Taking the plunge in turning

By Niraj M Wanikar, Chief Editor, CNCTimes.com, 2017-01-23 15:11:00

When using traditional turning methods on heat-resistant and hard materials such as super alloys large engagement angles and inconsistent chip load can occur at both tool entry and exit. Employing traditional plunge methods on such workpieces may also result in uneven rest materials with irregular surfaces.

Furthermore, Traditional Turning methods can cause adverse effects during the cutting process, such as heavy tool load, high and irregular cutting forces, vibration and poor chip control1. A key factor when high-speed machining these hard materials is maintaining a constant chip load, which remains vital when machining quality parts and prolonging tool life. In particular, if a chip load is too low or too high, that may cause the tool to wear faster causing many unwanted outcomes.

These unwanted outcomes may include chips so large that they cannot get out of the cutter's way fast enough. For example, if a tool is cutting deep down in a slot the chips will have a hard time getting out of the way quick enough, which may cause the tool to break. Another adverse out- come of a low chip load is a rubbing effect, which prevents the machine from making clean chips, and will also heat up both the tool and the material, drastically reducing tool life. Therefore, maintaining a constant chip load is crucial in the manufacturing process.

ProfitTurning™ Capabilities
ESPRIT features a new and innovative lathe roughing strategy, ProfitTurning™ which helps eliminate the adverse effects of traditional turning methods. ProfitTurning™ is a high-speed cutting method added as an additional cutting strategy in ESPRIT’s existing Roughing and Grooving cycles.
ProfitTurning™ is a productive and secure cutting method that enables manufacturers to make more efficient cuts with consistent chip loads and cutting forces, thereby reducing tool wear and decreasing cycle time. This is achieved using a toolpath algorithm based on an engagement control strategy, which allows for consistent cutting forces universally, and achieves the highest level of productivity.

Engagement control: Make reduced and constant engagements throughout the entire pass
Another way to eliminate negative effects in traditional plunging is to maintain reduced and consistent tool engagement. ProfitTurning™ breaks the cutting surface into manageable pieces, and uses round inserts to roll in and out of the cut to control the engagement at both tool entry and exit. With smooth roll-in movements and a smaller feed rate, the cutting force at tool entry can be significantly reduced and maintained at a constant level. The feed rate is also maximized during these straight line movements called - parallel moves - maintaining constant engagement, and then reducing engagement when exiting the cut.

Cut small, tricky areas with ease
Not all cutting areas are as smooth and easy to reach, such as the one featured in Figure 3. Fortunately, ProfitTurning™ provides cutting strategies for all small and uneven areas. These areas are often defined by part profiles, roll-in/out arcs, and the minimum trochoidal radius. The minimum trochidal radius is deter- mined by users to limit the size of trochoidal moves in small corners where a cutting tool cannot easily fit.

Another challenge in these difficult to reach areas is to keep constant tool engagement, so that the roll-in arc radius is not too large. To handle this challenge, ProfitTurning™ employs full trochoidal cutting inside these small areas until the tool reaches the “minimum trochoidal radius” as defined by the user. The mini- mum trochoidal radius then sets the size of the nonmachinable area at sharp corners, and the stepover is reduced to maintain constant tool engagement.

Benefits of ProfitTurning™
ProfitTurning™ uses round inserts or the full radius of groove tools to achieve higher feeds rates, in order to maintain a constant or near constant chip load. This is referred to as the chip thinning effect. In addition, Prof- itTurning™ reduces vibration and irregular cutting forces, which can result in poor surface finish and cutting tool damage by using round inserts with engagement control. In turn this makes ProfitTurning™ ideal for cutting hard materials and super alloys with thin walls.

Put to the Test!
Comparative testing of ESPRIT ProfitTurning™ was completed against conventional turning methods in collaboration with ESPRIT machine tool partners. The baseline for the test was established using a conventional ZigZag cutting strategy, and then compared to ESPRIT’s ProfitTurning™ strategy. The results were suc- cessful indicating a 25% reduction in cycle time using ProfitTurning™ as opposed to conventional cutting methods.

Another goal of the test cut was to evaluate tool life compared to traditional cutting strategies using ESPRIT ProfitTurning™. One part with two identical features was used in the test cut. One feature was cut with the traditional ZigZag technique and the other feature was cut with ProfitTurning™. During the test cut, TMAC4 (Tool Monitoring Adaptive Control) from Caron Engineering, was used to monitor the horsepower of the spindle.

Caron Engineering has over 30 years of experience in monitoring and controlling CNC machines, and TMAC is just one of their products. TMAC operates on the principle that the power required to cut a part increases as the tool life decreases. With the support of TMAC, we measured the difference in horsepower between ProfitTurning™ and conventional ZigZag strategies. For each strategy, we started with an air cut, then measured the horsepower for each pass. That data was then averaged together to show the overall horsepower value for each groove.

ProfitTurning™ Tool Selection
ProfitTurning™ uses round inserts or the full radius of groove tools. When using these round inserts, the entire cutting edge perimeter can be used when cutting, and the direction of the toolpath can be alternated to maximize the tool usage with higher efficiency, and to prolong tool life. Furthermore, round inserts can also tackle side loaded jobs, in which regular square inserts usually fail to accomplish. In addition, round inserts are suitable for materials with hardness levels of ISO-S and H5, such as heat-resistant super alloys.

In addition, when machining rigidity is also a factor when comparing round inserts to square inserts. Generally speaking, round inserts are more stout, making them the strongest inserts available, which also means they are less likely to produce harmonics during the cut, allowing for higher productivity. For example, Aerospace components are usually large, with increased radii and blending profiles designed to eliminate high stress points, which allows for round inserts to be used with ease.

Benefits of round inserts:
-The entire insert perimeter can be used when cutting
-The cutting direction can be alternated
-Effective engagement control with roll-in and out techniques
-Stronger cutting edge for tough materials
-Higher feed rates
-Side loaded cutting

Test Results
The first test cuts were made at the Mazak Technology Center in Gardena, California. The goal of this first test cut was to verify that the original toolpath motion worked properly with the proper feeds/speeds. The results showed that both the OD groove/contour and face groove were machined with the “alternate” parameter turned on when cutting the face groove. The OD cutting conditions and final results proved successful, and the surface finish was consistent with a high speed roughing cycle.

Equations of Business
In today’s manufacturing world a lot of money is spent on adopting and investing in new technologies. However, there still remains a decision on when to adopt those new technologies versus continuing to use traditional methods. Adopting ESPRIT’s ProfitTurning™ can increase cutting speeds and decrease cutting time, but what is the investment cost to use this new technology compared to traditional methods? We used a Sandvik Turning calculator to show users just that by setting priorities when choosing a cutting strategy.
We calculated the cost per part using ESPRIT ProfitTurning™ and round inserts (Table 1), and in parallel used a similar cost evaluation using the traditional ZigZag cutting method (Table 2) with the same round tool insert and holder. The final results showed that the unit price to cut one part using ProfitTurning™ costs 60% less than the unit price of using the traditional ZigZag cutting method.

Conclusion
The ProfitTurning™ cutting strategy in ESPRIT features a toolpath that maintains consistent chip load and cutting forces, allowing cutting speeds to be significantly increased. By employing controlled engagement techniques using round inserts, the ProfitTurning™ toolpath also reduces vibration and residual stresses, making it particularly useful for thin walls or hard materials, such as superalloys. This innovative cutting strategy results in significantly reduced machine cycle time and cost per part, allowing for increased productivity and making it the ultimate turning solution.

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