Tag: FEA

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

aluminum v steel table

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

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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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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)

Core deflection fill time graph

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

Core shift pressure graph

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

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Is this the correct Injection Molding Machine for your Tool?

By Bozilla
November 8, 2021

To start this discussion I’d have to first state that the size of the tool plays a large role when selecting an injection molding machine  More specifically, it is the projected area that is of concern and how the projected area, along with the pressure distribution over that projected area, creates clamp force

Selecting a machine based on clamp force (tonnage) is more common when you have a part with a large projected area; ie multi-cavity tools, bumper fascias, housewares and many other items

In today’s economic climate, it’s more important than ever to conserve energy  Many believe that using the smallest IMM is the best way to achieve this cost savings  However, there are reasons why a smaller machine isn’t always the most efficient machine

 Reason 1: If an optimum process is the objective, select a machine that does not allow the tool to exceed the clamp force and flash the tool (blowing open)  during an  ‘optimized’ process

We  have had many concerned customers consult with us about the process Their questions are directed at finding out why the part is warping or exhibiting cosmetic defects  Once I dig into the process, I typically find that the part is not packed sufficiently due to the tool blowing open  In order to keep the tool closed, they must pack with very little pressure for a very short time  Packing with too little pressure, too little time, or both can cause a loss of control with dimensional stability and/or cosmetic issues due to excessive shrinkage  These issues create problems that are caused because the tool is in an IMM that doesn’t have the proper clamp force requirement

In the image below the clamp force required to fill and make the part is 250 Tons  However, in order to pack the part out sufficiently and make a good part (meets tolerances, minimal cosmetic defects, minimal deflection, etc) the clamp force required during 2nd stage pack is 1,450 Tons  That’s a very big difference

clamp force plot

 

 Reason 2: You are able to make parts but the process window is so small that staying within the process window is difficult or impossible to maintain

The inability to stay within a process window could be caused by several issues, especially since there are so many variables in the molding process  However, if the machine does not have sufficient clamp force to stay closed during an optimum molding process, concessions will be made and

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Can Gate Location Really affect Part Warpage?

By Bozilla
August 17, 2021

Based on part geometry, gate location(s) will determine how the polymer fills the cavity  If the cavity doesn’t fill in a balanced/uniform fashion, the internal stresses will be anisotropic- meaning non-uniform properties  So it is important to place a gate in a location such that the polymer flowfront fills the cavity at a uniform rate and reaches the end of the cavity at all locations, including weld line locations, simultaneously

With simple part geometry, identifying an ideal gate location may be possible by using experience and examining the part  However, with more complex geometry and gating limitations (cooling line interference, ejector pin interference, slides, etc), it is nearly impossible to determine the appropriate gate location(s) without using FEA(flow simulation)  Not only can FEA(flow simulation) produce actual deflection results(warpage), it can also provide data that is a precursor to warpage-such as volumetric shrinkage and frozen-in stress which is typically due to a response from forcing the material into the cavity while the material is trying to freeze

gate location and part warpage courtesy of sciencedirectcom

Gate location(s) will determine polymer orientation  Based on that location, it will ultimately determine polymer shrinkage  Also, different regions of the part will cool at different rates(regions of the cavity near the gate that were first to fill will cool before regions furthest from the gate)

 

Why is this important?  Because there are 3 major components that contribute to warpage:

 ✔ Polymer Orientation

✔ Polymer Shrinkage

✔ Cooling Effects

 

Shrinkage and orientation are both directly correlated to injection location(s) on a part as it relates to processing conditions  Warpage due to cooling effects is  based on the rate of how the polymer cools on one side of the cavity relative to the other side Non-uniform cooling through the thickness will create warpage

Because gate location(s) directly correlates to the contributors of warpage, gate location is therefore extremely important in the tool creation process and ultimately the quality of the part

The injection molding professionals at Bozilla Corporation have over 20 years of experience assisting OEM’s, Tier 1 & Tier 2 suppliers, and Tool Shops to create quality parts that meet timing and goals

wwwBozillaCorpcom

 

About the author

Chris Czeczuga President Bozilla Corporation

Chris Czeczuga is a Plastics Engineer, Injection molding expert, Military Veteran and the President of Bozilla Corporation He has proven success with many OEM’s Tier

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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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Finite Element Analysis(FEA) – On Every Tool?

By Bozilla
March 3, 2021

Finite Element Analysis (FEA) has been available to the injection molding industry since approximately 1978 when Moldflow pty Ltd produced the first simulation software to be used to optimize all phases of design and production processes for injection molded plastic parts

Over the years, FEA has proven to be a successful, cost-saving optimization method used for injection molded tool manufacturing

 

injection molding trouble shooting

Prior to FEA, a typical method used to refine product and process was to cut tool steel and design a feed system based on experience with older, comparable tools This method is also known as the trial and error method

This type of “guessing” process has cost manufacturers thousands of dollars in re-tooling and time delays that could have been prevented if they had first utilized FEA to troubleshoot the product and process

The question remains, “Should FEA be used for every tool?”  The answer is YES! Whether it is a new tool replacing an old tool running the same part, a New Tool being built for a new part, or a new mold for an existing part, FEA can positively refine both the quality of mold and the process

FEA is a gift to plastics manufacturers in that it provides an inside look at both the product and process before any steel is cut or altered  The refinement of product and process allows the manufacturer to perfect their part and save both time and money by limiting or preventing future rework

Contact Bozilla Corporation to assist you in achieving a successful part based on your budget and timing goals for your next project  We will provide you with detailed project data empowering you to make the most informed decisions to create a high quality mold

Do you remember the cost of your last mold?  If the answer is “yes”, do you really want to pay for it again because of rework/redesign?  

The plastic injection molding experts at Bozilla Corporation have over 20 years of experience with Autodesk Moldflow software, feed system design and field experience We provide the highest degree of professionalism, knowledge and quality to every project  Contact Bozilla Corporation Today and Let’s get started!

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A Deeper Understanding Of Conformal Cooling For Injection Molds

By Bozilla
November 22, 2019

Conformal cooling has become the latest trend in the injection molding industry   As it compares to traditional gun-drilled cooling lines, it appears to be better, but is that always the case?  We will discuss the comparisons and application of both traditional cooling versus conformal cooling as it applies to heat removal of the polymer/part

When designing cooling for injection molds, several factors must be understood with regards to the properties of the tool steel such as the type of steel and its corresponding properties ie  thermal conductivity, thermal diffusivity, specific heat capacity and density   Those same properties must be considered for the coolant along with Reynolds number and flow rate

Thermal conductivity:

A measure of a materials ability to conduct heat as shown below:

Thermal Conductivity

Thermal diffusivity:

The thermal conductivity divided by the density and specific heat capacity (at constant pressure) as shown below:

Thermal diffusivity

In order to take advantage of these properties, certain guidelines should be considered such as the spacing between adjacent cooling circuits, thickness or cross section of the circuits and the spacing between cooling circuits and the cavity  The flow rate must be sufficient enough such that the coolant is turbulent (Reynolds number above 8000) in all regions of the circuits in order to have maximum heat removal

Conventional Cooling (gun-drilling):

Gun drilled cooling channels are straight holes cut through the tool steel  Because these are straight holes, it limits the regions in which holes can be cut such as in any action within the tool or small or difficult regions near the cavity of the tool  Implements can be used such as heat pipes (thermal pins), bubblers, baffles and small circuits and high heat-transfer materials  However, there are still regions within the tool that are difficult to implement cooling and these regions are typically accepted  They can cause issues within the mold such as parts sticking or controlling cycle time

Gun drilled cooling channels are very adequate when sized and spaced correctly  Basic guidelines will take advantage of the properties of both the coolant and the cooling channels:

  • The spacing of the cooling channel from center-line to center-line (pitch) should be no more than 3 times the diameter (3D)
  • The distance from the cooling channel to the cavity surfaces should be no more than 15 times the diameter (15D)

If these simple guidelines are maintained, there will be adequate

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