What is honing? · 2020-03-09 · machining, which is about 1/20th of that of general grinding...
Transcript of What is honing? · 2020-03-09 · machining, which is about 1/20th of that of general grinding...
What is honing? Honing processing is a polishing process mainly combining rotational motion and reciprocating motion on the cylindrical inner peripheral surface. Characteristic
1.Processing distortion is small at about 30 to 100m of low speed machining, which is about 1/20th of that of general grinding wheels. 2. General grinding is line contact processing. Honing is surface contact processing.
3. It acts as a lubrication as a sliding surface and an oil reservoir of a
rotating part.
Trend of honing processing!
In recent years, it has been mainly used in combination with
superabrasive grains (diamond · CBN), and it is showing great
effect in automobile industry etc.
Photo
Engine block production line
Benefit of honing processing!
Cycle reduction is possible. Example: Improvement of occupancy rate through production
automation and cycle shortening.
Improve circularity. Example: Engine cylinder intersection, within a few microns.
The surface roughness is stabilized. Example: Mainstream processing method for
automobile engine production.
Cost reduction. Example: Great combination cost reduction effect with superabrasive
grains (diamond · CBN).
1.6.1 Outline of Honing
(1) Honing basics
Honing is a technique in which a grinding stone is
pressed against a work surface while rotating and
reciprocating motion is applied to a grinding stone held
by a fixture and a workpiece and a grinding stone are
kept in a constant surface contact state while pouring a
large amount of working liquid, Shape, and surface
roughness of the workpiece. The honing has the largest
inner surface of the cylinder but also to the outer
surface and the flat surface.
Figure 16.01 shows the simplest method of internal
honing work. In other words, the cylindrical degree of
the hole is improved in the reciprocating direction from
the motion state of the grindstone, and the roundness is
improved in the rotating direction.
In Fig. 16.01, the axial distance, that is, the honing
stroke S, at which the whetstone moves on the work
surface is S = L + 2t - р.
Where L is the work piece length, t is the over travel,
and ℓ is the grindstone length. Also, on the honing
surface, a reciprocating motion is given to the
grindstone in the same way as the rotation, and a
specific intersecting meshed finished surface can be
obtained. (Figure 16.02). This mesh-like intersecting
angle is called (cross hatch angle).
Cross angle 2α = 2 tan - ¹ Vs / Vr・・・・・(2)
The synthesized speed of the circumferential speed V 1
and the reciprocating speed Vs is referred to as a
honing speed V.
VටV²r+V²s・・・・・・・・・・・・・・・(3)
Wheel expansion allows pressing between the grinding
wheel and the workpiece by pushing the expansion rod
inside the honing tool and extruding a conical cone
which is in contact with the wheel head and serves to
press the grindstone against the workpiece. (Fig. 16.01).
(2) Honing machine
The honing machine has a vertical shape in which the
processing hole is made vertical, and a horizontal shape
in which it is processed horizontally. For inner honing,
normal standing is used.
Many of the recent honing machines are fully
automated honing machines equipped with multiple
1.6 Honing
axes for high efficiency, automatic sizing devices,
automatic supply devices for workpieces, etc., as well
as high speed conveying devices and the like.
Recently, new control technologies such as automatic
corrections necessary for processing the optimum
hole shape in the honing process have been
developed, to ensure the elimination of defective
products and the stabilization of product precision.
In the automatic honing machine, as a basic method
(Fig. 16.03) for expanding the whetstone, the
grindstone is expanded with a constant pressure
against the workpiece by hydraulic pressure (1)
constant pressure expansion method (constant
pressure cut) and the expansion (2) machine
expansion method (constant speed cut) is carried out
while regulating speed by sending. In the machine
expansion method, since the control of the grindstone
expansion amount is simple, it is easy to digitize and
NC. Furthermore, cubic boron nitride (CBN) or
synthetic diamond 1 (SD), which is difficult to abrade
or wear away from abrasive grinding edge, which is
easy to maintain minute amount honing due to fine
incisions due to hard and tough properties Honing
machines of the machine expansion method using
super abrasive grinding wheels tend to increase.
In honing processing, it is basically important
that the grindstone follows the central axis of the
machined hole. From this it is clear that the
fixture always has the center of the grinding
stone at the center of the machining hole during
machining, the honing head and the machining
hole are self-aligned and the honing pressure
equals the whole machining hole by free cutting
Equipment is necessary.
Therefore, considering the weight and shape of
the workpiece, it is necessary to decide whether
to fix the fixture (rigid type) or swing type (float
type). In general, when the workpiece is
lightweight and compact, let it float. If the
workpiece is heavy in weight, float the honing
tool and fix the fixture. (Fig. 16.04).
In addition, when actually operating the honing
machine, the conditions to be provided by the
honing machine are satisfied, and the thermal
displacement amount and the work accuracy of
each part of the machine, the change of the
cutting speed due to the temperature rise, etc.
are necessary.
1.6.2 Honing mechanism
(3) Honing stones
The indication of the honing grindstone is displayed according to JIS R 6210 (vitrified grinding wheel) when conventional alumina material and silicon carbide abrasive grains are used. Superabrasive grains such as diamond and cubic boron nitride (CBN) abrasive grains are displayed according to JIS B 413 (diamond and cubic boron nitride wheel).
Fig.16.0 shows a display example of a honing
grindstone. FIG. 1 shows various shapes of a honing
grindstone. The mold type grinding stone prevents damage such as grinding wheel chipping, improving the grinding wheel life, and improving the effect of grinding wheel management greatly. Also, the abrasive grain reamer with superabrasive grains attached by electrodeposition method achieves high efficiency honing by passing the inner surface of the hole one or two times at low stroke speed, and high precision can be achieved even with drilled holes with notches It is easily possible.
Honing is as slow as 1 / 50th of the grinding process. Further, the workpiece and the grinding stone are processing methods for efficiently finishing
the surface of the workpiece in surface contact with the line contact of the grinding process. Such a cutting mechanism having such characteristics is fundamentally important for honing.
In honing, cutting is performed with the
grindstone and the workpiece in surface contact.
For this reason, except for green in the cutting
direction of the grinding wheel, since chips are
required to escape from the grindstone surface, it
is not easy to generate continuous chips,
resulting in massive chips. Of course, in this case
the discharge of the chips becomes a problem.
(1) Chip generation
Fig.16.06 and Fig. 16.07 show the case where
bearing steel is internally ground and honed with
CBN grindstone respectively. In internal grinding it
is a continuous chips of flow type, whereas in
honing bulky discontinuous type chips are mainly
used. Fig. 16.08 and Fig. 16.09 are honed cast
irons, both of which are granular sandy chips.
Fig. 16.10 and Fig. 16.11 are the observation of
the work surface of the grindstone at this time.
(2) Cutting mechanism of honing
In the vitrified honing grinding stone using conventional alumina and silicon carbide abrasive grains, (1) falling cutting (dressing period), (2) steady crushing cutting (steady cutting period), (3) eye It is known to take three forms of clogging (loading cutting). For example, in a honing grindstone that fills the pores of a vitrified grinding stone, the purpose of the loading cutting is to continue the cutting force while maintaining a constant value at all times because the loading depth from the grindstone surface is small. Figure 16.12 shows the four wear forms of the honing grindstone.
(3) Action of Metal Bond Wheel
which are harder and more tough than
conventional abrasive grains are actively
adopted. The bonding agent (bond) applied to this
is mostly metal bonds that have better abrasion
resistance than other bond types.
Figure 16.13 shows a cutting model diagram of a metal bonded grinding stone, and the generated chip abrades the front metal bond layer of the abrasive grain to make a crater. On the other hand, each abrasive grain is responsible for honing in two directions, so the
In recent honing processing, super abrasive
grains such as diamond and CBN abrasive grains
1.6.3 Honing condition and finishing performance
chips flow around the side of the abrasive grain and make a V-shaped groove as shown in Figure 16.14. This groove serves as a flow path, and the chips are conveyed behind the abrasive
grain and discharged. Therefore, if the grinding
stone width is wide, the chips which lose escape
place are interposed between the grindstone and
the workpiece, causing scratches on the
processed surface.
For this reason, in superabrasive metal bond whetstones, the width of the conventional alumina grindstone is 10 to 12 mm, whereas it is narrowed to 3 to 4 mm so that chips are easily discharged.
In order to raise the machining efficiency by honing work and to satisfy the accuracy of the target, it is necessary to select the correct grinding stone together with an appropriate honing condition. Figure 16.15 shows basic conditions that affect honing performance, and Table 16.02 shows honing characteristic values corresponding to four elements for processing purposes.
Figure 16.16 shows the results of internal diameter honing of mild steel as a hydraulic cylinder - part by constant pressure cutting method. The specification of WA grinding wheel is currently widely used in this part processing
and we are testing CBN and SD whetstone for
comparison. The crossing angle is changed by
changing the grinding wheel rotation speed with
the reciprocating speed constant and accordingly,
with a constant machining time, the traveling
distance increases as the crossing angle
decreases.
(2)Cross angle and finish performance
(3) Wheel pressure and finishing performance
When both the thrust and the circumferential force are
organized and compared by the expanding force of the
whetstone in both the constant pressure cut and the
constant speed cut and the expansion force is the same
as the constant pressure cut in constant speed cutting,
The machining efficiency shows the same value and
increases in proportion to the expansion force.
(4) Honing speed and finishing performance
The reciprocating speed of the grinding wheel is
limited from the machine and is currently in the range
of 5 to 25 m / min. Therefore, the grindstone rotation
speed is usually 15 to 40 m / min for a conventional
grinding wheel and 35 to 80 m / min for a super
abrasive grindstone Speed honing is preferable.
Figure 16.18 shows the specific material removal rate (㎤ / min / ㎠) as the chip removal efficiency per unit time per 1 ㎠ surface area. In the WA grinding wheel, there is a tendency that the efficiency tends to be the maximum in the vicinity of V = 60 m / min (2.alpha. = 30 degrees), but in superabrasive whetstones the specific material removal rate also increases as V increases. This is
proportional to an increase in the travel distance L
shown in the figure. On the other hand, the amount of
honing (㎤ / m / ㎠) at unit travel distance per 1 ㎠
surface area of the grinding wheel is higher for the
super abrasive grinding wheels as the 2 α becomes
larger. Therefore, in order to perform high efficiency
honing with honing operation with constant processing
time by super abrasive grinding wheels, the honing
speed must be increased and the number of abrasive
grain working cutting edges must be increased in order
to increase the running distance.
As compared with superabrasive grains, abrasive
grains are easy to break, and in the WA grinding
wheel with a large amount of wear abrasion, there
is a maximum value of honing amount in the
vicinity of an intersection angle of 30 degrees. On
the other hand, with superabrasive grinding
wheels, the honing amount tends to increase as
the crossing angle decreases, that is, as the
running distance increases
Figure 16.17 shows the finishing performance
against grindstone surface pressure, both grinding
wheel abrasion and honing value increases as the
wheel surface pressure increases. With the same
grinding wheel surface pressure, the honing amount
of the SD grinding wheel is smaller than that of the
CBN grindstone.
Figures 16.22 to 16.24 show the results of inner
diameter honing of gears by metal bonded CBN
whetstone in the case where the taking amount is
constant at 0.02 to 0.04 mm in diameter.
As shown in Figure 16.22, the processing time T
becomes shorter due to the increase of the
grindstone pressure Pn, but the grindstone wear
amount S also increases sharply in proportion to
Pn, so it is not preferable to simply set the high
pressure condition. Also in Fig. 16.23, when the
low pressure is 30 kgf / ㎠, T is greatly shortened
by increasing the grindstone rotation speed V,
which is efficient. Therefore, as a honing
condition, the grinding wheel surface pressure is
a lower pressure, and T is greatly shortened by
increasing the grindstone rotation speed, which is
efficient.
The smaller the crossing angle 2α, the shorter
the T is, the higher the efficiency is. This is due to
the influence of the grindstone rotation speed. In
Figure 16.24, as the grinding wheel reciprocating
speed V increases, T is shortened and high
efficiency is obtained, but S is increased on the
contrary. The lowering of the grinding wheel life
becomes conspicuous as the pressure increases.
(5) Constant speed cutting and finishing performance
It is the most ideal if a fixed speed cutting
method in which the grinding stone expands in
the radial direction at a constant speed, and if the
setting amount equal to the extension amount of
the setting can be obtained.
Figure 16.20 compares the honing amount W
with the set cutting depth d for the conventional
WA grinding wheel and the CBN grindstone. In
the CBN grindstone, the cutting amount of the
setting is almost satisfied, and in the WA grinding
stone, the cutting allowance is about 30 to 40%.
In addition, Figure 16.21 shows the relationship
between W and dressing wear S with respect
to d, indicating that the sum of W and S is
approximately equal to d . That is, in the
constant velocity incision, if the stiffness of the
grinding wheel incision system is sufficient, the
sum of W and S substantially matches d.
Therefore, super abrasive grains which are
superior in cutting ability compared to
conventional abrasive grains easily without
crushing or blurring, are very convenient for
constant speed cutting which forcibly removes the
margin by cutting amount .
1.6.4 Honing surface
(2)It is obtained from a unique mesh (cross hatch)
finished surface depending on the grindstone
rotation speed and the reciprocating speed and
plays a role of oil holding at the sliding surface
and rotating contact portion, giving a good
result of lubrication action.
(3) In addition to the usual honing finish surface,
a plateau surface finish that combines the
advantages of groove depth with coarse honing
and the smooth surface finish is possible.
(4) The processing strain of the honed surface
layer is small and excellent surface quality is
obtained.
(1) Characteristics of honing surface
The characteristics of the honed finished surface
are as follows.
(1) Surface finish of about 0.3 S or more can be
freely selected by appropriately combining
the grinding stone · honing speed · cutting
speed · honing oil agent etc.
(2) Display of finished surface roughness
On the honed surface, it is expected that the
surface shape and roughness value will differ
depending on the direction to be measured, since
there are peculiar intersecting marks of the marks
traveled by the abrasive grains. The grindstone is
actually measured in the case of the constant
pressure outer circumference honing, and it is said
that it may be measured from either the
circumferential direction or the axial direction,
except when it is peculiar that the intersection angle
2α is around 0 ° or 180 °.
(3) Surface roughness and grindstone selection
Figures 16.25 and 16.26 show the relationship
between grindstone grain size and finished
surface roughness for various work materials. That is, as the grain size of the normal honing
grindstone becomes finer, the finished surface
also becomes finer. However, when the amount
to be removed is relatively large and a good
finished surface is required, it is necessary to
efficiently remove the required margin with
coarse grain size by two-step machining and
finish the finish with finer grain size, so that
economical honing Processing is possible. In
Figure 16.27, it is more efficient to perform
general abrasive grinding than super abrasive
grinding to perform a fine surface finish of less
than 3 μm R (3 μRmax) or less.
Normally, the roughness of the honing surface is
measured in the axial direction, and Rmax and Rz
are used in Japan. In addition, the surface
roughness standards of each country are
exemplified as shown in Table 16.03.
Therefore, in case of needing a surface finish of 3 μm
Rt (corresponding to 3 μm Rmax) or less by honing
process of cast iron with large amount of taking-out
etc. in mass production etc., it is possible to perform a
high honing by coarse honing with super abrasive
grains and then finish honing with general abrasive
grains Efficiency, economical and stable quality parts
are guaranteed.
Table 16.04 shows how to select abrasive grain type
and grain size with respect to the desired surface
roughness for various work materials to be honed.
(4) Plateau Honing
The inner surface of the engine cylinder is honed at
the final stage. In this case, familiar operation is
substantially reduced by creating a surface finish
structure called plateau honing. The valley of the
honing surface with an appropriate interval provides
an ideal oil pocket, and as a result it has an effect on
consumption and life of engine oil. Figure 16.28
shows the plateau honing state of the inner surface of
the cylinder, the cross sectional profile of the finished
surface giving rise to the Abbott Contact Curve.
Abbott contact curves show the percentage of the
cumulative contact area with respect to the valley
depth of the cross-sectional curve of different cutting
finished surfaces and are controlled so that the
pattern of the curve falls within a certain intersection.
Figure 16.29 shows the plateau honing process.
In actual production, for example, coarse honing is
due to mechanical expansion and plateau honing is by
hydraulic expansion. In addition, it has two stages of
expansion mechanism with one axis, the set of two
different kinds of different honing stone are alternately
expanded.
When high speed honing is carried out by using super
abrasive grains,
the cutting temperature becomes high as a matter of
course, the influence of temperature and surface flow
on the depth and residual stress of the work-affected
layer is concerned. Figure 16.30 shows the results of
examining these. Depth 0 represents the machined
surface by honing, and the honing margin is about 30
μm. From this figure, tensile stress disappears when
honing, and residual compressive stress occurs.
(5) Residual stress on honed surface
Table 16.05 compares the finishing performance
when using GC (SC) wheels and diamond (D)
wheels, respectively, with plateau honing by
finishing honing after coarse honing.
1.6.5 Take off honing
(1) Guidelines for removal
In the honing process, it is scraped off from the first
high portion, and the final size is obtained in a state
where the whole is honed. Therefore, the honing
margin is usually determined by the pre-processing
precision.
In general, the minimum mating honing magazine is
theoretically given as the sum of the prefabricated
surface roughness twice amount and the
pre-processing dimensional error such as roundness,
cylinder degree, straightness and the like.
Although it is most economical to set the honing
margin as minimum as possible, for large holes with
large waviness of pre-machining or tape, twice the
sum of pre-machined surface roughness and
pre-machining dimensional error We need honing
margin of quantity.
(2) Take off ~ practical example of processing time
Normally, honing time for small parts is small, but it is
a problem in case of large parts. Table 16.07 is a
guideline for the time required to eliminate the
required margin
Table 16.08 and Table 16.09 show the removal
amount and processing time in various honing
operation examples using super abrasive grains.
In general, the cutting action and thermal stress
cause tensile residual stress, and the basini effect
produces compressive stress. Therefore, it can be
said that the influence of the basini effect is larger
than that of the cutting heat even in high speed
honing. In this figure, the depth of the influence of
the honing process is about 50 μm, and the depth of
the altered layer as a whole is dominated by the
machining as the pre-processing.
1.6.6 Processing precision
(1) Modification of cylindrical shape and circularity Generally, in honing processing, by floating either the tool or the workpiece, the honing
head and the processing hole are automatically aligned so that automatic cutting can be
continued. That is, by uniformly expanding the grinding stone to the inner surface of the hole,
the tool is further subjected to the reciprocating motion of the grinding stone having an
appropriate length and rigidity at the same time, The shape error occurring in the
pre-processing is corrected with the minimum allowance amount, and improvement in
geometrical shape accuracy such as cylinder degree, roundness, surface roughness and
the like is obtained.
In order to obtain accurate cylindricity by honing processing, it is necessary to accurately
adjust the stroke length and the stroke position. That is, the cylinder degree is closely
related to the number of abrasive particles passing through an arbitrary point on the
processed surface of the workpiece, that is, the honing amount. Before and after the
moment when the grindstone overruns at the end of the workpiece, the cutting amount
increases as the wheel surface pressure increases.
Also, it is known that the roundness is closely related to the surface roughness, and by
cutting the grinding stone and applying run-out or multistage honing equivalent to spark-out
of the grinding process, the finish surface roughness Roundness is also improved with
improvement.
(2) Automatic sizing device One of the reasons why honing has become widely used is that it is a processing method
that facilitates automatic sizing by in-process.
The automatic sizing in honing work is shown in Table 16.10.
However, the current automatic sizing is about the control of the machining allowance in the
strict sense, and it does not automatically control finish surface roughness, roundness,
cylinder degree, and the like.
(3) Multistage honing and high efficiency and high precision machining Injection pump parts (Fig.16.32) heat treatment after deep hole drilling and immediately
honing. The removal allowance is in the range of 0.1 to 0.215 mm depending on the hole
diameter.
By using this as a honing process divided into three or four stages, high precision can be
easily obtained. In this multistage honing, in the first step, the rate of removal is increased,
and in the subsequent step, a small amount of removal that emphasizes surface finish is
allocated.
Also, a CBN metal bond grinding stone having excellent cutting performance is used for the
work hard material.
As shown in Figure 16.33, surface roughness and geometric accuracy are improved in
stages by using fine grinding wheels. For example, the shape accuracy decreases to 1/2 for
each step, and the accuracy is improved.
In this processing, good results can be obtained from the viewpoint of improvement of
machinability and accuracy as compared with continuing pressurization by hydraulic
expansion by extending the honing tool slightly by machine expansion.
Furthermore, in this machining, the diameter measurement and the stroke position are
converted by the sizing station having the automatic feedback, and the cylindrical shape is
automatically corrected.
Practical application of adaptive control honing is desired because it mass-produces stable
parts with excellent uniformity and does not produce defective products. However, as a
practical matter, the reason why quality control is difficult during the honing process is
honing result cannot be reproduced. The reasons are listed below.
1) Friction force in cutting system
2) Rigidity problem in tools and workpiece systems
3) Changes in grinding performance during honing
4) The state of the sharp edge of diamond or CBN honing tool is unclear.
5) Changes in honing processing affected by the state of the grindstone working surface
caused by various wear forms
6) Variation of pre-processing dimension of workpiece
Here, regardless of the surface condition and honing condition of the honing grindstone, it
was produced by honing based on the linear correlation (Fig. 16.34) between the measured
values of the tangential force ratio μt and the surface roughness Rz It is intended to manage
the surface roughness by measuring the tangential component force Ft in the rotational
direction and the torque. (Figure 16.35)
In this case, however, the types of the grindstone, workpiece material and coolant are
limited.
In other words, if the surface roughness is finer or rougher than the required value, the
vertical component force (grinding wheel pressing force) Fn is corrected by increasing or
decreasing the hydraulic pressure.
However, since the machine cannot calculate Fn in the extended form, in this case, it is
nothing other than directly managing the surface roughness during machining.
Figure 16.37 shows a calibration chart when using the roughness sensor (Fig. 16.36)
attached to the groove of the honing head and an example of measuring the surface
roughness during honing.
1.6.7 Selection of honing stone
(1) Grindstone selection criteria In the honing grindstone, the selection of the correct honing grindstone becomes important
from the viewpoint of accuracy, efficiency and economy. Compared with conventional
abrasive grains, hard and tough superabrasive grains are excellent in abrasion resistance,
and the cutting edge of the abrasive grains is firm.
Particularly, it is easy to control the expansion amount of the grindstone even for minute
cuttings such as machine expansion method, so the practical application of superabrasive
grinding wheels such as diamond and CBN is rapidly expanding.
On the other hand, since honing has low speed and little heat generation due to processing,
active selection of diamond abrasive grains and the like is being put to practical use.
(a) Grindstone selection for work material
Table 16.11 shows the selection of general abrasive grinding wheels. In the case where
the work material is steel, alumina (Wa, A) abrasive grains are usually used, and in the
case of cast iron, silicon carbide (CG, C) abrasive grains It is selected as standard.
And, for the purpose of economical grindstone performance with less grinding wear
abrasion and excellent machinability, a processing grinding stone is used which softens the
degree of bonding of the grinding stone base body and fills the grinding stone pores with
sulfur (S). Table 16.12 shows selection of super abrasive wheels. CBN abrasive grains are
typically chosen for honing of heat treated hard steel whereas diamond (SD) abrasive
grains are selected for hard brittle materials, cast iron, mild steel and the like.
In order to facilitate the discharge of chips using a metal bond grinding stone or to promote
the cutting action of abrasive grains during constant pressure cutting by enlarging the
interval between abrasive grains, the concentration is preferably lower.
(b) Particle size selection for finished surface roughness
Table 16.13 and Table 16.14 show the particle size selection for finish surface roughness
for general abrasive grains and super abrasive grains.
In superabrasive grains, it is necessary to select a mesh number that is 1.5 to 2 times as
large as that of general abrasive grains on average.
(c) Example of selecting a honing stone
Table 16.5 shows selection examples of conventional grinding wheels and superabrasive
grinding wheels in honing of automobile parts. Whereas conventional whetstones handle
sulfur with vitrified bonds, metal bonds with the highest wear resistance among various
bond systems are standardized for superabrasive grains.
Particularly recently, bronze-based crushable metal bonds which promote the blade
function and emphasize machinability are frequently used.
(2) Performance evaluation of honing stone In honing processing, there is a honing ratio (cutting removal volume / grinding wheel
abrasion volume) corresponding to the grinding ratio in the case of grinding as a method for
evaluating the performance of the honing grindstone. That is, when a super abrasive
grinding wheel which is expensive compared with the conventional general grindstone is
used, a high honing ratio is desired.
However, pursuing only this makes it difficult to maintain favorable machinability.
Therefore, it is necessary to evaluate the total cost, such as shortening of processing time
besides grinding wheel cost, greatly decreasing the frequency of grindstone replacement
by improving the grinding wheel life, not only improving productivity but also saving labor
cost and overhead cost is there. Table 16.16 shows data on the honing ratio and the cutting
removal volume per unit time at that time, that is, the honing efficiency, for the example of
workpiece per set of grinding wheels with respect to grinding wheel life. Table 16.17 shows
this comparison in comparison between conventional grinding wheels and superabrasive
grinding wheels. At the same time, the average grinding wheel wear amount per workpiece
is also shown.
(3) Shape accuracy of super abrasive grinding wheel
With ordinary grinding wheels, the grindstone wears as the honing process progresses and
adapts to the machined surface, so that the precision of the imaginary cylinder formed by
the grindstone surface, that is, the cylindricalness of the honing head improves in a state
where the grindstone is attached to the honing head.
However, with super abrasive grinding wheels, wear is very low, so we can hardly expect
this cylindrical degree correction function. Therefore, for super abrasive grinding wheels
such as CBN, diamonds need to be delivered with accuracy of 0.010 mm or less in
cylindrical shape of honing head before use by truing. In general, a honing head is used as a
truing jig, a grinding stone is attached to the honing head, and the workpiece finished or a jig
having the same hole diameter as that of the workpiece is used to expand the honing head
so as to closely contact the grindstone Fix and sharpen the cylinder to a predetermined size
with reference to the center.
In order to ensure a better cutting action, it is possible to dress with a GC grinding wheel
with fine grain than the grain size used for the honing grindstone, soft wet GH hardness
without losing shape accuracy of the honing grindstone obtained by truing it is important to
remove metal bonds between abrasive grains to create small chip pockets. Besides this, as
a dressing method of a metal bond grindstone, there is a mist electric discharge machining
and the like.
1.6.8 Selection of the honing oil
(1) Procedure for selecting oils Generally, as a honing oil agent, a water-insoluble oil blended with a low viscosity mineral
oil as a base oil, various oiliness agents and extreme pressure additives is used. Basically,
the following three actions are required.
1) Lubrication at abrasive grain cutting edge application point
2) Cleaning action to carry out cutting and grinding wheel abrasion
3) Cooling action to reduce heat generation
Honing oil is included in the classification of JIS/ K2241 cutting oil.
In choosing the actual horn oil, it is selected in consideration of the viscosity, the type and
amount of additives, as well as the flash point, safety and hygiene, etc., based on the
working materials and horn conditions.
Viscosity affects processing efficiency and finished surface roughness.
Normally, when the viscosity is high, the finished surface roughness is improved, but the
working efficiency is lowered.
Addition of additives such as oiliness agents and extreme pressure agents gives good
results to the finished surface roughness and honing ratio, and in some cases troubles such
as scratches caused by the grindstone, chatter marks, grinding wheel defects and the like
can be prevented.
In addition, management of oil agent in honing processing is very important in minimizing
fluctuation in grindstone performance so that mass production can be performed stably with
high precision processed products without issuing defective products. The important
management items are as follows.
1) Filtration management of oil agent
Mixing abrasion powder and chips of the grindstone in the oil agent causes deterioration of
the finished surface or scratches. Also, these mixtures may adversely affect grinding wheel
life. Therefore, it is necessary to select an appropriate filtration device according to the
purpose of processing and always use the oil agent in a clean state.
2) Temperature control of oils
In order to reduce dimensional variations of workpieces and to maintain stable processing
performance, the viscosity of the lubricant must be constant. For this purpose, it is
necessary to control the temperature of the oil agent. For example, with a cooling device or
a humidifier, the oil agent is sent to the honing zone at a constant temperature of 20
degrees.
3) Property management of oil agent
The occurrence of various troubles can be prevented by periodically performing the property
management of the appearance, viscosity, additive concentration, sucking tail, inclusion and
the like of the honing oil agent beforehand to prevent deterioration of the oil agent.
(2) Practical use of water-soluble oil Along with the automation and labor saving of production lines, the need to convert from
water insoluble oil to water-soluble oil is persistent from fire prevention, environmental
hygiene, centralized refueling and the like in factories.
However, water solubilization by honing has various problems due to changes in oils,
machinery and grindstone performance, and it is currently difficult to put it into practical use.
Normally, when a water-soluble oil is used, a paste-like sticky substance adheres to the
surface of the whetstone, resulting in a severe clogging state, making normal honing difficult.
This is said to be due to a part of the surfactant contained in the water-soluble oil becoming
a water-insoluble sticky substance and adhering to the surface of the whetstone. The test oil
in Table 16.18 was used for the honing of the sintered alloy shown in Figure 16.39 for the
purpose of commercializing water-soluble oil. Experiments were conducted with varying
dilution concentrations for standard water insoluble oils as honing oil using an emulsion type
and a soluble type, which are superior to lubricity as compared with solution type.
Fig. 16.40, Fig. 16.41 and Fig. 16.42 show honing performance by diamond (SD), CBN
whetstone and conventional GC whetstone. Both of the grinding wheels are of high
emulsion type and good results are obtained especially for SD grinding wheels.
Both of the grinding wheels are of high emulsion type and good results are obtained
especially for SD grinding wheels. In addition, the finished surface roughness was the SD
and CBN grindstone for the GC grindstone of 0.8 to 1.5μmRz.
1.6.9 Single pass honing
As a recent honing technique, there is single pass honing (single pass honing or single
stroke honing). Unlike ordinary honing which repeatedly makes a stroke with a rotating
honing tool, it intends to remove all the removal allowance intensively with one stroke.
Figure 16.43 illustrates the single pass honing technique.
As a tool, an electrodeposition grinding stone of super-abrasive grains of a long life such as
diamond or CBN is used.
The feature of this processing method is that high precision high efficiency honing is easy for
blind holes or discontinuous holes.
For short chips of cast iron, very economical processing is possible, whereas for long chips
like mild steel and hard steel, or streaky adhesive chips such as bronze and aluminum,
electric Processing is not easy because the surface of the wearing tool tends to be clogged.
Furthermore, in this processing, attempts have been made to commercialize emulsion type
water-soluble oils from the necessity of lubricity and cooling properties. Further, this
processing method has a need for an automated line or a robotized machine because it is
easy to standardize at a high level in terms of process control.
1.6.10 Honing processing of fine ceramics
We will describe the machinability of various fine ceramics with honing process, the
performance of grindstone use and the selection of whetstone.
(1) Machinability of fine ceramics
Table 16.19 shows the characteristic values of various fine ceramics. That is, borosilicate
glass (SiO2), alumina (Al2 O3), silicon carbide (SiC), and two different types of silicon nitride
(Si3N4) of the same manufacturer under the same pressureless sintering method. Then,
these materials were honed, and from the detailed study results, the experimental result on
the machinability using the private grinding stone shown in Table 16.20, which was deemed
appropriate for each, is shown in Figure 16.45.
In other words, the abscissa shows the grindstone depth of cut d when one grinding stone is
regarded as one cutting tool and the ordinate shows the specific cutting resistance K 2
(GPa) and chip volume of unit volume the energy Ks (J /mm3) required for generation is
shown.
The material at the lower right in this figure has better machinability.
SiO 2 and Al 2 O 3 are better machinability than spheroidal graphite cast iron (FCD 50)
processed as a comparison, and SiC and Si3N4 are bad.
(2) Wheel finish performance
Figure 16.46 shows the effect of abrasive grain size on the processing of Al2O3 and Si3 N4.
When the particle size number is large and the abrasive particle diameter becomes small,
the specific cutting resistance becomes large, the cutting depth and the finishing ratio
become small, and the machinability of the grindstone deteriorates.
The finished surface roughness improves rapidly with finer grain size, and mirror surface
can be obtained by processing Si3N4 with # 1200 grindstone.
Figure 16.47 shows the machined surface profile for the case in Figure 16.46.
(3) Grindstone selection
In the grinding wheel specification table 16.20 selected for each kind of fine ceramics,
abrasive grain type is preferably high toughness among diamonds, and the bonding
agent is more suitable for resin bond or vitrified bond than metal bond with large
abrasive grain support power.
When using the FCD50 material in metal processing as a reference, the concentration
should be higher for Al2O3 and SiO2, better for machinability, and low enough for SiC
and Si3N4 with poor machinability. Regarding the grindstone strength бb, a range of бb
= 80 to 150 MPa, which is smaller than that of metal working, is appropriate for a fine
ceramic material, and бb is made smaller for a material with poor machinability so as to
improve machinability It is necessary to select emphasized metal bond.
1.6.11 Troubleshooting in honing processing
Troubles that occur at the site honing process often have duplicate causes. Therefore,
detailed analysis and examination are required.
Table 16.21 shows troubleshooting on honing accuracy. Tables 16.22 and 16.23 show
troubleshooting on honing finishing performance and superabrasive grinding wheels
when super abrasive grains such as diamond or CBN are used.
Table16 .21 Honing Troubleshooting -Processing precision-
Decrease concentrations ○ ○ ○ ○
Decrease granularity ○
Use a hard grindstone ○
Use a sharp grinding stone ○ ○ ○ ○
○
Sizin
g equ
ipment (plu
ggau
ge type
)
Check eccentricity between pluggauge and honing tool or honing
head
○
Increase pushing pressure ofplug gauge
○
Check plug gauge expansion
Honin
g conditio
nFixtu
re
○
○Increase over travel
Do well motion ○
○○
○ ○
○ ○ ○ ○
○
○
○
○
○
○
○
○
○
○
○ ○
○ ○
○
○
Check the rigidity of the honinghead and the guide wear
Right angle of pre-machinedshape
Change to flange mounting
○
Unstable
Straigh
tness is
difficult to
achie
ve
Variatio
n in
finish
ed dim
ensio
ns
Roundness Cylindrical degree AngleStraight
nessSize
Decrease cutting speed
○
The bo
ttom
is finish
ed
small be
cau
se o
f the blin
d
hole
Fau
lt in stac
k honin
g
Failu
re o
f the lan
d width
Unstable
To be
elliptic
al
Degradatio
nby sag in
notc
hed part
Uneve
n fin
ish o
fth
e w
hole
circ
um
fere
nce
Both
ends be
com
e large
r
Both
ends be
com
e sm
all
mac
hin
eW
ork
piece
Check centering accuracy of tool and workpiece
Check the universal movementof the tool
Devise a tool layout
Correctly match the angle and
pitch of the expansion cone and thewheel head
Reduce the gap between the wheel
head and the groove of the honinghead
Check fluctuation of strokeposition
Supe
r-abrasive
grindin
g stone
Increase rotation speed
Increase run-out
Reduce over travel
○
Support reinforcement againstlack of rigidity of workpieces
Provide a work guide for the tool toprevent movement of the
workpiece
Improve fitting squareness
Stabilize the mountingreference surface
○
Increase Concentration ○
○ ○
Use a mold type grindstone ○
○
Lengthen the grindstone length ○ ○
The precision of the shape of thegrinding wheel does not come out
○
○
Control to constanttemperature
○
Replace with appropriate oil ○
Honin
g oil
Change to flange mounting ○
Shorten the grindstone length ○ ○
Increase the grindstone width ○
Measures
Trouble
Table16 .22 Honing Troubleshooting -Honing finish performance-
○ ○ ○ ○ ○
○ ○ ○ ○ ○ ○ ○ ○
○ ○ ○ ○
○ ○ ○ ○ ○ ○ ○ ○ ○
○ ○ ○ ○ ○ ○ ○ ○ ○ ○
○ ○ ○ ○ ○If the efficiency is high, theprocessing accuracy will be
deteriorated
Too good
Too rough
Unstable
Scratches on the machined surface
Bad sharpness and long cycle time
Incre
asing c
uttin
g speed
Decre
asing c
uttin
g speed
Incre
asing ro
tation spe
ed
Decre
asing ro
tation spe
ed
Incre
asing h
onin
g speed
Incre
asing ru
n-out tim
e
Usin
g soft grin
dingsto
ne
Usin
g hard grin
dingsto
ne
Incre
asing gran
ularity
Decre
asing gran
ularity
Honin
geffic
iency
Super grain grindingstone
Checkin
g oil de
terio
ration
Checkin
g filtration o
f oil
Rese
lectin
g the o
il
Honing oil
Decre
aasing c
oncentratio
n
Chan
ging abrasive
from
diamond to
CB
N
Chan
ging th
e type
of abrasive
Usin
g mold type
Chan
ging to
high
viscosity
Honing condition
Fin
ising
surfac
e
Incre
asing c
oncentratio
n
Usin
g 2 ste
p honin
gTrouble
Measures
Table16.23 Honing Troubleshooting -Super grain grindingstone-
Trouble Cause
Clogging
Grain flatten
Grindingstone does not fit
Insufficient dressing of grains
Increasing granularity, Using soft grindingstone, Decreasing concentration.
Decreasing cutting speed, Increasing or Decreasing rotation speed
Supplying enough oil to the processed surface, Using washable oil
Reduce the grindstone width
Making a sufficient chip space on the grindstone working surface by dressing
measures
Grindingstone does not fit
Processing conditions do not match
Fault of honing oil
Too wide grindingstone width
Processing conditions do not match
Fault of honing oil
Using soft gridingstone,Decreasing concentration,Changing abrasive from diamond to CBN
Decreasing or increasing cutting speed, Increasing or Decreasing rotation speed
Supplying enough oil to the processed surface, Using lubricating oil
Short life ofgrindingsotne
Grindingstone does not fit
Chipped grindingstone
Fault of honing oil
Using hard grindingstone,Increasing concentration, Using larger grindingstone
Decreasing concentration, Using fine granularity, Using Metal mold type,Using plastic moldtype,Using lubricating oil
Removing chips and grind stone powder in oil to clean