Adjustable side milling cutter for grooving - carbide grooving insert
Another thing to consider is keeping plenty of extra hardware for the holder around because typically the screws holding the insert tend to be very tiny.
"Everyone wants to automate their process," said Mara. "We can’t get skilled people, so the logical step is to automate. End-of-arm tooling is not typically as dextrous as it needs to be for small parts, and robot accuracy may not be sufficient. It’s difficult to hold very small parts with a robot, especially for loading and unloading."
"The screw could be an M2.5 or smaller, and in some cases, they can be easily lost to the bottom of the machine or conveyor system," said Tonne. "The other thing I would recommend is using torque-limiting drivers at all times. If you overtorque an M2.5 screw, you’re going to strip it, and that will add a lot of extra time getting that screw out and changing the insert."
Looking for tooling that is purposely designed for small-part turning or microturning is a good place to start. These tools tend to have tighter tolerances and are more finely ground.
"Automation for small parts has historically been a challenge, but we are really starting to see some new and exciting advancements in automation," said Mara.
MOGAS makes the balls from chucked barstock: Bore out the main bore, mount it on a mandrel, turn the OD, then move the piece to another machine to pocket-mill a rectangular slot. The slots engage the valve stem as part of the rotation mechanism. The valve seats involve OD and ID turning only, with the ID a spherical radius to mate with the ball.
The enemy of precision machining is vibration and heat. Rather than heavy, deep cuts, small, higher-speed cuts can keep the workpiece as cool as possible, reducing heat deformation in the part. Any sort of deformation can make it difficult to maintain proper tolerances. According to Mara, Swiss machines usually use high pressure up to 2,000 PSI with water-based coolant to help keep the heat out of the part.
A conventional CNC lathe is good for general-purpose turning but usually has spindle speeds of only about 3,000 to 5,000 RPM, whereas a Swiss-style lathe can be in the 10,000- to 15,000-RPM spindle range. That higher RPM enables the machine to generate the surface speed needed to cut small-diameter parts efficiently.
Accordingly, MOGAS flood cools everything during turning ---work piece, mandrel, tool and tool holder. They run the milling dry, but flood the cutter and inserts for 15 seconds at every indexing stoppage. Horton won’t disclose the actual indexing frequency, but says it’s short enough to shock some people. “Nevertheless, we’re way ahead economically by burning through inserts in order to run faster. That’s a trade-off I’d take any day.”
"Sharp molded and ground cutting tool inserts provide less tool pressure and freer cutting," said Steve Easterday, Swiss applications engineer, Kyocera Precision Tools, Hendersonville, N.C. "Physical vapour deposition (PVD)-coated inserts provide excellent tool life and a sharper edge."
Some milling jobs feed at 200 IPM @ 2,500 SFM without catastrophic edge failure. Turning feeds up to 0.01 IPR @ 1,200 SFM are routine. “With the other ceramics we tried, whiskered or unwhiskered, the milling was not up to our standards,” said Hub Whitley.
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With small components, tool pressure is a primary concern. Very small parts can easily deform during turning operations.
A machine needs to have a rigid setup, regardless of whether it’s a conventional or Swiss machine, and it is vitally important that the correct tooling be used for small-part turning. EMEC
Operators need to be mindful of the cutting edge at all times. It needs to be sharp, and damage can occur very easily from general wear, handling, or even indexing.
"Many of today’s new machines come equipped to handle smaller parts," said Bill Mara, president, EMEC Machine Tools Inc., Mississauga, Ont. "One of the biggest challenges machine shops face when dealing with small-part turning is the machine’s capability to hold the parts effectively without damaging or distorting them, but that’s not really a problem anymore. For shops looking to get into parts that are smaller than 0.250 in. dia., a Swiss-style lathe is the way to go."
Based on success with the Inconel balls and seats, Horton is running the same Ingersoll ceramic insert to turn valve stems, and is doing a considerable volume of boring, too. “We’re pushing the envelope regarding boring Inconel with ceramics, with excellent results” says Horton. “We’ve heard that many shops avoid boring Inconel with ceramic inserts because the material doesn’t tolerate the recutting very well. With this particular Ingersoll grade and special attention to chip evacuation, our boring operations have been very successful.”
There are pluses and minuses to working in the machine shop at MOGAS Severe Service Ball Valves. On the plus side, there’s plenty of work despite the ongoing economic uncertainties; as part of a global corporation, the Houston-based process valve manufacturer is busier than ever. The backlog of orders is so extensive that the CNC department and manual machine shop must run 24/7 just to keep up.
Indeed, heat management in a broader sense helped to shorten cycle times in other ways. Keeping the tools just warm to the touch will shorten indexing downtime to a measurable degree. “We’re deliberately accepting high edge wear in exchange for higher throughput, which necessarily means more frequent indexing,” says Horton. “Naturally we want to avoid indexing delays due to inserts becoming too hot to handle right away.” Kippola added that he has seen processing at other plants delayed for 10 minutes or more, waiting for the tool to cool off enough to handle.
Another area of importance is measurement and inspection. Small components require different inspection methods than their larger counterparts, especially because of the microtolerances and tiny features.
Tonne agreed that when working with long parts, pinch turning is a great option. Pinch turning helps keep everything aligned. The external features are completed first to maintain that stability and then internal operations are performed.
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The principal parts in MOGAS ball valves are the balls and their mating valve seats. Such valves help control hot, corrosive process fluids found in refining, chemical and mining operations. Each valve has one ball and two valve seats that require precision machining for the valve to be truly leak-proof. The ball has a bore down its center, rotating the ball opens and closes the flow of material.
On the other hand, to fill all those orders MOGAS must machine a lot of “uncooperative” Inconel 718. That heat-resistant alloy is notorious for burning up tools and generating long, stringy chips with a proclivity for adhering to cutting edges. This limits cutting rates and necessitates frequent but unpredictable stoppages for indexing — considerably upsetting that round-the-clock schedule.
On a conventional lathe you may be able to turn a length-to-diameter (L:D) ratio of about 10:1, and that is only if the machine has a steady rest or similar supporting device. On a Swiss-style machine, the L:D can be as much as 20:1, making it possible to produce very difficult parts.
Four-part solution There were four parts to their solution: 1) retool with an Ingersoll ceramic insert, with special edge preparation; 2) inject some “out of the box” programming; 3) sacrifice edge life for exponential gains in feeds and speeds as a matter of strategy; 4) and control process heat to speed up edge indexing.
Micromachining, on the other hand, is classified by part diameters that are too small to be fixtured using a standard collet. In some instances, this could mean parts that are 0.1 in. to 0.02 in. dia. all the way down to the size of a human hair, depending on the equipment.
For shops looking to take on small-part turning operations, there are a number of things that can be done to ensure success.
"If their machine is equipped with HP coolant pumps, internal coolant through tooling is a must," added Easterday. "Make sure that the workpiece can be done on the machine you have. In many cases when you are dealing with long workpieces, adjustments need to be made. Extended guide nose bushings or the capability to pinch-turn can be helpful."
Another concern with small parts is they get washed away with chips. For example, part ejectors that put small parts into the conveyor may have issues separating them from chips. A vacuum that removes the part when the chuck opens and puts it in a separator is a good option.
"Shops have been cutting small parts forever and have found innovative ways to do it effectively," said Mara. "It’s important to remember that a machine needs to have a rigid setup, regardless of whether it’s a conventional or Swiss machine, and it is vitally important that the correct tooling is used."
Because of the low cutting speed required, built-up edge can be a problem. On larger parts burrs can be removed easily with the secondary processes, but it’s more difficult with small parts.
With a long part it’s always a good idea, especially with a small diameter, to try to grab it with the secondary spindle. While this may add a little bit of time, gripping and not letting the part hang out adds the stability needed to ensure tolerances are met.
Luminoso has a bachelor of arts from Carleton University, a bachelor of education from Ottawa University, and a graduate certificate in book, magazine, and digital publishing from Centennial College.
"Common mistakes can include incorrect cutting conditions like incorrect surface footage, too high feed rate, and too heavy depth of cut, which can result in incorrect tolerances that include part bending and poor finish," said Easterday.
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With small tools, a high-quality modular system, like Horn’s W&F Micro precision modular tooling, will allow operators to keep a close eye on the tool wear. Horn
"The No. 1 thing to consider is chip control," said Easterday. "Having the correct chipbreaker is key. The chip needs to be directed away from the workpiece."
Ceramic, but built for roughing A key factor in the performance of the Ingersoll AS20 ceramic is the toughness of the SiN substrate, combined with a very strong geometry and special edge prep. Unlike most ceramics, the AS20 is designed specifically for roughing, and in particular features a wide land. Top-face geometry puts more of the machining heat into the departing chip than into the tool, toolholder, or workpiece. This not only protects the insert, but also helps speed up indexing.
Faster machining, reliably In initial trials, the Ingersoll solution achieved slightly higher rates than other ceramics, but did so with much more reliability. Failure causes were edge wear (which was very predictable), not edge rupture (which is not.) “Performance was especially impressive on milling, with its interrupted cuts that often fracture brittle ceramics,” said Hub Whitley.
Last August, MOGAS CNC programmer/supervisor Zach Horton and his CNC team, together with Ingersoll’s Craig Kippola, attacked the problem head-on by seeking to find a faster, more reliable way to machine that most contentious material. As a result, they’re turning Inconel 718 valve balls four times faster than with carbide — and twice as fast as with any other ceramic they’ve ever tried. Similarly, the team improved rough milling rates by 5 to 1 over carbide, and again, 2 to 1 versus any other ceramic.
Chip control is essential for effective small-part turning where the chip needs to be directed away from the workpiece. Kyocera Precision Tools
Automation is slowly making its way into all aspects of the shop floor. However, when working with small parts, automation may not be the obvious next step.
"Because of this, the process needs to be planned to minimize tool pressure using sharp, positive tools," said Edwin Tonne, training and technical specialist, Horn USA Inc., Franklin, Tenn. "It’s important to look for well-defined cutting edges and a positive top rake. Fully sintered cutting tools can be problematic because they’re just not sharp enough to minimize the pressure. Look for finely ground cutting edges with plenty of clearance. A sharp wedge angle will help prevent deformation in the part. Form tools are a good choice because they can simplify the process."
Once the requisite stability was established, the MOGAS CNC team modified the programs for more aggressive toolpaths, and then turned to Kippola and Higby to optimize the final machining parameters. The critical detail of their strategy was to push machining rates, even at the expense of edge life. “Sure, ceramic inserts aren’t cheap, but the real potential for money saving is to speed up the chipmaking and let the rest fall where it may,” said Horton.
With very tight tolerances, it can be challenging to get the tool back to size after indexing. Monitoring and controlling the size after indexing the cutting tool is a must for small-part turning.
"For shops looking at turning long and thin parts, a conventional CNC lathe has its limitations and probably wouldn’t perform as needed," said Mara. "A Swiss-style machine offers the rigidity in the setup required to turn very small or long parts by doing the cutting as close as possible to the spindle nose and by feeding the material through a stationary tool as opposed to the tool moving across the part as on a conventional lathe. Choosing a Swiss-style machine is definitely the best option, if possible, for turning long, thin parts."
"With small tools, a high-quality modular system will allow you to keep a close eye on the tool wear," said Tonne. "If you have a feature that’s only 0.001 in. deep, and you lose the radius of your tool, you can have a problem on your dimensional tolerance, so keeping a close eye on the tool is very important."
Lindsay Luminoso, sr. editor/digital editor, contributes to both Canadian Metalworking and Canadian Fabricating & Welding. She worked as an associate editor/web editor, at Canadian Metalworking from 2014-2016 and was most recently an associate editor at Design Engineering.
Turning small parts is nothing new for many machine shops. Industries like automotive, aerospace, electronics, firearms, and medical are pushing the envelope when it comes to small-part production. Typically, any application requiring a workpiece smaller than 1 in. dia. is considered small-part turning.
“Many people think that whiskered ceramics are intrinsically tougher than unwhiskered ones, but that’s ‘old school’,” said Kippola. “Newer, unsupported ceramics exhibit vastly improved toughness because of the substrates themselves.”
"You may want to think about using a vision inspection system, offline gauges, and those sorts of devices," said Tonne. "These take more time than using a caliper or bench-type measurement tool. Getting the part to the right size and back up and running after tool indexing is also critical."
Kippola’s recommendation for both turning and milling: Ingersoll ceramic grade AS20 SiN inserts, running at roughly twice the speed of any other ceramic tried. To Horton’s surprise, the inserts were “unwhiskered” (no microscopic reinforcing fibers), with special edge preparation. Turning inserts are plain rounds, which rough at 1,200 SFM. Milling inserts, seated in a 2-inch shell mill, are notched for better gripping in the seat pocket to withstand the extremely fast rpm’s. Standard speed: 2,500 SFM.
Commitment to ceramics Together with lead man Hub Whitley, Zach settled on ceramic tooling to replace the carbide components. They tried a few grades on their own and achieved 50% to 100% productivity improvements, but edge failures were so unpredictable that they defeated process stability. So, they called Ingersoll’s Craig Kippola and Kirk Higby of tooling distributor Cutting Tools Inc. for specific recommendations on grades and machining parameters. “They solved past problems for us very well, so they were the natural ‘go-to guys’ this time around,” said Horton.
The outcome: a secure process for roughing Inconel, which runs twice as fast as with any other ceramic. For example, turning a ball that used to take an entire shift with carbide, and two hours with other ceramics, now takes an hour. A seat ring that once took an hour with carbide, and 30 minutes with other ceramics, is now completed within 15 minutes.
"When working with anything less than 0.250 in. dia., it becomes difficult to reach the correct speed for normal steel material," said Tonne. "And with RPM limitations on the machine, sharp cutting edges and very lubricious coatings are helpful. When it comes to depth to cut, typically the machine will perform a single finish pass. This needs to be balanced with tool pressure. First and foremost, keep your feeds very modest. Form tools and special tooling can help claw back some of the time."
Swiss-style CNC machines even can perform other operations like this tapping of a small-diameter brass shaft. Phuchit/iStock/Getty Images Plus
Chip control and evacuation can be cumbersome in small-part turning. For the most part, the biggest tool possible is the better option, but it’s important to remember that there must be enough room, especially in boring operations, for chip evacuation. High-pressure coolant can be a huge help with this.