Viewpoints: Getting Capability Right
Less maintenance, less floor space, and lower per-piece cost are goals for every production plant in the world. In the critically important automotive field, shorter innovation cycles, more models, faster model changes, and fluctuation in demand require a machining system for prismatic parts that can adapt quickly for today and tomorrow, while reducing the cost of piece parts as much as possible.
The way to accomplish this is to minimize operating and investment cost while maximizing production volumes, based on machining system productivity and availability. It's not simply a matter of producing more of one component, but more of several different parts that together make up a large volume of parts.
Machine companies have addressed this need with higher machine speeds and feeds. But those approaches may not actually result in faster part processing. The impressive speeds often are not achieved in practical application, and can actually reduce the life expectancy of machine components and raise the cost of operation and ownership.
For example, high speeds and feeds do affect machine performance, but not much. In one study I'm familiar with, an improvement in the axis dynamics, of jerk and rapid traverse, only gets the user another 1–2% of productivity. But an improvement in tool availability actually results in a 6% increase in productivity. Taking potentially higher maintenance costs for high-tech components into account, the pure dynamic advantage can also be a disadvantage.
In fact, the goal for a machining system is not top performance but continuous performance.
So, what is the best answer to optimum Total Cost of Ownership when it comes to volume machining systems? At our company, we've answered this question by developing the ModuleLine System. It's capable of a 60 m/min rapid, and acceleration in all axes of 8 m/sec2, but the focus is on low maintenance or maintenance-free components as much as it is on optimization of movement. For example, we use linear drives with wireless connections to provide a low-cost, low-maintenance alternative to rack-and-pinion drives with trailing cables. This change generates savings when you consider that a transfer unit in a three-shift operation can travel up to 6000 miles (9654 km) annually. Maintenance on cables, cable tracks, and drive units used in more conventional systems can cause total system downtime.
Flexibility is something machine builders like to talk about, but the user really does not see the flexibility of a system initially, and therefore may not see the benefit of a possibly higher price for that built-in flexibility. That's why a modular, unitized system is an effective approach. It achieves a low basic initial price with the use of standardized components, but when the system has to be expanded or changed, the advantages are huge, because it can be done quickly and cost-effectively.
Starting with machining centers (process modules), designed for dry or wet machining, a modular system typically has a number of pieces that can be added to reduce processing time, such as a swiveling table for five-sided work, a workpiece changer to connect to the part-handling automation, and a tool magazine located near or over the spindle, reducing toolchange times.
Simplifying automation and reducing the distance parts have to travel is another way to improve a system. But this approach still enables the user to have only one automation system for an entire installation.
With no rigid connections between machining modules, there is only a flexible supply and distribution system. It can be opened for extensions anytime by adding onto the linear transfer unit and adding a machining unit. And in case volumes drop, machining units can be taken out without disturbing material flow. If necessary, changes to the system layout can be carried out by drag and drop from a modular building system.
So there you have it. A modular, unitized system can give manufacturers productivity and flexibility for high-variety series components, from now into the future. Applying technology to achieve continuous production capability, in spite of volume and part-design changes, will permit a manufacturer to manage and reduce part cost—from the original investment, through operating costs, across the now-longer life cycle of the installation.
This article was first published in the October 2007 edition of Manufacturing Engineering magazine.