Using EIS, molders can easily raise the injection unit above the conventional clamp centerline to align the machine nozzle with a sprue bushing at the upper-end of the offset runner system required by this approach. These raising blocks can be removed for conventional injection.

One molder has found EIS to be helpful in precision molding electrical connectors and wire harnesses. Injecting into the parting line also helps this molder minimize the effects of fiber orientation in finished parts.

By involving the molding machinery supplier early on when designing it's standardized production cell systems, it had the time to plan ahead for EIS, and also for other customized processing specialties to help it meet its goals of quick product changeover and high quality parts.

Such cooperation helps this company manufacture some 7200 parts/day, seven days/week, with tolerances held to within .002 to .003 inch, even with 30 percent glass-filled engineering resins, while holding wall thicknesses to between .015 and .020 inch (Figure 2). It does so on 123 Battenfeld CD Series machines - that's 95 17-tonners and 25 38-tonners, plus three lab machines (Figure 3). It runs 240 different part numbers in 208 tools and in 47 different materials at 8-to 12-second cycles, around the clock, hands-off. each machine is calibrated alike, so tools can be swapped between machines if necessary.

The molder is the Packard Electric Div., General Motors Corp. (PE-Brookhaven, MS), the world's largest manufacturer of automotive power and signal distribution systems. PE presently enjoys a 22.4 percent global market share. Last year it supplied wiring sets for 11.3 million vehicles through its global network, which includes 160 facilities in 27 countries and on six continents.

Once a totally captive GM molding operation, PE's Brookhaven plant now supplies more than 100 different automotive and nonautomotive customers. It also must compete with outside vendors and other PE units in Warren, OH and Clinton, MS, even for GM's business. In fact, the two 60-machine units under the roof of PE's Premo (precision molding) operations in Brookhaven's 203,000-sq-ft facility often compete against each another for the same project booked by another GM unit.

Competitiveness, understandably, is very important. It definitely was important in 1986 when planning began.

Customized CIM

Battenfeld's field-programmable Unilog 4000 controllers on each machine provide Moog servovalved, closed-loop control over injection rate and holding pressure; during screw rotation, backpressure also is controlled. PE concentrated on part weight verification for 3-D process monitoring as a key to its zero-reject-rate goal. The control even integrates the parts bagging system (Figure 4).

To this end, Battenfeld supplied systems designed around Mettler scales for each production cell (Figure 5). The scales are enclosed, shielding them from the plant environment. The scales first weigh parts on contact, verifying ejection, and signaling initiation of the next cycle. Then the scale stabilizes and weighs again to within thousandths of a gram. The Unilog 4000's Quality Table software monitors the feedback. Remember, this takes place with each part in cycles averaging around 10 seconds.

Weighted parts are then conveyed to beside-the-press, good/bad-part bagging systems. The Unilogs select part quantities per bag. During a recent tour, it was hard to find a bad-part bag with anything in it.

In addition, the controllers interface with two Regloplas mold conditioning units that monitor tool steel temperatures, not fluid temperature, and up to two hopper dryers (from Novatec and Comet Plastic Equipment) in each cell. Temperature setpoints and readouts are displayed at the cell, or through PE's bi-directional host-computer network. Mold data set information also can be transmitted to and from each cell in this manner, as can production and diagnostic data.

Quick product change-overs were another Packard Electric goal. It wanted to run batches as small as 10 parts. To accomplish this goal, PE runs modular, single-cavity unit frame M.U.D.-type tooling equipped with uncomplicated manual cavity quick-disconnects.

Molds come from the division's tool engineering group. They are certified and ready for up to 150,000 cycles till PE's planned maintenance program kicks in. After its global benchmarking efforts in the 1980's when designing its facilities, PE found that single-cavity molds provide better cost and quality control.

QMC is accomplished in under 3 minutes on the company's 17-tonners, and under 5 minutes on the 38-ton machines. PE performs 75 to 80 inventory turns/year. It promises 24 hour delivery to its customers, and holds only 24 hours worth of inventory.

Battenfeld designed special purge shields to support QMC (Figure 6). The shields temporarily cover the nozzle openings on the fixed platens. When activated, material can be purged while the mold is being changed, so machine attendants ('precision molding coordinators," as they are called) don't have to worry about accidental contact. Nozzle drool is wiped automatically during changeovers.

Sprue and runner removal from PE's tunnel-gated connectors is important. Their positive removal must be accomplished for maintaining part-weighing accuracy. So, Battenfeld developed pneumatic swingarm pickers to fit inside the standard safety gates of PE's production machines. Clamp-driven mechanical pickers were considered, but pneumatics obviate the need for mold protection to be increased to overcome mechanical friction during the clamp-close cycle phase.

Brookhaven's annual uptime averages well-above its scheduled goal of 95 percent. But molding technology and economic conditions have changed since 1988. For example, cost and volume demands may lead the company to multicavity, hot-runner tooling. That's why PE and Battenfeld are working together to develop new cells for the company's next expansion.

-Carl Kirklan