Forum: It’s Just Not That Simple

Today’s Machining World Archives May 2011 Volume 07 Issue 04

It’s Just Not That Simple

I enjoyed reading the primer from the April 2011 issue “How it Works” piece on tool coating, but overall, the comments from various manufacturers are certainly over-simplified as far as the wear types observed on cutting tools. The most glaring omission is the truth behind the CVD or PVD question.

With the exception of easier to machine cast irons, PVD is the correct choice for coated tools. It’s not unlike the choice between using a carburetor or fuel injection on a gasoline engine. The carburetor is old technology—best in its day, but inferior at this point in time.

It may be true that in some limited applications, CVD coated inserts will run at higher cutting speeds, but the small potential for faster cutting is more than offset by the inconsistencies observed in tool performance from edge to edge and insert to insert.

Major tooling companies continue to push a plethora of CVD grades into the market. The main driver of this approach is that the cost of coating inserts by the CVD process is many times less than the cost to coat by PVD. Yet cutting tool companies routinely introduce all types of new CVD coating varieties and layers into the market at higher and higher prices. This approach is a winning strategy for tool manufacturers as they make higher profits and can keep their customers confused and captive with an incomprehensible variety of tool choices. Unfortunately, CVD inserts are almost always a losing strategy for machine shops.The significant majority of shops would be wise to confine their tool and insert selections to about three different PVD coating options and eliminate CVD entirely. With this approach, machinists will better understand tool applications and performance, and focus on correctly applying the tools for each operation. This approach always results in higher overall production rates. If anyone doubts the advantages of this—just take a look at the inventory of solid carbide endmills in most shops. You will find one, two, or perhaps three options (uncoated, TiN coated, and AlTiN/TiAlN coated). Ever wonder why just three options can quite successfully cut all the various operations and materials that need to be milled with a 1/8” to 3/4” diameter milling tool?

Be cautious, and don’t study this too hard. The next thing you will start to wonder is why the price of a typical insert is in the mid-teens per insert, when a solid carbide endmill that has twice as much carbide by weight, and obviously is much more labor intensive to manufacture, costs about half what a normal insert costs. A real puzzler that one.

Dave

Feeling Bad for Today’s Youth

In response to the feature from the March issue, “How the American Visa System Keeps Skilled Workers Out,” since the introduction of the U.S. Department of Education, this country has witnessed the greatest “dumbing of America” in our history. What happened to our vocational high schools, our company sponsored apprentice programs and Junior Achievement? They all seemed to work very well in my youth. I graduated from a vocational (machine shop) high school and completed a Ford Motor Company apprenticeship program. I feel sorry for the kids coming up today.

Gary Goins

Way to Keep Going

In response to your “Swarf” on Caltech’s sports teams continuing their efforts after 26 years of losing, I applaud them. Of course everybody wants to win, but I’m sure most of the players are in it for the fun of it. It’s not like they’re at Caltech on basketball scholarships and need to prove something. If they were a Division I team—then sure, castigate them on their record. But they’re not. This example also doesn’t compare at all with professional teams that don’t perform well. The players on professional teams are there for one reason—to play ball. Playing basketball for CalTech students is certainly not their primary reason for being there.

Kim

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