Subjective hearing sensation of process variations at a milling machine. How reliable will chatter marks be detected?

Intuition enables experienced machine operators to detect production errors and to identify their specific sources. A prominent example in machining are chatter marks caused by machining vibrations. The operator's assessment, if the process runs stable or not, is not exclusively based on technical parameters such as rotation frequency, tool diameter, or the number of teeth. Because the human ear is a powerful feature extraction and classification device, this study investigates to what degree the hearing sensation influences the operators decision making. A steel machining process with a design of experiments (DOE)-based variation of process parameters was conducted on a milling machine. Microphone and acceleration sensors recorded machining vibrations and machine operators documented their hearing sensation via survey sheet. In order to obtain the optimal dataset for calculating various psychoacoustic characteristics, a principle component analysis was conducted. The subsequent correlation analysis of all sensor data and the operator information suggest that psychoacoustic characteristics such as tonality and loudness are very good indicators of the process quality perceived by the operator. The results support the application of psychoacoustic technology for machine and process monitoring.

Proposed Stable Machining Condition Search Method Based on Machined Surface Information after End Milling

Chatter vibration in end milling remains a serious problem for manufacturing engineers. Chatter vibration often leaves a characteristic pattern or chatter mark on the machined surface. Chatter marks are generated by the relative displacement of the tool and the workpiece. Closer observation of chatter marks may prove useful in understanding chatter vibration. In this study, we investigated chatter mark patterns on end-milled surfaces. Based on these observations, we proposed and demonstrated the effectiveness of an iterative analysis method to identify stable machining conditions and minimize chatter vibration in various operations without use of sensors under specific conditions.

A Study on the Relationship Between the Variation of Rolling Parameters and the Vibration Characteristics of Twenty-High Rolling Mill

As a common defect in the production of high-quality steel strip, chatter marks are easily found on the strip surface which may resulting from inappropriate variation of rolling parameters of a twenty-high rolling mill and the quality of the strip surface can be significantly affected. Therefore, it is critical to understand the underlying relationship between the vibration mechanisms of chatter marks and rolling parameters, furthermore, an appropriate adjustment strategy of rolling parameters is needed to improve the quality of the strip surface. To addressing this problem, a dynamic model of the twenty-high rolling mill, coupling the vertical and horizontal vibrations (because of the variation in friction tension forces), is proposed to investigate the vibration characteristics under different rolling conditions. Based on this dynamic model, effects of rolling force, rolling speed and fluctuations of tension on the vibration of the twenty-high rolling mill are studied. Finally, a rolling parameter adjustment strategy is discussed and presented based on the research results.

The Effect of Roll Misalignment on Vibration Response of Roll Grinder

The chatter marks may be caused by the roll misalignment during the grinding process of roll grinder, which can affect the quality of the roll surface of the strip steel. Based on a doubly regenerative time delay grinding model, a 2-degree-of-freedom lumped parameter model of a roll grinder with the roll misalignment fault is presented to investigate the effect of a roll misalignment on its vibration responses. A Runge-Kutta numerical integration method is applied to calculate the vibration response from the presented model. The effects of the roll misalignment and the rolling speed are investigated. Moreover, an experiment setup is presented. Numerical results from the presented model are compared with experimental results to validate the presented model. It seems that the results may provide some guidance for the detection of the misalignment fault and monitoring of the operation state of the roll grinder.

Mechanism of the Strip Surface Chatter Marks with 1220 Cold Rolling Mill

Aiming at a 1220 strip surface, where the Cold Rolling Mill had chatter marks, on which the reasons for the formation was tracked tested for in-depth study. Based on the vibration test, the analysis was given to the dynamic characteristics of the rack [1-3]. It was found that had reaction to the mill that caused the forced vibration mill to further accelerate the formation of chatter marks. In the analysis of the mechanism on the chatter marks, the relationship between chatter marks spacing and vibration source was considered in successfully finding out the cause of the 1220 mill chatter marks generated, and then the chatter marks suppression measures were proposed with satisfied effects.

System Identification of a Grinding Machine Excited by an Active Tool Holding Device

Reducing the cost of manufacturing products can be realized by high performance, precise and productive machine tools. This goal is often obtained by the user increasing the adjustable machine parameters, which include the feed rate or the cut depth. Both will increase the grinding force during the grinding process, which can result in an excitation of the machine structure. If the excitation is too high, the machine structure can show an undesired dynamic behavior, which can cause the machine to vibrate. These vibrations can result in chatter marks on the work piece surface and if large enough can result in a production stop. One possibility to minimize the chance of excessive vibration is a conservative choice of machine parameters which are well below the optimal set for a particular machine. This paper presents an approach which shows the first results of an active tool holding device aimed at reducing unwanted vibrations resulting from an aggressive parameter choice.