Plastic Injection and Robots: High Efficiency and Minimized Wear Are Keys to Success

Robots have become key components to any successful plastic injection operation. Their primary purpose are to establish consistency in cycle time and reduce labor cost. This article will define key areas that define the profitability of any robotics operation, regardless of brand or the programming that defines a robot's efficiency within your process.

Takeout time:

Takeout time is one of the most crucial aspects of any robotics operation. Robots are designed to ultilize the precision of CNC machines...utilizing x, y and z plane setpoints to enter the mold, line up for cup placement on the parts, grip the runner for removal, remove the shot and exit the mold. The time that all of these motions take are absolutely crucial to the overall efficiency of your machine's cycle. Ascent and descent into the mold are should be maximized. Many company's fear the robotics precision, and in doing so slow their cycle times by entering and exiting well beneath the capacity and design of their robots capability. Consult the manufacturer of your equipment and let them establish the capacity of your takeout time. You will likely be surprised by the amount of time that can be removed from your cycle by maximizing the efficiency of robotic takeout time.

Cup Size and Placement

It is important to maximize your vaccuum system by matching cup size to 90% of total part area. Using too small of a cup can reduce your takeout time by increasing dropped parts and downtime associated with cycle failures. Your cups should be positioned on a level plane that matches the position of the cup once approach and touch-off has been completed. When using spring loaded cup shafts, full eject forward should move the springs to 50% of full retracted capacity. It is also important to recognize that cups come in different shapes as well as materials. Some cups are more tacky due to the material type used when they are molded and can improve extraction due to their gripping nature. Other applications (such as appliique molding) may be more suited to a cup with less gripping power for the purpose of improving separation. The shape of a cup can also improve or detract from your efficiencies.

Matching Ejection to Extraction

It is imperative that you learn the basics of part extraction...ejectors should move forward matching the speed of the robot when the two functions are performed bilaterally. Ejectors moving slower than End of Arm evacuation motion can result in cup separation..as well as an end of arm moving slower than ejection can create a bind or overcompressed condition resulting in part extraction failures.
When a robot is positioned prior to ejection, it is important to position it in a manner that assures that full contact has been made with the part to assure mating and extraction.. but remember, too much pressure at full ejection can cause the part to bind, and result in poor and failing part extractions.

Quite often you may find it necessary to enter delay timers during part extraction to assure that the parts mate well prior to backing away from the mold and exiting the mold area.. but it is also imperative to maximize these timers to assure that you aren't adding unneeded time to your removal process. Ejection speeds should be maximized in forward and retract motions, while equally matching robot backoff speed. Cycle repeatability is absolutely paramount to the success of your robotics operation. Fast removal of parts is great... but if your speeds are creating downtime. it defeats the purpose..

In closing, many companies fail to match the remaining programming to mold open. Part removal is your most crucial event. The rest of the cycle should be conducted in a manner that once gates are cut, parts are placed on conveyor, etc. your robot should move back over the mold for the next extraction just prior to mold full open to begin. There is no sense in beating up your equipment for the full robotics profile if the end results in the robot waiting on the mold to open. Following this protocol will reduce your maintenance times that are often associated with high speed wear and tear.

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Garrett MacKenzie: plastic411.com Editor & Technical Writer

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Plastic Injection and Robots: High Efficiency and Minimized Wear Are Keys to Success

Takeout time:

Cup Size and Placement

Matching Ejection to Extraction

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