Performing to extremes

As a manufacturer of high value, small batch instrumentation components for use in extreme aero-engine environments, Derby-based Rotadata necessarily follows a strict ‘right first time' policy, aided by investment in a new Mini Mill vertical machining centre from XYZ.
Rotadata designs, develops and manufactures a variety of measurement solutions especially for aero-engine customers around the world to record and measure pressure, temperature, strain, flow and vibration in the fan, combustor, turbine and compressor sections of gas turbine development rigs and engines, and in compressors and automobile engines. It's products need to perform at temperatures between -150ºC and in excess of 1000ºC at rotational speeds up to 130,000rpm and, with five-off is regarded as a big batch, there is little margin for error. Special project manager, Colin Dale expands: “Every gas turbine engine is different, even down to a slight difference in the angle at which incoming air hits the edge of the fan blade, and this influences our design response, the way in which we machine components and our choice of machine tool.” As such, the decision to invest in a 15hp/8000rpm XYZ Mini Mill 560 vertical machining centre (VMC) was led by versatility. “We need a machine tool that can be reconfigured in minutes rather than hours as machining times tend to be short and lead times are crucial. To further aid this requirement, the machine has also been fitted with a large vice that spans virtually the entire length of the 610mm x 370mm table and eliminates the need for dedicated fixturing. However, if necessary, fixtures can be designed and made in-house.” Small quick cuts

Although the machine has axes travels of 560mm, 400mm and 500mm respectively, Rotadata has successfully machined components measuring 414mm diameter and 300mm high on the Mini Mill 560. Solid Meehanite ribbed casting also ensures that the 3,100kg machine provides maximum rigidity when cutting tough aerospace alloys. “Much of the work we do relates to high temperature alloys and challenging new materials that may not be seen in a general production environment for several years. Rigidity is more relevant than spindle power, as our preferred high speed method is to take smaller cuts quickly, with the volumetric removal rate rather than the depth of cut being the key criteria. However, we have achieved feed rates up to 8m/min on stainless steels and titanium,” adds Dale. The Siemens 810D ShopMill conversational CNC fitted to the compact VMC provides smooth axes movements suited to Rotadata's preferred high speed machining techniques, although Dale also singles out the tool management aspect of the control for particular mention: “The Siemens system doesn't use tool numbers as such. Instead it identifies individual tools using up to 18 characters. It doesn't matter which magazine pocket a tool is loaded into as the control recognises what the tool is and where it is located in the tool changer. All our machining programs call for the tool rather than a specific tool location, which eliminates the risk of the wrong tool being selected and saves time when loading any of the 120 tools that can be stored in the control's memory.” Most of the cutting tools in use at Rotadata are solid carbide cutters are provided by MA Ford Europe, in which each flute is ground on a slightly different helix angle. This eliminates resonance and ‘chatter' and contributes to extended tool life. However, within the ‘tool wear' page of the Siemens control, a limit can be placed on how long a tool is in use before it is replaced by a sister tool. If there is no alternative available, the machine will stop and sound an alarm. While simple, this is an important feature, as expensive aerospace materials can be on lead times of more than a year and any mishap resulting from worn tooling could prove extremely costly. www.rotadata.com
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