Avoidance of collision-caused spindle damages—Challenges, methods and solutions for high dynamic machine tools

doi:10.1016/j.cirp.2011.03.031

CIRP Annals

Volume 60, Issue 1, 2011, Pages 425-428

https://doi.org/10.1016/j.cirp.2011.03.031 Get rights and content

Abstract

There are various reasons for collisions in the machining area during the production process. These collisions often cause damage to the tool, main spindle unit and machine axes. In industry different strategies are pursued to avoid serious and expensive consequences for the machine tool and the production process. This paper presents possible methods and solutions to prevent collisions and collision damages of machine tool components. In the focus of the accomplished considerations is the main spindle unit as one of the main components in the cutting process. A new technical solution for the avoidance of collision damage of motor spindles is introduced in this article. The functionality of the developed system under normal process conditions as well as in collision situations could be proved in various experiments.

Introduction

Various causes lead to collisions between moving components in modern metal-cutting machine tools. The most frequent sources of collisions are associated with mistakes caused by the operator during setting-up and operation of the machine tool, e.g. incorrect work piece positioning and tool election as well as programming errors of the numerical control. The arised damages caused to the concerned machine components cannot be neglected in most cases.

The appearing collision forces depend on the properties of the colliding machine parts (moving mass, rigidity) and the movement characteristics (direction of collision, speed of movement). Quite often, rapid speeds of 60 m/min and more (up to 120 m/min) can be reached in modern machine tools, particularly by using linear-direct drives in the feed axes. Resulting collision forces reach 100 kN and more. Depending on the intensity of the collision, the damages could lead to an immediate breakdown or reduced lifetime of the machine components resulting in failure of function after several hours. The main spindle unit is one of the machine tool components most susceptible to damage during a collision [1]. As depicted in Fig. 1, 60% of the damages caused to the main spindle unit result from overload in the form of collisions [2]. These damages can often lead to repair, service and replacement costs of up to 20,000 €. Rolling-element bearings, which are most commonly used, are extremely susceptible to damage. Due to the small contact surface areas between the races (both inner and outer) and the rolling-element, the maximum allowable interface pressure (ball bearing: 2000–2500 MPa; roller bearing: 1500–1900 MPa [3]) is exceeded when the collision forces are too high.

Section snippets

Avoiding collisions and the resulting damages

Since the beginning of the 1980s, various strategies have been followed to avoid serious collisions in machine tools. An increase in the complexity and productivity of machines over the years has led to a greater need for developing better protective measures.

Damage avoidance through collision protection system for motor spindles

Contact-based collision protection systems should respond to forces induced by external influences in case of overload and should not respond to normal operation conditions. This response can be made in an active manner by specifying the limiting values as in the case of sensor-based systems.

The system can also be made to respond passively by the mechanical placement of a switching threshold which disconnects the force flow when pre-defined limits are reached. Another way of inducing a passive

Conclusion and outlook

There are various strategies and technical solutions to avoid collisions and collision caused damages. This article presents a new developed spindle protection system. Its design enables to handle different collision situations by limiting peak forces at tool tip or loads at the spindle bearing.

The accomplished tests of a first prototype show a promising behavior under static conditions and in collision situations. The achievable mounting forces enable to withstand high axial and radial process

Acknowledgements

The authors thank the German AIF-Otto von Guericke e.V. for funding the project and the cooperational project partners Jakob Antriebstechnik GmbH and WZL RWTH Aachen.

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Avoidance of collision-caused spindle damages—Challenges, methods and solutions for high dynamic machine tools

Abstract

Introduction

Section snippets

Avoiding collisions and the resulting damages

Damage avoidance through collision protection system for motor spindles

Conclusion and outlook

Acknowledgements

Annals of the CIRP

Annals of the CIRP

Annals of the CIRP

Annals of the CIRP

Annals of the CIRP

Beeinflussbarkeit von Lebenszykluskosten durch Wissensaustausch–Produzieren mit Blick auf die Lebenszykluskosten

wt Werkstattstechnik Online