Molding Machine & Molding

8/17/2019 Molding Machine & Molding

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ONE – Basic of Injection Molding

Plastic injection molding, by definition, is the process of injecting plasticinto a mold (or mould in European circles), cooling the plastic, ejecting itfrom the mold, and packing the finished product for sale to the customer.

This sounds simple and in its basic form it is, but the process involved withmaking all this happen is actually quite complicated. lastic can be injectedinto the mold with low pressure, but typically is done under high pressureupwards of !",""" #$ cavity pressure.

There are many diverse types of injection molding and as many differenttypes of plastic injection molding machines to go with it. #ome of themore common types of plastic molding are standard mold injection, insertmolding, plastic extrusion, blow molding, multi-color or materialmolding, stac molding, and rotar! molding just to name a few. There

are custom plastics as well, from common every day plastic resinsto the more e%otic engineering grade resins used in most automobilestoday. There is even injection molding grade &metals& being e%perimentedwith and used these days. There are many types of injection molding machines all made for specificpurposes. There are the standard hori"ontal injection moldingmachines which range in si'e from a few tons all the way up to """ tonsand more. ou could drive car between the platens of a press that large.#ertical injection molding machines are often used for insert molding(although this can also be done hori'ontally) and share a common cover withtwo ejection halves of the mold. This allows for de*molding and loading of inserts in one half, while the other half is producing the ne%t shot of parts.There are also two and three shot injection molding machines forproducing multi*color or multi*material parts such as lenses for tail lightsand gear shift knobs with hard plastic inner core and a soft vinyl outcovering. The newest machines are &all electric versions& which stray fromthe standard hydraulic injection machines used now for years. Theseinjection molding machines are much more efficient and repeatable thentheir hydraulic cousins are. +ommon injection molding machinemanufacturers are $oshiba% &us!% 'incinnati% (eMaag% Engel% Nissei%

)BE% *rburg and Bo!, just to name a few. The basic steps to producing a plastic injection molded part on a standinjection molding machine are

• -eating the plastic resin to the required range of the product being

used.

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• eveloping the shot si'e through use of a reciprocating screw which

conveys the melted plastic to the front of the screw.

• $njecting the plastic into the mold under pressure to fill the cavity of

the mold.

• acking the plastic to create a full part inside the mold.

• +ooling the plastic in the mold through the use of cooling channelsmost commonly with water.

• Ejecting the cooled part from the mold.

• /epeating the process over and over again.

$+O – 'hoosing a Machine

+ommon injection molding machine manufacturers are &us!% $oshiba%

Nissei% Mitsubishi% Engel% #an (orn% (emaag% 'incinnati% &PM% )BE %

Nigata% ,andretto% eed% *rburg% and Bo!. There are also others, butthese listed cover of the most common injection molding machine

manufacturers. Each of these manufacturers supply the standard hori'ontal

hydraulic or toggle clamp injection molding machines, and may also supply

co-injection% multi shot, and the more recently desired all electric

injection molding machines.

0hat type of machine is best for you1 This depends entirely on what youare planning to do with it. 2irst you need to decide what your 3iche market

is going to be. ou then should research what types of products these

markets will require and what types of injection molding processes will

be required to create them. ou can do this yourself or have it done by a

consulting or research service. 4ased on what the research tells you, you

will then need to decide what type of machine you will need to perform those

services for your customers. 2or e%ample, if you decided to get into the

3iche market of automobile lenses, you will likely need a machine capable of

multi shot or co*injection molding. $f you are going to produce simple oneshot type molding products, or products that do not require any special

needs, you will be looking for standard toggle or h!draulic clamp

machines. $f your market will require some type of insert molding, you

could be looking for .ertical shuttle presses.


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ou will also need to decide if you will need new or used injection

molding e/uipment. This depends entirely on the level of consistency and

comple%ity of the products you are molding. There are pros and cons to

both avenues. 5lder used injection machines can fill a service if less

comple%ity and repeatability are required. 3ewer used machines oftenbecome available do to someone going out of business or simply changing

directions within the company, and these machines will be more current and

have more current technology. They will also typically be more reliable from

a maintenance point of view. 6sed equipment will be less e%pensive than

new and often fill the needs of the molder.

$f your business is cutting edge, or may be on the larger si'e, keeping up

with your competition becomes more of an issue. $n this case, purchasing

new equipment is probably the most common way to go. This will keep you

competitive with your competition and also maintain the average age of your

machines to something more desirable. 7gain this just depends on your

niche and business requirements. 8any businesses try to maintain around a

9" year average machine age to remain competitive in their fields.

:astly, if you want the latest technology for your plant, the &all electric&injection molding machines employing electric servo controls are the latest

to hit the market. $n the earlier years of their development, only small si'e

electric machines (up to around ;"" ton) were available, but now you can

easily find machines in the 9""" ton class and above that are &all electric&.

There are also -ybrid versions with electric injection units and hydraulic

clamp ends. The consistency and &shot to shot& repeatability of these

machines is currently unmatched in this area.

T-/EE * -ow to /educe #etup Times 6sing


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companies are not at full utili'ation of their equipment, management would

love and often pushes for the achievement of one minute changeo.ers on

all molds so they do not loose any machine time. 0hat management does

not always do is to support the idea with money saving devices or studies to

help the process technician and set*up people to achieve quicker moldchange o.er0s. This often produces frustration in with the technicians and

die setters who are trying to do a faster change over without some of the

fancy tools to do it with.


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personnel is paramount to the success of the mold change team and

reducing your setup times.

#ometimes when you=re not busy (ha*ha), get your video camera and film

the guys (or gals) doing a mold change. 0atch them go back and forth,

down the aisles, into the corners, on top of work benches, into the

maintenance area do'ens of times just to get parts, tools etc to do the mold

change. The first step is to separate your die set into two areas and those

are &internal and &e%ternal& components. $nternal components are things

that have to be done &during& the die set. E%ternal components are your pre

preparation and post cleanup operations. 7 very simple way to get started is

to do &before and after& video tapes. Tape a setup as you would normally do

them and then review these with your die setup team. 3ote each time that

someone leaves the frame of the picture and where they went at the time or

what they got, and how long they were gone. 0atch for any repetitive or

wasted steps and note them down. 4rainstorm ideas as a team on how to

eliminate these time losses. reparation and practice is the key to success,

just like in the 37#+7/ pits.

5ne of the easiest and most cost effective things you can do to aide quickmold change is to manifold your dies. Then all your set*up people need to

do is run the larger water feed lines to the manifolds, one in and out for

each half, and then the mold is ready to run. This can also be done for valve

gate hoses if you have them as well. This removes minutes, and in some

severe cases, hours of set*up time depending on your particular set up and

mold si'es. #tore your molds at the machine when practical. $nstall mold

racks right at the machine to reduce fork lift travel in the plant and to keep

handy the mold at the machine if at all possible. This can reduce time of

quick mold changes, as well as keep the molds from getting lost behindgaylords of material, stacked up high on a heavy duty rack or lost

somewhere in the shop. 7 well organi'ed storage area can be a great help

in optimi'ing your die setup times.

Then there are other simple yet very important ideas that help the set*up

people. +olor coding of all the waterlines to be blue > red for &in& > &out&.


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6se of colored wire ties and a unique molder invented product of waterline

safety tags for the disconnect fittings with a corresponding colored cap that

is installed on the tool under the water line plug assures proper hook*up. 7ll

these items ultimately help the process technician or set up person to

perform proper water hook*up=s.

256/ * The 4asic $njection 8olding rocess

The basic injection molding process, which is the process taking a polymeror generically a ?plastic resin@ from a solid state, heating it and changing itto a semi*liquid state, forming it into something, and cooling it back to asolid state. $njection molding is an e%tremely versatile and popular form of molding. 5ther processes include e%trusion, thermoforming, and blowmolding. This process can be used to create untold types of productsincluding toys, everyday items we use, medical items, and car parts. $tAs

uses are almost limitless and are ever e%panding day by day, as newtechnologies for both injection molding machines and engineered resins

are developed and implemented.

4ut, thatAs not why you are here visiting this page. 0e could spend all daydiscussing the different types or resins, their uses and applications, thevarious types of machines and their processes but we wonAt at this time. $hope that you are here because you want to understand the basic injectionmolding process and how it works. 4ased on that, we are going to take avery simplistic approach to this process and keep everything very generic.ou can get training through most of the injection molding machine

manufacturers and it can often be done as onsite training vs. offsite, but if you choose to do onsite training, it is important that you can create anenvironment where the staff that is being trained, can do so uninterruptedby their normal daily tasks. $ have seen many failed attempts at usingonsite training because proper arrangements were not made to cover thepersonnel involved in the training, and interruptions rendered the traininguseless. $f you are looking for a more advanced e%planation of injectionmolding, you will need to take some classes, seminars, workshops, or othermore advanced training in the area of injection molding. ou would thenlearn about basic polymer chemistry all the way through advanced

polymeri'ation and processing conditions and much more.

The basic injection molding machine is comprised of a few unique major

components. The major components of an injection molding machine are

the feed hopper or hopper, the screw and barrel, the barrel heaters

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, the no''le and no''le tip, the platens, the tie bars, the clamp, or clamping

mechanism (usually toggle type or hydraulic), the mold, and a whole lot of

electronics, hydraulics, andBor servo motors and controls, to make it all do

what it is designed for, over and over again. ou also will have a number of

e%ternal au%iliary equipment units, such as material dryers, mold heater orthermolators units for temperature control, hot runner controllers, valve gate

controllers, and other items required for your unique processes.

2$CE * 4asic lastic $njection 8olding 8achine rocess

Material Drying and Material Hoppers

Material (r!ing

epending on the resin you are using and whether or not it is a

?hydroscopic@ resin (absorbs moisture form the air), you may have to first

dry the resin. This is a process of removing any moisture from the individual

plastic pellets, so as to make them usable in the injection molding process.

This is done with a material dr!er, which is provided my many different

manufactures, and itAs sole purpose is to remove moisture from plastic. This

is accomplished by circulating heated ?dry@ air through the resin inside a

drying hopper at a manufacturer specified temperature. This causes the

plastic resin to release itAs moisture and most commonly this moist air is run

through the material dryer through a bed of molecular sieve (desiccant)

which retains the moisture inside the dryer bed and sends dry heated air

back out to the hopper. This air needs to be maintained at a dew point level

somewhere between *9" and *;" degrees 2. 7ny higher than this and you

run the risk of having wet material. The material can be checked for

moisture using a couple of glass slides and a hot plate, looking for small

pockets of gas in the pellet. This is done by heating the slides on the hot

plate to a high enough temperature to soften or melt the plastic you are

checking, laying a few pellets on one of the heated slides and sandwiching

the pellets between the plates. ou can then inspect the flattened pellets

between the plates for small gas bubbles which would indicate moisture. The

other method involves a lab device called a moisture analy'er, which isconsiderably more e%pensive but much more accurate. 5nce the plastic resin

is dry, which usually is anywhere from D *; hours on average, it is ready for

processing and we are going to feed the resin into the machine hopper to

begin the molding process.

$he Machine &opper


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These can be very small (shot hoppers) to very large in si'e but they all

serve the same purpose and that is to hold plastic pellets or resin, which will

be used in the injection molding process. The smaller shot hoppers, are

typically used when you are drying resin either in a me''anine or machine

side drying hopper. These small hoppers only bring a small amount of resineach cycle to the screw feed area, thus controlling the likely hood of the

pellets regaining moisture while waiting to be fed to the screw as can be the

case with small shot si'es and larger machine hoppers that are not being

dried on very humid days. The other very common method, but will require

some reinforcement of the hopper mount, is to mount a sufficiently si'ed

drying hopper directly over the feed throat of the machine. This method is

commonly used but presents itAs own challenges as they are much more

difficult to move out of the way when you have to inspect the feed throat.

#ome machine makers have added an air assisted hopper slide option to

aide in the process of moving the hopper out of the way as needed. 7ll of

these options, should be mounted on a magnetic drawer base. The purpose

of this unit is to try and eliminate any metal objects that may have gotten

into the material, virgin or regrind, and yes this does happen from time to

time. #ometimes itAs a malicious act but most of the time itAs carelessness

or disrepair that causes this to occur. 8etal and screws donAt mi% and it can

make a mess out of your molding process depending on where the metal

ends up. $t can get lodged in the screw, no''le or no''le tip, in your gates,

or simply scratch your beautiful mold surfaces should it make itAs way

through the entire system. Each case has itAs related costs to repair and

these magnetic bases can prevent much of it from ever happening.

Barrel, Screw, & Barrel Heaters

$he ,crew and Barrel

The reciprocating screw in injection molding or just ?screw@ resides

inside the barrel. $t is made up of two components which are the injection

molding screw and screw tip assembly. $t serves two purposes, the first

being to convey material forward in the barrel to the front of the injection

unit for each new shot, and two, inject the plastic under high pressure into

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the mold. $t is very important that these components are inspected for wear

at least yearly as they are very high tolerance components and very critical

to the injection molding process. 5ne way you measure your screw and

barrel performance is to record your recovery time and screw /8As, when

the screw and barrel are both new, and also note which resin thatmeasurement was performed with. Then at month intervals, check your

recovery times, and make sure that they remaining relatively the same. $f

you start noticing a longer recovery time (D"F or more), there is a chance

that you are starting to get some wear. The only way to know that for sure

is to remove the screw from the barrel, inspect them both and measure

them with micrometers and compare the si'e to the print. The manufacturer

can give you the recommended ma%imum where for your particular screw

and barrel but usually itAs around ."" * ."9" of an inch. There are three

main 'ones to most standard injection molding screws and these are the

feed, transition, and metering 'ones. ou can also get specialty injection

molding screws with mi%ing sections or other sections built to your own

specifications as needed. 8i%ing or barrier wave injection molding screws

would be an e%ample of a different flight options for a screw. The screw,

during the rotation phase, can also provide heat to the melting process

through friction, improving the quality of your melt. The injection pressure

applied by the screw is the heart of your process.

Barrel &eaters

The purpose of the barrel heaters is somewhat self*e%planatory, and that is

to ?heat the barrel@. The reason we need to do this is provide an

environment in which to begin the plastic processing portion of our cycle. $t

is imperative that your barrel temps are up to your ?set temperature@ for the

type of resin you are using, before turning the screw. ou will also want to

add some ?soak time@ to this to be sure that all of the solidified resin in the

barrel and on the screw has fully softened or melted. The result of not doing

this is usually a broken screw tip assembly or in some e%treme cases, even a

snapped of screw. ou=ll notice $ donAt mention how much time your soaktime will need to be, and that is because it will vary by the material you are

using and the efficiency of your barrel heaters. 3ormally, at least a half hour

of ?soak time@ is recommended for most plastics and this is commonly a

standard feature on most machines made in the last 9" *9G years. $f you

have the ability on your machine to ?bypass@ this part of the process, my

recommendation is donAt and that is from e%perience with seeing the results


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of people who have tried that and failed. 7t upwards of H9G"" for a screw

tip assembly and upwards of H9G,""" or more depending on the si'e of your

screw.

Barrel Temperature Control, Nozzles & Nozzle Tips

'ustom Injection Molding - Barrel $emperature 'ontrol

Each 'one of barrel heat is individually controlled and range from a couple of

'ones to or more depending on machine and barrel si'e. They are

controlled through the use of thermocouples which are attached in a central

location of each heating 'one and provide feed back to a controller which

turns electricity on and off to the heater bands, maintaining a constant

stable temperature for your process. Thermocouples come in two types on

most injection molding machines, types I > J. $t is always important to

make sure you have the correct type of thermocouple when replacing these

or you can have process issues due to inaccurate temperature readings.

#ame thing goes for heater band replacement. $f you replace a ;"" watt

band with one half the si'e or double the si'e, it can dramatically affect your

processing. ou also need to pay attention to the voltage of the heater

bands you are replacing as they typically will be one of three voltages which

are 9D", D;", or ;K" volt. These bands are not simply interchanged. $ have

seen 9D"v heater bands hooked up to D;" volt circuits, and turn cherry red

before they failed, which can be very dangerous. The opposite can also be

the case where a DD" volt band is used in place of a 9D" volt band and

though these will not turn cherry red, you might never get enough heat to

move plastic through it.

No""les and No""le $ips

The no''le and no''le tip are the e%it point for the plastic resin from the

screw and barrel on itAs way into the mold. 3o''les come in a multitude of

lengths and designs and you will need to know which is right for you and

your process. The most commonly used are the two piece no''le which

incorporates a separate body and tip. The reason for this is that you have

more versatility for use between the most common sprue bushing radii,


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which are L@ and M@, and also different material types which may require

different tip styles such as a continuous taper or reverse taper for nylons

resins and other high crystalline materials. $t also allows you to easily

change the tip opening si'e which can vary from mold to mold. ou always

want to use a tip orifice si'e that is equal to or slightly less than the spruebushing orifice in the mold to aide in leak prevention between these two

areas. $f you use a no''le tip that has a larger orifice si'e than your sprue

bushing, or is damaged, be ready to replace some heater bands as at some

point you will likely leak plastic between the tip seat and the sprue bushing

sea. This will then leak back over and cover your no''le and eventually the

barrel if itAs not caught in time, which causes unnecessary down time and

cost to replace destroyed heater bands and thermocouples. $t is very easy to

change tips during production with this type of no''le either due to a radius

change or if the tip has been damaged in any way. 3o''les and no''le tips

come in a variety of flow through styles as well, such as general purpose,

continuous taper, and a few others.

1I#E * 7 4asic +ustom lastic $njection 8olding 8achine

The Platens & Tie Bars

Platens

5n most machine there are two platens, referred to as the movable and the

stationar! platens. 8ost commonly you will have two stationary platens,

one front and one rear, and one moveable platen. The platens serve a couple

of functions. The first thing that it does is provide a place to attach your

mold. The platens will normally be drilled and tapped with threaded holes,

which in turn are used to attach clamps to the mold, holding it in place

during the entire molding process. #ome platens in less common cases, are

built with slots in them instead of drilled and tapped holes, and this is

actually a more versatile way to attach clamps to the mold. This was more

commonly used with European machines then it is on Iapanese or 7merican

machines. The placement of these holes are usually determined by an

industry standard unless otherwise specified by you for a given platen andmachine si'e. The si'es of the holes in the platens are typically determined

by the platen and machine si'e as well. The larger the machine, the larger

the bolt si'es required to clamp the molds into them. $Ave often been asked

how many clamps are required for a given mold. 0hile $Ave not really found

a ?hard rule@ about this, $ can tell you from e%perience that if you have one

clamp for every 9K inches of mold length, you will not drop a mold on the

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floor as long as it is properly attached. #o, on a mold of !@ in length, you

would have a total of 9D clamps, ! per side, and each per mold half. 3ow

this will vary some in different molding facilities and is meant only to be a

guideline. ou should follow whatever rules your company has set forth for

this procedure in your injection molding facility. There are also some ?through holes@ in the platen in a number of pattern options for ejector

rods. The use of these will be e%plained in a later section. These holes are

also laid out as per a specific standardi'ed location as with the threaded

holes for the clamps. There are multiple patterns available, which will

handle F of all standard molds.

The second function of the platen is to provide the steel to develop a

uniform force on the mold and move the mold halves or cover and ejector,

either to the open or closed position. $n the open position, parts can be

ejected and removed from the mold by means of an operator or by someother robotic means. $n the closed position, tonnage is applied to the mold

halves via the platens and this is when the plastic under high pressure is

injected into the mold. The term ?platen deflection@ is derived from the

amount of movement that is e%erted on and results from this injection

pressure being applied. 7 hydraulic clamp machine usually will resist the

platen deflection issue better than toggle clamp press because in a hydraulic

clamp press, the tonnage is developed by a large hydraulic ram located in

the very center of the movable platen. 5n a toggle press, the attachment

location of the toggles to the platen are more towards the outside edges anddeflection in the center of the platen is more common place. This can make

a difference when you are close to the press tonnage threshold on a given

mold, and puts the mold at risk for flash problems along the parting line

edges.

$ie Bars

The tie bars are the mechanism that actually develops the tonnage of the

press. Tie bars are made of steel. The si'e will vary from a few inches in

diameter on small machine up to well over D"@ in diameter on the very largepresses and the length is determined also by the type and si'e of the press.

The rods will be attached most typically with a very large nut on the outside

of both the front and rear stationary platens. There will be four tie bars in

the case of most common injection molding machines. The only place this

wonAt really apply is with some of the ?+@ type clamp mechanisms, which

arenAt very common in most standard injection molding machines. The way


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this tonnage is developed is by moving the movable platen forward until the

two mold halves contact each other and then high pressures are applied

causing the tie bars to ?stretch@. $t is this stretch and the force being

applied that will determine the final tonnage capability of an injection

molding machine. 5ften, this stretch is measured with a strain gage that islocated on the end of one or even all ; tie bars, and this stretch or ?strain@ is

measured to deliver an output back to injection molding machine controller

in order to get a ?tonnage reading@ from the machine. This is tie in with

safety mechanisms to avoid over stressing the bars which can literally cause

them to crack or snap, as well as feed back for the process itself. This

information can also be used by many newer machines that have the option

for ?auto tonnage setting@ of the machine, which takes most of the setup or

technician requirement out of the function as it is automatic.

Plastic n!ection Molding Mold Clamping Systems

Mold 'lamping ,!stems

+lamping your molds on the platens for the injection molding process is a

fairly basis principle and the methods used to accomplish this task are not all

that different from each other. The most common method is the use of

mold clamps. These clamps are usually made of forged or cast steel and

look like the picture shown here. 0hile this is a fairly common clamp style,

you can find a number of variations of this type of clamp. $t consists of the

clamp, an adjustment bolt, an attachment bolt, and a spacer or washer for

use on the attachment bolt.

The alignment of these clamps is critical to their

function and they must be used properly. The result

of not using these clamps properly, could mean the

difference of a mold remaining in your machine and

lying on the ground beneath it. The safety ha'ard of this is self e%planatory, not to mention the damage

that could be done to the mold or machine. $t is very important that the

clamp adjustment bolt is set the correct height which is level with the

clamping surface of the mold. ou can measure the clamp plate thickness

and if itAs 9 ?, set you adjustment bolt for 9@ height. This provides the most

surface contact with the clamp plate and results in the best clamping forces


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being applied. 7 small amount of error can e%ist without serious issues, but

level is still the desired and safest approach.

7nother important factor in proper attachment of a clamp is the depth of

the attachment bolt into the platen hole. The best rule of thumb used to

calculate this is ?one and a half times the diameter of the bolt being used

should be used as a depth into the platen hole@. $n other words, if you are

using a M@ inch attachment bolt, you should use a bolt length that will get

you at least one and one eighth of an inch into the platen. .NG % 9.G O

9.9DG or 9 9BK@. The formula applies to all bolt si'es being used. 8ake sure

you also account for the height of the spacer or washer you are using to

determine the bolt length needed. :etAs assume the spacer is L@ in

thickness. 0e already know we need to get 9 9BK@ depth into our platen. To

determine the length of the bolt required you need to make some

measurements. 2irst measure the height of your clamp plate. Then youneed to know the thickness of your clamp and add the spacer thickness to

that. :ets assume our mold clamp plate thickness is 9@. 5ur clamp

thickness is also 9@. 5ur spacer is L@. 0e total these amounts and then add

the thread depth needed to determine our bolt length or, 9@ P 9@ P L?P 9

9BK@ O !.DG@ or ! GBK@ bolt length required for our task.

This is important for a couple of reasons. The first is that if we are using

too short of bolts, we will likely strip the threads right out of the platen holes

when the mold is mounted on the platens. 7s the mold is opening, closing,

and ejector system running, you could literally strip the mold off the platens

and the mold could fall out of the press. oes this sound like the voice of

e%perience1 ThatAs because it is and $Ave seen it happen. The other problem

$Ave seen that ends with the same result is using bolts that are too long.

Each platen hole has a finite depth, meaning that you can hit bottom if the

bolt is too long. The result of this if you donAt notice is once again a loose

clamp and a dangerous situation, so pay attention these details and youAll

never have a problem. Jeep your platens holes in good condition too, as

this makes everyoneAs job simpler and safer.

5ther methods of clamping a mold to a press is using holes in the clamp

plates and bolting directly through them ou will need to apply the same

calculation to determine bolt lengths for this method as well. This method is

easier and safer than clamps, but requires precise hole placement in the

molds to line up with your press platen holes. The last common method is

hydraulic clamping, which is the fastest, safest, and most e%pensive method


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but well worth it if the investment is made as this is a great time saver,

saves wear and tear on the platens, and cuts down the risk of mistakes.

These are the types of financial decisions your company will have to make

for itself. 7nother less common and even more e%pensive clamping method

is magnetic platens or clamping plates that are added to your e%istingplatens and use e%tremely powerful magnets to hold the molds into place.

These are typically only used where time savings and quick mold change are

a way of life as their costs are tough to justify in many situations.

Custom Plastic n!ection Molding "!ection and Core Pull Systems

Ejector ,!stem

The sole purpose of your ejection system is to remove the finished custom

injection molded parts from the mold or die. The ejection system is

comprised of a hydraulically driven ejector plate, sometimes referred to asthe butterfly plate, and some type of ejector rod or bar, which is used to

drive the mold ejector plate forward, releasing the part from the cavity or

core of the mold, or so that it can be removed by an operator or a robot.

epending entirely on your mold and itAs requirements, there could be

anywhere from 9 to ; or more rods required to perform this task. 5ne

critical thing to remember is that if you are using more than 9 rod, it is

necessary that these rods are e%actly the same length. The reason for this

is so that the ejector plate is moved forward in a uniform manner, to avoid

causing the ejector pins to become scored and bound up. $f you are using

one rod, it usually is placed in the very center of the mold. $f two or more

are ejector rods are used, it is important that they a installed symmetrically

into the mold, such as opposite corners, directly above each other, all four

corners, or similar. These rods can be installed as loose or ?floating

components@ or tied*in. 7s the term indicates when tied*in, the rods are

attached at both the mold and machine ends of the rods, usually with bolts

or threaded rod stubs in the rod. 8olds that have return springs can be

used with loose or floating rods, as the springs are intended to provide the

return stroke of the mold ejector plate when the machine ejector plate is

retracted, allowing the rods to also be retracted out of the way. This is

especially useful if you run smaller molds with multiple ejection strokes and

little or no actions built into the mold.

0ith more comple% molds, the tie*in method is more appropriate and more

often used. The difference in using this method is that the machine is

controlling the entire stroke and it allows you to safely control the ejection of

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parts from molds that have actions built into them such as slides, suicide

core pins, or both. This also helps prevent damage to the tool, should

something go wrong with the injection molding process or machine. 0hen

coupled with a robot or operator removal, the rods can maintain the ejector

plate in the forward position until the robot or operator has removed thefinished injection molded part from the mold.

'ore Pulls

+ore pulls do e%actly what they sound like they would do, and that is to pull

cores out of parts which otherwise could not be molded any other way. 2or

e%ample, $f you wanted to create a hole in the top flange of a part and the

hole was not in ?die draw@, you would be able to use a movable core to

create this hole. Iust to clarify, die draw is anything that lies in the direction

of ?mold opening@, with sufficient draft for the part to be removed. $n thecase of a rectangular bo%, by adding some amount of draft, you can mold

this bo% without the aide of anything special besides the ejector system to

remove it from the cavity. 4ut, $f you would like to put a hole in the side of

the bo%, we need to use a core pull mechanism to do this. The process is

simple in the case of creating a hole. 5nce the mold is closed, we will use

the core pull system to drive a pin into the core wall, creating an area that

plastic must flow around during the filling of the cavity. This now creates a

hole in the side of the plastic part. 3ow if we were simply to open the mold

up, we would rip or tear away all the plastic behind this core pin during

ejection, leaving us with a useless part. 4ut, if we pull that core back up out

of the way before we open the mold, we can safely eject the part with no

damage to our hole. This is just one of the myriad of uses of the core pull

mechanism on the machine. $t can if desired, be used in certain mold design

configurations be used as a hydraulic ejector system addition as well.

,I2 * * Basic 'ustom Plastic Injection Molding Machine Process

The Machine Controller

Machine 'ontrols

This area or component of the custom injection molding process can become

quite e%pansive. There have been so many iterations of machine controls

over the last DG years, that itAs difficult to know where to start. ue to the

fact that there are so many machines still in use today from this same time

span, $ will only touch on the basics of the main changes in order to keep


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this flowing and on topic as much as $ can. The process of injection molding

in itAs basic sense has remained relatively unchanged since the beginning.

8olten plastic is injected under high pressure into a mold, creating a non*

3ewtonian flow condition, which is cooled, and then removed from the

mold. There are 9""As of control mechanisms to create these conditions butthey all end with the same purpose in mind and that is to produce a plastic

injection molded part.

$n the beginning, there were relaysQ 7ctually there were other things before

that too, but we will start there. /elays, limit switches, relays, and more

limit switches, were the flavor DG to !" years ago and $Am not referring to

the newer solid state types, but the very large and now impractical

mechanical relays used in many molding machines for years. 7s with now,

these machines were provided to you with a hydraulic and electrical

schematic or ?ladder diagram@ showing line after line of relays, some open,some closed, that all together made a required action occur. $n many ways,

$ felt troubleshooting these machines were much simpler in a lot ways than

with todayAs solid state control systems. $f your clamp wouldnAt close, you

just looked for that line in the ladder logic, started at the end of that circuit

which usually was a solenoid on a valve, activated the clamp close button

and checked for voltage at that point. $f there was none present at the

solenoid, you back tracked to the ne%t point along the circuit path which

might be a junction block. 3o voltage there and back you go again until you

found the first point where voltage was present, but not getting through tothe rest of the circuit. That point often would be a relay or relay contact that

had failed. /eplace or re*build the relay and off you went again.

3ow that is a simplistic approach to circuits of old, but they worked. There

werenAt any touch screens, or :E read*outs, or circuit boards. Everything

today is now touch screens, electronic control modules, programmable

controllers, and the like. Trouble shooting is now more often done to the

module level and then replaced if itAs not functioning properly with another.

$ would say that todayAs machine controllers are much more reliable than

those of old, but they are also much more e%pensive to maintain. $nstead of

replacing or rebuilding a burnt relay that cost a few bucks, you will likely

have to replace a HD""" module. This is one of the costs of progress.

$n a nutshell, the controller is the brain of the injection molding machine. $t

controls all of the functions of the injection molding machine and insures

that the machine does what it is programmed to do. $n the case of the


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newest machines, they are comprised of many sensors, such linear

measurement devices, thermocouples, pro%imity sensors, speed sensors and

many more. Think of these sensors as the nerves of your own body, or your

ears, eyes, nose, and tongue. ou react to what your senses tell you, just

as with the machine. The controller allows you to input certain set pointsinto it, which tells the machine what to do during the injection molding

process. The sensors provide feedback to the machine controller so that it

knows whatAs going on and when, and what to do ne%t based on a program

that tells the controller what to do with the information that it receives.

These set points that you have control over will be discussed more in a later

module on process setting and controls.

,I2 * Basic 'ustom Plastic Injection Mold

The function of the ?mold@ or ?mould@ depending on which spelling yousubscribe to in the injection molding process, is simply to be the vesselwithin which a plastic part is born. Think of the mold as the reverse imageof your finished part. 0hat $ mean by that is thisRif $ took a ball and $covered the entire surface of the ball with plaster and let it harden, and $then cut it e%actly down the middle into two halves and removed the ball,what $ would be left with is the basis of an injection mold. $t is a void orspace of some shape that is split into two sections so that we can injectplastic into that space to create a plastic part when it is removed from thismold. 0e refer to the halves of the mold as the cavity and core, or coverand ejector. The cavity and core can be either the front or back half of a

mold depending on the design. 8ost molds will have the cavity or cover of the mold mounted on the stationary platen and core or ejector of the moldon the movable platen. $n the case of molds that are built with cavity orcover ejection this would be reversed, and then we often would use the corepull system to run the ejectors forward. 0e will stick with the more commonconfiguration of the ejector half of the mold being located on the movableplaten and using the standard injection molding machine ejector system. The ?ejector@ or ?ejection@ half of the mold is what will ultimately cause thefinished plastic part, to be ejected from the mold. $t is comprised of a

number of components, some of which will be the ejector housing, ejectorplate, ejector pins, and water (cooling) lines. 7s design requires it, it mayalso have slides, cores, lifters, and other moving components that make upthe the ejection system. $t also is usually the core half of the mold. 4esidesbeing a critical part of the molded part, itAs only other purpose in life is partremoval or ?ejection@. lastic shrinks to varying degrees, and because of this we must build molds with sufficient draft to allow the part to easily slipoff of the core of the mold without damage to the parts plastic surfaces.


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raft needed for a given material or resin can vary greatly and you shouldconsult your material vendor for the specifications for the material you areusing for your specific application. raft can be as little as a couple of degrees, to something much more substantial depending the part design andmaterial requirements. 0hen a part is molded and then cooled, the ejector

plate of the mold is moved forward causing the ejector pins andBor lifters topush the part free of the mold, allow it to be removed by an operator orrobot, or to simply fall onto a chute or conveyor to be moved to itAs ne%toperation. The cover or core of the mold, e%cept when the part is cover ejected, doesnot typically have any moving parts. $t does however usually house theentry channel for the plastic into the mold. This is done through a numberof different methods, such as a sprue bushing and sprue, or a hot runnermanifold. The channels of plastic flow can be directly into the part itself orflow through a ?runner@ system, which is the most commonly used method.The runner system can be part of the hot runner manifold or a cold runnersystem that is cut into the surface of the mold itself. 0e need a separationpoint between the part and the runner and this is called the ?gate@. Thereare many ?gate@ configurations and again, this all depends on your partsdesign and requirements as how this will be performed. This half of themold will also require sufficient draft, as the part must release from thecavity as the mold opens which separates the two halves prior to ejection,with the part remaining on the ejector half of the mold. This half of themold the mold will also contain the horn pins which move any slides themold might have into place as the mold closes. The guide pins, which will

located in two up to all four corners of the mold, perform the task of keepingthe two halves aligned as the mold closes. 0hen the two halves are closedtogether, they create a void that will be filled with plastic to create thefinished molded part.

,E#EN S Basic Plastic Injection Molding Machine Process

Injection Machine 'ontroller 'lamp 3 Ejectors ,etting (escriptions

and 1unction

'lamp settings

$n the custom injection molding process, the clamp settings control thedistance the mold opens and closes to, where it slows down and speeds up,and other miscellaneous settings where you might perform other actionssuch as core pulling and ejection start points. 4ecause of the large varietyof machine types, $ will not attempt to cover every possible setting but onlythe main ones that are common to most machines. epending on the age


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and abilities of your machine, these could be digital settings in the controllerinterface on newer machines or limit switches on older ones, or in somecases a combination of both.. 'lamp open fast S where you want to start opening the mold quickly

'lamp open slow S where you want to start slowing down the clamp beforereaching full open.'lamp full open * where you want the machine to clamp to stop after eachcycleEject start S where you want to start your ejection movement if yourmachine has ?eject on the fly capability@, otherwise it will usually be at themold full open point.'lamp close fast S where you want to close the clamp at high speed'lamp close slow S where you want to slow down the clamp when closing(usually before engaging the guide or leader pins)

Mold safe S just before the mold halves first touch, usually a fewthousandths of an inch before 'ero. This is the safety feature to help protectyour mold from damage if it closes on a runner or part. The clamp is putinto a low pressure state at this set point to protect your mold. This settingis one of the most critical to be set correctly and precisely.+lamp fully closed S this is the point where the mold halves make contactand high pressure is applied to build full tonnage.+lamp speeds and pressures S most of the above functions also have aspeed and pressure setting. These will be set according to you needs andwill vary somewhat for each mold.

Ejector settings4

The ejector settings control the distance and speed of the ejector rodsduring the part removal process from the mold. The settings are crucial toyour molding process as they help determine a number of things such aswhether or not the part is going to remain in place for robot or operatorremoval, or be ejected completely into a bin or chute. They can in someinstances also help in determining part quality with how fast a part isremoved in some more sensitive parts and molds, or ensuring the cores

have been removed prior to ejection in order to protect the mold fromdamage. 7s with the clamp settings, depending on the age and abilities of your machine, these could be digital settings in the controller interface onnewer machines or limit switches on older ones, or in some cases acombination of both.

Eject start position S where the ejectors start their forward stroke.


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Eject forward position S the distance of travel the ejector rods will makeduring each stroke of ejection.Number of stroes S the number of times the ejectors will make a anentire ejection stroke each cycle, usually limited to not more than G repeats.Ejector dwell time or eject forward hold time S the length of time the

ejectors will be held forward after reaching itAs forward limit. 6sually onlyused with a single stroke condition.Eject retract position S the position the ejectors must be in prior to closingthe mold for the ne%t cycle.Eject speeds and pressures S most of the above functions also have aspeed and pressure setting. These will be set according to you needs andwill vary somewhat for each mold.

Injection ,ettings

Injection Phase

-igh pressure 9st #tage 4oost * epending on the area in which you live,you will hear a number of different terms used for this phase of the custominjection molding cycle. 3o matter what it is referred to as in your plant, itremains the same thing and serves the same purpose, and that is to injectmelted plastic into your injection mold. This in many ways is the mostimportant part of the basic injection molding cycle, as it has a great bearingon the initial cosmetics and si'e of your finished plastic injection moldedproduct. ou can control the hydraulic pressure and speed with which youperform this phase, and on most newer machines the ?fill@ or ?injectionphase@ can be broken down into 9" segments or more to aide in precise

control of this part of your injection molding process. 0e will get deeperinto the profile settings, what they are, and what you can do with them inthe troubleshooting segment of this series. 6nder normal plastic processingconditions we want to fill the part as close to the G *F full cavity rangeas we safely can, allowing for the natural resistance of the plastic to absorbthe remaining inertia of the screw. 0hen we reach the injection transfer or ?cut*off@ point setting, we are doing e%actly what it sounds like and that istransferring from fill or 9st stage pressure, to packBhold or Dnd stagepressure.The machine settings controlling these functions are

1ill Pressure S the pressure setting for fill or 9

st

stage. $n most processestoday, this would be set to the ma%imum of the machines ability which isusually between D""" and DG"" psi. The reason for setting this toma%imum, is so that you do not ?pressure limit@ this part of the process.2ill #peed S The speed control for the fill portion process. 0e want tocontrol the fill speed of our process and not the fill pressure.1ill ,peed Profile S these are the fill segments we spoke of earlier. Theseprofiles can have as few as D steps or many as 9G or more. G to 9" steps


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are usually more than sufficient to handle the processing conditions for mostprocesses.$ransfer% transition% or cut-off position S The point of transfer from 9st toDnd stage injection. This can be done on most newer machines by position(most common), hydraulic pressure, time (least accurate and repeatable),

and cavity pressure.

Pac Pressure Phase

ack or second stage pressure is used just as it implies. 0hen used properlyitAs purpose is to pack out the injection molded part. 7ssuming you followedthe G to F fill rule, you will use the pack pressure to fill out theremainder of your plastic part, until reaching the desired cavity pressure foryou process. Typically, there are only one or two segments for this functionbut $Ave seen up to five, and it will have independent time and pressuresettings for each. ack pressure if used correctly, will finish filling and ?packyour plastic into the cavity. 5ften the 9st step of this pressure will be ?equaltoo or slightly greater than@ your transfer pressure so as to prevent thescrew from bouncing back at transfer. 7gain, if you follow the G to F fillrule on the 9st stage filling process, you can even use a lower pressure packin many cases without creating a screw bounce situation. This bounce iscaused by two things, the first is overfilling the cavity in the 9 st stage of filland second, packing with too low of a pressure when the first conditione%ists. $f the inertia of the screw is fully e%pended before the cavity is fullyfilled as should be, the likelihood of this happening is low.

3ormal pack setting options, if your machine is so equipped are

Pac time S Typically, you will have one or two segments of time available if your machine has the pack option installed. This time should coincide withthe amount of time to finish filling and pack the cavity to itAs peak pressurefor the desired dimensions.Pac Pressure S settings for the pressure of each segment.Pac ,peed S this is not an option on all equipment but very useful if youhave it, especially if you are using your pack to finish filling and packing thepart. This will be a low speed option and on some machines itAs even limitedto G"F or less.

&old Pressure PhaseThe hold pressure phase of the process is meant to maintain the custominjection mold process pressure inside of the cavity until the gate or gatesfree'e off which then will be released, as pressure no longer need be appliedafter that point. 5nce gate free'e off has been attained, no further pressurecan be added or removed from the plastic inside the injection mold cavity, asthe gates basically act as a cork after that point of the process. 5nce gate


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free'e has occurred, and the hold pressure has been released from thecavity, the cooling portion of the cycle may begin. -old pressure on most newer machines is also provided in segments withindividual time and pressure settings for each. There is typically only one

hold speed for the entire hold pressure phase. This again is usually a verylow speed of less than !"F, as we are not trying so much to move plastic atthis point of the injection molding process as we are maintaining thatpressure in the mold cavity until the gates have fro'en preventing anyfurther pressure loss. $f your particular machine is not equipped with a packpressure option, you can sometimes use the first one or two segments of your hold pressure phase as ?pack pressure@. This again will depend on theabilities of your individual machine and controller capability. 8ost machinesbuilt in the last 9" S 9G years have at least G and 9" segments of holdpressure. The machine settings controlling these functions are&old ,peed S this is usually on one speed setting that covers all of the holdsegments.&old Pressure Profile S each segment of hold will have an independentpressure setting and can be ramped up or down for each segment change.&old $ime * each segment of hold will have an independent time settingand can be changed up or down for each segment change. 6se as few of these segments as necessary to provide a good molded product. 8anymolders have a tendency to take the approach that if there are 9" segmentsinjection hold pressure, that we should use 9" segments of injection hold

pressure. $n reality, most injection molding situations will require less thanD pressures segments and rarely more than G. #ome e%ceptions to thatmight be when you are using one or two segments as pack. -old pressurealso will most commonly remain the same over the profile or reduce to lowerpressures in each phase when using multiple segments. ,crew otate and Bac Pressure Phase

The screw rotate and back pressure portion of the process occurs during thecooling phase of the injection molding portion of the cycle. 4ack pressure isapplied as a resistance pressure to the screw as it rotates, while developing

the shot for the ne%t machine cycle. The purpose of the back pressure is toaide in providing a consistent density of the shot si'e as the screw rotatesand conveys plastic resin towards the front of the screw. This is veryimportant for the injection molding process ?shot to shot@ consistency that isrequired by todayAs high precision injection molding process requirements.5n most machines, back pressure is usually limited somewhere around theDGF mark of total system pressure. 4ack pressure in most cases is a veryimportant function of the molding process, but it also contributes the wear of


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the screw and barrel components, thus keeping this as low as possible andstill able to produce a consistent and homogenous melt stream is verydesirable. epending on the resin you are processing, this could be very lowin the range of G" #$ or upwards of !"" #$ or more. 4ack pressure alsocontributes ?mechanical heat@ to the melt stream and the higher the back

pressure is set, the more mechanical heat that will be added to the injectionmolding process through itAs use.

The machine settings controlling these functions are,crew ,peed S This setting controls the /8As that the screw turns at up to

the machine rated speed. This can be a few hundred /8As on a smaller

machine, but typically will be less than 9G" /8As on larger machines

without special options. This setting also contributes to the time that it take

to get the screw from itAs forward position during the injection molding

process and the full shot si'e position. The ideal condition is to get the

screw back to its full shot si'e position just prior to the opening of the mold

at the end of the cycle, to prevent e%cessive idle residence time for the

plastic in the barrel.

Bac Pressure ProfileS This function on most newer machines, is alsosegmented with individual pressure and position settings for each segment.

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