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机械设计英文翻译


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毕业设计(论文)外文翻译 (原文)

院 (系): 专

应用科技学院

业: 机械设计制造及其自动化 师俊峰 0501120417 应用科技学院 刘海涛 高级工程师

学生姓名: 学 号:

指导教师单位: 姓 职 名: 称:

2009 年

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Failure Analysis,Dimensional Determination And Analysis,Applications Of Cams And Mould INTRODUCTION Mechanical design is the application of science and technology to devise new or improved products for the purpose of satisfying human needs. It is a vast field of eng ineering technology which not only concerns itself with the original conception of the product in terms of its size, shape and construction details, but also considers the va rious factors involved in the manufacture, marketing and use of the product.People wh o perform the various functions of mechanical design are typically called designers, or design engineers. Mechanical design is basically a creative activity. However, in addit ion to being innovative, a design engineer must also have a solid background in the a reas of mechanical drawing, kinematics, dynamics, materials engineering, strength of m aterials and manufacturing processes. As stated previously, the purpose of mechanical design is to produce a product which will serve a need for man. Inventions, discoveries and scientific knowledge by themselves do not necessarily benefit people; only if they are incorporated into a desi gned product will a benefit be derived. It should be recognized, therefore, that a hum an need must be identified before a particular product is designed. It is absolutely essential that a design engineer know how and why parts fail so that reliable machines that require minimum maintenance can be designed.Sometimes a failure can be serious, such as when a tire blows out on an automobile traveling at high speed.On the other hand,a failure may be no more than a nuisance.An exam ple is the loosening of the radiator hose in an automobile cooling system.The conseq uence of this latter failure is usually the loss of some radiator coolant,a condition th at is readily detected and corrected. The type of load a part absorbs is just as significant as the magnitude. Generally speaking,dynamic loads with direction reversals cause greater difficulty than static loa ds,and therefore,fatigue strength must be considered.Another concern is whether th e material is ductile or brittle.For example,brittle materials are considered to be una cceptable where fatigue is involved. Many people mistakingly interpret the word failure to mean the actual breakage o f a part.However,a design engineer must consider a broader understanding of what appreciable deformation occurs.A ductile material,however will deform a large amou nt prior to rupture.Excessive deformation,without fracture,may cause a machine to fail because the deformed part interferes with a moving second part.Therefore,a part fails(even if it has not physically broken)whenever it no longer fulfills its required fu nction.Sometimes failure may be due to abnormal friction or vibration between two mating parts.Failure also may be due to a phenomenon called creep,which is the pl
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astic flow of a material under load at elevated temperatures.In addition,the actual s hape of a part may be responsible for failure.For example,stress concentrations due to sudden changes in contour must be taken into account.Evaluation of stress conside rations is especially important when there are dynamic loads with direction reversals a nd the material is not very ductile. In general,the design engineer must consider all possible modes of failure,whic h include the following. ——Stress ——Deformation ——Wear ——Corrosion ——Vibration ——Environmental damage ——Loosening of fastening devices The part sizes and shapes selected also must take into account many dimensional factors that produce external load effects,such as geometric discontinuities,residual stresses due to forming of desired contours,and the application of interference fit join ts. Cams are among the most versatile mechanisms available. cam is a simple two A -member device.The input member is the cam itself,while the output member is cal led the follower.Through the use of cams,a simple input motion can be modified i nto almost any conceivable output motion that is desired.Some of the common applic ations of cams are ——Camshaft and distributor shaft of automotive engine ——Production machine tools ——Automatic record players ——Printing machines ——Automatic washing machines ——Automatic dishwashers

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The contour of high-speed cams (cam speed in excess of 1000 rpm) must be det ermined mathematically.However,the vast majority of cams operate at low speeds(les s than 500 rpm) or medium-speed cams can be determined graphically using a large-s cale layout.In general,the greater the cam speed and output load,the greater must be the precision with which the cam contour is machined. DESIGN PROPERTIES OF MATERIALS The following design properties of materials are defined as they relate to the tens ile test.

Figure 2.7 Static Strength. The strength of a part is the maximum stress that the part can sust ain without losing its ability to perform its required function.Thus the static strength may be considered to be approximately equal to the proportional limit,since no plasti c deformation takes place and no damage theoretically is done to the material. Stiffness. Stiffness is the deformation-resisting property of a material.The slope of t he modulus line and,hence,the modulus of elasticity are measures of the stiffness of a material. Resilience. Resilience is the property of a material that permits it to absorb energy without permanent deformation. amount of energy absorbed is represented by the area underneath The the stress-strain diagram within the elastic region. Toughness. Resilience and toughness are similar properties.However,toughness is t he ability to absorb energy without rupture.Thus toughness is represented by the total area underneath the stress-strain diagram, as depicted in Figure 2.8b.Obviously,t he toughness and resilience of brittle materials are very low and are approximately eq ual. Brittleness. A brittle material is one that ruptures before any appreciable plastic defo rmation takes place.Brittle materials are generally considered undesirable for machine

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components because they are unable to yield locally at locations of high stress becaus e of geometric stress raisers such as shoulders,holes,notches,or keyways. Ductility. A ductility material exhibits a large amount of plastic deformation prior to rupture. Ductility is measured by the percent of area and percent elongation of a part loaded to rupture.A 5%elongation at rupture is considered to be the dividing line bet ween ductile and brittle materials. Malleability. Malleability is essentially a measure of the compressive ductility of a material and,as such,is an important characteristic of metals that are to be rolled int o sheets.

Figure 2.8 Hardness. The hardness of a material is its ability to resist indentation or scratchin g.Generally speaking,the harder a material,the more brittle it is and,hence,the l ess resilient.Also,the ultimate strength of a material is roughly proportional to its ha rdness. Machinability.Machinability is a measure of the relative ease with which a material can be machined.In general,the harder the material,the more difficult it is to mach ine. COMPRESSION AND SHEAR STATIC STRENGTH In addition to the tensile tests, there are other types of static load testing that provide valuable information. Compression Testing. Most ductile materials have approximately the same properties in compression as in tension.The ultimate strength,however,can not be evaluated f or compression.As a ductile specimen flows plastically in compression,the material bulges out,but there is no physical rupture as is the case in tension.Therefore,a d uctile material fails in compression as a result of deformation,not stress.

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Shear Testing. Shafts,bolts,rivets,and welds are located in such a way that shea r stresses are produced.A plot of the tensile test.The ultimate shearing strength is d efined as the stress at which failure occurs.The ultimate strength in shear,however, does not equal the ultimate strength in tension.For example,in the case of steel,th e ultimate shear strength is approximately 75% of the ultimate strength in tension.Thi s difference must be taken into account when shear stresses are encountered in machi ne components. DYNAMIC LOADS An applied force that does not vary in any manner is called a static or steady lo ad.It is also common practice to consider applied forces that seldom vary to be stati c loads.The force that is gradually applied during a tensile test is therefore a static l oad. On the other hand,forces that vary frequently in magnitude and direction are cal led dynamic loads. Dynamic loads can be subdivided to the following three categories. Varying Load. With varying loads,the magnitude changes,but the direction does n ot.For example,the load may produce high and low tensile stresses but no compress ive stresses. Reversing Load. In this case,both the magnitude and direction change.These load reversals produce alternately varying tensile and compressive stresses that are commonl y referred to as stress reversals. Shock Load. This type of load is due to impact.One example is an elevator droppi ng on a nest of springs at the bottom of a chute.The resulting maximum spring forc e can be many times greater than the weight of the elevator,The same type of shock load occurs in automobile springs when a tire hits a bump or hole in the road. FATIGUE FAILURE-THE ENDURANCE LIMIT DIAGRAM The test specimen in Figure 2.10a.,after a given number of stress reversals wil l experience a crack at the outer surface where the stress is greatest.The initial crack starts where the stress exceeds the strength of the grain on which it acts.This is us ually where there is a small surface defect,such as a material flaw or a tiny scratc h.As the number of cycles increases,the initial crack begins to propagate into a con tinuous series of cracks all around the periphery of the shaft.The conception of the i nitial crack is itself a stress concentration that accelerates the crack propagation pheno menon.Once the entire periphery becomes cracked,the cracks start to move toward t he center of the shaft.Finally,when the remaining solid inner area becomes small en ough,the stress exceeds the ultimate strength and the shaft suddenly breaks.Inspectio n of the break reveals a very interesting pattern,as shown in Figure 2.13.The outer annular area is relatively smooth because mating cracked surfaces had rubbed against
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each other.However,the center portion is rough,indicating a sudden rupture similar to that experienced with the fracture of brittle materials. This brings out an interesting fact.When actual machine parts fail as a result of static loads,they normally deform appreciably because of the ductility of the material.

Figure 2.13 Thus many static failures can be avoided by making frequent visual observations and replacing all deformed parts.However,fatigue failures give to warning.Fatigue f ail mated that over 90% of broken automobile parts have failed through fatigue. The fatigue strength of a material is its ability to resist the propagation of cracks under stress reversals.Endurance limit is a parameter used to measure the fatigue str ength of a material.By definition,the endurance limit is the stress value below whic h an infinite number of cycles will not cause failure. Let us return our attention to the fatigue testing machine in Figure 2.9.The test is run as follows:A small weight is inserted and the motor is turned on.At failure of the test specimen,the counter registers the number of cycles N,and the correspon ding maximum bending stress is calculated from Equation 2.5.The broken specimen i s then replaced by an identical one,and an additional weight is inserted to increase t he load.A new value of stress is calculated,and the procedure is repeated until failu re requires only one complete cycle.A plot is then made of stress versus number of cycles to failure.Figure 2.14a shows the plot,which is called the endurance limit or S-N curve.Since it would take forever to achieve an infinite number of cycles,1 mi llion cycles is used as a reference.Hence the endurance limit can be found from Fig ure 2.14a by noting that it is the stress level below which the material can sustain 1 million cycles without failure. The relationship depicted in Figure 2.14 is typical for steel,because the curve be comes horizontal as N approaches a very large number.Thus the endurance limit equ als the stress level where the curve approaches a horizontal tangent.Owing to the lar ge number of cycles involved,N is usually plotted on a logarithmic scale,as shown in Figure 2.14b.When this is done,the endurance limit value can be readily detected by the horizontal straight line.For steel,the endurance limit equals approximately 5 0% of the ultimate strength.However,if the surface finish is not of polished equalit
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y,the value of the endurance limit will be lower.For example,for steel parts with a machined surface finish of 63 microinches ( μin.),the percentage drops to about 4 0%. For rough surfaces (300μin. greater), or the percentage may be as low as 25%. The most common type of fatigue is that due to bending. The next most frequent is torsion failure,whereas fatigue due to axial loads occurs very seldom.Spring mat erials are usually tested by applying variable shear stresses that alternate from zero to a maximum value,simulating the actual stress patterns. In the case of some nonferrous metals,the fatigue curve does not level off as th e number of cycles becomes very large.This continuing toward zero stress means that a large number of stress reversals will cause failure regardless of how small the valu e of stress is.Such a material is said to have no endurance limit.For most nonferro us metals having an endurance limit,the value is about 25% of the ultimate strength. EFFECTS OF TEMPERATURE ON YIELD STRENGTH AND MODULUS OF E LASTICITY Generally speaking,when stating that a material possesses specified values of pro perties such as modulus of elasticity and yield strength, is implied that these values it exist at room temperature.At low or elevated temperatures,the properties of material s may be drastically different.For example,many metals are more brittle at low temp eratures.In addition,the modulus of elasticity and yield strength deteriorate as the te mperature increases.Figure 2.23 shows that the yield strength for mild steel is reduce d by about 70% in going from room temperature to 1000oF. Figure 2.24 shows the reduction in the modulus of elasticity E for mild steel as the temperature increases.As can be seen from the graph,a 30% reduction in modul us of elasticity occurs in going from room temperature to 1000 oF.In this figure,we also can see that a part loaded below the proportional limit at room temperature can be permanently deformed under the same load at elevated temperatures.

Figure 2.24
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CREEP: A PLASTIC PHENOMENON Temperature effects bring us to a phenomenon called creep,which is the increasi ng plastic deformation of a part under constant load as a function of time.Creep also occurs at room temperature,but the process is so slow that it rarely becomes signifi cant during the expected life of the temperature is raised to 300oC or more,the incre asing plastic deformation can become significant within a relatively short period of ti me.The creep strength of a material is its ability to resist creep,and creep strength data can be obtained by conducting long-time creep tests simulating actual part operati ng conditions.During the test,the plastic strain is monitored for given material at sp ecified temperatures. Since creep is a plastic deformation phenomenon,the dimensions of a part experi encing creep are permanently altered.Thus,if a part operates with tight clearances,t he design engineer must accurately predict the amount of creep that will occur during the life of the machine. Otherwise, problems such binding or interference can occur. Creep also can be a problem in the case where bolts are used to clamp tow part s together at elevated temperatures.The bolts,under tension,will creep as a function of time.Since the deformation is plastic,loss of clamping force will result in an un desirable loosening of the bolted joint.The extent of this particular phenomenon,call ed relaxation,can be determined by running appropriate creep strength tests. Figure 2.25 shows typical creep curves for three samples of a mild steel part und er a constant tensile load.Notice that for the high-temperature case the creep tends to accelerate until the part fails.The time line in the graph (the x-axis) may represent a period of 10 years,the anticipated life of the product.

Figure 2.25 The machine designer must understand the purpose of the static tensile strength te st.This test determines a number of mechanical properties of metals that are used in design equations.Such terms as modulus of elasticity,proportional limit,yield strengt h,ultimate strength,resilience,and ductility define properties that can be determined from the tensile test.

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Dynamic loads are those which vary in magnitude and direction and may require an investigation of the machine part’s resistance to failure.Stress reversals may requi re that the allowable design stress be based on the endurance limit of the material rat her than on the yield strength or ultimate strength. Stress concentration occurs at locations where a machine part changes size,such as a hole in a flat plate or a sudden change in width of a flat plate or a groove or f illet on a circular shaft.Note that for the case of a hole in a flat or bar,the value of the maximum stress becomes much larger in relation to the average stress as the si ze of the hole decreases.Methods of reducing the effect of stress concentration usuall y involve making the shape change more gradual. Machine parts are designed to operate at some allowable stress below the yield st rength or ultimate strength.This approach is used to take care of such unknown facto rs as material property variations and residual stresses produced during manufacture an d the fact that the equations used may be approximate rather that exact.The factor of safety is applied to the yield strength or the ultimate strength to determine the allow able stress. Temperature can affect the mechanical properties of metals.Increases in temperat ure may cause a metal to expand and creep and may reduce its yield strength and its modulus of elasticity.If most metals are not allowed to expand or contract with a c hange in temperature, then stresses are set up that may be added to the stresses from the load.This phenomenon is useful in assembling parts by means of interference fit s.A hub or ring has an inside diameter slightly smaller than the mating shaft or pos t.The hub is then heated so that it expands enough to slip over the shaft.When it cools,it exerts a pressure on the shaft resulting in a strong frictional force that preve nts loosening. TYPES OF CAM CONFIGURATIONS Plate Cams.This type of cam is the most popular type because it is easy to design and manufacture.Figure 6.1 shows a plate cam.Notice that the follower moves per pendicular to the axis of rotation of the camshaft.All cams operate on the principle t hat no two objects can occupy the same space at the same time.Thus,as the cam r otates ( in this case,counterclockwise ),the follower must either move upward or bi nd inside the guide.We will focus our attention on the prevention of binding and att ainment of the desired output follower motion.The spring is required to maintain cont act between the roller of the follower and the cam contour when the follower is movi ng downward.The roller is used to reduce friction and hence wear at the contact surf ace.For each revolution of the cam,the follower moves through two strokes-bottom dead center to top dead center (BDC to TDC) and TDC to BDC. Figure 6.2 illustrates a plate cam with a pointed follower.Complex motions can be pr oduced with this type of follower because the point can follow precisely any sudden
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changes in cam contour.However,this design is limited to applications in which the loads are very light;otherwise the contact point of both members will wear premature ly,with subsequent failure. Two additional variations of the plate cam are the pivoted follower and the offset sliding follower,which are illustrated in Figure 6.3.A pivoted follower is used when rotary output motion is desired.Referring to the offset follower,note that the amount of offset used depends on such parameters as pressure angle and cam profile flatness, which will be covered later.A follower that has no offset is called an in-line follower.

Figure 6.3 Translation Cams.Figure 6.4 depicts a translation cam.The follower slides up and down as the cam translates motion in the horizontal direction.Note that a pivoted fol lower can be used as well as a sliding-type follower.This type of action is used in c ertain production machines in which the pattern of the product is used as the cam. A variation on this design would be a three-dimensional cam that rotates as well as tran slates.For example,a hand-constructed rifle stock is placed in a special lathe.This s tock is the pattern,and it performs the function of a cam.As it rotates and translate s, follower controls a tool bit that machines the production stock from a block of the wood.

Figure 6.4

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Positive-Motion Cams.In the foregoing cam designs,the contact between the cam a nd the follower is ensured by the action of the spring forces during the return strok e.However,in high-speed cams,the spring force required to maintain contact may b ecome excessive when added to the dynamic forces generated as a result of accelerati ons.This situation can result in unacceptably large stress at the contact surface,whic h in turn can result in premature wear.Positive-motion cams require no spring becaus e the follower is forced to contact the cam in two directions.There are four basic ty pes of positive-motion cams: the cylindrical cam,the grooved-plate cam ( also called a face cam ) ,the matched-plate cam,and the scotch yoke cam. Cylindrical Cam.The cylindrical cam shown in Figure 6.5 produces reciprocating foll ower motion,whereas the one shown in Figure 6.6 illustrates the application of a piv oted follower. The cam groove can be designed such that several camshaft revolutions are required to produce one complete follower cycle. Grooved-plate Cam.In Figure 6.8 we see a matched-plate cam with a pivoted follow er,although the design also can be used with a translation follower.Cams E and F r otate together about the camshaft B.Cam E is always in contact with roller C,while cam F maintains contact with roller D.Rollers C and D are mounted on a bell-cran k lever,which is the follower oscillating about point A.Cam E is designed to provi de th e desired motion of roller C,while cam F provides the desired motion of roller D. Scotch Yoke Cam.This type of cam,which is depicted in Figure 6.9,consists of a circular cam mounted eccentrically on its camshaft.The stroke of the follower equals two times the eccentricity e of the cam.This cam produces simple harmonic motion with no dwell times.Refer to Section 6.8 for further discussion. CAM TERMINOLOGY Before we become involved with the design of cams, is desirable to know the it various terms used to identify important cam design parameters.The following terms r efer to Figure 6.11. The descriptions will be more understandable if you visualize the cam as stationary and the follower as moving around the cam. Trace Point.The end point of a knife-edge follower or the center of the roller of a roller-type follower. Cam Contour.The actual shape of the cam. Base Circle.The smallest circle that can be drawn tangent to the cam contour.Its ce nter is also the center of the camshaft.The smallest radial size of the cam stars at th e base circle.

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Pitch Curve.The path of the trace point,assuming the cam is stationary and the foll ower rotates about the cam. Prime Circle.The smallest circle that can be drawn tangent to the pitch curve.Its ce nter is also the center of the camshaft. Pressure Angle.The angle between the direction of motion of the follower and the no rmal to the pitch curve at the point where the center of the roller lies. Cam Profile.Same as cam contour. BDC.Bottom Dead Center,the position of the follower at its closest point to the ca m hub. Stroke.The displacement of the follower in its travel between BDC and TDC. Rise.The displacement of the follower as it travels from BDC to TDC. Return.The displacement of the follower as it travels from TDC or BDC. Ewell.The action of the follower when it remains at a constant distance from the ca m hub while the cam turns. A clearer understanding of the significance of the pressure angle can be gained b y referring to Figure 6.12.Here FT is the total force acting on the roller.It must be normal to the surfaces at the contact point.Its direction is obviously not parallel to t he direction of motion of the follower.Instead,it is indicated by the angle α,the pr essure angle,measured from the line representing the direction of motion of the follo wer.Therefore,the force FT has a horizontal component FH and a vertical component FV.The vertical component is the one that drives the follower upward and,therefore, neglecting guide friction,equals the follower Flood.The horizontal component has no useful purpose but it is unavoidable.In fact,it attempts to bend the follower about it s guide. This can damage the follower or cause it to bind inside its guide. Obviously, we want the pressure angle to be as possible to minimize the side thrust FH.A practi cal rule of thumb is to design the cam contour so that the pressure angle does not ex ceed 30o.The pressure angle,in general,depends on the following four parameters: ——Size of base circle ——Amount of offset of follower ——Size of roller ——Flatness of cam contour ( which depends on follower stroke and type of follower motion used )

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Some of the preceding parameters cannot be changed without altering the cam requirements, such as space limitations.After we have learned how to design a cam,we will discuss the various methods available to reduce the pressure angle. General all-steel punching die’s punching accuracy Accuracy of panel punching part is display the press accuracy of the die exactly. But the accuracy of any punching parts’ linear dimension and positional accuracy al most depend on the blanking and blanking accuracy. So that the compound mould of compound punching accuracy, is typical-ness and representation in the majority. Analysis of the die’s accuracy For the analysis of practicable inaccuracy during production of dies to inactivation, we could get the tendency when it is augmentation in most time. From this we coul d analyze the elements. When the new punch dies pt into production to the first cutte r grinding, the inaccuracy produced called initial error; if the die grinding more than t wenty times, until it’s discard, the inaccuracy called conventional error; and before the dies discard, the largest error of the last batch permit, called limiting error. at job sit e, the evidence to confirm life of sharpening is the higher of the blanking, punched h ole or punched parts. Because all finished parts had been blanked ,so it is especially for the compound dies. Therefore, the analysis of burr and measurement is especially important when do them as enterprise standardization or checked with <<the height of punching part>>. The initial error usually is the minimal through the whole life of die. Its magnit ude depend on the accuracy of manufacture, quality, measure of the punching part, thi ckness of panel, magnitude of gap and degree of homogeneity. The accuracy of manu facture depend on the manufacture process. For the 1 mm thicket compound punching part made in medium steel, the experimental result and productive practice all prove that the burr of dies which produced by spark cutting are higher 25%~~30% than pro duced by grinder ,NC or CNC. The reason is that not only the latter have more exact machining accuracy but also the value of roughness Ra is less one order than the fo rmer, it can be reached 0.025μm. Therefore, the die’s initial blanked accuracy depends on the accuracy of manufacture, quality and so on. The normal error of the punch die is the practicable error when the fist cutter gr inding and the last cutter grinding before the die produce the last qualified product. A s the increase of cutter grinding, caused the measure the nature wear of the dies are gradual increasing, the error of punching part increase also, so the parts are blew pro of. And the die will be unused. The hole on the part and inner because the measure of wear will be small and small gradually, and its outside form will be lager in the s ame reason. Therefore, the hole and inner form in the part will be made mould accor ding to one-way positive deviation or nearly equal to the limit max measure. In like manner, the punching part’s appearance will be made mould according to one-way ne
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gative deviation or nearly equal to limit mini measure. For this will be broaden the n ormal error, and the cutter grinding times will be increased, the life will be long. The limit error in punching parts the max dimension error which practicable allo wed in the parts with limit error. This kind of parts usually the last qualified product s before the die discard. For the all classes of dies, if we analyze the fluctuate, tende ncy of increase and decrease and law which appeared in the die’s whole life, we will find that the master of the error are changeless; the error that because the abrade of the cutter and impression will be as the cutter grinding times increased at the same t ime. And that will cause the error oversize gradually; and also have another part error are unconventional, unforeseen. Therefore, every die’s error composed of fixed error, system error, accident error and so on. 1. Fixed error At the whole process when the New punching die between just input production to discard, the changeless master error that in qualified part are called fixed error. Its magnitude is the deviation when the die production qualified products before the first cutter grinding. Also is the initial error, but the die having initial punching accuracy at this time. Because of t he abrades of parts, the die after grinding will be change t he dimension error. So the punching accuracy after cutter grinding also called “grin ding accuracy” and lower tan initial accuracy. The fixed errors depend on the element s factor as followed: (1) The material, sorts, structure, (form) dimension, and thick of panel The magnitude of punching gap and degree of homogeneity are have a important effect for the dimension accuracy. Different punching process, material, thick of panel, have completely different gap and punching accuracy. A gear H62 which made in ye llow brass with the same mode number m=0.34, 2mm thick and had a center hole, w hen the gap get C=0.5%t (single edge) , and punched with compound punching die, a nd the dimension accuracy reached IT7, the part have a flat surface ,the verticality of tangent plane reached 89.5°, its roughness Ra magnitude are 12.5μm, height of burr are 0.10mm; and the punching part are punched with progressive die, the gap C=7%t (single edge) , initial accuracy are IT11, and have an more rough surface, even can s ee the gap with eyes. In the usual situation, flushes a material and its thickness t is t he selection punching gap main basis. Once the designation gap had determined flushe s the plane size the fixed error main body; Flushes the structure rigidity and the three -dimensional shape affects its shape position precision. (2) punching craft and molder structure type Uses the different ramming craft, flushes a precision and the fixed error differenc e is really big. Except that the above piece gear example showed, the essence flushes the craft and ordinary punching flushes a precision and the fixed error differs outside
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桂林电子科技大学毕业设计用纸

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a magnitude, even if in ordinary punching center, uses the different gap punching, th e fixed error difference very is also big. For example material thicket=1.5mm H62 bra ss punching, selects C <= the 40%t unilateral I kind of small gap punching compared to select C <= 8%t (unilaterally) III kind of big gap punching, will flush a fixed err or to enlarge 40% ~ 60%, the precision at least will fall a level. Side in addition, wh ether there is picks builds a row of type side, flushes a error to have far to be bigge r than has builds a row of type to flush. Side not builds a row of type to flush. Side not builds a row of type to flush a precision to be lower than the IT12 level side, but most has builds a row of type to flush a precision in IT11 between ~ IT9 level, material thicket > 4mm flushes, the size precision can lower some. Different die’s stru cture type, because is suitable the ramming material to be thick and the manufacture precision difference, causes to flush a fixed error to have leaves. Compound die cente r, multi-locations continuous type compound die because flushes continuously to duplic ate the localization to add on the pattern making error to be bigger, therefore it flush es a fixed error compound punching die to want compared to the single location Big 1 ~ 2 levels (3)The craft of punching die’s manufacture The main work of punching die namely are raised, the concave mold processing procedure, to operates on the specification not to be high, can time form a more com plex cavity. But its processing surface approximately is thick > 0.03 ~ 0.05mm is the high temperature ablation remaining furcated austenite organization, degree of hardnes s may reach as high as HRC67 ~ 70, has the micro crack, easily when punching app ears broke the cutter or flaking. The Italian Corroder Corporation’s related memoir cal led "the line cut the processing contraction to have the disadvantageous influence to t he superficial gold, in fact already changed the gold constructions. We must use the stone powder to grind or the numerical control continual path coordinates rub truncate (cut to line) to make the precision work ". In recent years country and so on Switze rland and Japan, has conducted the thorough research to the electrical finishing equip ment and a bigger improvement, makes function complete high accuracy NC and the CNC line cutter, the processing precision may reach ± 0.005 ~ 0.001mm,even is smalle r. The processing surface roughness Ra value can achieve0.4 mum. According to the r ecent years to the domestic 12 production lines cutter factory investigation and study, the domestically produced line cutter processing precision different factory different mo del line cutter might reach ± 0.008 ~ ± 0.005mm, generally all in± 0.01mm or bigger so mewhat, was individual also can achieve± 0.005mm, the processing surface roughness R a value was bigger than1.6μm. However, the electrical finishing ablation metal surface thus the change and the damage machined surface mental structure character can not change, only if with rubs truncates or other ways removes this harmful level. Theref ore, merely uses electricity machining, including the spark cutting and the electricity p erforation, achieves with difficulty punching, especially high accuracy, high life punchi ng die to size precision and work components surface roughness Ra value request.

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桂林电子科技大学毕业设计用纸

第 16 页 共 17 页

With precisely rubs truncates the law manufacture punching die, specially makes t he high accuracy, the high life punching die, such as: Thin material small gap compo und punching die, multi- locations continuous type compound die and so on, has the size precision high, the work component machined surface roughness Ra value is smal l, the mold life higher characteristic. Its processing craft at present changed the electri cal fire by the past ordinary engine bed rough machining spark cutting or the electrici ty puncher rough machining, finally precisely rubs truncates, also from takes shape ru bs, optics curve rubs, the manual grid reference rubs gradually filters the continual pat h grid reference to rub and NC and the CNC continual path grid reference rubs, Proc essing coarseness may reach ± 0.001 ~ 0.0005mm, the processing surface roughness Ra value may reach 0.1 ~ 0.025 mum. Therefore, with this craft manufacture the die re gardless of the size precision, the work components surface roughness, all can satisfy die, each kind of compound request, the die is especially higher than the electrical fin ishing craft manufacture scale. (4) gap size and degree of homogeneity the flange and other sheet forming agene rally all must first punching (fall materi al) the plate to launch the semi finished materials, after also has the forming to fall t he material, the incision obtains the single end product to flush. Therefore punching t he work, including is commonly used punching hole, the margin, cut side and so on, regarding each kind of sheet pressing part all is necessary. Therefore punching the ga p to flushes a out form in precision to have the decisive influence. Punching the gap small and is even, may cause punching the size gain high accuracy. Regarding driva bility is curving and so on mould, the gap greatly will decide an increase flushes the oral area size error and the snapping back. The guenon-uniformity can cause to flush a burr enlarges and incurs cutting edge the non-uniform attrition. (5) ramming equipment elastic deformation In the ramming process After the punch press load bearing can have the certain elastic deformation. Altho ugh this kind of distortion quantity according to flushes the pressure the size to chang e also to have the obvious directivity, but on the pressing part, mainly is to has the volume ramming archery target stamping, embosses, the equalization, the pressure is ra ised, the wave, flushes crowds, the shape, the flange, hits flatly, thinly changes draw ability and so on the craft work punching forming flushes, has the significant influenc e to its ramming aspect size precision

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