Abstract
Load induced errors aroused by internal masses of machine tool components and external cutting forces are a main contributor that influences machining accuracy. A mathematical model for load induced errors identification of large-span crossbeam in heavy-duty machine tool was proposed. According to the identified load induced errors, a method for optimisation of the guideway camber curve on crossbeam by particle swarm optimisation was proposed. Geometric errors of y-axis along cambered crossbeam and noncambered crossbeam were calibrated, and multibody system theory was also introduced to predict theoretically the machining accuracy of machine tool with two kinds of crossbeam. The comparisons between two kinds of crossbeam show that after cambering, the geometric errors are decreased and can meet the requirements of ISO standard, and the machining accuracy is enhanced remarkably too. In addition, the indirect dynamic straightness error of z-direction along cambered crossbeam was measured by displacement sensors, and the response results show that even though at the start-stop moment, the straightness error is also within the reasonable range of ISO standard.
Highlights
The accuracy of machine tools is a critical factor that affects the quality of manufactured products and an important consideration for any manufacturer
Geometric errors are caused by mechanical imperfections in the machine tool structure and the misalignment of machine tool elements: they arise under cold-start conditions and all change gradually due to component wear [1]
The milling machine tool with cambered crossbeam has better machining accuracy than that with noncambered crossbeam, which illustrates the usefulness of the optimised camber curve theoretically
Summary
The accuracy of machine tools is a critical factor that affects the quality of manufactured products and an important consideration for any manufacturer. Zargarbashi and Mayer [14] developed a single set-up estimation of a fiveaxis machine tool based on Capball sensor measurement, which can estimate four tilt errors and centre line offsets of the rotary axes These methods cannot identify all six angular geometric error parameters of each rotation axis separately and quickly. External loads that cause errors in a machine include gravity (a function of the weight of the part to be machined), cutting load which arises from the cutting process, and axis acceleration load resulting from the displacement of the masses of the machine components [19] These errors are the load induced errors and badly affect the stiffness of a machine tool structure.
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