Tandem mold technology, a relatively new development, is beginning to be a growth business for T-Mould, a mold manufacturer based in Bad Salzuflen, Germany with an office in Grand Rapids, MI. The company does not build the tandem molds itself, but is the inventor and developer of the tandem technology.
"Because of our growing business we wanted to have an increased presence in North America," explained Wilhelm Kliewer, managing director of American T-Mould.
A tandem mold is similar to a stack mold in that it has two parting lines. The primary difference however, is that a tandem mold operates in an alternating process. "For each parting line you have a standalone process," explains Kliewer. "The material is injected into the first single face section, then hold and pack takes place. But before the cooling process starts we activate the Compact Locking System (CLS), which locks the parting line. At that point, the barrel retracts and we shoot in the resin into the second parting line. The benefit to the Tandem mold is that we utilize the dead cycle time - the cooling phase - to injection the resin into a second parting line."
T-Mould holds the world-wide patent rights for the Tandem technology processing method, which is an amalgamating process that implements the Compact Locking System (CLS), which T-Mould's customers purchase. "We do not have repeating license fees," Kliewer clarifies. "We offer a one-time purchase of the CLS on a particular tool."
The CLS is offered in four different sizes and in different variations. "We work with customers on which locking system is best to be used for the particular tool," Kliewer says. "We're all engineers, toolmakers and process engineers, so we help our customers calculate their needs and offer technical support around the product. We also collaborate with the various suppliers such as press manufacturers, systems manufacturers to support the requirements of the Tandem tool, and with the toolmaker to design a Tandem tool. For us it is not only important that they use the technology, but more importantly that it's used in a proper functional way to receive the real benefit from the Tandem technology."
The Tandem mold concept was introduced by T-Mould in 2003. Since then, the technology has been catching on for various applications. However, Kliewer notes, applications for the technology are unique, and typically the end user is looking for greater productivity. Applications span a wide range of markets including medical, appliance, automotive and electronics among others.
One of T-Mould's customers with an expertise in building connector molds, had a requirement for a 16-cavity connector mold. "The customer usually builds 8-cavity connector tools, and with 250 critical dimensions they know how to build and balance the tool," says Kliewer. "But when they tried to go to 16-cavity tool, it wasn't possible to balance the tool properly. They sacrificed quality and it resulted in a reduced process window."
The moldmaker then went with the Tandem mold process, which resulted in increased production and higher throughput. Utilizing the Tandem technology, the moldmaker essentially had one 8+8-cavity mold in which he could use the cooling time of parting line 1 to inject into parting line 2, and can process this 16-cavity tool. "He was also able to increase his process window," Kliewer added.
Another customer needed a mold built for a housing and lid. "Usually for this type of application you need two stand alone tools or a family tool that needs proper balancing," says Kliewer. "Whenever you have a family tool with two different parts, the question is what happens if you require different volumes? With Tandem tools you can lock each parting line independently and use either parting lines as a single face tool to get different volumes."
Another application required a housing and cover for keyboards, but it also required colored resin, as well as different volumes and different surface textures. "This product couldn't be done in a family mold," Kliewer explains. "Also it needed a good profile to fill well because of a class A surface requirement. By building a Tandem tool, the customer got a perfect color match, each with its own profile as stand-alone tools, and a much lower scrap rate."
As with any new technology, educating both moldmakers and end users about the benefits and suitability for various applications, can take time. Often, people are reluctant to use new mold technology. "The customers we work with are not afraid of technology and not afraid of working at a level where they can be more competitive," said Kliewer. "We have almost 800 applications worldwide where the Tandem technology is being used. Within the U.S. in the last year, American T-Mould has worked with many different customers on a number of applications."
In deciding whether a Tandem mold is appropriate, Kliewer notes that it is important to look at the overall program and what the end user requires. "We have several customers in the appliance industry currently looking at how often they might be able to use this technology in their applications," he says. "They begin looking at Tandem molds from the outset of the design. They also evaluate shot size and weight differential, for which Tandem technology can accommodate up to 60%. In other words you can have totally different weight relations. Every second shot you can get from a larger volume of material to a smaller volume. We have developed calculation programs that we use to calculate a Tandem process vs. a stand-alone mold to weigh the cost benefit of tandem vs. stand-alone. We are very honest about what we do - we don't pretend we can achieve something that we can't, but most of the time we can achieve a significant price reduction."