Several different processes aim at better part quality and reliability. For example, MuCell’s process can improve snap-fit parts, common in automotive applications. Because there’s no pack and hold, and the cooling cycle isn’t as harsh, parts are more accurate in terms of joining correctly, said Braig.
Consistent, repeatable, molded part production can be ensured through Scientific Molding and Design of Experiments, said Ryan Katen, general manager of Micro Mold. “Scientific Molding is the only way to have a repeatable process molding environment, if controls stay within a certain preset window in the manufacturing process.” It’s common in more technical molding environments with critical requirements, such as automotive, aerospace, and medical.
Designed for a polymer automotive front grille, this aluminum mold made by DRS Industries includes complex angles, eight slide/lifters, and a three-drop custom manifold. Featuring a Class A surface and an automotive specification grain where required, it demonstrates the abilities of aluminum tooling to make large, injection-molded parts.
Scientific Molding dissects the molding process into various components, to reduce, or eliminate as much as possible, any process variations, such as from one material lot to the next. Although it’s been around a long time, it wasn’t used frequently until the last 10 to 15 years, said Rob Cooney, manufacturing manager at Micro Mold’s sister company, Plastikos. With the increased pressure on US manufacturers to become more competitive and efficient, it’s become more of a requirement.
“If you’re not doing Scientific Molding, you’re not accounting for certain variables to ensure a process that has lot-to-lot repeatability,” said Cooney. “For example, customizing injection velocity is an important one. Another is hold time. If there’s too much hold time, cycle time will be too long, and if there’s too little, there will be too much process variation.”
Once a Scientific Molding process and baseline have been established, Design of Experiments comes into play. This approach tests the highs and lows of the impacts of intentional process changes such as warpage, or a part’s dimension, on the final part. It has become especially important during the last five to six years across all customer application areas, as the demand for increased quality and continuous improvement has risen, said Cooney.
Quality requirements are higher in industries such as medical and electronics, where tight tolerances and specifications must be met. “Form, fit, and function are critical dimensions on these parts and must be met 100 percent of the time, with no exceptions,” said Cooney. He continued:
For medical, there’s a long, comprehensive qualification process. Manufacturers have to prove they’re capable of producing parts consistently over a long-term period and everything that happens in production must be traceable. While strict, the requirements for even military and aerospace are not as stringent as medical applications.
In several industries, OEMs are converting parts from metal designs to plastic designs to reduce size and weight. As material development has continued to produce better mechanical properties in thermoplastics, they have replaced a lot of metal parts in the automotive industry, as well as in appliances and power tools, said Braig.
Metal-to-plastic part conversions are also occurring in medical equipment. For example, one Plastikos medical OEM customer wanted to explore more cost-efficient methods for producing a component within one of its medical pumps. The brass part had traditionally been machined, a costly and time-consuming process, said Cooney.
How else can you design a part to be manufactured without understanding the capabilities and limitations of the manufacturing process? Evidently it has been done, but it doesn't make sense. It seems that others have thought differently over the years, which is probably the basis for the whole "DFM" group of consultants who try to solve problems for those designing hard to manufacture parts.
Injection molding has been one of those areas where the first step of part design has been to determine the capabilities needed to produce the part features while designing those same features. That would determine which supplier was selected as well as what features of the part could be included. An analogy is deciding what one would ,ake for dinner based on what food was on hand and what was available to cook it with.
Theoption of including secondary operation types of actions while the part is molded is quite interesting, and it would allow a number of additional options for the initial design process.
Interesting point on the improved mold performance using aluminum due to its improved thermal conductivity. Do you know what type of aluminum they used? (QC-7?)
The use of Scientific Molding is a great way to produce repeatable parts on multiple machines. Documentation of separation of pack and hold as well as a documented gate seal study helps to produce parts consistently on different machines.
In regards to aluminum tooling, what is the effect of glass filled reins on the aluminum mold? Often times, it is necessary to use glass filled resins for metal replacement projects.
Ann, I assume your statement regarding aluminum or steel in the first paragraph is incorrect considering the text of the rest of the article. It is an interesting one, by the way. Recently there was an article on this site on Metal Injection Molding (MIM), which had a poor reputaiton, but has seen great improvements.
One observation is about the statement about increased pressure on manufacturing. This is a common statement, so my comment is not aimed at your article, particularly. There would be no increased pressure without advances in science and engineering. The statemnt seems to imply that these industries are standing still and being pushed by someone else. In reality US industry is among, if not the most , efficient in the world.
Another interesting point in your article is about the Scientific Molding process. I once worked for a company that made simulators, primarily for training. These included flight, military as well as industrial simulators. In general, the simulators were very accurate. They could often be driven faster than real-time. A secondard market was found for the industrial simulators in plant control. The simulator could run many scenarios with different feed stocks, etc. This would allow adjustment to the process before acutally consuming anything.
Finally, your article points out the need for design for manufacturing. Before the move toward outsourcing, there was a move toward integration. If you could design a part to be more easily manufactured, and you did it in the design phase, it was a very inexpensive change. If this had to be addressed later, it would be very costly. Perhaps we are moving back.
I heard an example of this recently. A manufacturer of space heaters, I think it was, brought their manufacturing back to the US. By a small redesign, one that eliminated a lot of fasteners, they were able to lower the time to manufacture. Since their market was mostly here, and since they could make changes to respond to market conditions more quickly, they have improved their competitiveness. A god example, I think.
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