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May 31, 2001
7 Min Read
Figure 1. Caco Pacific experienced frequent downtime processing an elastomer through this tool. A new ionization process impregnated the tool with zirconium nitride to enhance wear resistance.
When Covina, CA moldmaker Caco Pacific began having difficulties with the gate area of a 32-cavity mold, it knew what the problem was but didn't know how to fix it. "We had an abrasive material that was destroying the gate area," says Lou Rose, project manager at Caco Pacific. "And if the gate becomes damaged, you're talking about a very expensive cavity that's too complex to use gate inserts."
Though the company never determined the actual cause of the gate problem, it believed the abrasion was caused by a colorant, filler, or some other additive in the elastomer running through the tool. In this application (Figure 1) the material was eroding the gates by as much as .10 mm on the diameter within the first 100,000 cycles (Figure 2). It created a gate vestige that the customer found unacceptable.
After doing some research to find a solution, Caco Pacific came across a new company that uses a patent-pending process to impregnate tooling materials in such a way that it becomes harder, lubricious, and more corrosion resistant.
"With this process, the part was hard enough so that the abrasive aspect of the [elastomer] was deleted," Rose says. "We have run the part well over a million cycles and everything looks excellent due to the surface hardness and lubricity. And we didn't have to make any allowances for the procedure involved." He attributes this to the impregnation being performed at such a microscopic level that it reportedly doesn't significantly change the dimensions of the tool.
From Inspection to Ionization
The procedure Rose is referring to is a physical vapor deposition (PVD) process performed by Ionic Fusion Corp. (Longmont, CO). "Other companies do PVD but we've carried it a few steps further," says Rod Ward, president of the company.
What exactly do those few extra steps entail? At the heart of the process is enhanced ionic energy. An impregnating material is ionized and that energy is used to drive that material into the the mold steel, not only hardening it but making it more lubricious. Reportedly, those two factors combined in the metal allow a tool to run longer and without a mold release.
Finished components have a hardness of 83 to 85 Rockwell C, compared to 45 to 55 for standard molds.
Most of the impregnating materials used in the Ionic Fusion process are refractory metals. "They're the best to use because they're longer wearing," says John Petersen, vp and chief technology officer at Ionic Fusion. "However, different combinations of alloys can be used with this process." He lists titanium, tungsten, nitrides, carbides, and oxides as some examples. Most applications use nitrides, such as zirconium nitride. Reportedly, enough ionic energy is produced that the company can impregnate most metals and the result in the substrate is the same composition as the alloy. "The benefit of that is you can find exactly the right combination of corrosion resistance, wear resistance, and hardness," he says.
But to understand the process fully, you need to learn how it works. Vince Sciortino, vp of business development at Ionic Fusion, emphasizes that the process impregnates components of molds, not actual molds. "We request that we receive the components," he says. "Don't send the mold as a mold. Break it down."
The process begins when a customer's tool first arrives at the door and is inspected for shipping damage, nicks, and corrosion. Once the mold components pass inspection they are ultrasonically cleaned, a critical step because ions will be driven into the metal's surface. "You don't want oils or leftover residual plastics," Ward says. "We prefer coating virgin materials. That's where the process really shines."
Following the cleansing stage, the mold components are placed in a vacuum chamber. This releases water vapor and frees oxygen from the components and the chamber. Ionization is then ready to take place.
Figure 2. The .8-mm gate hole shown here created problems for Caco Pacific by continuously plugging up. Solving the problem through the use of a zirconium impregnation process reduced downtime by two-thirds.
The chamber uses a cathode that contains the agent to be impregnated into the mold steel. An arc, which can be likened to a lightning bolt, is then generated inside the chamber, thus ionizing the impregnating material.
"Basically, it takes an electron and then releases an ion of a certain energy," explains Petersen. "That ion attempts to get back to a balanced state so it's looking for electrons." This step is accelerated by magnetic devices and the impregnating material is then driven into the substrate.
According to Petersen, this process is performed close to the speed of light so there is no need to use high temperatures. Enough kinetic energy exists in the ions, allowing them to embed themselves, and fuse with the mold steel. Once the base coating is built up, it can be adjusted to be as thick as 85 Âµm, although most of the coatings are in the 1- to 3-Âµm range.
"As you're putting down the metal, you cycle different gases, nitrides, and oxides," says Ward. "We ionize those gases and then combine them. It's all done in a controlled plasma." The substrate is in the plasma and is applied uniformly around the chamber and the length of the component. "Basically, we get a uniform impregnation everywhere on the components," he says. "It can uniformly go down holes and around corners."
With the Caco Pacific part, Petersen says only the gate entry required coating, as this is where the plugged hole is located. Note in Figure 2 the gold color of the gate area. It's from the zirconium nitride, which was the impregnating material infused into the substrate. Once that material is impregnated into the structure of the substrate, Ionic Fusion can conformally build up to whatever thickness is needed, without changing any of the tool component's dimensions, unlike other types of coatings that may add layers to a tool.
Behind the Fusion
The hardness of a coated mold component is one of the most significant results. The finished components have a microhardness of approximately 83 to 85 Rockwell C, compared to standard molds that typically have a hardness of 30 to 55 Rockwell C. In addition, the process can be customized to meet a specific problem. This may involve a multilayered process consisting of pure metals, nitrides, carbon nitrides, carbides, oxides, and other alloyed metals.
"We can go back and forth between the layers to build a structure, similar to a super-alloy-type structure," Petersen says. "All of our impregnation processes are like that with the layers. It builds up the corrosion resistance on top and the bonding of the base metal on the bottom. We have a lot of flexibility."
Another feature is the low temperature required by the process. This can be useful when dealing with certain types of tools. "A lot of tools and steel are tempered, and once they're heat treated you don't want to reintroduce heat," explains Ward. "We can keep the temperatures down to 70 to 80F because it's a completely liquid-cooled process." He adds that ionic fusion also can add heat, if necessary. The maximum temperature used to date is 250C.
As for corrosion resistance, Sciortino uses the effects of PVC as an example. "Once you put PVC through one of your presses, it is very corrosive to the molding equipment," Sciortino says. "With this process, we can impregnate all the screws and barrels, sprue bushings, and check rings with a hardening material that can fight off the effects of PVC." He adds that this process can reduce the cost of the base metal because PVC molders normally have to buy stainless steel for molds. "If we eliminate the cost of stainless steel and go to a lower-cost hardened material, then the machining cost is lower," he says.
Ward sums up the difference between Ionic Fusion's process and the coatings other PVD processes produce. "We may go to 2 Âµm in thickness, but the key is impregnation into the substrate. It's not topicalâ€”it's integrated into the structure."
Caco Pacific's Rose understands that difference. His company has seen its downtime reduced by two-thirds by eliminating the gate problem. "The impregnation is so hard, it stands up to wear excellently," he says.
Ward says the company does plan to license the process, as well as set up in-plant leasing and purchasing programs.
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