The analysis of axis belt grinding for marine propeller vane

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					       THE ANALYSIS OF FOUR-AXIS BELT GRINDING FOR
                                 MARINE PROPELLER BLADE
                                                      J.Q. Wu*, Y. Huang
 *Chongqing Engineering Research Center for Material Surface Precision Machining and Whole Set Equipments, Chongqing
                     University, Chongqing, 400044 P.R.China, wujianqiang1019@163.com , 02367669667




Keywords: Marine propeller blade; Belt grinding; Abrasive            processing for propeller vane, solved the problem for vane’s
belt wear; Processing precision; Material removal rate.              processing difficulty, improved its quality, the consistency
                                                                     and interchangeability of the vane get better[5]. The most of
Abstract                                                             the material of the marine propeller vane is aluminum bronze,
Marine propeller blade is composite of the free form surface,        which has high strength and good wear resistance. In this
its machining method has been a difficult thing. The blade is        experiment, this paper analyzed the wear of the abrasive belt
processed by 4-axis belt grinding machine in this experiment,        and the processing precision and the material removal rate of
this paper analyze that the wear of the abrasive belt and the        the blade according to the grinding performance of the vane
processing precision and the material removal rate of the            material, the structural features of the vane, and the theory of
blade according to the grinding performance of the blade             4-aixs belt grinding machine.
material, the structural features of the vane, and the theory of
                                                                     2 The principle of 4-axis belt grinding machine
4-aixs belt grinding machine. Draw formulas with time for
                                                                     for vane processing
the belt wear height and the actual grinding depth. The life
expectancy of the ceramic abrasive belt is the longest, and its      Figure 1 depicts a theory that 4-axis belt grinding machine
the material removal rate is maximum in Three kinds of belt          process marine propeller vane, the machine has two axis for
and when the belt line speed is 30m/s or so, the material            linear and rotation movement separately         the axis which
removal rate is maximum.                                             parallel to the grinding head and perpendicular to the
                                                                     direction of the blade thickness is X-axis, can ensure the
1   Introduction                                                     processing of the blade in surface normal direction; the axis
Marine propeller is an important factor to determine the             which Perpendicular to the grinding head and along the
performance of a ship, its manufacturing accuracy affect the         direction of the propeller blade height is z-axis, can ensure the
quality of the propulsion system directly. Marine propeller          processing of the blade in endwise direction; the axis which
blade is composition of complex rational space surface, most         rotation around X-axis is A-axis, can ensure the processing of
of its processing method is that milling is carried out first, and   the blade in scallop direction, the axis which rotation around
then uses a large number of artificial grinding to                   Z-axis is C-axis, can ensure the processing of the blade in
complete[2,7]. These result in the processing take too much          scallop direction, ensures that a better fit with the surface
time and effect, and its processing precision is difficult to        when the grinding process the blade.
guarantee.
                                                                     3   Experiment equipment and method
Belt grinding has many advantages, its grinding efficiency is        The experiment is performed in 4-axis belt grinding machine
very high, it is a flexible grinding and compound processing         developed by ChongQing Three Grinding Samhida Co., Ltd.
technology include grinding, abrading and finishing. 4-axis          Figure 2 depicts that the machine is grinding the blade. In
marine propeller vane belt grinding machine was used in              grinding process, grinding head cut-in the workpiece from the
                                 1.Contact wheel 2. Marine propeller blade 3.Machine tool

                               Figure 1: The principle of belt grinding machine for 4-axis linkage


         Alloy desingnation          Alloy name               Al              Fe              Mn                 Cu

         ZCuAl8Mn13Fe3               8-13-3 xantal         7.9-9.0         2.0-4.0         12.0-14.5         Remainder


                                            Table1: Chemical composition of xantal

bottom of the blade, feeding along U-line direction of             4.1   The wear analysis of the belt in grinding for marine
Parametric line, after complete the feed for a cutting tool path   propeller blade
line, feeding along V-line direction of parametric line,
repeating the movement[1,8]. The diameter of the bottom of         There are three basic forms for the normal wear of the belt.
the blade is 303mm, its maximum width is 734mm, the                They are sticky caps, shed and blunt. The sticky cap is that
material of the blade is xantal. Table 1 shows its chemical        micro chip remain in the abrasive outer surface, hinder the
composition.                                                       particle continue to participate in cutting and reduce severely
                                                                   the grinding ability. The shed is that the abrasive grain will
                                                                   fall off from binding admixture when the force is exerted for
                                                                   the particle exceed its adhesive force in grinding, the belt
                                                                   grinding capacity will be reduce significantly or lost
                                                                   completely if the abrasive grain drop off too much. The blunt
                                                                   is that the abrasive grain tip is abraded into small plane
                                                                   because of which abrasive grain and the processing material
                                                                   rubbed repeatedly, then not only will reduce the amount of
                                                                   material removed, further increase the friction in particle and
                                                                   the heat caused by grinding in grinding area, and give rise to
                                                                   blunt further exacerbated and the workpiece burns. The blunt
                                                                   throughout the entire grinding process and is the most
 Figure 2: Marine propeller blade is grinded by abrasive belt.
                                                                   common wear form for belt in three kinds of wear form[5,10].
                                                                   Figure 3(a) shows the belt surface before grinding, Figure 3(b)
4   The analysis of the experiment results
                                                                   shows the belt surface in grinding, it can be see that the
                   (a) before wear                          (b) wearing            (c) the wear of the single abrasive grain

                                            Figure 3: the wear of the abrasive belt

abrasive grain is abraded into small flat and some abrasive
brain has fallen off Wear. Figure 3(c) shows the constitution       4.1.2   The impact of abrasive type on belt wear
diagram of the wear for a single abrasive brain, it can be see      Three different abrasive type belt were used according to the
that the abrasive grain is Similar to the taper has been            characteristics of the marine propeller blade material in this
planished. The processing system state will deteriorate if use      experiment, and compared the wearing capacity with each
the belt after the wear, affect seriously the machining             other. In Figure 4, the wear capacity of the ceramic grains belt
accuracy, surface quality and processing efficiency.                SK750X is less than other two kind of belt, the second is
                                                                    zirconia alumina abrasive grains belt ZK713X, and the wear
4.1.1    The impact of grinding time on belt wear
                                                                    capacity of alumina grain belt is more. The ceramic abrasive
In this experiment, the author calculate the belt's wearing         grains is composite of crystal include zirconia and alumina. In
capacity by means of which measuring the belt thickness in          grinding, the crystals make a very good toughness after that
certain time interval in different cross sections, and obtain the   the more soft zirconia differ into the crystals, can prevent the
line chart of the wear capacity and the time according to the       abrasive grains crushing under the heavy load, grit under the
wear of the belt. In figure 4, the wearing capacity δ increase      heavy broken. Alumina is very hard and tough, therefore the
coupled with the increase in time, The early stages of wear is      ceramic abrasive grains belt have a longer life expectancy
a fast wear stage, the belt surface is not completely flat belt,    than the other two kinds of belt in many processing situations.
some of the more prominent of the abrasive grain contact
with the workpiece broken rapidly because the load is too
large, at the same time, the internal stress and micro-cracks
are produced in the Repair progress of some abrasive grain[4].
After this stage, the belt wearing capacity δ keep a steady
linear growth, the belt wear come into the stable wear stage,
and has been in this stage before the end of the belt’s life. As
can be seen from figure 4, the line chart of the wearing
capacity and the time is approximate to straight line in the
stable wear stage. An equation can be written as:

             δ ≈ δ 0 + k it                    (1)


( δ 0 : The wear height in the early stages, k: A factor for belt
                                                                          Figure 4: The wear of belt for time and abrasive type
wear.)
                                             Pressure surface (mm)                    Suction surface (mm)
                           Profiles
                  Radius                  X5          X10        X15            X5           X10             X15


                      0.4R               2.94        3.00        3.05          3.25          3.32            3.21

                      0.5R               3.01        3.00        3.04          3.22          3.30            3.24

                      0.6R               3.03        3.03        3.07          3.19          3.15            3.26

                      0.7R               2.98        3.09        3.11          3.24          3.18            3.30

                      0.8R               3.05        2.98        3.07          3.27          3.12            3.24

                      0.9R               3.05        3.01        3.08          3.17          3.25            3.19

                      0.95R              3.94        3.06        3.04          3.26          3.31            3.24


                                      Table 2: The profile margin value of marine propeller blade


                                                                     contact point in the grinding process, the cutting contact point
4.2   The analysis of processing precision for marine                change from the point ‘b1’ to ‘b2’ after an interval because of
propeller blade                                                      the belt’s wear, therefore the inaccuracy is produced. Its value
The processing precision of marine propeller blade has a great       is equivalent to the height of the belt wear.
impact on the overall performance of the propeller include the
noise, the power loss and fatigue damage. The process of the             At the same time, the belt grinding precision of the blade is
belt process for propeller blade is complex, there are many          influenced by many factors include the elastic deformation of
factors that affect the grinding precision, the reason mainly        the blade, the contact roller and the belt and the stiffness of
concentrated in the belt's wear, elastic deformation of contact      the grinding machine. combined with the above factors on
wheel and the elastic contact problems of belt. In this              machining accuracy an equation can be drawn that relating to
experiment, firstly the propeller blade is processed by new          the actual belt grinding depth, as follows:
abrasive belt on the propeller blade pressure surface, then the                      d = d ' − δ − ∆h1 − ∆h2         (2)
suction side of the propeller blade is processed, the allowance
of both sides of the propeller blade retained as 3mm, finally                                         '
                                                                        (d: Actual grinding depth, d : Grinding depth in theory, δ:
measuring the surface residual, Table 2 shows Precision
marine propeller blade on the propeller has a great impact on        The height of the belt wear, ∆h1 : The elastic deformation
the overall performance. It can be see that the inaccuracy of
the suction surface is clearly larger the inaccuracy of the          value for contact roller in grinding, ∆h2 : The elastic
pressure surface in Table 2.
                                                                     deformation value for abrasive belt in grinding. )

In the process of belt grinding blades, the point ‘a’ that the
center of the contact roller is cutter location point in theory      The belt wear has greatest impact on the precision of the

that is generated by NC grinding program for the belt                blade in above factors, the elastic deformation value is

grinding of the blade, there is a cutting contact point formed       difficult to quantification, its effect within the accuracy of the

after adding a tool offset to cutter location point coordinate.      product requirement, therefore the formula can be simplified,

Figure 5 shows that the change of the position of the cutting        as follow:
                                                                    the material removal rate of blade decrease gradually later, in
             d ≈ d' −δ                         (3)
                                                                    Figure 6, the curve variation can be considered that the reason
  Equation (1) is substituted into Equation (3):                    why the early material removal rate increase is that the
                                                                    increase of belt line speed make the amount of the abrasive
             d ≈ d ' − δ 0 − kt               (4)
                                                                    grain which participate in grinding increase in unit time. Later
                                                                    stage, the incessant increase of grinding speed makes the
                                                                    frequency that abrasive grain in elastic abrasive belt is
                                                                    impacted by workpiece surface increases, Elastic belt yield
                                                                    which makes the actual penetraction depth of abrasive belt
                                                                    cutting edge reduce. The material removal rate of the blade is
                                                                    maximum when these two factors are relatively balanced.




                                                                     Figure 6: The material removal for line speed and abrasive
 Figure 5: The effect of belt wear on the processing precision                                   type
                            of blade
                                                                    4.3.2     The impact of abrasive grain type on material
In the marine propeller blade grinding process, the actual belt     removal rate
grinding depth is a function of time, the feed of the tool          Figure 6 can be drawn that the material removal rate of
should be chose according to the actual grinding depth of the       ceramic abrasive is maximal in three kinds of abrasive under
belt.                                                               the same conditions, the second is zirconia abrasive grains
                                                                    belt, and the material removal rate of alumina grain belt is
4.3     The analysis of process efficiency for marine
                                                                    minimum. These is caused because of the characteristics of
propeller blade
                                                                    the abrasive, the ceramic abrasive is manufactured by gel
Abrasive belt grinding efficiency is that mainly through the        method, every abrasive grain is constitute of alumina ceramic
material removal to calculate quantitatively its index. Marine      composed by many sub-micron grain[6,9]. In the grinding
propeller blade belt grinding removal rate is directly related to   process     its unique crystal structure avoid abrasive grain
blade production efficiency[5,6].                                   breaking fast, a new crystals form when the tiny crystals fall
                                                                    off the belt, the abrasive grain still maintain its sharpness,
4.3.1   The impact of belt line speed on material removal           therefore, the ceramic abrasive belt posses higher material
rate                                                                removal rate and better self-sharpening than the other two
Figure 6 shows that the removal rate arise with the growth of       kind of abrasive belt. Zirconia abrasive has higher hardness
belt line speed, the material removal rate of blade is              and toughness, new cutting edge form, its material removal
maximum when the belt line speed increased to 30m/s or so,          rate is higher than alumina abrasive belt. Alumina abrasive is
composed of many coarse crystals, the alumina abrasive is        [4] H.Huang, Z.M.Gong, X.Q.Chen. “Robotic grinding and
grind into facet slowly, the facet become lager slowly with      polishing for turbine-vane overhaul”, Journal of Materials
grinding, the role of abrasive cutting blades become smaller     Processing Technology, 127,pp. 140-145(2002).
which reduce the material removal rate.
                                                                 [5] Y.Huang, Z.Huang. “Modern Belt Grinding Technology
                                                                 and Its Application”, Chongqing University Publications,
5 Conclusion
                                                                 China 2009.
  In the process of belt grinding for marine propeller blade,
                                                                 [6] H.C.Kuo, W.Y.Dzan. “The analysis of NC machining
the amount of belt wear is increasing with time. In the early
                                                                 efficiency for marine propellers”, Journal of Materials
stage, the belt wear is faster, belt wear is approximate to a
                                                                 Processing Technology, 124, pp. 389-395 (2002).
linear function of time t in the steady wear stage. The new
belt should be disposed properly when semi-finishing and         [7] B.Ozturk, I.Lazoglu, H.Erdim. “Machining of free-form
finishing for marine propeller blade.the life-span of the        surfaces”, Machine Tools & Manufacture, 46, pp. 736-746,
ceramic grains belt is longer than the other two kind of belt,   (2006).
the second is zirconia abrasive grain, and the life-span of      [8] J.W.Park, J.G.Lee, C.S.Jun. “Near net-shape five-axis
alumina grain belt is less.                                      face milling of marine propellers”, International Journal of
  There are many factors that affect the grinding precision,     Precision and Manufacturing 23, pp. 5-12, (2009).
the reason mainly concentrated in the belt's wear, elastic
                                                                 [9] W.L.Wang, F.S.Pan, Y.J.Chen. “Investigation on abrasive
deformation of contact roller and the Elastic Contact
                                                                 belt grinding of stainless steel”, Journal of Chongqing
Problems of belt. The belt wear has a greatest impact on the
                                                                 University, 29, pp. 91-95, (2006).
machining accuracy, the actual belt feeding depth is
approximate to a linear function of time t.                      [10] H.Z.Zhong, X.M.Yang: “The research on wear for
  The removal rate of blade arise with the growth of belt line   abrasive belt” , Abrasives and Grinding, 16, pp. 4-8, (1991).
speed, and it is maximum when the belt line speed increased
to 30m/s or so, the material removal rate of blade decrease
gradually later, the material removal rate of ceramic abrasive
is maximal in three kinds of abrasive under the same
conditions. The second is zirconia abrasive grains belt, and
the material removal rate of alumina grain belt is minimum.

Acknowledgements
This research is supported by Chongqing municipal scientific
and technological project (NO.CSTC2008AB3014).

References
[1] L.C.Cao, J.Liu. “An integrated surface modeling and
machining approach for a marine propeller”, Int J Adv Manuf
Technol, 35, pp. 1053-1064, (2008).

[2] J.Carlton. “Marine Propellers and Propulsion”, EIsevier
Ltd Publications, U.S.A 2007.

[3] Y.J.Chen, Y.Huang, K.X.Zhu. “Study and application on
the abrasive grinding properties of precision abrasive belt”,
Journal of Chongqing University, 29, pp. 28-31, (2006).

				
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