Today’s manufacturers need sustainable manufacturing methods. But these techniques must not only conserve resources and result in a smaller carbon footprint, they must also be efficient and produce high-quality parts. This is the reality driving Freudenberg-NOK Sealing Technologies’ efforts to continuously improve net-shape molding technology.
Net-shape molding produces molded parts in such a way that the initial molded part is very close to the final, or net shape. The closer the initial part is to the final shape, the less scrap is produced. The ultimate goal is zero engineered waste. Not only does net-shape molding reduce the use of valuable resources, it eliminates finishing steps required by conventional molding methods. All told, we have found that the net-shape molding process is not only cost-effective but more robust and sustainable than other molding operations.
When we set out to implement our net-shape molding process, we found we needed improvements in three critical areas to achieve better quality and flexibility on behalf of our customers. These included increasing our understanding of material behavior; improving the valve-gated injection molding process; addressing injection-molding machine controls.
We first had to address our understanding of how our materials behaved during the development of the molding process. By critically measuring material properties, such as shear viscosity, density, and the pressure/volume/temperature (PVT) relationship under controlled lab conditions, our material scientists were able to develop accurate mathematical models that predicted how various materials behave during molding. To verify and improve these models, they then developed experimental procedures and molds to verify their findings.
Once the scientists were satisfied with the accuracy of their models, our manufacturing engineers used them to improve mold designs and the valve-gated injection molding process. For example, they used the simulation results to optimize the number of drops to include in the mold, sprue dimensions, and vent placement. Simulation results also allowed the engineers to select appropriate processing conditions, such as material temperature and injection speed.
In parallel with this work, we determined that we needed to improve our machine controls. One of the issues we were trying to control was the ongoing and unexpected interruption and shutdown of the molding machines whenever there was a system software update. While it’s a good practice to keep your software updated, the downtime we incurred was unacceptable. To resolve this issue, we isolated the machines from the company network, thus preventing system shutdowns. We also improved the man-machine interface. Instead of a separate display for the controllers and the injection molding machines, we developed a single user interface.
Perhaps one of the biggest changes we have made with our net-shape process has been our ongoing migration away from large multi-cavity injection molding machines to compact, single-cavity injection molding machines. These smaller, more nimble presses allow for more precise control of variables like pressure and temperature. Rubber does not have to flow as far in a single-cavity mold as it does in a multi-cavity mold. This means that we can run the process at a higher temperature, thus cutting cure time. Cycle times with the single-cavity molding process have been reduced compared with multi-cavity molding. We have also developed our own tooling and machine concepts to further optimize the single-cavity process.
Additionally, when multi-cavity machines break down they can take a significant portion of the plant’s manufacturing capacity with them. By using redundant single-cavity presses to produce components, we have improved our manufacturing flexibility and established a robust ability to maintain our manufacturing when we experience issues with one of the single-cavity presses.
Collaboration between research and development, engineering and manufacturing proved essential to improving the net-shape process now benefiting our customers. Continuous improvement and innovation remain the foundation of all of our industry efforts.
This article was first published in the December 2016 edition of Manufacturing Engineering magazine. Read “Quality, Sustainability Drive Net-Shape Molding Efforts” as a PDF.