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Making and measuring in micro MIM manufacturing
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Making and measuring in micro MIM manufacturing To be able to successfully form very small parts by micro metal injection moulding is not quite enough for series manufacturing. Dimensional measurement and quality evaluation requirements also need to be satisfied. These were among the objectives for a Japanese research group... tional force to another gear or device and is also a machine element for highaccuracy positioning. In recent years some advanced micro-manufacturing processes and micro-sized gears made of metals and some advanced ceramics have been manufactured [1]. Micro-planetary gear motors have also been made from nickel-ferrous (Ni-Fe) and nickel-based bulk metallic glasses by X-ray lithography & electro-deposition (direct-LIG) [2] and injection moulding [3], respectively. However, there is demand for microsized gears made of general-purpose durable materials for miniaturisation and reliability improvement of various products. In manufacturing terms the aim
is to achieve a high economic efficiency to satisfy industrial need. Micro metal powder injection moulding (μMIM) is useful for producing micro-sized and microstructured parts [4-5], but measuring the accuracy of micro-gears manufactured by μMIM has proved difficult. A micro-planetary gear made of 17-4PH stainless steel was manufactured by μMIM as part of the Osaka project. The quality of the ultra-compact planet gear was evaluated by measuring the variation in dimensions of the gear teeth with digital image analysis. The micro-planetary gear composed of three types of gearwheels manufactured by μMIM process is shown in Figure1. In
▶
0.55 0.3
1.82 1.2
0.15
1
T
he production of micro-size and micro-structured parts by metal injection moulding (MIM) requires more sophisticated techniques than conventional MIM. New techniques for the quality evaluation of tiny parts also need to be developed. A micro-planetary gear made of 17-4PH stainless steel has been developed by micro metal injection moulding (μMIM) processas part of a study carried out by researchers at Osaka Prefectural College of Technology in Japan that describes the method of fabrication and quality evaluation of ultra-compact planet gears. A gearwheel is a component within a transmission device that transmits rota-
1
(a) Planetary-gear set
(b) Planet gear
: mm
(c) Dimensions of planet gear
Figure 1. Micro-planetary-gear manufactured by MIM.
22
MPR October 2009
0026-0657/09 ©2009 Elsevier Ltd. All rights reserved.
this study, the accuracy of the planet gear with dimensions shown in Figure 1(c) was evaluated. The specification of the planet gear (as sintered) is shown in Table 1. The materials used for producing the ultra-compact gears were stainless steel 17-4PH water-atomised powder (D50=2μm) and poly-acetyl based binders. Powder loading of the feedstock was 60vol%. The feedstock was injection-moulded using a high-speed injection moulding machine (FANUC Ltd., S-2000i 50A). The green compacts were debound at 600ºC for two hours in a nitrogen atmosphere, and sintered at 1150ºC for two hours under argon. The sintered parts were also age-hardened at 480ºC for one hour. The accuracy of conventional-sized gears is generally evaluated by master gear meshing test or contact profilometry. However, in the case of compact gears it is difficult to manufacture the master gear and to measure the shape by contact. Therefore a noncontact shape measurement technique using advanced instruments such as laser displacement sensing and digital image analysis are considered
Table 1. Specification of planet gear (as sintered). Module, m [mm]
0.07
Number of teeth, z [teeth]
24
Pressure angle, α [°]
20
Tip diameter, da [mm]
1.82
Pitch circle diameter, d [mm]
1.68
Circular pitch, p [mm]
0.22
Tooth thickness, s [mm]
0.11
useful in evaluating the accuracy of ultracompact gears. In current Japanese Industrial Standards (JIS B1702-1 (1998)), it is applicable for only gears larger than module; m=0.5, and is not applicable for smaller gears. In this study, cross-sections of planet gear in each processing steps; green bodies, sintered parts and agehardened parts were observed after polishing by a digital microscope (Keyence Co., VH-8000). The shapes of gear teeth were measured by image processing software (Media Cybernetics Inc., Image Pro® Plus 4.5), and the accuracy classes of gear in each processing step were obtained from four shape deviations of
gear teeth; 1) Runout of tooth groove (Fr), 2) Single pitch deviation (fpt), 3) Accumulated pitch deviation (Fp) and 4) Tooth profile deviation (Fα) shown in Figure 2. The accuracy classes were decided from average deviation values for gear (m = 0.07; 10 specimens) using the gear accuracy standards software (Amtec Co, Ltd GearAccuracy). The quality of gear was evaluated also by Vickers hardness (10 specimens), sintered density (Archimedes’ method, 10 specimens) and microstructures. Though shrinkage in sintering is significant, it is necessary to focus on the change seen in each dimension from moulding, to green bodies and on to
1.005
r
r (mm)
rmax 0.999
Fr
rmin 0.993 0
5
10 15 20 25 Tooth No.
1) Total runout (Fr),
2) Single pitch deviation (fpt)
α
3) Accumulated pitch deviation (Fp),
4) Tooth profile deviation (Fα)
s
da df 5) Diameters of addendum circle (da), root circle (df) and tooth thicknesss (s) Figure 2. Four shape deviations and principle definition of gear teeth.
metal-powder.net
October 2009 MPR
23
0.2
da
-17%
df
2
s mms (mm) Tooth thickness,
Diameter of addendum circle, da (mm) df circle, m d (mm) Diameter ofdaroot f
2.5
-16%
1.5
1 Mold
0.1
0
Green As sintered After HT
Figure 3. Diameters of addendum circle (da ) and root circle (df ).
-16%
Single pitch dev. Fpt (μm) fptpitch Fp μm Accumulated dev. Fp (μm)
Fr μmF (μm) Total runout, r
15 10 5
Mold
Green As sintered After HT
Figure 4. Tooth thicknesss (s).
20
0
Mold
Green As sintered After HT
20 15 10
fpt Fp
5 0 Mold
Green As sintered After HT
Figure 5. Total runout (Fr). Figure 5. Total runout (Fr ).
sintered parts to be able to manufacture the final products within specified dimensional tolerance. Figure 3 and Figure 4 show the change in each processing step on diameters of addendum circle (da); root circle (df), and tooth thicknesss (s), respectively. These measuring results showed 0.5%
m Fα (μm) Fα dev., Tooth profile
20
and 16.4% of shrinkage in moulding and sintering, respectively, but no change in dimensions after age-hardening. Table 2 shows the specification of a planet gear calculated by considering the shrinkages in each processing step. Modules, m were obtained by assigning db, z and α to m=db/z cosα. Figures 5, 6 and 7 show the measuring results of four shape deviations. Figure 5 shows that Fr tends to increase with the developing MIM process. The mould
used in this experiment had a pin-shaped gate located in the centre of planet gear, which meant the “weld line” which is caused by interfluent in injection moulding has not affected the mould accuracy. However, moulding pressure might become non-uniform due to unstable filling in a tiny cavity. It was considered that the gear shape deformed and had an effect in the sintering and age-hardening stages. From Figure 6 it was found that fpt was smaller than Fp which is largely affected by injection moulding.
15
Table 2. Specification of planet gear calculated by considering the shrinkage. Mold Green As sintered After HT
10 5 0
Mold
Green As sintered After HT
Figure 7. Tooth profile deviation (Fα ).
24
Figure 6. Single pitch deviation (fpt ) and accumulated pitch deviation (Fp ).
MPR October 2009
Module, m [mm]
0.084
0.084
0.070
0.070
Base circle diameter, db [mm]
1.910
1.900
1.580
1.580
Pitch circle diameter, d0 [mm]
2.016
2.016
1.680
1.680
Circular pitch, p [mm]
0.264
0.263
0.220
0.220 JIS B 1702-1 (1998)
metal-powder.net
Table 3. Accuracy classes for four shape deviations in MIM process. Mold Green As sintered
P
After HT
Total runout, Fr
6
6
7
7
Single pitch deviation, fpt
6
6
6
7
Accumulated pitch deviation, Fp
5
6
7
7
Tooth profile deviation, Fα
8
8
9
9
ISO1328-1(1995), ISO1328-2(1997), JIS B1702-1,-2(1998)
(a) As-sintered
Table 4. Vickers hardness and relative density. As sintered
P (b) After HT Figure 8. Microstructures of ultra-compact gears.
Figure 7 shows only slight differences in Fα among processing steps. From the results of the four shape deviations shown above, accuracy classes for each processing step were obtained for gear with m=0.07 as summarised in Table 3. The accuracy classification of the ultra-compact planet gear manufactured by MIM has not come up to that of a precisely ground gear, which is equivalent to around five. However it is reviewed that the accuracy class of ultra-compact gear is around seven which is an acceptable level for generalpurpose applications from a practical point of view. While Fr, f pt and F p keep within seven in terms of accuracy, only Fα is lower level than eighth. One of the reasons may have been that the shape of the gear tooth might not have been a completely ideal involute curve. This would taker further investigation. There was also a theoretical problem in that the accuracy classification degrades significantly when the ultracompact gear (eg m=0.07) is identified as conventional-sized gear (eg m=7) by enlarging each dimension 100 times. Table 4 shows the measured results of Vickers hardness and relative density of planet gears as-sintered and after age-hardening. The age-hardening process achieved a 24% increase in
metal-powder.net
After HT
Vickers hardness, Hv
325
402
Relative density, p [%]
97.6
99.6
Vickers hardness. This is more than Hv=400 which is equivalent for hardness of 17-4PH stainless steels specified by Japanese standards (JIS G4305). Relative density also increased after agehardening. However there seemed to be no difference in microstructure between
as-sintered specimens and age-hardened ones. The authors have studied the tribological properties of MIM products and the wear properties were evaluated quantitatively with comparison to moulded examples, clarifying the wear mechanisms [6].
References [1] D Löhe and J Haußelt, Advanced Micro & Nanosystems, Vol.3 and 4, Microengineering of Metals and Ceramics, WILEY-VCH Verlag GmbH & Co. KGaA (2005). [2] http://www.mikrogetriebe.de/ [3] M Ishida, H Takeda, N Nishiyama, Y Shimizu, K Kita, Y Saotome and A Inoue, “Characterization of Super-precision Microgear made of Ni-based Metallic Glass”, Journal of Metastable and Nanocrystalline Materials, 24-25, 543-546 (2005). [4] K Nishiyabu, K Kakishita, T Osada, S Matuzaki and S Tanaka, “Micro Evaluation Method for Quality Improvement of Micro Metal Injection Molding by Direct Mixing-Injection Molding Machine”, EuroPM2005, 182-1-6 (2005). [5] K Nishiyabu, Y Kanoko and S Tanaka, “Innovations in Micro Metal Injection Molding Process by Lost Form Technology”, Trans Tech Publications Ltd., Materials Scinece Forum, Vols.534-536, pp.369-372 (2007). [6] K Kameo, K Nishiyabu, K Friedrich and T Tanimoto, “Sliding Wear Behavior of Stainless Steel Parts Made by Metal Injection Molding (MIM)”, Wear, 260, pp.674-686 (2006).
The Authors This feature is derived from Accuracy Evaluation of Ultra-Compact Gears Manufactured by Micro-MIM Process, a paper by Kazuaki Nishiyabu1,a, Ian Andrews1,b and Shigeo Tanaka2,b, given at EuroPM 2008 in Mannheim. 1Osaka
Prefectural College of Technology, 26-12 Saiwai, Neyagawa, Osaka 572-8572 Kogyo Co., Ltd., 26-1 Ikeda-kita, Neyagawa, Osaka 572-0073, JAPAN [email protected], [email protected], [email protected] 2Taisei
October 2009 MPR
25
Making and measuring in micro MIM manufacturing To be able to successfully form very small parts by micro metal injection moulding is not quite enough for series manufacturing. Dimensional measurement and quality evaluation requirements also need to be satisfied. These were among the objectives for a Japanese research group... tional force to another gear or device and is also a machine element for highaccuracy positioning. In recent years some advanced micro-manufacturing processes and micro-sized gears made of metals and some advanced ceramics have been manufactured [1]. Micro-planetary gear motors have also been made from nickel-ferrous (Ni-Fe) and nickel-based bulk metallic glasses by X-ray lithography & electro-deposition (direct-LIG) [2] and injection moulding [3], respectively. However, there is demand for microsized gears made of general-purpose durable materials for miniaturisation and reliability improvement of various products. In manufacturing terms the aim
is to achieve a high economic efficiency to satisfy industrial need. Micro metal powder injection moulding (μMIM) is useful for producing micro-sized and microstructured parts [4-5], but measuring the accuracy of micro-gears manufactured by μMIM has proved difficult. A micro-planetary gear made of 17-4PH stainless steel was manufactured by μMIM as part of the Osaka project. The quality of the ultra-compact planet gear was evaluated by measuring the variation in dimensions of the gear teeth with digital image analysis. The micro-planetary gear composed of three types of gearwheels manufactured by μMIM process is shown in Figure1. In
▶
0.55 0.3
1.82 1.2
0.15
1
T
he production of micro-size and micro-structured parts by metal injection moulding (MIM) requires more sophisticated techniques than conventional MIM. New techniques for the quality evaluation of tiny parts also need to be developed. A micro-planetary gear made of 17-4PH stainless steel has been developed by micro metal injection moulding (μMIM) processas part of a study carried out by researchers at Osaka Prefectural College of Technology in Japan that describes the method of fabrication and quality evaluation of ultra-compact planet gears. A gearwheel is a component within a transmission device that transmits rota-
1
(a) Planetary-gear set
(b) Planet gear
: mm
(c) Dimensions of planet gear
Figure 1. Micro-planetary-gear manufactured by MIM.
22
MPR October 2009
0026-0657/09 ©2009 Elsevier Ltd. All rights reserved.
this study, the accuracy of the planet gear with dimensions shown in Figure 1(c) was evaluated. The specification of the planet gear (as sintered) is shown in Table 1. The materials used for producing the ultra-compact gears were stainless steel 17-4PH water-atomised powder (D50=2μm) and poly-acetyl based binders. Powder loading of the feedstock was 60vol%. The feedstock was injection-moulded using a high-speed injection moulding machine (FANUC Ltd., S-2000i 50A). The green compacts were debound at 600ºC for two hours in a nitrogen atmosphere, and sintered at 1150ºC for two hours under argon. The sintered parts were also age-hardened at 480ºC for one hour. The accuracy of conventional-sized gears is generally evaluated by master gear meshing test or contact profilometry. However, in the case of compact gears it is difficult to manufacture the master gear and to measure the shape by contact. Therefore a noncontact shape measurement technique using advanced instruments such as laser displacement sensing and digital image analysis are considered
Table 1. Specification of planet gear (as sintered). Module, m [mm]
0.07
Number of teeth, z [teeth]
24
Pressure angle, α [°]
20
Tip diameter, da [mm]
1.82
Pitch circle diameter, d [mm]
1.68
Circular pitch, p [mm]
0.22
Tooth thickness, s [mm]
0.11
useful in evaluating the accuracy of ultracompact gears. In current Japanese Industrial Standards (JIS B1702-1 (1998)), it is applicable for only gears larger than module; m=0.5, and is not applicable for smaller gears. In this study, cross-sections of planet gear in each processing steps; green bodies, sintered parts and agehardened parts were observed after polishing by a digital microscope (Keyence Co., VH-8000). The shapes of gear teeth were measured by image processing software (Media Cybernetics Inc., Image Pro® Plus 4.5), and the accuracy classes of gear in each processing step were obtained from four shape deviations of
gear teeth; 1) Runout of tooth groove (Fr), 2) Single pitch deviation (fpt), 3) Accumulated pitch deviation (Fp) and 4) Tooth profile deviation (Fα) shown in Figure 2. The accuracy classes were decided from average deviation values for gear (m = 0.07; 10 specimens) using the gear accuracy standards software (Amtec Co, Ltd GearAccuracy). The quality of gear was evaluated also by Vickers hardness (10 specimens), sintered density (Archimedes’ method, 10 specimens) and microstructures. Though shrinkage in sintering is significant, it is necessary to focus on the change seen in each dimension from moulding, to green bodies and on to
1.005
r
r (mm)
rmax 0.999
Fr
rmin 0.993 0
5
10 15 20 25 Tooth No.
1) Total runout (Fr),
2) Single pitch deviation (fpt)
α
3) Accumulated pitch deviation (Fp),
4) Tooth profile deviation (Fα)
s
da df 5) Diameters of addendum circle (da), root circle (df) and tooth thicknesss (s) Figure 2. Four shape deviations and principle definition of gear teeth.
metal-powder.net
October 2009 MPR
23
0.2
da
-17%
df
2
s mms (mm) Tooth thickness,
Diameter of addendum circle, da (mm) df circle, m d (mm) Diameter ofdaroot f
2.5
-16%
1.5
1 Mold
0.1
0
Green As sintered After HT
Figure 3. Diameters of addendum circle (da ) and root circle (df ).
-16%
Single pitch dev. Fpt (μm) fptpitch Fp μm Accumulated dev. Fp (μm)
Fr μmF (μm) Total runout, r
15 10 5
Mold
Green As sintered After HT
Figure 4. Tooth thicknesss (s).
20
0
Mold
Green As sintered After HT
20 15 10
fpt Fp
5 0 Mold
Green As sintered After HT
Figure 5. Total runout (Fr). Figure 5. Total runout (Fr ).
sintered parts to be able to manufacture the final products within specified dimensional tolerance. Figure 3 and Figure 4 show the change in each processing step on diameters of addendum circle (da); root circle (df), and tooth thicknesss (s), respectively. These measuring results showed 0.5%
m Fα (μm) Fα dev., Tooth profile
20
and 16.4% of shrinkage in moulding and sintering, respectively, but no change in dimensions after age-hardening. Table 2 shows the specification of a planet gear calculated by considering the shrinkages in each processing step. Modules, m were obtained by assigning db, z and α to m=db/z cosα. Figures 5, 6 and 7 show the measuring results of four shape deviations. Figure 5 shows that Fr tends to increase with the developing MIM process. The mould
used in this experiment had a pin-shaped gate located in the centre of planet gear, which meant the “weld line” which is caused by interfluent in injection moulding has not affected the mould accuracy. However, moulding pressure might become non-uniform due to unstable filling in a tiny cavity. It was considered that the gear shape deformed and had an effect in the sintering and age-hardening stages. From Figure 6 it was found that fpt was smaller than Fp which is largely affected by injection moulding.
15
Table 2. Specification of planet gear calculated by considering the shrinkage. Mold Green As sintered After HT
10 5 0
Mold
Green As sintered After HT
Figure 7. Tooth profile deviation (Fα ).
24
Figure 6. Single pitch deviation (fpt ) and accumulated pitch deviation (Fp ).
MPR October 2009
Module, m [mm]
0.084
0.084
0.070
0.070
Base circle diameter, db [mm]
1.910
1.900
1.580
1.580
Pitch circle diameter, d0 [mm]
2.016
2.016
1.680
1.680
Circular pitch, p [mm]
0.264
0.263
0.220
0.220 JIS B 1702-1 (1998)
metal-powder.net
Table 3. Accuracy classes for four shape deviations in MIM process. Mold Green As sintered
P
After HT
Total runout, Fr
6
6
7
7
Single pitch deviation, fpt
6
6
6
7
Accumulated pitch deviation, Fp
5
6
7
7
Tooth profile deviation, Fα
8
8
9
9
ISO1328-1(1995), ISO1328-2(1997), JIS B1702-1,-2(1998)
(a) As-sintered
Table 4. Vickers hardness and relative density. As sintered
P (b) After HT Figure 8. Microstructures of ultra-compact gears.
Figure 7 shows only slight differences in Fα among processing steps. From the results of the four shape deviations shown above, accuracy classes for each processing step were obtained for gear with m=0.07 as summarised in Table 3. The accuracy classification of the ultra-compact planet gear manufactured by MIM has not come up to that of a precisely ground gear, which is equivalent to around five. However it is reviewed that the accuracy class of ultra-compact gear is around seven which is an acceptable level for generalpurpose applications from a practical point of view. While Fr, f pt and F p keep within seven in terms of accuracy, only Fα is lower level than eighth. One of the reasons may have been that the shape of the gear tooth might not have been a completely ideal involute curve. This would taker further investigation. There was also a theoretical problem in that the accuracy classification degrades significantly when the ultracompact gear (eg m=0.07) is identified as conventional-sized gear (eg m=7) by enlarging each dimension 100 times. Table 4 shows the measured results of Vickers hardness and relative density of planet gears as-sintered and after age-hardening. The age-hardening process achieved a 24% increase in
metal-powder.net
After HT
Vickers hardness, Hv
325
402
Relative density, p [%]
97.6
99.6
Vickers hardness. This is more than Hv=400 which is equivalent for hardness of 17-4PH stainless steels specified by Japanese standards (JIS G4305). Relative density also increased after agehardening. However there seemed to be no difference in microstructure between
as-sintered specimens and age-hardened ones. The authors have studied the tribological properties of MIM products and the wear properties were evaluated quantitatively with comparison to moulded examples, clarifying the wear mechanisms [6].
References [1] D Löhe and J Haußelt, Advanced Micro & Nanosystems, Vol.3 and 4, Microengineering of Metals and Ceramics, WILEY-VCH Verlag GmbH & Co. KGaA (2005). [2] http://www.mikrogetriebe.de/ [3] M Ishida, H Takeda, N Nishiyama, Y Shimizu, K Kita, Y Saotome and A Inoue, “Characterization of Super-precision Microgear made of Ni-based Metallic Glass”, Journal of Metastable and Nanocrystalline Materials, 24-25, 543-546 (2005). [4] K Nishiyabu, K Kakishita, T Osada, S Matuzaki and S Tanaka, “Micro Evaluation Method for Quality Improvement of Micro Metal Injection Molding by Direct Mixing-Injection Molding Machine”, EuroPM2005, 182-1-6 (2005). [5] K Nishiyabu, Y Kanoko and S Tanaka, “Innovations in Micro Metal Injection Molding Process by Lost Form Technology”, Trans Tech Publications Ltd., Materials Scinece Forum, Vols.534-536, pp.369-372 (2007). [6] K Kameo, K Nishiyabu, K Friedrich and T Tanimoto, “Sliding Wear Behavior of Stainless Steel Parts Made by Metal Injection Molding (MIM)”, Wear, 260, pp.674-686 (2006).
The Authors This feature is derived from Accuracy Evaluation of Ultra-Compact Gears Manufactured by Micro-MIM Process, a paper by Kazuaki Nishiyabu1,a, Ian Andrews1,b and Shigeo Tanaka2,b, given at EuroPM 2008 in Mannheim. 1Osaka
Prefectural College of Technology, 26-12 Saiwai, Neyagawa, Osaka 572-8572 Kogyo Co., Ltd., 26-1 Ikeda-kita, Neyagawa, Osaka 572-0073, JAPAN [email protected], [email protected], [email protected] 2Taisei
October 2009 MPR
25