Scientific troubleshooting increases molding efficiencies

There are many classes in scientific molding principles, but when it comes to the troubleshooting aspect of molding, information on applying scientific principles is lacking. That was the impetus for Tim Worthington to help molders apply scientific molding principles to troubleshooting through his business, Tim Worthington Consulting (www.timworthington.com).
   
As a plastic manufacturing and engineering specialist, Worthington has seen many troubleshooting guides, but most are "generic” rather than specific or scientific. Typically, if parts start to go bad during production, technicians begin to try and solve the problem by adjusting the process, rather than analyzing the problem to see if it’s the mold and/or the process.

Given that both the mold and the process are key to molding conforming parts, invariably Worthington finds that process technicians will start trying to correct the problem by changing the processing parameters only.
   
“The tool is sacred,” Worthington told PlasticsToday. “Nobody wants to touch the tool. We’re the only industry that tries to solve a tooling issue by adjusting the process…crazy! If it’s a tooling issue, then fix the mold.”
   
Worthington has developed a flow chart as his Molding Defects Troubleshooting Guide, but he emphasized that it helps to have an understanding of scientific molding principles to understand his troubleshooting flow chart.

Overview of the scientific troubleshooting process.
   
“Scientific injection molding principles teach us there are four plastics variables that should be controlled and monitored for a robust process,” explained Worthington: actual plastic melt temperature, actual plastic pressure, actual plastic flow rate (velocity), and actual cooling rate/time. The word “actual” is paramount.
   
Worthington’s troubleshooting techniques must involve investigation within these four variables, which are broken down further to Mold and Process for troubleshooting analysis. The Process portion is composed of four stages: (1) material (proper drying & regrind control), (2) heating (correlates to actual melt temperature), (3) filling (correlates to plastic pressure and flow rate or velocity), and (4) cooling (rate and time). The Mold portion is composed of hot manifold versus conventional runner system with overlaps in both with regard to cavity balance.

The steps for this analytical troubleshooting approach are quite simple:

1)    Define the problem: what is the actual definition of the specific defect? “Everyone has a different definition – be in agreement and on the same page,” Worthington said.
2)    Conduct the trend data over time – data determines decisions NOT emotion. “Once you define the defect, collect the trend data over time, which must be cavity or cavities specific,” he said. “If you don’t do that you’re spinning your wheels. If it’s a cavity-specific problem, then it’s probably a tooling issue.

“For example, does the defect occur every shot on a specific cavity only or does the defect occur every shot randomly on a specific cavity only or does the defect occur on all the cavities randomly, and so forth,” said Worthington. “Also is the mold a hot runner or conventional runner? Is it a family mold or a multicavity mold? Determine if it is Mold (cavity specific) or Process related.
   
“If it’s a cavity-specific problem, don’t change the process,” Worthington stressed. Never process around a specific cavity defect as you will be compromising all the other good cavities to eliminate a defect on only one cavity. “If the problem is random among cavities, it could be a process issue as well as a tooling issue.”

3)    What is the CAUSE of the specific defect? Use deductive reasoning to determine the cause. List all the probably causes of the defect and eliminate as per the Trend Data Over Time collection.
4)    The FIX is the easy part once the first three steps have been completed.  Do not be in denial, if the mold requires fixing, do it.
   
Too often solving molding/processing problems is done by trial and error rather than by scientifically analyzing the variables, collecting the trend data over time, and approaching the problem with science. “Do everything analytically – use deductive reasoning to determine the cause of the defect.”