Centerless Continuous Cylindrical Grinding with a Fold

Manuf. and Ind. Eng., 11(3), 2012, ISSN 1338-6549
© Faculty of Manuf. Tech. TUKE
Centerless Continuous Cylindrical Grinding
with a Fold Grinding Wheel
Stanislaw Legutko, Roman Siecla, Jacek Francka
Abstract
The paper presents the results of experiments involving centerless grinding with fold grinding wheels of various
characteristics. The objective of the investigation was to increase the productivity of centerless grinding of “pins” with the
diameters of Φ = (6 - 10) mm. Pins of this type are made of rolled rod materials. Standardized dimensions of the rods and
the relevant allowance values require several passes. An increase of the thickness of the layer removed in one pass will
allow for a significant increase of productivity. Selection of adequate characteristics of grinding wheels will make it
possible to increase the thickness of the ground layer and ensure correct parameters of the shaft top layer.
Keywords: grinding shafts, fold grinding wheel characteristics, ground layer parameters
1 Introduction
The shapes of workpieces in the process of centerless
grinding are, in principle, determined. In the case of longitudinal centerless continuous grinding, those are objects
of the type of “smooth shaft” or technologically similar
ones. The practical application of longitudinal continuous
centerless grinding requires the object to be easily brought
into the machining zone between the grinding wheel and the
work-rest wheel (Fig. 1) and equally easily taken out of that
zone.
In this respect, centerless grinding, due to its kinematics,
is an especially convenient kind of machining of any sort of
objects type pins - bolts. Centerless grinding of pins – bolts
is an operation in the technological process of those parts,
an operation than can be easily automated. The lack of
kinematic connections between the workpiece, e.g. a pin,
being machined and the assemblies of the centerless grinder
allows for continuous introduction of the workpieces into
the machining zone. The lack of kinematic connection of
the machined parts with the assemblies of the centerless
grinding machine results in indeterminable relocations of
the parts – pins, bolts in the machining zone. Those relocations cause definite changes in the shape of the removed
layer resulting in deviation from the workpiece roundness.
The process of centerless grinding is criticized. The problem is, however, that the undeniable advantages of the
process, first of all its easy automation and, consequently,
high productivity, make it still widely applied in practice.
Experimental works are conducted aiming, on the one hand,
at more profound cognition of the process itself and, on the
other hand, at its improvement [3, 6, 7].In that respect, the
Poznan University of Technology, too, has performed research works since many years [9, 11, 16].The purpose of
those works is to determine a model of centerless grinding
process and, basing on it, to find the best conditions of
performing it in respect of the quality of the machined part
[8].
8
Fig. 1 Operating principle of the centerless grinding
machine in the process of continuous cylindrical grinding:
1 - the ground workpiece – a pin, 2 – grinding wheel,
3 work-rest wheel, 4- - work-rest blade, 5 – steady bracket
used to adjust the height of the workpiece position, h - the
height of the workpiece position, v - workpiece resultant
speed, vfa - workpiece tangential speed, vw – travelling
speed, α - work-rest rake
The investigation conducted has enabled partial elaboration of a model [6, 8] which has made it possible to undertake fragment investigation in respect of the determination of the most advantageous conditions of continuous
centerless grinding [8, 12, 17]. Moreover, the results of those investigations have indicated the need of investigations
concerning increase of productivity. Fragments of investigations concerning productivity are discussed in the present
article. Figure 1 shows the principle of operation of a centerless grinding machine in the process of continuous grinding of shaft type objects.
2 Investigation program
and methodology
The program of investigation of fold grinding wheel
characteristics selection has been determined basing on the
results obtained in earlier experiments [3, 6, 12, 17]. It has
been found in those tests three zones could be distinguished
on the working surface of a grinding wheel. During the operation of the wheel, the zones change and they determine
the removed layer. The essential part of the machined
allowance is removed in the first, input, zone (1). In the
second zone (2), formation of the cylindrical surface of the
workpiece is formed. The third zone (3) constitutes an output fragment of the space between the grinding wheel and
the work-rest wheel and it is a continuation of the pin forming process.
Basing on the zones fund, a program of fold grinding
wheel characteristics selection has been elaborated. It has
been shown in table 1. In the selection of the grinding wheel
characteristics, attention was paid to the tasks of the individual zones.
Due to the correct parameters of the top layer of the
ground shafts obtained under the conditions existing so far,
the characteristics of the grinding wheel of the first test
series has been maintained in the third zone. In the second
test series, a grinding wheel of fewer granularities has been
adopted for zone (3) in order to obtain lower roughness of
the pin surface.
Tab.1 Program of investigation of fold grinding wheel
characteristics in the process of centerless grinding
For zone (1), the characteristics were selected as for
rough machining; for the second zone (2) as for forming
machining. The arrangement of the component wheels can
be seen in Fig.2.
In the production of pins, various raw materials are
used: 1 – rolled bars, 2 – peeled bars and 3 – drawn bars.
Fig.2 Arrangement of grinding wheels:
A – two grinding wheels arrangement,
B – three grinding wheels arrangement
For that reason, in the investigation program, the
individual kinds of raw materials have been incorporated
and adequate technological cycles elaborated; the cycles can
be found in table 2.
Note! The values of accuracy and roughness stated in
table 2 are ones obtained in production and, also the
required ones. Grinding tests were performed on two
centerless grinding machines, model ABS 3184 G. The test
pieces were pins with the diameters of Φ = (6 – 10) mm,
made of steel 45.
After cutting on a press, the pins were located in the
space between the grinding wheels one by one in order to
prevent their inclined positioning causing grinding wheel
chipping. Roundness deviation measurements were perfor-
med on a Talyrond 50 device and surface roughness measurements were effected on an ME 10 device [13].
Tab.2 The cycles of technological operations of centerless
grinding of shafts
3 Experiment results
The experiments were performed in two stages. Stage
one concerned investigation of the influence of the raw
materials on the accuracy and surface roughness. The tests
were performed in accordance with the cycles of technological operations presented in table 2. Stage two included
tests related to the selection of the component grinding
wheel characteristics stated in table 1.
Serie one
As has been proved by the investigations [1, 2, 6, 9], the
machining effects, particularly in the case of centerless
grinding, are closely related to the results of the previous
operation of the technological process under realization.
The results of the operation preceding centerless grinding
influence the selection of the adjustable settings of the
grinding machine as recommended by the norms. In this
respect, the purpose of the investigation was to determine
the influence of the semi-product quality after the operation
prior to the centerless grinding. The result of the investigation is the values stated in table 2. In this stage, the tests
were performed with two grinding wheels: rough grinding
was effected with a 99A46M7V wheel and finish grinding
with a 99A60K5V wheel (used in production nowadays).
Serie two
The pins to be tested were cut on a press and then
subjected to barrelling in order to break the edges. The pins,
in accordance with table 2, were subjected only to finish
grinding, each time ground in one pass. The tests in the
second stage were divided into two series. The first and the
second series included two test batches, “A” and “B”. The
first series, batch A consisted in grinding the pins with two
wheels; batch ‘B” with three wheels.
The test results assembled in table 3 have proved that, in
the first series, batch A, with the use of:
• rough grinding wheel granularity of “46”, the accuracy
obtained was – roundness deviation in the range of 0,25 mm
< Δ < 0,5 mm and surface roughness of 0,6 µm <Ra< 0,9
µm (test no 1);
• rough grinding wheel granularity of “30”, the accuracy
obtained was – roundness deviation in the range of 0,35 mm
< Δ < 0,75 mm and surface roughness of 0,8 µm <Ra< 1,05
µm (test no 2).
Furthermore, the tests results of the first series, batch
B, with the rough grinding wheel granularity of “30” and
the forming wheel granularity of “46” allow us to obtain the
following accuracy: roundness deviation of 0,45 mm < Δ<
0,55 mm and surface roughness of 0,50 µm < Ra < 0,65 µm
(test no 3). With the rough grinding wheel granularity of
“30” and that of the forming wheel of “54” the obtainable
9
accuracy is as follows: roundness deviation of 0,35 mm <
Δ< 0,45 mm and surface roughness of 0,30 µm < Ra < 0,45
µm (test no 4).
E-mail: [email protected]
[email protected]
[email protected]
Tab. 3 The results of accuracy and roughness testing after
the grinding process
References
[1]
[2]
[3]
[4]
The results obtained in the second series, batch A, for
all kinds of semi-products, with the use of:
finish grinding wheel granularity of “120” and rough
grinding wheel granularity of “80” were as follows: roundness deviation within the range of 0,25 mm< Δ < 0,4 mm
and surface roughness of 0,25 µm < Ra < 0,55 µm (test no
5). With the rough grinding wheel granularity of “46” and
the same of the finish grinding wheel the obtainable
accuracy is as follows: roundness deviation of 0,25 mm <
Δ< 0,35 mm and surface roughness of 0,35 µm < Ra < 0,55
µm (test no 6).
The test results of the second series, batch B are as
follows:
with the rough grinding wheel granularity of “54” and
the forming wheel granularity of “80” the obtainable
accuracy is: roundness deviation in the range of 0,25 < Δ <
0,45 mm and surface roundness 0,25 µm <Ra < 0,35 µm
(test no 7). With the rough grinding wheel granularity of
“30” and the forming wheel granularity of “100”, the
accuracy obtained was: roundness deviation in the range of
0,15 mm < Δ < 0,25 mm and surface roughness of 0,20
µm< Ra < 0,30 µm (test no 8).
4 Conclusions
Basing on the investigation results stated above, one can
say that the application of fold grinding wheels makes it
possible to reduce the number of passes in the process of
centerless grinding.
The application of various grinding wheel characteristics
makes it possible to obtain the required surface layer parameters. The results of the presented tests allow for the statement that it is advantageous to assemble grinding wheels
of three characteristics as has been stated in the results of
the second series, batch “B” .Generally, it can be said that
the fold grinding wheel arrangement should be as follows:
the rough grinding wheel should have coarse grains, the
forming one medium grains and the finishing wheel should
have fine grains.
Prof. DSc. Legutko Stanislaw, prof. h.c. M.Sc., PhD.,
Roman Siecla, M.Sc., PhD.,
Francka Jacek, M.Sc.,
Poznan University of Technology,
Institute of Mechanical Technology,
Street Pl. Marii Skłodowskiej - Curie 5, 60-965 Poznań,
Poland,
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