塑料模具设计中英翻译

2024-01-19 07:26:31 文档大全网 [ 字体：小中大 ] [ 阅读： ]

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模具设计,中英,翻译,塑料
Die Life and Die Failure

Proper selection of the die material and of the die manufacturing techniquedetermines to a large extent the useful life of forming dies. Die may have to bereplaced for a number of reasons such as changes in dimensions due to wear orplastic deformation deterioration of the surface finish breakdown of lubrication andcracking or breakage. In hot impression die forging the principal modes of the failureare erosion thermal fatigue mechanical fatigue and permanent plastic deformation. In erosion also commonly called die wear material is actually removed fromthe die surface by pressure and siding of the deforming material wera resistance ofthe die material die surface temperature relative sliding speed at the die/materialinterface and the nature of the interface layer are the most significant factorsinfluencing abrasive die wear. Thermal fatigue occurs on the surface of the dieimpression in hot forming and results in “heat checking”. Thermal fatigue resultsform cyclic yielding of the die surface due to contact with the hot deforming material.This contact causes the surface layers to expand and because of the very steeptemperature gradients the surface layers are subject to compressive stresses. Atsufficiently high temperatures these compressive stresses may cause the surfacelayers to deform. When the die surface cool a stress reversal may occur and thesurface layers will then be in tension. After repeated cycling in this manner fatiguewill cause formation of a crack pattern that is recognized as heat checking. Diebreakage or cracking is due to mechanical fatigue and occurs in cases where the diesare overloaded and local stresses are high. The dies are subjected to alternatingstresses due to load and unloading during the deformation process and this causescrack initiation and eventual failure. Die life and die failure are greatly affected by the materials properties of the diematerials under the conditions that exist in a given deformation process.Generally the properties that are most significant depend on the process temperature.Thus die materials used in cold forming processes are quite different from those usedin hot forming. The design and manufacture of dies and the selection of die materials are veryimportant in the production of discrete parts by use of metal forming processes. Thedies must be made by modern manufacturing methods from appropriate die materialsin order to provide acceptable die life at a reasonable cost .Often the economicsuccess of a forming process depends on die life and costs per piece produced. For agiven application selection of the appropriate die material depends on three types ofvariables:aVariables related to the process itself including factors such as size of the diecavity type of machine used and deformation speed initial stock size and temperaturedie temperature to be used lubrication production rate and number of parts to beproduced.bVariables related to the type of die loading initial speed of loading i.e. impact orgradual contact time between dies and deforming metal this contact time is especiallyimportant in hot forming maximum load and pressure on the dies maximum andminimum die temperatures and number of loading cycles to which the dies will besubjected.cMechanical properties of the die material including harden ability impact strengthhot strength if hot forming is considered and resistance to thermal to thermal andmechanical fatigue.

模具寿命与模具损坏

正确的选择模具材料和模具的制造技术，在很大程度上决定着成形模具的使用寿命。为着某些原因，模具可能不得不更换。例如，由于磨损或塑性变形而使尺寸发生改变，表面损坏、光洁度降低、润滑故障和裂纹即破裂。在热压模锻中，模具失效的主要模式是腐蚀作用、热疲劳、机械疲劳和永久性即塑性变形。腐蚀，通常也叫做模具磨损，实际上模具由于受到压力后模具表面上的材料发生剥落。变形材料的滑移、模具材料的抗磨性，模具表面温度、模具和材料接触表面的相对滑动速度以及接触层的性质，都是影响模具磨损的最主要的因素。热成形加工中会发生热裂效应，热疲劳都发生在模具模腔的表面。由于跟热变形材料接触，就在周期性屈服的模具表面引起了热疲劳。由于温度梯度的急剧变化，这种接触引起表面层的膨胀，而且表面层受到压应力的影响。在温度足够高的时刻，这些压应力可引起表面层的破坏。当模具表面冷却时，可发生反向应力，因而表面层将处于拉应力状态。这种状态循环往复将引起形成龟裂的模面，那就是作为识别热裂纹的特征。模具破裂或产生裂纹是由于机械疲劳，并且是在模具过载和局部应力高等情况下发生的。在变形加工过程中，由于加载、减载，模具承受着交变应力作用，这就将引起开裂并发生重大破坏。在给定的成形工艺条件下，模具材料的机械性能对模具寿命和模具的损坏影响很大。一般而言，最具影响的性能是取决于加工过程的温度。这样，用于冷却成形加工工艺的模具材料与用于热成形加工的材料有着极大的区别。对于金属成形加工工艺的小批、单件生产，模具的设计、制造和模具材料的选择是非常重要的。为着提供成本合理和具有令人满意的寿命的模具，必须用合适的模具材料和用现代的制造方法来制造模具。成形加工的经济效益常常是取决于模具寿命和所制造的每件模具的成本。根据上述应用，合适的模具材料的选择取决于以下三方面的因素：（a）与加工工艺本身有关的因素，包括模腔尺寸、所用机器形式和变形速度，毛坯尺寸和温度，要用的模具温度、润滑、生产率和要生产的零件数量。（b）与模具加载形式相关的因素，包括加载速度，即模具与正在变形的金属之间的冲击时间或逐渐接触的时间（在热变形加工中，这种接触时间显得特别重要），在模具上的最大载荷和压力，最大和最小的模具温度以及模具将要承受的加载周期的数目。（c）模具材料的机械性能，包括硬度、冲击强度、热强度（如果考虑热成形加工的话）和抵抗热疲劳和机械疲劳的性能。