How to Increase Uptime in Press Shops

Production schedules are relentless. The inability to satisfy them can severely impact the bottom line of a press shop, which must optimize productivity by eliminating downtime and increasing efficiency through the identification and use of next-generation lightweight tooling. Vacuum cups, end effector tooling systems and, in rapidly increasing numbers, magnets are all utilized to pick, place and secure different materials for stamping. These tools have advanced in design and operational capabilities in recent years, and astute shops should investigate whether their use of innovative components – combined with the latest robotics and system design – can help improve various stages of stamping operations. For example, one of the more recent noteworthy developments involves lightweight tooling systems, many of which are constructed of high-strength aircraft aluminum that can weigh up to 50 percent less than traditional steel components and help improve press shop performance in four critical areas:

• Vibration. Because of their smaller mass, lightweight aluminum end effectors reduce the amount of vibration that can occur during pickup and drop-off activities. Less vibration means less strain is placed on the lifting system, which equates to better positioning accuracy, less wear and tear, and reduced maintenance and downtime.
• Robot size. Lighter end effectors can be controlled by smaller robots. In turn, smaller robots work faster and more efficiently than the traditional high-payload robots that were required for pick-and-place operations using heavier tooling systems.
• Speed. In the world of end effector operation, lightweight means faster and, in fact, some of the new aluminum end effector models can perform their duties up to 30 percent faster than their heavier counterparts. Lighter components are also easier to change out, meaning a tool change that once took up to half an hour can now be performed in ten minutes or less. This increase in operating and changeover speed – combined with improved overall accuracy and efficiency – means higher production output and a healthier OEE.
• Operator safety. Handling heavy tools and heavy components can put a lot of physical strain on the operator. With the newest end effectors weighing up to 50 percent less than traditional tooling, the operator is less likely to incur a back strain or other type of repetitive-motion injury.

Looking closer, optimizing the efficiency and reliability of the system’s tool changers can significantly improve overall manufacturing performance. This is seen in the use of next-generation automatic tool-changing technology, which has grown in recent years thanks to the improved effectiveness of robots in these applications. Automatic tool-changing systems allow a robot to remove and drop off an end effector on a dedicated tool stand and replace it with another one in a streamlined process that requires no operator input. This operational efficiency can be a boon for plants that operate many different and unique part-moving jobs from the same area of the factory, which also helps to reduce potentially prohibitive setup costs.

Some shops incorporate a simplified “semi-automatic” approach to tool changes that uses both a robot and a human operator with a two-tool stand, rather than more complicated tool stands that can accommodate upwards of ten end effectors at once. In this two-tool system, the robot drops off one end effector and grabs the next one. While that process is being completed, the operator removes the end effector branches from the first tool stand and replaces them with whatever tooling is needed next. The benefit here is that the press can continue to run while the manual end effector change out is taking place, which improves uptime while simultaneously reducing the space that a five, ten or 15-tool stand would require. The lightweight, modular design of aluminum end effector parts also makes it easier to keep replacement parts in stock and on-site, which can help reduce the time needed to change out a tool from two hours to 15 to 30 minutes.

This combination of automatic and manual tool-changing processes has synthesized into what is known as the World Tool: the tool-changing setup is built around a strong main boom that is attached to an automatic tool changer controlled by a robot at one end and a manual tool changer – where smaller, lighter end effector branches are situated – at the other end. By using the World Tool, lighter components can improve production speeds by up to 30 percent, lighter components are safer and more ergonomically friendly to operators, and lighter components are less susceptible to excessive and expensive wear and tear.

THE IMPORTANCE OF VACUUM CUPS
Though they are the smallest components in an end effector system, the vacuum cups located at the end of the end effector branches have big responsibilities. With that in mind, the manufacturer must know the physical characteristics of the object that is to be lifted, moved and replaced, and how they can affect the type of vacuum cup that can be used in the application. These characteristics include:

• Material Type. Material types generally fall into one of two categories: porous or non-porous. Porous materials include such items as cardboard, wood and Styrofoam, all of which generally require higher vacuum flow but don’t require high-level vacuum generation in order to be lifted. Non-porous materials (steel, aluminum, hard plastic, etc.) require a lower vacuum flow to be picked up effectively.
• Surface Type. Surface types also fall into one of two categories: dry or oily. Most objects to be lifted and moved are dry, but there are classes of plastics that may have a fine oil on the surface. There are also examples of sheet metals that are treated with a rust-inhibitor before undergoing a stamping process that can leave an oily sheen on the surface. Selecting the correct tread on a vacuum cup will ensure the proper handling of different surface types.
• Contour. Determining the contour requires answering this question: Is it flat, or does it have rounded edges or curves? Some objects may simply have too many curves or undulations, which means a vacuum cup may not be able to be used. Also, objects that have too many closely-spaced holes are not compatible with vacuum cups.
• Shape. There have traditionally been two choices in vacuum-cup shape: round or oval. Round vacuum cups are usually the fallback style, but if the operation requires grabbing a very thin object, then a long oval vacuum cup may be required. However, new bell-shaped vacuum cups are growing in popularity because their bell-shaped body can easily adhere to convex or concave surfaces through a refined internal friction, or tread, pattern that can withstand high shear forces.  Within the various vacuum-cup families there are two design types: flat or bellows-style. The bellows-style vacuum cup has an accordion look that makes it more flexible, which allows it to pick up items that don’t have a consistent shape or are not well-aligned with the cup, though a higher vacuum flow is needed in these instances to remove the larger volume of air inside. Flat vacuum cups require a lower volume of air to be evacuated in order to create a strong grip, but flat cups are not as flexible as bellows-style cups.
• Durometer. One of several measures of the hardness of a material, durometer is typically used as a measure of hardness in polymers, elastomers and rubbers. Most vacuum-cup suppliers use the Shore A scale when testing for durometer. Higher numbers indicate harder materials, while lower numbers indicate softer materials. Both rubber and polyurethane-based standard cups on the market today will use this same scale to measure durometer:

– 30: Soft durometer ideal for use with contoured panels. It may, however, have a shorter life cycle than harder durometer vacuum cups.
– 45: A medium-hard rubber that will effectively seal and adapt to most contours, which makes it good for all-around usage. Generally has a longer operational life than a 30-durometer vacuum cup.
– 60: The hardest durometer is effective with extremely oily flat surfaces. Its usable life is longer than that of a 45-durometer vacuum cup.

Some suppliers of vacuum cups will color-code their products by durometer for easy identification, maintenance and replacement. When choosing a durometer for the application, remember that contoured parts, or those with sharp corners or edges, need a softer durometer so that the vacuum cups can hug the contours easier. Flat surfaces are ideal for a harder durometer because a vacuum cup constructed of that material will have stronger holding properties.

• Tread Pattern. Like the manufacturers of vehicle tires, all vacuum-cup suppliers have developed their own unique tread pattern. The design of the tread pattern helps determine the holding power or grip of the vacuum cup on the surface of the material to be transferred. What works in one application may not work in another, especially if the material’s surface is dry or oily. Some vacuum cups combine their unique treads with multiple durometers to help increase grip strength.
• Mounting Type. A wide range of mounting types are available: male/female Imperial NPT and Metric-G threads, square T-mount, and quick disconnect. New lightweight plastic-thread mounts are also coming to the market. Developers of vacuum cups have worked hard to create products that will satisfy the needs of the end user’s preferred mounting type. Before choosing a mounting type, it is wise to consult with the manufacturer to see what type of automation system is being used; if the vacuum cup doesn’t fit on the mount, the system won’t operate.

As far as supplying the air that allows the vacuum cups to operate, venturis are globally accepted. However, the configuration and operation of the venturi-based air-supply system has changed. Traditional systems operate with two air lines: one to create the vacuum that allows objects to be picked up and a second that adds air into the cup, allowing the part to drop. The second blowoff line can be unreliable in its operation, resulting in misplaced and uneven drops that can hamper the normal operating abilities of the robot and the overall tool-changing system. New single-line venturis feature vent holes in the air supply line. When these vent holes are closed, they allow the vacuum cup to grip the object being moved. When the vent lines are opened, they equalize the pressure in the air line and allow the part to be released. The single-line venturi not only simplifies the pick-and-place process, it also consumes 50 percent less air than a two-line setup for obvious economic and environmental benefits. Maintenance costs are also reduced since only one line must be serviced instead of two.

A RANGE OF TOOLING COMPONENTS
A variety of additional components and accessories can be used to optimize press shop performance even further. Many suppliers of equipment to press shops have diligently developed stamping-system components that look the same and have the same design to benefit end users with production locations all over the world: if a job is specified for a factory in Detroit, the manufacturer knows that the same components and systems can be used and are serviceable at a similar facility in China. Other innovations developed in recent years to help operators produce more stamped parts per hour while reducing overall system wear and tear include:

• Sheet-Metal Grippers. A reworked design makes the gripper lighter weight and more compact, but with no reduction in grip force. This allows them to function seamlessly with lightweight tooling components.
• Proximity Switch Mounts. Constructed of high-strength, glass-filled nylon to withstand the high sensitivity of the aluminum-sensing proximity switches that are used in increasingly popular robotic pick-and-place material handling lines.
• Rotaries. These can be used with end effector and sheet-metal grippers for an automated solution in tri-axis press applications. Low-profile rotaries also help ensure precision component positioning.

One final area to consider are the use of magnets as a way to pick, move and place parts and finished products. Ideally, powerful Rare Earth magnets can be used in applications where typical vacuum cups or grippers are not effective, such as lifting and moving heavy steel sheets, blanks, stamped parts and even complete assemblies in station-to-station, press-to-press and robotic pick-and-place systems.