Adopting new technologies generally involves lots of experimentation coupled with low expectations. Sloppiness, imprecise results, or outright failure are fine learning experiences when evaluating a novel system’s potential but completely unacceptable outcomes for production systems.
With additive manufacturing (AM) moving from prototyping and design labs into serial production, users demand higher levels of quality, repeatability, traceability, and output. And while 3D printer makers and other AM technology providers continue to improve their equipment, a new, advanced supply chain has emerged.
Just as traditional job shops work with a network of machine tool manufacturers, cutting tool makers, software vendors, and materials suppliers, AM users are learning that it takes a network of manufacturing technology providers to create a finished part.
An early dream of AM was direct print-to-use components – imagining a 3D part using digital design software, sending it to a 3D printer, and getting a finished, usable part within a few hours of ideation. While possible in some situations, users have found that building semi-finished parts and going through post-processing improves cost, quality, and productivity.
In the pages of the 2019 AM/3D Target Guide, several technology experts discuss where post-processing techniques fit into the maturing AM ecosystem. Experts highlight heat-treatment systems for thermoplastic AM parts, finishing fluids used in cleaning post-processes, and using AM to develop custom tooling. There’s also coverage of cutting-edge developments in AM systems and use cases showing how manufacturers can benefit from new equipment.
AM is still a cool, gee-whiz, sky’s-the-limit technology capable of revolutionizing any industry it touches. The growth of support industries and post-processing shows that it’s also maturing, making it more capable of producing complex parts quickly, cost effectively, and most importantly, reliably.— Elizabeth, Robert, Eric, & Michelle
Six-axis hexapod robots support stricter manufacturing accuracy requirements by precisely aligning and positioning manufacturing and quality assurance processes. Parallel-kinematic hexapod robots can move and position tools, workpieces, and complex components weighing a few grams to several tons in any spatial orientation. Integrating EtherCAT data on control connectivity eases integrating hexapods into automation systems.
In a parallel-kinematic system, Cartesian axes do not correspond to motor axes, requiring coordinate transformation that cannot be solved analytically. A computation-intensive, iterative algorithm recalculates complex hexapod kinematics for each step. The digital controller calculates and controls the individual motors in real-time, rather than forcing users to perform these tasks. Cartesian coordinates in the PLC determine shifts, rotations, reference system definition, and pivot point.
- PLC command of hexapod system
- Simplified path planning, trajectory generation; synchronize with other automation system devices
- No proprietary programming language
- Communicating with the hexapod via EtherCAT fieldbus protocol, the PLC defines the hexapod system’s Cartesian target position in space and receives feedback on actual positions.
The minimum permissible cycle time for the hexapod controller is 1ms. The object dictionary, process data object (PDO) mapping, and service data objects (SDO) are supported. PDOs and SDOs have been defined according to drive profile CiA402 for easy integration of the Cartesian axes of the hexapod within the PLC.
Since all drives act on the same platform, statuses of individual Cartesian axes are interdependent. To counter this, the PLC represents and treats each Cartesian axis as a separate axis, and the hexapod controller references or stops the axis for all axes simultaneously. Error messages from one Cartesian axis are mirrored on all other axes. The system maintains control and status words separately for each axis to prevent too much intervention with underlying standardized drive protocols. The axis with the lowest status level determines the system’s status, so to move the hexapod to a higher status level, all axes must reach minimum level.
Cyclic synchronous position (CSP) mode positions the hexapod using the EtherCAT master to specify the target Cartesian positions for the axes. Maximum hexapod vector velocity depends on the maximum possible velocity and acceleration of the individual struts, depending on the hexapod platform angle and commanded Cartesian target position. Users figure Cartesian axes via the PLC using the hexapod’s maximum value, hexapod velocity will deviate from the velocity calculated in the PLC – the greater the distance to be travelled, the greater the deviation. To avoid large tracking errors, reduce the target velocity and acceleration in the PLC for combined movements of the Cartesian axes. If the maximum vector velocity of the hexapod is exceeded when the target positions are specified, the stop mechanism integrated in the hexapod controller automatically takes effect. This puts the hexapod controller into an error state and stops the system with the maximum possible acceleration. The integrated interpolation mechanism ensures that the hexapod stays on the planned path.
Motion range, velocities
Service data objects are available to avoid exceeding vector velocity, providing users with the best possible support in trajectory planning. When querying the available travel range, the controller simultaneously calculates the maximum possible velocities and accelerations, distinguishing between translational and rotational components. Since these velocities and accelerations vary across the workspace, the system only determines values for the point at which the hexapod was located when the query started. Users should also configure maximum and reference velocities and accelerations for the axes in the PLC. The velocities can be taken from the hexapod data sheet. Acceleration values for translation axes can be read out directly via service parameter 0x19001502 using PI software PIMikroMove or PITerminal during initial commissioning. For rotational axes, maximum acceleration can be determined by transferring the ratio for linear axes.
The intelligent hexapod controller allows users to freely define and select reference coordinate systems for movement in space. Work coordinate and Tool coordinate systems are available via the EtherCAT. To configure coordinate systems, assume that the Tool coordinate system moves in the Work coordinate system.
Sub-indices correspond to coordinates of individual Cartesian axes. The Tool coordinate system can also be configured via an object. All values must be specified in micrometers or thousandths of a degree.
Initial hexapod system commissioning should be carried out via PI software. All required parameters are queried and can then transfer to the PLC via Ethernet and RS-232 interfaces. Even with the EtherCAT interface activated, users can send GCS commands at any time via Ethernet and RS-232 interfaces.
Automated surface finishing
Active Orbital Kit (AOK) 601 supports large-scale sanding and polishing processes and easily adapts to robot applications. Designed for automated surface finishing of very large surfaces, the kit is lightweight and provides single-source process quality.
It automates the industrial sanding process with individual control of rotational speed, contact pressure, and feed rate.
With a triple sanding head, the AOK/601 rapidly processes large surfaces while reducing abrasive consumption. It shortens cycle times and reduces costs by eliminating manual work steps.
Single-axis, digital drive
The XC2 PWM digital drive is a small form-factor, high-performance, single-axis motor drive for motion-control applications. It’s compatible with the Automation 3200 motion platform using the HyperWire motion bus. The XC2 can control brushless DC, brush DC, voice coil, or stepper motors up to 100VDC and 10A peak current capability.
The digitally closed current loop and servo-loop ensure positioning accuracy and rate stability, allowing loop closure rates up to 20kHz while permitting real-time digital and analog I/O processing, data collection, process control, and encoder multiplication.
The drive accepts square-wave encoder feedback at rates of up to 40 million counts-per-second. Sine-wave encoders can be multiplied up to 16,384 for high-resolution position feedback.
Each single-axis XC2 PWM digital drive has an optional I/O expansion board that includes a dedicated PSO output.
Airplane wings require hundreds, and sometimes thousands, of holes to be drilled in complex, fragile surfaces with high accuracy, posing two challenges for manufacturers:
- Developing a method of securing parts during drilling that doesn’t cause damage
- Providing an ergonomic work environment, customizable to each worker, that allows them to drill thousands of holes per day without injury
At Spirit AeroSystems in Tulsa, Oklahoma, these challenges were especially pronounced on the drilling stations for the wedge and cove-angle components of the Boeing 787 aircraft wing. Using input from operators and Bosch Rexroth aluminum structural framing, Spirit AeroSystems developed an ergonomic workstation that significantly improved quality, reduced worker injuries, and improved throughput.
The wedge structure is a composite piece of the airplane wing’s leading edge, and there are 10 variations of the part. Each wedge requires around 300 manually drilled holes and the typical production rate is six wedges per day – 1,500 to 2,000 holes per day – no small task for any operator.
“In the automotive industry, probably 90% of drilling is automated, with only about 10% of drilling operations being done manually. In the aerospace industry, the situation is almost the exact opposite,” says Brian Lewis, continuous improvement specialist at Spirit AeroSystems.
The original assembly workstation layout used a standard, flat table to hold the wedge during drilling. But the wedge is contoured, making it extremely challenging for the operator to drill hundreds of holes in precise locations. The part tended to rock back-and-forth on its curved edge, so the operator often had to hold the part with one hand while drilling with the other hand. The lack of control from one-handed drilling, coupled with the odd position of the part, often led to drill-starts where the hole is started in the wrong spot, marking the part and in some cases, producing an out-of-spec, elongated hole.
Additionally, drilling hundreds of holes per day – even on flat, stable parts – requires thoughtful workspace design to ensure good ergonomics. Wedge line operator James Wright was plagued by the effects of poor workstation ergonomics. So, he proposed a rotating fixture – inspired by a rotisserie – that would allow the part to be positioned at any angle and height, depending on the current operator’s preferences. What started as a napkin sketch was taken to Lewis, who accepted the task of making this concept a reality.
Having worked with Bosch Rexroth aluminum framing to build tables, workbenches, and holding fixtures for other areas of the factory, Lewis immediately enlisted the help of Spirit AeroSystems Design Engineer Matt Sheets and Jay Rogers of Pacific Integrated Handling (PIH), in Tacoma, Washington, to help design a wedge fixturing system. PIH is a distributor with more than 20 years’ experience applying Bosch Rexroth aluminum framing to specialized tooling and fixtures.
Based on Wright’s sketch, the team designed the wedge fixture with aluminum framing for structural support, along with a counterbalance system to ease rotation of the wedge – an incredibly heavy part. The fixture is infinitely adjustable in height, and the ability to rotate the wedge allows each operator to set the workpiece at a comfortable drilling angle. To accommodate variations in wedge designs, one wedge end is supported by a Bosch Rexroth size 25 ball rail, allowing the width of the fixture to be adjusted to the wedge’s length.
A workstation design that once required five people to complete five units per day, now has three people completing six to seven units per day. Put another way, on an 8-hour shift, man-hours per part fell about 54%, from 8 hours per part to less than 4 hours. And the company has been able to reallocate resources from the wedge area to other operating stations. Since the fixture was put in use, rework in this area has been reduced by 80%.
Possibly the most important outcome of this new fixture is the improved ergonomics. With the previous workstation design, operators experienced back problems from bending over or leaning in to drill holes, and soreness in the upper body was a common complaint.
“The improvement in ergonomics was immediate,” Wright says. “This fixture, and the ability to adjust it to my specific needs, has really made a difference in my physical well-being. Other areas are looking to replace their old, ‘dinosaur’ tooling and fixtures – typically made of steel – with lighter, more cost- effective, and more ergonomic designs made from Bosch Rexroth aluminum framing.”
Cove-angle carousel fixture
A cove angle is also a part of the Boeing 787 wing – a structural member used in the front slats to produce lift. Like the wedge, there are 10 variations to the cove angle, and each variation requires drilling 168 holes. Cove angles require operators to drill a pilot hole and then a second hole to the specified size.
In the original cove angle workstation, operators drilled one part at a time on a typical, flat workbench. This was inefficient, since no real work was occurring every time the operator had to offload one part and load the next. Damage from drill-starts and out-of-round holes resulted in high rework and scrap rates.
The solution to these issues – a rotating carousel fixture – drew inspiration from a fixture that Sprit AeroSystems had implemented on a smaller scale in the Boeing 737 program – essentially the same part but made from aluminum rather than composite.
Cove angles are approximately 12ft long x 2" wide, making them ideal for loading onto a carousel, supported by Bosch Rexroth aluminum framing that holds five parts at a time. The carousel rotates and locks into place while the operator drills each part and moves in and out, to be closer to or farther away from operators to meet ergonomic preferences.
A monitor mounted to the structural framing displays work instruction and layout of each part. With feedback from a linear encoder, the monitor can be moved down the fixture along the part’s length. As the monitor moves, the drawing displayed corresponds to its position along the part, providing instructions specific to that exact spot on the part. After finishing one part, the operator rotates the carousel and works back along the length of the fixture on the next part.
Although inspired by a B737 program solution, the much larger cove-angle carousel fixture was especially challenging to design and manufacture. One difficulty was making a fixture that could rotate while maintaining enough stiffness to support the pressure from drilling.
Spirit AeroSystems completely outsourced the design and manufacturing to PIH, and the PIH team worked with designers and operators at Spirit AeroSystems to provide a turnkey solution that met the operators’ requirements for ergonomics and simplicity, while meeting Spirit’s cost and timeframe goals.
Since the fixture’s implementation, productivity in the cove angle area has increased by 50%, and like the wedge area, ergonomics vastly improved. The cove angle fixture’s ability to handle five parts at a time also reduced floor space and improved part-flow through the line.
Both the wedge and cove angle fixtures greatly improved ergonomics for the operators, improving productivity and quality. The return on investment (ROI) for these projects was well within the three-year timeframe set by management, based on increased throughput and reduced quality costs. Not only did these projects exceed the company’s ROI target, worker compensation issues also decreased. As a bonus, upper management at Spirit AeroSystems was impressed with the amount of input and level of engagement the operators demonstrated in the design and realization of these two fixturing projects.
Aircraft turbines produce high output by highly compressing air in the combustion chamber. Within the engine, the high-pressure turbine sits behind the combustion tube, subjecting it to great stress from exposure to the pressure generated by combustion energy and temperatures higher than 1,832°F (1,000°C).
Hollow cooling structures in high- pressure turbine blades and nozzle guide-vanes are manufactured using the lost wax process, with molten metal poured into a mold made by a wax model of the component. A heat-proof core in the model enables manufacturers to create parts that have hollow structures. However, a foreign object or processing defect in the hollow structure can reduce heat dissipation, potentially resulting in engine failure. Manufacturers inspect the inner part of the turbine blade’s hollow structure during manufacturing and engine maintenance to prevent such flaws.
Mini borescopes with a diameter of 3mm or less were used to inspect the hollow structures inside turbine blades for residues, scratches, and cracks. A rod lens in the mini borescope provided good-quality images but suffered from drawbacks that slowed inspection, including:
- Rigid, easily damaged, long, thin lens on insertion tube
- Small images difficult to see without a monitor
- A camera unbalances the scope, making it difficult to use
- Non-articulated insertion tube; can’t look around inside hollow structures
- Insufficient illumination from weak light guide
Thin videoscope advantages
Unlike a mini borescope, thin fiberscopes and videoscopes are flexible and offer articulation. A fiberscope is made of a bundle of glass fibers, while videoscopes have a built-in image sensor. Both have a 2.4mm OD insertion tube and articulation at the distal end.
Fiberscopes are cost-effective, although images acquired through the glass-fiber bundle have a mesh-like appearance that can make it difficult for users to detect tiny defects.
Videoscopes acquire images via a sensor providing bright, clear images with no mesh-like appearance. By electrically amplifying image signals, videoscopes enable users to observe deep inside a hollow structure with a wide field of view (FOV) and sufficient brightness, even with limited light intensity. This makes it easier for users to detect residues, scratches, and other defects.
The Olympus IPLEX TX videoscope’s insertion tube has a protective resin layer and 2.4mm OD. The insertion tube’s multilayered structure prevents resin surface damage from irregularly shaped parts, improving durability.
An ordinary videoscope needs to be entirely replaced when its insertion tube gets damaged, but a detachable insertion tube allows quick replacement on the IPLEX videoscope.
Inspecting hollow structures inside turbine blades presents significant challenges that can be overcome by using a videoscope with a small-diameter insertion tube. With durability, high image quality, and articulation, inspectors can easily maneuver inside these narrow structures, viewing, recording, and archiving images.