To maintain the required precision in the micrometer range, significant investment is required. The climate in the production shops is precisely controlled to 0.1 degree Kelvin and the machines are fitted with temperature sensors all the way to the base. If it is very cold outside, the machine base cools down when the machine is turned off. The machining centre then has to run empty for several hours until the entire system is once again at a uniform temperature level. Wandinger remembers, "In the early days we had a window in the production shop, and sunlight used to come through the shutters onto one of the machines. This beam of sunlight caused such significant temperature expansion that precision production was out of the question".
Wandinger's precision demands are certainly extreme. "If we were to produce to DIN tolerances, we would have gone out of business a long time ago. We are often operating in tolerance ranges between two and three micrometres - not just for drilling, but for contour milling too". Contactless tool measurement systems from Blum-Novotest are used on all the machines. Wandinger remembers, "At the beginning we calibrated the tools manually by touch, but even the slightest contact can destroy the tiny tool cutting edges or totally break off the tool, and we quickly moved over to laser systems". Wandinger has been using Blum equipment for 15 years now, initially arriving as part of a Chiron system and impressing from day one.
As the LaserControl measurement systems have to be located in the working space in the machining centres, the optics need to be protected. Blum uses several methods to do this. On the one hand, the laser optics are mechanically protected by a shutter during machining. A pneumatically actuated shutter piston moves in front of the optical inputs and outputs. When the shutter opens for measurement, a sudden blast of air is released to clear the device of dirt and chips. During measurement, a stream of barrier air reliably protects the optics from contamination, for example caused by drops of coolant being thrown off. This enables excellent in-process reliability to be achieved. Unlike other laser measurement systems, the laser beam on the Blum devices is focused, in other words the beam is extremely thin at a particular point between the laser transmitter and receiver. The models in the Nano NT series reach a beam thickness of just a few micrometres. On unfocused systems with a greater beam thickness, it is possible that the measuring system will "miss" the actual drill when determining the tool length and only detect the significantly thicker shaft. If these incorrect tool values are then used for milling, when using such small drills a tool breakage and a rejected workpiece are almost inevitable, as in a worst case scenario the axis may still be moving rapidly when the drill comes into contact with the workpiece. Even if the tool does not break, the wrong length is being used, which results in dimension deviations on the workpiece.
An extremely powerful electronic system, which Blum-Novotest calls "NT technology" allows such fast measurements that each blade on a tool running at its rated speed can be individually monitored for breakage. Even the tiniest breaks and wear to the blade can thus be detected. Alongside the shutter system, this intelligent electronics is the reason why the systems in the machine work reliably despite the use of coolant. Thanks to plausibility tests and the "pulling" measurement from the laser beam, falling or discharged coolant has no influence on the measurement. Wandinger has Blum Micro Compact NT or Nano NT type measuring systems on all his machining centres. They differ in terms of the transmitter to receiver distance, allowing some of them to measure larger tools. Tool breakage monitoring is also an important application for the Blum measuring systems. Between two machining cycles, for example between drilling of two holes, the tool spindle briefly moves to the laser measurement system, which measures whether the drill is still in place. At 30,000 rpm, even a very minor resonance, e.g. due to a 2 micrometer imbalance, can cause a 100 micrometer drill to break, demonstrating how important breakage detection is.
Wandinger calls it "total breakage" - for example if the drill intended to pre-drill a hole, is no longer in place. In a worst case scenario, all of the downstream tools could also break as a result. The costs of a "total breakage" - but also of an individual broken tool - are far from negligible, as a single one of these highly sensitive tools can cost anywhere between 25 and 180 Euro, in some cases as much as 250 Euro. In addition, the forces resulting from collision with the workpiece can also jeopardise the accuracy of the spindle, possibly causing further high costs. And we should not forget the costs of the blank, which can be very high depending on the material being used. For Wandinger, it is important that the laser measurement systems are fitted directly in the working space, ideally immediately adjacent to the tool holder. "This enables all influences, such as temperature-related expansion of the machine, to be measured and taken into account. The thermal expansion of the spindle and the tool fitting, as well as the speed-related displacement of the spindle, can also be compensated, which is essential when accuracy levels of less than ten micrometres are required". The measurements that can only be carried out in the working space also include concentricity tests at operating speed; sometimes it is not until the drill is being calibrated on the machine that incorrect labelling on the packaging is noticed. "You are trying to fathom why your 100 micrometre holes have a diameter of 120 micrometres, until you measure the tool diameter and identify the fact that the incorrect drills have actually been supplied", Wandinger said.
"I am fascinated by how accurately tools can be measured", he continues. "This has a direct impact on costs. For instance, we once had a workpiece that had to have 960 tiny holes drilled in it. At this diameter, the feed rate is 1.5 millimetres per minute. So if I slow down the movement a tenth of a millimetre too early above the surface of the workpiece when approaching a drilling point, I will be drilling nothing but air for four seconds before the drill actually gets to the workpiece. With 960 holes, this adds up to more than an hour of 'dead drilling'. However, if I have measured the length of my drill to an accuracy of a few micrometres, I can get closer to the surface at high speed, saving lots of time - and ultimately production costs".
"We are extremely satisfied with the laser measurement systems from Blum", Wandinger concludes. "Because the tools are measured directly in the machine, we can achieve a level of precision that is at the very limits of what is technically feasible. That is why we had to acquire a scanning electron microscope back in 2004 so that we could inspect our workpieces. We have reached the limits of conventional measurement methods. The contactless measurement technology and extreme accuracy of the Blum tool measurement systems are the only way we can achieve these tolerances - to say nothing of the robustness that is possible by fitting such a precise piece of measuring equipment where chips are flying and cooling lubricant is spraying around. In most cases, we can now make the very first part a good part, and this is thanks largely to the LaserControl equipment".