Illustrated Sourcebook of Mechanical Components Part 13 ppt

Fabrication Tips 24- 1 7 required. In no case should the cor- ner radius be less than thickness of material for a one-operation draw. When the ratio of “height divided by diameter” exceeds %, it will be necessary in most cases to reduce the flat blank to the finished shell by using two or more draw dies of proportionately decreasing diame- ters. In some cases, one or more an- nealing operations will be necessary between first and finish draw opera- tions. The necessity of annealing de- pends to a large extent on the work- ability of the metal being drawn. Determination of the number of reductions necessary to draw a shell with ratios (height divided by diam- eter) greater than % cannot be done by hard and fast rules. In general, for ductile materials, with generous corner radius in the shell, the re- quirements are: 1. Height equals % to 1Y’ times the diameter of the shell-two reductions will be required. 2. Height equals 1% to 2 times the diameter of the shell-three re- ductions will be required. 3. Height equals 2 to 3 times the diameter of the shell-four re- ductions will be required. It may be necessary to anneal the shell when more than two reductions are required. When corner radius is less than four thicknesses of mate- rial, add one or two flattening dies and operations, depending on corner radius desired. For less-ductile materials, it is more difficult to predict the number of operations required. In general, the measure of ductility of the ma- terial (percent of elongation or per- cent reduction of area) will determ- ine the maximum reduction possible in one operation. Finish of edge depends on the “height divided by diameter” ratio and on the material being drawn. For relatively shallow shells where the “height divided by diameter” ratio is not over 1/3, it’is possible to produce an edge within commercial tolerances without requiring finish- ing operations. That is, the height and uniformity of the edge depends on the size of blank used. For higher shells it is not possible to do this, and one of the following finish- ing operations will be required: 1. Flange trim and finish draw 2. Pinch trim (Fig. 2). 3. Machine trim (Fig. 3). 4. Wedge or “shimmy”-die trim (not suitable for small quanti- ties). A “Draw Reduction Table” offers a simple means of determining per- cent of draw reduction and flat- blank diameter. By dividing the in- side shell height by the mean shell diameter, a height-diameter ratio is (Fig. 1). obtained. Find this ratio in Col. I of the table. Directly opposite in Col. I1 find the percent of reduction of diameter (a measure of the amount of cold-working to be done in drawing the flat blank into a shell). Directly opposite in Col. 111, find the Blank-Draw ratio. Multiply the mean shell diameter by this fac- tor to obtain the approximate flat blank diameter. It must be understood that this table can only be used with round straight-sided shells or cups. Shells or cups with flanges must be inves- tigated by other methods. Care must be used when attempting to predict the number of operations required to produce a flanged shell or cup. EDGE-TRIMMING METHODS n 0 Partly Drawn Shell Flange Trim Die Finish Drawn Shell Fig. 1 -FLANGE TRIM AND FINISH DRAW. This method is satisfactory for most shells, particularly diameters greater than 2 in. Only one additional die-a trimming die-is required. Draw with Flange Flattening Die Pinch Trim Die Fig. 2-PINCH TRIM DIE. This method will produce a shell with uniform height, but the inside edge is considerably rounded. The flange must be flat- tened to a sharp corner, which will require one or two dies. Finished Draw Machine Trim, Lathe or Grind Finished Shell Fig. 3-MACHINE OR BOX TRIM. Tooling cost is generally low, but this method is slow. The best-appearing edge is produced, and sometimes this method is the only practical one. 24- 18 Tonnage for Air Bends Capacity ratings of press brakes are based in air bends in which dies do not strike solidly on the metal. All pressure is used in forming-none in coining or squeezing. Roy F. Dehn Air-bend dies produce a bend with an inside radius approximate- ly 15% or 5/32 of the die opening. This means that less than an 8- times die opening must be used if a smaller radius is desired-requir- ing higher tonnage. Press ratings are based on die openings of 8 times the material thickness up to about 36 in. plate. Die openings up to 10 or 12 times are used for forming heavier thick- nesses of plate. If the die opening is too large, an excess amount of metal is drawn into the die, causing a curve to form in the metal each side of the point radius. If the metal is formed over a die opening less than 8 times the plate thickness, there is danger of frac- turing the metal in the heavier thicknesses, unless a small amount of preheat is applied. Effective width of die opening When the punch radius is equal to or less than the material thick- ness, the effective width of die opening to use with the tonnage table, page 99, is die width W. When the punch radius is greater than the plate thickness, the ef- fective width of die opening to use with the tonnage table is 2 times X shown on sketch. Pressure per foot Check tonnage required from table to be sure it is within the capacity of the machine, making allowance for coining and drawing forces required on other than air- bend dies. Bending pressure is proportional to the ultimate strength of the ma- terial for the same thickness and die opening. The inside radius of a bend is approximately 5/32 of the die opening and is about the same for varying thicknesses of material bent on the same die set. Heavier thicknesses of plate con- tain higher carbon content in or- der to maintain full ultimate strength. This results in more bending fractures which can be reduced by 10 or 12 times die open- ing or the use of special flanging steel. High tensile steel plates are usu- ally formed over 10 to 12 times die opening. The manufacturers of special steels usually recommend the radi- us of die opening to use with their materials. Bends across grain will show less breakage than when bent in line with the grain of the plate, es- pecially in the thicker plates. It helps to avoid cracks by rounding the edges of thick plates at each end of the bend, on the outside of the bend. Approximate spring back: Low carbon steel, lo to 2' 0.40 to .50 carbon steel, 3" to 4O Spring steel annealed, loo to 15O The same size of press brake, as formerly used for bends of 8 times plate thickness in mild steel, is suitable for 12-times bends in the popular low-alloy steels. If less flange width is required, a smaller die opening must be con- sidered, and this will affect the tonnage rating needed. Forming practice Material bent on too wide a die opening may not come square. Re- hitting with dies set closer in trying to square up the bend frequently overloads the press. The forming of channel or offset bends may require more than six times the load needed for a single right angle bend in the same material. To adjust a mechanical press Effective width of die opening I I brake ram and bed parallel under load follow these three steps: 1. With the eccentrics on bot- tom center, adjust right hand pit- man or screw (or pitman with drive motor) 0.015 in. or 0.025 in. above left-hand end. 2. Run both screws down to- gether until left hand end bottoms in die and stalls adjusting motor. 3. Release adjusting clutch on cross shaft and run right hand screw down until it stalls. Ram and bed are then parallel under pressure and it is only nec- essary to back up adjustment for the thickness of the material. Another method is to use a short test piece under each end of the press, adjusting until equal results are obtained on both ends. Use wide enough test pieces so that the unit pressure will not be high enough to indent the dies. Another method is to start with a shallow bend and run the adjustment down between strokes, until the desired angle is formed. However, one must check for equal angles at both ends of the bend. Dies should preferably be of a closed height so that the adjusting screws project about one to three inches. If a load is put on one end of the press so that it is substantially performed by one pitman, it should be limited to half the press ca- pacity to avoid overloads. Reprinted with permission from American Machinist, A Penton Media Publication Fabrication Tips 24- 19 24-20 Tonnage vs Stroke of Press Brakes This chart can be used to check the capacity of press brakes, because it shows tonnage available at different points in the stroke. Roy F. Dehn Data are based on a die opening sult the press-brake manufacturer work to be done on mechanical width W, and are correct for the with regard to the limiting effect press brakes rated with a bottom usual Drcmortions of width of die of the available flywheel energy. stroke capacity equal to 150% of opening to material thickness. Distance A is punch travel re- quired to make the bend, and equals 40% of die width W. Full tonnage to make the bend is re- quired at 0.7 A above bottom, where W, or width of die opening = 8 or more. Also, under these conditions, 0.7 A = 0.28 W. Problem: What length of % in. mild steel plate can be bent on a 320-ton brake with a 5-in. stroke? Solution: A 3-in. die opening would nor- mally be used. Therefore the height above bottom for full tonnage = 3 x 0.28 = 0.84 in. Percentage of stroke abcve bot- tom stroke = 0.084 -+ 5 = 16.8%. Enter the chart at 16.8% of stroke above bottom stroke and draw a dash line to the stroke-ca- pacity curve. Drop down a dash line and read the tonnage available at 16.8% of stroke equals 1.3 times full capac- ity, or 1.3 X 320 = 416 tons. From the chart “Tonnage for air bends,” (AM-March 28, ’66, p99) find that the pressure to bend 3/s- in. plate in a 3-in. wide die equals 24 tons per foot. Then, 416 +- 24 = 17 ft, or maxi- mum length of air bend that can be made on the 320-ton brake, using %-in. mild steel plate. This value would have to be ad- justed upward or downward for other materials. If alloy-steel plate is to be bent on extra-wide die openings, con- This chart may be used also-for mid-stroke capacity. . Tonnage vs stroke I Mid - stroke I 50 r“ 45 ,E 35 e + 40 0 + + 2 30 8 25 20 u, 15 w > 0 al L c y. 0 z 9) 10 25 0 0 Overload knockout setting _I Percent capacity above bottom of stroke 160% Bend work diagram T 1 . A = 0.4 W A = 0.28 W A= distance punch travels Punch travel A = 0.4W Reprinted with permission from American Machinist, A Penton Media Publication Fabrication Tips 24-2 1 Tonnage Chart for Various Bend Angles Roy F. Dehn terial must be bent to less than a 90' bend angle, and then the accompanying chart provides a means of estimating the tonnage in relation to that required for a 90° air bend. The chart published earlier (AM Example: What is the percentage -March 28, '66, p99) gives the of tonnage for a 90° bend thatis tonnage per foot to produce 90' required to bend plate to an inside air bends in various plate thick- bend angle of 175O? nesses and using various die open- According to the tabulation, the ings. In many cases, however, ma- percentage is 50%. Now cross check this by using the curve AEP. Solution: Follow the 175O inside bend an- gle to the right until the dash- line extension cuts curve AEP. Drop down to the scale for 100% air bend tonnage, and read that 50% of that tonnage is required. If the full 90° bend in 2 in. plate requires 171 tons per foot, a 175' bend will require 50% of it, or 85 tons per foot. Tonnage vs bend angle \ \ \ \ \ \ Inside bend ongle \ \ \ Values given are based on punch radius not greater than plate thickness, and for material with up to 65,000 psi ultimate tensile. For higher strength materials, in- crease tonnage values in direct gro- portion. Bend inside angle 175O 170° 160° 1 50° 1200 900 yo of 900 Bend air bend slope tonnage 2%" 50 50 65 100 90 15O 100 30 O 100 450 100 \ 4L I *O 40 6o J D Reprinted with permission from American Machinist, A Penton Media Publication 24-22 Press Tools for Bending Don R. King s election of a suitable method is the initial step in de- signing press tools for parts that require bending. Often, for a given shape, there are several possible methods. To select the one best suited to your job, we give here schematic drawings of press tools to serve as a refer- ence guide. These are classified according to standard arrangements to produce basic bend configurations. Notes under each sketch give the advantages and dis- advantages of the particular design. In most cases, the bend is shown as accomplished at the last station of a progressive die, in order to indicate the relationship of cut off. Of course, the construction may apply to intermediate stations, wh,ere the bend includes only part of the strip, or is turned parallel to the direction of feed. Dimensions ''32'' on certain sketches are likely to be critical in respect to part di- mensions. They should be checked for limitations of die wall thickness or space. RIGHT-ANGLE BENDS No. 1 Good location and alignment Inclined ejection possible Slight tendency for part to creep No scrap waste No. 3 Alignment may depend on stock fit in stripper Push-through ejection is possible Some tendency to creep Scrap slug wasted long cut-off punch required No. 2 Good location and alignment Inclined ejection preferred Scrap slug wasted No creep if other punches are engaged large spring space needed in punch holder I Straddle heel -2' desirable No. 4 Inclined ejection required Tendency to creep No scrap waste Punch sharpening more difficult than other designs Large spring space needed in punch holder Reprinted with permission from American Machinist, A Penton Media Publication Fabrication Tips 24-23 RIGHT-ANGLE BENDS . continued No. 5 Requires inverted pierce and notch operations No creep if other punches are engaged No scrap loss Good ejection r He0 vy rr Must be guided spring No. 7 More complicated and costly than other designs Eliminates scrap slug, when farming downward is necessary No creep occurs Stroddle - - - - ' '-stock bee/ lifter No. 6 For bends with short legs only No creep if other punches are engaged No scrap loss More difficult to reshorpen Large spring space needed in punch holder k- x-4 No. 8 limited to thin material and short farming travel Eliminates scrap slug, when inside form-up is necessary No ACUTE-ANGLE BENDS . 10 Suitable only for moderately acute angles No scrap waste Some distortion of stock is likely No. 9 Not suited to parts of all proportions Resharpening die may cause difficulty Scrap slug is wasted Distortion of stock and creep are possible spring stop No. 11 No scrap waste Not suited to parts of all proportions Resharpening may cause some difficulty Distortion of stock bid creep are likely 24-24 ACUTE-ANGLE BENDS . continued Slide I No. 12 Widest adoptability - Good-quality bend; are produced More costly than other dies Inversion of design is possible 1-1 tssq n\\\\w Gam I Opfionol for ejector slide OBTUSE-ANGLE BENDS No. 14 Inclined ejection is desirable Scrap slug wasted Some difficulty in resharpening No. 16 Good-quality bends produced on short legs and sharp corners Stock distortion occurs on long legs or when angle is close to 90' no. 13 Inclined ejection is required Some difficulty in resharpening Special backup heel may be needed Large spring space required in punch holder I HI?OVY' - - Must be guided No. 15 More complicoted and costly than Scrap slug is eliminated when form other designs down is necessary \ neovy spring No. 17 Desirable design when bend radius is large, because Usually unsuited to angles greater than 120" follow wiper minimizes stock out of control Fabrication Tips 24-25 OBTUSE-ANGLE BENDS - Continued Distorted' cut No. 18 Good design only when angle is close to 90" Bends of good quality produced regardless of leg length or radius No. 19 Good-quality bends when legs are short Push-through ejection is possible Scrap slug is wasted large spring space needed in punch holder CHANNELS No. 20 Good location and alignment of bends Inclined ejection is desirable Scrap slug is wasted long cutoff punch is required I spring sfop . Possible to cbm ouf ond continue progressive operotbns No. 21 Good design for cross-transfer operation Inclined ejection is desirable Large spring spoce needed in, punch holder 'A No. 22 Same notes as for No. 20 above Introducing an idle station avoids thin die wall ACUTE CHANNELS No. 23 Good quality bends are produced Special ejection requirements must be met, but inversion Cross-transfer or cut-and-carry progressive Closely fitted guides or nest are required on 2nd operation moy help operation may be employed 2nd Operation I st Operation 24-26 ACUTE CHANNELS - continued No. 24 Good quality bends produced; even 90” bends Not used for heavy stock or extreme acute angles Special ejection means are required in springy material Shorr heavy spring I WINGED CHANNELS b , Radius required on par f Radius required’ on porf No. 26 Bends usually of poor quality, but die cost is low Distortion remains from “slip forming” unless Not suited to pdarts of all proportions straightened by spanking ‘Pivoted die members No. 20 Bends of fair quality Do not use for heavy stock Die more difficult to construct, but useful for odd angles No. 25 limited to small parts Fair-quality bends produced, but wings will not large spring space may be required in punch holder be square unless spanked 7 Firsf operotion No. 27 Bends of best quality produced Two operotions are required; these may be cross-transfer or cut-and-carry progressive Optional spank 1st Operotion 2nd Operation No. 29 Fair quality bends Useful for odd wing angles Inversion of design is possible Die may be cross-transfer or cut-and-carry progressive type [...]... plunger pump ha5 screw ad/ustment of stroke length Change of crankpin positlonalters capacity of pump oil for actuatlon of diaphragm w s tho llquld handled MRERIWCP and propartlonlng p of coupling for adfusrlng stro of s DIAPHRAGM pump with boll suction ond dirchorge valves Is built with stationary or movable base, is motor driven through beam HOR means of variatlan of the crankpin posEtion DUPLE end... after passing tangency of the bend, re- Fabrication Tips FIG 4 covery takes place and produces a small amount of overbending Extension of this reasoning led to the construction shown in Fig 4 Controlled movement of the wiper is introduced by means of springs and stops The amount of movement required is very small A few thousandths past tangency will correct a considerable angle of springback, and the... setting are of some help FIG 1 FIG 2 “SPANKING THE BEND Another means of giving a more definite “set” to the material is illustrated in Fig 2 Here “spanking” of the bend area occurs at the bottom of the stroke Careful stroke adjustment is required to prevent abnormally high pressures S6me improvement may be gained by altering the spanking radius to reduce the area of contact, but this partially defeats... extrusions with sections like those shown in Fig 1 The greatest proportion of these jobs is done on the tangent bender due to the capabilities of the machine, its relatively high production rate, and the quality of work attainable Material-Use of wing-type and stretch bending machinery involves processing parts made from various grades of these materials: (1) Low carbon steel ( 2 ) Stainless steel ( 3 )... uniformity of forming from end to end of the bend is possible This method cf fold-action radius bending requires a much greater overbending allowance as well as a means of checking the unwinding of the bend when the bender wing swings down Radius bend-wipe action In this type of wing-action radius bending, Fig 5, the pipot point, or wing swing center, corresponds exactly with the center of the radius... Another method uses a temperature-sensitive switch to feed fuel directly into the intake manifold of the engine ILLUSTRATED S O U R C E B O O K of MECHANICAL COMPONENTS SECTION 26 PUMPS Pumps: Major Classes and Types 26-2 How Pumps Work 26-5 Centrifugal Pumps 26-6 Rotary Pumps 26- 12 Reciprocating Pumps 26- 13 Pump Applications 26-17 Pump Selection 26-23 Other Considerations in Choosing Pumps 26-25 Priming... up much of the mystery and confusion surrounding pump classes and types You might call it your road map to the world of pumps Based on often-used standard classifications, it incorporates a number of useful facts that are a big help in pump selection and application Three classes of pumps find use today -centrifugal, rotary and reciprocating Note that these terms apply only to the mechanics of moving... problems of class and type Each classification is further subdivided into a number of different types, diagram left For example, under the rotary classification we have cam, screw, gear and vane pumps Each is a particular type of rotary pump To go one step further, let's take a brief look a t a fuel-oil pump in wide use today It is a rotary three-screw type available with rotors of a number of different... compare, detail for detail, a number of makes Broad breakdown in diagram comes in handy then Our next consideration is a wide statement of the general characteristics of a given class of pumps Table, above left, does just this for us For example, if we want to handle relatively small ca- Dacities of clean, clear liquids at high head, we can refer i the table In any problem of this type we must remember o... the bottom of the boy’s bucket The result is a workable pump for imparting energy to a liquid a t one point to cause it to move to another Long of major importance in the pumping field, reciprocating units today are finding many new uses, particularly in the fields of metering and proportioning, and where extremely high pressures are needed Direct-acting steam pumps, lop left, have two sets of valves . advantages of the particular design. In most cases, the bend is shown as accomplished at the last station of a progressive die, in order to indicate the relationship of cut off. Of course,. obtained. Find this ratio in Col. I of the table. Directly opposite in Col. I1 find the percent of reduction of diameter (a measure of the amount of cold-working to be done in drawing. difficult to predict the number of operations required. In general, the measure of ductility of the ma- terial (percent of elongation or per- cent reduction of area) will determ- ine the