Materials that require threads to be milled rather than tapped are usually very complex alloys created for components or parts designed for long-term use. These alloys are typically created with a higher-than-average hardness, abrasiveness and heat resistance. In the last 10 years, there has been more demand for materials suitable for challenging aerospace/defense applications, such as nickel alloys (Inconel), stainless steels, titanium and even aluminum.
The part runs or volume of threads in the aerospace and defense industries using these materials are typically lower than found in automotive, for example. But the cutting demands can be greater. The tough materials in aerospace applications require using solid carbide cutting edges on the thread mill in order to get a quality thread, without scrapping parts, substantially challenging tool life and longevity of the tool’s cutting edge(s).
Based on today’s requirements for thread cutting tools, single-plane thread milling cutters are an excellent option.
There are three key considerations that require attention for a successful thread milling operation, including chips, feed and stability. ZGF-S-Cut, Emuge’s latest single-plane type cutting tool is ideal for hard metals and exotic materials designed to resist cuts or fractures. This tool features three rows of cutting teeth, where the first tooth has a truncated form and acts as a rougher, removing most of the material for the following cutting teeth to finish the rest of the profile. These tools are designed to be run with a left-hand spindle rotation. A climb milling routine effect will result when combining this rotation with the 10-degree left-hand flute helix angle on the cutter. The thread mill is programmed in a counter-clockwise rotation but enters from the top of the hole in a conventional clockwise milling routine path. The climb milling routine effect has proven to be very beneficial for maximizing tool life and creating an excellent, stable cutting action throughout the entire length of thread. Dedicated to producing one size thread pitch only, these tools also feature a multi-layered TiAlN-T46 proprietary coating, providing superb cutting-edge protection for increased tool life in abrasive and edge wearing materials.
When combining a ZGF-S-Cut tool with an Emuge FPC milling chuck, the setup is further optimized for successful thread milling in exotic materials. The FPC’s precision holding power allows for shanks starting as small as 3mm or 1/8" to be rigidly held in its exclusive holding system. The FPC system achieves full contact of the shanks by pulling a slightly tapered sleeve into the body of the holder, using its patented internal 1:16 worm gear system to create optimal rigidity, vibration dampening, concentricity, machining speed and tool life for carbide cutting tools. This achieves a successful cutting action in very hard or difficult materials, especially with a three-axis, simultaneous tool-path movement.
It is this particular combination of a ZGF-S-Cut tool with the FPC holder that allows for the tools to run unattended for longer periods of time. Cycle times are reduced because there are fewer passes and machine stops required to compensate/gage the tool and produce a thread.
Other thread mill options are the Emuge ZGF-Z Thread Mills. These cutters offer a single row of teeth and an increased number of cutting edges via the Z geometry. In almost every case, when comparing the cycle time of Emuge standard single plane cutters with the ZGF-Z cutters featuring an increased number of flutes, there is a reduction in cycle time of about 50 percent to 70 percent, just by going from three to five flutes.