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Compiled by Don Rosato
Keyword Abstract: metal, metal plastic composites, overmolding, nylon 66, electronic conductors, cable harness, automatic transmission control systems, automotive, HydroPlast Structures, SmartLok, connection technology, automotive structural components, car doors, front-end modules, Solid Freeform Fabrication, Shape Deposition Manufacturing, DuPont, Asahi Dow, Engel, ZIMK, Carlisle Engineered Products, Vari-Form Inc.
Metal-Plastic Composite Assemblies
ZIMK GmbH, a supplier to the semiconductor and electronics industry is using the latest 'ergonomic' technology from Engel for its metal-plastic composite parts. The company, which specializes in the development and manufacture of high quality metal-plastic composite parts mainly for application in the automotive and electromechanical markets is overmolding stamped metal parts with a DuPont 35% glass fiber reinforced nylon 66 to produce flat multiple conductors. The conductors are used for example in automatic transmission control systems for various makes of automobiles. The ZIMK cable harnesses are produced in fully automatic, production cells.
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Cable Harness Overmolding
(Source: ZIMK GmbH) |
To maximize efficiency, ZIMK operates the injection molding machine with a two-station rotary table and two bottom mold halves (two-cavity ZIMK manufactured molds). While the stamped metal parts are being overmolded in the first bottom mold half, the robot removes the finished composite parts from the second one, this now being freely accessible at the front of the machine, and places new parts-collected from a sliding table magazine feed system-into the cavities in readiness for the next overmolding process (the robot is equipped with a dual purpose gripper head for these two functions). These stamped metal parts are extremely intricate, not to say 'flimsy'. In one series, they are only 0.6 mm thick, with 15 conductors measuring only 1.2 to 1.8 mm in width, and these are also angled within their overall length of around 60 mm. Nevertheless, the robot is able to pick them up and transfer them to the mold cavity with reproducible accuracy. The robot does this with the aid of a special gripper, which pulls each individual part slightly taut to permit accurate placement in the mold cavity. The demolding side of the robot likewise features a special time-saving device: the necessary sprue-separating cutters are incorporated directly in the gripper head and remove the sprue in a sprue removal station located immediately in front of the stacking unit. The parts are then accurately stacked in trays and discharged from the production cell on a conveyor belt. This highly sophisticated system was developed by Engel's automation specialists at Dietach in close collaboration with project engineers at ZIMK using a new generation of vertical rotary table machines, an Engel Insert 330V/90 and complete automation peripherals (Engel ERC 34/1 F linear robot and Engel ETS 4 tray server).
Located immediately downstream of the automated injection molding cell is a fully automated finishing and testing station developed by ZIMK production specialists. The overmolded metal parts are re-stamped in this station to remove connecting webs which served to hold the individual conductors together prior to nylon overmolding. Removal of the webs ensures the individual conductivity of the conductors. These flat 'cable harnesses' are then subjected to a fully automatic 100% functional testing before they are finally passed as 'reliable' components for installation-in an automatic transmission control system, for example.
HydroPlast Structures and SmartLok Plastic-Metal Hybrid
HydroPlast Structures and SmartLok connection technology was developed in by U.S. based custom molder Carlisle Engineered Products and U.S. steel company, Vari-Form Inc., to combine plastics and metals for in a single cost-effective molding process. The Hydroplast technology, which combines injection molding with hydroformed tubular steel parts rather than sheet metal, was used to produce a prototype front end for the Nissan Xterra. Carlisle has commercialized SmartLok parts. The patented SmartLok connection, an integral tie formed in the injection molding process, joins the plastic and metal components of the structure. Proprietary tooling creates the SmartLok Connection between the metal tube and plastic, enabling significant load transfer between the two materials providing excellent resistance to bending, compression and torsional loads, high energy absorption, dimensional stability and low part weight. Compared to current hybrids, these products need less plastic, since none is needed to provide stiffening in the steel beam. The metal tube can be overmolded with 30% glass-filled Asahi Dow nylon/polyphenylene ether alloy.
Other Multi-Material Plastic to Metal Forming Processes
There are other methods of forming multi-material, metal replacing, plastic parts that do not involve injection molding. The most common alternative known as Solid Freeform Fabrication (SFF) involves the use of a layered manufacturing process in which the plastic part is produced by depositing multiple layers one on top of the another to produce the necessary geometry. Shape Deposition Manufacturing (SDM) is one example in which parts are fabricated by depositing layers of material in a 'Y' build orientation while machining each layer in the X-Z directions to give the component 3-dimensional shape. By changing the materials used during layer deposition spatial variation of the parts material properties can be achieved. Selective laser sintering, a rapid prototyping technique in which multi-materials are used has been developed to produce multi-material parts or objects. '3D Printing' is another layered manufacturing process that can be used to produce heterogeneous objects. In this process 3-dimensional objects are fabricated by printing various materials in different locations, through separate ink-jet nozzles. Though SFF processes are considerably slower, more expensive and less accurate than injection molding they are useful in part rapid prototyping, and can in some cases form objects that are not possible using multi-material molding approaches. |
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