Forming DiesForming 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 material 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 some 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 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 channels 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 die 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 drawing specifications. Where limited production is required, and a liberal tolerance is allowed in a stamping, a solid form die can be used.Drawing DiesDrawing is a process of changing a flat, precut metal blank into a hollow vessel without excessive wrinkling, thinning, or fracturing. The various forms produced may be cylindrical or box-shaped with straight or tapered sides or a combination of straight, tapered, or curved sides. The size of the parts may vary from 0.250″(6.35mm)diameter or smaller, to aircraft or automotive parts large enough to require the use of mechanical handling equipment.Die Design PrinciplesCoining Dies. In backward extruding dies the punch is always smaller in diameterthan the die cavity in order to give theclearance between punch and dieequaling the desired wall thickness ofthe part to be produced. The punch isloaded as a column. To minimizepunch failure it is desirable to coin theslugs to a close fit in diameter to assureconcentricity. Figure 8-66 illustrates acoining die to prepare a slug forbackward extrusion. Coining the slugto fit the diepot and coining the upperend to fit and guide the free end of the punch will minimize punch breakage of the extruding die.Backward Extrusion Dies. A typical backward extrusion die is shown in Figure8-67. The use of a carbide die cavitywill minimize wear due to excessivepressures. The carbide insert is shrunkinto a tapered holder. The holder has a1◦ side taper that prestresses thecarbide insert to minimize expansionand fatigue failure. The inserts arewell supported on hardened blocks.The extruding punch is guided by aspring-loaded guide plate which inturn is positioned by a tapered pilotingring on the lower die. Ejection of thefinished part from the die is bycushion or pressure cylinder. Figure 8-68illustrates a backward extrusion die withan unusual punch penetration ratio of 5：1 made possible with a modified flat-endpunch profile.Forward Extrusion Dies. Figure 8-69 is an example of a typical forwardextrusion die in which the metal flows inthe same direction as the punch, but at agreater rate owing to change in the cross-sectional area. The lower carbide guidering 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 anotherforward extrusion die in which the punch creates the orifice through 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 upper extruding punch is guided by a spring-loaded guide plate into which the guide sleeve is mounted. To maintainconcentricity between the punch anddie, the punch guide sleeve iscentered into the die insert.Punch Design.The mostimportant feature of punch design isend profile. A punch with a flat endface and a corner radius not over0.020″(0.51mm) can penetrate threetimes its diameter in steel, four to sixtimes its diameter in aluminum. Apunch with a bullet-shaped nose orwith 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 requires a 4µ in.(0.10µm) 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 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 die ring is shrunk into the shrink ring or die shoe. The die shoe is normally in compression. A shrink fit of 0.004″per in.(0.004mm 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 shrink 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 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，通常被认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。