Design of An Active Workpiece Holder

AbstractMilling is one of the most used machining processes thanks to its high flexibility and high achievable quality. The performance of milling machines is constantly increasing, improving the convenience and increasing the competitiveness of this operation. However, the trend of performance improvement has found a technological limit: self-excited vibrations due to the dynamics of the system machine-workpiece-tooling (i.e. chatter). Chatter is the most dangerous dynamic phenomena that could happen during milling; due to its regenerative nature, it could lead the machine and the tooling system to a heavy fault or to the disruption of the workpiece. This paper develops an active workpiece holder that avoids chatter vibrations by a smart actuation of the workpiece. The design of the workpiece holder is a difficult task due to strict product requirements and the need to create a decoupled structure. The decoupling of the structure is a fundamental requirement of the product because this affects the controllability of the system. Axiomatic Design Theory is used to support the definition of the product requirements and the product architecture. After the definition of the optimal structure of the workpiece, the design features are integrated in order to obtain a functional decoupled structure

Investigation and Correction of Actual Microphone Response for Chatter Detection in Milling Operations

Integrating sensors in machine tools for monitoring purpose entails dealing with different issues, not only related to accessibility and safety but also to measureable bandwidth and linearity of the sensors. Those factors could be related to the sensor itself but also to sensor–machine interaction that could drastically affect sensor performances and reliability. This paper presents a dedicated experimental investigation of the actual response of microphone transducer inside the machine-tool chamber, highlighting the effects of the machine-tool chamber in altering response linearity. The identified response is then processed with specifically developed equalization filters to correct the measured response and rescale the amplitude of frequency contributions, as required by most chatter detection techniques. The main aspect of both the experimental identification procedure and the development of an effective correction approach are presented and discussed. Finally, the technique is tested in processing signals acquired in experimental chatter tests to estimate the achievable improvements

Intelligent Fixtures for Active Chatter Control in Milling

AbstractThe mitigation of chatter vibrations in milling has collected the interest of several researches in the last decades. One of the most industrially oriented alternatives is represented by active fixtures, complex mechatronic devices capable of actuating the workpiece during machining operations, with the purpose of stabilizing the process by generating counteracting vibrations. Most of the previous works show different fixture architecture and model based control techniques. This paper deals with the development and testing of such an active fixture, presenting the main design aspects and the features of the black-box control-logic used. Experimental tests are presented to show the achievable chatter mitigation

Speed-varying Machine Tool Dynamics Identification Through Chatter Detection and Receptance Coupling

AbstractTool-tip Frequency Response Function (FRF) represents one of the essential inputs to predict chatter vibration and compute the Stability Lobe Diagram (SLD). Tool-tip FRFs are generally obtained for the stationary (non-rotating) condition. However, high speeds influence spindle dynamics, leading to a reduced accuracy of the SLD prediction. This paper presents a comprehensive method to identify speed-varying tool-tip FRFs and improve chatter prediction. First, FRFs for a screening tool is identified by a novel technique based on a dedicated experimental test and analytical stability solution. Then, a tailored receptance coupling technique is used to predict speed-varying tool-tip FRFs of any other tool. Proposed method was experimentally validated: chatter prediction accuracy was demonstrated through chatter tests