Generalized cutting force model for peripheral milling of wood, based on the effect of density, uncut chip cross section, grain orientation and tool helix angle

R Curti,G Goli,B Marcon,L Denaud,M Togni,R Furferi

doi:10.1007/s00107-021-01667-5

Abstract

The influence of the grain angle on the cutting force when milling wood is not yet detailed, apart from particular cases (end-grain, parallel to the grain, or in some rare cases 45°-cut). Thus, setting-up wood machining operations with complex paths still relies mainly on the experience of the operators because of the lack of scientific knowledge easily transferable to the industry. The aim of the present work is to propose an empirical model based on specific cutting coefficients for the assessment of cutting force when peripheral milling of wood based on the following input: uncut chip thickness and width, grain angle (angle between the tool velocity vector and the grain direction of the wood), density and tool helix angle. The specific cutting coefficients were determined by peripheral milling with different depths of cut wood disks issued from different wood species on a dynamometric platform to record the forces. Milling a sample into a round shape (a disk) allows to measure the cutting forces toward every grain angle into a sole basic diameter reduction operation. Force signals are then post-processed to carefully clean the natural vibrations of the system without impacting their magnitudes. The experiment is repeated on five species with a large range of densities, machining two disks per species for five depths of cut in up- and down milling conditions for three different tool helix angles. Finally, a simple cutting force model, based on the previously cited parameters, is proposed, and its robustness analysed.

Highlights

The cutting forces on the workpiece observed during wood machining are induced by three main components in the cutting mechanisms: the required new surface generation energy, the friction of the chip on the tool, and the mechanical energy dissipation inside the chip, as clearly presented by Atkins (2005)
The method consists in machining a wood specimen into a round shape in order to cut it with every possible grain angle
Two replicates were performed for each cutting condition, on two different specimens machined into different slabs; each one providing averaged cutting forces to compute a corresponding specific cutting coefficient Ks

Summary

Introduction

The cutting forces on the workpiece observed during wood machining are induced by three main components in the cutting mechanisms: the required new surface generation energy, the friction of the chip on the tool, and the mechanical energy dissipation inside the chip, as clearly presented by Atkins (2005). From an engineering point of view, high cutting forces are more likely to introduce tool deflection or vibrations and to increase the defects of the part. Prior to machining, modelling and simulating of the cutting forces could be a great help for manufacturers in order to set the feed speed and the revolution per minute of the tool to stay within the machine spindle power range, verify their fixture, optimize both the material and cycle time (linked to the energy consumed during the process) as well as the final quality of their production. Tools manufacturers express their wish to use cutting forces models to run the right tools for the right applications as well as providing the optimized cutting parameters range depending on the operation to perform

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Conclusion