Grinding advances: Improvements in technology now make grinding an option for finishing exotic materials and 3D-printed parts

Aerospace parts manufacturers face numerous machining and finishing challenges, one being the introduction of new alloyed materials. To increase fuel efficiency and produce lighter planes, incorporating materials that are lighter, stronger, and can better manage heat is crucial. While these alloys have amazing characteristics, they can sometimes be difficult to process, resulting in the need for grinding expertise and the latest technologies. Without optimizing the grinding process, parts made with these new alloys may have poor surface quality, internal metallurgical damage, increased part cycle times, and higher manufacturing costs.

Another challenge is bottlenecks on the manufacturing floor. Some customers use wire electric discharge machining (EDM) to carve profiles and shapes into various aerospace components. While EDM is effective for parts with faces that are tough to access, grinding may be a better option for many operations. Wire EDM machining is initially less expensive than grinding, however, using EDM can take a long time to complete a part. Grinding is much faster in removing material, and while it may be more expensive upfront, the benefits of grinding – saving production time, unclogging bottlenecks, and having a smooth-running line – almost always offset the cost and result in a substantially more efficient process.

Grinding vs. machining
Aerospace components generally have very low Ra surface finish requirements and tighter dimensional tolerances, as well as precise complex shapes and forms. Grinding is much better at producing these precision parts and holding necessary shape and dimensional tolerances due to the way the material is removed. During grinding and machining, the material ground off is removed as chips. In grinding, much smaller chips are created which allows for more precise shapes and smoother surface finishes, while machining produces significantly larger chip formations.

Due to the larger chips and aggressive cuts of material, traditionally, machining has generated higher material removal rates (MMR) than grinding. With newer grinding technology, this isn’t necessarily true. For example, new Norton TQX grain technology has been able to hit Q’ (Q- prime specific material removal rate) values of >3in3/min/in in creepfeed grinding of aerospace components, which is usually the max Q’ achieved with ceramic grain bonded wheels. These values rival those of machining processes. Figure A (pg. 30) shows the improvement of TQX versus other ceramic grains. With the other ceramic grains, as Q’ is increased, G-ratio (the volume of material removed from the work per unit volume of wheel wear) declines and eventually bottoms out at about 3.5in3/min/in. Alternatively, TQX can increase G-ratio with increased Q’ up to 2.5in3/min/in and maintain this high G-ratio at Q’s over 2.5in3/min/in, but in this case, TQX reaches a Q’ of 5.5in3/min/in. This new technology challenges machining processes, producing parts with improved quality and eliminating the need for further finishing processes.

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