Abstract
This paper presents an accurate machining feedrate prediction technique by modelling the trajectory generation behaviour of modern CNC machine tools. Typically, CAM systems simulate machines’ motion based on the commanded feedrate and the path geometry. Such approach does not consider the feed planning and interpolation strategy of the machine’s numerical control (NC) system. In this study, trajectory generation behaviour of the NC system is modelled and accurate cycle time prediction for complex machining toolpaths is realised. NC system’s linear interpolation dynamics and commanded axis kinematic profiles are predicted by using finite impulse response (FIR)–based low-pass filters. The corner blending behaviour during non-stop interpolation of linear segments is modelled, and for the first time, the minimum cornering feedrate that satisfies both the tolerance and machining constraints has been calculated analytically for 3-axis toolpaths of any geometry. The proposed method is applied to 4 different case studies including complex machining toolpaths. Experimental validations show actual cycle times can be estimated with > 90% accuracy, greatly outperforming CAM-based predictions. It is expected that the proposed approach will help improve the accuracy of virtual machining models and support businesses’ decision-making when costing machining processes.
Highlights
With the introduction of concepts like virtual manufacturing [1] and digital twins [2], building process models and predicting actual machining process conditions in the computer environment has become paramount in attaining higher productivity and throughput in today’s manufacturing
This paper models the non-stop interpolation behaviour of modern numerical control (NC) systems and predicts feedrate profiles along high-speed machining (HSM) toolpaths by considering the real-time path blending behaviour of NC systems
As seen in Eq 1, the filter contains an integrator, which acts to smooth the input signal. These two features of 1st-order finite impulse response (FIR) filters are appealing from a NC system perspective, since G-codes can be convolved through a series of such filters to generate smooth velocity profiles
Summary
With the introduction of concepts like virtual manufacturing [1] and digital twins [2], building process models and predicting actual machining process conditions in the computer environment has become paramount in attaining higher productivity and throughput in today’s manufacturing. Modern NC systems are equipped with propriety algorithms that interpolate these lengthy series of short CL blocks smoothly These algorithms are called Look-ahead or Compressor functions and are capable of generating a non-stop motion with a time optimal feedrate profile [10] that respects kinematic limits of the machine [12, 13]. Predicting feedrate profiles along short segmented complex toolpaths for high-speed machining (HSM) is a challenging task This is due to the fact that look-ahead modules of NC systems alter jerk limits on the fly as it blends series of CL lines to generate a non-stop smooth continuous feed motion. This paper models the non-stop interpolation behaviour of modern NC systems and predicts feedrate profiles along HSM toolpaths by considering the real-time path blending behaviour of NC systems.
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