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1、STAMPING Journal Key design principles for successful deep drawing成功深拉伸模的关键设计准则By Art Hedrick, Contributing WriterMay 30, 2001Successful deep drawing depends on many factors. Ignoring even one of them during die design and build can prove disastrous.成功深拉伸模依赖很多因素. 在模具设计和制造中忽略其中任何一个因素都会导致灾难性的后果 .Succe
2、ssful deep drawing depends on many factors. Ignoring even one of them during die design and build can prove disastrous. However, regardless of the many factors involved, the most important element to a successful deep drawing operation is initiating metal flow. The following are key elements affecti
3、ng metal flow, and each of them should be considered when designing, building, or troubleshooting deep drawing stamping dies:成功深拉伸模依赖很多因素. 在模具设计和制造中忽略其中任何一个因素都会导致灾难性的后果. 尽管在深拉伸工艺中有很多因素要考虑, 然而决定成功的最重要的因素源于金属的流动. 以下列出一些影响金属流动的关键因素, 这其中任何一种在深拉伸冲压模具的设计, 制造或者在故障诊断中都应当考虑.1. Material type 材料类型2. Material t
4、hickness 材料厚度3. N and R values N 和 R 值4. Blank size and shape 展开平板的尺寸和外形5. Part geometry 零件的几何尺寸6. Press speed (ram speed) 冲床速度 ( 压头速度)7. Draw radii 拉伸圆角8. Draw ratio 拉伸率9. Die surface finish 模具表面的光洁度10. Die temperature 模具的温度11. Lubricant 润滑12. Draw bead height and shape 拉延阻筋的高度和形状13. Binder pressur
5、e 压边圈的压力14. Binder deflection 压边圈的变形15. Standoff height 平衡垫片 ( 上下压边圈之间) 厚度Because thicker materials are stiffer, they hold together better during deep drawing. Thicker materials also have more volume, so they can stretch longer distances.由于较厚的材料刚性好, 因此在深拉伸时, 不易断裂. 又由于较厚的材料有更大的容积, 所以它们能拉延更长.The N val
6、ue, also called the work hardening exponent, describes the ability of a steel to stretch. The R valuethe plastic strain ratiorefers to the ability of a material to flow or draw. Blank sizes and shapes that are too large can restrict metal flow, and the geometry of parts affects the ability of metal
7、to flow. Press speeds must allow time for materials to flow.N 值也叫冷作硬化指数, 它是描述钢材拉伸能力的指标. R值也叫塑性变形系数-用来度量材料的流动和拉伸能力的. 展开平板的尺寸和形状若太大都阻碍金属的流动, 以及完成品零件的几何外形也影响金属的流动能力. 冲床的速度应容许留出金属流动所需足够的时间.Die surface finishes and lubricants are important because they can reduce the coefficient of friction, allowing mat
8、erials to slide through tools more easily. Die temperatures can affect the viscosity of lubricants.模具表面光洁度和润滑也是重要的, 因为它们能够减小摩擦系数, 容许材料更容易流入型腔. 模具的温度能够影响润滑剂的黏(滞) 度As a controller of metal flow, draw bead height and shape can cause materials to bend and unbend to create restrictive forces going into a
9、 tool. Increasing binder pressure exerts more force on a material, creating more restraint on material going into the tool.作为控制金属流动的拉延阻筋的高度和形状能够通过弯曲和拉直材料产生在模具内的限制阻力. 增加压力圈的压力可施加在材料上更多的力, 产生更多的约束来限制材料的流动.The remaining key elements affecting metal flow are examined in more detail in the remainder of t
10、his article. To illustrate the principles of metal flow, this article examines two basic draw shapes, round and square. All deformation modes that occur in any given part shape are present in one of these common shapes.其余影响金属流动的因素在这篇文章剩余部分进一步详细的分析研究. 为了说明金属流动的原理, 本文从分析两种基本的拉伸形状圆形和正方形入手. 任何给定形状的零件的所有
11、变形模式都可用这两种基本形状之一的变形来描述.Figure 1 图一In the illustration of incorrect draw ratio (L), the too-small post would cause metal to thin to the point of failure, while the correct draw ratio (R) will result in a successfully deep drawn part. 为了说明不正确的拉伸率(L), 太小的型芯凸模将导致金属变薄直到开裂, 反之, 正确的拉伸率(R)会得到成功的深拉伸零件.The dr
12、aw ratio is among the most important elements to be considered when attempting to deep draw a round cup. The draw ratio is the relationship between the size of the draw post and the size of the blank. The draw ratio must fall within acceptable limits to allow metal to flow.拉伸圆杯件时, 在众多最重要因素当中首先要考虑的是拉
13、伸率. 拉伸率体现型芯凸模尺寸和零件展开尺寸之间的关系. 拉伸率必须在容许金属流动的可接受的极限内.During forming, a blank is forced into circumferential compression, which creates a resistance to flow. If the resistance is too great, the cup fractures. If the post is too small or too far from the blank edge, the metal stretches and thins to the p
14、oint of failure. If the post is the appropriate distance from the blank edge, and the die entry radius is acceptable, the metal can flow freely, progressively thickening as it enters the die cavity (see Figure 1).当压型时, 平板四周若有强迫压缩力作用时, 将阻挠金属的流动. 如果这个阻力太大, 杯子会被拉破. 如果型芯太小或离平板外边缘太远, 金属将被拉伸变薄直至断裂点. 如果型芯离
15、平板外边缘适当的距离, 同时材料切入凸凹模圆角合理的话, 金属能够自由的流动, 并且当它进入凹模型腔时, 厚度不断增加(参见图一).When a very tall small-diameter part is being processed, draw reductions likely will be necessary (see Figure 2). A draw reduction is a process in which a part is first formed within acceptable draw ratio limits and then is progressiv
16、ely reduced or reshaped to a desired shape and profile.当拉伸一个细长零件时, 分阶段拉伸是非常有必要的(参见图二). 分阶段拉伸是一种工艺过程, 也就是首次拉伸采用合理的拉伸率拉伸, 然后依此递减拉伸或整形到理想的形状或轮廓. Figure 2 图二Reduction percentages for various thicknesses of draw-quality steel. 不同厚度拉伸钢材的分阶段拉伸递减百分比.The most important factor to remember when performing draw reductions is that all of the material necessary to make the final part shape must be present in the first draw. Figure 3 is a reduction chart for the first, second, and thir
