In April 2013, precision engineering company Columbia Precision installed its first vertical turning lathe (VTL) — a Mazak Megaturn Nexus 900M — as part of a £2 million investment in new plant and software.
This machine increased to 1m the maximum diameter of component that can be accommodated on a lathe at the sub-contractor’s factory in Aston, Birmingham. The previous maximum was 400mm, although 630mm can be turned on the table of a Matsuura MAM72 six-pallet machining centre.
The arrival of the VTL allowed Columbia to take on extra work turning larger aero-engine rings up to the machine’s full capacity. However, its three-jaw chuck was unable to hold the thin-wall components for machining without introducing distortion, out-of-roundness and eccentricity.
To address the problem, the engineer in charge of the machine — Colin Peach — turned to Salisbury-based work-holding specialist 1st Machine Tool Access-ories (
www.1mta.com).
The latter’s applications engineers proposed an Abbott master plate, pre-drilled and keyed to accommodate three standard, curved segments that spread the clamping pressure evenly around the circumference of the rings, either by holding on the inside or the outside.
This US-made work-holding system can maintain the required circularity and dimensional accuracy of the components, and the cost was well under half that of a multi-jaw compensating chuck offered by another supplier.
Catherine Kelly, general manager of 1st MTA, said: “The idea behind the master plate system, which can be machined to fit over any lathe chuck, is that it becomes a universal fixture that increases the machine’s holding capacity, while still allowing smaller components to be secured.”
Different sets of three segments can be machined to accommodate a variety of component sizes and types; nine sets of segments are currently in use at Columbia. A set can be removed and three more segments bolted onto the plate for the next production run in less than 30min, according to Mr Peach, allowing high productivity to be maintained ‘round the clock’.
Engine rings currently being machined by Columbia range in diameter from 650 to 720mm and typically have a 15mm wall thickness; they also feature a 5.5mm-wide external groove. The rings are produced mainly from cast or forged Jethete — an aircraft-grade stainless steel, but also from Inconel and Incoloy nickel-based alloys.
Five rings are machined from each blank in a cycle time of about 2hr. Each component is successively grooved and parted off on the Mazak after the full outside and inside diameters of the blank have been turned. The rings are then split to produce 10 half-sections for an aero-engine.
“By clamping the rings at 125psi using the Abbott master plate system from 1st MTA, we are easily able to hold the required dimensional tolerance of ±0.1mm and 0.15mm roundness, which would be impossible using the VTL’s standard three-jaw chuck,” concluded Mr Peach.