THEORY OF SHEARING• Shearing is the method of cutting sheets or strips without forming chips. • The material is stressed in a section which lies parallel to the forces applied. • The forces are applied by means of shearing blades or punch and die. Critical stages in shearing 1. Plastic deformation. 2. Penetration. 3. Fracture. 1. Plastic deformation: The pressure applied by the punch on the stock material tends to deform it into the die opening when the elastic limit is exceeded by further loading, a portion of the material will be forced into the die opening in the form of an embossed on the lower face of the material and will result in a corresponding depression on its upper face. This stage imparts a radius on the lower edge of the punched out material. This is called the stage of “plastic deformation”. 2. Penetration stage: As the load is further increased, the punch will penetrate the material to a certain depth and force an equally thick portion of metal into the die. This stage imparts a bright polished finish on both the strip and the blank or slug. This is “penetration stage”. 3. Fracture stage: In this stage, fracture will starts from both upper and lower cutting edges. As the punch travels further, these fractures will extend towards each other and eventually meet, causing complete separation. This stage imparts a dull fractured edge. This is the “fracture stage”. 1 1. Press Force calculation: The essential considerations are: • Cutting force • Stripping force • Ejection force 1. Cutting force “Cutting force is the force applied on the stock material in order to cut out the blank or slug”. This determines the capacity of the press to be used for particular tool. The area to be cut is found by multiplying the length of cut by stock thickness. Cutting force (F) = L x S x T max L = Length of periphery to be cut in ‘mm’. S = Sheet thickness in ‘mm’ T max = Shear strength in N/mm2 Shear and tensile strengths for most materials are not the same. Shear strength for: Aluminum is approximately 50’% of its tensile strength Cold roll steel is approximately 80% of its tensile strength Stainless steel is approximately 90% of its tensile strength 2. Stripping force The main purpose of a stripper is to the part material from the ends of the punches. This function occurs at the Withdrawal phase of the cutting process. Stripping force varies based on part material type and thickness as well as punch to die clearance. Most applications do not exceed 10% of the cutting force. If the die has more than one punch the stripping force for that die is the sum of stripping forces required for each punch. Striping force = 10% - 20% of cutting force (F) Movement of stripper Ystr = t + 2 Where Y sIr = Movement of stripper t= Thickness of stock Spring deflection (Y) Y = (3 to 4) Y str = (3 to 4) (t+2) Where Y = Total spring deflection at F max load 3. Ejection force The force required to eject the component from the punch. Ejection force = 10% cutting force (F) Press force = Cutting force + stripping force The following table gives the shear strength (T max = 0.2 for tensile strength σ max ) of several materials. Material Steel with 0.1% carbon Steel with 0.2% carbon content (deep draw steel) Steel with 0.3% carbon T max in N/mm2 240 - 300 320 - 400 360 - 420 2 140 90 .250 20 . It is expressed in N/ mm2 If 'c' is 0. 45 .120 20 .320 120 .9% carbon Silicon steel Stainless steel Copper Brass Bronze German silver (2 .01.900 450 .560 550 . Material I II Type of edge III IV V 3 .450 200 .015) x 'C' constant = 0.20% Ni.50 70 .550 350 .Steel with 0. when punch is entered in to the die opening. which yields a better and cleanest work piece. The usual practice 'c' will be conceded as 0.450 300 .75% Cu) Tin Zinc Lead Alluminium 99% pure Alluminium manganese alloy Alluminium silicon alloy Paper & card board Hard board Laminated paper or rosin impregnated paper Laminated fabrics Mica Plywood Leather Soft rubber Hard rubber Celluloid 450 . If 'c' is 0.30 20 . Cutting clearance: It is the small amount of gap maintained between the side of the punch and the corresponding die opening on one side of the edge.700 700 .20 20 . but finish wil.005 or 0.40 100 . So the cutting clearance should expressed as the amount of clearance per side Clearance for sheet thickness up to 3 mm Clearance for sheet thickness above 3 mm cxsx max √ T 10 max √T10 (1.l not b good.01 Ii is also expressed in terms of % of stock thickness (s) per side C=c x t Since the edge characteristics. T max.40 7 7 20 .4% carbon Steel with 0. dimensional accuracy and die life depends upon Clearance its value should be taken according to the requirements.5 x s) x (s-0. but requires a higher cutting force and considerably more energy.400 350 .20 30 .6% carbon Steel with 0. Shear strength 80% UTS.120 150 .005 we get a clearance.60 40 .90 100 .60 2.400 360 .120 50 .01 as the case may be. the cutting force energy as its minimum. 0 7. carbon steel Duraluminium. polished and also for close tolerances Type V . tool life for average sheet metal work.Less radius Normal burr.60 0.5% 11% 8. Bronze 6 12 18 +10 24 30 36 42 48 +20 54 60 80 +30 110 130 140 180 +50 200 220 240 320 360 +100 450 500 600 900 +200 High carbon Card board.70 0.30 0. rubber and Bronze Clearance on both sides in microns 7 4 2 14 5 3 21 +10 6 +5 4 +3 28 8 5 35 10 6 42 12 8 49 14 9 56 +20 16 +10 10 +8 63 18 12 70 20 15 100 +30 24 +15 10 +12 120 30 22 140 36 27 160 40 30 200 +50 44 +25 40 +20 230 50 45 250 56 48 270 60 53 350 70 60 400 +100 200 +50 60 +20 540 90 60 600 100 60 700 1000 +200 Sheet thickness S in mm 0.large radius / Die roll.2 2.0 2.8 2.Type II .5% 2% 2% 1% 1% 3 1/2% 2 '1/2% 1% 1% 1% Type I .90 1. Aluminum 5 10 15 +10 20 25 30 35 40 +20 45 50 70 +30 80 110 120 160 +50 180 200 210 280 320 +100 360 400 500 700 +200 med.Normal Radius/die roll Burr free For Components to be formed later Type IV .5 2. for precision stamping Mild steel.20 0.0 6.+10 -17 20 25 30 +10 34 35 42 +15 52 62 70 77 +25 90 98 105 122 77 +25 157 175 210 +50 4 .2 1.Steel (SAE 102O) Steel (High carbon) Stainless steel Copper (1/2 hard) Copper (annealed) Brass (1/2 hard) Phosphors bronze Lead Aluminum (Hard) Aluminum (250) Magnesium 21% 26 1/2% 22 1/2% 25% 26% 21% 25% 22% 20% 17% 16% 12% 18% 12. steel.5% 2% 4. complete secondary shear Recommended for accuracy for soft materials And for hard materials the die life reduces considerably. Normal burr Max. Recommended total shearing clearance.5 5. Brass. alloy steel plastics paper.large dished radius large burr . Type III . High Laminated leather.only for structural rough work.0 magnesium alloys ---.0 3.10 0.5 1. reamed. Brass. hard.0 4.0 1.40 0. Signs of secondary shear.80 0.8 3.1/2% 9% 13% 9% 14 1/2% 9% 6% 9% 14 1/2% 10 1/2% 8% 6% 6% 11. for good quality components to be shaved.50 0. Copper.5 4.5% 7% 10% 7% 4% 6 1/2% 12% 4% 3 1/2% 3% 3% 4 1/2% 5% 6% 3% 2 .Negligible radius Normal burr. 0 14.5 1.” An amount of 3mm land for stock thickness up to 3mm and the thicker materials equal to their thickness has proved to be good practice. The die wall below the land is relieved at an angle for the purpose of enabling the blanks or slugs to clear the die. An angular clearance of 1.5 .0 13. the die is made to desired part size and the clearance is subtracted from (applied to) the punch size as shown in figure A. When the metal is punched out from the functional part and the metal around the opening is scrap. The straight wall is called “The Land.0 20. when the slug is discarded and the punched opening is functional. Generally.5-2 5 2 2.0 800 1100 1200 1600 1700 +300 2100 2300 2700 2900 3400 +500 3600 4200 4400 1000 1300 1400 1800 1900 +300 2500 3000 3000 3200 3800 +500 4000 4600 4800 1100 1400 1600 2000 2200 +300 2800 3300 3300 3500 4100 +500 4300 5000 5200 Applying Clearance Given diagram illustrates how to apply clearance to obtain correct size of hole and blank.0 11.5 1. To avoid brakeage of cutting edge of the die plate die walls are kept straight only to a certain amount from the cutting edge.5-3 2.50 per side will meet the usual requirements Pitch punches (side cutters) Allowance for stock cut off at the side of the strip Stock thickness t (mm) Allowance for stock cut off f (mm) Width of strip after cropping (W1) W1 = D + 2a 5 <1.0 12.0 19.0 15.8.0 17.0 9. Determination of punch and die size Piercing Piercing punch = Pierced hole size Die = Hole size + total clearance.0 16.0 10. the required clearance is applied (added to) the die opening as shown in figure B. Soft thicker materials above 3mm require more angular clearance.0 18. Blanking Blanking punch = Blank size-total clearance Die = Blank size Land and angular clearance. soft materials require greater angular clearance than hard materials. 25 2.5 . say at least 75%.2T -I. + g = 0 + 2a +g Distance between the guides before cropping stage Bt = W2 + X = D + 2a -I.20.30 3.pass.50 s.5-2. the clearance B will follow the following rule: 6 . for C > 63 mm s = thickness of strip B = Clearance between successive blanks or clearance between the edge of the strip and blank Here where C= L +B – lead or advance of the die L = Blank length W= Width of the strip H = Blank width or height .5 Gap for forwarding (g) 0.Width of strip before cropping (W2) T .6 0.row single-pass layout have been explained.4-1.5 1. Scrap bridge: It may be appreciated for the economical production of blanks.75 mm. following formulae used: = 1. Generally for strips whose thickness exceeds 0. Stock thickness (t) mm <0.25 s. E2 = (0 + 2a + f + 2T) Distance between the guides after cropping stage 81 = W.00 3.625 mm.X where D = Governing dimension of the die opening 2T= Total tolerance of the strip a = Margin Allowance of stock cut-off g = gap for forwarding the strip x =Clearance 0. For strips with thickness equal to or less than 0.5 2.5-3.5 0. Instead following Table is to be used.8 0. Strip width W (mm) 0-75 75-150 150-300 ≥ 300 Dimensions B (mm) 1.75 So far the parameter for single. the utilization of the strip should be of high.f -I. the above formulae are not to be used. for C < 63 mm = 1.1 mm.5 0.5-1.3-0.0 3.1-0. In case the layout is decided to be double – row double. as shown in the bellow fig. Economy factor: Stock material conservation being a decisive factor in press working. Economy factor = Area of blank x number of rows x 100 Width of strip x pitch 5. they will be subjected to compression stresses. The same can be written in the form of equation: a = LH A CW where L = length of blank H = height or width of blank C = advance or lead W = width of strip Generally. Buckling of Punches. Hence the max force.1(c). Utilization factor is the ratio of the blank area to the total area of me strip utilized to create a single blank. designer has to take every possible means to attain this. namely. But if due to consideration of these stresses are over loaded during designing of the tool.Single row double pass B = 1.25 t The variants. single-row double-pass or double-row double-pass are basically strip layout designed to improve the utilization factor. Side-thrust or Lateral Forces 7 .50 t Double row Double pass with curved lines B=1. Fb = [ π ² × E × I ] Lp² Fb= Maximum Force beyond which buckling occurs. When ever the punches are coming in to contact for shearing the sheet in the press tool. B=1.25 t Double row Double pass with straight and curved lines[ as in fig 4. with out satisfying the accuracy requirement of the component. E= Modulus of Elasticity (For steel Modulus of Elasticity varies from 200 to 220 GN /m²) I = Moment of Inertia in mm4 (different section details are given in last pages) Lp = Length of punch in mm The ultimate condition is when. Buckling Force = Cutting Force required for the operation = Shear force on the punch. which a punch can withstand without buckling can be calculated by using the formula. then thin punches may tends to brake. the utilization factor is aimed at 70 – 75% • • • 4. 8 ..Figure illustrates the shear. Effect of Die Clearance on Lateral Forces Bellow equation gives an approximation of the side thrust or lateral force generated when cutting or shearing. The formula to be used for this calculation is given bellow.l3.+ln 7. The purpose of shaving is • To improve the dimensional accuracy of the piece part. and compressive forces that occur during the cutting process. Or minimum =0.. Shank Location The resultant force of all the cutting forces acting on different punches should pass through the shank centre. lbf (kN) T = material thickness. By applying the following two methods: • • By calculation By graphical method (polygon of forces). The amount of lateral force varies with the cutting clearance and material.. in. lbf (kN) 6. Centre point of shank location can be found by calculating the x and y coordinates for the point.04 s. The width of the scrap web removed by shaving operation is the shave allowance. It is done by removing (shaving) a small amount of material from the previously cut edge....33 x T F v = cutting force. (mm) P = penetration.+ln Y = (l1y1)+l(2y2)+(l3y3)………. tensile. Shaving Shaving is the secondary cutting operation. X = (l1x1)+l(2x2)+(l3x3)………..l2. When applying this equation.. typically 0. From the die plate references to the centroide of different split profiles of the die cutting area length of which is taken as l1.+(ln xn) l1+l2+l3……………….. (mm) F H = side thrust.. in. Shave allowance for steel A = C+0. = FH T–V FV where: C = clearance... • To improve the flatness of the piece part.+(ln yn) l1+l2+l3……………….. • To improve the cut edge characteristics of the piece part. adjustments for the type of material and die conditions must be made. C .08.. A1 = C/2 or minimum 0. In practice the formula used is as follows: F = L x S x T max F = Blanking or shearing force (tones or kg) L =Total of outer and inner shear periphery lengths (in. • Compound nature tooling.08mm. A = Shave allowance for single shaving operation is employed. as small as 60% of the material thick can be pierced. Special fine blanking presses and custom tooling produce parts that are too complex to make accurately by conventional stamping.04. Vee ring force & Counter force: The most important factor for determining the type of machine to be used is the shear force. or N/mm²) If Shear force FS = ‘x’ tones then. copper. shaving • Components remain very flat. C = Cutting clearance used for previous cutting operation (prior to shaving). counter bores. it is necessary to keep up side down in the shaving. A = C or min 0. Fine blanking: Fine blanking is a unique metal forming process founded on the technology of metal stamping. Relation between Shear forces.015mm are achievable. • Holes with a dia. Vee ring pressure FR = 50% of ‘x’ (shear force) Or 9 . A1= Shave allowance for second shaving operation is employed. in. The striking force required for shaving operation is two to three times that of the stripping force required for the blanking. or mm) s = Material thickness (in. • Material up to 15mm thick can be fine blanked. Shaving allowance for brass. This ensures superior positional accuracy between features.04. or mm) T max =Tensile strength (t. coined • chamfers. extrusions. • Virtually any metal can be fine blanked • Components can have features such as countersinks. 8.A1= C/2 or min 0. and offsets. • Eliminates the need for secondary processes like reaming. weld projections. Features of fine blanking are: • Components of very high accuracy are attainable tolerances of ±0. semi-piercing. piercing. German silver etc. • Tooling prices are competitive compared with conventional tooling. Note: To improve the flatness of blank used to produce a better square cut edge. /sq. 1-15 15.6-7 7.4 5.6 to 0.7 0. Rm = Tensile strength.8 s clearance is 1.4 1.4 0.3-3.6 0.8.7 2.5 5. 10 . But in case of minimum die roll Vee may be adopted on both sides even though sheet thickness is less then 4 mm.8-4. Typical fine blanking tool.2 s clearance 1 % of s For punch diameter 0.8-4.5 a 1 1.4 0.FR= lr x h x Tmax FR = vee ring force.7 2 r 0.1-9 9.2% of s.1-11 11.2 h 0.5 3 3.1 6.6 0. 10 11 12 13 14 15 16 Material thickness 4.6 1.3 0.2 h 0.8 2 2.8 1 1. 1 2 3 4 5 6 On die plate Sl no.6 0.3-3.4 0.2 2.8 to 1.6 4.8 r 0.2 6. when the sheet thickness is more than 4 mm. Counter pressure FG = 50% of Vee ring pressure Or FG = As x Qg FG= counter force As= part surface without inner forms and holes Qg= Selected force (20-70N) Total Press force F = FS + FR +FG tones Note: • • • Materials between 30-50N/mm² tensile ratio =30-50% of ‘x’ For harder materials FR= 100% of ‘x’ The common requirement of the Vee-ring must be implied on die and pressure plate.25 s clearance is 0.4 1.5-3.2.8 r 0.3-2.2 Material thickness 2.2 0.8-3.4 0.2 0.2 1. 7 8 9 On guide plate Sl no.7 3.7 3. Vee ring indenter: On guide plate Sl no.1-20 a 2.6 Material thickness 1 -1.2 1.5% of s For punch diameter 0. h = height of vee ring.2 3. Lr = length of vee ring.9 h 0.7 0.7 1.2 0.7 0.5 0.8 2 2.4 Cutting force: For punch diameter over 1.5 a 1.2 3.4 0.1-13 13.9 1.6 0.2 0.4 0.5-5. Die block 15. Punch holder with adjusting plate 9. Top back-up block 5. Rmax R max = SE 2σy R min could be calculated by following formula. ri > 4t. Adjusting plate 12. Bend allowance. Bottom plate 3. ri = 2 to 4t. Guide bushing Bending: Bend allowance is a term which describes how much material is needed between two panels to accommodate a given bend. Rmin 11 . Ejector 14. Punch retainer with adjusting plate 13.5t Calculation for R max and R min. Piercing punch retainer 16. Radius which produces a permanent. R max could be calculated by following formula. Guide pillor 7. Punch 8. Bend development. Determining bend allowance is commonly referred to as “Bend Development” or simply “Development”. is fairly easy to predict and calculate for many standard circumstances. K = neutral axis offset (k factor) For ri < 2t. Top plate 2. Guide bushing 11. k = 0.4t k = 0. Guide plate 4. Blank length = circumference at neutral axis + straight lengths Neutral fiber: L = 2 πα (Ri + k x s) 360 Ri = internal radius S = sheet thickness α = angle of bend.33t k = 0.1. Bottom back-up block 6. The above formula therefore gives the condition for R max. In order to obtain a permanent set the stress which occurs on bending must be higher than yield point of the material. while being oftentimes tricky to determine for all cases. V-Ring plate 10. 3 Bending Force Bending force for Edge bending or Wiping die. 01. no permanent deformation takes place.7 09.2 11. Brass 0. Stainless Steel 0.4 08. Pad force: Fp = 0. (Kg/mm ) L = Span = rd + rp + c C = Die clearance. Deep drawing tool 0. Gun Metal 1.5 02. Aluminum half hard 1.4 10. Brass 0. 12 . German Silver 0. Construction steel 2. Aluminum pure 0.27 05. Copper 0.Bending or channel bending: Force required Fs = 2 times force required for edge bending.45 06. If ri is greater than the R max.33 x Su x W x t L W = width of stock Su= ultimate tensile strength. Mild steel 1. Bending force Fb: 0. Aluminum hard 0.5 12. rd= die radius rp=punch radius.4 07.0 04.5 03.5 x Fb Total force: Fn = Fb + Fp 2 2 U .R min = C 3 S S = sheet thickness C = Constant referred to the following table. 6 4.5 4.8 50 4.0 7.3 7.8 Material Aluminium 3003-0 CRCA (SAE 1008) BRASS (dead soft)70/30 Dead soft stain less steel 13 .7 3.05-0.0 3.5 70 4.5 5.8 7.8 8.0 5.8 30 3.µ) Rc = radius of curling µ = co efficient of friction (0. The following formula is also frequently used for V.8 x Tmax x w x s2 4 x Rc x (1 .6 6.1 60 4.0 7.2 4.0 6.1) Off-setting or joggling: Force required for off setting is 3 times the bending force (90º bend) if off setting is 6t and more.667 x Su x W x T2 L Pad force: FB = 0.8 x W x t x Su V .3 4.0 10 2.0 80 4.2 40 3.0 5.2 3.Bending force: 0.0 4.0 20 3.2 8.2 5. 8-10 times the V – bending force (90º bend) if offset is less then 6t Spring Back Degrees of spring back Degrees of bend 5 2.2 x Su x W x t2 L Curling: Force required for curling Fc = 0.1 7.4 6.4 90 4.3 8.4 x W x t x Su Total load: FN = 0.9 5.Bending Force: FB = C x Su x W x t2 L C=1+4t L L = Width of opening. FB = 1.7 6.8 4.0 5.5 4.3 8.bending.7 5. 5-2) π d t Ssh Embossing/Beading Force for embossing Fe = Su t L L = height of embossing or bead Su = uts Bottoming force Fb=Sy A A= plan area of bottoming zone Sy=yield of strength 14 . Forming: Flanging B = A + 5t for t < 1.9.20 mm = t/3 for t > 1.2 mm Pre pierced hole size.2 mm H = 4t where t is 0.25 mm 5 R = t/4 for t < 1.25 mm 5 H = 3t for t > 1. 5) π d t Ssh Force required for hole flanging after pre-punching the hole: Ff = (1. d= Force required for direct piercing and flanging (with single stepped punch) Ff = (2-2.2 mm 4 =A+t H = t where t > 1.9 to 1. 7 Upto 0.4-0.4-0.7 Over0.7 Over0.7 Upto 0.4-0.7 Over0.7 Upto 0.4-0.4 over 0.4 0.7 --Pc 1-12 6-10 20 100-120 70-100 100-120 70-100 60-80 -100-150 70-90 60-80 120-150 100-120 70-100 180-250 125-160 100-120 220-300 160-200 120-150 --- Material 99% of Al Al alloy Brass 63% Cu Soft copper Hard copper Pure nickel German silver Steel Stainless steel Silver Gold 35-45 30-40 120-150 35-40 28-42 30-40 120-150 35-40 ---- 60-80 --- 250-320 150-180 120-150 60-90 --- Note: Pressures for 0.4-0.7 Over0.4 0.7 are the excess pressures given up to 0.4-0.7 -Upto 0.4 0.7 -Up to 0.4 Flattening (planishing) Force required for flattening Ff = A × P A = surface area of flattening portion P = surface pressure Calculations for tool elements Movement of stripper Ystr = t + 2 Where Y sIr = Movement of stripper t= Thickness of stock 15 .4 0.7 Over0.Coining: Force of coining Fc=A Pc A = total area of deformed surface (mm²) Pc = surface pressure (Kg/mm²) Coining pressure p in kg/mm2 Ultimate tensile stress Kg/mm² 8-10 18-32 29-41 21-24 -40-45 Kind of coining Letter and pattern 5-8 15 20-30 20-30 30-50 30-60 Both sides 8-12 35 150-150 80-100 100-150 160-180 Light coining 5-8 14 20-30 10-25 -25-35 Heavy coining For depth mm Up to 0.4 0.4-0.7 Upto 0.4 0.4 0. Force developed under this deflection 25-35 kg/cm2 Expected life of rubber blocks =b 3 lakh cycles where rubber blocks are used. Deflection =40% of it’s original height.6D to allow for bulging. Press Tool design check list 16 .Spring deflection (Y) Y = (3 to 4) Y str = (3 to 4) (t+2) Where Y = Total spring deflection at F max load Sharpening allowance 'S' is provided on the tools Y max = [(3 to 4) (t +. Space between blocks should be more than 1.2)] + S Rubber blocks: Shore hardness recommended 65-68 Possible Max. are they large enough for needed rigidity. involved and to the press working equipment to be used? 2. hardening.Preliminary planning 1. Has it been determined whether shedder provision is needed on any forming punches? 16. Have any necessary clearance holes in die block or stripper been checked for transport of blanks or slugs? 31. Have the sizes of all springs been calculated? 36. for adjustability. has the die block been Specified to be finished square on all sides 21 Have edges of die openings been designed a minimum distance of 1 to 11/2 times block thickness from outside edge of block 22 Have the punches and dies been designed sectional. Have any hardened punches been designed to be mounted in a soft plug. Provided the intended service requires it. preferably. location. for spacing far enough apart. Are idle s stations needed in a planned-progressive die? 3. Is the correct side of the blank up with respect to any shaved portions? 6. combined with bending or forming? Die plate and punch plate 20. Have any notching punches been located and. And to avoid miss feeds? 38 Have bolt heads in die plates been set sufficiently below the top surface to permit maximum die sharpening? 39 Have any necessary air vent holes been located? 40 Are stop or bumper blocks needed anywhere? 17 . if any. Have bushing decisions been checked as to need. for easy construction. provide with heel blocks or other backup support? 15. If die setup are to be used. heat treatment. Are any finger stops so located as to avoid cutting on only one edge of the die? 24. Check for required dimensional accuracy be realized from the planned stock strip layout? 4. Punch planning 14. Have heel punch fillets been made as large as possible? 19. are they stepped to reduce total shearing pressure? 17. Where small pierce or blank punches are to be grouped closely together. Have any pilot-hole punches been suitably located? 13. or not to exceed 450 7. Have the design feature been checked against the shut height of the closed die? 10. and replacement? 23. for easy replacement? 11. Have proper provisions been made for clamping the die set to press? 9. been located at next-to-last station and. Have adequate provisions been made for scrap disposal? 28. where feasible. Has the blank been developed with due regard to best grain direction. for means of removal from blind holes. sharpening. and optimum length? 37 Has the planned piloting practice been checked as to removability to facilitate punch grinding. unguided length. Has the centerline of pressure been properly established? 12. and far enough apart? 33. Have spanking punches. for advisable staggering to prevent miss assembly? 29. to stresses and Strains. Have any needed release or vacuum pins been checked as to location and action? 34. Is the punch plate sufficiently thick to support all punches adequately? 30. Will any forming be done across the grain (optimum). Have unavoidable delicate projections been designed as inserts. Have blank hole. Will inserts and bushings be planned wherever needed to-facilitate die making. If punches must be used having more than about 4-in. Have needed scrap cutters been suitably located? 27. if needed. have spacers or filler plates been considered? 18. or easy Replacement of worn or broken sections? 25. Has a selected die set been checked for parallelism of mounting surfaces? For of guideposts in their bushings? 26. scrap hole clearances been checked? 35. Has the final sequence of operations been thoroughly checked and established. Has doweling been checked for sufficient size to withstand shearing action. Is material utilization maximum? 8. rather than pressed directly into a hardened punch plate? General design details 32. Can the burr be so placed as to require no removal? 5. 4. Avoid the use of blind holes when possible. mass. Use sectional dies if the design is considered to be hazardous 7.41 Has a thorough check been made to ensure safety to the operator. 3. Avoid use of large masses. the die. Use sufficiently oversize stock to insure freedom from surface defects and decarburization after grade selection is made. Use fillets at base of keyways to minimize stress concentration. Use steps of taper whenever possible. Avoid thin-walled areas. If design permits. 9. Avoid sharp re-entrant angles. incorporate a hole to facilitate Spring Selection Steps 18 . because they tend to alter uniformity of cooling. Generous fillets should be used whenever possible to minimize stress Concentration during heat treatment. Some of the basic rules for design. 6. 5. directly related to heat treatment. Heat treatment is the most severe operation any tool or die must go through and it is necessary that ease or safety in heat treatment be given every possible consideration when designing tools and dies. and the press? Heat treatment. method of fabrication. Increase cross section in such areas if possible. surface area. Avoid drastic changes in cross section. also square inside corners. are given in the following slides 1. • • • Design is the sum total of many variables among which are geometry. surface finish. and heat treatment. 8. material used. 2. Then choose the figure nearest the compressed length “H” required by the die design from the appropriate charts of spring supplier. Read corresponding free length. etc. or ExtraHeavy Load. X Step 7 Select springs as follows: 1. Medium. For best economy and saving of space. The free length “C” must comply with the length determined in Step 3.short run. Hardness conversion 19 . Step 1 Estimate the level of production Required of the die . Divide “R” in Step 6 by the number of springs to be used (if known) in order to get the rate per spring. 2. constant production.I n determining the length of a spring. Step 3 Determine free length “C” as follows: Decide which load classification the spring should be selected from -Light. or an Extra Heavy Load spring having a free length equal to eight times the travel. choose Light and Medium Load springs or the Heavy Load spring having a free length equal to six times the travel. the number of springs required will be substantially increased. If ratios lower than these are used because of height limitations. divide “R” from Step 6 by the rate of the spring you select for the correct number of springs. If the number of springs is not known. Step 5 Determine “X” (initial compression) by using the following formula: X = C-H-T Step 6 Determine “R” (total rate for all springs in N/mm) by using the following formula: R= L. Heavy. Step 4 Estimate total initial spring load “L” required for all springs when springs are compressed “X” inches or millimeters. Then refer to the spring supplier catalogs for springs having the desired rate. Step 2 Determine compressed spring length “H” and operating travel “T” from the die layout. it should be remembered that maximum delivered spring load is obtained by selecting longer springs. Vickers .HV Rockwell. c Brinell 20 . c Brinell Vickers .HV Rockwell. 940 920 900 880 860 840 820 800 780 760 740 720 700 690 680 670 660 650 640 630 620 610 600 590 580 570 560 550 540 530 520 51 0 500 490 480 470 460 450 440 430 420 68 67 67 66 65 65 64 64 63 62 61 61 60 59 59 58 58 57 57 56 56 55 55 54 54 53 53 52 51 51 50 49 49 48 47 46 46 45 44 43 42 767 757 745 733 722 710 698 684 680 656 647 638 630 620 611 601 591 582 573 564 554 545 535 525 51 7 507 497 488 479 471 460 452 442 433 425 41 5 405 397 410 400 390 380 370 360 350 340 330 320 310 300 295 290 285 280 275 270 265 260 255 250 245 240 230 220 210 200 190 180 170 160 150 140 130 120 110 100 95 90 85 41 40 39 38 37 36 35 34 33 32 31 29 29 28 27 27 26 25 24 24 23 22 21 20 18 15 13 11 9 6 3 0 - 388 379 369 360 350 341 331 322 313 303 294 284 280 275 270 265 261 256 252 252 243 238 233 228 219 209 200 190 181 171 162 152 143 133 124 114 105 95 90 86 81 21 .