WO2009015029A1 - Procédé de moulage de structures complexes utilisant un matériau sacrificiel - Google Patents

Procédé de moulage de structures complexes utilisant un matériau sacrificiel Download PDF

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Publication number
WO2009015029A1
WO2009015029A1 PCT/US2008/070519 US2008070519W WO2009015029A1 WO 2009015029 A1 WO2009015029 A1 WO 2009015029A1 US 2008070519 W US2008070519 W US 2008070519W WO 2009015029 A1 WO2009015029 A1 WO 2009015029A1
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WO
WIPO (PCT)
Prior art keywords
sacrificial component
molding
binder
sacrificial
debinding
Prior art date
Application number
PCT/US2008/070519
Other languages
English (en)
Inventor
Majid Entezarian
Original Assignee
Phillips Plastics Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Phillips Plastics Corporation filed Critical Phillips Plastics Corporation
Publication of WO2009015029A1 publication Critical patent/WO2009015029A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28B7/00—Moulds; Cores; Mandrels
    • B28B7/34—Moulds, cores, or mandrels of special material, e.g. destructible materials
    • B28B7/342—Moulds, cores, or mandrels of special material, e.g. destructible materials which are at least partially destroyed, e.g. broken, molten, before demoulding; Moulding surfaces or spaces shaped by, or in, the ground, or sand or soil, whether bound or not; Cores consisting at least mainly of sand or soil, whether bound or not
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F3/1017—Multiple heating or additional steps
    • B22F3/1021—Removal of binder or filler
    • B22F3/1025—Removal of binder or filler not by heating only
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
    • B22F3/225—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip by injection molding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F5/00—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product
    • B22F5/10—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product of articles with cavities or holes, not otherwise provided for in the preceding subgroups
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28B1/00—Producing shaped prefabricated articles from the material
    • B28B1/24—Producing shaped prefabricated articles from the material by injection moulding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C33/00—Moulds or cores; Details thereof or accessories therefor
    • B29C33/44—Moulds or cores; Details thereof or accessories therefor with means for, or specially constructed to facilitate, the removal of articles, e.g. of undercut articles
    • B29C33/448—Moulds or cores; Details thereof or accessories therefor with means for, or specially constructed to facilitate, the removal of articles, e.g. of undercut articles destructible
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/16—Making multilayered or multicoloured articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/17—Component parts, details or accessories; Auxiliary operations
    • B29C45/40—Removing or ejecting moulded articles
    • B29C45/44—Removing or ejecting moulded articles for undercut articles
    • B29C45/4457—Removing or ejecting moulded articles for undercut articles using fusible, soluble or destructible cores
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • C04B35/63—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B using additives specially adapted for forming the products, e.g.. binder binders
    • C04B35/638—Removal thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
    • B22F2998/10—Processes characterised by the sequence of their steps
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/60—Aspects relating to the preparation, properties or mechanical treatment of green bodies or pre-forms
    • C04B2235/602—Making the green bodies or pre-forms by moulding
    • C04B2235/6022—Injection moulding
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/60—Aspects relating to the preparation, properties or mechanical treatment of green bodies or pre-forms
    • C04B2235/602—Making the green bodies or pre-forms by moulding
    • C04B2235/6028—Shaping around a core which is removed later
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
    • C04B2235/74—Physical characteristics
    • C04B2235/77—Density

Definitions

  • Powder injection molding is a process that uses fine metal or ceramic powder to create a wide variety of parts.
  • the process includes combining the powder with a binder to form a feedstock.
  • the feedstock is injected into a mold and cooled to create a green part.
  • the binder is removed from the green part to form a brown part.
  • the brown part is sintered to form a final part that is ready to be used alone or in combination with one or more other parts.
  • PIM provides a number of advantages, it also suffers from a number of problems.
  • One problem associated with PIM is that it is difficult to prepare parts that have complex shapes such as undercuts and the like.
  • attempts have been made to remedy this problem past approaches still suffer from a number of drawbacks.
  • One approach is to insert mold the part using a sacrificial component.
  • the sacrificial component is preformed and inserted into the mold manually or robotically.
  • the PIM feedstock is injected into the mold and surrounds the sacrificial component.
  • the part is removed from the mold and processed to eliminate the sacrificial component.
  • the part is eventually sintered to give it strength and rigidity.
  • a multi-shot process is used to form the sacrificial component and inject the PIM feedstock.
  • the multi-shot process involves creating the sacrificial component and the part as one or more shots in the same press.
  • the sequence and number of shots can be varied as desired.
  • the sacrificial component may be formed by injecting sacrificial material in one or more shots.
  • the PIM feedstock may also be formed in one or more shots. The shots may be ordered so that the sacrificial component is formed first then the part.
  • the shots may be ordered so that a portion of the part is formed initially, the sacrificial component is formed, and the remainder of the part is formed.
  • Each of these steps may include one or more shots, e.g., the initial portion of the part may be formed in one or more shots.
  • the green part may undergo further processing to remove the sacrificial component, debind the part, and/or sinter the part. It should be appreciated that the processes described herein may include any number and/or combination of these additional steps in any order. For example, debinding and removing the sacrificial component may occur simultaneously or separately from each other. If these steps are performed separately, they may be performed in any order.
  • an insert molding process is used and the sacrificial component is heated before it is placed in the mold.
  • the insert molding process involves preforming the sacrificial component in one press, heating the sacrificial component, placing it in the mold of another press, and injecting the PIM feedstock into the mold.
  • the green part may undergo further processing (e.g., debinding, sintering, etc.).
  • the sacrificial component may be heated using any suitable method or process.
  • the sacrificial component may be transported through a furnace or oven that heats it.
  • the sacrificial component may be heated using a hot plate.
  • the sacrificial component may be heated in a continuous, semi-continuous, or batch-wise process.
  • plastic injection molding process may be similar to any of the PIM processes except that plastic is used instead of metal and/or ceramic powder and the steps of debinding and sintering may be eliminated.
  • the plastic injection molding process may also include heating a preformed sacrificial component before placing it into the mold and forming the sacrificial component and the part in a multi-shot process.
  • the processes described herein may provide a number of advantages.
  • One potential advantage is that the processes reduce the number and/or severity of defects in the final part. It has been discovered that a large temperature difference between the sacrificial component and the PIM feedstock contributes to the formation of defects. Heating the preformed sacrificial component or forming the sacrificial component in a multi-shot process reduces the temperature difference between the sacrificial component and the PIM feedstock thereby reducing the number and/or severity of defects in the part.
  • insert mold Insert molding, and the like are used herein to refer to molding processes where one component of the part is preformed in one molding press and then is inserted, either manually, robotically, or otherwise, into another molding press where the final part is made.
  • multi-shot multi-shot molding
  • Multi-shot molding may use one or more of the following technologies to form a multi-component part - robotic transfer within the same press, coinjection, core toggle, rotary platen, rotary stack, and/or indexing plate.
  • Preferred technologies for multi-shot molding include rotary platen, indexing plate, and/or core toggle.
  • references to molding the feedstock or a part "around” or “over” a sacrificial component or sacrificial material should not be interpreted as requiring the feedstock to surround the sacrificial component. Rather, references such as this should be interpreted as indicating that the feedstock or part contacts, even in a minor way, the sacrificial component or sacrificial material.
  • FIG. 1 is flow diagram of one embodiment of a process for molding a part.
  • FIG. 2 is a flow diagram of one embodiment of an insert molding process for forming a green part.
  • FIG. 3 is a flow diagram of one embodiment of a multi-shot molding process for forming a green part.
  • FIGS. 4-6 are cross-sectional views of different embodiments of parts that were formed using a two-shot molding process. DESCRIPTION
  • FIG. 1 shows a flow chart of one embodiment of a PIM process 100 for molding a part.
  • the process 100 begins by compounding metal and/or ceramic powder 102, binder 104, and/or additives 106 at step 108 to form a feedstock. It is desirable to include as much powder 102 in the feedstock as possible while minimizing the amount of binder 104. However, the feedstock should have sufficient binder 104 to allow the feedstock to flow at the molding temperature smoothly into the die without any segregation. It is also desirable for the viscosity to be constant or nearly constant over a range of temperatures. In one embodiment, the ratio of the binder 104 to the powder 102 is about 0.3 to 0.9 or, desirably, about 0.5 to 0.7.
  • the powder 102, the binder 104, and the additives 106 may be compounded 108 in any suitable manner.
  • the powder 102, binder 104, and/or additives 106 may be combined in a manner that creates a shearing action that helps coat each particle and uniformly distribute the materials. This may be accomplished using a Z blade mixer, planetary mixer, or other suitable equipment.
  • the feedstock may be granulated or fed directly to the molding operation 110. If the feedstock is granulated, it is processed to create solid pellets that can be fed into the mold later in the process 100. The solid pellets make it simple and easy to store and transport the feedstock.
  • Any suitable metal and/or ceramic powders 102 may be used in the process 100. The primary limitation on the powder 102 is that it should be capable of forming a rigid structure upon sintering. Suitable metal powders may include powders of low-alloy steels to stainless steels, soft magnetic alloys to tool steels, Ni-super alloys to titanium, tungsten, ferrous and non- ferrous alloys, or any suitable combinations thereof. Suitable ceramic powders may include powders of alumina, zirconia toughened alumina, zirconia, and other oxides, nitrides, carbides, or combinations thereof.
  • the process 100 has the advantage that very little, if any, powder 102 or other raw material ends up as scrap. In contrast, alternative processes that involve machining and the like produce a significant amount of scrap. The reduced amount of scrap associated with the process 100 helps to make it more economical and efficient.
  • the powder 102 may include particles having any suitable size and/or shape. In general, it is desirable to incorporate as much powder 102 in the part as possible. Also, it is often desirable to provide a range of powder sizes because although fine powders tend to sinter more readily than coarser powder, the smaller particles are more expensive and may present other limiting factors. In one embodiment, the powder may have a mean diameter of about 5 to 15 microns.
  • the powder 102 may have any one or more of the following features.
  • the powder 102 may have a particle size distribution (i.e., a mixture of lower cost large particles and higher cost small particles) that is tailored for high packing density and low cost.
  • the particles may be spherical or predominantly spherical to resist agglomeration in the feedstock.
  • the particle shape may provide sufficient interparticle friction to prevent the part from collapsing when the binder is removed.
  • the particles may also be clean of other substances that may cause unpredictable interactions with the binder 104, additives 106, or other components used in the process 100.
  • Any suitable binder 104 may be used in the process 100.
  • the binder 104 should provide suitable rheological properties to allow the molten feedstock to be injected into the mold.
  • the binder 104 should also be capable of being removed from the green part at the debinding step 112 of the process 100.
  • the choice of binder 104 may depend on which process is used to remove it.
  • the binder 104 may be removed catalytically, thermally, or chemically. Binders that can be removed catalytically include polyacetal based binders used with BASF's Catamold feedstock. Binders that can be removed thermally include plastics such as polyethylene and polypropylene as well as stearic acid, micropulvar wax, and/or paraffin wax. Binders that can be removed chemically (e.g., with a solvent) include waxes and the like.
  • the binder 104 may include a single material or a combination of different materials.
  • the binder 104 may include a polymer material.
  • the binder 104 may also include an organic material, desirably, an organic polymeric material.
  • the binder 104 may be selected to allow it to degrade at different rates during the debinding process 112.
  • the binder may be a polyacetal based plastic binder.
  • the binder may be any one or combination of the binders described in U.S. Patent No. 5,362,791 to Ebenhoech et al. (the '791 Patent), the entire contents of which are incorporated herein by reference.
  • the feedstock compounded at step 108 is molded into a part at step 110.
  • the part may be made using an improved insert molding process 120.
  • the part may be prepared using a multi-shot process 130.
  • the insert molding process 120 includes the steps of molding the sacrificial component 122, heating the sacrificial component 124, and molding the part around the sacrificial component 126.
  • the sacrificial component is preformed in a separate molding press.
  • the sacrificial component may be preformed immediately prior to being placed in the part mold or it may be preformed much earlier and, potentially, at a different geographical location.
  • the insert molding process 120 is an improvement over conventional insert molding processes because the sacrificial component is heated before it is placed in the part mold. Heating the sacrificial component in this manner reduces the number and/or severity of defects in the part.
  • the sacrificial component should be heated enough to prevent it from prematurely cooling the feedstock but not so hot that the sacrificial component becomes deformed. If the sacrificial component is heated too much the molten feedstock will heat it too much and deform it resulting in a malformed part. If the sacrificial component is not heated enough, it will prematurely cool the feedstock and cause cracks and/or other defects. A balance should be reached where the sacrificial component is heated to a temperature that is low enough to prevent deformation but high enough to prevent the part from cracking.
  • the sacrificial component may be heated using any suitable method.
  • the sacrificial component may be heated in a furnace.
  • the sacrificial component may be heated on a hot plate.
  • the sacrificial component may be heated in a continuous, semi-continuous, or batchwise process.
  • Any suitable sacrificial material may be used to make the sacrificial component.
  • the sacrificial material should be capable of being removed from the green part.
  • the sacrificial material may be the same as the binder 104 or may be a separate material.
  • the sacrificial component may also be made of a single sacrificial material or multiple sacrificial materials. Different sacrificial materials may be combined so that different parts of the sacrificial component degrade at different rates. The choice of which sacrificial material depends largely on which method is used to remove the sacrificial material.
  • the multi-shot process 130 includes the steps of molding the sacrificial component in one or more shots 132 and molding the part in one or more shots 134.
  • the sacrificial component and the part are molded in the same press.
  • One of the advantages of this process 130 is that the feedstock is injected before the sacrificial component can cool, which fosters temperature stability between the feedstock and the sacrificial component. Thus, the sacrificial component does not cause cracks in the part. However, the shot of feedstock can be delayed long enough to allow the sacrificial component time to solidify.
  • Another advantage of the process 130 is that the step of placing the sacrificial component in the mold is eliminated. This may increase the throughput rate of the process 130 as well as eliminate the cost of labor and/or robotic equipment that would otherwise be needed to place the sacrificial component in the mold.
  • Yet another advantage of the process 130 is that concerns related to shrinkage of the sacrificial component are greatly reduced because the sacrificial component is not allowed to cool significantly. In contrast, shrinkage concerns are much greater in conventional insert molding process because the insert has been allowed to cool before it is put into the mold.
  • An additional advantage of the process 130 is that part to part variation may be minimized for hydroscopic materials because the components molded by each shot do not absorb significant amounts of moisture. Also, part to part variation may also be minimized for semi- crystalline materials because crystalline formation doesn't occur until the entire part is cooled. [0044]
  • the various shots of sacrificial component and feedstock may occur in any order. In one embodiment, the sacrificial component may be completely formed in one or more shots and then the part may be formed in one or more shots. In another embodiment, the multi-shot process 130 may include forming a portion of the part may first, forming the sacrificial component next, and finally forming the remainder of the part.
  • the processes 120, 130 may be carried out using any suitable equipment.
  • single screw extruders may be used to inject the sacrificial component and/or the feedstock into the die cavity.
  • the temperature of the screw and the nozzle may be controlled to melt the binder in the feedstock and the sacrificial component so that they can be injected into the die cavity.
  • the die temperature may also be controlled at a lower temperature that allows the part to cool and become rigid.
  • the tooling for the PIM equipment is similar to that of traditional injection molding equipment with one major difference.
  • the PIM tooling is oversized to allow for shrinkage when the part is sintered.
  • the binder 104 is removed from the green part to form a brown part.
  • the binder 104 may be removed catalytically, thermally, chemically, or using any other suitable process.
  • the preferred method is to remove the binder 104 catalytically.
  • Catalytic debinding involves feeding green parts into an oven heated to 110-140° C in the presence of a catalyst.
  • the catalyst may include gaseous nitric acid and/or oxalic acid.
  • the catalyst breaks down the binder 104 into small volatile molecules. These molecules have a relatively high vapor pressure and diffuse rapidly out of the part. Binder removal proceeds from the outside inward thereby preventing pressure build-up in the interior of the part. This promotes a very uniform and rapid debinding from the exterior surface into the center of the part.
  • the binder decomposition front moves inward at a rate of 1-2 mm per hour making catalytic debinding much faster than other techniques. Furthermore, unlike other debinding techniques, there is no limit on the thickness of the part that can be debound.
  • the small molecules generated by the process have a high vapor pressure, which greatly minimizes the potential for capillary condensation and allows thick part sections to be debound.
  • Catalytic debinding has another advantage over other debinding techniques.
  • Equipment has been developed for catalytic debinding that allows it to be operated on a continuous basis instead of a batchwise basis. It should be appreciated, however, that the catalytic debinding process can also be operated on a semi-continuous or batchwise basis as well.
  • Thermal debinding involves passing the green part through a furnace or other heat source that melts, decomposes, and/or volatilizes the binder 104.
  • the debinding process may remove all or substantially all of the binder. Any remaining binder residue may be removed during sintering. If thermal debinding is used, the binder 104 should be capable of melting, decomposing, and/or volatilizing at elevated temperatures.
  • the binder 104 may include several ingredients which melt, decompose, or volatilize at different temperatures to prevent the disruption of the part as it is thermally debound.
  • Chemical debinding involves dissolving the binder 104 with a solvent.
  • a suitable solvent is trichloroethane.
  • the part may be heated to further volatilize the solvent and/or binder 104.
  • suitable solvents include hexane and water.
  • the debinding process 112 reduces the strength of the green part significantly. Thus, after debinding, care should be exercised when handling the brown part.
  • the debinding step 112 depicted in FIG. 1 is also used to represent the step of removing the sacrificial component. It should be appreciated, however, that the binder and the sacrificial component may be removed at the same time or at different times. In one embodiment, the binder may be removed first and the sacrificial component removed subsequently. In another embodiment, the sacrificial component may be removed first and the binder removed subsequently.
  • the sacrificial component may be removed using any of the same processes used to remove the binder 104.
  • the sacrificial component and the binder 104 may be removed catalytically.
  • the sacrificial component and the binder 104 may both be polyacetal based.
  • the brown part is sintered to form the finished part at step 114.
  • Sintering refers to the process in which the separate powder particles weld together to provide strength and rigidity to the finished part. Sintering involves heating the brown part to a temperature that is slightly below the melting point of the powder 102. If the temperature reaches the melting point of the powder 102, the brown part will lose its shape and slump. The temperature should be carefully controlled to prevent this from happening.
  • the part may be sintered in a reducing atmosphere to prevent the powder 102 from oxidizing. This is especially a concern when the powder 102 includes metal.
  • the reducing atmosphere may also reduce any metal oxide that exists on the surface of the powder particles.
  • the composition of the reducing atmosphere depends on the particular powder 102 being used.
  • a hydrogen atmosphere may be used for many metal parts. If the powder contains an iron/carbon alloy (e.g., carbon steels), then it may be desirable for the atmosphere to contain a carbon compound or compounds so that the carbon content of the atmosphere is in equilibrium with the carbon content of the powder. This prevents the atmosphere from carburizing or decarburizing the metal.
  • the part may also be sintered in a vacuum.
  • the brown part is very porous. As the part is sintered it shrinks substantially. For example, the part may shrink about 20 wt%. Although the shrinkage is large, it is also uniform, provided that the feedstock was of uniform density.
  • the finished part typically has a density closely approaching the theoretical density for the material.
  • the finished part may have a density of at least about 95 wt%, at least about 97 wt%, or, desirably, at least about 98 wt% of the theoretical density of the material.
  • the mechanical properties of the finished part are also similar to the mechanical properties of a fully dense part (e.g., a wrought metal part).
  • the part may be sintered in any of a number of suitable furnaces or ovens. In one embodiment, the part may be sintered in a batch vacuum furnace, continuous atmosphere furnace, and/or batch atmosphere furnace.
  • the size and weight of the final part are consistent from part to part.
  • the variability of dimensions and weights from part to part is minimal. Close tolerances of dimensions and weight may reduce or eliminate the need for secondary machining processes which can be costly and difficult. Tolerances as small as +/- 0.003 inch per linear inch can be obtained without secondary processing.
  • the part After the part has been sintered, it may be removed from the furnace and used without any further processing. Alternatively, the parts may be subjected to additional secondary operations such as heat treatment to harden the part, surface coating the part, hot isostatic pressing until the part reaches full density, glass beading cleaning to remove impurities from the sintered surface, and tumbling to smooth off sharp edges and remove barbs.
  • additional secondary operations such as heat treatment to harden the part, surface coating the part, hot isostatic pressing until the part reaches full density, glass beading cleaning to remove impurities from the sintered surface, and tumbling to smooth off sharp edges and remove barbs.
  • the processes 100, 120, 130 or any of the individual steps in the processes 100, 120, 130 may be operated on a continual, semi-continual, or batchwise basis.
  • the molding machines used to create the part and/or the sacrificial component may be highly automated and run continuously.
  • a sintering furnace may also be provided that has a large throughput and is capable of running continuously as well.
  • FIGS. 4-6 show conceptual examples of parts that may be made using the processes described herein. The different methods that may be used to make each part are considered in turn. It should be appreciated that the sacrificial components described herein may be provided as either a separate insert that undergoes additional heating before being placed in the mold or as a separate shot in a multi-shot process.
  • the part 151 may be molded in a number of different ways.
  • the sacrificial component 152 is initially formed on a metal core pin 154.
  • the feedstock 150 is then molded around the components 152, 154.
  • the components 152, 154 may be combined and formed entirely out of the sacrificial material.
  • the resulting sacrificial component may be formed as an insert or in one or more shots of a multi- shot process.
  • a part 153 may be molded by first molding the sacrificial components 156, 158 as separate shots.
  • Metal core pin 160 may be used to support the sacrificial components 156, 158.
  • the feedstock 150 is then molded around the components 156, 158, 160 to form the part. It should be appreciated that the pin 160 may be replaced by sacrificial material.
  • a part 155 that is even more complex may be prepared using a process that is similar to that shown in FIG. 5.
  • the part 155 illustrates some additional features that may be molded as part of the processes described herein.
  • plastic injection molding processes are not limited to PIM processes. They may also be applicable to plastic injection molding. The same concepts related to the use of the sacrificial component may be applied to plastic injection molding. It should be appreciated that plastic injection molding processes may not include the steps of debinding and sintering.
  • the processes may be used to make any of a number of complex features.
  • the processes may be used to make undercut features in PIM parts.
  • the processes may be used to make features such as re-entrant angles, multi-shaped blind holes, screw threads, surface profiles, perpendicular holes, intricate cavities, and undercuts.
  • the processes described herein may be used to make any of a number of plastic, metal, or ceramic, parts.
  • the processes may be used to make high tolerance parts such as those make in the automotive field for turbocharger, valve train, gearbox, seat- adjustment, fuel injection and sensor systems parts.
  • the parts may also be used in the following fields: medical, dental, firearms, and aerospace, to name but a few.
  • One technology area where it may be very desirable to use parts made using the processes described herein is pressure sensing systems.
  • the processes may be used to make a pressure sensor that is used to sense the brake fluid pressure in an automobile.
  • the word “or” when used without a preceding "either” shall be interpreted to be inclusive (e.g., “x or y” means one or both x or y).
  • the term “and/or” shall also be interpreted to be inclusive (e.g., "x and/or y” means one or both x or y).
  • a stated range of 1 to 10 should be considered to include and provide support for claims that recite any and all subranges or individual values that are between and/or inclusive of the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less (e.g., 5.5 to 10, 2.34 to 3.56, and so forth) or any values from 1 to 10 (e.g., 3, 5.8, 9.9994, and so forth).

Abstract

L'invention concerne un certain nombre de procédés qui peuvent être utilisés pour former des pièces complexes avec des dégagements et similaires. Dans un mode de réalisation, un procédé à cycles multiples est utilisé pour former le composant sacrificiel et injecter la charge PIM. Les procédés décrits ici peuvent réduire le nombre et/ou la sévérité des défauts dans la pièce finale. Le composant sacrificiel est moulé dans une presse de moulage et la pièce est moulée sur celui-ci dans la presse de moulage.
PCT/US2008/070519 2007-07-20 2008-07-18 Procédé de moulage de structures complexes utilisant un matériau sacrificiel WO2009015029A1 (fr)

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