INTEFIX project offers innovation to the aviation industry
INTEFIX project had worked on the specific case studies that focused on the aviation industry. First study case focused on production of thin-walled curved workpieces typical for structural parts of airplanes, while the second one was dedicated to machining of aircraft turbine support structures. Project team looked into specific technical problems appearing during production process of desired elements, worked out tailor made solutions. Positive results were identified on various levels like production process timing or accuracy, to name just a few.
Production of thin-walled curved workpieces typical for structural parts of airplanes
Main technical issue
The case study is focused on production of thin-walled curved workpieces typical for structural parts of airplanes. The current issue in the workpiece clamping and subsequent machining is changeable workpiece stiffness. The existing clamping strategy and machining strategy caused large local deformation of the part. As a results of this state, the workpiece wall thickness was out of tolerance and subsequently also part weight was out of tolerance. This caused part weight changes which is also undesirable.
Proposed technical solution
Workpiece clamping: New fixtures with integrated support and clamping function were developed. The workpiece is clamped using a vacuum. Concurrently, suitable control for automatic position setting of the fixtures was developed. Suitable thickness measurement sensor was selected and integrated into the machine tool. The new fixture elements are autonomous and plug-and-produce ready, with integrated safety to monitor the minimal workpiece clamping force.
Machining planning: Suitable tools and cutting conditions for roughing and also finishing operations were selected and optimized. The main criterion for tool selection is minimization of the cutting force in the surface normal direction. The main criterion for cutting condition settings was chatter avoidance during thin wall machining. The method was developed for adaptive modification of finish tool path with respect to current workpiece thickness and deformation.
Process automation: the integration of thickness measurement sensors in order to control the precision of the workpiece and subsequent modification of the tool path for finishing operations; development of one software for quick and easy workpiece inspection and thickness measurement.
Main advantages of the solution
The main advantages for end-user could be summarized as:
- The fixture plug-and-produce system is universal for clamping of various workpiece types. The developed LECLIN software based on metrology HMI enable quick and intuitive alignment, inspection and thickness measurement of the workpiece.
- The wall thickness accuracy was improved. The wall thickness stayed within dimensional tolerance ±0.05 mm. Thus, the part weight also stayed within defined tolerance of maximum +1 kg.
- The bottom side machining time was reduced of about 15%.
- The price of the whole solution was reduced about 25% on this demonstration case study.
Machining of Aircraft Turbine Support Structures
Main technical issue
The main objective is the control and minimization of the deformation of large, complex geometry and low stiffness workpieces during the setup and clamping process in order to achieve improved precision during the subsequent operations: machining, welding, assembly…
The workpiece in study is the Tail Bearing House (TBH) of a turbine (1900 mm in diameter, 350 mm in height and common thickness of 6-10 mm), and the machining operation to control is the turning of the flanges. This structural component is made by welding different forged and cast components that are machined afterwards. The welding produces deformations and distortions, so the fixture has to adapt the clamping of the workpiece to avoid additional deformations and hyperstatic load states; in order to assure suitable precision and to fulfil the requirements for subsequent assembly process.
The precision and tolerances required in the workpiece are ±0.2 mm for general diameters; ±0.05 mm for reference dimensions within turned features; and ±0.015 mm for reference holes. The fixture tolerances must be related to the part tolerances in the contact areas.
Proposed technical solution
In order to solve the problems and limitations explained above it has been decided to develop a system with integrated sensors and actuators to correct and control the deformations of the workpiece; improving the precision and performance of the machining process. The development of the clamping unit has been done based on an existing flexible clamping element developed by Roemheld, adding different subsystems.
The solution comprises a series of intelligent clamping units able to detect and correct the position of the workpiece, with the following characteristics:
- Integration of sensors (displacement and force) in the clamping unit to detect undesirable deformations.
- Integration of actuators in the clamping unit to counteract the deformations by modifying and adapting the position of the yaws and the clamping force.
- Achieve an automatic position correction based on the measurement of the position and force sensors.
Main advantages of the solution
The developed intelligent clamping unit aims at substituting the current manual clamping elements in order to obtain the following improvements in the setup of the workpiece:
- Achievement of an automatic clamping and position correction based on the measurement of the displacement and reaction force in the clamping unit
- The positioning precision of the clamping unit depends on the stiffness of the workpiece and in the case of the TBH it is below 0.01 mm.
- Using the force control in the clamping unit, it can achieve a reaction force precision of ±8N with a positioning repeatability within 0.01 mm
- Using the position control in the clamping unit, it can achieve a repositioning precision of 0.007 mm.
- Reduction of workpiece exchange and set-up time by the introduction of the clamping units, being this independent of the number of units. With the developed clamping unit it takes just 4 seconds the setup, while using the mechanical clamping elements the set up takes up to 15-20 minutes.
- The clamping unit allows keeping the same clamping and holding forces of the mechanical units.
