How to choose correct turning insert

There are many parameters to consider when choosing a turning insert. Carefully select insert geometry, insert grade, insert shape (nose angle), insert size, nose radius and entering (lead) angle, to achieve good chip control and machining performance.

You will get efficient and thoughtful service from Guangzhou Ruiyi Technology Co., Ltd..

• Select insert geometry based on selected operation, for example finishing
• Select the largest possible nose angle on the insert for strength and economy
• Select the insert size depending on the depth of cut
• Select the largest possible nose radius for insert strength
• Select a smaller nose radius if there is a tendency for vibration

l = cutting edge length (insert size)

RE = nose radius

Nose angle

Turning insert geometry

Turning geometries can be divided into three basic styles that are optimized for finishing, medium and roughing operations. The diagram shows the working area for each geometry based on acceptable chip breaking in relation to feed and depth of cut.

Roughing

High depth of cut and feed rate combinations. Operations requiring the highest edge security.

Medium

Medium operations to light roughing. Wide range of depth of cut and feed rate combinations.

Finishing

Operations at light depths of cut and low feed rates. Operations requiring low cutting forces.

ap

The above example illustrates the offer for steel—there are other options available for all material groups.

Turning wiper geometry

Use wiper inserts for improved surface finish with standard cutting data, or, maintained surface finish at substantially higher feed rate.

The -WMX wiper geometry is First Choice, and is a good starting point for most applications. When conditions change, there is always a productive alternative.

Choose a positive wiper geometry to lower forces and maintain productivity in case of vibration problems.

Choose wiper geometry as follows:

-WL: For improved chip control when moving to a lower fn/ap.

-WF: Improves chip control at a lower fn/ap. Also for lower cutting forces when vibrations occur.

-WMX: Always First Choice in the wide chip application area. Provides maximum productivity, versatility and the best results.

-WR: When a stronger edge line is needed—for example, for interrupted cuts.

Are you looking for tool recommendations?

Find our cutting tools here chevron_right

Need advice?

Ask us a question chevron_right

Want to learn more about the basics of metal cutting?

Register for our free e-learning chevron_right

Turning insert grade

The insert grade is primarily selected according to:

• Component material (ISO P, M, K, N, S, H)
• Type of method (finishing, medium, roughing)
• Machining conditions (good, average, difficult)

The insert geometry and insert grade complement each other. For example, the toughness of a grade can compensate for lack of strength in an insert geometry.

Turning insert shape

The insert shape should be selected relative to the entering angle accessibility required for the tool. The largest possible nose angle should be selected to provide insert strength and reliability. However, this has to be balanced against the variation of cuts that need to be performed.

A large nose angle is strong, but requires more machine power and has a higher tendency for vibration.

A small nose angle is weaker and has a small cutting edge engagement, both of which can make it more sensitive to the effects of heat.

Cutting edge strength (Large nose angle)

• Stronger cutting edge
• Higher feed rates
• Increased cutting force
• Increased vibration

Less vibration tendency (Small nose angle)

• Increased accessibility
• Decreased vibration
• Decreased cutting force
• Weaker cutting edge

Turning insert size

Select insert size depending on the application demands and the space for the cutting tool in the application.

With a larger insert size, the stability is better. For heavy machining, the insert size is normally above IC 25 mm (1 inch).

When finishing, in many cases the size can be reduced.

How to choose insert size

1. Determine the largest depth of cut, ap
2. Determine the necessary cutting length, LE, while also considering the entering (lead) angle of the tool holder, the depth of cut, ap and the machine specification
3. Based on the necessary LE and ap, the correct cutting edge length, L and IC for the insert can be selected

Turning insert nose radius

The nose radius, RE, is a key factor in turning operations. Inserts are available in several sizes of nose radius. The selection depends on depth of cut and feed, and influences the surface finish, chip breaking and insert strength.

For more General Turning Insertsinformation, please contact us. We will provide professional answers.

• Ideal for small cutting depth
• Reduces vibration
• Weak cutting edge
• Generally better chip breaking

• High feed rates
• Large depths of cut
• Strong edge security
• Increased radial forces

Depth of cut and cutting forces

The relationship between nose radius and depth of cut affects vibration tendencies. The radial forces that push the insert away from the cutting surface become more axial as the depth of cut increases.

It is preferable to have more axial forces than radial. High radial forces can have a negative effect on the cutting action, which can lead to vibration and bad surface finish.

As a general rule of thumb, choose a nose radius that is equal to or smaller than the depth of cut.

Positive or negative turning insert style

A negative insert has an angle of 90° (0° clearance angle), while a positive insert has an angle of less than 90° (for example, 7° clearance angle). The illustration of the negative style insert shows how the insert is assembled and tilted in the holder. Some characteristics of the two insert types are listed below:

Positive turning insert

• Single sided
• Low cutting forces
• Side clearance
• First Choice for internal turning and for external turning of slender components

Clearance angle

Negative turning insert

• Double and/or single sided
• High edge strength
• Zero clearance
• First Choice for external turning
• Heavy cutting conditions

Clearance angle

Entering angle for turning

The entering angle, KAPR (or lead angle, PISR), is the angle between the cutting edge and the feed direction. It is important to choose the correct entering/lead angle for a successful turning operation. The entering/lead angle influences:

• Chip formation
• Direction of cutting forces
• Cutting edge length in cut

Large entering angle (small lead angle)

• Forces are directed toward the chuck. There is less tendency for vibration.
• Ability to turn shoulders
• Higher cutting forces, especially at the entrance and exit of the cut
• Tendency for notch wear in HRSA and case-hardened workpieces

Small entering angle (large lead angle)

• Increased radial forces directed into the workpiece will cause a tendency for vibration
• Reduced load on the cutting edge
• Produces a thinner chip = higher feed rate
• Reduces notch wear
• Cannot turn a 90° shoulder

Are you looking for tool recommendations?

Find our cutting tools here chevron_right

Need advice?

Ask us a question chevron_right

Want to learn more about the basics of metal cutting?

Register for our free e-learning chevron_right

Achieving Good Turning Quality

Learn to achieve high-quality turned components by mastering chip control and cutting data. chevron_right

Thread Turning Inserts

Learn how to select the correct thread turning inserts and shims for optimal threading. chevron_right

Internal Turning

Internal turning machines the inner diameter of workpieces and addresses tool and setup considerations. chevron_right

External Turning

External turning shapes the outer workpiece diameter with high demands on process quality. chevron_right

For as long as there’s been tungsten carbide (which is roughly nine decades), machinists have been brazing small hunks of it to steel shanks and then grinding a sharp edge on the result. These brazed carbide tool bits and boring bars are easy to make, customizable to the application, and inexpensive. Unfortunately, their effectiveness depends on the machinist’s brazing and grinding skills. And since the tool must be removed from the mill or lathe for sharpening, they also lead to significant and costly machine downtime.

HSS tool bits present a similar story. They’ve been around even longer than brazed carbide. They’re much less expensive than carbide and there’s no need for brazing—just sharpen the tip however you want and get cutting. Sadly, you won’t be cutting very long or very quickly because HSS boasts a cutting speed of just one-fourth that of tungsten carbide, and even less compared to some of the newer, coated grades. HSS might be fine for hobbyists with loads of time on their hands, but carbide is the first choice for professional machine shops.

That statement extends to HSS rotary tool bits such as end mills, drills, and reamers, all of which are used daily throughout the manufacturing industry. That’s a shame. Yes, these tools are less expensive than their solid carbide alternatives, but as mentioned, they’re also far less wear-resistant, predictable, and productive. These factors explain why leading cutting tool manufacturers emphasize the importance of carbide tooling to their customers and why many have stopped offering HSS cutting tools altogether.

That leads us to indexable carbide inserts, the workhorses of the machining industry. As with old-fashioned brazed tools, indexables also utilize small bits of carbide. The difference is how they’re attached. Rather than a permanent braze, indexable tooling relies on a screw or clamp to secure the carbide insert to the tool body. When the edge becomes worn, swapping it out only takes seconds. More importantly, there’s no loss of position or need to “touch off” the tool. Just remove the old insert, stick in a fresh one, and get to work.

Where machinists and toolmakers once had to grind special shapes into their brazed or solid carbide tools, they now have the option of buying off-the-shelf indexable inserts in a huge variety of geometries and styles. Need to cut a 1/16” wide groove in a shaft? How about an Acme thread, or a 45-degree chamfer around a part periphery? These and other insert shapes are readily available, no grinding necessary.

Indexable cutting tools are especially important on CNC machinery, where the need to keep spindles turning at all times is critical. Here, machinists rely on indexable drills—often with coolant running through them—to make holes quickly, followed by indexable boring bars to finish machine them. Indexable face mills true up large flat surfaces; indexable end mills rough out pockets and cut slots; indexable profiling tools trace complex part shapes. There’s very little that can’t be machined with indexable cutting tools.

But how do you know what carbide inserts and cutter bodies to buy? And why are there so many different grades of carbide inserts out there? Good questions; we’ll start with the second one first. Unlike a few decades ago, when machinists had just a few grades to choose from, there are now dozens of inserts grades, coatings, and chip-breakers available.

Many of these are tailor-made for specific materials or material groups. For instance, a shop making aerospace components can greatly increase efficiency by purchasing carbide inserts designed for tough, heat-resistant superalloys (HRSA) such as Inconel and Hastelloy. The same is true for medical shops, which tend to cut corrosion-resistant, biocompatible materials like 316 stainless steel, cobalt chrome alloy, and titanium. Automakers can dial in their processes by using inserts optimized for cast iron and low carbon steel, while oil and gas producers benefit from tooling that excels in duplex steel.

Simply put, if there’s an alloy out there, the chances are excellent that a material-specific carbide grade is available to cut it. However, some shops machine aluminum one day, iron the next, and titanium the day after that, often in low quantities. Does this mean they need to bloat their tool crib with dozens upon dozens of different carbide insert grades and geometries, many of which will only be used occasionally?

Probably not. Just as there’s no shortage of indexable carbide tooling optimized for certain materials, there’s also no shortage of excellent general-purpose cutting tools. These represent a middle ground between performance and the tool crib bloat just mentioned. That said, the decision to go the material-specific route is a delicate balancing act—if a job’s going to be in the machine for more than a few days or is sure to come around again in a month or two, it almost always makes sense to buy carbide inserts designed for that material.

Last but not least is the whole topic of insert nomenclature. It’s a deep subject, one filled with exceptions and cutting tool-specific rules. Regardless, most manufacturers follow the ANSI or ISO tool identification system (and sometimes both). We won’t get into the details here except to say that it uses an alphanumeric code to specifies an insert’s shape (round, square, triangular, etc.), clearance angle (neutral to positive), tolerance (some inserts are pressed to size, while others are ground), the size of the locating hole (if any) and clamping method, its size and thickness, corner radii, and various other defining features (see the chart above for an example).

Complex naming systems aside, however, choosing the right insert for your machining application isn’t as difficult as it might appear. That’s because cutting tool manufacturers have developed online tool advisors that walk machinists and programmers through the tool selection process. For example, Kennametal.com has a collaborative space that prompts users to answer questions about the metal removal process (milling, turning, or holemaking), the machine tool that will be used, workpiece material and removal amount, and expected depths of cut. It then generates a machining strategy along with insert and toolholder suggestions, ordering information, product availability, feed and speed recommendations, and more.

Long story short, carbide insert selection is much easier than it once was, even though the number of cutting tool options has grown exponentially since the days of brazed carbide and HSS tool bits. Download a catalog, log in to Kennametal.com or give your local cutting tool representative a call. You’ll be making chips in no time.

If you are looking for more details, kindly visit High Feed Milling Inserts.