Sheffield-based Tecomet (formerly Symmetry Medical) has installed three Hermle trunnion-type five-axis machining centres for manufacturing stainless-steel medical components.

These machines were supplied between March and July 2016 by Gosport- based Geo Kingsbury Ltd (www.geokingsbury.com) — the sole UK agent for the German manufacturer.

Full production started in early October 2016 and is ramping up to round-the-clock high-volume manufacture.

In view of Tecomet’s vast product range, two of the Hermle C 400 machining centres have 87-tool magazines, allowing all component variants to be produced with a single set of cutters, thereby minimising down-time. The other machine has a standard 38-tool magazine and is reserved for larger batch quantities.

Components are manufactured from two grades of 316 stainless-steel forgings produced on the Sheffield site. These generally undergo two operations, although some require only one.

Programs are long, as the components have complex shapes to match the human anatomy, and some cycles run to 300,000 lines of code.

Machining operations are mainly three-axis types, with the other two axes positioned and clamped; some components require 4+1-axis cycles. Operations generally involve taper milling, slotting, drilling and tapping and take
between 25 and 90min.

Tecomet production engineer Steve Jackson said: “Hermle C 400 machines were chosen for this latest production cell because we know their pedigree. We installed a pair of smaller C 22 U five-axis machines a couple of years ago to produce medical instruments, and their installation has proved very successful.”

The Hermle C 400 is one of a new range of machines that offer the same high quality as other Hermle five-axis models built by the German manufacturer; however, they are offered with fewer options to lower their price.

This means that the C 400 with its 850 x 700 x 500mm work envelope costs about the same as the ‘fully featured’ C 22 U (450 x 600 x 330mm work envelope) while offering over three-times the working volume.

Mr Jackson said that any restriction in the specification of the latest three Hermle machines does not affect production. Through-spindle coolant delivery (essential for machining stainless steel) is provided, as are tool measuring and tool-breakage monitoring.

Minimal idle times are ensured by an acceleration rate of 6m/sec₂ to a rapid-traverse rate of 35m/min in all linear axes. The trunnion tilt rate is 25rev/min (through +91 to -139deg), while C-axis positioning is at 35rev/min. Control is via a Heidenhain iTNC 530.

Having the larger machining capacity for about the same price is useful to Tecomet; it means that more components can be fixtured at a time, leading to fewer tool changes per part and hence more-efficient production.

The bigger size may also prove useful for the growing amount of non-medical work that the company undertakes; this includes the forging and casting of turbine blades, along with the machining of actuators and gimbals.

Furthermore, the ability of the Hermle C 400s to undertake full five-axis milling has future-proofed Tecomet’s investment in them, providing maximum flexibility for the machines to be used for other work.