HOW MUCELL® MICROCELLULAR FOAMING TECHNOLOGY FOR INJECTION MOLDING MAKES THINGS STRONGER AND LIGHTER

The MIT-developed technology, called MuCell, makes plastics super strong but extra light.

Here's one thing that often gets lost in the shuffle when debating the sexier points of green transportation: the simplest way to make a car, plane, whathaveyou more eco-friendly is just to make the whole damn thing lighter. All well and good, but how do you make sure that those industrial-grade plastic parts maintain their strength once you lighten them up? A technology developed at MIT called MuCell, and now being explored by automakers like Ford and Cadillac, has an answer. And that answer is: just add bubbles.

No, seriously: adding tiny bubbles of nitrogen or carbon gas into the normal injection-molding manufacturing process results in plastic that's just as rough-and-tumble, but up to 10% lighter (according to estimates from Ford Motors, who's very keen on using the technology). But wait: how does removing material from the part with these bubbles not make it weaker? The truth is that designers always massively "over-spec" the mechanical tolerances for these parts -- usually 50-100%. So the relatively small reduction in material strength introduced by the bubbles is negligible, because the part was designed from the get-go to be much stronger than it'll ever need to be in practice.

Still, that 10% weight reduction could help Ford meet its goals of eventually shaving off anywhere from 250 to 750 pounds from an average car. Ford is hoping to incorporate the MuCell-made plastic into all its vehicles by 2020. Luxury brands like Cadillac are circling, too. So why are they suddenly interested in MuCell's microcellular foaming technology, which was actually invented nearly two decades ago at MIT before being commercialized by Trexel? Two simple words that matter now much more than they did in 1995: "Sustainability initiatives," says Levi Kishbaugh, VP of Engineering at Trexel. "Automakers like Ford have sampled the MuCell process over the past decade and have achieved good results, and now they are taking the next steps toward widespread adoption." Kishbaugh says that when MuCell is incorporated into part design and mechanical tolerances from the get-go (rather than applied downstream in the process), even greater weight reductions can be achieved while maintaining part strength: "20% or even more in many cases."

Bonus: Not only does MuCell result in weight-optimized designs, it also uses less manufacturing material too. (Bubbles are mostly empty space, remember.) This isn't to say that car manufacturers should give up on next-gen battery technology and other gee-whiz green engineering initiatives. But the small stuff -- like zillions of microscopic nitrogen bubbles in a Ford manufacturing facility -- matters, too.

COMMENTARY:   The MuCell Molding Technology is licensed by Trexel, Inc., Woburn, MA, the world leader in the development and commercialization of the MuCell Molding Technology. MuCell Molding Technology is available as a retrofit to installed injection molding equipment and as an option on selected new injection molding machines (only on licensed OEM's). All MuCell-capable machines--new and retrofitted--are also capable of conventional, non-foaming operation.

According to Trexel engineer Levi Kishbaugh, the Trexel MuCell™ microcellular plastics injection molding technology conversion kits average between $150,000 to $300,000 per plastic injection molding machine.  All installation and training is done onsite by Trexel engineers.   

Trexel's MuCell microcellular plastics injection molding technology is patented, offers barriers to entry, offers lower plastics material melting viscosity (energy savings and faster injections), generates savings in both materials and producing cycles, does not require any changes to existing raw materials, and the payback period is quite impressive.

Trexel markets the MuCell foam injection molding technology products to OEMs and end-users through a network of sales representatives located in the U.S., Germany, Australia, Japan, China, Korea and Singapore. 

Trexel began as Axiomatics Corp in 1982 and changed its name to Trexel, Inc. in 1996.  Trexel is located in Woburn, Massachusetts, investor and employee privately owned, claims to have over 300 MuCell plastic injection models installations, and the President and CEO is Steve Braig.   Revenues are not available.

Courtesy of an article dated April 1, 2011 appearing in Fast Company Design

====================================================================  

The following information was "lifted" off of Trexel's website.   Looks like the techies at MIT are on to something, and Trexel is going to make a lot of money, while helping manufacturer's make things faster, lighter and more economically.

The MuCell™ Molding Technology

The MuCell™ Molding Technology uses low-cost, environmentally friendly supercritical fluids (SCFs) of atmospheric gases (CO₂ and N₂) as physical blowing agents to produce a low viscosity polymer melt. This low viscosity melt is subsequently used advantageously by the molder to reduce cycle times, improve dimensional stability, produce microcellular foam and to reduce weight of most injection molded parts. Initially developed as a method of producing relatively thin extruded sheet and tubes, the MuCell Molding Technology now encompasses a broad range of patented molding techniques that can reduce product costs, improve processability and increase the performance of molding machines.

Processing Improvements

Many processing enhancements are possible with the new MuCell Molding Technology, resulting in attractive cost savings for molders. For example:

• The use of SCFs as blowing agents with the MuCell process lowers the viscosity of the material by up to 50%, which allows for substantial decrease in melt temperatures (as much as 78^o on the centigrade scale, 140^o on the Fahrenheit scale)¹ while maintaining flowability.^{2 
  1}In tests, polypropylene (PP) dropped from approximately 430^o to 300^o F (approximately 220^o to 150^o C), polystyrene (PS) dropped from approximately 430^o to 260^o F (approximately 220^o to 125^o C), and polysulfone dropped from approximately 700^o to 560^o F (approximately 370^o to 295^o C). 
  ²With 0.020 in (0.5 mm) PS plaque, the standard mold filling flow-to-thickness ratio improves from 50:1 to 270:1.
• Because of the low melt viscosity in the MuCell process, the injection pressure can be reduced up to 50%, as shown in Figure 1:

• The low melt viscosity in the MuCell microcellular process permits molders to reduce clamp tonnage up to 60%. Consequently, molders can increase the number of cavities without increasing clamp tonnage, which can significantly improve production efficiency. Likewise, larger parts can be molded without increasing clamp tonnage, which also can improve production efficiency.
• Because of the uniform and controlled internal gas pressure inherent in MuCell Molding Technology, the MuCell process can eliminate sink marks while either reducing or eliminating hold time.
• The combination of low viscosity, uniform internal gas pressure, and low molded-in stress results in much lower post-mold warpage. Because of these attributes, the MuCell process typically results in a significant reduction in cooling time and thus cycle time.
• Because of the low injection and clamp pressure requirements of the MuCell process, it is possible to switch from steel molds to aluminum or other lower-cost materials and more-cost-effective methods of manufacturing.

Product Improvements

The advantages of microcellular foam material result from the uniformly sized and evenly distributed microscopic cells. With the MuCell Molding Technology, molders can foam complex, three-dimensional objects with solid skins and microcellular foamed cores (skin/core cross sections) with excellent dimensional tolerances. The MuCell process permits molders to produce parts with substantially lower densities than with conventional foam molding technologies.

The controlled weight reductions characteristic of the MuCell process can be quite impressive, as illustrated later in this paper in the applications section.

The MuCell™ Process Expands Molding Capabilities

Generally molders use foamed materials and weight-reducing processes (such as gas-assist) for two primary purposes: to reduce product costs and to improve product quality. Cost reductions and product quality improvements are achieved in a number of ways, including reducing raw material, improving processing (e.g., reducing fill pressure and reducing cycle time), and enhancing product characteristics (e.g., eliminating sink marks). The application and effectiveness of conventional foaming, gas-assist, and other technologies, however, are often constrained by cost limitations, control complications, product-design challenges, and other factors. Trexel's successful adaptation of the MuCell™ technology for injection molding gives molders expanded capabilities. With the MuCell process, product designers can specify lightweight, polymer-saving molded foam materials for products for which conventionally foamed materials would be impossible and for which other lightweighting techniques (such as gas-assist) might be ineffective or not cost effective.

MuCell Molding Technology and Conventional Foaming

Only a very small percent of injection molded products are foamed today, perhaps less than 5%. In addition, injection molded products that are foamed are generally limited to 0-5% weight reductions. In comparison, the MuCell microcellular molding technology can achieve density reductions of up to 60%.

The use and expansion of conventional thermoplastic foams is limited primarily by the large size of the cells that characterize materials produced by standard foaming techniques and the lack of uniformity of those cells. Large cells necessitate relatively thick part cross sections to ensure that the cells are contained within the material, which prevents thin-wall foaming. (Thin cross sections are often flawed by breaks and holes.) In addition, large, non-uniform cells introduce brittleness, which decreases mechanical properties (e.g., strength, toughness, and fatigue). In contrast, the microcellular foam material produced with the MuCell Molding Technology does not contain large voids. For instance, while thin wall foaming below 0.100 in (2.54 mm) is seldom successful with conventional foaming processes, the microscopic, uniformly sized cells produced by the MuCell microcellular foam process enable molders to foam materials with cross sections as thin as 0.020 in (0.5 mm). With the MuCell Molding Technology, molders can produce high-volume, thin-wall parts without significant loss of mechanical properties.

Traditional foam processes also can produce material inconsistencies due to the inherent difficulty of controlling the levels, uniformity, and release of blowing agents (such as in the use of CBAs). The precisely controlled-MuCell process, however, improves consistency and reduces variability.

The MuCell microcellular foam process is less sensitive to material composition than conventional foaming processes, which enables molders to use more cost-effective resin grades. Since the blowing agent is not "ignited" to liberate the gas in the MuCell Molding Technology, all materials can be foamed with the same atmospheric-gas blowing agents, without limitations caused by high processing temperatures. For example, high-temperature materials such as polysulfone and polyehterimide-which are difficult to foam with conventional techniques-are suitable for the MuCell process. (With the MuCell Molding Technology, weight reductions of up to 25% on parts with wall thicknesses of 0.100 in/2.54 mm have been achieved with these high-temperature materials.)

The MuCell Molding Technology and Gas-Assist

Although gas assist is an effective technique for both reducing product weight and improving product functionality, the technology is limited by bubble placement, bubble size, and part complexity, which generally restricts the use of gas assist to the production of thick parts (unless special part designs are used). With the MuCell Molding Technology, the entire part is foamed with microscopic cells, without requiring the injection of holes or voids, as in gas-assist. Because the MuCell molding process is a precisely controlled density-reduction process, weight reduction is achieved without the need to address either gas bubble placement or size. In addition, control of closed-loop gas voids is eliminated since the cross-section structure is homogeneous.

The MuCell process is not limited by part complexity. Because the MuCell microcellular foamed structure is homogeneous, it is not necessary to design methods of injecting gases. (Few if any modifications are required to existing molds to apply the MuCell Molding Technology.) With the MuCell Molding Technology, the weight reduction is uniform and consistent and occurs throughout the part.

As noted above, the MuCell process is suitable for thin walling. While gas-assist generally is not effective for parts thinner than 0.150 in (3.8 mm), the MuCell technology can be applied to complex, three-dimensional parts, with sections as thin as 0.020 in (0.5 mm), and once again no major mold modifications are required.

Advantages attributed to gas-assist processes--such as a reduction in fill, pack, and hold pressure and a resultant reduction in clamp tonnage--are also realized by the MuCell process, but for different reasons. In gas-assist, the injected gas provides some of the fill, pack, and hold pressure (thereby reducing the overall pressure); in MuCell processing, the overall pressure is reduced because of the low melt viscosity and internal gas pressure.

Applications of the MuCell™ Molding Technology

The MuCell Molding Technology is suitable for a broad range of thermoplastic polymers. Because the MuCell process uses an inert gas it is less sensitive to material composition than conventional foaming processes and more-cost-effective resin grades often can be applied.

Trexel has applied the MuCell™ microcellular foam process to numerous applications on commercial injection molding equipment in Trexel's production-scale test laboratory. To date, the high-temperature engineering resin polyphenylsuflone (trade name Radel), nylon, polycarbonate (PC), polycarbonate/acrylonitrile butadiene styrene (PC/ABS), polyethylene (PE), Acetal, polypropylene (PP), and thermoplastic elastomers (TPEs), such as Santoprene and Kraton, have been foamed.

Currently, extruders and molders around the world are developing and introducing new and innovative microcellular foam products for a variety of industries, including the automotive, medical device, consumer goods, and electronics industries. Applications for injection molding microcellular foam material include a wide range of automotive, food service, and electrical markets.

Analysis of cost reductions due to MuCell

Figure 5 demonstrates from actual applications how MuCell has reduced costs. Obviously, cycle time and material reduction has been the greatest benefit for the applications run to date, but other significant cost reductions include colorant reduction, energy consumption reduction and tooling costs.

On each commercial trial run with MuCell, the customer has performed a Return on Investment analysis. Figure 6 is a summary on some of the parts run along with their savings / year and payback of the initial investment in terms of time. As you can see, the savings per year is based only on cycle time or material savings. Ancillary savings such as reduced energy consumption or reduced capital cost is not considered.

Implementing the MuCell™ Molding Technology

The MuCell™ microcellular foam process follows four basic steps:

1. Gas dissolution: A supercritical fluid (SCF) of an atmospheric gas is injected into the polymer through the barrel to form a single-phase solution. Equipment designed for the MuCell process allows for the rapid dissolution rate required.
2. Nucleation: A large number of nucleation sites are formed (orders of magnitude more than with conventional foaming processes) where cells will grow. A large and rapid pressure drop is necessary to create the large number of uniform sites.
3. Cell growth: Cells are expanded by diffusion of gas into bubbles. Processing conditions provide the pressure and temperature necessary to control cell growth.
4. Shaping: Mold design controls part shape. No modifications are required for most molds.

Equipment

The MuCell™ molding technology can be retrofitted easily to installed equipment with low-cost hardware and software modifications. Adapting the MuCell process to injection molding requires the following changes or additions:

• A SCF metering system with sufficient capacity to deliver the blowing agent to the screw at the volume and pressure required for the MuCell process. (Trexel's Equipment Division supplies properly configured pump systems for SCF delivery and other proprietary components to licensees.)
• A Trexel-designed screw for creating a single-phase solution of the blowing agent and polymer and possibly a new barrel.
• Minor software and system modifications to create and maintain the uniformity of the single-phase solution throughout the injection molding cycle.

Trexel has entered into commercial license agreements with Engel, Inc., Milacron, Arburg, Ferromatik, to supply new injection molding equipment capable of utilizing Trexel's proprietary MuCell™ microcellular foam process. Retrofit packages for installed equipment are also available on selected equipment. Additionally, EPCO has also taken licenses and is capable of retrofitting installed equipment. As noted above, all MuCell-capable machines--new and retrofitted--are also capable of conventional, non-foaming processing.

 

 

Conclusion

The MuCell™ molding technology permits molders to produce new and innovative products while reducing product costs. The MuCell process can be used to mold complex, thin-walled microcellular foam parts with dramatic weight reductions. Product improvements include the elimination of sink marks, lower post-mold warpage, and skin-core cross sections. Process improvements include reduced processing temperature, reduced injection pressure, reduced clamp tonnage, and reduced cycle time.

The MuCell Molding Technology uses supercritical fluids (SCFs) of atmospheric gases as physical blowing agents--not CBAs, hydrocarbon-based physical blowing agents, nucleating agents, or reactive components. The MuCell process, which can be retrofitted to existing equipment, is available in selected new injection molding machines; all MuCell-capable machines also can be used for conventional, non-foaming processing.

The materials and process savings associated with the MuCell Molding Technology will become even more pronounced during the next 3-5 years as products and tooling are specifically designed for this breakthrough technology.

Patents and patents pending in Asia, Europe, and North America cover Trexel's MuCell Molding Technology. 

By TwitterButtons.com  

 

Comments

[Cyan Merk]

Continuous progress and improvement on ideas and equipment is a good sign that the industry is still on progress and must be aware of these changes as long as there are chances.

[John Smith]

Plastic Injection Moulding is the most common method of quality plastic products and part manufacturing. It is ideal for producing high volumes of the same object. Thanks for sharing this nice and wonderful information about plastic injection moulding machine. Looking forward for more such blogs from your side.

[Tsven]

Has anyone yet to experience a corrosive result when molding long strand PP glass resin into a Dyna Blued injectin mold?

[Tommy]

Home Mold Testing,

Thank you for your feedback. Yes, the injection equipment must be of good quality in order for the MuCell injection molding technology to perform the best. Hope you will continue to visit my blog regularly. Tommy

[home mold testing]

Its necessary to use better equipment.I agree with your article.Its very helpful for all.

[Bill Palmer]

Can MuCell using PETE be used for manufacturing airplane parts for model airplanes? Can it make a wing 3'x8"x1.5" with a hard shell on the outside and a low density core on the inside weighing in at a few ounces?

[Tommy]

MTD, thanks for your compliments.

[MTD Micro Molding]

Thanks for sharing this article. The injection molding industry is very competitive. Therefore, it's important to continue to evolve and use the best equipment that's available.