The robotics industry has been undergoing a demographic shift. It started with industrial applications but there’s been significant growth with customer-service robots, personal-assistant robots, unmanned aerial vehicles (or drones), and “driverless” vehicles. Despite the shifting landscape, industrial robots remain critical in a market expecting to reach $500 billion in sales revenue by 2025.
One industry continuing to rely on robots and automation is automobile manufacturing. This industry was one of the first to embrace robotics/automation to enhance and optimize manufacturing times and schedules. Packaging, pharmaceutical and aerospace industries also continue to use automation.
Manufacturers in these industries and can enhance their experience with automation applications such as the metal-stamping and metal-assembly industries.
In the metal-stamping industry, there are commonly used styles of press lines on which parts are formed:
- Progressive: these lines run smaller parts not requiring automation or end of arm tooling (EOAT) to move the part from die to die as they progress down the line. An EOAT acts as the robot’s “hand”, holding a part in place or moving to the next station in a manufacturing process.
- Transfer: these lines feature three-axis transfer rails transferring the part from die to die and powered mechanically or from a servo motor. Mechanically powered transfer lines have a fixed motion relative to the press’s Ram timing, while servo-powered transfer allows the motion to be programmed and optimized for the best possible throughput or stroke per minute.
- Tandem: these lines feature 4 to 7 presses arranged in a row. The part-transfer process in a tandem press is configured as a three-axis pick-and-place system or through a six-axis robot between each individual press.
No matter the type of press line that is used, stamped parts are not always completed parts. The stamping will need to be welded or assembled before it becomes a finished part. These requirements transform the metal-stamped part into a metal-assembly process. Robots and robotic EOAT ensure the efficiency and accuracy of the metal-assembly process.
In the beginning…
A traditional die design process starts with the end user working with the die maker to create the die designs. After review-and-revision, the end user approves the die and CAD drawings are created. The tooling supplier receives the agreed-upon die data and creates a tooling design and working simulation of the automation tooling. A Corrective Actions Report (CAR) makes note of any clearance or clash issues during the simulation. The CAR is sent to the die manufacture, who resolves any clearance or clash issues before shipping the dies.
A fully designed and functional die set can cost upwards of $200,000, while the cost for the end effectors is less than 10% of that upfront cost. System designer and end user devote more attention to the more expensive component, but all parts must work in harmony to create a functional and reliable system. If the automation-tooling supplier was involved earlier in the design process, costly time and rework of the die modifications can be avoided.
So, the end-effector supplier is allowed to merge into the design process upon receipt of a process sheet with suggested grab and grip points where the Finger Tooling or EOAT are needed. The supplier designs the system’s touch points, simulates the motions needed (clamping, lifting, pitch, unclamp, etc.) and works with the die manufacturer to ensure the end effectors work harmoniously with the already-produced die. The die manufacturer determines if the dies and end effectors are compatible and able to deliver what the end user needs. If modifications are needed, a corrective-action report is created. When all modifications are made, simulations are performed to see if the system can perform as expected.
With the necessary back and forth between the die and end-effector constituencies, it benefits the end user and system designer to incorporate the EOAT supplier at the outset.
The 4 Things to consider
Finding and implementing the perfect end-effector system is reliant on the user giving due consideration to four critical areas.
1. Operating environment
There are two basic industrial-manufacturing environments where robotic-reliant part-handling systems will be used:
- Press shop: the press shop is where part-stamping is performed, though the definition of the press shop has been evolving in recent years. Old-school setups have a “transfer press” operation, a linear operation that relies on non-robotic automation. More press shops are incorporating “tandem” lines, using robots to perform their various functions. End effectors in a tandem line need to be compatible for use with robots.
- Body Shop: parts that have been stamped are married together via welding, gluing, etc. The body shop is a robot-reliant facility, with modular end-effector systems developed to meet the needs of the specific applications, requiring precise positioning and holding of parts.
2. Operating parameters
There are three major operating parameters to be assessed and quantified before the best end effector can be selected:
- Cycle time: the movement or operations the end-effector system can perform to complete a part. A typical transfer press performs at a rate of 15-22 spm. The efficiency of the system design improves the spm rate. Advances in digital-design and simulation capabilities allow die and end-effector designers to perform interference studies, pointing out potential bottlenecks in the part-moving process, which can then be designed out of the system before it becomes active, optimizing the spm abilities.
- Weight: The weight of the parts plays a huge role in determining the type of end effectors being used. It is important the designer of the EOAT, or transfer fingers, understands the tooling needs to be designed as robust and as light as possible, so it performs with no drops, vibrations or misplacements, and handles thousands of transfer cycles without fatiguing or breaking down.
- Reach: How far the end-of-arm tools must extend to perform their required task determines which end-effector solution is best for the job. The idea is to limit the amount of offset load and/or weight of the EOAT or transfer finger. Keeping the EOAT or transfer finger as small (minimum offset load) as possible reduces the deflection, resulting in a better automation cadence and more efficient throughput.
3. Which end effector?
There are two options, the first is Modular Tooling, which is gaining in usage and acceptance. This requires less design time because the end effector can be built from CAD components, resulting in better design consistency, offering more flexibility if changes in product design are ever needed. Modular tooling requires fewer custom parts, leading to reduced assembly time. The finished product has less overall weight with reduced startup times and quicker recovery if a crash should occur during operation.
The second end-effector design option is Welded Construction. While this method brings high levels of durability and reliability, its design and operational characteristics pale in comparison to those offered by modular tooling. This method has fewer standard components in a CAD library, taking longer to design the end effector. This makes it more difficult to factor in or predict future design changes, while variations can exist among design teams. Building a welded end effector requires more customized parts, resulting in longer assembly times and a heavier part and corresponding longer startup times. Crash-recovery time can also be longer with a welded part.
4. Ancillary components
There are ancillary components that can be used with the end-effector system to consider:
- Vacuum cups and magnets: These components contact the part or finished product that needs to be held or moved. Vacuum cups are available in a variety of sizes, shapes, treads, flexibility levels, materials of construction, and connections to vacuum sources. Magnets are used in applications where there is insufficient surface area to pick and place the part with vacuum cups.
- Grippers/powerclamps: Sheet-metal grippers or powerclamps hold the parts. Lightweight sheet-metal grippers are ideal for part-handling in a press shop. The gripper’s internal mechanism prevents opening when air pressure is lost. Sheet-metal grippers come in an array of grip styles with multiple contact-point options. Powerclamps are often used when part handling in the body shop with an enclosed pneumatic toggle-lock, and power clamps with integrated open/close sensing can secure a part even when air pressure is lost.
- Venturis: Venturis supply vacuum to an end-effector system’s vacuum cups. Traditional systems operate with two lines, one creates the vacuum that retrieves parts and a second adding air to the cup, allowing the part to drop. Single-line venturis require 50% less air, reducing operating and maintenance costs.
Conclusion
Robotics in workholding and pick-and-place applications in industrial manufacturing will not be going away. It’s important that industrial manufacturers design and deploy a compatible automation tooling/end-effector system involving automation tooling/EOAT suppliers in the design process from the start, knowing all of the variables and options that are in play, and using the latest digital-design technologies.