“There are a few different Trochoidal strategies, all with very slight differences. By engaging the entire flute length of the cutter (ap) and reducing the width of cut (ae), this milling method can deliver huge benefits.”
By Swarf Guru Joe Reynolds: Original article can be viewed at: http://read.mtdatmach.com
I started my cutting tool journey in 1995 designing and manufacturing taps, milling inserts and bodies. The industry has evolved tremendously over the last 20 years and I’ve been heavily involved in cutting tools throughout this period. In this special feature, I’m taking a look at the modern trends in machining processes and how cutting tools have evolved in line with machine tool technology.
The biggest influence on cutting tool development is the new material technology, legislation, the end product of the manufacturing process and of course the machine tool technology being applied. Trains, planes and automobiles are continually being made lighter, meaning materials need to be lighter without the reduction of component integrity. We know that Ti-5553 and Ti6-4v titanium, aluminum and CFRP are being widely used in the aerospace sector to make stronger, more robust and ultimately lighter and more efficient aircraft. The automotive sector is also a long way down this road.
Global statistics indicate that 2-3% of the total family car weight was made from aluminum in 1980. By 2020, this will be 25%. This fact is indicative as to why cutting tool manufacturers have significantly increased their offering of high helix, positive geometry end mills. From an indexable perspective there is a rise in sharp polished inserts, PCD tooling and new lubricated coatings.
I don’t have the page space to discuss all the trends throughout my career, so let’s focus on one machining process that can be applied to most industry sectors and material types, Trochoidal milling.
The name Trochoidal milling comes from describing a curve (trochoid). By definition, it is ‘a curve traced by a point on a radius of a circle rotating along a straight line or another circle’. We don’t need to worry ourselves with that too much; we want to concentrate on what really matters….Metal Removal Rates (MRR).
There are a few different Trochoidal strategies, all with very slight differences. By engaging the entire flute length of the cutter (ap) and reducing the width of cut (ae), this milling method can deliver huge benefits. The benefits include increased productivity (reduced cycle time), extended spindle life (reduced stress on the spindle), significantly increased tool life, increased chip removal, reduced horsepower demands upon your machine (HP) and increased process reliability. To get the best out of this strategy, you will need to speak with your CAM vendor.
Many cutting tool manufacturers are focusing on Trochoidal milling and even investing in dedicated literature for the strategy. Tamworth based Industrial Tooling Corporation (ITC) have a catalogue of products and strategic advice from their partners Widia and BIG KAISER. The VariMill range of end mills is perfect for high performance Trochoidal milling. UK manufacturer ITC also produces a number of end mills perfect for optimized roughing and Trochoidal strategies.
What are the Limitations?
During the infancy of Trochoidal milling, excessively long chips were often an issue that would cause the tool to choke and fail. This has been overcome by introducing chip breakers in the flutes that significantly reduce chip size. A good example of this would be the F1105LLL chip-breaker from HAIMER, the CIRCULARLINE range from WNT and the Mirage CB from UK based Quickgrind.
I’m not making out that Trochoidal milling is a new strategy, but as with anything in machining, you have to continue to evolve and improve the process and strategy, especially with the evolution of machine tool, material and CAM system technology.
Early CAM systems were great for milling external features but when it came to internal features, they often fell short. This was down to tool-path movement as cutters entered a corner from a straight line motion. The arc of tool contact increases and the cutting parameters no longer coincide with the set arc of contact. If the tool path doesn’t adjust accordingly then vibration, chatter and ultimately tool failure is a certainty.
Modern CAM systems don’t have these issues. They are finely tuned packages that increase productivity with the use of tool-path optimization strategies for specific internal and external features. Now, intelligent CAM calculations seamlessly maintain a constant correlation between the cutting parameters and chip thickness.
What should I do next?
If you have so far failed to implement Trochoidal milling or any other advanced machining strategy you are in for a treat. If you use CAM, get your vendor to provide training and direction on Trochoidal milling. If you are not using this strategy, it is likely that you are programming on the CNC control and not via a CAM system. If this is the case, visit www.MTDCNC.com and look at the various CAM suppliers. Some will offer a ‘free-of-charge’ introductory trial period. However, limited experience will prevent you from optimizing the package and getting the best results.
Speak with you tooling supplier or visit our website for more information and videos on appropriate tooling. The right tool most certainly won’t be the cheapest, but the benefits will far outweigh the cost of the applying the correct tools. Cutting tools are a small investment when looking at the overall contribution of overheads to the cost per part. Despite this, the benefit of the right tool will ramp-up your productivity and reduce your overall cost-per-part whilst delivering all the benefits I mentioned at the start of the article. The Guhring Diver is a tool I see a lot in the field. This is because it is a multi-purpose tool that can aggressively ramp, plunge in the Z-axis like a drilling motion and it is a proficient Trochoidal milling tool.
Most, if not ‘all’ round tool manufacturers have products honed for Trochoidal milling.
One final thing…. please invite your cutting tool suppliers in to help you and don’t buy on price. The technical expertise and product quality is what you pay for – when you get it right you’ll realize it’s worth every penny.
A Note from Colibri Spindles:
Colibri’s unique HSM Jet Spindle line (coolant driven high speed spindles with real-time RPM monitoring) are used extensively in Trochoidal milling processes, especial for applications that require small cutting tools (0.5mm to 5.0mm). ISCAR’s solid carbide and MULTI-MASTER product line is equipped with suitable tools, as well as multi-flute tools for Trochoidal milling.