JPS63252639A - Die for molding rim - Google Patents

Abstract

PURPOSE:To reduce the cost of a casting mold and to improve molding accuracy by bonding an inside layer made of a Bi-Sn alloy having the die surface coinciding with a product shape and the thickness equal to the thickness of a product to a high-rigidity back up body by casting. CONSTITUTION:A hollow male board 13 is fashioned in accordance with a prototype 10 and a male mold 15 transferred with the curved face 11 of the prototype 10 is previously formed. Sheet wax 16 is separately stuck to the prototype 10 and a model 18 of the back up body 4 is fashioned by the outside surface 17 of the wax and flask, then the back up body 4 is cast of a cast iron. Runners 21 are bored to the body 4 and said body is mated with the mold 15, by which a casting mold having a cavity 22 is obtd. A Bi-Sn alloy is cast into the cavity 22 to form a die 1. The inside layer 5 made of the Bi-Sn alloy forms the exact die surface and the time required for forming the same is shortened. The need for correcting the casting mold is eliminated and the cost of the casting mold is reduced; in addition, the molding accuracy of the product is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to improvements in molds used in rim molding (RIMJ or reaction injection molding).

(Prior Technology J Synthetic resin products used in motorcycles and other vehicles have traditionally been manufactured by injection molding, but recently rim molding has been increasingly adopted. Because the injection pressure is low, it requires smaller equipment than conventional injection molding, and has the advantage that the mold does not need to have much durability or rigidity, so it is a material that is easy to process as a mold material. The mold production cost is low, and it is convenient for producing parts when producing a relatively large number of models in small quantities, such as motorcycles.

(Problem to be solved by the invention J) However, similar to conventional injection molds, rim molding molds first scrape off the mold surface corresponding to the product shape from a metal material by copying, etc., to eliminate unevenness. Next, the remaining cut surface is smoothed by mainly manual surface finishing.Although this cutting and finishing process slightly shortens the processing time, it is effective for products with complex three-dimensional shapes. It took a considerable amount of time and effort to make the gold.

On the other hand, with the m-spraying type, which is a simple one-piece model, it is often impossible to thermally spray items with deep grooves or a female shape. In the case of molds, there are many places where the thickness cannot be uniform and electroforming is not possible for molds with complex shapes.

Next, there is a method of molding a low melting point alloy such as a zinc alloy and forming it to match the model, but since it shrinks during solidification, there is a large difference in dimensions and accuracy compared to the model. These alloys were manufactured as block inserts of a certain size regardless of the product shape, so they had a large mass and not only wasted expensive alloys but also had a significantly larger amount of shrinkage. Furthermore, since the thickness of the alloy is not constant along the product shape, even if a certain amount of shrinkage is allowed for the master model, there will be an irregularity in the amount of shrinkage during solidification depending on the location, and if the amount is uniform all around. After solidification, finishing process is required.

Also, during iRIM molding, the difference in wall thickness caused distortion due to the difference in thermal expansion between the molds, which was not desirable in terms of the ff variation of the product.

(Means for Solving the Problems J) The present invention has been made in view of the above points, and the mold surface is formed of smooth metal, which not only eliminates the need for cutting and finishing. The highly accurate mold has a structure that can be manufactured easily and in a short period of time, and the means for achieving this are as follows:
It consists of an inner layer made of B1-Sn alloy with a thickness equal to the mold surface that matches the shape of the product to be molded, and a highly rigid back-up body, and is characterized by the fact that both parts are joined by internal casting. shall be.

(Since the above-mentioned means are provided, the inner layer with the molding surface is reinforced with each solid layer and has high rigidity, and the molding surface is B1
- It can be formed with high precision due to the non-shrinkage property of the Sn alloy.

(Example) Examples of the present invention will be described below with reference to the drawings.In Fig. 1, (1) is a mold of the present invention, which forms a cavity (3) together with another mold (2). The rim of the desired product is then formed within this cavity.

The mold tl) is equipped with a back-up body (4) made of cast iron and an inner layer (5) made of a B1-Sn alloy inside it. ! (5) has a curved surface (6) on the mold surface.

The lining means of the same alloy is made by casting into the inner surface of the back-up body (4) (the force is solidified in the runner).

The illustrated curved surface (6) is a single curved surface for mere illustration, and a curved surface with a complicated shape can be easily formed in the same way as this curved surface (6). The formation of this curved surface and the lining can be carried out by the steps ω to ① shown in FIG.

In FIG. 2, in the first step (2) (lI is the original shape made from a suitable mold material, this original form III is the same as the product shape and its curved surface old) becomes the basis of the curved surface (6).

This curved circle is compared to the shape of the product shown by the virtual mu.
The yield is expected to be tv due to the cooling of the tree after molding. However, in this specification, the shape immediately after molding will be described as the product shape.

Based on this original form tllll 'e, in the second step (■), a female mold 03 is made, and from this, in the third step (■), a mold circle is taken with the curved surface (ill) transferred with serum, and in the fourth step (■), it is fired and a male mold is made. Make 09.

On the other hand, the female @ type is made through the steps of ■, ■, and ■. First, sheet wax ue with a thickness of 5 to 25+w is pasted on the prototype Ilα, and the outer surface (in) and a roughly rectangular frame (not shown) surrounding this are used to create a tuck-up body ( 4) Create a model.

This model is shown in (18) in the 6th step ■, and a mold is made with the casting frame θj, sand) and the model 0 barrel,
As a result, the entire back-up body (4) shown in (2) is cast.

Then, when a runner eI) is formed on this body (4) during drilling or casting, and it is fitted with the male mold Q51 gold of (■), the sheet wax (161 part) becomes a blank space, and
As shown in the figure, a mold with a cavity (two metals) is formed. Then, as shown in the ninth step (2), when B1-Sn alloy hot water (c) is poured, a cast iron 6-cup body (4) is formed.
The inner surface of the B1-Sn alloy j@ (51) is integrally fixed and lined, and at the same time, a curved surface (6) corresponding to the curved surface 0υ of the original shape (lol) is formed on the inner surface, as shown in Figure 1. The mold (1) shown is completed.

The B1-Sn alloy has the property of faithfully filling the cavity without shrinkage during casting, and it is possible to create a mold surface that accurately reproduces the original mold. In addition, since the inner layer of old-Sn alloy has a uniform thickness along the product shape, there is no distortion due to unbalanced mass, and there is no need for finishing work such as correction of the casting punch shape. Similarly, a product with good precision can be obtained without distortion due to the difference in thermal expansion during RIM molding.

This alloy is commercially available under trade names such as Cellokast and SK Cast, and has a melting point of about 150°C, while the reaction temperature for rim forming is 50 to 70°C, so it is sufficiently durable.

The surface roughness of the mold surface (6) can be improved by polishing to give it a metallic luster, but as shown in Figure 3, for example, if hard chrome plating (6aJ) is applied, the mold surface Both durability and surface roughness can be further improved.

In addition, a cooling water jacket (4aJ) or a pipe may be provided around the inner layer in the backup body (4).

Next, when manufacturing another mold (2) in Fig. 1, this time, using the mold (1) as a reference, the inner surface (6) is the thickness of the product + the mold (
Apply sheet wax to the inner layer thickness of 2), and place the mold (1)
It can be produced in a similar way, but it can also be done.

(Effects of the Invention) As described above, in the present invention, since the mold surface '1 is formed with equal thickness by casting Bi-Sn alloy, an accurate mold surface can be easily made in a short period of time, and accuracy can be improved. High quality rim molding can be done at low cost.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view of an embodiment of the present invention, Fig. 2 is a manufacturing process diagram of a mold, and Fig. 3 is a longitudinal sectional view of another embodiment. Body (5)...inner no. Figure 2 a

Claims (1)

[Claims] A rim consisting of an inner layer made of a Bi-Sn alloy having a thickness equal to the mold surface that matches the shape of the product to be molded, and a highly rigid backup body, the two members being joined by casting the inner layer. Molding mold.