Last 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.
It increased to one metre the maximum diameter of component that can be accommodated on a lathe at the subcontractor’s factory in Aston, Birmingham. The previous maximum was 400 mm, although 630 mm 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 at Columbia, Colin Peach, turned to workholding specialists, 1st Machine Tool Accessories.
The supplier’s applications engineers proposed a solution by US-based Abbott Manufacturing, a 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 clamping on the inside or the outside.
The US-manufactured workholding system is able to maintain the required circularity and dimensional accuracy of the components, while the cost was well under half that of a multi-jaw compensating chuck offered by another supplier.
Catherine Kelly, General Manager of 1st MTA, commented, “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 on to the plate for the next production run in less than half an hour, according to Mr Peach, enabling high productivity to be maintained around the clock.
Engine ring diameters currently being machined at Aston range from 650 to 720 mm and measure typically 15 mm from outside diameter to bore, with a 5.5 mm 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 approximately two hours. 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.
Mr Peach concluded, “By clamping the rings at 125 psi using the Abbott master plate system from 1st MTA, we are easily able to hold the required dimensional tolerance of ± 0.1 mm and 0.15 mm roundness, which would be impossible using the VTL’s standard 3-jaw chuck.”
The range of Abbott Master Plates are available from 1st MTA. If you have any questions or queries about the products mentioned in this article, please don’t hesitate to contact us on 0800 783 0510 or enquiries@1mta.com.
