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 dgraham@secotools.com.

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