Design of a five-axis ultra-precision micro-milling machine—UltraMill. Part 1: Holistic design approach, design considerations and specifications

High-accuracy three-dimensional miniature components and microstructures are increasingly in demand in the sector of electro-optics, automotive, biotechnology, aerospace and information-technology industries. A rational approach to mechanical micro machining is to develop ultra-precision machines with small footprints. In part 1 of this two-part paper, the-state-of-the-art of ultra-precision machines with micro-machining capability is critically reviewed. The design considerations and specifications of a five-axis ultra-precision micro-milling machine—UltraMill—are discussed. Three prioritised design issues: motion accuracy, dynamic stiffness and thermal stability, formulate the holistic design approach for UltraMill. This approach has been applied to the development of key machine components and their integration so as to achieve high accuracy and nanometer surface finish

Identification and control for micro-drilling productivity enhancement

Micro-hole drilling (holes less than 0.5 mm in diameter with aspect ratios larger than 10) is gaining increased attention in a wide spectrum of precision production industries. Alternative methods such as EDM, laser drilling, etc. can sometimes replace mechanical micro-hole drilling, but are not acceptable in PCB manufacture because they yield inferior hole quality and accuracy. The major difficulties in microhole drilling are related to the wandering motions during the inlet stage, high aspect ratios, high temperature, etc. However, of all the difficulties, the most undesirable ones are the increases in drilling force and torque as the drill penetrates deeper into the hole. This is mainly caused by chip-related effects. Peck-drilling is thus widely used for deep hole drilling despite the fact that it leads to low productivity. Therefore, in this paper, a method for cutting force regulation is proposed to achieve continuous drilling. A proportional plus derivative (PD) and a sliding mode control algorithm will be implemented and compared for controlling the spindle rotational frequency. Experimental results will show that sliding mode control reduces the nominal torque and cutting force and their variations better than PD control, resulting in a number of advantages, such as an increase in,drill life, fast stabilization of the wandering motion, and precise positioning of the holes. (C) 1999 Elsevier Science Ltd. All rights reserved.X1135sciescopu

A mechanistic model of cutting forces in micro-end-milling with cutting-condition-independent cutting force coefficients

Complex three-dimensional miniature components are needed in a wide range of industrial applications from aerospace to biomedicine. Such products can be effectively produced by micro-end-milling processes that are capable of accurately producing high aspect ratio features and parts. This paper presents a mechanistic cutting force model for the precise prediction of the cutting forces in micro-end-milling under various cutting conditions. In order to account for the actual physical phenomena at the edge of the tool, the components of the cutting force vector are determined based on the newly introduced concept of the partial effective rake angle. The proposed model also uses instantaneous cutting force coefficients that are independent of the end-milling cutting conditions. These cutting force coefficients, determined from measured cutting forces, reflect the influence of the majority of cutting mechanisms involved in micro-end-milling including the minimum chip-thickness effect. The comparison of the predicted and measured cutting forces has shown that the proposed method provides very accurate results.X111839sciescopu

DEVELOPMENT OF A VIRTUAL MACHINING SYSTEM, PART 1: APPROXIMATION OF THE SIZE EFFECT FOR CUTTING FORCE PREDICTION

In this three-part paper, components of a virtual machining system for evaluating and optimizing cutting performance in 21/2axis NC machining are presented. Part I describes a new method of calculating cutting-condition-independent coefficient and its application to the prediction of cutting forces over a wide range of cutting conditions. The prediction of the surface form error and transient cutting simulations, described in Parts 2 and 3, respectively, can be effectively performed based on the cutting force model with the improved size effect model that is presented in Part 1. The relationship between the instantaneous uncut chip thickness and the cutting coefficients is calculated by following the movement of the center position of the cutter, which varies with nominal feed, cutter deflection and runout. The salient feature of the presented method is that it determines the cutting-condition-independent coefficients using experimental data processed for one cutting condition. The direct application of instantaneous cutting coefficient with size effects provides more accurate predictions of the cutting forces. A systematic comparison of the predicted and measured cutting forces over a wide range of cutting conditions confirms the validity of the proposed mechanistic cutting force and size effect models. (C) 2002 Elsevier Science Ltd. All rights reserved.X1155sciescopu

DEVELOPMENT OF A VIRTUAL MACHINING SYSTEM, PART 2: PREDICTION AND ANALYSIS OF A MACHINED SURFACE ERROR

In part 2 of this three-part paper, a newly developed method that predicts the three-dimensional machined surface errors generated during the peripheral end milling process is presented. From the cutting force prediction system of Part 1, since the uncut chip thickness is calculated by tracing the movement of the cutter, the positions at which the cutting edges pass over the workpiece surface can readily be obtained. In this part of the paper these positions are used to construct surface error maps. In addition, by using the estimated locations of the peak and valley values of the cutting force component normal to the machined surface, a quantitative analysis of the machined surface error is given and followed by theoretical explanations. A series of machining tests on aluminum workpieces were conducted to validate the effectiveness of the model. The predicted cutting forces and surface errors were found in good agreement with their measured counterparts. (C) 2002 Elsevier Science Ltd. All rights reserved.X1131sciescopu

DEVELOPMENT OF A VIRTUAL MACHINING SYSTEM, PART 3: CUTTING PROCESS SIMULATION IN TRANSIENT CUTS

In Parts I and 2 of this three-part paper, a mechanistic cutting force model was developed and machined surface errors for steady cuts under fixed cutting conditions were predicted. The virtual machining system aims to simulate and analyze the machining and the machined states in a general flat end-milling process. This frequently involves transient as well as steady cuts. Therefore, a method for simulating the cutting process of transient cuts needs to be developed to realize the virtual machining system concept. For this purpose, this paper presents a moving edge-node (ME) Z-map model for the cutting configuration calculation. The simulation results of four representative transient cuts in two-dimensional pocket milling and an application of off-line feed-rate scheduling are also given. In transient cuts, the cutting configurations that are used to predict the cutting force vary during the machining operation. The cutting force model (Part 1) and surface error prediction method (Part 2) were developed for steady cuts; these are extended to transient situations using the ME Z-map model to calculate the varying cutting configurations efficiently. The cutting force and surface errors are then predicted. To validate the feasibility of the proposed scheme, the measured and predicted cutting forces for transient test cuts were compared. The predicted surface error maps for transient cuts were constructed using a computer simulation. Also, off-line feed-rate scheduling is shown to be more accurately performed by applying the instantaneous cutting coefficients that were defined in Part I.. (C) 2002 Elsevier Science Ltd. All rights reserved.X1132sciescopu

Consumption of an aqueous cyanophyta extract derived from Arthrospira platensis is associated with reduction of chronic pain: results from two human clinical pilot studies

Gitte S Jensen,1 Victoria L Attridge,1 Steve G Carter,1 Jesse Guthrie,2 Axel Ehmann,2 Kathleen F Benson1 1NIS Labs, 2Cerule LLC, Klamath Falls, OR, USA Objectives: The aim of this study was to evaluate the effects of consumption of an aqueous cyanophyta extract (ACE) from Arthrospira platensis on chronic pain in humans, in two clinical pilot studies. Design and interventions: The two pilot studies each involved 12 subjects experiencing chronic pain. The initial study followed an open-label 4-week study design involving consumption of 1 g ACE per day. A subsequent placebo-controlled, single-blind, crossover study involved consumption of 500 mg ACE, 250 mg ACE, or 0 mg ACE (placebo) per day for 1-week duration, separated by 1-week washout period. Subjects: Adult subjects of both sexes, with chronic joint-related pain for at least 6 months prior to enrollment, were recruited after obtaining written informed consent. Outcome measures: Visual analog scales were used to score pain at rest and during physical activity for each person's primary and secondary areas of chronic pain. An activities of daily living questionnaire was used to collect data on physical functioning. Results: The data showed rapid reduction of chronic pain in people consuming ACE, where the reduction in pain scores for each person's primary pain area reached a high level of statistical significance after 2 weeks of consumption (P<0.01), both when at rest and when being physically active. Secondary pain areas when physically active showed highly significant improvements within 1 week of consumption of 1 g/d (P<0.001) and borderline significant improvements within 1 week of consuming 500 mg/d (P<0.065) and 250 mg/d (P<0.05). This was accompanied by an increased ability to perform daily activities (P<0.05). A small but significant weight loss was observed during the 4-week study, as the average body mass index dropped from 31.4 to 29.4 (P<0.01). Conclusion: Consumption of ACE was associated with reduction of chronic pain, as well as a dose-dependent increased ability to perform activities of daily living. Keywords: activities of daily living, pilot study, placebo-controlled study, Spirulin

Index, sources and derivation of key indicators of local authority social services

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