CA2179323A1 - Synthetic resin mold for synthetic molding and methods - Google Patents
Synthetic resin mold for synthetic molding and methodsInfo
- Publication number
- CA2179323A1 CA2179323A1 CA002179323A CA2179323A CA2179323A1 CA 2179323 A1 CA2179323 A1 CA 2179323A1 CA 002179323 A CA002179323 A CA 002179323A CA 2179323 A CA2179323 A CA 2179323A CA 2179323 A1 CA2179323 A1 CA 2179323A1
- Authority
- CA
- Canada
- Prior art keywords
- layer
- mold
- heat
- polyimide
- thickness
- Prior art date
- Legal status (The legal status 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 status listed.)
- Abandoned
Links
Classifications
-
- 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
- B29C33/56—Coatings, e.g. enameled or galvanised; Releasing, lubricating or separating agents
-
- 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
- B29C33/38—Moulds or cores; Details thereof or accessories therefor characterised by the material or the manufacturing process
- B29C33/40—Plastics, e.g. foam or rubber
-
- 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
- B29C33/38—Moulds or cores; Details thereof or accessories therefor characterised by the material or the manufacturing process
-
- 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
- B29C33/42—Moulds or cores; Details thereof or accessories therefor characterised by the shape of the moulding surface, e.g. ribs or grooves
-
- 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
- B29C33/56—Coatings, e.g. enameled or galvanised; Releasing, lubricating or separating agents
- B29C33/565—Consisting of shell-like structures supported by backing material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
- B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B33—ADDITIVE MANUFACTURING TECHNOLOGY
- B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
- B33Y70/00—Materials specially adapted for additive manufacturing
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Moulds For Moulding Plastics Or The Like (AREA)
Abstract
The present invention relates to compositions produced by Stereolithography Apparatus (SLA), generally known as a form of Rapid Prototyping, and more particularly to a method and product allowing the protection of photoformed compositions, utilized as mold inserts, for thermoplastic injection and blow molding. These mold inserts can be made from start to finish without traditional machining practices. In a preferred embodiment, the mold insert has three component parts. The parts are a photoformed shell, a cooled heat conductive backing and a conformal protective Polyimide exterior coating.
Description
2 1 7q3~3 BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to compositions produced by Stereolithography Apparatus (SLA), generally known as a form of Rapid Prototyping, and more particularly to a method and product allowing the protection of photoformed compositions, utilized as mold inserts, for thermoplastic injection and blow molding. These mold inserts can be made from start to finish without traditional machining practices.
Steroeolithography is one of several available methods of producing rapid prototype models. The process allows complex shapes to be reproduced in polymer resin, going from computer data to finished product within a period of 24 hours. Rapid prototyping techniques are increasingly being used by industry to produce models in a fraction of the time required for more conventional manufacturing methods.
To produce a stereolithography model, the product must be modelled with a computer aided design (CAD) package. The stereolithography model is manufactured by scanning a laser across the surface of a tank of liquid polymer resin. The CAD model ~J~I~b~.se directs this laser.The resin is sensitive to the laser light and solidifies in a thin layer, in the scanned areas. Each scan builds up a thin layer of solidifed resin, representing one of the cross sections of the model. Between the scanning of each layer, the developing model is "dunked" beneath the surface of the resin, leaving a layer of liquid to be solidified in the next scan.
2i 7~323 The resin is partially cured and is finally cured by placing the model in an oven.
After this, the model is cleaned up by hand and finished according to it's intended application.
Another form of Stereolithography has been termed Solid Ground Curing (SGC).
The Cubital System uses this technology to combine layer additive and layer subtractive process to produce patterns. The finished parts are produced in photopolymer resin, similar to stereoltithography is appearance A typical process layer is produced in the following steps:
1 ) An ultraviolet lamp exposes a photosensitive resin (similar to those used instereolithography) through a mask. The mask is created on a charged glass plate using a toner similar to xerographic or laser printing techniques.
2) The unexposed resin is vacuumed up from the exposed layer.
The present invention relates to compositions produced by Stereolithography Apparatus (SLA), generally known as a form of Rapid Prototyping, and more particularly to a method and product allowing the protection of photoformed compositions, utilized as mold inserts, for thermoplastic injection and blow molding. These mold inserts can be made from start to finish without traditional machining practices.
Steroeolithography is one of several available methods of producing rapid prototype models. The process allows complex shapes to be reproduced in polymer resin, going from computer data to finished product within a period of 24 hours. Rapid prototyping techniques are increasingly being used by industry to produce models in a fraction of the time required for more conventional manufacturing methods.
To produce a stereolithography model, the product must be modelled with a computer aided design (CAD) package. The stereolithography model is manufactured by scanning a laser across the surface of a tank of liquid polymer resin. The CAD model ~J~I~b~.se directs this laser.The resin is sensitive to the laser light and solidifies in a thin layer, in the scanned areas. Each scan builds up a thin layer of solidifed resin, representing one of the cross sections of the model. Between the scanning of each layer, the developing model is "dunked" beneath the surface of the resin, leaving a layer of liquid to be solidified in the next scan.
2i 7~323 The resin is partially cured and is finally cured by placing the model in an oven.
After this, the model is cleaned up by hand and finished according to it's intended application.
Another form of Stereolithography has been termed Solid Ground Curing (SGC).
The Cubital System uses this technology to combine layer additive and layer subtractive process to produce patterns. The finished parts are produced in photopolymer resin, similar to stereoltithography is appearance A typical process layer is produced in the following steps:
1 ) An ultraviolet lamp exposes a photosensitive resin (similar to those used instereolithography) through a mask. The mask is created on a charged glass plate using a toner similar to xerographic or laser printing techniques.
2) The unexposed resin is vacuumed up from the exposed layer.
3) The remaining voids where the unexposed resin was removed is filled with liquid wax, and a chill plate then hardens the wax.
4) The resin/wax layer is the milled down by a cutter to a precise thickness.
5) A new layer of resin is applied, and the process continues.
When complete, the soluble wax is usually removed by dissolving it in a mild acid solution or a solution of soap and warm water.
There has been an increasing requirement to create molds for injection molding rather than a part using the SLA. Both the cavity and core are produced by Stereolithography. It is an a very fast method to obtain a complicated shape with detailed topography. Injection molding is an excellent way to repoduce the obverse of that complicated shape in one shot. Common injection moulding processes can then produce functional plastic parts.
There are three properties of the photoformed molds which reduce their efficiency in injection molding of thermoplastics. The three characteristics are compressive strength, heat deflection temperature and heat transition temperature.
The stereolithographic molds by themselves undergo a change in mechanical properties respective glass te",peralures. In most cases the glass temperatures are less than 130 degrees Centigrade. Stereolithography molds tend to chip when the part is ejected after exceeding these temperatures.
The other critical temperature to the SLA mold is the heat deflection temperature.
The heat deflection temperature of the cured photopolymer is the temperature at which the polymer softens and begins to creep. These deflection temperatures are typically less than 100 degrees Centigrade for stereolithograpy inserts. Heat deflection effect will change the topography of the thermopl~.stic part produced.
Accuracy in the thermoplastic part produced by the insert is further degraded by the compressiblity of the cured SLA resin.
In order to address these temperature problems the SLA resin core and cavity have previously been coated with a 125 micron layer of copper used to protect the core and cavity from heat stress during the injection moulding of relatively high temperature resins such as Polycarbonate.
This process has produced a relative small number of parts before the delamination of the the thin copper coating. The copper absorbs the heat more readily than the sul,st,ale. The copper film expands at a faster rate than the sub~ te. The coppper coating shears off the sul)slrale after approximately fifty parts are produced.
Nickel is an other protective coating material which tends to crack after a small number of parts are produced.
In order to fully utilize the efficencies of stereolithograpy compositions for injection mold inserts there is a need to protect the photoformed insert with an outermost layer of the cavity or core wall consisting of a substance with excellent heat resistance low heat conductivity high tensile strength and high elongation durability against heating cooling cycles an abrasive resistant surface with polishability and be thin in cross section. The protective coating must not require curing at temperatures that exceed the glass transition and heat deflection tel"peralures of the photofo""ed insert. The high heat resistance of the prolecti~/e layer is desireable because the greater the variety of thermoset and thermoplastic resins can be for the injected molded part. The outermost layer must a glass temperature greater than 200 degrees Centigrade.
2 1 7q323 -Photopolymer such as describe above are used by and not limited to the followingStereolithography Appartus:
1. 3D Systems Inc., U.S.A.
2. CMET, JAPAN - SOUP 600, 850x 3. D-MEC (Sony Group), Japan - SCS 1000HD
4. Laser 3D, France - SPL 1000, 5000 5. EOS Gmbh, Germany - STEREOS 400, 600 6. Teijin Seiki, Japan - Soliform 300, 500 7. Cubital, Isreal - Solid Ground Curing The Disclosure The ~ ess The mould creation process is the main factor in creating functional and technical prototype plastic parts. The functional prototypes, ty-pically two to five parts are needed in the product development cycle for:
1) product planning a) working principle verification b) functional principle optimization 2) m~mlf~ctllring process planning a) m~mlf~cture sequence assembly planning b) layout pl~nning c) resource planning The technical prololy~es, typically three to twenty parts are needed in the product development cycle for:
1) product planning a) cll~tomer acceptance verification b) fatigue strength verification 2) m~mlf~cturing process application The goal of our research project was to produce both functional and technical pr~tolyl,es in numbers less than fifty parts in the engineering resin identified for final m~nllf~ctllre - Polycarbonate. The chosen test part was breast shield adapter for a mother's breast milk pump. Two parallel three--limen.cional CAD solid models were produced, one with PRO/engineer and the other with AutoCad R12 (Advanced Modeling Extension). The AutoCAD produced STL file proved unsatisfactory for the Stereolithography a~al~lus (SLA) and had to be l.,cleatt;d using a third party application working within AutoCAD R12.
21 7~323 s Once the part was created by the designer and all the structural and cosmetic features have been designed into the part, it is then sent to the Stereolithography appal~us (SLA).
The SLA creates real three--limen~ional parts from the computer model. The parts which can be made of acrylic or epoxy, address only the plu~lties of form and fit, but do not fill the above requirements of functional and tec~ical prototypes listed previously. They are quite brittle and will not with~t~ntl heat sterilization. The process that has been developed takes a dirre~c.,l route from the step above. Instead of creating a part using the SLA, a mould is created using the SLA. Previously, only one side of the mould was created by this process.
Here, both the cavity and core are produced by Stereolithography. The mould can then be used to create functional plastic parts.
The PRO/engineer CAD model is sent to another package called PRO/mold that creates the core and cavity of a mould. In PRO/mold, the core and cavity are adjusted for shrink allow~ces of a plastic injection moulding process. The location of the ejector pins to strip the plastic part, from the mould are added. Cooling lines, used to keep the mould cool during the injection moulding process, may be added if necessary. The time to pclr~ ll this function is about one day for the breast shield adapter.
The mould core and cavity are then sent to the SLA to be built. The building time of the SLA parts also depends on the size of the part. This time is real time as the SLA can operate day and night and it does not need to have a model maker present. Simlllt~neously, a mould maker is prep~;l-g mould shoes that will hold the SLA core and cavity in the injection moulding m~r~hine and m~king ejector pins for the mould.
The SLA core and cavity are then coated with a 125 micron layer of copper used to protect the core and cavity in the injection moulding m~chine; This is a key part of the process.
The mold halves were ready for the next phase one week after the CAD solid model geometry was complete.
The coated core and cavity are then fitted into the shoes, which the model maker has made, and the shoes are placed in the injection moulding m~Ghine. The ejector pins are also placed in the mould shoes. The injection moulding m~hine parameters, such as temperature and s~ule, are adjusted and the first parts are made. The setup time is about two hours. Up to forty-four functional prototypes of the breast shield adapter have been created by this process.
.
Concluslons The prototypes of the breast shield adapter, created by this process, are functional and could be used for hospital efficacy testing. Consumer focus groups can be provided with these ploto~y~es for acc~ce verification. Sales staff can use these prototypes for marketing and obtaining orders before product production commences.
Designers will gain from this process because it reduces the risk associated with the final part design for production mould m~nllf~chlring- Mech~nic~l dçsigners can check that the parts function propt;lly. Product integrity staffcan conduct environment~l stress analysis at the earliest possible stage in the development process.
2 1 7~323 The process has reduced the time to create functional plotoly~e plastic parts by a factor of at least 15, and reduces the cost of making proto~pe moulds by 80%.
The process applies to the wide spectrwn of Thermoplastics having melt t~ el~ s less than Polycarbonate. This group includes ap~lo~illlately 80% of all Thelmoplastics. Mould Makers can now produce both core and cavity inserts by this process.
[1] Yeung M. and McKeen J., "Rapid M~mlf~ctllrin~ of Plastic Injection Moulds for Prototype ABS Parts", on the proceeding of "1995 SLA User's Group Conference", Tampa, FL, U.S.A., March 1995.
[2] McKeen J. and Yeung M., "Rapid Mould M~mlf~ctllnn~", on the procee~ling of "Rapid Prototyping and Manufacturing '95", Dearborn, MI, U.S.A., May 1995.
In a preferred embodiment the mold insert has three component parts. The parts are a photoformed shell a cooled heat conductive backing and a conformal protective Polyimide exterior coating. The mould insert consists of a stereolithograpy apparatus photoformed shell which is filled by heat conductive backing and cooling ducts. The backing material has a co",pressive strength equal or greater than the compressive strength of the hardened photofor",ed shell ",ate,ial. Typically this greater than Cold cure two part epoxy matrix combined with alluminium fragments of random shape and size is used for the baking material and copper or alluminium tubes for the cooling ducts.
Other techniques to attempt to reduce the operating temperature of the photopolymer in a mould the core and cavity inserts have been hollowed out or or a shell is photoformed.
The shell is then filled with a conglomerate mixture of alumium fragments in a polymer. Heat conductive ducts can be installed in the conglomerate prior to the polymer harding. These ducts can then be cooled with water in allelllpl to keep the photoformed shell below it heat deflection and glass transition temperatures. This water cooling is applied when photoformed shells and backing are installed in an injection moulding machine and the photoformed shell is in cyclic contact with a thermoplastic to produce a part with the topography of shells obverse shape. Although the photoformed shell is cooled by the backing material it is still subject to surface heating which reduces its number of part cycles.
The exterior of the shell is protected by a flourinated polyimide layer which is the outermost layer of the cavity or core wall. Polyimides have been used as coatings in the electronics field because they are high thermally stable dialectric. The other propertys that makes Polyimides excellent for a protective coating used in conjunction with injection moulding is the fact that are abrasive resistant there surface is slippery and can be polished.
~ 1 7~323 The p~oble", in the past has been these Polyimides have been applied in a solvent solution such as gamma-Butyrolactone. Typically solutions such as this require final cure te",perdlures in between 200 and 350 degrees Centigrade. Application of these Polyimide films to a Stereolithography mould would require curing at temperatures at least 70 degrees greater than the glass transition temperature of the Photopolymer sul,slfate. When the temperature of the photoformed shell is exceeded the mechanical properties of the subslfate would be degraded. The coated photopolymer would be unuseable as a mould material as it woud be unable to withstand the pressure of injection moulding. First a photoformed shell is made and the consisting of a substance with excellent heat resistance, low heat conductivity, high tensile strength and high elongation, durability against heating cooling cycles, an abrasive resistant surface with polishability and be thin in cross section. The protecti~/e coating must not require curing at temperatures that exceed the glass transition and heat deflection temperatures of the photofor"~ed insert. The high heat resistance of the protective layer is desireable because, the greater the variety of thermoset and thermoplastic resins can be for the injected molded part. The outermost layer must a glass temperature greater than 200 degrees Centigrade.
The flourinated polyimide powder such as LARC cp-1, but not limited to, are solvent soluble. It is mixed with solvents that are volitile at tempertatures below the glass transition temperature of the hardened photoformed composition. Typically these solvents are Tetra Hydro Furan, Ethyl Acetate, Acetone, Isobutal Keytone, Cloroform and a combination of Ethyl Acetate and Acetone. These solvents are typically drawn off at room temperature. In fact this drawing of process should not be accelerated because it may cause bubbling or bli~leri,1g in the polyimide coating. A final heat may be applied up to the glass temperature of the photopolymer to draw off residule solvent and to cure the polyimide coating.
The solvent mixture can be have up to 16.0% solids. The amount of solids can be reduce to accommodate desired layer thickness and required viscosity for the application technique.
Thickness of the conformal coating of polyimide can vary from 20 microns up to .005 inch.
The favoured application technique is eleclroslatic spray coating. This allows many thin conformal coats to be applied one after another.
Simple hand sprayers or air brush guns can be used. Even application with a paintbrush.
21 7~323 In a second embodiment there is no backing material filling the photoformed shell. In a third embodiment a adhesive is used between the shell and the exterior coating.
An adhesion promoter such as Hexamethyle di silazane (H.M.D.S), tradename -H~dro~ella~e may be used. A expoxy resin mixed with a hardner may be used to promote adhesion of the polyimide solution to the hardened photofor"led shell.
When complete, the soluble wax is usually removed by dissolving it in a mild acid solution or a solution of soap and warm water.
There has been an increasing requirement to create molds for injection molding rather than a part using the SLA. Both the cavity and core are produced by Stereolithography. It is an a very fast method to obtain a complicated shape with detailed topography. Injection molding is an excellent way to repoduce the obverse of that complicated shape in one shot. Common injection moulding processes can then produce functional plastic parts.
There are three properties of the photoformed molds which reduce their efficiency in injection molding of thermoplastics. The three characteristics are compressive strength, heat deflection temperature and heat transition temperature.
The stereolithographic molds by themselves undergo a change in mechanical properties respective glass te",peralures. In most cases the glass temperatures are less than 130 degrees Centigrade. Stereolithography molds tend to chip when the part is ejected after exceeding these temperatures.
The other critical temperature to the SLA mold is the heat deflection temperature.
The heat deflection temperature of the cured photopolymer is the temperature at which the polymer softens and begins to creep. These deflection temperatures are typically less than 100 degrees Centigrade for stereolithograpy inserts. Heat deflection effect will change the topography of the thermopl~.stic part produced.
Accuracy in the thermoplastic part produced by the insert is further degraded by the compressiblity of the cured SLA resin.
In order to address these temperature problems the SLA resin core and cavity have previously been coated with a 125 micron layer of copper used to protect the core and cavity from heat stress during the injection moulding of relatively high temperature resins such as Polycarbonate.
This process has produced a relative small number of parts before the delamination of the the thin copper coating. The copper absorbs the heat more readily than the sul,st,ale. The copper film expands at a faster rate than the sub~ te. The coppper coating shears off the sul)slrale after approximately fifty parts are produced.
Nickel is an other protective coating material which tends to crack after a small number of parts are produced.
In order to fully utilize the efficencies of stereolithograpy compositions for injection mold inserts there is a need to protect the photoformed insert with an outermost layer of the cavity or core wall consisting of a substance with excellent heat resistance low heat conductivity high tensile strength and high elongation durability against heating cooling cycles an abrasive resistant surface with polishability and be thin in cross section. The protective coating must not require curing at temperatures that exceed the glass transition and heat deflection tel"peralures of the photofo""ed insert. The high heat resistance of the prolecti~/e layer is desireable because the greater the variety of thermoset and thermoplastic resins can be for the injected molded part. The outermost layer must a glass temperature greater than 200 degrees Centigrade.
2 1 7q323 -Photopolymer such as describe above are used by and not limited to the followingStereolithography Appartus:
1. 3D Systems Inc., U.S.A.
2. CMET, JAPAN - SOUP 600, 850x 3. D-MEC (Sony Group), Japan - SCS 1000HD
4. Laser 3D, France - SPL 1000, 5000 5. EOS Gmbh, Germany - STEREOS 400, 600 6. Teijin Seiki, Japan - Soliform 300, 500 7. Cubital, Isreal - Solid Ground Curing The Disclosure The ~ ess The mould creation process is the main factor in creating functional and technical prototype plastic parts. The functional prototypes, ty-pically two to five parts are needed in the product development cycle for:
1) product planning a) working principle verification b) functional principle optimization 2) m~mlf~ctllring process planning a) m~mlf~cture sequence assembly planning b) layout pl~nning c) resource planning The technical prololy~es, typically three to twenty parts are needed in the product development cycle for:
1) product planning a) cll~tomer acceptance verification b) fatigue strength verification 2) m~mlf~cturing process application The goal of our research project was to produce both functional and technical pr~tolyl,es in numbers less than fifty parts in the engineering resin identified for final m~nllf~ctllre - Polycarbonate. The chosen test part was breast shield adapter for a mother's breast milk pump. Two parallel three--limen.cional CAD solid models were produced, one with PRO/engineer and the other with AutoCad R12 (Advanced Modeling Extension). The AutoCAD produced STL file proved unsatisfactory for the Stereolithography a~al~lus (SLA) and had to be l.,cleatt;d using a third party application working within AutoCAD R12.
21 7~323 s Once the part was created by the designer and all the structural and cosmetic features have been designed into the part, it is then sent to the Stereolithography appal~us (SLA).
The SLA creates real three--limen~ional parts from the computer model. The parts which can be made of acrylic or epoxy, address only the plu~lties of form and fit, but do not fill the above requirements of functional and tec~ical prototypes listed previously. They are quite brittle and will not with~t~ntl heat sterilization. The process that has been developed takes a dirre~c.,l route from the step above. Instead of creating a part using the SLA, a mould is created using the SLA. Previously, only one side of the mould was created by this process.
Here, both the cavity and core are produced by Stereolithography. The mould can then be used to create functional plastic parts.
The PRO/engineer CAD model is sent to another package called PRO/mold that creates the core and cavity of a mould. In PRO/mold, the core and cavity are adjusted for shrink allow~ces of a plastic injection moulding process. The location of the ejector pins to strip the plastic part, from the mould are added. Cooling lines, used to keep the mould cool during the injection moulding process, may be added if necessary. The time to pclr~ ll this function is about one day for the breast shield adapter.
The mould core and cavity are then sent to the SLA to be built. The building time of the SLA parts also depends on the size of the part. This time is real time as the SLA can operate day and night and it does not need to have a model maker present. Simlllt~neously, a mould maker is prep~;l-g mould shoes that will hold the SLA core and cavity in the injection moulding m~r~hine and m~king ejector pins for the mould.
The SLA core and cavity are then coated with a 125 micron layer of copper used to protect the core and cavity in the injection moulding m~chine; This is a key part of the process.
The mold halves were ready for the next phase one week after the CAD solid model geometry was complete.
The coated core and cavity are then fitted into the shoes, which the model maker has made, and the shoes are placed in the injection moulding m~Ghine. The ejector pins are also placed in the mould shoes. The injection moulding m~hine parameters, such as temperature and s~ule, are adjusted and the first parts are made. The setup time is about two hours. Up to forty-four functional prototypes of the breast shield adapter have been created by this process.
.
Concluslons The prototypes of the breast shield adapter, created by this process, are functional and could be used for hospital efficacy testing. Consumer focus groups can be provided with these ploto~y~es for acc~ce verification. Sales staff can use these prototypes for marketing and obtaining orders before product production commences.
Designers will gain from this process because it reduces the risk associated with the final part design for production mould m~nllf~chlring- Mech~nic~l dçsigners can check that the parts function propt;lly. Product integrity staffcan conduct environment~l stress analysis at the earliest possible stage in the development process.
2 1 7~323 The process has reduced the time to create functional plotoly~e plastic parts by a factor of at least 15, and reduces the cost of making proto~pe moulds by 80%.
The process applies to the wide spectrwn of Thermoplastics having melt t~ el~ s less than Polycarbonate. This group includes ap~lo~illlately 80% of all Thelmoplastics. Mould Makers can now produce both core and cavity inserts by this process.
[1] Yeung M. and McKeen J., "Rapid M~mlf~ctllrin~ of Plastic Injection Moulds for Prototype ABS Parts", on the proceeding of "1995 SLA User's Group Conference", Tampa, FL, U.S.A., March 1995.
[2] McKeen J. and Yeung M., "Rapid Mould M~mlf~ctllnn~", on the procee~ling of "Rapid Prototyping and Manufacturing '95", Dearborn, MI, U.S.A., May 1995.
In a preferred embodiment the mold insert has three component parts. The parts are a photoformed shell a cooled heat conductive backing and a conformal protective Polyimide exterior coating. The mould insert consists of a stereolithograpy apparatus photoformed shell which is filled by heat conductive backing and cooling ducts. The backing material has a co",pressive strength equal or greater than the compressive strength of the hardened photofor",ed shell ",ate,ial. Typically this greater than Cold cure two part epoxy matrix combined with alluminium fragments of random shape and size is used for the baking material and copper or alluminium tubes for the cooling ducts.
Other techniques to attempt to reduce the operating temperature of the photopolymer in a mould the core and cavity inserts have been hollowed out or or a shell is photoformed.
The shell is then filled with a conglomerate mixture of alumium fragments in a polymer. Heat conductive ducts can be installed in the conglomerate prior to the polymer harding. These ducts can then be cooled with water in allelllpl to keep the photoformed shell below it heat deflection and glass transition temperatures. This water cooling is applied when photoformed shells and backing are installed in an injection moulding machine and the photoformed shell is in cyclic contact with a thermoplastic to produce a part with the topography of shells obverse shape. Although the photoformed shell is cooled by the backing material it is still subject to surface heating which reduces its number of part cycles.
The exterior of the shell is protected by a flourinated polyimide layer which is the outermost layer of the cavity or core wall. Polyimides have been used as coatings in the electronics field because they are high thermally stable dialectric. The other propertys that makes Polyimides excellent for a protective coating used in conjunction with injection moulding is the fact that are abrasive resistant there surface is slippery and can be polished.
~ 1 7~323 The p~oble", in the past has been these Polyimides have been applied in a solvent solution such as gamma-Butyrolactone. Typically solutions such as this require final cure te",perdlures in between 200 and 350 degrees Centigrade. Application of these Polyimide films to a Stereolithography mould would require curing at temperatures at least 70 degrees greater than the glass transition temperature of the Photopolymer sul,slfate. When the temperature of the photoformed shell is exceeded the mechanical properties of the subslfate would be degraded. The coated photopolymer would be unuseable as a mould material as it woud be unable to withstand the pressure of injection moulding. First a photoformed shell is made and the consisting of a substance with excellent heat resistance, low heat conductivity, high tensile strength and high elongation, durability against heating cooling cycles, an abrasive resistant surface with polishability and be thin in cross section. The protecti~/e coating must not require curing at temperatures that exceed the glass transition and heat deflection temperatures of the photofor"~ed insert. The high heat resistance of the protective layer is desireable because, the greater the variety of thermoset and thermoplastic resins can be for the injected molded part. The outermost layer must a glass temperature greater than 200 degrees Centigrade.
The flourinated polyimide powder such as LARC cp-1, but not limited to, are solvent soluble. It is mixed with solvents that are volitile at tempertatures below the glass transition temperature of the hardened photoformed composition. Typically these solvents are Tetra Hydro Furan, Ethyl Acetate, Acetone, Isobutal Keytone, Cloroform and a combination of Ethyl Acetate and Acetone. These solvents are typically drawn off at room temperature. In fact this drawing of process should not be accelerated because it may cause bubbling or bli~leri,1g in the polyimide coating. A final heat may be applied up to the glass temperature of the photopolymer to draw off residule solvent and to cure the polyimide coating.
The solvent mixture can be have up to 16.0% solids. The amount of solids can be reduce to accommodate desired layer thickness and required viscosity for the application technique.
Thickness of the conformal coating of polyimide can vary from 20 microns up to .005 inch.
The favoured application technique is eleclroslatic spray coating. This allows many thin conformal coats to be applied one after another.
Simple hand sprayers or air brush guns can be used. Even application with a paintbrush.
21 7~323 In a second embodiment there is no backing material filling the photoformed shell. In a third embodiment a adhesive is used between the shell and the exterior coating.
An adhesion promoter such as Hexamethyle di silazane (H.M.D.S), tradename -H~dro~ella~e may be used. A expoxy resin mixed with a hardner may be used to promote adhesion of the polyimide solution to the hardened photofor"led shell.
Claims (20)
1) A layered structure consisting of two layers. The first layer has a surface carrying the defined topography of the final structure. The second layer is a conformal exterior coating for the first having heat insulative characteristics. The second layer has heat-deflection and heat transition temperature higher than the heat deflection and heat transition temperature of the first layer. The process of adhereing the layers to each other and the curing of the second layer requires heating up to but not exceeding the glass transition temperature and heat heat deflection temperatures of the first layer.
2) A structure according to claim 1 wherein said first layer is a synthetic resin.
3) A structure according to claim 2 wherein the said second layer is a synthetic resin.
4) A structure according to claim 1 wherein the first layer has been formed by coating a solution of a Photoformed composition derived from a photopolymer resin.
5) A structure according to claim 4) wherein the said second layer has been formed by coating a solution of a precursor of a linear high-molecular weight polyimide on the said first layer.
6) A structure according to claim 1) wherein said second layer exceeds the firstin the following charaturistics - low heat conductivity, excellent heat resistance, high tensile strength and high elongation, durability against heating cooling cycles, high surface hardness and excellent wear resistance, easy coating on a mold body, satisfactory adhesion to the mold body, surface polishability, and excellent anticorrosion during formation of the heat insulating said second layer during molding of synthetic resins. The said first layer of claim 1) has the form and utility of a mold body or insert used in the
7) A structure according to claim 1) wherein said second layer has a compressive strength greater than the compressive strength of said first layer.
8) A structure composed of three component parts:
a) a first shell layer carrying the defined topography of the structure.
b) a backing or filling material to fill said shell and c) a second exterior layer to comformal coat the combination of said first shell layer and baking material.
a) a first shell layer carrying the defined topography of the structure.
b) a backing or filling material to fill said shell and c) a second exterior layer to comformal coat the combination of said first shell layer and baking material.
9) A mold for synthetic resin molding comprising a mold body made of a synthetic resin said mold having provided on the cavity wall thereof a polyimide layer, wherein said polyimide layer has a thickness of from 0.02 to 2 mm, has a heat conductivity of not more than 0.002 cal/cm multiplication dot sec multiplication dot degree(s) C., has a glass transition temperature of not less than 200 degree(s) C., has an elongation at break of not less than 10%, and has an adhesive strength of not less than 500 g/10 mm to the cavity wall.
10) The mold according to claim 1, wherein said mold body has thereon a plating material from the group consisting of chromium and nickel on which said polyimide layer is formed.
11) The mold according to claim 1 or 2, wherein said polyimide layer has a polished smooth surface.
12) The mold according to claim 1, wherein said mold is a mold for injection molding.
13) The mold according to claim 4, wherein the thickness of said polyimide layer is increased from a gate portion toward a resin flow end.
14) The mold according to claim 4, wherein said polyimide layer has a relativelysmall thickness at the portion where a relatively high inner pressure is applied immediately after the cavity is filled with the synthetic resin, relatively a large thickness at the portion where said inner pressure is relatively low.
15) The mold according to claim 3, wherein said mold is a mold for blow molding.
16) The mold according to claim 3, wherein said mold is a mold for injection molding.
17) The mold according to claim 8, wherein the thickness of said polyimide layer is increased from a gate portion toward a resin flow end.
18) The mold according to claim 8, wherein said polyimide layer has a relativelysmall thickness at the portion where a relatively high inner pressure is applied immediately after the cavity is filled with the synthetic resin, a relatively large thickness at the portion where said inner pressure is relatively low.
19) The mold according to claim 4, wherein the thickness of said polyimide layer increased from a gate portion toward a resin flow end.
20) The mold according to claim 1, wherein said mold is a mold for blow molding references.
[1] Yeung M. and McKeen J., "Rapid Manufacturing of Plastic Injection Moulds for Prototype ABS Parts", on the proceeding of "1995 SLA User's Group Conference", Tampa, FL, U.S.A., March 1995.
[2] McKeen J. and Yeung M., "Rapid Mould Manufacturing", on the proceeding of "Rapid Prototyping and Manufacturing '95", Dearborn, Ml, U.S.A., May 1995.
[1] Yeung M. and McKeen J., "Rapid Manufacturing of Plastic Injection Moulds for Prototype ABS Parts", on the proceeding of "1995 SLA User's Group Conference", Tampa, FL, U.S.A., March 1995.
[2] McKeen J. and Yeung M., "Rapid Mould Manufacturing", on the proceeding of "Rapid Prototyping and Manufacturing '95", Dearborn, Ml, U.S.A., May 1995.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002179323A CA2179323A1 (en) | 1996-06-14 | 1996-06-14 | Synthetic resin mold for synthetic molding and methods |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002179323A CA2179323A1 (en) | 1996-06-14 | 1996-06-14 | Synthetic resin mold for synthetic molding and methods |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2179323A1 true CA2179323A1 (en) | 1997-12-15 |
Family
ID=4158425
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002179323A Abandoned CA2179323A1 (en) | 1996-06-14 | 1996-06-14 | Synthetic resin mold for synthetic molding and methods |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2179323A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20150037453A1 (en) * | 2012-03-06 | 2015-02-05 | Krones Ag | Stretch blow molding machine with rapid prototyping components |
-
1996
- 1996-06-14 CA CA002179323A patent/CA2179323A1/en not_active Abandoned
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20150037453A1 (en) * | 2012-03-06 | 2015-02-05 | Krones Ag | Stretch blow molding machine with rapid prototyping components |
| US9085098B2 (en) * | 2012-03-06 | 2015-07-21 | Krones Ag | Stretch blow molding machine with rapid prototyping components |
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