the anatomy of an end mill for titanium |
modern machine shop
Titanium is often characterized as a challenging workpiece material. Certainly, machining this material is a challenge to milling machines, cutting tools and workholding accessories that are suitable for machining more common materials such as mild steel, cast iron or aluminum.
All of the features of the VariMill II ER solid carbide end mill are tailored for the conditions encountered in milling titanium. The grooves on the shank are part of the Haimer SafeLock system that prevents it from being pulled out of the holder under the extreme forces generated when machining this material.
Eccentric relief gives the cutting edges lasting strength and sharpness for the shearing action that promotes high metal removal in titanium. The geometry of the tool nose is engineered for effective center cutting.
Titanium is often characterized as a challenging workpiece material. Certainly, machining this material is a challenge to milling machines, cutting tools and workholding accessories that are suitable for machining more common materials such as mild steel, cast iron or aluminum. With appropriate machines, cutters and related equipment, however, machining titanium can be a successful and profitable operation for the knowledgeable and committed machine shop.
The key is understanding the nature of titanium and the somewhat complex interactions among the components of the machining system that titanium calls for. Examining one end mill family specifically designed and engineered for titanium milling brings out many of these interactions. That is, the features and characteristics of these end mills reflect the implications of a complete system optimized for titanium machining.
This representative end mill family is VariMill II ER from Widia (Latrobe, Pennsylvania). It is the five-flute expansion of the original four-flute VariMiIl, hence the II. The five flutes are unequally spaced. ER stands for eccentric reliefthe version of this end mill that is best-suited for titanium because the eccentric relief gives the cutting edges extra strength for the high feeds at relatively low rpms that titanium requires. Though primarily designed for roughing and finishing applications in titanium aerospace parts, it can be used for slotting, ramping and plunging of titanium and stainless steel in virtually any industry.
David Buchberger, who represents Widia through Hi-Speed Corp. (Thousand Oaks, California), specializes in advising aerospace shops in titanium cutting. He explains why this cutter work so well in titanium. For example, the correct cutting edge for titanium is important because this material tends to work-harden, he says. Titanium quickly loses what low malleability it has when beaten by cutting speeds that are too high. Titanium likes a big chip to clear material before it hardens. A strong, sharp edge, with the thrust of a rigid, high-torque machine structure to power it, can shear the titanium effectively, he says. The eccentric relief on the edges of the VariMill II ER creates positive orientation on the radial and axial angles of this edge, which promotes this shearing action.
The underlying foundation for strong, sharp edges, however, has to be a tool with a strong, thick core that makes the entire tool rigid. For this reason, the flutes are more open at the tip of the tool where space for chip evacuation is needed, but as the core runs up to the shank, it becomes heavier to provide integrity to the tool and resistance to deflection, Mr. Buchberger explains.
The flutes are unequally spaced to create a consistently variable impact on the workpiece that breaks up any regular frequency that might match a harmonic in the machine structure to create vibration, detectable as chatter. Of course, other sources of chatter, such as weaknesses in the machine structure or clamping methods, must be addressed in the system.
The coating on the end mill plays a role as well. The VariMill II ER end mills are coated with AlTiN (aluminum titanium nitride), which helps keep the edges sharp by resisting cracking and, more importantly, making surfaces that contact the workpiece smooth and slick so they generate less frictional heat. Heat buildup accelerates deterioration of the cutting edges, so controlling friction reduces one of the negative factors that shortens tool life, Mr. Buchberger says.
Because these end mills are designed to be center-cutting, an inspection of the flat end of the tool shows a strong web across the root. This design eliminates a dead spot in the center that might drag across the floor of a pocket or bottom of a slot. The edges along the tip must also be prepped for sharpness and strength.
As a standard item, the VariMill II ER end mill offers the Haimer SafeLock anti-pullout clamping feature on tools 0.5 inch (12 mm) and larger in diameter. This system gives the tool more stability and greater concentricity in the holder, in addition to countering pullout forces, so its benefits are multidimensional, Mr. Buchberger says.
He adds that the primary concern for the programmer is having the correct speeds and feeds. The concept is to spin the tool slowly and take big bites. A surface speed of 160 to 200 fpm is the best range. He says this is more important than elaborate toolpath strategies.
Finally, he stresses that any approach to machining titanium must be a complete systemthe right tool, the right machine, the right clamping and so on. When shops take care to do titanium milling right and invest in the appropriate technology, which includes carefully chosen cutting tools, they will have a system that makes machining titanium no more challenging than other operations, he says. The challenge is understanding a systematic approach and implementing it fully in the first place. He also suggests working with a cutting tool supplier who will base tooling recommendations on a review of the entire titanium machining operation. Any weak link in the process can be disastrous. No cutting tool is the best or right choice if other elements of the system are sub-optimal, he concludes.
Finally there is an alternative to ballnose endmills for finishing 3D parts. The combination of finishing tools shaped to provide more cutting surface and a CAM system with the ability to apply them on a five-axis machining centercan dramatically reduce finishing cycle times while delivering better surface finishes.
what is the most productive end mill in titanium? |
modern machine shop
Personnel from Boeing's Research & Technology group recently answered readers' questions. One reader asked the following. To see the list of experts taking questions from readers right now, see our Ask An Expert page.
We are machining a 0.423-inch diameter Ti Beta C rod into a 0.375-inch hex. We use a 6-flute carbide end mill at a feed rate of 8.7 ipm and a 0.024-inch depth of cut. No finish pass is needed. We tried an insert cutter that went 3 times as fast, but the interrupted cut tended to tear the material. Can you recommend an end mill we can use for this job that will allow a much faster feed rate than we are now getting?
For instances where we are taking very light radial cuts (0.050 inch or less), we use either 1-inch diameter 10-flute tools or 0.75-inch diameter 8-flute solid carbide end mills for finishing titanium parts. The key with these tools is never to touch a corner. We run them at 400 sfm with a 0.003-inch chip load. We go 46 to 48 ipm when cutting with the side of the tool.
If cutting with the bottom of the tool, back off to 300 sfm but maintain the 0.003-inch chip load. When cutting with the bottom of the tool, do not ramp to depth into a part, as there is not enough chip clearance. You should either create a start spot with a different tool, or start off of the part and feed onto it. Limit axial depth of cut to 0.030 inch, but feel free to maximize your step over. Full slots are possible in this situation.
Our primary experience is with titanium 6Al-4V, so your parameters may need to be adjusted for your material. We achieve 90+ minutes of tool life with these parameters as long as our radial engagement is 0.050 inch or less and we never touch a corner. You can buy cutters such as these from Fullerton, Data Flute, Robb Jack and Onsrud, among others. The cutters are a little bit expensive, but they run really fast and in most instances we find that the extra cost is more than worth it, because they are so productive they end up saving a lot of cost in the end.
To make the transition to hard turning, you'll need to switch from carbide to CBN inserts, but that is easier (and more economical) than you might think. It's making the jump to much higher surface speeds that might scare you off. It needn't. Here's why.
Running rotary milling cutters at the proper speeds and feeds is critical to obtaining long tool life and superior results, and a good place to start is with the manufacturer's recommendations. These formulas and tips provide useful guidelines.
high efficiency milling for titanium made easy with helical
Titanium is a notoriously difficult material to machine, especially in aggressive toolpaths, such as those associated with High Efficiency Milling (HEM). Helical Solutions new line of tooling, the HVTI-6 series of end mills for titanium, is optimized specifically for this purpose, and proven to provide 20% more tool life than a competitors similar tool.
At face level, these new Helical end mills for titanium feature corner radius geometry, 6 flutes, and are Aplus coated for optimal tool life and increased cutting performance. But there is much more to these end mills than the typical geometry of standard 6 flute tools. The HVTI-6 was designed with a combination of a unique rake, core, and edge design that give it a leg up over standard 6 flute tools for milling titanium while cutting HEM toolpaths. Click here to watch the HVTI-6 in action!
The design of the HVTI-6 was the result of significant testing by the Harvey Performance Company Innovation and New Product Development teams. These teams spent many months testing tools, doing in-depth analysis on materials and tool geometry, and pushing these tools through dozens of hours in the cut at testing sites across the country.
The new HVTI-6 cutter experienced higher metal removal rates (MRR) and 20% longer tool life while performing HEM in Titanium when compared to a standard 6 flute tool offered by a Helical Solutions competitor. This type of tool life improvement will produce huge cost savings on tooling, as well as shortened cycle times and lower cost per part.
The Harvey Performance Innovation team targeted Titanium grade Ti6Al4V for their testing, which accounts for the vast majority of the Titanium being machined in North America. The test part was designed and programmed to allow for a more defined agility test of the tool, taking the tool into key geometry cutting exercises like tight corners, long straight line cuts, and rapid movement.
Many hours were spent with Lyndex-Nikken, manufacturers of high-quality rotary tables, tool holders, and machining accessories, at their Chicago headquarters. By working with the team at Lyndex-Nikken, the Harvey Performance Company team was able to test under optimal conditions with top-of-the-line tool holders, work holding, and machining centers. Lyndex was also available to provide their expert support on tool holding techniques and were an integral part of the testing process for these tools. Video of the impressive test cuts taken at the Lyndex facility can be seen below.
While the standard 6 flute tools offered by Helical will still perform to high standards in Titanium and other hard materials (steels, exotic metals, cast iron), the HVTI-6 is a specialized, material-specific tool designed specifically for HEM toolpaths in Titanium. Advanced speeds and feeds for these new tools are already available in Machining Advisor Pro, and the complete offering is now available in the Helical CAM tool libraries for easy programming.
To learn more about the HVTI 6 Flute End Mills for Titanium, please visit the Helical Solutions website. To learn more about HEM techniques, download the HEM Guidebook for a complete guide on this advanced toolpath.