22 Jun Resolving Processing and Part Performance Issues
Imagine the following scenario: you’re a processor with a processing and part performance issue to resolve. You adjust and change processing parameters to no avail, and the problems persist. You might even face some added difficulties by attempting to process around the issue.
Unfortunately, this scenario is all-too-common – but luckily, all hope is not lost. An injection molding issue could be process-related or come from decisions made in prior phases of the product launch. There are four essential pillars to consider to successfully problem solve and find a solution: part design, mold design, processing, and material. And if your issue isn’t resolved no matter how many processing changes you try – and your part design and mold design are solid – it’s likely it is, in fact, the material that’s causing the problem.
Let’s break down the potential issues that may arise, the four pillars to consider when solving a problem, and four case studies where changing the material was the ultimate solution.
Potential Processor/Molder Issues
Process technicians are expected to reduce or eliminate many issues through processing every day. Sometimes these issues are genuinely process set-up issues. However, trouble begins when we process around issues and feed parameters beyond the recommended ranges the material suppliers have given. Potential issues include:
- Cracking/breakage
- Material degradation
- Short shots
- Part imperfections
- Burning
- Splay
- Black specks
- Blemishes
- Flash
- Sticking in the tool
- Extended cycle time
- Nucleation
- Filler
- Part warpage
- Dimensional stability
- Shrinkage
Four Pillars to Consider
Shortcuts in the design process can result in issues that can be avoided by analyzing four pillars: part design, mold design, processing, and material. Decisions made in these four areas contribute significantly to the issues later found at the press, which are then considered processing issues. Using these four pillars and involving all parties at each step ensures a smoother launch.
Part Design
When it comes to part design, we ask questions about wall thickness, FEA simulations, and mold analysis. We also pay close attention to how the part was designed; designing as if the part were metal can be a big mistake – you must make changes when designing with plastic instead. Other areas to pay attention to include sharp angles, flow length, weld lines, sink marks, and gate vestige.
Mold Design
Thinking about mold design is the next step. As a processor, you usually have your own mold-building shop or partner with a nearby shop to create these molds. There’s a lot of thought that goes into a mold design, such as cooling line placement to make sure that there’s a consistent surface temperature on the mold during processing. Gate size, cold and hot runners and their size, the length and kind of cavitation you may have, and draft are other areas to consider.
Processing
When you’re at the press and an issue pops up, we tend to call it a processing problem automatically. And when it comes to processing, there are many areas where we can potentially place the blame. At PolySource, we aim to understand the actuals rather than the set points so we really know what’s going on, but we also must look outside the standard processing. We look at the drying of the material, how and where we do that, and who sets up where this mold will run. We must also consider machine selection, including the barrel capacity, clamp tonnage, and screw design. Other processing conditions to consider are melt temperature (set vs. actual), mold temperature (set vs. actual), injection speed, pack time, pack pressure, screw speed, back pressure, cooling time, and decompression.
Material
At last, we get to the material. We continue asking many questions and center around how the material was selected. In some cases, the fundamental problem is that the material chosen is readily available as a house resin or what has been classically used in other parts by the OEM. Other times, a material is selected because it has the right cost profile. As the saying goes, sometimes we try to make a silk purse out of a sow’s ear. But if you’re dealing with variation, consistency, and uniformity issues, it’s time to consider if you’re working with a suitable material.
Ultimately, when it comes to the four pillars, it’s important to remember that one isn’t more or less important than the other. All four must be considered – without taking shortcuts.
The Design Funnel for Material Selection
At PolySource, our role starts with a clean sheet of paper and asking many questions. We begin with our design funnel to capture as much information as possible, starting at the broadest part of the funnel to gather information about the physical, chemical, and thermal requirements. We ask questions about how the material will be used and what it will be exposed to, as well as flatness, color, and appearance. From there, we can start to get a little more detail; for example, if there’s a lot of chemical resistance required, that helps us to understand we’ll likely be looking at a semi-crystalline resin, and we can think about things like impact and weather. We also must avoid potentially expensive oversights by considering regulatory requirements. This comprehensive line of questioning ensures that we pick the correct material.
Case Study #1: Mixed Glass PA6 Compound Solves Part Problems
Throughout the years, there have been many instances where customers have approached PolySource, desperate to solve an issue, and the solution ended up being a material change.
In one such case, a customer was using 30% glass-reinforced PA6 for flat parts for bezels, housings, and internal structural parts. This material was a house resin that met all performance criteria – and the customer’s price point. However, it was not meeting dimensional stability requirements. The part needed to be flat, but with warp occurring, the device could not be assembled.
Upon analysis, PolySource determined that there were no issues with part design or mold design. Processing was not the issue either – and processing around the problem didn’t work – so we started to ask questions about the material. Semi-crystalline materials are known for their anisotropic shrink; adding a little glass makes it even worse. In this case, no mold flow had been completed, and because of the gate location and the way it would flow into this mold, there was a lot of fiber alignment. We began to consider a glass and mineral mix.
Ultimately, PolySource recommended a mixed glass or mineral/glass PA6 compound. This material would result in reduced fiber alignment and continue to meet all other performance criteria despite reduced strength and toughness. With slightly reduced mechanicals, the part still met specifications.
Case Study #2: High Flow, Low Viscosity 32-Melt Polycarbonate for an Optical Lens
Another notable example was using a 20-melt polycarbonate standard material for an optical lens. Multiple cavitations made this case slightly different, as this part had an eight-cavity tool. The molder could not fill the part; 80% of the barrel was already being utilized, but this machine had to be used.
The usual tweaks did not work: going up in temperature to improve the flow resulted in material degradation and black specks, and injecting faster led to splay, maximized machine pressure, flash, and brittle parts. The processor attempted a workaround by blocking off cavities to resolve the issue, but the increased cost associated with this made it an unreasonable solution.
As with the first case study, an analysis concluded no issues with part or mold design. Regarding processing, everything tried had negative results, although we did determine that completing an initial mold flow could have caught the issue sooner.
PolySource was able to recommend a higher flow, lower viscosity 32-melt polycarbonate. This material filled the part with recommended processing conditions while avoiding material degradation, black specks, flash, and brittle parts. The original cost quotes were able to be met as all cavities could be used. The part still met all mechanical requirements with no increased cost on resin – only a slight change within the resin family to lower viscosity was needed.
Case Study #3: Modified Existing Formulation Reduces Torque
In this case, an automotive seat adjustor using an unscrewing mold with 50% GF PA66 had an issue with parts sticking on the unscrewing core during molding. The problem was so bad that the unscrewing motor was burning out around 100 shots because of the amount of torque it took to unscrew the core. Everything the customer tried had a negative effect: packing it less caused the parts to be too small and led to voids resulting in weakness; overpacking showed some improvement but caused flash. A cold mold led to high internal stress and dimensional changes with stress relaxation. Playing with the melt temperature proved problematic as well – going up in temperature shrunk the part and caused more sticking, whereas going down in temperature led to short shots and the mold not filling.
Part design, mold design, processing, and material all checked out – this issue was an unanticipated problem that occurred when molding in production. Making a wholesale material change would be the path of least resistance given the nature of the automotive industry, where a lot of specification, validation, and approvals must occur. We started to think about how we could reduce the sticking and adhesion to the core and came up with a solution: a little extra mold release.
Adding mold release to the existing formulation was a minor change by the OEM that still met automotive specifications. The results showed no plate out, no secondary operation concerns, and the unintended improvement of reduced torque in end-use. With some trial and error, slightly modifying an existing formulation was just the ticket to solving the issue.
Case Study #4: Glass-Reinforced PP Meets Requirements for Stiffness, Impact, and Heat Resistance
In this last example, a customer using GF PA66 to create a radiator fan had a big concern: he had no window to process this material. There was extreme variability – flash, short shots, and splay were all occurring with a large amount of variation within a lot. The processor was focused on the material and asked PolySource for help.
Our analysis concluded that the part design and mold design were both solid. We focused on drying and analyzed the moisture content, discovering it was out of range to meet the customer’s part requirements. The customer did not have the drying capacity to meet production needs. We concluded that the customer needed to add more dryer capacity or change material.
After performing a deep dive on the actual application requirements, PolySource was able to recommend glass-reinforced PP. This material met application requirements for stiffness, impact, and heat resistance. Another effect of this change was a significant cost reduction, as the material didn’t have to be dried and cost less per pound – and the processor didn’t need to buy another dryer!
Conclusion
The four design pillars come together with three people: the OEM, the processor, and the material supplier. Using your resin supplier to work with your OEM to review issues is vital to the success of your project. In addition, various cost-efficient, time-saving tools are available to us to deploy before a mold is made, including FEA and mold analysis. Utilizing these tools often pays for itself by avoiding costly issues down the road, cutting down on total project costs substantially. Keeping the four pillars in mind, working with your supplier and OEM, and completing an upfront analysis will ensure you get the best material and design in the shortest amount of time.
At PolySource, we’re called “The Fixers” for a reason. We’re known for our extensive questioning – it’s all a part of our relentless pursuit to get it right. Whether you’re looking for the best material for your application or need to fix a current issue, we’re here to help.
