In the middle of the 1980s DECKEL MAHO in Pfronten achieved a breakthrough in the field of controlled five-axis operation on milling machines with its MH 700 S mill and drill centre. “Continuously controlled axes in the head and table equipment and the respective advances in CNC and CAM technologies were revolutionary developments for that time”, recalls Alfred Geißler, Managing Director of the DECKEL MAHO Pfronten GmbH.
The swivel head with controlled B-axis was a crucial development
What made the machine so special was the combination of an NC swivel rotary table, the program-controlled change of the spindle position from horizontal to vertical and a tool changer with a magazine that could accommodate up to 36 tools. This made it possible to completely machine even complex workpieces in a single setup in unmanned operation through breaks and into the night. “The prerequisites for the technical implementation of this 5-axis technology were the availability of backlash-free drive equipment in the rotary axis and the use of direct measuring systems in both the rotary and the linear axes”, explains Geißler. In addition 5-axis machining placed high demands on the computing power of CNC controls, which had not been possible to fulfill formerly.
A decisive step forward on the success path of 5-axis machining was the development of a swivel head with a controlled B-axis. It was introduced in the P-Series in the middle of the 1990s and reflected the pioneering role of the company. “The B-axis with a swivel plane of less than 45° made it possible to carry out simultaneous milling in five axes with a high degree of stability due to machining in the rotation point of the axis”, stresses Geißler the importance of the development. This meant excellent milling results were always achieved regardless of the direction of the processing forces. It was not until the introduction of this swivel head that simultaneous movement of all five axes could be realised and free-form, cylindrical or spherically curved surfaces could be milled in a time-saving way without patterning.
However, the DMG MORI manager did concede that the majority of 5-axis applications were concerned less with 5-axis simultaneous machining of free-form surfaces and more with spatial positioning. “This means that as soon as a drill or milling tool is positioned in the required angle to the workpiece, actual machining is carried out with a maximum of three axes.”
Production in a single setup with increased precision
Geißler went on to tell us that the main motivation for the use of 5-axis technology was the trend towards reducing the number of parts that in turn led to increasing complexity of the individual workpieces. “The availability of 5-axis machining followed by 5-axis simultaneous machining reinforced this trend enormously. So it was in fact an interdependency between the market and technology”, explains Geißler. This resulted in multi-axis milling operations gaining a foothold firstly in prototype construction and then in tool and mould making and especially aircraft construction and more and more in serial production as well.
The special attraction of 5-axis machining is that it enables production in a single setup and of course the increased precision that goes hand-in-hand with this. Because it costs time and money and inevitably leads to loss of accuracy every time a machine is re-tooled. Added to this is the fact that complex components, with traverse bores and undercuts, for example, just cannot be produced economically on a three-axis machine.
5-axis machining also improves surface quality and reduces production time. This can be seen clearly on the example of an inclined surface: where a 3-axis machine would have to machine this in many small cutting steps, five-axis positioning means that the tool can be positioned at the required angle to this surface and can remove the material in a single step. All positions of a workpiece can be reached with five axes. In addition tools can be used more efficiently because inclining them with the same feed rate means that longer cutting lengths are possible and this in turn reduces cutting forces.
The trend towards 5-axis machining continues unbroken
The advantages are obvious and have also convinced users. “DECKEL MAHO Pfronten alone has sold a good 15,000 5-axis machines on the market to date and thus contributed greatly to the status of DMG MORI as the world’s technological and market leader in the 5-axis sector”, says Geißler.
And the trend towards 5-axis machining continues unbroken. The speed with which DMG MORI introduces innovations in this sector remains consistently high, as diverse developments in the duoBLOCK® Series clearly prove. The latest exponent in this respect is the 4th generation DMC 125 U duoBLOCK® that is equipped with a fast rotary pallet changer in its standard version for setting up parallel to primary processing time. According to DMG MORI rigidity has been increased here by 30 %. At the same time energy consumption has been reduced to the same extent. “The entire periphery of the machine offers enormous potential for saving energy”, says Geißler. An efficient cooling unit with cold water admixture instead of a device that is permanently in operation, for example, brings considerable savings. The cutting fluid pump will be equipped with a speed governor in future and will therefore only consume the amount of energy needed for actual machining.
In order to boost the flexibility of the 5-axis milling machine and reduce machining times, the developers have also re-engineered the B-axis. It has been equipped with even bigger bearings which should increase rigidity by 20 %. The internal cable track also ensures there are fewer interfering contours.
Step-by-step the standard DMU and monoBLOCK®-machines will also be equipped with the new speedMASTER spindle that was developed within the cooperation. High cutting performance, a long lifecycle and a high level of accuracy thanks to the large spindle bearings plus optimised sealing against cutting fluid are the highlights mention by DMG MORI here.
And how does the Managing Director of DECKEL MAHO see the future? “As a machine manufacturer DMG MORI has very little scope for improvement where the effective working area between the cutting edge and workpiece in classic 5-axis machining is concerned. The focus is more on the process environment.” Key words here include meaningful simulation and collision control as well as programming and operation. The company is also working on the combination of processes with the ULTRASONIC or LASERTEC Series. The latest topics in this respect are laser structuring or the new hybrid machine LASERTEC 65 3D for additive manufacturing.
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