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1、Forming Dies Forming dies, often considered in the same class with bending dies, are classified as tools that form or bend the blank along a curved axis instead of a straight axis. There is very little stretching or compressing of the material. The internal movement or the plastic flow of the materi
2、al is localized and has little or no effect on the total area or thickness of the material. The operations classified as forming are bending, drawing, embossing, curling, beading, twisting, spinning, and hole flanging. A large percentage of stampings used in the manufacturing of products require som
3、e forming operations. Some are simple forms that require tools of low cast and conventional design. Others may have complicated forms, which require dies that produce multiple forms in one stroke of the press. Some stampings may be of such nature that several dies must be used to produce the shapes
4、and forms required. A first consideration in analyzing a stamping is to select the class of die to perform the work. Next to be considered is the number of stampings required, and this will govern the amount of money that should be spent in the design and building of the tools. Stampings of simple c
5、hannels in limited production can be made on a die classed as a solid form die. It would be classified under channel forming dies. Others-the block and pad type-are also channel forming dies. Such operations as curling, flanging, and embossing as well as channeling employ pressure pads. A forming di
6、e may be designed in many ways and produce the same results; at this point the cost of the tool, safety of operation, and also the repairing and reworking must be considered. The tool that is cheapest and of the simplest design may not always be best because it may not produce the stamping to the dr
7、awing specifications. Where limited production is required, and a liberal tolerance is allowed in a stamping, a solid form die can be used. Drawing Dies() diameter or smaller, to aircraft or automotive parts large enough to require the use of mechanical handling equipment. Die Design PrinciplesCoini
8、ng Dies. In backward extruding dies the punch is always smaller in diameter than the die cavity in order to give the clearance between punch and die equaling the desired wall thickness of the part to be produced. The punch is loaded as a column. To minimize punch failure it is desirable to coin the
9、slugs to a close fit in diameter to assure concentricity. Figure 8-66 illustrates a coining die to prepare a slug for backward extrusion. Coining the slug to fit the diepot and coining the upper end to fit and guide the free end of the punch will minimize punch breakage of the extruding die.Backward
10、 Extrusion Dies. A typical backward extrusion die is shown in Figure 8-67. The use of a carbide die cavity will minimize wear due to excessive pressures. The carbide insert is shrunk into a tapered holder. The holder has a 1 side taper that prestresses the carbide insert to minimize expansion and fa
11、tigue failure. The inserts are well supported on hardened blocks. The extruding punch is guided by a spring-loaded guide plate which in turn is positioned by a tapered piloting ring on the lower die. Ejection of the finished part from the die is by cushion or pressure cylinder. Figure 8-68 illustrat
12、es a backward extrusion die with an unusual punch penetration ratio of 5：1 made possible with a modified flat-end punch profile.Forward Extrusion Dies. Figure 8-69 is an example of a typical forward extrusion die in which the metal flows in the same direction as the punch, but at a greater rate owin
13、g to change in the cross-sectional area. The lower carbide guide ring is added to maintain straightness. The nest above the upper carbide guide ring serves as a guide for the punch during the operation. Figure 8-70 illustrates another forward extrusion die in which the punch creates the orifice thro
14、ugh which the metal flows. The extruding pressure is applied through the punch guide sleeve. Combination Extruding Dies. A typical combination forward and backward extrusion die is shown in Figure 8-71. In this die, the two piece pressure anvil acts as a bottom extruding punch and a shedder. The upp
15、er extruding punch is guided by a spring-loaded guide plate into which the guide sleeve is mounted. To maintain concentricity between the punch and die, the punch guide sleeve is centered into the die insert.Punch Design.() can penetrate three times its diameter in steel, four to six times its diame
16、ter in aluminum. A punch with a bullet-shaped nose or with a steep angle will cut through the phosphate coat lubricant quicker than a flat-end punch. When the lubricant is displaced in extrusion, severe galling and wear of the punch will take palce. The punch must be free of grinding marks and requi
17、res a 4 in. (0.10m) finish, lapped in the direction of metal flow. The punch should be made of hardened tool steel or carbide. In some backward extrusion dies a shoulder is provided on punch to square up the metal as it meets this shoulder.Pressure Anvil Design. The function of the pressure anvil is
18、 to form the base of the diepot, to act as a bottom extruding punch, and to act as a shedder unit to eject the finished part. Heat treatment and surface finish requirements are the same for pressure anvils and for punches.Diepot Design. To resist diepot bursting pressure, the tool steel or carbide d
19、ie ring is shrunk into the shrink ring or die shoe. The die shoe is normally in compression. A shrink fit of 0.004per in.( per mm) of diameter of the insert is desirable. Material, heat treatment, and finish requirements of the diepot are the same as for the punch. The recommended material for shrin
20、k rings is a hot-worked alloy tool steel which is hardened to Rc 50-Rc 52. A two-piece diepot insert is sometimes used for complex workpiece shapes.Punch Guide Design. The guide ring minimizes the column loading on the punch above the diepot. The spring-loaded guide sleeve pilots the punch into the
21、diepot and maintains concentricity between them. The guide ring can also act as a stripper. The proper use of guide sleeves permits higher penetration ratios.成型模成型模具，通常被以为是与弯曲模属于同一类，被作为工具，沿着弯曲的轴线而非直线轴线使工件半成品成型或弯曲。材料有超级小的拉伸和紧缩。材料的内部运动或塑性流动是定域化的，并已很少或几乎没有阻碍材料的总面积或厚度。操作成型的分类为弯曲，拉伸，压花，卷曲，弯边，扭曲，旋压，和孔翻边。用
22、于制造冲压件产品的专门大一部份需要一些成形操作。一些简单的成型，需要工具的本钱低，常规设计。其他的一些可能复杂的成型，这需要在一个紧缩冲程中能够产生多种形式的模具。表现一些冲压件性质的几种模具必需用于生产所需的形状和形式。在分析一个冲压进程时，第一考虑的是来完成那个工件的模具品级的选择。下一个要考虑的是冲压件的数量，这将支配的钱应该被花在工具的设计和制造上的数量。用于固定产品上的一些简单的途径生产的冲压件，能够通过被归类为固体成型模具的模具来制造。它将被归类为通道成形模。其他的一些类型模块式和垫板式也是通道成形模。卷曲，翻边，压花如此的操作，和应用通道的压力垫是一样的。成型模具能够和通过许多方
23、式来设计，而且产生相同的结果；在这一点上的工具的本钱，操作平安性，还有维修和改造，这些必需被考虑。该工具是最廉价和最简单的设计不必然是最好的，因为它可能可不能产生符合制图标准的冲压件。在一个冲压进程中，有许诺有限的产量是和丰硕的公差的要求的方面，也能够应用固体成型模。拉伸模拉伸是一种将一种平面的、预先切割完的金属坯料转化为中空容器，而且使其没有皱纹、变薄、或压裂。成型生产的各类形式能够是圆筒形的或立方体或棱锥形的侧边或混合直线、圆锥的组合、或曲边。零件的尺寸可能会有所不同，转变能够从0.250（6.35毫米）直径或更小的，到需要足够大的机械设备来搬运的飞机或汽车上的零件。模具设计原那么压印模具
24、。在反挤压模中，冲头的直径小于模腔，为了使凸凹模之间的间隙等于部件所需的要生产壁厚。冲头是一个圆柱的。为了最大限度的减少冲头失效，最可取的是压印嵌条紧密配合尺寸，以保证同心度。图8-66说明压印模具预备一个嵌条作为反挤压塞。压印塞来适应空心模和压印的上端以适应和引导冲头的自由端，将减少挤压凸模的断裂。反向挤压模具。一个典型的反挤压模具如图8-67所示。一种硬质合金模腔的利用，将减少由于过度的压力造成的磨损。硬质合金刀片被缩小为一个锥形座。那个锥形座有一个1侧锥角，来保证施加预应力时，硬质合金刀片减少膨胀和疲劳失效。这将是专门好的支持硬块。挤压冲头是由下模锥形环依次定位的一个弹簧导板来导向。从模
25、具中推出完成的部件是用缓冲器或压力缸。图8-68显示了一个不寻常的渗透率比为5:1，与修改后的平头冲头的反向挤压模具。正挤压模具。图8-69是在同一方向的金属流动的冲头的典型的正向挤压模具的一个例子，但由于在横截面面积的转变，以一个更大的速度。较低的硬质合金导环被添加来维持直线度。上硬质合金导环以上的嵌套用作冲头的操作期间的导向。图8-70说明了另一个正挤压模，通过金属流动冲压创建孔。挤出压力被施加通过上述冲头导套。组合挤压模具。一个典型的组合向前和向后挤压模具如图8-71示。在这两个模具中，两片压砧别离作为底部挤压凸模和顶出。上部挤压冲头被引导由一个弹簧加载的导板安装到其中的导向套筒。为了维
26、持冲头和冲模之间的同心度，在冲头导套的中心插入模具添加物中。凸模设计。凸模设计的最重要的特点是端部轮廓。一个mm）的冲头，在钢中，能够穿透其直径的三倍，其在铝中，能够穿透其直径的四到六倍。一个子弹形的凸头，或与一个峻峭的角度的冲头穿过的磷化膜润滑剂的速度比平端冲头速度快。当在挤出进程中润滑剂的流离发生时，严峻的擦伤和磨损会发生。冲头必需无磨痕和需要一个4in.（0.10M）的修整，沿着金属流动方向被研磨。冲头应该用硬化工具钢或硬质合金来制作。在一些反向挤压模具中，一个模肩应该被设置，来使金属变平，与轴肩一样。压力砧的设计。压力砧的功能是，来形成空心模的基部，作为挤压冲头的底部，并作为一个顶出装
27、置直到完成部件。作为压砧和为了穿孔，热处置和表面光洁度要求是相同的。空心模设计。为了抵抗空心模爆破压力，工具钢或硬质合金模具环收缩到收缩环或模座中。模具座一般是抗压的。插入物的过盈配合的尺寸为每英寸0.004（0.004mm每毫米）是可取的。空心模的材料，热处置，和光洁度的要求是和冲头是相同的。收缩环的推荐材料是热加工的合金工具钢，其硬化至Rc 50到Rc52。有时，两个空心模插入是被用于复杂工件的形状。冲头导轨的设计。在空心模上，导向环是最大限度地减少冲头上的柱状载荷。弹簧导套引导冲头进入到空心模，并维持它们之间的同心度。导向环也能够作为一个冲孔模板。导套的正确利用，使更高的穿透率成为可能。
