Friday, October 26, 2012

Thinking More Positive About Negative Cutters

By Todd Miller, Manager, Rotating Products

At Seco, we are constantly seeking out new ways for our customers to save money and still productively produce quality products. Such commitment has enabled us to continuously add new dimensions to the world of metalcutting where “one size does not fit all.” Consider our brand new take on negative cutter design.
Double Octomill
Negative cutters have been around for years and are quite popular, given they help reduce manufacturing costs by allowing the use of double-sided inserts. However, they prove most effective in steel and cast iron applications. Today, we’ve managed to re-engineer the traditional negative cutter to handle a wider range of applications by using modern, high-positive insert geometries – creating a hybrid negative/positive cutter style. 

This hybrid cutter style retains its strength for roughing operations, generates downward cutting pressure, which pushes the part into the fixture, and provides the economy of multiple cutting edges while reducing cutting forces, maintaining good chip evacuation and providing excellent surface finishes.

There are three common configurations for cutter bodies — positive/positive, negative/negative and positive/negative – all having advantages and disadvantages in different applications, which you can read about here.

By taking a negative cutter body and introducing a high-positive insert geometry, we’ve created a highly effective positive cutting rake angle. The effective cutting rake angle is calculated by adding the radial rake of the cutter body and the cutting rake angle of the insert. With a positive cutting rake angle in a negative cutter, users benefit in multiple ways – freer cutting action as well as reduced power consumption and heat generation, all of which leads to longer tool life in addition to the increase in usable cutting edges.

Square 6
The hybrid combination also takes into account several other design factors in addition to cutter body geometry, including the cutting insert’s geometry, effective cutting rake and edge preparation. 

Cutter body geometry, or the positioning of the cutting edge of the insert, involves lead, axial rake and radial rake angles. The lead angle is the approach the cutting edge takes as it enters the workpiece. It also controls the direction of the axial and radial cutting forces, as well as affects chip thickness, tool pressure and tool life. The axial rake is the insert’s angle along the central axis of the cutter assembly, while the radial rake is the insert’s angle in relation to the periphery of the cutter. In a hybrid negative/positive geometric configuration, the cutter rake angles both remain negative. It’s the introduction of the positive insert geometry that makes the difference.

Insert edge preparation also plays a key role in the new hybrid negative/positive approach. In typical milling cutters for steel and cast iron operations, negative T-land edge protection sufficiently applies, while in tougher applications involving titanium, Inconel or superalloy materials, the inserts are honed and do not include the negative T-land, enabling them to be sharper and cut freer. These tougher workpiece materials are where some of the most significant cost reductions can be found using the new hybrid technology. While in most situations, double negative cutters are not effective for these tougher materials. But now, these materials can be machined successfully using the hybrid style with honed-only inserts.

Additionally, these designs now incorporate integrated wipers of various sizes on each insert. This should be considered when machining different materials. For instance, longer wipers tend to produce more tool pressure and increased heat. Therefore, when working with tougher materials, such as superalloys, a shorter wiper is recommended for roughing to help reduce work hardening and excessive heat. In steel and cast iron roughing applications, a longer wiper can save valuable machining time thanks to its freer cutting action that produces a nice surface finish in just one pass.    

Currently, several Seco customers are finding success using negative cutter bodies with the new hybrid negative/positive configuration. Such cutter bodies include the Double Octomill, a highly versatile and economic face milling cutter with 16 numbered cutting edges, and Square 6 line of shoulder milling cutters. And stay tuned as we look to develop even more ways for our customers to productively and profitably machine quality products.

Watch the Double Octomill in action.
Watch the Square 6 in action.

About the Author
Todd is the manager of rotating products for NAFTA, responsible for solutions and applications involving face, square shoulder and disc milling. Todd and his team of product experts are dedicated to providing a consistent, high-level of support to Seco customers throughout the United States, Canada and Mexico. In his spare time, Todd likes to bowl and cheer on the University of Michigan football team. Contact Todd at

Wednesday, October 10, 2012

The Low-Down on Insert Coating Processes and Materials

By Don Graham, Manager of Education and Technical Services

Few materials have had a greater impact on our economy and industrialized culture than cemented tungsten carbide. Hard and wear-resistant, this material is used for products as interesting and varied as ballpoint pen balls, fishing rod guide rings, wear parts, dental drill bits, armor-piercing shell cores and, most significantly, cutting tools

In fact, coated cemented carbides are the most widely used cutting tools on the market today. After all, they bring high levels of productivity to the manufacturing process, which, in turn, makes many of the products we use everyday more affordable. However, with today’s vast array of advanced coating processes and coating materials, it’s not always easy to determine the best insert grade for your application. 

The Seco TP2500 is a great example of a CVD-coated insert.  
The best place to start is with your workpiece material because the type of material you are machining will play a key role in determining whether you need a coated or uncoated carbide insert. 

Coated carbide inserts are a must for working with ferrous materials such as iron, cast iron, steel or stainless steel. When machining super alloys, you’ll want to use a coated insert most of the time, especially when cutting alloys with medium to high machinability ratings. Titanium alloys also benefit with coatings, especially when not using high-pressure coolant.   

Uncoated carbide inserts are ideal for applications involving non-ferrous materials, such as aluminum. In fact, because aluminum can be soft and lead to built-up edge, it’s best to make use of an extremely sharp, uncoated cutting edge. Other materials not requiring a coated insert include brasses, bronzes, many composite materials and wood.  Having said that, however, productivity and tool life can be dramatically improved with the use of an appropriate diamond coating.

The insert selection process becomes tricky when trying to pick the right coating type. After all, every application is different and you must take both coating processes and coating materials into consideration. And, while there is no simple answer to “How do I choose the right insert coating?” understanding coating processes and coating materials help take some of the ambiguity out of the selection process.  

Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD) are the two main coating processes for carbide inserts, each one providing interesting features and benefits. For example, CVD coatings are thick (typically 9 – 20 microns) and highly wear resistant, making them ideal for steel and cast iron machining as well as widely used in turning operations. Unfortunately, however, such thick coatings can compromise edge toughness. PVD coatings are thin (typically 2 – 3 microns) yet tougher and typically smoother than CVD coatings. Consequently, they are useful for machining materials, such as superalloys, titanium alloys and difficult-to-machine stainless steels, that typically notch or chip cutting edges. 

Chemical Vapor Deposition (CVD) Coatings

CVD-coated inserts work well in turning, milling and drilling applications involving ferrous materials. In fact, we recommend CVD-coated inserts over PVD-coated inserts if you are turning, milling or drilling steels and cast irons.   

Characteristics of CVD Coating Types:    

TiN Coatings

• Excellent build-up resistance
• Easy to tell what insert corners have been used
• Effective at lower speeds
• Excellent on gummy materials
• Excellent for threading and cut-off operations

TiC Coatings

• Excellent wear resistance
• Effective at medium speeds
• Excellent on abrasive materials

 Al203 Coatings

• Excellent crater resistance
• Effective at high speeds and high heat conditions

Physical Vapor Depositions (PVD) Coatings

The Seco TS2000 is great example of a PVD-coated insert.
PVD-coated inserts are ideal for turning, milling and drilling applications involving high-temperature alloys, titanium alloys and stainless steel. We recommend using PVD-coated inserts when turning high-temperature alloys; however, if the alloy is on the softer side and you can machine at higher speeds, a CVD coating is preferred. 

Characteristics of PVD Coating Types:    

TiN Coatings

• Excellent build-up resistance
• Broad application range
• Effective on high-temperature alloys
• Effective on stainless steels

TiCN Coatings

• Harder than TiN coatings
• Effective on end mills
• Sometimes used in milling applications where the work material is abrasive

TiAIN Coatings

• Harder and more stable than other PVD coating types
• Becomes harder and more stable with time
• Effective on high-temperature alloys and stainless steels
• Effective on abrasive irons at lower speeds

This is just the tip of the iceberg when it comes to information involving CVD and PVD-coated inserts. Seco currently offers approximately 75 different insert grades, many of which incorporate multiple coatings, so trying to select the right one for your operations can seem like an overwhelming task, but this is where our expert staff can help. We live metal cutting and take pride in working closely with our customers to provide solutions that increase productivity and profitability, so don’t ever hesitate to contact us.  

About the Author  
Don is the manager of education and technical Services for Seco, responsible for all educational activities for the NAFTA market, new product testing and various other technical functions. Outside of work, he enjoys making maple syrup, restoring antique tractors and farming. Contact Don at