In simple terms, the LaserControl NT is an optical measuring system for tool setting and tool monitoring. As well as providing basic tool breakage control, the systems capture data such as tool length, radius, wear, cutting edge bursts and spindle and tool carrier accuracy at nominal spindle speeds. They also compensate for spindle displacement at high speed and can detect and correct tool clamping errors.

 

It was in the mid-1990s that MTU Aero Engines purchased its first laser system. Existing machines were gradually upgraded, while new machines were acquired with LaserControl NT already installed. A number of machines also have contact touch probes supplied by Blum. In terms of quality assurance, the Blum systems are said to make a major contribution to the manufacture of all MTU engines, which include the new GP7000 family, taking responsibility for the low-pressure turbine, the intermediate turbine casing and high-pressure turbine components.

 

A major role in aero engine manufacture is played by so-called ‘blisk machining’. This involves integral rotor construction in which the disk and blade form a one-piece component, rendering blade roots and disk grooves superfluous. Heinz Baumgartner, blisk production team leader for the medium pressure compressor for the TP400 engine programme, explains: “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.”

 

It takes between 15 and 60h to make one blisk, depending on size of component and type of machining required. Parts produced are worth between €30,000 and €60,000. This makes the constant monitoring of the tools used to machine them so important. Each component can require the use of 10 different tools – from the humble twist drill to expensive special-purpose tools. In the past, occasionally the wrong tool was fitted, resulting in substantial losses. With the laser the company can be confident that such mistakes cannot happen.

 

Baumgartner continues: “Our ultimate goal is to achieve the greatest possible machine utilisation. The longer the machines run, the more we can keep costs down. This can only be achieved by working unmanned weekends.”

 

This is also why the production experts at MTU 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 use by cutting unnecessary stoppages. The function is built in to the Blum measuring cycles as standard.

 

Most of the machines 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. All kinds of tools are measured with the laser measuring systems – the smallest has a diameter of 1.2mm; the largest cutter head is currently 250mm.

 

MTU also sees benefits from the NT technology introduced by Blum in 2003 which has eliminated problems previously caused by coolant.  Walter Strohmeir, user support representative for NC engineering with MTU Aero Engines, comments: “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 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.”

 

MTU has also been able to use LaserControl to help solve a problem that occurs in day-to-day practice – due to 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.