Physicomechanical Nature of Acoustic Emission Preceding Wire Breakage during Wire Electrical Discharge Machining (WEDM) of Advanced Cutting Tool Materials

The field of applied wire electrical discharge machining (WEDM) is rapidly expanding due to rapidly increasing demand for parts made of hard-to-machine materials. Hard alloys composed of WC, TiC and Co are advanced cutting materials widely used in industry due to the excellent combination of hardness and toughness, providing them obvious advantages over other cutting materials, such as cubic boron nitride, ceramics, diamond or high-speed steel. A rational choice of the WEDM modes is extremely important to ensure the dimensional quality of the manufactured cutting inserts, while roughness of the machined surface on the cutting edge is of great importance with regards to the application of wear-resistant coatings, which increases tool life. However, the stock control systems of CNC WEDM machines, which are based on assessment of electrical parameters such as amperage and voltage, are unable to timely detect conditions at which a threat of wire breakage appears and to prevent wire breakage by stopping the electrode feed and flushing out the interelectrode gap (IEG) when hard alloys with high heat resistance and low heat conductivity, such as WC, TiC and Co composites, are being machined, due to the inability to distinguish the working pulses and pulses that expend a part of their energy heating and removing electroerosion products contaminating the working zone. In this paper, the physicomechanical nature of the WEDM of hard alloy WC 88% + TiC 6% + Co 6% was investigated, and the possibility of using acoustic emission parameters for controlling WEDM stability and productivity were explored. Acoustic emission (AE) signals were recorded in octave bands with central frequencies of 1–3 and 10–20 kHz. It was found that at the initial moment, when the dielectric fluid is virtually free of contaminants, the amplitude of the high-frequency component of the VA signal has its highest value. However, as the contamination of the working zone by electroerosion products increases, the amplitude of the high-frequency component of the AE signal decreases while the low-frequency component increases in an octave of 1–3 kHz. By the time of the wire breakage, the amplitude of the high-frequency component in the octave of 10–20 kHz had reduced by more than 5-fold, the amplitude of the low-frequency component in the octave of 1–3 kHz had increased by more than 2-fold, and their ratio, coefficient Kf, decreased by 12-fold. To evaluate the efficiency of Kf as a diagnostic parameter, the quality of the surface being machined was investigated. The analysis of residual irregularities on the surface at the electrode breakage point showed the presence of deep cracks and craters typical of short-circuit machining. It was also found that the workpiece surface was full of deposits/sticks, whose chemical composition was identical to that of the wire material. The presence of the deposits evidenced heating and melting of the wire due to the increased concentration of contaminants causing short circuits. It was also shown that the wire breakage was accompanied by the “neck” formation, which indicated simultaneous impacts of the local heating of the wire material and tensile forces. Due to the elevated temperature, the mechanical properties the wire material are quickly declining, a “neck” is being formed, and, finally, the wire breaks. At the wire breakage point, sticks/deposits of the workpiece material and electroerosion products were clearly visible, which evidenced a partial loss of the pulses’ energy on heating the electroerosion products and electrodes. A further increase in the contamination level led to short circuits and subsequent breakage of the wire electrode. It was shown that in contrast to the conventional controlling scheme, which is based on the assessment of amperage and voltage only, the analysis of VA signals clearly indicates the risk of wire breakage due to contamination of the working zone, discharge localization and subsequent short circuits. The monotonic dependence of WEDM productivity on AE parameters provides the possibility of adaptive adjustment of the wire electrode feed rate to the highest WEDM productivity at a given contamination level. As the concentration of contaminants increases, the feed rate of the wire electrode should decrease until the critical value of the diagnostic parameter Kf, at which the feed stops and the IEG flushes out, is reached. The link between the AE signals and physicomechanical nature of the WEDM of advanced cutting materials with high heat resistance and low heat conductivity in different cutting modes clearly shows that the monitoring of AE signals can be used as a main or supplementary component of control systems for CNC WEDM machines.

Application of Polydioxanone Sutures in the Nuss Procedure

Background/Purpose The Nuss procedure is the most common surgical repair for pectus excavatum (PE). Surgical steel wires are used in some modifications of the Nuss procedure to attach one or both ends of a support bar to the ribs. During follow-up, wire breakage was found in some cases. Patients with wire breakage may undergo prolonged bar removal surgery and may be exposed to excessive radiation.In this study, we had a series of patients who received polydioxanone suture (PDS) fixations instead of steel wires. This retrospective study was conducted to explore the differences between these two fixation materials in the incidence of related complications and efficacies. Furthermore, we attempted to observe whether the two materials lead to similar surgical efficacy in the Nuss procedure, whether they have divergent effects on the bar removal surgery, and whether PDS can reduce the risks due to steel wire breakage as expected. Methods We retrospectively studied PDS and surgical steel wires as fixation materials for the Nuss procedure in children with congenital PE and reviewed the outcomes and complications. A total of 75 children who had undergone Nuss procedure repairs and bar removals from January 2013 to December 2019 were recruited to participate in this study. They were divided into three groups: the PDS group, the unbroken wire (UBW) group, and the broken wire (BW) group, according to the fixation materials and whether the wires had broken or not. Moreover, we selected the duration of operation (DO), intraoperative blood loss (BL), bar displacement (BD), postoperative pain score (PPS), and incision infection as the risk indicators and the postrepair Haller index (HI) as the effectiveness indicator. These indicators were statistically compared to determine whether there were differences among the three groups. Results One BD occurred in the PDS and BW groups while none took place in the UBW group. No incision infection was found in any of the groups. The PDS group had the shortest DO, while the DO in the UBW group was shorter than that in the BW group (p < 0.05). BL in the PDS group was less than that in the other two groups (p < 0.05). Additionally, no difference was observed in BL between the BW and UBW groups (p > 0.05). The PPS of the PDS group was less than that of the BW group (p < 0.05), whereas no differences were found between the other two groups. No statistical difference emerged in HI among the groups (p > 0.05). Conclusion PDS fixation results in a similar repair outcome and shows certain advantages in the DO, BL, and PPS; also, PDSs are safe and effective in the Nuss procedure. Level of evidence Level III.

A Comparison Of Efece Systems With Tension Band Wiring For Patella Fracture Fixation In Cadavers

Background: EFECE Systems are newly-defined internal fixation systems, which are suitable for patella fracture fixation. The aim of this study was to compare the fixation strength of EFECE Systems with tension band wiring for transverse patellar fracture simulation on fresh frozen cadaver models. Methods: Quadriceps tendon-patella-patellar tendon (QT-P-PT) complex was prepared from human cadavers. After simulation of a transverse patella fracture, in Group 1, 5 patella were fixed with a pair of 1.2 mm EFECE wires and 4 EFECE devices. In Group 2, 5 patella were fixed with a pair of 1.2 mm Kirschner wires (K-wire) and a cerclage wire according to the tension band technique.Using a testing device with custom-made jaws, increasing distraction force was applied to these QT-P-PT complexes. Extension of these complexes with the distraction forces was observed. The maximum distraction force and the elongation during maximum force were evaluated. Results: After 5 experiments with the EFECE Systems, there was no EFECE wire breakage or EFECE wire-EFECE device catching failure. The median maximum force was 740 N (720-810N). During maximum distraction force the median extension was 2.5 mm (1.6-2.5 mm).After 5 experiments with the tension band technique, there was no K-wire breakage. The median maximum force was 330 N (240-510N). During this maximum distraction force the median extension was 3.4 mm (2.2-3.8 mm).Conclusions: Based on the biomechanical advantages, patella fracture treatment with EFECE systems may constitute a reasonable alternative in the treatment of patella fractures.

A Comparison of Efece Systems With Tension Band Wiring for Patella Fracture Fixation in Cadavers

Background: EFECE Systems are newly-defined internal fixation systems, which are suitable for patella fracture fixation. The aim of this study was to compare the fixation strength of EFECE Systems with tension band wiring for transverse patellar fracture simulation on fresh frozen cadaver models. Methods: Quadriceps tendon-patella-patellar tendon (QT-P-PT) complex was prepared from human cadavers. After simulation of a transverse patella fracture, in Group 1, 5 patella were fixed with a pair of 1.2 mm EFECE wires and 4 EFECE devices. In Group 2, 5 patella were fixed with a pair of 1.2 mm Kirschner wires (K-wire) and a cerclage wire according to the tension band technique.Using a testing device with custom-made jaws, increasing distraction force was applied to these QT-P-PT complexes. Extension of these complexes with the distraction forces was observed. The maximum distraction force and the elongation during maximum force were evaluated. Results: After 5 experiments with the EFECE Systems, there was no EFECE wire breakage or EFECE wire-EFECE device catching failure. The median maximum force was 740 N (720-810N). During maximum distraction force the median extension was 2.5 mm (1.6-2.5 mm).After 5 experiments with the tension band technique, there was no K-wire breakage. The median maximum force was 330 N (240-510N). During this maximum distraction force the median extension was 3.4 mm (2.2-3.8 mm).Conclusions: Based on the biomechanical advantages, patella fracture treatment with EFECE systems may constitute a reasonable alternative in the treatment of patella fractures.

A Comparison of EFECE Systems With Tension Band Wiring for Patella Fracture Fixation in Cadavers

Background EFECE Systems are newly-defined internal fixation systems, which are suitable for patella fracture fixation. The aim of this study was to compare the fixation strength of EFECE Systems with tension band wiring for transverse patellar fracture simulation on fresh frozen cadaver models.Methods Quadriceps tendon-patella-patellar tendon (QT-P-PT) complex was prepared from human cadavers. After simulation of a transverse patella fracture, in Group 1, 5 patella were fixed with a pair of 1.2 mm EFECE wires and 4 EFECE devices. In Group 2, 5 patella were fixed with a pair of 1.2 mm Kirschner wires (K-wire) and a cerclage wire according to the tension band technique. Using a testing device with custom-made jaws, increasing distraction force was applied to these QT-P-PT complexes. Extension of these complexes with the distraction forces was observed. The maximum distraction force and the elongation during maximum force were evaluated.Results After 5 experiments with the EFECE Systems, there was no EFECE wire breakage or EFECE wire-EFECE device catching failure. The median maximum force was 740 N (720-810N). During maximum distraction force the median extension was 2.5 mm (1.6-2.5 mm).After 5 experiments with the tension band technique, there was no K-wire breakage. The median maximum force was 330 N (240-510N). During this maximum distraction force the median extension was 3.4 mm (2.2-3.8 mm).Conclusions Based on the biomechanical advantages, patella fracture treatment with EFECE systems may constitute a reasonable alternative in the treatment of patella fractures.