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March 8, 2004

6 Min Read
Flexible end-of-arm tooling aids molding process

The combination of an articulating-arm robot and flexible end-of-arm-tooling can deal economically with a variety of part-removal and manipulation challenges.

A wide variety of standard end-of-arm-tooling components are available to choose from in putting together custom part-handling systems.

EOAT forlabel insert molding

A triple-action EOAT uses a combination developed for an insert molder. With limited space, the EOAT first picks up and inserts the label. The label is then swiped with another motion of the EOAT for charging in the mold. The swiping motion created by the EOAT reduces the size of the charging unit vs. charging in one stationary mode. The final gripping EOAT motion removes the finished plastic bottle, with inserted label, from the mold. Such complex EOAT concepts can be best served with3-D drawing services (see CAD graphic).

EOAT for metal insert molding

The photo and CAD graphic illustrate the use of end-of-arm-tooling for placement of metal inserts and removal of the insert molded parts. Note the multiple insert carriers and the gripper for the runner system. This is an example of a system built of standard components that may be less expensive and easier to maintain than a custom unit.

EOAT for small parts

For quick action and tight spaces, a stock retracting vacuum arm (RVA) is used to remove a small telecommunication part from a mold. The lightweight, thin cylinder EOAT components grab and automatically retract to remove the parts.

While much time and thought go into the purchase of an injection molding machine or robot, a robot?s end-of-arm tooling (EOAT) is often a last-minute consideration.

Given that a robot is only as good as its ability to pick, place, move, handle, hold, and manipulate a part, there are clear reasons for moving the end effector to a higher priority. EOAT is a relatively inexpensive part of the entire workcell, but it is an integral part of the molding operation and could be a costly operational expense if not set up correctly.

A Proper Start

To determine the tool that best meets both part and production needs, a meeting of the minds with maintenance, purchasing, and production departments is needed. Project requirements should be spelled out and agreed to. The goal is to get the most effective EOAT for the application, keeping the other parts of the workcell in mind.

Starting with the mold, determine whether or not minor changes can be made to it for more effective removal of the part. Here are some items to review that can help remove the part from the mold with less effort:

  • Ejector pins must have enough travel to push the part forward and the proper shape so the finished product is not marked unnecessarily.

  • The addition of a small radius to a square corner on the part may help free the part from the mold.

  • Changing the material temperature may allow the part to eject more freely and to be removed after ejection with less chance of marking the surface or deforming the part.

Questions to Answer

With the mold design optimized for ejection, how much pulling and/or twisting force is required to break the part loose? What movement functions can the robot provide to pick the part from the mold and place it in a container or on a conveyer? What movements does the EOAT need to make in addition to the robot?s movements? Can the robot reach the farthest point or is an extension arm required? Are there enough air/vacuum circuits and electrical I/Os available on the robot to connect the EOAT? Is the robot capable of moving at the speed required for the mold cycle time?

EOAT must be designed with these conditions or limitations in mind. In addition, the combined weight of the part and the EOAT must not exceed the robot?s payload specification.Knowing the above conditions, think about the part itself. Consider the weight, texture, available places to grip the part without mold obstructions; the temperature of the part upon ejection; and the physical size that needs to be maneuvered out of the press to the conveyer.

Types of EOAT

When choosing end-of-arm tooling, consider the following characteristics:

  • Lightweight EOAT helps meet robot payload requirements and reduces robot maintenance costs.

  • Flexible/modular EOAT allows for fine adjustments to the job and can be re-used on future projects.

  • Strong/rigid EOAT holds parts firmly and better withstands many cycles.

  • Modular components are often less expensive than ordering a one-of-kind custom tool, and spare parts are more readily available.

Vacuum cups are generally the least expensive method of grabbing a part and come in many varieties and materials. Elastomeric compounds and silicon vacuum cups handle high temperatures. Silicon is also good for holding rough surfaces. Polyurethane wears very well. For an application that requires oil resistance, consider polyurethane, nitrile rubbers, or vinyl. To avoid marking the surface of a part, the best choices are nitrile rubbers or silicon in a cup with bellows.

If only vacuum cups are used on the EOAT (no grippers), be sure the speed of the robot will not create a shear force on the cups that causes the part to drop during a swift or twisting motion. In some cases, a basic gripper can be used to secure the part during transport.When a part sticks in the mold?even if it happens only occasionally?pneumatic grippers are normally required. Grippers are also used when a part doesn?t have sufficient surface area for a vacuum cup, or if the part is very heavy. Grippers come in a selection of lengths and rotations.

Make sure the part is gripped on a noncritical surface if esthetics is important. Some applications may benefit from a sensing circuit?a sensor that makes sure the grippers or cups are holding the part and sends a signal to the robot to proceed with its motion.For applications that require a twisting or prying motion to remove the part from the mold, or to move the part and EOAT out of the mold area, special air cylinders can be added to the tool to gain this additional motion over and above the capability of the robot itself. The cylinders move the EOAT independently of the robot?s motion.

Flexible EOAT Installations

In the auto industry, special care must be given when handling a Class A surface part so as not to mark the surface. A nonmarking acetal gripper finger mounted on the EOAT should be used in this case instead of vacuum cups.

Another example of a how EOAT can interface with a complex molding process involves a two-shot mold with a nylon and rubber combination part. A multiple-function EOAT removes the nylon part from the operator side and moves it to the nonoperator side to be overmolded with rubber. During the movement, the EOAT rotates and adjusts the spacing before placing the nylon into the overmold cavity. The nylon/rubber part is then removed from the nonoperator side as part of the sequence. This complex tool helps maintain a short cycle time and provides several functions that the robot is not capable of alone.

If your technical departments have the time and capability, you can select the components and build your EOAT in-house. If time and skill are constraints, look for a full-service supplier that can supply the components, build, and install the EOAT. Only a few suppliers handle both components and building of EOATs. These suppliers are found quite easily on the web by searching for ?EOAT.?

Editor?s note: Richard Petz is general manager of SAS Automation Ltd.

Contact information
SAS Automation Ltd., Xenia, OH
Richard Petz
(937) 372-5255; www.sasgripper.com

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