GB2403927A

GB2403927A - Controlling flow of resin into a mould cavity using sensors

Info

Publication number: GB2403927A
Application number: GB0421177A
Authority: GB
Inventors: John H Moore; Steven A Beal
Original assignee: JHM TECHNOLOGIES Inc
Current assignee: JHM TECHNOLOGIES Inc
Priority date: 2001-05-31
Filing date: 2002-05-31
Publication date: 2005-01-19
Anticipated expiration: 2022-05-31
Also published as: GB0421177D0; GB2403927B

Abstract

A method and apparatus for moulding composite articles are disclosed. There may be at least one skin 16 with a back side 54 and a front side 52, which defines a portion of a mould cavity. A pressure sensor 66 has a portion extending through the skin 16 into the cavity to generate a signal indicative of pressure in the cavity. A control unit controls injection of resin into the cavity in response to the signal generated by the sensor. Deflection sensors may be mounted to the back sides of upper and lower skins 20, 16 defining the cavity therebetween. The sensor, mounted on a deformable skin, may generate a signal indicative of skin deformation. The sensors, which may be connected to a CPU, stop or slow the flow of resin if the resin pressure builds up to deform the skins.

Description

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METHOD AND APPARATUS

FOR MOLDING COMPOSITE ARTICLES

field of the Invention

The present invention relates to a method of molding and molding apparatus for use in the molding of composite articles. More particularly, the invention relates to a method and apparatus for use in resin transfer molding.

Background of the Invention

Resin transfer molding (Rl is a process in which dry fiber reinforcement is loaded into a mold cavity. The surfaces of the mold cavity defLue the ultLmate configuration of the article being fabricated. Resin is injected under pressure or drawn under vacuum into the mold cavity to saturate the fiber reinforcernert. After the resinated fiber reinforcement is cured, He finished article is removed from the mold.

Recently, RTM molding has been performed in a rind cavity or lower 1> mold and a skin fomung the upper mold. Such a molding process is disclosed in United lLincdom Patent Application 9?319,90'A. The flexible upper mold I sun is typically made from a composite material. The upper sled is formed - over an inverted male mold pattern. 1 hen, a calibration layer of sheet wax.

defining the mold cavity is laid over the upper slim and a bolster slain is formed over the calibration layer. The exposed face of He bolster sun is shrouded with a frame. The pattern is separated and the calibration layer is removed.

The upper skin is then used as pelt of the upper mold half. However, the sky has a short life expectancy and next slans can be replaced only by reapplying the sheet wax and rebuilding the upper slain from a calibrated wax surface.

- 95 This requires the tooling to be out of production for a lengthy period of time depending upon the size of the mold. Additionally, the flow of resin occasionally bac.l;s up as it is blown through the fiber reinforcement in the mold cavity. thereby causing an outward deformation of the slim and loss of tolerance in He article being formed.

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Brief Description of the Invention

The invention is directed to a novel molding apparatus, a method of fornin=, the apparatus, and a method of using the apparatus to form a composite article. The apparatus includes a semi-flexible slain supported on a lower frame and a serru-rigid upper mold half. The lower frame includes a peripheral flange which surrounds an opening for receiving the cavity of the lower slain. The flange has a contour which is formed to mirror- the corresponding structure.of the slain. A vacuum is used to draw the lower sldn tightly against the flange of the frame and an inner peripheral edge of the flange. The upper mold is formed by applying calibration sheet wax within the cavity of the lower skin. A suitable tooling surface material is applied to {he sheet wax followed by a casting of additional materials to form the upper mold half. Ike slain is then structurally supported by building a trussworl: across the bacl; side of the skin to make the upper mold halt semi-rigid. peripheral flange With vacuum ports is formed similar to the flange on the frame to permit a vacuum to be drawn to draw the upper mold tightly against the lower-sldn.

Deflection sensors are mounted to the back sides of the upper and lower sl;in.

The sensors are connected to 2 CPU to stop or slow the flow of resin if the resin pressure builds to deform the slovens.

Brief Description of the Drawing

The invention will now be ex.planed in further detail with reference to the embodiments shown in tle drawings in which: FIG. 1 is a partial sectional view and schematic of the molding apparatus in accordance with Me invention; FIG. is a perspective vied' of the frame and flange for the lower mold half in accordance with the invention; FIG. 3 is a crosssectional exploded viewer of the upper and lower mold halves; FIG. is a cross-sectional view of Be upper and lower mold halves of 3Q the aup&-atus in accordance with the invention; A ÀeÀe :: . À. :. A: 3 À. A: FIG. 4B is a partial cross-sectional view of the upper resold half in accordance with the invention, FIG. is a cross- sectional view of a mechanical sensor in accordance with the invention, and FIG. 6 is a flowchart showing, methods of forming the apparatus in accordance with tile invention.

Detailed Description of the Preferred Embodiments,

As show in FIG. 1, an apparatus 10 for resin transfer molding (RTM) includes a lower mold half 17 having a frame 14, a lower cavity slain 16, and an upper mold half 18 having a semi-rigid mold slain 20. The sl;ins of the apparatus 10 form a cavity 22 (FIG. 4) or plenum for molding an article of composite material.

As shown in FIGS. 2,; and 4, the lower frame 14 includes a support flange 94 supported on a tubule base 96. Tile flange 94 is formed to extend peripherally around a cavity portion 8 of the lower slain 16 (FIG. 4). The support flange 24 has a top surface 30 which is contoured to match a peripheral flange 44 of tile cavity slain 16. A pair of spaced apart seals 32, 33 or rubber gaskets extend longitudinally alone, the top surface 39. plurality of openings 34 for drawing a vacuum are positioned between the seals 32 33 and extend through the support flange 24 to a manifold 36 formed on an underside of the flange 94. The manifold 36 is connected by a conduit 38 to a vacuum pump 40 and control unit 42. When the pump 40 is activated, the peripheral flange 44 is drawn against the support flange 24 and the slain is drawn tightly against an inner edge 46 of the support flange 24 to provide rigidity to the sldn 16. The 2 ironer edge ó6 is formed to nest securely against the shin 16. 'me support flange 24 is fondled by hand lay-up on the back side of the skin 16. The seals are installed and then resinated cloth is laid on to for a rumor image of the back side of the flange of the skin. Depending upon the size of the article beige molded, it may be necessary; to provide a composite form 4S extending_ So under a cente; of the cavil:' skin i6. The form 48 acts lil;e a sling to support a middle portion of Me cavity, skin 16.

À À e. ce :: À. :e I: 4 À. A: As shown in FIG. 3, the caving skin 14 is formed with the per meter - flange 44 extending outwardly rrom the cavity portion 28. The skin 16 has a front side 52 and a back side 34. The front side:2 of the cavity portion 50 has the sltape of one side of the article to be formed. The cavity skin 16 is formed on a male mold pattem 56 by a suitable mower such as hand lay-up, vacuum bagging, vacuum form therrnoset or thermoplastic sheet. The mold pattern has the shape of the article being formed. The front side 52 of the sldn 16 is formed on the patter The mold also forms the Lange. A pair of gaskets me placed on the portion or the mold forming the flange to form recesses on the i flange of the skin to receive seals 32 of the frame as discussed below.

In most applications the molded article win have an outer layer of gel; coat. In such applications, the gel coat 56 is applied to the front side of the cavity portion 78 of the skin. Once the gel coat 56 has cured on the cavity portion US, reinforcement fibers 60 Ore then fitted to Me cavity form The reinforcement fibers SS may be fiberglass, ararnid, carbon or synthetic fibers which are laid on the gel coat 56 in the cavity portion 8 of the slain. After the slain 16 has been fitted with the reinforcement fibers IS, the skin is placed on the frame with the underside or the peripheral flange 44 of the slow resting on the support flange 4 of the rrarne. The inner edge 46 of the support flange ?4 of the frame 14 extends around the back side of the cavity skin 16 where the cavity portion 28 begins. When a vacuum is drawn, tile cavity skin 16 is locked onto the frame 14 and the support flange 24 provides the skin with great rigidity.

As shown in FIGS. 4A and 4B, the upper mold half 18 includes an 2 upper slain 0 which is backed bit a truss frame 60 having a flange 6,' contairung another set of vacuum seals 64 65. The skin is formed in 1 he same manner as described in GB 2,319,205 A. The truss Game 6G extends across a baclc side 6 of the slain 20 to malice the skin semi-rigid. The Eame 60 may be formed of a suitable rigid material such as metal and is permanently affixed by resin to the sldn The frame 60 houses a vacuum manifold 64 which extends about the flange 62 of the uppe: slant I"ne manifold 64 is connected to the t' .. Àe À.. ....

pump 40. Seals 63, 65 are mounted to the flange 6. The upper mold half 18 and lower mold half lq have registry guides such as a dowel as known in the al! to maintain the upper and lower mold halves IS, 12 in proper position.

After the upper mold half 18 is placed over the cavity skin 24, a vacuum is drawn on the upper half to lock the upper mold half on the front side of the cavity skin flange.

As shown in FIG. 1, a vacuum is created in the cavity through a port in the center of the upper mold half 18 orn either a catchpot 59 mounted di,ectly on We top of the port or through a tube feeding to a resin trap as is known in. i the art. After the mold halves have been installed and registered, a vacuum on the flange of the lower skin is drawn by pump 63. Then a vacuum on We; cavity is drawn, typically 0.5 bar, and resin is injected from a supply of resin 51 through ports is, 45.

As shown in FIG. 4A, pressure sensors, such as a pressure transducer I 5 66, are mounted to both the back sides of the upper and lower mold skins for detecting the pressure within the cavity. The sensor may be pressure transducer 66 or a mechanical valve 68 (FIG. 1) whirls reacts to a change in pressure. The pressure transducer 66.has a probe which passes through the slan into the cavity. The pressure transducer is able to detect small changes in So pressure of.1 bar or less. A suitable pressure transducer is produced by Micron Instruments of Simi Valley, California The pressure in the cavity is less than the ambient pressure surrounding the clans. The CPU receives the signals from the sensors, and if there is a positive gain in pressure' the CPU operates a valve to slow or stop the flow of resin before there is a deflection of q5 the skins. When one or more of tile sensors sense an increase of pressure at too high a rate or above a threshold pressure, the CPU acts to reduce or stop the flow of resin.

As shown in FIG. 5, the pressure sensor may be a mechanical valve 68 having a housing 70 and a piston 7. cavity pressure diaphragm 74 is 3G mounted on one end of the piston 72. The housing is mounted to the skin by mold Ibsen nag 75 to be in direct contact with the cavity. One su. ace of We À 6 ' "any ' i piston 72 is in a chamber 73 which is connected to the vacuum source 63. A pilot poppet 74 is mounted opposite the piston 79. The pilot poppet 74 is connected to the pump power air supply 76 for a resin pump 78. The pilot poppet 74 is in a normally closed position providing control for the power supply air flowing to tile pump 78. The piston 72 is removable through the chamber 7o to close the poppet 74.

When the cavity 20 is placed under vacuum' the pressure is exactly the same in both the cavity 29 and the vacuum connection port which is durectly cormected to the vacuum source 6; drawing central vacuum. Since the pressure is the same on the cavity diaphragm 74 and in the chamber 73, the piston will rernam in a neutral state in which the piston 72 is not in contact with the pilot poppet 74. If the pressure ir' the cavity 22 increases over the vacuum source pressure, the piston 72 will move to open the pilot poppet 74. Once the piston 7 is lifted from its neutral position, the pilot poppet will release the air holding 'e pneumatically powered resin pump supply line opera In an alternative embodiment of the pressure control apparatus, the piston is spring biased against the pressure diaphra - . When the inner mold cavity pressure is greater than the biasing force of the spring, the piston will move to trigger the pilot poppet as above. The sensitivity of the system using o0 this valve is limited to the biasing resistance of the spring. In the previous embodiment, where the vacuum pressure is applied to one side of the valve, minimal changes in mold cavity pressure will result in movement of the piston to trigger the poppet.

When the lealc signal is lost a signal is sent to sever the resin pump Mom its power supply air and the resin pressure intensified by the resin pump is immediately lost. This allows the cavity pressure to become negative again and the piston den returns to the normal position operating the poppet. The leak signal then is restored and We r esin pump power supply is restored to allow the pump to again bed pumping. This operation continues in a "closed loop" until the mold cavity is filled.

À l' ^ A À À a À , 7 À As shown in FIG. 1, the valve 68 or sensor 66 may be used with molds ha,irlg multiple injection ports 53' 5. The injection ports 53, SS are spaced successively inwardly from the peruneter of the mold towards the center exit vent 56. Resin is injected in the outermost injection points first. When the j valve 68 senses a positive increase of cavity pressure pilot pressure is sent to a diversion valve 90 to close the initial peruneter injection point and to open a succeeding inner injection point(s) to further the resin flow to the center while maintamng a negative cavity pressure. The injection mall also be accomplished by using the electronic sensors 66 and CPU to control the flow.

lo After the injection is complete, the mold is held with the vacuum on the vacuum frame holding the cavity mold and upper mold to maintain closure of the mold halves until the resin cures within the mold cavity. After the prescribed cure time has elapsed, the upper mold half is lifted off the cavity and the molded product is removed.

As set forth in FIG. 6 in greater detail with respect to the description of the apparatus, the method includes forming a se=-fle.;ible slain on a male mold pattern for use in defining a cavity for a lower mold half. A contoured flange for supporting the skin on a frame is then formed. The flange has the contour and an Inner surface to mate with the back side of a flange. A next step is forming a semi-rigid upper mold half. The serningid mold half may be formed by laying calibration wax over the mold pattern and casting the skin on the calibration wax. A trussworl; frame with a vacuum manifold on a Lange is mounted to the bacl; of the upper slain. The next step is to place the lower skin onto the flange of the frame and to place the upper mold half on top of the lower slain. A vacunrn is drawn through the contoured surface of the lower skin and through the outer fl&cre OI the upper mold half to close 'e mold halves. Finally resin is injected into the caviny.

Additionally a method of controlling the injection of the resin includes mounting a pressure sensor in a portion of the cavity, generating signals indicative of the pressure at intervals dream, the injection process, noting the À a.- ee; 8 ' ... .- . ' . rate of change of the pressure within the caviny' and controlling injection of resin into the cavity in response to pressure sensed by the sensors.

Thus disclosed is an apparatus and method for RTM rnoldg which is less expensive than conventional methods. The cavihy of the mold can be easily replaced at a fraction of the cost of conventional tooling methods. The cavity can be duplicated at minimal expense, thus multiple caviler sldus may be used each simultaneously. A gel coat and reinforcement fiber can be applied while other skins are molding products in the mold fires and the slau can be replaced without having to remove the mating half from production. ;

Claims

À see e e e e q

CLRIMS

1 1 An apparatus for molding an article compasmg: 2 at least one skin having a back side arid a fioot side, said front side 3 defir log a portion of a mold caviar, 4 - a pressure sensor mounted to a back side of said skin and hang a. ; portion extending Trough said skin into "d canter, said sensor generating a 6 signal indicative of pressure resaid cavity; and 7 a control nut for controlling the Section of resin into said cavity in 8 response to said signal generated by acid sensor.

1 2. The apply of Cohn wherein mid sensor is a pressure 2 transducer.

1 3. The apparatus of claim I wherein said sensor is a valve having a 2 membrane mounted in said cavity. ; 1 4!. A me&oaf of controlling a molding process ccnprmag Me steps 2 of: 3 mounting a sensor on a deformable side defying a portion of & mold 4 cavibr; ingesting resin into said cavity; 6 sensing defonnation of said skin with said sensor, 7 generating a signal indicative of deformation; and 8 controlling We flow of resin in response to said signal. Àe. À

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À . À . À 1. 5. A mold for molding an article by ream transfer molding, said 2 mold comprising: 3 a lower mold half having a flame ant a semi-flexible skin, salt Bame, 4 havlug a flange for supporting said slain, said flame farther haying a manifold I connected to a plurality of apertures fanned in said flange; -6 a vacuum pump connected to said manifold for drawing a vacuum 7 through said apertures on a bay side of said skin; and 3 8 an upper mold half having a surface spaces apart from a front side.: 9 surface of said skin to form a mold cavity for forming said article.

1. The mold half of claim further having at least one pressure 2 sensor extending Trough said sldn mto said cavity for sensing &e pressure 3 vermin the cavity and a controller far conhol]ing &e flow of resin in said cavity 4 in response to pressure sensed in said cavity.

1. The mold of claim wherein said upper mold half comprises a 2 son and a trusswork mounted to a back side of said skin.

1 8. The mold of claim 6 wherein said flange of said Dame teas a 2 contoured surface adapted to conform to said back side of a portion of said 3 skin. . 1 al. The mold of claim S wherein said flange has an mnerpenpheal - 2 - edge formed to nest agamst a back side of a portion of said skin. ÀÀ À:

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1 - - 10. A method of molding an article, said method comprising the 2 steps of: 3 forming a slab having a peripheral flange extending around a mold 4 cavil; placing said saw m a lower frame; 6 placing an Upper mold havmg a flange on Me upper surf ce of said 7 flange of said skin; 8 drawmg a vacuum through said lower frame on a back side surface of 9 stud flange of said slug and drawmg a vacuum Trough said upper mold on an upon surface of said flange of said skin; and 11 drawing resin through a plenum formed between said skm and said 12 upper mold to form the article.

1,. The method of claimed further comprising drawing a back side 2 peripheral portion of said cavity against a peripheral edge of said frame to 3 provide rigidity to said skm.

I I. The method of claim 10 further comprising forming said upper 2 mold from a senu-Dexible skin and Conning a framework on a back side of said 3 skin to provide rigidity to said mold.