By Chad Miller, Product Manager – Turning and Advanced Materials
|MR6 chipbreaker for medium-rough turning|
Chips can be extremely detrimental to your tools and production process, especially long chips formed during turning operations. The good news is there are tooling solutions and best practices for dealing with problematic chips.
By way of background, it’s important to understand what causes chips and the problems they create. Long, stringy chips commonly form when machining materials with low amounts of carbon, such as mild-steel and austenitic stainless steel. These types of materials are soft and gummy, and do not form martensite that would allow their chips to easily break away.
When these types of chips form, they can tangle around the tool and workpiece and form bird nests, which can increase heat in the material that, in turn, leads to poor surface finishes, tool breakage, machine downtime and thus increased production costs. A build-up of chips hinders process efficiency and creates safety issues. Operators must stop machines to untangle dangerously sharp chips from around tooling as well as constantly empty chip hoppers. Not only are these extra steps time-consuming, they make unattended lights-out operations impossible.
Today’s chipbreaking technology eliminates many of these issues by effectively controlling the formation of chips so they break off and move out of the cut zone. Here are a few general chipbreaking best practices:
|MF2 chipbreaker for semi-finishing and finishing|
• Match the chipbreaker to the application. The first basic rule of controlling chips is to understand that not all chipbreakers are alike. There are many different shapes and geometries of inserts available in positive and negative rakes. Proper selection depends on the type of workpiece material and turning operation being performed.
When finishing, for example, strict chip control is essential. Finishing chipbreakers are specially designed for smaller depths of cut usually less than 0.060" and relatively low feed rates of 0.003"-0.012" in/rev. These chipbreakers are narrow in the front and have a pit or dimple and a very large rake angle at the nose. Compare this to a roughing chipbreaker, which typically has negative T-lands for edge strength and for breaking chips at heavier depths of cut.
However, whether roughing or finishing, the key to truly effective chipbreaking is the right combination of tool geometry, grade and coating paired with proper coolant, all of which is based on the application at hand.
• Increase the depth of cut, if possible. Depth of cut significantly affects chip formation. Smaller depths tend to produce spiral-shaped chips, while larger depths generate the more desired comma-shaped chips. To create chips that break off and quickly evacuate, cutting tools should run at their maximum allowable depths of cut.
• Increase the feedrate. One of the most common mistakes machinists make is not feeding tools hard enough, which often results in poor chipbreaking. As a rule of thumb, the minimum feed rate in turning applications should not be less than the chipbreakers recommend feed rate, and the maximum feed rate should not exceed the tool’s nose radius to ensure ideally shaped chips.
These are just a few of the general considerations for effective chipbreaking. At Seco, we have a complete assortment of chipbreaker geometries that includes both negative and positive rake inserts and can help you find the right solution for each of your applications. To learn more or discuss a specific chipbreaking challenge, please feel free to contact me.
About the Author
Chad manages Seco's turning and advanced materials product lines, including all CBN and PCD products. When he's not helping customers implement advanced metalcutting solutions, you can find him training for and running 5K, 10K and 1/2 marathon races and triathlons.