Improving the quality of surface in the polishing process with the magnetic abrasive powder polishing using a high-frequency induction heating source on CNC table

10 Pages·0.751 MB·English

by  Mirian S.S.

IntJAdvManufTechnol
DOI10.1007/s00170-010-3109-1
ORIGINAL ARTICLE
Improving the quality of surface in the polishing process
with the magnetic abrasive powder polishing using
a high-frequency induction heating source on CNC table
Seyed Saeed Mirian&Alireza Fadaei&
Seyed Mohsen Safavi&Mahmoud Farzin&
Mahmoud Salimi
Received:1October2010/Accepted:30November2010
#Springer-VerlagLondonLimited2010
Abstract In this research, polishing flat surfaces has been 1 Introduction
donebyusingacompletelynewandinnovativemethod.In
this method, rotary magnetic tool that carry magnetic Avariety of research has been done in this field, based on
abrasive powders, is placed in a very strong thermal which a new approach has been proposed in this paper, by
induction field, and magnetic rotary tool frequently change using the fact that heating and cooling of the abrasive
its direction from clockwise (CW) to counterclockwise powder can improve the process of polishing. The whole
(CCW) and CCW to CW. The frequency of changing experiments carried out indicate success of the method in
rotation direction is an important parameter of this the average air gaps. Review of the previous works carried
innovation method. The intended pieces for polishing out indicates that no measure has been so far undertaken
operations have been placed on a synchronic two-axis aboutplacingtherotarymagneticabrasivepowderinavery
Cartesian CNC table, and the gap between rotary magnetic intense thermal electromagnetic field and using the energy
tool and the sheet surface can be controlled by a power resulting from this field for polishing. While associating a
transmissionscrew operatinginthedirectionofthevertical kind of effective frictional brushing, it is a new subject to
axis.Severalexperimentshaveprovedhighperformanceof which the research work done has been paid. In this
the new proposed method in the process of polishing. innovativemethodofpolishing,rotatingofmagneticrotary
tool and meanwhile powering on–off of high-frequency
Keywords High-frequency induction heat source induction heat source (HFIHS) will cause the abrasive
(HFIHS).Data acquisition mechatronics.Abrasive powder powders frequently getting hot and cold. This heating and
polishing.Numerical control.Air gap cooling of powders, helps the powders to be more fragile
and the sharp edges of the powders will increase. At the
Nomenclature same time, temperature shock of this frequent heating and
HAPP Heating-assisted powder polishing cooling will affect polishing process and the abrasive
PLC Programmable logic control powder will act more efficiently. In this point of view, this
MAP Magnetic abrasive polishing proposed method is an innovative method that no other
HFIHS High-frequency induction heating source referencespaidonit.Theotheradvantageofthisinnovative
CNC Computer numerically controlled methodiscoolingandheatingofabrasivepowders inshort
RMT Rotary magnetic tool cycle times. Short cycle time of heating and cooling of
abrasive powders is source of temperature shocking of this
method. This temperature shock can help to improving of
polishing process and using of HFIHS will cause
: : : : Several advantages in comparison to other heating
S.S.Mirian(*) A.Fadaei S.M.Safavi M.Farzin
M.Salimi methods that the major advantages are listed below:
IsfahanUniversityofTechnology,
1-1 HFIHS can cause the heating process in short cycle
Khomeynishahr,Iran
e-mail:[email protected] times in comparison with other methods.
IntJAdvManufTechnol
1-2 After powering off of HFIHS, rotating of magnetic moved up and down by a power transmission screw, and
rotary tool can help the cooling of abrasive powders can change the distance between magnetic tool and the
in short cycle times. surface of the circular flat pieces. Due to some restrictions,
1-3 In this method of temperature shocking system, no just polishing the top of circular flat pieces has been
other facilities like oven and furnace is needed. considered in the present research, and polishing of three-
1-4 Thismethodismorecosteffectivethanothermethods. dimensional pieces with this new method, has been
postponed to the next research works. Furthermore, in this
proposed system, the polishing forces were measured with
and without the presence of HFIHS by using a data
2 Literature review acquisition system as well as system of monitoring the
currentpassingthroughthesteppermotordrives(whichisa
Special feature of MAP method is to create surfaces with symbol of the forces).
desirable or flat high-quality curve, without having direct These forces have been measured in two following
contactofthepolishingtoolwiththeintendedsurfaces[1]. In cases,
mostoftheresearchdone,theworkpieceintendedtoperform
the polishing operations is being rotated, in which forced 1. The powder and the magnetic tool are not placed in an
passing of the abrasive particles over the rotating workpiece inductive thermal electromagnetic field.
has caused the workpiece surface to be polished [2]. 2. The powder and the magnetic tool are placed in an
Furthermore, combination of this polishing method with inductive thermal electromagnetic field
automatic computer numerically controlled (CNC) table, to
The difference between these forces in the two cases
automatically move the workpiece, is the topic on which
above, as well as the quality of polished surface, is one of
manynewresearchhavebeencarriedout[3,4];andavariety
output parameters of the experiments.
ofworkshasbeenprovidedaboutmathematicalmodelingof
The main components of this proposed system are:
this polishing method, among which ref [5] can be cited.
Also, in many cases, researchers have used the magneto- 3-1 Two-axis CNC table, whose spindle in the Z
rheologicalgelinsteadofabrasivepowderfortheprocessof direction can be moved by a power transmission
polishing, among which the refs [6, 7] can be cited. screw that can adjust the gap distance between the
In research work conducted by Dabrowski et al. [6], tool and workpiece.
workpiece and magnetic head have simultaneously rotated, By using two stepper motors whose drives are
duetowhichperformanceofthismethodhasbeenincreased. controlledbyaPCbasecontroller,tableiscapableof
Ref [8] also has made internal polishing of austenitic automatically moving on relevant proposed route.
steel capillary tubes by this method. Furthermore, ref [9] This system shown in Fig. 1
has polished the inner surface of aluminum–ceramic
equipment using this method. Cooling and heating of
abrasive powders with HFIHS in short times, and conse-
quently, a temperature shock condition is a new topic that
no other reference paid attention to it.
3 Introduction of system and components
In the proposed method, there is the ability to move flat
sheets in the horizon plane through designing and con-
structing a two-axis Cartesian CNC table.
Due to some restrictions, just polishing the flat sheets
has been studied in the present research, and polishing the
three-dimensional sheets has been postponed to the next
research works.
In the proposed method, it will be possible to move the
circularflatpiecesinhorizonplanebytheuseofatwo-axis
automatic CNC table.
Furthermore, the third axis of system (Z), on which
three-phasemotorofmagnetictoolhasbeenplaced,canbe Fig.1 Equipmentcontrollingtableandspindle
IntJAdvManufTechnol
3-2 Mechatronic set of the system includes drive and clockwise rotation of the system's spindle and
programmable logic controller (PLC) to control the controlling the corresponding time.
speed, direction, and frequency of the three-phase
3-6 Abrasive powder
motor driving the magnetic head, as well as stepper
Abrasive powder used in this system includes the
motor drives with data acquisition equipment and
materials requiredinsandblastsystems,withbrand of
pulsegeneratoranddirectcurrent(DC)powersupply.
grate steel and size of 70 μm. Each component will
Figure 2 shows this complete set.
be separately described as follows:
3-3 High-frequency induction heating source
CNC table
This system (as shown in Fig. 4) has a copper coil
In this table, which is made by an innovative
that abrasive powder will insert in this coil and when
mechanism without using LM and ball screw, guide
this source run it can immediately heat the abrasive
pin, pulley time, and timing belt are to be used. By
powder. Thisheating source can frequently be on and
using two stepper motors with accuracy of 1.8 deg/
off by PLC and this action will affect the polishing
pulse, this table is capable of automatically moving
process. The heated abrasive powder could act better
with various well-known motion trajectories in CAD/
than normal powder and this is the main difference
CAM applications.
between this method and previous methods.
These methods include the following:
3-4 Special magnetic rotary tool, in which high-intensity
magneticdiscsareplacedatmaximummodeofabout & zigzag,
8,400 gausses; and the number of magnetic discs & spiral motion from inside to outside,
inside it will determine the vertical magnetic field & spiral motion from outside to inside,
intensity. & one-way method of motion.
3-5 Software collection and computer Inthecrossoftwoguidepinsofx,y,oneholder
It includes the following software: has been prepared, on which the intended flat
workpieces can be placed before the process of
& Labview for monitoring polishing forces; polishing. Furthermore, the spindle placed in the
& Mastercam for extracting CNC code related to the system, which is responsible for carrying the
automatic motion magnetic head; rotating magnetic head, has the ability to move up
& Mach3 to convert the CNC code into motion and down and thus to change the air gap between
pulses, and to send them on the PC base controller the rotating magnetic head and the workpiece, by a
of the table's driving system; and cast-iron plate connected to the power transmission
& Ladder master for programming logic controller of screw in the direction of z axis.
three-phasemotorsystemandcontrollingspeedand The spindle can be fully controlled by its
directions of successive clockwise and counter- inverter and PLC, with regard to the speed,
Fig.2 Completeset
IntJAdvManufTechnol
direction, and the amount of rotation which is AsshowninFig.3,theflatsheetforpolishingis
among the parameters affecting the process of located on top of the container, and under the flat
polishing. CNC table, as well as inverter and sheetisavacantspacethattheabrasiveslurryfilled
spindle are shown in Fig. 1. it. Figure 4 shows this object schematically. In this
Mechatronic set method, top and bottom of sheets will be polished
This set includes two stepper motor drives with with two different methods. Top of sheets will be
PC base controller to convert the CNC motion polished with HAS (heating-assisted system) and
codes into pulse-width modulation (PWM) for bottom of sheet will be polished by effect of
drives using the Mach3 software. Furthermore, abrasive slurry. This slurry abrasive is magnetic
three-phase motor inverter and the system's PLC sensitive and wants to move toward the magnetic
are among other components of the system. DC rotary tool and existing of flat sheet, prevent this
power supply is used for operating stepper motor motion and thus cause to polishing of bottom side
drives; and data acquisition card is also used for of sheet. In this kind of polishing one can compare
measuring and recording the polishing forces, by these two kinds of polishing with another and thus
getting and recording data of current passing at the same time heating-assisted polishing and
through each drive (in each 0.01-s-interval times). traditional use of abrasive slurry in polishing, will
Furthermore, PLC is responsible for controlling be possible.
three-phase motor. Another duty of PLC is control- High-frequency induction heating source
ling (on–off) high-frequency induction heating The induction heat source works at 220 V
source. The frequency of on–off of this heating electricity and its working frequency is equal to
source is one of important parameters. The time of 100 kHz. Its maximum voltage and current inten-
heating could not select more than 10 s because it sity are 12 A and 220 V, respectively. The
may melt the powder and it could not select lower maximum input power is equal to 9.5 kW and a
that 0.5 s because in this case the abrasive powder tank with at least 50 L of water, as well as a pump
couldnotbeheatedperfectly.Theoptimumtimeof with discharge capacity of 2 L/min and head of
on-off of this system that obtained during experi- 0.1 MPa are needed, in order to cool the copper
ments was 3-s on and 7-s off that this cycle coil. With minor change in the hand steering pedal
frequently repeated. Figure 3 shows the block of the thermal source, the system can be automat-
diagram of complete set during experiments. ically controlled by the pulses sent from the PLC.
Fig.3 Completeblockdiagram
ofsystem
IntJAdvManufTechnol
Thus,thePLCoutputscontrollingtheprocessinclude to the three-phase motor, direct coupling with the
y0 and y1 for creating successive clockwise and motor shaft is used, and that the motor output is
counterclockwiserotationsoftheset'sspindle,aswell directly transferred to the rotating magnetic tool.
as output y2 for switching the pedal of induction Computer and software collection
heating source. As is shown in Fig. 4, during the MastercamsoftwarehasbeenusedtoextractCNC
processofpolishing,whiletherotarymagnetictoolis motion codes by well-known methods and strategies,
placedwithinthecoppercoiloftheinductionheating such as the different methods of pocket and center
source, sheet is moved by CNC table in accordance contourasclockwiseorcounterclockwise.Thepieces
withtheproposedCAD/CAMstrategy;andpolishing selected for polishing operations include sheets with
occurs by hot magnetic abrasive particles. 150-mmdiameter;andtoextractmotioncodesinthe
The abrasive particles will have two motions software, the intended CAD geometry is drawn as
(rotation and transitional motion) which include circles with diameters of 150 mm. Furthermore, the
rotation around the vertical axis (to follow rotation intended CAM will include the use of known pocket
of the magnetic tool) as well as traversing the methods on the related CAD as well as extraction of
direction (to follow the magnetic tool). Polishing CNC codes related to any strategy. One of the
operationsoftheflatsurfacehappenfasterandeasier, strategies including a spiral motion from inside to
due to successive hot and cold temperatures of the outside in the clockwise system is shown in Fig. 8
abrasive particles within the copper coil of induction Furthermore, programming of the set's PLC
machine, as well as their successive clockwise and controller is done by ladder master software. It
counterclockwise rotations. includes control of speed, direction, and time of
In Fig. 5 high-frequency heating source during clockwise and counterclockwise rotations of the
heating of abrasive powder is shown. magnetic rotary head. This software also controls
Magnetic rotary tool the switching pedal of the high-frequency induction
This tool has been so designed and built that a heating source, and programs the system's PLC,
certain number of magnetic discs with specified field which is the type of vigor with eight inputs and six
intensity can be fed within it, and the intended test outputs, with the ladder logic method.
can be done. Magnetic abrasive powder
Themorenumberofdiscs,thehigherrotatingfield Different abrasive powders, including steel
intensity, and consequently the stronger abrasive grate powders for sandblasting, and sintered
brush. powder of aluminum oxide and iron carbonyl,
Thistool,intermsoffieldintensity,isverystrong, have been used during stages of relevant experi-
andasisshowninFig.6,iscapableofcarryinga 5- ments. Due to their high melting temperature and
kg mass in the case that the magnetic discs (whose resistance against melting in high-frequency
structurehasbeendescribedinFig.7)havefilledone induction heating environment, it is necessary to
half of it. It should be noted that to connect this tool use aluminum oxide and steel grate.
Fig.4 Polishingofbottom
andtopsidebytwodifferent
methods
IntJAdvManufTechnol
Fig.7 Specialstructureofarotatingmagnetictool
manually powered transmission screw; and the effect of
Fig.5 Inductionheatingsourceduringheatingofabrasivepowder
which can be observed on the intended outputs, including
4 Complete set the surface smoothness and polishing force. PLC, as a
central system controller, can switch the pedal of induction
As is shown in Fig. 3, since rotating magnet tool is placed source. It also can make the abrasive powder hot and cold.
inside copper coil of the induction heating source in this Furthermore, the frequency of successive switching of the
innovative method, it is impossible for the rotary magnetic high-frequency induction heating source is another input
head to be moved on the plane XY. So, the workpiece parameter in the series of the experiments conducted.
shouldbeautomaticallymovedbytheCNCtableunderthe The gap can be changed with axis-z manually powered
head. Furthermore, the amount of air gap between the transmission screw, whose effect can be observed on the
rotary magnetic tool andsurface of sheet (in whichpowder intended outputs, including the smoothness of the surface
of abrasives are placed), isone ofthe important parameters
of the set of tests which can be changed with axis-z
Fig. 6 High magnetic power of a rotating head to keep a 5-kg cast-
ironweight Fig.8 CAD/CAMstrategyrequiredforpolishingthesheetsurface
IntJAdvManufTechnol
and polishing force. The three-phase motor drive related to 6. Parameter of handling tool in each step over, in each
the set's spindle, on which a volume is embedded, is ofthemotiontrajectories,from3/4oftooldiameterto
capable of creating rotational speeds, from 5 to 14,00 rpm. 0.1 of tool diameter;
The successive clockwise and counterclockwise rotation 7. Induction field intensity of the high-frequency induc-
of the magnetic tool at different times is another parameter tion heating source;
beingcontrolledbyPLC,andisoneimportantparameterin 8. Induction field voltage;
the set of experiments conducted. PLC program of the 9. Conducting experiments and acquiring data about the
inverter is so planned that it can create a wide range of currentofdrivers(thepolishingforcesandthecurrent
different frequency modes of the spindle's clockwise and of the stepper motors), as well as measuring surface
counterclockwise rotations. However during the experi- smoothness in the following cases:
ments carried out, only eight cases have been actually
a. without heating induction field
considered. Furthermore, 32 analog input channels and
b. in the presence of heating induction field
eight digital inputs can be received in data acquisition card
10. Frequency and time of switching pedal of the high-
of the system, among which two analog input channels are
frequency induction heating source.
actually used to measure the polishing forces (ch0, ch1).
The channel ch0 measures the polishing forces in the As is clear, the use of statistical methods or design of
direction x, proportional to current of motor, x; and the experiments using Taguchi approach with these experi-
channel ch1 measures the polishing forces in the direction ments will actually include a great number of experi-
y, proportional to current of motor, y. ments. So, it was decided that it is selected among a
The third analog channel Ch2 can be also used for limited range of I/Os, including four inputs parameters in
measuring and recording the current of the three-phase four levels of access, and outputs in two levels, including
motor spindle. two parameters of surface smoothness and current of
As the central controller of the system, PLC can fully stepper motor drives to be selected proportional to the
control the three-phase motor. Furthermore, depending on polishing force. Input parameters have been listed in
which PLC input is active, the time of clockwise and Table 1.
counterclockwise rotations of the magnetic head rotating In addition abrasive temperature indeed is the key
arounditselfcanbecontrolled.Forexample,whenthePLC- factor that affects the performance of this kind of
relatedinput×3isexcited,thespindlemotorwillsuccessively polishing. By use of a non contact temperature mea-
rotate for 5 s CW and 5 s to CCW. These clockwise and surement system (infrared system) the mean temperature
counterclockwiserotations of the rotating magnetic tool and of abrasive particles has measured in various frequen-
consequently powder of abrasives as well as frequently cies of heating operation and listed in Table 2. As it is
heating and cooling of magnetic abrasive powder have mentioned before, under the flat sheet is a container
significanteffectsontheprocessofpolishing.PLChasbeen which is filled with a slurry abrasive .This slurry can
so programmed that the least time of clockwise and polish the sheet from bottom side and is an identification
counterclockwiserotationisfor0.5sbystimulating×0;and for comparing the quality of surface with another side of
the most time occurs in the stimulation ×7 (i.e., constant sheet (top side) that is in contact with hot abrasive
clockwise rotation of 3,600 s). The complete set of experi- particles
mentsinputsaresuchbelow:
1. Air gap between the magnetic rotary tool and the
workpiece surface (from 0.5 to 10 mm for every Table1 Constantparametersduringtheexperiments
0.5 mm of a experiment) can be changed for total of
Value Parameter
20 experiments;
2. Rotational speed of the magnetic device connected to 220V Inductionheatsourcevoltage
a three-phase motor (from 5 to 1,400 rpm with an 18A Inductionheatsourcecurrent
increase of 100 rpm totally for 14 experiments); Spiralpocketfrominsideto Motiontrajectory
3. Frequency and time of clockwise and counterclock- outsideinclockwisesystem
20 Numberofthemagneticdiscs
wise rotations of the three-phase motor (from 0.5 to
providingmagneticfield
3,600 s);
200mm/min Motionfeedoftable
4. FeedrateintheCNCtable,toautomaticallymovethe
3/4ofthetools'diameter Distancebetweencasesof
workpiece (very varied, from 10 to 1,000 mm/min);
pass-overinautomatic
5. Numberofthediscssupplyingrotatingmagneticfield motionoftable
(20 discs);
IntJAdvManufTechnol
Table2 Meantemperature
conditionsbasedonfrequency Frequency 0.05Hz 0.1Hz 0.2Hz 0.5Hz 0.75Hz 0.9Hz 1HZ
MeanT(°C) 550°C 500°C 430°C 400°C 390°C 370°C 350°C
Relevantexperimentswiththedataacquisitionrelatedto Finally, conditions of the experiment tests which lead to
these experiments are performed in four output cases as optimization of the output values is a separate subject that
follows: will be separately discussed in other papers. Here, just a
few important figures and results are discussed.
1. Measuring the polishing forces without high-frequency
Among the total parameters affecting the experiments,
induction heating source
the effect of air gap is examined on the two outputs, i.e.,
2. Measuring the polishing forces with high-frequency
surface roughness and current passing through the stepper
induction heating source
motors (proportional to the polishing force). These results
3. Measuring the surface smoothness without high-
are examined in the two following cases:
frequency induction heating source
4. Measuring thesurfacesmoothnesswithhigh-frequency 1. The rotary magnetic tool is not placed in a thermal
induction heating source induction field;
2. The rotary magnetic tool is placed in a inductive
heating field.
Furthermore, the parameter of airgap was considered as
input for the set of experiments. As is shown in Fig. 9, highest attainable surface
So, four series of experiments were totally designed and smoothness without high-frequency induction source
carried out, whose results will be analyzed in the next occurs for the lowest gap (i.e., 1 mm), and increase in the
section. It should be noted that a rotational speed of testing time will lead to better results.
500rpmhasbeenselectedforthespindle,andafeedrateof According to this diagram, it is clear that almost all the
200 mm/min for the table in all these experiments. diagrams follow the same trend in the case of the presence
of high-frequency induction field, and that rotational speed
of 500 rpm has been selected for the rotary magnetic head
5 Analysis of the results in all these experiments. Furthermore, a frequency of once
every 5 s has been selected for clockwise and counter-
Dataanalysisandresultsoftheexperimentsconductedwere clockwise rotations of the rotary magnetic tool. The effect
obtainedbythestatisticalmethodssuchasvarianceanalysis ofairgaponsurfaceroughnessinthepresenceofmagnetic
andexaminationofinputfactorsaffectingtheprocessoutputs, thermal induction field is shown in Fig. 10. As it is clear,
including current of the stepper motors and surface smooth- firstly low air gap (1 or 2 mm) has little effect on the
nessofthegroundpieces,aswellastheequationsbetweenthe smoothness of final surface in these circumstances; and
inputsandoutputsoftheregressionmethod. secondly, the best surface smoothness is related to air gap
Fig. 9 Diagram of changes in
thesurfaceroughness,basedon
changesinairgapandthe
testingtime
IntJAdvManufTechnol
Fig.10 Effectofairgap
onsurfaceroughnessinthe
presenceofthermalinduction
field
of 5 mm. According to the diagram, it seems that frequent theabsenceofthefield.Presenceofthermalinductionfield
hot temperatures of abrasive powder in low air gaps not practicallyhaslittleimpactforhighergaps.Soaccordingto
only don't help the created quality of surface, but also the sum of these diagrams, it can be concluded that
reduce the quality of surface, due to the local corrosions induction heat source has little effect in improving the
and sintered powder in the area; while this problem doesn't qualityofsurfaceforlowgaps(1and2mm)andhighgaps
exist in the air gap of 5 mm or more. Comparison of the (10-mm high); and best performance of induction heat
above diagram with the diagram of Fig. 9 shows that if the source occurs in the medium gaps.
rotary magnetic head is placed in thermal induction field, As is shown in Fig. 11, minimum current passing
the surface roughness will be achieved. In this case, it will through the stepper motors (and thus the least polishing
beapproximately0.12μmatbest,whileinthediagram(9), force in this case) occur for high gaps. It suggests that in
quality improvement of relevant surface for a gap of 5 mm thiscase,highairgapscannotleadtohigh-qualitysurfaces.
has been reported to be approximately 0.2. Similarly, it is Furthermore, it is clear that in the early stages of polishing
clear that for the air gap 7.5 mm, the surface quality in the operations (i.e., until the first 30 min), minimum air gap
presence of a thermal induction field is better than that in (1 mm) can draw maximum current from the motors; and
Fig.11 Effectofairgap
onthepolishingforceswithout
inductionheatsource
IntJAdvManufTechnol
Fig.12 Effectofairgap
onthepolishingforcesinthe
presenceofinductionheat
source
then,almostalldiagramswillobtainsimilarbehavior.So,it 2. Thesurfacequalityimprovementoccursfortheaverage
can be concluded that for air gap of 1 mm, almost the air gaps in this method.
highest volume of polishing takes place until the first 3. Maximum polishing forces occurs in the least air gaps,
30 min of polishing operations. Descending movement of butthisdoesnotnecessarilymeanthatthesurfacequality
the diagram for intervals of 2, 5, and 7.5 mm is also improvementoccursinthesamedistances.
indicatedthatintheseairgaps,increasedtimeofoperations
will lead to less current passing through the motors.
Therefore, it can be concluded that increased time in the References
process will cause surface quality improvement.
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