Transcript Metallurgy-Disk-Broaching.ppt

An Examination of Metallurgical
Features in Broached Turbine Disks
Ernesto Gutierrez-Miravete
(with material from C. Cook – CCAT)
Rensselaer at Hartford - CCAT
Presented at CINVESTAV-Queretaro
December 2010
Broaching
• Broaching is an orthogonal machining process
consisting in the unidirectional travel of a
specially designed tool to create the desired
machined shape in a single pass of the tool.
• The broaching action is obtained by designed the
tool as a series of increasingly larger, specially
designed teeth
• The process can be used for internal or external
machining and for flat, round or contoured
surfaces
• View BCI Video
Advantages and Limitations
Advantages
Limitations
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• Workpiece must be suitable
for broaching
• No obstructions along the
direction of tool motion must
be present
• Starting hole required (internal
broaching)
• Material must withstand high
thrust forces and be firmly
supported
• Rigid machines and
workholders required
High Productivity
Close Tolerances
Good Surface Finish
Economical Operation
Versatility
Broaching of Disks
Broached Grooves in Disk
A
A
BOSS Modeling
4140 As Broached Microstructure
4140 As Broached Microstructure
4140 As Broached Microstructure
4140 As Broached Microstructure
As-Broached Microstructure
Summary
• Tempered Martensite Microstructure
• Smooth, good quality machined surface
• Highly deformed zone near machined
surface (thickness ~ 15 micrometer;
shear strain > 2), undeformed structure
below
• White Layer ( < 5 micrometer thick). This
may result in premature fatigue failure!
Shot Peening
• Shot Peening is a mechanical surface
treatment process designed to induce
compressive stresses near the surface of
materials.
• The process directs a swarm of high velocity
small shots against the surface
• Fatigue life improvements have been
documented to result
• See related video and Howard’s Thesis and
Anason’s Project
As-Peened Microstructure of
Broached Sample
As-Peened Microstructure of
Broached Sample
As-Peened Microstructure of
Broached Sample
As-Peened Microstructure
Summary
• Tempered Martensite Microstructure
• Surface somewhat rough but still as
satisfactory as the machined surface
• Compressive deformed zone under peened
surface (thickness ~ 50 micrometer)
• White Layer still there but its potential
deleterious effect may well be fully eliminated
by the residual stress from shot peening.
Conclusion
• Broaching is a fast, efficient machining process
• Broached microstructures in steel exhibit
white layers and highly deformed near surface
regions
• Shot peening of broached surfaces produces
thick, compressively loaded near surface
regions