Machining with tool–chip contact on the tool secondary rake face—Part II: analysis and discussion

The forces, chip thickness, and natural tool–chip contact length in machining with a double-rake-angled tool are predicted in Part II of the present study. It is revealed that in comparison with a single-rake-angled tool, a double-rake-angled tool increases the forces, especially the thrust force. However, the increase in chip thickness and tool–chip contact length is not significant under the input conditions specified in the present study. The effect of seven input variables of the proposed model is quantitatively investigated. The predicted variations of forces, chip thickness, and natural tool–chip contact length are in good agreement with theoretical and experimental results obtained by other researchers. The interrelationships among the resultant force, the chip thickness, and the natural tool–chip contact length are established, which provides a new and promising method to estimate the tool–chip contact length by employing the resultant force. It is demonstrated that the model can also be extended to study the problem of machining with a groove-type chip breaker tool.     

FORCES AND TEMPERATURES IN HARD TURNING

In precision machining, due to the recent developments in cutting tools, machine tool structural rigidity and improved CNC controllers, hard turning is an emerging process as an alternative to some of the grinding processes by providing reductions in costs and cycle-times. In industrial environments, hard turning is established for geometry features of parts with low to medium requirements on part quality. Better understanding of cutting forces, stresses and temperature fields, temperature gradients created during the machining are very critical for achieving highest quality products and high productivity in feasible cycle times. To enlarge the capability profile of the hard turning process, this paper introduces prediction models of mechanical and thermal loads during turning of 51CrV4 with hardness of 68 HRC by a CBN tool. The shear flow stress, shear and friction angles are determined from the orthogonal cutting tests. Cutting force coefficients are determined from orthogonal to oblique transformations. Cutting forces, temperature field for the chip and tool are predicted and compared with experimental measurements. The experimental temperature measurements are conducted by the advanced hardware device FIRE-1 (Fiberoptic Ratio Pyrometer).     

Sculpture surface machining: a generalized model of ball-end milling force system

A new mechanistic model is presented for the prediction of a cutting force system in ball-end milling of sculpture surfaces. The model has the ability to calculate the workpiece/cutter intersection domain automatically for a given cutter location (CL) file, cutter and workpiece geometries. Furthermore, an analytical approach is used to determine the instantaneous chip load (with and without runout) and cutting forces. In addition to predicting the cutting forces, the model also employs a Boolean approach for a given cutter, workpiece geometries, and CL file to determine the surface topography and scallop height variations along the workpiece surface which can be visualized in 3-D. The results of model validation experiments on machining Ti-6A1-4V are also reported. Comparisons of the predicted and measured forces as well as surface topography show good agreement.     

带传动中各力关系式的图解法研究

提出用图解法建立摩擦型带传动中的各力关系式,并通过引入传动能力系数对各力关系进行深入探讨,为带传动的设计计算理论和工作能力的研究提供了新的工具。     

Circumventing mental health stigma by embracing the warrior culture: Lessons learned from the Defender's Edge program.

Despite considerable efforts on the part of the Department of Defense, Department of Veterans Affairs, and the wider mental health community, mental health stigma continues to be a significant barrier to seeking help by service members, highlighting the need for newer modes of thought. A significant factor contributing to this stigma is the fundamental difference between traditional mental health approaches and the warrior culture. As a mental health prevention initiative, the Defender's Edge (DEFED) program was specifically developed to fit within the United States Air Force Security Forces (SF) charged with ground combat operations while deployed to Iraq. DEFED adopted a strengths-based philosophy and integrated a psychologist into the SF culture. Evaluative feedback from 192 program participants is presented, demonstrating high programmatic acceptability and feasibility suggestive of success in circumventing mental health stigma. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Discrete element method (DEM) modelling of evolving mill liner profiles due to wear. Part I: DEM validation

Since the early 1990s the discrete element method (DEM) gained considerable success in its ability to predict the power draw and the load behaviour in mills as affected by operating conditions. The DEM can also be used to design milling equipment and predict the breakage of particles. A detailed validation of this method is required in order to produce accurate results. In this paper, we assess the ability of the DEM to predict forces exerted by the mill charge on liners. Data obtained on an experimental two-dimensional mill designed in order to record the normal and tangential forces exerted on an instrumented lifter bar was available. The measured results are compared to the DEM simulated results. Good agreement has been found in terms of amplitude of forces and positions of shoulder and toe at low speed.     

Model of slice-push cutting forces of stacked thin material

Adding slicing to push cutting processes can significantly reduce cutting forces. Creating an appropriate model for the calculation of forces is necessary to completely understand manufacturing processes. In this investigation, a model detailing the cutting forces of stacked thin material using an asymmetrical knife is developed. Equilibrium of forces and frictional effects at the cutting edge are analyzed to determine the components in vertical and horizontal direction of the total cutting force, and their dependency on the slice-push ratio. The friction effects of the new model are based on Coulomb friction. For comparison purposes, an existing shear friction model is extended to discuss the new presented Coulomb friction model. To support the findings, the newly developed model is experimentally verified.     

Determination of forces in high speed blanking using FEM and experiments

The increasing demand for micro-formed and stamped parts such as connectors in the electronic industry is forcing manufacturers to push the speed limit of conventional press technologies to improve throughput. Designing dies/tooling for higher speeds and obtaining extended tool life requires a thorough understanding of the process. This paper discusses an experimental study of the interaction between punch, stripper plate and sheet material at various blanking velocities up to 1600 mm/s. The effect of velocity on punching force is also studied. A methodology to obtain high strain and strain rate dependent material flow stress data using blanking test and finite element modelling is presented.     

Modelling of temperature and forces when orthogonally machining hardened steel

This paper initially considers heat generation in single-point metal cutting and the direct/indirect techniques employed to measure cutting temperatures. The development of analytical models of the cutting process is briefly reviewed, including more recent work involving finite element (FE) methods. Details are given of the different FE packages and formulation methods used by different researchers. Following on from this, an FE model is presented using FORGE 2® to simulate cutting forces and temperature distributions when orthogonal turning a hardened hot work die steel, AISI H13 (52HRC), with polycrystalline cubic boron nitride (PCBN) tooling. Experimental data from infrared chip surface temperature measurements and cutting force output are used to validate the model. Good correlation was obtained between experimental and modelled results for temperature; however, the FE analysis underestimated feed force results due to a lack of adequate workpiece property data and simplistic tool/chip friction assumptions.     

半圆形防波堤抗滑移稳定浅析

基于二维随机波浪对半圆形防波堤作用的物理模型试验和相关理论，分析不同水深下影响半圆形防波堤抗滑稳定的因素，找出堤体滑移失稳破坏和不同水深下滑移方向不同的原因。