Articles: Technology Notebook

Custom vs. modular EOAT for injection molding
By John Westbeld, engineering manager for SAS Automation

Most end-of-arm tooling (EOAT) can be constructed of standard modular components. The demands of some applications, however; go beyond the scope of modular elements, and require true custom construction. How can you tell when it's time for custom EOAT? 

You may have been building your own EOAT for years but you have a couple of molds where the parts stick and they need to be pried off of the cores. Do you have operators pulling the parts from the mold or do you have a custom EOAT designed and manufactured specifically for your application to remove those parts from the mold?

Straightforward pick-and-place molding applications usually have straightforward EOAT made of modular robotic EOAT components. The more complex the molded parts are, the more likely they will need manipulation to remove the parts from the mold. Also, molds that were designed with little thought of EOAT or robotic automation can pose problems as well. 

Identifying when you need a custom EOAT

Any of the following production challenges can be met with a custom EOAT:
  • The part is sticking to the core and needs to be pried off.
  • One corner of the part needs to be lifted first so the part can rotate before it can be removed cleanly.
  • The part needs to be shuttled a certain direction to be removed cleanly from the core.
  • The part needs to be rotated parallel to the mold face to clear the core.
  • The Class A surface of the part cannot be touched with standard components or it will be marred. 
  • The part geometry does not lend itself to be removed with standard modular robotic EOAT components.
  • The surface texture is so rough that vacuum cups are ineffective.
  • The part has to be manipulated outside of the mold to place it into packaging.
  • You have an in-mold labeling (IML) application and you need to place labels into the mold.
  • You have an insert molding application and are trying to insert threaded inserts into the mold.
  • You need to perform downstream automation on the part after it is removed from the mold (degating, assembly; deflashing, vision systems, etc). 
  • Multiple cavities of any of these applications only increase the complexity.

Custom EOAT Adds Capabilities
A custom EOAT can be designed to manipulate parts off of the mold. There are a wide variety of pneumatic actuators that are typically used to add capabilities to gripping mechanisms on the EOAT. These extra motions are used to pry; rotate, shuttle, and secure the parts. 

The word "custom" carries with the it connotations of expensive and unreliable. Expense depends on multiple considerations. How much does it cost in cycle time and labor to have an operator remove the parts from the mold? Can the operator monitor several IMMs or is the operator limited to one press in order to remove the parts manually? 

Continued on next page
 

  

Custom vs. modular EOAT for injection molding (continued)

Reliability is a function of design. Make sure that your vendor has custom EOAT design capabilities. They will have proven concepts from manipulating the parts for most applications. They can also walk you through the process of design, manufacture, assembly, functional testing, and installation of custom EOAT.

Several applications illustrate ways of meeting EOAT challenges with custom equipment. The first involves electrical panels in a two-cavity mold. The challenges were to secure the parts mechanically, absorb the ejector stroke so the parts will not fall on ejection, shift the parts closer to each other to fit in divided dunnage, keep the EOAT envelope as close to the part envelope as possible, and cope with parts that are porous with ridges and required special handling. 

The custom EOAT shown above left is designed and manufactured to remove electrical panels from a two-cavity mold. The parts are porous and have ridges on them so vacuum cups could not be used to secure the parts. Mechanical grippers with custom jaws were used to secure the parts. Since vacuum confirmation switches could not be used for part verification, photo-electric sensors were used. 

The ejector stroke of the press had to be absorbed by the EOAT so the parts would not fall upon ejection. A custom rod/bearing/spring assembly was designed into the base plate of the EOAT to absorb the ejector stroke with precision. This also kept the EOAT envelope within the part envelope. 

The EOAT was required to place the parts into divided dunnage on a conveyor. The center-to-center part spacing in the mold was not the same as the center-to-center part spacing in the dunnage, however. 

One part needed to be shifted toward the other to achieve this spacing. This was accomplished by a slide cylinder assembly. 

The second example involves door frames in a two-cavity mold and is shown on p.2. The challenges included securing the parts with mechanical grippers requiring part compliance, a requirement that the new EOAT weigh less than the existing EOAT, and dealing with glass-filled parts requiring special handling. 

The parts have several support ribs on them, so vacuum cups are not an option. Mechanical grippers were used to secure the parts and ultrasonic sensors were used to detect part presence. 

The system this EOAT is used on is very old so the robot and IMM repeatability were obstacles to overcome. The grippers were mounted on individual compliance devices to accommodate the tolerances in the system and align the grippers to the parts. 

To reduce the weight relative to the existing EOAT a custom plate was designed with lightning features such as holes, chamfers, and radii. The plane was thick enough to ensure a robust, rigid frame. 

These are a few of the many applications in which custom EOAT enabled system automation. Most injection molders have several custom EOAT in their shops for complicated molds. For applications in which neither manual nor modular EOAT are good options, custom EOAT is an excellent alternative. 

Contact Information
SAS Automation, Xenia, OH
(937) 372-5255; www.sasgripper.com

 

Plastics Machinery & Auxiliaries May/June 2006 Edition
Reprinted with permission from Canon Communications LLC