锻模材料与工作性能最佳耦合的基础研究/Basic Research in Best Coupling State between Material and Wo

2018-11-28 03:49:35

machine heat stress Die 锻模



锻模是制造业中重要的基础工艺装备。在利用它成形锻件时,其承受脉冲的热负荷和脉冲的机械负荷。型腔表面在热负荷的反复作用下可能会发生四种形式的损伤:热疲劳、相变、回火和塑性变形。型腔表面在机械负荷的作用下主要发生脆性破裂、机械裂纹、机械磨损和塑性变形四种损伤。这些损伤严重影响锻模的寿命。
生产实践表明,如何提高锻模的寿命是个综合性问题。其研究内容涉及到锻模的材料与工作性能的耦合问题。本文将以锻模为研究对象,对此耦合问题进行基础研究。
研究内容分为四个部分。第一部分是在锻模的实验研究、生产经验和调查统计的基础上,分析其失效形式和失效机理,得出引起锻模失效的最根本原因是负荷。因此,要提高锻模的寿命,必须了解作用在锻模上的各种负荷及其影响锻模寿命的机理。
第二部分是用有限元方法分析热锻模热力过程,这一部分是本文的主体部分。首先,将热锻模热力过程划分成吸热过程和散热过程的交替循环,并建立锻模的吸热模型和散热模型。为了得到锻模的热平衡状态,提出试探法的新思路求解最佳工作节拍。并按此工作节拍仿真出锻模在其工作过程中的温度场。其次,根据温度场的变化求解锻模的温度应力。温度应力即为热负荷使锻模产生的应力。再次,根据机械负荷求解锻模的机械应力。最后,将温度应力和机械应力按时间和空间进行叠加,得到锻模的综合应力。得到了综合应力,就能从微观上真实反映锻模的失效原因。
第三部分是以一具体实例——终锻模为例,用第二部分提供的研究方法分析热锻模热力过程,得到锻模温度场、各种应力场的数据。根据温度场的变化规律,将锻模划分为波动区、平衡区和下降区,并通过超调量——深度曲线确定了波动区的厚度。根据应力场的数据,得出结论:锻模的失效主要是温度应力引起的,其失效形式主要是塑变失效和热疲劳失效。
第四部分讲述了提高热锻模寿命的有效途径:选用梯度材料、加强强化层性能、润滑冷却和预热。并说明只有将这些因素综合考虑,才能使锻模在最佳耦合状态下工作,寿命得到有效提高。



Forging die is important basic technics equipment in manufacturing. When it is used to forge workpieces, it endures pulsing heat and machine load. Surface of die occurs four damnification such as thermal fatigue, phase change, temper and plastic distortion under heat load. Surface of die occurs four damnification such as brittleness break, machine crack, machine wear and plastic distortion under machine load. All damnification influences severely life of die.
Manufacture and practice show that how to improve life of die is a complex problem. Its research content comes down to coupling of material and working properties. In order to investigate the coupling problem, forging die is as research object in the thesis.
These are four parts in research content. In the first part, it is concluded that load is the most fundamentality reason leading to disablement of die after experimentation research, manufacture experience and stat. Thus, load and its action should be found out to improve life of die.
In the second part which is main body, forging die’s heat-force process is simulated by FEM(finite element method). Firstly, forging die’s heat-force process is divided into alternate loop of decalescence process and heat-lossing process. The models of decalescence and heat-lossing are established. Exploring method is first put forward to get best working rhythm for heat balance of die. Temperature field of die is simulated under the rhythm. Secondly, temperature stress is solved by change of temperature field, and it is from heat load. Thirdly, machine stress is solved by machine load. Finally, integrated stress is gotten from temperature and machine stress added as time and space. Integrated stress can reflect really disablement reasons of die in microcosmic.
In the third part, an example of final-die is investigated for heat-force process of die, and data about temperature field and several stress field are gotten. Die is divided into three parts, wave zone, balance zone and descending zone as change disciplinarian of temperature field, and thickness of wave zone is gotten by curve of overtaking-depth. It is concluded that disablement of die is mainly by temperature stress and disablement form is mainly plastic and thermal fatigue disablement from data of stress.
In the last part, ways to improve life of die are grads material, consolidating surface, labrication and warm-up. If those reasons are consider, life of die is improved as best coupling state.