Economical 5-axis cell for producing medical components

Sheffield-based Tecomet, formerly Symmetry Medical, has installed three Hermle trunnion-type 5-axis machining centres for manufacturing stainless steel medical components. The machines were supplied between March and July 2016 by sole UK agent, Kingsbury. Full production started in early October 2016 and will quickly ramp up to around-the-clock, high volume manufacture.

In view of the vast product range, two of the Hermle C 400 machining centres have 87-tool magazines, allowing all component variants to be produced without changing cutters, so minimising downtime. The other machine has a standard, 38-tool magazine and is reserved for larger batch quantities.

Components are produced from two grades of 316 stainless steel forgings produced on the Sheffield site. Generally, they 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 3-axis with the other two positioned and clamped, while some components require 4+1-axis cycles. They involve taper milling, slotting, drilling and tapping and take between 25 and 90 minutes.

Tecomet production engineer Steve Jackson said, “Hermle C 400 machines were chosen for this latest production cell because we know how good they are.

“We installed a pair of smaller C 22 U 5-axis machines a couple of years ago to produce medical instruments and the installation has proved very successful.

“We have also been impressed with the service from the UK agent, Kingsbury. The support is second to none. If we have a problem on a machine or need help with an application, they are on it like a flash.”

The Hermle C 400 is one of a new line of machines that are of equivalent high quality to other 5-axis models built by the German manufacturer but are offered with fewer options. This lowers the price, so the 850 x 700 x 500 mm capacity machine costs approximately the same as the 450 x 600 x 330 mm capacity, fully-featured C 22 U but offers well 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 well as tool measuring and breakage monitoring. Minimal idle times result from 6 m/s2 acceleration to 35 m/min rapids in all linear axes. Trunnion swivel is 25 rpm through +91 / -139 degrees, while C-axis positioning is at 35 rpm. Control is provided by 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 alternative work the subcontractor undertakes. The Sheffield firm already forges and casts turbine blades and machines actuators and gimbals.

Furthermore, the ability of the Hermle C 400s to perform full 5-axis milling has future-proofed the investment, providing maximum flexibility for the machines to be deployed onto other work. To find out more about the benefits of 5-axis milling, see our complete guide to 5-axis CNC Machining.

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