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Previously given Paper 09ATC-0232 delivered at the SAE Aerotech conference in Seattle in 2009 reports on the E6000 machine installing slug rivets with the EMR. Paper 2015-01-2491given at the SAE conference in Seattle in 2015 reports on index head rivets being installed with screw driven squeeze process. This paper reports on the screw driven squeeze process installing unheaded slug rivet which is a more complex process. We also report on improvements to the fixture automation.

Large-scale aerostructures are commonly constructed using multiple layers of stacked material which are fastened together using mechanical methods. Ensuring the interface gaps between these materials are kept within engineering tolerances is of utmost importance to the structural integrity of the aircraft over its service life. Manual, right angle feeler gauges are the traditional method for measurement of interface gaps, but this method is tedious and mechanic dependent. A portable hand tool utilizing low-coherence interferometry has been developed to address these issues. The tool uses a right-angle probe tip which is inserted into a previously drilled hole and driven through the depth of the material. A line scan of data is collected and analyzed for the presence of interface gaps. To measure the consistency of the gap around the circumference of the hole, the tool is rotated by the operator and additional scans are collected.

Electroimpact has produced a new in-process inspection system for use on drilling and fastening systems. The system uses a high-accuracy, non-contact, laser system to measure the flushness of installed fasteners. The system is also capable of measuring part normality and providing feedback to the machine for correction. One drawback to many automatic inspection systems is measurement error. Many sources of measurement error exist in a production environment, including drilling chips, lubrication, and fastener head markings. Electroimpact’s latest system can create a visualization of the measured fastener for the operator to interpret. This allows the operator to determine the cause of a failed measurement, thus reducing machine downtime due to false negatives. Electroimpact created a custom C# WPF application that queries the point-cloud data and analyzes the raw data. A custom “circle Hough transform” scoring algorithm is used to find the center of the nosepiece (pressure foot).

Automated fiber placement of pre-impregnated (pre-preg), thermoset carbon materials has been industrialized for decades whereas dry-fiber carbon materials have only been produced at relatively low rates or volumes for large aerospace structures. This paper explores the differences found when processing dry-fiber, thermoset, carbon materials (DFP) as compared to processing pre-preg, thermoset materials with Automated Fiber Placement (AFP) equipment at high rates. Changes to the equipment are required when converting from pre-preg to dry fiber material processing. Specifically, the heating systems, head controls, and tow tension control all must be enhanced when transitioning to DFP processes. Although these new enhancements also require changes in safety measures, the changes are relatively small for high performance systems. Processing dry fiber material requires a higher level of heating, tension control and added safety measures.

A new style of all electric riveting machine has been developed with saddle hoppers that does not require a track between the hoppers and the fingers. This enables feeding square rivets without difficulty. The upper ram has a bent knee which allows the rivet fingers to be brought up to the hopper and rotated 30 degrees rather than the rivet sliding down a track, which minimizes jamming that occurs with some fasteners in the track, and increases reliability. A mixture of fasteners can be loaded side by side in the hoppers, increasing flexibility. The rivet feeding is accomplished by bringing the rivet fingers to the hopper. The machine uses a power drawbar to change out different rivet fingers. A small industrial robot is incorporated into the machine to complete different sized coupons and also complete small assemblies. In larger machines larger robots or CNC positioners can be used to scale up the use of the machine.

With typically over 2.3 million parts, attached with over 3 million fasteners, it may be surprising to learn that approximately two out of every three fasteners on a twin aisle aircraft are fastened by hand. In addition the fasteners are often installed in locations designed for strength and not necessarily ergonomics. These facts lead to vast opportunities to automate this tedious and repetitive task. The solution outlined in this paper utilizes the latest machine vision and robotics techniques to solve these unique challenges. Stereo machine vision techniques find the fastener on the interior of an aerospace structure and calculate the 6DOF (Degrees of Freedom) location in less than 500ms. Once the fastener is located, sealed, and inspected for bead width and gaps, a nut or collar is then installed. Force feedback capabilities of a collaborative robot are used to prevent part damage and ensure the nut or collar are properly located on the fastener.

The advent of accuracy improvement methods in robotic arm manipulators have allowed these systems to penetrate applications previously reserved for larger, robustly supported machine architectures. A benefit of the relative reduced size of serial-link robotic systems is the potential for their mobilization throughout a manufacturing environment. However, the mobility of a system offers unique challenges in maintaining the high-accuracy requirement of many applications, particularly in aerospace manufacturing. Discussed herein are several aspects of mechanical design, control, and accuracy calibration required to retain accurate motion over large volumes when utilizing mobile articulated robotic systems. A number of mobile robot system architectures and their measured static accuracy performance are provided in support of the particular methods discussed.

Electroimpact has retrofitted two E4100 riveting gantry machines and two more are in process. These machines use the EMR (Electromagnetic Riveter) riveting process for the installation of slug rivets. We have improved the skin side EMR to provide fast and reliable results: reliability improved by eliminating a weekly shutdown of the machine. In paper 2015-01-2515 we showed the slug rivet injector using a Synchronized Parallel Gripper that provides good results over multiple rivet diameters. This injector is mounted to the skin side EMR so that the rivet injection can be done at any position of the shuttle table. The EMR is a challenging application for the fingers due to shock and vibration. In previous designs, fingers would occasionally be thrown out of the slots. To provide reliable results we redesigned the fingers retainer to capture the finger in a slotted plastic block which slides along the outside diameter of the driver bearing.

Figure 1 Global 7000 Business Jet. Photo credit: Robert Backus. The customer’s assembly philosophy demanded a fully integrated flexible pulse line for their Final Assembly Line (FAL) to assemble their new business jets. Major challenges included devising a new material handling system, developing capable positioners and achieving accurate joins while accommodating two different aircraft variants (requiring a “flexible” system). An additional requirement was that the system be easily relocated to allow for future growth and reorganization. Crane based material handling presents certain collision and handover risks, and also present a logistics challenge as cranes can become overworked. Automated guided vehicles can be used to move large parts such as wings, but the resulting sweep path becomes a major operational limitation. The customer did not like the trade-offs for either of these approaches.

In many existing AFP cells manual inspection of composite plies accounts for a large percentage of production time. Next generation AFP cells can require an even greater inspection burden. The industry is rapidly developing technologies to reduce inspection time and to replace manual inspection with automated solutions. Electroimpact is delivering a solution that integrates multiple technologies to combat inspection challenges. The approach integrates laser projectors, cameras, and laser profilometers in a comprehensive user interface that greatly reduces the burden on inspectors and decreases overall run time. This paper discusses the implementation of each technology and the user interface that ties the data together and presents it to the inspector.

A new high speed forming process for fatigue rated index head rivets used in wing panel assembly using ball-screw based servo squeeze actuation has been developed. The new process is achieved using a combination of force and position control and is capable of forming to 40,000 lbs at rates of up to 200,000 lbs/second whilst holding the part location to within +/− 10 thousandths of an inch. Multi-axis riveting machines often have positioning axes that are also used for fastener upset. It is often the case that while a CNC is used for positioning control, another secondary controller is used to perform the fastener upset. In the new process, it has been possible to combine the control of the upset process with the machine CNC, thus eliminating any separate controllers. The fastener upset force profile is controlled throughout the forming of the rivet by using a closed loop force control system that has a load cell mounted directly behind the stringer side forming tool.

Aircraft assembly systems which require tooling or machinery to pulse or move between multiple positions within a factory can be positioned with high repeatability without high performance foundations or sweeping out large areas of floorspace. An example shows a system of large left and right-hand frames which are positioned at 3 sequential manufacturing steps and then recirculated to the start of production via a central return aisle. The frames are 41 ton actual weight and are 72′ long, similar to a rail car. The system achieves rectangular motion for the recirculation path. The supporting and moving system incorporates low-cost rail in a floor with minimal preparation and simple to use controls. The system is also easily reconfigured if the manufacturing system needs to be altered to meet rate or flow requirements.

Automated countersink measurement methods which require contact with the workpiece are susceptible to a loss of accuracy due to cutting debris and lube build-up. This paper demonstrates a non-contact method for countersink diameter measurement on CFRP which eliminates the need for periodic cleaning. Holes are scanned in process using a laser profilometer. Coordinates for points along the countersink edge are processed with a unique filtering algorithm providing a highly repeatable estimate for major and minor diameter.

The process of robotic automated fiber placement has been enhanced by combining the technologies of an accurate articulated robotic system with a modular Automated Fiber Placement (AFP) head. The accurate robotic system is comprised of an off-the-shelf 6-axis KUKA Titan KR1000L750 riding on a linear axis with an option for an additional part rotator axis. Each of the robot axes is enhanced with secondary position encoders. The modular fiber placement head features a robotic tool changer which allows quick-change of the process heads and an onboard creel. The quick-change fiber placement head and simplified tow path yields terrific process reliability and flexibility while allowing head preparations to occur offline. The system is controlled by a Siemens 840Dsl CNC which handles all process functions, robot motion, and executes software technologies developed by Electroimpact for superior positional accuracy including enhanced kinematics utilizing a high-order kinematic model.

Starting in 2003 Electroimpact began development on a comprehensive kinematic and compensation software package for machines with large envelopes. The software was first implemented on Electroimpact's Automatic Fiber Placement (AFP) equipment. Implementation became almost universal by 2005. By systematically collecting tracker measurements at various machine poses and then using this software to optimize the kinematic parameters of the machine, we are able to reliably achieve machine positional accuracy of approximately 2x the uncertainty of the measurements themselves. The goal of this paper is to document some of the features of this system and show the results of compensation in the hope that this method of machine compensation or similar versions will become mainstream.

A frame-clip riveting end effector has been developed for installing 3.97mm (5/32) and 4.6mm (3/16) universal head aluminum rivets. The end effector can be mounted on the end of a robot arm. The end effector provides 35.6 kNt (8000 lbs) of rivet upset. Rivets can be installed fifteen millimeters from the IML. The clearance allowed to rivet centerline is 150 millimeters. The riveting process features a unique style of rivet fingers for the universal head rivet. These fingers allow the rivet to be brought in with the ram. This differentiates from some styles of frame-clip end effectors in which the rivet is blown into the hole. The paper shows the technical components of the end effector in sequence: the pneumatic clamp, rivet insert and upset. The end effector will be used for riveting shear ties to frames on the IML of fuselage panels.

Spirit AeroSystems' process of producing carbon fiber nacelle panels requires heat and high force plus a high level of dynamic accuracy. Traditionally this would require large and expensive custom machines. A low cost robotic alternative was developed to perform the same operations utilizing an off-the-shelf 6-axis robot mated to a servo-controlled linear axis. Each of the 7 axes is enhanced with secondary position encoders and the entire system is controlled by a Siemens 840Dsl CNC. The CNC handles all process functions, robot motion, and executes software technologies developed for superior dynamic positional accuracy, including enhanced kinematics. The layout of the work cell allowed the robot to span two work zones so that parts can be loaded and unloaded while the robot continues working in the adjacent zone.

Precision hole inspection is often required for automated aircraft assembly. Direct contact measurement has been proven reliable and accurate for over 20 years in production applications. At the core of the hole measurement process tool are high precision optical encoders for measurement of diameter and countersink depth. Mechanical contact within the hole is via standard 2-point split ball tips, and diametric data is collected rapidly and continuously enabling the system to profile the inner surface at 0 and 90 degrees. Hole profile, countersink depth, and grip length data are collected in 6 seconds. Parallel to the active process, auto-calibration is performed to minimize environmental factors such as thermal expansion. Tip assemblies are selected and changed automatically. Optional features include concave countersink and panel position measurement.

Automated Fiber Placement (AFP) machines typically consist of 3 linear and 3 rotary axes of motion in order to manufacture complex shapes. These axes are generally orthogonal and semi-coupled. In these designs, a linear axis move will not affect the rotary axes orientation whereas a rotary axis move will affect the Tool Center Point (TCP) location with respect to the linear axes position. The wide range of motion required to maintain the compaction-axis normality needed for carbon fiber layup tends to prevent all of the rotational axes from passing through the TCP. The location and arrangement of these rotational axes has a great effect on the AFP machine performance and controllability during high speed layup. This paper presents a unique kinematic AFP axes design consisting of replacing the 3 orthogonal rotary axes with 3 tool-center-point-intersecting coupled-axes which decouple the linear axes from the rotary axes.

Wing and fuselage aircraft structures require large precise tools for assembly. These large jigs require periodic re-certification to validate jig accuracy, yet metrology tasks involved may take the tool out of service for a week or more and typically require highly specialized personnel. Increasing the time between re-certifications adds the risk of making out-of-tolerance assemblies. How can we reduce jig re-certification down time without increasing the risk of using out-of-tolerance tooling? An alternative, successfully tested in a prototype tool, is to bring automated metrology tools to bear. Specifically, laser tracker measurements can be automated through a combination of off-the-shelf & custom software, careful line-of-sight planning, and permanent embedded targets. Retro-reflectors are placed at critical points throughout the jig. Inaccessible (out of reach) tool areas are addressed through the use of low cost, permanent, shielded repeatability targets.