A general approach to simulating workpiece vibrations during five-axis milling of turbine blades

In the present paper the chatter instability of variable speed machining is studied. Though, there exist numerical methods for the computation of the stability lobes for variable speed machining, especially in turning processes the potential of an active spindle speed variation for chatter suppression is mostly unexploited. In the case of a slowly time-varying spindle speed, which is practicable on a real machine tool, the stability behavior with a time-varying spindle speed is connected to the stability behavior with constant spindle speeds. This so-called frozen time approximation helps to understand the stabilizing mechanism of turning with spindle speed variation. Strategies for tuning the parameters of the speed variation for an optimal stabilization are developed. The results presented here are useful for a practical implementation of variable speed machining to increase the productivity without any negative effect due to the variation of the spindle speed.

Application of spindle speed variation for chatter suppression in turning

Orbital drilling is a highly complex machining operation. Due to the tool helical trajectory, the chip thickness is highly variable along the cutting edges and during the tool revolution. This can be made even more difficult by the cutting tool geometry, which can be also very complex. This explains why cutting forces are very difficult to model and to estimate for different cutting tool geometries. The aim of this study is to develop a cutting forces model depending on the tool geometry and cutting conditions in order to control the final quality of the machined borehole. First, the geometry of the chip is modelled taking into account the parameters defining the trajectory and the tool geometry. A cutting force model, based on the instantaneous chip thickness, is then set up. An experimental study validates the modelling through measurements of cutting forces made during orbital drilling tests. From this modelling, it is possible to optimise the cutting parameters and the geometry of the cutting tool in order to control the loading on the tool and thus the final quality of the borehole.

Modelling of cutting forces in orbital drilling of titanium alloy Ti–6Al–4V

Chatter avoidance in cutting highly flexible workpieces

https://ercnsm.osu.edu/sites/ercnsm.osu.edu/files/uploads/658.pdf

Determination of forces in high speed blanking using FEM and experiments

The numerical simulation of machining process is a key factor in the control of parts machining process. Its development aims at improving the process reliability and reduces the time spent during the process planning stage. In this context, we use a specific time domain simulation allowing modeling the dynamics of a thin wall part turning operation. After having introduced the basics of the proposed approach we present a specific cutting test that has been designed to specifically measure and control the dynamics of the part and the cutting conditions of a finishing toolpath. The influences of the cutting speed and damping coefficient on the chatter occurrence are discussed. In order to better control the simulation uses, an analysis of the simulation parameters influences on the simulated results is proposed.

/pdf/dynamic-study-of-thin-wall-part-turning-179k9j6mlq.pdf

Dynamic Study of Thin Wall Part Turning

Virtual Machining: a General Approach to Deal with Flexible Workpieces.

A new blanking process that involves punch speed up to 10 ms
 −1 has obvious advantages in increased productivity. However, the inherent dynamics of such a process makes it difficult to develop a practical high speed punch press. The fracture phenomenon governing the blanking process has to be well understood to correctly design the machine support and the tooling. To observe this phenomenon at various controlled blanking speeds a specific experimental device has been developed. The goal is to measure accurately the shear blanking forces imposed on the specimen during blanking. In this paper a new method allowing the blanking forces to be measured and taking into account the proposed test configuration is explained. This technique has been used to determine the blanking forces experienced when forming C40 steel and quantifies the effect of process parameters such as punch die clearance, punch speed, and sheet metal thickness on the blanking force evolution.

/pdf/high-speed-blanking-an-experimental-method-to-measure-4bg2b8ihyq.pdf

High Speed Blanking: An Experimental Method to Measure Induced Cutting Forces

Punching process is increasingly used in industry. The punching speeds increase induces the generation of new mechanisms which are characterized by high strain rates like strain rate hardening of materials. The increase of the punching speeds also involves the formation of adiabatic shear bands (ASB). These effects result in improving the cutting quality. The critical releasing speed of the observed phenomena depends on the workpiece material properties and on the process parameters. To understand and identify the activated mechanisms, a high speed punching device has been developed. The proposed device enables the user to regulate a gap between punch and die of about 0.1 mm with a precision of 0.02 mm. In this paper we will present various aspects related to the design of the punching device and an analysis of measurements obtained for a micro alloy steel S600M.

/pdf/experimental-study-of-a-high-speed-punching-process-4b0cl7nhef.pdf

Experimental study of a high speed punching process

The invention relates to a platen for measuring force with inertial compensation and comprising a base plate (4), an upper plate (5) and piezoelectric force sensors bridged together by each of the plates (4, 5), characterised in that the lower plate (5), intended for rigid interaction with a part to be machined of a machining tool, is triangular and in that the number of sensors is at least three, and in that it further comprises a set of six single-axis accelerometers (10-15), three of which (10, 11, 12) are oriented in the direction of the platen body while the three others (13, 14, 15) are located in the plane of the platen, two of the latter accelerometers (13, 14) being perpendicular to one of the sides thereof while the last one (15) is parallel thereto. The measuring method that uses the platen comprises identifying the sensor by a least square method in order to define the mass (m) of the assembly and the position of the centre of gravity thereof, and processing by calculation the measuring signal value of the platen in order to derive the value of the cutting force by subtracting, from the measure value, the calculated value of the mass-type inertia forces multiplied by the acceleration.

Arnaud Larue

Papers

Dynamic Study of Thin Wall Part Turning

Virtual Machining: a General Approach to Deal with Flexible Workpieces.

High Speed Blanking: An Experimental Method to Measure Induced Cutting Forces

Experimental study of a high speed punching process

Platinum and method for measuring a cutting force