issue: June 2008 APPLIANCE Magazine Manufacturing Technology Simplified Assembly	Share  Printable format  Email this Article  Search
Multifunctional assembly technology may reduce manufacturing costs and assembly time by replacing traditional joining techniques.

The process, called Injected Metal Assembly (IMA), is a specialized molten-metal injection technology created by FisherTech, a division of FisherCast Global Corp. (Peterborough, ON, Canada; www.fishercast.com). According to the company, the technology reduces assembly to a single-step operation and, in some instances, can reduce production costs by 70%. “The IMA process enables the manufacturer to eliminate a premanufactured component from an assembly by replacing it with a zinc alloy component which is die cast directly onto another part as it is joined to it,” explains Meinrad Machler, chief technology officer of FisherCast Global. “The alloy can replace a more expensive material, and the IMA process eliminates the previous joining operations.”

In one case, a food mixer manufacturer was able to join three components in one operation by connecting them with an injected zinc alloy hub. According to Machler, the OEM was using multiple operations to assemble a zinc alloy die-cast gear and a sintered iron bevel gear to a steel shaft as part of the mixer’s motor drive assembly. The gears were press fit onto the shaft, and then drilled and pinned through and across to obtain the required drive.

Using a custom fixturing tool, the IMA process allowed the OEM to join the three motor drive components in one assembly step. “The components are automatically positioned by the tool in correct relationship to each other,” Machler explains. “A shot of molten zinc alloy is injected into a cavity at the intersection of the components. As the molten metal solidifies and shrinks towards its theoretical center, a strong locking action occurs, forming a permanent mechanical joint in a matter of milliseconds. The strength of the hub joining the components is in excess of 130 Nm.”

As a result, Machler says, the appliance manufacturer was able to reduce labor from the six individuals needed for the original production process to one IMA system operator. In addition, 1100 sq ft of plant floor space was freed for other uses, and consumable items were eliminated.

While these production savings are a major benefit, Machler says that OEMs can also gain accuracy. “The tooling…is built to exceedingly close tolerances. This ensures part-to-part consistency in the assembly,” he explains. “Where the positioning of one component to another is critical, the IMA process joins them with repeatable precision of true position and circular runout.” In the case of the food mixer motor drive, tolerance on the shaft position was within 0.004 in. total indicator reading (TIR), and the concentricity of the outside diameters of the gears to the shaft’s outside diameter is 0.002 in. TIR.

Machler claims the process can replace most joining techniques, including welding, press fitting, drilling and pinning, crimping, stamping, adhesive bonding, gluing, brazing, swaging, and staking. It can join several different types of materials, ranging from steel and nylon to plastics and rubber. “Although the alloy injects at temperatures up to 815°F (430°C), bonding and solidification speeds of the zinc alloy prevent component materials from thermally degrading,” Machler says. “Any heat distortion stresses are short-term because solidification behavior of the zinc mitigates them within seconds.”

Possible appliance applications include placing a magnet and soft iron core onto a steel stamping in small electric motors, or casting eyelets onto a stainless-steel plate in a dishwasher door latching system. Whatever the end use, Machler says the key is evaluating the use of the process at the design concept of a project. “This allows maximum cost savings and functionality to be incorporated into the design,” he says.