5-Axis Machining Advantages
- Virtually perfect mold surfaces bypass several steps that add to mold production lead times
- Roughing, semi-finishing and finishing operations can be performed on the mold in the hardened state
- Time on the spotting press to verify core/cavity alignment is reduced to hours instead of days
- Molds produced with zero stock machining run longer and more efficiently
A Way of Life
Eifel has built an arsenal of top of the line 5-Axis CNC machining centers that include a DMG MORI DMU105, a Hermle C40U, a Hermle C30U and a DMG MORI DMU100P. Successful zero stock machining relies on a strategic synergy arising from a coordinated implementation of advances in four broad areas of manufacturing technology—super-rigid, super-accurate machine tools for high speed machining; workpiece fixturing that is flexible and highly repeatable; rigid holders for cutting tools with exceptionally accurate radius at the tip; and CAM software capable of producing tool paths for high-accuracy machining in the lights-out mode.
At Eifel, zero stock machining became “a way of life” around 2005. A pair of Hermle 5-Axis VMCs represents Eifel’s main resources for zero stock machining. A Hermle model C40 was installed in 2008; a slightly smaller model C30 was installed in 2011. The new machine has high-pressure, through-the-spindle coolant delivery, a feature that has proven valuable for milling and drilling the latest generation of coated carbide cutters with coolant holes. Otherwise, the machines are similar. Both feature a rotary table in a trunnion supported at both ends for the fourth and fifth axes. "We chose these machines for their extreme accuracy and rigidity,” Mr. Hecker says. The trunnion-style configuration is especially important at Eifel because 3+2 machining is the shop’s preferred mode. In this mode, the rotary axes are used to orient the work piece so that cutting can be performed in three axes (X, Y and Z).
According to Mr. Hecker, 3+2 machining is ideal for molds with small, deep pockets and numerous undercuts. One of the main benefits is being able to reach work piece features with a shorter, more rigid cutting tool assembly. A shorter, stiffer tool enhances high speed machining (HSM) techniques that are at the heart of the zero-stock machining concept. HSM involves taking light cuts at high feed rates with closely spaced stepovers. “A stiff, short tool will withstand higher feed rates without deflection so we can achieve the optimum chip load at the optimum depth of cut—even for cutters under 1 mm in diameter,” Mr. Hecker notes. This also helps the shop get the full productivity from the 18,000RPM spindles on these machines.
Eifel’s reliance on 3+2 machining has implications for CAM programming, too. For all zero-stock machining, the shop uses PowerMill from Autodesk. According to Gary Schulz, the shop’s manufacturing manager, this software has features of particular value for this machining strategy. One, he says, is the variety of options for approaching the work piece surface with the cutting tool. “When reaching into tight spaces at the bottom of a deep pocket, your approach angle may be limited, so it is best to have several choices. It’s all about protecting the cutting edge of the tool as it contacts the workpiece,” Mr. Schulz explains.
The other software capability that shines is visualizing the stock model. PowerMill displays material left behind by the operations performed with the previous cutter. This allows the programmer to choose “rest machining” options for the next smaller cutter. “This feature helps us be sure that this cutter will not encounter unexpected material,” Mr. Schulz says.
Finally, advanced collision detection provides another layer of protection in the 3+2 operations. Mr. Schulz says that it is easy to think only of the work piece surface and the tool tip when planning for 3+2, thereby neglecting to consider nearby geometry and the shape of the entire tool assembly. Collision detection, he explains, catches the oversights that might otherwise lead to broken tools or spindle nose crashes. To say that zero-stock machining is a “lifestyle” for a mold shop is no exaggeration. Behind this lifestyle is a set of “philosophical principles” that Mr. Hecker believes are essential. These principles fall into three categories: People, Process and Technology.
Most importantly, this approach creates a shop environment in which a capable workforce can sense its empowerment and vitality. “This is the kind of shop lifestyle that is attracting a new generation of young talent to mold manufacturers,” Mr. Hecker says. Ultimately, that is the renewal on which every future depends.