Use of flow simulation at the front end of a project can save a mountain of money, as long as the technology is used properly.

The ability to analyze a molding project prior to cutting steel is one of the most powerful technological advances our industry has experienced. Many companies have invested in this capability, perhaps to validate their own design, to market their materials, or to crunch the time frame from PO to PPAP. Regardless of the reason behind the purchase, improperly using the technology not only hinders project development, but also can cause those involved to form a poor opinion of molding analysis capability as a whole. Keeping the suggestions below in mind should help improve the accuracy and efficiency of your analyses.
 
1. Have a plan
Good intentions are often ruined by poor planning. The decision to run an analysis is a good one. Now, what are the exact expectations of the analysis project? Perhaps the part design is frozen, and the molder simply wants to evaluate its intended gating design for required fill pressure and necessary tonnage. Warp could be a concern, where the molder would like to evaluate different gating approaches, and how those approaches affect fiber orientation in a glass-filled system. Whatever the desired output, defining specific analysis goals eliminates wasted time and resources, and keeps the entire project launch team on the same page regarding expectations. If someone asks you to “do a flow analysis,” make sure they define exactly what they are asking for.
 
2. Understand the targeted machine’s capabilities
It’s a very uncomfortable situation when one is putting a $150,000 tool with valve gates through its virgin sampling, only to find the press does not have enough pressure to fill the mold. The process engineer glances at the tooling engineer, the tooling engineer looks at the design engineer, the design engineer stares at the project manager, and . . . well, you get the picture. Now, before we all get carried away, make sure the pressure-limiting situation is real. To quote consultant/trainer John Bozzelli, “The goal is to fill the cavity as fast as you can, as far as you can, under control.” Many tools have been falsely deemed “pressure limited,” when in fact transfer position has been improperly set, the screw overtravels transfer position during boost, and material slams the end of the cavity before the pressurization phase is enacted. This is an improperly designed process, not a pressure-limited situation.
 
With that said, tools are often built that cannot be molded with a logically optimized process due to lack of available pressure. Sometimes this can be rectified by feed system or part geometry changes, but even if the fix is that simple, it’s another trip to the toolroom, another sampling, and more time wasted. Understanding the maximum available plastic pressure, injection rate, and tonnage are key to analysis success, as they are used to identify red flags prior to tool design and build.

3. Reverse engineer with accurate data
Unfortunately, many projects never hit the molding analysis stage until after the mold is shot, a problem is identified, and the panic button is about to be pushed. Analysis is then requested to identify the root cause of the pressure drop issue, warp problem, or other defect. When performing an analysis to baseline an existing issue, it is extremely important to have all current data available. This means specific feed system dimensions, cooling system layouts, fill and pack profiles, cooling times, and melt temperatures. The ramp between stages of fill and pack is often a large player that goes unidentified, but can cause major part dimension fluctuations.
 
Relying on machine setpoints is another common mistake. Perhaps the machine is out of calibration, and the 4000-psi plastic pressure is actually providing 7000 psi to the tool, or vice-versa. Utilizing an exterior process evaluation unit that will allow an accurate plastic pressure trace to be recorded for reference is invaluable. Remember that plastic variables are what matters, not machine settings.
 
4. Analyze the correct part geometry
This one surprises people, but anyone who has enough years in the industry recalls at least one situation in which something has gone awry with the geometry. While working as a project engineer for a molder several years ago, a tool shop accidentally cut the incorrect shrink rate into two large automotive tools we had sourced to them, although the desired shrink rate was documented in writing. The ensuing fiasco that came about after measuring the initial part samples and discovering the root of the problem was quite memorable, to say the least. Whatever the situation, make sure the part data is current, and that it matches the most recent revision. The pretty flow analysis PowerPoint that you spent hours putting together looks wonderful, until someone in the meeting looks at the first slide and says, “Those ribs were eliminated two revisions ago.” Wasted time can never be recouped.

5. Get some experience
A tooling manager I used to work for was not a big fan of air travel and often commented that, when getting on a plane, he “liked to see a bit of gray hair in the cockpit.” Experience matters. Make sure the person you have designated as your analysis professional carries a solid molding pedigree. Several schools now offer top-flight plastics engineering programs that provide a high level of plastic theory. However, theory is a complement to hands-on experience, not a replacement.
 
If you have intelligent and educated engineers assigned to manage your molding analysis work, invest the time to get them on the shop floor for a while. Just walking around for a few days with a molding technician isn’t enough. Get them in jeans and steel toes, and get them dirty. Have them trained to hang tools, start jobs, and learn how to process in an industrial setting.
Next, get them some time in the toolroom. The lab setting many experience in their degree programs is a great start, but when they take their first job at a molding shop where clamp force stretches to 3000 tons or more, gas-assist programs are being run, inmold decorating and two-shot molding are common, or sequential valve gates and insert molding are utilized every day, there is a culture shock.
 
Understanding processes and limitations in both molding and tooling will broaden their knowledge, bridge the gap between theory and industry, and create some bonding between all departments, helping eliminate the perception of engineering sitting in the ivory tower and throwing projects over the wall.

Never before has there been a greater premium placed on accuracy, quality, and speed than there is today. Customers have a choice of vendors, and the winners of the battles for business will be those using knowledge, hard work, and technology to support their customers, gain their trust, and earn their business. A proper analytical approach saves time, and time is money.