How to choose the robot end tool (EOAT)

- Sep 13, 2019-

Today's injection molding companies focus on the choice of injection molding machines or robots. However, few people have paid attention to the use of robotic end tools (EOAT). In fact, EOAT is a very important part of the injection molding process.


If the injection molding company wants the robot to be able to automate the entire process of picking, placing, moving, handling and holding the product, they must seriously consider the choice of the end tool system (EOAT) that best suits their robot.


The multi-joint robot and the flexible end tool are connected together to economically move a variety of products.


EOAT choice


What kind of end tool system (EOAT) can meet the needs of products and production? In general, in order to select the most efficient EOAT system, injection molding companies must first consider the opinions from the maintenance department, the procurement department and the production department. At the same time, they should also consider other factors that affect the release of the product. Specifically, these factors are:


1. In order to avoid unnecessary marks on the product, proper correction of the mold should be considered to make the product more convenient to be removed. In order to make the article easy to demold, the shape of the pin is generally required to be appropriate, and at the same time, the pin must have sufficient stroke so that it can push the article forward.


2. In the design of the appearance of the product, it is easier to demold by adding a small chamfer.


3. Changing the temperature of the material not only makes the release of the product easier, but also reduces the chance of deformation or deformation of the surface of the product after demolding.


After optimizing the design and revision of the mold, you must also understand the following issues:


1. How much tension or shear is required to remove the product?


2. Take the product out of the mold, put it in a container or put it on a conveyor belt. What operations can the robot provide? What supplementary actions does the EOAT system need to work with the robot?


3. Can the robot reach the farthest point?


4. Do you need to install an extension arm?


5. Is there enough air/vacuum circuit and current input and output on the manipulator so that it is connected to EOAT?


6. Can the manipulator achieve the speed required by the molding cycle?


After fully considering the above conditions and factors, the EOAT system can be designed and selected. When choosing an EOAT system, the following aspects should also be considered: the weight and texture of the product, whether the product has a suitable position for clamping, whether the product is obstructed by the mold, the temperature at which the product is ejected, The area in contact with the tool when placing the article on the conveyor. Finally, it should be noted that the total weight of the product and EOAT cannot exceed the load range of the robot.


Use of EOAT


Different types of end tools (EOAT) have different characteristics. For example, lightweight EOAT can meet the needs of the robot load range and reduce the maintenance cost of the equipment; flexible, combined EOAT not only makes the operation have good adjustability And can be used again in later production; sturdy, rigid EOAT can hold the product firmly and has a long service life; EOAT made up of standard parts is often cheaper than custom-made special tools, and Its accessories are usually also easier to buy.


Multiple standard end tool parts


In general, the use of vacuum chucks to grab articles is one of the cheapest methods. Vacuum chucks are available in a variety of materials and can be made from different materials. Among them, the suction cup made of elastomer and silicone rubber can be operated at high temperature, the suction cup made of silicone rubber is very suitable for grasping the surface rough product; the suction cup made of polyurethane is very durable. In addition, in actual production, if the suction cup is required to have oil resistance, it is conceivable to use a material such as polyurethane, nitrile rubber or vinyl-containing polymer to manufacture the suction cup. Generally, in order to prevent the surface of the product from being scratched, it is preferable to select a suction cup with a bellows made of nitrile rubber or silicone rubber.


In the case of EOAT using a vacuum chuck (without clamp), it should be noted that the movement speed of the robot should not be too high, otherwise a shear force will be generated on the suction cup, which will make the product fall easily during the rapid twisting process. . In some cases, a clamp can be used to ensure safe delivery of the product. In view of the possibility that "the article adheres to the mold", a clamp can usually be installed to solve this problem. When the surface area of the product is too small or the product is too heavy to use the vacuum chuck, the same problem can be solved by using a clamp.


If the product is very strict in appearance, the clamped portion cannot be the outer surface. To solve this problem, a sensing circuit can be installed. After confirming that the clamp or suction cup has gripped the product, the sensor sends a signal to the robot to enable it to proceed to the next step.


In the case where the manipulator has limited athletic ability and needs to be manually twisted or tilted to demold the product or remove the product and EOAT from the molding zone, a special cylinder capable of moving the EOAT alone without relying on the robot operation can be added. This problem has been improved.


The end tool for in-mold labeling can perform three actions: in a limited space, EOAT picks up and inserts the mark and then fixes the mark in the mold. This operation can reduce the size of the device compared to static labeling devices. The last action of EOAT was to remove the branded plastic bottle from the mold.


In general, care must be taken in the handling of Class A surface products when injecting automotive parts. In order to avoid scratches on the surface, the use of a vacuum chuck must be absolutely prohibited. At this time, it is conceivable to install a clamp made of acetal on the EOAT to effectively avoid scratching the surface of the article.


So how do you use EOAT for complex machining processes? To illustrate this problem, we exemplify an example of "overmolding with nylon and rubber." In this example, a multi-functional robotic end tool (EOAT) is used to move the nylon product from the operator's hand to the side away from him. During the movement, the EOAT is rotated at a certain angle, and when it is adjusted to a suitable position, the nylon is placed in a cavity that is overmolded with rubber. After the injection molding is completed, the nylon/rubber product is taken out by EOAT. In this example, the molding cycle is greatly shortened by using such an end tool, and it also provides an operation that cannot be performed by a single robot.


In the production of small products, the operation speed is very fast, but the operation space is small. At this time, the small electronic parts can be taken out from the mold by using a retracting vacuum arm (RVA for short). This EOAT is lightweight and comes with a small cylinder that grips the product first and then moves it back by automatic retraction.


Of course, for injection molding companies, in terms of time and ability, it is entirely possible to choose the parts to assemble their own EOAT for their own production needs. If you are limited by time and technology, you can find a supplier that can provide full service.