Importance of reference angle in plastic mold design

Time:2019-09-25 09:26:04 / Popularity: / Source:

Mold reference angle seems to be a very simple problem, but even friends who have rich experience in plastic mold design may have had problems with large or small problems due to reference angle.
A cube with 6 faces; a set of common molds, is also with 6 faces, as shown below.
Mold is installed on injection moulding machine, side where worker takes product is operation side, back side of operation side is non-operation surface. Upper side named sky side, and lower side named ground side. Right angle side formed by ground side and non-operation side is mold reference angle. Position of reference angle in 2D group diagram is as follows:
plastic mold design 
Distinction between reference angles of molds is generally not wrong. For us, when ordering mold bases, we usually require molding supplier to cut C10 chamfer on reference angles of all stencils.
There have been such mistakes: when designer orders mold base, reference angle position in 3D is correct, and molding supplier processing is also processed with that reference angle. But when reference angle is cut, it is reversed and cut to the opposite side of reference angle. Position of reference angle in the map that designer officially sent to CNC machining is not in the position of mold ordering map. Reference angle of 2D machining diagram of mold blank that is sent to mold room is also placed in wrong position. However position placed is not at the corner where molding supplier is wrong. This mold is processed by single angle of reference angle. When drilling thimble and transporting water, deep hole drill only touched chamfer on the stencils and reference on the drawing. Then screw ejector pin was all wrong. In short, this mess set. It’s useless to fight and problem still needs to be solved. Later, mold was changed back by designer, and template was drilled with hundreds of holes.
From mistakes, reviewing mistakes is to sum up lessons learned. First look at the picture below. Position of reference angle in machining diagram is set to an unreasonable problem.
plastic mold design 
Reference angle of insert is on the right side according to assembly reference of injection moulding, it can be seen that shape of insert is not very regular. And we just remember that to match mold benchmark, it must be unique, so reference angle is placed on the right, and code in 3D is also on this side. Actually, material is bigger than this shape by about 20 mic, and be copper. It is actually expensive! When material come back, it is square, and it has been ground according to size of material. First CNC and use the right side of part to take number of processing. Then wire-electrode cutting whose 2D drawing come from us. Wire-electrode cutting according to position of reference angle in the figure, after two processes are finished, processed parts are 20 mic smaller than drawing size. Cylinder hole is also cut, and everything is partial. Welding can't be burned back. In addition, welding performance of beryllium copper is not so good. If it is heated, it is a big flaw. Even if it is a little bit of welding, it will burn out to swelling. Because of misunderstanding, there is no solution, and final result is refueling. But experience must be accumulated and lessons must be learned.
Some of following experiences and suggestions may have limitations and are not recognized by everyone. They are just for reference only.

Processing method of number of molds is generally based on internal requirements of molding supplier.

It is divided into a single-edge fetching process for reference angle and a fetching process for four-sided segment. At present, more molding supplier use a fetching process for four-sided segment and feel that accuracy of four sided segment is high, and it is nothing more than a double touch. However, there are also some well-known mold molding supplier that use single-edge fetching process for reference angle. They say that precision they make is also very high. Therefore, four sided segment are better or worse than single-edge fetching process. No comment, strictly in accordance with company's internal requirements, certainly yes.

For mold parts, if side that is consistent with direction of reference angle of injection moulding is a right-angled side, it is definitely based on this.

If part is shaped, but shape still has a right angle side, use right angle as machining reference angle.

If part is shaped and does not have any right-angled edges, you can cut a vertical edge at the bottom. Reference is machined before machining, and CNC cutting or wire-electrode cutting.

As shown below:
plastic mold design 
In addition, part in the above picture is a push block with a slope around it. In fact, I personally feel that it doesn't matter if part is not used for this part. Slope around is all one slope, or it can be divided into four-sided. Sticking this picture is just an idea.

In figure below, shape of insert has a slope, so two red faces perpendicular to each other are cut out as reference.

plastic mold design 

Look at picture below, mold is divided into two pieces and a fetching process for four-sided segment is adopted.

So when we design 2D processing drawing, we adopt a fetching process for two-sided segment instead of dividing the mold.
plastic mold design 
It can be seen from above picture that mold sealing position seems to be very small, and edge of mold is close to glue side. In fact, at the beginning, sealant position of about 20mm was left. After mold steel was fixed, it was said to cancel. Later, it was said that it would not be canceled and it was suspended first. After a few tossing, shape of product sent over became larger. Only the former mold steel will be used. Anyway it is also a plane model, dont need to worried.
In short, when designing and manufacturing mold, it is necessary to ensure that 3D, CNC machining number, milling machine, deep hole drilling, wire cutting number of design are consistent and unique. Reasonably arrange process and reasonably select processing benchmark. Assembly standard of mold is always certain. Even if your machining standard does not match mold reference, it will not be reversed or misplaced under normal circumstances because assembly standard and machining standard are not matched. However, we should try our best to avoid wrong installation when designing. For example, guide post on reference corner side of standard mold frame is asymmetrical with other three guide posts, slightly offset by 3~5mm or 2mm. It is to avoid fatal destruction of mold caused by 180° anti-mold.

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