GB2411618A

GB2411618A - Controlling moulding process using sensor

Info

Publication number: GB2411618A
Application number: GB0510891A
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: 2005-09-07
Anticipated expiration: 2022-05-31
Also published as: GB2411618B; GB0510891D0

Abstract

A method of controlling a moulding process, for moulding composite articles, is disclosed. The method comprises the steps of mounting a sensor on deformable skin defining a portion of a mould cavity, injecting resin into the cavity, sensing deformation of the skin with the sensor, generating a signal indicative of deformation and controlling the flow of resin in response to the signal.

Description

241 1618 h!ErOD AND APPARATUS Meld of the Invention The present insertion

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 In,tention

Resin transfer molding (Rl is a process in which dry fiber reinforcement is loaded into a mold cavity. The surfaces of the mold cavity define He ultimate configuration of the article being fabricated. Resin is _. . _ _ _. _. . - ' . . __- ' --.-- ----- - T injected under pressure or dragon under vacuum into the mold cavity to saturate the fiber reinforcement. After Be resinated fiber reinforcement is cured, the finished article is removed from tibe mold.

Recently, RTM molding has been performed in a rigid cavity OI lower mold and a skin forming the upper mold Such a molding process is disclosed in United I;ingdorn Patent Application r7,319,20SA. The flexible upper mold slan is typically made from a composite material. The upper skin is formed over an inverted male mold pattern. Then, a calibration layer of sheet wax defining the mold cavity is laid over the upper slain and a bolster slain is formed over the calibration layer. The exposed face of the bolster she is shrouded with a frame. The pattern is separated and the calibration layer is removed.

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

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 fiefonnation of the slim and loss of tolerance in He article being formed.

ir;cf 1SCrip+ O,C lo *C.od.;g h c. (;rst pact oft,c-t 1 pow. - d a method of controlling a molding process compr=mg the steps 2 of: 3 mounting a sensor on a defonnable skin defying a portion of a mold 4 cavity; injechug lean into said canter, 6 sensing deformation of said sldn with said sensor, 7 generating a signal indicative of deformation; and 8 controlling Me flow of resin in response to said signal.

At amour at oLd - a pixel 'e 1 iS Avid - ( an apparatus for molding as article cord: 2 at least one skin having a back Side and a front de' said front side 3 defining a portion of a mold cagily; 4 a pressure sensor mounted to a back side of said sldn Id hang a 5_ portion tohsaid sldn intro said cavity. said sensor aUng AL _ 6 BigDBl indicative of plebe m said cavity; sad 7 a control emit far controlling the injection of resin into stud cavity is 8 response to said sigasl generated by said sensor.

1 troll said sensor is a pressures 2 transducer.

1 61 said sensor is a valve havmg a 2 membrane mounted in said cavity. At.

I do Throw - 'ok of pxt._ APT 1 is pm,d can mold for molding an Uncle by ream transfer molding, said 2 mold comprising: 3 a lower mold half having a fiche and a semi-flexible skin, salt flame 4 having a flange for supporting said slain, said frame further hat a manifold connected to a plurality of apexes formed m said flange; 6 a vacuum pump connected to said manifold for drawmg a vacuum 7 Trough said apertures on a back side of said slain; slid - an--upper mold hardhat a surface-paced---from a i-sidc 9 surface of said skin to form a mold cavity for forming said oracle.

1 The mold navy ureter haves at least one pressure 2 sensor extending Trough said skin into said cavity for sensing the pressure 3 within Me cavity and a controller for controlling the flow of resin ire said cavity 4 in response to pressure sensed in said cavity.

I Pricer. said upper mold half comprises a 2 skin and a trusswork mounted to a baclc side of said skin.

I irC(crally Add flange of said frame teas a 2 contoured surface adapted to conform to said bulk side of a portion of said 3 skin.

I i,2fy Mid flange has an inner penphezal 2 edge formed to nest against a back side of a portion of said skin Amok I t; 1 ts po.dQl method of molding an article, "d method comb the 2 steps of: 3 forming a sldn having a peripheral flange exg around a mold 4 cavil, placing said skm m a lower theme; 6 placmg an upper mold havmg a fudge on the upper space of said 7 flange of said skin; --4. dry vaunt thaw He ab0.sid. _ __ 9 said flange of said sldu and drawing a vacuum through said Upper mold on upper surface of said flange of said BlCiR; and 11 drawing resin Trough a plenum formed between said skm Bald said 12 upper mold to firm the article.

1 The method bay father comprise drawing a back side 2 peripheral portion of said cavity against a peripheral edge of said frame to 3 provide rigidity to said sldn.

1 The method fiercer comprise forming said upper 2 mold Tom a semi-Dexible skin and fommg a framework on a back side of said 3 sldn to provide rigidity to said mold. lo.

The invention is directed to a novel molding apparatus, a method of forming the apparatus, and a method of using the apparatus to form a composite article. The apparatus includes a seni-flexible skin supported on a lower frame and a semi-rigid upper mold half. The lower frame includes a peripheral flange which surrounds an opening for receiving the cavity of the lower skin The flange has a contour which is formed to or the corresponding structure of the slain. A vacuum is used to draw the lower sldn tightly against the flange of Me frame and an inner peripheral edge of the - 10 flange. The upper Blond is fomed-by appalibrabon suet wax wlbin the cavity of the lower skin. A suitable tooling surface material is applied to the sheet wax followed by a casting of additional materials to form the upper mold half Tile slow is then structurally supported by building a ttusswork across the bacl; side of the shin to make the uppermold half semi-rigid. A 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 skin.

Deflection sensors are mounted to the back sides of the upper and louver skins.

The sensors are connected to a CPU to stop or slow the flow of resin if We resin pressure builds to deform the slcins.

Brief Description of the Drawling

The inflection will now be explained in further detail with reference to the embodiments shown in the drawings in which: FIG. 1 is a partial sectional view and schematic of Me molding apparatus in accordance with the invention; FIG. 2 is a perspective view of the frame and flange for the lower mold half in accordance with the invention, FIG. 3 is a crosssectional exploded view of the upper and lower mold halves, FIG. 4A is a cross-sectional view of Me upper and lower mold halves of Me apparatus in accordance with the invention; FIG. 4B is a partial cross-sectional view of the upper mold half in accordance with the invention; FIG. 5 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 the invention.

Detailed Description of the Preferred Embodiments

As shown in FIG. 1, an apparatus 10 for resin transfer molding PRIM includes a lower mold half 1r' having a frame 14, a lower cavity skin 16, and an upper mold half 18 hatting a senii-rigid-in 20. The skins of the apparatus 1Q form a cavity 29 (FIG. 4) or plenum for molding an article of composite material.

As shown in FIGS. I, 3 and 4, the lower frame 14 includes a support flange 74 supported on z tubular base 26. 'Ike flank e 94 is formed to extend penpherally around a cavity portion 98 of the lower slain 16 (FIG. 4). The support flange 94 has a top surface 30 which is contoured to match a peripheral flange 44 of the cavity slain 16. A pair of spaced apart seals 39, 33 or rubber gaskets extend longitudinally along the top surface Ad. A plurality of openings 34 for drawer a vacuum are positioned between the seals 39, 33 and extend 00 through the support flange 24 to a manifold 36 formed on an underside of the flange 24. 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 94 and the slain is drawn tightly against an inner edge 46 of the support flange 24 to provide rigidity to the slain 16. The o: inner edge 46 is formed to nest securely against the Skin 16. The support flange 94 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 form a mirror image of the back side of the flange of the skin. Depending upon the size of the article being molded, it may be necessary to provide a composite form 4S extending under a center of the cavity skin 16. The form 48 acts lilce a sling to support a middle portion of the cavity, skin 16. i . J 'Y

As shown in FIG. 3, the cavity skin 14 is formed with the perimeter flange 44 extending outwardly from the cavity portion 08. The skin 16 has a front side 52 and a back side 54. The front side S of the cavity portion 50 has the shape of one side of the article to be formed. The cavity slain 16 is formed on a male mold pattern 56 by a suitable manner such as hand lay-up, vacuum bagging, vacuum form thennoset or thermoplastic sheet. The mold pattern has the shape of the article being formed. The front side S of the slain 16 is formed on the pattern. The mold also forms the Dange. A pair of gaskets are placed on the portion of the mold forming the flange to form recesses on the - 10 - - - flangefthls elf flee frame as discussed be ow.

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 28 of the skin. Once the gel coat 56 has cured on the cavity portion 2S, reinforcement fibers 60 are there fitted to Me cavity form The reinforcement fibers 58 may be fiberglass, aramid, carbon or synthetic fibers which are laid on We gel coat 56 in the cavity, portion 28 of the slain. After the slain 16 has been fitted with the reinforcement fibers 38, the slain is placed on the frame with the underside of the peripheral flange 44 of the skin resdog on the support flange 24 of the frame. The inner edge 46 of the support flange 24 of the frame 14 extends around the back side of the cavity skin 16 where the cavity portion 28 begins. When a vacunrn is drawn, the cavity skin 16 is locked onto the frame 14 and the support fiance 4 provides the skin witl1 great ngidity.

As shown in FIGS. 4A and 4B, the upper mold half 18 includes an upper skin 0 which is baclced by a truss frame 60 having a flange 62 containing another set of vacuum seals 64, 65. The slain is formed in the same manner as described in GB 2,319,205 A. The truss harne 60 extends across a back side 6 of the skin 20 to mal;e the skin semi-rigid. The frame 60 may be formed of a suitable rigid material such as metal and is p- nanently affixed by resin to the slcm. The frame 60 houses a vacuum manifold 64 which extends about the flange 6 of the upper slant I-ne manifold 64 is connected to the

J

pump 40. Seals 63, 65 are mounted to the flange 62. The upper mold half 18 and lower mold half 12 have registry guides such as a dowel as known in the art to maintain the upper and lower mold halves 18, 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 ire the center of tile upper mold half 18 from either a catchpot 59 mounted directly on the top of Me port or through a tube feeding to a resin trap as is known in the'art.AfEerthe molhale8''have bee-irtstalled and register - , a vacuurn _ the flange of the lower skin is drawn by pump 63. Then, a vacuum on the cavity is drawn, typically 0.5 bar, and resin is injected from a supply of resin 51 through ports 53, 55.

As shown in FIG. 4A, pressure sensors, such as a pressure transducer 66, are rnoulted 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) wluch reacts to a change in pressure. The pressure transducer 66 has a probe which passes through the skin into the cavity. The pressure transducer is able to detect srn all changes in 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 the slrins. When one or more of the 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 79. A cavity pressure diaphragm 74 is molested on one end of the piston 72. The housing is mounted to the slain by mold insert ring 75 to be in direct contact with the cavity. One surface of the piston 72 is in a chamber 73 which is connected to the vacuum source 63. A pilot poppet 74 is rlloullted opposite the piston 72. 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 the pump 78. The piston 72 is movable through the chamber 73 to close the poppet 74.

When the cavity 29 is placed under vacuum, the pressure is exactly the same in both the cavity 22 and the vacuum connection port which is directly connected to the vacuum source 63 drawing central vacuum. Since the -- 10 pressi-s We same- on the" cavity diaphragm 74 and in Ace chamber lithe piston will remain in a neutral state in which the piston 72 is not in contact with the pilot poppet 74. If the pressure in the cavity 29 increases over the vacuum source pressure, the piston 72 will movie to open the pilot poppet 74. Once the piston 70 is lifted from its neutral position, the pilot poppet will release the air holding tle pneumatically, powered resin pump supply line open.

an alternative embodiment of the pressure control apparatus, the piston is spring biased against the pressure diaphragm. When the inner mold cavil:, 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 this Valve is limited to the biasing resistance of Me 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 QS from 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 then returns to the normal position opening the poppet. The leak signal then is restored and the resin pump power supply is restored to allow the puny to a rain bean pumping. 'his operation continues in a "closed loop" until the D: old cavity is filled.

As shown in FIG. 1, the valve 68 or sensor 66 may be used with molds having multiple injection ports 53 55. The injection ports 53, 55 are spaced successively inwardly from the perimeter of Me mold towards the center exit vent 56. Resin is injected in the outermost injection points first. When the 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 Ad to open a succeeding inner injection point(s) to furdler the resin flow to the center while mtnining a negative cavity pressure. The injection may also be accomplished by using the electronic sensors 66 and CPU to control the flow.

10 - bate, Reweld is held win ti=YMmn) an the vacuum frame holding the cavity mold and upper mold to maintain closure of the mold halves until be 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 seDii-fJexible slain on a male mold pattern for use in defend a cavity for a lower mold half. A contoured flange for supporting the skin on a frame is then fondled. The flange has the contour and an idler surface to mate with the back side of a flange. A next step is SO forming a germ-rigid upper mold half. The semi-rigid mold half may be formed by laying calibration wax over the mold pattern and casting the stun on the calibration wax. A trussworl frame with a vacuum manifold on a flange is mowlted to the bacl; of the upper skin. The next step is to place the lower skin onto tile flange of the frame and to place the upper mold half on top of the o5 lower skin. A vacuum is drawn through the contoured surface of the lower sled and through the outer flange of the upper mold half to close the mold halves. Finally, resin is injected into the cavity.

Additionally a method of controlling the injection of the resin includes mowlting a pressure sensor in a portion of the cavity, generating signals indicative of the pressure at intervals during be injection process, noting the 1\ rate of change of the pressure within the cavity, 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 molding which is less expensive than conventional methods. The cavity of the mold can be easily replaced at a fraction of the cost of conventional tooling methods. The cavity can be duplicated at mirurnal expense, talus multiple cavity skins may be used each simultaneously. A gel coat and reinforcement fiber can be applied while older sl;ins are molding products in the mold flames and the slcin can be replaced without having to remove the mating half from production.

Claims

CLAIlS 1 1. method of controlling a molding process capnsiDg the pB 2 of:

3 mowing a sensor on a deformable c deEmmg a portion of mold 4 cantor.

injecting rem into said cantor, 6 smug defonnadon of said don with said scosor, 7 geneg a dgoal indicative of defonnada; and g controlling Me flow of resin m response to Bud dgnel.