1、常州工學院畢業設計(論文外文文獻學院機電學院專業班級10成型一學生姓名高麗君指導教師陳懷國A.Mold ComponetsMolds used in injection molding consist of two halves;one stationary and one movable.The stationary half is fastened directly to the stationary platen and is in direct contact with the nozzle of the injection unit during operation.The mova

2、ble half of the mold is secured to the movable platen and usually contains the ejector mechanism.There are many possible mold designa,including multiple piece molds for complicated parts.On production molding equipment many articles may be shot at the same time by the use of multiple cavity molds.Th

3、e use of a balanced runner system carries the plastic from the sprue to each individual cavity.At this poin the material passes through a gate into the cavity.The gate is a restriction,smaller then the runner,to provide for even filling of the mold cavity and to allow the products to be easily remov

4、ed form the runner system.With most injection molding system,the articles can be snapped away from the runner or sprue without additional trimming.Prouducts that have been injection molded can usually be identified by finding where the gate was broken off.The gate will usually be located at the edge

5、 or parting line of an object or in the center of cylindrical product.Molds are expensive,as are the machines.Yet,once the product has been designed, molds made,and production stared,articles can be produced in quantity at low cost.Virtually all thermoplastics can be injection molded through variati

6、ons in mold and machine design.Compression,Injection,and Die-Cast MoldPos. No.Denomination StandardDIN ISO1Plate,plain16760-16753-22Plat,drilled V16760-2/3Support pillar DIN ISO1007310073 4Centring sleeve1675994495Locating guide pillar1676180176Locating guide busch1671680187Ejector pin,cylindrical h

7、ead1530-A67518Shouldered ejector pin,cylindrical head1530-C8694 9Ejector pin,conical head1530-D/10Flat ejector pin1530-F869311Ejector sleeve16756840512Sprue puller insert16757/13Sprue bushing16752-11007214Angle pin/840415Locating unit,round and falt/840616Locating ring1676310907-110907-2 17Thermal i

8、nsulating sheet167131560018Cooling connectors16766/B Mold ConstructionThe construction of the mold for injection molding begins with the working drawing. From it the tequirements for the mold can be specified.These would include the material from which the mold should be made,the availability of equ

9、ipment for machining the mold,and the mold capacity of the die set on the machine.Cold rolled steel is an ideal material for laboratory molds,since it machines well,is fairly inexpensive,and holds up well for nozzle pressure and wear.Its major disadvantage is that it will rust quickly unless protect

10、ed by mold telease or wax during storage.Complicated常州工學院mold cavities need specialized machining and polishing,therefore,circular cavities which can be turned and polished on the lathe require less equipment and machining skill.Similar molds may also be machined from aluminum,and they have the adva

11、ntage of not rusting.Excessive wear develops on the sprue due to the high nozzle pressure on the soft aluminum,but this can be overcome by the use of a steel cover plate on the top of the mold.Another method of mold construction is by the casting process using an aluminum filled epoxy resin.This typ

12、e of mold is particularly suited to products of intricate design and products that are difficult to machine.The cast epoxy is strong and gives good surface detail, however,it is brittle and should have a steel top plate attached to absorb the wear of the nozzle.A pattern of the product must be secur

13、ed or made and placed on a mold plate.The drag of a small steel flask is placed around the pattern and the epoxy resin is poured to fill the mold half.When this half of the mold has been cured,the cope is placed over it and the remainder of the mold poured.Upon curing,the flask is removed,all surfac

14、es machined smooth,dowel pinholes drilled,and dowels inserted.A steel cap plate should be bolted to the top halves and the sprue,runners,and gates machined.Instructions for mixing,pouring,and curing the aluminum filled epoxy should be followed according to the manufacturers specifications.2.Hot Runn

15、er SystemsHot runners are classified according as they are heated:insulated-runner systems(it is not described in this articleand genuine hot-runner systems.The latter can be further sub-classified according to the type of heating:internal heating,and external heating.Heating is basically performed

16、electrically by cartridge heaters,heating rods,band heaters,heating pipes and coils,etc.To ensure uniform flow and distribution of the melt, usually a relatively elaborate aontrol system comprising several heating circuits and an appropriate number of sensors is needed.The operating voltage is usual

17、ly220V to240V,but small nozzles frequently have a low voltage of5V,and also15V and24V operating voltage.Runner systems in conventional molds have the same temperature level as the rest of the mold because they are in the same mold block.If,however,the runner system is located in a special manifold t

18、hat is heated to the temperature of the melt,all the advantages listed below accrue.Runner manifolds heated to melt temperature have the task of distributing the malt as far as the gates without damage.They are used for all injectionmolded thermoplastics as well as for crosslinking plastics,such as

19、elastomers and thermosets.常州工學院In the case of thermoplastics,these manifolds are usually referred to as the hot-runner system,the hot manifold,or simply as hot runners.For crosslinking plastics,they are known as cold runners.A.Hot-Runner SystemsHot-tunner systems are available as standard units and

20、it is hardly worthwhile having them made.The relevant suppliers offer not only proven parts but also complete systems tailored to specific needs.The choice of individual parts is large.B.Economic Advantages and Disadvantages of Hot-Runner Systems1.Economic AdvantagesSavings in materials and costs fo

21、r regrind.Shorter cycles;cooling time no longer determined by the slowly solidifying runners; no nozzle retraction required.Machines can be smaller because the shot volume-around the runners-is reduced,and the clamping forces are smaller because the runners do not generate reactive forces since the

22、blocks and the manifold block are closed.2.Economic DisadvantagesMuch more complicated and considerably more expensive.More work involved in running the mold for the first time.More susceptible to breakdowns,higher maintenance costs(leakage,failure of heating elements,and wear caused by filled mater

23、ials.3.Technological AdvantagesProcess can be automated(demoldingbecause do not need to be demolded.Gates at the best position;thanks to uniform,precisely controlled cooling of the gate system,long tlow paths are possible.Pressure losses minimized,since the diameter of the runners is not restricted.

24、Selective influencing of mold filling;needle valve nozzles and selective actuation ofthem pave the way for new technology(cascade gate system:avoidance of flow lines,in-mold decoration.Shorter opening stroke needed compared with competing,conventional three-platen molds.Longer holding pressure,which

25、 leads to less shrinkage.4.Technological DisadvantagesRisk of thermal damage to sensitive materials because of long flow paths and dwell times,especially on long cycles.Elaborate temperature control required because non-uniform temperature control would cause different melt temperatures and thus non

26、-uniform filling.C.Design of a Hot-Runner System and its ComponentsHot-runner molds are ambitious systems in a technological sense that involve high technical and financial outlay for meeting their main function of conveying melt to the gate without damage to the material.D.Externally/Internally Hea

27、ted SystemsThe major advantages and disadvantages of the two types.E.Externally Heated System1.AdvantageLarge flow channel cause low flow rare and uniform temperature distribution.2.DisadvantageThe temperatures required for external heating have to be very much higher.For PA66, for example,the mold

28、temperature is approximately100and the manifold temperature is at a temperature difference of approximately170from the mold block,which means.Special measures required for fixing the hot-runner nozzles to the gates because of the considerable themal expansion.Risk of disruption if this is not adepan

29、tely resolved.Higher heating power(over500W per100mm line for a typical cross-section measuring40·7mm2.Insulation from the mold block.Large,unsupported ateas and therefore,with large-surface molds,risk of bowing of the mold platen on the feed side if this has not been designed thick enough and

30、thus,as a direct consequence,the mold becomes very heavy.F.Internally Heated SystemA frozen layer of plastic forms on the inner surface of the channel and functions as aninsulation layer.The heat requirement of the system is much lower(toughly55W per100mm length of inside tube.The temperature differ

31、ences between mold and manifold blocks are negligible; therefore measures that would have been necessary for large heat expansion are not needed.The hot manifold of an internally heated system if a compact block that is bolted tightly to mold.Consequently,the mold is very rigid and no measures are r

32、equired for centering the nozzles and gates.This also allows the plate on the machine side to be manufactured as one block consisting of fixed mold with inbuilt manifold and corresponding rigidity.The melt volume is small and so the dwell times of the flowing melt are short.On the other hand,the flo

33、w rates are very much greater and this can damage the material.It is not advisable to use internally heated systems for sensitive materials.When deciding on a certain system,advice can be obtained from suppliers.3.Forming TheoryThe confidence level in successfully forming a sheetmetal stamping incre

34、ases as the simplicity of the part's topography increases.The goal of forming with stamping technologies is to produce stampings with complexgeometric surfaces that are dimensionally accurate and repeatable with a certain straindistribution,yet free from wrinkles and splits.Stampings have one or

35、 more forming modes that create the desired geometries.These modes are bending, stretch forming and drawing.Stretching the sheetmetal forms depressions or embossments. Drawing compresses material circumferentially to create stampings such as beer cans.As the surfaces of the stamping become more comp

36、lex,more than one mode of forming will be required.In fact,many stampings have bend,stretch and draw features produced in the form die.The common types of dies that shape material are solid form,stretch form and draw.Solid Form The most basic type of die used to shape material is the solid form die.

37、This tool simply displaces material via a solid punch"crashing"the material into a solid die steel on the press downstroke.The result is a stamping with uncontrolled material flow in terms of strain distribution.Since"loose metal"is present on the stamping,caused by uncontrolled

38、material flow,the part tends to be dimensionally and structurally unstable.Stretch Form Forming operations that provide for material flow control do so with a blankholder.The blankholder is a pressurized device that is guided and retained within the dieset.Stampings formed with a blankholder may beD

39、raw The draw die has earned its name not from the mode of deformation,but from the fact that the material runs in or draws off the blankholder surface and into the punch. Although the draw mode of deformation is present in draw dies,some degree of the stretch forming and bending modes generally also

40、 are present.The architecture and operational sequence for draw dies is the same as stretch-form dies with one exception.Material flow off the blankholder in draw dies needs to be restrained more in some areas than others to prevent wrinkling.This is achieved by forming halfmoon-shaped beads instead

41、 of lock steps or beads found in stretch-form dies.The first stage of drawing sheetmetal,after the blank or strip stock has been loaded into the die,is initial contact of the die steel with the blank and blankholder. The blank,round for cylindrical shells to allow for a circumferential reduction in

42、diameter,is firmly gripped all around its perimeter prior to any material flow.As the press ram continues downward,the sheetmetal bends over the die radius and around the punch radius.The sheetmetal begins to conform to the geometry of the punch.Very little movement or compression at the blank edge

43、has occurred to this point in the drawing operation.Air trapped in the pockets on the die steel is released on the press downstroke through air vents.The die radius should be between four and10times sheet thickness to prevent wrinkles and splits.Straightening of sheetmetal occurs next as the die con

44、tinues to close.Material that was bent over the die radius is straightened to form the draw wall.Material on the blankholder now is fed into the cavity and bent over the die radius to allow for straightening without fracture.The die radius should be between four and10times sheet thickness to prevent

45、wrinkles and splits.The compressive feeding or pulling of the blank circumferentially toward the punch and die cavity is called drawing.The draw action involves friction,compression and tension.Enough force must be present in drawing to overcome the static friction between the blank and blankholder

46、surfaces.Additional force is necessary during the drawing stage to overcome sliding or dynamic friction and to bend and unbend the sheet from the blankholder surface to the draw wall.As the blank is drawn into the punch,the sheetmetal bends around the die radius and straightens at the draw wall.To a

47、llow for the flow of material,the blank is compressed.Compressionincreases away from the die radius in the direction of material flow because there is more surface area of sheetmetal to be squeezed.Consequently,the material on the blankholder surface becomes thicker.The tension causes the draw wall

48、to become thinner.In some cases, the tension causes the draw wall to curl or bow outward.The thinnest area of the sheet is at the punch radius,and gradually tapers thicker from the shock line to the die radius.This is a probable failure site because the material on the punch has been work-hardened t

49、he least, making it weaker than the strain hardened material.The drawing stage continues until the press is at bottom dead center.With the operation now complete,the die opens and the blankholder travels upward to strip the drawn stamping off of the punch.Air vents provided inflat or female cavities

50、 of the punch allow air to travel under the material asit is lifted by the blankholder.The stamping will have a tendency to turn inside out due to vacuum in the absenceof air vents.4.Injection mold designThe plastic injection mold is in the present all plastics mold,uses the broadest mold,can take s

51、hape the complex high accuracy,plastic product.Under only is sketchily introduces.The design plastic injection mold first must have the certain,understanding to the plastic, the plastic principal constituent is a polymer.Like we often said the ABS plastic then is the propylene nitrile,the pyprolylen

52、e,the styrene three kind of monomers uses the emulsion,the main body or aerosol gathers the legitimate production,enable it to have three kind of monomers the high performance and may the compression molding,injects under the certain temperature and the pressure to the mold cavity,has the flow disto

53、rtion,the obtaining cavity shape,after guarantees presses cooling to go against becomes the plastic product.The polymer member assumes the chain shape structure generally,the linear molecule chain and a chain molecule thought is the thermoplastic,may heat up the cooling processing repeatedly, but pa

54、sses through heats up many members to occur hands over the association response,including forms netted the build molecular structure plastic usually is this,cannot duplicate injects the processing,also is the thermosetting plastics which said.Since is the chain shape structure,that plastic when proc

55、essing contracts the direction also is with the polymer molecular chain under the stress function the orientation and the cooling contraction related,must be more than in the flow direction contraction its vertical direction in contraction.The product contraction also with the product shape,the runn

56、er,the temperature,guarantees presses factor and so on time and internal stress concerns.In the usual book provides the shrinkage scope is broad,considers is product wall thickness,the structure and the determination casts the temperature pressure size when the practical application and the orientat

57、ion.The common product if does not have the core strut,the contraction correspondingly wants big.The plastic casts the mold basically to divide into the static mold and to move the mold.In the injection molding machine injection one side belt runner set is the static mold,the static mold has the run

58、ner wrap,the back,the template composition generally,the simple mold(is specially static mold does not have core moldalso to be possible not to use the back, straight took over the use of the thick template to be possible.The runner set is a standard letter generally,only if the special reason,does

59、not suggest the cancellation.A runner set of use is advantageous in installs the mold,the replacement is convenient,does not need oneself to polish.Some special molds runner wrap may use to drill or with the taper line shears.When the partial molds must the static mold drawing of patterns,but also must add on the static mold drawing of patterns organization.Moves the mold the structure for to move the template generall