Robot workcell for injection moulding plastics

Citation

(2010), "Robot workcell for injection moulding plastics", Industrial Robot, Vol. 37 No. 2. https://doi.org/10.1108/ir.2010.04937baf.002

Robot workcell for injection moulding plastics

Article Type: Mini features From: Industrial Robot: An International Journal, Volume 37, Issue 2

Inject Plastics is a trade injection moulder producing a huge variety of plastic parts. Not unusually, the project in question concerned programming a robot for high speed, high precision work, in a fully automated workcell. Less commonly, it involved a powerful six-axis robot already installed alongside an injection moulding machine, rather than designing the cell layout from scratch.

A family owned business established in 1986, Inject Plastics is based in a modern 13,000 ft² factory on the town’s industrial estate, adjacent to the Barr & Paatz premises. It invests continually in leading edge technology and is equipped with the latest microprocessor-controlled Demag injection moulding machines, with clamping forces ranging from 35 to 300 tonnes, enabling it to produce plastic parts up to a kilogram in weight. Unlike many injection moulding companies, which tend to employ simple three-axis Cartesian fixed automation systems for demoulding, Inject Plastics also boasts a six-axis, Stäubli RX 90L industrial robot, with a reach of almost 1,200 mm, a maximum payload capacity of 6 kg and an impressive repeatability of ±0.025 mm.

“Cartesian systems are OK for loading and unloading, but not sufficiently adaptable to perform the other operations and movements frequently required, such as rotating the moulding or assembling components,” says Inject Plastics MD, Richard Bromley. “A six-axis robot, with its full range of accurate and repeatable motion over a wide work envelope, provides the ideal, cost-effective automation solution.”

Industrial robots can also be reprogrammed and redeployed for other processing tasks, an inherent flexibility that was exploited by Barr & Paatz on this project. On behalf of a trade customer, Inject Plastics produces precision mouldings for scratch-resistant safety goggles and the Stäubli robot was previously used as a pick and place device in a process that involved laying paper-thin plastic film inside the moulding tool and injecting plastic onto the back. However, a product redesign necessitated adding film to both faces of the optical moulding, creating a three-layer sandwich, which meant fully automating the more complex process.

Since the robot and some safety guarding were already installed, revising the whole cell layout for optimum performance was impractical, so Barr & Paatz had to work within existing parameters and add ancillary equipment for such functions as film handling, bonding and gate cropping. The robot specialists also incorporated new loading mechanisms, extra guarding and safety interlocks, as well as air filtration equipment that enables the workcell to operate in a dust-free environment.

The moulded goggle lenses are curved to eliminate optical distortion, but the robot starts by configuring the end-of-arm tooling to pick up flat plastic film, which is achieved by first docking the tool into a custom-powered drive configuration that mechanically flattens the shape. Once the tool is in the flat figuration, the robot collects two separate strips of plastic film, one on either side, and then returns to the drive station to reconfigure the tool into a curved format.

When the moulding machine is open and ready, the robot rotates the end effector 90° and removes the finished product by means of vacuum cups, then flips back 90° and loads the new film onto each face of the mould, ready to produce the next three-layer optical lens. Finally, the robot deposits the finished product onto the exit conveyor and is ready to start the whole cycle again.

“The whole process is completed without the product being touched by human hand, which contributes to its optical integrity. Quite frankly, it would be impossible to produce these parts to the required standard and in the quantities involved, using manual procedures,” concludes Richard. “Robotics eliminates the costly labour element from the process and it’s fair to say that the operator’s skill set has actually increased, since he has had to become familiar with the working kinematics of the robot.”

For further information, please visit the web site: www.barr-paatz.co.uk