Previous Page conventional mold and have to be compensated by material savings Thus, material losses in a corresponding eight-cavity mold could be reduced from 12 to 3% [6.47] In cases where multiple gating is needed for certain moldings (e.g headlamp reflectors), production without cold-runner cassettes is often not conceivable [6.46] Cold-runner technique for thermosets is also used in the so-called common-pocket process (Figure 6.62) A combination with this process is the RIC technique (Runnerless Injection Compression), which reduces scrap to a minimum in a simple way At the same time flashing is diminished The plasticated material flows through a temperaturecontrolled runner into the slightly opened mold and is distributed there The material is pushed into the cavities and formed by the clamping motion of the mold The material distributor penetrates the tapered sprue bushing and closes it against the parting line Temperature control keeps the material in the runner fluid and ready for the next shot [6.48] Figure 6.62 Cold runner mold Bucher/Mueller system with tunnel gate [6.47] 6.11 Special Mold Concepts 6.11.1 S t a c k M o l d s A special mold design has come into use, the stack mold, for molding shallow, small parts in large quantities such as tape cassettes Here, cavities are located in two or more planes corresponding to two parting lines and are filled at the same time (Figure 6.63) A molding machine with an exceptionally long opening stroke is needed An increase in productivity of 100% as one might expect from doubling the number of cavities cannot be realized because of the time needed for the longer opening and closing strokes The increase in productivity is about 80% [6.49] The clamping force should be 15% higher than for a standard mold [6.49] Hot manifolds are now employed exclusively A stack mold with two parting lines has three main components, a stationary and a movable mold half, and a middle section It contains the runner system (Figure 6.64) Ground connection Figure 6.63 Stack mold with hot manifold [6.47] A, B Parting lines; 1-3 Leader for center plate; 4a-4b Mold plates; 7-8 Cores; 9-10 Mold plates; 11 Leader for mold plates; 12 Leader bushing; 15 Heater for sprue; 16 Hot manifold; 17 Sprue to molded part; 18 Mold plate, as per 9; 19-23 Central sprue to machine as extended nozzle; 24 Sprue; 27 Stripper ring; 28 Ejector pins; 29-35 Ejector system; 39 Retainers; 42 Heated nozzle; ^ Interlocks The mold section mounted on the movable platen and the center section are moved in the direction of the machine axis during demolding With this, the extension is removed from the nozzle The extension has to be sufficiently long that no leakage material can drop onto the leader pins and stick there during mold opening This would impede their proper functioning [6.53, 6.54] For this reason many stack molds are operated today with telescopic extensions and without nozzle retraction While the outer section on the clamping side is mounted on the movable machine platen and moves positively with it during mold opening and closing, special elements are necessary to guide and control the movement of the center section Because of the frequently large size of the molds utilizing the whole platen area, center sections are attached to the tie bars or are guided by means of guide bars with guide shoes [6.53, 6.54] (see Figure 6.64) Today the motion is primarily produced by toggles or sometimes by racks (Figure 6.65) Previously systems were employed which used separate hydraulic cylinders for moving the center section Toggle and rack control open at both parting lines smoothly and simultaneously Toggle controls also offers the option of using, within a certain range, opening strokes of different lengths This allows the molding of parts with one height in one stack and parts with a different height in the other one The curves of the opening path can be Sprue Figure 6.64 Stack mold [6.16] Hot runner system for stack mold manifold and sprues and gates molds The sprue is normally mounted at the level of the mold center and feeds the melt into the middle of the hot runner manifold From there, the melt is distributed uniformly to all cavities of both mold daylights Movement with hydraulic cylinder Figure 6.65 Movement with toggle Movement with racks Methods of moving center section of stack molds [6.55] Figure 6.66 Toggle mechanism for stack molds [6.55] Movable clamping platen Stationary clamping platen Stripper ring Ca l mp ram Clamping unit Stripper plate Rack or lever system Figure 6.67 Ejector drive for stack molds [6.55] adjusted within a wide range depending on pivotal point and toggle geometry At the same time ejection is actuated by the same elements that move the center section Various kinds of toggle control are shown with Figure 6.66 The rack control in Figure 6.67 is less rigid and permits a gentle start and build-up of demolding forces because of springs in the pulling rods connected to the crank drive 6.11.2 M o l d s for M u l t i c o m p o n e n t Injection M o l d i n g There are a large number of multicomponent injection molding techniques, in terms of processes and of names, which are explained in Table 6.6 [6.56, 6.57] 6.11.2.1 Combination Molds Two-component combination injection molding in which two melts are introduced into the cavity in succession via separate gating systems requires special mold techniques since those areas of the mold that become filled by the second melt must be blocked off when the first material is injected, in order that it does not penetrate into those areas Table 6.6 Definition of several multicomponent injection molding processes Process name Definition Multicomponent injection molding All injection molding methods in which two or more materials are processed Several melts are injected via several gate systems into Composite injection molding the cavity in succession 2-Color injection molding As above, but using one material in different colors Multicolor injection molding Same as 2-color injection molding, but using more than colors 2-Component sandwich injection molding Two melts are injected in succession through a gate system, to form a core and outer layer Bi-injection Two melts are injected simultaneously via two gating systems into the cavity This separation has allowed the development of two-component combination injectionmolded parts, such as housings with integrated seals The separation may be effected in either of two ways: by the rotating mold systems shown in Figure 6.68 and by the non-rotating core-back technique shown in Figure 6.69 [6.57-6.59] Molds with Rotating Mold Platen or Rotating Mold Half A rotating mold has several gating stations and different cavities For a two-colored part, the first colored section is created by injection at the first mold position After sufficient time has elapsed for the melt to cool, the mold opens and the mold-part section turns 180° into the second position The mold closes to form the second cavity into which the second color or another material is injected via a second injection position In the first mold position, meanwhile, the first molded-part section is being created again In a similar fashion, three-colored parts can be made using three injection and mold positions and rotations of 120° The mold is rotated either by means of a standard rotary platform that can be attached to the machine, irrespective of the mold, or by means of a rotary device integrated into the mold that allows a rotary plate to operate The advantage of the standard rotary platform is its universal method of use, and in the smaller and less expensive design of the molds used Usually the mold platen on the ejector side is designed to be the rotating side since rotation of the nozzle-side mold platen is more complicated in terms of gating system and rotating system These molds require high precision mold making but are dependable in operation and not require any elaborate melt feed [6.57, 6.60] Typical applications are car tail light covers [6.60], three-colored keyboards [6.61], and the vent flaps of the Golf motorcar [6.62] Non-rotary mold system Core/back technq i ue Rotary mold systems Rotary platform Rotary mold Spiders or cores Transfer technique Figure 6.68 Rotary mold systems for composite injection molding Figure 6.69 Core-back technique Molds with Rotary Cores or Spiders In this technique, only part of the ejector- or nozzle-side cavity with injected premolding is rotated (Figure 6.70) Both mold platens remain in position Molds with Transfer or Insert Technique After the pre-molding is made in the first cavity, it is transferred by a handling device or by hand into the second cavity and molded to produce the final part with a second material The term transfer technique is also used to describe using a different machine for molding to produce the final part Generally, these molds are preferred to rotary molds for economic reasons because the complicated rotary device can be dispensed with, and usually more cavities can be accommodated on the mold platen Furthermore, thermal separation of the pre-molding and final-molding positions is easier to accomplish (particularly important for thermoplastic-thermoset laminates) Disadvantages are the need for precise centering of the pre-moldings [6.57] Molds with Retractable Slides and Cores (Core-Back Molds) With comparatively low mold costs, it is possible to produce multicolor or multicomponent injection molded parts in one mold without the need for opening the machine in between and further transport of a molded part by means of the core-back technique The cavity spaces for the second material are first closed by movable inserts or cores and are opened only after the first material has been injected The components can be arranged beside, above, or inside each other This method does not suit material pairs that will not join or bond to each other since it is not possible to produce effective undercuts for interlocking with the injection partner Furthermore, injection in these molds can only be carried out sequentially and not in parallel as in other methods This results in longer cycle times [6.57] Separate temperature control of the cores or inserts is beneficial since the temperature of the impact surface onto which the second melt is injected can be controlled more accurately [6.64] In combination injection molding, the rotary mold systems often employ hot runners for the pre-molding so as to yield a gateless pre-molding, since the gate interferes during Rotary platform technique, schematic [Source: Nefctal, 1997] Figure 6.70 [6.63] Overmolding by the rotary technique Here: toothbrush made of two components rotation or transfer [6.64, 6.65] and would otherwise have to be removed prior to transfer The choice of method for a particular molded part must be established individually from technical and, economic aspects for every application It must be remembered, however, that rotary mold systems are generally more expensive because of the need for two cavities and from the machine point of view, need a large distance between tie bars in order to be rotatable Rotary molds do, however, offer greater design freedom and the possibility of thermal separation of the kind required for the manufacture of rubberthermoplastic combinations (e.g PA/SLR) 6.11.2.2 T w o - C o m p o n e n t S a n d w i c h Injection M o l d s In contrast to combination injection molding, sandwich molding theoretically does not require a special mold technology and may be performed with standard injection molds Two melts are injected through a joint gating system into the cavity, to form a core and an outer skin The melts meet in an adapter between the nozzle peaks of the injection units and the sprue bushing of the mold It should be noted that all deviations from rotationally symmetrical molded-part geometry with central gating cause non-uniform core material distribution 6.11.2.3 Bi-lnjection M o l d s In this injection molding method, two different melt components are fed into the cavity simultaneously through different gating systems The weld line is affected by the positions of injection and wall thicknesses in the mold as well as by the injection parameters of the two components [6.68] References [6.1] KegelanguB, SchirmanguB, RinganguB, BandanguB Technical Information, 4.2.1, BASF, Ludwigshafen/Rh., 1969 [6.2] SpritzgieBen von Thermoplasten Publication, Farbwerke Hoechst AG, Frankfurt/M., 1971 [6.3] Sowa, H.: Wirtschaftlicher fertigen durch verbesserte AnguBsysteme Plastverarbeiter, 29 (1978), 11, pp 587-590 [6.4] Kohlhepp, K G.; Mohnberg, J.: SpritzgieBen von Formteilen hoher Prazision, dargestellt am Beispiel von Polyacetal Kunststoff-Berater, 10 (1974), pp 577-584 [6.5] Crastin-Sortiment, Eigenschaften, Verarbeitung Publication, Ciba-Geigy, Basel, August 1977 [6.6] Christoffers, K E.: Formteilgestaltung, verarbeitungsgerecht Das SpritzguBteil VDIVerlag, Dusseldorf, 1980 [6.7] TunnelanguB, AbreiB-Punkt-AnguB Technical Information, 4.2.3, BASF, Ludwigshafen/Rh., 1969 [6.8] Thonemann, O E.: AnguB- und Anschnitt-Technik fur die wirtschaftliche Herstellung von SpritzguBteilen aus Makrolon Plastverarbeiter, 14 (1963), 9, pp 509-524 [6.9] Kunststoffverarbeitung im Gesprach, 1: SpritzgieBen Publication, BASF, Ludwigshafen/Rh., 1979 [6.10] SpritzguB-Hostalen PP Handbook Farbwerke Hoechst AG, Frankfurt/M., 1980 [6.11] Vorkammer-PunktanguB-Isolierverteiler Technical Information, 4.2.4, BASF, Ludwigshafen/Rh., 1969 [6.12] Durethan BK Tech Ringbuch der Farbenfabriken, Bayer AG, Leverkusen, 1967 [6.13] Goldbach, H.: HeiBkanal-Werkzeuge fur die Verarbeitung technischer Thermoplaste (ABS, PA, PBT, PC) Plastverarbeiter, 29 (1978), pp 677-682, and 30 (1979), pp 591-598 [6.14] Gauler, K.: HeiBkanalsysteme mit Ventilanschnitten Kunsstoffe, 87 (1997), 3, pp 338-340 [6.15] Homes, W.: KaskadenspritzgieBen vermeidet Bindenahte Kunststoffe, 86 (1996), 9, pp 1269-1272 [6.16] Husky: Husky-HeiBkanalsysteme Werkschrift der Husky Injection Moulding Systems Ltd., Bolton, Canada, D-62507 Wiesbaden-Igstadt, Phone: +49 611 950 850 [6.17] Leidig, K.; Poppe, E A.; Schinner, K.: Technische Kunststoffe: Die Top Ten der SpritzgieBprobleme Schwierigkeiten mit HeiBkanalen (8), DuPont de Nemours GmbH, D-61343, Bad Homburg [6.18] Eiden, G.: Werkzeuge fiir die Herstellung von Prazisionsteilen aus technischen Thermoplasten Reprint of 8th Tooling Conference at Wiirzburg: Der SpritzgieBformenbau im internationalen Wettbewerb September 24-25, 1997 [6.19] Braun, P.: Innenbeheizte HeiBkanalsysteme Kunststoffe, 87 (1997), 9, pp 1184-1886 [6.20] HeiBe Seiten Plastverarbeiter, 48 (1997), 10, pp 96-98 [6.21] Braun, P.: Universelles HeiBkanalsystem Osterr Kunststoffzeitschrift, 28 (1997), 5/6, pp 98-102 [6.22] Sander, W.: Homogene Schmelze-Temperaturverteilung mit Standard-Elementen Plastverarbeiter, 42 (1991), 12, pp 55-59 [6.23] RoBbach, R.: Schmelzefilter fur den SpritzgieBer Kunststoffe, 85 (1995), 2, pp 193-195 [6.24] Zimmermann, W.; Hack, K.: Einfaches HeiBkanal Schmelzeleitsystem fiir SpritzgieBwerkzeuge Plastverarbeiter, 44 (1993), 4, pp 18-22 [6.25] Konstruktionszeichnung H Weidmann AG, Raperswil/Schweiz [6.26] HeiBkanalsystem - Indirekt beheitzter Warmeleittorpedo C.2.1 Technische Kunststoffe, Berechnen - Gestalten - Anwenden Publication, Hoechst AG, Frankfurt/M., October 1979 [6.27] Mit Microelektronik Temperaturen genau regeln Plastverarbeiter, 41 (1990), 5, pp 78-80 [6.28] Der HeiBkanal Publication, Plastic Service GmbH, Mannheim [6.29] Catalog Firma Hotset, Ludenscheid [6.30] Publication Tiirk und Hillinger, Zuttlingen [6.31] Warmeverluste an HeiBkanalblocken - Reflektorbleche schaffen Abhilfe Plastverarbeiter, 37 (1986), 4, pp 122-123 [6.32] Schauf, D.: AnguBloses Entformen von SpritzguBteilen In: Das SpritzgieBwerkzeug VDIVerlag, Dusseldorf, 1980 [6.33] Krehwinkel, T.; Schneider, Ch.: Kaltkanaltechnik-pro und contra In: SpritzgieBen und Extrudieren von Elastomeren, VDI-Gesellschaft Kunststofftechnik, VDI-Verlag, Dusseldorf, 1996 [6.34] Cottancin, G.: Gummispritzformen mit dem Kaltkanalverfahren Kautschuk Gummi Kunststoffe, 33 (1980), 10, pp 839-841 [6.35] Kaltkanaltechnologie beim ElastomerspritzgieBen Publication, Klockner Ferromatic Desma, Werk Achim, 1983 [6.36] Schneider, Ch.: Das Verarbeitungsverhalten von Elastomeren im SpritzgieBprozeB Dissertation, RWTH, Aachen, 1987 [6.37] MaaB, R.: Die Anwendung der statistischen Versuchsmethodik zur Auslegung von SpritzgieBwerkzeugen mit Kaltkanalsystem Dissertation, RWTH, Aachen, 1995 [6.38] Cottancin, G.: Gummispritzformen fiir das Kaltkanalverfahren Gummi, Asbest, Kunststoffe, 33 (1980), 9, pp 624-633 [6.39] Bode, M.: SpritzgieBen von Gummiformteilen In: SpritzgieBen von Gummiformteilen VDI-Verlag, Dusseldorf, 1988, pp 1-33 [6.40] Cottancin, G.: Gummispritzpressen mit dem Kaltkanalverfahren Gummi, Asbest, Kunststoffe, 33 (1980), 9, pp 624-633 [6.41] Lommel, H.: Einfliisse der ProzeBgroBenverlaufe un der Werkzeuggestaltung auf die Qualitat von Elastomerformteilen Unpublished report, IKV, 1984 [6.42] Holm, D.: Aufbau von Werkzeugen fiir SpritzgieBmaschinen In: SpritzgieBen von Elastomeren VDI-Verlag, Dusseldorf, 1978 [6.43] Benfer, W.: Rechnergestiitzte Auslegung von SpritzgieBwerkzeugen fiir Elastomere Dissertation, RWTH Aachen, 1985 [6.44] Menges, G.; Barth, R: Erarbeitung systematischer Konstruktionshilfen zur Auslegung von Kaltkanalwerkzeugen AIF-AbschluBbericht, IKV, Aachen, 1987 [6.45] Kloubert, T.: Reduzierung von ausgehartetem AnguBmaterial beim SpritzgieBen von rieselfahigen Duroplasten - Kaltkanaleinsatz und Partikelrecycling Dissertation, RWTH, Aachen, 1996 [6.46] Niemann, K.: Kaltkanaltechnik-Stand und Einsatzmoglichkeiten bei Duroplasten AnguBminimiertes SpritzgieBen, SKZ, Wiirzburg, June 23-24, 1987 [6.47] Gluckau, K.: Wirtschaftliche Verarbeitung von Duroplasten auf SpritzgieBmaschinen in Kaltkanalwerkzeugen Plastverarbeiter, 31 (1980), 8, pp 467^69 [6.48] Braun, U.; Danne, W.; Schonthaler, W.: AnguBloses Spritzpragen in der Duroplastverarbeitung Kunststoffe, 77 (1987), 1, pp 27-29 [6.49] Hotz, A.: Mehr-Etagen-SpritzgieBwerkzeuge Plastverarbeiter, 29 (1978), 4, pp 185-188 [6.50] Hartmann, W.: SpritzgieBwerkzeuge in Etagenbauweise mit "Thermoplay"HeiBkanaldiisen fur Verpackungs-Unterteile aus Polystyrol Plastverarbeiter, 32 (1981), 5, pp 600-605 [6.51] Moslo, E R: Runnerless-Moulding SPE-Journal, 11 (1955), pp 26-36 [6.521 Moslo, E R: Runnerless-Moulding New York, 1960 [6.531 Lindner E.; Hartmann, W.: SpritzgieBwerkzeuge in Etagenbauweise Plastverarbeiter, 28 (1977), 7, pp 351-353 [6.54] Schwaninger, W.: Etagenwerkzeuge insbesondere als Alternative zum Schnellaufer Der SpritzgieBprozeB, Ingenieurwissen, VDI-Verlag, Dusseldorf, 1979 [6.55] Publication, Husky [6.56] Eckardt, H.: MehrkomponentenspritzgieBen - Neue Werkstoffe und Verfahren beim SpritzgieBen VDI-Verlag, Dusseldorf, 1990, pp 149-194 [6.57] Langenfeld, M.: Werkzeugtechnik zur Herstellung von Mehrkomponenten-SpritzgieBteilen Mehr Farben - Mehr Materialien - Mehr Komponenten - SpritzgieBtechnik, SKZ, Wurzburg, May 1992, pp 83-102 [6.58] Eckardt, H.: Verarbeitung von TPE auf SpritzgieBmaschinen und Moglichkeiten der Anwendung des Mehrkomponenten-SpritzgieBens Thermoplastische Elastomere im Aufwartstrend, SKZ, Wurzburg, October 1989, pp 95-123 [6.59] Kraft, H.: "Erweiterte Anwendungsbereiche fur das Mehrkomponenten-SpritzgieBen" In: Kunststoffe, 83 (1993), 6, pp 429-433 [6.60] Bodeving, C : "Horizontalmaschine mit Drehtisch" In: Kunststoffe, 85 (1995), 9, pp 1244-1254 [6.61] "Beweglich aus dem SpritzgieBwerkzeug" In: Plastverarbeiter, 36 (1985), [6.62] "Vollbewegliche Lufterklappen bei jedem Spritzzyklus" In: Plastverarbeiter, 44 (1993), [6.63] Netstal News No 31, Netstal-Maschinen AG, Nafels/Schweiz, April 1997 [6.64] "HeiBkanaltechnik beim Mehrkomponenten-SpritzgieBen" In: Plastverarbeiter, 45 (1994), 10 [6.65] Krauss, R.: SpritzgieBtechnik fur die Mehrfarbentechnik In: Konstruieren von SpritzgieBwerkzeugen, VDI-Verlag, Dusseldorf, 1987, pp 6.1-6.18 [6.66] Mehr-Rohstoff-Technologie Publication Battenfeld, Meinerzhagen, September 1996 [6.67] "Combimelt-Technologie fur Mehrfarben und MehrkomponentenspritzguB" In: KGK Kautschuk, Gummi, Kunststoffe, 49 (1996), 7-8 [6.68] Johannaber E; Konejung, K.: Mehrkomponenten-Technik beim SpritzgieBen Mehr Farben - Mehr Materialien - Mehr Komponenten - SpritzgieBtechnik, SKZ, Wurzburg, May 1992, pp 7-20