C G = Center of gravity Imbalance
C G = Center of gravity Imbalance
Rotation speed ω
Rotation speed ω
e
Fig. 2: Unbalanced
Fig. 3: Balanced
C ω = Center of gravity balance hole
Fig. 1
U = Res. Unbalance F = Res. Centrifugal force
BIG DAISHOWA tool holders are designed for high-speed machines. If a rotating tool holder (Fig. 1) is not rotationally symmetrical, imbalance occurs (Fig. 2). As a result, when the rotational speed is increased, non-symmetrical centrifugal forces occur at the tool holder and the cutting tool, causing vibration and premature spindle bearing failure. To correct for the imbalance, the tool is balanced by various methods such as drilling (Fig. 3), milling or grinding a flat, moving the center of mass as close as possible to the center of the axis of rotation.
standpoint and oftentimes isn’t even necessary. Today’s balancing machines are realistically only sensitive enough to pick up on a minimum of around 0.5 g-mm. In light of this issue, a new standard dubbed ISO 16084 has been developed. This standard considers (what seems like) every possible variable that influences balance in a tool holder/spindle system and was compiled by a joint team of industry experts and academics. Like ISO 1940-1, the operator will only have to define a few variables to physically describe the holder and speed/balance requirements while the machine does the calculation work and spits out results in the familiar terms of gram millimeter (g-mm). But unlike ISO 1940-1, this standard remains viable for any size tool holder or speed and only asks that you define whether or not you require standard balance quality or fine balance quality (rather than G6.3, G2.5, and so on). You will find that the new standard is more lenient for small tool holder/high speed situations, to the point where the permissible unbalance is achievable. This
leniency is even more apparent as you decrease speed and increase size. The reality is, we as an industry have been manufacturing all tool holders based on a strict standard that was never even designed with tool holders in mind. Since ISO 1940-1 is usually the stricter standard, you may be asking yourself: what’s wrong with the old standard if it’s worked so far, or what’s wrong with a tool holder being more balanced than it probably needs to be? A few things. Besides the fact that the math behind ISO 1940-1 breaks down and becomes impossible to achieve at smaller sizes and higher speeds, this also means that for years we have spent countless dollars and hours tricking ourselves into needlessly over- balancing tool holders in some cases. Clearly, the transition to ISO 16084 will not happen overnight and it may not directly affect everyone but be on the lookout for it as it slowly gains headway. Future impact The tendency in machining has been toward faster and faster, and there’s no reason to believe
that this trend will change anytime soon.
Developments in 3D printing technology, hybrid processes, and rapid digitalization and interconnectivity will greatly impact the manufacturing sector, no doubt. But that’s not to say that machining’s role will disappear, or even necessarily diminish. Rather, there will be a continued shift toward high-speed machining to better complement and keep up with these processes. If you can make it faster, you can make it for cheaper. And if you can make it for cheaper, you have an edge over your competition. Shops are in a constant race with each other, and those who don’t adapt easily to the constant advances in technology are left in the dust. With higher speeds becoming more of a necessity, proper understanding and implementation of these strategies is essential to survival.
CONTRIBUTOR Jack Kerlin is an Application Engineer at BIG DAISHOWA. jack.kerlin@us.bigdaishowa.com
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