Mollart wins aerospace turbine shaft contract

The win involves the machining of key operations on a family of turbine shafts machined from a forged blanks weighing up to 800 kg and up to 2,200 in length. Managing director Guy Mollart (pictured) pays tribute to the company's workforce for their efforts in supporting the securing of the order: "We had to produce sample parts for final approval, which meant we needed total support from our workforce involved in the project. Over the Christmas period, they showed their dedication by giving up parts of their holiday to come in and ensure the customer would take delivery directly after the break." Operations director Mike Pragnell explains how the contract was secured, which involves working closely with the forging supplier. "It was our ability to combine three essential elements of our business in deep hole drilling and the associated tooling development, expertise for special bore production and our large capacity turning and boring capability. However, most influential in the customer's mind, was the security of our track record with other blue-chip customers in machining very difficult alloy materials that are used in ultra-high functionality and demanding applications." An initial proving trial was performed in September that involved machining the first of the alloy steel free-issue forged components of some 2,200 mm overall length and weighing up to 800 kg, which were supplied in the rough turned and heat-treated condition. Following the successful machining operations, it took some three months to carry out evaluation, which included a strict, full quality audit of the Mollart business. This was followed with sample part production before Christmas, leading to the issue of the first production batches involving two parts per week. Prior to machining on Mollart's Weiler E90 CNC lathes with 6 m bed length, each high cost forging has to be fully qualified by Mollart engineers to determine there is no distortion from heat treatment so that it will fully clean up when turned and bored. The forged blank is basically a tube with a trumpet-shaped end having a 50 mm thick flange of 500 mm dia at the mouth of the cone shape, which merges into the main body of the turbine shaft that has to be profiled turned to 160 mm dia. A main bore is some 84 mm dia by 1,800 mm deep from the flanged end, and a further bore is produced 44 mm dia to a total depth of 1,900 mm. The part is then relocated and a bore of 70 mm dia is counterbored to 96 mm dia. There are also a series of steps, cones, and internal/external tapers at the conical end of the shaft that have to be machined. Currently, overall production time is running at 40 hours per shaft. As part of the contract, Mollart's engineering team developed a special ejector drill head, cartridge and insert, design to produce the main 84 mm bore, as well as the special conical forms required at the bottom of the bore.