Getting your parts at a consistent quality AND price are of course, your and your molder’s goal. Injection velocity is one process setting that can make or break your ability to do that.
While an optimum velocity (or velocities) would have been determined at the beginning of the mold’s production, with each start-up, variations in cosmetics may occur. A common tendency is to process visual defects out of the molding cycle. This is because the parts are scheduled, the mold is hung, and the production schedule cries out for these parts to be run. A look at any molding defect chart will show a reduction of injection velocity as a cure for defects like jetting, burns and flash.
The only problem with that is reducing injection velocity adds to cycle time. Adding to the cycle time means a variance to manufacturing standard. The processor may swallow that variance to standard the first time through, but subsequently the longer cycle time will equate to a price increase to you the customer. If no price increase is passed on, the molder makes less margin and has to make it up elsewhere or suffer. How do you not increase injection velocity? Problems like jetting, burns and flash are mold problems not processing problems. Look for a molder that has good mold maintenance; secondly look for a molder that has in-house capabilities and can address the issue mechanically rather than through processing.
Having mold design, maintenance and repair under the same roof as injection molding continues to stand out as a means to efficient operation, superior problem solving and a more efficient solution for both supplier and customer.