TU Darmstadt Cellular machining offers flexibility, low cost-per-part

Editor: Barbara Schulz

An independent study at the Technische Universität (TU) Darmstadt in Germany shows that customers who invest in multiple, affordable CNC machine tools instead of one or two high-end, special purpose machines benefit in many respects. By Stephan Möller, MBMC

The TU Darmstadt report, entitled ‘Cellular Manufacturing to enable Lean Machining’, was prepared by Stefan Seifermann (front left), Jörg Böllhoff (third right), Eberhard Abele and Joachim Metternich (not pictured) as well as technician Christoph Schwarz (2nd row right).
The TU Darmstadt report, entitled ‘Cellular Manufacturing to enable Lean Machining’, was prepared by Stefan Seifermann (front left), Jörg Böllhoff (third right), Eberhard Abele and Joachim Metternich (not pictured) as well as technician Christoph Schwarz (2nd row right).
(Source: Scheibner/PTW)

A recent report from the Technische Universität (TU) Darmstadt in Germany demonstrates that the use of several, modestly priced CNC machine tools arranged in a cellular configuration can offer significant benefits over the use of more expensive special-purpose machines configured for “done-in-one” operations. The cell-configuration studied at the university features two Haas Super Mini Mill 2 CNC machining centres and a Haas SL-10 CNC lathe.

Transferring the principles of lean to machining operations

The idea for the research was based on a perceived absence of the principles of lean manufacturing applied in widespread machining operations in manufacturing companies of all sizes. Although deployed widely in assembly and process engineering environments (typically in the volume automobile manufacturing sector), the principles of flow as a central element of lean manufacturing have not often been transferred successfully to machining operations, and are rarely to be found at all in Europe.

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In essence, cellular manufacturing is the grouping of heterogeneous equipment (in this case, CNC machine tools) to manufacture a family or group of similar parts. Typically, the concept involves the arrangement of machines in a U-shape to aid flow and balance work-in-progress with “takt” time (the average unit production time needed to meet customer demand).

To demonstrate the potential advantages, a cellular reference production line has been established at the PTW’s Process Learning Factory (CiP). The “done-in-one” line features two, high-specification machine tools: a 4-axis CNC horizontal machining centre with tombstone fixture, and a CNC multi-axis automatic turning centre. The competing line, a machining cell, features two Haas Super Mini Mill 2 3-axis machining centres and a Haas SL-10 2-axis CNC lathe, as well as two, general purpose CNC machining centres and a CNC lathe supplied by another machine tool manufacturer. The report notes that the investment for the two machines in the “done-in-one” line totaled €780,000, while that for the six CNC machine tools in the cell configuration was just €340,000.

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