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Castable Bulk Metallic Glass Strain Wave Gears: Towards Decreasing the Cost of High-Performance Robotics

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ABSTRACT

The use of bulk metallic glasses (BMGs) as the flexspline in strain wave gears (SWGs), also known as harmonic drives, is presented. SWGs are unique, ultra-precision gearboxes that function through the elastic flexing of a thin-walled cup, called a flexspline. The current research demonstrates that BMGs can be cast at extremely low cost relative to machining and can be implemented into SWGs as an alternative to steel. This approach may significantly reduce the cost of SWGs, enabling lower-cost robotics. The attractive properties of BMGs, such as hardness, elastic limit and yield strength, may also be suitable for extreme environment applications in spacecraft.

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Prototyping bulk metallic glass flexsplines.(a) Suction casting over brass inserts was used to create a cup from a Ti-based BMG. (b) Comparing the outer shape of the BMG cup to a machined steel flexspline. (c) The minimum thickness of the cup using suction pressure was 2 mm. The wall was thinned via conventional machining. (d) EDM was used to machine the teeth in the flexspline resulting in the final shape, shown. (e) Attempts were made to cast the teeth of the flexspline using and EDMed mold, shown in the inset. (f) Comparison of fully prototyped BMG flexspline with a steel version. (g) An assembled, functioning SWG utilizing a BMG flexspline from (f). (h) DSC trace of three BMG alloys cast into flexsplines. The lower two plots were prototyped using lab-grade material while the other plot is from a commercially cast part. (i) XRD scans of three BMG alloys cast into flexsplines, showing mostly amorphous microstructure even in fairly large parts.
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f2: Prototyping bulk metallic glass flexsplines.(a) Suction casting over brass inserts was used to create a cup from a Ti-based BMG. (b) Comparing the outer shape of the BMG cup to a machined steel flexspline. (c) The minimum thickness of the cup using suction pressure was 2 mm. The wall was thinned via conventional machining. (d) EDM was used to machine the teeth in the flexspline resulting in the final shape, shown. (e) Attempts were made to cast the teeth of the flexspline using and EDMed mold, shown in the inset. (f) Comparison of fully prototyped BMG flexspline with a steel version. (g) An assembled, functioning SWG utilizing a BMG flexspline from (f). (h) DSC trace of three BMG alloys cast into flexsplines. The lower two plots were prototyped using lab-grade material while the other plot is from a commercially cast part. (i) XRD scans of three BMG alloys cast into flexsplines, showing mostly amorphous microstructure even in fairly large parts.

Mentions: To evaluate the potential, we performed a feasibility study to see if BMGs could be successfully manufactured into flexsplines from a variety of different alloys. Two BMG alloys were used for the prototyping, a Zr35Ti30Cu8.25Be26.75 (GHDT) known for its high toughness and a new Ti-based BMG, Ti40Zr20Cu10Be30, which is a low-density alloy (4.8 g/cm3) with a high glass forming ability (~16 mm)18. This alloy was based on two previously developed BMG metal matrix composites, DV1 (Ti48Zr20V12Cu5Be19), and V0 (Ti53Zr27Cu5Be15)1920. To create the Ti-based BMG used here, the vanadium was removed (which was initially added to composites to provide a beta stabilizing effect) and the titanium was replaced with beryllium (to reduce the volume fraction of the second-phase microstructure and to create a monolithic glass). New alloy variants were created by attempting to decrease the percentage of dense elements, such as zirconium and copper, while maximizing the low-density element beryllium. The process was stopped at the composition Ti40Zr20Cu10Be30, where the density could no longer be lowered without the critical casting thickness of the alloy decreasing below the minimum required to cast the flexspline prototype shown in Fig. 2. The new alloy was characterized using DSC and X-ray diffraction as compared to several other BMGs and the hardness and elastic constants were also measured. The DSC curve demonstrates the Ti-BMG does not have as wide of a supercooled liquid region as GHDT and shows some evidence of crystal phases forming in the prototyped flexspline, but the alloy is still remarkable for its low density and high glass-forming.


Castable Bulk Metallic Glass Strain Wave Gears: Towards Decreasing the Cost of High-Performance Robotics
Prototyping bulk metallic glass flexsplines.(a) Suction casting over brass inserts was used to create a cup from a Ti-based BMG. (b) Comparing the outer shape of the BMG cup to a machined steel flexspline. (c) The minimum thickness of the cup using suction pressure was 2 mm. The wall was thinned via conventional machining. (d) EDM was used to machine the teeth in the flexspline resulting in the final shape, shown. (e) Attempts were made to cast the teeth of the flexspline using and EDMed mold, shown in the inset. (f) Comparison of fully prototyped BMG flexspline with a steel version. (g) An assembled, functioning SWG utilizing a BMG flexspline from (f). (h) DSC trace of three BMG alloys cast into flexsplines. The lower two plots were prototyped using lab-grade material while the other plot is from a commercially cast part. (i) XRD scans of three BMG alloys cast into flexsplines, showing mostly amorphous microstructure even in fairly large parts.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121900&req=5

f2: Prototyping bulk metallic glass flexsplines.(a) Suction casting over brass inserts was used to create a cup from a Ti-based BMG. (b) Comparing the outer shape of the BMG cup to a machined steel flexspline. (c) The minimum thickness of the cup using suction pressure was 2 mm. The wall was thinned via conventional machining. (d) EDM was used to machine the teeth in the flexspline resulting in the final shape, shown. (e) Attempts were made to cast the teeth of the flexspline using and EDMed mold, shown in the inset. (f) Comparison of fully prototyped BMG flexspline with a steel version. (g) An assembled, functioning SWG utilizing a BMG flexspline from (f). (h) DSC trace of three BMG alloys cast into flexsplines. The lower two plots were prototyped using lab-grade material while the other plot is from a commercially cast part. (i) XRD scans of three BMG alloys cast into flexsplines, showing mostly amorphous microstructure even in fairly large parts.
Mentions: To evaluate the potential, we performed a feasibility study to see if BMGs could be successfully manufactured into flexsplines from a variety of different alloys. Two BMG alloys were used for the prototyping, a Zr35Ti30Cu8.25Be26.75 (GHDT) known for its high toughness and a new Ti-based BMG, Ti40Zr20Cu10Be30, which is a low-density alloy (4.8 g/cm3) with a high glass forming ability (~16 mm)18. This alloy was based on two previously developed BMG metal matrix composites, DV1 (Ti48Zr20V12Cu5Be19), and V0 (Ti53Zr27Cu5Be15)1920. To create the Ti-based BMG used here, the vanadium was removed (which was initially added to composites to provide a beta stabilizing effect) and the titanium was replaced with beryllium (to reduce the volume fraction of the second-phase microstructure and to create a monolithic glass). New alloy variants were created by attempting to decrease the percentage of dense elements, such as zirconium and copper, while maximizing the low-density element beryllium. The process was stopped at the composition Ti40Zr20Cu10Be30, where the density could no longer be lowered without the critical casting thickness of the alloy decreasing below the minimum required to cast the flexspline prototype shown in Fig. 2. The new alloy was characterized using DSC and X-ray diffraction as compared to several other BMGs and the hardness and elastic constants were also measured. The DSC curve demonstrates the Ti-BMG does not have as wide of a supercooled liquid region as GHDT and shows some evidence of crystal phases forming in the prototyped flexspline, but the alloy is still remarkable for its low density and high glass-forming.

View Article: PubMed Central - PubMed

ABSTRACT

The use of bulk metallic glasses (BMGs) as the flexspline in strain wave gears (SWGs), also known as harmonic drives, is presented. SWGs are unique, ultra-precision gearboxes that function through the elastic flexing of a thin-walled cup, called a flexspline. The current research demonstrates that BMGs can be cast at extremely low cost relative to machining and can be implemented into SWGs as an alternative to steel. This approach may significantly reduce the cost of SWGs, enabling lower-cost robotics. The attractive properties of BMGs, such as hardness, elastic limit and yield strength, may also be suitable for extreme environment applications in spacecraft.

No MeSH data available.


Related in: MedlinePlus