How to design a mold for plastic injection molding?

First, pre-processing of product

Many mold designers?take a product and start to rush into mold. In fact, don't rush to split mold after getting?a?product. The most important thing is to check product structure, modification of?product tolerance and draft. Some products will also have a step?difference. When you have processed parting surface of product in the early stage, structure and position of gate can be basically determined.?Of course, these are ultimately confirmed with customer.

Second, confirm product's unreasonable parts

Some mold designers?may ask, is it possible for me to start designing mold after I have analyzed product structure? Answer is of course not. If you want to avoid trouble to make changes?in the design, then you must understand customer's requirements for mold.

Third, tonnage and model type of injection molding machine used by customer

If this confirmation is not accurate, you can't confirm entrance diameter of mold's sprue sleeve and locating ring, size and position of ejector hole,?even size of?mold base, and even height of mold, etc.?You have worked hard to design a?set of mold structure?and?also have a sense of accomplishment, but?mold can not be produced when delivered to customer. If?thickness of mold is not compatible with customer's injection molding machine, customer will not accept the mold you designed.

Fourth, analyze problem of product, as well as product line, product materials and shrinkage

It is not taken for granted that plastic shrink rates?of ABS must be 0.5%. This must be confirmed with customer. It is necessary to know what grades materials are ultimately used for production, whether or not to add any modified materials. When conditions permit, it is best to be familiar with assembly relationship of product and use of product, etc. This information is very helpful for future design of mold. Because only by?understanding these, you know which ones are appearance and which are non-appearances. Which areas of?draft angles can be increased and which areas cannot be changed. Even including structure of some products, if you understand actual assembly relationship and use of product, you will know which reverse structure can be canceled or changed to another simple form. It is important to keep in mind that process of making a mold is a process of simplification of complex problems. I often see that some people are?proud that they?have finished?a complicated structure. It is very ignorant. Because many product engineer?may design some unreasonable structures due to their own experience.?If you?can't correct them as a downstream process, they may always think that?their?design is okay. Then progress of our product designer?will be very slow. As shown in figure below, position of slanted top where product designer?doesn’t?consider?carefully, must be put forward by our mold designers.

Five, mold waterway

Only after understanding customer's requirements before design, you can have a predictable design waterway. You have worked hard to design a?set of mold,?but?you will find that customer needs to add other standards inside mold: date stamp, lettering insert, exhaust inserts. At that time, if you change it again, it is estimated that you will be tired and half dead, because your waterway, ejector, and screws are all already in layout.

Six,?after mastering above information, you can design mold.

First is parting mold. This process is estimated to be a process that everyone likes. Because of sense of accomplishment. Principle of parting surface?is simple, that is, parts?that can be stretched out is not scanned, or other advanced commands are used. Secondly, when you want to parting surface, you need to have a big picture?and?try to simplify parting surface. If it is not a precision mold, those 0.1~0.5 insertions can be avoided. In addition, parting surface?must follow a principle, that is, try to follow product trend. Parting surface?that was made in that way will be more conducive to fitter master fitting mold. When using UG software,?it's important to remember principles of each command, so?you know when you can use that command. Many times it's?not?important that you don't?know how to?use software, but you won't learn to use software. Same command, experienced people will have a variety of flexible usage, which is the most obvious in UG. In a word, important thing is idea, not?the?tool itself. When doing parting surface, you only need to know that angle of insertion surface can be large, area of collision surface can be large, and width of occipital can be wide. It is necessary to fully consider?actual mold of?parting surface?that you are do?now?is finished in the future, master who is responsible for fitting mold?in the workshop will not be jealous of you.

It is also necessary to consider layout?of slider and lifter while making parting surface, because those also involve modification of parting surface. Typical slider structure?is a trigonometric function relationship. This is fine if you can calculate it more times, but make sure that angle of oblique guide column?is not too large, try to achieve 25 degrees or less. Principle of inclined guide column?is that it can be thick, not too small, because inclined guide column?must be strong. In addition, slider is also divided into many variegated structures, such as upper inclined slider, inner suction slider, cylinder pumping, front mould?slider, slider with reverse ejector, slider with lifter, and so on.?These special structures make full use of trigonometric function relationship, purpose is to achieve demouding of product buckle, normal opening and closing of mold.

Followed by lifter, lifter?is more flexible, but angle of typical lifter?is not too big, try not to exceed 15 degrees. Of course, you have to do 20 degrees,?life is hard to guarantee, and movement will be very smooth. Specific principle refers to trigonometric functions and theoretical mechanics. There are many evolutions for?shape of lifter, for example,?slanted lifter,?large lifter?with a round bar,?small lifter?with a splicing platform, lifter?under top block, lifter?on slider, and so on.?All of these structures target on?one?purpose, using trigonometric functions?to make product's undercut. This shows how important it is to learn trigonometric functions!

As for various special structures, people think of it. You can make full use of your imagination. No matter what kind of structure, you can just think about it. After?thinking, go to bold design. Maybe you have a new invention, but after designing, it is necessary to?verify relationship of trigonometric function, which is to simulate opening and closing of mold under actual simulation, and to consider whether?there will be problems during?injection molding. Next step is layout?of mold structure. These contents are to be sorted out in advance. According to actual situation of product, different types of mold structure?are selected, for example, two-plate mold, three-plate mold, hot runner and so on.

All mold structure?types are designed to be able to achieve mass production of product. When choosing a mold base, we must fully consider considerations just mentioned.

After selecting mold base, we have to consider inlay of mold. Principle of inlaying is to simplify processing, save materials and facilitate product molding, such as exhaust. For parts?where you feel that there is very?thin on the mold, it must be set separately and easy to replace in the future. When inlaying, consider strength and workability?of insert, designability of waterway in the future. After inlay is finished, it is necessary to add standard parts. Principle of adding standard parts is kay parts?first, then local?parts,?and try to arrange balance symmetry. Generally, it is necessary to add on?ejector?parts?first. When adding mold ejector pins, it is necessary to consider layout?of waterway. Under normal circumstances, it is necessary to give priority to layout?of mold ejector pins, then generally design waterway, and adjust waterway ejector according to actual situation to balance these?two. Principle of mold ejector pins?is to add to the place where holding force is strong. In addition, it should be added to bone position?and?place where?strength structure is better, so as to avoid whitening or imbalanced ejector.

Actually principle of waterway?is principle of ejector. Because in general, place where product is tight is also hot spot of product and part where?cooling needs to be strengthened, This contradiction needs to be adjusted?well. As for whether to use a ejector,?a top block or a push plate, specific analysis is needed. This should be analyzed in combination with structural characteristics of product. For example, if product is easy to stick to front mold, it is necessary to consider whether to add reverse buckle in back mold, or to add ejector?to front mold. These are natural things, but many mold designers?will not think comprehensively. Why? It is because there is no adequate analysis of product structure, and there is no practical consideration for?state of product during injection molding process. This is the key to problem. After eject?waterway has been added, the rest are?some messy?standard parts. You should?consider symmetrical balance when adding. After design of the whole set of molds is completed, following checks must be done. First is draft analysis of inserts to see if there is any undercut, followed by interference check for?various parts of mold, which is the most important.?and?interference check of the parts of the mold is the most important. Then there is simulation of mold opening and closing action. If?mold is not too clear, it must be simulated. In addition, machinability of various parts of mold and assembly process of mold. Please do not work hard to design a clever structure, theoretical calculations are no problem.?After processing, result?is that it?can not be installed?(especially structure of tunnel slider), or poor assemble.

General process is over. In fact, molding?design?is a matter of contradiction. If you want to design a perfect one, cost of mold will be high. If you want to design a simple one, you may have to change product or strength of mold, and service life will have an impact. So molding?design?is not absolute. As long as you find?a?balance point, mold you designed is successful. Therefore, structure designed by others may not be suitable for you. As long as you follow above molding?design?points, we can design a more reasonable mold structure.