Two of the major objectives a molder has entering a project are to preserve the material properties the customer is seeking and to produce a part to print. Mold flow analysis (MFA) is a critical tool for designing successful parts and tools for plastic injection molding. But it’s only as good as the expertise of the team conducting it, and their ability to interpret the data it generates.
A well-designed and analyzed MFA can help you build tooling that consistently produces high-quality parts at a reasonable cost. A poorly done MFA, on the other hand, can result in recurring part quality problems, expensive and time-consuming tooling changes, and endless frustrations for you and your molder.
So how can you ensure better quality results from your mold flow analyses? Here is one big mistake to avoid and several proven strategies that you should consider for better MFA outcomes.
Is the material you’re planning to use well-characterized?
A well-characterized resin has a detailed profile that describes all its properties including its physical, mechanical, thermal, and electrical characteristics. An engineer at your molder can feed this data into MFA software to deliver a prediction of how a tool will perform in a production environment.
Conversely, if a resin isn’t well-characterized, the MFA won’t be as accurate leading to problems during sampling and production. This, especially, is a situation where your molder’s ability to interpret an MFA can provide a lot of value or create a lot of headaches.
Don’t rely only on a phase 1 MFA from your toolmaker
Today, it’s common to see a mold flow analysis included in tool costs. What most customers don’t realize is that it’s usually only a phase 1, or preliminary, MFA.
“It helps them determine the gate location for the tooling and allows for verification of shear rate, fill pressure, clamp requirements, knit line and trapped air locations, and warp prediction. A phase 1 MFA also assumes that the tool will cool uniformly, which means it provides a good estimate of warp but won’t accurately predict how the part will warp in a production environment,” explains NBP Engineering Manager Dan Manning. If a Phase 1 MFA predicts issues in the current tool design, the next step is to take a much deeper dive.
A phase 2 MFA is much more comprehensive. “We model the cooling lines and incorporate a more complete tool design,” he continues. “When we re-run the analysis, we’re able to move from a prediction of uniform cooling to an actual cooling model. Often, that reveals hot spots in the tooling that may lead us to reposition cooling lines or use high thermal conductivity materials to help it cool faster.”
Why does this matter? Because hot spots in the tool can affect the product integrity, the ability to meet the part print, and lead to longer cycle times which in turn results in higher part prices.
A more detailed MFA can also help engineers verify the location of cooling lines, the impact of warp, material shrinkage values, the selected material feed system, and the balance of the runner if one is present.
“Molding processes don’t always produce the results we expect them to,” Manning advises. “That’s why it pays to do an in-depth analysis to surface and solve any potential problems – before the customer has tooling built.”
Don’t rely on molders who only use rules of thumb and experience to optimize part designs and tooling
Some molders don’t fully embrace the value of mold flow analyses. Instead, they tend to rely on rules of thumb and past experience to predict how the material will behave in a customer’s tooling. That approach can be very risky, warns Vice-President of Sales Joseph Mechery:
“They create this very expensive tool based on their rules of thumb. They bring the tool into sampling and use your molded product to begin their troubleshooting. That usually leads to expensive and time-consuming tool corrections and do-over loops.”
He adds that these molders usually have several rounds of tool modifications baked into their pricing. But the bigger issue is that it can cause costly delays:
“Every time you need to make a steel change, it tends to be very time-consuming. Some tools are very large and require some very precise steel changes. Chances are, they’re going to delay production of your part by weeks if not months,” he points out. “Not to mention the amount of avoidable rework that is being done to a brand-new tool with steel being added or removed in the process”.
If you’re transferring challenging tools, ask your new molder to do MFAs
It isn’t uncommon that the reason behind moving a tool can stem from a molder being unable to produce a desirable part. A smart molder can utilize an MFA to reverse engineer valuable adjustments to transfer the tool more quickly into production and begin producing parts successfully.
“We can take the drawings of the tooling, along with the current locations of the gate and cooling lines and plug them into an MFA. We can then start playing ‘What if?’ with them,” Mechery indicates. “What if we moved the gate here or added more cooling there?”
“This process can help us in many ways. Once we plug in the inherited scenario and correlate what we are seeing in the molded part, we can confidently simulate the changes we recommend and verify their influence before making those necessary changes. This will help get a part into production more quickly, even if the previous molder was having problems with it,” he adds.
Take advantage of every opportunity to learn from the MFA process
Your plastic injection molder should be willing to provide you with a detailed walk-through of the MFA results – in layman’s terms. That can help you understand what the data means and the justification for any changes the molder is recommending.
“Here at New Berlin Plastics, we walk our customers through the entire MFA report and help them understand it. We present it in such a way that they don’t need to be injection molding experts. It helps them understand what we’re predicting, what the outcomes are, and any risks we see. That helps them make better-informed decisions about any part or tooling recommendations,” Mechery emphasizes.
“The process of reviewing the MFA and being able to understand the consequence of a design or feature helps any engineer or designer level up their knowledge of injection molding. That knowledge will serve them well throughout their career. They can also incorporate what they’ve learned into their next part design,” he concludes.
Contact us to learn more about our MFA process and how we can help you get your parts into production quickly and cost-effectively.