Productivity Of Machining Operations Research Articles

A hybrid physics and data-driven model for spindle fault detection

Machine tool spindles must be periodically monitored to ensure the accuracy and productivity of machining operations. This paper presents a spindle fault detection model that is based on the combination of physics-based simulation and a machine learning network. The spindle imbalance and the wear of the race and ball are incorporated into the digital model of spindle dynamics, and the resulting vibrations at sensor locations are predicted at different speeds. A Gated Recurrent Unit Network (GRU) is trained to recognize the faults using the simulated and a few experimental vibration spectrum data. The model gave 97.6% fault detection accuracy when it is tested on faulty spindles.

Autoregressive Spectrum Analysis of Vibration and Condition Monitoring of Self-Propelled Rotary Tool

Self-propelled rotary tools are being rediscovered for their applications in machining of ‘difficult-to-machine’ materials or for general improvement in the productivity of machining operations. The vibration characteristic and the occurrence of chatter during high speed cutting will induce the deterioration of precision and machining surface, tool wear and tool life. This paper deals with the identification of the vibration in SPRT cutting system with AR time series model. The experiment and deduction method provide a sound foundation for improving the structure with high antivibration strength, which could reduce the relative vibration between tool and workpiece in the alloweable scope.

Modeling of cutting forces in a face-milling operation with self-propelled round insert milling cutter

Rotary tools are being rediscovered for their applications in machining of ‘difficult-to-machine’ materials or for general improvement in the productivity of machining operations. While, a detailed analysis of application of rotary tools in turning operations has been done, their application in the generation of plain surfaces has received limited attention. This paper deals with the modeling of cutting forces in a face-milling operation performed using self-propelling inserts. The proposed model incorporates differences in the machining mechanics of self-propelling inserts due to the difference in their geometry and rotation in a static force prediction model in a face-milling operation with stationary inserts. The predicted values of cutting forces evaluated by the proposed model are in excellent agreement with the experimental value than those predicted using the static force model as it is.

Robust Machining Force Control With Process Compensation

Force control is an effective means of improving the quality and productivity of machining operations. Metal cutting force models are difficult to accurately generate and, thus, there is large uncertainty in the model parameters. This has lead to investigations into robust force control techniques; however, the approaches reported in the literature include known process changes (e.g., a change in the depth-of-cut) in the model parameters variations. These changes create substantial variations in the model parameters; thus, only loose performance bounds may be achieved. A novel robust force controller is presented in this paper that explicitly compensates for known process effects and accounts for the force-feed nonlinearity inherent in metal cutting operations. The controller is verified via simulation and experimental studies and the results demonstrate that the proposed controller is able to maintain tighter performance bounds than robust controllers that include known process changes in the model parameter variations.

An Investigation of Variable Spindle Speed Face Milling for Tool-Work Structures With Complex Dynamics, Part 2: Physical Explanation

Part 2 of this paper focuses on the explanation, both on theoretical grounds and through model simulations, of why the technique of variable spindle speed machining is an effective tool for increasing the quality and productivity of machining operations. In particular, Part 2 explains why, by disturbing the regenerative and forced vibration excitation frequencies which generate large amplitudes of vibration during constant speed machining, variable speed machining has the potential to reduce the vibration of the tool-work system and be robust with respect to the cutting process dynamics. The explanation is based on the work done by the cutting forces, the chip load variation, tool-work displacements, cutting forces, and workpiece surface error generated by both constant and variable speed machining. By investigating the effects of regeneration and forced vibration during variable speed machining on the vibration of tool-work systems having different cutter diameter-to-workpiece width ratios, it has been shown that variable speed machining is also robust with respect to the geometry of the tool-work system. This work concludes that variable speed machining is safer to use than constant speed machining when the effects of the tool-work dynamics and geometry on the vibration of the cutting process are hard to determine.

High-speed milling of advanced materials

The productivity of machining operations can be increased and the quality of products can be improved by using higher cutting speeds than applied conventionally. However, High-Speed Milling (HSM) is much more than just the high revolution speed of the spindle of the machine tool. In this paper utilization of HSM in the manufacturing of the products made of different advanced materials is described. Results are based on the collaborative investigation performed by VTT and HUT in close cooperation with Finnish industry. Utilizing HSM in manufacturing of electrodes for electric discharge machining (EDM) does not permit the special properties of graphite as a workpiece material to be ignored. However, high chip removal volumes with economical tool life for relatively small end mills can be achieved when milling electrodes involving precise details. Polymer-matrix composites such as carbon and glass fibre, which are usually considered difficult or even impossible to machine, have been high-speed milled by using advanced carbide and diamond tools. Tests for materials used typically in model and prototyping manufacturing have been performed in order to determine the minimum reliably achievable thickness/height -ratio for thin ribs. The most interesting application field of HSM is the finishing operations of tool steels. Products made of hardened tool steel and comprising three-dimensional surfaces have successfully been milled with special cubic boron nitride (CBN) end mills without any significant tool wear.