5 clearly shows that the settings of the process parameters in Experiment 5 achieved the highest grey relational grade. Therefore, the fifth experiment provides the best multiperformance characteristics amongst the nine experiments. This experiment produced minimal sample damage, a small weld depth and short welding time. Although Experiment 6 had a smaller weld depth than Experiment
5. It was not the best experiment because weld width was smaller and weld depth was considerably smaller thereby making the adhesion force extremely weak and weakening the bond between the pieces. The results show that Experiment 5 has larger weld width and good weld depth. A large weld width indicates large amount of melted material between the two pieces, which provides the
Please cite this article as: K. A. Hubeatir, Laser transmission welding of PMMA using IR semiconductor laser complemented by the Taguchi method and grey relational analysis, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.167
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Fig. 7. (a) illustrate the relation between welding width and welding speed for three thicknesses. (b) illustrate the relation between the welding depth and welding speed for three different thicknesses.
Table 2 The results of all experiments for different thickness and welding speed. No. Exp.
L9
1 2 3 4 5 6 7 8 9
Mean value
Thickness mm
Welding speed mm/min
Welding width mm
Welding depth mm
2.6 2.6 2.6 3.7 3.7 3.7 4.3 4.3 4.3
44 113 150 44 113 150 44 113 150
1.1806 1.3033 0.8922 1.3351 1.3164 0.8536 1.1792 1.0649 0.9919
36.5 20 16 24.3 10.2 4.53 38 20 9.2
Table 3 L9 experimental design with signal-to-noise ratio determination of welding depth and width. No. Exp.
1 2 3 4 5 6 7 8 9
L9
Mean value
S/N ratio
Thickness mm
Welding speed mm/min
Welding width mm
Welding depth mm
Welding width mm
Welding depth mm
2.6 2.6 2.6 3.7 3.7 3.7 4.3 4.3 4.3
44 113 150 44 113 150 44 113 150
1.1806 1.3033 0.8922 1.3351 1.3164 0.8536 1.1792 1.0649 0.9919
36.5 20 16 24.3 10.1 4.53 38 20 9.2
0.1442 0.18503 0.068469 0.10743 1.3071 0.72895 0.82265 0.7871 0.683
31.246 29.376 23.213 28.093 27.293 26.523 27.717 27.538 27.107
Fig. 8. the main effect plot of S/N ratio for welding depth. Fig. 9. the main effect plot of means for welding depth.
strongest weld. Meanwhile, weld depth was selected on the basis of the principle ‘‘the smaller, the better” because a large depth causes damage between the two pieces and produces a hollow area between them due to porosity formation, which makes weldment
extremely weak. Thus, a high depth of welding reflects the size and shape of the weld seam and the eventual porosity that may arise due to the heating of the polymer beyond its decomposition
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Table 6 The optimum value of each level, the symbol‘‘*” indicates the optimum parameter level. Process parameter
Thickness Welding speed
Average grey relational grade for each factor level Level 1
Level 2
Level 3
0.41238 0.39663
0.6733* 0.60865
0.53416 0.6145*
temperature, thereby reducing the strength of the welding line [6]. The grey analysis results appear in good agreement with the Taguchi method results. The grey relation provides an explanation for each experiment and identify the best one based on both responses. By contrast Taguchi method merely provides the optimum parameters for each response.
Fig. 10. the main effect plot of S/N ratio for welding width.
- Optimum value for each level The optimum value for a process parameter level can be calculated by taking the average of the grey relational grade for each factor level. The optimum values for the levels are listed in Table 6.
6. Conclusions
Fig. 11. the main effect plot means for welding width.
Table 4 Value of normalization calculation for welding depth and width. No. Exp.
1 2 3 4 5 6 7 8 9
Normalized value Welding width
Welding depth
0.06114 0.0941 0 0.03145 1 0.5332 0.60888 0.58018 0.4961
0.0437 0.5243 0.641 0.399 0.813 1 0 0.5243 0.839
The welding speed is considerably affect both the welding line width and depth in inverse manner. Besides that the welding line strength has been affected by welding width, the increase in weld depth weakens its strength due to the formation of bubbles and porosity. Taguchi method shows that the best strength is occurred at sample thickness 3.7 mm. from the grey relational analysis the optimum process parameters for best welding are determined at welding width (1.3164 mm) and depth (10.2 mm) these results shows a good agreement with the Taguchi method results. The effect of transparent pieces thickness is slightly affect on welding strength due to high transmission ratio at laser wavelength 808 nm.
Acknowledgements The author is particularly grateful to University of Technology, Laser and Optoelectronics Engineering Department, for the financial support and providing the equipment and devices to the present research work.
Table 5 The value of deviation sequence, gray relational coefficient and gray relational grade calculation for welding depth and width. No. Exp.
1 2 3 4 5 6 7 8 9
The deviation sequence
Gray relational coefficient
Welding width
Welding depth
Welding width
Welding depth
0.93886 0.9059 1 0.96855 0 0.4668 0.39112 0.41982 0.5039
0.9563 0.4757 0.359 0.601 0.187 0 1 0.4757 0.161
0.3475 0.3556 0.3333 0.34047 1 0.51717 0.56109 0.54358 0.4980
0.3433 0.5125 0.5821 0.4541 0.7278 1 0.3333 0.5125 0.7564
Gray relational grade
Order
0.3454 0.43405 0.4577 0.3973 0.8639 0.7586 0.44719 0.5280 0.6273
9 7 5 8 1 2 6 4 3
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[14] Jaschke P, Wippo V, Bluemel S, Staehr R, Dittmar H.(Laser Machining of Carbon Fiber-Reinforced Plastic Composites); ‘‘In: ”Advances in laser materials processing: technology, research and applications‘‘ (Jonathan Ls), 2nd edition, CHP 6,p.121-152, United kingdom,Woodhead Publishing 2018. [15] A. Bauernhuber, T. Markovits, J. Takács, Investigating the pulse mode laser joining of overlapped plastic and metal sheets, Phys. Proc. 83 (2016) 1094– 1101. [16] V. Kagan, R. Bray, W. Kuhn, Laser transmission welding of semi-crystalline thermoplastics—Part I: Optical characterization of nylon based plastics, J. Reinforced Plastics and Compos. 21 (12) (2002) 1101–1122. [17] M. Ilie, E. Cicala, D. Grevey, S. Mattei, V. Stoica, Diode laser welding of ABS: Experiments and process modeling, Opt. Laser Technol. 41 (5) (2009) 608–614. [18] M. Aden, Influence of the laser-beam distribution on the seam dimensions for laser-transmission welding: a simulative approach, Lasers Manuf. Mater. Process. 3 (2) (2016) 100–110. [19] J.D. Van de Ven, A.G. Erdman, Bridging gaps in laser transmission welding of thermoplastics, J. Manuf. Sci. Eng. 129 (6) (2007) 1011–1018. [20] S. Singare, S.G. Chen, J.J. Zou, N. Li, Laser transmission welding of thermoplastic: experimental investigation using polycarbonate, in: Advanced Materials Research 2015, pp. 63-69. Trans Tech Publ. [21] S ß . Kasman, I.E. Saklakoglu, Determination of process parameters in the laser micromilling application using Taguchi method: A case study for AISI H13 tool steel, Int. J. Adv. Manuf. Technol. 58 (1–4) (2012) 201–209. [22] A. Freddi, M. Salmon, Introduction to the Taguchi Method. In: Design Principles and Methodologies, Springer, 2019, pp. 159–180. [23] S. Campanelli, G. Casalino, N. Contuzzi, A. Ludovico, Taguchi optimization of the surface finish obtained by laser ablation on selective laser molten steel parts, Proc. CIRP 12 (2013) 462–467. [24] B. Shanmugarajan, R. Shrivastava, P. Sathiya, G. Buvanashekaran, Optimisation of laser welding parameters for welding of P92 material using Taguchi based grey relational analysis, Defence Technol. 12 (4) (2016) 343–350. [25] K. Hubeatir, M. AL-Kafaji, H. Omran, Deep Engraving Process Of PMMA Using CO2 Laser Complemented By Taguchi Method vol. 1 (2018) 012068. [26] N. Kumar, R. Rudrapati, P.K. Pal, Multi-objective optimization in through laser transmission welding of thermoplastics using grey-based Taguchi method, Procedia Mater. Sci. 5 (2014) 2178–2187.
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Laser transmission welding of PMMA using IR semiconductor laser complemented by the Taguchi method and grey relational analysis Kadhim A. Hubeatir Laser and Optoelectronics Engineering Department, University of Technology, Baghdad, Iraq
a r t i c l e
i n f o
Article history: Received 8 July 2019 Received in revised form 8 September 2019 Accepted 29 September 2019 Available online xxxx Keywords: Semiconductor laser Laser transmission welding Polymer Taguchi method Grey relational analysis
a b s t r a c t Laser transmission welding involves localized heating and non-contact techniques at the interface of two polymer pieces to be joined. The welding quality is very sensitive to speed welding, thickness and welding line width and depth. This work presents the laser transmission welding of Poly(Methyl Meta acrylate) PMMA polymer transparent and oblique slabs. A semiconductor laser with 808 nm wavelength, 2 W output power and a 2 mm beam diameter was used. Three different transparent slabs with dimensions 40 60 mm and thickness (2.6, 3.7, 4.3 mm) were fixed tightly onto oblique slab (dark color). Three different selected speeds (44, 113, 150 mm/min) of the welding process were applied to the prepared samples. Results indicate the welding line width and depth were inversely proportional to the welding speed while the transparent slab thickness have little effect. Nine experiments were performed for the three different thickness at different speeds. Taguchi method and grey relational analysis were used to determine the optimum values for welding speed, width, depth and thickness during these nine experiments. The results exhibit good agreement with those of the Taguchi method and grey relational analysis. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Materials Engineering & Science.
1. Introduction Laser transmission welding (LTW) technology has attracted considerable interest in recent years. It is typically used to join similar thermoplastic materials at high speed and precision without the use of adhesives. A moving laser source penetrates the upper transparent material and then absorbed by the oblique surface of the lower material. Therefore, the entire or a considerable proportion of the laser beam’s thermal energy is absorbed by the opaque material thereby producing the required heat at the interface between the two materials [1]. Bappa Acherjee, Arunanshu S. Kumar [2] studied (LTW) of polycarbonate to ABS, the effect of laser power, welding speed, stand off distance and clamp pressure on weld strength and track width is investigated. The weld strength is significantly depend on these above factors. Xiao Wang et al. [3] studied laser transmission spot welding with poly(methyl methacrylate) (PMMA) by using the pulsed Nd: YAG laser. The influence of the peak voltage, defocusing distance and welding type, on welding quality have been investigated. L.
E-mail address: [email protected]
S. Mayboudi et al. [4] examined the thermal modeling aspects of LTW of thermoplastics for joining plastic parts. Lab joint geometry was modelled for semi crystalline (polyamide-PA6) and amorphous (polycarbonate PC) materials. Experimental and theoretical studies have been conducted to estimate the optical properties of materials, such as the absorption coefficient of laser, the absorbing part and light scattering by the laser transmitting part. Annamaria Visco and Cristina Scolaro [5] used a diode laser source with awavelength of 970 nm (Lambda Scientific Systems) and small amounts of carbon nano particles. A morphological study of the welded area was performed. The laser energy produced a thermal effect on the heat-affected zone. Thereby smoothing the surface at a depth of approximately 1.5 mm. Moreover, surface roughness decreased and the permeability of the joint to biological fluids was enhanced. Adhish Majumdar et al. [6] presented thermal analysis of the LTW process for thermoplastics using the finite element method in addition to heat transfer equations, An original approach was used to calculate phase transformation phenomena, such as melting, evaporation or decompostion and solidification, of a polymer. MD shakibul, Mohd. Anecs Siddiqui [7] investigated welding processes, such as hot gas welding, fraction welding and hot plate
https://doi.org/10.1016/j.matpr.2019.09.167 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Materials Engineering & Science.
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welding. Various important polyvinyl chloride welding parameters, such as temperature, speed and equipment requirements, were discussed. important developments in the field of plastic welding to assist in the future improvement of plastic welding, Plastic manufacturing parts are regularly used in many industries. Parts made of polymeric materials and composites can satisfy today’s highly demanding requirements. Plastics exhibit good corrosion resistance, excellent strength-to-weight ratio and the ability to achieve good finish. Plastics can be categorised into thermosets and thermoplastics. Amongst the two, only thermoplastics are weldable. Annalisa Volpe et al. [8] succeeded in microwelding transparent PMMA layers using femtosecond laser pulses at 1030 nm in the megahertz region. They intended to utilise localized heat accumulation to weld layers without preprocessing the sample and any intermediate absorbing media by focusing femtosecond (fs) laser pulses on the interface. The fs laser welding of PMMA samples was successfully demonstrated, and the samples were tested via leakage tests for application to the direct laser assembly of microfluidic devices. The laser welding of transparent materials with micrometre precision is attracting the interest in various applications, particularly in the assembly of biomedical devices. The effect of laser beam on plastic adhesion was investigated to determine the optimum condition for plastic adhesion. CO2 and Nd:YAG lasers have been used experimentally by Sung Jin Park et al. [9]. Their experimental results showed that Nd:YAG laser is the most suitable for plastic adhesion. Three adhesion parameters, namely input power, working time of the laser beam and pulse per second, were systematically adjusted for suitable adhesion. The relationships between adhesion surface of the laser beam and the three aforementioned parameters have been determined. Bappa Acharjee et al. [10] reviewed an experimental investigation of the diode laser transmission welding of dissimilar thermoplastics namely PMMA and Bacrylonitrile butadiene styrene (ABS). The effects of laser welding parameters, such as laser power, welding speed, standoff distance and clamp pressure, on weld strength and weld width were investigated using response surface methodology. A mathematical model established the correlation between the process parameters and the responses. The adequacy of the developed models was tested using the sequential F-test, lack-offit test and ANOVA. All three techniques were used to find the optimum solutions accordance with the desired optimization criteria. In the this study, a semiconductor laser with a wavelength of 808 nm, an output power of 2 W and a laser spot size of 2 mm is used in the LTW of a transparent PMMA piece with different thicknesses and an oblique PMMA piece. The semiconductor laser is considerd an appropriate choice for performing PMMA welding compared with other lasers. The effects of welding speed on weld width and depth at different thicknesses are determined to be inversely proportional. The Taguchi method was used to the find solutions in accordance with the desired optimization criteria. In addition, grey relational analysis is implemented to identify the region in the graphics where the optimal condition is found. 1.1. Laser transmission welding (LTW) background Since the 1980s, LTW of plastic parts has played an increasingly role in industrial mass production due to advancements in processes and machine technologies. Therefore, LTW is an established process for thermoplastics [11]. In LTW the heating of two plastic parts and the joining operation of the two parts occur in a single step. Consequently LTW requires joining parts with different optical properties. One part should exhibit high transmittance for laser radiation, whereas the other part should exhibit high absorbance at the wavelength of the laser [11–14].
Laser plastic welding is a method of bonding two or more thermoplastic components. Although, a method for joining thermoplastic is available, laser plastic welding exhibits several apparent advantages, such as higher joining quality, minimal resulting flash or particulates, higher-quality controls and less stress to components; moreover, components can be welded into complex and intricate shapes [15]. Laser transmission welding is a new technology used in industry. It enables the fast and efficient joining of plastics utilising the merits of laser technology [16]. M. Ilie et al. [17] studied the laser beam weldabillity of ABS plastic by combining experimental and theoretical aspects. An optical model was used to determine the attenuated laser beam by the first material in oreder to obtain the laser beam profile at the interface. The authors have used this information as input data for a thermal model based on the first principles of heat transfer and utilises the temperature variation laws of material properties. The evolution of the temperature field within the two components can be estimated. In LTW, a material that is transparent to the laser wavelength lies on top of an absorbent material. The laser beam penetrates through the transparent component with minimal energy loss and melts the surface of the absorbent material. Heat is transferred under such condition to plasticise the adjacent surface of the transparent material [18]. An ideal transparent polymer for LTW have a low laser absorbance to avoid energy loss, a low scattering level to provide a maximum energy flux at the weld interface and a high resistance to thermal degradation. Laser welding of polymers is successfully used in numerous applications, in the automotive, electronics and telecommications industries, medical devices technology, human care and household devices. The advantages of laser as a tool for joining plastics are as follows: - Laser-welded joints can resist high mechanical loads. - Welding can be precisely localised due to the high density of energy within a small spot. - Minimal thermal and mechanical stresses are applied. - Optional online process monitoring is available. - Weld seams with high visual quality are produced. - Particle-free welding is possible. - No surface damage is produced. - Meanwhile, economic advantages include the following: - Faster product development. - Higher flexibility. - Shorter cycle times and simple product solutions. However, the complexity and poorly understood interaction between laser and transparent materials are amongst the major limitions of this technique [13,19].
2. Materials and methods Three samples of PMMA with different thicknesses for the transparent and absorbent layers with high purity bought from scientific burea having the following specifications: thermal conductivity(0.19–0.24 w/m.k), melting point (130 °C), density 1.15–1.19 g/cm3 , optical absorption 7–20% from UV-Mid IR and refractive index (1.49). Samples were prepared with dimensions of 40*60 mm and thicknesses of 2.6, 3.7 and 4.3 mm using a diamond saw. The two pieces to be welded together were placed in the required configuration. They were fixed using a clamping system to hold them in place during welding and ensure good conduction of heat between the parts. Consequently, uniform adherence was achieved between two pieces over the irradiated area. The first piece was made of PMMA material that was transparent to a
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semiconductor laser at 808 nm and 2 Watt output power. By contrast, the second piece was absorbent. The incident laser radiation on the top surface was partialy reflected and partialy absorbed in transparent part. The remaining energy was transmitted down to the absorbent part. The laser radiation absorbed in the absorbent part produced heat. This heat was conducted to the transparent part, and a welding line was formed at the interface between them, where temperature exceeded the melting temperature of PMMA. A controllable one dimensions (1D) stage was designed using a programmable Arduino microcontroller connected with a blank CDROM driver. The speed of the movable stage could be varied using software with PC or manually using variable resistance. the experiment setup includes the semiconductor laser (808 nm, 2 W o/p) with a beam diameter of 2 mm. The laser was fixed with a perpendicular holder onto a movable stage. Three different speeds, 44, 113 and 150 mm/min, were applied to each sample with varying thicknesses. Good welding was achieved between the two pieces in all samples. The welding width and depth were measured with an optical microscope model Olympus BX51M-Japan and an optical scanner. the Arduino microcontroller with driver designed to control the movement of the one-axis stage with desirable speed. Nine experiments were performed for three different thicknesses of transparent PMMA at different selected speeds (44, 113 and 150 mm/min). The Taguchi method and grey relational analysis were used to determine the optimum values for welding speed, width, depth and thickness at this laser power and wavelength during the nine experiments. Different process parameters considerably influenced the quality of the weld formed. The most important parameters used were laser power, welding speed, beam diameter or spot size, transparent piece thickness and laser wavelength. the transmittance and absorbance of the material used (PMMA) have been measured using UV–Visible spectrophotometer (modelMetertech SP 8001). Particularly the laser absorption characteristics of the bottom pieces and the high transmittance of the transparent the top pieces measured at the operating wavelength. Therefore, to be joined successfully two polymers from the same plastic family (i.e. similar resin properties and melting temperature) is used. Otherwise, one part may melt or burn, whereas the other is unaffected.
The results of the calculations are presented in Table 1: 4. Multi- objective optimization using grey relational analysis In grey relational analysis, experimental data that measure the features of the quality characteristics of a product are firstly normalized from zero to one. This process is known as grey relational generation. Subsequently, grey relational coefficients are calculated based on normalised experimental data to represent the correlation between the desired and actual experimental data. Then, the overall grey relational grade is determined by averaging the grey relational coefficient that corresponds to selected responses. The overall performance characteristic of the multiple- response process depends on the calculated grey relational grade. This approach converts a multiple-response optimization problem into a single-response optimization situation, where the objective function is the overall grey relational grade. The optimal parametric combination is then evaluated by maximizing the overall grey relational grade [25]. 4.1. Normalization of the experimental response results Data preprocessing involves transferring the original sequence to a comparable sequence. For this purpose, the experimental results are normalized within the range from zero to one. Normalization can be implemented using three different approaches. If the expectancy is the smaller the original sequence should be normalized as follow:
vi ðkÞ ¼
The experiment design used was based on the Taguchi method using an L9 orthogonal array. The effects of two parameters, thickness and welding speed, on the welding process were considered in this study. For each parameter, three levels were selected to perform the nine experiments. The responses of the considered were welding width and depth. The signal-to-noise ratio (S/N) of welding depth was considered ‘‘the smaller, the better” and calculated using the following equation:
"
S 1 ¼ 10log10 N n
n X
# y2i
ð1Þ
i¼1
Similarly, the S/N of welding width was considered ‘‘the larger, the better” and calculated using the following equation:
" # n S 1X 1 ¼ 10log10 N n i¼1 y2i
ð2Þ
where n is the number of experiments, and y is the experiment value [20–24].
ð3Þ
where vi is the value after grey relational generation (data preprocessing), max v0i is the largest value of v0i (k), and min v0i is the smallest value of v0i (k) [25]. 4.2. Grey relational coefficient and grey relational grade From the pre-processed data, the grey relational coefficient is calculated to express the relationship between the ideal and actual normalized experimental results. The grey relational coefficient can be expressed as follows:
ni ðkÞ ¼ 3. Taguchi optimization methodology
maxv0i ðkÞ v0i ðkÞ maxv0i ðkÞ minv0i ðkÞ
Dmin þ f:Dmax D0i ðkÞ þ f:Dmax
ð4Þ
where ,ni (k) is a grey relational coefficient, and D0i (k) is the deviation sequence of the reference sequence v0*(k) and Dmax ¼ highest v alue of D0i ðkÞ, Dmin ¼ smallest v alue of D0i ðkÞ, f is the distinguishing or identification coefficient: fe(0, 1), and 0.5 is generally used. After obtaining the grey relational coefficient, we typically regard the average of the grey relational coefficient as the grey relational grade. The grey relational grade is defined as follows:
ci ¼
g 1X
g
ni ðkÞ
ð5Þ
k¼1
where, ci is the Grey relational grade for a particular experiment number, k is the number of responses and ni(k) is the Grey relational coefficient for a particular experiment number and number of responses [24–26]. 5. Results and discussion The effects of welding speed on weld width and depth were determined using a semiconductor laser with a wavelength of
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Table 1 L9 Taguchi design of experiment. No. Exp.
1
2
3
4
5
6
7
8
9
Thickness mm Welding speed mm/min
2.6 44
2.6 113
2.6 150
3.7 44
3.7 113
3.7 150
4.3 44
4.3 113
4.3 150
808 nm and an output power of 2 W. The results were classified into three groups according to thickness. Group 1 includes the samples with a thickness of 2.6 mm applied at three different speeds 44, 113 and 150 mm/min on the surface of the transparent PMMA. The welding width measured in this experiment is shown in Fig. 1, where the sample number 1, 2 and 3 refer to applied three welding speeds. This figure shows that welding width is inversely proportional to the welding speed Moreover, welding depth exerts the same effect (i.e. inversely proportional)., as shown in Fig. 2 Group 2 includes samples with a thickness of 3.7 mm, when the same incident laser power (2 W) and the three different welding speeds mentioned earlier (numbered 4, 5 and 6) were applied. The measured welding width and depth are shown in Figs. 3 and 4, respectively. Finally, Group 3 includes samples with a thickness of 4.3 mm when the same three different welding speeds are applied. Fig. 5 shows the weld width for samples 7, 8 and 9. The weld depth for this experiment is shown in Fig. 6. The weld diameter: depth ratio considerably affected joint quality, such that welding performance was improved. The relation between welding speed and weld width for all three samples at different thicknesses is shown in Fig. 7. This figure indicates that weld width is inversely proportional to welding speed for all three samples. Therefore, weld width, as a function of the applied welding speed at a constant laser power on the top transparent PMMA pieces, slightly depends on its thickness, the transmittance of the transparent pieces with different thicknesses (2.6, 3.7 and 4.3 mm) at this wavelength change from (86–92%) respectively measured by (UV–Visible) spectrophotometer .The reduction in the transmission percentage as a function of wavelength changed less slightly [26]. Due to laser energy melting a thin layer of plastic in both parts. When welding speed is low, molecular diffusion will have plenty of time to occur with high width and depth to form a solid joint as the melt layer solidifies [2–4]. In LTW, the danger of overheating increases due to the laser transmitting surface of the joint, which limit the thickness of the transparent pieces. The welding width to depth ratio considerably affects the quality of the joint, such that welding performance is improved and weld strength is increased as compared with Wang et al. [3]. This relationship between weld strength and width can be achieved using different parameters, such as laser power and speed. Therefore, weld width is more efficient on the tensile strength of the samples, which increases welding quality as compared with Azhikannickal et al. [13]. Table 2 summarises the results of all the experiments for different thicknesses and welding speeds,
thereby providing the values of weld width and depth for all the cases at the same laser power of 2 W and the same wavelength with a laser spot diameter of 2 mm. 5.1. First point. Taguchi optimization The results of the calculations are presented in Table 3. - Effects of parameters on weld depth The S/N and mean plot for weld depth with respect to plate thickness and welding speed are presented in Figs. 8 and 9. As shown in these figures, the best value for S/N is occurred at a thickness of (3.7 mm). This thickness is resulted in the best interaction between the laser beam and black plate. In addition, the minimum weld depth, imposed the least plate damage. The figure also shows that the weld depth decreased with increasing welding speed because the interaction time between the laser and plate became shorter. 5.2. Second point. Effects of parameters on weld width The S/N and mean plot for weld width versus plate thickness and welding speed are illustrated in Figs. 10 and 11. As indicated in these figures, the minimum welding width occurred at a thickness of (2.6 mm and 4.3 mm). At a thickness of 2.6 mm, the transmission of the laser beam was high, and thus, the heat applied by the laser beam was rapidly absorbed by the black plate, thereby producing low weld width and high depth. By contrast when the thickness was 4.3 mm, the transmission was less than that at 2.6 mm, such that the interaction between the laser beam and black plate was reduced. Thus this is leading to a smaller weld width. When the thickness was 3.7 mm, weld depth became smaller and weld width was wider compared to those in the other cases.This caused minimal sample damage, and therefore, could be used to achieve high-quality welding. The figures clearly indicate that the weld width decreases with increasing welding speed. On the basis of the Taguchi method, we determine that the best welding was obtained at a thickness of 3.7 mm, as shown in the aforementioned figures. 5.3. Third point. Grey relational analysis The normalized values are listed in Table 4: The grey relational coefficient and grey relational grade results are presented in Table 5:
Fig. 1. group 1 weld width of transparent thickness 2.6 mm with welding speed 44,113,150 mm/min respectively.
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Fig. 2. Welding depth when the transparent thickness 2.6 mm as a function of three different welding speed 44,113,150 mm/min respectively. 5X.
Fig. 3. group 2 weld width of transparent thickness 3.7 mm with welding speed 44,113,150 mm/min respectively.
Fig. 4. Welding depth when the transparent thickness 3.7 mm at welding speed 44,113,150 mm/min respectively . 5X.
Fig. 5. Group 3 weld width of transparent thickness 4.3 mm with welding speed 44,113,150 mm/min respectively.
Fig. 6. Welding depth when the transparent thickness 4.3 mm as a function of three different welding speed 44,113,150 mm/min respectively. 5X.
On the basis of the experimental performance, Table 5 clearly shows that the settings of the process parameters in Experiment 5 achieved the highest grey relational grade. Therefore, the fifth experiment provides the best multiperformance characteristics amongst the nine experiments. This experiment produced minimal sample damage, a small weld depth and short welding time. Although Experiment 6 had a smaller weld depth than Experiment
5. It was not the best experiment because weld width was smaller and weld depth was considerably smaller thereby making the adhesion force extremely weak and weakening the bond between the pieces. The results show that Experiment 5 has larger weld width and good weld depth. A large weld width indicates large amount of melted material between the two pieces, which provides the
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Fig. 7. (a) illustrate the relation between welding width and welding speed for three thicknesses. (b) illustrate the relation between the welding depth and welding speed for three different thicknesses.
Table 2 The results of all experiments for different thickness and welding speed. No. Exp.
L9
1 2 3 4 5 6 7 8 9
Mean value
Thickness mm
Welding speed mm/min
Welding width mm
Welding depth mm
2.6 2.6 2.6 3.7 3.7 3.7 4.3 4.3 4.3
44 113 150 44 113 150 44 113 150
1.1806 1.3033 0.8922 1.3351 1.3164 0.8536 1.1792 1.0649 0.9919
36.5 20 16 24.3 10.2 4.53 38 20 9.2
Table 3 L9 experimental design with signal-to-noise ratio determination of welding depth and width. No. Exp.
1 2 3 4 5 6 7 8 9
L9
Mean value
S/N ratio
Thickness mm
Welding speed mm/min
Welding width mm
Welding depth mm
Welding width mm
Welding depth mm
2.6 2.6 2.6 3.7 3.7 3.7 4.3 4.3 4.3
44 113 150 44 113 150 44 113 150
1.1806 1.3033 0.8922 1.3351 1.3164 0.8536 1.1792 1.0649 0.9919
36.5 20 16 24.3 10.1 4.53 38 20 9.2
0.1442 0.18503 0.068469 0.10743 1.3071 0.72895 0.82265 0.7871 0.683
31.246 29.376 23.213 28.093 27.293 26.523 27.717 27.538 27.107
Fig. 8. the main effect plot of S/N ratio for welding depth. Fig. 9. the main effect plot of means for welding depth.
strongest weld. Meanwhile, weld depth was selected on the basis of the principle ‘‘the smaller, the better” because a large depth causes damage between the two pieces and produces a hollow area between them due to porosity formation, which makes weldment
extremely weak. Thus, a high depth of welding reflects the size and shape of the weld seam and the eventual porosity that may arise due to the heating of the polymer beyond its decomposition
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Table 6 The optimum value of each level, the symbol‘‘*” indicates the optimum parameter level. Process parameter
Thickness Welding speed
Average grey relational grade for each factor level Level 1
Level 2
Level 3
0.41238 0.39663
0.6733* 0.60865
0.53416 0.6145*
temperature, thereby reducing the strength of the welding line [6]. The grey analysis results appear in good agreement with the Taguchi method results. The grey relation provides an explanation for each experiment and identify the best one based on both responses. By contrast Taguchi method merely provides the optimum parameters for each response.
Fig. 10. the main effect plot of S/N ratio for welding width.
- Optimum value for each level The optimum value for a process parameter level can be calculated by taking the average of the grey relational grade for each factor level. The optimum values for the levels are listed in Table 6.
6. Conclusions
Fig. 11. the main effect plot means for welding width.
Table 4 Value of normalization calculation for welding depth and width. No. Exp.
1 2 3 4 5 6 7 8 9
Normalized value Welding width
Welding depth
0.06114 0.0941 0 0.03145 1 0.5332 0.60888 0.58018 0.4961
0.0437 0.5243 0.641 0.399 0.813 1 0 0.5243 0.839
The welding speed is considerably affect both the welding line width and depth in inverse manner. Besides that the welding line strength has been affected by welding width, the increase in weld depth weakens its strength due to the formation of bubbles and porosity. Taguchi method shows that the best strength is occurred at sample thickness 3.7 mm. from the grey relational analysis the optimum process parameters for best welding are determined at welding width (1.3164 mm) and depth (10.2 mm) these results shows a good agreement with the Taguchi method results. The effect of transparent pieces thickness is slightly affect on welding strength due to high transmission ratio at laser wavelength 808 nm.
Acknowledgements The author is particularly grateful to University of Technology, Laser and Optoelectronics Engineering Department, for the financial support and providing the equipment and devices to the present research work.
Table 5 The value of deviation sequence, gray relational coefficient and gray relational grade calculation for welding depth and width. No. Exp.
1 2 3 4 5 6 7 8 9
The deviation sequence
Gray relational coefficient
Welding width
Welding depth
Welding width
Welding depth
0.93886 0.9059 1 0.96855 0 0.4668 0.39112 0.41982 0.5039
0.9563 0.4757 0.359 0.601 0.187 0 1 0.4757 0.161
0.3475 0.3556 0.3333 0.34047 1 0.51717 0.56109 0.54358 0.4980
0.3433 0.5125 0.5821 0.4541 0.7278 1 0.3333 0.5125 0.7564
Gray relational grade
Order
0.3454 0.43405 0.4577 0.3973 0.8639 0.7586 0.44719 0.5280 0.6273
9 7 5 8 1 2 6 4 3
Please cite this article as: K. A. Hubeatir, Laser transmission welding of PMMA using IR semiconductor laser complemented by the Taguchi method and grey relational analysis, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.167
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Please cite this article as: K. A. Hubeatir, Laser transmission welding of PMMA using IR semiconductor laser complemented by the Taguchi method and grey relational analysis, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.167