Rough and tough - high-efficiency roughing versus high-speed roughing

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Achieving a high metal removal rate (MRR) is the goal, and it is how we reduce cycle time. Higher axial-cut depths require lower radial-cut depths to allow for reliable chip evacuation. By reducing the radial depth of cut, one can increase the tool flute count and increase the metal removal rate. It also enables use of chip thinning calculations to increase the cutter feed rate to maintain chip thickness. A thicker chip will also pull more heat away from the tool (see Figure 3).

Setting feed rates for maximum material removal

Without spikes in material removal rates, setting feed rates for maximum material removal becomes much easier. A shop can use data from the tool supplier or simply start milling and increase feed rates slowly to a level with which operators are comfortable. It is recommended to do this after making the first pass around a block, in case the stock size ends up being a little different than what was programmed.

When machining moulds with complex 3D shapes, using a large depth of cut will leave larger “stair steps” in the roughed model. In such situations, machinists should take advantage of step-up functionality so that the roughed stock has a consistent stock allowance. Adaptive clearing uses a strategy of constant cuts with a repositioning move. The inherent benefit is that a climb cutting direction is maintained, whereas in traditional roughing operations there may be periods of conventional milling cuts. Because of this, there may be more retracts than some people are accustomed to when the reposition is over a greater distance. Generally, rapid retracts are fastest. However, stay-down parameters also can be modified. With these parameters, the tool will not retract to the top of the stock but rather stay down as it repositions. In many cases, it is desirable for the tool to lift slightly to avoid dragging the floor during repositioning moves, which could generate premature tool wear.

Increasing metal removal rates, decreasing cycle times and improving cutting consistency is easier with adaptive clearing strategies. These strategies are simple to implement and test, as they do not require special tooling or a special mill, working as well on entry-level mills as on the fastest high-performance mills. They also are available for a wide range of CAD systems. ETMM

Reprinted with permission from MoldMaking Technology, Gardner Business Media, moldmakingtechnology.com

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