Project Readiness Package Rev 06 Nov 2010

Project Summary

Pull-type rivets are extensively used in the aerospace industry for assembly fabrication or repair when only one side of a part can be accessed. Unlike common hardware store "pop" rivets, these rivets made by Cherry Aerospace have high dimensional tolerances and high strength materials to meet demanding aerospace applications. These rivets are mass-produced in large quantities, making 100% inspection currently impossible. A sample of parts per lot are currently inspected manually, but a higher proportion of inspected parts is desired which would require implementation of an automated inspection system. We wish to design and construct an inspection tool to measure and validate critical rivet dimensions at high speed in high volumes, and consolidate the inspection data for use in real time statistical process control. Project sponsored by Cherry Aerospace, Precision Castparts Corporation, SPS Fastener Division.

Administrative Information:

Project Name: Cherry Rivet Inspection System
Project Number: TBD
Project Track: n/a
Project Family: n/a
Parent Roadmap: n/a
Planning Term: Fall 2010
Start Term: Winter 2010
End Term: Spring 2011 / Faculty: Alan Raisanen (RIT)
Industry Guide: Rich Drinker (PCC-SPS Fastener Div.)
Project Customer: PCC – SPS Fastener Division
Project Sponsor: PCC – SPS Fastener Division
Project Budget: approximately $7-10K

Project Context:

Aerospace pull-type rivets such as those shown in Fig. 1 are commonly used in applications where only one side of a component can be easily accessed, or for convenient repairs to airframe components. Close-tolerance holes are drilled in the materials to be fastened, countersinking is applied as required, the rivet is inserted into the holes with the materials clamped tightly together, and tensile force is applied to the rivet mandrel. This plastically deforms the rivet body, crushing the rivet against the materials and establishing a tight mechanical bond. When a pre-determined tensile force is obtained, the mandrel snaps off, leaving a core of high shear strength material at the center of the plastically deformed rivet head. Maximum shear strength and clamping force, and controllable break-off force, are enabled by tight control over rivet geometrical parameters such as diameter, concentricity, roundness, and perpendicularity.

Cherry Aerospace, a division of Precision Castparts Corporation (PCC), SPS Fastener Division makes pull-type rivets for demanding aerospace applications. Key geometrical parameters of these rivets are measured manually by technicians using micrometers and other metrology instruments. Due to customer demand and the large number of rivets being produced daily, it is impractical to perform a 100% inspection of all rivets produced. Instead, a sample of the rivets is measured per lot of rivets produced. Approximately 125 pieces per lot are inspected in about 90 minutes, with a maximum number of 35 lots per day being sampled using current personnel resources. Cherry Aerospace would like to be able to sample up to 54 lots per day without increasing personnel resources, which implies implementation of an automated inspection process. A dimensioned mechanical drawing illustrating a typical Cherry Aerospace rivet product is shown in Fig. 2, with typical geometrical parameters which must be measured.

Cherry Aerospace would like to set up a means of inspecting these rivets and compare this inspection data with design values. This inspection fixture should be highly automated and usable by Cherry personnel with minimal training. Data analysis and databasing capability enabling statistical monitoring of rivet quality as well as tracking trends in dimensional variation should be included in the deliverables package. For the production operators, a "go/no-go" indication should be given to indicate whether a lot of rivets should be released to the customer, flagged for additional measurements or sorting, or discarded as noncompliant.

Construction of the inspection system hardware is probably most readily accomplished by use and integration of commercial off the shelf (COTS) components such as optical measurement sensors (optical micrometers) and stepper-motor driven linear and rotation motion stages. One potential architecture, illustrated in Fig. 3, is based on COTS optical micrometer sensor such as those offered by Keyence (LS-7000 series) and other manufacturers. A narrow beam of light is projected between the micrometer heads, and the part to be measured is inserted into the beam. The diameter of the part inserted is readily measured to better than ±0.00002 inches accuracy. A stage will need to be designed and constructed to accurately register the rivet to be inspected, and a linear translation stage will need to be constructed to systematically move the rivet through the optical beam of the sensor. A rotational stage will also need to be constructed to spin the rivet through the beam to measure out-of-round conditions. The workholding fixture should be easy to load and unload and present the rivet for measurement accurately, so considerable thought will need to be given to design a V-block or collet-type holding fixture that is easy to use. A map of the diameter versus X-coordinate of the entire rivet can then be readily constructed in suitable data acquisition software such as LABVIEW or even an EXCEL spreadsheet equipped with macros. This software should be capable of comparing design intent specifications obtained from mechanical drawings to the measured data, and flagging any out-of-spec conditions. A database of rivet measurements should be constructed enabling extensive statistical process control methods to be implemented, such as process-induced drift of dimension.

Customer Needs Assessment and Engineering Specifications:

A rudimentary Phase 1 House of Quality is illustrated here. Students engaged in this project are encouraged to contact the customer for interviews and input to further populate the list of customer requirements and develop a much more extensive list of engineering specifications. Upon initial analysis, most of the performance of the inspection system will be driven by the resolution and speed of the X-θ stage linear/rotation motion system, and the performance of the optical micrometer sensor. This project will require a significantly greater budget than most MSD projects, as these laser sensors retail for $6-8K depending on the exact model. Students are encouraged to use open source software or standard industrial software packages for control, data collection, and analysis. A complete training package is required to assist Cherry Aerospace engineers and technicians in setting up an SPC process for spot inspection of rivet lots and quality control.


Project Interfaces:

This project is a stand-alone task specific to Cherry Aerospace. Many elements of this project are shared with a second PCC project, "Thread Roll Die Inspection System". Both projects would benefit by being run concurrently with strong interaction between teams in hardware and software development to maintain a unified system architecture, or by being run sequentially so that lessons learned developing one system could be incorporated in the second system.

Staffing Requirements:

Position Title / Position Description
Lead Engineer (IE) / The Lead Engineer is an industrial engineer responsible for maintaining project schedule, coordinating project tasks, and systems integration. The lead engineer should have strong leadership ability and communications skills. The lead engineer will be responsible for establishing realistic compromise device architecture and engineering parameters to meet desired performance objectives using commercially available components such as sensors and stepper drives. Basic familiarity with mechanical engineering concepts is required. The lead engineer should have taken the DPM course.
Mechanical Engineer (ME) / This mechanical engineer will be responsible for designing and implementing die holding fixtures to present rivets to the inspection system for measurement. This fixture will need to accurately register against datum points on the rivet, and be simple enough to be used by Cherry Aerospace technicians with little training. Fixtures for a number of different rivet sizes will be required. Experience in reading mechanical drawings, solid modeling, and fabrication processes will be required.
Mechanical Engineer (ME) / This mechanical engineer will be responsible for designing and implementing the machine frame and the X-θ motion stages for scanning the rivet through the optical micrometer. Analysis of mechanical error in these systems will be crucial. This task will require specification and fixturing of linear and rotary bearings, leadscrews, and integration with stepper motor drives. Experience in solid modeling, design tolerancing, and LABVIEW or other programming environment will be helpful.
Optional Computer Engineer (CE) / The inspection fixture will use stepper motor drives interfaced with a computer to provide the X-θ scanning motion required to map the rivet. This could be implemented from scratch by a suitable computer engineering resource. However, this task has been performed by many other MSD teams and the solution may simply be ported over from one of these prior solutions. COTS open-source robotic solutions also exist.
QFD Engineer (IE) / The QFD engineer will be an industrial engineer responsible for setting up an automated data analysis system and implementing the rivet sampling and inspection plan. A quality monitoring methodology will need to be designed and integrated with the customer operation. Experience in data collection, analysis, and quality control methodologies will be helpful. Experience in a programming environment such as LABVIEW or EXCEL macros will be very useful.

Project Constraints:

Usage of commercially available optical sensors and stepper motor drives is very highly recommended but not strictly required. Budget will be available for purchase of these items or parts for their fabrication, within reason.

Required Faculty / Environment / Equipment:

Describe resources necessary to support successful Development, Implementation and Utilization of the project. This would include specific faculty expertise for consulting, required laboratory space and equipment, outside services, customer facilities, etc. Indicate if required resources are available.

Category / Source / Description / Resource Available (mark with X)
Faculty / Dr. Alan Raisanen / Optical Sensor and motion stage advice / X
Dr. Wayne Walter / Motion systems and automation / X
Environment / Test area / Setup of optical and electrical tests / X
Equipment / Machine Shop / Fabrication / Welding of mechanical components / X
Interferometer / Validation of system die measurements / X
Materials / Sensor / Maser Sensor from Keyence or equivalent / Purchase
Motion stage / Precision ballscrews, stepper motors, and related components / Purchase
Other / Control and Data acquisition / Stepper motor control and acquisition of data from laser sensor - PC based / purchase

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