IDEA OF NONCIRCULAR GEARS MANUFACTURED OF

KOMISJA BUDOWY MASZYN PAN – ODDZIAŁ W POZNANIU
Vol. 28 nr 2
Archiwum Technologii Maszyn i Automatyzacji
2008
PIOTR KRAWIEC∗
IDEA OF NONCIRCULAR GEARS MANUFACTURED
OF SINTERED POWDER METALS
In this elaboration the possibility of manufacturing of noncircular gear-wheels of sintered
powder metals used in uneven-running transmissions and in hydraulic machines has been presented. The technology conception of shaping of sintered powder metal products for chosen
wheels forms has been also presented. Advantages and limitations of proposed solution have been
specified.
Key words: powder metallurgy, noncircular gears, manufacturing technologies
1. INTRODUCTION
Application of noncircular gears in machine construction is known from 50-tiess of the last century [5]. However the significant limitation of their general
usage were problems connected with geometrical features designing, gear kinematics and also with available their manufacturing techniques. Application of
numerical methods, especially referring to outline envelope optimization, became the base for solving of problems connected with designing of unevenrunning gears variations. While matters connected with manufacturing, especially with accuracy, are significant problems till now. Amongst noncircular wheels
manufacturing methods there can be distinguished as follows: cutting forming
(milling, chiseling) and as well forming on CNC electro-erosion machines [3].
Relatively new conception of noncircular gears manufacturing is the idea their
production with metal powders sintering method.
History of powder metallurgy dates on the beginning of the XIX century. But
the beginning of common application of this method falls on the Second World
War time. This technology is the subject of extremely dynamic development
mainly thanks to application in such branches of industry as: electrical, automotive, machine construction, armaments industry, and for manufacturing of highproductive cutting tools. Powder metallurgy, in comparison to traditional manufacturing methods, has the following advantages:
∗
Dr inż. – Chair of Basics of Machine Design, Poznan University of Technology.
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− it is „no waste” technology, and material losses are on a few percentage
level,
− products manufactured with this method are characterized with high accuracy of designed shape enabling elimination (limiting to minimum) of expensive
and labour-consuming cutting machining,
− there is the possibility of manufacturing of complicate shape gears, cams
and clutch elements etc.
− thanks to application of proper instrumentation there is possible obtaining
of products characterized with repeatable geometrical, material and strength
features,
− there is the possibility of components connecting, which cannot be united
by melting because of big differences in their freezing temperatures or because
of mutual solubility lacking,
− there is possible to obtain metal-ceramic composite materials,
− efficiency of large-lot production considerably exceeds efficiency of production carried out with classical methods.
Interesting statement of technical-economical rate of production of one ton of
products manufactured with cutting machining and with metal powders sintering
method is presented in elaboration [10]. It is unequivocally arising from this
statement that manufacturing with usage of powders pressing and sintering
should have more common application in lot production especially in large-lot
production than machine cutting.
Table 1
Technical-economical rate of production of 1 ton of workpieces [10]
Wskaźniki techniczno-ekonomiczne produkcji 1 tony wyrobów [10]
Number
1
2
3
4
5
6
Technical-economical rate
Material consumption index
Material utilization coefficient
Quantity of technological operations
Production surface [m2]
Labour consumption (man-hours)
Quantity of blue-collar workers
Production of one ton of
workpieces
Machine
Pressing and
cutting
sintering
4.00
1.00
0.25
0.99
25÷40
4÷8
3.46
1.69
930
86.70
0.35
0.07
Manufacturing method of sintered metal powder machine elements is commonly attributed to obtaining of machine elements in mass production and to
production of workpieces with nontypical material properties [12]. This method
can be also the alternative to classical methods of chipless forming which need
the complex manufacturing process and special tools. The examples of such
elements are cams and noncircular envelope gears used in hydraulic machines
Idea of noncircular gears...
87
[13], belt transmissions with periodical changeable ratio [4, 8]. Exemplary configuration of such transmission with gear of ellipse shape and gear assembled
off-center is presented in Fig. 1.
Fig. 1. Uneven-running belt transmission with off-center gear
Rys. 1. Nierównobieżna przekładnia cięgnowa z kołem mimośrodowym
One of leading center dealing with elaboration of technology and manufacturing of machine elements of sintered metal powders is Metal Forming Institute
in Poznań [14, 15, 16], thanks to which there was possible to elaborate brief
foredesign and technological assumptions for manufacturing of sintered powders
gears used in uneven-running belt transmissions.
2. FORMING TECHNOLOGY OF SINTERED METALS POWDERS
PRODUCTS
Forming technology of sintered metals powders products consists of the following stages:
– pressing, consisting of three operations that is powder charge, proper
matching (composition densification) and pressed profile pushing out,
– sintering, consisting in integrating of pressed or loosely charged metal
powder particles in temperature lower than their melting temperature, into solid
body,
– finishing, consisting in calibration process, machine cutting, chemical-heat
and surface treatment of sinters.
For manufacturing with sintered metals powders method there were chosen
three noncircular pulleys shown in Fig. 2a–c.
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a)
b)
c)
Fig. 2. Noncircular wheels of uneven-running transmission: a) wheel of elliptic envelope, b) wheel
of oval shape envelope, c) wheel of near-circular envelope
Rys. 2. Koła nieokrągłe przekładni nierównobieżnej o obwiedni: a) w kształcie elipsy, b) w kształcie owalu, c) zbliżonej do okręgu
Basing on information concerning previously manufactured workpieces [15]
(Fig. 3a) there was accepted that required material features of noncircular wheels
could be obtained by single forming operation. Process flow diagram of sintered
metals powders workpieces manufacturing is presented in Fig. 3b.
Basing problem in designing of sintered powder products is choice of proper powder. Actually in the market there are available a number of products. Referring to a big experience in this matter in MFI Poznan there were chosen
a powder under the name Astaloy Mo of company Hoganas S.A. [15].
Chemical composition and physical characteristic of this material are given in
Table 2.
Necessary powder mass for manufacturing of one workpiece is determined
from dependence
M =V ⋅ς ⋅c ⋅k
p
t
ς
s
where: V – product volume,
ςt – product theoretical density,
cς – product density coefficient,
ks – powder loss coefficient in manufacturing process (ks = 1.01÷1.02).
(1)
Idea of noncircular gears...
89
Fig. 3. Manufacturing of sintered powders machine elements in Metal Forming Institute in Poznan:
a) exemplary machine elements, b) process flow diagram of sintered metals powders in one shaping
operation [15]
Rys. 3. Wytwarzanie elementów maszyn z proszków metali w INOP Poznań: a) przykładowe elementy
maszyn, b) schemat technologii wytwarzania w jednej operacji kształtowania [15]
Press choosing should be carried out basing on unit pressure determined experimentally (taking into account required product density) and area.
Table 2
Chemical composition and physical characteristic of material Astaloy Mo of company Hoganas S.A.
Skład chemiczny i cechy fizyczne materiału Astaloy Mo firmy Hoganas SA
Chemical composition and physical characteristic of material Astaloy Mo
Chemical composition %
C
O
S
Mn
Mo
<0.01
0.1
–
–
1.5
Bulk density
Flow
Density
green
Densification
pressure
Strength green
[g/cm3]
[sec/50g]
[g/cm3]
[MPa]
[MPa]
3.10
24
7.12
400÷800
15
Physical characteristic
Mechanical presses enable obtaining of thrust up to about 1 MN. In case of
necessity of thrusts over 0.6 MN application there is necessary to use hydraulic
presses.
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90
Required thrust value of press Fp is determined from dependence:
Fp = F j ⋅ A
(2)
where: Fj – press unit pressure determined experimentally depending on required
product density,
A – area.
For carrying out of pressing manufacturing process there is necessary elaboration of new or adaptation of known pressing tools. In pressing tool designing
process there should be met the following rules [6]:
− the whole volume of chamber must be uniformly charged with mixture of
powders and additives,
− density distribution in pressed product must be uniform (material uniformity),
− densification must be carried out uniformly and simultaneously in such
a way that product should have identical material properties in all its volume,
− ready product must leave die without damages,
− punches movements must be controlled in such a way to ensure the repeatability and accuracy of profiles manufacturing,
− punches used in pressing tools should transmit comparable loads to ensure
their durability and wear resistance,
− tool should be easy assembled in the press to limit setup time,
− costs of instrumentation should be adequate to its durability and efficiency.
Pressing tool design is based on solutions included in elaborations [1, 2, 6, 11].
Geometrical, material, and strength characteristics choosing process by FEM and
simulation of pressing tool (Fig. 4c) were carried out in CAD 3D [9].
Main elements of pressing tool, analogical to plastic forming and plastic materials forming, are: dies, punches, cores.
Dimensions of inner die profile can be determined from dependency given in
[1, 11, 12]
d m = z n ± 0,5 Δd − z r ± zsp + z k + zoc
(3)
taking into account the fact that inner die profile will be equidistant (curve parallel) to ready product profile
z mw = z n ± 0,5 Δz − zr ± zsp + z k + zoc
where: zn
∆z
zr
zsp
zk
zoc
– nominal profile of sinter,
– nominal profile deviation,
– radial elastic expansion of stamping after pressing, (about 0,2%),
– dimensional changes in sintering process (taken empirical),
– allowance for sizing, (in range of 0,25÷0,5),
– changes of dimensions during heat treatment (taken empirical).
(4)
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91
Minimal dimensions of die inner profile zmz can be determined from dependency [1, 11, 12]
kr + ν ⋅ p
dm = dm
(5)
kr − ν ⋅ p
taking into account the fact that term
kr + ν ⋅ p
denoted as k will be the value
kr − ν ⋅ p
of outer profile withdrawal from inner profile of die.
Z mz = Z mw ⋅ k
(6)
where: Zmw
ν
p
kr
– inner profile of die,
– Poisson ratio,
– pressing pressure,
– die allowable tensile stress equal to kr = Re0,2/x, where: Re0,2 –
proof stress, x – safety factor (5÷6).
Because of technical-economical reasons, for noncircular wheel shown in
drawing 4a, there is advisable shaping of outer profile in the shape shown in Fig.
4b.
Height of loading chamber H can be determined from dependency [7]
H = h⋅ z
(7)
where: h – height of stamping,
z – proportion of pressed density to bulk density of stamping.
Table 3
Chosen process parameters of sinter metals powder noncircular wheels manufacturing
Wybrane parametry procesu technologicznego wytwarzania kół nieokrągłych
ze spiekanych proszków metali
Parameter
Wheel from Fig. 2a
Wheel from
Fig. 2b
Wheel from
Fig. 2c
Product volume V [cm3]
Powder mass Mp [kg]
Powder mixing time (100kg) t [h]
Press thrust P [kg]
Sintering temperature T [°C]
Sintering time t [h]
Product density ζt [g/cm3]
Roughness Ra [µm]
100.02
0.72
about 1 h
470 000
1120
30 min
7.1
2.5
42.41
0.31
about 1 h
200 000
1120
30 min
7.1
2.5
33.47
0.24
about 1 h
15 000
1120
30 min
7.1
2.5
Chemical-heat treatment
Cyaniding carbonizing – depending on hardness
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a)
b)
c)
Fig. 4. Pressing tool unit: a) noncircular pulley, b) outer and inner profiles of die, c) pressing tool:
1 – upper plate, 2 – pilot, 3 – pilot sleeve, 4 – die block, 5 – sliding wedge, 6 – spring, 7 – guide
posts, 8 – main plate, 9 – wedge of bottom slide, 10 – pulling plate, 11 – slider, 12 – sleeve 13 – core,
14 – die, 15 – punch, 16 – backing plate
Rys. 4. Zespół prasownika: a) koło pasowe nieokrągłe, b) zarys zewnętrzny i wewnętrzny matrycy,
c) prasownik: 1 – płyta górna, 2 – pilot, 3 – tuleja prowadząca, 4 – płyta matrycowa, 5 – klin suwliwy, 6 – sprężyna, 7 – słupy prowadzące, 8 – płyta główna, 9 – klin suwaka dolnego, 10 – płyta ściągająca, 11 – suwak, 12 – tuleja, 13 – rdzeń, 14 – matryca, 15 – stempel, 16 – płyta mocująca
Idea of noncircular gears...
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Statement of determined process parameters of particular stages of noncircular wheels, from drawing 2a–c, manufacturing is presented in Table 3.
3. CONCLUSIONS
Basing on elaborated conception there is well-grounded formulation the following thesis: there is a possibility of manufacturing of noncircular wheels by
metals powders sintering method.
Such process is characterized by high costs especially in piece and small series production. Because of traditional engineering process complexity there is
recommended to make its instrumentation on numerically-controlled machines.
For reduction of determined press thrusts there is recommended to design hybrid
gears composed of core made of steel and toothed-wheel rim made of sintered
metals powders. Full information concerning the correctness of elaborated design-technological process could be taken from manufacturing of exemplary
noncircular gears. But because of lack of interest in single elements manufacturing by „industry” and high costs such attempt wasn’t carried out.
Natural continuation of discussed subject will be manufacturing of noncircular gears with methods Rapid Prototyping/Rapid Tooling RP/RT.
RENDER THANKS
Author thanks to Mrs. Hanna Wiśniewska-Weinert PhD Eng. from Metal
Forming Institute in Poznan for consultation and the possibility of getting acquainted with practical manufacturing process of sintered metal powder workpieces.
LITERATURA
[1] Adamczak S., Aleksanderek F., Wytwarzanie części maszyn z proszków metali, Warszawa,
WNT 1969.
[2] Adamczak S., Lesniak R., Wyroby spiekane z proszków metali – Katalog informator, Warszawa, Wyd. Ministerstwa Przemysłu Samochodowego „WEMA” 1973.
[3] Domek G., Krawiec P., Metody kształtowania pasowych kół zębatych, Mechanik, 2007,
r. 80, nr 8–9, s. 684–687.
[4] Dudziak M., Przekładnie cięgnowe, Warszawa, PWN 1997.
[5] Fuentes A., Litwin F.L., Gear Geometry and Applied Theory, Cambridge, Cambridge University Press 2004.
[6] Hoganas AB, Poradnik metalurgii proszków, cz. 1, 2, 3, 1997.
[7] Kotschy J., Technologia spieków, Kielce, Wyd. Politechniki Świętokrzyskiej 1977.
[8] Krawiec P., Nieklasyczna przekładnia cięgnowa z pasem zębatym, Przegląd Mechaniczny,
2005, nr 4, s. 25–26.
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[9] Krawiec P., Projektowanie napędów i elementów maszyn z CAD, Poznań, Wyd. Politechniki Poznańskiej 2007.
[10] Kulszewicz I., Proć T., Przemysł metalurgiczny w Polsce – wyroby z proszków żelaza, w:
Wybrane technologie obróbki plastycznej, Poznań 1996, s. 29–34.
[11] Missol W., Spiekane części maszyn, Katowice, Wydawnictwo Śląsk 1978.
[12] Nowacki J., Spiekane metale i kompozyty z osnową metaliczną, Warszawa, WNT 2005.
[13] Stryczek J., Koła zębate maszyn hydraulicznych, Wrocław, Oficyna Wydawnicza Politechniki Wrocławskiej 2007.
[14] Weinert H., Leszczyński V., Stojanov A., Sewastianow S., Kuczma V., Sposób otrzymywania elementów kształtowych, patent 191806 PL.
[15] Wiśniewska-Weinert H., Leshchynsky V., Ozwoniarek J., Kędzia Ł., Lisowski J., Technologie wytwarzania części dokładnych ze spiekanych materiałów proszkowych, Obróbka
Plastyczna Metali, 2006, t. 17, nr 3, s. 37–42.
[16] Wiśniewska-Weinert H., Plewiński A., Lisowski J., Stan obecny metalurgii proszków
i perspektywy rozwoju zapotrzebowania rynku na części wykonane z materiałów proszkowych, Obróbka Plastyczna Metali, 1998, t. 9, nr 1, s. 5–14.
Praca wpłynęła do Redakcji 31.03.2008
Recenzent: prof. dr hab. inż. Hubert Latoś
KONCEPCJA WYTWARZANIA KÓŁ NIEOKRĄGŁYCH
ZE SPIEKANYCH PROSZKÓW METALI
Streszczenie
Przedstawiono możliwość wytwarzania kół nieokrągłych, stosowanych w przekładniach nierównobieżnych oraz maszynach hydraulicznych, ze spiekanych materiałów proszkowych. Zaprezentowano koncepcję technologii kształtowania wyrobów ze spiekanych proszków metali dla wybranych
zarysów kół nieokrągłych. Wykazano zalety i ograniczenia proponowanego rozwiązania.
Słowa kluczowe: metalurgia proszków, koła nieokrągłe, technologia wytwarzania