Investigation of ignition temperature, time to ignition and chip morphology after the high-speed dry milling of magnesium alloys

Abstract

Purpose -The purpose of this paper is to determine time-to-ignition of magnesium alloy chips and the ignition-preceding stages as well as to examine chip morphology. The tests were conducted according to the following pattern: directly after a milling operation, after ignition using a special test stand located outside the machine tool and after intensive oxidation which prevented ignition. Design/methodology/approach -Milling is a machining process widely used in the manufacturing of various parts that are applied, e.g. in the aircraft industry. Milling is used for both roughing and finishing machining. In the dry machining of magnesium alloys, spontaneous ignition can occur; therefore, the analysis of chip temperature in the cutting area is of great significance. Additionally, time-to-ignition and chip morphology are crucial when considering the safety of magnesium alloy machining processes. Findings -The experimental results demonstrate the effect of parameters of the milling process on time-to-ignition of chips made of magnesium alloys AZ31 and AZ91HP. The experiments also involved examining the morphology of a selection of chips produced at the maximum cutting velocity vc and feed per tooth fz. In addition, we analysed the morphology of both ignition products and chips subjected to high temperature where ignition did not occur. Practical Implications -Based on the time-to-ignition and chip morphology results, it is possible to indicate both safety levels in machining and the efficient range of parameters in the milling of aircraft parts made of magnesium alloys. Originality/value -The paper presents a new approach to assessing safety in milling operations. The results of the tests of chip flammability (time-to-ignition) which were run at a special test stand placed outside the machine tool enabled determination of both safety and efficiency range of the milling process.

The Analysis of Deformability, Structure and Properties of AZ61 Cast Magnesium Alloy in a New Hammer Forging Process for Aircraft Mounts

“…The research concentrated on a new forming process of forging an aircraft mount ( Figure 1 a) manufactured from a billet in the form of a sand-cast preform from a high-strength AZ61 grade magnesium alloy. Currently, aircraft mounts presented in Figure 1 b are manufactured by machining from cast elements or by multi-stage forging from wrought billet [ 28 , 29 , 30 , 31 ]. This technology is particularly time, labor, and energy-consuming.…”

The potential of SLM technology for processing magnesium alloys in aerospace industry

“…Another process which significantly reduced the grain size was machining with simultaneous cooling of the treated surface with liquid nitrogen [30]. However, there is a risk that fine chips that are formed during machining may ignite [13]. Grain refinement in magnesium alloy after ECAP process resulted in better mechanical strength, whereas machining improved the hardness of the near-to-surface layer almost two times.…”

“…Purging a molten metal with inert gases (Ar, SF6) in the casting process alone reduces the number of contaminants in the material and increases material elongation from 4 to 7% [12]. An additional problem in the processing of magnesium alloys is the risk of ignition and difficult extinguishing both at elevated temperature and when the material is loose; for example, it has the form of powder or chips [13]. Due to safety reasons caused by the risk of ignition, the use of magnesium alloys in cabin structure was prohibited [14].…”

Analysis of deburring effectiveness and surface layer properties around edges of workpieces made of 7075 aluminium alloy

“…Optimization of machining strategy to diminish the size of burrs by reducing the feed per tooth is not always recommended. In the case of magnesium alloys, at low feed per tooth, chip fractions may occur which are subject to ignition (Kuczmaszewski et al, 2016).…”