Extruded Plastic Sheets Palletized by a Robot

Alliance Automation, LLC has developed an automated robotic sheet stacker at the end of a plastic sheet extruder line for the thermoforming industry.

THE PROBLEM

A typical environment for a plastic thermoforming plant that extrudes its own plastic in-house includes ambient temperatures that can exceed 95°F.

Two operators unloading 80lb to 150lb sheets of plastic that are freshly extruded at 300°F and placing it on a pallet can be a very demanding and challenging task.

In the current labor market, this is not a position that is easy to fill.

Alliance Automation, LLC in Flint, MI, was presented with this opportunity to develop an automated solution to solve this problem.

Two stations allowed for the operator to load and unload parts while the robot worked on the opposite station, reducing cycle time.

EXISTING EQUIPMENT

When looking at an application like this, the customer typically already has an existing extruder with some type of conveyor where the operators unload the sheets and stack them. The pallet is stacked until it is approximately 36” tall and weighs over 2,000lbs. These sheets are then moved to the thermoforming machine, where they are molded and take shape. The extruder machine also may be old with outdated controls. Scrap material is picked by hand and placed to the side, and operators use a guide to stack sheets consistently with a setup shown below.

OBSTACLES

Customer orders determine the production need where length, width and thickness can vary drastically. For example, we will analyze an extruder that makes sheets with a 10’ width. At the end of the extruder are blades that cut the sheet width and a shear mechanism that cuts the desired sheet length. Below is an example of various sizes that can run on one line.

There are two significant obstacles when looking at automating this process. The first consideration is the large variety of sheet sizes, and the second is handling the scrap material. The system has to adapt and pick only the main sheet and ignore and dispose of the scrap material.

Another obstacle is integrating a new robot system with an old extrusion line. Communication between the systems can be difficult and requires some innovation to do so.

SOLUTION

Alliance Automation developed and integrated a robot system at the end of the extruder line to automatically unload and stack the sheets onto two pallets.

The system consists of a custom conveyor, robot system, scrap conveyor, two pallet stations, and safety devices. The conveyor is 120” wide and designed to reach the back end of the extruder right against the shear mechanism. At the end of the conveyor is a pop-up mechanism to stop the sheet and scrap pieces. Presence sensors are integrated on the shear and in the conveyor to track the sheet as it moves through the system.

A Fanuc M-900iA/260L robot with a 3.1m reach and 260kg payload is located on the side of the conveyor. On the end of the robot is a custom end-of-arm tool equipped with multiple rows of suction cups, 13 individually controlled valves, laser sensors, and a retractable failsafe mechanism.

There are two pallet stations that the robot loads. This allows the robot to continually stack one side while the other side can be unloaded and loaded with a new pallet by a forklift driver. Sensors built into the pallet stations verify that a pallet is loaded and when a pallet is full.

CYCLE

A complete cycle starts with the shear mechanism that cuts a sheet, the pop-up stop is activated, and the conveyor speeds up. The sheet and scrap then run into the stop and wait for the robot. The robot determines what valves to use and only picks up the main sheet, leaving the scrap. The robot moves up, and the pop-stop retracts, allowing the scrap pieces to continue down the conveyor and onto a scrap conveyor into a bin. The robot then moves to one of the active pallet stations and stacks the sheets. This operation will continue until the stack height reaches 36”. An audible alarm alerts the forklift driver that a pallet is finished and needs to be replaced. The system repeats this cycle, providing full pallets of stacked plastic sheets.

CUSTOMER BENEFITS

Automating this process gives the immediate customer benefit and an improved bottom line. The return on investment (ROI) for this type of system is dependant on labor rates and number of shifts. Assuming average labor rates and two shifts per day, the breakeven point is approximately one year. This ROI estimate doesn’t include efficency improvements and other beneficial metrics that can vary by company.

In a labor shortage, this isn’t about replacing employees with automation. However, it allows the company to use the employees elsewhere to keep up with production. There is a detrimental cost to not running because there is a lack of employees.

The customer also realizes increased throughput and more consistency. The extruder can run at capacity, while the robot can easily keep pace. The pallets are stacked quickly and identical to one another.

The more automation that a customer implements, the more skilled and comfortable employees get with automation. Growth in production technology and employee knowledge of that technology has benefits that will be realized long term.

FUTURE FOR THERMOFORMING

With demand remaining high for custom thermoformed plastic products and an unpleasant production environment for a dwindling workforce, automation projects like this are necessary to stay competitive and installing an automated robotic sheet stacker system can be an excellent solution.

ABOUT THE INTEGRATOR

Alliance Automation, LLC is a robot systems integrator located in Flint, MI USA and specializes in various automation applications. For more information about robotic plastic sheet stacking, please contact us.

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