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2 Journal of Machine Engineering

2 2015

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Real-Time Compensation of Machine Tool Thermal Error Including Cutting Process

Horejs O., Mares M., Hornych J.

Journal of Machine Engineering

2015

Vol. 15, No. 3

5--18

The challenge to be addressed by this paper is to extend the common machine tool thermal compensation models considering only internal heat sources to include the effects of the cutting process. Although real-time software compensations of thermal errors exist, the majority of these models only presume machine tools under load-free rotation of the main spindle without any reference to rough machining. The machining process is completely neglected in spite of the fact that it represents a significant heat source and causes workpiece inaccuracy. This paper presents a real-time compensation of three-axis vertical milling centre thermal errors including the cutting process effect. The simulation is based on dynamic modelling using transfer functions. The model was implemented into a standard CNC controller of a three-axis vertical milling centre to compensate for thermal errors in real time. The inputs of the compensation algorithm are the spindle rotational speed, the 5 temperatures of the machine structure and spindle power. A reduction of thermal errors achieved by using the new approximation TF model including cutting process impact is up to 79% for steel cutting tests with different cutting conditions.

Advanced Thermal Error Compensation of a Floor Type Machining Centre Allowing for the Influence of Interchangeable Spindle Heads

Mares M., Horejs O., Hornych J.

Journal of Machine Engineering

2015

Vol. 15, No. 3

19--32

Thermal errors caused by internal and external heat sinks and sources may cause more than 50% of machine tool (MT) total error. Demands on machining accuracy and machine time utilization are still increasing. Therefore, research on thermal behaviour of MT structures is crucial for successful manufacturing. Direct (measuring between tool and work-piece) and indirect (predictive models) approaches to compensation of thermo-dependent tool centre point (TCP) displacement can be used to reduce sensitivity to heat flow or temperature control of MT and its environment. Thermal error indirect compensation is one of the techniques widely employed to reduce thermal errors due to its cost-effectiveness and ease of implementation. This paper is a continuation of scientific work on the modelling of complex MT thermal behaviour using a dynamic method with a physical basis: thermal transfer functions (TF). Previously published works focusing on middle-sized MTs are extended here to include heavy-duty MT application. Particular attention is paid to issues concerning compensation of thermal errors caused by interchangeable spindle heads.