Tag: injection molding expert

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

reclaimed plastic

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

lose control of the process

 

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

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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:

homopolymer chain

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:

copolymer chain

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

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Creating a Virtual Plastics Injection Molding Window

By Bozilla
April 27, 2022

Since the inception of plastic injection molding, creating a robust injection molding process has always been a challenge As time has progressed, the design of plastic parts has become more detailed and intricate, the tolerances have become tighter and the boundaries of injection molding standards are being pushed to their limits The combination of each one of these factors is making it more and more difficult to create and maintain a robust molding process

Initially, it wasn’t difficult to design a basic injection molding window that would result in a robust molding process However, with the advent of increasingly demanding factors it has become more difficult to design a process molding window that is large enough to be robust and create consistently good parts As a matter of fact, not only is it difficult to create a wide process molding window, it’s nearly impossible to create a suitable molding window- Period We will discuss how and why it is necessary to first create a virtual injection molding window and how that data can be translated to the floor in order to have the best injection molding window possible

Let’s begin with understanding what a molding window (or process window) is Typically, a molding window is comprised of three major factors: Fill time (or fill speed), Mold Temperature and Melt Temperature Each of these factors has the greatest impact on the injection molding process

Graphs below will illustrate the impact of each

The influence of each factor:

  • Fill Time (fill speed): As fill speed decreases, the material moves into and through the cavity slowly which allows the cooling effects of the tool steel to have more time to influence and cool the temperature of the plastic resulting in a higher viscosity response and a greater pressure to fill the cavity Conversely, as the fill speed increases, the material will shear thin (the viscosity will decrease) significantly, but ultimately the plastic will resist filling the cavity and require a greater pressure to fill the cavity Somewhere between filling extremely slow and filling extremely fast is a sweet spot that requires low pressure to fill the cavity If plotted out in a graph, it will be a u-shaped curve where the lowest point is typically a good fill speed

molding window pressure

  • Mold Temperature: The mold temperature is highly influential with regards to having the material fill the cavity The thickness of the part relative to the flow length is an important relationship with regards to the impact of the mold
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How Experienced And Knowledgeable Is Your Analyst?

By Bozilla
August 4, 2021

In this economic climate, it is critical to create higher quality processes and parts while keeping costs as low as possible This typically means getting analysts involved in the beginning phases of a project Because a mold typically costs in the range of $12,000 to above $200,000, spending less money up front with analytical work will save you from costly tool re-work at the end of a project

More businesses are turning to mold flow analysts to provide in-depth, technical knowledge before, during, and after the course of their project Whether the analyst is internal or is a hired consultant, it is extremely important to know what type of experience and knowledge they have in order to take full advantage of their expertise

What basic requirements should an Injection mold flow analyst (example: Autodesk Moldflow) have when analyzing the injection molding process

Qualities of an injection molding analyst

  1. Injection molding knowledge: What type of focus does your analyst have in the injection molding sector? For instance, are they knowledgeable about mold design, polymers, and flow, etc?

Having an analyst that fully understands the scope of their position is an absolute necessity In order to have a comprehensive understanding of their job, analysts must be knowledgeable in all aspects of the injection molding process This includes injection molding processing, mold design, part design, and polymer chemistry and properties(eg a plastics engineer)

Plastics engineer

Plastics Knowledge: Is the analyst a Plastics Engineer or will a Plastics Engineer be involved?

Without a full understanding of polymers, it is extremely difficult to understand polymer behavior during processing This understanding begins at a molecular level and extends far beyond standard processing knowledge  A Plastics Engineer is able to identify the differences between polymers and each polymer’s flow characteristics This information can be used in conjunction with the simulation software to optimize the analyzation process Therefore, it is crucial to have a Plastics Engineer involved with plastics processing

injection molding worker

Injection Molding Experience: Has the analyst ever run an injection molding machine or been formally trained on one?  Does he/she understand ancillary equipment such as thermolators/chillers?

Without injection molding experience, it is difficult to properly analyze such a process

A mold flow analyst is typically required to identify and understand polymer flow behaviors within the injection mold Frequently, this can involve analyzing the 1st stage, 2nd stage, and cooling stages of the injection molding process If your analyst must survey these phases of the

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