Multiscale Analogue Modelling of Clinching Process to Investigate Thickness Tolerance and Tool Misalignment.

NEED-The effect of dimensional variability of sheet thickness (tolerance) and tool misalignment is poorly understood for the clinching process. Finite element analysis (FEA) is valuable but requires a lot of and is difficult to verify in this situation due to the asymmetrical geometry and nonlinear plasticity. OBJECTIVE-The objective of this work was to determine the effect of thickness tolerance, tool misalignment and sheet placement (top vs. bottom) in the clinching process, by use of analogue modelling with plasticine. METHOD-Experiments used a scaled-up punch and die, with plasticine as the analogue. Thickness tolerances were represented by sheet thicknesses of 11 and 7 mm, 12 and 8 mm, 8 and 12 mm and 13 and 9 mm for upper and lower sheets, respectively. Two types of lubricant were tested between sheets: glycerine and silicone oil. Angular variability was also introduced. Measured parameters were interlock (also called undercut) and neck thickness. Analogue results for deformation were compared with microscopy of metal clinching. FINDINGS-The results reveal that the multiscale analogue model is an efficient tool for studying the effect of dimensional deviation on a clinch joint. Thickness tolerance showed a critical relationship with interlock, namely a reduction to about half that of the nominal, for both maximum and least material conditions. Increased angular misalignment also reduced the interlock. Compared with glycerine, silicone oil tests showed reduced interlock, possibly the result of a lower coefficient of friction. ORIGINALITY-This work demonstrates the usefulness of analogue modelling for exploring process variability in clinching. The results also show that significant effects for sheet placement are ductility, lubricant (friction), thickness of samples and tool misalignment.

The Effects of Cooling and Shrinkage on the Life of Polymer 3D Printed Injection Moulds.

3D Printed Injection Moulds (3DIM), commonly used for low volume production and prototyping purposes, are known to fail abruptly and have a comparatively shorter life than conventional moulds. Investigating the underlying critical factors affecting failure may help in reducing the risk of abrupt failures and possibly prolong the 3DIM tool life. A hypothesis that the cooling time of the Injection Moulding (IM) process is a critical factor for 3DIM tool failure has been proposed. The failure hypothesis has been validated by theoretical calculations, FEA simulations and experimental investigations. Experiments were performed using two different materials for the 3DIM tool (Visijet M3-X and Digital ABS) and an engineering thermoplastic (Lexan 943-A) as the moulding material. Results showed that cooling time was a critical factor on tool life and managing the thermal loading on a 3DIM tool could lead to increased tool life. The paper identifies cooling time as the critical factor affecting 3DIM tool life and presents a cooling regime that could possibly lead to prolonged tool life.

Assessment of the Effect of Cleanliness on the Visual Inspection of Aircraft Engine Blades: An Eye Tracking Study.

Background-The visual inspection of aircraft parts such as engine blades is crucial to ensure safe aircraft operation. There is a need to understand the reliability of such inspections and the factors that affect the results. In this study, the factor 'cleanliness' was analysed among other factors. Method-Fifty industry practitioners of three expertise levels inspected 24 images of parts with a variety of defects in clean and dirty conditions, resulting in a total of N = 1200 observations. The data were analysed statistically to evaluate the relationships between cleanliness and inspection performance. Eye tracking was applied to understand the search strategies of different levels of expertise for various part conditions. Results-The results show an inspection accuracy of 86.8% and 66.8% for clean and dirty blades, respectively. The statistical analysis showed that cleanliness and defect type influenced the inspection accuracy, while expertise was surprisingly not a significant factor. In contrast, inspection time was affected by expertise along with other factors, including cleanliness, defect type and visual acuity. Eye tracking revealed that inspectors (experts) apply a more structured and systematic search with less fixations and revisits compared to other groups. Conclusions-Cleaning prior to inspection leads to better results. Eye tracking revealed that inspectors used an underlying search strategy characterised by edge detection and differentiation between surface deposits and other types of damage, which contributed to better performance.

Frequency and duration of ambulance officer exposure to nitrous oxide and methoxyflurane in New Zealand.

OBJECTIVE: Nitrous oxide (Entonox®) and methoxyflurane (Penthrox®) are inhaled analgesics administered in paramedicine. Occupational exposure to nitrous oxide has been associated with negative health effects, and may inhibit professional capability. The effect of occupational exposure to methoxyflurane has not yet been clearly determined. This study identifies the frequency and duration of ambulance officer (AO) occupational exposure to nitrous oxide and methoxyflurane to provide a foundation for future assessments of occupational toxicity risk. METHODS: A retrospective database review of Patient Report Forms (PRFs) in 11 months between February 2016 and February 2018 was conducted. Nitrous oxide was available for the first 5 months studied, followed by 6 months methoxyflurane availability. AO-specific measures of attendance, rate of inhaled analgesic use, and duration of analgesic use were determined. Subgroup analysis by AO qualification and rostered work hours was undertaken. RESULTS: A total of 46,759 PRFs were examined, identifying 1,033 cases of nitrous oxide administration and 1456 cases of methoxyflurane was administration. There was a significant increase in the proportion of cases where inhaled analgesia was administered following the replacement of nitrous oxide with methoxyflurane. Relative risk of exposure to methoxyflurane compared with nitrous oxide was 1.22, while median duration of each exposure remained unchanged (32 vs. 33 min). CONCLUSIONS: Methoxyflurane via the Penthrox® inhaler was more likely to be administered than nitrous oxide. Most AOs are infrequently exposed to inhaled analgesics and are exposed for durations slightly greater than previously reported. Relative risk of exposure was greatest for lower-qualified AOs. Peak number of exposures and duration values suggest a subset of AOs with higher occupational health risk.

Analysis of Raised Feature Failures on 3D Printed Injection Moulds.

BACKGROUND: Polymer-based 3D Printed Injection Mould (3DIM) inserts are used as a cost-effective method for low volume injection moulding (50-500 parts). However, abrupt failure leading to a short tool life is a common shortcoming of 3DIM. Need: The underlying causes of raised feature failures on 3DIM are not well known. Failure is commonly attributed to bending or shearing of raised features on the tool. Understanding the causes may help in delaying the failure and increasing tool life. APPROACH: Tool failure was analysed from a first-principles perspective, using pressure and temperature fields as determined by mould flow simulation. Experimental results were also obtained for two types of tool material (Visijet M3-X and Digital ABS) with polycarbonate (Lexan 943A) as the part material. FINDINGS: Results find against the idea that pin failure in 3DIM tools is caused by bending and shear failures induced by injection pressures. We also conclude that failure of raised features is not necessarily an abrupt failure as mentioned in the literature. Originality: The generally accepted explanation for the failure of raised features in 3DIM tooling is that injection pressures cause bending and shear failure. This paper disconfirms this notion on theoretical and experimental grounds.

A Methodology for Harmonizing Safety and Health Scales in Occupational Risk Assessment.

Successful implementation of Health and Safety (H&S) systems requires an effective mechanism to assess risk. Existing methods focus primarily on measuring the safety aspect; the risk of an accident is determined based on the product of severity of consequence and likelihood of the incident arising. The health component, i.e., chronic harm, is more difficult to assess. Partially, this is due to both consequences and the likelihood of health issues, which may be indeterminate. There is a need to develop a quantitative risk measurement for H&S risk management and with better representation for chronic health issues. The present paper has approached this from a different direction, by adopting a public health perspective of quality of life. We have then changed the risk assessment process to accommodate this. This was then applied to a case study. The case study showed that merely including the chronic harm scales appeared to be sufficient to elicit a more detailed consideration of hazards for chronic harm. This suggests that people are not insensitive to chronic harm hazards, but benefit from having a framework in which to communicate them. A method has been devised to harmonize safety and harm risk assessments. The result was a comprehensive risk assessment method with consideration of safety accidents and chronic health issues. This has the potential to benefit industry by making chronic harm more visible and hence more preventable.

Serum fluoride levels in ambulance staff after commencement of methoxyflurane administration compared to meta-analysis results for the general public.

OBJECTIVES: Ambulance officers administering methoxyflurane as an inhalational analgesic may be exposed to trace vapor. Fluoride is a methoxyflurane metabolite, and has been associated with acute renal failure in anesthesia patients and skeletal fluorosis with chronic elevated serum levels from other sources. However, there has been no direct measurement of serum fluoride in occupationally exposed ambulance officers. Thus, this study directly measures serum fluoride over a prolonged period in order to determine renal toxic and skeletal fluorosis risk to ambulance officers who are administering methoxyflurane. MATERIAL AND METHODS: Serum inorganic fluoride concentrations were measured in a prospective observational study of 12 emergency medical technicians (EMTs). The study took 7 serum fluoride measurements over 24 months. A meta-analysis of healthy adult serum fluoride ranges was also conducted. RESULTS: The typical healthy adult serum fluoride range was determined to be 0.21-2.11 µmol/l (p < 0.001). The EMTs' baseline median (IQR) serum fluoride concentrations were 0.4 µmol/l (0.2; 1.0) with maximum 1.6 µmol/l. The EMTs' overall median serum fluoride was 0.4 µmol/l (0.2; 1.3) with maximum 4.0 µmol/l, usually within healthy reference ranges. All results were ≤10% of the suggested single-dose renal toxic threshold. One result was above a threshold for skeletal fluorosis. The highest measured serum fluoride was 24% of the lowest level associated with radiologic evidence of fluorosis. There was no evidence overall of increasing serum fluoride levels. CONCLUSIONS: There was no evidence that EMTs' exposure to methoxyflurane resulted in sustained increased serum fluoride. These results imply EMTs' occupational safety from acute renal toxicity when activated carbon filtration is used on patient exhalation. However, 1 serum fluoride result above a skeletal fluorosis threshold suggests that the risk of mild skeletal fluorosis cannot be excluded. Int J Occup Med Environ Health. 2021;34(6):767-77.

Methoxyflurane toxicity: historical determination and lessons for modern patient and occupational exposure.

AIM: Historically methoxyflurane was used for anaesthesia. Evidence of nephrotoxicity led to abandonment of this application. Subsequently, methoxyflurane, in lower doses, has re-emerged as an analgesic agent, typically used via the Penthrox inhaler in the ambulance setting. We review the literature to consider patient and occupational risks for methoxyflurane. METHOD: Articles were located via PubMed, ScienceDirect, Google Scholar, Anesthesiology journal and the Cochrane Library. RESULTS: Early studies investigated pharmacokinetics and considered the resulting effects to pose minimal risk. Pre-clinical rodent studies utilised a species not vulnerable to the nephrotoxic fluoride metabolite of methoxyflurane, so nephrotoxicity was not identified until almost a decade after its introduction, and was initially met with scepticism. Further evidence of nephrotoxicity led to abandonment of methoxyflurane use for anaesthesia. Subsequent research suggested there are additional risks potentially relevant to recurrent patient or occupational exposure. Specifically, greater than expected fluoride production after repeated low-dose exposure, increased fluoride production due to medication-caused hepatic enzyme induction, fluoride deposition in bone potentially acting as a slow-release fluoride compartment, which suggests a risk of skeletal fluorosis, and hepatotoxicity. Gestational risk is unclear. CONCLUSIONS: Methoxyflurane poses a potentially substantial health risk in high (anaesthetic) doses, and there are a number of pathways whereby repeated exposure to methoxyflurane in lower doses may pose a risk. Single analgesic doses in modern use generally appear safe for patients. However, the safety of recurrent patient or occupational healthcare-worker exposure has not been confirmed, and merits further investigation.

Communication Adjustment in Engineering Professional and Student Project Meetings.

BACKGROUND: communication is important for project teams. There is a need to better understand how members respond to communication at project meetings, and how this affects the team roles the participants adopt. METHODS: observational data were collected from (a) two engineering organisations and (b) five university engineering student teams. A mixed methods approach was used, comprising observations (recorded with the interaction diagram method), questionnaires and interviews. RESULTS: participants adjusted their communication style to the behaviour of other people and to different communication settings. This happened with three different dynamics: micro-level (grounding processes in conversation), mezzo-level (emotional and rational regulation) and macro-level (over a period of time). Originality: a new theory was presented for the process of team behaviour during project meetings; specifically, role adoption and communication behavioural changes. Participants change their team roles within three different dynamics: at the macro-, mezzo- and micro-levels, corresponding to the organisation, project and meeting, respectively. The changing of team roles in project meetings arises from rational and emotional regulation. The findings have the potential to assist managers and supervisors to better understand and manage the team dynamics on their projects.

Team Role Adoption and Distribution in Engineering Project Meetings.

Team communication plays a vital role in engineering management, however, there is a paucity of work that examines how team roles emerge as a response to the communicative processes between participants. This research explored role adoption using qualitative methods comprising observations, questionnaires and semi-structured interviews. Five student teams doing final year projects at a university in New Zealand were observed during the academic year and then interviewed at the final stage of project completion. A number of team roles in the engineering context were identified for students and their supervisors: Explorer; Initiator; Facilitator; Active and Passive Information Provider; Outsider; Active and Passive Connector; Passive Collector; Arbitrator; Gatekeeper and Representative. Personal factors, such as social sensitivity, were correlated with the choice of team behaviour pattern. In addition, the team roles could be arranged in circular order to create a circumplex, the two axes of which were identified as Personal Agency/Communion and Social engagement/Social disengagement.

Texture Evolution in AA6082-T6 BFSW Welds: Optical Microscopy and EBSD Characterisation.

One of the difficulties with bobbin friction stir welding (BFSW) has been the visualisation of microstructure, particularly grain boundaries, and this is especially problematic for materials with fine grain structure, such as AA6082-T6 aluminium as here. Welds of this material were examined using optical microscopy (OM) and electron backscatter diffraction (EBSD). Results show that the grain structures that form depend on a complex set of factors. The motion of the pin and shoulder features transports material around the weld, which induces shear. The shear deformation around the pin is non-uniform with a thermal and strain gradient across the weld, and hence the dynamic recrystallisation (DRX) processes are also variable, giving a range of observed polycrystalline and grain boundary structures. Partial DRX was observed at both hourglass boundaries, and full DRX at mid-stirring zone. The grain boundary mapping showed the formation of low-angle grain boundaries (LAGBs) at regions of high shear as a consequence of thermomechanical nature of the process.

Interaction Diagrams: Development of a Method for Observing Group Interactions.

Recording of team meeting's processes with electronic devices can be problematic because of the invasiveness of the process: issues with privacy; interpretation difficulty with noise or quiet speech; and distortion of participants' behaviour. There is a need for less intrusive methods. We developed the interaction diagram method by extending the directed graph nature of sociograms to capture the time sequence of events, including the identification of the person, communication behaviour, and duration of interactions. The method was tested on engineering team meetings. Data processing by quantitative and qualitative analysis is shown to be feasible. Several team roles were observed in the engineering context: Initiator; Passive collector; Explorer; Information provider; Facilitator; Arbitrator; Representative; Gatekeeper; Connector; and Outsider. The work provides a graphical representation of the record of the interaction flow during meetings. It does this without needing video recording. It is also an efficient method, as it does not require subsequent transcription or coding. It provides a procedure to quickly analyse communication situations, identify group roles, and compare group activity at different meetings.