GB2108422A - Compression moulding and coating plastics sheet - Google Patents

Abstract

Coated, compression moulded reinforced plastics articles are produced by transferring reinforced plastic sheet in mould parts (18) between a main press (10) and auxiliary presses (12, 14). In the main press (10) the sheet (30) is compressed and cured to be formed into a desired shape, and the formed part is coated, and in the auxiliary presses (12, 14) other operations such as charging the sheet, closing and opening the mould (18) and removing the moulded article (30) are performed. Between the main and auxiliary presses are arranged transfer devices to supply the moulds to them. On the transfer devices levelling devices (52) for supporting the upper mould (48) are provided, and during the transfer the coated SMC part is compressed and cured in the mould (18) by suitably controlling the levelling devices (52). This method can be applied to mass production of automobile parts. <IMAGE>

Description

SPECIFICATION Method for producing sheet moulding compound parts by compressing The invention relates to a method for producing sheet moulding compound (hereinafter referred to as SMC parts), by compressing, more particularly it relates to a method for producing SMC parts by compressing and coating in the mould to improve the productivity.

SMC sheets, which are thermosetting plastics such as unsaturated polyester resins, reinforced with composite material, such as glass fibre, have been recently applied to parts of automobiles or the like instead of metal sheets. Heretofore, the SMC parts have been produced by conventional hydraulic press systems, and their typical operational stroke and time diagram is as shown in Figure 1 of the accompanying drawings. The process consists of charging a SMC sheet A, closing a mould B, gelling the SMC sheet, flowing the filling the SMC sheet into the mould cavity C, compressing and curing the SMC sheet D, opening the mould E, removing the formed SMC part F. The cycle is then repeated.

When the SMC parts are used as parts of auto mobiles of the like, they serve to reduce the assemb ling processes and lighten weights, and the like, but they necessitate longer cycle times for producing parts. Various researches have been tried to shorten the cycle time, but the special property of the SMC materials such as curing of the chemical reactions made it impossible to shorten the cycle time by any significant amount.

Furthermore, on most of the surfaces of the SMC parts produced by compressing, there are generated small pinholes and sink marks or the like, and exterior parts, such as exterior body panels of automobiles or the like, need to be coated to improve their surface quality. When the SMC parts are coated in the forming process, their surface pit defects such as pinholes and sink marks can be removed, and pit finding and pit filling in the ensuing processes are eliminated to reduce the overall cost, but the cycle time is still further lengthened by the need for coating as well as compressing and curing the coated parts.

The present inventors have analyzed the above cycle time diagram for overcoming these shortcom ings. It was found that the compressing and curing times occupy somewhat more than half of the cycle time, and the remaining time is occupied by the pressless operations such as charging the SMC sheet, closing and opening the mould, and the like.

Consequently, the effection forming efficiency is not high. In addition, in the compressing and curing the SMC sheets a predetermined large press power is needed, but in the pressless processes the opera tions can be adequately performed by a much smaller power than the compressing power, without requiring such a large force. Furthermore, as shown in Figure 1, in the compressing and curing the operation can be performed within an extremely short stroke, but the pressless operations require a longer stroke. It follows that conventional SMC compression systems were uneconomically constructed and of low production rate.

The SMC material is heated to be gelled or softened, compressed to be flowed and filled into a mould cavity, and further compressed and heated to be cured and formed into a desired shape conforming with the mould cavity. In this manner, the SMC parts are produced, but the long curing time necessitates a long cycle time as above mentioned. Furthermore, coating the formed SMC part in the forming process causes the cycle time to be still further lengthened.

Accordingly, if the compressing and curing operation and the other pressless operations are separated, and the compressing and curing the coated SMC part is performed during transferring the mould for connecting operations, the productivity may be greatly improved.

An object of this invention is to improve a new and useful method for producing coated SMC parts by compressing.

Another object of this invention is to provide a method for producing coated SMC parts by compressing, which can improve the productivity and reduce the cycle time to approximately one half of the cycle time, even though the SMC parts are coated in the forming process.

A still further object of this invention is to provide a method for economically producing coated SMC parts by compressing without raising the cost in proportion to the productivity, though the coated SMC parts can be produced in a high production rate, such as to double the rate of conventional productivity.

Briefly stated, according to the method coated SMC parts can be economically and/or productively produced by effectively separating operations to a mainly compressing and curing operation and the other operations, and connecting the both operations with transferring the moulds between them and compressing and curing the coated SMC parts by suitably controlling levelling devices equipped on each transfer device during transferring the mould.

The invention will be further described with reference to the accompanying drawings in which: Figure 1 is a typical conventional cycle time diagram for forming SMC parts; Figure 2 is a schematic fragmentary sectional side view of an embodiment of an apparatus for carrying out the invention; Figure 3 is a schematic fragmentary sectional view of levelling devices of the apparatus in Figure 2; and Figures 4 to 6 are respective schematic fragmentary sectional side views of steps in the forming SMC parts using the apparatus in Figure 2.

The invention is now described in the following with referring to an embodiment of the invention.

Figure 2 shows an exemplary embodiment of a preferred system of the invention, which comprises a main press equipment 10, two auxiliary press equipments 12, 14, two transfer devices (not shown), associated parts. The main equipment 10 is compactly constructed of predetermined large press power and short stroke, and is used for compressing and curing a SMC sheet 16 in a mould device 18 or the like. It has a predetermined large press power and short stroke hydraulic cylinder 20 on the upper frame 22, and is provided with a rigid moving platen 24 between uprights 26. The platen 24 is arranged to be slidably moved in the vertical direction against the lower frame 28 by the cylinder 20 according to a servo control system (not shown) or the like. In the lower surface of the platen 24 there is mounted a suitable injector (not shown) such as a conventional injector.The inlet of the injector is connected by a flexible hose (not shown) to a coating source (not shown) for supplying coating materials such as simple compound liquid coating or two compound liquid coating as disclosed in U. S. application No.

814502 or 852625 (Japanese Application No. 53- 65862 or 53-142136, Japanese Laid - Open Application No. 54-36369 or 54-81398). The outlet of the injector is removably connected to a sprue (not shown) located in the upper surface of the mould 18 so as to enable the coating materials to be coated over the compressed SMC part 30 in the mould 18.

Between the platen 24 and the lower frame 28 is placed said mould 18 which has been closed so as to lower to a predetermined height in the auxiliary equipments 12, 14. In the mould 18 the SMC sheet 16 is cosmpressed into the mould cavity 32 is to be formed to a desired shape and coated in the mould 18 as above mentioned. The auxiliary equipments 12, 14 are symmetrically constructed to the main equipment 10 and arranged on opposite sides of the main equipment 10. They are simply constructed of predetermined small power and long stroke, and used for pressless operations such as charging the SMC sheet 16, closing and opening the mould 18 and removing the SMC part 30, and the like. On the lower frame member 40, they are respectively provided with a plurality of predetermined small power and long stroke lift cylinders 34, 36 for moving the upper frame member 38.The upper mould 42 is demountably secured to said beamed shaped upper frame member 38 by clamping devices 44,46 and is suitably moved by the lift cylinders 34,36. The lower mould 48 is securely mounted on a bolster 50 and arranged so as to be placed to a determined position on the lower frame member 40 or the lower frame 28. The bolster 50 is respectively arranged reciprocably to traverse between the main equipment 10 and auxiliary equipments 12, 14 by each of transfer devices (not shown) such as hydraulic cylinders or the like, and the mould 18, coupled by closing the separable upper mould 42 onto the lower mould 48, is suitably carried with it.

At the four corners of the bolster 50 levelling devices 52, such as servo mechanical actuators, are respectively vertically equipped so that they support the upper mould 42 parallel with the lower mould 48 and these are also transferred with the bolster 50 while supporting the upper mould 42 parallel with the lower mould 48. Each of the levelling devices 52, as shown in Figure 3, comprises a predetermined power hydraulic actuator 54, a control unit 56 and a positioning rod 58 for operating the actuator 54 to the required position, and the like. In operation, a servo valve 60 operated by a pulse motor 62 of the control unit 56 actuates the vertically fixed hydraulic actuator 54, the movement of the moved rod 64 is fed to the servo valve 60 through the positioning rod 58, and the rod 64 is moved to a determined position by the instructions of the pulse motor 62 respectively.Thus, each rod 64 of the hydraulic actuator 54 is suitably controlled as the speed is accurately moved in parallel by the required amount according to the input pulse numbers from a control box (not shown).

As shown in Figure 3, the levelling devices 52 are respectively equipped with a locking device 46 such as a locking cylinder or the like on an upper portion of the cylinder rod 64. The upper mould 42 is removably clamped onto the levelling devices 52 so as to cure the coated SMC part 32 by a required force. In this manner, the upper mould 42 removably supported by the levelling devices 52 in contact with spherical surfaces is vertically moved with high accurate positioning control and speed control according to the predetermined programmed control. Description with respect to structures such as temperature control means of the moving platen, guiding members and the like are omitted, but they may be constructed in suitable manner in accordance with normal practice in the art. Reference numeral 68 shows traverse rails for transfer devices.

The operation is described below with reference to Figures 4to 6.

At first, as shown in Figure 4 a suitable size SMC sheet 16 is charged onto the lower mould 48 in the auxiliary equipment 12, in which the upper mould 42 has been raised to the predetermined height by the lift cylinders 34, 36. Then the upper mould 42 is lowered against the lower mould 48 by simultaneously moving the lift cylinders 34, 36. At the predetermined height the upper mould 42 is removed from the upper frame member 38 by clamping the clamping devices 44,46, and smoothly put on to the levelling device 52. The levelling devices 52 actuate the hydraulic actuators 54 and lower the upper mould 42 with uniform speed so as to lightly press the SMC sheet 16, as shown in Figure 5, by controlling the pressure and position according to the programmed commands. Thus, the upper mould 42 is uniformly closed parallel to the lower mould 48.

As the upper mould 42 and the lower mould 48 are suitably heated as above mentioned, the SMC sheet 16 is softened and fluidized to be flowed and filled into the mould cavity 32 only by loads, which may be as small as the weight of the upper mould 42.

Therefore, the auxiliary equipments 12, may be adequate if of a determined small power and simple structure. The flowing and filling timing, rate, and the like are controlled through the levelling devices 52 by the programmed commands in the control box. As the upper mould 42 is controlled by the levelling devices 52, the SMC sheet 16 can be precisely and uniformly flowed and filled into the mould cavity 32.

During this time, in the main equipment 10 and SMC sheet 16 in the mould 18, which has been closed in the another auxiliary equipment 14 as above mentioned, is compressed and cured by the large press power hydraulic cylinder 20 to be formed into a desired shape, as shown in Figure 4. After the SMC sheet 16 is compressed and cured, the main cylinder 20 is unloaded and the upper mould 42 is slightly, for instance 1 - 6 mm, opened by raising the levelling devices 52 parallel with the lower mould 48.

At the same time, the upper mould 42 is locked to the levelling devices 52 by the locking devices 66. If necessary, the upper mould 42 may be locked to them beforehand. Then, the injector mounted in the platen 24 is operated and the coating materials are injected from the injector over the SMC part 30 through the sprue connected to the injector. As the upper mould 42 is kept with parallel to the lower mould 48 in the desired small gap by controlling the levelling devices 52, the coating materials are evenly spread over the SMC part 30 with uniform thickness.

After coating, the platen 24 is raised to a determined height and the upper mould 42 is lowered so as to close the mould 18 by withdrawing the levelling devices 52. As the main equipment 10 is used for compressing and curing the SMC sheet 16, and coating the formed SMC part 32 in the mould 18, it can be sufficiently performed by the predetermined large press power and short stroke hydraulic cylinder 20, without the long stroke and large press power cylinder such as conventional systems. Consequently, there is not required the large size and highly rigid structure as before, and can be compactly constructed as shown in the Figures.

Then as shown in Figure 5, the mould 18 is carried out to the auxiliary equipment 14 by the transfer device. During the transfer, the upper mould 42 locked to the levelling devices 52 is lowered parallel with the lower mould 48 by controlling the levelling devices 52 according to the programmed speed and pressure controls, and the coated SMC part 30 is further compressed and cured by the predetermined force. As the force of compressing and curing the coated SMC part 30 needed is approximately from one tenth to one fifth of the SMC compressing force, the coating operation is sufficiently performed by the levelling devices 52 without operating in the main equipment 10. Therefore, the operation can be performed during the transfer of the mould 18, and the cycle time needs to be lengthened by at most, a small timing, although the SMC part 30 is coated.On the other hand, another mould 18, which has been closed as above mentioned in the other auxiliary equipment 12, is simultaneously carried into the predetermined position in the main equipment 10 by the other transfer devices. During transferring of the mould 18, the upper mould 12 is being continuously closed onto the lower mould 48 in parallel manner by controlling the levelling devices 52 in succession to the preceding operation as above mentioned, and the SMC sheet 16 is being continuously flowed and filled into the mould cavity 32, and it is carried to the main equipment 10 before starting to cure.So, all operations can be continuously connected to the progress of the SMC chemical reactions, and the SMC sheet 16 can be easily flowed and filled into all the corners of the mould cavity 32, although the compressing and curing operation and the pressless operations are separated and respectively performed. In the main equipment 10, as shown in Figure 6, the SMC sheet 16 is compressed and cured likewise as above mentioned. On the other hand, in the auxiliary equipment 14 the levelling devices 52 raise the upper mould 42, the lift cylinders 34,36 are lowered, and the clamping devices 44,46 clamp the upper mould 42 to fix beneath the upper frame member 38 and raise the upper mould 42 to the determined height. Then, the SMC part 30 is knocked out by a discharge device (not shown), removed from the mould 18 and next SMC sheet 16 is charged onto the lower mould 48 as above mentioned.

In this manner, by being interchangeably transferred to the main equipment 10 and auxiliary equipment 12,14, and being continuously flowed and filled out into the mould cavity 32 during the transfer of the mould 18, the SMC sheets 16 are formed into the desired configurations and dimensions, are coated in turn.

Therefore, as the compressing and curing operation in the main equipment and the other pressless operations in the auxiliary equipments are performed at the same time, the forming cycle can be reduced to approximately one half of the conventional time, depending upon the materials and forming dimensionsorthe like. Further, as the SMC sheet is continuously flowed and filled into the mould cavity with uniform speed by controlling the levelling devices with the upper mould parallel with the lower mould during the transfer, and the SMC part can be continuously formed from the charging to the compressing and curing, the SMC part with uniform thickness and strength can be precisely produced.Furthermore, conventional SMC compressing systems are uneconomically constructed of a predetermined large press power and long stroke, but as the equipments are respectively designed to be compactly or simply constructed as above described, this system can be economically constructed without raising the cost in proportion to the productivity, although the productivity can be approximately doubled. In addition, the small volume of the main press cylinder causes the compressibility of the hydraulic oil to be less and to improve the responsiveness, positioning accuracy, pressure controlling accuracy and the product quality. These advantages become clear since the system does not require both the large power and long stroke.

In the above embodiment, the levelling devices are not limited to the servo hydraulic cylinder system, and other high accuracy systems, such as electro motor actuator systems or the like, may be used.

Furthermore, in the above embodiment an injector is mounted in the moving platen of the main equipment so as to be used in common for all the moulds, but alternatively an injector may be mounted in each of the moulds to coat the SMC parts. As a result, the above mentioned in mould coating the SMC parts may be performed partially or wholly during the transfer of the moulds.

Furthermore, in the above embodiments, the moulds are carried simultaneously between the main equipment and auxiliary equipments, but they may be respectively carried to them according to the schedules. They may be designed to be carried by using conventional rapid die changers or the like.

And furthermore, in the plant where a plurality of the main equipments and auxiliary equipments are arranged, the moulds handling system may be provided to deliver the moulds to them according to the computer control system. In addition, the above producing systems may be designed to produce a plurality of the SMC parts at once.

While the invention has been illustrated and described as embodied in the press equipments, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the scope of the present invention.

Claims (8)

1. A method for producing SMC parts by compressing, which comprises: separating operations of producing SMC parts into a mainly compressing and curing operation for forming a SMC sheet into a desired shape in a mould and the remaining substantially pressless operations of charging the SMC sheet in the mould, closing and opening the mould, removing the SMC part, and the like; performing the mainly compressing and curing operation in a main press equipment and the remaining operations in auxiliary press equipments respectively at the same time; connecting both operations by transferring the mould charged with the SMC sheet between said press equipments as required; and compressing and curing the coated SMC part, which is coated in the forming process, by controlling the mould during transfer of the mould from the main equipment to the auxiliary press equipments.

2. A method as claimed in claim 1, wherein said compressing and curing the coated SMC part is performed in succession to the preceding operation during transfer of the mould after the operations of compressing and curing the SMC sheet and coating the formed SMC part to the operations of opening the mould and removing the SMC part.

3. A method as claimed in claim 1, wherein during transfer of the mould from the operation of closing the mould to the operation of compressing and curing the SMC sheet, the SMC sheet is being flowed and filled into the mould cavity, and during transfer of the mould from the operation of compressing and curing the SMC sheet and coating the SMC part to the operations of opening the mould and removing the SMC part, said compressing and curing the coated SMC part is performed in succession to the preceding operation.

4. A method as claimed in claim 2 or 3, wherein levelling devices for supporting the upper mould half so as to flow and fill the SMC sheet into the mould cavity is mounted on a transfer device, said compressing and curing of the coated SMC part being performed by controlling the levelling devices to maintain the upper mould half parallel with the lower mould half during transfer of the mould.

5. A method as claimed in claim 4, wherein the levelling devices are equipped with locking devices for removably locking the upper mould half, said compressing and curing the coated SMC part is performed by locking the upper mould half to the levelling devices with the said locking device.

6. A method as claimed in claim 5, wherein the mainly compressing and curing operation is performed in the main press equipment which is compactly constructed of predetermined large press power and short stroke, the remaining operations being performed in the auxiliary press equipments which are simply constructed of predetermined small power and long stroke, a plurality of the auxiliary press equipments being arranged adjacent to the main press equipment, and the said compressing and curing of the coated parts being performed in transfer devices which are arranged between the press equipments.

7. A method as claimed in claim 6, wherein the mould charged with the SMC sheet is transferred from the auxiliary press equipment to the main press equipment by a transfer device, and simultaneously the mould charged with the SMC part is transferred from the main press equipment to another auxiliary press equipment by another transfer device.

8. A method of producing SMC parts by compression substantially as hereinbefore described with reference to Figures 2 to 6 of the accompanying drawings.