Coatings, Geometry, Substrate - Magic Bullets In Precision Machining

In most shops there are three magic bullets that can make a job go better:

• Tool Coatings
• Tool Geometry
• Tool Substrate (material)

Are you guilty of magical thinking?

Magic Bullet Number 1 - Coatings

Tool coatings are important technologies that help us get longer tool life, thus longer operating uptime and therefore more billable production (dollars) per day in our shops. But, just as cold medicine is not the cure for heart attacks, tool coatings are not always the solution for an underperforming job. On a job with interrupted cuts, the tool material - its strength and grain structure are often far more important than coating on the tool. But if the last problem that the shop had was cured with a new "super coating" you can bet that that new coating will be first to be suggested on this newest problem at hand.

Magic Bullet Number 2 - Geometry

Geometry is a critical component of every machining operation. Geometry is the determinant of power required, as well as strength of the tool edge and the setup. Geometry has an important role on surface finish, and in confined spaces (deep holes, parting off, grooving, etc.) the ability to control the chip with geometry alone is an important means of assuring success. While rake angles tend to be fairly typical for certain work-piece materials, there are situations where a change in geometry can solve the problem of chip clogging, rough finish, or poor tool life. Once a shop has "learned" that changing geometry can make a problem go away in a material, they tend to over generalize that lesson. While it is likely that the geometry change was effective because of the particulars of the operation, not just because of the work-piece material, changing angles jumps to the head of the line the next time a shop runs into difficulties, especially if it is the same material. Geometry and chip control is a crucial aspect of machining success, particularly in deep holes, grooves, bores and cutoffs, but it is not the only one.

Magic Bullet Number 3 - Substrate and Material Issues

What the tool (or work-piece) is made of is another area that can mean success or failure to a difficult job. The advent of micrograin carbides was an event celebrated by machine shop owners everywhere, and developments in this area continue to improve our bottom lines. The same too, for work piece materials. Once a shop finds out that supplier "A's" material machines fine on a job, they immediately prefer it, often times without identifying which aspects of the provision of the material are aiding their production. Some suppliers have multiple process paths to make some items, and service centers often shop the world for price or delivery, bringing the full range of global variability to bear on your job. Consistency in supply is important, but it goes well beyond the name on the tag, to parameters of the processing and sourcing of the material itself.

It's not a single magic bullet. For each workpiece material, feature to be produced, machine tool, there is an optimum combination of tool substrate, geometry, and coating to produce the part to print with a minimum of downtime and management hassle. Looking for a magical single solution is generally the wrong approach.

Editor's Note: CR4 would like to thank Milo for sharing this blog entry, which originally appeared here.