Solid carbide and indexable tools have their pros and cons. Choosing the correct tool for milling aluminum can be easy at times, such as using an end mill to finish the floor of a pocket or using an indexable face mill to deck off the top of a part. But then, there are applications where choosing a tool can become more complicated because of the different CAM software + machine tool capabilities. A large determining factor when deciding what tool to use for a roughing strategy is how much metal you can remove or your “material removal rate”. Material removal can be quantified by using the following formula:

Material Removal Rate (M.R.R.) = (Radial Depth Of Cut) x (Axial Depth Of Cut) x (Feed Rate)

So if we machined a piece of aluminum, assuming all factors except the tool parameters are the same, with a five flute 1/2" solid carbide end mill and a two flute 1.0" indexable end mill, we can see that the metal removed with the indexable tool is over twice that achieved by the solid carbide tool:

the numbers tell us that size matters for milling aluminum

So, for roughing applications, we want to use the largest possible cutter that the application or machine tool will allow without chattering or stalling. This is one of the reasons why the machine tool is so critical! Large taper spindles with secure mounting such as dual contact are great for taking larger radial and axial depth of cuts without creating chatter. Small tools with a large radial and axial depth of cut may create chatter, limiting the engagement of the tool. Part designs also may be complex and CAM programs would only engage a cutting tool for a minimal amount of time.

When should you consider an indexable milling cutter vs. a solid carbide Tool?

This has many variables and while each situation should be assessed on a case by case basis, there are two factors that come to mind when deciding when to use an indexable tool over a solid carbide tool – price and reliability. The replacement cost of a solid carbide tool over the 1/2"-5/8" range can start getting expensive. Indexable tooling should start being considered at this point. While indexable tooling starts at diameters as little as 3/8", you may not always see the cost benefits on diameters this small. Cutting diameter sizes starting somewhere in the range of 5/8"-3/4" is where you start seeing good financial benefit.

The initial dollar value, however, may not be your determining factor. Process reliability such as chip management, tool changes, or taking advantage of a more reliable (sturdy) set-up may outweigh the benefits of aforementioned cost savings. Solid carbide end mills can create small, difficult to manage chips that can get into areas such as way covers, causing damage or requiring additional maintenance time. However, chips created with indexable tooling (due to the feed rate and depth of cuts) tend to be heavier and more manageable. Tool changes can be a determining factor as well. Although aluminum tooling with advanced coatings tend to have exceptional tool life, the ability to change insert corners after a certain lot or quantity for process reliability may also be a determining factor. Indexable tooling also offers multiple radii, coatings or substrates (such as PCD) to potentially add value to your application. 

Here are some pros and cons on solid carbide and indexable tooling, to help you weigh your decision:

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