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Almanac: The state of automation

DTI Globalwatch : 21 October, 2006  (Technical Article)
A beam-mounted pin marker for date coding and other marking requirements increases robot utilization, all within the existing molding cycle. Automation has been the next big thing in molding for several years, but it wasn
Processors facing increased competition are relying on new automation strategies to maximize machine utilization and part quality while continuing to reduce labor and scrap costs. The selection and flexibility of robots, combined with lower costs for automation technology, are providing processors an even greater advantage than previously possible. The ability of the robot to control the entire workcell has been further advanced by simple graphical programming for pick-and-place routines. In addition, Internet connectivity offers enhanced operation with immediate access to system status, alarm messages, manuals, and so on.

Following are several evolving trends in robots and automation:
1. Flexibility. Today’s top-entry, electric traversing robots are fitted with six degrees of freedom. Molders used to consider automation only for high-volume jobs, especially for specialized downstream workcells. Now flexible automation workcells are being developed that allow quick changeover of end-of-arm tooling, stored programs, and downstream workstations where savings can be realized for each application.

Most typical are top-entry, traversing robots fitted with EOAT rotations that allow great freedom to accomplish many secondary functions. Most basic CNC robots can provide simple part removal and conveyor placement in less than 10 seconds, offering additional overall molding cycle time to accomplish many part handling or added-value tasks in the downstream workcell. Commonplace extra work performed by the primary workcell robot includes degating, cavity separation, insert loading, box or tray filling, weighing, assembly, and QC handling.

2. Added cycle time, added savings. In some fast-cycle applications, a robot replacing the automatic parts-drop (gravity) method may add some mold-open cycle time. With better SPC and production monitoring controls, management is now able to calculate the robot’s advantages to help ship more good-quality product with lower labor and scrap costs and increased machine utilization than without it, despite the impact to cycle. Molders, mold designers, and process engineers are learning how proper mold and workcell design can support efficient robotic systems.

3. Payback. Plastics robots’ features and flexibility increase while their prices continue to fall, further reducing payback periods and enhancing the profitability with their use.

4. CNC robots. Electric top-entry robots are the baseline for the majority of molders and are often considered a necessary component with a new molding press. Pneumatic robots, once the only available technology, are now becoming a much less desirable choice when flexibility is necessary. Pneumatic robots cannot run as fast and inherently have more shock and wear from point-to-point and stop control. Additionally, pneumatic robots often require the user to climb up on the press to set the stops for each mold setup, whereas electric-drive robots allow the positions to be set from the floor and stored for future runs.

Most robots’ vertical stroke in the mold comes down to the centerline. After part removal, it’s important to stroke down below the press centerline to a more workable secondary equipment height. Therefore, it is best to have longer vertical strokes and an electric NC or servodrive on the vertical axis to allow one position of the vertical stroke to meet the press centerline and an additional vertical stroke and multiple positions to release or stack parts below the centerline. The electric drives also allow positioning control to secondaries.

5. Servo robots. Many vendors use the word “servo” loosely. A properly controlled CNC or induction motor or frequency motor with multiple inverter motors can operate similarly to that of true servomotors. The true 3-D servo with proper control can allow curved motions. Servodrives are not always faster than frequency motors, but curved motions may help.

For example, when a rectilinear robot moves into a mold, it must move down and then forward, whereas a curvilinear servo robot can move down and forward simultaneously to save time. Once it clears the safety gate of the press, the robot can move diagonally down to secondaries instead of over and down, again, with potential time savings. However, many applications with longer cycles may not need the luxury of servo when flexible CNC robots for reduced costs are available.

6. Speedy linear robots. With research and development into new materials such as carbon fiber composites, some robot vendors offer lighter-weight construction and direct-drive, high-speed servos to reduce part removal times to less than .6 second. With these new capabilities, the mold and EOAT must be designed to optimize cycle reduction.

7. Articulating robots. In the past, articulating robots were rarely used for part removal, but rather for downstream assembly, specialized degating, or added-value applications. Historically, the more expensive articulating robots have been slower, required more mold daylight, required side-entry operation and removal of the safety gate, used more workcell floor space, and had a cumbersome programming language unfamiliar to the typical molding technician. However, in the post-mold workcell, articulating robots are often considered now.

Linear robots can also offer six axes of freedom and provide a competitive solution for many applications. Sometimes, more than one linear robot may be used in a workcell to meet cycle requirements, yet still remain more cost-effective than an articulating robot.

8. Terminology. The SPI Robot Interface AN-116, currently version 4.0, is standard for molding machines and robots; it provides a handshake of signals and inhibits to allow safe operation and control between a robot and molding machine. Any robot manufacturer can supply the robot with a simple connector, which is then plugged into the standard SPI robot interface of the molding machine to complete the handshake. Almost identical is the Euromap standard E-12 interface to accomplish the same handshake.

One term to know is robot referencing. This refers to a homing sequence generally used with an electric-drive robot to recalibrate and reference itself to a home position. Operators will reference a robot before starting it into an automatic cycle or teaching a new sequence. Some vendors allow custom “homing” or reference routines to allow the unskilled operator simply to push one button after a workcell alarm to home the robot safely and restart the automatic cycle.

9. Windows of justification (return on investment). ROI for plastics automation has remained about the same over the years. Note, however, that several manufacturing cost factors have increased while robot prices have fallen. In essence, costs for labor, resin, mold steel, transportation, insurance, and workers’ compensation have risen, while the available high-quality labor pool has shrunk. This imbalance with lower robot costs has offered faster automation payback periods or increased profit through the utilization of robots. (See “Where Your Robot ROI Comes From.”)

10. Simpler, easier controls. Many vendors now offer graphical operator interfaces to quickly teach simple pick-and-place routines and set timers. Advanced workcell programming may be accomplished offline and some vendors offer online peripheral workcell programming. It is the robot controller that acts as the central workcell command. An advanced controller that allows customization via sequence or line programming is essential to maximizing workcell flexibility, assigning I/Os, and performing faster changeovers, easier workcell integration, and setup storage.

With the increasing trend among molders to make greater use of robots for tasks beyond simple pick and place and quick mold changeover, the robot control’s teaching capability, memory capacity for setups, power to control the complete workcell, and user friendliness for the average mold technician have become important factors.

11. Downstream opportunities. A wider range of technical downstream applications offer less risk and faster lead times with greater complexity. Insert loading applications have always been an important and justifiable application for robots. The rate of new applications using inserts and robots is increasing. Now bolts, nuts, appliqués, textiles, paint films, blades, pins, and plastic parts are commonly loaded into presses as inserts that cannot otherwise be efficiently or consistently run with labor. Also, multicomponent or two-shot molding may use the same robot to handle the finished parts and also pick and place the substrate parts.

12. Inmold labeling. Inmold labeling is now becoming more prevalent in North America as molders look for ways to reduce costs and offer more value. It requires a thorough knowledge of the process as well as involvement at the early stages of the project from all suppliers of the system. Working with experienced suppliers is critical to the overall success of the system. It is not something that should be considered after the mold is made and the part is in production, as the various components are dependent on each other.

David Preusse, president of Wittmann Inc. (Torrington, CT), has an engineering degree from University of Lowell, an MBA from Pepperdine University, and 20 years of experience in plastics automation. Wittmann manufactures auxiliary products such as robots, mold temperature controllers, material handling and drying systems, granulators, chillers, and water systems. Contact Preusse at or (860) 496-9603.
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