CASE STUDIES
Mack Molding
The selection of case studies shown below represents only a few examples of Mack Molding’s industrial manufacturing services and how they have helped customers resolve challenges and move product to market. It is not intended to provide a comprehensive listing of Mack Molding’s involvement in any industry.
Air Conditioner Base
Improved performance. Lower part cost. Fewer tools. In a compression-to-injection conversion of a residential air conditioner base, Mack Molding accomplished all three.
It takes a lot of confidence to walk into the offices of the country’s largest residential AC supplier and suggest that you can replace an integral component of their top-seller with a part that is just as good, but less expensive. Especially when that component has already gone through a major conversion from metal (100% controlled in-house) to compression molded plastic. Especially since that conversion required a major inside sales effort. And especially when that compression-molded product had yet to experience even one failure in the field.
But Mack Molding personnel, backed by a technical team with extensive knowledge about polymer performance, plastics processing, and computer modeling that confirms the plastic injection molding solution, were convinced the base could be produced with the same or higher quality at a lower price. (On left: To demonstrate the part’s muscle, engineers parked a Suzuki Vitara on top of two injection molded bases without damaging the parts.
Today, most AC bases are still formed from metal. But there’s a problem with rust. So many OEMs are beginning to look at plastic replacements to gain corrosion resistance and the ability to consolidate several parts into one. Compression molding has been one option because it yields excellent strength-to-weight ratios by blending relatively inexpensive commodity resins with glass. But there’s room for improvement.
In this particular case, there were four significant challenges – cost, structural integrity, UV stability, and a seamless integration of the injection part into the production line.
Reduce costs by 15%
Compression molded material is inherently stiff and fairly low-cost. Processing, press tonnage and tooling were Mack Molding’s three opportunities to reduce overall costs on this program.
First, injection molding eliminated the machining that was necessary with the compression part. Previously, about 50 openings had to be machined into the solid molded part. The base was redesigned for injection molding, with Mack Molding adding lifters, shutoffs and core pins in the tool to incorporate all the previously machined features and eliminate that process.
Savings #1
Next, gas-assist was chosen to add more structure to the part. Injection molding material generally doesn’t have a flex modulus as high as compression molding material. Mack Molding was able to make up the difference by using gas-assist, which located tubular gas channels throughout the base and gave a structural cross-section to the part. This also allowed Mack Molding to mold the base in a smaller press with less clamp tonnage.
Savings #2.
Today, there are three different base sizes that run in presses ranging from 700-1500 tons. All molds are filled from a single gate.
The final cost-saving opportunity was in tooling. The OEM was rebuilding the compression tools after every 100,000 parts or so. With plastic injection molding, Mack Molding estimated the tools wouldn’t need to be rebuilt until after 250,000 pieces.
Savings #3.
Mack Molding is running seven molds – three for the largest base, which is the highest volume; two for the medium-sized based and two for the smallest. The Company can also handle the OEM’s volume expectations with fewer tools than that required for compression molding. Not only do compression tools have to be rebuilt more frequently than injection molds, they also require a longer cycle time to mold the part. Gas-assist injection molding resulted in fewer tools overall, all of which have a longer lifespan.
The bottom line? A total part cost savings of 15%.
Improve performance
Beyond lower part cost, lower tooling cost and longer tooling life, gas-assist injection molding offers more detail and better resin disbursement than compression molding. This is particularly important when using a glass-filled material, which is often required for structural applications.
When compression molding the AC base, the resin tended to move down into the bottom of the ribs, while the glass primarily remained in the main level of the part. So when the part had a load placed on it, the bottoms of the ribs (where the glass didn’t reach) were inclined to crack. Injection molding produced a more homogenous glass/resin mixture that flowed throughout the entire part, so even the finest detail, including the ribs, had glass in it. This provided improved structure and strength.
The structural integrity of the part had to be proven through creep tests over 1000 hours at high and low temperature variations and a falling ball impact test. The material also had to be F1 rated for UV stability. Mack Molding sampled about 30 different resins – everything from 20-40% regular glass, and several versions of long-glass and glass-filled nylon – before settling on glass-filled polypropylene.
Mack Molding engaged in a significant R&D effort with several material suppliers that took many hours of press time, tons of material, hundreds of impact tests, and thousands of hours of creep testing to develop a custom-compounded material that met the product requirements. The Company also performed multiple iterations of moldflows to determine where to put the gas channels. In fact, Mack Molding did all the modeling for the injection design, including glass orientation modeling, gas channel placement and warpage.
Integrate seamlessly into production
The overriding goal was to implement this compression-to-injection conversion with minimal design change so the OEM could transition from old part to new without impacting production. Assembly line tooling, layout and work instructions had to remain the same.
Other areas where conversion from compression to injection molding should be considered include appliance, heavy truck, lawn & garden, and consumer products. This technology can apply to a lot of other applications, including heat pumps, swimming pool heaters, and any other outdoor appliance that sits on a base with electrical and mechanical components bolted to it.
For more information, contact sales.south@mackmolding.com.
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AC Cover
Up to $1.4MM Annual Savings, SPI Award
Due quality issues with the cosmetic top cap for its top-of-the-line residential air conditioner, the top became an ideal candidate for Mack Molding’s expertise.
The Challenge
In addition to cutting costs, the customer’s redesign team wanted to streamline manufacturing by consolidating the original multi-piece assembly into a single part. Formerly, the cover was built of five separate parts, requiring three molds to produce each part. The parts then had to be glued, often leading to loose louvers that contributed to a number of problems. As a result there were productivity gains that were possible just through mold reduction alone.
The Solution
The eventual new top cap design involved design, processing and assembly changes. Injection molding produces fast molding cycles for a high volume part with cosmetic requirements. External gas is also used, however, to produce the cavity texture and improve part ejection from the tool. External gas-assist molding also lowers the injection pressure required to fill the part, reducing press size requirements along with costs.
The material choice for the new design is a UV stabilized polycarbonate resin for strength, impact, long-term aging, cosmetics and the color stability required for an outdoor application.
The most impressive technical aspect of the project is reflected in the part’s geometry changes and how they work with the tool design. Slide lines in the tool combine with style lines on the side of the part, eliminating any interruption in texture appearance. Because the louvers are now integral to the part, its structural aspects and strength properties are improved. Most of the core side ribs that were previously needed have been eliminated, as well as the associated sink and flow disruptions.
The absence of any read-through on the top surface results in a better overall appearance. Additionally, there is better screw-hole alignment for assembly and increased structural integrity.
The bottom line? The redesign yielded a top cap that will cost up to $1.4 million less per year to produce. It also won the Building & Construction category of the Society of the Plastics Industry’s annual plastics design competition.
The redesign team included staff members from the customer, Mack Molding, Advanced Innovative Design and Delta Mold.
For more information, contact sales.south@mackmolding.com.
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Splice Enclosure
The Challenge
The Challenge- Replace existing splice enclosure, which had reached its limitations in both size and weight
- Achieve quick turnover from part design to market introduction
- Find a less expensive way to manufacture the product
The Solution
The customer’s new splice enclosure design replaces galvanized cast iron and steel with lightweight structural foam, engineering resin and strategic aluminum strengthening components. Designed by customer, the new box weighs 29 pounds, a 55 percent weight reduction from the previous design.
Through the combined efforts of the customer, Mack Molding, GE Plastics (Now SABIC) and prototyping specialists at Ferriot Inc. of Akron, Ohio, the new splice enclosure design was completed and the prototype introduced to the AFL sales force in less than two months. Once approved for production, Mack Molding coordinated a fast-track effort to develop, manufacture and commission the very innovative tooling required to produce the splice enclosure. The product was in full production less than six months after the first sketch was made.
This is an excellent example of how plastic can perform in markets currently dominated by castings and welded parts. Plastic has reduced the weight of this box from 65 pounds in its previous design to 29 pounds, a tremendous relief to field service personnel who are hoisting these units up utility poles to install them.
For more information on this or other Mack Molding industrial case studies, contact sales.south@mackmolding.com.
