Quality Test & Inspection: Casting Company Opens Its Testing Labs
The "lab" is more of a labyrinth than just a laboratory. Each corridor feeds room after room. And each room holds sophisticated, multifunctional testing equipment. In one room, a scanning electron microscope (SEM) is engaged in nondestructive test (NDT) analysis. In another, banks of creep-rupture machines conduct testing of aerospace alloys at blazing temperatures. Contact and noncontact, destructive and nondestructive, chemical and physical, Howmet Casting (Whitehall, MI) testing laboratory seemingly can do it all. And do it well.
These labs must be good because it is here that testing is done on parts, both massive and miniscule, that power jets, generate electricity and operate in corrosive and destructive environments.
Many of the parts tested here will operate in environments that are at, or slightly above, the theoretical melting point of the metal. Because of this, the engineering and metallurgy that goes into these parts have to be exact, as does the testing.
Chemistry, says Bill Carothers, manager of the lab, drives mechanical properties, and mechanical properties drive performance of the engine. Turbine engine builders, for instance, have much to gain. "They want to squeeze every bit of horsepower that they can possibly get out of an engine. So they push the material to its absolute limits to improve fuel economy and thrust."
By running the engine hotter, it becomes more efficient, and efficiency is critical as fuel costs continue to increase. "If they can get more efficiency out of these gas turbines, their customers are going to help their bottom line," says Gail Cole, director of the lab.
For years, the experienced specialists at Howmet and the sophisticated equipment they operate were available only to internal customers-the Howmet casting plants. Recently, that testing capability has become available to the outside world-mostly customers and suppliers related to the investment casting industry but also to other aerospace, power generation, biomedical and automotive industries. Their services have ranged from testing high-precision ceramics to investigating NASCAR racing parts. Soon, a new computer system will further open up Howmet's testing to the outside world.
Out on LIMSAt the testing laboratory, each process is tied to a Laboratory Information Management System (LIMS). The LIMS, developed in the late 1970s, operates on a mainframe computer that lets other Howmet facilities monitor the progress of their testing, print certification reports, query historical data and do statistical trend analyses. "It is a vital tool for us to link our production plant to the laboratory and to support process control and problem solving," says Carothers.
The LIMS is now being replaced with a new Web-based system that upgrades its capabilities. This is an important move as Howmet's testing lab looks to be even more competitive with other commercial testing labs. Scheduled for launch during 2005, the new LIMS will allow all of Howmet's customers to confidentially track the progress of their testing via the Internet.
A busy place
The lab, the official name of which is the Technical Services department, is kept busy testing castings, raw materials and virtually anything that can come into contact with parts-such as pattern materials, cores, melting crucibles, mold materials and post-cast finishing materials-from Howmet's production facilities, as well as for parts that were built by outside companies.
The chemistry lab, for instance, analyzes about 15,000 samples per year. This translates to hundreds of thousands of tests, because a single sample may be analyzed for one element or the entire periodic table.
With aerospace investment castings, it is not only the part that gets tested but anything that comes into contact with the part is also tested. "Much of this is not required by our customers," says Cole, "but there are a lot of tests that we do to control our own materials and processes."
In addition, many customers require samples to be taken from multiple locations on a part for analyzing trace elements. For instance, the lab conducts atomic absorption tests that analyze elements to the parts-per-
million level. "The part may be analyzed for several trace elements," says Carothers. "With superalloys, the big two are lead and bismuth. These are very detrimental even at the parts per million level." If an extraneous material gets into the part, it can be disastrous to part performance.
"Much of the testing that we do is concerned with trace element control," says Cole. "There are other elements like sulfur that are detrimental to corrosion resistance of turbine blades. We have to know if those elements are there."
For Technical Services to meet its customers' needs, both inside and out, the labs must be able to do myriad tests and do them when needed. "We try to be a one-stop shop," says Cole. "We try to do everything that our production plants and external customers need so they don't have to use several different labs."
While a multitude of testing is done every day, everything has a purpose. "We don't do testing for the sake of science," says Cole. "Most testing is done to support manufacturing." For example, thermal expansion testing is done on every batch of core material. The core is the part of the investment casting that forms the hollow cavity. "We have to make sure that the thermal expansion is the same every time," says Carothers. "Otherwise you may get thin walls or even ‘kiss out' from a core."
Primarily, the testing lab is called on to do master-heat qualification or remelt testing of the alloy. This usually involves conducting full chemistry and mechanical property testing to ensure the alloy meets customer design requirements. However, the laboratories also provide failure analysis of parts and defect characterization for problem solving. "Our customers may have a problem with an unknown contaminant or defect on a part, and send it to us to identify the root cause," says Carothers. "We will perform a variety of tests to identify the source conclusively. We use investigative tools, such as a SEM, to study the defect at high magnification and determine its chemical composition. We then get that information back to the production plants and they can implement the corrective action to prevent reoccurrence."
First article testing is also one of the lab's specialties. When investment castings are made for the aerospace and industrial gas turbine industries, the manufacturing process must be validated with first article testing. This often includes a full chemistry and mechanical testing from samples taken from the part. It also includes an extensive metallographic cut-up plan to characterize its metallurgical integrity. All of the testing results must be documented in a single report.
Aerospace often requires NDT, such as fluorescence penetrant testing and radiographic inspections. Tom Jones, the lab's quality manager, works on the development of new technologies such as digital radiography and advanced ultrasonic inspection.
Jones says, "I'm here as an engineering resource for all of our manufacturing plants, and for helping to address current NDT issues as well as implement new technology. If a plant is struggling with how to use digital radiography or what kind of equipment to buy, then I will work with them."
In the area of advanced ultrasonic inspection, technical support was provided to a Howmet plant implementing a phased-array ultrasonic inspection of castings for an F-22 fighter. Jones says, "I am also working on a project funded by the U.S. Air Force to improve the accuracy of our ultrasonic wall thickness measurements on single-crystal castings. We use the grain orientation of the single crystal to correct the sound wave velocity and therefore the wall measurement. Because the
single-crystal materials are anisotropic, the sound velocity can vary up to 20%. That translates to variability in wall measurements. By applying this correction, the variability in wall measurement has been reduced to 5%."
The lab is accredited to ISO 9001: 2000, AS9100, National Aerospace Defense Contractors Accreditation Program and ISO/IEC 17025. The laboratory is also in the process of obtaining certification from the American Association for Laboratory Accreditation.
Turn, turn, turnDespite having so much more testing, the labs still must do the work on a timely basis. Turnaround time is critical. Typical turn times are 3 days or less, and to accomplish that, the lab is staffed for three shifts during the week with additional weekend coverage. "When I started in the 1980s," says Cole, "our manufacturing cycle time was 12 to 16 weeks from the time a pattern was made to the time a casting was shipped. Now we can make solid parts in 1 week and cored parts in 2 to 3 weeks. This huge reduction in cycle time put pressure on us to reduce our testing cycle time. We streamlined our lab operations and staffed to meet these demands. If we are not done with the testing when the part is ready to ship, that can be a big problem. We might get test samples less than 3 days before the parts are scheduled to ship, or sometimes, the parts are already on the shipping dock and they need same-day service. That is the heroics that a lab has to jump through once in a while." Q
sidebar: Howmet's Self-Imposed TestingHowmet Tech Services department does a number of tests not required by their customers. These include:
• Raw materials are tested to ensure process control. These materials are primarily wax, monoshell, core, crucible and finishing materials.
• Chemistry and physical testing make up the majority of this testing. Examples include:
- Trace element control for sulfur, lead, bismuth and other trace elements.
- Thermal expansion of core material lots to control radial core position.
- Ceramic creep of monoshell to control part dimensions.
- Particle size distribution of monoshell flours, to control viscosity and plate weight for correct shell build.
- Ash content of wax, to prevent casting inclusions.
Testing capabilities include:
• The chemistry lab conducts inductively coupled plasma, spark emission, optical emission, X-ray fluorescence, atomic absorption, carbon and sulfur, O-N-H gas analyses and X-ray diffraction tests.
• The mechanical testing lab conducts room temperature and elevated
temperature tensile and creep rupture tests, hardness and heat treatment of test material.
• The physical testing lab conducts sieve analysis, particle-size distribution, thermal conductivity, thermal expansion, ceramic creep and modulus of rupture tests.
• The microanalysis lab conducts optical microscopy, microhardness, image analysis, scanning electron microscope and microprobe analyses.