5.3工具设计的工业实践毕业课程设计外文文献翻译、中英文翻译

资料来源：书籍文章名：Extrusion书刊名：English for Die & Mould Design and Manufacturing作 者：刘建雄王家惠廖丕博主编出版社：北京大学出版社，2002章 节：Chapter 5 Extrusion页 码：P86P105文 章 译 名： 5.3工具设计的工业实践5.3 Industrial Practice in Tool Design5.3.1 Dummy BlocksIn common with the die, the container, and mandrel when used, the dummy block sees the highest temperatures through its contact with extruded metal. For heavy metal extrusion the members of this component rank second only to the dies, because of plastic deformation of the block above the softening temperature of the steel used.Most dummy blocks are turned from plain cylinders with a thickness of 0.50.75 of theirdiameter. The overall diameter of the dummy block depends on whether extrusion is intended withor without a skull. In aluminium extrusion the dummy block leading edge diameter may be 0.5 mm smaller than that of the container, whereas to obtain a good complete skull in brass extrusion the difference between container and dummy block diameters would not be less than 1 mm.In heavy metal extrusion the dummy block is usually ejected from the press with the extrusion discard at the end of each cycle to permit cooling and to avoid wasting press time. Any skull is then cleared by passing a larger diameter cleaning pad through the container.In aluminium extrusion the dummy block may be of the “combination” type, one block simultaneously pushing the billet but with a slightly larger diameter trailing edge cleaning the detritus left behind on the container bore. A desire to increase productivity by billet-to-billet extrusion has led to the use of dummy blocks fixed to the ram, and having some means of preventing air entrapment between the back end of the extruded billet and the front end of the next one.Various attempts have been made in heavy metal extrusion to vary the shape of the front face of the dummy block, to increase yield by reducing the discard volume, and at the same time to influence the flow pattern in the billet, in some cases these attempts have been combined with shaping the extrusion die. In one significant case the use of spherical dummy blocks was seen to reduce extrusion defect and increase yield when compared with conventional dummy blocks. In addition, the technique gave explanation of a particular type of defect (waviness) seen during the latter part of extrusion of very wide thin sections, by the way in which dummy blocks act on the dead metal zone.5.3.2 DiesOf all the tooling components the extrusion die is of paramount importance to the extrusionprocess, since its design defines the extruded product as regards accuracy and consistency of shape and dimension of the cross-section, and linearity and freedom from twisting of the extruded length. The design must also take account of any tendency for apart of the section not to “fill” the die orifice, and also the variations in dimensions implicit between front and back of one extruded length and between successive extrusions. Thin ends of limbs and thin parts of a section adjacent to thicker parts will not “fill” even at relatively slow extrusion speeds unless the die design corrects this tendency.Only for copper sections, which are subsequently heavily cold drawn, is detailed consideration of this problem not so important. For all other extruded metals the control of “differential flow” is vital.In general, solutions to the above problems have been developed empirically, by trial- and-error methods, over decades, for basically flat plate dies. Dies based on flat plates but with profiled or bell-mouthed entry to the shape defining die orifice are only widely used for high temperature shape extrusion, e.g. steel, nickel or titanium alloy.1. Die Layout and Container SizeExperience gained by commercial extruders has to a large extent defined which sections can be extruded under given conditions of temperature and available press power.Of the various expressions formulated to relate minimum extruded area to available press power, the following empirical form seems easily usableP/A = k (b ln (A/a) + c)(5.1)where “P” is the press force, “A” is the cross-sectional area of the billet, “a” is the extruded cross-sectional area and “k”, “b”, “c” are constants.This form ignores the billet/container friction losses and any effect of conicity of die entry. For relatively high extrusion ratios the expected minimum in extrusion pressure for a flat die is confirmed, and except for very large values of billet length to diameter ratio, in direct extrusion the above equation is adequate for simple copper and brass sections.For a single hole die the circumscribing circle center would normally be placed at the die center, although highly asymmetric sections are sometimes displaced with a thick part of the shape out towards the edge follower section (e.g. a round) on the other side of the die to balance flow.The orifices in multihole dies should be positioned so as to minimize flow control problems. Where possible, sections should be positioned with their centers of gravity on the same diameter to equalize the exit speeds of separate strands (compare Figs. 5-4 (a) and (b). Where a section includes a large tongue, it can be of value to position the orifices with their centers of gravity(a) W(d) C(b) C(e) C(c) Wfurthest from the die center, to overcome a tendency for the metal to extrude faster over the tops of tongues. Thus the layout in Fig. 5-4 (e) is preferred to that in Fig. 5-4 (c). The requirement for aluminium extrusions that one surface of the product shows the best possible surface finish may, however, alter the design to ensure that this surface does not touch the runoutAn extrusion dimension can be up to 3% smaller than the die orifice for reasons including effects of thermal expansion and deflections of the die under load. Even for simple shapes the differences between die orifice and the extrusion dimensions are not totally accounted for by thermal expansion, and a “shrinkage allowance” must be determined for each extruded alloy, the form of which is best decided for each alloy and extrusion temperature from measurements on a wide variety of extruded sections and their dies, taking into account elastic deflection and/or plastic collapse of the die orifice and variations during extrusion of a series of billets.5.4Cold Extrusion of Steel5.4.1 Nomenclature and Tool Assembly DrawingsThere are four basic extrusion operations (shown in Fig. 5-5), namely, forward rod-extrusion, can-extrusion, forward tube-extrusion and open-die extrusion. The complete tool for can-extru- sion is shown in Fig. 5-6; this can be used also for the other types, although a separate special tool can be used for forward rod-extrusion (Fig. 5-7).ContainerPunch ProductContainerPunchBilletBilletCounter punchProductMandrel(a) backward can-extrusion(b) forward tube-extrusion(c) forward rod-extrusion(d) open die-extrusionFig. 5-5 Basic extrusion operationsPressure pad PunchStripping platesProduct Die insertCounter punch Die stress ringPressure padEjectorFig. 5-6 Tool set for can-extrusionFig. 5-7 Tool set for forward rod-extrusion5.4.2 PunchesThe punch is the portion of the tool that forms the internal surface of the workpiece in a can-extrusion, or that pushes the workpiece through a die in rod, tube or open die extrusion.In can extrusion the punch is highly stressed by compressive and bending loading, and atthe same time subjects to heavy wearing and increases in temperature at the punch nose. Compressive stresses of over 2200 N/mm2 can occur and on the return stroke, tensile stresses are encountered due to the stripping action.In forward rod- and tube-extrusion the punch does not suffer much from wear but the compressive stresses are similar to can extrusion punches.In open die-extrusion where the extrusion ratio is less than 15%, the punch loads are of necessity comparatively low and there are no wear and stress problems.1. Punch StressesThe stress on the punch is equal to the punch load Fe divided by the cross-sectional area A0. Due to buckling caused by eccentricity, the allowable stress that can be used is reduced as the punch length to diameter ratio increases (Fig. 5-8). In practical terms this means that the higher the extrusion stresses, the more important it is to reduce eccentricity and to keep the length/diameter ratio of the punch to a minimum. When all else fails with normal tool steels, solid carbide punches should be considered.z(N/mm2)30002500200015001000500Forward Extrusione= eccentricitydp=punch diameterBackward Extrusion2. Design0123456 789 10 11 l/dFig. 5-8 Buckling limitations of steel punchesFig. 5-9 shows the various possible designs of punches and punch/mandrel configurations for tube extrusion.A point that needs great attention is that for can-extrusion punches the axiom “attention to detail is all important, in that every aspect of design, manufacture, assembly and treatment in service” must be considered, and methodically and carefully acted upon.Rod punch6Tube punch6Tube punch6Tube punch23145Can punchh1Integral mandrel Fixed mandrel Floating mandrelFig. 5-9 Punch and punch/mandrel configurations1-punch nose 2-stem 3-shank 4-shoulder 5-shankhead 6-mandrelFig. 5-10 shows the design details for a can-extrusion punch with variations for the method of fixing and stripping. Stripping is necessary for many automatic presses where an occasional workpiece sticks to the punch rather than in the die with consequential damage to the immediate and subsequent tooling.h2 h3 h2 depends onlength and travelh3Flatness important and TIRRtm1mhh1maximumdepth of can of stripper bushShort type punchFig. 5-10 Punch details for can-extrusionThe design of punches for rod-extrusion is comparatively simple because punch pressures are lower than with can extrusion (normally less than 2,000 N/mm2). The essential features are the close clearance between punch and die bore to avoid burrs on the upper side of the workpiece, and the necessity to avoid seizure between punch and die because of the elastic radial expansion of the punch, for which a compromise must be made between the two features.In tube-extrusion, there are three main types of punch/mandrel. The first is an integral punch which is mainly used for thin-wall extrusions or for short extrusions where thelength/diameter ratio of the mandrel is less than 1.51 (Fig. 5-9).Fig. 5-11 shows the details, of which it is worth noting the slight taper from d1 (at the nose) to d of an included angle of less than 1. This helps to extract the tool from the workpiece. This is important because there is no possibility of a stripper being used.h3h4 d4flatness importanth2Design Datad1, d2 according to the preformed cup or tubed1max = d0.01 L1d3 = d2+0.5mmd4 = 1.2 d2 to d2h11.5dh1penetration depth in dieh3 = d3h4 0.5d4R1 = 0.5 (d1d)R2 = according to final shape = 15to 30Eccentricity TIR d1, d2 ,d3 tod3 0.01mmh1Fig. 5-11 Integral punch and mandrelIt is also important to ensure that the radius between the mandrel and punch should be free from scratches or score marks as the stress concentrations are dangerous at this point.The punch with inserted mandrels is shown in Fig. 5-12 with the fixed mandrel details shown on the right hand side and the movable one on the left. As with the integral mandrel, the working portion of the mandrel should be slightly tapered to facilitate stripping, although it is possible to design a special arrangement of stripper in conjunction with an in-built subsidiary motion of the press. d5d3flatness important and TIR1.0md1Transition radii as large as possible without scratchesDesign Datad1 and d2 according to the final shape of componentd1 = according to the die bored3 = 1.3dd4 = 1.3dd5 = 1.6dh1 depends on the die boreh2 = 1/2d4h3 d3h4 = (0.7 to 1) d3h5 8d = 5to 10 = 15to 3 = 5to 15R1 = 0.3 (d1d)Fig. 5-12 Punch with inserted mandrelThe movable mandrel allows it to move in the direction of the extruded tube, thus reducing the tensile stress in the mandrel. Inserted Belleville type washers can be used to reduce the shock on the return stroke.3. Materials and ManufactureMaterials arent mainly considered in this chapter, but it is necessary to stress the extreme importance of correct selection of materials and their control, initial machining, heat treatment and finish machining.A few points worth noting are:(a) Select only those suppliers who can guarantee the quality and consistency of their material supply;(b) Do not hardness-test highly stressed regions of the tool;(c) Avoid heavy roughing cuts and deep sharp cuts;(d) Allow for decarburization and distortion from heat treatment;(e) Use EDM only when grinding is very difficult or impossible;(f) Avoid center holes, so use extensions which can be subsequently ground off;(g) Blends at changes of section should be polished.4. Operational AspectsIt cannot be stressed too much that what happens to a tool in service is important to the tool designer as well as the production staff and operators. The immediate feedback to the designer of this information means that modifications can be made and recorded, thereby preventing re- occurrence of the problems.However well the tools are designed, it is always possible to improve them, or reduce costs, as the performance of tools is dependent on so many variables that it cannot be predicted entirely from the drawing board.5. The Failure of Punches and Their CausesIn general, trouble may occur in any or all of three forms, as follows:(1) Pickup and WearPickup (i.e. the welding together of slug material and tool) will usually occur as a result of shortcomings in the surface coating and lubrication of the slug, but may also arise if the tools have an unsuitable geometry, a poor surface finish or too low a hardness. The surface quality of the product will then deteriorate rapidly owing to the appearance of scratches and score lines and the tool will soon become so damaged that it cannot be reclaimed. Repolishing of tools is at bestusually only a temporary remedy, however, and the trouble should therefore be corrected at sourcefor example, by attention to the original surface condition of untreated slugs as influenced by the annealing and cleaning procedure, prior to surface coating.Some overall wear of tools is bound to occur, to a degree which is mainly influenced by the number of components produced. Since the extent to which wear can be tolerated depends on the length of run and the dimensional accuracy and finish required in the components, the decision whether remedial action should be taken is dictated by the economics of the situation. If a significant reduction in the rate of wear is in fact sought, then the solution rests primarily with tile tool material and its heat treatment condition, or possibly with the use of hard surfacing procedures such as nitriding or other methods.(2) Plastic DeformationThe problems arising under this heading consist of permanent bending of punches or mandrels, and swelling of punches or necking of mandrels.Bending arises mostly from eccentricity in preformed slugs or poor guidance of the tools in the press, and less frequently from non-uniform lubrication.Swelling and necking are basically the result of stresses in the tool which are too high for the material to sustain elastically. These may occur if the extrusion loading is too great (for example, from excessive friction, deficiencies in slug material and slug preparation, or too high an extrusion reduction) or because the tool material is unsuitable (incorrect choice of material or heat treatment).A point of interest is that new punches for can-extrusion are often found to upset by a few hundredths of a millimetre after some tens of products have been made, and it is known that if the punch is then re-ground to its original size the subsequent performance is enhanced.(3) FractureSince punches are usually made from materials which, in the heat-treated condition, are of intrinsically low ductility, the amount of plastic deformation that they can tolerate is severely limited. For the same reason any features which have a local stress raising effect are highly undesirable, whether arising from tool design, manufacturing imperfections (for example, excessive grain size, grinding marks, scratches, etc.) or from the quality of the tool material (for example, poor carbide distribution). A further point is that cold extrusion tools are subjected to cyclic stressing, that is, they are in a fatigue situation, which may intensify the bad effects of stress raisers and low ductility.Fracture (usually most common in can-extrusion punches) is therefore always of a brittle rather than of a ductile nature, and manifests itself in different ways and in different areas,according to the factors giving rise to it.6. Monitoring SystemsMeasurement and analysis of loading conditions in single and multistation machines is possible on a continuous basis and can be used to prevent overloading of the tools.5.4.3 DiesThe die is the item of t