plastic injection molding better quality parts is just the beginning

8/12/2019 Plastic Injection Molding Better Quality Parts is Just the Beginning

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Plastic Injection Molding Better QualityParts Is Just The Beginning...

July 16, 2013

When I first got started in mold making for plastic injection molding companies in

Melbourne in 1989, I was surprised by the high capital investment required just to start a

molding business.

The cost to purchase new machines was high so injection molders always tried to get the

lowest price possible but for some reason the cost of long set up times, making reject

parts and energy consumption were not much of an issue.

Today, however, it is a different story. Plastic injection molding companies are under

constant pressure to make better quality parts at lower prices with shorter

delivery lead times.

So as a molder, why would you settle for a cycle time of 30 seconds when it is possible to

have 24 seconds. Whats more, why would you invest hundreds of thousands of dollars in

machinery and moulds that will not live up to expectation?

In short, if you are involved with plastic injection molding as a process technician, business

owner, engineering manager or mold maker then we would like to save you five years of

learningso that you can:

Produce better quality parts

Reduce cycle times Reduce set up times

Reduce your energy bill

Save plastic material

After all, in order to deal with the pressure of todays overseas competition and increasing

energy costs it is essential that you have a well managed business that uses as few

resources as possible while still adding value to your customers. In other words, having a

lean manufacturing business.

So if you desire flawless production (as in the video below) here you can read about the

best ideas and techniques for increasing productivity that we have learned and developedover the past 20+ years.

Lean Manufacturing Principles And TheirBenefits

Lean manufacturing principles were used to create lean techniques that aim to build and

maintain the most efficient manufacturing business possible.

One of the key principles in lean manufacturing is to view things from the customers

perspective. Getting and using feedback from customers about your product line willensure you make products that satisfies their needs.


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Whats more, customer feedback ensures resources are not wasted on making a product

that has features that they are not interested in and not willing to pay for.

How Can Lean Manufacturing Principles Benefit

Injection Molding?

Many people initially believe that lean techniques are mostly about cost reductions. In

fact, they provide the one feasible way to cut costs while also shortening lead

times and times to market, improving quality, and providing customers with

exactly what they want precisely when they want it.[1]

One of the principles used to achieve these benefits is to eliminate all waste in a

manufacturing process. Waste is any action that does not add value to the end

customer.Click here to learn about the 4 most common mistakes in injection molding.

In injection molding, the most obvious example of waste is making defect parts.

A less obvious example is energy consumption used to make each part. Just because you

use 30% more energy than your competitor, it doesn't mean customers are willing to pay

more for your parts. They will go for the cheapest price.

This is why molders need to identify areas of waste.

There are literally dozens of examples of waste in plastic injection molding plants such as

longer than necessary cycle times due to poor part design, poor mold design or operator

incompetence.

Click here to learn how to reduce cycle time and save costs.

Another example is the lack of training in proper molding techniques. Insufficient training

can result in costly mold and machine damage.

When properly implemented, lean manufacturing principles can deliver many benefits.

Some other benefits include:

Higher employee morale (which naturally improves productivity)

Establishing a reputation as a quality and reliable supplier (this will increase yourcustomer base)

Given these benefits, one would think lean implementation would be standard practise in

the industry but this is not the case. During the past 20 years western plastic injection

moulding companies preferred to move some or all of their manufacturing operations

offshore to low cost countries such as China, India, Malaysia, Vietnam and the Philippines.

Fortunately, this trend is showing signs of reversing mainly due to the realization that

profit margins were not as high as expected because of ongoing quality issues and other

unexpected costs. As a result, injection molding and mold making industries are slowly

recovering in many western countries such as Australia and America.
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As this trend continues, it will not be sufficient to just sit back and wait for a full recovery.

Long term survival of an injection molding company hinges on the ability to eliminate

waste across the entire firm and make parts that satisfy customers needs.

Lean manufacturing principles provide a vehicle to see where waste exists and how to

eliminate it. One would expect that these principles will grow in popularity now thatoff shoring has not lived up to expectations.

Lean Techniques

One of the most common techniques is lean 5s.Click here to learn how lean 5s can benefit

your injection molding business.

Another common technique is the 7 wastes.Click here to learn how the 7 wastes can

benefit your injection molding business.

Challenges

Convincing Upper Management

The biggest challenge is getting long term commitment from upper management. They

need to understand how the long term benefits of implementing a lean manufacturing

program outweigh the short term inconvenience of modifying the way employees think and

participate in a firm.

Guaranteeing Worker Job Security

Workers naturally feel threatened by any change in their job roles especially one that

involves cost cutting. Thats why it is critical that upper management guarantee job

security at the beginning of a lean program and keep this promise.

Over time employees will gain confidence in the changes as they see the benefits of a

program. The result will be constructive participation by all employees.

Additional Comments

To be most effective using lean manufacturing principles the concept needs to be

embraced across the entire company. A lean manufacturing program should cover all

aspects of the business. It can be applied to office environments as well as manufacturing

processes.

Just cherry picking certain areas for improvement will not give long term sustainable

benefits to the company.
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4 Injection Molding Mistakes To Avoid

Avoid the most common injection molding mistakes if you are starting a plastic injection

molding manufacturing business and begin on the correct path. Understand that injection

molding is not as easy as it looks and there are so many hidden costs that are not visible

until you are already in too deep.

1. Poor Project Management

At the start of any new molding project, there are a number of people that need to come

together to discuss the best way to design and make a new part. Part designer, mould

designer, mold maker, moulding technician, plastic supplier, machine supplier , relevant

management staff and the end user need to discuss and find solutions to any possible

impediments to an efficient manufacturing process and product application.

Such things as part design must be analysed by all people so that potential manufacturing

and application issues are eliminated before making a mould.

Projects that start on the wrong foot almost never fully recover from mistakes because it is

simply too costly and time consuming to do so. The result is a high manufacturing cost, a

sub-standard product and tension between people.

2. You Get What You Pay For

Buying a cheap mould (especially from a low cost country) is a guaranteed way of having

ongoing quality and productivity issues.

Common issues with cheap injection moulds are the use of sub-standard steel, poor mold

design and poor mold building. The worst part about these issues is that they cannot be

fixed unless a new mold is made.

Whats more, a poor quality mould will damage a moulding machine so maintenance costs

will be high.

Similarly, buying cheap machines will also give ongoing part quality and productivity

issues. If buying a used molding machine then make sure it has been fully reconditioned

and tested before delivery so no time is wasted troubleshooting upon mould

commissioning. Click here to learn how to buy used machines that work.

3. Lack of Training

The plastic injection molding process is complicated and often management do not

appreciate this fact. Consequently, process technicians do not get the training they need to

be able to set up molds and make parts efficiently and consistly.
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The time and cost spent troubleshooting issues could have been put toward proper training

techniques in the beginning so that problems could have been avoided in the first place.

4. No Lean Manufacturing Program

This is the biggest injection molding mistake by far. A lean manufacturing program would

not only solve the 3 previously mention mistakes but also would address other

inefficiencies in an injection molding company. All waste would be eliminated over time.

The decision to implement a lean program must come from top management so that every

single person in the company cooperates and contributes to a better bottom line and

happier working environment.

Lean Manufacturing Example - How To

Make Your Injection Molding Business5% More Productive Immediately AndSave Costs

Here is a lean manufacturing example that will get injection molders at least 5% more

productivity immediately without spending a dollar.

The technique I use in this example is based upon my 5% Rule.

My 5% Rule says that most injection moulding machines can give at least 5% more

productivity because cycle times have not been optimized.

Have you ever noticed in a manufacturing company how a certain culture exists whereby a

particular level of production becomes acceptable and few people are willing to question

how much more productivity is possible with the existing machinery?

The machine operator might have become complacent because the management have also

become complacent or the management dont have the technical background to

understand how the process could be improved. Instead management are considering

investing hundreds of thousands of dollars in new machinery with new technology.

Before investing in new equipment why not see how much more productivity

your existing machinery has to offer?

Cycle Time Reduction

If cycle time is reduced by 5% then productivity will increase by 5%.


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Take, for example, an injection molding machine producing a food container part.

If the annual requirement of this part is 400,000 then with 5% more productivity this

machine will produce 420,000 parts which is 20,000 more parts per year. And if each

product sells for $2 then this is an increase of $40,000 in sales revenue per year per

machine - a tidy return for very little investment of time.

Whats more, if there are ten machines in your company with the same production

requirements the extra sales revenue will be $400,000 per year.

And how do I expect to achieve this 5 % extra productivity immediately without any

investment of money?

Let me explain with a lean manufacturing example.

Lean Manufacturing Example

Consider the same injection moulding machine producing a food containers with a cycle

time of 9.1 seconds. If the cycle time is reduced by 5% then the cycle becomes 8.6

seconds which means some part of the cycle needs to be reduced by 0.5 seconds. In the

injection moulding process there are typically 6 phases that occur during each cycle.

The 6 phases:

1. Mould closing

2. Injection of plastic into the mould

3. Holding of plastic in the mould to allow proper formation of the container

4. Cooling of the container so that it is rigid enough to eject from the mould

5. Opening stroke of the mould

6. Ejection time; the container can be physically ejected off the mould

The following is a real life example performed on an injection molding machine in

Melbourne, Australia running a 2 cavity mould.

The 9.1 second cycle time had the following breakdown:

Phase (seconds)

1. Closing 1.3

2. Injection 1.2

3. Hold 2.0

4. Cooling 2.1

5. Opening 1.5

6. Ejection 1.0

Total 9.1

In order to reduce the cycle time by 0.5 seconds, the first thing considered was the phase

that would have the smallest effect on part quality. This was the ejection time.


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In this example the ejection was started 0.2 seconds earlier while the mould was still in

the opening stroke. There was no need to wait for the moving side to completely stop

before starting the ejection stroke. therefore, the ejection time was reduced to 0.8.

Additionally, the opening and closing times were reduced by 0.1 each saving another 0.2

seconds by reducing the opening stroke.

Another 0.1 was subtracted from the cooling time which achieved our target of 0.5

seconds. Although the part shrinkage was slightly more it was still within the quality limits

and made no difference to the end user.

Here is a summary of the changes:

1. Closing 1.3 reduced to 1.2

2. Injection 1.2 unchanged

3. Hold 2.0 unchanged

4. Cooling 2.1 reduced to 2.05. Opening 1.5 reduced to 1.4

6. Ejection 1.0 reduced to 0.8

Total cycle changed from 9.1 to 8.6 seconds without effecting quality

Additional Comments

From this case study one can see that there are 6 parameters that could be used to share

the 0.5 second reduction in cycle time. This means there are several combinations that

could be used to reduce the cycle time. For example, in the above example as it turns out

the hold time could have been reduced by 0.2 seconds without any change in part quality.

Its a matter of looking at each mould and machine combination on a case by case basis.

To see what works best. In some cases the mould and machine might already be operating

at their limits so it is not possible to reduce cycle time.

Also, on some molding machines the plasticizing screw recovery time will have an effect on

cycle time if the machine doesn't have a shut off nozzle.

Injection moulding companies have millions of dollars invested in machinery and tooling so

it is vital to get the most out of them. The right mindset is important to run efficiently as

possible so as a factory owner, manager, leading hand or moulding technician you should

be asking yourself how can I improve productivity by 5% today?

Exercise

I would like you to choose one moulding machine in your company that is producing a part

with a stable cycle time and attempt to reduce that cycle time by 5% by using the above

lean manufacturing example as a guide.


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And once you have established a 5% cycle time reduction on a particular machine, try

reducing the cycle time by another 5% until quality issues become your limiting factor. Use

this approach on every machine in the company. Target one machine per week and just

see how much more productivity can be achieved. You might be surprised how much

difference it could make.

Lean 5s The First Step To ImprovingProductivity

A plastic injection molding company practising the lean 5s method will benefit by having

faster set up times, reduced operating costs, a visually attractive workspace and higher

employee morale.

What Is Lean 5s About?

It is about people organising their workspace into a safe and structured layout so that

tools such as allen keys and eye bolts are easy to find and use.

Broken or lost tools are replaced or fixed so that tasks are completed quickly. 5s

eliminates time wasting because tools are easy to locate and are in good working order.

Steps In 5s Lean

There are 5 steps:

1.Sorting

Sorting involves collecting the tools you need and discarding the tools you dont need.

The tools needed should be sorted into 3 categories. The first are the tools that are used

daily, the second are the tools that are used only occasionally and the third are the tools

that are used once or twice a year.

In injection molding some of the tools a die setter needs daily are allen keys, a torque

wrench and eyebolts.

Tools required occasionally are used for machine maintenance such as tapping a hole in a

platen and tools required once or twice a year are for machine servicing or repair.

2.Straightening out or simplifying

This means organizing the workspace so that all tools belong to a dedicated trolley, board

or cabinet so that they are easy to find, use and return.

For tools used on a daily basis, shadow boards are common (right). They are usually

secured to a wall which is easy to see from a distance and are located in a convenientposition such as next to a molding machine.


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3.Shining or Sweeping

This means cleaning everything in the workspace so that it is free of residual oil, dirt , dust

or anything else that is not supposed to be present(right).

This helps to promote a safer and more enjoyable work environment.


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4.Standardizing

Standardizing is about implementing practices that are consistent throughout the work

place. All workspaces must have common rules that are easy to use so that everything is

kept well organized.

For example, at the end of shift all shadow boards should be checked and any missing

tools found so that the next shift doesnt have to waste time searching.

5.Sustaining

This is about doing the previous 4 steps in the long term.

5s will only work if management are committed to it.

One way of doing this is for one manager to manage by walking around and report on the

tasks that have not been done and holding people responsible.

Additional Comments

The biggest benefit of implementing a 5s program is that the results can be seen

immediately.

Having a workplace that is clean, safe, neat and tidy makes everyone feel better and what

is even better is that this can be used as a motivational tool for the company to implement

the next lean manufacturing method.

The Benefits Of The 7 Wastes

A plastic injection molding company using the 7 wastes method will benefit by having

reduced costs, higher profits and will produce better quality parts.

What Are The 7 Wastes About?

It is a lean method which identifies key areas of waste in a manufacturing process.

It is about identifying which steps add value and which steps do not.

The 7 areas analyzed are:

Defects

Over Production

Over Processing Waiting


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Transportation

Motion

Inventory

1.Defects

It takes just as much time and energy to produce a defect part as it does to

produce a good part.

Making a defect part is costly because not only does the part need to be made

again which uses more material and time, other jobs which were scheduled to go

into that molding machine have to be delayed, potentially blowing out delivery lead

times and having to deal with angry customers.

If your reject rate is 10% then your production time is 10% longer and you use

10% more material your customer will not reimburse you for this.

2.Over Production

Over production means producing parts before they are required.

If an assembled part is made up of 2 pieces and one part has a shorter cycle time

than the other then this is over production.

There is waste in this process in two ways.

The first is in having to hold extra inventory of the slower cycling part so that the

assembly station does not have to wait.

The second is the extra time it takes to make the part with the longer cycle time.

Why not modify the part and mold design so that both parts cycle at the faster

cycle?

3.Over Processing

Over processing is seen as any extra unnecessary step that does not add value to

the process.

An injection molder is expected to produce parts that fall within certain quality

specifications for his customer to accept them.

If the specified part weight is 15.0 grams plus or minus 0.3 grams then its better

to aim for the lower range of 14.7 grams to save material cost (assuming nothing

else is effected).

The customer will not pay more if the parts are in the upper range even though it

cost more to make.

4.Waiting

Waiting for materials, equipment or people is a sign of poor planning if it happenson a regular basis.


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Waiting adds to the manufacturing cost of each part made because it is effectively

increasing cycle times.

5.Transportation

Moving raw plastic material to a molding machine and then moving the moldedpart to the storage area is transportation.

Although transportation is necessary,the most efficient path is not always taken.

This is a result of poor factory layout.

Every time something is transported, not only does it take time and energy, it is

also at risk of being damaged or lost and having to be made again.

To minimizing transport study your factory layout.

6.Motion

Unnecessary movements are a waste of motion.

If tools are not in their proper place and a die setter needs to go searching for

them then this is wasted motion.

7.Inventory

Inventory relates to raw materials and finished goods.

Having more inventory than required ties up money that could be used for other

things.

Having an excess of plastic material not only ties up money, it consumes valuable

floor space.

Additional Comments

The 7 wastes is a powerful method in identifying and eliminating waste in the

entire manufacturing process.

But it is more than this.

The seven wastes is also about encouraging people to think differently about their

work environment. When this mind set is reinforced over time, huge benefits will

naturally flow to both the injection molder and their customers.

Plastic Injection Molding MachineSelection Why It Is Important

If you select the right plastic injection molding machine you will make quality partsconsistently and profitably.It will also help you keep your costs low which will make you


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more competitive. You will be able to sell more parts, earn more money and at the same

time establish a reputation as a quality manufacturer.

Even better, you will have the security of long term customers.

How To Keep Your Costs Low:

Minimize reject rate (set a target


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that the injection molding machine can automatically adjust to normal variation in the

plastic material viscosity.

Insufficient injection pressure will produce short moldings.

The injection units screw diameter governs the available maximum injection pressure so itis critical to choose the correct diameter when buying a plastic injection molding machine.

Mistake #4

Inadequate Clamp Tonnage

If clamp tonnage is too low then it will be difficult to produce quality parts. Low clamp

tonnage means inconsistent weights, flash, short shots, wall section variation, poor surface

finish and size variation.

Machine and mold wear will be excessive.

Mistake #5

High Energy Consumption

Have you ever noticed how there is almost no difference in your cars fuel consumption

with 2 people in it compared to just 1 person? A moulding machine is the same. A small

mold will require almost as much energy to open and close the platen compared with a

medium size mold. A properly selected plastic injection molding machine will use power

very efficiently.Click here to learn about how to reduce your energy bill on your existing

machinery by changing parameters in the plastic injection molding process.

The type of machine design also plays a significant role in power consumption. There are 3types of machine designs: fully hydraulic, fully electric and hybrid machines. Hybrid

machines are partly electric and partly hydraulically operated. Selection largely depends

upon the type and quantity of parts to be molded.

Machine Selection Process

1. Know the plastic parts you intend to mold

2. Select machine type: Hydraulic, hybrid or electric

3. Calculate clamp tonnage requirements

4. Calculate the injection unit size.

1.Know The Plastic Parts You Intend To Mold

The process of selecting the right machine starts with knowing the particular plastic parts

that will be moulded by the machine. Molding parts that are not suited to the machine will

result in frustration with on-going quality problems, slow cycle times and machine and

mold damage.

You should know the part:

Plastic material

Weight
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Length x width x height

Average wall section

Gate location

Maximum flow length from the gate

Estimated cycle time

Quality requirements Annual quantity requirements

In addition you should also know the mould size and weight.The correct part information

will then allow you to find the injection unit size, clamp tonnage requirements and machine

type.

2.Select Machine Type

Types of plastic injection molding machine designs available:

Fully Hydraulic Fully Electric

Hybrid - combination of hydraulic and electric drive

Fully Hydraulic Machines

The types of hydraulic machines available are defined by the type of clamp design, type of

hydraulic pump design and the presence or absence of an accumulator.

Clamp design is either a toggle clamp or by hydraulic ram.

Hydraulic pump design can be a constant displacement pump (also called fixeddisplacement pump), a variable displacement pump (also called a piston pump) or a servo

pump (also called frequency control or RPM control) .

If an accumulator is present then some machine manufacturers use it to drive the entire

machine, while others use it for the injection stage only. Accumulators are required for

molding of parts which have wall thicknesses in the range of 0.3mm to 0.8mm this is

known as thin wall molding.

Accumulators might also be required for moulding thicker parts but this must be checked

on a case by case basis.

Which one is suitable for you?

It depends on your priorities.

Here are some criteria to consider before selecting a hydraulic moulding machine:

Buy a new or used machine

Purchase price

Energy efficiency

Plastic material to be processed

Part design

Mould design Clean room requirement


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Cycle time requirement

Hold time requirement

Local service agent capability

If low power consumption is a priority then choose a hydraulic machine with a servo pump

as this is the most energy efficient of the fully hydraulic machines. A servo pump will onlyoperate when the machine requires movement, the rest of the time it is using minimal

power. However, the purchase price is 10%-15% higher than a hydraulic machine with a

constant displacement pump or even a variable displacement pump.

Keep in mind a servo pump control will only save you power if you have long

cooling times or machine inactive times such as long take out time for robot.

Fully Electric Plastic Injection Molding Machines

Every movement of the machine is done with direct drive electric servo motors only

drawing power when movement is required so they are very energy efficient. Electricmachines have excellent repeatability which virtually guarantees consistent part quality.

This makes them suitable for molding medical devices.Click here to learn more about

medical injection molding.

Electric machines are suited to clean room operations because there is no hydraulic oil that

can leak on to the floor.Click here to learn more about electric molding machines.

Hybrid Plastic Injection Molding Machines

A hybrid plastic injection molding machine uses a combination of hydraulic drive and

electric direct drive. The hydraulic drive is used to generate fast injection speeds when

moulding thin wall parts. The rest of the machine uses electric drive servo motors and

each axis of the machine has its own dedicated motor. For example, the mould

opening/closing stroke has its own motor.

These injection molding machines are very energy efficient

3.Calculate Clamp Tonnage Requirements

Clamp tonnage requirements for your plastic injection molding machine can be calculated

by:

By experience injection molders and machine manufactures have thisinformation

Computer simulation using software such as Mold Flow

By a simple calculation Projected Area X Average Cavity Pressure X Number of

Cavities. (Click here to find the machine clamp tonnage for plastic parts made from

polypropylene).

In order to find the tonnage using the simple calculation the following part information is

required:

Plastic material

Length x width x height

Projected area (length X width)
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Average wall section

Gate position

Maximum flow length from the gate

Number of cavities in the mold

The average cavity pressure is also required and this information is available in someplastic injection molding machine manufacturers hand book for certain materials.

Most injection molded parts average cavity pressures lie in the range of 300-800 bar. Parts

with long flow paths and thin walls will have pressures in the upper range while parts with

short flow lengths and thicker wall sections will have much lower pressures.

Plastic material selection also influences the cavity pressure.

In addition, you need to know the mold weight and size so that you can check that the

mold will physically fit into the machine and that the machine can carry the mould weight.

4.Calculate The Injection Unit Size

To select the right unit for your plastic injection molding machine you must know part:

Plastic material

Cycle time

Cooling time

Shot weight (part weight, cold runner weight and number of cavities)

Peak injection pressure requirement

Plasticizing rate

Injection rate Hold time and pressure

For a specific tonnage machine, manufacturers usually offer 2 injection units to choose

from. Both units usually have 3 different screw diameters on offer. In order to select the

correct diameter the shot size must be calculated as a percentage of the barrel capacities

and must lie between 15% and 80% so that good quality parts can be made.

Most barrels are rated in grams of general purpose polystyrene (GPPS). To calculate the

shot capacity for materials other than for GPPS the density needs to be known (which is

available in most molding books or can be found online by doing a search).

Lets assume we have a barrel with a screw diameter of 56mm and the capacity is 510

grams of GPPS. What is the barrel capacity for polypropylene (PP)?

Density of GPPS = 1.06 grams per cubic centremeter

Density of Polypropylene = 0.91 grams per cubic centremeter

Calculation to find barrel capacity for PP is:


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(Density of PP/Density of GPPS)xBarrel capacity of GPPS grams

=(0.91/1.06)x510 grams=438 grams PP

So maximum barrel capacity for this 56mm screw diameter is 438 grams.

Next we need to make sure the shot size is within the maximum and minimum limits of

between 15% and 80%.

If the shot size for the injection mould is 110 grams then the shot size as a proportion of

the total barrel capacity is:

=(110/438)x100= 25%

which is within limits.

Next, the following 3 criteria must be confirmed to be within limits of the injection unit

with the 56mm diameter screw.

Injection pressure

Plasticizing rate

Injection rate

These can be found in one of 2 ways:

The first is by experience - perhaps you have a similar part in production in which case you

can read the pressure directly off the screen. Be sure to check the screw diameter is the

same.

The second is by computer simulation but keep in mind the results are only as good as the

information that is entered. It is advisable to check these results against some real life

examples.

Just remember, the screw diameter selected is crucial to long term part quality

and productivity.

Click here to learn more about screw selection.

"How To Buy Used Injection Molding

Machines That Work"

"Let Improve-Your-Injection-Molding.com get the right used injection molding machines

for you - it is the easy way to grow your company on a budget"

Hello,

If you are like many injection moulding companies you may be searching for the perfect

blend of price, delivery time, quality, reliability and backup service.
http://www.improve-your-injection-molding.com/injection-molding-screws.htmlhttp://www.improve-your-injection-molding.com/injection-molding-screws.htmlhttp://www.improve-your-injection-molding.com/injection-molding-screws.html


19/41

If you are becoming frustrated in your search for the ideal used injection molding

machines for sale then we might have the answer for you.

And we ship to any country.

Click here to skip down to the Quoting Contact Form

We Source The Right Machines For Your Needs

We find the right machines for the particular plastic parts you intend to mold. We do the

work so you get the best used injection molding machines. This means you will produce

high quality parts consistently and profitably.

And this will win you the respect of your customers so you'll get repeat orders and feel a

terrific sense of satisfaction.

When searching for used machinery we will target younger machines so that we can

ensure that the continuity of supply for the electronic equipment and control can still be

sourced.

Get Fully Tested Molding Machines

All moulding machines are fully tested before delivery - so you know you are buying

machines that will work and be safe to use. All machines are run and engineering parts are

checked for the need to be replaced or refurbished. This will ensure they will be able toproduce your plastic parts to the specified quality.

You won't have to suffer the time and frustration of troubleshooting and employees will be

free to perform their daily tasks without interruption.

Best of all, the machines will start satisfying customers orders and earning you money

immediately.

Fully tested machines will give you 5 to 7 years production - giving you time to save for

the capital investment required to buy into new technology machines. Its important to

keep in mind that machine life depends upon cycle time, materials being processed and

age of the machine.

Energy Savings

Significant energy savings are possible with some models of machines saving you lots of

money. New servo pump and control can be retrofitted to specifically designed machines

normally of German origin.

Fast Delivery And Commissioning Service
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Machines are normally ready for shipping in about 4 weeks but can be as little as 2 weeks

if already completed and in stock. Once machines have been shipped to your country

an experienced engineer will be be on his way to commission the machine- this is

all part of the purchase price.

On top of that, you have the added security that it will function nearly as well as a newmachine.

It doesn't matter which country you are located it, a commissioning service is all part of

the cost.

With such a short delivery lead time, you can start taking orders from your customers

straight away. And the sooner you complete each order, the sooner you will get paid -

avoiding cash flow problems.

Fair Final Payment Terms

Final payment not required until you see the completed shipping documents. This gives

you the security to know you will get your machines.

Some machine suppliers require final payment 5 days BEFORE shipping.

12 MONTH GUARANTEE

12 month Guarantee on labour (Warranty). We must be confident you will be satisfied.Only a really honest and established company would give a guarantee like that on a used

machine. Most other machine suppliers will not give any guarantee at all if you are lucky

you will get 30 days.

So it must be everything we say it is. If it wasn't we would be foolish to offer such a long

guarantee.

All used injection molding machines will be inspected and tested by us. At the completion

of inspections and tests the machines will normally require additional repairs and parts to

be installed that will bring them up to the standard that we will support.

It is critical that these additional repairs are carried out to ensure that our 12

month guarantee on repair labour can be given. Just purchasing a machine that has

been reconditioned by some international warehouse seller does not guarantee that the

machine has been repaired correctly and that all functions are operating properly.

This is why we must inspect each machine that we supply to our customers. It is normal

for us to reject at least 50% of the machines we inspect.

Only the best used injection molding machines we will offer to our customers and stand

behind them for the duration of their production.


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Training Free Of Charge

On-site training after machine installation is free of charge. For one full day your molding

technicians will learn how to use the machine more efficiently so you will be moreproductive and you will earn more money and your machine and moulds will last longer.

What's more, your molding technicians can apply this knowledge to every machine in your

company so productivity will get even better.

Free Help By Email And Phone

If you get stuck you can get help and advice so you will never be left on your own. We

make sure you won't have to struggle.

All Machine Manuals Supplied

The manuals will ensure you get long term productivity out of the machine because it

holds information about:

Correct oil grades

When to replace filters

Maximum mold weight

Minimum mold size

All used injection molding machines must have full electrical drawings, hydraulic drawings

and operational manuals otherwise we will not support the purchase of it.

Mold And Machine Package Option

If you require new molds for your machines we can offer these as a package.

There are a number of advantages to this:

It is cheaper than buying them separately

Eliminates interfacing problems

Will produce quality parts consistently and profitably

Will be easy to setup and maintain

Both mold and machine are guaranteed

Nows The Time To Get A Quote


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If you know what machines you need we can probably quote based upon your

specifications. Keep in mind that not all machine manufacturers can supply the technical

information and backup needed to keep the machines operational and the customer

supported at all times.

We have a reasonable selection of well known brands that we will support and sell but notall brands will be offered to our customers. Continuity of spare parts, backup information,

technical information and troubleshooting are most important to us and our customers.

If, however, you want to know what the best used injection molding machines are for the

plastic parts you intend to mould then we draw upon 10 years of experience in helping our

customers get the right machines. This means we do the hard ground work for you so that

you can start producing the best quality parts consistently and profitable in the shortest

delivery time. All of this at a reasonable price.

When you order used injection molding machines from us you can rest assured that all

priority equipment is measured and replaced if necessary. The machine is completely

checked over, run, tested and every function operated for its performance capability

piece of mind to know that you will get long term repeatability.

Take a peek at what one of our customers had to say :

Approximately five years ago I was faced with the problem that the moulding machines I

had were too old, inefficient and unreliable. For my company to remain viable, I had to

upgrade my machines.

After careful consideration of the options, I decided the most affordable option was to buyrefurbished used injection molding machines out of Singapore.

I had been using Improve-Your-Injection-Molding for breakdown, repair and servicing on

existing machinery, and as they were offering the service of going to Singapore to check

the machines as they were being refurbished to ensure their quality was as anticipated,

that is what I did.

The first machine I purchased, a KM 360 B Kawaguchi, arrived in August 2007. I was

impressed with the condition and performance of this machine. It achieved a 40% power

saving over my existing machines running the same product at the same rate. Since then I

have purchased another 5 KM series Kawaguchi machines out of Singapore ranging in sizefrom 50 to 280 tonne.

All these machines have proven to be very reliable and user friendly, producing good

quality, consistent product. These machines have allowed us to broaden the type of work

we can do successfully, into more complex multi-cavity tooling and enabled us to use a

greater range of materials, including engineering plastics.

In the first half of 2010 I purchased an L/T Demag Ergotech 200, which had been

refurbished in my factory. This is also proving to be a very good machine.

Overall I have been very pleased with the technical advice, service and back up provided

to my company over the ten years that it has been operating.


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Alan Myers

Managing Director

MT Containers Limited

[email protected]

What's more, when you contact Improve-Your-Injection-Molding.com you can be sure you

are starting a business partner relationship not just contacting a machine supplier.

This gives you the confidence to know that we stand behind every machine that we sell

because we know the quality of the machines in your company is crucial to your on-going

success.

How exactly do you find out the price of used injection molding machines and molds ?

Fill out the Contact Form below including as much information as possible about the

machines and molds you are interested in.

Plastic Injection Molding Process -

Energy Saving TechniquesThe plastic injection molding process can start saving you money immediately.

I am about to show you how to use the molding process more efficiently.

An important part of the plastic injection molding process are the process parameter

settings such as hold time and screw plasticizing time. Process parameters give direct

control over part quality and cycle time.Click here to read about how plastic drying also

influences part quality.

But they also have another function.

Process parameters can heavily influence the energy consumption of a molding machine.

By experimenting with process parameter settings you can potentially cut

thousands of dollars a year off your energy bill.

A recent case study we performed on a 260 ton Sumitomo hydraulic injection moulding

machine showed that the electrical energy cost per part was reduced by 23% just by

changing molding process parameters.Click here to find out about another way of

reducing costs by fixing flash quality problems.

And click here to find out how to save costs by eliminating short shot quality issues.
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This result was achieved during a 6 hour production run. A small investment in time for

such a large, ongoing return.

We want to help you get the same result by showing you how easy it is to do.

Case Study

Equipment used:

260T Hydraulic injection molding machine with single cavity mold

Chiller unit

An energy meter (see figure 1) Also called a watt meter

Procedure

Disconnected moulding machine from mains power via circuit breaker and then connected

the energy meter to the machines power supply.

Once barrel heaters and hydraulic oil were up to temperature production commenced and

continued for one hour before the first energy consumption readings started.

A photo of the part produced is in figure 2.

In the first test, the amount of energy consumed during a 30 minute period was measured

with the original plastic injection molding process parameter settings.Cycle time was 18.0

seconds. See table 1 below for a list of all parameters.

The electricity cost per part was calculated to be 2.39 cents.

For the 2nd test we chose to double the RPM speed of the plasticizing screw. At the end of

the 30 minute period we could see that this reduced energy consumption by 3.5% (without

effecting quality) so the cost per part reduced to 2.31 cents. Cycle time remained at 18.0

seconds.


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In test 3 cycle time was reduced by increasing the mould opening and closing speeds.

Although the energy consumption slightly increased during the 30 minute time interval,

the production quantity actually increased from 100 parts to 120 parts so the cost per part

went down to 2.06 cents.

Test 4 was to cut cooling time by 3 seconds from 8.7 to 5.7 seconds and the cost per partreduced again to 1.85 cents. A 23% reduction in cost compared to test 1.

Test 5 involved increasing the fill time from 1.2 second to 1.65 seconds and reducing the

cooling time so that the cycle time remained the same as test 4 at 12.0 seconds. The

result was an increase in cost per part to 1.93 cents.

All these results are in Table 1 below.

RESULTS

TEST NO. 1 2 3 4 5

PROCESS

CHANGE

INITIAL

SETUP

INCREASED

SCREW

RPM

SAME AS 2

& REDUCED

MOULD

OPENING &

CLOSING

TIMES

SAME AS

3 & CUT

COOLING

TIME

SAME AS 4 &

INCREASED

INJECTION

TIME

CYCLE TIME

seconds18.0 18.0 15.0 12.0 12.0

INJECTION TIME

seconds1.2 1.2 1.2 1.2 1.65

HOLD TIME

seconds

2 stages

0.8 0.2

2 stages 0.8

0.2

2 stages 0.8

0.2

2 stages

0.8 0.2

2 stages 0.8

0.2

HOLD PRESSUREbar

2 stages504 420

2 stages 504420

2 stages 504420

2 stages504 420

2 stages 504420

COOLING TIME

seconds8.7 8.7 8.7 5.7 5.25

PLASTICIZING

SPEED rpm125 250 250 250 250

PLASTICIZING

TIME seconds5.0 2.55 2.55 2.55 2.55

BACK PRESSURE 4 stages 4 stages 224 4 stages 224 4 stages 4 stages 224


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bar 224 224

224 56

224 224 56 224 224 56 224 224

224 56

224 224 56

INJECTION

PRESSURE bar

Set to

maximum

Set to

maximum

Set to

maximum

Set to

maximum

Set to

maximum

MOLD OPEN TIME

seconds1.5 1.5 1.1 1.1 1.1

MOLD OPEN

STROKE mm450 450 250 250 250

MOLD CLOSE

TIME seconds1.3 1.3 1.1 1.1 1.1

EJECTION

STROKE mm70 70 70 70 70

EJECTION TIME

seconds1.0 1.0 1.0 1.0 1.0

BARREL

TEMPERATURES

C

235-230-

210-205

235-230-210-

205

235-230-210-

205

235-230-

210-205

235-230-210-

205

MOLD HOT TIP C 230 230 230 230 230

ENERGY

CONSUMPTION

PER 30 MINS kwhr

13.3 12.85 13.75 15.45 16.1

ENERGY

CONSUMPTION

PER 1 HOUR kwhr

26.6 25.7 27.5 30.9 32.2

TARIFF $ PER

kwhr0.18 0.18 0.18 0.18 0.18

PARTS MADE PER

HOUR200.0 200.0 240.0 300.0 300.0

MATERIAL 15.2 15.2 18.2 22.8 22.8


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CONSUMPTION

PER HOUR kg/hr

ENERGY

CONSUMPTION

PER Kg kwhr/Kg

1.75 1.69 1.51 1.36 1.41

COST PER HOUR

$/hr4.79 4.63 4.95 5.56 5.80

COST PER PART

$/part0.02394 0.02313 0.02063 0.01854 0.01932

COST PER PART

cents/part2.39 2.31 2.06 1.85 1.93

COST

REDUCTION PER

PART cents

0.0 0.081 0.332 0.540 0.462

% COST

REDUCTION PER

PART

ZERO 3% 14% 23% 19%

Results

The results for this experiment show that for this particular machine producing this part,

energy consumption was reduced by up to 23% from the original settings. This translates

directly into a 23% saving in electricity costs per part. And this was done just by changing

some of the parameters in the plastic injection molding process.

If your annual electricity cost for this machine and part was $10,000 then that

translates into a saving of $2,300 per year.

Imagine if all of your machines could have at least a 10% reduction in cost then this would

mean tens of thousands of dollars in savings per year. That's capital that can be used to

grow your business.


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More importantly, the results show that the machine uses energy more efficiently at faster

cycle times. This is one benefit of fast cycling thin wall injection molding.

Click here to learn more about the benefits of thin wall injection molding.

In test 1 the kwhr per kg of polypropylene was 1.75 at a cycle of 18.0 seconds. In test 4the kwhr per kg reduced to 1.36 at a cycle time of 12.0. So there is a double benefit of

having the fastest cycle time possible: the most obvious is the increased production output

but the hidden benefit is the reduced electricity cost. It is cheaper to make parts at

faster cycle times with hydraulic machines.

Conclusion

The fact is, it easy for an injection molder to reduce electricity costs on existing hydraulic

machines just by adjusting parameters in the plastic injection molding process.

The ability to reduce costs without having to invest in expensive new technology machines

is totally in your control.

Plastic Dryers, Moisture MeasurementAnd Part Quality

Plastic dryers are used to remove moisture (water) that has been absorbed either onto the

surface of plastic pallets or into the plastic pallets internal structure before they go into the

injection molding machine to make parts.

There are 2 groups of plastics. The first group will only hold water on its surface (such as

polypropylene) while the second group will absorb it into its internal structure (such as PET

polyester).

Drying is required to ensure good quality parts are made consistently. Plastics with excess

moisture levels will react when processed in the molding machine barrel and will produce

by-products that will effect such things as impact strength in the finished molded part.

Plastics ThatNeedTo Be Dried Before Processing:

1. SAN

2. PVC

3. ABS

4. PPO

5. ACRYLIC

6. ACETAL

7. PPS
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8. POLYCARBONATE

9. PET POLYESTER

10. PEI

11. POLYURETHANE

12. NYLON

13. PBT POLYESTER

Plastics 1 to 7 need to be dried for cosmetic reasons only. Excess moisture will cause

bubbles, flow lines or surface defects in the molded part. However, their mechanical

properties are not affected by moisture.

Excess moisture in the plastics 8 to 13 will affect the mechanical properties in the molded

part. The part will have reduced impact and tensile strength but will not show any cosmetic

defects. This fact is very important to know so that moulders do not rely upon visual

checks to ensure the quality of the molded part.

Why It Is Important To Measure Moisture Level After

Drying.

Processing plastic pallets in an injection molding machine that have not been dried to the

required level can lead to disastrous consequences in the field. Parts that look good are

not necessarily strong enough to function properly. This means you are not just wasting

time producing rejects but more importantly are likely to damage your companys

reputation as a quality supplier.

Just because the plastic material is dried at the recommended temperature and length of

time doesnt mean the material is dry enough to process. If the desiccant dryer has not

been maintained properly then the plastic material may still have too much moisture and

may need to be dried for a longer period of time.

Thats why it is critical that the moisture content is measured before processing.

This should be done on a daily basis so that moisture can be eliminated as a

reason for any part quality issues.

Moisture Measurement Methods.

There are 2 different systems of moisture measurement - massed based and sensor based

instruments.

Sensor based (usually Karl Fischer) are the most accurate because they will only measure

the moisture level in the pallets. However, the massed based systems will measure the

moisture level along with other volatiles produced during the analysing process giving afalse reading.


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The appeal of massed based systems are their lower purchase price compared with sensor

based and are easier to use. But these are not reasons to use this type of instruments

because they do not give accurate and repeatable results.

Additional Comments

As an injection moulder you spend millions of dollars in equipment such as molding

machines, moulds and chillers so there is no excuse not to spend a bit more on quality

plastic dryers and moisture measuring equipment.

Whats more, material cost is an injection moulders largest ongoing expense so itis critical

that waste is eliminated.

Medical Device Injection Molding

The medical device injection molding process is used to produce parts because of it ability

to produce large quantities with consistent quality and low unit costs.

Medical injection molding also offers a large degree of freedom in part design so many

different shapes and sizes can be produced.

On top of this, the range of plastic materials available for medical injection molding is large

for both commodity materials such as PP and engineering materials such as PVC.

However, medical injection molding is not without its challenges and to be successful the

following issues require serious consideration.

Medical injection molding requires a high degree of cleanliness so factory buildings with

clean rooms are a necessity. The injection molding process, part assembly and packaging

take place inside a clean room.

Clean rooms are significantly more expensive to build compared with factory buildings in

other plastic injection molding industries such as automotive.

Other cost requirements for medical device injection molding are for rapid prototyping

equipment, quality injection molding machinery, robotics, injection molds and equipment

for the vast array of secondary operations.

In addition to this, the ISO 13485:2003 quality management system certification is a

requirement to do business with Australian, Japanese, American and European medical

industries. The certification costs tens of thousands of $US and takes several months to

implement.

Annual ongoing audits and costs are required to maintain the certification. Click here to

learn morehttp://www.standards.org/standards/listing/iso_13485

Despite all of the costs of the certification, the 2 main benefits are: potential for more

customer leads and improved efficiency within the organization. These are invaluable.
http://www.standards.org/standards/listing/iso_13485http://www.standards.org/standards/listing/iso_13485http://www.standards.org/standards/listing/iso_13485http://www.standards.org/standards/listing/iso_13485


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Additional Comments

To be successful in medical device injection molding, molders must provide a full range of

services. Not only must they produce quality medical devices on time, but also must beable to add value to the devices by providing secondary operations.

In addition to this, they must be involved in the development of any new medical device so

any potential manufacturing pitfalls can be eliminated before the project is started.

Machine Clamp Tonnage Calculator ForPolypropylene.

Correct Clamp Tonnage

What is the right clamp tonnage for a mould producing a particular part?

Getting the right clamp tonnage can be tricky. Just because a moulding machine can

produce a clean looking part without flash it doesnt mean the clamp is enough.

For any particular part, there are a range of clamp tonnages than can produce parts that

appear to be ok.

But what about the weight?

The correct clamp tonnage will produce parts to the target weight consistently over an

extended period of time. This is assuming that the process parameters have been setup

correctly and optimized so that consistent fill times are maintained and hold pressure is

not excessive.

If process parameters are not optimized then clamp tonnage will need to be higher than is

necessary. This uses extra electrical energy and increases the rate of wear in the mould

and machine.

Clamp Tonnage Calculator

Use the following clamp tonnage calculator to get an estimate of the tonnage required to

mould a part. It has been validated with molds making containers for both thin wall and

thick wall parts.

Square & Rectangular Parts:(mm) Round Parts:(mm)


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Length: 0

Diameter: 0

Width:0

Max Flow Length

From Gate:0

Max Flow Length

From Gate:0

Wall Thickness:

0.50

Wall Thickness:

1.10

Number of Mold

Cavities:0

Number of Mold

Cavities:0

Material Flow Index

(MFI): 25

Material Flow Index

(MFI): 15

Answer: Metric Tons Answer: Metric Tons

Selecting Injection Molding Screws

Using the right injection molding screws is crucial to making quality parts consistently and

with maximum production output.

To select the right screw, details of the particular part to be moulded must be known (that

is, part material, weight, size and wall thickness). The basic mould design is also

important so that flow length from gate, shot weight and runner system are all taken into

consideration.

Choosing a screw without knowledge of the parts is like buying a car without any

preference for performance and handling requirements.

Screw Design


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The basic design of any screw has 3 zones along its length:

1. Feed zone

2. Transition zone

3. Metering zone

The feed zone conveys the solid plastic pellets which are fed from the hopper to the

transition zone where they are compressed by a change in screw geometry. This

compression forces the pellets to melt through the action of pushing up against each

other. This is called shearing. The metering zone then conveys the melt to the front of the

screw ready for injection into the mould cavity.

In the transition zone the material is compressed by the change in the depth of the screw

channels from the feed zone to the metering zone. The ratio of the change in depth is

called the compression ratio and is usually between 2 and 3 for plastics such as PP and PE.

The length of the transition zone is typically 4 to 7 x the screw diameter in a general

purpose screw.

Another aspect of screw design is the length to diameter ratio (L/D) meaning how long it is

compared to its diameter. As an example, the L/D ratio for PP and PE is in the range 20-

30:1.

When it comes to general purpose screws, longer screws are usually preferred because

they will produce a better quality melt and therefore produce better quality parts

General Purpose Screws (GPS)

The advantage of a GPS is that they can be used with most plastic materials such as PP,

PE, Nylon, PET and PC so they are very flexible and good for moulding companies that

mould a variety of different materials.

The disadvantage is that, for some materials, part quality and productivity rates will be

lower compared to more advanced injection molding screw designs such as the barrier

screw.

Barrier Screws

This type of screw provides a better quality melt at a faster rate compared with a GPS.

There are many different designs of barrier screws, the difference being in the varying of

the flight depths and channel widths.

The exact design chosen must be in line with the application.

Double Flight Screws


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Although double flight screws have a different design, they are an alternative to barrier

screws. They are also designed to deliver a high quality melt at fast rates.

The design ensures the plastic is fully melted before it reaches the compression zone,

which is not the case in a GPS.

Double flight injection molding screws can be used in technical parts for PP and thin wall

technical parts in PA which does not plasticize well with barrier screws.

Screw Diameter

The screw diameter is important for 2 reasons. The first reason is that it determines the

maximum available injection pressure, the smaller the diameter the higher the available

pressure. This is critical for parts that have thin walls and a long flow length and for plastic

materials that are difficult to inject.

The second reason is the diameter determines the maximum shot size available. The

smaller the diameter, the smaller the shot size.

It can be seen that there is a conflict between shot size and injection pressure when

selecting a screw diameter. Initially it might seem advantageous to choose the largest

diameter so that there is more flexibility in the types and size of parts that can be made in

one machine but this is the wrong way to think about it.

The screw diameter should be chosen in line with the application otherwise quality and/or

productivity rates will suffer. The injection unit must be capable of generating enough

injection pressure (with some in reserve) to maintain consistent fill times and as a

consequence, maintain the quality.

Wear Resistant Injection Molding Screws

Serious thought should be given to using a heat-treated screw and barrel as these will

provide longer life than non heat-treated parts. This is especially important when the

material contains some level of reinforcement as this is much more abrasive and will wear

out the screw and barrel sooner than material without reinforcement.

Once the screw and barrel start to wear, part quality will start to suffer and it will only be a

matter of time before a replacement will be needed. This is a large cost, not just because

of the cost of the replacement screw but for the loss in production.

Screw Tip

The tip is a non-return valve at the front of the screw which allows the melt to pass

through during the plasticizing stage but stops the melt from back flowing into the screw

during the injection stage.


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There are 2 basic designs the ball check valve and the sliding ring check valve. The ring

check valve is generally preferred because it allows an easier path for the melt to pass

through compared to a ball check valve. Therefore, a ring check valve is suited to shear

sensitive materials such PC.

However, the disadvantage of the ring valve is their tendency to wear, so the ring checkvalve condition should be checked on a regular basis. A typical sign of wear is inconsistent

cushioning during processing.

Additional Comments

The fact is, in todays competitive environment, injection molding manufacturers need to

be making parts as efficiently as possible in order to keep manufacturing costs down and

delivery times short.

Using the right injection molding screws for your parts will play a significant role in this.

Injection Mold Design - A Little KnownBut Costly Mistake

Correct injection mold design is crucial to having a profitable business. A proper design will

ensure quality plastic parts will be produced for the intended life of the mould at the

expected cycle time.

If you have a question about mold design either scroll to the bottom of the page orclick

here to skip down to the form.Your question and my answer to it will then be part of this

page for others to read.

Correct injection mold design has the following benefits:

Quick mold setups

Faster cycle times

Quality parts

Low reject rate

High productivity

Long mold life

Long molding machine life

Higher employee morale

Unfortunately, many mold designs have some fundamental flaws which prevent the

Click here to learn aboutinjection molder from achieving a higher level of productivity.

what makes a competent injection mold designer.

he most common injection mold design mistakes you can avoidBy learning about one of t

Click here to learn aboutwaste and help make your company grow and be more profitable.

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One of the Most Common Mistakes

Thin Back Plates

Most molds have 2 back plates with one on the fixed side and one on the moving side.

Figure 1 shows the back plates in between the molding machines platens.

The back plates have 3 main functions:

To hold the mold in the moulding machine using clamps

To form part of the runner system

Support the entire mould against excessive platen deflection

If the back plates are too thin then the resultant repetitive deflection during each cycle

eventually causes the following part quality problems:

Flashing Shorting

Weight variation

Voids

Sink

Balancing issues

These quality problems occur because the platens do not provide enough support to

d clamp tonnage.stabilize the mould against cavity injection pressure an

Whats more, repetitive deflection causes wear inside the mould. One of the things mould

wear does is reduce the effectiveness of the venting. Poor venting will also result in rejectparts especially in multi cavity moulds.


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Its important to keep in mind that during the injection molding process most machines will

have some amount of platen deflection. Platen deflection is not necessarily a bad thing,

however, if the deflection is extreme then part quality will deteriorate over time. This can

happen over a period of years, months or weeks depending upon the injection mold design

and selection and condition of the moulding machine.

Platen deflection is usually worse on the fixed side platen because of the weakness created

by the location ring diameter and the larger recess behind it. The diameter is quite large in

most machines as it is clearance to allow the machine injection unit nozzle to connect to

the mould (see figure 1).

On top of that, if the fixed half of a mold is a cavity (as opposed to a core) then this adds

to the weakness of the system. A cavity is naturally weak because of its shape.

The combination of these 2 weaknesses require an extra thick back plate on the

fixed side to strengthen a mold.

Case Study

Figure 2 is a rectangular lid made from a 2 cavity mold. The lid started to severely flash

after only 8 weeks from mould commissioning. An investigation found that there was toomuch platen deflection so the fixed side back plate was replaced on the mold.

The original plate was 90mm (see figure 5) while the new plate was 150mm. The thicker

back plate bought the deflection within a manageable level so that quality problems were

eliminated.

The main clue to the problem was the pattern of radial brown hard marks found on the

back plate see figure 3. This pattern was a clear indication of too much platen deflection

causing the mould to wear on the shut off faces of the cores and cavities resulting in part

flash. Figure 4 gives a closer view of the hard marks.


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Additional Comments

Relating part quality problems to excessive platen deflection is not that difficult once you

know where to look and what to look for.

This type of issue happens in all types of injection moulds from fast cycling thin wall

moulds to slow cycling single cavity moulds and the sign is the same for all of them.

Look for radial lines of hard marks on back plates and also on shut off surfaces of cores

and cavities.

Figures 6, 7 and 8 are more examples of the hard mark pattern produced when large

platen deflection is present.


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Example of Good Injection Mold Design


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Figures 9, 10 and 11 show a 4 cavity lid mold designed with an extra thick back plate on

the fixed side 150mm thick.

This mould has produced millions of quality parts without any problems. Note the hard

mark pattern on the back plate in figure 9, it is completely different to the pattern in the 2

cavity (figure 3).

This is how the hard marks on a properly designed mould should be.

plastic injection molding better quality parts is just the beginning

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