When it comes to critical jet-engine parts, today’s manufacturers strive for zero-scrap production. Nowhere else is that goal more important than at the deburring and finishing stages of production. These operations come at a critical time and, if not performed correctly, could lead to scrapping parts for which manufacturers have already invested significant time and money.
Among such critical jet-engine components are blisk-rotor discs and blades typically made from hard nickel, titanium and other alloys. The surface finish on the interlocking “fir-tree” patterns machined into these parts, for example, requires deburring and finishing to specific requirements.
In terms of jet-engine part finishing, manufacturers often rely on spindle- and Sutton-type deburring and finishing systems that, between the two, offer various size and weight capacities. Other than manual operations, large-scale spindle-type systems are, for the most part, the most consistent way to finish components such as turbine discs and blades. The machines not only finish parts much faster and more efficiently when compared to manual or standard vibratory-type finishing, they provide a simple, stable, consistent and predictable process.
Unlike vibratory and centrifugal barrel-type finishing systems where parts move freely, those in a spindle machine are mounted to spindles that submerge and rotate into a tub of deburring media (slurry) that’s also rotating. This double-rotation action allows the slurry to permeate into a part’s crevices and other hard-to-reach areas to remove all burrs and produce consistent surface finishes throughout.
More Than Rounding Sharp Corners
After machining, blisk-rotor discs and blades often need a specified radius imparted on all cut edges. These radii perform functions such as improving airflow and/or making that section of the part stronger and more wear resistant.
For discs, operators mount the part onto the machine’s spindle, after which the machine tilts the part down into a bath of media (aluminum oxide or preformed), water and cleaning chemistry. This configuration ensures media accesses all of a part’s surfaces, including fir-tree patterns on discs, for generating uniform finishes.
Blades, for instance, often come with a long list of radii measurements as well as surface-finish and other geometric specifications. The challenge, however, is to prevent removing too much material on one part section that could affect the performance or requirements of other features.
This is why aerospace OEMs often rely on finishing-machine suppliers and application laboratories. Such companies test with the intended parts and determine the right process parameters for finishing to the specified requirements and cycle times without jeopardizing other sections.
Control and Traceability
Today’s finishing machines have more advanced controls and operate at much quieter levels to fulfill A&D manufacturing facility safety requirements. They also provide process tracking for traceability to show exactly what finishing operations the part went through, and confirm the machine performs those operations consistently for every part.
Programmable logic controller screens on machines indicate the special surface-finishing media recipe. Jet-engine components may involve 20 different process parameters, all of which must be stored, tracked and kept accurate.
For traceability, manufacturers ensure finishing recipes follow part numbers. They label the specific finishing mixture with the associated part number, allowing them to verify the right mix is used for the right parts.
Experienced supervisors will lock out other recipes to prevent mix-ups that result in scrapped parts. Shops will also connect finishing machines digitally and oversee the whole process using enterprise resource planning systems.
Adding to that stability, the finishing machines rigidly fixture each part in a repeatable orientation within the media, so the process is identical and consistent. Shops can add custom timers that indicate required preventive maintenance or that the process media needs to be changed to prevent any variations that could affect consistency.