Five-axis VMC cuts machining cycles by up to 20%

A 5-axis CNC vertical machining centre, with a trunnion-mounted table, has reduced machining cycles by up to 20% and halved changeover times for milling toolholder bodies.

Swedish tooling manufacturer, Seco, which has factories in 13 countries, has designated its UK subsidiary in Alcester, Warwickshire, as a European centre for the manufacture of semi-standard toolholders in its MDT (multi-directional turning) range.

To mill the toolholder bodies, a Hermle 5-axis C 30 U vertical machining centre with bespoke fixturing has been supplied by UK agent, Geo Kingsbury Machine Tools, following machining trials at its Gosport technical centre.

Until recently, Seco Tools (UK) specialised in producing custom tooling and grinding custom insert profiles in batches of typically 1- to 5-off for the UK market.

This is essentially a job-shop activity which is carried out cost-effectively on standard vertical machining centres by interpolating the three linear axes, while the rotary positions of a 2-axis NC table are moved to various predetermined angles and clamped.

However, on an MDT toolholder there are features that require simultaneous 4-axis and in some instances 5-axis machining, for which the Hermle with its trunnion-mounted rotary table is ideal.

Additionally, the higher throughput of semi-standard and standard toolholders in batches of up to 200-off dictated the installation of a production centre with higher speeds and feeds as well as quick changeover.

The latter was particularly important due to the hundreds of MDT tooling variants in four product families, for which a suite of nine quick-change Erowa fixtures was supplied.

Commented Roy Organ, custom tools specialist at Alcester, "Hermle machines are becoming the standard 5-axis production centre within the Seco Group, as they are used at our factories in Sweden, Germany, the USA and shortly at Seco Pune India, where three machines are to be installed.

They have excellent accuracy and repeatability, partly because the fourth and fifth axes are integral, not add-ons, and also because the mineral-cast bed minimises vibration." He added: "Access for changing tools, fixtures and components is good, and there are the added advantages of interchangeability of machine programs between our divisions, and commonality of post-processor software." Custom tools supervisor, Andy Horsnall, continued, "We find that the 18,000 rev/min spindle and 45m/min linear rapids (rapid traverses) of the Hermle translate into cycle time reductions of between 10 and 20% compared with our standard VMCs.

Where we are able to use 4- and 5-axis interpolation to good effect for what would otherwise be carried out using three axes, the savings can be greater still." Even more dramatic has been a halving of changeover time from one job to another, thanks to the pneumatic fixtures supplied by Geo Kingsbury.

Other options included as part of the turnkey package were 4-arc-second accuracy for both of the rotary axes, tool length measuring with offsets sent automatically to the Heidenhain control, tool breakage detection and high-pressure, through-tool coolant.

To machine an MDT toolholder, a pre-milled steel blank is fixtured and the appropriate program for milling of the head shape and insert pocket is downloaded by DNC to the Hermle.

The pocket requires serrations to be milled on the bottom to mesh with a similar feature on the insert, this being a particular characteristic of the MDT design.

Certain models require a sweep to be machined below the pocket to simulate the radius of a groove, for example, in which case 4-axis interpolation is needed; and if the sweep is chamfered, all five axes have to be employed simultaneously.

Installation of the Hermle machine has resulted in a significant increase in the production of semi-standard products at Alcester for the Seco Group, not only of MDT products for which a 15-day turnaround is offered, but also of thread mills for the USA and gap blades for European markets.

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