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When new technology emerges in today’s rapidly changing market, it is vitally important to look past the buzzwords and focus on the real life results it can have on your bottom line. Driven at the center of gravity technology is one such technology that moldmakers should look into before purchasing their next machine tool.

By reducing vibration, driven at the center of gravity provides much higher quality of surface finishes. Photos courtesy of Mori Seiki.

Underlying Technology
Many moldmakers have likely heard of driven at the center of gravity technology and understand that it enables superior surface finish textures and extended tool life, but to fully comprehend the benefits, one must understand the underlying technology.

An object’s center of gravity can be defined as the average center of its mass. This also is the object’s balance point. During movement, application of force at a point other than the center of gravity will cause strain and a tendency to rotate. This basic principle is very simple to demonstrate and understand. When a pencil is placed on a level surface and pushed at its center, it will roll forward. On the other hand, if pushed at just one end, the pencil will tend to rotate. While the forces opposing the pencil’s movement are uniformly distributed, the force causing movement is being applied unevenly.

Tool life is dramatically increased through driven at the center of gravity technology.

While a very basic idea at its core, the center of gravity is typically ignored in traditional machine design. A machining center axis is typically defined by a pair of linear guides and driving mechanism, usually a ballscrew and servo motor combination. With a proper understanding of center of gravity, common sense would dictate placing the ballscrew in the center of the axis. This would balance the driving force and avoid twisting the axis during movement. Unfortunately, this ideal scenario is often impossible to achieve within a machine tool.

Obviously, a single ballscrew drive cannot be placed in the center of an axis when another machine component must occupy that space. In many machine designs, a fourth axis table or tool spindle is located in the center of an axis. Traditionally, machine tool builders have compromised and mounted the ballscrew on the left or right side of the center of gravity, creating an unbalanced loading of the driven components. While this was not a significant detractor to overall quality levels in the past, it has become an Achilles heel to the potential for high performance afforded by other breakthroughs in machine design.

Machines with driven at the center of gravity technology use twin ballscrews to move components along their simulated center of gravity.

All materials, even metals, possess a degree of elasticity, causing them to deflect when subjected to stress. In the context of machine tool design, the greater the force generated by an imbalanced drive, the greater the deflection. This causes a dramatic effect in regards to vibration of the tool tip, as the metal between the driving point and the tool tip deflects, causing both inaccuracy and reduced quality of finish.

Machine Tool Design
Driven at the center of gravity technology works to reduce vibration and its negative effects by driving movement through a simulated center of gravity. By implementing twin ballscrews equidistant from the actual center of gravity, driven at the center of gravity effectively eliminates deflection as the machine moves along its axes. In terms of the previously mentioned analogy, it would be the equivalent of applying equal pushing force at both ends of the pencil, causing it to move uniformly.

Advantages
The application of driven at the center of gravity technology provides multiple benefits to today’s moldmaker. Efficiency is improved through increased speed, as machine components can accelerate much faster without imparting vibration to the tool tip.

Additionally, the much superior surface textures achieved through driven at the center of gravity technology result in dramatic reduction, if not outright elimination, of hand finishing/polishing operations. This results in significant savings, both in time and cost. In fact, the elimination of this bench work can be the single most critical factor in keeping mold work in the U.S. Obviously, components that require many hours of hand polishing are very sensitive to the cost of labor. When driven at the center of gravity eliminates this labor-intensive process, domestic moldmakers no longer suffer a disadvantage relative to those regions with lower labor costs.

Machines with driven at the center of gravity technology use twin ballscrews to move components along their simulated center of gravity.

Reducing vibration also improves tool life. This provides significant value when cutting large cavities in which it is difficult to complete the cut with a single tool. When a tool requires replacement during a machining process, the component being produced often exhibits blemishes that must later be removed. Thus, enabling the cutting of large cavities with a single tool serves to further reduce or eliminate polishing time.

Benefiting from What Lies Beneath

When new technology becomes available, manufacturers need to look past the buzzwords to find where the true benefits lie. With driven at the center of gravity technology, a revolutionary new approach to machine design has provided dramatic reductions in machine vibration. Through driven at the center of gravity, today’s moldmaker stands to achieve increased quality while saving the time and money required to be competitive in a global market.