Maintenance of Injection Molds

15 M a i n t e n a n c e of Injection M o l d s Injection molds represent a major investment for plastics processors They constitute a large position of the company's assets and are the basis for production, economic success, and technical development For these reasons, injection molds must be in good working order and ready for use In practice, however, situations frequently arise in which defects and improper maintenance of injection molds cause major disruptions to current production, occurring particularly during modifications This reduces the actual working time of the injection molding machines and continually impedes proper, planned production Against this background, back in 1992, an industrial survey by the Institute for Plastics Processing (IKV) in Germany [15.1] showed that on average almost 7% of possible production time was lost due to damage to injection molds (Figure 15.1) Comparison with the results from 1973 clearly show that this figure has more than doubled in twenty years As opposed to that, the proportion of machine-related downtimes is much lower Technological developments in injection-molding machines have lowered the proportion by as much as one third In view of this situation, it is difficult to understand why injection molding shops, which would frequently have to maintain as many as 1000 molds, still employ the "fire brigade" approach, by which is meant that a mold is only repaired when it has failed The industrial survey mentioned above [15.1] showed that only 30% of injection molding shops carry out preventive maintenance at fixed intervals In these shops, again, only one third of the maintenance data is recorded and evaluated systematically It follows from this that only 10% of injection molding shops perform preventive maintenance founded on a sound database [15.1] Downtime [%] 4.4% Injection molding machn i es 6.1% 2.9% Figure 15.1 Change in production downtimes 1973 Injection mod ls Year 6.8% 1992 The situation just described may be used to illustrate the deficits arising during the maintenance of injection molds (Figure 15.2) The state of the art is such that while damage and cost data are recorded, they often cannot be combined with each other While such information, which represents invaluable experience for mold-making, is Work preparation Design State of the art Maintenance/ mold making Production Downtimes Repair times Downtime causes Repair costs Inspection report Spare parts Maintenance report Archiving/documentation Data evaluation/weak point analysis Choice of strategy Figure 15.2 State of data acquisition and evaluation Experience feedback Experience feedback Data capture archived, it merely serves documentation purposes The goal should be, however, to use this invaluable practical experience as a basis for preparatory work and design Much as damage to molds is of interest, its causes are even more important It turns out that, of the most frequent causes of damage, wear comes top of the list This is followed by set-up errors and operating errors The similarly relatively high proportion of design errors can, among other things, often be attributed to poor communication between those responsible for mold maintenance and mold design [15.2] (no feedback or archiving) Since every injection mold is unique, it is not possible to generalize about maintenance Commonplace are maximum possible standardization, the use of mold standards, easy accessibility and exchangeability of parts on the injection molding machine where possible, and the wear-resistant construction of friction pairings But there are invaluable hints to be gained for individual molds, particularly from use It will be shown below how these signs of weak points taken from production can be recorded so as to reduce costs and to optimize processes in production and mold-making 15.1 A d v a n t a g e s of M a i n t e n a n c e Schedules Figure 15.3 compares the work processes involved when the "fire brigade" and the preventive strategies are employed, in terms of attainable machine utilization and resultant downtimes Examples from shop practice prove the efficacy of performing scheduled preventive maintenance Constant monitoring of the throughput times of maintenance jobs or actual repair times (Figure 15.4) permit measures to be taken so as to increase efficiency (e.g., Disruption Report Start of repairs Startup Passed parts Scrap "Fire brigade" l psed time Production Ea strategy till reported Maintenance job Standstil Standstil Waiting for repairs Repairs Scrap Production Startup Passed parts Preventive strategy Production Preventive maintenance Startup Production Production time gained Figure 15.3 Time scheme for application of different maintenance strategies Fraction [0A] 1989 1990 1991 Up to Up to 10 Up to 15 Up to 20 Over 20 Repari times [hours] Figure 15.4 Decreasing repairs over the years investment in new machining equipment) and decrease the throughput times for maintenance and for production through reducing downtimes This effect is reinforced by purposeful preparation of the measures to be implemented (e.g., provision of equipment and spare parts), much as when set-up preparations are made when molds are changed As may be seen in Figure 15.4, the proportion of quick repairs has increased in our example while the proportion of longer-lasting ones has receded over the years, as a result This clearly illustrates the success of the measures implemented 15.2 Scheduling Mold Maintenance 15.2.1 D a t a Acquisition The choice of molds to examine first necessitates the acquisition of detailed data Since various factory studies revealed that a great deal of acquired data are not used, particular value should be attached to goal-oriented or need-oriented data acquisition The goal of data acquisition must be the provision of informative maintenance data in the form of feedback to staff in design, work preparation and mold making (Figure 15.2) Data on mold maintenance is essentially required in two areas The first is the control and monitoring of the direct and indirect costs that arise It should be possible to report on all molds, a particular class of molds, an individual mold, or a functional group The second is selective weak-point analysis, which requires detailed data acquisition Here, a distinction needs to be made between the damage that occurs and its actual cause [15.4] The mold data can be stored in a type of lifetime As shown in Figure 15.5, the data for each individual mold should be recorded in the form of a lifetime data record Item is the mold identification number To be able to schedule maintenance measures or intervals, the number of cycles needs to be known as it is a wear-determining factor (item 2) It is also important to establish if the maintenance measure is scheduled or nonscheduled (item 3) For referencing purposes, the functional system where the damage occurred must be noted (item 4) Description of the damage (item 5) and, where possible, the cause (item 6) should be coded for the weak-point analysis Space is also required for a brief comment The costs are entered into item 8, separated according to direct and indirect costs, for the purposes of evaluation The mold lifetime can be kept for all injection molds by a central unit and forms a good basis for informative evaluations To illustrate the need for cost-related data acquisition, two evaluations of a mold resume will now be presented In the first, the maintenance activities were assigned to the various functional groups The sum of the activities and the relation to the total instances of damage are shown in Figure 15.6 In this example, repairs to the demolding system were the most frequent (50%), followed by mold cavities at 14% The other functional groups sustained much less damage, amounting to less than 10% However, reporting mold damage in terms of the number of repairs is not satisfactory It is important to link each event with the time for repair and the costs incurred In this example, it made sense to use the available data to weight the damage susceptibility of certain modules according to the number of maintenance hours incurred This afforded the possibility of making a concrete, value-based evaluation Recording an event in the mold lifetime Mold lifetime Unschedue ld Cycles Date ID No.: Key Category Abbrev.: Door handle Ma int costs Indirect Direct System date 123.456 123.457 123.458 123.459 Cycles: ISchedue lc n/y Gate Figure 15.5 Data in a mold lifetime Cavity Temperature control Demolding Leader/locating Power transmission lWear Setup error Material failure Jammed Fracture Initiate job Reverse job Temperature control 4% Demod ln ig 50% Cavity 43% Cavity 5% Gate 1% Leader and locating 6% Temperature control 5% Gate 5% Leader and locating 5% Others 25% After evau l ato i n of a modl lifetime I 100% = 70 reparis Figure 15.6 Damage frequency for a single injection mold Demolding 21% After evau l ato i n of 830,000 cyce ls 100% = 539 man itenance hours Figure 15.7 Maintenance hours expended on a single injection mold Application of this approach to the same injection mold yielded the distribution of maintenance hours that is shown in Figure 15.7 This modified damage distribution is based on a total of 539 maintenance hours for a mold that carried out roughly 830,000 cycles in the production period concerned This analysis differs enormously from that based on the number of activities While mold cavity and demolding still constitute the most damage, their ratio is now reversed: demolding: cavity: previously 50% - now 21%, previously 14% - now 43% This reversal is logical considering that an ejector can generally be replaced very quickly, but a repair to what often is a polished or chrome-plated mold cavity is relatively time-consuming From the economics point of view and for the purpose of establishing a work-benefit ratio of maintenance measures, the analysis shown in Figure 15.7 must be considered to be more informative Conventional data acquisition using forms still serves a purpose, especially if it is only a temporary measure A company will resist the unavoidable effort involved until it recognizes the advantages that this approach has to offer [15.5] Although computer support should be the long-term goal, despite the considerable work involved for evaluation, forms can be used with great effect in a pilot project or for multiple instantaneous records Generally, however, there is no extra work involved for the company as most already perform data acquisition, even if this does not always satisfy the criteria for an evaluation 15.2.2 D a t a Evaluation a n d W e a k - P o i n t Analysis A major goal of data acquisition and evaluation is to illustrate the failure modes of injection molds This goal is served by the answers to the various questions, such as: - What are the most common types of damage? Which functional system of an injection mold is most frequently affected by damage? Which molds are the most susceptible? What are the most common causes of damage? Which types of damage cause the most trouble? Maintenance costs [%] The financial effects will not be discussed in detail here Instead, the focus will be on technical aspects and possible consequences A determination of the proportion of the most serious types of damage and their causes can reveal, for instance, that only five types account for more than 50% of all failures [15.6] This provides those responsible in mold making with a direct starting point for eliminating the weak points A "Pareto Principle" can be derived from this relationship; it states that a small number of monitored types of damage will incur by far the most costs [15.7] Also known as the "ABC method", this can be illustrated as shown in Figure 15.8 This tool can considerably reduce the amount of work involved in that it restricts attention to the greatest causes of costs incurred by molds on the one hand (Figure 15.8, top) and investigates only the most important types of damage for these on the other (Figure 15.8, bottom) To make acquisition and evaluation of the various types of damage ascertained as easy as possible, a numbering system should be employed for the various types, just as was done for the various mold parts For the sake of clarity, initially no more than 10 types of damage should be identified per functional system Implemented as a numbering system, this means that ejector fracture would have a two-digit number (e.g., 41 where = demolding system and = ejector fracture) For five functional systems, this would allow fifty different types of damage to be described The particular advantage of this is unambiguous identification of damage during data acquisition - employees are not using Ca l ss CCa l ss B Ca l ss A Ca l ss A: 10% Molds 75% Costs Ca l ss B: 25% Molds 15% Costs Ca l ss C: 65% Molds 10% Costs Maintenance costs [%] Number of molds [%] Figure 15.8 ABC analysis of damage Ca l ss CCa l ss B Ca l ss A Mold damage [%] Ca l ss A: 10% Damage 75% Costs Ca l ss B: 25% Damage 15% Costs Ca l ss C: 65% Damage 10% Costs their own descriptions for the same type of damage Furthermore, the numbering system allows direct classification and access to the corresponding work plan It also helps to smooth the transition to a computer-based support system 15.2.3 C o m p u t e r - B a s e d S u p p o r t Crucial to the use of a computer system are the functions provided for data evaluation, which must suit the case at hand A peculiarity arises from the fact that injection molds are not fixed permanently in one place, but rather have to be tracked as movable inventory A computer system must therefore be able to accommodate the respective status with more detailed information (e.g., in the mold department for repair until approx .) This information serves production control for planning subsequent production orders as well as maintenance in the planning of preventive measures From the point of view of the prime aim of a maintenance analysis, a computer system must be in a position to provide the following functions: - acquisition of all relevant data in a mold lifetime, - support for ABC analyses for all molds, mold groups, functional systems, and mold damage, - comprehensive support in the evaluation of lifetime data, - presentation of percentage types of damage for a single mold or mold group, - possibility of classifying damage within a functional system, - presentation of the proportion of a certain type of damage in a mold group, - presentation of the maintenance measures for the service life in cycles, - comparison of intervals between occurrences of a particular type of damage, - presentation of the frequency of the damage that has occurred with the goal of weakpoint analysis, - tracking of repair times, comparison of in-house/external share, etc The ultimate goal of the evaluations must be to eliminate primarily those weak points that incur the highest costs An example of such a presentation is shown in Figure 15.9 This allows the costs of the different functional systems of a specific mold to be compared If a functional system becomes noticeable because of extremely high maintenance, it must be possible to call up more detailed information on the proportions of the various types of damage The special advantage of this presentation comes to the foreground when an evaluation can be performed separately on the basis of direct and indirect costs In this case, those weak points whose direct costs were not high enough to cause concern can be uncovered if they lead to indirect costs in the form of lost profit contributions due to equipment downtimes 15.3 S t o r a g e a n d C a r e of Injection Molds Injection molds have a limited service life (Table 15.1) Appropriate measures can greatly extend this, however Such measures can be classified on the basis of: - maintenance, - storage, and - care Evaluation of a mold lifetime ID No.: 123.456 Abbrev.: Door handle 250.000-500.000 Cycle maintenance costs yirect Mold cycles Gate Cavity Temperature control Demolding Leader and locating Damage cause tables: Leader and locating Cavity (4-cavity model) Figure 15.9 Weak point analysis based on mold lifetime Contamination Corrosion Demolding Temperature control Gate Table 15.1 Numbers of molded parts obtainable with various mold materials [15.8] Material Zinc alloys Aluminum Aluminum Copper-beryllium Steel Attainable number Casting Casting Rolled Surface hardened 100,000 100,000 100,000-200,000 250,000-500,000 500,000-1,000,000 To be able to quickly fall back on ready-to-use molds, the following demands on storage and care must be fulfilled: - every mold must be stored along with one molded part and a mold card in its own, easily accessible space in the mold store, - only ready-to-use, complete, clean molds may be stored The purpose of also storing a molded part (usually the last one from previous production) and a mold card bearing the article number and the mold number is to allow the mold to be uniquely identified The mold card should also bear all the information needed for setting up the mold and starting up the injection molding machine Information in this category includes the following: - mold design (split, sliding split, unscrewable mold etc.), dimensions of the mold and the molded part, mold mounting equipment, injection molding machine suitable for production, shot weight (injection volume), suitable plastic, rules on material pretreatment, processing temperatures, mold temperature and heat-control medium (water, oil, etc.), cycle times, injection pressure, follow-up pressure, dynamic pressure, injection speed, screw speed, cylinder equipment (sliding shut-off nozzle, non-return valve), maintenance intervals, number of pieces produced This list could be extended and thus matched to the special needs of a factory Instead of on a mold card, much of this information, such as the settings for the injection molding machine, could be stored on external data storage media that could be read into the control unit prior to production startup Mold changes can only be performed quickly if the molds are ready for use when they leave the stores and can go into production without the need for major assembly or cleaning work Every mold must therefore be a self-contained unit, i.e., it must not be made of parts that are required for other molds Parts or groups of parts that are "loaned" or "borrowed" often disappear or are needed elsewhere just when the mold is scheduled for use The consequences are unnecessary, incalculable, and often time-consuming downtimes Cleaning work also delays the start of production It should therefore be kept to a minimum This means that special care has to be taken of the molds (discussed later) and imposes specific demands on the store, its cleanness and particularly the ambient conditions Damp and unheated rooms promote corrosion Once rust has begun to attack the mold, maintenance becomes very time consuming and very expensive Often it is impossible The mold store should therefore be kept at a constant temperature where possible, and dehumidified Not much equipment is required for this, and it soon pays for itself Important to the accessibility of the molds is also the size of the store It is essentially determined by the vehicles available in the factory (e.g., forklift) and the maneuvering space When a job is complete, the mold may only be returned to storage when its suitability for future use has been checked The last parts produced with it can provide an indication of its condition They must be examined for dimensional stability and closely scrutinized This will provide information about the state of the mold surface, the level of seal in the mold parting line (perhaps flash formation on the molded part) and the working order of the ejectors, ejector bushes, etc If no deficiencies are found, the maintenance work then takes the form of the general care measures described below Maintenance of Cooling Lines Cooling lines must be cleaned thoroughly to eliminate scale, rust, sludge, and algae Since these deposits decrease the diameter of the channels, measuring the flow rate is a way of checking the system A pressure-controlled valve is installed between mold and water line and a defined pressure drop is set, which has to be the same for each examination If the flow rate was measured with the new mold, a comparison with any new measurement after a production run provides information about the degree of clogging of the cooling channels For cleaning, the cooling lines are usually flushed with a detergent because mechanical removal of the deposit is generally not feasible due to the geometry of the system Detergents and special cleaning equipment are marketed by several producers [15.9, 15.10] A solution of hydrochloric acid (20° Be) with two parts water and a corrosion inhibitor has been successfully used The nipples, bridges, bolts and feed lines (tubes) outside the mold are also checked for damage and replaced where necessary, provided they stay on the mold Before the mold is stored, water has to be removed with compressed air and the system dried with hot air Care and Maintenance of the Mold Surfaces After the end of production, the mold must be carefully cleaned of any adhering plastic residue The work is independent of the type and amount of molding material It is advisable to use soap and water for removing material remnants and other deposits The mold then has to be dried carefully Rust spots from condensed water or aggressive plastics have also to be removed before storage Depending on the degree of chemical attack, abrasives for grinding and polishing (car polish) may be suitable Removal of residual lubricants from movable mold components is also part of the cleaning operation Degreasing detergents for this are available on the market Care and Maintenance of the Heating and Control System This work is particularly important for hot-runner molds After each production run, heater cartridges, heater bands, and thermocouples should be checked with an ohmmeter and the results compared with those on the mold card Accidental grounding should be investigated, too The control circuits are easily tested with an ammeter installed in the circuit A check should also be made to ensure that lines, connections, insulation, and main lead cleats are in proper working order Care and Maintenance of Sliding Guides The guides on movable mold parts require particularly careful cleaning and must be washed with resin-free and acid-free lubricants Also check the level of seal in the cylinder in the case of hydraulically actuated slides and cores Care and Maintenance of the Gate System Start checking at the nozzle contact area, which is subjected to very high loads during operation Check also any special nozzles belonging to the mold In the case of temperature-controlled gates that are not generally demolded with every shot, it is necessary - to an extent depending on the plastic processed - to flush the gating system until the end of production with a plastic that has wide processing latitude Care Prior to Storage At the end of each maintenance work, the mold has to be carefully dried and lightly greased with noncorrosive grease (petrolatum) This is especially important for movable parts such as ejector assembly, slides and lifters, etc For extended storage, the mold should be wrapped in oil paper Greasing and wrapping of the mold in oil paper is crucial when the mold store does not satisfy the demands above and below AU observations and maintenance work are recorded on the mold card [15.11, 15.12] 15.4 Repairs a n d Alterations of Injection Molds Injection molds can be subjected to extreme conditions during operation This gives rise to wear symptoms that are due to rolling, sliding, thrusting, and flowing movements A survey of the various kinds of wear, their causes and symptoms is provided in Figure 15.10 Manifestation, progression, results Seizing, cratering, grooving, running, clearance, chatter marks Rolling wear with and without slippage Pitting, peeling, spoiling, rippling, seizing, grooving Wear by shock Break out, peeling, pitting Vibrational wear Roughenn ig seizing, oxide fluttering, fretting Particle, sliding and rolling friction wear Grooving, break out, rolling tracks Sliding friction wear Erosive wear Characteristic Sliding friction Abrasive With and without lubrication (metals, plastics, solids) Type of wear Initial conditions Counter-particle Particle furrowing a) Grooving, break out, furrowing embedding, smoothing a) b) b) Flat grooves, washout Hydroabrasive wear, radiation wear, other erosive wear Figure 15.10 Overview of types of wear [15.13] Waves, cavities, piercing, washout The consequences of wear are dimensional inaccuracy, flawed surfaces and flash on the molded part Before the damage can be repaired, the cause must be determined Remedial measures require a detailed knowledge of the cause of damage The following are possible: - simple mechanical finishing, - replacement of parts or modules, - deposition of material Leaky parting planes are typical injection molding damage When this is not very extensive, it can be eliminated by grinding However, this is limited by the tolerances imposed on the molded-part dimensions Minor damage to the mold surface (pits) that can be attributed to impact can be remedied by reboring, remilling, and then setting pins or wedges Once the flaw has been treated, the mold is heated and the drill hole or groove closed with a cold insert (slightly overdimensioned) The repaired spot is then rendered flush with the mold surface by grinding or polishing It is important to use the same type of material for this repair work, as the repaired area should have the same material properties as the rest of the mold surface Damage to functional and mounting parts, such as guide pins and bushings, ejectors, locating flanges, nozzles, etc., should not be repaired These are normally standard parts (see Chapter 17) available in various dimensions and can thus be replaced cheaply Doing this means that the molds will function perfectly and avoid any major risks The repairs described so far will often be inadequate and material will have to be deposited because, e.g., edges or corners have broken off Welding is necessary in such cases Repair welds to injection molds should always be preceded by heating to keep thermal stress and the formation of internal stress as low as possible Preheating avoids compression and shrinkage in the weld zone and, above all, prevents heat from being dissipated so quickly from the weld area that hardening sets in (as when heated parts are quenched in oil or water) The preheating temperature (at which the workpiece must be kept during welding) depends on the material to be welded, and in particular on its chemical composition Steel manufacturers provide details of this During welding, the workpiece must be kept at the preheating temperature When welding is complete, it is cooled to between 80 and 100 0C and then reheated again to the normalizing temperature [15.14] Welding repairs are performed by the TIG method and welding with coated electrode wires TIG (tungsten inert gas) offers distinct advantages The following basic rules must be observed for repair welding: - The electrode wire material should be of the same composition as the mold material, or at least similar Ensuing heat treatment of the weld results in equal hardness and structure [15.14] - The amperage has to be kept as low as possible to prevent reduced hardness and coarse structure [15.14] - The preheating temperature must be above the martensite-forming temperature It can be taken from the respective temperature-time phase diagram for the steel It should not be considerably higher, however, since it increases the depth of burn-in [15.14] - During the entire welding process, the mold must be kept at the preheating temperature This is particularly the case for several deposits - At edges, the molten material needs to be supported This can be effected with copper pieces or copper guide shoes that can be water-cooled if necessary Very recently, lasers have been used for repair welding of molds Mostly these are pulsed solid-state lasers, e.g., ND-YAG lasers, with laser capacities of 50-200 Watt for hand welding The great advantage of laser welding over "conventional welding" is that low amounts of energy are applied with extreme precision to the welding site Due to the very short welding impulses (1-15 milliseconds max.), the heated zone is very small, in the order of a few hundred millimeters Thermal stress on the mold is therefore slight Laser welding is more or less distortion-free [15.15] Figure 15.11 shows which welding depths and seam widths are possible with lasers Only relatively minor damage can be repaired in one working operation Spot welding Seam welding Up to mm Up to mm Spot diameter 0.2-2 mm Diameter: depth ratio = 1:3 for small diameter = 1:1 for large diameter 0.2-2 mm Figure 15.11 Possible welding depths and seam widths in laser welding [15.15] The electrode wire material is generally < 0.5 mm in diameter, a small portion of which is melted onto the mold with every welding pulse The wire material is available in different thicknesses and compositions The welding process itself is observed through a stereomicroscope fitted with a proper shield Due to the expected and actual difficulties inherent in all forge welding techniques, the calls for "cold metal-deposition processes" are understandable One such process is electrochemical metallizing for depositing all kinds of metals and alloys on almost all metallic materials Dimensional corrections up to several tenths of a millimeter are possible with this method on flat surfaces, shafts, and in drill holes [15.16] The steps required in effecting a repair (Figure 15.12) vary with the type and extent of the damage Major damage (deeper than 0.5 mm) is first rebored and the hole sealed with pins Then the damaged area, e.g., minor damage, is ground out in a hollow and sandblasted or electrochemically cleaned with a so-called preparatory electrolyte An area treated in this way, free of grease and oxide, is optimally prepared for metal deposition Figure 15.12 Working stages in electrochemical metal deposition [15.16] Flaw; Pins inserted; Cavity ground out; Cavity metallized with rapid-depositing electrolyte; Leveling of metal filling (mechanical); Transition to intact surface, covered with hard finishing layer The repair area is then sealed off with galvanic sealing tape and the ground-out hollow is filled with a fast-depositing metal such as copper or nickel and mechanically flattened The damaged area is then ready for sealing flush to the mold surface with an appropriate covering metal [15.16] Sealing is carried out by soaking a graphite anode surrounded with an absorbent material in the desired high-performance electrolyte and moving it across the area to be coated Under direct current, the metal is deposited onto the cathode, i.e., the mold surface There are also micro-cold or deposit welding devices [15.17, 15.18] on the market that operate on the principle of resistance pressure welding The most common application of this process is spot welding Resistance pressure welding uses the heat generated by the electric current in overcoming the electric resistance at the point of contact with the parts to be welded At the points of joining, the parts become pasty and are pressed together without the need for additional materials [15.19] For repair welding of molds, e.g., filling out of hollows, one "part for welding" is replaced, e.g., by a steel tape which covers the hollow During welding, the electrode is rolled along the steel tape, and pressed at the same time against the area to be repaired The steel tapes are available in thicknesses of 0.1 to 0.2 mm For deeper hollows, the process has to be repeated For minor repairs, e.g., to edges or corners, the steel tape is replaced by metal powder or metal paste [15.17] The repaired areas can then be machined afterwards and polished to a high finish Hardening and coating are also possible Metal-depositing processes are risky ways of effecting repairs, require dexterity and good knowledge of material behavior and the actual process employed References [15.1] Michaeli, W.; Feldhaus, A.; Eckers, C ; Lieber, T.; Pawelzik, P.: Instandhaltung von SpritzgieBwerkzeugen - Ergebnisse einer Befragung von SpritzgieBbetrieben Prospectus, IKV, 1992 [15.2] [15.3] [15.4] [15.5] [15.6] [15.7] [15.8] [15.9] [15.10] [15.11] [15.12] [15.13] [15.14] [15.15] [15.16] [15.17] [15.18] [15.19] Feldhaus, A.: Instandhaltung von SpritzgieBwerkzeugen - Analyse des Ausfallverhaltens und Entwicklung angepaBter MaBnahmen zur Steigerung der Anlagenverfiigbarkeit Dissertation, RWTH, Aachen, 1993 Hackstein, R.; Richter, H.: Optionale Instandhaltung - untersucht am Beispiel von Spritzund DruckguBmaschinen FB/IE 24 (1975), 5, pp 267-273 Oltmanns, P.: EDV-Unterstutzung zur Instandhaltung von SpritzgieBwerkzeugen, Unpublished report, IKV, Aachen, 1993 Mexis, N D.: Die Verfugbarkeitsanalyse in der Investitionsplanung Verlag fur Fachliteratur, Heidelberg, 1991 Wilden, H.: Werkzeugkonzeption In: Der SpritzgieBprozeB VDI-Verlag, Diisseldorf, 1979, pp 87-109 Taubert, D.: Wirtschaftliche Bewertungskriterien fur die geplante Instandhaltung, VDIBerichte, No 380, 1980, S 13-19 Rheinfeld, D.: Werkzeug soil in Ordnung sein VDI-Nachrichten, 30 (1976), 31, p Reinigungsgerate fur Kuhlkanale Kunststoffe, 54 (1974), 3, p 112 SpritzgieBen-Werkzeug Technical information, 4.3, BASF, Ludwigshafen/Rh., 1969 Kundenzeitschrift Arburg heute, 10 (1979), 16, June 1979 Oebius, E.: Pflege und Instandhaltung von SpritzgieBwerkzeugen Kunststoffe, 64 (1974), 3, pp 123-124 Brandis, H.; Reismann, J.; Salzmann, H.; Spyra, W; Klupsch, H.: HartschweiBlegierungen Thyssen Edelstahl, Technical report, 10 (1984), Ml, pp 54-75 Rasche, K.: Das SchweiBen von Werkzeugstahlen Thyssen Edelstahl, Technical report, (1981), 2, pp 212-219 Schmid, L.: ReparaturschweiBen mit dem Laserstrahl Paper presented at the 8th Tooling conference at Wlirzburg: "Der SpritzgieBformenbau im internationalen Wettbewerb", Wurzburg 24 1997-25 1997 Elektrochemischer Metallauftrag Prospectus, Baltrusch und Mtitsch GmbH & Co., KG, Forchtenberg Prospectus, Joisten und Kettenbaum GmbH & Co., Joke KG, Bergisch Gladbach Fachkunde Metall Verlag Europa-Lehrmittel, Nourmney, Vollmer GmbH & Co., HaanGruiten, 1990 Prospectus, Schwer & Kopka GmbH, Weingarten