Often, when we work with a customer on tool life and finish problems, we start by looking at the process they’re using to machine their parts.
Let’s take milling as an example. First, we need to look at what machine type will be used and how the part will be fixtured. Are we working on a vertical or horizontal machine? We do not see as many problems on vertical machines as we do horizontal ones, however, they do exist on both styles.
Horizontal machining center example – First, we need to check perpendicularity. Is the tombstone positioned correctly and is it sitting perpendicular to the spindle? If not, correct this before running any parts. Many shops will attempt to fix this issue by shimming parts.
Don’t do that!
Please do not program in a taper to offset the problem on the fixture. All of these tactics are used; however, the problem still exists and needs correcting to ensure that you produce a quality part and maximize tool life and part integrity. Fix the problem by correcting the fixture itself. Vertical/horizontal challenges – A common problem on either type of machine is machining or feeding tools, such as milling cutters, away from your locators or away from your table. This often causes chatter and poor tool life. It may not seem like an issue, but when possible, always feed in the direction toward your locators and into the table. Most forces on vertical machines will already be in the table but you should always look at the direction of your feed to keep it toward your locators and the most solid part of your fixturing.
Other challenges occur when using circular interpolation. You will not always be able to keep feed forces toward your locators or down into the table. You can, however, make sure that your cuts are started so that feed forces going in that direction are the strongest for your part and the fixturing. This will also help decrease chatter.
Maximizing the strength of your feed directions and keeping your tools as short as possible will let you feed at higher rates and maintain proper tool life. Simple checks similar to this will help increase productivity and tool life by simply reviewing your processes and sticking to basic machining principles.
CMR Consulting miker2468@aol.com
Mike Ramsey, president of CMR Consulting, retired from Kennametal Inc. as vice president, global machine tool industry sales, after 39 years of service in sales and marketing. He can be reached at miker2468@aol.com.
