Construction Injection Molds Classification

classification or types of mold injection very depend on what we need to make the plastic parts, because every parts have specific and unique design. when design molds we must see what the influencing factor like geometry, number of cavities, ejection principle, plastic material and shape of parts.

The basic classification of mold based on construction shown on picture below


1. Standard Molds
the standard mold is the most simple design, basically the standard molds is same as two plate molds construction, they divided in two side : cavity side and core side, cavity side is the side that construct to flowing plastic material from nozzle to cavity parts, basically they consist of sprue, runner.

core side construct to make shape for core, demolding system and ejection system, at this side we design ejection system.
standard mold have one parting line, and have one opening direction. this type of mold use in all kinds of plastic parts that doesn't have undercut, inner and outer screw.
Light brown color little and straight in ejection system is shown ejector pin.



2. Slide mold
development from this mold type is the used slider parts in various molds types, basic slide mold is transfer horizontal movement of mold to vertical movement, this types of molds is used to make parts with undercut, you should see more at the post when we need slider for learn more.




3. Three plate molds
basically three plate molds has two parting line, and floating plate, floating plate support by support pin, Since the mold has two parting planes, the runner system can be located on one side of floating plate or make special plate that attach in floating plate, we called runner plate, see post about runner plate. Three plate molds are used because of their flexibility in gating location. this types of molds is flexible even use in multiple cavity.

note : floating plate also called cavity plate or plate number 3, to know more the different between two plate mold and three plate mold see the posting about Basic and Types Molds Construction

4. Split Cavity Mold
basically the split cavity is same as 2 plate standard mold, but the cavity have split block to make undercut product or external threads.


this type of mold use when the slider is not enough to make the undercut or the threads. the disadvantages of this mold is when use for little parts, the construction will difficult.








5. Mold With Screw Device

this mold special to make thread forming, the core can be rotate when demolding process, both internal or external threads can be forming by this type mold.





from those picture we can see that they have gear device, the gear will rotate when form thread.





6. Stripper Ejector Mold
this type of mold have special purpose to make a cup shape without undercut, stripper ejector will make ejection more easy, same movement and power at the product and without a lot of marks in product






Molds with complex and difficult design can be integrated or combined one to the others mold type.

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Introduction to Mold Engineering of Thermoplastic

most electrical, and home appliances made from plastic, one of technology to make plastic product is using mold, specially injection mold of thermoplastic, basically when thermoplastic material heated, they will change of state, thermoplastic material will become soft, melt and flowable, when cooled again, they become solid again.

What is Injection Mold ?
there are some definition of injection mold

is a manufacturing technique for making parts from both thermoplastic and thermosetting plastic materials in production (wikipedia.com)

A manufacturing process for forming objects, as of plastic or metal, by heating the molding material to a fluid state and injecting it into a mold.(www.answer.com)

Herbert Ress, 2002 : an injection mold is arrangement, in one assembly a number of cavity spaces built to shape of the desired product, with the purpose of producing plastic parts in large number

this blog define injection mold is manufacturing process to make plastic product that have cavity spaces to shape the product by heating and injection pressure.

Types of Injection Molds
based on how injection mold would be processed wikipedia.org devide injection mold as 7 types until now, they are
1. Reaction injection molding
2. Liquid injection molding
3. Gas assist injection molding
4. Co-injection molding
5. 2-Shot Injection Molding
6. Fusible core injection molding
7. Rapid injection molding

based on type of opening method and runner system, The DIN ISO standard 12165, "Components for Compression, Injection, and Compression-Injection Molds" classifies molds on the basis of the following criteria:
1. standard molds (two-plate molds)
2. split-cavity molds (split-follower molds) stripper plate molds
3. three-plate molds
4. stack molds
5. hot runner molds

depending on material to be injected classifies as :
1.thermoplastic injection molds
2.elastomer molds
3.thermoset molds
4.structural foam molds

picture below shown 3 plate mold type with cold runner system and ejection system
click the picture to enlarge




closed Condition
picture below shown 3 Plate Molds Types in 3D design, in closed position with support pin, puller bolts, leader pin or positioning pin.


you can also learn more about basic pin construction at post about pin in molds
Opening Condition
then the construction molds of 3 plate type when opening is like picture below

picture below is shown three plate condition when open


we also can learning more about ppening Sequence, why and how the molds open, and explaining each molds opening step or sequence at post about opening construction

those opening sequence is just for 3 plate type, 2 plate type is more easy becouse just have one opening parting line.

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Top Plate, Stripper Plate,Sprue Bush and Runner Lock Pin Design

at the picture below you will see a set of Top plate until stripper plate design related with runner flow, at this picture support pin exclude. the mold type in this picture is 3 plate type.

the runner system accommodates the molten plastic material that coming from barrel, and guide it into mold cavity, the dimension, configuration, shape, and system connection with mold cavity will affect filling process.



as see from that picture, red plate indicate isolated plate, it's doesn't matter you use isolated plate or not, but you must see more in injection machine, if it needed isolated plate give it. number 1 and 2 in black plate it's indicated top plate for number 1 and stripper plate for number 2, those picture shown 3 open mold type.
after injection, in ejection process stripper plate will open because puller bolt pull it( not include at those picture).

runner ejector set will needed to push runner, after ejection, but if you use arm robot or manual take the runner by hand operator it doesn't needed. runner ejector set always contains spring, those spring will push pin in ejector set and will push the runner.

runner lock pin function is to pull runner when ejection begin still in top plate, if runner adhere in stripper plate, the robots or operator will difficult to take the runner, because no ejection system for runner in stripper plate.

when design the runner system and ejection system for runner in 3 plate type of mold you should use those mold accessories.

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Types of Runner depending temperature

there are various concept and type of runner, here we will give explain about runner type depending on the temperature control, we could divide in 3 type :
1. Standard runner system
2. Cold runner system
3. Hot runner system

standard runner system are directly machined into the mold plates (plates 2 or plate 3) but we can also make in special plate that called runner plate, this plate usually use in 3 plate mold type and attached in plate three(cavity plate)
at this picture below shown that runner directly machined in plate three


but picture below shown special plate called runner plate, those runner plate will attached in plate three, you can see from this plate that mold will have 4 cavity od product.


Cold runner system
this runner system have similar use with hot runner, but in different temperature, the temperature between 80-120 C, this Cold runner system used in reactive material such us rubber and thermosets type of plastic.
the difficulties in Cold runner system is
- high pressure consumption, so design more expensive
- because material is reactive, a little different temperature make different viscosities, this will make every cavity have different time to full fill.

Hot Runner System
this system should be viewed as extended nozzle in form of block, the hot runner system contains : sprue bush, runners, gate and extended nozzle, the advantage of hot runner is
- they can completely eliminate runner scrap, so there are no runners to sort from the parts,
- no runners to throw away or regrind and remix into the original material.
- no loss of melt and thus less energy and work input
- easier for fully automatic operation
- very good quality because melt can be transfered into the cavity at the optimum site

the disadvantages are :
- high cost
- thermal isolation from the hot runner manifold block is problematic

Hot runners are popular in high production parts, especially with a lot of cavities

there is 3 type of Hot Runner are :
1. the insulated hot runner,
Insulated runner molds have oversized passages formed in the mold plate
Heated type Hot runner
2. the internally heated hot-runner system,
3. the externally heated hot-runner system
internally heated and externally heated. The first is characterized by internally heated, with the heat being furnished by a probe and torpedo located in the passages. This system takes advantage of the insulating effect of the plastic melt to reduce heat transfer (loss) to the rest of the mold. The second consists of a cartridge-heated manifold with interior flow passages, look at picture below to learn more

this picture take from http://www.scudc.scu.edu

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When we need slider parts in Mold Design

second previous post i have post about the slider parts and construction in complete mold base , then now i give a little brief when we need slider in mold design, basically we design mold from our customer, first is we must look the parts that we will make by plastic mold, look mare at the drawing so we can know about tolerance and critical point of parts, seconds is define the parting line, first parting line is between core and cavity parts, and after that if the parts have side form we must define slider parting line, look picture below



from those parts we know that we need slider parts, side hole and other shape that can not form by core and cavity became slider parts. below is picture in 3D modeling,look at the hole shape in side, those shape need slider part.



and how the construction of slider, more about construction mold you can see by clicking mold construction or molds parts in quick topic, basically here i give slider 3D modeling and parts name, those parts names i take from Misumi standard mold design


you can use this tutorial for education and others purpose but still write copyright from this site.

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Mold Handling Picture after Assembly

Picture below show 3 plate mold after assembly, the position indicate ready to handling by crane, eye bolt was attached at center of mold plate.

after assembly process, make sure you has attached the tension link in 3 plate mold type or safety bolt or magnet in 2 plate type of mold this to prevent mold plate falling down when handling up with crane, when design eye bolt for handling, give bolt hole about 1 cm more to cavity direction from center line of mass of mold, it's commonly in plate 3 or 4 depending on how wide each mold plate, why it's must move about 1 cm ? the reason is same as safety bold, by move those bolt position when handling with crane mold base will decline about 5-30 degree, and top plate in upper position, this method make more secure when handling.

at this picture below, number 1 is eye bolt position in ready position to handling, and tension link (2) was attached.



from where we know that those mold is three plate, from the characteristics of three PLATE MOLD we can see from picture that :
1. Attached tension link, tension link function is o pull plate number 3 or cavity plate then by puller bolt, cavity plate will also pull the second plate, and cut the runner from nozzle.
2. second plate, it's indicate that those mold is 3 plate mold type, why because in 2 plate type, second plate is doesn't use. second plate is necessary when gate type is pin point gate.
3. runner plate, if you see more carefully, between second plate and third plate attached runner plate, in 2 plate mold type, runner plate does not use, because runner attached in third plate.

green arrow show injection nozzle machine where must be attached and indicate flow of plastic material during injection process.

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