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Injected metal saves manufacturing steps.

Have you overlooked the process of injected-metal assembly (IMA[TradeMark])? The process can assemble small parts of many materials and shapes, with few technical limitations. After "shots" of hot metal fill cavities and gaps in components held by special fixtures, completed assemblies come from Fishertech[Rights] IMA machines ready to use.

According to Fishertech, Div Fisher Gauge Ltd, Peterborough, Ontario, Canada, IMA equipment can replace operations such as crimp, press fit, shrink fit, stake, swage, rivet, adhesive bond, solder, braze, and weld. It overcomes problems with these methods, yet works at speeds up to 1000 assemblies/hr or higher. Also, it often eliminates secondary machining operations.

Because molten metal fills gaps between components, you can relax some tolerances of mating parts. The process virtually eliminates material waste, and can form additional shapes while joining parts. You can combine several parts instead of producing them separately, thus reducing inspection procedures, stocking, and handling. IMA fits right into the JIT concept.

Typical components now being joined include: disk and shaft, gear and shaft, electric-motor rotors, pins and plates, laminated stampings, metal hubs in elastomer or ceramic disks, abrasive points, cable terminations, bridged mountings, and interval positioning of parts along wires or shafts. The versatile process can join elastomers, paper, fibers, and glass.

Process in action

In operation, parts to be assembled are positioned accurately in correct relationship and held firmly by a tool mounted on the operating head of the IMA machine.

Next, the machine injects molten metal into the cavity where the parts meet. The metal flows in and around physical features such as grooves, knurls, undercuts, splines, keys, lugs, ridges, and holes.

The metal solidifies in milliseconds to create a strong, permanent lock. Finally, the machine ejects a ready-to-use assembly, which usually may be handled safely without gloves.

Typically, assemblies can be as large as 6" dia, but larger items have been accommodated in some cases. Although holding fixtures can limit workpiece size, parts can be assembled to shafts and cables of long length.

The basic consideration must be the amount of molten metal that an IMA machine can inject. Today's models have capacities of I oz, 2 oz, and 4 oz (equivalent to 0.3 in', 0.6 in and 1.0 in Accuracy and cost saving

How precise is the process? It largely depends on the accuracy of the fixtures. In many cases it's better than conventional assembly methods. For example, if the ID of a stamping or the OD of a shaft must be held to close tolerances to achieve concentricity, injected metal has the advantage. Also, if several parts must be positioned in relation to each other-particularly if they are currently joined in separate operations-IMA will probably do a better job than previous methods.

The process can be carried out on semiautomatic hand-fed machines, or it can be part of an automated production line. It lends itself to automated cells, is clean, and relatively quiet. The manufacturer says the process is nontoxic and requires no special cleaning or chemical preparation of parts before their use in the injected-metal system.

The bottom line is lower cost than most conventional methods, and Fishertech offers a low-cost prototype tool program to produce samples for customer evaluation. In looking at new designs or redesigns, consider that the process can eliminate further machining, finishing, straightening, deburring, etc. Furthermore, you often can use the IMA tool as a checking station.

There is virtually no wasted material, and there is a more subtle materials saving, too. Fishertech says dramatic savings are possible simply because of reduced component inventory for assemblies.

For example, in an assembly containing a shaft, the basic shaft stock diameter may be reduced from a hub or pinion diameter to the journal diameter, with injected metal forming the pinion or hub. Thus, you can get along with fewer stock sizes. Speed and strength

Rates vary from a few hundred to over 1000 assemblies per hour, depending on part complexity, number of parts, orientation of functional surfaces, and degree of orientation. The automatic portion of the cycle takes from 0.5 sec to 1.0 sec, the balance of process time being that required to load parts and unload assemblies.

Injected-metal assemblies are permanent, because joints are formed of solid metal-sometimes lead alloy, but usually a zinc alloy. Fishertech's test data show that many joints are stronger than the components being joined. A company engineer says, Zinc alloy has an average tensile strength of 41,000 psi; compression strength of 60,000 psi; Brinell hardness of 82; and Charpy impact strength (1/4" X 1/4" bar) of 43 lb-ft. Properly designed zinc-alloy joints beat high-tensile-steel shafts in our destructive shear tests."

He adds, "Our process is consistent. Once initial samples have been made and checked, results are predictable. Zinc alloy has desirable fluidity, strength, ductility, and shrinkage characteristics-and they all repeat reliably."


In most cases, IMA machines install right in the assembly line to help reduce material-handling costs. The machines are easy to run, requiring minimum operator skin. Furthermore, the machines are easy to install and require no unusual services or pollution-control equipment, according to Fishertech.

Either manual or automatic methods may serve for feeding parts to the machines. With delicate, valuable, or difficult-to-feed parts, Fishertech recommends careful hand loading and unloading-or a combination of manual and automatic feeding. Less-sensitive but highly accurate assemblies can be produced on fast-running automated IMA machines using vibratory feeders, hoppers, magazines, pick-and-place units, or reels of wire stock.
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Author:Miller, Paul C.
Publication:Tooling & Production
Date:Jul 1, 1990
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