Structural foam plastic molding is an injection molding process that utilizes a foaming agent that mixes with the base resin in the polymer melt before being injected into the mold. This mixture becomes a combined polymer/gas melt. This process allows for less volume of plastic than a solid injection molded part to completely fill the mold, or a “partial fill” method. The lesser polymer volume requires less clamping pressure on the molds. This is often described as a low-pressure molding process. Due to the lower pressure and forces involved, the structural foam process allows very large parts and/or multiple parts to be produced on a single machine and in a single cycle. Additionally, cost-effective tooling solutions can be utilized for these large or multi-cavity molded products.
As the foamed plastic flows through the mold, the surface cells burst and a solid skin is formed against the walls of the mold while the core of the part cools to a cellular structure. This results in a part that typically weighs 20% less than a solid plastic part, is 3 to 4 times more rigid, and is produced with less molded-in stresses. Parts may weigh up to several hundred pounds.
From a conversion perspective, structural foam molding can replace wood, metal, concrete, and fiberglass. It can also have significant advantages in relation to alternative processes such as rotational molding, die-cast, stamped metal, smc, thermoforming, rim, and fiberglass layup... The results? Significant reduction in cost and increases in productivity.
The structural foam process allows the production of rigid plastic products which have a cellular foamed core surrounded by an outer skin forming a total integral structure. Products molded with the structural foam process have a high strength to weight ratio and are 3 to 4 times more rigid than solid parts of the same weight.
There are numerous benefits to selecting structural foam or gas assist molding. Structural foam molding is an excellent conversion alternative for wood, metal, concrete, and fiberglass. It can also offer a significant ROI in comparison to other processes such as rotational molding, RIM, thermoforming, die-cast, injection, and SMC. The result is a significant reduction in cost and a vast increase in productivity. The following are the key benefits of structural foam molding:
- 20% less weight than high-pressure parts
- 3-4 times more rigid than solid parts
- Substantial cost reductions
- Low mold cavity pressure allows lower-cost tooling
- High stiffness-to-weight ratio
- High dimensional stability
- Capable of molding parts as thin as .156″ thick or greater
- Low warp and part stress
- Multiple molds can run simultaneously
- Functions as an excellent substrate for high quality painted finish applications
- Virtually any thermoplastic can be foamed
- Multi-nozzle Structural Foam
- Single-nozzle Structural Foam
- Gas Assist Molding
- Gas Counter Pressure
- Structural Web
The gas assist molding process utilizes nitrogen to hollow out large, thick, wall sections. The gas does not mix with the resin but instead forms continuous channels through the hotter, less viscous, sections of the melt stream. This allows molding of thick wall sections without sink marks and without the characteristic swirl appearance of structural foam.
In gas assist molding, the gas will displace the polymer in thicker areas to hollow out the part. The nitrogen gas does not mix with the resin but instead forms a continuous channel through the hotter, less viscous sections of the melt stream. The gas maintains internal pressure throughout the cooling cycle.
The process is a low-pressure injection method. A “partial fill” method of resin fill is used. The gas is then utilized to fill and pack out the remainder of the part. The nitrogen is typically injected into the process at relatively low pressures. At DeKALB, we utilize Uniloy Springfield Structural Web and Bauer Gas Assist technologies in our processes.
Key Benefits of the Gas Assist Molding Process
- Design freedom utilizing thick and thin wall sections
- Hollow gas channels increase stiffness and reduce cooling time
- Improved aesthetics (low warp, no sink marks, etc.)
- Reduced cavity pressure equals lower tonnage, more efficient machines
- Significantly reduced cooling and overall cycle time
DeKALB Molded Plastics is proud of the world-class quality reputation that it has established in the structural plastics industry. Our team is dedicated to providing products and services that exceed customer expectations with a high focus on continuous improvement. Our high commitment to quality is achieved by adhering to clearly defined standards that help to control all process variables.
To ensure all products consistently meet your expectations, our highly skilled team is trained to utilize the most modern methods of quality assurance:
- ISO 9001:2015
- Statistical process control
- Team-oriented problem solving
- Gage R&R studies
- Continuous improvement
- Dimensional layout
- Gage measurement systems
- Advanced Quality Planning (AQP)
- Color measurement system