Titanium machining FMS solution proves its worth

The installation of an FMS providing machining of 18 variants of left and right hand titanium ribs, pylons and engine mounting brackets has demonstrated a reduction in costs of some 40%

The installation of a true flexible manufacturing system (FMS) in the UK providing on-demand machining of 18 variants of left and right hand titanium ribs, pylons and engine mounting brackets has demonstrated a reduction in costs of some 40% following installation and commissioning in 2008. It has taken just two years to create a payback on the original £5.3 million investment. Spindle up time has been maintained at between an impressive 97% and 98% and operational equipment effective (OEE) performance is running at 75%. The system runs through a 24 hour day, 6-day shift system which has two operators during the day and one overseer at night. The turnkey project installation performed by Mitsui Seiki of the four machine based system comprises two Toyoda-Mitsui Seiki HU80A 4-axis and two HU80A-5X, fully simultaneous 5-axis, trunnion style horizontal machining centres. The system operates in totally ‘lights-out' conditions to automatically produce on-demand a range of titanium components supplied in random order.  The four machines have an output equal to six previous twin-spindle 4-axis machines and the new installation enabled eight people to be redeployed. On current production schedules with the previous methods, 16 people would have been required. Central to the selection of the system and its installer, was the ability to meet strict production and quality demands and the contract was placed following extensive investigation, stringent testing and prove-out. Among the trials Mitsui Seiki had to full face mill a slot in a titanium billet using a 125mm cutter with 8mm depth-of-cut without coolant. Spindle deflection was also checked using a 40mm cutter to produce an 8mm full slot followed by two half cuts each side. As part of the procedure the system supplier also had to demonstrate its ability to fully integrate the turnkey system to produce the difficult to machine and highly demanding range of titanium components. The machines are integrated with a Fastems 24 pallet system and rail guide vehicle that utilises a common 800mm square pallet across both 4- and 5-axis machines. A Fastems central tool storage and gantry holding 1,024 tools is included supported by two, 6-axis Fanuc robots to manipulate up to 10 tools at a time both in and out of the machine's individual 60 tool magazines. Tool information is carried via chip data storage in each toolholder which is interfaced with Mitsui Seiki tool life control software and its cutting load monitoring. In order to maintain a consistent production environment, Renishaw NC-4 non-contact tool setting and tool breakage detection is incorporated. Spindle temperature monitoring and spindle vibration sensors are also important elements in the control of quality and machine performance. The system was installed around the pallet stacker system comprising a stacker crane with a two level rail-guided vehicle 24.8m long by 4.4m high. It has a lifting carriage for pallet handling that feeds one of the two loading stations with 90° pallet tilt and turn for single and multiple part loading according to the planned schedule of work.  The two pairs of 4- and 5-axis machines are also incorporated with the Fastems tool storage and gantry system. Here, the track-mounted Fanuc R2000i 6-axis robots were installed to transport up to 10 tools at a time between the toolstore and the on-board, 60 tool magazine that is fitted to each machine to account for the random feed of material and production scheduling of parts. Key to machining success is a bespoke coolant and five micron filtration system that comprises five subsystems developed in conjunction with coolant system specialist FSE. The system operates at up to 200 bar pressure with 35litres/min external supply around the spindle, a tool wash at 50litres/min and a cascade flood swarf clearance at 100litres/min. There is also a Z-axis bed wash that uses 50litres/min.  As part of the coolant system is a recognised industry ‘first' whereby the volume can be varied up to 70litres/min with pressures up to 120 bar fed through the spindles of each machining centre to suit the machining requirements. Also through the PLC controlled system, which monitors both flow and pressure, built-in intelligence automatically adjusts the system to suit the tools being used to prevent or delay the onset of any built-up edge on the tools and maintain an ‘in-cut' life of one hour. As an example of swarf generated when machining a titanium pylon, its raw unmachined weight is reduced from 29kg to just 8kg. Every 24 hours 400kg of titanium swarf is removed from the system. Coolant flow and its control was also seen as an important element due to the amount of heat generated under cut and to maintain the general +0.05mm tolerance and specific tolerances for geometry and size on the components. The pylon machining process involves left and right hand components requiring seven main operations. Initial datums are first prepared on the FMS followed by rough machining and heat treatment. Parts are then put through the system for semi-finish and then finish machining before the two halves are assembled. Final machining of the assembly is then carried out in the system.  Processes include the boring and drilling of holes between 6mm and 50mm diameter, contour and plunge milling with cutting speeds varying between 65 and 100m/min and feed per tooth between 0.2 and 0.8mm/min. At this time cutting rates when milling are 450mm/min at a surface speed of 80m/min. However, the design, construction and build quality of each machine is to such a standard that they are capable of delivering higher levels of productivity as new developments in tooling become available. The two Toyoda-Mitsui Seiki HU80A 4-axis machines under Fanuc 31iM-5A control have strokes of 1,200mm x 950mm x 900mm, a B-axis index of 0.001° and can accept a maximum workpiece diameter of 1,170mm. Meanwhile, the two 5-axis HU80A-5X Fanuc 31iM-5A controlled machines have 1,200mm in X, 1,000mm in Y and 1.050mm in Z. In addition, the 5X version also has a full B-axis table with 0.001° positioning and an A-axis, high torque trunnion mounted table, able to position between +20° and –115° with a workpiece diameter of 1,200mm. Due to the design of the machine, high levels of thrust from the spindle are accounted for because the cutting point is always maintained close to the pivot of the tilting table. Both machines are fed with a common 800mm by 800mm pallet system which is located and pulled down using a T-clamp that creates an even loading of the pallet and maintains a maximum error tolerance of just 10 microns over the datum surface. This pallet sits on highly accurate four-point taper cone. The 8,000revs/min spindles on each machine are driven by 26kW motors and gearbox able to develop in excess of 1,000Nm of torque through the highly rigid HSK100A tooling taper that is ideal to meet the rigorous demands when cutting titanium. With linear scale feedback, any possible error in the drive system is overcome from influences of temperature or longer term wear enabling a resolution of 0.001 mm to be maintained. The B-axis rotary encoder also has a resolution of one micron and the A-axis has precision scales. The 60 position tool magazine on each machine will accept tools weighing up to 25kg, 650mm tool length and 125mm diameter. Exchange time for tool-to-tool is six seconds. Manning levels involve two people on day shift who load and unload pallets. They also have responsibility to inspect work and change tooling, preset tools and perform general housekeeping duties. During the night, an overseer maintains a watch on the system. www.2DCNC.co.uk

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