Faster cycle times produce cost savings: multiple, interconnecting machining centers can bring results.

For years, transfer lines and special part-specific machine concepts have been the process capabilities of choice and the low-cost solutions for high-volume machining. Today, manufacturers must contend with the large number of model offerings and volume variability, which forces a change in this philosophy.

Machining centers have probably become about as productive as they ever will be for high-volume, variable parts production.

The introduction of machining centers with one or two spindles, with manufacturing cycle times of less than one minute per part, approaches the effective boundaries of machining centers. This is especially true for machining aluminum parts, where the productive time of machining centers is less than 30 percent of the total cycle time. Tool changes and pallet changes account for about 70 percent of the total cycle time.

To reduce time lost due to tool-change, multiple parts are machined in the same pallet. The compact orientation of multiple workpieces in a pallet affects the spindle accessibility to the part, thus requiring multiple clamping of the part. This adversely affects the process capability and the quality of the part. In addition, machining compound angles also often requires multiple clampings of the same part to access all of these features.

An alternative to machining palletized parts requiring multiple clampings is to substitute multiple, interconnected machining centers to achieve production rates similar to that of dedicated machine tools. While conversion of this type system to another part is much easier than it is for a dedicated machine, users still are confronted with some limitations:

* Most segmented machining processes are configured in series so that when one machine goes down, the entire process is disabled.

* Investment costs are higher when compared to that of a dedicated line. For example, many parts on passenger vehicles are being developed from aluminum rather than steel or cast iron. Features with compound angles must be machined, which often requires multiple clampings. More clampings influence process capability and increase machining costs.

Shorter, more productive cycle times, longer tool life, and elimination of coolant costs/maintenance can reduce per-piece production costs for the manufacturer. The flexibility of the system ensures that it is readily adaptable to different model parts, again saving costs for the customer.