Synergistic approaches to ultra-precision high performance cutting

Lars Schönemann,Daniel Berger,Timo Dörgeloh,Oltmann Riemer,Ekkard Brinksmeier,Rudolf Krüger,Per Schreiber,Berend Denkena,Johannes Hochbein,Nasrin Parsa,Christian Schenck,Bernd Kuhfuß

doi:10.1016/j.cirpj.2019.12.001

Abstract

Diamond milling allows for the flexible production of optical and high precision parts, but suffers from poor setup and production speeds. This paper presents recent advances that aim towards achieving high performance (HPC) and high speed cutting (HSC) in ultra-precision machining. After a short introduction, the benefits of high speed cutting for both metals and brittle-hard materials are shown. Thereafter, novel mechatronic devices are presented that enable an automated balancing of the applied air bearing spindles and the application of multiple diamond tools on one tool holder and by thus, contribute to HPC. These developments are supplemented by a novel linear guiding system based on electromagnatic levitation that, along with a dedicated model-based control system, enables fast and precise movements of the machine tool. After presenting the recent developments in detail, their synergistic performance is assessed and an outlook to future developments is given.

Highlights

Ultra-precision machining with diamond cutting tools has been known for decades for its usability in generating metal optical surfaces for technical mirrors and molds [1]
Without viable means to quickly balance the high speed spindle, the machine setup is a tedious and time-consuming process and cannot be applied economically. This is similar to the application of multiple diamond cutters on a single milling tool: having more cutting edges engaged in the material process allows for faster movement of the feed axes which, in turn, requires a fast-actuating slide and bearing concept, like the electromagnetic linear guide presented in Section “Increasing the feed velocity using electromagnetic levitation technology”
This paper summarizes the current state of developments of the Research Unit FOR1845 on ultra-precision high performance cutting made by the Universities of Bremen and Hannover over the past years

Summary

Introduction

Ultra-precision machining with diamond cutting tools has been known for decades for its usability in generating metal optical surfaces for technical mirrors and molds [1]. Adiabatic shearing, caused by thermal softening of the machined material, leads to reduced heat transfer into the workpiece, reduced mechanical stresses and improved surface finish during conventional high speed cutting [22]. The use of high rotational speeds is a challenge for setting up diamond fly-cutting due to a relatively large rotating mass, i.e. the tool holder, due to the quadratic influence of the angular velocity V on the centrifugal force Fcen. This leads to a significant reduction of the permissible residual specific unbalance eper to achieve the same rotor balancing grade G (see Eq (2)) with increasing rotational speed [33]:. To amplify the unbalances of the system in X-direction, the coupling joints are disconnected from the top plates (measuring state)

Experimental setup

20 Â 25 Â 12 mm3

Findings

Summary and outlook