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A Robot Cell to Die Cast For

July 22, 2008
Die-cast products comprise the bulk of mass-produced items manufactured by the metalworking industry, from alloy-based children’s toys to automotive engine parts, and the integrated design of a die-casting work cell is critical to ...

Die-cast products comprise the bulk of mass-produced items manufactured by the metalworking industry, from alloy-based children’s toys to automotive engine parts, and the integrated design of a die-casting work cell is critical to make these products at competitive rates.

As with other manufacturing processes, robots have become a vital component in automated die-casting cells, and there are many factors that must be considered when designing an automated cell.

The size and shape of the product drives the design of the dies used in die casting, and the shape and size of the die help to define the size and capabilities of robots that are used to service diecasting machines. The use of robots also relies on the reach they will have to have and the accessability of the cast product.

Almost all manufacturers today rely on 3D CAD software packages to design die-casting systems, the dies they use and the products made on the systems. 3D data also is critical for accurate end-effector design for robots and for the design of storage racks or conveyor pallets that are used to hold or transport finished product.

However, the savings associated with 3D CADbased integrated design and simulation tools for die-casting systems is negligible compared with the cost of problems that could occur on the plant floor if the system is not validated prior to building it.

Time is at a premium during installation, so spending time up front during the engineering phase of a project to create a quality system is worth it. Plus, the benefits of simulation can be realized even at the end of a product life cycle because it can be re-used to validate placing the next generation of products and dies into the existing system.

Since safety is a major concern in die-casting operations, the main job of a robot is to keep humans from being exposed to the extreme heat and emissions generated by the casting process.

Most robot OEMs offer a foundry series of robots that can be built with heatresistant materials. In addition, the selection of end-effector component materials should be based on heat resistance because these parts interact with products as they exit dies in which temperatures are high.

Besides die-cast product shape and size, factors such as temperature, payload and force requirements have to be considered when designing an end-effector for a robot.

To ensure that the endeffector will have the proper clearance within a die, 3D product, fixtures and die models should be consulted during the design process.

Also, clamping surfaces typically are based on quality and finish requirements of the part and should be determined with the customer.

Floor space required to automate die-casting operations depends on partprocessing needs and the design and size of peripheral equipment.

Robotic simulation ensures that end-effector designs are suitable for all robot tasks and associated equipment. In cases where gates, risers or biscuits need to be removed from parts, the robot end-effector may need specific force compensation or a compliance device.

Floor space needed to automate a die-casting operation depends largely on part processing requirements as well as peripheral equipment design and sizes.

The most effective way to ensure that enough space is earmarked for robotic automation is by using a simulation of all the robotic operations.

A significant benefit of robotic simulation is the ability to test multiple product styles and dies to develop a layout configuration that can be common to several product designs so that changeover time and associated costs are reduced.

3D CAD-based integrated design and simulation tools validate automated diecast cell designs prior to system build.

While environmental conditions are important in choosing a robot, payload, reach and part access within the die also are key factors. The mass, center of gravity and moments of inertia about the mounting face of the robot all combine to determine the robot model that must be used to handle the payload capacity – the part size – for which the cell is designed.

Mass data for payload analysis can be generated from mechanical design CAD packages as long as the data entered into the system for material properties is accurate. The mass data that is generated then can be entered into a payload-calculation program that would determine the robot model needed to deal with the payload requirements.

Other factors that drive robot selection are the direction of die travel (horizontal or vertical), gantry versus floor-mounted robots based on equipment size and access, and cycle time requirements.

The time it takes for one cycle of the press and the unload time drive production rates on die-casting systems.

Once this data is known, process design must focus on ensuring that the press spends a minimum wait time on other pieces of automation. The time spent by the robot after unloading a part from the dies should not exceed the time needed by the press to cycle and generate a new casting.

Robot simulation in conjunction with external robot controller software can help generate accurate robot motion cycle time. The use of virtual controls to replicate real-world conditions allows for evaluation of both individual processes and coordinated activities of robots within a system.

Once a product is extracted from a die, it may need to cool – by liquid quenching or air-cooling – before further processing, or it may need to be transferred to other equipment. For liquid-cooled operations, equipment could be as simple as a quench tank into which the robot dips hot parts. For air cooled operations, a small fixture or buffer stand may need to be designed so that the robot can unload the parts. For either of these options, robotic simulation validates reach and location, and ensures that designs will transfer into reality.

Some cast parts, such as engine components, may have metal gates, runners or flash that are required for the casting process but must be removed afterwards.

Often, casting plants use “knockoff” stands to remove gates, and the process usually has specified directional requirements for how the excess material is removed. For this, robot simulation must be used to ensure that the robot can access the desired knockoff position without reach issues.

Flash, an unwanted metal formed at the parting lines of two die plates, generally is removed using a trim press or a CNC machine. A robot loads the casting into the press or machine and waits for the equipment to cycle before unloading the finished part. Again, robot simulation ensures there is sufficient opening and clearance to enter the machine.

Die-cast parts often are transferred out of a system in several ways based on customer requirements.

Some parts transfer to conveyors for further processing, while others are robotically transferred to palletizing racks. Robotic simulation ensures that a robot can reach all extremes of all pallets at all heights and can be used to analyze cycle time based on stack pattern requirements.

All design elements of robotic/ automation workcells should be evaluated for safety issues. All aspects of the cell, from robot and operator tasks to workcell layout, to controls and electrical designs are analyzed and, in some instances, integrated into a virtual world to ensure safety.

A growing trend in making human and machine interactions safer is the use of 3D virtual manufacturing involving CAD designs, simulated controls and virtual robotic and ergonomic simulations.

While it is important to validate die-casting automation in a virtual environment, it is even more imperative to ensure that control engineers and robot programmers make safety a priority.

PLC software must have the capability to conduct safety checks between software and hardware and provide proper handshakes between the robot, press and safety devices.

Safety devices such as light screens, perimeter guarding, safe distance calculation, robot base limit switches and hard stops need to be carefully designed, programmed and debugged for safe cell operation.

Programming robots is a task well left to an expert. While most robot motion is primarily simple material handling, there are situations where delicately extracting a hot part out of a die or trimming operation is a must and involve considerable pathteaching skills.

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