PROJECT 99.08
INTELLIGENT TOOLING
OF METAL FOAMS
TEAM MEMBERS:
Glenn GardnerAndrew Graybill
103 Harter Hall34 Prospect Avenue
Newark, DE 19717Newark, DE 19711
(302) 837-8508(302) 456-9167
Jeff RousheyJoseph C. Staley
57 North Chapel36 Continental Avenue
Newark, DE 19711Newark, DE 19711
(302) 455-1670(302) 266-7108
CUSTOMER:
Chin-Jye (Mike) Yu Harald Eifert
Program Manger Executive Director
Fraunhofer Resource Center Fraunhofer Resource Center
Tel: (302) 369-6752 Tel: (302) 369-8057
Fax: (302) 369-6753 Fax: (302) 369-6753
EXECUTIVE SUMMARY
The production of metal foams is a state-of-the-art process with possible applications in a variety of industries. The powder production process is currently the only method for producing metal foams. The process involves mixing metal powder with a small quantity of foaming agent, and then extruding this mixture into a solid. This solid is placed within a mold and heated in a furnace, which causes the foaming agent to sublimate and the metal to expand and fill the mold cavity.
Our mission is to design and assemble a sensor system which will signal that the aluminum foam has risen to fill the entire mold cavity. Our main customer for the project is Fraunhofer Resource Center, and possible future customers include the automotive, aerospace, and building/construction industries.
Our wants for this project are: high percentage of successful foams, system reliability, system simplicity, and low cost. We desire a high percentage of successful foams so that material and labor waste will be minimized. We would like the system to be simple and inexpensive so that it will be embraced by industry in the future, and we hope to build a reliable system which has a long service life and generates foams with homogeneous properties.
We will be designing the system under some constraints which have been given to us by Fraunhofer. We must fabricate our system for less that $8000, our system must be able to operate within the confines of the furnace and at the furnace temperature of 700 degrees C, and we must use a LabVIEW interface to alert the user that the foaming process is complete.
We began the generation of our concepts by performing system level benchmarking. We benchmarked systems for casting and molding monitoring, high temperature monitoring, and materials level monitoring. We learned that the system would most likely be composed of a sensor to determine the completion of the foaming process, amplifiers/attenuators to alter the output signal of the senor, and a terminal board to channel all data into the LabVIEW data acquisition card.
Our functional level benchmarking was focused on researching sensors. We considered resistance, current , piezo-electric, optical fiber, eddy current, temperature, and many other sensors for monitoring the foaming process. Any signal altering devices needed in the system would depend on the output of the sensor.
Once we had found many sensors which could possibly detect the completion of the foaming process, we needed a method of comparing these sensors. We established a list of metrics according to our wants, and then determined target values for each of these metrics.
Next, we needed to generate complete concepts which would be compared with one another using our metrics. We determined that a complete concept would have to accomplish four critical functions: sense foaming process completion, alter the sensor output signal, channel the signals into the data acquisition card, and use LabVIEW software to alert the user of the completion of the foaming process. The most important critical function is the detection of the foaming process completion. As a result, the sensor is the most important component in each system.
The concept which best accomplished our task based on the metrics was the completion of an electrical circuit. A battery is used to create a driving voltage, and electrical contacts are placed on the side and top of the mold. When the metal foam rises to the top of the mold, it contacts the copper electrode and completes an electrical circuit. Current then flows through the upper electrode, and a voltage signal is sent to the LabVIEW data acquisition card via a terminal board. Some major advantages of this system were low number of signal alterations, low programming time, and low cost. The only disadvantage of the system according to the metrics was the necessity of mold alterations in order to implant the electrical contact sensors.
Once we had determined that the electrical contact system was our best solution, we began a detailed design of the system. The system would consist of a copper mold, two copper electrical contacts, a ceramic insulator, copper wire, a terminal board, and a battery. The ceramic insulator is a cylinder which is used to isolate the upper electrode from the surrounding copper mold (see appendix for diagrams).
We performed tests on metal foam samples to ensure that they were capable of conducting electricity. We found that a cold foamed sample conducts electricity with nearly no resistance, and a hot foamed sample (700 degrees C) conducts electricity with a resistance of approximately 2.1 ohms. These tests gave us confidence that our solution was feasible and would indeed work.
We also considered some future problems that might be encountered using the system. We considered that the ceramic cylinder surrounding the upper copper electrode might possibly be cracked during foaming due to the thermal expansion of copper. We have devised experiments which will demonstrate whether or not thermal expansion will cause us any problems in the final system.
Our team plans to order all materials and perform all remaining experiments during the winter semester so that we will be ready to fabricate our system when we return for the Spring Semester.
PRELIMINARY DESIGN REPORT CONTENTS
I. INTRODUCTION
A. Process Background
- Problem Background
- Problem Description
- Customers
- Main Customers
- Projected Customers
- Wants
1)High Percentage of Successful Foams
2)System Reliability
3)System Simplicity
4)Low Cost
- Constraints
II. CONCEPT GENERATION
- System Benchmarking
1)Die Casting / Injection Molding
2)High Temperature Monitoring
3)Materials Level Monitoring
- Functional Benchmarking
1)Capacitance / Resistance / Electrical Conductivity Sensors
2)Piezo-electric Transducer
3)Thermocouple
4)Optical Fiber
5)Eddy-Current
- Derivation of Metrics / Target Values
1)Dimensions
2)Number of Surface Defects
3)Sensor System Life
4)Maximum Operating Temperature
5)Number of Signal Alterations
6)Programming Time
7)Setup Time
8)Number of Mold Alterations
9)Cost
- Concept Discussion / Identification of Critical Functions
1)Electric Circuit Completion
2)Piezo-Electric Force sensor
3)Thermocouple Array
4)Optical Fiber
5)Eddy-Current Position Sensor
III. CONCEPT SELECTION
- Evaluation Against Metrics
1)Electric Circuit Completion
2)Piezo-Electric Force Plate
3)Thermocouple Array
4)Eddy-Current Position Sensor
5)Optical Fiber
- Working Model – Electric Circuit Completion
1)Copper Mold
2)Ceramic Insulator
3)Copper Electrode
4)Copper Wire
5)Terminal Board
6)Battery
- Testing of Electric Circuit Completion Concept
1)Cold Sample Testing
2)Hot Sample Testing
- Other Considerations / Plans for Spring
1)Possible Problems
2)Next Semester
APPENDIX
I. INTRODUCTION
A. PROCESS BACKGROUND
The production of metal foams is a state-of-the-art process with possible applications in a variety of industries. A powder metallurgical method for producing metal foam was invented at the Fraunhofer Institute of Applied Materials in Bremen, Germany. Upon perfection of this procedure, metal foam could prove to be an integral material in the automotive, construction, and aerospace industries.
The powder production process is currently the only method for producing metal foams. The process begins by mixing metal powder with a small quantity of foaming agent. After the foaming agent is evenly mixed throughout the matrix powder, a compaction or extrusion process produces a semi-finished, “foamable” product that can be worked into sheets or profiles. Upon completion of the metal working stage, the semi-finished product is placed in a mold and heated within a furnace at a temperature near the melting point of the matrix material. At this temperature, the foaming agent starts its decomposition, thus the foaming process begins. This decomposition releases gases into the material, causing it to expand and fill the mold cavity. As a result, we achieve a material with very desirable properties: decreased density, increased stiffness, high level of energy absorption, fire retardancy, and excellent sound damping characteristics. Upon conclusion of foaming, the foamed material forms a closed outer layer. If the piece is sectioned, the porous structure within becomes visible. A flow chart of the powder production process can be seen to the right.
B. PROBLEM BACKGROUND
At this stage in the research and development of metal foams, it is difficult to achieve optimal levels of the desirable properties mentioned above. But, it is known (through trial and error) that in order to optimize these desirable properties, the foaming process should be terminated (removed from furnace) at the instant the foam has risen to fill the entire mold cavity. Presently, the proper foaming time is approximated by experience. This results in a large quantity of wasted material due to overaging of the samples. Overaging, with respect to metal foams, is defined as the collapse of the foam due to escape of foaming gas. It would be of great benefit to Fraunhofer if a system was devised to signal completion of the foaming process.
C. PROBLEM DESCRIPTION
Our mission is to design and assemble a sensor system which will signal that the aluminum foam has risen to fill the entire mold cavity, thus yielding the most desirable properties. We will be using a copper mold with outer dimensions of 4” x 4” x 1”. All data will be displayed for the user on a LabVIEW interface. This system must have the ability to withstand a temperature of 700 C, the temperature at which foaming takes place for Aluminum foams.
- CUSTOMERS
i. Our customers are as follows:
1)Dr. Chin-Jye (Mike) Yu
Program Manager, Metal Foams
Fraunhofer Resource Center-Delaware
2)Harald Eifert
Executive Director
Fraunhofer Resource Center-Delaware
3) Bernard M. McGuiness
Laboratory Research Assistant
Fraunhofer Resource Center-Delaware
4) Jim Adkins
Laboratory Coordinator
Fraunhofer Resource Center-Delaware
ii. Projected future customers:
5)Automotive Industry
6)Aerospace Industry
7)Building/Construction Industry
E. WANTS
1)High Percentage of Successful Foams
This want was expressed by each customer. A successful foam is defined as one which produces a final product of target value dimensions. The greater the percentage of successful foams, the less material waste. Less material waste means cost reduction, which is attractive to any business or organization.
2)System Reliability
System reliability is defined as the ability of the system to perform its desired functions consistently over a long period of time. A reliable system will endure the harsh conditions associated with metal foaming and ensure all data collected are valid. The automotive, aerospace, and building/construction industries would like a system which will last for several years to ensure a large return on their capital investment. Fraunhofer would like a reliable system since it will enable them to achieve a greater degree of homogeneity regardless of temperature.
3)System Simplicity
System Simplicity is defined by a overall ease of operation and implementation. The automotive, aerospace, and building/construction industries would like a system which will be easy to apply to their existing methods of production. Fraunhofer would also like a system which will be easy to set-up, which can accelerate up the research process.
4) Low Cost
Low cost can be described as minimizing the total cost of the system.
Fraunhofer, a non-profit organization, would like a solution at minimal expenditure. A large scale implementation of our system could prove to be expensive. Therefore, the automotive, aerospace, and building/construction industries would find this want of utmost importance.
F. CONSTRAINTS
1)Cost
Fraunhofer would like us to achieve a solution for less than eight thousand dollars.
2)Operating Temperature
The designed system must be able to withstand the thermal stresses and extreme temperatures conditions associated with the metal foaming process. For our case of Aluminum foam, the system must be able to sustain temperatures up to 700 C.
3)LabVIEW Interface
Any proposed solution must use LabVIEW as the data acquisition software. Therefore, compatibility is a necessity.
4)Limit of Furnace Design
The size of the sensory component must be of suitable dimensions that it can be placed inside the furnace with the mold. Also, the sensory component should not be so large that it interferes with the heat transfer to the mold, thus hindering the foaming process.
II. CONCEPT GENERATION
A. SYSTEM BENCHMARKING
Our team began the generation of concepts by benchmarking systems related to our task of monitoring the metal foaming process. The team looked at other materials production processes such as injection molding and die-casting. Methods that monitor the level of materials inside containers and high temperature monitoring systems were also used as benchmarks.
1) Die Casting / Injection Molding
The casting and molding industries were benchmarked since our design project also involves a material production process. We found that these industries monitor the progress of their processes by visual inspection (source: General Die Casters, Inc.), linear position sensors (source: Visitrak, Inc.), and piezoelectric force sensors (source: AMP, Inc.). These methods helped to give us ideas on how to use sensors with computer software to alert an operator that the metal foaming process is complete.
2) High Temperature Monitoring
The Pyrotrace (source: Bricesco), a system we found that monitors the temperature inside kilns, uses a software package named Pyrographics and presents the temperature data in graph form. This system serves as a model of high temperature data acquisition and how signals from a sensor system must be amplified/attenuated and conditioned by a terminal board before it can be handled by a computer’s data acquisition card. Our team was also interested in the materials used in high-temperature monitoring processes. A ceramic material named Macor (source: JANDEL Engineering, Ltd.) was found to be used as an insulator in high temperature sensing applications.
3) Materials Level Monitoring
Many methods are used to monitor the level of materials inside containers. Ultrasound, eddy-current, resistance, capacitance and photoelectric sensors can be placed on the external sides of tanks to sense material levels. These systems can constantly monitor the level inside a container, or act as a trigger when a certain level was reached. The idea of using these different types of sensors aided our team in the generation of concepts. However, a system that monitors material levels near our operating temperature constraint could not be found.
B. FUNCTIONAL BENCHMARKING
Sensors that could be used to signal the completion of the metal foaming process were benchmarked.
1)Capacitance/Resistance/Electrical Conductivity Sensors(source:
Turck, Inc.)
These sensors can detect changes in the resistivity, capacitance, or conductivity of the metal foam. Electrodes can be placed so that, as the metal foam rises, it contacts the electrodes and completes an electrical circuit.
2)Piezo-electric Transducer (source: Turck, Inc.)
A force plate that utilizes piezo-electric technology can sense the force that the foam exerts on the top of the mold when it rises to touch it.
3)Thermocouple (source: Turck, Inc.)
Thermocouples would sense an abrupt change in temperature as the foam rises and touches the top of the mold.
4)Optical Fiber (source: Turck, Inc.)
An optical fiber can send a light beam into the mold, which reflects off the foam and is detected by a photoelectric sensor. When the foam reaches the top of the mold, the light would not be able to be reflected into the detector and this would signal that the process is complete.
5)Eddy current detector(source: Turck, Inc.)
A detector placed on the top of the mold would sense the change in eddy-currents given off by a source as the foam rises in the mold. This could sense the linear position of the foam from the detector.
C. DERIVATION OF METRICS
The metrics for our design project were derived from our customers' wants. The importance of each Metric to each Want was rated. These ratings were then used in SSD to give each Metric a total weighting. The team then assigned engineering target values to each metric. The results are shown in the table below.
Wants to Metrics Cross-correlationQuality Metrics / High % / System Reliability / System Simplicity / Low Cost / Score / SSD Weight % / Target Value
Dimensions / A / d / d / d / 9 / 9.890 / 4" X 4" X 1"
#Surface Defects / A / d / d / d / 9 / 9.890 / 0
Sensor Sys. Life / C / a / c / c / 12 / 13.187 / 5 years
Max Op. Temp / B / a / d / c / 13 / 14.286 / 700 C
# Signal Alterns. / D / d / a / d / 9 / 9.890 / 0
Progrmg. Time / D / d / a / d / 9 / 9.890 / 20 hours
Set-up Time / D / d / a / d / 9 / 9.890 / 30 minutes
#Mold Alteratns / D / d / a / d / 9 / 9.890 / 0
Cost / C / c / c / a / 12 / 13.187 / $2,000
91
Use / a / to Denote Very Strong Correlation / Score= / 9 / pts.
Use / b / to Denote Strong Correlation / Score= / 3 / pts.
Use / c / to Denote Weak Correlation / Score= / 1 / pts.
Use / d / to Denote No Correlation / Score= / O / pts.
1)Dimensions of the foamed sample
The dimensions of the final foamed products created by our design must be correct to ensure a high percentage of successful foams. Any type of void caused by insufficient foaming time would result in improper dimensions of the finished product. If the product is left in the oven too long, it will collapse and the dimensions will not be correct. The target value that the team derived is simply the inside dimensions of the mold. If the finished product's dimensions do not meet the target value, it is an undesirable product for the customers.
2)Number of Surface Defects