Fixture system for workpiece adjustment

Main technical issue
The case study is focused on improvement of the productivity and accuracy  of large workpiece production through the shortening of the workpiece setup  and clamping time. The current situation in the workpiece adjustment is based  on extremely time-demanding manual setting, when the operator has to find  optimal zero point of the workpiece manually – scribing operation and to fix the  workpiece.

Proposed technical solution
The new proposed solution is a comprehensive solution that automates workpiece  adjustment and clamping process. It is achieved by the development of:

  • Modular active fixtures with centralized control for workpiece leveling. Fixtures allow precise automatic positioning of the workpiece in regards to  the machine tool coordinate system. The active fixtures are designed as a  compact mechanism that is equipped with a ball screw connected with a  servo motor, gearbox and ball nut directly connected with the movable part  of the unit. The mechanism is also equipped with linear guideways for better  stiffness and a brake located on the linear guideways.
  • Modular fixtures for workpiece automatic clamping in adjusted position  without deformation and with demanded clamping force. The unit for  clamping in additional points consists of two main parts. The first part is an  hydraulic work support that can touch the workpiece very slightly and can  be fixed in that position. The second part is a swing clamp that can fix the  workpiece on the work support by closing the clamping force circuit.
  • Active vibration reducer (AVR) as an alternative clamping unit for places  where above-mentioned fixtures cannot be used. It is a device composed  of one acceleration sensor and one inertial shaker, within an enclosure.  This device can be attached to a vibrating structure and it modifies the  mechanical impedance of the structure, thus avoiding vibrations.
  • Modular fixtures for workpiece automatic clamping and its controlled predeformation,  the fixtures is equipped with position and pre-deformation  force sensor. The fixture is a combination of the new modular active fixture  equipped with a force sensor and clamping part.
  •  Control system with HMI for above-mentioned fixtures control and cooperation  with a machine tool CNC. It consists of the main electrical cabinet with the  main control PC (Beckhoff industrial PC) and I/O for control of hydraulic, static  fixtures, dynamic fixtures (AVR), an hydraulic circuit, a portable screen with  developed software LECLIN and a connection with the machine tool control  system.

Main advantages of the solution 

The proposed process of levelling and clamping of the demonstration part was  performed in approximately 15 minutes, conventional levelling, scribing and  clamping operation take about 60 min depending on the operator’s skills. Based  on the results, it can be concluded that the automatic workpiece levelling is  much faster compared to manual levelling. Position accuracy of the unit is 6 µm  with the direct position measurement system. The unit is capable to achieve 5000  N loading force during the movement, stroke 50 mm and, due to the integrated  brake, more than 5000 N loading force during machining. (See table page 18)  The developed solution can be used for adjusting and clamping different  workpieces which makes the solution universal. Despite the fact that the initial  investment is relatively high, the proposed leveling and clamping system is cost effective.  The key financial benefits are the ability to reduce clamping time  significantly and its universal design suitable for different types of workpieces.



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