Several considerations must be weighed during these conversions. Plastikos began its evaluation with prints of the part and two options: a single piece with molded threads, or a two-piece molded assembly.
Analysis revealed that the single-piece option with molded-in threads would need a tougher, stronger, more costly material to prevent the threads from tearing during the core-pull process. It would also mean a more complex, higher-risk tool design, which might cause difficulty during molding in filling out the threads with the stronger resin material. Instead, Plastikos recommended installing a separate threaded component after molding the part, for a relatively low cost and little complexity.
This option allowed the customer to use a more familiar material and a simpler mold design.
This example underlines the importance of engaging the mold making, molding, and material supply people, as well as the parts designer, up front, said Katen. “It’s best to get in with the customer early on, even when they’re at the paper napkin sketch stage. Several customers will say I have an idea -- is this feasible? What would you need to make it more feasible?”
For example, Micro Mold recommends part designers use consistent thicknesses wherever possible. A lot of thick-to-thin changes can cause problems in manufacturing, such as trouble filling out thicker walled areas.
The example also illustrates some of the controversy surrounding whether integrating multiple steps within a single molded part is always a good idea. There can be design engineering and design limitations to consider when incorporating more features into a tool, said Myers. “The industry has been seeing more multi-shot applications. But is the facility set up for it? Is the product’s application geared toward it?”
Reducing or eliminating post-processing handling does lead to reduced labor costs, said Clinton McDade, senior designer of plastic products for Schaefer Systems International. A single part from the machine that’s ready to package may look like the ideal solution from this perspective. “But to make this part in one piece, sometimes complexity must be added into the mold, such as moving slides to avoid die-lock,” he said. “This can lead to increased mold cost, longer part cycle times, and more downtime for mold maintenance, all directly affecting speed and cost. This one-part product may also require a higher tonnage machine, with its higher overhead rate.”
The two pieces of a two-part product can be made in less expensive, open/shut molds that run on smaller machines with lower overhead rates. On the other hand, manufacturing this final product requires two machines and two cycle times, in addition to the time required for handling and assembly.
“Regardless of how you juggle the manufacturing variables, the ultimate result must be a part that meets the customer’s functional needs,” said McDade. A two-piece product may make the most sense from the standpoint of manufacturing variables, “but if the product’s ultimate application subjects it to cyclic loading or temperatures, the fastening mechanisms could introduce a failure mode not present on a one-piece design.”
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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