Deburring is an option that is critical to quality. When its importance is minimized, serious quality and safety issues case arise. Removal of burrs should be considered during process design and should also be part of an organization’s training regimen. Learning to properly remove burrs should be considered as important as learning to use micrometers and calipers.

“Very important is the amount of coolant that can be provided and ensuring that the coolant stream direction maximizes the chip evacuation out of the cutting zone,” said Bernd Fiedler, senior product manager-solid end milling, at Kennametal, Fuerth, Germany. “Sometimes high-pressured air can be a good option to remove chips out of the working area and prevent chip clogging, especially in pockets. ”

“There are several general indicators that chip formation is insufficient,” Fiedler said. “Chips are very curled or rippled, have no uniform edge, or they are deeply colored. For instance, when the side that rolls over the cutting edge is no longer shiny but shows color changes.”

Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.

Enlarging a hole that already has been drilled or cored. Generally, it is an operation of truing the previously drilled hole with a single-point, lathe-type tool. Boring is essentially internal turning, in that usually a single-point cutting tool forms the internal shape. Some tools are available with two cutting edges to balance cutting forces.

These strategies change the way a machinist tackles a job, and it’s becoming popular for machinists to use multi-flute end mills—those with five or more flutes—to do both roughing and finishing, eliminating the need to fill up the tool carousel with an array of different end mills. These modern strategies mitigate the need to bury the tool into a part and any worries about getting chips clogged up in the flute gullets, which can lead to a broken end mill and the failure of the part in progress.

With a higher number of flutes, though, chip formation and evacuation become concerns. Mitigate these concerns by adjusting radial engagement and table feeds to the application and target material; choosing the correct tool for a specific application; and selecting tools tailored for a high number of flutes—for example, those with a specific core design enabling bigger flute space toward the front end, or a design that optimizes chip formation.

“All the CAM systems have different names for this type of programming,” he said. “HEM, VoluMill—there’s all sorts of them. If you really want to give it a blanket name it’d be ‘optimized roughing.’ These CAM systems have made it so easy, you just say this is my percentage of diameter width of cut and it does a lot of the back figuring for elevated surface footages and correcting of feed rates. It figures the tool path for you. It’s just made it so much easier for the small guy to be competitive.”

How can the use of multi-flute end mills lead to higher productivity if they take such small bites of metal? “Because the normal operation of the multi-flute is decreased radial engagement, let’s say less than 25 percent of the diameter, the arc of contact is smaller,” said Horn’s Tonne. This allows the use of two to three times the normal cutting speed range.

Tonne also agreed the software enables processes that lead to higher productivity. With trochoidal milling “you have some unproductive time in the cut but [the process] more than makes up for it because you can take a really big axial DOC, even with a small end mill,” he said.

Newer software and machining techniques can even help make an older machine perform like a shiny new model. “If they have machines even with moderate speed, a lot of times an older machine that has moderate capabilities—if it’s partnered with a new machining strategy—can still take advantage of modern high-efficiency machining and toolpath strategies,” said Strauchen. “The best way to figure it out is to bring specialists in that are savvy with modern programming techniques … and help customers maximize what they have.”

Depending on the lay, a burr may not be detectable visually or by feel, making it easy to overlook. This is often the case with close-tolerance holes. When a burr is left on the edge of a hole, plugs and thread gages may not fit properly, resulting in rejected parts.

The higher the number of flutes per given diameter, the smaller the flute space on the end mill, Fiedler said. Depending on the material and its specific chip formation behavior, sufficient chip evacuation is critical and needs to be closely observed. In general, cut-off material moves down to the core and then breaks or rolls into chips, but it’s helpful to know how to read different materials and their tendencies. Steels up to 45 HRC, depending on the type of alloy, tend to roll and then break. Hardened steels are brittle and create thin chips. In general, stainless steels have less tendency to roll, but this is also heavily dependent on the alloy. Cast iron breaks into dust particles. Titanium tends to curl and fills up the available flute space quickly.

Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.

Sometimes, burrs can be eliminated by programming a machine’s CNC to add a deburring operation while the part is on the machine. Examples include programming a chamfering tool to take a pass along the edge of a hole, milling a chamfer on a sharp edge and programming a radius on the edge of a part.

Is there a limit on the number of flutes for one end mill? The primary method of manufacturing end mills is grinding using automatic NC grinding machines, said OSG’s Hashizume. As long as they are manufactured using such machines, the capabilities of CAD/CAM applications and the grinding machines themselves (especially the size of the grinding wheel) impose limitations on the number of flutes it is possible to create. “The larger the OD of the end mill manufactured, the bigger the space that can be used for one cutting edge, and the more cutting edges that can be manufactured,” said Hashizume. The maximum number of flutes depends on the diameter of the tool, Tonne agreed.

It seems that many engineers, operations leaders and machinists no longer value the skills needed to properly remove burrs. Only after a part fails do they begin to emphasize deburring.

After many rejections and many dollars spent investigating, we found that burrs left from machining were getting trapped between the parts, causing erroneous measurements. We eliminated the burrs, and the problem went away.

“In a typical, traditional approach, when machinists use end mills for more material [removal], more roughing, and if the tool is buried more, the fewer flutes they would use,” said Drew Strauchen, executive vice president at GWS Tool Group, Tavares, Fla. “With conventional wisdom, roughing uses two- or three-flute end mills and semi-finishing and finishing operations uses more flutes—four, five and beyond.”

The DOC can also be increased. For example, the machinist could run a process using a 5/8" (1.6-cm) diameter, two-flute end mill on titanium 6AL-4V at 130 sfm using full slotting and 1× the diameter DOC for productivity of 1.49 in³/min. (24.4 cm3/min.). Doing the same process with an eight-flute end mill with 230 sfm and 0.019" (0.048-cm) radial engagement or width of cut and 2× the diameter depth of cut increases productivity to 1.57 in³/min. (25.7 cm3/min.). “So, the net gain on productivity is significant,” said Tonne.

It is easy for machinists, programmers and engineers to get lost in the possibilities and forget about simple, but necessary, processes like deburring. Very few parts, if any, don’t need to be deburred. Nearly every machining process leaves some sort of burr that must be removed.

He was given a die grinder, a box full of burr bits and 5 minutes of instruction and then was set free to remove burrs from a $250,000 component. In his zeal to do an excellent job, he removed far more material than was required and altered the geometry of the part. We were able to salvage the part, but it severely interrupted the schedule, almost delaying shipment to the customer.

There’s even more encouraging news for smaller shops when it comes to multi-flute end mills and CAM software. “They’re great tools for low power and smaller taper machines like 40-taper because with multi-flutes we’re taking deep axial cuts and balancing the radial forces by using the length of the tool for stability,” said Matt Clynch, national product specialist-milling, Iscar USA, Arlington, Texas. “With those smaller taper machines, if we take deep radial cuts with the large widths of cut it would start to bend and the assembly topples.”

From what he’s seen in the industry, 20 flutes on a 1.25" (3.18-cm) tool is the maximum. “With that many flutes, the radial engagement due to the limited usable flute volume is much less than 10 percent,” he said. “So, you start to diminish the practicality in most applications or limit your work to pure finishing and not much else.”

End mills, traditionally made with two to four flutes, are used in one of the oldest mechanized machining processes—milling. Cutting-edge software, machine tools, novel strategies, ever-improving techniques and design updates in the tools themselves keeps milling useful in the 21st century. The machinist who masters the art of these metal eaters can save their shop time and money while producing superior parts.

Stringy portions of material formed on workpiece edges during machining. Often sharp. Can be removed with hand files, abrasive wheels or belts, wire wheels, abrasive-fiber brushes, waterjet equipment or other methods.

Deburring is often performed by hand with simple tools, giving some the impression that it is a task that does not add value. This attitude and the desire to cut costs have created an environment that minimizes the importance of developing and cultivating effective deburring processes, as well as training on the proper techniques.

By adding flutes, the machinist can decrease the feed per flute and still maintain the same feed compared to an end mill with a lower flute count. For example, for a four-flute end mill running 0.002" (0.005-cm) per flute, substitute a five-flute end mill and maintain the same feed with decreased pressure per flute. “So, you get a little more flexibility in your tool wear without decreasing your productivity,” Tonne said. “The linear feed rate can stay the same and the cycle time will stay the same but you’re decreasing the section each flute has to take.”

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“But using a multi-flute end mill with high-speed techniques and low radial engagement you can mill a slot or any kind of feature in it,” Tonne said.

Don’t equate cycle time with tool life, though, said Clynch. Just because a machine ran six hours, that doesn’t mean it used six hours of tool life. The end mill may have only been engaged with the workpiece a fraction of that time due to the short arc of contact. “Pay close attention to this to make sure you are getting the maximum [life] out of your tools,” he said. “If not, you may be leaving money on the table!”

Deburring is almost always considered a secondary operation performed after machining, by hand and off the machine. A better option is to develop machining processes that eliminate the need to deburr off the machine.

Tonne agreed with Strauchen that modern CAM software is what helps make possible processes like trochoidal milling and high dynamic milling. “CAM software has gotten really good at high dynamic milling, where it’s managing the chip thickness,” he said. “So, you can use that in a roughing operation.”

Burrs can cause issues in downstream machining processes by preventing proper location of the part in a fixture or result in erroneous measurements when a burr interferes with a metrology device.

I experienced a situation with one of my employers where a newly hired employee was assigned to deburr an extremely expensive part. The “new guy” was not a machinist and had little experience around machine tools or machining. It was decided he should deburr until he completed his training as a machine operator.

Dynamic milling relies on the ability of CAD/CAM software to create a trochoidal milling program; a milling machine to read complicated trochoidal programs at high speed; and a machine that can rapidly move the spindle and table.

“Once these conditions are met, it is possible that not only high efficiency is achieved, but also that tool life and the life of the machine spindle are greatly extended,” said Hashizume. “In such an environment, it is less important to consider chip evacuation by enlarging the chip pocket of the end mill, but rather how to increase the number of flutes to increase the tool rigidity and feed rate to achieve high efficiency.”

When I worked for a manufacturer of power steering gears, an automated assembly machine was a continual source of part failures. The machine screwed ball joints into the steering unit and then verified that the parts had been assembled correctly. If a part went in farther than expected, the machine alerted us about a bad part.

“There are many modern machining techniques and strategies that really turn [that wisdom] on its head,” said Strauchen. Now, faster machines with more horsepower and faster, more precise spindles have made possible aggressive machining strategies like high-efficiency milling (HEM), also known as dynamic milling, and trochoidal milling.

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Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.

I worked in an aerospace shop that made hydraulic components. The components had small orifices that could easily become blocked by burrs if they were to break free. Blockage of the orifices could result in a failure of an aircraft’s hydraulic systems—a potentially life-threatening event.

Deburring small, intricate parts is almost an art form, requiring fine motor skills, an understanding of critical part features and attention to detail. In some industries, like aerospace, deburring has been considered a trade and there have been people who have spent their entire careers at the burr bench.

Edwin Tonne, training and technical specialist, Horn USA Inc., Franklin, Tenn., said the perceived application for multi-flute end mills is for semi-finishing and finishing workpieces. “But, actually, if the shop is willing to re-program the job multi-flutes can be used to rough and to pocket as well,” he said.

Deburring is an important skill; it should be given attention because removal of burrs is critical to safety and quality.

The question is how can a machinist seemingly defy the laws of physics and use the speed of a higher-flute tool without clogging it with chips and causing it to break? The answer is in new programming strategies. Today, CAD/CAM software, with sophisticated toolpath generation built in, allows programmers to generate more efficient toolpaths that are speedy but prevent the tool from getting into danger zones. The software’s approach is very specific, so the mill is never over-engaged with the part. Users can tell CAM software, “I don’t want to exceed this amount of tool engagement,” and the application will create the toolpath necessary to ensure the tool never gets engaged beyond the point he defined.

However, Clynch offers several cautions. When using this strategy, a machine tool’s acceleration/deceleration rates have to be higher because with the smaller moves the tool makes, the machine has to ramp up and down more to adjust the speed. The machine tool needs more memory for longer programs and it also needs enough “look-ahead,” or buffer space, to run smoothly. If the machine can’t read the code fast enough, it jerks, stalls or dwells trying to keep up, he said.

What to do if chip formation doesn’t look right? “Unfortunately, there is not a simple answer to this. It depends on the application and material,” said Fiedler. In the case of chips changing their color, the coolant supply into the work zone needs to be improved. Vibration might be the cause of all this, so the tool and workpiece clamping need to be checked. Modifying the feed rates and axial DOC can also help. Curling and ruffling of chips often indicates feed rates are too high, so adjusting the feed rates can help, but it is important to maintain sufficient average chip thickness

Using these tools in an HEM/VoluMill environment (toolpath software from Celeritive Technologies, Moorpark, Calif.) will mitigate assembly disasters, he said. This approach can make the smaller tapered machines competitive with larger taper machines. “The metal removal rates we can achieve are very close if they aren’t in fact beating the standard way to rough material out on bigger taper machines like 50-taper and HSK A100,” Clynch said. As a result, a wider segment of the industry can be competitive because smaller taper machines are less expensive and easier to learn.

In contrast to the linear radial toolpath in conventional machining, trochoidal milling uses a spiral (or D-shaped) toolpath with a low radial DOC to reduce load and wear on the tool. Since trochoidal milling uses a tool to machine a slot wider than its cutting diameter, the same tool can be used to create slots of varying sizes. This can free up space in the tool carousel and save time on tool changeouts, depending on the requirements of the part.

Burrs left on parts can also injure workers. Most of the recordable injuries at our shop are lacerations to hands. Many of these injuries come from parts that were not properly deburred. Therefore, removing burrs before moving parts to the next operation is critical to maintaining a safe working environment. It is given considerable attention at our shop.

Lots of attention is given to improving machining processes. New productivity-boosting developments for drills, mills, boring tools and turning tools abound. Advanced milling and turning techniques are always under development, and software companies regularly announce new features that promise to slash cycle times. Machine tool builders and CNC manufacturers are creating ever-faster machines and controls capable of keeping pace with advanced machining techniques.

Don’t forget about the material you’re removing, said Clynch. “In theory there is not a limit, but you’ve got to have some place for the chip to form correctly,” he said. For normal, everyday materials like ISO P, ISO M, and high-temperature alloys there has to be a limit on the number of flutes. The rule of thumb is for every millimeter in diameter of a tool you get one flute, he said. For example, for tools with a ½" (12.7-mm) diameter, the maximum flute number to be effective is 12 and for tools with a 1" (25.4-mm) diameter the maximum flute number to be effective is 25. “For practicality that’s a good way to do it,” Clynch said.

A host of methods exist for deburring parts, such as this motorized brush from the Deburring Applications Laboratory at Matrix Design LLC. Image courtesy of Alan Richter.

In other situations, special-purpose deburring tools can be purchased. These tools are made with retractable blades that deburr both sides of a through-hole. Many machine solutions exist to support deburring in the machine tool.

Science of measurement; the principles on which precision machining, quality control and inspection are based. See precision machining, measurement.

In the not-so-distant past, young tool and die apprentices were trained to deburr parts for journeyman tool and die makers. It was a practical activity that taught patience and hand skills.

“Dynamic milling is defined as a method that is done with a large axial depth of cut (DOC) and small radial DOC to reduce the engagement time of the cutting edge of an end mill, which reduces the force load on the tool and spindle and the generation of cutting heat, while increasing the amount of material removed,” said Tyler Hashizume, product engineer II, OSG USA Inc., St. Charles, Illinois.

The newer processes enabled by modern CAM software are a boon for machining hard materials that need to be machined with low radial engagement, which otherwise would risk breaking the end mill. For example, when machining steel greater than 50-60 HRC, a two-flute end mill probably will snap.

By eliminating the need to change out one mill for another and employing more cutting-edge techniques, today’s machinists can go faster, which leads to increased productivity.