MACHINERY''''S HANDBOOK 27th ED Part 9 pptx

PUNCHES, DIES, AND PRESS WORK 1331 and shearing ordinary metals not over 1 ⁄ 4 inch thick, the speeds usually range between 50 and 200 strokes per minute, 100 strokes per minute being a fair average. For punching metal over 1 ⁄ 4 inch thick, geared presses with speeds ranging from 25 to 75 strokes per minute are commonly employed. The cutting pressures required depend upon the shearing strength of the material, and the actual area of the surface being severed. For round holes, the pressure required equals the circumference of the hole × the thickness of the stock × the shearing strength. To allow for some excess pressure, the tensile strength may be substituted for the shear- ing strength; the tensile strength for these calculations may be roughly assumed as fol- lows: Mild steel, 60,000; wrought iron, 50,000; bronze, 40,000; copper, 30,000; alumi- num, 20,000; zinc, 10,000; and tin and lead, 5,000 pounds per square inch. Pressure Required for Punching.—The formula for the force in tons required to punch a circular hole in sheet steel is πDST/2000, where S = the shearing strength of the material in lb/in. 2 , T = thickness of the steel in inches, and 2000 is the number of lb in 1 ton. An approx- imate formula is DT × 80, where D and T are the diameter of the hole and the thickness of the steel, respectively, both in inches, and 80 is a factor for steel. The result is the force in tons. Example:Find the pressure required to punch a hole, 2 inches in diameter, through 1 ⁄ 4 -in. thick steel. By applying the approximate formula, 2 × 1 ⁄ 4 × 80 = 40 tons. If the hole is not circular, replace the hole diameter with the value of one-third of the perimeter of the hole to be punched. Example:Find the pressure required to punch a 1-inch square hole in 1 ⁄ 4 -in. thick steel. The total length of the hole perimeter is 4 in. and one-third of 4 in. is 1 1 ⁄ 3 in., so the force is 1 1 ⁄ 3 × 1 ⁄ 4 × 80 = 26 2 ⁄ 3 tons. The corresponding factor for punching holes in brass is 65 instead of 80. So, to punch a hole measuring 1 by 2 inches in 1 ⁄ 4 -in. thick brass sheet, the factor for hole size is the perim- eter length 6 ÷ 3 = 2, and the formula is 2 × 1 ⁄ 4 × 65 = 32 1 ⁄ 2 tons. Shut Height of Press.—The term “shut height,” as applied to power presses, indicates the die space when the slide is at the bottom of its stroke and the slide connection has been adjusted upward as far as possible. The “shut height” is the distance from the lower face of the slide, either to the top of the bed or to the top of the bolster plate, there being two meth- ods of determining it; hence, this term should always be accompanied by a definition explaining its meaning. According to one press manufacturer, the safest plan is to define “shut height” as the distance from the top of the bolster to the bottom of the slide, with the stroke down and the adjustment up, because most dies are mounted on bolster plates of standard thickness, and a misunderstanding that results in providing too much die space is less serious than having insufficient die space. It is believed that the expression “shut height” was applied first to dies rather than to presses, the shut height of a die being the dis- tance from the bottom of the lower section to the top of the upper section or punch, exclud- ing the shank, and measured when the punch is in the lowest working position. Diameters of Shell Blanks.—The diameters of blanks for drawing plain cylindrical shells can be obtained from Table 1 on the following pages, which gives a very close approximation for thin stock. The blank diameters given in this table are for sharp-cor- nered shells and are found by the following formula in which D = diameter of flat blank; d = diameter of finished shell; and h = height of finished shell. (1) Example:If the diameter of the finished shell is to be 1.5 inches, and the height, 2 inches, the trial diameter of the blank would be found as follows: Dd 2 4dh+= Machinery's Handbook 27th Edition Copyright 2004, Industrial Press, Inc., New York, NY 1332 PUNCHES, DIES, AND PRESS WORK For a round-cornered cup, the following formula, in which r equals the radius of the cor- ner, will give fairly accurate diameters, provided the radius does not exceed, say, 1 ⁄ 4 the height of the shell: (2) These formulas are based on the assumption that the thickness of the drawn shell is the same as the original thickness of the stock, and that the blank is so proportioned that its area will equal the area of the drawn shell. This method of calculating the blank diameter is quite accurate for thin material, when there is only a slight reduction in the thickness of the metal incident to drawing; but when heavy stock is drawn and the thickness of the finished shell is much less than the original thickness of the stock, the blank diameter obtained from Formula (1) or (2) will be too large, because when the stock is drawn thinner, there is an increase in area. When an appreciable reduction in thickness is to be made, the blank diam- eter can be obtained by first determining the “mean height” of the drawn shell by the fol- lowing formula. This formula is only approximately correct, but will give results sufficiently accurate for most work: (3) where M = approximate mean height of drawn shell; h = height of drawn shell; t = thickness of shell; and T = thickness of metal before drawing. After determining the mean height, the blank diameter for the required shell diameter is obtained from the table previously referred to, the mean height being used instead of the actual height. Example:Suppose a shell 2 inches in diameter and 3 3 ⁄ 4 inches high is to be drawn, and that the original thickness of the stock is 0.050 inch, and the thickness of drawn shell, 0.040 inch. To what diameter should the blank be cut? Obtain the mean height from Formula (3) : According to the table, the blank diameter for a shell 2 inches in diameter and 3 inches high is 5.29 inches. Formula (3) is accurate enough for all practical purposes, unless the reduction in the thickness of the metal is greater than about one-fifth the original thickness. When there is considerable reduction, a blank calculated by this formula produces a shell that is too long. However, the error is in the right direction, as the edges of drawn shells are ordinarily trimmed. If the shell has a rounded corner, the radius of the corner should be deducted from the fig- ures given in the table. For example, if the shell referred to in the foregoing example had a corner of 1 ⁄ 4 -inch radius, the blank diameter would equal 5.29 − 0.25 = 5.04 inches. Another formula that is sometimes used for obtaining blank diameters for shells, when there is a reduction in the thickness of the stock, is as follows: (4) D 1.5 2 41.5× 2×+ 14.25 3.78 inches=== Dd 2 4dh+ r–= M ht T = M ht T 3.75 0.040× 0.050 3 inches== = Da 2 a 2 b 2 –() h t += Machinery's Handbook 27th Edition Copyright 2004, Industrial Press, Inc., New York, NY 1334 PUNCHES, DIES, AND PRESS WORK In this formula, D = blank diameter; a = outside diameter; b = inside diameter; t = thick- ness of shell at bottom; and h = depth of shell. This formula is based on the volume of the metal in the drawn shell. It is assumed that the shells are cylindrical, and no allowance is made for a rounded corner at the bottom, or for trimming the shell after drawing. To allow for trimming, add the required amount to depth h. When a shell is of irregular cross-sec- tion, if its weight is known, the blank diameter can be determined by the following for- mula: (5) where D = blank diameter in inches; W = weight of shell; w = weight of metal per cubic inch; and t = thickness of the shell. In the construction of dies for producing shells, especially of irregular form, a common method to be used is to make the drawing tool first. The actual blank diameter then can be determined by trial. One method is to cut a trial blank as near to size and shape as can be estimated. The outline of this blank is then scribed on a flat sheet, after which the blank is drawn. If the finished shell shows that the blank is not of the right diameter or shape, a new trial blank is cut either larger or smaller than the size indicated by the line previously scribed, this line acting as a guide. If a model shell is available, the blank diameter can also be determined as follows: First, cut a blank somewhat large, and from the same material used for making the model; then, reduce the size of the blank until its weight equals the weight of the model. Depth and Diameter Reductions of Drawn Cylindrical Shells.—The depth to which metal can be drawn in one operation depends upon the quality and kind of material, its thickness, the slant or angle of the dies, and the amount that the stock is thinned or “ironed” in drawing. A general rule for determining the depth to which cylindrical shells can be drawn in one operation is as follows: The depth or length of the first draw should never be greater than the diameter of the shell. If the shell is to have a flange at the top, it may not be practicable to draw as deeply as is indicated by this rule, unless the metal is extra good, because the stock is subjected to a higher tensile stress, owing to the larger blank needed to form the flange. According to another rule, the depth given the shell on the first draw should equal one-third the diameter of the blank. Ordinarily, it is possible to draw sheet steel of any thickness up to 1 ⁄ 4 inch, so that the diameter of the first shell equals about six- tenths of the blank diameter. When drawing plain shells, the amount that the diameter is reduced for each draw must be governed by the quality of the metal and its susceptibility to drawing. The reduction for various thicknesses of metal is about as follows: For example, if a shell made of 1 ⁄ 16 -inch stock is 3 inches in diameter after the first draw, it can be reduced 20 per cent on the next draw, and so on until the required diameter is obtained. These figures are based upon the assumption that the shell is annealed after the first drawing operation, and at least between every two of the following operations. Neck- ing operations—that is, the drawing out of a short portion of the lower part of the cup into a long neck—may be done without such frequent annealings. In double-action presses, where the inside of the cup is supported by a bushing during drawing, the reductions possi- ble may be increased to 30, 24, 18, 15, and 12 per cent, respectively. (The latter figures may also be used for brass in single-action presses.) When a hole is to be pierced at the bottom of a cup and the remaining metal is to be drawn after the hole has been pierced or punched, always pierce from the opposite direction to Approximate thickness of sheet steel 1 ⁄ 16 1 ⁄ 8 3 ⁄ 16 1 ⁄ 4 5 ⁄ 16 Possible reduction in diameter for each succeeding step, per cent 20 15 12 10 8 D 1.1284 W wt = Machinery's Handbook 27th Edition Copyright 2004, Industrial Press, Inc., New York, NY PUNCHES, DIES, AND PRESS WORK 1335 that in which the stock is to be drawn after piercing. It may be necessary to machine the metal around the pierced hole to prevent the starting of cracks or flaws in the subsequent drawing operations. The foregoing figures represent conservative practice and it is often possible to make greater reductions than are indicated by these figures, especially when using a good draw- ing metal. Taper shells require smaller reductions than cylindrical shells, because the metal tends to wrinkle if the shell to be drawn is much larger than the punch. The amount that the stock is “ironed” or thinned out while being drawn must also be considered, because a reduction in gage or thickness means greater force will be exerted by the punch against the bottom of the shell; hence the amount that the shell diameter is reduced for each drawing operation must be smaller when much ironing is necessary. The extent to which a shell can be ironed in one drawing operation ranges between 0.002 and 0.004 inch per side, and should not exceed 0.001 inch on the final draw, if a good finish is required. Allowances for Bending Sheet Metal.—In bending steel, brass, bronze, or other metals, the problem is to find the length of straight stock required for each bend; these lengths are added to the lengths of the straight sections to obtain the total length of the material before bending. If L = length in inches, of straight stock required before bending; T = thickness in inches; and R = inside radius of bend in inches: For 90° bends in soft brass and soft copper see Table 2 or: (1) For 90° bends in half-hard copper and brass, soft steel, and aluminum see Table 3 or: (2) For 90° bends in bronze, hard copper, cold-rolled steel, and spring steel see Table 4 or: (3) Angle of Bend Other Than 90 Degrees: For angles other than 90 degrees, find length L, using tables or formulas, and multiply L by angle of bend, in degrees, divided by 90 to find length of stock before bending. In using this rule, note that angle of bend is the angle through which the material has actually been bent; hence, it is not always the angle as given on a drawing. To illustrate, in Fig. 1, the angle on the drawing is 60 degrees, but the angle of bend A is 120 degrees (180 − 60 = 120); in Fig. 2, the angle of bend A is 60 degrees; in Fig. 3, angle A is 90 − 30 = 60 degrees. Formulas (1), (2), and (3) are based on extensive experiments of the Westinghouse Electric Co. They apply to parts bent with simple tools or on the bench, where limits of ± 1 ⁄ 64 inch are specified. If a part has two or more bends of the same radius, it is, of course, only necessary to obtain the length required for one of the bends and then multiply by the number of bends, to obtain the total allowance for the bent sections. Example, Showing Application of Formulas:Find the length before bending of the part illustrated by Fig. 4. Soft steel is to be used. For bend at left-hand end (180-degree bend) Fig. 1. Fig. 2. Fig. 3. L 0.55 T×()1.57 R×()+= L 0.64 T×()1.57 R×()+= L 0.71 T×()1.57 R×()+= L 0.64 0.125×()1.57 0.375×()+[] 180 90 × 1.338== Machinery's Handbook 27th Edition Copyright 2004, Industrial Press, Inc., New York, NY 1340 PUNCHES, DIES, AND PRESS WORK it is constructed. The reinforcing members must be able to resist the deflection of the sheet, and its own deflection. There is a relationship between duct width, reinforcement spacing, reinforcement size, pressure, and sheet thickness. For constant pressure and constant duct size, the thicker sheet allows more distance between reinforcements. The higher the pressure the shorter the spacing between reinforcements. Joints and intermediate reinforcements are labor intensive and may be more costly than the savings gained by a reduction in wall thickness. Thicker duct wall and stronger joints are more cost effective than using more reinforce- ment. The following material illustrates various joint designs, used both in duct work and other sheet metal asseblies. Sheet Metal Joints Plain Lap and Flush Lap: Raw and Flange Corner: Allowances for Bends in Sheet Metal Square Bends Gage Thick ness Inches Amount to be Deducted from the Sum of the Outside Bend Dimensions, Inches 1 Bend 2 Bends 3 Bends 4 Bends 5 Bends 6 Bends 7 Bends Formed in a Press by a V-die 18 0.0500 0.083 0.166 0.250 0.333 0.416 0.500 0.583 16 0.0625 0.104 0.208 0.312 0.416 0.520 0.625 0.729 14 0.0781 0.130 0.260 0.390 0.520 0.651 0.781 0.911 13 0.0937 0.156 0.312 0.468 0.625 0.781 0.937 1.093 12 0.1093 0.182 0.364 0.546 0.729 0.911 1.093 1.276 11 0.1250 0.208 0.416 0.625 0.833 1.041 1.250 1.458 10 0.1406 0.234 0.468 0.703 0.937 1.171 1.406 1.643 Rolled or Drawn in a Draw-bench 18 0.0500 0.066 0.133 0.200 0.266 0.333 0.400 0.466 16 0.0625 0.083 0.166 0.250 0.333 0.416 0.500 0.583 14 0.0781 0.104 0.208 0.312 0.416 0.521 0.625 0.729 13 0.0937 0.125 0.250 0.375 0.500 0.625 0.750 0.875 12 0.1093 0.145 0.291 0.437 0.583 0.729 0.875 1.020 11 0.1250 0.166 0.333 0.500 0.666 0.833 1.000 1.166 10 0.1406 0.187 0.375 0.562 0.750 0.937 1.125 1.312 Fig. 6. Plain Lap The plain lap (Fig. 6 ) and flush lap (Fig. 7 ) are both used for var- ious materials such as galvanized or black iron, copper, stainless steel, aluminum, or other metals, and may be soldered, and/or riv- eted, as well as spot, tack, or solid-welded. Lap dimensions vary with the particular application, and since it is the duty of the drafts- man to specify straight joints in lengths that use full-sheet sizes, transverse lap dimensions must be known. Fig. 7. Flush Lap Fig. 8. Raw and Flange Corner The raw and flange corner (Fig. 8) is generally spot-welded, but may be riveted or soldered. For heavy gages it is tack-welded or solid-welded. Machinery's Handbook 27th Edition Copyright 2004, Industrial Press, Inc., New York, NY PUNCHES, DIES, AND PRESS WORK 1341 Flange and Flange Corner: Standing Seam: Groove Seam: Corner Standing Seam: Double Seam: Slide-Corner: Button Punch Snap Lock: Fig. 9. Flange and Flange Corner The flange and flange corner (Fig. 9) is a refinement of the raw and flange corner. It is particularly useful for heavy-gage duct sec- tions which require flush outside corners and must be field- erected. Fig. 10. Standing Seam The standing seam (Fig. 10) is often used for large plenums, or casings. Before the draftsman is able to lay out a casing drawing, one of the items of information needed is seam allowance mea- surements, so that panel sizes can be detailed for economical use of standard sheets. Considering velocity levels, standing seams are considered for duct interiors: 1″ seam is normally applied for duct widths up to 42″, and 1 1 ⁄ 2 ″ for bigger ducts. Fig. 11. Groove Seam The groove seam (Fig. 11) is often used for rectangular or round duct straight joints, or to join some sheets for fittings that are too large to be cut out from standard sheets. It is also known as the pipelock, or flat lock seam. Fig. 12. Corner Standing Seam The corner standing seam (Fig. 12) has similar usage to the stand- ing seam, and also can be used for straight-duct sections. This type of seams are mostly applied at the ends at 8″ intervals. Fig. 13. Double Corner Seam The double corner seam (Fig. 13) at one time was the most com- monly used method for duct fitting fabrication. However, although it is seldom used because of the hand operations required for assembly, the double seam can be used advantageously for duct fittings with compound curves. It is called the slide lock seam. Machines are available to automatically close this seam. Fig. 14. Slide Corner The slide-corner (Fig. 14) is a large version of the double seam. It is often used for field assembly of straight joints, such as in an existing ceiling space, or other restricted working area where ducts must be built in place. To assemble the duct segments, oppo- site ends of each seam are merely “entered” and then pushed into position. Ducts are sent to job sites “knocked-down” for more effi- cient use of shipping space. Fig. 15. Button Punch Snap Lock The button punch snap lock (Fig. 15) is a flush-type seam which may be soldered or caulked. This seam can be modified slightly for use as a “snap lock”. This types of seam is not applicable for aluminum or other soft metals. This seam may be used up to 4″ w.g. by using screws at the ends. The pocket depth should not be smaller than 5 ⁄ 8 ″ for 20, 22 and 26 gage. Machinery's Handbook 27th Edition Copyright 2004, Industrial Press, Inc., New York, NY 1342 PUNCHES, DIES, AND PRESS WORK Pittsburg: Flange: Hem: Flat Drive Slip: Standing Drive Slip: Flat Drive Slip Reinforced: Double “S” Slip Reinforced: Flat “S” Slip: Fig. 16. Pittsburgh The Pittsburg (Fig. 16) is the most commonly used seam for stan- dard gage duct construction. The common pocket depths are 5 ⁄ 16 ″ and 5 ⁄ 8 ″ depending on the thickness of sheet. Fig. 17. Flange The flange (Fig. 17) is an end edge stiffener. The draftsman must indicate size of the flange, direction of bend, degree of bend (if other than 90°) and when full corners are desired. Full corners are generally advisable for collar connections to concrete or masonry wall openings at louvers. Fig. 18. Hem The hem edge (Fig. 18) is a flat, finished edge. As with the flange, this must be designated by the draftsman. For example, drawing should show: 3 ⁄ 4 ″ hem out. Fig. 19. Drive Slip This is one of the simplest transverse joints. It is applicable where pressure is less than 2″ w.g. This is a slide type connection generally used on small ducts in combination of “S” slips. Service above 2″ inches w.g. is not applicable. Fig. 20. Standing Drive Slip This is also a slide type connection. It is made by elongating flat drive slip, fasten standing portions 2″ from each end. It is applica- ble for any length in 2″ w.g, 36″ for 3″ inch w.g., and 30″ inches at 4″ w.g. service. Fig. 21. Drive Slip Reinforced This is the reinforcement on flat drive slip by adding a transverse angle section after a fixed interval. Fig. 22. Double “S” Slip The double “S” slip is applied, to eliminate the problem of notching and bending, especially for large ducts. Apply 24 gage sheet for 30″ width or less, 22 gage sheet over 30″ width. Fig. 23. Plain “S” Slip Normally the “S” slip is used for small ducts. However, it is also useful if the connection of a large duct is tight to a beam, column or other object, and an “S” slip is substituted for the shop standard slip. Service above 2″ inches w.g. is not applicable. Gage shall not be less than 24, and shall not 2 gage less than the duct gage. When it is applied on all four edges, fasten within 2″ of the corners and at 12″ maximum interval. H Machinery's Handbook 27th Edition Copyright 2004, Industrial Press, Inc., New York, NY PUNCHES, DIES, AND PRESS WORK 1343 Hemmed “S” Slip: Other Types of Duct Connections Clinch-bar Slip and Flange: Clinch-bar Slip and Angle : Flanged Duct Connections Angle Frame, or Ring: Flanged End and Angle: Formed Flanges: Fig. 24. Hemmed “S” Slip This is the modified “S” slip, by adding hem and an angle for reinforcing. The hem edge is a flat, and finished edge. Hemmed “S” slip is mostly applied with angle. The drive is generally 16 gage, formed a 1 inch height slip pocket and screws at the end. Notching and bending operations on an “S” slip joints can be cum- bersome and costly, especially for large sizes. Tied each section of the duct within 2″ from the corner at maximum 6-inch interval. Fig. 25. Clinch-bar Slip and Flange The clinch-bar slip and flange (Fig. 25), uses the principle of the standing seam, but with a duct lap in the direction of airflow. These slips are generally assembled as a framed unit with full corners either riveted or spot-welded, which adds to the duct cross-section rigidity. Reinforcement may be accomplished by spot welding the flat-bar to the flange of the large end. Accessibility to all four sides of the duct is required because the flange of the slip must be folded over the flange on the large end after the ducts are connected. Fig. 26. Clinch-bar Slip and Angle The clinch bar slip and angle (Fig. 26), is similar to clinch bar slip (Fig. 25), but it has a riveted or spot-welded angle on the large end. This connection can also have a raw large end which is inserted into the space between the angle and the shop-fabricated slip. Matched angles (minimum of 16 ga) are riveted or spot welded to the smaller sides of the ducts, to pull the connection “home.” Fig. 27. Raw Ends and Matched ∠s Any of the following flanged connections may have gaskets. The draftsman should not allow for gasket thicknesses in calculations for running length dimensions, nor should he indicate angle sizes, bolt centers, etc., as these items are established in job specifications and approved shop standards. Generally, angles are fastened to the duct sections in the shop. If conditions at the job site require consider- ation for length contingencies, the draftsman should specify “loose angles” such as at a connection to equipment which may be located later. The most common matched angle connection is the angle frame, or ring (Fig. 27). The angles are fastened flush to the end of the duct. Fig. 28. Flanged Ends and Matched ∠s The flanged end and angle (Fig. 28), is often used for ducts 16 ga or lighter, as the flange provides a metal-to-metal gasket and holds the angle frame or ring on the duct without additional fastening. The draftsman may indicate in a field note that a round-duct fitting is to be ″rotated as required″.This type of angle-ring-connection is con- venient for such a condition. Fig. 29. Formed Flanges Double flanges (Fig. 29), are similar to Fig. 21, except that the con- necting flange has a series of matched bolt holes. This connection, caulked airtight, is ideal for single-wall apparatus casings or ple- nums. The flanges are formed at the ends of the duct, after assembly they will form a T shape. Mating flanges shall be locked together by long clips. In order to form effective seal, gasket is used with suitable density and resiliency. At the corners 16 gage thickness steel corner are used with 3 ⁄ 8 ″ diameter bolts. Machinery's Handbook 27th Edition Copyright 2004, Industrial Press, Inc., New York, NY 1344 FINE BLANKING Double Flanges and Cleat: Clinch-type Flanged Connections: Fine Blanking The process called fine blanking uses special presses and tooling to produce flat compo- nents from sheet metal or plate, with high dimensional accuracy. According to Hydrel A. G., Romanshorn, Switzerland, fine-blanking presses can be powered hydraulically or mechanically, or by a combination of these methods, but they must have three separate and distinct movements. These movements serve to clamp the work material, to perform the blanking operation, and to eject the finished part from the tool. Forces of 1.5–2.5 times those used in conventional stamping are needed for fine blanking, so machines and tools must be designed and constructed accordingly. In mechanical fine-blanking presses the clamping and ejection forces are exerted hydraulically. Such presses generally are of tog- gle-type design and are limited to total forces of up to about 280 tons. Higher forces gener- ally require all-hydraulic designs. These presses are also suited to embossing, coining, and impact extrusion work. Cutting elements of tooling for fine blanking generally are made from 12 per cent chro- mium steel, although high speed steel and tungsten carbide also are used for long runs or improved quality. Cutting clearances between the intermediate punch and die are usually held between 0.0001 and 0.0003 in. The clamping elements are sharp projections of 90- degree V-section that follow the outline of the workpiece and that are incorporated into each tool as part of the stripper plate with thin material and also as part of the die plate when material thicker than 0.15 in. is to be blanked. Pressure applied to the elements containing the V-projections prior to the blanking operation causes the sharp edges to enter the mate- rial surface, preventing sideways movement of the blank. The pressure applied as the pro- jections bite into the work surface near the contour edges also squeezes the material, causing it to flow toward the cutting edges, reducing the usual rounding effect at the cut edge. When small details such as gear teeth are to be produced, V-projections are often used on both sides of the work, even with thin materials, to enhance the flow effect. With suitable tooling, workpieces can be produced with edges that are perpendicular to top and bottom surfaces within 0.004 in. on thicknesses of 0.2 in., for instance. V-projection dimensions for various material thicknesses are shown in the table Dimensions for V-pro- jections Used in Fine-Blanking Tools. Fine-blanked edges are free from the fractures that result from conventional tooling, and can have surface finishes down to 80 µin. Ra with suitable tooling. Close tolerances can be Fig. 30. Double Flanges and Cleat Double Flanges and Cleat (Fig. 30) is identical to (Fig. 29), but has an air seal cleat. The reinforcements is attached to the duct wall on both sides of the joint. Fig. 31. Bead Clinch and Z Rings Clinch-type flanged connections for round ducts, 16 ga or lighter, are shown in Fig. 31. The angles or rings can be loose, as explained in Flanged End and Angle, (Fig. 28). The draftsman should indicate flange sizes, bend direction, and type of assembly. An example such as the flange lap for a field assembly of a 10-gage casing corner would be written: 1 1 ⁄ 2 ″ flange out square on side with 9 ⁄ 32 ″∅ bolt holes 12″ CC. At the beginning and ending angles are connected by rivets or welding. The bolt will be 5 ⁄ 16 ″ ∅ at 6″ maximum spacing 4″ w.g Machinery's Handbook 27th Edition Copyright 2004, Industrial Press, Inc., New York, NY [...]...Machinery's Handbook 27th Edition FINE BLANKING 1345 Dimensions for V-projections Used in Fine-Blanking Tools V-Projections On Stripper Plate Only Material Thickness 0.040-0.063 0.063-0. 098 0. 098 -0.125 0.125-0.157 0.157-0. 197 0.157–0. 197 0. 197 –0.248 0.248–0.315 0.315–0. 394 0. 394 –0. 492 0. 492 –0.630 All units are in inches V-Projections On Both Stripper... Hardness Engineering Grades of Low Alloy Steel Castings 70,000 45,000 26 150 80,000 50,000 24 170 90 ,000 60,000 22 190 100,000 68,000 20 2 09 110,000 85,000 20 235 120,000 95 ,000 16 245 150,000 125,000 12 300 Normalized and tempered Normalized and tempereda Quenched and tempered Quenched and tempered Good weldability Medium strength with high toughness and good machinability For high temperature service Certain... usually pumped through strategically placed holes in the electrode or in the workpiece Vacuum flushing is used when side walls must be accurately formed and straight, and is seldom needed on numerically controlled machines because the table can be programmed to move the workpiece sideways Flushing needs careful consideration because of the forces involved, especially where fluid is pumped or sucked through... 8.40 8.71 8. 89 2.07 … 1.83 7.30 10.20 8.80 7.80 … … 4.50 18.85 6.40 Melting Point Vaporization Temperature °F °C °F °C 1220 1710 2 696 198 0 660 93 0 1480 1082 4442 2450 N/A 2350 1202 2300 4748 2651 2500 2730 2750 3200 6 098 790 1285 650 1260 2620 1455 1371 1500 1510 1700 3370 420 … 5520 4710 6330 290 0 2 595 3500 … 2025 3870 10,040 490 0 1110 2150 5560 2730 … … … 590 0 10,670 1663 3260 593 0 90 6 Conductivity... Machinery's Handbook 27th Edition 1358 ELECTRICAL DISCHARGE MACHINING cially if the graphite is infiltrated with copper, so an efficient exhaust system is needed for machining Compressed air can be used to flush out the graphite dust from blind holes, for instance, but provision must be made for vacuum removal of the dust to avoid hazards to health and problems with wear caused by the hard, sharp-edged particles... punch attached to it, as shown, and it withstands the pressure exerted in the cutting or forming action when the press is operated The closed height of the die is adjusted to permit the cutting edge to penetrate into the material to the extent needed, or, if there is a punch, to carry the cutting edges just past the punch edges for the cutting operation After the sharp edge has penetrated it, the material... Machinery's Handbook 27th Edition ELECTRICAL DISCHARGE MACHINING 13 59 Wire EDM.—In the wire EDM process, with deionized water as the dielectric fluid, carbon is extracted from the recast layer, rather than added to it When copper-base wire is used, copper atoms migrate into the recast layer, softening the surface slightly so that wirecut surfaces are sometimes softer than the parent metal On wire EDM machines,... wire EDM applied to grinding machines is termed EDG The process uses a graphite wheel as an electrode, and wheels can be up to 12 in in diameter by 6 in wide The wheel periphery is dressed to the profile required on the workpiece and the wheel profile can then be transferred to the workpiece as it is traversed past the wheel, which rotates but does not touch the work EDG machines are highly specialized... shape defined by the pattern, so that the flask and the sand halfmold can be lifted from the pattern plate Matching half molds made by these procedures are assembled into a complete mold, with cores inserted if needed With both mold halves still held by vacuum, molten metal is poured through the sprue cup into the mold, the plastics film between the mold surfaces being melted and evaporated by the hot... on and off times in this cycle were halved, as shown in the second data row in Table 1, the duty cycle remained at 40 per cent, but the frequency doubled to 20 kHz The result was that the peak current remained unaltered, but with only half the on time the MRR was reduced to 0.7 in.3/hr, the electrode wear increased to 6.3 per cent, and the surface finish improved to 300 µin Ra The third and fourth rows . 0.416 0.520 0.625 0.7 29 14 0.0781 0.130 0.260 0. 390 0.520 0.651 0.781 0 .91 1 13 0. 093 7 0.156 0.312 0.468 0.625 0.781 0 .93 7 1. 093 12 0.1 093 0.182 0.364 0.546 0.7 29 0 .91 1 1. 093 1.276 11 0.1250 0.208. corner (Fig. 8) is generally spot-welded, but may be riveted or soldered. For heavy gages it is tack-welded or solid-welded. Machinery's Handbook 27th Edition Copyright 2004, Industrial Press,. Fig. 24. Hemmed “S” Slip This is the modified “S” slip, by adding hem and an angle for reinforcing. The hem edge is a flat, and finished edge. Hemmed “S” slip is mostly applied with angle.