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The next robotics frontier.

Today's servo robots can do a lot more than demold parts. They can also help you automate secondary operations - everything from decorating and assembly to inspection and packaging.

Robots have long demonstrated their capacity to enhance productivity in injection molding operations by allowing faster cycle times, reducing scrap, and slashing direct labor content. Yet pulling parts out of the machine and placing them on a conveyor or in a tote isn't all today's robots can do. The next frontier of injection molding automation stretches well beyond these basic functions to the labor-intensive realm of secondary operations.

Since decorating, machining, assembly, packaging, and many other post-mold operations tend to be simple, repetitive tasks, they often lend themselves to automation. When one or more of these value-adding operations can be performed robotically, the results can be dramatic: Both direct and indirect labor content drop. Robots perform most individual operations more reliably and consistently than human hands, boosting post-molding productivity. And robots essentially eliminate the time spent transferring production from one station to the next, further increasing production rates while reducing work-in-process. What's more, automation can save valuable floor space. Robots permit secondary steps to be placed close together and performed in an uninterrupted sequence, allowing redundant work-staging areas to be dedicated to more productive purposes.

There are essentially no restrictions on the size or type of injection molded parts that can be handled robotically. Applications range from tiny optical components to large automotive body panels. All post-part-removal automation applications typically fall into two categories: "Simple" applications for injection molding robots are those that can be performed by the robot itself using end-of-arm tooling and/or equipment that is mounted on the robot's traverse beam. In a "complex" post-mold application, the parts-removal robot typically hands parts off to a separate automation station. The functions performed in these "complex" applications may require more time than is available between mold-open cycles, and may involve larger or more extensive equipment adjacent to the press.

SIMPLE POST-MOLD TASKS

Nowadays, servo-driven, traverse-type robots are the norm for automating the "simple" category of post-mold operations, which are always preceded by robotic demolding. These applications are generally engineered to take advantage of robot waiting time in between mold-open cycles. As compared with pneumatic drives, servo motors excel in precision and speed and multiple-positioning capability, enabling robots to stop at several stations along each axis.

Degating is the most common post-mold application. The robot removes parts and runners in one piece from the mold, holding either the parts or the runners in the end-of-arm tooling. The robot arm then traverses out of the press and presents the shot to nippers mounted on the end of the traverse beam. Upon degating, the sprue drops into a bin or a grinder, and the robot traverses to another station, where the parts may be either dropped into a bin or placed carefully on a conveyor, table, or shuttle (stacking is also possible). Alternatively, if the robot tooling grasps the runner instead of the parts, then the parts drop when degated, and the sprue is discarded at the next station.

The ability of servo-driven robots to position themselves at numerous stations allows them to separate parts from multi-cavity molds. The robot can place different part types from family molds in different bins, on different conveyors, or in different fixtures on downstream assembly equipment. Parts from bad cavities can be isolated and discarded. Robots can also be programmed to automatically discard or otherwise isolate parts whenever the injection molding machine's controller signals that quality-related process parameters have not been met.

Implementation of less well-known, but increasingly important, "simple" post-mold applications is already on the upswing at larger captive molding companies. If the general pattern of robotics adoption holds true, these will likely be employed by an expanding base of smaller custom molders seeking a competitive advantage. Here are a few such applications:

* Machining - Simple machining operations can be performed by a drilling or milling head mounted on the traverse beam or floor-mounted immediately adjacent to the press. Holes, bores, slots, lands, and similar features can often be machined with the help of a robot more cost-effectively than adding complex core actions to mold tooling.

* Quality Control - Numerous QC functions also lend themselves to "simple" levels of integration with robotics. Dimensional checks can be performed with either go/no-go gauging, with a contact-type variable gauge, or with vision systems capable of generating numerical results. Gauge feedback enables the robot to automatically isolate out-of-tolerance parts, and gauging data can be fed directly into SPC/SQC systems. Other QC tests that robots perform include weighing and leak testing.

* Packaging - Bagging machines can be integrated with parts removal. Delicate or sensitive parts that require further downstream processing, such as optical lenses, can be robotically bagged for temporary protection. Parts can be bagged in single or multiple units or in bulk for intermediate protection or distribution, and even as final packaging. Consumer-assembled products, such as toys and exercise equipment, often require bags of various small parts and hardware. Robots can bag such parts very reliably.

* Other tasks - Relatively common, single-station functions include flexing of living hinges as they come out of the mold and closing one-piece snap-caps for liquid packaging.

COMPLEX JOBS TAKE TEAMWORK

For the "simple" applications cited above, cost-effectiveness demands that cycle times for the part-removal robot be determined by the press cycle - not vice versa. So if the secondary operations cannot be performed within that interval, it is preferable to pass the part off to another automated workstation.

The most common of these complex applications are boxing and loading trays and magazines. Boxing can involve varying degrees of complexity, from a single item placed per box to individual packages filled and arranged in cartons in multiple levels and rows. Depending on the level of automation desired, full integration may involve numerous stations to shuttle cartons in and out of the boxing station, to expand fiat boxes, to seal bottoms and tops, and to store and stack the packed boxes. Trays and magazines used to arrange parts for downstream processing or assembly can be loaded, stacked, and conveyed, or shuttled.

Robots also excel at assembly. Snap-fitting of parts is common, as are ultrasonic welding and adhesive bonding. Parts with molded threads can be screwed together robotically. Automated workstations can be used to place hardware, including springs, clips, and spacers, and to torque threaded fasteners. Once they've completed the assembly, robots can then aid in quality control by checking for presence and proper placement of features on finished assemblies. As a rule of thumb, as many as three assembly procedures can often be integrated near the injection molding machine. Beyond that number, floor space tends to become restricted, so any additional automated assembly procedures are usually located in other areas of the plant.
POST-MOLD ROBOTIC OPERATIONS

INTEGRATION LEVEL FUNCTION EXAMPLES

Simple Automation: Degating Drop sprue into
granulator.
One post-mold Flex/Close Flex living hinge. Snap
operation is performed shut one-piece closures.
by the parts-removal Multiple Separate parts from family
robot or one down- Positioning molds. Isolate parts from
stream device. bad cavities. Isolate
parts
 if production parameters
 are not met. Place parts
in
 separate bins or on
 conveyors. Place parts in
 fixtures or trays. Stack
 parts.

 Machining Drill, mill, degate, trim
 gate vestige.

 Quality Check dimensions with
 Control vision system or contact
 gauging. Check for
presence
 of features using vision
 systems, contact gauges,
or
 sensors. Weigh and count
 parts. Perform
 leak/pressure testing.

 Bagging Bag single parts for
 protection.
 Bag multiple parts for
 shipping.
 Bag family-mold parts.

Complex Automation: Packaging Load and stack trays. Box
Parts-removal robot parts with single or
works with secondary multiple layers per box.
equipment Insert Feed inserts. Grip
inserts.
 Molding Place inserts in tool.
 Confirm insert placement.
 Extract finished parts.

 Serialization Deliver parts to laser or
 & Decoration impact printer,
 self-adhesive labeler, hot
 stamper, or pad printer.

 Assembly Deliver parts for
 (one to three ultrasonic welding or
 operations is adhesive bonding. Screw
 typical) parts together. Snap fit
 parts. Place metal
 fasteners.


Another assembly-related application - robotic loading of inserts into a mold for insert molding - differs from other examples of "complex" applications in that it adds value before, not after, the product is molded. Inserts are generally placed by the same end-of-arm tooling that is used for parts removal, but additional automated equipment is required upstream to deliver the inserts to the robot and position them properly.

Decorating and labeling stations - for hot stamping, pad printing, or applying pressure-sensitive labels - can also be fed by parts-removal robots. Stations may be integrated to perform art serialization by time, date, or sequential numbering using laser or impact printers.

When deciding which operations to automate, don't overlook opportunities for robots to work together. For example, two adjacent injection presses might each be equipped with a robot for parts removal. One of those robots could be a relatively simple pneumatic robot, while the other is a high-speed servo-driven model. If the servo robot has spare cycle time, it may be possible to integrate the two, so that the pneumatic robot hands off to the servo robot, which then adds value to production from both presses through a secondary operation. Ideally, servo-driven robots should be performing work during the entire molding cycle.

BEFORE YOU AUTOMATE

To get the biggest productivity gains from automation, it's important to carefully consider several implementation issues beforehand. For one thing, remember that today's injection molding robots are likely to last up to 20 years in service, during which time numerous changes in your production requirements may occur, and numerous opportunities to enhance productivity may present themselves. Selecting robots on the basis of both present and potential future needs can cost more but may save money down the road. For example, servo-driven robots, while up to 80% more expensive than pneumatics on initial purchase, are much more flexible for integrating post-mold processes and can thus become more economical in the long run.

The same holds true of today's sophisticated, user-friendly control systems, which can be reprogrammed more readily than older or simpler systems to perform different tasks. Purchasing a robot with higher speeds and longer strokes also provides more flexibility, allowing the integration of more processes within a given cycle time and work envelope.

You will need to select your robotics vendor carefully. It is important to distinguish between suppliers who are mere hardware vendors and those who are capable of engineering complete automation solutions. Even "simple" secondary operations, such as drilling, bagging, and degating, involve fairly complex hardware and software engineering, plus a solid understanding of injection molding production, in order to provide the correct interlocks, sequencing, and positioning between system components. As a molder, you probably don't want to act as your own systems integrator, trying to resolve conflicts between equipment from several different vendors. Instead, select an automation vendor who will do this for you, managing the project from the planning stages to the training of your production personnel.
COPYRIGHT 1996 Gardner Publications, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1996, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Article Details
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Author:Mallon, John, IV
Publication:Plastics Technology
Date:Oct 1, 1996
Words:1824
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