JPS6010891B2 - Method of manufacturing molded cavity - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a mold cavity for injection molding thermoplastic parts.

In particular, the present invention provides a method of manufacturing a thermoset mold cavity made by transfer molding a thermoset plastic material using inverted mold sections.
The fabrication and assembly of injection molds and the fabrication and assembly of master molds have traditionally been expensive and complex in terms of time, convenience, and economy.

Mold cavity materials are not readily available in the commercial market;
Special equipment is required, and the fabrication and assembly of these tools has necessarily been excluded from the actual production line of other parts. The time required for manufacturing the cavity prototype is also
It was also one of the limiting factors in production research and development activities. Conventional mold cavities for producing thermoplastic parts are made from the following materials:

These include plain machined copper, plain machined aluminum and brass, cast zinc, cast aluminum, cast beryllium copper, sprayed metal shells on various backing materials, and the like. Cavities have also been made using lightning technology. All of the above methods require expensive specialized materials and time-consuming processing methods to create a mold cavity that can withstand the conditions of injection molding. Only recently, even thermoplastic materials have been used experimentally (
(but only in connection with compression molding).

EuropeanPlas polyimide cavity
ticNews (May, 1975), according to which a cavity in polyimide material is fabricated by compression molding, and this mold can be used to compression mold thermoplastics. This method has rather obvious drawbacks. That is, it requires a pelletizing press to preform the polyimide material, requires a recirculating air oven to remove flash from the cavity, and is capable of post-curing the polyimide molding at temperatures as high as 25,000 ℃. All of these are characteristics of the compression molding process, and are part of the reason why injection molding production is increasingly emphasized as opposed to compression molding. The present invention provides a low-cost alternative to molds as forming tools, which makes it particularly advantageous for the fabrication of prototypes and the production of blanks for plastic parts.

In addition, it provides a suitable tooling structure as a production aid. This alternative uses two-step three-dimensional cross-linking, instead of traditional epoxy, steel or non-ferrous alloys to construct the mold cavity. Using a reinforced, low-shrinkage thermoset material, it requires only machining equipment and a transfer press, both of which are common mechanical elements in the production of plastic parts.
The methods used for this can be summarized as follows.

1 A model with dimensions slightly larger than the desired thermoplastic final product is made according to specifications, along with an undercut ejector bushing and a hole-forming pin.

2. Guide pins are provided to position the shoe on the model, and the insert is placed using the positioning holes in the model.

3. A hole large enough to accommodate the required volume of thermoset material is machined into the lower mold half.

4. The dimensions of the bushing and insert are such that when both mold halves are clamped together, they are tightly clamped in place by the underside of the hole.

5. The model is fixed onto the replaceable temporary plate of the upper half of the model with screws that pass through this plate and enter the model.

6. Both mold halves are closed loosely by hand and tightly clamped together.

The thermosetting material is transfer molded into the hole that houses the model and all inserts. The molded cavity is then cured. 7. Once curing is complete, the mold halves are separated by manually operating the machine again (if available) to remove the mold from the mold cavity.

8 When the thermoset tool has cooled sufficiently, a new wound channel and gate are machined into it and an ejection device is created, and the tool thus made can produce injection molded thermoplastic parts. It can be used to

Next, the drawings will be explained in detail.

As shown in FIG. 1, two mold sections, an upper mold half 1 and a lower mold half 2, are fabricated to make the thermosetting mold cavity of the present invention.

The upper half mold 1 is composed of a base 3 and a temporary plate 4.

The component model 5 is fixed at a predetermined position on the temporary plate 4 by screws 6 passing through this plate. The lower mold half 2 is constructed in the form of one fixed base 7 or in the form of a two-component base consisting of a standard main section 8 and a further plate 9.

A wound canal 10 for injecting the thermosetting material and a space 11 sufficient to fill the injection amount of the thermosetting material to be injected are provided on the fixing table 7.
Or it is machined into a separate plate 9 to form the lower half mold. A cap screw 12 passing through the fixing base 7 or the main section 8 and entering the flanged insert 13 holds the thermoset molding cavity 14 in its bolt shape. The lower mold half is prepared for subsequent grinding of the parting line surface. The part model 5 shown in FIGS. 1 and 2 includes an insert 15 for making any desired holes in the final thermoplastic part and a pre-drilled pilot hole 19 for the ejector pin and as an ejector pin guide. A useful bush 16 is arranged.

The insert and footwear are provided with an undercut 17.
The bushing is placed on the part model using guide pins 18;
The insert 15 is placed into place by placing it in a hole in the model. Regarding molding of the cavity, the upper half mold 1 with the part model attached is always placed in the position occupied by the lower half mold using a transfer molding press (for example, Bussman Plastomat,
10 hawks, 100 tons clamping force, or S Ke751,
50 tons clamping force).

All inserts 15, which will later become holes during molding, and inserts 16, which act as ejector pin guide pushes, are placed on the model 5. This reversal of the position of the mold halves is necessary so that the inserts and bushings placed on the part model 5 are held in contact with the surface of the model by their own weight and gravity. Similarly, the lower mold half 2 is mounted on the machine in the position always occupied by the upper mold half.

At this point, the space 11 machined into the lower mold half is centered directly above the model. The molding press is then closed (preferably manually) and the mold halves are gradually brought together and tightly clamped together.

In this respect, the model and each insert are held firmly in place within the machined space. When both mold halves reach the required temperature for transfer molding the thermosetting material, the thermosetting material is poured into this space and cured. Suitable ventilation channels are created in the lower mold half 2 in which the machined space 11 is located so that air and molding gases can escape from the space 11 while the thermosetting material is being injected to ensure complete filling of this space. Make sure to secure it. Once curing is complete, the press is opened to gently separate the mold halves and the model is removed from the molded thermoset cavity.

When both mold halves have cooled to room temperature, machine work to grind the parting line surface or drill and drill for ejector pin holes.
Able to perform J-me work. The new runner and gate are then machined into the mold tool, the ejector is assembled, and the cavity is ready for use. In one preferred embodiment of the invention, the thermosetting plastic material used is a two-stage, three-dimensional, low-shrinkage reinforced phenolic material called FiriteFM4004.

FioripFM4004 is FioriteCorpo
ration, and has the following properties]. Tensile strength = 5 states / Secret impact strength (notch test) = 1 Rib / Leg bending strength = 9 states / Fence bending modulus = 16800 N / Ground solidity (Rockwell M scale) FMIOO compressive strength =
26 / secret thermal conductivity = 13 × 10-℃al no see /℃
/ Skin molding temperature = 143-177q0 Molding pressure (transfer) = 6.89-20.6 MPa Molding shrinkage % = 0.
15-0.30% linear expansion coefficient = 1.4xlo-5in/
in/°C.The advantages offered by this type of material are many.

Reinforced thermoset phenolic plastics are not new materials, but they are inexpensive and readily available. Its structure is a three-dimensional, cross-linked polymeric structure and is therefore durable, offering the added advantage of being able to withstand the wear and corrosion normally associated with injection molding processes. At forming temperatures, its coefficient of linear expansion is very close to hardened steel. Furthermore, since this thermosetting material is transfer molded to form the mold cavity, no special bulleting equipment is required, no flash occurs in the holes, and the post-curing process and equipment are easy to use. It's unnecessary. This cavity can be made entirely on site. The thermoplastic part or master model 5 to be produced is made of a material capable of withstanding the same range of temperatures as the thermoset material to be transfer molded into the bolster.

When using Fiberite FM4004, this temperature is in the range 160-175 pm and the material used for the model is steel. Additionally, the pattern must be large in size to include allowance for shrinkage of the thermoset material after molding the tool and for shrinkage of the polymeric material used in molding the final thermoplastic part. insert(
13, 15, 16) are made of steel, yellow steel or aluminium, and are firmly affixed to the model of the part during the pouring of the thermosetting material.

The guide pin 18 can be removed after the thermoset mold cavity has been molded. A flanged metal insert 13 is provided to retain the thermoset molding within the bolster. Retention of the bushing and insert in the thermoset molding is achieved by a combination of undercuts 17 and natural shrinkage of the thermoset material during the curing process. The dimensions of the hole machined in the lower mold half are 4 holes x 65 holes x 25.5 holes when using the solid base 7.
It was willow. However, in the case of the two-component lower mold, the thickness is 17.
A separate board 9 of the material frame was used. The dimensions of the holes machined in the 17 ribs were 3 broadsides x 15 broadsides.

The volumes of injectable material in the B-order sman and S-ke transfer presses referenced above are 140 and 1, respectively.
It's number 10. Provision must be made in the lower mold half to compensate for shrinkage of the thermoset material, since the thermoset hole will shrink below the parting line surface by a certain percentage of the depth of the hole. After transfer molding the tool, grinding is required to bring the hole surface and separation line surface to the same level. When using two separate plates, the advantage is that the same main section 8 can be used when making different tools by simply changing the volume of the bore 11.

Once the bolster platform has been constructed, the temporary plate 4 of the upper mold can be optionally replaced with a new plate of the same overall dimensions to act as a closing surface for the upper mold.
If necessary, a new plate 9 with holes 11 can be fitted to the lower mold half to produce new tools for different parts. The ejector pin holes in the lower mold half can be recessed with standard steel pins to mold new cavities, and if such holes are properly placed, the ejector pin holes in new parts can be reused. can do. By using a ready-made Bols base and ejector plate system, a new half mold can be produced on average as follows: production stage
Creating the average time (time) model 1
6 Fabrication of plates for the upper and lower radii 10 Reconstruction of the ejector and table work 16 Molding of the thermoset tool hole in the transfer molding press 1 Total of 4 hours Machining the gate into the thermoset material and molding the part Although possible, in the preferred embodiment, steel or preferably yellow steel is inserted into the thermoset material where the gate is to be machined.

Although each of the molded sections shown in FIG. 1 is compatible with the die set of the model, it should be understood that the invention is not limited to any particular bolster configuration.

[Brief explanation of the drawing]

FIG. 1 shows both mold sections and the part model and insert in place during transfer molding of thermoset material according to the invention. Figure 2 shows the part model and the insert and protruding bush placed on it. 1... Upper half mold, 2... Lower half mold,
3... Base, 4... Temporary board, 5... Parts model, 6
...Screw, 7...Fixing base, 8...Standard main division, 9
...Another board, 10... Runway, 11... Hole, 12... Cap screw, 13... Flange insert, 14... Molded thermosetting cavity, 15... Insert, 16...Fush, 17...Undercut, 1
8... Guide pin, 19... Pilot hole. FIG. IFIG. 2

Claims (1)

[Claims] 1 A recess is formed in at least one of a pair of openable and closable radii, a passage communicating with the outside is formed in the recess, a protrusion having an undercut is provided in the recess, and a part model to be manufactured is placed in the recess. is fixed, the pair of radii are closed, and a thermosetting plastic having a three-dimensional cross-linked polymer structure is flowed into the recess through the passage, and the thermosetting plastic that has been flown is cured. A method for manufacturing a mold cavity for injection molding a thermoplastic part, the method comprising the steps of: applying heat to the half molds to separate the pair of half molds.