The Continuous Flow Continuum

Workpieces that require operations that can be performed on a turning center and a machining center can often be produced more efficiently on a multi-process machine tool that combines machining center and turning center capabilities. By completing all of these operations in one setup, the time and labor associated with handling, waiting and change-over are greatly reduced or eliminated.

Columns From: 1/1/2006 Modern Machine Shop, ,

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Mark Albert

Mark has been writing his Mark: My Word column every month since January, 1981.

Workpieces that require operations that can be performed on a turning center and a machining center can often be produced more efficiently on a multi-process machine tool that combines machining center and turning center capabilities. By completing all of these operations in one setup, the time and labor associated with handling, waiting and change-over are greatly reduced or eliminated. Inaccuracies that can occur when a workpiece is refixtured are also minimized. These are some of the key advantages of the done-in-one concept.

Passing pieces from one process step to the next without batching partly finished workpieces in between is also the idea behind continuous flow production, one of the most important goals in lean manufacturing. Making complete parts on a multi-process machine is one way to achieve continuous flow. For this reason, shops and plants may need to consider multi-process machines as a step toward waste-free production.

However, there are many ways to achieve a continuous flow of parts requiring more than one machining operation as process steps. A cell that allows an operator to transfer parts directly from a lathe to a mill can create continuous flow. Adding robotic part transfer, pallet changers, pallet shuttles and other automation can further enhance a lean cell.

The point is, multi-process machines can be seen as part of a “continuous flow continuum” in terms of the technology choices for implementing lean manufacturing. Looking at multi-process machines in the context of lean is important because the methodology of lean manufacturing forces planners to look at the entire value stream in a coherent, disciplined effort to find and eliminate activities that do not add value.

Analyzing the value stream should help planners see where multi-process machines fit in. Hitting a certain takt time (how often a part must be produced to meet customer requirements) may not be possible without the efficiency of multi-processing. Of course, analysis may show that a multi-process machine is not appropriate if, let’s say, the milling and turning operations are difficult to balance across a family of parts. A machining cell in which extra lathes or mills can be pulled in or out might be the better choice.

Thinking of multi-process machines as part of a continuous flow continuum is a guard against the notion that done-in-one is a cure-all or is right for every application. Likewise, this thinking is a strong reminder that these machines have tremendous potential to contribute to lean manufacturing.

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