Quality is of the utmost importance to the aerospace industry. Small wonder then, that leading engine manufacturers MTU Aero Engines use the LaserControl NT optical measuring system from Blum-Novotest on over 100 machines. The process stability the laser helps to achieve the best possible manufacturing results.
"When your car develops engine problems, you simply pull over and wait for a mechanic. But when jet engines fail in an aircraft, the lives of several hundred people are potentially at risk. That is why we at MTU attach the highest priority to quality! All our components must satisfy the close tolerances that we specify - often to within just a few hundredths of a millimetre," explains Walter Strohmeir, user support representative for NC engineering with MTU Aero Engines in Munich, Germany. In addition to supporting machine operators with virtually every aspect of NC machining, his responsibilities include the programming of CNC routines and procuring machines and the peripherals to go with them.
To fully meet the production engineering demands of aero engine manufacture, the machining centres at MTU rely on non-contact laser measuring systems supplied by Blum-Novotest. In simplest terms, the LaserControl NT is an optical measuring system for tool setting and tool monitoring. As well as providing basic tool breakage control, the LaserControl NT systems capture data such as tool length, radius, wear, cutting edge bursts and spindle and tool carrier accuracy at nominal spindle speeds. The systems also compensate for spindle displacement at high speed and can detect and correct tool clamping errors.
"Way back in the mid Nineties, LaserControl NT won out against strong competition in the selection process at MTU Aero Engines as being the system integrator with the most knowledge. MTU subsequently purchased its first laser system and the existing machines were gradually upgraded, while new machines were acquired with LaserControl NT already installed," says Daniel Czujek from the Technical Sales Department of Blum-Novotest and MTU support engineer. Today, MTU Aero Engines has over 100 Blum laser systems in use across the company. Around 300 to 350 MTU employees work with LaserControl NT in three-shift operation.
A number of machines are also equipped with contact touch probes supplied by Blum. In terms of quality assurance, the Blum systems make a major contribution to the manufacture of all MTU engines. They include the new GP7000 family of aero engines that the Munich firm produces, taking responsibility for the low-pressure turbine, the intermediate turbine casing and high-pressure turbine components. The GP7000 family of aero engines is used in the long-haul sector, including scheduled services of the Airbus A380 since August 2008. In its class, this jet engine is a benchmark in terms of reliability, fuel consumption and noise emissions.
A major role in aero engine manufacture is played by so-called ‘blisk machining'. Blisks marry the concept of maximum performance and minimum weight. The process involves integral rotor construction in which the disk and blade form a one-piece component, rendering blade roots and disk grooves superfluous. "The chief advantages of blisks are their substantial weight saving, increased service life, decrease in the number of components through higher stage loading and the reduction in the amount of maintenance that is required. Most parts are made from titanium. For tool setting and monitoring we deploy LaserControl NT throughout the entire blisk production line," explains Heinz Baumgartner, blisk production team leader for the medium pressure compressor for the TP400 engine programme. He supervises virtually all of the machining operations that are involved in 'blisking'. Almost half of his team of 19 work with the Blum systems.
Blisk facts and figures are impressive: It takes between 15 and 60 hours to make one blisk, depending on the size of the component and the type of machining that is required. The parts that are produced are worth between €30,000 and €60,000Euros. This makes the constant monitoring of the tools that are used to machine them so vital. If there is a problem in the production process because of a faulty, worn or incorrectly fitted tool and the work is scrap, things rapidly get very expensive. Each component can require the use of 10 different tools - from the humble twist drill to expensive special-purpose tools. At MTU there was the odd occasion when the wrong tool was fitted in error, resulting in substantial losses. With the laser they can now be confident that such mistakes cannot happen again.
The laser systems also help maximise the utilisation of the machines. After all, in modern production facilities with low employee numbers there is not an operator on every machine all of the time. One operator is often responsible for several machining centres, so without a reliable monitoring system, if there is a problem with a tool it can take a long time for the fault to be found. The tool may be broken or it may be worn or its cutting edge may have broken, ruining the surface of the component. This is particularly true on weekends when running the machines unmanned on Saturdays and Sundays is essential because of the production costs of the products.
"Our ultimate goal is to achieve the greatest possible machine utilisation. This means working toward the industry standard of 5,000 hours per annum. The longer the machines run, the more we can keep costs down. This can only be achieved by working unmanned weekends," explains Heinz Baumgartner -This is also why the production experts at MTU Aero Engines plan to take a different approach to tool breakage in future, one in which the laser measuring system will again take centre stage. What is proposed is to interpret the error message, so if the laser detects a broken tool, a sister tool will be fitted automatically. This degree of automation will further enhance machine utilisation by cutting unnecessary stoppages to an absolute minimum. The function is built in to the Blum measuring cycles as standard.
The excellent process stability that the laser system offers delivers benefits in other areas as well. Most of the machines equipped with LaserControl, no longer require tool presetting devices. Some machining centres are operated in parallel, but MTU's objective is to dispense with tool pre-setters altogether, so when the machines are fitted with new tools, the laser will capture the tool data to the nearest micron, directly on the machine. This will eliminate human error when operators manually enter tool data that has first been logged on the pre-setter, such as keying errors and transposed numbers. Measuring directly on the machine is in any case much more accurate, as the data is recorded in the actual clamping situation and at working speed. All kinds of tools are measured with the laser measuring systems. The smallest has a diameter of just 1.2mm, while the largest cutter head is currently 250mm.
MTU also sees significant benefits from the NT technology introduced by Blum in 2003 which has completely eliminated problems previously caused by coolant. "On this basis we can now theoretically move to the laser with the tool dripping with coolant and it still works perfectly. Together with the tool cleaning jets that were installed a few years ago, this solution represents a real quantum leap in process reliability. The good direct contact we have established over the years with Blum is a major contributing factor. The same goes for the custom cycle that Blum has written to allow special purpose tools with their non-standard profiles to be measured," says Walter Strohmeir.
MTU has also been able to use LaserControl to help solve a problem that occurs in day-to-day practice - because of the long operating hours, the machines can experience thermal growth that adversely affects machining quality. LaserControl compensates for this effect by calibrating between machining steps. This means that the thermal growth in the machine axes or spindle is found by calibration and stored in the controller as an additive zero offset.
"For us, it is the process reliability the LaserControl NT offers that is its most important feature. The excellent cooperation with Blum is another vital factor for our business because they understand what we want and can deliver it quickly. And they are always giving us useful hints, like how we can measure the tools even faster. Above all, the laser measuring systems give us the reliability and confidence we need for our machining processes," sums up Walter Strohmeir with evident satisfaction. Passengers too should enjoy peace of mind thanks to the high quality standards set by MTU Aero Engines, at least whenever their flights are powered by engines from MTU.