Case Study | Case Hardening for Production Quantities:
Bridge Tooling

Normally an Aluminum Tooling Mold’s life expectancy can be several thousand to 1 million + plastic parts if using an unfilled resin and simple part geometry. Difficult shut offs, undercuts developed by using mechanical slides, lifters or handloads does affect wear and tear on an Aluminum Mold.

With the right knowledge an Aluminum Mold can be groomed and enhanced in worn areas cheaper than a soft tool. A soft tool is a mold not made out of hardened or heat treated steel alloys. Even P-20, pre-tempered steel is considered a soft tool. This can be surprising to people, especially when we are all lead to believe that Aluminum is “soft” and “inferior”. Nothing could be further from the truth. Aluminum Tooling Myth 1 clearly shows that the hardness levels of Aluminum is comparable to P20.

Not All Injection Molds are Created Alike

PHOENIX PROTO inherited a customer’s problem P20 molding tool that was never able to run correctly, much less efficiently enough to justify the exorbitant cost of $125,000. This particular Mold was completed with 4 cavities, a hot runner system and cavity detail that was “Cut in Solid”. “Cut in Solid” means that you basically “get what you get” with no adjustments, and as is. On top of that issue, the P20 Mold was a very large one as was 4 feet high. A large tool like that would require a 400 Ton press. The actual component was the size of a bottle cap, about 1 ½ inches in circumference. That is an enormous amount of wasted material; a guesstimate would be ½ ton worth of unused P 20.

The size of the injection molding press needed was also overkill in the injection molding best known practices. Generally for cost savings, the smallest sized injection molding press is used. Especially for small parts that even as a family tool could be built to run in a much smaller injection molding press.

Poor Tooling = Lost Revenue

Generally you would expect that a 4 cavity Injection Mold would have a better piece price than a 2 cavity Injection Mold. This problem Mold experienced such a great amount of scrap that any output gains were essentially lost. To make matters worse, a hot runner system’s costs are generally justified through reduced scrap from runner waste and potential increased cycle times from not waiting on the part to cool.

Once again this Mold defied common Moldmaking 101 logic. The tool ran so inefficiently at a 40 second cycle with such large amounts of scrap the cost of the hot runner system was insult upon injury. Add in that the resin selected was Polypropylene. Unfilled resin’s generally run smoother in process than more complex filled resins. This tool seriously jeopardized our customer’s project from every angle.

New Aluminum Tooling

We normally will take a worn, problem, etc tool and fix it up. We then maintain it till end of life to help our customer’s bottom line while they are working with us to create a Aluminum Tool that will better suit their needs. In this case, PHOENIX PROTO recommended that we build a new Aluminum Mold in 7075 material. We suggested an Ampco core, and “case hardened” the cavity detail with a process called Nituff which took the Aluminum from an initial soft state,
to a 58 Rockwell hardness. The hardness process penetrated the aluminum just .0003 which treated it as a case hardness and protected wear surfaces and life expectancy. We also used a cold runner system (Tri-Plate with a single gate drop) to further reduce cost for our customer.

Faster Cycles and Less Scrap from Aluminum Tooling

The new Aluminum Mold reduced the original cycle time from 40 seconds to 24 seconds. Scrap was also reduced as the process ran smoother allowing for even fills on every part shot. Aluminum’s natural thermal conductivity reduces “hot spots” and “cool spots” in a Mold. Aluminum heats and cools evenly, which is why it is a favorite in the Cookware Industry. The reduction in cycle time and scrap took the piece price from $0.15, down to $0.12. That might not seem like much, but when multiplied by several hundred thousand it adds up.

800,000 Plastic Components From a Aluminum Mold

We initially guaranteed the mold to run 250,000 parts since the resin to be used was Polypropylene. The customer eventually was able to get 800,000 parts with regular maintenance and grooming. This new Aluminum tool saved our customer thousands of dollars, not just in part costs, but thousands of dollars in future mold repairs from the original steel mold.

Cost Savings of Aluminum Prototype -vs- P 20 Steel Alloy
Description Price EAU Program Life – 4 YR’s Cycle Piece Cost
4 – Cavity Production Mold $125,000.00 200,000 800,000 40 $0.15
P-20 Cavities
Hot Runner
Cam Slides
2 – Cavity Bridge Tool $39,000.00 200,000 800,000 24 $0.12
Aluminum Cavities
Ampco Cores
Cam Slides
Teflon Hardness Coated
Savings $86,000.00 $24,000.00
Total Savings $110,000.00

*Both Ampco® and Nituff® are registered trademarks of their respective owners.