Avoiding assembly costs by letting the mold do it

By: 
September 28, 1998


All of these parts are produced in one cycle, by one machine, without postmold assembly. Using the multishot technique called In-Mold Assembly, the automotive air vents are made in three shots, the locking electrical connectors are two-shot molding, and the two-shot small gear and connecting rod assembly are used in an electric toothbrush.

You've heard of in-mold decorating, and in-mold labeling, and in-mold deflashing, but have you heard about a technique to streamline the way to a finished product? It's called In-Mold Assembly, and its purpose is to deliver a finished and assembled part at the end of every molding cycle. Developed by Fickenscher & Co. GmbH of Selb, Germany, the technology has been trademarked, licensed exclusively, and brought to the United States by Fickenscher America, Richmond, IN.

Fickenscher America's president Don Birdsall and marketing vice president Mark Elder have been trying to convince U.S. companies that dropping a fully assembled, articulating product made of three, four, seven, or more parts out of a mold is not magic, but a real-world process.

Now some automotive companies are starting to take notice. They have contracted with Fickenscher America to use this process. The inventor, Fickenscher & Co. GmbH, is a well-known toolmaker specializing in multishot tools; what Fickenscher America has done is license the technology to mold parts (not to build the tools themselves) outside Europe.

"We took the opposite approach of most U.S. companies, choosing to transplant the entire German process into our company, then work with Fickenscher as our technology partner and toolmaker," says Birdsall. "The German company has such a good reputation in multishot molding in Europe that we felt it appropriate to adopt the name, too."

Where the Process Fits

The process is already widely established in Europe for the automotive, toy, and electronics industries. "Toy figures with articulating arms, legs, and heads were the first products done with In-Mold Assembly," explains Elder. "Today, complex parts such as locking electronic connectors, gear assemblies, and dashboard air vents are made for companies including Volkswagen, Mercedes Benz, Siemens, and Braun."

You can just visualize the manufacturing savings, estimated at 10 to 30 percent, in spite of increased tooling cost. There's no more postmold assembly, with its work-in-progress inventories, labor, floor space, fixtures, tracking procedures, robotics, and storage. Quality assurance is another cost and time saver. "Because you get an operable part out of the mold, you can check the entire assembly's quality at the machine," Birdsall explains. You don't have to wait to solve the problem.

The design advantages are intriguing as well. The first-class fit is one example. "Who has not had a dashboard air vent whose vanes would not hold position?" Birdsall asks. "With In-Mold Assembly, you don't have the stack-up of error in component tolerances that leads to loose fits. You can design in the fit you want to result in the right amount of friction. With all the components molded and assembled at the same time on the same machine, in one mold, you get a high degree of consistency."

Another project in process is a part with a living hinge that did not last. With In-Mold Assembly, two-component molding creates a part with a fully mechanical hinge, plus position detents (not available in the original) to hold the lid. The customer got a superior product at a comparable price.

Fickenscher America's injection molding cell for In-Mold Assembly consists of a 100-metric-ton Ferromatik Milacron with three injection units.

How It Works

In-Mold Assembly is a multishot injection molding process resembling progressive stamping. The first shot produces a preform; the second (or third or fourth or fifth) produces the finished product. The preform moves to a new cavity after each shot. After the first shot, all shots use a mold geometry created partly by the steel cavity and partly by the molded surface of the preform or previous shot. Because each shot is a different material, with a different melt temperature, no bonding occurs between material in successive shots. "This molding technique has quality assurance built right into it," says Birdsall. "If any shot is short, you'll find out right away, because the finished part won't articulate."

To serve as the horsepower behind this molding process, Birdsall purchased a Ferromatik Milacron K100S-3F injection molding machine, identical to the 20 or so that were custom built for Fickenscher Germany. In this way, the two partners can speak a common language when discussing the process. "If the Germans build and trial a tool for us," says Birdsall, "they can send us a data cartridge from their machine that we can drop into ours."

The base machine is customized around the demands of the rotary tooling. It has exceptionally wide platens and tiebar spacing for its size, tiebar extensions, and a proportionally controlled ejector stroke to accommodate the large tools. While Fickenscher declined to discuss details of the tool, Ferromatik Milacron's Bob Hare says that rotary molds can be electrically or hydraulically powered, and control may be open or closed loop, with speed and position feedback provided to the machine control via a rotary encoder in closed loop mode. Other features that relate to the tooling are a manually controlled double core-pull circuit that terminates at the moving platen with connections to the mold ejectors, and another CRT-controlled double core-pull circuit with connections to the mold. Despite the level of mold action and the extra resin processing, there is virtually no cycle time penalty because the machine has the reserve hydraulic and control capacity to handle simultaneous operations.

    Part Guidelines
    Fickenscher America's Mark Elder offers these tips to those considering In-Mold Assembly.
  1. Apply the process to a product already in production. This will provide you with a clear cost and function comparison, and you will have a backup source.
  2. Don't worry about a major redesign of a part. Revisions are not likely to be requested in the show surface of the part.
  3. Your product must be able to satisfy performance requirements with commodity plastics or conventional engineering resins. But it may combine flexible, rigid, and elastomeric materials.
  4. Components that move relative to one another must be of materials with a melt temperature difference of at least 50 deg F.
  5. Practically, parts should fit into an 8-inch square when placed in the as-molded position. However, there is no theoretical size limit to what could be done.
  6. Parts can use a maximum of four different materials or colors, although two or three are most common.
  7. A practical minimum for cost justification is 250,000 parts/year, although quality and other issues could drive this lower.
  8. Insert molding is not recommended due to the risk of mold damage.

Molding Air Vents

Fickenscher America has contracted with a Tier One to produce the first in-mold assembled automotive air conditioning vents in North America, for one of the Big Three. The parts are created in a multicavity hot runner mold. "The original design called for a snapfit part, with a frame that retained the vanes and snapped into a cosmetic housing," says Birdsall. "The new three-component molding, with PBT vanes and PP link and housing, will cost much less than the original part."

The K100, with 100 metric tons of clamp, forms the heart of the molding cell. Its three injection units (two horizontal and one vertical) are all capable of independent operation. Its accumulator-based hydraulic system supports clamping, injection, and ejection simultaneously. The machine uses a D-M-E hot runner control and has a Colortronic material handling system.

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