Injection Molding Archives

Tag: Injection Molding

Recycled Resin- The Question and the Caution

By Bozilla

October 27, 2023

By: Bozilla Corporation

My customer doesn’t like using any recycled material

Working with a Tier 1 supplier to a major OEM, there was a discussion with the molders on the floor, people molding the parts on the injection molding machine, and their personal experiences

Their experience with recycled resins is the inability to maintain a controlled injection molding process

Because they are responsible for the quality of the part they are molding, they make decisions (call an audible) and replace the recycled resin with a locally available equivalent virgin resin This protects them from producing unacceptable

Losing Control of the Process

Recycled plastic goes through several processes when it is reclaimed In layman’s terms, it gets beaten up

Here is the rundown:

In the first phase of the plastic recycling process, the material goes through the injection molding process, which partially degrades the material (molecular weight reduction) Then, it is potentially exposed to UV, temperature fluctuations, or chemicals, which contributes to the degradation process Next, the plastic is ground up and typically cleaned with a thermal or chemical process, further degrading the material Finally, the reclaimed plastic is ready to, again, be beaten up in the injection molding machine

Loss of injection molding process control

It is essential to know that the reclamation process breaks the polymer’s molecular structure down, making it lesser quality because the properties of that original polymer have been degraded Recycled resin has a smaller molecular weight( length of chains) and varying viscosity, making it unpredictable Virgin resin has molecular weight consistency/control with much less variation, giving it consistent properties

This lack of consistency, or better stated, lack of control of the recycled resin will affect the quality of your part

Do you see some reasons why you may reconsider using recycled plastic for your part?

Industry Response

Now, the response in the industry and all industries to using recycled materials is, when possible, to take a certain percentage of recycled material and blend it in with the virgin resin

However, it is essential to note that the percentage of added recycled material vs part quality is not a 1:1 ratio, eg, adding 20% of recycled resin does not equate to 20% loss of properties For instance, you can test the recycled resin of 1 lot of material, and it may meet specs, but the next lot is completely different, thus knocking the process out of control This lack of conformity

Medical Device Success-Faster to Market/Optimal results

By Bozilla

August 14, 2023

Let’s face facts

Medical device failure can be a devastating event Encountering negative physical and financial consequences is not the path a #medical company wants to take

Alleviate device failure

Should cost be the primary determining factor when developing and manufacturing a medical device?

Could that upfront cost savings result in more significant money expenditure due to law suites, fines, and time lost? Let’s consider a new approach

You can avoid expensive law suites, FDA fines, and loss of time by considering additional factors during the initial stages of development

These factors include:

Polymer choice
Consulting with an experienced #molding professional
Part design optimization utilizing experienced plastic engineers

You must have noticed that the word ‘experienced’ is used multiple times If you desire to manufacture a device successfully, it is vital to choose professionals who know what they are doing, from design creation to manufacturing Otherwise, you are at a greater risk of device failure

If cost is the only determining ingredient driving your decisions on any of the above considerations, you are putting your company and the patient at risk Gambling on any of the three factors above will reduce the chances of a successful medical device

Let’s get into it

Polymer choice

What is significant about polymer choice?

Let’s recognize that an FDA-approved polymer is mandatory for most medical devices

From the polymer options the FDA endorses, which is best for your particular design? If you allow cost to drive this decision, it may come out poorly

At this stage, you should already be consulting a plastics engineer with extensive polymer knowledge The choice of polymer and its durability will depend on the device’s intended usage and exposure to environmental stresses

Injection Molding Consultant

It is critical to have an experienced injection molding professional guide you when developing a design for a device A consultant with a plastic engineering degree is a significant advantage

Hold up if you are cringing because the costs in your head are adding up Let’s get through this bit, and I will show you how it saves you money in the long run

An experienced injection molding professional should have these qualifications:

A minimum of 10 years in the injection molding industry
Exposure to multiple industries, eg, automotive, caps and closures, medical, housewares, etc
Fully understand how a polymer will respond during the injection molding process ( this will also affect your choice of polymer)

STOP doing this to Cooling Circuits!

By Bozilla

May 2, 2023

STOP ignoring the importance of proper cooling circuit design for injection molding Cooling circuit design is typically not heavily weighted with regards to importance in the injection molding industry Cooling circuits need to be designed properly and the importance of the design must not be overlooked A common practice is to simply ‘place cooling in the mold’ and not much more Sometimes it is taken a step further where the practice is ‘to place as much cooling in the mold as possible’ This is a better practice but is it the best? We are going to discuss the importance of proper cooling circuit design and the implications of overlooking this important practice

Cooling Circuit Diameter

Is the diameter of the cooling circuit important? It certainly is In fact, the diameter of the cooling circuit must be a part of a larger consideration such as circuit spacing, pressure drop and flow rates A larger diameter may be thought to cool better since it is larger, which is somewhat true, however it will take up more space due to its larger diameter so it may be difficult to route in tighter locations

The spacing of larger cooling lines can be increased based on the diameter which can result in fewer cooling lines hence less gun—drilling, ie a cost savings but this is not always the better condition if the mold design is complex or small Larger cooling lines will also have a lower pressure loss resulting in less power required to pump the water through the circuit This is a big plus but the difference in pumping efficiency may be negligible It is also important to understand that varying cooling circuit diameters within the same mold will only be as efficient as the smallest diameter of that circuit due to the higher pressure loss within the section containing the smaller diameter The flow may be turbulent in the portion with the smaller diameter yet may take flow away from the larger diameter portion resulting in a laminar flow condition in the section with that larger diameter

The Importance of Balanced Cooling Circuits

Optimal designed cooling circuits are the driving force behind productivity and cycle times

If your cooling circuits are not as working as efficiently as they can be, they will be costing you precious time and money Balancing cooling circuits plays a tremendous role in cooling efficiency

So why do the cooling circuits need to be balanced and what exactly does that mean?

In short, all circuits are not created equal If cooling circuits are not equally balanced, then the flow rate

Lean Tool Validation for Injection Molding

By Bozilla

April 19, 2023

Lean Tool validation for injection molding means developing a more efficient process that benefits the environment; Reduces CO2, and saves costs Bozilla uses “cutting-edge” proprietary techniques developed over 21 years in the injection molding industry to determine if a tool can be optimized and brought back to life in its most efficient state

A typical scenario entails a company contacting Bozilla to make a tool more efficient or bring a tool back to life We would ask them to send us everything about the tool, including CAD drawings, 3D part and tool drawings, machine process settings, current tool status, and other pertinent information about the tool

Bozilla will investigate all areas of inefficiency, outline suggestions, and provide a proposal During the beginning phase, there will be no up-front cost The company then determines which recommendations can be practically implemented, and Bozilla provides a cost and time estimate Should the customer accept the proposal, the work can begin immediately

Some examples of tools Bozilla has efficiently improved include those that have been cut wrong (tool dimensions did not match part specifications/dimensions), fouled cooling channels, a poorly designed feed system(both hot and cold), cycle times that are excessive or are known to be inefficient and even tools that have been sidelined due to inefficiency

Once the project has started, the type of work performed is analytical where Bozilla models the current design and conditions in a virtual world using Autodesk Moldflow Insight

Initially, our team would identify areas of the process that can be optimized, make those changes and continue to further optimize the process Once the process has been deemed efficient (based on the tool design, coolant flow rate, and other factors), the customer will have an opportunity to review and make as many changes as possible, which may or may not include tool modifications (such as adding cooling lines) It is not always apparent that a tool is underperforming unless a thorough investigation is performed Each potential issue is identified accordingly, and proposed changes are provided to create a streamlined, lean running tool that will be lean and profitable

Some examples of proposed changes may include instrumenting the tool correctly, determining pump efficiency, reducing cycle times, increasing temperature control, minimizing process variation, reducing energy consumption (creating less CO2), recapturing costs from tools

Is Using MFR the Best method for Material Selection?

By Bozilla

December 1, 2022

When a material selection comes down to flow rate, is using the (Mass Flow Rate) MFR or Melt Index (MI) the best choice? To answer this, we need to understand why the Melt Index test initially came about

The Origin of the Melt Index Test Method (ASTM D-1238)

ASTM D 1238: Test Method for Flow Rates of Thermoplastics by Extrusion Plastometer

Before there were standards to test polymers, there was a need to determine the differences in how polymers would flow when melted A method was created to keep all polymers on the same level playing field This method places the material in an Extrusion Plastometer or Melt Indexer

The standard has the barrel of the melt indexer heated to a specific temperature The user would obtain a resin sample and place it in the barrel where a piston would be inserted A specific load would be placed on the piston, and the melted polymer would be extruded through a capillary die (with a particular orifice size) The extrusion would take place for 10 minutes, and the amount of polymer would be weighed in grams yielding an output in g/10 minutes

Having MFR data for all materials allows one to compare them side-by-side, giving a respective idea of how each will flow with the other

The limitation of this test method is that it is, in fact, one point on the viscosity curve and is at a shear rate of nearly zero, which is not indicative of the injection molding process

When materials experience shear during injection molding, shear rates may be experienced up to and possibly exceeding 100,000 1/sec Some materials become more viscous at higher shear rates, but these are uncommon

So how do we compare materials at these higher shear rates?

Since the inception of the melt indexer (1950s), a much more accurate test method was designed using a Dual Capillary Rheometer

A dual capillary rheometer can produce a series of viscosity data points over a range of shear rates, such as the image below

A Rheology curve provides exact viscosity data based on specific shear rates at specifically tested temperatures Notice how the Melt Index MFR point does not provide any data relating to the injection molding process A curve like this will allow one to understand the exact behavior of the material and shear rate

Using Aluminum for Injection Molds?

By Bozilla

July 14, 2022

Aluminum tooling has significant benefits when compared to steel tooling because of the cost of aluminum as well as the ease of manufacturing Aluminum tools can be cut much quicker than steel saving a lot of time and money These benefits can result in shorter cycle times and price-per-part savings However, there are some drawbacks of aluminum such as being a softer metal which can cause mold deflection and also having a fatigue limit which can be catastrophic In order to better understand the advantages and disadvantages of utilizing aluminum for injection molds we will take a closer look at the properties of both aluminum and steel

Let’s compare the properties of aluminum to steel

Table of Aluminum v Steel properties

The above table compares the properties of aluminum and steel Based on this table, we can determine the following

Density: Aluminum is 279 times less dense than Steel

Hardness: Aluminum is much softer than steel

Thermal Conductivity: Aluminum is 655 times more conductive than Steel

Thermal Diffusivity: Aluminum has 79 times the thermal diffusivity than Steel

Yield Strength: Aluminum has almost half of the yield strength of Steel

Poissons Ratio: Aluminum deforms more than Steel

Advantages of Using Aluminum for Injection Molds

Now that we’ve compared aluminum to steel, we can take a look at the advantages of using aluminum for injection molds based on the above properties

Density:

Aluminum is 279 times less dense than steel resulting in a lighter end product As the cost of shipping is increasing dramatically, the weight of any product will have a direct impact on shipping costs and must be kept low as possible

Hardness:

The softer aluminum reduces machining hours and wear and tear on machining components

Thermal Conductivity and Diffusivity:

Thermal conductivity and diffusivity is extremely important in injection molding as it directly impacts the cycle time Aluminum is 655 times more conductive and 799 times the diffusivity of steel which results in a significant reduction in cycle time, faster start-up times, reduction in response times to process temperature changes, and mold change times

The faster thermal recovery of aluminum also modulates the cyclic ‘highs-and lows’ of the tool temperature during processing As the melt is injected into the mold, the heat must be removed as quickly as possible Aluminum is able to process the heat out of the tool much faster than steel resulting in a more stable mold temperature and thus a more stable process

Disadvantages of Using Aluminum for Injection Molds

Poissons Ratio:

The Poissons Ratio of Aluminum is 033 and Steel

Homopolymer vs. Copolymer

By Bozilla

May 24, 2022

Material selection for an injection molding application can sometimes prove to be very challenging What happens if you identify a material then find that it can be supplied as a homopolymer or a random copolymer Is there a difference? The answer is YES The choice made for your project can affect part quality

The Homopolymer:

A homopolymer has the same base unit which causes the molecular chain to have a high degree of consistency and size However, length can vary depending on how long the polymerization process is allowed to occur

The high degree of consistency in a homopolymer creates a high degree of regularity When many of these changes flow and combine, they are able to create a very tight entanglement and when they cool and shrink, they also have a high degree of crystallinity which increases shrink

The Copolymer:

A copolymer, as shown in the image above, has more than one base unit and each base unit is a different size There can be more than two base units Due to the variation in size of the base units, the copolymer chains will be spaced much further from each other and have a higher degree of irregularity And similar to the homopolymer, the length of the molecule will depend on how long the polymerization process is allowed to occur

The high degree of irregularity does not allow the polymer chains to form a tight structure, leaving a lot of space between the molecular chains Therefore, when the polymer flows, there can be alignment but there will be more irregularity and not as tight of a structure which prevents excessive shrinkage

When comparing the two types of polymers, assuming each is the same length (same molecular weight, per se) the homopolymer will be much more organized and structured therefore creating more mechanical strength and chemical resistance but have high shrinkage The copolymer will have more random orientation which will create space between the molecules allowing for easier chemical attack and less mechanical strength and also have lower shrinkage Of course, we could discuss these comparisons in much more detail but we will stick to the basics for now

As material selection relates to injection molding, the properties of the material is a crucial factor

The major properties when comparing homopolymers to copolymers are:

shrinkage
chemical resistance
mechanical strength

Each of these properties must be considered with regards to the outcome of part quality

For example, when injection molding

The Reality of Core Shift- Is this happening to You?

By Bozilla

March 23, 2022

Core shift is not always obvious or suspected Recently, Bozilla Corporation was called upon to investigate a part that was warping differently and more than expected The customer had a flow simulation conducted by a third party and the warpage results did not match the actual part data Sometimes part warpage does not match the flow simulation and in many cases, it is easily explained However, after a quick investigation, the underlying cause of the excessive deflection was not easily understood It was time for our Team to troubleshoot

(The animations and images presented in this article do not represent the Customers actual part file and is just an example of how core deflection occurs)

To begin the investigation, we compared the floor process to the simulation, which is standard operating procedure They matched fairly well They are never a perfect match but were very close We then looked at the part data and tool design then compared it to the data utilized in the flow analysis The data matched This was good news because through process of elimination, we were nearing the target

We then began taking a closer look at the part along with the flow simulation results We noticed that there were long features extending from the core side of the tool that the polymer had to flow around and down The features were thin so they did not have cooling in them therefore it was suspected that these long cores were heating up excessively causing the polymer to stress relieve and therefore warp However, the simulation software accounted for this to some degree and we did not see a trend that suggested the hot core feature was contributing to additional deflection

Having a long history with examining many polymers and how they behave in varying geometries caused us to take a closer look at the differential pressure within the cavity as it flowed around and along the long core features We discovered a significant pressure differential that occurred on either side of the core We also learned that the polymer did not freeze uniformly around that core during the 2nd stage pack process Having differential pressure and non-uniform freezing threw up a few flags

We had to investigate the impact of the differential pressure and non-uniform freezing on these features We knew it was time for a core-deflection analysis The customer was fairly confident that the P-20 tool steel was robust enough to

Accuracy of Flow Simulation on Plastics Injection Molding machine

By Bozilla

March 15, 2022

I have recently been exposed to multiple articles and discussions regarding the implementation of flow simulation on injection molding machines This is an intriguing topic which I advocate Currently, this new combo method is proving difficult to line up the results from the analysis with the actual process on the injection molding machine In order to successfully utilize this capability on an injection molding machine, several factors must be understood

For those who have read my previous articles, you may appreciate that I strongly promote having the right person for the right job In other words, the simulation engineer must have a complete and comprehensive understanding of plastics in order to be able to properly simulate the plastics injection molding process

My suggestion is to always have a degreed Plastics Engineer with floor experience perform simulations on plastic parts The reason for this advocation is to ensure that the simulation engineer virtually takes on the role of the process engineer This makes certain that the simulation will properly emulate the injection molding machine process on the part being molded Unfortunately, this is not always the case and the articles I have recently read do not touch on this very important factor A virtual simulation cannot simply be executed, have the results taken to the floor, input into the injection molding machine and expect the molded part to perfectly match the simulation results It’s not that easy due to many variables which must be considered

For example, the simulation engineer (with the proper degree and experience) will understand the limitations and boundaries of the intended injection molding machine for that particular simulated part It is not always necessary to know every specification of the machine and to input that specific data into the simulation Most machines have a wide variation of capabilities that the simulation engineer will take into consideration The simulation will then be executed with all of the necessary variables factored in for the injection molding machine, thus maintaining a high degree of accuracy between the simulation and the floor

The difficult task is discovering those unintended variables that affect the process on the floor, eg material batch changes, colorant issues in the polymer, tool temperature variations that the press cannot record, physical changes within the tool such as polymer sticking to action within the tool, cold gates not opening and flowing when desired, cosmetic issues at the gate or

Key Factors in a Reliable Plastics Injection Molding Simulation Report

By Bozilla

November 30, 2021

I have written in a prior post about the key factors necessary in a plastics injection molding optimization analyst Now, I would like to discuss the importance of a skillfully assembled simulation report Jennifer Schmidt spoke of the key ingredients of a trustworthy injection molding simulation report in her talk at the Plastics Technology Molding 2021 conference In this brief, I will discuss the valuable information she provided and add additional feedback If you want a successful outcome for your tool, these key components are essential to consider

1Software

What version is being used and is the software up to date? Look for signs that the analyst is using an older version of software which will alter the results on the report, and ultimately the floor results

Typically, the output file(s) of the software contain the release version of the software It might not be the absolute latest release of the software, but is should be a proven release which is typically a year old or less

2 Type of Mesh used: Consider the type of mesh that used for the part and the runner

Is the mesh type appropriate for the part geometry?
Is it precise enough in critical areas to capture important details?
Is the correct technology being used for the part geometry/runner combination, ie midplane, Dual-Domain, 3D or a specialty mesh used?
Will the report allow access to display the mesh?
Does the filling animation, weld lines and sink marks reveal insights into the mesh quality?

Consider: Simulations of the same part with the same material and same mesh density, but different mesh types for the part and runner, may produce different results for pressure at the fill-to-pack switchover point, which could make quite a difference in what occurs in an actual molding environment

There are many factors to consider and only a seasoned user with the proper education in the software will be able to make these determinations in order to provide the best analytical outcome

3 Material Data: An accurate molding prediction requires good material data

What was the material data in the simulation based on?
Was data on the actual material available?
Was the data a substitute?-a resin of the same generic family but has a

Plastics Engineering, Simulation and Consultation

Tag: Injection Molding

Recycled Resin- The Question and the Caution

Losing Control of the Process

Here is the rundown:

Loss of injection molding process control

Industry Response

Medical Device Success-Faster to Market/Optimal results

STOP doing this to Cooling Circuits!

Cooling Circuit Diameter

The Importance of Balanced Cooling Circuits

Lean Tool Validation for Injection Molding

Is Using MFR the Best method for Material Selection?

Using Aluminum for Injection Molds?

Homopolymer vs. Copolymer

The Reality of Core Shift- Is this happening to You?

Accuracy of Flow Simulation on Plastics Injection Molding machine

Key Factors in a Reliable Plastics Injection Molding Simulation Report

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