Beyond the Router:
Machining and Fabrication Processes
by Pete Daumeyer

omputer Numerical Controlled (CNC) machinery is everywhere. CNC fabrication of plastic shapes is becoming more common in the performance plastics industry. We are seeing more routers everywhere, and soon most distributors will have at least one router somewhere in their organization. Many distributors already have several routers in different locations.

But what about other fabrication equipment? Besides cutting a 2-dimensional shape out of a sheet of acrylic, what are some machine shops or part manufacturers doing with performance plastics? What different machinery are they using to turn that rod, blank or plate of polymer into a finished part?

Most machine shops simply mill or turn parts. Most of the machines are CNC, but there are still “manual” mills and lathes in use. Manual machines usually have some type of computer control, however, and the measurements are still precise. Let’s take a closer look at the machinery.

Mills and lathes
Mills are like small routers, but with more power. A mill will run the same RPMs as a router, but the torque is much higher, allowing harder cuts into the product. A part is held down to a table, and the tool runs at a high RPM, cutting into the plastic shape. Even extreme mills can turn the table, so that the endmill located in the tool can turn and cut the part at extreme angles.

Lathes are the opposite of mills. With lathes, the part turns or spins at a high rate of speed and a static tool is introduced to pull material away from the part. The shape of the semi-finished part is always a rod.

Milling a plate
Milling a plate of FR-4 at Atlas Fibre, you can see water and chips splashing everywhere.
Mills generally start with three axes, while lathes rotate around one axis and introduce a tool at a second axis. Some mills can turn the tool at an angle or completely horizontal to get into the sides of the plastic. Some lathes, likewise, can introduce the tool at different angles to have different effects on the material. As parts get more complex, more axes are involved in the cutting phase of the parts.

Mills have a table that is usually smaller than a router, because most machined parts don’t need to come out of full sheets. In most CNC mills, the table stays motionless while the tool moves around the part. Some mills move the table back and forth, adding more movement to the part and, thus, more axes of cutting can be processed. Most mills have a 20″ x 40″ table for the part to be held down to, providing a fair size footprint.

Atlas Fibre machining
Through the spindle turning of thermosets at Atlas Fibre machining.
In addition, most CNC mills come with automatic tool changers, allowing for the quick change of tools and endmills (the part cutting the plastic). When selecting tools for the job, you want to pay attention to the depth of cut, the diameter of the tool and the angle or radius at the bottom of the tool. Most tools are made of carbide steel and some even have special coatings for the product they are cutting.

As for lathes, there are two ways to present a part to the tool. For a smaller part, a long rod can be introduced from the back or side of the lathe and will come through the spindle. A rod feeder is usually attached to the side of the lathe, with a series of rollers on which the back of the rod can continue to spin while the front of the rod is machined. The part is then chopped off and the rod is extended a certain length so the lathe can start working on the next part. This process is usually CNC-driven now, with multiple rods placed in a feeder, so that the machine can turn parts continuously until it runs out of rods.

Large parts will have to be chucked up, which means working on only one part at a time. A larger diameter rod is cut into a certain length and then installed by hand into the chuck. Then it will begin to spin with tools introduced to cut material out and create the part. Chucking goes up to 10″ on most CNC equipment; however, some large parts can get a much heavier diameter chucked up for cutting.

Next-level machines
Your fabrication options increase with next-level machine tools. A 7-axis mill-turn machine can run endmills into a part and then spin the part for static tools to cut the full circumference of the part. Likewise, there are lathes with live tooling, where the part will stop rotating and an endmill can be introduced to cut holes or different shapes into the sides of the part. A mill-turn is more like a complete machining center, whereas a lathe with live tooling is still a lathe.

Horizontal mills exist, where instead of the X axis being up and down, it is positioned horizontal into a part. Horizontal mills turn the table on their side. In fact, they are called “tombstones” for the way the stand up and hold the part. Multiple tombstones can help accommodate part removal and replacement, thus speeding up the activity and allowing for continuous machining. A small benefit of a horizontal mill is the assist you get from gravity with chip removal.

Screw machines are for smaller parts. Like a lathe, a small rod comes through the spindle and can be cut on one side, then moved to a separate position and the part can be cut on the back side. A finished part, machined on the front and back ends, as well as turned down on the circumference, is the output from this type of machine.

Staying cool
Coolant is a big issue with machines. While all metal should be cut with some type of oil to keep the part cool and the cut lubricated, most plastics should not. The oils can contaminate a part or effect its structural properties. Thus, when cutting plastics, either water or sometimes just plain air is forced onto the part to keep it cool and lubricated while being machined. Most machines have flexible hoses for the coolant to be directed at the tool, while some machines have “through the spindle” coolant. The end mill will be hollow with holes to allow the coolant to be sprayed on the part.
“A little bit of knowing about how the plastic you are selling is being machined can go a long way to helping your customer find the right solutions for their needs.”
Tidying up
As for the chips coming off the parts, an additional part for both tools would be a chip removal auger and conveyor. The auger is at the bottom of the machine and rotates, pulling the chips to one end of the machine. The chips then go to a conveyor, which pulls them out of the machine and dumps them, usually into a bin or garbage can for recycling. This keeps the inside of the machine relatively clean.
The more you know, the more you can help customers
The next time you speak with your customer, you will know a little bit more about how parts are being machined. Whether parts are being turned or milled, the next time the doors of the machine close, you will know what is going on inside it. A little bit of knowing about how the plastic you are selling is being machined can go a long way to helping your customer find the right solutions for their needs.
Pete Daumeyer is a territory manager for CartierWilson LLC and chair of the IAPD Editorial Committee. For more information, contact CartierWilson LLC at 34194 Aurora Road, Suite 231, Solon, OH 44139-3801 USA; phone (813) 431-2308, fax (770) 644-0008, peter@cartierlwilson.com or www.cartierwilson.com.