Article From: MoldMaking Technology
Posted on: 12/8/2010

Myths have always been around: the world is flat and the sun revolves around the earth— to name a few. The world of manufacturing is no different with its own false beliefs. Today we have the myth that aluminum tooling is “junk tooling or for prototypes only”. This is a stereotype that has grown from earlier grades of aluminum—alloys that were gummy, difficult to cut and improperly used in a manufacturing environment.

The development of aircraft grade 7075 aluminum brought forth a durable and quality product. In 1998 the SPE and Douglas Bryce wrote “Plastic Injection Molding: Mold Design and Construction Fundamentals” that discussed the quality of 7075 and the capacity to produce millions of parts. However, many manufacturers did not follow his recommendations. Instead, many chose the wrong aluminum alloy and did not follow good tooling practices. Unfortunately, the damage to aluminum’s reputation had already been done.

Cost factors are forcing manufacturers and major OEMs to take a second look at aluminum. Back in 1991 IBM did a five-year study on aluminum tooling with many credible findings. Currently, Honda’s ongoing aluminum tooling study is a success and other companies are taking a renewed interest in the cost savings that aluminum has to offer. Unfortunately, old beliefs are hard to overcome.

Myth #1: Aluminum tooling is just for prototypes and low volumes

Aluminum can be used for production volumes: The mistaken belief that only steel alloys such as H-13, S-7, stainless steel or P20 steel should be used for production molds can be a costly one. An aluminum mold can provide volumes between 100,000 up to 1,000,000 components. This is due to current aluminum grades that are heat treated as part of their creation process resulting in a 6 – 18RC hardness. Surface coating treatments can harden aluminum up to 56 – 62RC depending upon the process. When these hardness levels are compared to P20’s 28 – 32RC and 420 stainless steel’s 34 – 38RC (pre-heat treated), this estimate of 1,000,000 seems conservative.

Myth #2: Limited resin types can be used in an aluminum mold prototype

All resin types can be used on aluminum: Aluminum’s excellent thermal conductivity allows resins to flow more evenly than steel. Certain resins like clear acrylics and polycarbonates often have processing issues due to hot and cold spots in a mold. Aluminum’s even heat dispersion reduces these areas resolving bubble and other aesthetic issues. Other high-temperature resins can run successfully in aluminum with cartridge heaters that are normally used with steel molds. Difficult-to-fill resins with a high viscosity rate also benefit from even heating as it reduces sheer stress upon the material by balancing the flow of material with a hot runner system. Glass-filled and other abrasive resins can be run with success as long as special care is taken to either hard coat or steel insert critical areas. Glass-filled resins can actually run more efficiently with aluminum due to its consistent thermal conductivity that assists in the flow of resin. PVC is often incorrectly believed to be abrasive, when in fact it is corrosive. That is why stainless steel alloys are chosen over P20. Both stainless steel and aluminum are corrosion-resistant by nature. Aluminum forms a 0.000001 (microinch) self-healing layer as a reaction to oxygen called aluminum oxide. The chromium in stainless steel reacts the same way to oxygen forming a layer called chromium oxide. Some of the newer grades of aluminum have chromium added for even greater corrosion resistance. There are surface hardening processes that work well with PVC that can increase component output.

Myth #3: Aluminum cannot be used for production quantities

The word “production” is subjective, as aluminum can achieve high volumes: How does “100,000 – 1,000,000 + production-quality plastic parts” sound? Not exactly short-run or low-volume. For many projects this is more than enough for the entire project until the next design change or upgrade. Of course higher production quantities can be achieved depending upon the resin and design. Aluminum tooling is also perfect for keeping marketplace share when bridge tooling is needed. An added benefit is that if the tool life is exceeded, aluminum is forgiving and easy to maintain or enhance in order to get those last few plastic parts until the hardened steel production tool is ready.

Myth #4: Aluminum tooling has limited textures and finishes versus steel alloy tooling

Unlimited surface finishes: Almost any surface finish or texture that can be applied to a steel mold can be applied to an aluminum mold. This includes Class A diamond finishes (SPI A-1), which are required for chrome plating. Certain grades of aluminum are more suitable for this, which may also require a hard coating process to enhance this finish. Bead blasting or any aesthetic texture finish can also be achieved with success.

Myth #5: Aluminum tooling has process issues

Faster process cycles: As mentioned above, the thermal conductivity is a benefit that eliminates many processing issues. Fast and even heating and cooling results in less shrink and warpage issues from uneven heat dispersion. Less scrap is a cost savings, but cycle times are also reduced by 30 percent on average, bringing down overall piece price. In order to run aluminum, a molder will need good tooling practices and maintenance routines to extend the tool life and fully realize all of the cost and time savings. This includes watching parting lines and shutoffs for wear to eliminate parts sticking and excessive wear. A sticking part can damage aluminum tools worse than steel. However, if the tool was built correctly and maintained to industry standards, it is not a common occurrence.

Myth #6: Can’t make tool modifications to soft tools like aluminum molds

Design modification: Commonly, many projects in the planning and design verification stages go through some sort of design modification. Aluminum could not be easier to modify or groom for maximum efficiency when during the build or when the tool is running parts, modifications to the initial design or to troubleshoot production issues are necessary. Welding aluminum has become very successful recently, which allows consideration for even cosmetic changes as well.

Myth #7: Aluminum tooling cannot handle complex designs

No design restraints: Complex design geometries that require under cuts, which require mechanical slides, lifters or hand loads can be done just like in a steel mold. Careful project planning, a strong knowledge of mold design, along with experience in machining aluminum means there is no reason to not expect aluminum to maintain critical dimensions. Steel inserts can be used to further maintain critical areas for higher volume projects. This can all be done in less time than traditional tooling because aluminum can be cut faster than other alloys.

Myth #8: Aluminum tooling is too expensive

Lower overall cost: Cost is the 800 lb gorilla everyone wants to talk about. While aluminum costs more per pound than P20 and other steel alloys, aluminum is lighter in weight so the cost per pound usually is less in total cost. Aluminum is easier and faster to cut than steel; and, polishes faster, which reduces build time by weeks with substantial cost savings. Even hard coating aluminum does not add to the final cost of the tool significantly. Improved thermal conductivity cuts down process issues, with less scrap and faster cycle times, which reduces the overall per piece price. Then factor in less machine wear and less electrical costs due to improved efficiencies. Moreover, when the tool is no longer needed, aluminum is easily recycled.

Summary

In today’s economy and business climate every company that wants to stay lean and competitive in the marketplace needs to seriously consider the cost savings from aluminum tooling. Although there have been many improvements in the grades of aluminum alloys, proper design, tooling and molding practices need to be considered to truly reap the benefits of this alloy. In 35 years of aluminum tooling, the last five have been the most notable due to the attention that aluminum has finally been given. Like most successful innovations that are born from the need to survive, aluminum tooling is not just the bridge to a faster product launch or the cost savings necessary for the planned budget; it is a successful alternative to steel tooling with huge benefits that will continue to advance and influence the future of the plastics industry.

Contributor:
Robert Lammon is Director of Operations for Phoenix Proto Technologies.

For More Information:
Phoenix Proto Technologies
(269) 467-8300, ext. 300
bob.lammon@phoenixproto.com
phoenixproto.com

Article From: MoldMaking Technology, Sherry Baranek , Senior Writer from MoldMaking Technology magazine
Posted on: 12/1/2008

“Using aluminum tooling instead of traditional tools steels reduces cycle time and costs, but requires up-front, open communications between moldmaker, molder, material supplier and hot runner manifold supplier.”

Moldmakers and molders looking to find an alternative to traditional tool steels should seriously consider using aluminum. Aluminum tooling offers a myriad of benefits: it is easier to cut and it cools at a much more rapid rate than tool steels, which reduces cycle times—resulting in reduced costs at the OEM level.

This article will present the challenges and benefits of using aluminum tooling from four perspectives: moldmaker, molder, material supplier and hot runner manifold supplier.

Mold Manufacturer

According to Chris Jones, president of Rapid Die & Engineering (Grand Rapids, MI)—a plastic injection mold manufacturer specializing in a wide variety of automotive components—aluminum tooling is gaining in prominence. “The end result of using aluminum tooling is to reduce costs to the OEM,” he emphasizes. “We do see a reduction in costs in the tooling—which will vary from molder to molder and how we build the tool. Each injection molder has their own tooling standards. The moldmaker must take this into account when quoting and ultimately building the mold. These tooling standards fundamentally drive the overall design and cost of the tool. But it can run anywhere from 15 to 25 percent savings on tooling, or greater, depending on simplicity.”

“Also, because of the ability to cool aluminum at a nice even rate, the theory is that cycle times will drop,” Jones adds. “Reduction in cycle time is dependent on each individual molder. Each injection molder has their own process (which can vary greatly depending on personnel, equipment available at that location and materials being molded). Their individual process can impact the cycle time. For example, some injection molders are looking at lowest cost tooling up front and not considering the piece part cost over the lifecycle of the production run. This can greatly impact cycle time. If using valve gates you can reduce cycle time and increase the process window, but they cost more up front. One molder may use valve gates whenever possible and another may not at all. The savings in tooling and a drop in cycle times will produce parts quicker.”

Another benefit is that it is easier to cut aluminum than steel. “You still have to invest in specialized tooling for optimal chip removal and you have to think differently with regards to processing, chip rate, chip load, etc., but the learning comes pretty easy. The major learning curve lies with the molder to teach their people to take care of the tooling and be gentle with it.”

As for the longevity of aluminum tooling, Jones points out that he has some tools still running with well over 100,000 shots on them. “The criteria for aluminum tooling is changing. In the past the mainstay was prototype tooling. You would get 50, 100 maybe 1,000 parts for all the testing and different departments and then build a steel production tool. Today aluminum tooling is being used for 50,000, 100,000 and even 200,000 shots for production. The average will depend on the demand. The demand (or volume) will dictate if today’s aluminum tooling fits the project. Throw into the mix modern surface coatings that can extend the aluminum tool life and you have yet one more thing to consider in the decision-making process.”

Molder

Mike Kleinert, Vice President of W.K. Industries (Sterling Heights, MI)—a full-service prototype and production mold/molding house that builds hundreds of aluminum tools per year—agrees with Rapid Die’s Jones that aluminum is an up-and-coming mold material, especially with prototype runs. “There seems to be a push in the industry to use aluminum for production tools,” Kleinert states. “There are good applications for aluminum tooling: for less complicated parts and parts that use a non-abrasive material like a polypropylene or a TPO, then aluminum is a good metal. However, when you get into higher volumes with more abrasive materials (e.g. glass-filled, ABS) that take a lot of pressure to fill a part, the aluminum is going to have a certain amount of life. The question is, ‘What is the life of tool going to be?’ and I don’t know that anyone has the answer to that. To guarantee an aluminum tool for so many pieces I would say is a risky statement.”

As for running an aluminum tool, Kleinert believes a little bit of vigilance goes a long way. “Any good molder recognizes that aluminum is obviously a softer metal than traditional tool steels so there needs to be a little more TLC,” he advises. “But you can’t be afraid of it either. It needs to be watched a little more than normal. It does require some additional awareness, but that is the case whether using aluminum or steel. Things can happen with either material, and the operator needs to be aware of what he is doing.

“It also is critical the mold be designed and built properly,” Kleinert continues. “Remember, the tool builder builds the tool, but the molder has to live with it. I think it is a great idea that all parties involved work collectively as a whole—that could save any finger-pointing later and ensure the molder is going to be more aware of what he will be receiving.”

Material Supplier

Anthony Negrelli, President of Clinton Aluminum & Stainless Steel (Clinton, OH)—a supplier of aluminum and stainless steel—notes that aluminum is now being utilized for production versus the old mentality of just for prototype work. “There are various grades of aluminum, and utilizing the correct grade of aluminum with number of parts required and plastic requirements will result in cost savings, he explains (see Chart 1).

Negrelli points out that a “leading” automotive manufacturer has performed a three-year study (see Benefits Sidebar) and found the following to be true:

The strongest aluminum is a 7000 series. The leading manufacturer had a third party study review various mill products.

Alumold produced by Alcan Aluminum and Hokotol produced by Aleris offer the highest, hardness, tensile and yield strength.

They recommend that an aluminum injection mold made from a 7000 series aluminum alloy can have a 2,000,000+ shot
life per tool [note: a 2618 cast aluminum (Duramold 2 and M1) has a recommended shot life of 100,000 hits].

There are some challenges to working with aluminum tooling, Negrelli adds, which include maintenance, the need to improve toolmakers’ skill sets with manufacturing an aluminum mold, and the need to continue to improve processes to texture and repair aluminum molds. The mills are working on improving the welding process for the 7000 series material, but still the current practices are acceptable. See Myths Sidebar for some common myths about aluminum tooling.

Manifold Supplier

Rich Oles, President/CEO of PSG Plastic Service Group, Inc.—a manufacturer of hot runner manifold systems and controllers—agrees that there has been a resurgence in the use of aluminum tooling in recent months. “We have had increased inquiries as to our experience and products offered for aluminum tooling.” Oles notes (see Figure 1). “This is a cycle we (along with our industry) have seen before. It seems about a decade ago there was a similar buzz in our industry. The major differences today are that new aluminum grades have increased performance and reliability, faster machines and software are available for designing and producing the molds, and a better understanding of the requirements of aluminum tooling and knowing the production goals give mold manufacturers a better direction.

“When you combine the above with early involvement (mold design phase) from the manifold supplier and moldmaker, the mold can be designed once to use standard manifold components that are typically lower in cost without sacrificing performance,” Oles continues (see Figure 2). “This is also the preferred method for all mold builds. Unfortunately it’s not the industry standard—yet.”

Currently when molding with aluminum tooling the most common solution for a runner system is the cold runner, Oles explains. “The reasons vary but the most common are cost and the general opinion ‘simple (overall design) is always better,’” he says. “With aluminum tooling having lower volumes in most cases, it becomes harder to justify the added cost of a hot runner manifold system.

“However, hot runner systems have a number of benefits that are not realized in most cases,” Oles continues (see Figure 3). “The general issues are: higher cost, nozzle tips freezing off completely (stopping flow) and damage to the aluminum tooling from installation and thermal expansion. In most cases, the added value of having a similar process in prototype and production can be significant but not considered. To offset the cost of a hot runner manifold system, early communication and planning can allow the hot runner system to be recycled from the aluminum (prototype) tool into steel (production) tooling. Recycling prototype manifolds into production is possible as long as drop locations don’t change. Using valve gates increases cost but opens up the processing window and can reduce cycle times.”

Using a nozzle sleeve or cooling bushing as a thermal isolation barrier is one method to prevent nozzle tips from freezing off, Oles adds (see Figure 4). “The sleeve isolates the colder aluminum from the increased temperatures of the nozzle tip,” he comments. “This creates the ‘layer’ of thermal isolation so the tip can flow and then freeze off completing the cycle and starting over again. Another variation of this application is to use the ‘cooling’ bushing to ‘warm or heat’ the gate point instead of cooling it. By warming the gate point area it decreases the delta in temperature from the bushing to the nozzle tip. The result is easier and consistent start-ups for molding.

“With standard equipment found in most injection molding plants, you can warm water to approximately 160oF,” Oles continues (see Figure 5). “This requires a separate circuit, and we don’t recommend looping more than three bushing onto one circuit (depending on shot volume and material set temperatures). The last thing you want to see is someone climbing into the press and taking a torch to the gate point in the aluminum tool because the gate has frozen off. Using aluminum increases the thermal demands on the nozzle tip area. Aluminum displaces the heat at the point of contact with the nozzle tip quicker than steel requiring the nozzle to heat cycle more often.”

An additional benefit from the nozzle sleeve or cooling bushing is a replaceable gate point. “Replacement would take the place of reworking the aluminum mold in the case of damage allowing leakage,” Oles emphasizes. “When using aluminum damage can occur during the assembly process (of a cold sprue or hot runner system) because the aluminum has a lower hardness than the components being installed. Sharp edges from components installed are the likely areas damage can and will occur if not handled with great caution. When using a nozzle sleeve or cooling bushing, once installed it does not need to be removed. The nozzle interfaces with the sleeve rather than the parent aluminum. The result: preventing damage to the aluminum tooling (see Figure 6).”

A Collaborative Effort

Aluminum tooling can be a viable alternative to traditional tool steels, with open communications between the parties involved: moldmaker, molder, material supplier and hot runner manifold supplier. PSG’s Oles recommends all four parties set a clear goal for the mold build and project requirements. “Collaborate, listen and learn from each other to achieve the goal at hand,” he stresses. “Aluminum tooling emphasizes the need for excellent up-front communications and selecting the correct components for the system.”

When designed and engineered properly, high-strength aluminum has become a mainstream tooling material

Article From: MoldMaking Technology, Jay Gawitt , Director of Mid-West Sales from Yarde Metals, Ron Smierciak, Marketing Manager from Alcoa Forgings & Extrusions
Posted on: 5/1/2011

The December issue’s Dispelling Aluminum Tooling Myths article by Robert Lammon underscores that today’s high-strength aluminum alloys can be a successful alternative to steel tooling. The article went through eight industry misconceptions, mainly related to durability, when considering aluminum for production injection mold tooling. The article touched upon solutions that mold builders and processors alike are using to take advantage of the benefits of high-strength aluminum. Used today for the cycle time advantage, high-strength aluminum alloys are making an impact in automotive, commercial and industrial injection molds as a competitive alternative to steel.

Breaking down these myths even further, one must consider the range of aluminum products that are commercially available for the moldmaking industry. During the mid-1980s aluminum manufacturers were taking advantage of high-strength aerospace aluminum plate and pursuing applications in the area of prototype injection mold tooling. By taking advantage of aluminum’s superior machining performance, prototype mold builders could design, machine and build molds in mere days and have tangible parts to show customers.

At the same time, aluminum alloys in the 2000 and 5000 series also were utilized for prototype tooling driven mainly by cost. As cast products, these aluminum materials had less processing, and therefore cost about half that of 7000 series material at the time. The mechanical properties of these materials were sufficient for the prototype parts they were producing, albeit significantly less hard than 7000 series aluminum.

The cycle time benefit when using aluminum was largely overlooked since prototype tools provided product designers and engineers the plastic component they desired. Changes to the plastic component for fit and form were re-engineered and applied to the steel tool design for the production tool. However, as mold shops began to use 7000 series aluminum, it was quickly realized that these alloys possessed higher hardness, improved machining characteristics and a cycle time advantage. With efforts to better understand how to polish, texture and repair these materials, molders began benefiting from the properties of high-strength aluminum.

Today’s High-Strength Aluminum

One of the important developments of 7000 series aluminum has been consistent through thickness strength across sections of material in excess of 8 inches. 7000 series alloys are characterized by the primary alloying element, zinc. Other elements including magnesium and copper in combination with zinc produce the highest strength family of aluminum alloys. Advancements in alloy development has led to 7000 series aluminum alloys with improved properties through the entire thickness of a finished mold block.

Rolled plates of these alloys provide excellent strength in thickness sections up to 8 inches. Forged mold block takes advantage of recently developed alloys that maintain through thickness strength. To develop the strength properties of 7000 series aluminum, it must be hot worked from a starting ingot: slabs for rolled plate and ingots for forged blocks. The building up of properties in high-strength aluminum involves both mechanical processes (rolling, forging or extruding) and thermal processes (heat treat, quenching and aging).

To acquire the higher yield strength of today’s high-strength aluminum, the manufacturing flow path involves these basics metalworking steps:
• Ingot casting: 7000 series aluminum requires precise measurement of the alloying constituents (zinc, copper and magnesium), by weight percentage as developed by the aluminum manufacturer.
• Hot working (mechanical process): Depending upon the output gauge, aluminum is either hot rolled to plate sizes, typically 8 inches and below or hot forged for thicknesses greater than 8 inches.
• Heat treatment and quench (thermal process): To assure dispersion of alloying elements and a rapid cooling of the heat treated aluminum to build the strength characteristics in the 7000 series alloy matrix
• Cold work (mechanical process): A process to reduce residual stress by stretching the plate or by cold compressing in a large forging press.
• Temper (thermal process): A solution heat treatment and the artificial aging process.

Aluminum Challenges and Strategies

Bob Lammon, Phoenix Prototype, said it well, “Like most successful innovations that are born from the need to survive, aluminum tooling is not just the bridge to a faster product launch or the cost savings necessary for the planned budget; it is a successful alternative to steel tooling with huge benefits that will continue to advance and influence the future of the plastics industry.”
The challenge remains how to tap into the process efficiency of aluminum. With impressive improvements in cycle time—as much as 60 percent in some cases—knowledge and training in the plastics processing industry can’t happen soon enough.

As evidence with the much reported successes at Honda reaches molders, the barriers to adoption of high-strength aluminum are beginning to weaken. In the case of the one production part that has exceeded 600,000 parts, the mold not only performed better than expected, it has fortified the notion that aluminum tooling can, in fact meet manufacturing and quality requirements.

A key element to successful implementation of an aluminum tooling strategy needs to focus on the benefits that aluminum tooling can deliver for components that make the most sense and will have the highest success rate. Components that make the most sense for first-time aluminum usage include unfilled, general-purpose resins, such as polypropylene or polyethylene, though not limited to these; flat geometry over deeply drawn parts; and, generous draft angles for ejection.

Summary

The adoption of productionized aluminum tooling as an alternative to steel does require open communication between the aluminum manufacturer and supplier, the mold shop and molder. Not all aluminum alloys are created equal; just as not all steels are created equal. Designed and engineered properly, high-strength aluminum is beginning to take a foothold as a mainstream tooling material for years to come.