Module 2: Adaptive clamping devices
In the DynaMill project the development of adaptive clamping devices is divided in five technology levels as shown in Figure 6.
Technology levels of clamping devices in DynaMill (Figure 6)
Locator/ positioning approaches in clamping devices
The second module aims at hardware development. To improve the hardware is important, because using better process parameters just causes less exciting, but does not change the physical dynamic characteristics in itself. If the thin walled work pieces are very flexible and/or poorly supported, deflections and vibrations will occur, which cannot be compensated only with parameters. To improve the clamping situation the most effective approach in many cases is to teach the knowledge of just building better clamping devices with regard of vibrations and continuum mechanics.
Objectives of locator/positioning approaches in clamping devices
Passive damping systems in clamping devices
Secondly the damping in clamping devices will be enhanced. Most of the existing clamping devices are designed to be very stiff, but provide only poor or no damping, leading to vibrations with very high amplitude when excited with even small loads. The enhancement of damping in clamping systems would provide an increased stability range of the work pieces. However the design of systems with enhanced damping is challenging. For damping being velocity proportional motion is in principle mandatory which contradicts stiffness. However structure borne wave damping concepts work without the drawback of much reduced stiffness aiming at high frequency energy dispersion.
Objective of passive damping systems in clamping devices
Adaptive locator systems in clamping devices
The next step of the clamping design module is the development of adaptive locator systems. The efficiency of a clamping system is determined by the time required for changeovers, pointing at issues of positioning and handling. Therefore, designers often try to develop clamping systems for machining front and rear sides in one clamped position. Large thin-walled structures often require backside locators in the middle of the work piece, causing the necessity to reclamp when machining the backside. In clamping systems with movable components (higher automatization) the reference of the first setup can be kept.
An other aspect of this topic is adaptive opening and locking of degrees of freedom of the locators, see Figure 7. With this technique the modal characteristics of work pieces can be manipulated, thus shifting and keeping the eigenfrequencies of the work pieces in stabile regions. An application will be compensation of modal shifts resulting from material removal. That way milling of thin walled work pieces can be kept stable by manipulating the locators of the clamping devices only.
Manipulation of the modal characteristic by adjusting the degrees of freedom in clamps, modal analysis via FEM for a ø20mmx500mm steel rod (Figure 7)
Objectives of adaptive locator systems in clamping devices
Sensor Integration in clamping devices
The forth step of the adaptive clamping device module deals with sensor integration in clamping devices. Accelerometers and force sensors (eg strain gauges or piezo), clamping systems are capable of monitoring vibration behavior of work pieces during machining. With a visualization of these signals in the frequency range dynamically stable parameters in the design process could easily be found. With monitoring of the clamping forces deformations caused by the clamps could be reduced plus slipping out could be detected.
Objectives of sensor Integration in clamping devices
Active clamping devices
Active clamping systems have the potential to improve the machining of thin-walled components by canceling vibrations regardless of the excitation. Active clamping devices provide an universal plug&play solution stabilizing vibrating systems without the need of adjusting of the process. Combined with stable cutting parameters active clamping devices provide further enhanced process performance. Because of the high complexity of these systems up to now ready for production concepts still do not exist. In DynaMill the efforts in developing active system will only be limited to scientific approaches, too. However the development of this promising future technology will be brought a step forth.
Objective of active clamping devices