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An Experimental Investigation of Laser Cladding
An Experimental Investigation of Laser Cladding G. Chryssolouris ( I ) , S . Zannis, K. Tsirbas, C. Lalas Laboratory for Manufacturing Systems and Automation Department of Mechanical Engineering and Aeronautics University of Patras, Greece
Abstract Laser cladding uses a laser beam to fuse materials with enhanced metallurgical properties on a substrate. A thin layer of the substrate is molten achieving good metallurgical bonding with the added material. In this paper experimental data from an industrial application of laser cladding are presented and discussed. The material of the substrate was an aluminum alloy and the cladding material was copper based powder. Under constant laser power and beam diameter, experiments were performed using various powder feed rates, process speeds and gas supply. The dimensions of the clad as well as the alloying and dilution depth were measured. The experimental data were analyzed in order to obtain a working range for the process parameters.
Keywords: Laser, cladding, experiments
1 INTRODUCTION In order to improve the properties of mechanical parts several surface treatment methods are available for industrial use [2]. When applying these techniques problems often arise such as porosity, poor bonding of the added material to the substrate, mixing of the added material with the substrate, excessive thermal distortion of the workpiece etc. A technique that may overcome some of the above problems is that of laser cladding (Figure 1) [ I , 3, 4-61,
important parameters that influence the quality of the cladding. In [9] experiments were carried out to establish a relationship between process speed and the clad width and depth. In this paper, experimental data from the industrial application of laser cladding are presented and discussed. The effect of the process speed, powder feeding rate and gas supply on the clad geometry as well as on the alloying and dilution depth is investigated (Figure 2). Clad geometry includes two main regions, namely the clad and the alloying zone. Clad height (h), width (w) and depth (d) define the final geometry of the clad after the end of the process. In the alloying zone the added material and the molten substrate are mixed. The sum of the alloying zone thickness (a) and the clad depth (d) define the clad dilution (D).
Figure 1: The laser cladding process Laser cladding is the process that uses a laser beam to fuse a material with enhanced thermal and mechanical properties on a substrate. The added material is introduced into the process directly, using inert gases such as argon or helium. Laser cladding can achieve excellent metalluraical bondina between the substrate and the added materGl while t h e cladded layer is relatively pure. Although the process is relative new a number of experimental and theoretical studies have been reported in the literature [5, 7 - 141. In [7] the effect of the piocess speed on the clad height, width and depth for various laser powers was investigated. In [8] experiments showed that the specific energy and the powder density are two
Figure 2: Clad characteristics
In the cladding process discussed in this paper the substrate was rotated and the laser beam and the powder delivery system remained stationary (Figure 3). A C 0 2 laser Of 6.5kw was used in the The laser beam was delivered to the workpiece through a set of 5
mirrors. The beam delivery system resulted approximately in a 10% loss of the laser source output power.
Top View). The substrate was heated up and partially molten by the laser beam. The powder was delivered through a powder nozzle and with the help of a carrier gas. Because of the geometry of the process (Figure 4) the laser beam was heating both the substrate and the powder particles. 3 EXPERIMENTAL RESULTS The focus of the experimentation was the effect of powder feed rate (m'), process speed (u) and gas supply (9') on the clad characteristics (Figure 2). Several experiments were performed in order to establish trends and a working range (Figures 5, 6, 7) of the process parameters within the experimental range (Table 2). PROCESS PARAMETER
EXPERIMENTAL RANGE
Powder feed rate - m' (a/min)
15 - 100
Figure 3: Experimental set-up The focal length could be varied resulting in laser spot diameters of 5, 7 and 9 mm. The laser beam was positioned at 45Oto the horizontal and perpendicular to the surface to be cladded. The powder feeder was inclined to the surface to be cladded (Figure 4).
I
Process speed - u (mm/min)
I
250 - 1170
I
I
Gas SUPP~Y- a' Wh)
I
200-1000
I
Table 2: Experimental conditions. Powder feed rate=30g/min, Laser power=5700W, Process speed=300 mmlmin, Laser beam diameter=5mm
+Alloying +Dilution
100
250
400
550
700
850
1000
la
Gas supply - g' (I/h)
Gas supply=7OOI/h Powder feed rate=6Og/min, Laser Power=5700, Laser beam diameter=5mm
-
E E 4 0
+Width -4- Depth
c
p 3 W
c
s 2
Figure 4: Clad formation
+Alloying +Dilution
1 m
0 1
7l
The cladding powder (Table 1) was delivered to the target point through a nozzle of 2 mm radius. The density of the powder was 8.73g/cm3 and its grainsize was 45-90 pn.
b0 400
SUBSTRATE: A319, (IS0 AISi7Cu4) Material wt (%)
I I
I I
Si 7-8
Cu 3-4
I I
Other 3.4
I I
Al (min) 84.6
Wt (%)=[(Weight of component per unit volume) / (Weight of substrate per unit volume)]*100
600
800
1000
Process speed - u (mmlmin)
Gas supply=2001/h, Laser p o w e ~ 5 7 0 0 W Process speed=400 mmlmin, Laser beam diameter=5mm
I
F 7 ,
W
POWDER Material wt (%)
I
Ni I Co 1161 8
I I
Mo I Fe I Si I Cr I Cu (min) 6 1 3 1 3 11.51 59.5
Wt (%)=[(Weight of component per unit mass) / (Weight of powder per unit mass)]*lOO
-A- Depth
t j 3 g 2
+Alloying
6 1 - 0 3 25
35
45
55
65
Powder feed rate - m' (g/min)
Table 1: Substrate and powder composition The center point of the powder delivery spot was behind the laser beam center point on the substrate (Figure 4,
Figure 5:Clad characteristics vs a) gas supply, b) process speed, c) powder feed rate.
4 DISCUSSION In many industrial applications, cladding depth (Figure 2) is the most important parameter because a "good" cladding process must have enough depth for the clad to be entrenched into the base material. On the other hand, alloying depth should be kept at a minimum level because of the poor material properties of the alloying zone. Clad height can be reduced by secondary processes, e.g. grinding, while clad width is mostly determined by the laser beam diameter. The main parameters (Table 4) affecting clad height are the powder feed rate (m') and process speed (u). When low powder feed rates are used, clad height is low and adherence is high, due to the substantial melting of the substrate. As the powder feed rate increases, the powder mass does not get impinged deep in the molten pool and it forms a clad with increased height (Figure 5c). However, after a certain point of powder feed rate increase, less powder is molten and a clad will be difficult to form. On the other hand the increase of the process speed decreases clad height (Figure 5b) due to the reduction, per unit length, of powder supplied to the process. The influence of gas supply on the clad height seems to be minimal (Figure 5a and Table 4).
Figure 7: Alloying depth versus process speed The Statistical Design Of Experiments [Illwas used to quantify the effect of the process speed (u), powder feed rate (m') and gas supply (9') on the clad characteristics. The experiments of the L9 matrix were performed and the results were recorded (Table 3).
Clad width is mainly affected by the laser beam diameter, since the laser beam size defines the size of the region that is molten. However, from the three parameters examined here, gas supply seems to have the greatest effect (Table 4). As the gas supply to the process is increasing, the area is cooling much faster due to rapid flow of inert gas on the process area, thus decreasing clad width (Figure 5a). An increase of the powder feed rate may reduce the clad width (Figure 5c), since more laser power will be absorbed by the powder particles. Thus the energy reaching the substrate is reduced leading to smaller clad widths. The increase of process speed may reduce the clad width (Figure 5b), due to the smaller amount of energy reaching the substrate per unit length. Gas supply and powder feed rate have major influence on clad depth (Table 4). By increasing gas supply the clad depth decreases (Figure 5a) for the same reason as in clad width. By increasing powder feed rate to about 40g/min, clad depth rapidly decreases reaching a nearzero value (Figure 6). Further increase of powder feed rate has no significant impact on clad depth, since the excessive powder reduces substantially the laser energy reaching the substrate. For the same reason, process speed shows no significant influence on clad depth at high powder feed rate values (>40g/min). However, when the powder feed rate is below 40g/min, and as the process speed increases, clad depth also increases (Figure 6). This is because, as the speed increases, the time available for mixing phenomena to occur between clad and substrate decreases. Thus there is increased clad depth and reduced alloying depth (Figure 7). Gas supply shows little or no effect on the alloying depth (Table 4), since it does not affect mixing phenomena which create the alloying zone. On the other hand, alloying depth shows a slightly increasing trend with increasing powder feed rate until a certain limit (about 40g/min) (Figure 5c). This is because increasing powder feed rate contributes to the impingement of the powder particles at the bottom of the molten pool and hence their mixture with the molten substrate. When higher powder feed rates are used, the molten pool becomes saturated with powder particles and the alloying depth remains constant (Figure 5c).
Table 4: Process parameter importance.
The increase of the gas supply reduces the dilution depth (Figure 5a) due to the rapid flow of inert gas, which cools the process area. Process speed does not seem to have
an important effect on dilution depth (Table 4) since the clad depth increases while the alloying depth decreases at the same time. By increasing the powder feed rate, more energy is absorbed by the powder particles. Therefore less energy is available for substrate melting and the molten pool depth is reduced, having a negative effect on the dilution depth (Figure 5.c). 5 CONCLUSIONS Several process parameters effect the size and the geometry of the clad. Clad height is governed by the process speed and the powder feed rate. Clad width is mainly affected by the laser beam diameter, but the increase of gas supply, powder feed rate and process speed reduces its size. Clad depth is reduced with the increase of gas supply and powder feed rate up to a point, after which their effect is minimal. For low values of powder feed rate, increasing process speed increases clad depth. The increase of process speed may decrease the alloying depth, whereas the gas supply has little effect. The increase of the gas supply may reduce the dilution depth. Process speed does not affect dilution depth while increasing powder feed rate may have a negative effect. Therefore, in order to achieve an optimum clad result, in terms of increased clad depth and minimum alloying zone, powder feed rates should be kept low and process speed should be high. 6 ACKNOWLEDGEMENT The work reported in this paper was partially supported by the project BE97-5024, "Innovative Coatings on Light Alloys".
7
REFERENCES Chryssolouris, G., 1991, Laser Machining - Theory and Practice, Springer - Verlag. Chryssolouris, G., 1992, Manufacturing Systems Theory and Practice, Springer-Verlag, 275-276 and 306-31 1. Chryssolouris, G., Sensors in Laser Machining, ClRP Annals, Vol. 43, No. 2 (1994), 513-519. Chryssolouris, G., 1994, 3-D Laser Machining: A Perspective, Proceedings of the 26th ClRP International Seminar on Manufacturing Systems "Laser Assisted Net shape Engineering/LANE' 94", 405-409. Heuvelman, C. J., Konig, W., Tonshoff, H.K., Meijer, J., Kirner, P.K., Rund, M., Schneider, M.F., Van Sprang, I., 1992, Surface Treatment Techniques by Laser Beam Machining, STC E, 41/2, p. 657 Ricciardi, G., Cantello, M., Laser material interaction: absorption coefficient in welding and surface treatment, STC E, 43/1, p. 171 Yellup, J.M., 1995, Laser cladding using the powder blowing technique, Surface and Coatings technology, 121-128. Xinwei Wu, Beidi Zhu, Xiaoyan Zeng, Xiang Hu, Kun Cui, 1996, Critical state of laser cladding with powder auto-feeding, Surface and Coatings technology, 200204. Voltz, R., 1992, Producing hard facing layers on aluminium alloys with high power COP laser, Laser treatment of materials, 399 - 404. [ l o ] Picasso, M., Marsden, C.F., Wagniere, J.D., Frenk, A,, Rappaz, M., 1994, A simple but realistic model for laser cladding, Metallurgical and materials transactions, Vol. 25B, 281-291.
111 Jouvard, J.M., Grevey, D.F., Lemoine, F., Vannes, A.B., 1997, Continuous wave Nd:YAG laser cladding modelling: a physical study of track creation during low power processing, Journal of laser applications, Vol. 9, 43-50. 121 Yevko, V., Park, C.B., Zak, G., Coyle, T.W., Benhabib, B., 1998, Cladding formation in laser beam fusion of metal powder, Rapid Prototyping Journal, Vol. 4, NO.4, 168-184. [I31 Bamberger M., Kaplan W.D., Medres B., Shepeleva L., 1998, Calculation of process parameters for laser alloying and cladding, Journal of laser applications, Vol. 10, N o l , 29-33. [I41 Hu C., Baker T.N., 1998, A semi-empirical model to predict the melt depth developed in overlapping laser tracks on a Ti-6AI-4V alloy, Journal of Materials Processing Technology (94), Elsevier Science, 116122. [I51 Phadke, M.S., 1989, Quality engineering using robust design, Prentice Hall, New Jersey.
Abstract Laser cladding uses a laser beam to fuse materials with enhanced metallurgical properties on a substrate. A thin layer of the substrate is molten achieving good metallurgical bonding with the added material. In this paper experimental data from an industrial application of laser cladding are presented and discussed. The material of the substrate was an aluminum alloy and the cladding material was copper based powder. Under constant laser power and beam diameter, experiments were performed using various powder feed rates, process speeds and gas supply. The dimensions of the clad as well as the alloying and dilution depth were measured. The experimental data were analyzed in order to obtain a working range for the process parameters.
Keywords: Laser, cladding, experiments
1 INTRODUCTION In order to improve the properties of mechanical parts several surface treatment methods are available for industrial use [2]. When applying these techniques problems often arise such as porosity, poor bonding of the added material to the substrate, mixing of the added material with the substrate, excessive thermal distortion of the workpiece etc. A technique that may overcome some of the above problems is that of laser cladding (Figure 1) [ I , 3, 4-61,
important parameters that influence the quality of the cladding. In [9] experiments were carried out to establish a relationship between process speed and the clad width and depth. In this paper, experimental data from the industrial application of laser cladding are presented and discussed. The effect of the process speed, powder feeding rate and gas supply on the clad geometry as well as on the alloying and dilution depth is investigated (Figure 2). Clad geometry includes two main regions, namely the clad and the alloying zone. Clad height (h), width (w) and depth (d) define the final geometry of the clad after the end of the process. In the alloying zone the added material and the molten substrate are mixed. The sum of the alloying zone thickness (a) and the clad depth (d) define the clad dilution (D).
Figure 1: The laser cladding process Laser cladding is the process that uses a laser beam to fuse a material with enhanced thermal and mechanical properties on a substrate. The added material is introduced into the process directly, using inert gases such as argon or helium. Laser cladding can achieve excellent metalluraical bondina between the substrate and the added materGl while t h e cladded layer is relatively pure. Although the process is relative new a number of experimental and theoretical studies have been reported in the literature [5, 7 - 141. In [7] the effect of the piocess speed on the clad height, width and depth for various laser powers was investigated. In [8] experiments showed that the specific energy and the powder density are two
Figure 2: Clad characteristics
In the cladding process discussed in this paper the substrate was rotated and the laser beam and the powder delivery system remained stationary (Figure 3). A C 0 2 laser Of 6.5kw was used in the The laser beam was delivered to the workpiece through a set of 5
mirrors. The beam delivery system resulted approximately in a 10% loss of the laser source output power.
Top View). The substrate was heated up and partially molten by the laser beam. The powder was delivered through a powder nozzle and with the help of a carrier gas. Because of the geometry of the process (Figure 4) the laser beam was heating both the substrate and the powder particles. 3 EXPERIMENTAL RESULTS The focus of the experimentation was the effect of powder feed rate (m'), process speed (u) and gas supply (9') on the clad characteristics (Figure 2). Several experiments were performed in order to establish trends and a working range (Figures 5, 6, 7) of the process parameters within the experimental range (Table 2). PROCESS PARAMETER
EXPERIMENTAL RANGE
Powder feed rate - m' (a/min)
15 - 100
Figure 3: Experimental set-up The focal length could be varied resulting in laser spot diameters of 5, 7 and 9 mm. The laser beam was positioned at 45Oto the horizontal and perpendicular to the surface to be cladded. The powder feeder was inclined to the surface to be cladded (Figure 4).
I
Process speed - u (mm/min)
I
250 - 1170
I
I
Gas SUPP~Y- a' Wh)
I
200-1000
I
Table 2: Experimental conditions. Powder feed rate=30g/min, Laser power=5700W, Process speed=300 mmlmin, Laser beam diameter=5mm
+Alloying +Dilution
100
250
400
550
700
850
1000
la
Gas supply - g' (I/h)
Gas supply=7OOI/h Powder feed rate=6Og/min, Laser Power=5700, Laser beam diameter=5mm
-
E E 4 0
+Width -4- Depth
c
p 3 W
c
s 2
Figure 4: Clad formation
+Alloying +Dilution
1 m
0 1
7l
The cladding powder (Table 1) was delivered to the target point through a nozzle of 2 mm radius. The density of the powder was 8.73g/cm3 and its grainsize was 45-90 pn.
b0 400
SUBSTRATE: A319, (IS0 AISi7Cu4) Material wt (%)
I I
I I
Si 7-8
Cu 3-4
I I
Other 3.4
I I
Al (min) 84.6
Wt (%)=[(Weight of component per unit volume) / (Weight of substrate per unit volume)]*100
600
800
1000
Process speed - u (mmlmin)
Gas supply=2001/h, Laser p o w e ~ 5 7 0 0 W Process speed=400 mmlmin, Laser beam diameter=5mm
I
F 7 ,
W
POWDER Material wt (%)
I
Ni I Co 1161 8
I I
Mo I Fe I Si I Cr I Cu (min) 6 1 3 1 3 11.51 59.5
Wt (%)=[(Weight of component per unit mass) / (Weight of powder per unit mass)]*lOO
-A- Depth
t j 3 g 2
+Alloying
6 1 - 0 3 25
35
45
55
65
Powder feed rate - m' (g/min)
Table 1: Substrate and powder composition The center point of the powder delivery spot was behind the laser beam center point on the substrate (Figure 4,
Figure 5:Clad characteristics vs a) gas supply, b) process speed, c) powder feed rate.
4 DISCUSSION In many industrial applications, cladding depth (Figure 2) is the most important parameter because a "good" cladding process must have enough depth for the clad to be entrenched into the base material. On the other hand, alloying depth should be kept at a minimum level because of the poor material properties of the alloying zone. Clad height can be reduced by secondary processes, e.g. grinding, while clad width is mostly determined by the laser beam diameter. The main parameters (Table 4) affecting clad height are the powder feed rate (m') and process speed (u). When low powder feed rates are used, clad height is low and adherence is high, due to the substantial melting of the substrate. As the powder feed rate increases, the powder mass does not get impinged deep in the molten pool and it forms a clad with increased height (Figure 5c). However, after a certain point of powder feed rate increase, less powder is molten and a clad will be difficult to form. On the other hand the increase of the process speed decreases clad height (Figure 5b) due to the reduction, per unit length, of powder supplied to the process. The influence of gas supply on the clad height seems to be minimal (Figure 5a and Table 4).
Figure 7: Alloying depth versus process speed The Statistical Design Of Experiments [Illwas used to quantify the effect of the process speed (u), powder feed rate (m') and gas supply (9') on the clad characteristics. The experiments of the L9 matrix were performed and the results were recorded (Table 3).
Clad width is mainly affected by the laser beam diameter, since the laser beam size defines the size of the region that is molten. However, from the three parameters examined here, gas supply seems to have the greatest effect (Table 4). As the gas supply to the process is increasing, the area is cooling much faster due to rapid flow of inert gas on the process area, thus decreasing clad width (Figure 5a). An increase of the powder feed rate may reduce the clad width (Figure 5c), since more laser power will be absorbed by the powder particles. Thus the energy reaching the substrate is reduced leading to smaller clad widths. The increase of process speed may reduce the clad width (Figure 5b), due to the smaller amount of energy reaching the substrate per unit length. Gas supply and powder feed rate have major influence on clad depth (Table 4). By increasing gas supply the clad depth decreases (Figure 5a) for the same reason as in clad width. By increasing powder feed rate to about 40g/min, clad depth rapidly decreases reaching a nearzero value (Figure 6). Further increase of powder feed rate has no significant impact on clad depth, since the excessive powder reduces substantially the laser energy reaching the substrate. For the same reason, process speed shows no significant influence on clad depth at high powder feed rate values (>40g/min). However, when the powder feed rate is below 40g/min, and as the process speed increases, clad depth also increases (Figure 6). This is because, as the speed increases, the time available for mixing phenomena to occur between clad and substrate decreases. Thus there is increased clad depth and reduced alloying depth (Figure 7). Gas supply shows little or no effect on the alloying depth (Table 4), since it does not affect mixing phenomena which create the alloying zone. On the other hand, alloying depth shows a slightly increasing trend with increasing powder feed rate until a certain limit (about 40g/min) (Figure 5c). This is because increasing powder feed rate contributes to the impingement of the powder particles at the bottom of the molten pool and hence their mixture with the molten substrate. When higher powder feed rates are used, the molten pool becomes saturated with powder particles and the alloying depth remains constant (Figure 5c).
Table 4: Process parameter importance.
The increase of the gas supply reduces the dilution depth (Figure 5a) due to the rapid flow of inert gas, which cools the process area. Process speed does not seem to have
an important effect on dilution depth (Table 4) since the clad depth increases while the alloying depth decreases at the same time. By increasing the powder feed rate, more energy is absorbed by the powder particles. Therefore less energy is available for substrate melting and the molten pool depth is reduced, having a negative effect on the dilution depth (Figure 5.c). 5 CONCLUSIONS Several process parameters effect the size and the geometry of the clad. Clad height is governed by the process speed and the powder feed rate. Clad width is mainly affected by the laser beam diameter, but the increase of gas supply, powder feed rate and process speed reduces its size. Clad depth is reduced with the increase of gas supply and powder feed rate up to a point, after which their effect is minimal. For low values of powder feed rate, increasing process speed increases clad depth. The increase of process speed may decrease the alloying depth, whereas the gas supply has little effect. The increase of the gas supply may reduce the dilution depth. Process speed does not affect dilution depth while increasing powder feed rate may have a negative effect. Therefore, in order to achieve an optimum clad result, in terms of increased clad depth and minimum alloying zone, powder feed rates should be kept low and process speed should be high. 6 ACKNOWLEDGEMENT The work reported in this paper was partially supported by the project BE97-5024, "Innovative Coatings on Light Alloys".
7
REFERENCES Chryssolouris, G., 1991, Laser Machining - Theory and Practice, Springer - Verlag. Chryssolouris, G., 1992, Manufacturing Systems Theory and Practice, Springer-Verlag, 275-276 and 306-31 1. Chryssolouris, G., Sensors in Laser Machining, ClRP Annals, Vol. 43, No. 2 (1994), 513-519. Chryssolouris, G., 1994, 3-D Laser Machining: A Perspective, Proceedings of the 26th ClRP International Seminar on Manufacturing Systems "Laser Assisted Net shape Engineering/LANE' 94", 405-409. Heuvelman, C. J., Konig, W., Tonshoff, H.K., Meijer, J., Kirner, P.K., Rund, M., Schneider, M.F., Van Sprang, I., 1992, Surface Treatment Techniques by Laser Beam Machining, STC E, 41/2, p. 657 Ricciardi, G., Cantello, M., Laser material interaction: absorption coefficient in welding and surface treatment, STC E, 43/1, p. 171 Yellup, J.M., 1995, Laser cladding using the powder blowing technique, Surface and Coatings technology, 121-128. Xinwei Wu, Beidi Zhu, Xiaoyan Zeng, Xiang Hu, Kun Cui, 1996, Critical state of laser cladding with powder auto-feeding, Surface and Coatings technology, 200204. Voltz, R., 1992, Producing hard facing layers on aluminium alloys with high power COP laser, Laser treatment of materials, 399 - 404. [ l o ] Picasso, M., Marsden, C.F., Wagniere, J.D., Frenk, A,, Rappaz, M., 1994, A simple but realistic model for laser cladding, Metallurgical and materials transactions, Vol. 25B, 281-291.
111 Jouvard, J.M., Grevey, D.F., Lemoine, F., Vannes, A.B., 1997, Continuous wave Nd:YAG laser cladding modelling: a physical study of track creation during low power processing, Journal of laser applications, Vol. 9, 43-50. 121 Yevko, V., Park, C.B., Zak, G., Coyle, T.W., Benhabib, B., 1998, Cladding formation in laser beam fusion of metal powder, Rapid Prototyping Journal, Vol. 4, NO.4, 168-184. [I31 Bamberger M., Kaplan W.D., Medres B., Shepeleva L., 1998, Calculation of process parameters for laser alloying and cladding, Journal of laser applications, Vol. 10, N o l , 29-33. [I41 Hu C., Baker T.N., 1998, A semi-empirical model to predict the melt depth developed in overlapping laser tracks on a Ti-6AI-4V alloy, Journal of Materials Processing Technology (94), Elsevier Science, 116122. [I51 Phadke, M.S., 1989, Quality engineering using robust design, Prentice Hall, New Jersey.