GB2108895A - Compression moulding reinforced plastics sheet - Google Patents

Abstract

Reinforced plastics sheet is compression moulded by transferring mould devices between a main press (10) and auxiliary presses (12, 14). In the main press (10) the SMC sheet is compressed and cured to a desired shape, and in the auxiliary (12, 14) press operations such as charging the sheet, closing and opening the mould, and removing the moulded article, are performed. On the transfer devices levelling devices (52) for supporting the upper mould (24) are provided, and during the transfer the sheet is continuously flowed and filled into the mould cavity in succession to the preceding operation by controlling the levelling devices (52) and the operation is connected to the following compression operation before starting to cure. 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, such as parts of automobiles or the like, by compressing.

SMC sheets, which are thermosetting plastics reinforced with composite material, such as unsaturated polyester resins reinforced with 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 or softening the SMC sheet, flowing and 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 automobiles or the like, they serve to reduce the assembling 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 make it impossible to shorten the cycle time by any significant amount.

The present inventors have analyzed the above cycle time diagram for overcoming these shortcomings. It was found that the compressing and curing times occupy somewhat more than one half of the cycle time, and the rest is occupied for the pressless operations such as charging the SMC sheet, closing and opening the mould, and the like. Consequently, the effect in forming efficiency is not high. In addition, in the compressing and curing of the SMC sheets a predetermined large press power is needed, but in the pressless processes the operations 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 in the pressless operations the operations required a long stroke.It follows that conventional SMC compression systems were uneconomically constructed and of low production rate.

As the SMC material is charged in a suitably heated mould, it is softened and fluidized, and becomes gelled and flowable. And by applying a small power onto it, it can be easily caused to flow into and fill the mould cavity. Further heated, as it starts to cure and expand, the compressing power is gradually increased so as to suppress the expansion according to the process of chemical reaction. The curing further proceeded, as it starts to contract, a predetermined large power is applied and kept on the mould until the complete end of the curing. In this manner, the SMC parts are produced, but the long curing time obliges to lengthen the cycle time as above mentioned.

Accordingly, if the compressing and curing operation and the other pressless operations are separated, and the other operations are performed during the compressing and curing operation, the production rate can be duplicated. However, as the SMC chemical reactions are continuously proceeding, the operations should be continuously performed to form the SMC sheet into a desired shaped part.

An object of this invention is to provide a novel and useful method for producing SMC parts productively by compressing.

Another object of this invention is to provide a method for producing SMC parts by compressing, which can improve the productivity and reduce the cycle time to approximately one half of the conventional time by effectively separating operations to the compressing and curing operation and the other pressless operations, and performing respectively them at the same time, and precisely produce the SMC parts by controlling levelling devices and continuously flowing and filling the SMC sheet into the mould cavity during transferring the mould for connecting the both operations.

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

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

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 is a diagram of the typical conventional cycle time of 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; Figure 4~Figure 6 is a respectively schematic fragmentary sectional side views of each step of forming SMC parts in the apparatus in Figure 2.

The invention is now described in the following with reference 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), and associated elements.

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. It has a predetermined large press power and short stroke hydraulic cylinder 20 on the upper frame 22, and is provided with a stiff 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.

Between the platen 24 and the lower frame 28 is placed the mould device 18 which has been closed, by lowering to a predetermined height in the auxiliary equipment 12. In the mould 18 the SMC sheet 16 is compressed into the mould cavity 30 to be formed to a desired shape. The auxiliary equipments 12, 14 are symmetrically constructed to the main equipment 10 and arranged transversally 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 32, 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 predetermined 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 the 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 removed upper mould 42 onto the lower mould 48, is suitably carried with them.

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 to the lower mould 48 and are transferred with the bolster 50 in the state of supporting the upper mould 42 with parallel to 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 the 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 of the instructions of the pulse motor 62 respectively.Thus, each rod 64 of the hydraulic actuator 54 is suitably controlled as the speed and precisely moved in parallel by the required amount according to the input pulse numbers from a control box (not shown). In this manner, the upper mould 42 supported by the levelling devices 52 in contact with spherical surfaces is vertically moved with high accuracy positioning control and speed control according to the predetermined programmed control.

Description with respect to structures such as temperature amendment means of moving platen guiding members and the like is omitted, but they may be constructed in accordance with accepted practice in the art. Reference numeral 66 shows traverse rails for transfer devices.

The operation is described below with reference to Figures 4 to 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 unclamping the clamping devices 44, 46, and smoothly put on 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 4, by controlling the pressure and position according to the programmed commands. Then, the upper mould 42 is uniformly closed and parallel to the lower mould 48. As the upper mould 42 and the lower mould 42 are suitably heated as above mentioned, the SMC sheet 16 is softened and fluidized to be flowed and filled into the mould cavity 30 only by the loads as small as the weight of the upper mould 42. Therefore, the auxiliary equipments 12, 14 are sufficient if of a predetermined 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, and filled into the mould cavity 30.

During this time, in the main equipment 10 the SMC sheet 16 in the mould 18, which has been closed in 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. As the main equipment 10 is used merely for compressing and curing the SMC sheet 16 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, it is not required the large size and sufficiently stiff structure as before, and can be compactly constructed as shown figures.

When the SMC sheet 16 is completely compressed and cured, as shown in Figure 5 the platen 24 is raised and the mould 18 is carried out to the auxiliary equipment 14 by the transfer device, and simultaneously the another mould 18, which has been closed as above mentioned in the another auxiliary equipment 12, is carried into the predetermined position in the main equipment 10 by the another transfer device. During transferring the mould 18, the upper mould 42 is being continuously closed onto the lower mould 48 with parallelism 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 30. It is carried to the main equipment 10 before starting to cure. So, all operations can be continuously connected according to the SMC chemical reactions proceeds.Therefore, the flowing and filling time, particularly the gel-time, can be made as long as possible, and the SMC sheet 16 can be easily flowed and filled into all the corners of the mould cavity 30, though the compressing and curing operation and the remaining stages are separated and respectively performed. In the main equipment 10, as shown ih Figure 6, the SMC sheet 16 is compressed and cured likewise as above mentioned. 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 32 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 30 during the transfer of the mould 18, the SMC sheets 16 are formed into the desired configurations and dimensions, 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 time can be reduced to approrimately one half of the conventional time, depending upon the materials and forming dimensions or the like. And, as the SMC sheet is continuously flowed and filled into the mould cavity with uniform speed by controlling the levelling device to keep the upper mould parallel with the lower mould during the transfer, and the SMC part can be continuously formed from the time of charging to the time of compressing and curing. The SMC part with uniform thickness and strength can thus be precisely produced.Furthermore, conventional SMC compressing systems are uneconomicafly 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, though 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 arise since the system does not require both large power and long stroke.

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

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 well known quick 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 (6)

1. A method for producing SMC parts by compressing, which comprises: separating operations of producing SMC parts into a compressing and curing operation for forming a SMC sheet into a desired shape in a mould and the remaining pressless operations of charging the SMC sheet in the mould, closing and opening the mould, removing the SMC part, and the like: performing the both types of operations respectively in a main press equipment and auxiliary press equipments at the same time; connecting the operations by transferring the mould charged the SMC sheet to said press equipments; and flowing and filling the SMC sheet into the mould cavity by precisely controlling the closing of the mould during transferring the mould to the press equipments.

2. A method as claimed in claim 1, wherein during transferring the mould from the operation of closing the mould to the operation of compressing and curing the SMC sheet, said flowing and filling operation is continuously kept on the preceding operation.

3. A method as claimed in claim 2, wherein levelling devices for supporting the upper mould half so as to flow and fill the SMC sheet into the mould cavity are mounted on a transfer device, and said flowing and filling operation is performed by controlling the levelling devices to maintain the upper mould parallel with the lower mould during transfer.

4. A method as claimed in claim 3, wherein the compressing and curing operation is performed in the main press equipment which is compactly constructed of predetermined large press power and short stroke, the remainder operations are performed in the auxiliary press equipments which are simply constructed of predetermined small power and long stroke, a plurality of the auxiliary press equipments are arranged adjacent to the main press equipment, and said flowing and filling operations are performed in the transfer devices which are arranged between the press equipments.

5. A method as claimed in claim 3 or 4, wherein the mould charged the SMC sheet is transferred from the auxiliary press equipment to the main press equipment by the transfer deyice and simultaneously another mould is charged the SMC part is transferred from the main press equipment to another auxiliary press equipment by another transfer device.

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