153 research outputs found
Investigation of Collision Welding by High-Speed Imaging
Collision welding bases on the oblique collision of two joining partners at high relative
velocities. Until today, the mechanisms of collision welding are not yet fully understood
due to the variety of phenomena occurring during the collision. One of these phenomena is
the cloud of particles whose influence on bond formation has been neglected concerning
its stored thermal energy. For the investigation of this influence, a collision welding model
test rig was used which allowed the precise adjustment of the process parameters. The
process observation was implemented by an image intensifier camera to visualize the
ongoing collision and the occurring process phenomena. In this manuscript the developed
methodology and the results of high-speed process observation are presented. The findings
confirmed previous research regarding the shape formation of the cloud of particles and
the influence on bond formation. It was found that the temperature of the cloud of particles
depends strongly on the collision angle. Furthermore, an accumulation of the cloud of
particles during the collision process was recorded which might influence the steadiness of
the welding process
Soft sensor approach based on magnetic Barkhausen noise by means of the forming process punch-hole-rolling
The relevance of the magnetic Barkhausen noise (MBN) and the non-destructive characterization of material properties in near surface layers, has increased in recent years.With the development of new signal processing techniques, the method was further developed into a powerful evaluation technique and is used in various areas of online and offline measurement. In addition to the established use in the detection of grinding burn, the method is increasingly used in the context of soft sensors for property controlled processes, due to its short analysis times. By a detailed description of a soft sensor concept for the novel forming process punch-hole-rolling this work focuses on the offline characterization of the process specific cause-effect relationships. This is done by analyzing the process interactions as well as the surface layer state by a metallographic investigation. Additionally a non-destructive characterization by means of MBN was done and correlated with the surface layer state. This provides important findings for the use of a MBN-sensor in a soft sensor concept and the potential integration into the forming process
In-situ-measurement of the friction coefficient in the deep drawing process
The surface texture plays an important role in the tribological behaviour of deep drawn components. It influences both the process of sheet metal forming as well as the properties for post processing, such as paint appearance, bonding, or corrosion tendency. During the forming process, the texture of the sheet metal and therefore its friction coefficient, changes due to process related strains. This contribution focuses on the development and validation of a tool to investigate the friction coefficient of the flange region of deep drawn components. The influence of biaxial strain on the friction coefficient will be quantified through a comparison of the experimental results with a conventional friction test (stand). The presented method will be applied on a cup drawing test, using a segmented and sensor-monitored blankholder. This setup allows the measurement of the friction coefficient in-situ without simplification of the real process. The experiments were carried out using DX 56D+Z as sheet metal and PL61 as lubricant. The results show a characteristic change in the friction coefficient over the displacement of the punch, which is assumed to be caused by strain induced change of the surface texture
Prediction of the Evolution of the Surface Roughness in Dependence of the Lubrication System for Cold Forming Processes
Lubricants for cold forging operations do not only enable a reliable forging process, but also affect the results of forging processes. A sound lubrication decreases the occurring forces and may result in a smooth specimen surface. However, some lubricants are known to increase the initial surface roughness of the specimen as a consequence of the forming. Therefore, the decision which lubricant should be used is of special interest for near-net shape operations. The paper at hand presents the results of a finite element investigation of the first stage of an industrial rod extrusion process which was investigated with two different lubrication systems. The numerical investigations focus on a reliable prediction of the development of the surface roughness in due consideration of the lubricant
Correlation of same-visit HbA1c test with laboratory-based measurements: A MetroNet study
BACKGROUND: Glycated hemoglobin (HbA1c) results vary by analytical method. Use of same-visit HbA1c testing methodology holds the promise of more efficient patient care, and improved diabetes management. Our objective was to test the feasibility of introducing a same-visit HbA1c methodology into busy family practice centers (FPC) and to calculate the correlation between the same-visit HbA1c test and the laboratory method that the clinical site was currently using for HbA1c testing. METHODS: Consecutive diabetic patients 18 years of age and older having blood samples drawn for routine laboratory analysis of HbA1c were asked to provide a capillary blood sample for same-visit testing with the BIO-RAD Micromat II. We compared the results of the same-visit test to three different laboratory methods (one FPC used two different laboratories). RESULTS: 147 paired samples were available for analysis (73 from one FPC; 74 from the other). The Pearson correlation of Micromat II and ion-exchange HPLC was 0.713 (p < 0.001). The Micromat II mean HbA1c was 6.91%, which was lower than the 7.23% from the ion-exchange HPLC analysis (p < 0.001). The correlation of Micromat II with boronate-affinity HPLC was 0.773 (p < 0.001); Micromat II mean HbA1c 6.44%, boronate-affinity HPLC mean 7.71% (p < 0.001). Correlation coefficient for Micromat II and immuno-turbidimetric analysis was 0.927 (p < 0.001); Micromat II mean HbA1c was 7.15% and mean HbA1c from the immuno-turbidimetric analysis was 7.99% (p = 0.002). Medical staff found the same-visit measurement difficult to perform due to the amount of dedicated time required for the test. CONCLUSION: For each of the laboratory methods, the correlation coefficient was lower than the 0.96 reported by the manufacturer. This might be due to variability introduced by the multiple users of the Micromat II machine. The mean HbA1c results were also consistently lower than those obtained from laboratory analysis. Additionally, the amount of dedicated time required to perform the assay may limit its usefulness in a busy clinical practice. Before introducing a same-visit HbA1c methodology, clinicians should compare the rapid results to their current method of analysis
Closed-loop control of product properties in metal forming
Metal forming processes operate in conditions of uncertainty due to parameter variation and imperfect understanding. This uncertainty leads to a degradation of product properties from customer specifications, which can be reduced by the use of closed-loop control. A framework of analysis is presented for understanding closed-loop control in metal forming, allowing an assessment of current and future developments in actuators, sensors and models. This leads to a survey of current and emerging applications across a broad spectrum of metal forming processes, and a discussion of likely developments.Engineering and Physical Sciences Research Council (Grant ID: EP/K018108/1)This is the final version of the article. It first appeared from Elsevier via https://doi.org/10.1016/j.cirp.2016.06.00
Numerical and Experimental Investigation of the Innovatory Incremental-Forming Process Dedicated to the Aerospace Industry
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