[0001] This invention relates to a lapping tool of the wet type for performing lapping of
a surface of a work using abrasion grain, and more particularly to a lap structure
of a lapping tool.
[0002] A lapping tool of the wet type performs surface treatment with a mixture of abrasion
grain and lap liquid interposed between a work and a lap. Conventionally, a lapping
tool of the wet type has a lap structure which has a suitable hardness like that of
cast ion and has abrasion grain bitten in the surface of the lapping tool itself.
[0003] However, since such a holding member as cast iron for holding abrasion grain is made
of a material softer than abrasion grain, also the holding member itself is abraded
by lapping and cannot maintain a predetermined shape. Accordingly, where a high surface
accuracy is required, correction working to correctly work the tool is necessitated
as occasion calls.
[0004] Accordingly, a high cost is required when lapping for a special shape with which
a high cost is required for correction working is performed.
[0005] The present invention has been made in view of such a situation as described above,
and it is an object of the present invention to provide a lap structure of a lapping
work which is superior in wear and abrasion resisting property and maintains a lap
shape for a long period of time without requiring any correction working.
[0006] In order to attain the object described above, according to the present invention,
there is provided a lap structure of a lapping tool of the wet type wherein lapping
is performed for a surface of a work using abrasion grain to finish the surface of
the work, constructed such that a particle holding layer wherein a particle holding
member softer than the abrasion grain embeds and holds hard particles in a substantially
uniformly dispersed condition is formed on a lap surface, that a surface of the particle
holding layer is polished so that flat surfaces of the hard particles polished together
are exposed to the surface of the particle holding layer, and that the abrasion grain
is held on the surface of the particle holding member between the exposed hard particles.
[0007] Since the flat surfaces of the dispersedly embedded hard particles are exposed discretely
to the surface of the particle holding layer, the abrasion grain abrades the particle
holding member other than the hard particles at an initial stage so that recessed
portions are formed between the hard particles, and the abrasion grain is admitted
in the recessed portions and bites into and is held by the particle holding member.
Consequently, the surface of the work is lapped by the abrasion grain thus held in
the particle holding member.
[0008] Since the hard particles are exposed at the flat faces thereof to the surface of
the lap, the lapping tool is superior in wear and abrasion resisting property and
the lap shape is maintained for a long period of time.
[0009] Accordingly, also in working for which a high surface accuracy is required, correction
working, which is working in which correction of the tool is performed as occasion
calls midway of working, is not required, and reduction of the cost can be achieved.
[0010] Where nickel is used for the particle holding member and diamond is used for the
hard particles, the lapping tool can be suitably used for works made of iron, particularly
works made of a base material of an SUS material to which Cr is plated or works made
of an SUS material processed by nitriding or other cast ion works.
[0011] Where the lapping tool laps a surface of a non-circular work, conventional reciprocating
lapping while the lap is turned as occasion calls is impossible, since, according
to the present invention, the lap shape is always maintained by the hard particles,
working with a high degree of accuracy can be performed only by reciprocating movements
of the lapping tool which does not involve any turning motion, and no correction working
is required, either.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a top plan view of a lapping tool according to an embodiment of the present
invention.
[0013] FIG. 2 is a vertical sectional view of the lapping tool.
[0014] FIG. 3 is an enlarged sectional view showing a structure of a surface of a lap of
the embodiment.
[0015] FIG. 4 is an enlarged sectional view of the surface of the lap illustrating a process
of forming the lap surface structure.
[0016] In the following, an embodiment of the present invention shown in FIGS. 1 to 4 will
be described.
[0017] In the present embodiment, the present invention is applied to a lapping tool 1 for
finishing an outer peripheral face of a piston ring, and as shown in FIGS. 1 and 2,
an inner peripheral face of a lapping machine 2 in the form of an elliptic cylinder
forms a lap surface 3.
[0018] A holder 5 in the form of a flattened elliptic column is fixedly mounted at a lower
end of a support shaft 4 which is inserted from above in the lapping machine 2, and
piston rings 6 each of which is a work are fitted and held in three grooves formed
along a circumferential direction on an outer peripheral face of the holder 5.
[0019] Each of the piston rings 6 is made of wear and abrasion resisting cast iron formed
as an elliptic ring, and an elliptic outer peripheral face of it is to be lapped.
[0020] Also other members such as a member formed from a base material of an SUS material
and plated with Cr or a member of an SUS material processed by nitriding are suitable
as such works.
[0021] Some gap is left between the outer peripheral face of the holder 5 and the inner
peripheral face of the lapping machine 2, and the piston rings 6 fitted on the outer
peripheral face of the holder 5 extend outwardly from the outer peripheral face of
the holder 5 and are held in pressure contact with the inner peripheral face of the
lapping machine 2, that is, the lap surface 3 under a predetermined lapping pressure.
[0022] The holder 5 having a center axis aligned with the lapping machine 2 is moved upwardly
and downwardly so that the outer peripheral faces of the piston rings 6 are slidingly
contacted with the lap surface 3 to lap the outer peripheral faces.
[0023] The lap surface 3 of the lapping machine 2 is shown in an enlarged scale in FIG.
3.
[0024] A particle holding layer 11 is formed on the surface of a base member 10 of the lapping
machine 2, and in the present embodiment, the particle holding layer 11 is constructed
such that diamond particles 13 which serve as hard particles are embedded and held
in a substantially uniformly dispersed condition in nickel 12 which serves as a particle
holding member softer than SiC (normally called carborundum) 14 serving as abrasion
grain.
[0025] The diamond particles 13 are polished at surfaces thereof into flat faces and exposed,
and the exposed faces of the diamond particles 13 lie substantially in a plane and
the SiC 14 is received in abraded recessed portions between the diamond particles
13 and bites in and is held by the nickel 12.
[0026] Here, the particle size of the diamond particles 13 is 150 to 250 µm and is approximately
200 µm in average. The SiC 14 as abrasion grain has a diameter around or less than
30 µm. The particle size of the abrasion grain is selected in accordance with a step
stage of lapping working.
[0027] A process of forming the lap surface 3 of such a structure as described above is
illustrated in FIG. 4.
[0028] First, as seen in (1) of FIG. 4, soft nickel 12 in which diamond particles 13 are
dispersed and mixed substantially uniformly is electro-deposited on the surface of
a base member 10 using a popularly industrialized technique.
[0029] Then, the surface of the particle holding layer 11 is polished as seen in (2) of
FIG. 4 until it has the thickness of approximately 100 µm.
[0030] By the polishing, also the diamond particles 13 are polished so that flat faces of
them are formed and exposed to the surface. The ratio (diamond density) of the total
area of the exposed flat faces of the diamond particles 13 to the overall surface
area of the particle holding layer 11 is approximately 60 to 80 percent.
[0031] Lapping working is started with such a surface condition of the lap as described
above.
[0032] Piston rings 6 fitted with and held by the holder 5 are inserted into the cylinder
of the lapping machine 2, and the piston rings 6 are moved back and forth in upward
and downward directions to start lapping working with a mixture of SiC 14 and lapping
liquid interposed between the piston rings 6 and the lap surface 3. Then, at an early
stage after the lapping working is started, the nickel 12 is abraded by the SiC 14
so that recessed portions between the diamond particles 13 are formed, and the SiC
14 is admitted into and held in the recessed portions as seen in (3) of FIG. 4 while
the SiC 14 simultaneously bites into and is then held by the nickel 12 which forms
the bottoms of the recessed portions.
[0033] Thereafter, the lap surface 3 keeps its condition shown in (3) of FIG. 4, and the
outer peripheral faces of the piston rings 6 are lapped by the SiC 14 admitted in
the recessed portions between the diamond particles 13.
[0034] Since the flattened faces of the diamond particles 13 are exposed to the lap surface
3, the lap surface 3 is superior in wear and abrasion resisting property, and the
lap shape is maintained for a long period of time.
[0035] Accordingly, in finishing the outer peripheral surfaces of the piston rings 6, no
later correction working need be performed additionally. Consequently, improvement
in productivity can be achieved.
[0036] And, the lapping tool is suitable for mass production and can be produced at a reduced
cost.
[0037] By the way, if a surface of a work to be worked has a circumferential face, then
the plane pressure accuracy can be maintained readily by performing reciprocating
lapping working while the lap is turned as occasion calls as in the prior art. However,
if the piston rings 6 as works have an elliptic shape as in the present embodiment
or have some other special shape, then reciprocating lapping working which involves
turning motion of the lap cannot be performed, and consequently, it is difficult to
maintain the plane pressure accuracy.
[0038] In particular, when lapping working which does not involve turning motion of the
lap is performed, if the lapping plane pressure is locally high, then where the tool
is low in wear and abrasion resisting property, abrasion proceeds only at the location
of the tool in a short time and the shape of the tool is varied. Besides, even for
reworking to an over-size, the working cost is increased.
[0039] The lapping tool 1 of the present embodiment can perform surface working of such
a non-circular work as described above with a high degree of accuracy only by reciprocating
movements of the lap since the diamond particles 13 exposed to the lap surface 3 maintains
the lap shape and is superior in wear and abrasion resisting property.
[0040] And, where the work has an elliptic shape like the piston rings 6 in the preset embodiment,
the working time can be reduced and the productivity can be enhanced by lapping the
entire elliptic profile at a time as in the case of the lapping tool 1 in the present
embodiment.
[0041] Summarized the present invention seeks to provide a lap structure of a lapping tool
which is superior in wear and abrasion resisting property and maintains a lap shape
for a long period of time without requiring any correction working.
[0042] The lap structure of a lapping tool of the wet type wherein lapping is performed
for a surface of a work using abrasion grain to finish the surface of the work is
constructed such that a particle holding layer 11 wherein a particle holding member
12 softer than the abrasion grain 14 embeds and holds hard particles 13 in a substantially
uniformly dispersed condition is formed on a lap surface, that a surface of the particle
holding layer 11 is polished so that flat surfaces of the hard particles 13 polished
together are exposed to the surface of the particle holding layer 11, and that the
abrasion grain is held on the surface of the particle holding member 12 between the
exposed hard particles 13.