Automated injection cell shuffles nine molds.

Automated Injection Cell Shuffles Nine Molds

A new injection molding cell with a hot-runner manifold for two materials reportedly can change any of nine multicavity molds in less than 6 min. The key is an automated approach that involves changing only the core/cavity plates of the molds. What's more, the system is totally integrated: electronic controls at every phase of the molding process report to a central cell-monitoring computer system.

A major Midwestern tractor manufacturer is the first processor to take advantage of the automated cell, which is being used to produce two-material sealing rings for tractor hydraulic systems. The manufacturer (which prefers not to be identified) expects to double its current production capacity by reducing downtime during mold changes and speeding finished-parts handling.

The production cell comes from Battenfeld GmbH of W. Germany (represented in N. America by Battenfeld of America, W. Warwick, R.I.). It includes two three-axis robots on a single boom for parts removal, degating, and stacking; a mobile mold changer with preheating and service stations; mold-storage racks; automated materials handling; a two-material injection machine; and the "double" hot-runner system that accommodates two materials.

The customer's specifications called for complete mold changes - including preheating - in under 6 min. To monitor this, the injection machine controller and a robot controller have been linked to a management information system (MIS) that logs all operating conditions. Custom software provides the molder with a variety of SP/QC reports, including X-bar, R, and histogram charts. Soon a second injection cell will be added and linked to the MIS.

NEW MOLD-CHANGING APPROACH

The sealing-ring assembly produced at the cell consists of a stiffener ring of 40% glass-filled polycarbonate, onto which a sealing lip of TP urethane is molded. A total of nine different sealing ring assemblies of 53 to 99 mm diameters are produced in 23-25 sec cycles in four-cavity molds - a process that requires close tolerances. Nevertheless, automated mold changing and parts handling, along with a special mobile parts rack for post-curing, reportedly allow for almost operator-free production. In fact, around 40,000 sealing-ring assemblies are produced on weekends at the plant, without any operators at all.

Conventional mold-changing systems change an entire mold and are typically equipped with individual hot-runner manifolds for each mold. In the new cell, only the core/cavity plates of the mold are changed. Two movable-side mold-base assemblies operate interchangeably with the double hot-runner system. While one mold-base assembly is in operation, the other is being prepped for a mold change. Since the cell uses only one hot-runner system and two interchageable mold bases, the mold-changing system can use any of nine different core/cavity plates during production-run changeovers.

The mobile, rail-guided mold-changing system is equipped with a rotary table and special gripping device to supply the machine with core/cavity plates. The mold changer places the core/cavity plates in a service station where they are bolted to the mold-base assembly manually, and then brings the plates to a preheating station. After preheating, core/cavity plates are automatically installed in the machine.

With the help of a cell controller from Battenfeld, preheating of molds starts automatically 3 hr prior to a new production run. After a run, used core/cavity plates are returned to the preheating station (which also acts as a cooling station), and are then returned to a mold-storage rack.

The cell's unusual mold-changing system is expected to provide considerable cost savings in machine startup time, preheating costs, and space savings.

PARTS HANDLING WITH A TWIST

Two three-axis robots remove finished parts from the mold and place them on a mobile parts-removal rack. The first gripper robot removes all four parts and brings them to a degating station. It places two parts in the degating station and proceeds to a waiting position while the second gripper robot removes the parts after degating. This sequence is repeated for the next two parts that were formed in the cycle. When the second robot has all four parts, it places them in the mobile parts rack.

This configuration requires only two punch-and-die sets for degating instead of four (one for each part), which reportedly reduces costs and makes it easier to convert the degating station to a new mold run. Once full, the parts rack is manually moved to a curing oven, where parts are cured for 16 hr at 293 F. For production without operators, a second degating station is on standby to accommodate a mold change.

The parts-removal rack is a series of poles onto which the sealing rings are placed. For maximum packing density within the curing oven, the racks have been constructed with an odd number of poles. With the help of a sophisticated robot control system, the Unilog 9000 BS, the parts-stacking robot determines where the finished rings should be placed on the rack. The system takes into account the odd number of stacking poles and the part diameter to achieve the maximum number of parts per rack - approximately 14,800 parts at one time.

MIS TIES IT ALL TOGETHER

Overseeing the automated cell operation is Battenfeld's BDE management information system (MIS) configured on hardware from Digital Equipment Corp. (DEC). The system provides reports on machine status, shift production, part data, and order status, as well as hourly, weekly, yearly and lifetime production. The MIS computer can store 24 hourly reports, 50 shift reports, 30 daily reports, 200 part-data files, 2000 current and future orders, and 2000 setpoints. Custom software for SP/QC can massage this data into any number of standard reports or graphic representations that allow managers to evaluate the data easily. (CIRCLE 10)

PHOTO : Two parts-removal robots work in unison to stack parts (left), after a two-step degating process finishes each part form a four-cavity mold

PHOTO : Mold-changing carriage of the automated cell takes mold cavities from the deposit to the preheating station and then to the service station, and installs them in the press.