A Smart Tool Holder Calibrated by Machine Learning for Measuring Cutting Force in Fine Turning and Its Application to the Specific Cutting Force of Low Carbon Steel S15C

Real-time monitoring of the cutting force in the machining process is critical for improving machining accuracy, optimizing the machining process, and optimizing tool lifetime; however, the dynamometers are too expensive to be widely used by machine tool users. Therefore, this paper presents a simple and cheap apparatus—a smart tool holder—to measure the cutting force of turning tools in the finishing turning. The apparatus does not change the structure of the turning tool. It consists of a tool holder and a piezoresistive force sensor foil, and transmits the signal through Bluetooth wireless communication. Instead of dealing with the circuit hardware, this paper uses the Artificial Neural Network (ANN) model to successfully calibrate the warm-up shift problem of the piezoresistive force sensor. Such a software method is simple, and considerably cheaper than the hardware method. For the force measurement capability of the smart tool holder, the cross-interference between orthogonal forces are very small and thus can be ignored. The force reading of the smart tool holder possesses high repeatability for the same turning parameters and high accuracy within the experiment groups. The authors apply the smart tool holder to cut the low carbon steel S15C, and to determine its specific cutting force in fine turning. The resulting fine turning force model agrees very well with the measurement. Its mean absolute deviation is 3.87% and its standard deviation is 1.55%, which reveals that the accuracy and precision of the smart tool holder and the fine turning force model are both good.

Cutting Forces and Tool Wear Investigation during Turning of Sintered Nickel-Cobalt Alloy with CBN Tools

This article describes issues related to the machining of parts made of sintered nickel-cobalt alloy. Longitudinal turning with a CBN (cubic boron nitride) tool was analyzed. The results of experiments showed the influence of cutting parameters in the field of finishing machining on the values of cutting forces and specific cutting force, taking into account the wear of the cutting edge. Measurements and analysis of the topography and roughness parameters of the machined surface, as well as the cutting tool wear, were presented. The microscopic examination showed that the average grain size of the sintered nickel-cobalt alloy was 3.22 ± 0.1 (μm). The presence of the hardening state variability of the material during machining, as well as the value of the cutting force fluctuation as a function of the tool wear VB, were stated. The specific cutting force values increased to a small degree for the tool wear in the range of VB = 0–0.2 mm, and reached similar values in the range kc = 5500–7500 N/mm2. The specific cutting force values increased significantly for wear VB > 0.2 mm and were characterized by a large variability. The occurring phenomena were analyzed and several explanations were proposed. A recommendation was developed for the machining of parts made of sintered nickel-cobalt alloy. The Taguchi method was used in the experiment methodology.

Feeling Machine for Process Monitoring of Components with Stock Allowance

To realize the increasing automation and flexibilization of production, it is necessary to monitor component-specific characteristics under fluctuating production conditions. Signals with a high correlation to the process quality have to be evaluated. In machining, the process force is an important measurand, which is sensitive to changes in the process. Feeling machines with force-sensitive machine tool components are therefore a promising signal source to monitor the machining. However, the force is also sensitive to non-critical process fluctuations such as stock allowance. Consequently, it is necessary to perform signal pre-processing and generate features that increase the robustness of the monitoring. In this paper, the material-specific cutting force was investigated for the first time concerning its suitability for process monitoring of parts with a stock allowance. The sensitivity of confidence limits was evaluated based on the normed bandgap. For the investigation, face turning processes of 20MnCr5 were carried out. The results show that the use of material-specific cutting force improves the sensitivity of the confidence limits to process errors. In this context, the feeling machine can be used to substitute the dynamometer for process monitoring.

Effect of Tool Rake Angle and Crystal Orientation on Ductile Mode Cutting of Hard/Brittle Materials

The effects of negative rake angles on the ductile mode cutting of soda glass and sapphire were studied. In addition, the machining mechanism was studied using a groove-cutting model based on the orthogonal cutting theory. It was found that the specific cutting forces in ductile mode cutting increase on both the soda glass specimen and on the sapphire specimen when the rake angle of the tool becomes negative. The difference between the experimental data and theoretical data of the specific cutting forces becomes large when the tool has a high rake angle on the negative side. This is attributed to effects of the roundness of the edge, the effects of the roundness of the nose, and the plowing mechanism, which causes plastic flow of the work material to both sides of the groove. The specific cutting force of sapphire depends on the cutting direction against the crystal orientation. The specific cutting force of sapphire depends on the cutting direction in terms of the crystal orientation. The anisotropy of the cutting force of sapphire also depends on the rake angle of the tool.

Comparison on various machinability aspects between mixed and reinforced ceramics when machining hardened steels

The hard turning process has an attracting interest in different industrial sectors for finishing operations of hard materials. However, it still presents disadvantages with respect to process capability and reliability. This paper describes a comparison of surface roughness, specific cutting force and flank wear between mixed ceramic CC650 (Al2O3 (70%) + TiC (30%)) and reinforced ceramic CC670 (Al2O3 (75%) + SiC (25%)) cutting tools when machining in dry hard turning of AISI 4140, treated at 52 HRC using the response surface methodology (RSM). A mathematical prediction model of the machining responses has been developed in terms of cutting speed, feed rate and cutting time parameters. Experimental observations show that the surface roughness obtained with the mixed ceramic insert significantly improved when compared with reinforced ceramic insert with a ratio of 1.44. In the same way, insert CC650 has better performance compared to reinforced ceramic inserts CC670, in terms of the specific cutting force and flank wear.