Accuracy of HEDELIUS machining centres

Many factors work together to achieve a specific workpiece accuracy. On the one hand, there are the machines themselves. The design, components and software have an influence on the processing result. However, many accompanying factors must also be taken into account, from the location of the machine, measuring devices, clamping devices and tools to the qualification of employees.

Design
Design
In the first phase of any new development of a machining centre, criteria such as stability, accuracy, dynamics, automation capability, space requirements, transport dimensions and manufacturing costs pose conflicts of objectives and must be weighted depending on the planned area of application. Designed as universal machining centres for a wide range of applications in machine and tool making, HEDELIUS places greater emphasis on stability and accuracy in the design phase. As a result of this process, the special design of the TILTENTA machining centres was created with the constantly projecting Y axis and the resulting high rigidity and precision over the entire traversing range of the Y and Z axes. The results were so impressive that the compact 5-axis machining centres of the ACURA series were also developed based on this design.
Measuring systems
Measuring systems
HEDELIUS only uses direct length measuring devices for position detection of the X, Y and Z axes. For example, the position control loop comprises the complete feed mechanism. This is known as closed loop operation. Mechanical transmission errors can thus be detected by the linear encoder on the feed axis and adjusted via the control electronics.

This eliminates a number of possible sources of errors:
  • Positioning errors due to the heating up of the ball screw
  • Reversal errors
  • Kinematic errors due to slope errors with the ball screw
Direct linear encoders are thus essential for machines that require high positioning accuracy and machining speeds. All HEDELIUS machining centres are fitted with direct measuring systems as standard.
Assembly groups
Assembly groups
Critical assembly groups such as mobile stands, beds and turn-tilt table units are manufactured and measured in-house at HEDELIUS. As a result, we not only always focus on quality, but also recognise the possibilities and limits of modern machining in everyday use. This process knowledge is constantly incorporated into the improvement of our products and into the advice we give our customers.
Guides and straightness
Guides and straightness
The alignment of the guideways requires special care and experience. HEDELIUS uses prepared roller guideways from German and Swiss manufacturers. Fine alignment with optical measuring technology means that the Y-axis rails, for example, are assembled with a maximum straightness of 5 µm. At the end of assembly, the positioning accuracy, repeat accuracy, straightness and backlash of the linear axes are finally checked and documented via a laser interferometer. For example, the positioning accuracies of the linear axes are regularly below 6 µm in accordance with ISO 230-2. We would be happy to provide you with an insight into internal processes and acceptance protocols on a factory tour.
Measuring systems on round axes
Measuring systems on round axes
For 5-axis machining centres, the accuracy of the measuring systems has a significant influence on the angularity and parallelism of surfaces and holes. For this reason, HEDELIUS also uses direct angle sensors in the centre of each axis of rotation in the integrated rotary tables, the swivel spindle drives and the rotary swivel table units. On request, we can measure the positioning accuracy of rotational axes with a resolution of ±1" using laser-based angle measuring devices and calibrate the axes to the highest positioning accuracy. As a result, positioning accuracies of less than ±5" can be achieved even with series components. On some models, it is also possible to optionally equip the C-axis with angle measuring devices in a higher accuracy class in order to increase the positioning accuracy to below ±2.5".
Circular form deviation
Circular form deviation
The Renishaw ballbar test has established itself as a fast and simple test method for the accuracy of machining centres. Within a few minutes, the measurement provides information on the interplay of two linear axes and the accuracy of a circular movement. Slip-stick-free roller guideways combined with direct distance measuring systems and high angular accuracy enable the milling of fits in a quality of IT7 and better in most cases, which reduces production times and the number of spindle tools required. We would be happy to provide a demonstration of the high level of circular accuracy with our Renishaw ballbar system.
Precision spindle chiller and temperature compensation
Precision spindle chiller and temperature compensation
To remove the heat generated in the milling spindle, HEDELIUS equips its ACURA 65 series machining centres, for example, with active spindle chillers. In order to optimally control the cooling output, the spindle chiller has a temperature sensor attached to the machine bed, which permanently records the current bed temperature and specifies the setpoint of the cooling temperature based on this. Thanks to active cooling in combination with the high control accuracy of ±0.2 Kelvin, increased thermal stability is already achieved as standard. However, since the spindle cooling cannot remove all the heat, HEDELIUS optionally installs temperature sensors on the spindle, mobile stand and, in some cases, also on the rotary axes to compensate for structural displacements via the control.
Coolant temperature control
Coolant temperature control
Consistent environmental conditions are required to achieve consistent manufacturing results. To achieve the highest accuracy and reproducible results, it is important to maintain a consistent workpiece temperature during machining. Any heat input into the workpiece and the tool can lead to the permissible tolerances being exceeded, thus turning the workpiece into scrap. The quality requirements for the workpiece are then no longer met. Active, controlled cooling of the cooling lubricant counteracts heat input into the material and tool. The HEDELIUS coolant systems can therefore be optionally equipped with an integrated immersion cooler for temperature control of the cooling lubricant.
3D measuring probe and laser
3D measuring probe and laser
For accuracy and set-up optimisation, a 3D measuring probe is an indispensable part of modern production. The field of application of a 3D touch probe extends from the preparatory measurement, such as determination of the allowance, regulating measurements during machining, such as readjustment for fits, to monitoring measurement at the end of the program for creating logs. Almost all machining centres today are also equipped with a switching tool probe or a laser for tool measurement.

Possible applications include:
  • Measurement of allowances with fluctuating blank dimensions, such as for cast or sawn parts
  • Determining the workpiece orientation for establishing a coordinate rotation
  • Adjustments to the machining process, e.g. tool deflection, workpiece deformation and thermal effects
  • Testing of special features
  • Tracking of deviations in characteristics via logs
  • Determining tool wear and tool breakage
Kinematic measurement cycle
Kinematic measurement cycle
If complex parts are to be manufactured precisely and with reproducible accuracy over long periods of time, the position of the round axes in relation to the linear axes must be checked regularly. This so-called "transformation chain" causes permanent changes due to thermal influences such as weather or process influences and should therefore be calibrated regularly. With software options such as the KinematicsOpt cycle in Heidenhain machines or the cycle 996 in Sinumerik machines, this calibration can be carried out by machine operators themselves within a few minutes.
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