Groove and groove-turn operations require secure insert clamping, rigid toolholding to be successful

The appropriate tooling geometry for the operation ensures the chip is controlled and easily exits the groove.

As with most turning applications, tool choice for a grooving operation depends on the details.

As a rule, the widest insert possible should be used to provide the strength necessary to handle the widely varying forces created during the various phases of the cut. A wide insert also has more mass to handle the heat generated, especially at the bottom of the groove.

However, an equally important factor in all grooving operations is toolholding.

For radial grooving operations, the toolholder needs to have the proper depth-of-cut capability to complete the groove, while securely clamping the insert in place. Choosing a toolholder with the shortest cutting depth for the job is best because a highly rigid tool will have a longer lifespan.

The more rigidity and clamping force on the insert, the longer it will last.

For groove-turning operations, the rigidity of the toolholder is even more important because the forces created during this operation are oriented at 90 degrees to where the tool’s strength lies. A toolholder with the shortest cutting depth should be used.

The Insert

“Insert choice itself depends on the workpiece material and any cycle time requirements,” said Kurt Ludeking, product manager, Walter USA. “By having the appropriate geometry for the operation, the chip will be controlled, and it will easily exit the groove. These radial grooving operations can be done very effectively with either short, single-edge inserts or with longer, two-edge inserts.”

Traditionally, grooving inserts have had only one cutting edge. Manufacturers have been reluctant to use multiple-edge inserts for fear that the additional edges will be damaged by chips leaving the work zone.

“When creating a deep groove, many machinists tend to use a single-sided insert because they fear a tool failure that can destroy the insert. They feel that, if this occurs, the other sides of the insert can’t be used anyway, so why add the costs associated with multiedged inserts,” said Steve Geisel, senior product manager for Iscar Tools Canada. “Our inserts are twisted, though, and this allows a double-sided insert to be used, even in deep grooving.”

Using a multisided insert means that the insert just needs to be indexed rather than switched out, saving time. The cost of the insert also is spread out over more cutting edges.

“We have a grooving tool that has five cutting edges,” said Geisel. “Having five cutting edges can be economical because you are spreading the cost of the insert over the five edges. It’s important to look at cost per edge in your operation, not just cost per insert.”

For groove-turning, the correct insert has a long, two-edge style because longer inserts are better able to resist the side forces generated.

“The geometry of the groove-turning insert is critical,” said Ludeking. “It needs to have very good chip control properties in both the radial and axial cutting directions. Inserts for groove-turning are designed with a chip breaker form around all the cutting edges; however, the form may vary significantly from the front of the insert to the sides to handle the different flow of the chips in axial and radial grooving.”

The cutting edge’s geometry and strength determine how the shearing action performs during the cutting process.

A sharp, positive cutting edge shears the workpiece material with low cutting pressure and, as a result, generates less heat and work-hardening. However, a sharp edge also is more likely to chip when exposed to interruptions in the cut and higher feed rates. An insert with a strong, negative cutting edge geometry better withstands these high forces and interruptions, but it generates more heat.

Using a Chip Breaker

According to Ludeking, chip breakers should be used in most situations, unless a short-chipping material, such as cast iron, is being machined.

“In most situations, a chip breaker geometry is very useful,” said Ludeking. “The chip breaker folds the chip so that its width is less than the width of the groove, and this is important to minimize the contact between the chip and the walls of the groove. This contraction of the chip prevents scratching of the groove walls to maintain a good surface finish.”

Walter USA has created a multifunctional chip breaker, which has a form that varies around the insert’s cutting edge.

“The geometry on the front edge is designed for optimum chip form in radial operations and provides short, tight chips that are easily evacuated even when cutting low-carbon steels like 1018,” said Ludeking.

The different geometries on the sides of the insert were designed for the axial turning phase of groove-turning.

“Because the forces and material flow are different than in radial operations, the edge geometry and position of the chip breaking elements need to be different to get proper chip control,” said Ludeking. “Finally, the corners of the insert are also different in form so that the insert leaves a good surface finish during axial turning operations.”

If an insert with a chip breaker is not used, a peck cycle that stops the cutting process to enable the operator to clear the chips needs to be used, which reduces productivity.

Other Design Aspects

More than just the insert geometry needs to be considered during grooving to create a productive, stable cutting operation. A securely held insert improves chip flow and surface finish.

“We have found that a dovetail pocket design is well-suited to grooving because it uses the toolholder itself to help absorb the cutting forces,” said Geisel. “This design also doesn’t rely on an insert screw or upper clamp to hold the insert in the pocket. When the upper jaw is removed from the setup, chips are no longer obstructed and flow out of the zone easily.”

This is even more important when wide inserts are used.

“The wider the insert, the more cutting forces are created. When a screw is used to hold the insert in the pocket, and these cutting forces grow, more pressure is put on that clamping screw,” said Geisel. “This creates a risk of breaking the heads off the clamping screw and having the insert come out while it’s in the cut. If this happens, you can destroy the insert, toolholder, or even the workpiece.”

An upper jaw is stronger than a screw, but chips can come in contact with the upper jaw and fail to exit the groove correctly. Chips can then pack in the groove, damaging the insert, holder, and part. This is especially prevalent in deep grooving operations.

“The deeper the groove, the more important it is to get the chips out easily. And, you don’t want to be damaging the surface finish of the groove’s walls. If you do, you will have to remachine those walls,” said Geisel.

Coated Tools

Coating imparts heat and wear resistance to a tool. In a grooving operation, the coating provides a barrier designed to keep heat away from the core of the insert, preventing deformation of the cutting edge that ultimately causes insert failure.

The coating also helps keep heat from the workpiece, lessening the chances of work-hardening.

“Walter uses PVD [physical vapor deposition] coatings for most of the grooving insert line for a number of reasons,” said Ludeking. “Since PVD coatings are thinner and adhere to sharp cutting edges better, the cutting edges can be sharper than with a typical CVD- [chemical vapor deposition-] coated tool. The advantage is that the cutting edge generates lower forces, which in turn create less heat and therefore less wear.”

A byproduct of adding a coating to the tool is a very smooth surface, enabling chips to flow better.

“PVD coatings also are less susceptible to built-up edge [BUE], which is common when cutting stainless steels and high-temperature alloys,” said Ludeking.

The coating choice depends on the material you are machining, of course.

“If you are machining INCONEL®s and other high-temp alloys, we recommend using a PVD-coated insert because it is very thin. If you are machining steel, you should use a CVD-coated insert, and for aluminum, you can use an uncoated insert,” said Geisel. “And, for each of these materials, we also need to use the correct grade. This all adds up to an insert that is matched to a manufacturer’s workpiece material, geometry, and lot size.

Troubleshooting

The success or failure of any cutting operation is not solely dependent on tool choice. Using the tool correctly means using the proper cutting data and tool paths.

Simply put, when improper speeds and feeds are used, bad things happen.

“Depending on how far the cutting parameters are from the recommended values, there can be a wide range of [negative] effects,” said Ludeking. “At the very least, tool life will be reduced. Improper parameters also can lead to chipping of the cutting edge, severe chip control problems, and poor surface finish.”

A worst-case scenario is insert fracture and damage to the workpiece or the toolholder.

Proper programming and tool path generation also need to be employed.

“Grooving actually is more technical than many people think,” said Geisel. “There is more to it than simply moving to the location and plunging into the material. If you aren’t programmed and set up correctly, it doesn’t matter how advanced your tooling is — you are set up for failure.”