“If you are cutting to small major diameters on the face, where the grooves generally aren’t that deep, the chips are not an issue,” says Drape. “But in ID grooving applications where the groove is deep into a bore, then we need to get coolant in, and also need to break down the chip so it can evacuate.”

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“Exotic materials are not for production jobs—these are low volume applications,” says Tom Ficker, regional sales manager for Cogsdill Tool Products, Inc., with responsibility for Canada. “The problem with precision grooving in high nickel alloys is that you beat down on the grooving insert almost from the get-go.”

Both TungUniversalSlot and TecTangentialSlot are indexable slot milling cutters with unique insert features. Traditional slot milling cutters require two different shapes of inserts in pairs, using one shape for the right corner and the other for the left, in order to complete the slot profile. Both TungUniversalSlot and TecTangentialSlot incorporate a double-sided insert, allowing one side to be used for the right hand and the other for the left hand. TungUniversalSlot has six cutting edges per insert and TecTangentialSlot 4 cutting edges per insert. These insert features contribute to significant improvement of cost-effectiveness with less tool investment and inventory management.

“You need the chips to be able to freely get out of the bore and away from the cutting action so they do not interfere with the machining process.”

“It would be preferable to take an indexable insert into small grooves, because it would be more economical. But you often have to go with a one piece design, using a brace tool with a carbide or carbon steel cutter brazed to it.”

Loosely, any milling tool. Horizontal cutters take the form of plain milling cutters, plain spiral-tooth cutters, helical cutters, side-milling cutters, staggered-tooth side-milling cutters, facemilling cutters, angular cutters, double-angle cutters, convex and concave form-milling cutters, straddle-sprocket cutters, spur-gear cutters, corner-rounding cutters and slitting saws. Vertical cutters use shank-mounted cutting tools, including endmills, T-slot cutters, Woodruff keyseat cutters and dovetail cutters; these may also be used on horizontal mills. See milling.

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As a result, Cogsdill’s tools are better suited to high production lines, an area that has seen some big changes of late. Only a few years ago, small bores were typically 4 mm, but now leading vendors are delivering off-the-shelf bore grooves to 2 mm, with specialty applications going much smaller. This has resulted in new abilities—and challenges—when it comes to grooving very small parts, as well as increased demand.

Cost-effective double-sided inserts with multiple cutting edges, with one side for the right hand and the other for the left hand

“The grades Iscar uses for our inserts depend on how fast the machine spindle can spin,” says Iscar Tool’s Geisel. “10,000 rpm sounds high but remember you are working with very small parts, around .100 in. in diameter. So that 10,000 rpm with a .100 in. diameter works out to be about 260 sfm…we need to design and produce the insert out of carbide grades with coatings that can run at such speeds.”

Managing chip generation in tight spaces has always been a challenge, because the smaller the hole the harder it is to get the chip out. One approach is to plum or port the tool to get coolant out. There are also advanced tools, like Kennametal’s AF-GUP insert geometry for grooving and turning, that are specially designed for these challenges.

Engagement of a tool’s cutting edge with a workpiece generates a cutting force. Such a cutting force combines tangential, feed and radial forces, which can be measured by a dynamometer. Of the three cutting force components, tangential force is the greatest. Tangential force generates torque and accounts for more than 95 percent of the machining power. See dynamometer.

“The geometries are not standardized, but there are ways to create space at the head of the tool to promote chip flow,” says Stewart. “Sometimes the actual grooving tooth on the cutting tool will have a chip breaker on it—this will help the chip move out and get flushed with coolant.”

In addition, the insert cutting edge is designed to generate light cutting force and stable cutting even under heavy chip load. The inserts are available in grade AH3135 boasting high fracture toughness and AH120 with wear resistance for long tool life in various materials.

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“Slow feeds can be a good idea, depending on the material,” says Bokum Tool’s Stewart. “With smaller sizes a weaker tool neck will want to deflect, especially with carbide, and with increased distance to the groove, feed speeds need to be adjusted downward.”

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.

“The challenge with grooving is that below 1.5 mm it is difficult to make a tool that is strong enough,” says John Stewart, VP of engineering at Bokum Tool in Madison Heights, MI. “The overall determining factor is: What does a groove look like in a hole that size? If it is proportionally very similar to a larger hole then it is theoretically possible to get very small, but it really comes down to the strength of the tool itself.”

“The cutting process produces pressure on the work piece and on the tool. Controlling the pressure during machining dictates how successful we will be [in producing an effective cutting tool]. We can control cutting pressures by controlling the width of the grooving insert; the wider the insert, the more pressure it will produce. We also grind positive rakes on the inserts to control the pressure and to act as a chip former to control the chip shape and size.”

“There are companies that require face grooves with major diameters as small as 0.2 mm,” says Duane Drape, national sales manager for Horn USA Inc., in Franklin, TN. “This is mostly aluminium, but I have had customer requirements to get that small with steel at 50 + Rockwell.”

Hydraulics, given their need to control pressure, create demand for inside diameter (ID) and outside diameter (OD) grooving seals and threads, as well as relief grooves. In the automotive sector, miniature grooving applications include fittings for air bags and fuel injection components.

How best to approach grooving a small part has a lot to do with the materials involved: repeat, high volume applications tend to be with softer metals, with specialty one-offs applying to higher value applications, often with tougher alloys.

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“This is a double-sided insert that works well with slow cutting forces,” says Kaufmann. “The GUP insert geometry is advanced and versatile, with excellent metal removing rates.”

Ability of the tool to withstand stresses that cause it to wear during cutting; an attribute linked to alloy composition, base material, thermal conditions, type of tooling and operation and other variables.

ID grooving in particular can be an issue with small parts, says Steve Geisel, senior product manager for Iscar Tools Inc., Oakville, ON.

Solid carbide grooving tools are usually L-shaped. Part of the challenge is that even the non-cutting, or “leg” part has to fit into the bore diameter. Given that the bottom of the L, or the “foot” has to be even smaller, strength becomes an issue, as does the fact that groove depth is limited. As a result, with bores of less than 2 mm in diameter the best tools are now constrained to a groove depth of around 0.2 mm.

Geisel concurs with John Stewart that the challenge for tooling suppliers is to make a strong, rigid cutting tool or insert.

“It is important to keep speeds as low as possible when you have small-sized parts,” says Igor Kaufmann, a member of Kennametal Inc.’s global team for turning tools. When grooving miniature parts, Kaufmann emphasizes that the tools still need to fit axially and apply radial force to the bore. As a result, it is hard to ensure that the tool is strong enough, which then leads not only to chatter issues but also challenges with breakage and chip evacuation.

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Metal-removing edge on the face of a cutter that travels in a plane perpendicular to the axis. It is the edge that sweeps the machined surface. The flat should be as wide as the feed per revolution of the cutter. This allows any given insert to wipe the entire workpiece surface and impart a fine surface finish at a high feed rate.

“As a tooling manufacturer, we are being pushed to produce tooling able to groove in smaller, and smaller diameters. Our PICCO line can produce grooves in diameters from as small as 2 mm (.08 in.) and we can go smaller by special request.”

The problem with carbide is that reducing deflection increases the risk a tool will break, so it’s important to preserve the strength of the neck of the tool. Tool monitoring is also recommended, because with small cutting edges it can be hard to see or hear when a tool breaks.

A frequent issue is whether or not to go with inserts or solid carbide tools. Inserts can be indexable or have only one edge for single use. Inserts tend to be less expensive, but usually can’t get into the smallest bores, and are not as strong as solid-carbide tools.

Another approach is to compress chip width, thus ensuring it doesn’t lodge in the groove and result in tool failure. Either way, when it comes to grooving small parts, the combination of slow feed rates, proper tool selection, and a strategy for chip evacuation is the best way to ensure success.

If the chip created by the grooving tooth is wider than the finished groove, then you can minimize the possibility that the chip will stay in the groove. But when it comes to harder metals the challenge isn’t chip control so much as creating the chip in the first place. “At 1.5 mm you need to have a tool that is strong enough to create the chip,” says Stewart. “But from there, with a strong alloy like Inconel, it is relatively easy to control the chip. In the case of aluminium and softer materials, where the chip is continuous, it creates greater headaches because the material balls up.”

But replaceable inserts, single edge, can still get to some small diameters. More cost effective than a solid carbide tool, they can also deliver better axial depth. That said, solid carbide tools are usually more expensive, toolholders aren’t, and there is a risk the holder might break after a dozen or so uses.

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When grooving small pieces, cutting pressure tends to be relatively high. Aside from slowing feed rates, it can also help to use high lubricity coolants that work well in tight spaces.