Purchasing Basics:Robots for press-side handling

Molders, custom and proprietary, are increasing their demand for automation to get the parts out of the mold and get them on their way through the plant. There are many reasons to consider automation, and it's important to focus on your own priorities among these reasons. Here are some of the benefits automation projects focus on achieving. Which are your priorities?

Once the objectives have been communicated to the potential vendors, you will find that many of them have detailed information requests that will help you through the process, probably in more detail than nearly any other purchase. If you are automating an existing molding operation, one very good place to start is with a video of your process as it presently exists. Even if it's not a new part, start with part information.

The Part and Mold
What is the part or parts? What does it weigh, how many are in a cycle, and how delicate is it? Is the sprue molten on ejection, formed, or is there no sprue? How many cavities are in the mold? Is the mold hot or cold runner? When the mold opens, how is the part oriented in the mold? If the mold is not already built, is there opportunity to influence the orientation because of the robotic handling? How is the part ejected from the mold? Can the ejector stroke be set so that parts are not dropped but are held? Where is the part gated? Is it hot when it comes out of the mold?

What specific functions have been identified as desirable? What sequences do you need the robot to repeat?

If it is to be used for many different parts, how often are molds changed? By what means? Does your process require traceability, so that parts from different cavities need to be kept separate?

The Machine
Specify the machine by manufacturer and age. What tonnage is it, and what is the control method and control voltage? Is it presently attended by an operator? Is it an insert application, requiring loading of inserts as well as removal of parts? Do you want the robot to load the inserts? Or could the inserts be loaded into a tray by the robot, and the tray loaded into the machine by an operator? An operator-loaded fixture reduces the overall cost of automation, although the operator is not eliminated. However, the consistent press cycle benefit still applies.

Get out your measuring tape. Most robot vendors have a whole series of measurements around your molding machine they need to have. Ask for a blank sheet and fill in the dimensions, or communicate in writing all the details on the machine's dimensions, such as distances for clearance-overhead obstructions, top of the platen to top of the safety gate, mold centerline to floor, platen edge to outside of safety gate, thicknesses of platen halves and mold halves, tiebar diameter, guide pin length on both sides, and so forth.

All these measurements will help determine the envelope in which the robot can operate. Is there enough room beside the press for a side takeout robot? It's faster, but also restricts access at the rear of the press, has a more limited work envelope, and requires a larger, more awkward main arm.

Programming
Will this be a robot in a permanent application that is programmed at the robot manufacturer's factory on a hardware basis? Pneumatic robots are usually programmed that way. Will you need to change programming frequently so that a software approach (servo robots) is better? Will the operator need to learn how to interface with the robot's controls, or will a programming specialist be available? Is offline programming or programming via a teach pendant more important to you?

Cycle Time

The overall estimated cycle time is important, but the mold open time is also critical. Only a small part of that overall cycle can be devoted to mold extract. If the robot is expected to use only 21/2 seconds out of a 20-second cycle for part takeout, for example, the robot manufacturer needs to know this. If this is a new project, you can work from reasonable cycle time estimates based on other projects. Most of all, be sure that your candidate vendors understand what your objectives are as they prepare proposals for your evaluation.


With our thanks . . .
. . . to a number of companies who provided material for this article. They include CBW Automation,Conair,Fanuc Robotics,Remak North America,Wittmann Robots, and Yushin America.

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