The demand for titanium components by the aerospace industry began as a whisper about 15 years ago and steadily grew to a sustained, raucous shout over the last five and likely won’t quiet for several more. Since Mitsui Seiki participated in an OEM’s research more than a decade ago to develop the machine tool technology to optimally cut this very hard and relatively difficult material, the knowledge base in the industry has evolved to the point at which we are all up to speed about the machine tool requirements—the ability to do low-frequency machining without chatter, a suitable design and robust structure of optimal height-to-width ratios on columns and tables to handle the high bending moments, ideal ballscrew locations for axis stability and hand scraping over all to provide the accuracy needed to make quality parts from this challenging material. We’ve also learned a lot about the best cutting tools, feeds and speeds, through-coolant spindles, motors, tool taper interface sizes and styles, and coolant fluids and systems for Ti applications.
Where industry is now, at least in aerospace where I spend a lot of my time, is the phase of refining the Ti machining process—continuously improving it, squeezing the cycle time out of it, and of course doing it all more efficiently with no impact on floor space. In essence they want to produce more on less floor. Here are the areas that have made the greatest contributions recently in Ti machining:
Cutting tools—Most leading cutting tool manufacturers have been putting and continue to put significant resources in R&D for new solid carbide end mills and indexable inserts for cutting Ti. Like the trend in general, they have their “go-to” proven grades, and they are now tweaking the styles with a special radius, a special grind, a special coating. As an example, new 1″ (25.4-mm) diameter seven-flute high feed end mills with a special grind are being used now on engine mount parts at an OEM facility that are allowing us to run at 357 sfm (109 m/min) at 1363 rpm and a feed rate of 80 ipm (2032 mm/min) , with a 0.9″ (22.9 mm) axial depth and a 0.1″ (2.54-mm) radial depth. It’s not taking that deep of a cut, but it moves through the material fast. A conventional end mill would fall apart in these conditions.
Cutting and toolpath strategies—One way to achieve better cycle times is by carefully analyzing cutting strategies and CAM toolpaths. I’ve seen notable improvements using trochoidal milling, essentially a peel milling approach that uses a series of circular cutting paths at the full depth of cut.
Coolant and coolant handling—Moving chips out of the cutting zone is critical in Ti applications. New biostable blends are coming on the scene that are particularly friendly to these high-pressure coolant cutting conditions with enhanced lubricity technology that can extend tool life, improve finishes, are corrosion resistant and are economical to use. Relevant to coolant, I’m seeing more centralized systems being installed out in the field, even among smaller companies serving their FMS, cells, or a certain department. In addition to the benefits of having fewer and more efficient pumps, less power usage, longer coolant life and easier recycling, this is one of the ways to save space on the shop floor. Coolant tanks near a machine can sometimes double the space requirement of the machine tool alone, plus you need space for maintenance access. Often, central filtration systems can be placed out of the production area entirely. Some figures cite a 25% floor space savings, which of course means you can increase production by 25% by that strategy alone.
Machine tool versatility—Machine tools with multi-functionality is a trend we have been seeing and reading about for many years. However an added functionality to note with regard to Ti machining is deburring within the machining center’s work envelope using brushes with ceramic particles in them. Deburring is one of those operations that is most always done outside of the machine by a person sitting at a bench. Now it can be a programmable process.