Tag: plastics injection molding

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 itpolymer choice for medical devices

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)
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End Part Failure due to Mold Filling Imbalance

By Bozilla
June 7, 2023

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

shear in polymer

How does

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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

furnace of the plastometer and extrusion plastometer

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

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

rheology curve

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

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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


 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


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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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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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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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

Plastics injection molding optimization

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

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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


Injection Molding simulation software


  • 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

Mesh quality for injection molding

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

Material Data for injection molding


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
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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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Valve Gates and Sequencing-for injection molding

By Bozilla
August 24, 2021

Valve Gates are invaluable as they relate to their primary design purpose and have many important functions

 They can:

✔ Eliminate waste that cold runners create

✔ Eliminate vestige

✔ Be sequenced

✔ Eliminate weld lines

✔ Control filling patterns

However, users should be aware that there are a few potential issues that could come with using valve gates and sequencing

valve gates for injection molding

 Vestige v Witness Marks

Valve gates can minimize or completely remove vestige by direct gating on the part  They do leave witness marks on the part where the valve gate tip seats into the cavity but with proper grinding or surface finish, it can be minimized or completely hidden

 Controlling the Fill Pattern v Machine Stroke Programming

When multiple valve gates are used to fill a part, it may be necessary to time the sequencing in order to create a more uniform filling pattern  It is extremely important to understand that if the valve gates are sequenced, then the flow rate input must also match the demand of the feed system

For example: If your tool has four valve gates and you initially open two valve gates, then open the next two valve gates, the IM machine must deliver twice the flow rate when the two additional valve gates are opened in order to maintain equal flow rates through all nozzles in the feed system

If the machine stroke is not profiled to compensate for the flow rate demand, the properties of the polymer will change in the cavity due to different filling rates  This could translate into non-uniform shrinkage and stress which directly translates into warpage  It can also cause surface finish variations as shown in the picture below

Nozzle and machine pressure for injection molding

Cascade Sequencing (eliminate weld lines) v Machine Stroke Programming

If the intention is to sequence the valve gates as the flow front passes by in order to remove weld lines, then the same concerns arise if the machine stroke is not programmed to compensate for the additional flow rate demand as additional nozzles are opened

Cascade sequencing can also create back-flow and uneven packing along with uneven stress even if the machine stroke is profiled to compensate for flow rate

Cascade sequencing removes weld lines, therefore the potential problems that accompany it must be weighed  Cascade sequencing should be used as a last resort when trying to eliminate weld lines

Valve Pin Control

Hot runner manufacturers have now developed controllers to

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