Machine controls today allow for extensive dynamic tuning of machine performance. The most common values to look at when considering machine dynamics are speed and acceleration. Equally important as each of these is jerk.
Jerk describes how quickly the nominal acceleration is reached. The higher the jerk, the faster the rate of acceleration. A machine’s jerk is limited by its mechanical structure and stiffness. Higher jerk makes the movement of the axes much more aggressive. While this increases productivity, it also can introduce vibration that negatively affects surface finish or accuracy.
Achieving the best possible dynamic tuning of a machine is a matter of finding the optimal compromise between speed, accuracy and surface finish. Usually, these judgments are made by the operator. In a roughing operation, it would make sense to maximize speed and pay less attention to accuracy and surface finish. In semi-finishing and finishing operations, the opposite would hold true. The maximization of machine dynamics by application has traditionally relied heavily on the knowledge of the operator.
Today, many machine builders are beginning to offer software that simplifies the adjustment of machine dynamics. For instance, an Operator Support System has been developed2 whose software shows a triangle including speed, accuracy and surface finish. Users can easily adjust priorities and the software calculates optimal dynamic performance of the machine as dictated by a job’s specific requirements.
Software such as the aforementioned can provide tremendous benefit in achieving high surface finishes while still getting the maximum levels of productivity out of a machine. In best case scenarios, the software not only takes into account the machine itself, but also the weight of the workpiece and tooling, toolpaths and other variables specific to a part. This ensures the surface finish required by a mold, without an unnecessary compromise of productivity.
Already, machine builders have taken dramatic steps in developing software to help moldmakers optimize their machining processes. Further advancements will soon continue this development.
In the realm of minimizing vibration, current software exists mostly as a reactive tool. It provides tremendous value, but the machine operator must make judgments and set parameters based upon the feedback given by the software. The next evolutionary step in smart software will allow the machine to act much more proactively.
For instance, when vibration levels begin to increase, the machine will automatically vary spindle speeds and feedrates to bring them back down into an acceptable range. Software also will likely contain the ability to slightly alter machine programs, analyze the resulting vibration rates throughout a job and suggest an optimal solution.
While many mold manufacturers pay close attention to the benefits afforded by advancements in machine hardware, progress in the realm of software also provides significant opportunity for process improvement. By understanding and taking advantage of the latest software technologies, moldmakers will be able to get the most out of their machine investments, achieving the perfect balance of surface finish and productivity.