handbook of die design 2nd edition phần 3 docx

is immersed in the tank as well. When exposed to the shock wave, the part is forced to take on the shape of its die. This process may be found useful for all tube-forming processes that alter the tube’s profile and shape, such as complex forming, bulging, and expanding. 3-4-3 Forming With Explosives Explosive forming is not really a new process, but very similar to electromagnetic forming described in Sec. 3-4-1. It has been around for years with differing results. Some consider it a superb method of manufacturing, others have lost their buildings to it in an explosion. It is a process in which safety cannot be overemphasized. The energy, derived from explosives can be of tremendous intensity and the use of such force for forming processes is certainly tempting. During the forming process, the explosive material, either in pieces or encapsulated, is placed in a water-filled tank alongside or within a die with the material to be formed. The charge, when detonated, prompts release of a great amount of steam and gas during a rela- tively short time interval. Such an action creates a strong shock wave in the liquid medium, which affects the part to be formed by forcing it to take on the shape of the die. Objects suitable for utilization of such manufacturing process are mainly tubes, which may be bulged, expanded, or squeezed to tight tolerances and formed into uneven shapes. Metal plates may be drawn to wildest shapes, many of them unattainable otherwise. 3-4-4 Superimposed Vibrations Ultrasonic waves, when applied to the molten metal, promote the development of addi- tional currents within its mass, which in turn produce a more effective mixing, which results in an improved homogeneity of the metal. When applied to the metal as it begins to METAL STAMPING DIES AND THEIR FUNCTION 143 FIGURE 3-58 Section view of a pillar subpress die. Suchy_CH03.qxd 11/08/05 10:36 AM Page 143 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. METAL STAMPING DIES AND THEIR FUNCTION solidify, ultrasound dissolves microfractures, removes gaseous entrapments, and drives out impurities. In solidified metals, high-intensity ultrasound repairs the structural defects by bringing the material into the stage of plastic deformation and rearranging its structure. Application of ultrasound reduces friction between metal particles, which in turn allows for a free movement of metal layers with respect to each other. This aids the forming process and improves homogeneity of the outcome. The speed of the forming is increased as well, with lessened friction between the material and its tooling, which subsequently decreases the wear of the latter. Ultrasound enhances mechanical properties of materials, increases their hardness, pre- vents structural changes due to deformation, and lowers stresses caused by manufacturing processes, while improving the quality of the product’s surface. Many brittle materials, such as bismuth, were possible to form only after ultrasound was added to the process. This is explained by the effect of vibrations on a metal crystal, which, under their influence, develops a series of linear defects, which lower its yield stress range. When applied to the forming process, ultrasonic vibrations greatly reduce the amount of force necessary for the alteration of metal. 144 CHAPTER THREE FIGURE 3-59 Cylindrical subpress die. Suchy_CH03.qxd 11/08/05 10:36 AM Page 144 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. METAL STAMPING DIES AND THEIR FUNCTION However, this type of manufacturing is not widely practiced as yet. Its possible nega- tive effects on the equipment, on the manufacturing personnel, and perhaps on the fabri- cated part has not yet been fully assessed. 3-4-5 Lasers and Their Application Lasers operate on the basis of a concentration of their output to a small area of operation, approximately 0.002 to 0.010 in. diameter (0.05 to 0.25 mm). One of their advantages is the absence of contact between the tool (laser) and the workpiece. The laser cutting process is fast, achieving high quality, burrless edges. The high temper- ature of the process quickly heats up the material in the path of the laser ray, causing the metal to melt and evaporate on contact. The surrounding material has no time to respond to such a sudden wave of heat, which is the reason for the cut surface’s lack of distortion. 3-5 FINEBLANKING Fineblanking is a special form of blanking, which not only produces finished edges on a cut part, but also works to close tolerances, attaining a superb consistency over high volumes of production. Fineblanking is performed in a cutting die, yet it is a process quite similar to cold extrusion. In fineblanking (Fig. 3-60), the material to be pierced is firmly retained by a pressure ring, which, on descending of the ram, partially enters the material with its grips. The punch follows down, piercing an opening in the sheet. The pressure of the retaining ring is not METAL STAMPING DIES AND THEIR FUNCTION 145 FIGURE 3-60 Fineblanking principle. Suchy_CH03.qxd 11/08/05 10:36 AM Page 145 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. METAL STAMPING DIES AND THEIR FUNCTION immediately released. Instead a counterpressure to a die pad is applied, from the bottom. This pressure drives the blanked part up, along with the punch. At the die-bushing level, the pressure ring releases its grip on the metal and the blank can be ejected from the die by the still-rising bottom pressure pad. This process uses tight clearances between the punch and the die, which amount to some 0.5 percent of the material thickness. While being taken down and up through the die, blanks have their cut edges forced into conformity with the surface of the opening. This smoothes the cut edge, making it even and uniform. One possible disadvantage can be a tapered edge of blanked parts, which is due to a fric- tion between the blank and the die opening. This taper is greater with thicker materials, or with those of higher carbon content. The burr appears on the punch side, while the oppo- site edge is rounded, as shown in Fig. 3-61. One definite advantage is the high precision of the work. Openings of 0.125 in. diame- ter (3.18 mm) can be produced even in 0.187 in. (4.75 mm) thick sheet, with the hole tol- erance ranging ±0.0004 in. (0.010 mm). 146 CHAPTER THREE FIGURE 3-61 Fineblanked part. FIGURE 3-62 Shape of the grip. Suchy_CH03.qxd 11/08/05 10:36 AM Page 146 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. METAL STAMPING DIES AND THEIR FUNCTION The work-retaining efficiency of grips is relevant to the quality of the cut. Their shape digs into the material before the punch descends to cut it. This in itself not only provides for controlled positioning of the sheet under the punch, but also stretches the sheet mater- ial in all directions, to prevent distortion. The grips are most often located on the face of a pressure pad, bordering the punch along its entire shape. With materials thicker than 0.156 in. (4.00 mm), or where rounding of cut edges is to be kept to a minimum, additional grips may be located on the upper surface of the die. The shape of the grip, as shown in Fig. 3-62, has two variations: either 45°–45° angles on both sides, or a 45°–30° angle combination. The height h 1 depends on the material thickness and its quality. It may vary along these recommended sizes: h 1 = 0.167t for hard materials h 1 = 0.333t for softer materials The distance off the edge of the punch a depends on the height of the grip and its percentile value should be: a = (0.6 to 1.2)h The height of the pressure pad behind the grip’s edge is usually relieved, or: h 2 = h 1 + 0.020 in. (0.5 mm) METAL STAMPING DIES AND THEIR FUNCTION 147 Suchy_CH03.qxd 11/08/05 10:36 AM Page 147 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. METAL STAMPING DIES AND THEIR FUNCTION Suchy_CH03.qxd 11/08/05 10:36 AM Page 148 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. METAL STAMPING DIES AND THEIR FUNCTION CHAPTER 4 149 METAL STAMPING DIES, THEIR CONSTRUCTION, AND ASSEMBLY 4-1 TOLERANCING SYSTEMS Manufacturing of parts cannot be absolutely precise. If such be the case, the cost of com- ponents would be horrendous. Already the differences in straightness or flatness, surface finish, the existence of tooling marks or tooling grooves, burrs, chips, and similar, can ren- der the component unacceptable by too harsh a standard. Yet, all these discrepancies can sometimes be present and for this reason designers and manufacturers devised a certain area of benevolent acceptance, called a tolerance range. This tolerance range specifies the amount of deviation a part can possess and still be accept- able and function well within an assembly. Different manufacturing fields use a different tolerance ranges. Where ±0.031 in. (0.79 mm) can be unacceptable in die work, the same tolerance range is too tight for, let us say, in steel constructions. For comparison, quite precise tolerances for glass cutting are: x.xxx ±0.015 in. x.xx ±0.031 in. fractions ±0.062 in. x.xx ±0.40 mm x.x ±0.80 mm x ±1.5 mm Minimal tolerances in woodworking, where NC equipment is utilized, are approxi- mately: x.xxx ±0.062 in. x.xx ±0.125 in. fractions ±0.25 in. and more x.xx ±1.5 mm x.x ±3.2 mm x ±6.5 mm Every manufacturing field adjusts the tolerance ranges to suit its needs. The fits, how- ever, are a rather different story, as they always involve two parts, assembled together. Here the tolerance range must be somewhat standardized and often quite precise. After all, we are not fitting wooden shafts into openings drilled through glass. Suchy_CH04.qxd 11/08/05 10:49 AM Page 149 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Source: HANDBOOK OF DIE DESIGN 4-1-1 Types of Fits in Assembly of Parts The inch-based measuring system has one great advantage––it may establish several layers of dimensions for easy application of tolerances. In die design, we most often have: x.xxx ±0.005 in. x.xx ±0.010 in. x.x ±0.015 in. Fractions ±0.031 in. which translates into metric system’s three layers only roughly, as follows: x.xx ±0.13 mm x.x ±0.25 mm x ±0.40 mm These tolerance ranges are rather common in metal fabricating field. The general range of tolerances, as published by the American Standards Association in 1925 (ASA Standard B4a 1925) runs as shown in Table 4-1. The use of this table is based on the hole dimension being the nominal size, toleranced on the plus side, with negative tolerance range equal to zero. The shaft is handled in the opposite way, its tolerance ranges being negative, with plus tolerance equal to zero. However, we will discuss the current American shop practice with regard to toleranc- ing, later in this chapter. In metric environment, the basic representation (IT) of ISO tolerancing system comes in eighteen levels of accuracy. For levels IT 5 through IT 16, a simple formula can be used, (4-1) iDD= 0 45 0 001 3 . +. 150 CHAPTER FOUR TABLE 4-1 Tolerance Ranges Per ASA Std. B4a-1925 Hole Shaft Class of fit Clearance Interference tolerance tolerance 1. Loose fit 0.0025 +0.0025 −0.0025 2. Free fit 0.0014 +0.0013 −0.0013 3. Medium fit 0.0009 +0.0008 −0.0008 4. Snug fit 0.0000 +0.0006 −0.0004 5. Wringing 0.0000 +0.0006 +0.0004 6. Tight 0.00025D +0.0006 +0.0006 7. Medium force 0.0005D +0.0006 +0.0006 8. Heavy force 0.001D +0.0006 +0.0006 D 3 D 3 D 3 D 3 D 3 D 3 D 3 D 3 D 3 D 3 D 3 D 3 D 2 3 D 3 D 3 D 2 3 D 3 D 3 D 2 3 Suchy_CH04.qxd 11/08/05 10:49 AM Page 150 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. METAL STAMPING DIES, THEIR CONSTRUCTION, AND ASSEMBLY where D is the geometric center with respect to all combined tolerance ranges, in. or mm and i is the unit of tolerance, in micrometers (µm). The upper allowable deviation is described as es or ES. This is the difference between the given basic diameter and its maximum deviation from this number. The lower deviation is ei or EI, and it is the difference between the basic diameter and the lower tolerance range. Both these abbreviations are taken from French, where es/ES is described as écart superieur and ei/EI is écart inferieur. The relationship between the two variations applies as follows. Notice the differentia- tion between shafts and holes by assigning capital letters to the latter. For shafts ei = es − IT es = ei + IT For holes ES = EI + IT EI = ES − IT where IT is the basic tolerance range. Selected IT values are given in Table 4-2. Every punch or die, or any other shape of an object to be mounted per specific require- ments, is considered a shaft in this description. The same way, every opening of any shape is considered a hole. The dimensional variations described above are used as alphabetically/numerically coded. These values are applied to the holes and shafts in the following manner: For shafts, a through h = upper tolerance range, es j through z = lower tolerance range, ei For holes, A through H = lower tolerance range, EI J through Z = upper tolerance range, ES Tolerance ranges A & a and Z & z present the widest differences of the whole arrangement. They vary the most from the zero-middle line and this way they allow for the loosest fits. The closer to the zero line, the tighter the dimensional tolerances become. The zero value of tolerance ranges can be observed with J & j denominations, where their deviations in either direction are equal and therefore they cancel each other out. Some recommended shaft/hole variations are presented in Table 4-3. Table 4-4 depicts the actual values of selected tolerance ranges. METAL STAMPING DIES, THEIR CONSTRUCTION, AND ASSEMBLY 151 TABLE 4-2 Selected Basic Tolerance Range (IT) Values (Metric) Dimension range Basic tolerance range in micrometers (µm) (mm) Levels of accuracy From To 1 2 3 4 5 3 6 1 1.5 2.5 4 5 6 10 1 1.5 2.5 4 6 10 18 1.2 2 3 5 8 18 30 1.5 2.5 4 6 9 30 50 1.5 2.5 4 7 11 Suchy_CH04.qxd 11/08/05 10:49 AM Page 151 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. METAL STAMPING DIES, THEIR CONSTRUCTION, AND ASSEMBLY 152 CHAPTER FOUR TABLE 4-3 Some Generally Recommended Metric Tolerance Ranges for Shafts and Openings Shaft Opening h6 D8 E8 F8 G7 H7 J7 K7 M7 N7 h7 H8 J8 K8 M8 N8 h8 D9 E8 F9–F8 H8 h9 D10–D9 E8 F9–F8 H9–H8 h11 D11 H11 Opening Shaft H6 f6 g5 h5 j5 k5 m5 n5 H7 d8 e8 f7 g6 h6 j6 k6 m6 n6 H8 d10–d9 e9 f9–f8 h9–h7 j7 k7 m7 n7 H10 h10–h9 H11 d11 h11 TABLE 4-4 Selected Basic Tolerance Deviations (Metric) Shaft (mm) Upper deviation, es (micrometers) From To defghj 36−30 −20 −10 −40±IT/2 610−40 −25 −13 −50±IT/2 10 18 −50 −32 −16 −60±IT/2 18 30 −65 −40 −20 −70±IT/2 30 50 −80 −50 −25 −90±IT/2 Upper Opening deviation, ES (mm) Lower deviation, EI (micrometers) (micrometers) From To DEFGHJ J 36+30 +20 +10 +40±IT/2 +5 to +10 610+40 +25 +13 +50±IT/2 +5 to +12 10 18 +50 +32 +16 +60±IT/2 +6 to +15 18 30 +65 +40 +20 +70±IT/2 +8 to +20 30 50 +80 +50 +25 +90±IT/2 +10 to +24 Suchy_CH04.qxd 11/08/05 10:49 AM Page 152 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. METAL STAMPING DIES, THEIR CONSTRUCTION, AND ASSEMBLY [...]... the die height which can be used up for subsequent sharpenings The height of the die life depends on the number of pieces the die has to produce and on the number of expected sharpenings during the die button’s existence in the die The height of this area is a debatable subject In order to prolong the life of a die, a considerable die- life size may be chosen, which may be expected to provide for many... cross-section of the die, and by studying details of punches and bushings, we can discover what this tool is really doing and how it is producing producing high-quality, close-toleranced parts each time the ram of the press slides down Majority of such work is done by components of the die, which are punches, die buttons, forming blocks, cutoff shears, special arrangements, and others The die blocks, die shoes,... (25.400 − 25 .38 7 = 0.0 13 mm) With 0.0005 in (0.0 13 mm) being the lowest possible interference and 0.00 13 in (0. 033 mm) being the highest, we have an acceptable level of press fit for the two metal parts However, dimensions of actual products are rarely found on either extreme side of their tolerance range but are rather somewhere in between Therefore, it is not important in which section of the tolerance...Suchy_CH04.qxd 11/09/05 6 :39 PM Page 1 53 METAL STAMPING DIES, THEIR CONSTRUCTION, AND ASSEMBLY METAL STAMPING DIES, THEIR CONSTRUCTION, AND ASSEMBLY 1 53 4-2 DIE COMPONENTS, THEIR FABRICATION, AND ASSEMBLY A die, as mounted in the press, is a complex-action mechanism, producing parts in predetermined sequence The lower half of the die, mounted on the lower die shoe, is firmly attached to the... form of draft, most often in the vicinity of 1.5 to 2° taper 4-2-2-1 Slug Removal The three types of slug relief are as shown in Fig 4-14; a tapered and counterbored relief with a die life (also called “land”), and a relief that is tapered through with no die life Each of these designs has its advantages and disadvantages For example, the tapered relief controls the movement of flat slugs through the die, ... the above text, are added here 4-2 -3- 1 Variations of Punch and Die Cutting Diameter As already mentioned, the cutting portion of the punch is always the size of the opening to be pierced The opening in the die amounts to a total of the punch size, plus metal-cutting clearance Metal-cutting clearance is the difference between the size of the punch and that of the die This term is not to be confused... centering of the punch during the die operation The tolerance range of the guide bushing’s inner openings is not as precise as that of cutting areas The opening itself is usually made +0.001 in (0. 03 mm) greater than the size of the punch, with tolerance of +0.001/−0.000 (+0. 03/ −0.00 mm) Mounting of guide bushings in the stripper plate is the same as mounting of any other die member (Fig 4-26) The head... discrepancy between the recommended variation of 0. 035 mm and the calculated variation of 0. 033 mm is due to rounding of converted numerical values This interference is acceptable, and yet the ranges of tolerance for the two vital dimensions are not out of the ordinary Through such evaluation we may assess that if the two parts were to be made to the fullest extent of their tolerance ranges, they still could... punches It also restrains the rest of the strip from moving along with the upper half of the die by keeping it positioned on the face of a die block The die block contains all bushings, forming dies, or cutting inserts It is supported by another backup plate positioned between this block and the lower die shoe All cutting, forming, and other material-altering punches and dies are assembled into their respective... process of inserting punches and dies into their openings in blocks is aided by the presence of a lead The lead is a 1/4 in wide band on the circumference of the punch shank (or die) , which is slightly smaller in diameter, for an easy entry of the large part into the smaller, press-fit opening 4-2-1-1 Depth of the Counterbore Versus the Height of the Punch Head When comparing the thickness of the punch . +0.0006 +0.0006 8. Heavy force 0.001D +0.0006 +0.0006 D 3 D 3 D 3 D 3 D 3 D 3 D 3 D 3 D 3 D 3 D 3 D 3 D 2 3 D 3 D 3 D 2 3 D 3 D 3 D 2 3 Suchy_CH04.qxd 11/08/05 10:49 AM Page 150 Downloaded from. of the metal. When applied to the metal as it begins to METAL STAMPING DIES AND THEIR FUNCTION 1 43 FIGURE 3- 58 Section view of a pillar subpress die. Suchy_CH 03. qxd 11/08/05 10 :36 AM Page 1 43 Downloaded. rights reserved. Any use is subject to the Terms of Use as given at the website. Source: HANDBOOK OF DIE DESIGN 4-1-1 Types of Fits in Assembly of Parts The inch-based measuring system has one