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Improved performance of electroplated grinding wheels using a new method of controlled grain size sorting
Journal of Manufacturing Processes 30 (2017) 336–342
Contents lists available at ScienceDirect
Journal of Manufacturing Processes journal homepage: www.elsevier.com/locate/manpro
Technical Paper
Improved performance of electroplated grinding wheels using a new method of controlled grain size sorting Yushan Lyu a , Haiyue Yu b,∗ , Jun Wang a,c , Guowei Zhao a , Zhizhen Liu a a b c
School of Mechanical Engineering, Shenyang Ligong University, Shenyang, PR China School of Mechatronic Engineering, Changchun University of Technology, Changchun, 130012, PR China School of Mechanical Engineering and Automation, Northeastern University, Shenyang, PR China
a r t i c l e
i n f o
Article history: Received 9 May 2017 Received in revised form 19 September 2017 Accepted 3 October 2017 Keywords: Sorting grains Hydraulic power Protrusion height Grinding wheel Surface roughness
a b s t r a c t The protrusion heights of grains on electroplated grinding wheel are uneven. This phenomenon has a negative influence on the grinding performance of electroplated grinding wheel. In this paper, CBN and diamond grains were sorted by hydraulic power method. Four kinds of electroplated grinding wheels were fabricated with selected and unselected CBN diamond grains. Then, the surface roughness of workpieces ground by the four kinds of grinding wheels were investigated and analyzed in contrast experiments. The experimental results show that the grains sorting method using hydraulic power can homogenize the size of grains; and lower ground surface roughness has been obtained by the electroplated grinding wheels with the help of the new method of controlled grain size sorting. © 2017 Published by Elsevier Ltd on behalf of The Society of Manufacturing Engineers.
1. Introduction The electroplated grinding wheel could be used in the filed of high efficiency grinding due to its good properties of high hardness, high thermal conductivity, high wear resistance and high chemical inertness [1]. But the grains on most electroplated grinding wheels are single-layer and are not typically dressed. Therefore, the protrusion heights of grains on the single-layer grinding wheel mainly depend on the original state of grains. Due to the geometrical flexibility of grains, high transverse surface roughness of the workpiece could be produced by the electroplated grinding wheel without dressing. To homogenize the protrusion height of grains, some studies on dressing monolayer superabrasive wheels were conducted. Ghosh et al. [2] developed a touch-dressing method for brazedtype single-layer CBN wheels, and finally obtained transverse surface roughnesses were Ra = 1 m and Ra = 1.5 m when material hardened IS103Cr1 was ground; Bing Guo [3] developed a novel conditioning technique for copper bonded diamond grinding wheels. During the conditioning process, the conditioners were continuously dressed by the means of electrolytic inprocess dressing (ELID). The protrusion height of grains can be
∗ Corresponding author. E-mail address: [email protected] (H. Yu).
homogenized by this method to a great extent. In addition, a constant wheel peripheral envelop surface exhibiting flattened diamond grains with a run-out less than 2.5 m was achieved, and the grinding performance of the grinding wheels was promoted [4]. Ho et al. [5] removed tall diamond grits which were found by scratch mechanism on the surface of grinding tool. This novel method can improve diamond disk performance. Kitzig et al. [6] developed a novel ultrasonic-assisted dressing method for electroplated grinding wheels. Through this process, the diamond grains of an electroplated grinding wheel were successfully conditioned/fractured by hitting with an ultrasonic-assisted diamond dresser. Then, numerous sharp cutting edges and similar grains’ protrusion were generated. Experimental analyses have shown that the grinding of tungsten carbide with fractured electroplated D251 diamonds enabled fine surface roughness (Ra < 0.1 m and Rz < 0.8 m). Laser technique was also applied to increase the smoothness of the wheel surfaces, thus increasing the homogenization of protrusion height. Dold et al. [7] conducted a laser touch dressing study to cut the diamond grains within a defined grain protrusion without any thermal damage on the nickel bond. Genyu Chen et al. [8,9] presented an online tangential laser profiling method for single layer abrasive wheel. This method mainly consisted of a pulsed fiber laser, a surface grinder, a motorized three-dimensional (3D) translation stage, laser displacement sensors and a laser power meter. It could be seen as special dressing method. The single-layer
https://doi.org/10.1016/j.jmapro.2017.10.004 1526-6125/© 2017 Published by Elsevier Ltd on behalf of The Society of Manufacturing Engineers.
Y. Lyu et al. / Journal of Manufacturing Processes 30 (2017) 336–342
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Fig. 2. The force analysis for the grain. Fig. 1. Schematic view of sorting grain device.
grinding wheel dressed by this method not only obtain homogenized protrusion height of grains, but also achieve lower mean circular runout and the axial gradient error. The positive clearance angles of grains (2.4◦ ) can also be obtained [10]. However, some problems generated in dressing process are unavoidable. Obviously, a lot of abrasives will be waste and loss. Besides, the grain damages, including micro-fractured, macrofractured, flat and break flat, will be generated by high temperature or mechanical force. In addition, some dressing process are complex and time-consuming. For electroplated grinding tools, the protrusion heights of grains are determined in the stage of fabricating process. Internal electroplate method (or inner galvanizing method) [11–13] is one of the most effective ways to improve the homogeneous protrusion height of grains. Nevertheless, this method is mainly used for diamond dressing roller because of its higher cost and more complex process than general plating method. To solve the issue, a kind of rolling grain method also was present [14]. But for the rolling grain method, the macro and micro fractures of grains may occur in the process of pressing grains due to the high force generated. It is difficult to obtain more consistent protruded heights of grains due to the elastic recoveries of the abrasive grains and the wheel matrix. But above all, grains’ damages, lower consumption rate of grains and complex process must be avoided when the homogeneous protrusion heights of grains are obtained. To attain it, a new method was used to sort the grains of CBN and diamond with the help of hydraulic power in this paper. Several electroplated grinding wheels were fabricated with unselected and selected grains. To compare in experiments better, the distribution of grains on these grinding wheels are the same with the help of mask-based lithography. The ground surface roughnesses using these grinding wheels were investigated to verify the advantages of grinding wheels with selected grains. 2. Sorting grains 2.1. The basic principle of sorting grains The grains was sorted with the help of hydraulic power, the schematic view of sorting grains is shown in Fig. 1. The grains spurt from the jet in the sorting box, whose movement in the liquid is also shown in Fig. 1. When the horizontal speed of grain reaches zero, the grain will sink vertically [15]. The fundamental principle is: grains with different size fall from the same height within the liquid initially. A while later, these grains will locate in different
position under the action of gravity, liquid resistance and buoyancy force. Then, the grains with different size will be distinguished. The liquid in Fig. 1 is plating solution which can prevent grains from contaminating in the sorting process. The purpose of mixer in Fig. 1 is to keep the grains uniform in the liquid. 2.2. The theoretical analysis of sorting grains As shown in Figs. 1 and 2, The movement of grains in the liquid will be influenced by the combined action of gravity (G), liquid resistance (Fvgx and Fvgy ) and buoyancy force (Fa ) when the grains spurt from the jet nozzle at a velocity (vg0 ) and angle (␣) in the sorting box. To analyze the movement of grains easily, the following assumptions are made: (1) all grains are spherical particle; (2) the movement of each grain is independent; (3) The pressure gradient force is ignored. Therefore, the gravity (G), liquid resistance (Fvgx and Fvgy ) and buoyancy force (Fa ) of movoment grain are analyzed, respectively [15]. The buoyancy of grain is: Fa =
3 Dp g 6
(1)
The gravity of grain: 3 Dp p g 6
G=
(2)
The liquid resistance:
⎧ v 2 ⎪ ⎨ Fvgx = C0x A gx 2
⎪ ⎩F
vgy = C0y A
(3)
vgy 2 2
Where: A is the meeting area of flowing of grain and A = 4 Dp 2 . Dp is the grains diameter. p is the density of the grain; is the density of the liquid; C0x and C0y are the resistance coefficient, g is the gravitational acceleration. According to Newton’s second law, with the help of Eqs. (1)–(3), the force balance equation for the grain in the liquid is:
⎧ dvgx vgx 2 ⎪ ⎪ 6 Dp 3 p dt = − 4 C0x Dp 2 2 ⎨
⎪ D 3 2 ⎪ ⎩ Dp 3 p dvgy = 6 p p p − g − C0y Dp 2 vgy 6
dt
p
4
2
.
(4)
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Y. Lyu et al. / Journal of Manufacturing Processes 30 (2017) 336–342
Where: C0x and C0y are the resistance coefficient of sorting liquid. Because of the low speed of liquid in Fig. 1, the grain is in laminar region. So, the resistance coefficients are [16]: C0x =
24 24 , C0y = . Rex Rey
(5)
Where: Rex and Rey is the Reynolds number and its mathematical expression is: Rex =
DP vgx DP vgy , Rey = .
(6)
Where is the viscosity coefficient of the liquid. Putting the Eq. (6) into the Eq. (5), then putting the Eq. (5) into the Eq. (4), the Eq. (4) can be rewritten as:
⎧ dv 1 ⎪ ⎨ Dp 2 p gx = −3 · vgx 6
dt
6
dt
⎪ ⎩ 1 Dp 2 p dvgy = 1 D2 p − g − 3 · vgy
.
(7)
6
The integral conditions of Eq. (7) are as following:
⎧ ⎧ dx dx ⎨ vgx |t=∞ = dt |t=∞ = v0 cos ˛ ⎨ vgx |t=∞ = dt |t=∞ = 0 ⎩
vgy |t=∞ =
⎩
dy = v0 sin ˛ | dt t=0
x|t=0 = 0
and
vgy |t=∞ =
dy | =C dt t=∞
y|t=0 = 0
(8)
−)g
P Where: C = (18 Dp2 , which is a constant velocity when the gravity (G) and liquid resistance (Fvgy ) reach equilibrium with the buoyancy force (Fa ). By the use of the integal conditions, the Eq. (7) can be solved, and the movement trajectory equation of enjected abrasive grain can be obtained, as follows:
⎧ ⎪ ⎪ ⎪ p · Dp2 ⎪ ⎪ x = vg0 cos ˛ · ⎪ ⎪ 18 ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ p − gDp2 y=
⎛ −
⎜
· ⎝1 − e
p · Dp2
· t + vg0 sin ˛ −
18 ⎪ ⎪ ⎪ ⎛ ⎞ ⎪ ⎪ 18 ⎪ ⎪ − · t 2 ⎪ p Dp ⎜ ⎪ · Dp2 ⎟ ⎪ ⎪ · · ⎝1 − e p ⎠ ⎪ 18 ⎪ ⎩
·t
⎟ ⎠
p − gDp2
p ·D2
(10)
.
At this point, the movement of the grain is in the y direction only, as seen in Fig. 1. Therefore, its movement displacement in the y direction is:
y|
p D2 p
t=3 18
≈
p Dp2 18
0.99vg0 sin ˛ + 2
diameter (m)
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
366–370 370–374 374–378 378–382 382–386 386–390 390–394 394–398 398–402 402–406 406–410 410–414 414–418 418–422 422–426
Table 2 The measured result of diamond grains (45/50 mesh). group
diameter (m)
group
diameter (m)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
< 340 340–344 344–348 348–352 352–356 356–360 360–364 364–368 368–372 372–376 376–380 380–384 384–388 388–392 392–396
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
396–400 400–404 404–408 408–412 412–416 416–420 420–424 424–428 428–432 432–436 436–440 440–444 444–448 448–452 452–456
p · Dp2 18
,
H ≥ y| t=3
p Dp2
(12)
18
2.3. The results of sorting grains
be obtained. But, when the movement time (t) is t = 3 · 18p , the movement displacement in the x direction will reach 99% of the theoretical value, namely
18
group
<310 310–314 314–318 318–322 322–326 326–330 330–334 334–338 338–342 342–346 346–350 350–354 354–358 358–362 362–366
18
If the movement time (t) in the Eq. (9) is considered to be infinite, then the biggest movement displacement in the x direction will
p · Dp2
diameter (m)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
t ≥3·
(9)
xmax ≈ 0.99vg0 cos ˛ ·
group
It can be seen from Eqs. (10) and (11) that the grains can be sorted successfully using the device in Fig. 1 when the movement time (t) and the jet nozzle hight (H) in the Fig. 1 meet the follow conditions:
⎞
18
Table 1 The measured result of CBN grains (45/50 mesh).
p − gDp2 18
(11)
The grains of CBN and diamond are 45/50 mesh and came from the same batch. These grains were sorted respectively using above method. Before sorting, the diameters of massive grains are measured by CCD for CBN and diamond grains. As seen in Fig. 3, the shape of grains is polyhedron instead of sphere. Therefore, the diameter of grain is defined nominally. For a grain, its picture was obtained by a CCD camera firstly. Then, its picture was demarcated by standard scaleplate. The size of the grain can be measured by the software (VMM2.2C). The mean value of measured maximum and minimum length of the grain is its nominal diameter. The diameters of grains are grouped as shown in Tables 1 and 2. Based on the statistics analysis of measured results are shown in Fig. 4. The diameters of grains obey the normal distribution basically. The mathematical expectation and standard deviation −
−
of CBN and diamond is: X CBN = 364.5 m, CBN = 21.1 m; X dia = 391.8 m, dia = 21.9 m. The grains of CBN and diamond in Tables 1 and 2 are sorted by the above method. The results are shown in Fig. 5. Jet nozzle was placed in the middle of grain collector, which was perpendicular to the direction of jetting. However, there were also grains on both sides of the direction of jetting. This phenomenon can be explained
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Fig. 3. The grain’s shapes used for electroplated grinding wheel under microscope.
Indeed, the deviations of the diameters got smaller after sorting. The diameters of the selected CBN and diamond were more homogeneous, whose deviations are reduced by about 50%. This means that the grains because more uniform in size. The grinding wheels with the homogenized grains must have good performance in the experiments of ground roughness. To verify this, four grinding wheels with the same grain density were fabricated.
3. Design and fabrication of grinding wheels The diameter and thickness of the grinding wheel hub is 100 mm and 15 mm, respectively. The material of the wheel hub is AISI 1045 steel, its surface hardness is HRC50. The radius runout of the wheel hub is less than 3 m, its surface roughness is Ra = 0.8 m. To contrast the grinding performance of different grinding wheels scientifically, the grain density and distribution on grinding wheel surface must remain the same to the greatest extent. Therefore, the mask-based lithography technology was used for fabricating the grinding wheels, and sulfamic acid nickel plating solution was adopted [17,18]. Fig. 6 showed an electroplated grinding wheel fablicated for experimantal investigation. With the help of the mask-based lithography technology [15], the grain distribution of the wheel surface was enforced as uniform random, and the grain density is 1.77 mm−2 . Four kinds of electropalted grinding wheel used for contrast grinding experiments have been shown respectively in Table 3.
4. Investigation of grinding experiments 4.1. Experimental setup Fig. 4. The analysis results of grains.
by the irregular shape of grains. It’s worth noting that the location of grains collector was fixed in the two processes of sorting. The grains in the marked grids by yellow rectangle were picked and measured. After analyzing of results, the standard deviation of each grid was similar. The grains in the grid with red rectangle for CBN and diamond grains are picked and used in the fabrication of the grinding wheels. The mathematical expectation and standard deviation −
of CBN and diamond in red rectangle were: X CBN = 374.43 m, −
CBN = 11.0 m; X dia = 394.27 m, dia = 10.7 m.
The grinding surface roughness is one of main parameter to reveale the surface topography characteristics and the performance of grinding wheel. So, the contrast experiments of grinding roughness were conducted with the four kinds of grinding wheels. The Ra values of the transverse surface roughness of the ground workpieces corresponding to each grinding parameter were measured by NDT120 surface roughness tester. In the present investigation, three measuring regions of workpieces surface were carried out after grinding. In the experiments, the vertical machine center DMU50 and the workpiece (10mm × 115 mm) of AISI 1045 with 45 HRC were used in the experiments. The experimental conditions for each grinding wheel are summarized in Table 4.
340
Y. Lyu et al. / Journal of Manufacturing Processes 30 (2017) 336–342
Fig. 5. The sorting results of two kinds of grains.
Table 3 The grinding wheels used in experiments with 100 mm diameter. Serial number of grinding wheel
1
2
3
4
grains
selected diamond
selected CBN
unselected diamond
unselected CBN
Table 4 Condition for grinding experiments. type
content
Grinding mode Cooling fluid Workpiece speed vw (mm/s) Grinding depth ap (m) Wheel speed n (r/min) Grinding width
Surface grinding (Up-grinding) Water-based emulsion 5, 10, 15, 20, 25 50, 60, 70, 80, 90 3000, 3500, 4000, 4500, 5000 10 mm
Fig. 7. The surface roughness after different grinding times (ap = 50 m, vw = 5 mm/s, n = 5000r/min).
Fig. 6. The material of object grinding wheel.
4.2. Results and discussion Before carring out the experiments at different grinding parameters, the four kinds of the grinding wheels were investigated to obtain the grinding stability of the grinding wheels. Fig. 7 reveals the changes of the surface roughness with the number of grinding passes, in which the surface roughness decreased progressively when the number of grinding passes increased. The surface roughness decreased progressively when the number of grinding passes increased. The surface roughness was beginning to stabilize after 20 grinding passes. The surface rough-
ness was basically stable until the grinding times exceed 30 grinding passes. Before 30 grinding passes, the Ra of the four kinds of grinding wheels decreased gradually. And then it is to maintain stability after 30 grinding passes. The roughness dropped about 50 percent compared to initial value. The phenomenon may be attributed to the pull-out of grains which had less holding force. The fractured and wear of grains occurred faster in the beginning of grinding are also important reasons [19–21]. The effect of grinding parameters on surface roughness for the four kinds of wheels were studied when their grinding performance were relatively stable. The results of measures were shown in Fig. 8. Obviously, the grinding wheels with selected grains perform better than the unselected grinding wheels in Fig. 8. The roughness ground by the grinding wheel 1 decreased about 19.2 percent than the grinding wheel with unselected diamond at different grinding parameters. Coincidentally, the decreased value between the selected and unselected CBN grinding wheel is 19.8 percent. The impact extent of sorting grains using hydraulic power is the same for the CBN and diamond grains in the aspect of grinding roughness because of the close value. The grinding wheels with selected grains had better homogeneity of protrusion heights than the grinding wheels with selected grains. The better homogeneity of protrusion heights would lead to better surface topography of workpiece. The deep grooves were easy to find in the surface of the workpiece ground by the grind-
Y. Lyu et al. / Journal of Manufacturing Processes 30 (2017) 336–342
341
Fig. 8. Effect of grinding parameters on surface roughness for the four kinds of wheels.
ing wheels with unselected grains, which were caused by the grains with higher protrusion heights. But the surface topography of workpiece ground by the grinding wheels with selected grains was smooth relatively. Therefore, the superiority of the grinding wheels with selected grains had been proven. The smaller mathematical expectation would lead to smaller surface roughness when the grain densities are the same based on common knowledge. In addition, the roughness values of surfaces
ground by grinding wheel with CBN grains pattern are always bigger than values ground by the corresponding grinding wheels with diamond grains as shown in Fig. 8. But the mathematical expectations of selected and unselected CBN grains are always smaller than the corresponding diamond grains. The difference of shape between the two kinds of grains can explain the results. As seen in Fig. 3, the homogeneity of diamon grains’ shape are better than the
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Y. Lyu et al. / Journal of Manufacturing Processes 30 (2017) 336–342
CBN grians. Therefore, the inhomogeneity of CBN grains may have negative effect on their protrusion heights. The values of roughness increase with the increase of grinding depth and workpiece speed in Fig. 8. These results are as expected because an increase in workpiece velocity and grinding depth will cause an increase in the uncut chip thickness which yields an increase in surface roughness. The surface roughness became better due to reduced undeformed thickness of single grain as the wheel speed increased. 5. Conclusions This paper presents a kind of method to homogenize the protrusion height of grains on the electroplated grinding wheel based on hydraulic power sorting, whose feasibility was proved by theoretical analysis and experiments of grinding roughness. The diameters of the selected CBN and diamond were more homogeneous, whose deviations are both reduced by about 50%. The values of surface roughness ground by the grinding wheels with selected grains were all reduced by about 19%, which were brought by better homogenous protrusion heights of selected grains. In the future, not only the size but also the shape of grains sorted by using hydraulic power method will be conducted. In this way, the shape of grains combining with engineered grinding wheel will be studied. Acknowledgement The authors gratefully acknowledge support for this work from Chinese National Natural Science Foundation. (Grant No. 51175352) References [1] Li Z, Ding W, Shen L, Xi X, Fu Y. Comparative investigation on high-speed grinding of ticp/ti-6al-4 v particulate reinforced titanium matrix composites with single-layer electroplated and brazed cbn wheels. Chin J Aeronaut 2016;29(5):1414–24. [2] Ghosh A, Chattopadhyay AK. Experimental investigation on performance of touch-dressed single-layer brazed cBN wheels. Int J Mach Tools Manuf 2007;47(7):1206–13. [3] Zhao Q, Guo B. Ultra-precision grinding of optical glasses using mono-layer nickel electroplated coarse-grained diamond wheels. Part 1: ELID assisted precision conditioning of grinding wheels. Precis Eng 2015;39:56–66.
[4] Zhao Q, Guo B. Ultra-precision grinding of optical glasses using mono-layer nickel electroplated coarse-grained diamond wheels. Part 2: Investigation of profile and surface grinding. Precis Eng 2015;39:67–78. [5] Ho JK, Tsai CH, Tsai MY, Yeh TS. Novel method to remove tall diamond grits and improve diamond disk performance. Int J Adv Manuf Technol 2014;75(1–4):1–14. [6] Kitzig H, Tawakoli T, Azarhoushang B. A novel ultrasonic-assisted dressing method of electroplated grinding wheels via stationary diamond dresser. Int J Adv Manuf Technol 2016;86(1):487–94. [7] Dold C, Transchel R, Rabiey M, Langenstein P, Jaeger C, Pude F, et al. A study on laser touch dressing of electroplated diamond wheels using pulsed picosecond laser sources. CIRP Ann Manuf Technol 2011;60(1):363–6. [8] Zhou C, Deng H, Chen G, Wang Y, He J, Du H. Study of the grinding performance of laser-trued and dressed bronzed-bonded diamond grinding wheels. Int J Adv Manuf Technol 2016;85(9–12):2797–803. [9] Chen G, Deng H, Zhou X, Zhou C, He J, Cai S. Online tangential laser profiling of coarse-grained bronze-bonded diamond wheels. Int J Adv Manuf Technol 2015;79(9–12):1477–82. [10] Warhanek M, Walter C, Huber S, Hänni F, Wegener K. Cutting characteristics of electroplated diamond tools with laser−generated positive clearance. CIRP Ann Man Technol 2015;64(1):317–20. [11] Guo X, Huang W, Fu J, Liu X, Qi S. A research on ticking – abrasives with diamond and Cbn Tools whiling and electrolyte flowing in the dies cavity. J North China Inst Astronaut Eng 2000;10(2):19–21. [12] Cui ZM, Liu ZR, Zhang HY. Manufacturing technique of high precision intricate diamond dressing roller. Mater Sci Forum 2006;532–533:492–5. [13] HANS SUPERABRASIVE MATERIALS CO., LTD. Diamond dressing Roller, http:// www.hansinc.com/diamond-dressing-rollers#!, 2017 4 5. [14] Yu N, Lyu YS, Wang J. Some researches on the issue in the manufacturing of electroplated CBN grinding tool. Mach Des Manuf 1996;(1):49–51. [15] Changyin D, Wanli L, Shengtian Z. Analysis and application of model for solid particle movement in Newton fluid. J China Univ Pet: Ed Nat Sci 2007;31(5):55–9. [16] Ning W, Qi Z, Zhanqing Q. Evaluation on calculation methods of solid particle settling velocity in fluid. Oil Drill Prod Technol 2000;22(2):51–4. [17] Lu YS, Zhao CY, Wang J, He Y, Kou ZH. Design and fabrication of the superabrasive grinding wheel with phyllotactic pattern. Adv Mater Res 2012;472:2354–60. [18] Yu HY, Wang J, Lu YS. Simulation of grinding surface roughness using the grinding wheel with an abrasive phyllotactic pattern. Int J Adv Manuf Technol 2016;84(5):861–71. [19] Yu HY, Lu YS, Wang J. Study on wear of the grinding wheel with an abrasive phyllotactic pattern. Wear 2016;358:89–96. [20] Shi Z, Malkin S. An investigation of grinding with electroplated CBN wheels. CIRP Ann Manuf Technol 2003;52(1):267–70. [21] Ding WF, Xu JH, Chen ZZ, Su HH, Fu YC. Wear behavior and mechanism of singlelayer brazed CBN abrasive wheels during creep-feed grinding cast nickel-based superalloy. Int J Adv Manuf Technol 2010;51(5–8):541–50.
Contents lists available at ScienceDirect
Journal of Manufacturing Processes journal homepage: www.elsevier.com/locate/manpro
Technical Paper
Improved performance of electroplated grinding wheels using a new method of controlled grain size sorting Yushan Lyu a , Haiyue Yu b,∗ , Jun Wang a,c , Guowei Zhao a , Zhizhen Liu a a b c
School of Mechanical Engineering, Shenyang Ligong University, Shenyang, PR China School of Mechatronic Engineering, Changchun University of Technology, Changchun, 130012, PR China School of Mechanical Engineering and Automation, Northeastern University, Shenyang, PR China
a r t i c l e
i n f o
Article history: Received 9 May 2017 Received in revised form 19 September 2017 Accepted 3 October 2017 Keywords: Sorting grains Hydraulic power Protrusion height Grinding wheel Surface roughness
a b s t r a c t The protrusion heights of grains on electroplated grinding wheel are uneven. This phenomenon has a negative influence on the grinding performance of electroplated grinding wheel. In this paper, CBN and diamond grains were sorted by hydraulic power method. Four kinds of electroplated grinding wheels were fabricated with selected and unselected CBN diamond grains. Then, the surface roughness of workpieces ground by the four kinds of grinding wheels were investigated and analyzed in contrast experiments. The experimental results show that the grains sorting method using hydraulic power can homogenize the size of grains; and lower ground surface roughness has been obtained by the electroplated grinding wheels with the help of the new method of controlled grain size sorting. © 2017 Published by Elsevier Ltd on behalf of The Society of Manufacturing Engineers.
1. Introduction The electroplated grinding wheel could be used in the filed of high efficiency grinding due to its good properties of high hardness, high thermal conductivity, high wear resistance and high chemical inertness [1]. But the grains on most electroplated grinding wheels are single-layer and are not typically dressed. Therefore, the protrusion heights of grains on the single-layer grinding wheel mainly depend on the original state of grains. Due to the geometrical flexibility of grains, high transverse surface roughness of the workpiece could be produced by the electroplated grinding wheel without dressing. To homogenize the protrusion height of grains, some studies on dressing monolayer superabrasive wheels were conducted. Ghosh et al. [2] developed a touch-dressing method for brazedtype single-layer CBN wheels, and finally obtained transverse surface roughnesses were Ra = 1 m and Ra = 1.5 m when material hardened IS103Cr1 was ground; Bing Guo [3] developed a novel conditioning technique for copper bonded diamond grinding wheels. During the conditioning process, the conditioners were continuously dressed by the means of electrolytic inprocess dressing (ELID). The protrusion height of grains can be
∗ Corresponding author. E-mail address: [email protected] (H. Yu).
homogenized by this method to a great extent. In addition, a constant wheel peripheral envelop surface exhibiting flattened diamond grains with a run-out less than 2.5 m was achieved, and the grinding performance of the grinding wheels was promoted [4]. Ho et al. [5] removed tall diamond grits which were found by scratch mechanism on the surface of grinding tool. This novel method can improve diamond disk performance. Kitzig et al. [6] developed a novel ultrasonic-assisted dressing method for electroplated grinding wheels. Through this process, the diamond grains of an electroplated grinding wheel were successfully conditioned/fractured by hitting with an ultrasonic-assisted diamond dresser. Then, numerous sharp cutting edges and similar grains’ protrusion were generated. Experimental analyses have shown that the grinding of tungsten carbide with fractured electroplated D251 diamonds enabled fine surface roughness (Ra < 0.1 m and Rz < 0.8 m). Laser technique was also applied to increase the smoothness of the wheel surfaces, thus increasing the homogenization of protrusion height. Dold et al. [7] conducted a laser touch dressing study to cut the diamond grains within a defined grain protrusion without any thermal damage on the nickel bond. Genyu Chen et al. [8,9] presented an online tangential laser profiling method for single layer abrasive wheel. This method mainly consisted of a pulsed fiber laser, a surface grinder, a motorized three-dimensional (3D) translation stage, laser displacement sensors and a laser power meter. It could be seen as special dressing method. The single-layer
https://doi.org/10.1016/j.jmapro.2017.10.004 1526-6125/© 2017 Published by Elsevier Ltd on behalf of The Society of Manufacturing Engineers.
Y. Lyu et al. / Journal of Manufacturing Processes 30 (2017) 336–342
337
Fig. 2. The force analysis for the grain. Fig. 1. Schematic view of sorting grain device.
grinding wheel dressed by this method not only obtain homogenized protrusion height of grains, but also achieve lower mean circular runout and the axial gradient error. The positive clearance angles of grains (2.4◦ ) can also be obtained [10]. However, some problems generated in dressing process are unavoidable. Obviously, a lot of abrasives will be waste and loss. Besides, the grain damages, including micro-fractured, macrofractured, flat and break flat, will be generated by high temperature or mechanical force. In addition, some dressing process are complex and time-consuming. For electroplated grinding tools, the protrusion heights of grains are determined in the stage of fabricating process. Internal electroplate method (or inner galvanizing method) [11–13] is one of the most effective ways to improve the homogeneous protrusion height of grains. Nevertheless, this method is mainly used for diamond dressing roller because of its higher cost and more complex process than general plating method. To solve the issue, a kind of rolling grain method also was present [14]. But for the rolling grain method, the macro and micro fractures of grains may occur in the process of pressing grains due to the high force generated. It is difficult to obtain more consistent protruded heights of grains due to the elastic recoveries of the abrasive grains and the wheel matrix. But above all, grains’ damages, lower consumption rate of grains and complex process must be avoided when the homogeneous protrusion heights of grains are obtained. To attain it, a new method was used to sort the grains of CBN and diamond with the help of hydraulic power in this paper. Several electroplated grinding wheels were fabricated with unselected and selected grains. To compare in experiments better, the distribution of grains on these grinding wheels are the same with the help of mask-based lithography. The ground surface roughnesses using these grinding wheels were investigated to verify the advantages of grinding wheels with selected grains. 2. Sorting grains 2.1. The basic principle of sorting grains The grains was sorted with the help of hydraulic power, the schematic view of sorting grains is shown in Fig. 1. The grains spurt from the jet in the sorting box, whose movement in the liquid is also shown in Fig. 1. When the horizontal speed of grain reaches zero, the grain will sink vertically [15]. The fundamental principle is: grains with different size fall from the same height within the liquid initially. A while later, these grains will locate in different
position under the action of gravity, liquid resistance and buoyancy force. Then, the grains with different size will be distinguished. The liquid in Fig. 1 is plating solution which can prevent grains from contaminating in the sorting process. The purpose of mixer in Fig. 1 is to keep the grains uniform in the liquid. 2.2. The theoretical analysis of sorting grains As shown in Figs. 1 and 2, The movement of grains in the liquid will be influenced by the combined action of gravity (G), liquid resistance (Fvgx and Fvgy ) and buoyancy force (Fa ) when the grains spurt from the jet nozzle at a velocity (vg0 ) and angle (␣) in the sorting box. To analyze the movement of grains easily, the following assumptions are made: (1) all grains are spherical particle; (2) the movement of each grain is independent; (3) The pressure gradient force is ignored. Therefore, the gravity (G), liquid resistance (Fvgx and Fvgy ) and buoyancy force (Fa ) of movoment grain are analyzed, respectively [15]. The buoyancy of grain is: Fa =
3 Dp g 6
(1)
The gravity of grain: 3 Dp p g 6
G=
(2)
The liquid resistance:
⎧ v 2 ⎪ ⎨ Fvgx = C0x A gx 2
⎪ ⎩F
vgy = C0y A
(3)
vgy 2 2
Where: A is the meeting area of flowing of grain and A = 4 Dp 2 . Dp is the grains diameter. p is the density of the grain; is the density of the liquid; C0x and C0y are the resistance coefficient, g is the gravitational acceleration. According to Newton’s second law, with the help of Eqs. (1)–(3), the force balance equation for the grain in the liquid is:
⎧ dvgx vgx 2 ⎪ ⎪ 6 Dp 3 p dt = − 4 C0x Dp 2 2 ⎨
⎪ D 3 2 ⎪ ⎩ Dp 3 p dvgy = 6 p p p − g − C0y Dp 2 vgy 6
dt
p
4
2
.
(4)
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Where: C0x and C0y are the resistance coefficient of sorting liquid. Because of the low speed of liquid in Fig. 1, the grain is in laminar region. So, the resistance coefficients are [16]: C0x =
24 24 , C0y = . Rex Rey
(5)
Where: Rex and Rey is the Reynolds number and its mathematical expression is: Rex =
DP vgx DP vgy , Rey = .
(6)
Where is the viscosity coefficient of the liquid. Putting the Eq. (6) into the Eq. (5), then putting the Eq. (5) into the Eq. (4), the Eq. (4) can be rewritten as:
⎧ dv 1 ⎪ ⎨ Dp 2 p gx = −3 · vgx 6
dt
6
dt
⎪ ⎩ 1 Dp 2 p dvgy = 1 D2 p − g − 3 · vgy
.
(7)
6
The integral conditions of Eq. (7) are as following:
⎧ ⎧ dx dx ⎨ vgx |t=∞ = dt |t=∞ = v0 cos ˛ ⎨ vgx |t=∞ = dt |t=∞ = 0 ⎩
vgy |t=∞ =
⎩
dy = v0 sin ˛ | dt t=0
x|t=0 = 0
and
vgy |t=∞ =
dy | =C dt t=∞
y|t=0 = 0
(8)
−)g
P Where: C = (18 Dp2 , which is a constant velocity when the gravity (G) and liquid resistance (Fvgy ) reach equilibrium with the buoyancy force (Fa ). By the use of the integal conditions, the Eq. (7) can be solved, and the movement trajectory equation of enjected abrasive grain can be obtained, as follows:
⎧ ⎪ ⎪ ⎪ p · Dp2 ⎪ ⎪ x = vg0 cos ˛ · ⎪ ⎪ 18 ⎪ ⎪ ⎪ ⎪ ⎪ ⎪ ⎨ p − gDp2 y=
⎛ −
⎜
· ⎝1 − e
p · Dp2
· t + vg0 sin ˛ −
18 ⎪ ⎪ ⎪ ⎛ ⎞ ⎪ ⎪ 18 ⎪ ⎪ − · t 2 ⎪ p Dp ⎜ ⎪ · Dp2 ⎟ ⎪ ⎪ · · ⎝1 − e p ⎠ ⎪ 18 ⎪ ⎩
·t
⎟ ⎠
p − gDp2
p ·D2
(10)
.
At this point, the movement of the grain is in the y direction only, as seen in Fig. 1. Therefore, its movement displacement in the y direction is:
y|
p D2 p
t=3 18
≈
p Dp2 18
0.99vg0 sin ˛ + 2
diameter (m)
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
366–370 370–374 374–378 378–382 382–386 386–390 390–394 394–398 398–402 402–406 406–410 410–414 414–418 418–422 422–426
Table 2 The measured result of diamond grains (45/50 mesh). group
diameter (m)
group
diameter (m)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
< 340 340–344 344–348 348–352 352–356 356–360 360–364 364–368 368–372 372–376 376–380 380–384 384–388 388–392 392–396
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
396–400 400–404 404–408 408–412 412–416 416–420 420–424 424–428 428–432 432–436 436–440 440–444 444–448 448–452 452–456
p · Dp2 18
,
H ≥ y| t=3
p Dp2
(12)
18
2.3. The results of sorting grains
be obtained. But, when the movement time (t) is t = 3 · 18p , the movement displacement in the x direction will reach 99% of the theoretical value, namely
18
group
<310 310–314 314–318 318–322 322–326 326–330 330–334 334–338 338–342 342–346 346–350 350–354 354–358 358–362 362–366
18
If the movement time (t) in the Eq. (9) is considered to be infinite, then the biggest movement displacement in the x direction will
p · Dp2
diameter (m)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
t ≥3·
(9)
xmax ≈ 0.99vg0 cos ˛ ·
group
It can be seen from Eqs. (10) and (11) that the grains can be sorted successfully using the device in Fig. 1 when the movement time (t) and the jet nozzle hight (H) in the Fig. 1 meet the follow conditions:
⎞
18
Table 1 The measured result of CBN grains (45/50 mesh).
p − gDp2 18
(11)
The grains of CBN and diamond are 45/50 mesh and came from the same batch. These grains were sorted respectively using above method. Before sorting, the diameters of massive grains are measured by CCD for CBN and diamond grains. As seen in Fig. 3, the shape of grains is polyhedron instead of sphere. Therefore, the diameter of grain is defined nominally. For a grain, its picture was obtained by a CCD camera firstly. Then, its picture was demarcated by standard scaleplate. The size of the grain can be measured by the software (VMM2.2C). The mean value of measured maximum and minimum length of the grain is its nominal diameter. The diameters of grains are grouped as shown in Tables 1 and 2. Based on the statistics analysis of measured results are shown in Fig. 4. The diameters of grains obey the normal distribution basically. The mathematical expectation and standard deviation −
−
of CBN and diamond is: X CBN = 364.5 m, CBN = 21.1 m; X dia = 391.8 m, dia = 21.9 m. The grains of CBN and diamond in Tables 1 and 2 are sorted by the above method. The results are shown in Fig. 5. Jet nozzle was placed in the middle of grain collector, which was perpendicular to the direction of jetting. However, there were also grains on both sides of the direction of jetting. This phenomenon can be explained
Y. Lyu et al. / Journal of Manufacturing Processes 30 (2017) 336–342
339
Fig. 3. The grain’s shapes used for electroplated grinding wheel under microscope.
Indeed, the deviations of the diameters got smaller after sorting. The diameters of the selected CBN and diamond were more homogeneous, whose deviations are reduced by about 50%. This means that the grains because more uniform in size. The grinding wheels with the homogenized grains must have good performance in the experiments of ground roughness. To verify this, four grinding wheels with the same grain density were fabricated.
3. Design and fabrication of grinding wheels The diameter and thickness of the grinding wheel hub is 100 mm and 15 mm, respectively. The material of the wheel hub is AISI 1045 steel, its surface hardness is HRC50. The radius runout of the wheel hub is less than 3 m, its surface roughness is Ra = 0.8 m. To contrast the grinding performance of different grinding wheels scientifically, the grain density and distribution on grinding wheel surface must remain the same to the greatest extent. Therefore, the mask-based lithography technology was used for fabricating the grinding wheels, and sulfamic acid nickel plating solution was adopted [17,18]. Fig. 6 showed an electroplated grinding wheel fablicated for experimantal investigation. With the help of the mask-based lithography technology [15], the grain distribution of the wheel surface was enforced as uniform random, and the grain density is 1.77 mm−2 . Four kinds of electropalted grinding wheel used for contrast grinding experiments have been shown respectively in Table 3.
4. Investigation of grinding experiments 4.1. Experimental setup Fig. 4. The analysis results of grains.
by the irregular shape of grains. It’s worth noting that the location of grains collector was fixed in the two processes of sorting. The grains in the marked grids by yellow rectangle were picked and measured. After analyzing of results, the standard deviation of each grid was similar. The grains in the grid with red rectangle for CBN and diamond grains are picked and used in the fabrication of the grinding wheels. The mathematical expectation and standard deviation −
of CBN and diamond in red rectangle were: X CBN = 374.43 m, −
CBN = 11.0 m; X dia = 394.27 m, dia = 10.7 m.
The grinding surface roughness is one of main parameter to reveale the surface topography characteristics and the performance of grinding wheel. So, the contrast experiments of grinding roughness were conducted with the four kinds of grinding wheels. The Ra values of the transverse surface roughness of the ground workpieces corresponding to each grinding parameter were measured by NDT120 surface roughness tester. In the present investigation, three measuring regions of workpieces surface were carried out after grinding. In the experiments, the vertical machine center DMU50 and the workpiece (10mm × 115 mm) of AISI 1045 with 45 HRC were used in the experiments. The experimental conditions for each grinding wheel are summarized in Table 4.
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Fig. 5. The sorting results of two kinds of grains.
Table 3 The grinding wheels used in experiments with 100 mm diameter. Serial number of grinding wheel
1
2
3
4
grains
selected diamond
selected CBN
unselected diamond
unselected CBN
Table 4 Condition for grinding experiments. type
content
Grinding mode Cooling fluid Workpiece speed vw (mm/s) Grinding depth ap (m) Wheel speed n (r/min) Grinding width
Surface grinding (Up-grinding) Water-based emulsion 5, 10, 15, 20, 25 50, 60, 70, 80, 90 3000, 3500, 4000, 4500, 5000 10 mm
Fig. 7. The surface roughness after different grinding times (ap = 50 m, vw = 5 mm/s, n = 5000r/min).
Fig. 6. The material of object grinding wheel.
4.2. Results and discussion Before carring out the experiments at different grinding parameters, the four kinds of the grinding wheels were investigated to obtain the grinding stability of the grinding wheels. Fig. 7 reveals the changes of the surface roughness with the number of grinding passes, in which the surface roughness decreased progressively when the number of grinding passes increased. The surface roughness decreased progressively when the number of grinding passes increased. The surface roughness was beginning to stabilize after 20 grinding passes. The surface rough-
ness was basically stable until the grinding times exceed 30 grinding passes. Before 30 grinding passes, the Ra of the four kinds of grinding wheels decreased gradually. And then it is to maintain stability after 30 grinding passes. The roughness dropped about 50 percent compared to initial value. The phenomenon may be attributed to the pull-out of grains which had less holding force. The fractured and wear of grains occurred faster in the beginning of grinding are also important reasons [19–21]. The effect of grinding parameters on surface roughness for the four kinds of wheels were studied when their grinding performance were relatively stable. The results of measures were shown in Fig. 8. Obviously, the grinding wheels with selected grains perform better than the unselected grinding wheels in Fig. 8. The roughness ground by the grinding wheel 1 decreased about 19.2 percent than the grinding wheel with unselected diamond at different grinding parameters. Coincidentally, the decreased value between the selected and unselected CBN grinding wheel is 19.8 percent. The impact extent of sorting grains using hydraulic power is the same for the CBN and diamond grains in the aspect of grinding roughness because of the close value. The grinding wheels with selected grains had better homogeneity of protrusion heights than the grinding wheels with selected grains. The better homogeneity of protrusion heights would lead to better surface topography of workpiece. The deep grooves were easy to find in the surface of the workpiece ground by the grind-
Y. Lyu et al. / Journal of Manufacturing Processes 30 (2017) 336–342
341
Fig. 8. Effect of grinding parameters on surface roughness for the four kinds of wheels.
ing wheels with unselected grains, which were caused by the grains with higher protrusion heights. But the surface topography of workpiece ground by the grinding wheels with selected grains was smooth relatively. Therefore, the superiority of the grinding wheels with selected grains had been proven. The smaller mathematical expectation would lead to smaller surface roughness when the grain densities are the same based on common knowledge. In addition, the roughness values of surfaces
ground by grinding wheel with CBN grains pattern are always bigger than values ground by the corresponding grinding wheels with diamond grains as shown in Fig. 8. But the mathematical expectations of selected and unselected CBN grains are always smaller than the corresponding diamond grains. The difference of shape between the two kinds of grains can explain the results. As seen in Fig. 3, the homogeneity of diamon grains’ shape are better than the
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CBN grians. Therefore, the inhomogeneity of CBN grains may have negative effect on their protrusion heights. The values of roughness increase with the increase of grinding depth and workpiece speed in Fig. 8. These results are as expected because an increase in workpiece velocity and grinding depth will cause an increase in the uncut chip thickness which yields an increase in surface roughness. The surface roughness became better due to reduced undeformed thickness of single grain as the wheel speed increased. 5. Conclusions This paper presents a kind of method to homogenize the protrusion height of grains on the electroplated grinding wheel based on hydraulic power sorting, whose feasibility was proved by theoretical analysis and experiments of grinding roughness. The diameters of the selected CBN and diamond were more homogeneous, whose deviations are both reduced by about 50%. The values of surface roughness ground by the grinding wheels with selected grains were all reduced by about 19%, which were brought by better homogenous protrusion heights of selected grains. In the future, not only the size but also the shape of grains sorted by using hydraulic power method will be conducted. In this way, the shape of grains combining with engineered grinding wheel will be studied. Acknowledgement The authors gratefully acknowledge support for this work from Chinese National Natural Science Foundation. (Grant No. 51175352) References [1] Li Z, Ding W, Shen L, Xi X, Fu Y. Comparative investigation on high-speed grinding of ticp/ti-6al-4 v particulate reinforced titanium matrix composites with single-layer electroplated and brazed cbn wheels. Chin J Aeronaut 2016;29(5):1414–24. [2] Ghosh A, Chattopadhyay AK. Experimental investigation on performance of touch-dressed single-layer brazed cBN wheels. Int J Mach Tools Manuf 2007;47(7):1206–13. [3] Zhao Q, Guo B. Ultra-precision grinding of optical glasses using mono-layer nickel electroplated coarse-grained diamond wheels. Part 1: ELID assisted precision conditioning of grinding wheels. Precis Eng 2015;39:56–66.
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