Recycled Resin- The Question and the Caution

Posted on October 27, 2023 by Bozilla

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, e.g., 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 may continue throughout the entire recycled resin being used.

The typical response to this situation is to combine a certain percentage of recycled material with virgin resin. By combining the recycled materials (uncontrolled variation of molecular weight) with virgin resin, which is very controlled, the blend will allow the process to maintain control, thus allowing the part to meet specifications. There may be a loss of 5% of the properties, so it will still make and meet standards.

However, you are still using recycled material, and 20% of the material has a history of being degraded. Unfortunately, properties will be lost, influencing the quality of the part.

The $10 million question is, how do you start using more recycled and less virgin resin?

This is typically not an easy question to answer, but there are ways the industry can address it.

The industry can adapt by designing parts to accept more variation, allowing increased content of recycled material. For example, the part could be globally or locally thickened in order to allow for more process variation without loss of part quality.

This is just one example, but the industry has the potential to address this in many other ways.

That’s the question, and that’s the caution.

Currently, material suppliers are working with recyclers to have test methods put in place to address these issues with recycled materials. The caution is that these test methods reveal the problem vs. fix the problem. How do the recyclers/material suppliers create quality control with regard to molecular weight variation? Suppliers might say they can test the material with an MFR flow test. Unfortunately, an MFR flow test is a zero viscosity test, which does not capture the true shear rate the material will experience during the injection molding process.

However, there are better ways to measure Rheology since it is necessary to know the molecular weight variation. But, there is no way to correctly measure this vital detail on recycled material because there is so much fluctuation in its properties.

So, with recycled material, even though you may be able to create a good test method, there’s no way to create consistency because of the history of the recycled material.

In other words, there is still no consistency in recycled materials. Until this is addressed, using recycled materials for injection molding must be managed smartly.

RELATED ARTICLES:

Is using MFR for material selection the best choice?

Medical Device Success-Faster to Market/Optimal results

Posted on August 14, 2023October 27, 2023 by Bozilla

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, e.g., 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)
Understanding how a polymer will perform in the field
Recognize that virtual optimization is critical to the success of your device

The value of an injection molding consultant can’t be understated. They will have full knowledge of the injection molding process, which can impact the part quality and integrity of the mold for long-term usage, the effect the injection molding process has on the polymer as it relates to the design, and be able to troubleshoot any issues that arise during the simulation stage.

This type of information is priceless for achieving a successful device. Using a plastics professional will reduce time to market and increase patient success.

Virtual part optimization

Without Virtual Optimization of the device design, you will be driving a car on only two wheels, which someone can do, but the risk is high.

First, it is vital for your device’s success to employ an individual skilled at optimizing part design. If the supplier has “thrown in” a flow analysis for no cost, granny, get your gun!

Time after time, outsourced optimization provided by suppliers is performed by individuals with limited knowledge of the software, experience, or skills. These individuals lack a thorough understanding of all of the following: injection molding, polymers, processes, and other critical factors needing consideration to produce a successful device. This lack of skills and knowledge leads to unnecessary design iterations, time loss, and poor quality. It’s a hot mess, and no one wins. For a device to succeed in the medical industry, optimizing a design requires an experienced professional who will pinpoint concerns and offer beneficial, feasible suggestions to improve the design as needed.

Can you see where I am going with this? If all the possible and probable kinks and flaws are addressed in the beginning stages of part design, the patient, medical company, and everyone involved has a good day. You will save money from the repercussions of law suites, fines, and lost time (faster to market). Success is yours!

The small investment upfront utilizing the skillset and experience of a skilled plastics engineer, injection molding consultant, and an experienced optimization specialist will get you to market faster, maximize quality and eliminate any financial repercussions from faulty devices. The team at Bozilla Corporation meets all three criteria necessary for you to effectively complete your goals and timing and get to market faster. Contact us today and let’s get started!

Contact Bozilla Corporation today and let’s discuss how we can successfully contribute to your project. Bozilla Corporation’s Injection molding Team has over 21 years of experience analytically and on the floor. We specialize in optimization, consulting, engineering, troubleshooting and Autodesk Moldflow software training. Additionally, our plastics engineers have a full understanding of polymers and how they influence an injection molded part. Your success is our success. Our skilled Team is focused upon meeting the goals and timelines of our customers.

#medicaldevicemanufacturing #injectionmolding

www.BozillaCorp.com, 800-942-0742, info@BozillaCorp.com

About Bozilla Corporation: https://youtu.be/-0xzsMWzxB4

End Part Failure due to Mold Filling Imbalance

Posted on June 7, 2023June 12, 2023 by Bozilla

Is Part quality and performance of your injection molded part important? Do you enjoy spending that extra time and money having your tool reworked? How about the pleasure of explaining the faulty part to your OEM? Let’s get real. Balance your tool analytically before mold steel is cut-NO EXCEPTIONS! If you ignore this step, there is a decent chance of experiencing an unfavorable result on complex or seemingly simple tools.

Let’s discuss mold balance.

When can a mold-filling imbalance occur? These imbalances may be due to gate location(s) on the part, part geometry, or a combination of both. Unless it is analyzed in flow simulation software, it is extremely challenging to determine how a part will fill.

What creates an imbalance?

In a single cavity tool, an imbalance can occur when one location of the cavity finishes filling while another has yet to fill.

In a multi-cavity tool and family tool, the same imbalance may occur within each cavity, but an imbalance may also arise from cavity to cavity.

How can imbalances cause problems with part quality and performance?

It is crucial to understand polymer flow. A plastic engineer excels at possessing polymer knowledge. Applying this expertise during the virtual optimization stage of your injection molded part will provide significant insight into an imbalance, which can affect part quality and performance.

Where can an imbalance occur?

As the cavity fills, the temperature of the polymer flowing through the tool must not fluctuate to keep the properties of the polymer consistent throughout the cavity. If flow velocity isn’t uniform in any region of the cavity, hesitation can occur and cause the polymer to cool down. As the polymer cools, a frozen layer will form on the mold walls. This frozen layer forms more rapidly in slower-moving regions and exceptionally fast in areas where the flow has stopped. Once the cavity produces enough pressure to continue filling these hesitating regions, the flow will begin to move again. However, the polymer is now cooler and will create tremendous shear stress as it continues to fill the remainder of the cavity. THIS SHEAR STRESS WILL CREATE THE POTENTIAL FOR PART DEFLECTION AND EVEN PART FAILURE.

If imbalances occur in a multi or family tool, the entire cavity experiencing the hesitation is at risk for this increased shear stress. The imbalance also causes the hesitating region of the cavity to become non-uniformly packed, which translates into non-uniform shrinkage, another precursor to part warpage.

How does shear stress cause quality and performance issues?

When polymer experiences shear stress, the naturally ‘coiled’ molecules are stretched out and frozen into the ‘stretched out’ position within laminates (layers) of the part depending on when and how fast it cools. This process of coiling and uncoiling is called frozen-in stress. Sometimes the stress is so great that the forces can break the molecules.

Frozen-in stresses in a part occur when the molecules are stretched out or broken, and the material cools and solidifies with those molecules in place. Therefore the part now contains a frozen-in level of stress. If these regions of the part have outside forces applied to them, it takes little effort for the part to fail. For example, have you ever purchased a 5-gallon bucket at a home improvement store and had the bottom crack after minimal use? Bye-bye, $10. This story represents a real-life example of how frozen-in stress can cause failure in the field. High-stress regions are usually the first to fail when additional loads are applied in the field as the part functions.

Over time, the stressed molecules can naturally relax into their naturally coiled position. Stress will lessen, and thermal cycling can accelerate this process. For example, the same bucket you purchased has yet to be used and is left outside. It will experience daily thermal cycles allowing the molecules to move and relax, resulting in a wrinkly, warped bottom. Therefore, both time and thermal cycling can relieve the frozen-in stress of a part, causing cracking and/or warpage. e.g., many headaches for you.

Shear stress is invisible

Most of the time, there will be no apparent signs of shear stress or other problems. Shear stress is typically invisible unless the part is so severely stressed that it cracks at the time of molding. Have you examined a clear plastic part, e.g., a CD case, and noticed a rainbow pattern? That is shear stress.

Eliminate shear stress

One of the best ways to prevent shear stress is to avoid an imbalance in the tool. Imbalance in a cavity or a multi (or family) tool can be prevented by performing a mold-filling analysis beforehand. An analysis will provide more insight into the process and the final product so that neither time nor money is lost when creating the tool for any part.

In conclusion, an imbalance in a cavity or a tool can cause molded-in stress, resulting in warpage/deflection or part failure in the field. Are you willing to risk not running an analysis upfront for that expensive mold and having a whole load of problems with your OEM when the parts fail in the field? Do yourself and your company a favor; perform a mold-filling analysis now. You can thank me later. The Bozilla corporation team saves their customers’ jobs and reputations, one part at a time.

Contact Bozilla Corporation today and let’s discuss how we can successfully contribute to your project. Bozilla Corporation’s Injection molding Team has over 20 years of experience analytically and on the floor. We specialize in optimization, consulting, engineering, troubleshooting and Autodesk Moldflow software custom training and mentoring. Additionally, our plastics engineers have a full understanding of polymers and how they influence an injection molded part. Your success is our success. Our skilled Team is focused upon meeting the goals and timelines of our customers.

www.BozillaCorp.com, 800-942-0742, info@BozillaCorp.com

About Bozilla Corporation: https://youtu.be/HIUfzwf1x90

About the Author:

Chris Czeczuga is a Plastics Engineer, Injection molding expert, Military Veteran and the President of Bozilla Corporation. He has proven success with many Fortune 500 companies throughout the injection molding industry. A graduate from UMass Lowell, he is Expert Certified with Autodesk, has 20+ years of field experience, intimate knowledge of injection molding part, tool and feed system design. Bozilla Corporation’s success is built on providing the highest level of injection molding simulation and consulting advice to businesses who have short lead times, require an efficient, cost-effective molding process, and desire to produce a correct part the first time.

STOP doing this to Cooling Circuits!

Posted on May 2, 2023 by Bozilla

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, i.e. 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 will be different in each circuit resulting in differential heat removal from each circuit and a non-uniformly cooled mold.

The cooling circuits within the mold are rarely all the same. In fact, they are typically different in total length, diameter and may also contain various amounts of bubblers or baffles.

When circuits are balanced, that means that they have the same pressure drop across them. If they have different pressure drops, and are hooked up to the same manifold, the flow rate will be different for each circuit. The circuits with the higher pressure drop will experience the lowest flow rate causing them to be less efficient than their counterparts.

Reasons Cooling Circuits would not be Balanced:

Flow lengths are not equal
Diameters are not equal
The addition of bubblers or baffles
Number of turns in a circuit (circuits hooked up in series)

A typical cooling system has a supply manifold with hoses running to the mold and hoses running out of the mold to a return manifold.

Below is a simplified illustration of a cooling system with a series of 5 cooling circuits, each with a different diameter, all hooked up to the same two manifolds with short hoses.

Cooling Circuit 1 (pic manifold)

This example is not far from what can actually occur. Because the circuits are hooked up to the same manifold, the manifold will deliver the coolant according to the pressure drop as seen in the next image. The coolant will always favor the circuit with the lowest pressure drop or path of least resistance.

Cooling Circuit 2(pic-circuit pressure drop)

Notice how the smaller diameter circuit (on the top of the image) has the greater pressure drop resulting in the highest pressure requirement and the larger ―”circuit (bottom of the image) has a very low pressure drop. The varying diameters will have a tremendous effect on flow rates.

The resulting flow rates are as follows:

Cooling Circuit 3 (pic circuit flow rate)

With a total inlet flow rate (into the manifold) of 4 gallons per minute, observe how the largest circuit (bottom of image) has the highest flow rate at 1.33 gallons per minute and the smallest circuit (top of the image) has a flow rate of 0.319 gallons per minute. That’s more than 3 times more flow rate than the smaller circuit.

Above all, when it comes to heat transfer, we need to have a Reynolds number above 5000 in order to have turbulent flow (0-2000 is laminar flow, 2000-5000 is transition flow and 5000+ is turbulent flow).

When the flow rates vary through circuits, some circuits may no longer have turbulent flow causing the circuit to be very inefficient and sometimes useless. Circuits with low flow rates are also prone to fouling, another hidden cost. The image below shows the corresponding Reynolds numbers for the circuits.

Cooling Circuit 4 (pic-circuit Reynolds number)

The smallest cooling circuit (top of image) only has a Reynolds number of 4379 while the largest cooling circuit has a Reynolds number of 9118! All circuits need to have a Reynolds number higher than 5000, preferably 8000 and higher. Imagine how inefficient a mold would be with these cooling circuits.

Unfortunately, imbalanced cooling circuits exist in many molds today especially with the incorporation of conformal cooling designs and the increasing complexity of injection molds.

In summary, cooling circuit design is extremely important and needs to be given more attention. Properly designed cooling circuits will:

Be less prone to fouling
Require less frequent maintenance due to less fouling.
Have greater efficiency resulting in shorter cooling times which will decrease cycle times dramatically.
Provide more uniform cooling (fewer hot spots) which can decrease issues such as part sticking.

STOP ignoring the importance of proper cooling circuit design.

Bozilla Corporation considers both pressure drop and circuit balance when analyzing cooling circuit designs in Injection Molds and in Thermoforming Molds. We believe in making every effort to help our customers save money. The next time you design your mold, call Bozilla Corporation and we’ll work with you to make your mold more efficient.

www.BozillaCorp.com, 800-942-0742, info@BozillaCorp.com

About Bozilla Corporation: https://youtu.be/Xz-5gJYQ_MY

About the Author:

Lean Tool Validation for Injection Molding

Posted on April 19, 2023April 20, 2023 by Bozilla

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 that have been shelved or sidelined, and many more.

After a full analytical investigation, final results based on all accepted changes are provided as an overall solution package.

This lean validation system was created due to repeat customer requests to find a solution to make their current tools more efficient or to find a means to render shelved tools usable again.

Are you aware that your tool may not performing efficiently?

Contact Bozilla Corporation for a Lean tool evaluation today.

www.BozillaCorp.com / 800-942-0742

Is Using MFR the Best method for Material Selection?

Posted on December 1, 2022December 1, 2022 by Bozilla

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 at the processing temperature used during molding. When two materials are compared, this curve will tell them if one material will flow more readily.

Currently, most testing takes place on an injection molding machine fitted with a unique die head that has a rectangular slit and is instrumented accordingly to acquire all of the necessary data for broad-spectrum rheology testing. The benefits of testing on an injection molding machine include the consideration of melt homogeneity and material degradation. Utilizing an injection molding machine for rheology testing is the best and most comprehensive method used today.

In conclusion, the ASTM D1238 Melt Index Test Method (MFR) is a great way to compare one material to another using zero shear flow rates. However, the reality is that when materials are injection molded, the shear rates are far from zero. At higher shear rates, it’s imperative to understand flow behavior of a polymer. The only way to do this is to look at and compare the rheology curve produced by the dual capillary rheometer or, better yet, a properly outfitted injection molding machine.

Bozilla Corporation utilizes completely tested rheology curves for every project to gain a thorough understanding of the polymer chosen for the application. Using this data provides the most remarkable accuracy when analyzing projects within the Autodesk Moldflow software when investigating polymers for project application and project troubleshooting.

Contact Bozilla Corporation today and let’s discuss how we can successfully contribute to your project. Bozilla Corporation’s Injection molding Team has over 20 years of experience analytically and on the floor. We specialize in optimization, consulting, engineering, troubleshooting and Autodesk Moldflow software training. Additionally, our plastics engineers have a full understanding of polymers and how they influence an injection molded part. Your success is our success. Our skilled Team is focused upon meeting the goals and timelines of our customers.

www.BozillaCorp.com, 800-942-0742, info@BozillaCorp.com

About Bozilla Corporation: https://youtu.be/HIUfzwf1x90

About the Author:

Part 2: Can Moldflow Validate the Quality of your Part?

Posted on September 30, 2022October 27, 2022 by Bozilla

Part 2: Can Moldflow Validate the Quality of your Part?

In Part 2 we will continue our discussion of utilizing the Moldflow software to ensure the part does not fail in the field. (Part 1: Can MoldFlow Validate the Quality of Your Part?)

Is the gate in the best location?

In many cases, the customer provides a part with a suggested gating location. The gating location is sometimes determined during the part design process and is designed based on the assumed gate location. However, the pre-determined gate location may not always be the best location for several reasons:

The gate location may not provide a balanced filling pattern which can cause severe velocity changes to the flow front or an undercut scenario where the flow direction changes after the frozen layer on the wall has been established which causes tremendous shear within the part laminae. Both of which can cause part deformation or even failure.
If the gate location creates an imbalanced filling pattern it can create a pressure spike which will also create a clamp tonnage spike. Both of which lead to issues mentioned in aforementioned bullet.
The gate location may not be in the best location with regards to the material freezing back to the gate which is essential for proper part packing. Some regions of the part may not be able to be packed due to a poorly selected gate location. This can cause excessive volumetric shrinkage in isolated regions of the part which can lead to sink marks or even voids. In the images below there is a wheel for a drawer carrier which is failing due to internal voids. There is a cut-away showing the voids which are revealed in the analysis where the high volumetric shrinkage shows the regions where the voids can potentially occur:
Has the tool design been verified?
This may seem like a redundant question but there are times when the tool may undergo some design changes which may affect the outcome of the part design such as:
- Cooling inserts added
- Rerouting of cooling lines
- Cavity orientation changes
- Feed system changes (perhaps due to cavity orientation changes)
- d possibly other tool design changes
Many businesses integrate a final tool review before or at the initial trial run, so if this is not standard procedure it is highly recommended. If anything HAS changed, the mold filling analyst will need to re-optimize the process based on those changes.
Has the material been qualified/verified? (Keep the material supplier involved)
This is another point that is typically not considered when trialing a tool but is absolutely critical. We have had several customers reach out to us with various conditions of part failure only to find that the batch of material that they were utilizing has changed and was compromised.
The material could have a specified glass content that may change from batch to batch. In some cases, the chemical binder used for binding the glass fiber to the polymer may be re-formulated and cause a situation where the polymer can bond to the tool resulting in a part that does not release properly during ejection.
We always recommend having the material supplier closely involved when both trialing a tool and during initial production start-ups.
Once an analysis has determined the optimum processing conditions for the part, the part will naturally contain inherent stress from the molding process. It is this stress that may be the ultimate cause of failure in the field and must be kept to a minimum.
Frozen-in stress coupled with functional stress imparted during usage may cause the part to fail and this must be headed off before the parts ever make it to the field.
This is when it’s vital to run a post process using FEA.
Perform post-molded CAE performance tests utilizing real-world stress loads to ensure the parts do not fail.
The Autodesk Moldflow software has the functionality to export the in-molded stresses from the injection molded process. This allows the user to import those stresses into a CAE software such as Ansys or Nastran which will allow them to run specific performance tests on the part while considering the in-molded stress from the injection molding process. The process of exporting the data and running the post-molded tests in a CAE software can be both time consuming and costly, therefore the risk/reward ratio should be considered.
Should you forego this testing? Perhaps, but what if the part fails in the field? Part failure could have easily been discovered and mitigated with this testing process. Again, if possible, we highly recommend performing the post-molding CAE performance tests in order to further increase the potential for part success in the field.
Because the frozen-in stress is accounted for in the analysis, the analysis may reveal that the part would fail when it normally wouldn’t have failed if the frozen-in stress was not accounted for. The inherent frozen-in stress due to the injection molding process is crucial data to consider in order to create a successful part.
Bear in mind that each one of the points discussed should be performed, at a minimum, on a first-generation tool. Engineers should consider conducting an analysis on a second-generation tool considering as many of these points as possible as an ‘insurance policy’ moving forward.
We have touched on a few of the key points of how to remedy the potential failure of parts in the field but there are many more to consider. We would like to emphasize the importance of reviewing these points in order to mitigate part failure. Once the tool is at the initial production run, it is very costly to make any changes that will influence the quality of performance of the part in the field.
Bozilla Corporation has performed this unique set of analyses and identified many potential causes of failure long before the parts were ever manufactured.
Bozilla Corporation’s Plastics Injection Molding Team has over 20 years of experience analytically and on the floor. We specialize in optimization, consulting, engineering, troubleshooting, mentoring and Autodesk Moldflow software training. Additionally, our plastics engineers have a full understanding of polymers and how they influence an injection molded part. Your success is our success. Our skilled Team is focused upon meeting the goals and timelines of our customers.

About the Author:

Can Moldflow Predict Part Quality? (Part 1)

Posted on September 2, 2022October 27, 2022 by Bozilla

This subject contains a significant amount of important information so it will be broken into two parts.

Part 1: Can Moldflow Validate the Quality of Your Part?

The short answer is YES. Validating your plastic injection molded part before it enters the field is the purpose for which the Moldflow software was created.

A well trained and seasoned user of the Moldflow software should be able to take a part through the entire injection molding optimization process and validate each of the factors that will ensure the part meets the design criteria. i.e. quality of the part.

Injection molding design validation

For most parts, the criteria is very similar:

The part must meet design tolerances and must have minimal deflection/warpage.
Weld lines must form in acceptable places or perhaps weld lines are not allowed on specified surfaces.
Air traps must be kept to a minimum and/or be vented properly.
The process must have a large molding window so that any minor variations will not cause the part to fall out of specification.
The design of the part must meet injection molding standards (correct draft, not have any regions that are die-locked, must have correct thickness ratios, etc.)
The design of the mold must allow for adequate filling and cooling along with many other criteria such as proper ejection (that will not deform the part) and so-on.

Why is injection molded part failing

What happens if you believe your part design and process is optimized properly only to find out that it fails in the field? This is a very common situation.

The purpose of the Moldflow software is to mitigate such a situation. I’ll explain.

In order to understand if a part is going to be molded correctly, the analyst must utilize the software to correctly optimize, at a minimum, each one of the following points.

1. Is the part filling at the right speed?

It is critical to fill the part with the proper flow front velocity (screw velocity profile). As the cavity is filling, the flow front of the polymer can cool off or heat up; both of which are critical with regards to how much stress is imparted in the polymer as it fills. Too much stress during the molding of the part can cause excessive post-molding stress relaxation and deflection.

2. Is the feed system designed correctly?

An improper feed system design can control cycle time or cause the pressure requirement to fill the cavity to become too high. Also, if the gate is not properly designed, it can freeze prematurely, not impart enough shear in the polymer to assist in the filling of the cavity or impart too much shear and damage the material or create cosmetic defects.

3. Is the cavity being packed effectively?

There are two primary factors when packing a part, pack pressure and pack time. The pack pressure controls the magnitude of shrinkage the part exhibits upon ejection and the pack time controls the variation of shrinkage in the part. Volumetric shrinkage is an important contributor to part deflection.

An over-packed part can cause flash in the tool and/or cause any action in the tool to stick. It can even cause the part to stick in the tool which can cause costly down-time and potential damage to the tool.

An under-packed part can cause excessive shrinkage, sink marks or even worse, voids.

If the 2nd stage packed is not optimized, it can create an excessive amount of stress in the part. This stress will reveal itself after the molding process (post-molding) as part warpage or even part failure in the field.

4. Is the part dimensionally stable?

A dimensionally stable part means the part will not deform during post-molding due to external stresses such as exposure to temperature cycling or a significant deformation during an assembly process. If the process has been optimized, the part will have minimal molded-in stress and be able to withstand a higher degree of post molding stress and not undergo a permanent deformation.

This brings us to the end of Part 1. In Part 2, we will continue discussing these critical points and also how to take the calculated stress data in Moldflow and export it so further post-molded tests can be conducted in FEA software.

Services

In addition to our Optimization service, we offer a live On Demand Mentoring Service that can coach your Team through all of these points so you have a thorough understanding of the usage of the Moldflow software. The details can be found at: https://bozillacorp.com/services/subscription-for-moldflow-support-services/

For more information, support with your Tool Design, assistance Troubleshooting any of your Plastics Injection Molded projects, or Autodesk Moldflow Training or Mentoring contact the Team at Bozilla Corporation.

Bozilla Corporation’s Plastics Injection Molding Team has over 20 years of experience analytically and on the floor. We specialize in optimization, consulting, engineering, troubleshooting and Autodesk Moldflow software training. Additionally, our plastics engineers have a full understanding of polymers and how they influence an injection molded part. Your success is our success. Our skilled Team is focused upon meeting the goals and timelines of our customers.

www.BozillaCorp.com, 800-942-0742, info@BozillaCorp.com

About Bozilla Corporation: https://youtu.be/HIUfzwf1x90

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Using Aluminum for Injection Molds?

Posted on July 14, 2022October 31, 2022 by Bozilla

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 2.79 times less dense than Steel

Hardness: Aluminum is much softer than steel.

Thermal Conductivity: Aluminum is 6.55 times more conductive than Steel

Thermal Diffusivity: Aluminum has 7.9 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 2.79 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 6.55 times more conductive and 7.99 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 0.33 and Steel is 0.29 which simply put: Aluminum is more elastic than Steel. Higher elasticity can translate into issues as aluminum has a fatigue limit where steel does not.

The image above illustrates the difference in fatigue limits of steel versus aluminum. The fatigue of steel (stress) reduces slightly during the early cycling phase and then levels off and is able to continue cycling without the onset of further fatigue. However, when looking at the fatigue of aluminum (stress), it continues to decrease as cycling continues which ultimately leads to failure.

Yield Strength:

The yield strength of aluminum is nearly half that of steel which could result in failure of the mold should the pressure and stresses within the mold get too high..

If the tool has any individual core components which can deform, we have to consider how much they will deform and how many cycles the tool will experience before the cores will ultimately fail. An aluminum tool that has any deformation will have a finite life span.

Even if there are no individual core components to deflect within the tool, the tool itself can deflect as seen below.

If there is high cavity pressure, then the aluminum tool will want to deflect much more than a steel tool. If this kind of deflection occurs, then the machine platens will have to take on the burden of the tool flexing which can put excessive wear and tear on a machine. It might even be necessary to create a steel frame enclosure for the aluminum tool to ensure deformation does not get translated to the machine platens. In some cases, the machines platens must be thicker to accommodate the tool deflection.

In summary, with regards to injection molds, aluminum has significant benefits when compared to steel.

Advantages:

Lower Density = Lower shipping costs
Lower Hardness = Faster milling time, less wear and tear, reduced time to manufacture.
Thermal properties = More stable process, faster start-ups, faster process response times and faster cooling/cycle times.

Disadvantages:

More elastic = mold deformation, mold core deformation and Injection Molding Machine wear
Fatigue limit = A lifespan on the mold and internal components i.e. Potential for mold cores and even mold failure

Understanding the benefits and disadvantages and weighing them both carefully will provide the knowledge and insight of when to utilize the aluminum tool over the steel tool. Without this knowledge the decision can potentially lead to higher over-all costs and even the catastrophic failure of the tool.

If core deflection is a concern, Bozilla Corporation can run an analysis and identify any core deflection and the magnitude of that deflection via simulation analysis.

For more information, support with your Tool Design, assistance Troubleshooting any of your Plastics Injection Molded projects, or Autodesk Moldflow Training contact the Team at Bozilla Corporation.

www.BozillaCorp.com, 800-942-0742, info@BozillaCorp.com

About Bozilla Corporation: https://youtu.be/HIUfzwf1x90

Homopolymer vs. Copolymer

Posted on May 24, 2022October 31, 2022 by Bozilla

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 a thick part using a homopolymer, the part will have:

Pro’s:

chemical resistance
mechanical properties

Cons:

A high degree of shrinkage which may cause internal stress, cracks or even voids.

If the same part is injection molded with a copolymer, the part will have:

Pro’s

Less internal stress and possibly no voids.

Cons:

Reduced chemical resistance
Reduced mechanical properties

Knowing the difference between the two polymers is critical with regards to the impact on final part quality.

Fortunately, flow analysis simulation can identify the shrinkage variation as well as the flow characteristics between the two types of polymers. Because the characteristics of each type of polymer is different, the injection molding process for each will also be different.

A skilled analyst can develop an optimized injection molding process for either of these types of polymers and provide critical insight into the part quality with respect to each.

Without the critical insight of the analysis, the potential for reduced part quality or even part failure exists.

For more information, support with your Tool Design, assistance Troubleshooting any of your Plastics Injection Molded projects, or Autodesk Moldflow Training contact the Team at Bozilla Corporation.

www.BozillaCorp.com, 800-942-0742, info@BozillaCorp.com

About Bozilla Corporation: https://youtu.be/HIUfzwf1x90

Losing Control of the Process

Here is the rundown:

Loss of injection molding process control

Industry Response

The $10 million question is, how do you start using more recycled and less virgin resin?

That’s the question, and that’s the caution.

Cooling Circuit Diameter

The Importance of Balanced Cooling Circuits

Reasons Cooling Circuits would not be Balanced:

Part 2: Can Moldflow Validate the Quality of your Part?

Is the gate in the best location?

Has the tool design been verified?

Has the material been qualified/verified? (Keep the material supplier involved)

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Part 1: Can Moldflow Validate the Quality of Your Part?

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