Optimization of 5-axis milling processes using process models

Productivity and part quality are extremely important for all machining operations, but particularly for 5-axis milling where the machine tool cost is relatively higher, and most parts have complex geometries and high quality requirements with tight tolerances. 5- axis milling, presents additional challenges in modeling due to more complex tool and workpiece interface geometry, and process mechanics. In this paper, modeling and optimization of 5-axis processes with cutting strategy selection are presented. The developed process models are used for cutting force predictions using a part-tool interface identification method which is also presented. Based on the model predictions and simulations, best cutting conditions are identified. Also, for finish process of a complex surface, machining time is estimated using three machining strategy alternatives. Results are demonstrated by example applications, and verified by experiments

Quality characteristics and phenolic compounds of European pear cultivars

Background: Pear fruits are an important source of plant secondary metabolites and one of the major sources of dietary phenolic compounds.Materials and Methods: The aim of this study was to determine the individual phenolic compounds and some quality characteristics of the flesh and peel of the fruit in four pear cultivars. The phenolic  composition of these pear cultivars was determined by high performance liquid chromatography with diode array detection (HPLC-DAD).Results: The fruit flesh firmness ranged from 35.2 to 85.8 N in the pear cultivars. The soluble solids content was higher in the flesh, while titrate-able acidity, vitamin C, individual phenolic compounds and total phenolics were generally higher in the peel. Arbutin, chlorogenic acid and epicatechin were detected as major phenolic compounds in the peel and flesh of pear fruits. Arbutin, chlorogenic acid and epicatechin of the flesh and peel ranged from 834.8 to 937.9 mg kg-1; from 332.1 to 460.7 mg kg-1; and from 77.2 to 104.0 mg kg-1 for ‘Seckel’ pear fruits, respectively. The highest total phenolics were found to be in the peel and flesh of the ‘Flemish Beauty’ pear fruits.Conclusion: Because of the higher level of antioxidant components in the peel of pear fruits (all phenolic compounds and vitamin C) consumption of unpeeled pears, after proper washing, is recommended to maximize the dietary benefit.Key words: Arbutin, Chlorogenic acid, Flesh and Peel, HPLC, Pear cultivars, Vitamin

Microwave-induced nonequilibrium temperature in a suspended carbon nanotube

Antenna-coupled suspended single carbon nanotubes exposed to 108 GHz microwave radiation are shown to be selectively heated with respect to their metal contacts. This leads to an increase in the conductance as well as to the development of a power-dependent DC voltage. The increased conductance stems from the temperature dependence of tunneling into a one-dimensional electron system. The DC voltage is interpreted as a thermovoltage, due to the increased temperature of the electron liquid compared to the equilibrium temperature in the leads

Discrete Cutting Force Model for 5-Axis Milling with Arbitrary Engagement and Feed Direction

5-axis machining operations bring new challenges for predicting cutting forces. Complex tool workpiece engagements and tool orientations make it difficult to adapt 3-axis process models for 5-axis operations. A new model is developed to predict cutting forces with arbitrary tool/workpiece engagement and tool feed direction. A discretization approach is used, in which the tool is composed of multiple cutting elements. Each element is processed to determine its effect on cutting forces, and global forces are determined by combining the elemental effects. Cutting tests are conducted to verify force predictions, where the tool/workpiece engagement is provided through a geometric software application

Machining strategy development in 5-axis milling operations using process models

Increased productivity and part quality can be achieved by selecting machining strategies and conditions properly. At one extreme very high speed and feed rate with small depth of cut can be used for high productivity whereas deep cuts accompanied with slow speeds and feeds may also provide increased material removal rates in some cases. In this study, it is shown that process models are useful tools to simulate and compare alternative strategies for machining of a part. 5-axis milling of turbine engine compressors made out of titanium alloys is used as the case study where strategies such as flank milling (deep cuts), point milling (light cuts) and stripe milling (medium depths) are compared in terms of process time by considering chatter stability, surface finish and tool deflections

Chatter avoidance via structural modification of tool-holder geometry

Chatter is a self-excited vibration that can occur during milling operations causing undesirable consequences such as poor surface finish and increased levels of tool wear. One possible solution to this problem is to optimise the dynamics of the machine by tuning parameters such as tool stickout length, e.g. by using receptance coupling substructure analysis. Unfortunately, experimental limitations of the method, such as the requirement to model interface dynamics and the inefficient optimisation process, have hindered its advancement to the industrial sector. This paper looks to resolve these issues by proposing a new structural modification method for chatter avoidance. Firstly, tool-holder diameter is investigated as a potential tuning parameter: a new experimental dataset demonstrates that this design parameter can have a significant and valuable impact on the chatter stability. Secondly, the direct structural modification method is introduced, allowing the tool-holder diameter to be modelled without any knowledge of the interface behaviour between tool and tool-holder. Thirdly, the inverse structural modification method is proposed, allowing tuning and stability optimisation by solving a single equation. Lastly, a new tunable-mass tool-holder is presented, allowing the dynamics of a milling machine to be tuned for each tool diameter and length range with a single tool-holder . This eliminates the need for manufacturers to purchase a wide range of tool-holders, a significant financial investment

A single-molecule method for measuring fluorophore labeling yields for the study of membrane protein oligomerization in membranes

Membrane proteins are often observed as higher-order oligomers, and in some cases in multiple stoichiometric forms, raising the question of whether dynamic oligomerization can be linked to modulation of function. To better understand this potential regulatory mechanism, there is an ongoing effort to quantify equilibrium reactions of membrane protein oligomerization directly in membranes. Single-molecule photobleaching analysis is particularly useful for this as it provides a binary readout of fluorophores attached to protein subunits at dilute conditions. However, any quantification of stoichiometry also critically requires knowing the probability that a subunit is fluorescently labeled. Since labeling uncertainty is often unavoidable, we developed an approach to estimate labeling yields using the photobleaching probability distribution of an intrinsic dimeric control. By iterative fitting of an experimental dimeric photobleaching probability distribution to an expected dimer model, we estimate the fluorophore labeling yields and find agreement with direct measurements of labeling of the purified protein by UV-VIS absorbance before reconstitution. Using this labeling prediction, similar estimation methods are applied to determine the dissociation constant of reactive CLC-ec1 dimerization constructs without prior knowledge of the fluorophore labeling yield. Finally, we estimate the operational range of subunit labeling yields that allows for discrimination of monomer and dimer populations across the reactive range of mole fraction densities. Thus, our study maps out a practical method for quantifying fluorophore labeling directly from single-molecule photobleaching data, improving the ability to quantify reactive membrane protein stoichiometry in membranes