微观结构级铁合金切削模型的建立

微观结构级铁合金切削模型的建立

BY

LEONID CHUZHOY

理学学士，俄亥俄州大学，1985

理学硕士，俄亥俄州大学，1985

THESIS

Submitted in partial fulfillment of the requirements

for the degree of Doctor of Philosophy in Mechanical Engineering

in the Graduate College of the

University of Illinois at Urbana-Champaign, 2001

Urbana, Illinois

摘要

摘要

诸如铸铁和钢等的钢铁材料在当今工业中应用广泛。如，铸铁广泛应用在内燃机、用于制造内燃机机座（内燃机引擎铸模带有内燃发动机汽缸的铸制金属区）的重型设备、排气集管、变速箱和其它零件中。为达到精确的尺寸和几何要求，许多钢铁和铸铁零件需要经受各种形式的切削加工，这些切削加工的费用往往会超过铸造或锻造的花费。充分理解材料的切削性能对降低加工成本和提高产品质量至关重要。各种铁合金的不同微观结构对其性能和机械加工特性具有显著影响。

本研究项目建立了铁合金切削加工仿真的微观结构级模型，该微观结构模型将下列四个主要要素集成到一个有限元结构中：微观结构仿真，材料模型，材料描述和材料流动断裂模型。微观结构仿真模块将各个单独的成分组织成一个基于微观结构成分、结晶粒度大小和分布的微观结构组成。材料模块用于解决各种成分对大的应变、应变速度、温度、损伤和加载路径影响等与切削加工相关的因素的反应。材料描述部分提供了一个参数化的材料模型，该参数用来定义依赖应变速度和温度的各个单独阶段的行为。材料流动和断裂模块则周期性地检查各个晶粒的破坏、定位变形的晶格边界并生成新的边界。该模型基于微观结构、各个成分的性质、刀具几何尺寸和工艺参数来计算各个阶段的应力、应变、温度和破坏。该微观结构模型已在球墨铸铁的切削加工中进行了验证。

在对各种不同材料如铸铁的加工过程中，接近切削影响区域的材料受到了反向载荷的作用，这表明了它自己在持续材料软化（MSRL 效应）。此外，裂缝在刀具的下面和前面产生。为了计算与MASL 效应相关的参数，应用球墨铸铁的单独成分进行了同轴反向加载实验和仿真。该模型在对球墨铸铁试样的反向加载实验中得到验证。为确定与各个成分断裂相关的参数，进行了锯齿形试样的实验与仿真研究。在验证阶段，仿真中球墨铸铁的反应与实验数据有着很好的一致性。

该微观结构模型在对球墨铸铁及其两个组成成分（珠光体和铁素体）的仿真中得到了验证。对三种材料进行了直角切削的实验与仿真研究。将测量的切屑形态和切削力与模型预测结果进行比较，发现它们之间有很好的相关性。此外，该微观结构模型对珠光体、铁素体和球墨铸铁的切屑形成机理以及切屑形状与切削力之间的关系给出了合理解释。

微观结构级铁合金切削模型的建立

ABSTRACT

Ferrous materials such as cast iron and steel are commonly used in industry today. Cast iron, for example, is used in engine and heavy equipment manufacturing for engine blocks, exhaust manifolds, transmission cases, and many other parts. To meet stringent dimensional and geometrical requirements many steel and cast iron parts undergo extensive machining with the cost of machining often exceeding the cost of casting or forging. Understanding material machinability is important for reducing machining costs and improving product quality. Heterogeneous microstructure of many ferrous alloys has pronounced influence on their properties and machinability.

This research project developed a microstructure-level model for machining simulation of ferrous alloys. The microstructure-level model for machining consists of four main elements integrated into the finite element structure: microstructure simulation, material model, material characterization, and material flow and fracture model. The microstructure simulation module assembles individual constituents into a composite material based on micro-structural composition, grain size, and distribution. The material module accounts for response of each constituent to high strains, strain rates, temperatures, damage, and effects of loading paths associated with machining. The material characterization part provides the material model with parameters to define strain rate and temperature dependent behavior of individual phases. The material flow and fracture module periodically examines each grain for damage, locates deformed grain boundaries, and generates new boundaries. The model computes stress, strain, temperature, and damage in each phase based on microstructure, properties of individual constituents, tool geometry, and process parameters. The microstructure-level model was demonstrated on machining of ductile iron.

During machining of heterogeneous materials such as cast iron, the material around the machining-affected zone undergoes reverse loading, which manifests itself in permanent material softening(MSRL effect). In addition, cracks are formed below and ahead of the tool. To calculate the parameters associated with the MASL effect, uniaxial reverse loading experiments and simulations were conducted using individual constituents of ductile iron. The model was validated with reverse loading experiments of ductile iron specimens. To determine the parameters associated with fracture of each constituent, experiments and simulation of notched specimens were performed. During the validation stage, response of simulated ductile iron was in good agreement with the experimental data.

The microstructure-level model was validated on machining of ductile iron and two of its constituents: pearlite and ferrite. Orthogonal cutting experiments and simulation were conducted of the three materials. The measured chip moephology and machining forces were compared with the model predictions, and a good correlation between them was found. In addition, the microstructure-level model explained chip formation mechanisms and relationship between chip formation and the machining forces for pearlite, ferrite, and ductile iron.