(12) United States Patent
`Marx et al.
`
`US006547210B1
`(10) Patent No.:
`US 6,547,210 B1
`(45) Date of Patent:
`Apr. 15, 2003
`
`EP
`H.
`JP
`WO
`WO
`
`FOREIGN PATENT DOCUMENTS
`() 466 664 A 9/1991
`1 * º º
`()7 304057
`11/1995
`WO 90 08637 A 8/1990
`WO 93 17820 A 9/1993
`OTHER PUBLICATIONS
`Jack Avery, “Section 5.5: Multicomponent Molding,” Injec
`tion Molding Alternatives: A Guide for Designers and
`Product Engineers, Hanser Gardner Publishers, 1998, pp.
`113–117.
`
`(54) SACRIFICIAL INSERT FOR INJECTION
`MOLDING
`(75) Inventors: Jeffrey G. Marx, Downingtown, PA
`(US); Bradley R. Heckendorf.
`Menomonie, WI (US); Brian L.
`Norberg, Durand, WI (US)
`(73) Assignee: Wright Medical Technology, Inc.,
`Arlington, TN (US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`(21) Appl. No.: 09/505,962
`(22) Filed:
`Feb. 17, 2000
`(51) Int. Cl." .................................................. B28B 728
`(52) U.S. Cl. .......................................... 249/175; 249/63
`(58) Field of Search ............................ 249/63, 64, 175;
`264/317
`
`(*) Notice:
`
`(56)
`
`(List continued on next page.)
`Primary Examiner—Christopher A. Fiorilla
`°7)
`ABSTRACT
`Sacrificial inserts and molds for use in injection molding &l?º
`disclosed. In one embodiment a sacrificial insert includes a
`water-insoluble insert which has a melting temperature
`9.
`p
`greater than the injection molding melt temperature of the
`e
`base material being molded. In another embodiment, a mold
`References Cited
`includes one or more of a sacrificial insert configured to
`U.S. PATENT DOCUMENTS
`gu
`form interior features of the object; a sacrificial insert
`3,731,901 A 5/1973 Holdredge, Jr. ............. 249/180
`3,882,220 A
`5/1975 Ryder ......................... ... configured to form interior and exterior features of the
`a?oodoss A
`6/1978 Wolf
`object; and a combination of a sacrificial insert configured to
`4343,757 A.
`8/1982 Popplewell ................. 264/221
`form exterior features of the object and a tool configured to
`4,464,324 A 8/1984 Hager ..........
`.... 264/221
`form interior features of the object. In another embodiment,
`4,614,627 A 9/1986 Curtis et al. ...
`... 264/46.6
`a multi-shot iniection molding process includes: providing a
`2- - - 2
`J
`g p
`p
`9.
`4,743,481 A 5/1988 Quinlan et al. ............... 428/36
`support base containing a tool; injecting a first material into
`4,752,857 A * 6/1988 Khoury et al. .............. 361/321
`the support base to form an integral tool and sacrificial
`4,827,589 A 5/1989 Friedrichs .....
`... 29/156.4 R
`insert; separating the tool from the sacrificial insert; retain
`?º º
`tº. º et al. .
`- - sº:* ing the sacrificial insert in the support base, or inserting the
`2- - -->
`/
`
`anes … / sacrificial insert into another support base optionally having
`4.956,142 A
`9/1990 Mangone, Jr
`264/318
`a further sacrificial insert or tool; injecting a second material
`4900146 A 2/1991 Deibig et al... ... Soiss;
`into the support base containing the sacrificial insert to form
`5,089,186 A 2/1992 Moore et al. ................. 264/25
`an integral sacrificial insert and molded object; and destruc
`5,143,665 A 9/1992 Clubbs et al. .............. 264/221
`tively disengaging the sacrificial insert from the molded
`5,169,577. A 12/1992 Feichtinger
`object without substantially damaging the molded object. In
`5,173,237 A 12/1992 Kidd .......................... 264/221
`another embodiment, a sacrificial insert is used to injection
`5,176,866 A 1/1993 Tanaka et al. ....
`... 264/219
`mold a metal or ceramic object.
`5,242,646 A 9/1993 Torigoe et al. ............. 264/219
`(List continued on next page.)
`
`4,938,679 A 7/1990 Pietrorazio .................. 425/437
`
`- - - - -
`
`-
`
`-
`
`- -
`
`-
`
`
`
`1 Claim, 1 Drawing Sheet
`
`PETITIONERS' EXHIBIT 1107
`
`PAGE 1 OF 7
`
`

`

`US 6,547,210 B1
`Page 2
`
`U.S. PATENT DOCUMENTS
`5,997,230 A 12/1999 Dodd et al. ................. 411/383
`5,248,552 A 9/1993 Moore et al. ............... 428/323
`OTHER PUBLICATIONS
`5,249,618 A 10/1993 Burkarth et al.
`Mike Tolinski, “Process Selection for Multi-Shot Molding,”
`5,433,912 A 7/1995 Schulz et al. ............ 264/297.2
`-
`Molding Systems, vol. 56, No. 1, Jan. 1998, pp. 30–35.
`5,595,771 A
`1/1997 Foltuz et al. .....
`... 425/443
`& 4
`-
`-
`-
`-
`33
`5,614,232 A
`3/1997 Torigoe et al. ............. 425/545
`Choosing a Multi-Material Molding Process".
`5,630,977. A
`5/1997 Catalanotti et al. ......... 264/318
`P. Coates, “Multi-Shot Values,” Plastics and Rubber
`5,656,234 A 8/1997 Kaneishi et al. ............ 264/572
`Weekly, No. 1789, Jun. 4, 1999, p. 7.
`5,658,515 A 8/1997 Lee et al. ......
`... 264/219
`J. Hahn, “Case Study for Multi-Shot,” Antec *99 Confer
`5,681,518 A 10/1997 Ashcraft .......
`.... 264/221
`ence Proceedings, New York City, May 2–6, 1999, pp.
`5,702,660 A 12/1997 Allott et al. ...
`... 264/242
`406—410.
`§: º ". | Wººl al. .......... sº J. Tinson, “Multi-Shot Injection Moulding,” Medical
`5,906,234. A
`5/1999 Mastrorio et al. ............ º: Device Technology, No.3, Apr 1998, pp. 26–28.
`5,972,269 A * 10/1999 Barros et al. ............... 264/221
`* cited by examiner
`
`Ill CI al. ...............
`
`2- - -->
`
`
`
`-
`
`-
`
`-
`
`PAGE 2 OF 7
`
`

`

`U.S. Patent
`US. Patent
`
`Apr. 15, 2003
`Apr. 15, 2003
`
`US 6,547,210 B1
`US 6,547,210 B1
`
`
`
`
`
`&
`
`PAGE 3 OF 7
`
`PAGE 3 OF 7
`
`

`

`1
`SACRIFICIAL INSERT FOR INJECTION
`MOLDING
`
`US 6,547,210 B1
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention relates to injection molding in
`general, and in particular to molding with sacrificial inserts,
`particularly for ceramic and metals.
`2. Description of the Known Art
`Injection molding is used to manufacture articles of
`complex geometry. This method is useful for plastic parts as
`well as metal and ceramic parts prepared by powder injec
`tion molding. Injection molding while being generally eco
`nomical for large volumes of parts can be uneconomical for
`short-run or prototype production. Moreover, obtaining cer
`tain features such as undercuts and blind holes in certain
`orientations in an injection molded part is either difficult or
`impossible, or requires complex and expensive tooling.
`There are numerous examples of the use of complex
`tooling solutions such as expanding cores, see, e.g., Holdred,
`“Expandable Core Assembly,” U.S. Pat. No. 3,731,901;
`Catalanotti, and Tarahomi, “Injection molding method and
`system with expandable cavity element,” U.S. Pat. No.
`5,630,977; Pietrorazio, “Collapsible core for molding clo
`sures having interrupted interior threads and the like,” U.S.
`Pat. No. 4,938,679; and Mangone, “Apparatus and method
`for molding three dimensional articles,” U.S. Pat. No. 4,956,
`142, and slides, e.g., Schulz, Kaiser, and Temesvary, “Pro
`cess for injection molding arcuately-shaped hollow articles,”
`U.S. Pat. No. 5,433,912; Kaneishi, Kiboshi, Mio, and Fukui,
`“Mold apparatus and injection molding method for produc
`ing hollow-structured article by injection molding,” U.S.
`Pat. No. 5,656,234; and Foltuz; and Cohan, “Modular mold
`for injection molding and method of use thereof.” U.S. Pat.
`No. 5,595,771, for the production of otherwise difficult
`geometry’s of injection molded parts. These tooling solu
`tions allow for the molding of some geometries, but there are
`limitations to the complexity of parts possible, and the cost
`of such tools may be prohibitive.
`The known art is also replete with examples of the use of
`expendable patterns in the forming of complex shapes. The
`casting industry commonly uses “lost wax,” and “lost foam”
`processes. In these processes, a mold is formed around a
`shaped material of wax, injection molded plastic, or poly
`meric foam. It is the purpose of this material to form the
`cavity and be vaporized upon casting of the molten metal.
`See, e.g., U.S. Pat. No. 5,906,234.
`U.S. Pat. Nos. 5,614,232 & 5,242,646 to Torigoe et al.
`describe methods for making fasteners by injection molding
`in which a sacrificial stem mold is used for defining exterior
`contours. U.S. Pat. No. 5,824,250 to Whalen et al. describes
`gel cast ceramic manufacturing using a fugitive mold. U.S.
`Pat. Nos. 5,248,552 & 5,089,186 to Moore et al. describe a
`method for removing a core from a cast molded product,
`which is an inert particulate material with a water soluble
`carbohydrate binder. U.S. Pat. No. 5,681,518 to Ashcraft
`describes an injection molding process in which a plurality
`of different mold components (including core components)
`of defined contour are formed and combined.
`U.S. Pat. No. 5,176,866 to Tanka and U.S. Pat. No.
`5,173,237 to Kidd describe molding cores that use low
`melting point alloys which may be removed from a molded
`article by heat, such as hot oil. U.S. Pat. No. 4,614,627 to
`Curtis et al. describes a method for molding a golf club head
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`which uses a fusible core which can be melted out after the
`injected material sets. U.S. Pat. No. 5,143,665 to Cubbs et
`al. describe a sacrificial mold used to mold composite
`materials, plastic or metals.
`There is a need, however, for a molding system which
`utilizes a sacrificial insert which is capable of forming
`interior features of an injection molded article, and which is
`able to maintain fidelity of the features being molded under
`the conditions of injection molding. There is also a need for
`a mold combination which can use different combinations of
`sacrificial parts and permanent parts to provide optimum
`economy when molding articles, particularly articles having
`complex geometries which are difficult to mold with con
`ventional molds, such as those described above and short
`run or prototype molded objects. There is also a need for a
`multi-shot process which can economically produce short
`run parts having complex features not normally attainable
`with conventional multi-shot molds.
`SUMMARY OF THE INVENTION
`One object of the invention is to overcome the disadvan
`tages of the known art described above. Another object of
`the invention is to provide a sacrificial insert for injection
`molding an object, and a mold which includes the sacrificial
`insert. Yet another object is to provide a method of injection
`molding an object using a sacrificial insert. Still another
`object of the invention is to provide a method for producing
`an object by multi-shot injection molding the object using a
`sacrificial insert. Yet another object of the invention is to
`provide a method for forming a molded ceramic object or a
`molded metal object by injection molding using a sacrificial
`insert.
`In order to achieve the foregoing and further objects, there
`has been provided according to one aspect of the invention,
`a sacrificial insert for injection molding an object from a
`base material, which includes, a water-insoluble insert
`which has a melting temperature greater than the injection
`molding melt temperature of the base material. According to
`another aspect of the invention, there has been provided a
`mold for making an object by injection molding, which
`includes, a support base and the sacrificial insert described
`above, and optionally a tool.
`According to yet another aspect of the invention, there has
`been provided a method of injection molding an object
`formed of a base material, which includes: providing a mold
`having the sacrificial insert described; providing the base
`material in a flowable state; flowing the base material into
`the mold and into contact with the sacrificial insert; solidi
`fying the base material in the mold to form the molded
`object; and destructively disengaging the sacrificial insert
`from the molded object without substantially damaging the
`molded object.
`According to still another aspect of the invention, there
`has been provided a method of removing a sacrificial insert
`from a molded object, which includes, subjecting the sac
`rificial insert described above and the molded object to a
`treatment sufficient to destroy the sacrificial insert and
`enable it to be removed from the molded object without
`substantially damaging the molded object.
`According to a further aspect of the invention, there has
`been provided a mold for making an object by injection
`molding comprising one or more of: a sacrificial insert
`configured to form interior features of the object; a sacrifi
`cial insert configured to form interior and exterior features of
`the object; and a combination of a sacrificial insert config
`ured to form exterior features of the object and a tool
`configured to form interior features of the object.
`
`PAGE 4 OF 7
`
`

`

`US 6,547,210 B1
`
`3
`According to yet another aspect of the invention, there has
`been provided a method for producing an object comprising,
`multi-shot injection molding the object which injection
`molding includes: providing a support base containing a
`tool; injecting a first material into the support base to form
`an integral tool and sacrificial insert; separating the tool
`from the sacrificial insert; retaining the sacrificial insert in
`the support base, or inserting the sacrificial insert into
`another support base optionally having a further sacrificial
`insert or tool; injecting a second material into the support
`base containing the sacrificial insert to form an integral
`sacrificial insert and molded object; destructively disengag
`ing the sacrificial insert from the molded object without
`substantially damaging the molded object.
`According to a further aspect of the invention, there has
`been provided a method for forming a molded ceramic
`object, which includes: providing a mold having a sacrificial
`insert; providing a ceramic injection molding feedstock;
`flowing the ceramic feedstock into the mold and into contact
`with the sacrificial insert; solidifying the ceramic material in
`the mold to form an integral green molded ceramic object
`and sacrificial insert; and subjecting the integral green
`molded ceramic object and sacrificial insert to a treatment
`sufficient to destroy the sacrificial insert, whereby the sac
`rificial insert can be separated from the molded ceramic
`object without substantially damaging the molded object.
`According to a further aspect of the invention, there has
`been provided a method for forming a molded metal object,
`which includes: providing a mold having a sacrificial insert;
`providing a metal injection molding feedstock; flowing the
`metal feedstock into the mold and into contact with the
`sacrificial insert; solidifying the metal material in the mold
`to form an integral green molded metal object and sacrificial
`insert; and subjecting the integral green molded metal object
`and sacrificial insert to a treatment sufficient to destroy the
`sacrificial insert, whereby the sacrificial insert can be sepa
`rated from the molded metal object without substantially
`damaging the molded object.
`Further objects, features and advantages of the present
`invention, will become readily apparent from detailed con
`sideration of the preferred embodiments which follow.
`
`DESCRIPTION OF THE DRAWINGS
`FIG. 1 depicts various sacrificial inserts according to one
`embodiment of the invention.
`FIG. 2 depicts an integral molded object/sacrificial insert/
`tool.
`FIG.3 depicts the molded object after the sacrificial insert
`has been destructively removed and the tool has been
`removed.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`The present invention provides a method for injection
`molding objects, such as parts, with complex geometries.
`This method allows complex features, particularly interior
`features, to be added to the object by insert molding with a
`sacrificial insert. Injection molding using conventional
`molds is well known, as described in “Injection Molding
`Handbook” by D. V. Rosato et al. (Chapman & Hall
`Publishing, 2" edition, 1995) which is incorporated by
`reference in its entirety.
`The sacrificial insert is prepared from a material that will
`be removed in a later step. By using the present invention,
`the complexity of tooling may be reduced, and features
`
`4
`previously un-moldable can now be molded. Objects with
`undercuts, and objects which would need numerous slides
`and other complex features in the tool can be molded
`directly. A number of similar objects may be molded with
`the same, or fewer tools with the differentiating features
`added with the use of sacrificial inserts. The present inven
`tion makes it possible to mold a small number of parts, e.g.,
`prototypes with a sacrificial insert(s) in a common mold
`base.
`As used herein, “sacrificial insert” is defined as one or
`more component(s) designed to form the interior, exterior
`and both interior and exterior features of the product being
`molded. The sacrificial insert is designed to be destructively
`removed from the product without substantially damaging
`the product after molding. The sacrificial insert can be
`shaped to form both the female and male mold cavity which
`forms the outer surface of the molded object. The sacrificial
`insert can also be shaped to be placed in a mold cavity to
`form the interior features of molded objects. The sacrificial
`insert can also include features of conventional molds such
`as runners for feeding the material being injected into the
`mold.
`A “tool” is defined as one or more durable component(s)
`such as metal, which may be attached, permanently or
`removably, to the support base to form interior and/or
`exterior features of the product being molded or of the
`sacrificial insert being molded. Unlike the sacrificial insert,
`the tool is designed to be used for molding more than once.
`The tool can be those well known in the art, such as mold
`cavities, cores, collapsible cores, multi-piece elements, etc.
`A “support base” is defined as a metal cavity that serves
`to support the “sacrificial insert” and “tool.” In some
`instances, the support base has no details, and the sacrificial
`insert and tool are the components which actually form the
`details of the product being molded. In other instances, the
`support base may be used to form exterior features of the
`product being molded, or the sacrificial insert.
`A “mold” is defined as comprising at least a combination
`of two or more of the support base, tool and sacrificial insert.
`“Interior feature(s)” are defined as any feature on the
`inner surface or aspect of the object, such as the undercut of
`a threaded object or lip.
`“Exterior feature(s)” are defined as any feature on the
`outer surface or aspect of the object.
`One embodiment of the invention provides a method and
`mold for the manufacture of complex parts such as in
`ceramic, metal or plastic injection molding, with the use of
`a sacrificial insert, and optionally one or more tools. The part
`is injection molded with one or more sacrificial insert(s).
`Following molding, sacrificial insert(s) are removed by a
`process that does not substantially damage the molded part
`or object. The tool, if present, is removed and may be saved
`for subsequent injection molding operations—thus giving
`shape features to the final part.
`According to one preferred embodiment, the sacrificial
`insert is configured (i.e., shaped) to form the interior
`features, and optionally the exterior features, of the object
`being molded. For example, sacrificial inserts, such as a
`sacrificial mold cavity and an insert for forming an interior
`cavity of the object, are prepared to fit in a support base for
`injection molding. Following molding, the molded object
`and the sacrificial insert(s) are ejected together from the
`support base. The sacrificial insert is then removed from the
`part by a process that does not detrimentally affect the
`molded object. For the next object to be molded, new
`sacrificial inserts are fitted into the support base, and another
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`PAGE 5 OF 7
`
`

`

`US 6,547,210 B1
`
`10
`
`20
`
`25
`
`30
`
`35
`
`5
`object is injection molded as described above. Although,
`using new sacrificial insert(s), such as a mold cavity, for
`each object being molded may not seem obviously economi
`cal; for prototypes and short production runs, it is more
`economical than time consuming and expensive machine
`tooling required for permanent molds made from more
`typical materials such as metals.
`If a tool is used, the tool may be used to form interior and
`exterior features of the object being molded. A particularly
`preferred embodiment is using a sacrificial insert to form
`exterior features and using a tool to form interior features. If
`the tool cannot be readily removed from the molded object
`without damaging the molded object, the tool may a multi
`piece tool or a collapsible core as described above.
`15
`The sacrificial insert may be prepared by any method of
`production including: injection molding, machining, com
`pression molding, etc. It is preferred that the insert be
`comprised of a polymeric material. This polymeric material
`may be either thermoplastic or thermoset. It is further
`preferred that the insert be injection molded. In the case of
`injection molding of the insert, the insert may be molded
`dense, or with a blowing agent to reduce weight and improve
`surface finish. In one embodiment, the sacrificial insert is
`injection molded from a thermoplastic with a high melting
`point. Preferred materials include polyacetal, sold under the
`tradename, Delrin", polypropylene, polysulphone, nylon,
`polyurethane, polycarbonate, and polystyrene.
`The sacrificial insert may be removed by mechanical,
`thermal, non-aqueous solvent, catalytic, sublimation,
`enzymatic, acid, base or other means of destruction or
`combinations thereof which destructively disengage(s) the
`insert without substantially damaging the molded object.
`“Substantially without damaging the molded object” is
`defined as the molded object not being degraded mechani
`cally and having no more than minor cosmetic surface flaws,
`e.g., scratches. Preferably the object has no surface flaws.
`Preferred combinations of sacrificial inserts/destruction
`methods include polyacetal/nitric acid atmosphere,
`polypropylene/heat, and polysulphone/acetone.
`In a preferred embodiment, the sacrificial insert is water
`insoluble, and the melting temperature of the sacrificial
`insert is greater than the injection molding melt temperature
`of the base material that is being molded. A water-insoluble
`insert will not dissolve or disperse when contacted with an
`aqueous solution. In the case where the base material being
`injection molded is a ceramic or metal powder, the injection
`molding melt temperature is the temperature at which the
`binder melts. The difference between the melting tempera
`ture of the insert and the injection molding melt temperature
`may be, for example, >100°F., preferably *200°F. Other
`temperature differences can also be used. In this regard,
`polysulphone is particularly preferred for some applications
`in view of its relatively high melting temperature. This
`higher temperature prevents or reduces deformation of the
`insert during the injection molding operation.
`Preferred combinations of sacrificial insert/material being
`molded include, polyacetal/ceramic, polypropylene/
`ceramic, polysulphone/ceramic, nylon/ceramic,
`polyurethane/ceramic, polycarbonate/ceramic, polystyrene/
`ceramic, polyacetal/metal, polypropylene/metal,
`polysulphone/metal, nylon/metal, polyurethane/metal,
`polycarbonate/metal, and polystyrene/metal
`Another preferred aspect of the invention is directed to
`multi-shot molding which can be used to produce one or
`more sacrificial inserts, which sacrificial inserts are then
`used subsequently in the multi-shot injection molding pro
`
`65
`
`40
`
`45
`
`50
`
`55
`
`60
`
`6
`cess to form the molded object preferably in the same
`molding cycle. In this aspect, the sacrificial insert is formed
`in the same process that forms the final molded object.
`Multi-shot processes are known in the art, and examples can
`be found in “Injection Molding Alternatives: A Guide for
`Designers and Product Engineers”, Section 5.5: “Multicom
`ponent Molding” by Jack Avery (Hanser Gardner
`Publishers, 1998, pages 113–117); “Process Selection For
`Multi-Shot Molding” by Mike Tolinski (Molding Systems,
`volume 56 number 1, January 1998, p 30–35); “Multi-Shot
`Values” by P. Coates, (Plastics and Rubber Weekly,
`No.1789, 4” June 1999, p.7); “Case Study for Multi-Shot”
`by J. Hahn, (Antec *99 Conference Proceedings, New York
`City, 2"–6” May 1999 p.406; and “Multi-Shot Injection
`Moulding” by J. Tinson, (Med. Device Technol, No.3, April
`1998, p.26–8), all of which are incorporated by reference
`their entireties.
`In a typical multi-shot process, the object to be molded is
`made from more than one material. A first material is
`injected into a first mold to form a first molded object. The
`first molded object is then removed from the first mold, and
`inserted into a second mold, typically by rotating the mov
`able portion of the mold from the first mold to the second
`mold, into which a second material to be molded is injected
`to form the final molded object. The final molded object is
`thus a combination, e.g., laminate, of the first and second
`materials. Additional analogous molding steps using third,
`fourth and additional materials can also be employed. These
`steps preferably all occur within the same molding cycle.
`In the present invention, the first molded object may be
`the sacrificial insert. The sacrificial insert is formed by
`providing a support base and tool to form a mold. The
`material which forms the sacrificial insert is then injected
`into the mold to form the sacrificial insert. The sacrificial
`insert is then separated from the tool in a manner which does
`not harm the sacrificial insert. The insert can be retained in
`the same support base, and a different tool can be employed
`for the next molding step, such as by rotating a platen
`containing the support base and sacrificial insert into place
`with another stationary tool, or alternatively, rotating a
`platen containing another tool into place with the stationary
`support base containing the sacrificial insert. Alternatively,
`the insert can be removed from the support base and inserted
`into another support base which may contain additional tools
`and sacrificial inserts. A material which will form the
`molded object is then injected into the support base con
`taining the sacrificial insert formed at the beginning of the
`process, as well as optional tools and additional sacrificial
`insert to form an integral sacrificial insert(s) molded object.
`As with conventional multi-shot processes, additional inject
`ing steps can be used with additional materials to form the
`final molded object. The final molded object is then destruc
`tively disengaged from the sacrificial insert(s) without sub
`stantially damaging the final molded product.
`Another aspect of the invention provides a method for
`molding ceramic or metal objects, using sacrificial inserts.
`According to this embodiment, a feedstock of a ceramic or
`metal is first prepared. The feedstock may or may not
`include one or more binders admixed with the ceramic or
`metal powder. In a preferred embodiment, a polymeric
`binder is present. Other additives can include processing
`aids such as water, plasticizers such as glycerin, release
`agents, and debinding aids. Fine ceramic or metal powders
`are preferably hot mixed with the polymeric binder, if
`present, and the other processing aids, if present. The
`mixture is then cooled and granulated to form the feedstock.
`Techniques and compositions for forming ceramic or metal
`
`PAGE 6 OF 7
`
`

`

`US 6,547,210 B1
`
`15
`
`20
`
`30
`
`25
`
`7
`feedstocks are well known in the art, and are described, for
`example, in U.S. Pat. No. 5,997,230, which is incorporated
`by reference in its entirety.
`The feedstock is then heated to a temperature that is just
`above the temperature at which the binder starts to flow. The
`feedstock is fed into an injection molding machine where it
`is directed into a mold containing one or more sacrificial
`inserts. The feedstock becomes a solid molded object upon
`cooling. After the feedstock has solidified, the one or more
`sacrificial inserts are destroyed without substantially dam
`10
`aging the molded object to form a green molded ceramic or
`metal object. The methods of destruction can be those
`described above.
`If a polymeric binder is used, then according to a pre
`ferred embodiment, the one or more sacrificial inserts are
`destroyed by heating to a temperature at which the insert
`decomposes or melts. At the same time, the heating also
`debinds the green molded object.
`After destruction of the insert and optionally debinding,
`the molded object is then heated to a temperature to effect
`sintering. Sintering temperatures for most ceramics of rel
`evance to this invention are preferably in the range of about
`1100° C. to about 1600° C., and preferred sintering tem
`peratures for metals are in the range of about 800 to about
`1400° C.
`The present invention may be more easily understood by
`reference to the following non-limiting examples:
`Example 1
`Cylinders of Delrin" were machined such that they
`would fit into the inner diameter of a cylindrical cavity
`support base. These Delrin" cylinders were machined with
`a bored and tapped inner dimension, as shown in FIG. 1. A
`35
`hole was drilled through the side to mate with the gate of the
`support base. In the center of the support base, a tool in the
`shape of a pin was screwed into the cavity half of the support
`base.
`A ceramic injection molding feedstock was prepared as
`described above according to the following formulation:
`586 g Al2O3
`37.7 g parrafin wax
`48.47 g polypropylene
`5.09 g stearic acid
`17.23 g Fusabond@
`The ceramic feedstock was injection molded into these
`cylinders and around the central pin. The resulting cylinders
`had a cylindrical internal bore, and a cylindrical outer
`surface. The integral molded object/sacrificial insert/tool
`had a green injection molded ceramic, with a Delrin"
`exterior and a central pin. The interface between the Del
`rin" and injection molded ceramic had the threaded con
`formation from the tapped Delrin". The composite molded
`object/sacrificial insert/tool is shown in FIG. 2.
`Cylinders prepared in this fashion were subjected to nitric
`acid vapor at a temperature of 110° C. for four hours in a
`specially designed nitrogen atmosphere oven. The effect of
`this treatment was to catalytically decompose the Delrin"
`insert leaving behind the ceramic injection molded object
`with a threaded outer surface given to the object by the
`insert. The green ceramic object was then debound in
`heptane at 60° C. to remove wax, heated to 600° C. to
`remove the polypropylene and sintered at 1550° C. The
`features given to the part by the sacrificial insert were
`retained in the final sintered part as shown in FIG. 3.
`
`8
`Example 2
`Cylinders of polypropylene were injection molded in a
`cylindrical support base with a central pin to yield polypro
`pylene cylinders with a hollow bore. The bores of these
`polypropylene cylinders were tapped to give internal
`threads, and the gate section was drilled through to the
`interior to yield sacrificial inserts. The central pin in the
`support base was switched to a pin (i.e., tool) with a smaller
`diameter. The polypropylene sacrificial inserts were then
`inserted into the support base, and a ceramic composition
`identical to Example 1 was injection molded between the pin
`tool and the polypropylene insert. The resulting cylinders
`had a cylindrical internal bore, and a cylindrical outer
`surface. The interior was comprised of green injection
`molded ceramic, with a polypropylene exterior. The inter
`face between the polypropylene and injection molded
`ceramic had the threaded configuration from the tapped
`polypropylene. The ceramic injection molded portion of this
`article was partially debound with the use of heptane at 60°
`C., and the article was thermally debound at 600° C. and
`sintered at 1550° C. During the thermal debinding and
`sintering step, the polypropylene sacrificial insert is ther
`mally destroyed, leaving the ceramic article.
`Example 3
`Cylinders of polysulphone were injection molded into a
`blank cylindrical support base with a threaded central pin to
`yield polysulphone cylinders with internal threads. A gate
`section was drilled through to the interior to yield a sacri
`ficial insert. The threaded central pin in