A vision of computer-aided casting in the year 2000.
Let's take a look into the crystal ball to see how foundries will make castings in the next century. It is timely to do so now because the year 2000 is just around the corner.
Casting is nearly as old as our civilization, and process procedures often are the results of centuries of experience. The image of foundrymen sitting at a computer does not convey the historic sense of "art" and "craft" that has produced the complex and wondrous castings that contributed to our technological civilization.
But we must be realistic, not romantic. The traditional approach is being replaced by more modern and scientific methods now that our industry is subject to strong international competition. Look at our children playing with their Nintendo computer games. For them--the generation of the future--the picture of the foundryman at a computer would be very attractive.
We can expect a generation change to occur along with the technological change. We "old-timers" must learn to gracefully accept the coming tide of the future. Actually, it is necessary to be more than graceful. It is necessary to create the future.
Many of the coming trends are visible, if we look in the right place.
A good place to start is with the computers that will be used in business. Let's look underneath the hood, so to speak, and see what will be available in the future. According to a recent issue of BYTE magazine, a review of microprocessor performance since 1972 shows that the processing capability, or speed, has been changing at an exponential rate, increasing by a factor of 10 every eight years.
Until now, this increase in speed has been attained primarily by a steady rise in transistor density, known as "Moore's Law." In addition to this factor, microprocessor manufacturers are experimenting with the parallel execution of multiple instructions which will increase the speed several times more.
If these trends continue, by the year 2000, microprocessors will operate at a speed of 100-200 millions of instructions per second (MIPS). In other words, the average personal computer will have the processing speed and power of workstations now marketed by, among others, IBM, Hewlett Packard, Sun and Silicon Graphics.
The availability of this tremendous computational power at a low price can be expected to have an enormous impact on business and industry, especially in areas where the cost of high-performance computing has been prohibitive, such as casting, forging and other metalworking industries.
Before we portray how the foundry of the future will operate, we must examine the steps required to produce a typical commercial casting today.
Currently, the casting process is riddled with human judgment errors, requiring costly redesign and remakes. These remake iterations are required because the internal properties of the solidifying metal in the mold and rigging cavities are largely unknown. Predicting the part properties is somewhat akin to a "black art."
Successful casting of a high-quality part on the first try is improbable for complex castings unless an accurate computational model and engineering analysis are used. This, in turn, requires the use of accurate product data, including three dimensional (3-D) geometry, domain-specific features, material properties, tolerances and finishing information. This product data will enable the generation of process data for actual manufacture. Ideally, process and product data should be considered concurrently in the overall part and process design cycle.
A new methodology, the Rational Product and Process Design (R|center dot~|P.sup.2~|center dot~D) has been developed to address this problem of process and product design in a concurrent engineering context. This, and other methodologies, will enhance today's casting process.
Now, we turn our attention to casting in the year 2000. The improved casting procedure is shown in Fig. 1.
Casting will consist of five steps:
1. send an electronic drawing to the foundry;
2. prepare a quotation;
3. design the mold or die;
4. make the pattern and cores, and;
5. pour the castings and verify.
1. An Electronic Data Representation Is Sent to the Foundry
Some foundrymen and engineers today are familiar with computer-aided design and drafting (CAD) programs, and with the advantages of this approach for the design of parts and for plotting of construction prints. In fact, the more powerful and popular computer-based CAD programs have nearly replaced the engineer working with a T-square, vellum and pencils at a drafting table, much like calculators have replaced the slide rule.
What many foundrymen are discovering is that several organizations are trying to establish a product data exchange standard for transfer of electronic data between CAD programs. At present, it is usually not possible for one CAD program to supply data compatible with another without special file translation packages.
Thus, if the customer has a different CAD program (and possibly a different computer) from the foundry, no direct communication is possible.
There are two choices: redo the drawing in the desired CAD format or invest in CAD platforms that are compatible. Both alternatives are costly and time consuming. A direct product data exchange standard is desirable and could also be used in computer-aided casting.
Motivated by the Department of Defense's Computer-Aided Acquisition and Logistic Support (CALS) initiative, a product data exchange model for casting is being developed that will comply with the Standard for the Exchange of Product Model Data (STEP). The data modeling activity is being carried out under the auspices of the IGES/PDES Organization (IPO), an ANSI-accredited standards body responsible for product data exchange standards. Both the American government and industry see a need for a unified standard for product data exchange.
Product Data Exchange
Product data exchange emerges from the need to extend the scope of the Initial Graphics Exchange Specification (IGES) to include all aspects of the product in addition to geometry. IGES is currently in use for interchanging graphical data between dissimilar CAD systems. Complete product data information will be exchanged within the next level of standardization. STEP will eventually specify all aspects of the product data requirements throughout the entire product life cycle.
Most STEP developments are being performed under the International Standards Organization (ISO) 10303 activity. As of this writing, STEP is now a Draft International Standard (a worldwide standard). STEP will permit electronic transfer of information about a product, including its geometry, topology, material specification, tolerances, features, surface finish and the manufacturing process. The IGES/PDES Organization (developers of IGES) leads the U.S. effort with its Product Data Exchange Using STEP (PDES) activity.
By the next century, almost all business and technical data transactions will be computerized. Data will be stored and transmitted electronically. Shared databases will be prevalent because they reduce costs and turnaround time, as well as improve access and integrity of information. Electronic exchange and storage require a workable format and proper organization so that recipients will understand the information contained in electronic files.
STEP provides the enabling information technology to facilitate the exchange of product engineering information via computer. It also helps shorten the lead time because of faster access to product information. For example, a customer can send an electronic version of its product to the foundry with the necessary information to produce the part. STEP will provide for similar information exchange between the foundry and its pattern, mold and core shops.
From the technical viewpoint, product engineering data can also be transferred to process modeling systems in a neutral format so it does not need to be translated. This facilitates the computer-aided manufacture of castings.
The Department of Defense is a stakeholder in neutral product data exchange. Its CALS initiative looks toward STEP to support the effective representation of product-related activities during product design, logistics, manufacturing and use.
To be able to exchange product engineering information, aspects of the product domain are analyzed. An application protocol (AP) methodology identifies and formalizes data attributed to the manufacturing application (in this case, casting). The AP then defines the standard format for the exchange of product data.
An AP for casting is being developed. The initial stage involves creating activity diagrams showing information flow. Data modeling to organize different information elements follows. All these activities are being done in coordination with the Manufacturing Technology Committee of the IGES/PDES Organization (IPO). Input from AFS is being used in part of this effort.
Projecting all of this activity into the next century, electronic transfer of part information under STEP will be the predominant method of transferring the customer's part geometry, tolerances and material requirements. A blueprint, if required, will be made by the foundry from the electronic file.
2. The Foundry Prepares a Quotation
After receiving information about a casting from a potential customer, a quotation will be prepared from the electronic STEP file. A quick quotation can be generated by a knowledge-based computer program that uses cost guidelines applied to the design. The quotation can be obtained quickly and easily, and cost estimates may be more accurate and reliable than with current hand calculations.
With advanced computers and software, a 3-D solid model of the casting will be generated from its electronic STEP file. The 3-D image can be rotated to any desired position. It is also possible to "look inside" the part at any position by "slicing away" exterior layers. Once the 3-D model is made, it is easy to calculate the weight of the casting or a certain part of it. The modulus (surface to cross-sectional area ratio) is also easily calculated at various points.
The STEP information allows the foundryman to estimate the size of risers needed to feed the castings. A parting line and the sprue, runners and gates may also be incorporated at this time. All this information is helpful in accurately pricing the casting by determining the amount of metal in the final part, the yield of the casting and probable labor costs incurred in production. Setup or tooling costs must also be estimated and amortized over the production run.
3. The Foundry Designs Mold or Pattern
Now we will look at how future foundrymen will design molds for castings. We will focus on sand casting, but most of the principles involved can be extrapolated to other casting processes.
The customer has placed an order with the foundry in the year 2000. With a foundry engineer at the design station, a parting line is established, and a sprue, runners, gates and risers are set in place either by an expert adviser or by hand. The dimensions of the pattern are automatically increased, according to empirical formulas established earlier for this alloy, to allow for thermal contraction of the casting as it cools after solidification.
A simulation is performed for a detailed analysis of the casting. This is done to check on the viability of the mold and pattern design. The simulation will show the probable presence of shrinkage or microporosity. Coupling with other software allows for the calculation of residual stresses and part distortion. It may also be possible to predict the occurrence of hot cracks or hot tears and to show the microstructural characteristics (and mechanical properties) throughout the casting.
To date, computational and visualization technology has been applied primarily to the simulation of the flow dynamics and solidification kinetics of the casting. Two examples of a 3-D simulation are shown in Fig. 2-3. Figure 2 shows a simulation for a typical piston obtained with a modeling, simulation and analysis system. Figure 3 illustrates the simulation of an exhaust manifold. Simulation capability is expected to grow as computers become more powerful and less costly.
The simulations fall into one of two categories. The first category is problem identification. In other words, a foundry has experienced problems in producing a casting and is asking what can be done to eliminate a defect. The second category is preventive. In this case, a foundry does a simulation before the pattern is made (or the mold is cut) to ensure the pattern design is correct.
The latter is becoming more prevalent as foundrymen and their customers learn in more detail about the benefits of a casting simulation. There are even cases where a potential customer wants the results of a simulation with the quotation, before an order is placed.
As the capabilities of numerical simulation programs improve and the cost of computer simulation falls (with decreased cost of computational speed, as noted above), it will become more cost-effective to test out a pattern design with computer simulation. Only after the simulation is made will the pattern be cut and metal poured. In this way, the expensive trial-and-error method to designing complex patterns is eliminated. The power that STEP provides from its 3-D solid representation is what assures transferability.
The design of the pattern and mold is now complete. A pattern is then made based on exported STEP data that has been enhanced to include the rigging. Then, the castings are poured. If all goes well, defect-free castings are produced the first time. However, problems often occur, especially with complex shapes. Therefore, it is sometimes necessary to redesign the mold. Risers may be added or increased in size, or perhaps relocated. Chills may be used. The gate design may be changed to direct the flow of liquid metal into the mold. Another simulation may be needed to check the design viability.
4. The Foundry Makes the Pattern and Cores
Now that the part design and mold parameters have been established and an order is placed, the foundry makes the pattern and cores. It is possible to envision an electronic transfer of the pattern and core designs directly from the foundry's workstation. A few foundries already use CAM packages to produce their molds and patterns in this way.
In other words, we can imagine the foundryman of the future will simply press a function key on his computer to automatically download the STEP files containing the pattern and core mold designs to CNC machines (either at the foundry or at another company), which will cut the patterns and cores.
5. Castings Are Poured
The foundry is now in a position to pour castings. Future foundries will be highly automated and process sensors will record relevant process information (metal temperature, dissolved gas content, metal cleanliness, mold temperature, pouring and cycle times, etc.) that provide an operational process database. This information is correlated automatically with casting performance for statistical process control (SPC). Assuming that Steps 1-4 have been done properly, the foundry is producing high-quality castings from the very first metal poured.
Concurrent Design Process
The five process steps described above have been considered as separate activities because this is how they are generally done at this time. In the future, the procedure may be different. We envision a greatly enhanced computational capability, and a "seamless" electronic data transfer network between customer and foundry. These important advances make it much easier to design the product and process concurrently. By considering an example, let's see how it works:
The foundryman of the future has just received a STEP file from a potential customer. This file is loaded into a workstation where a 3-D representation of the part is viewed. By using a computer and a feature-based program, a parting line is assigned, and the size and location of the needed risers, gates and runners are established.
A simulation for the casting using this mold and part design is started. This simulation runs in the computer background while the foundryman does other tasks. A few hours later, the simulation is complete.
An examination of the results shows the initial design may have problems. There may be a high probability of hot cracks along a long thin section, shrinkage porosity at a boss or "Tee" section, or perhaps an isolated hot spot that is not fed properly.
Whatever the problem, the foundryman calls the customer and sends files to the design engineer that show the problem. Together, the customer and foundry make design changes and start once more with the revised product design. This procedure may require several iterations until a promising simulation is obtained. Only at this point is a quotation made.
As shown in Fig. 4, the concurrent design of the product and the process is accomplished, and many potential problems are eliminated long before a pattern or mold is made or castings are poured. This approach helps eliminated costly production problems and usually results in significant cost savings. Elimination of design problems "up front" in the engineering process also reduces the time required to bring a component design into production.
This conclusion will not be news to foundrymen and engineers who have worked together on the concurrent design process. Unfortunately, this sensible cooperative approach to design is now more the exception than the rule. With proper software development, however, a computer-aided casting system can promote the concurrent design approach, thus making casting easier and more efficient.
The overall workstation-based, computer-aided casting scenario presented here is highly probable, but to our knowledge, no one is working on a total solution. A simulation program for several casting processes has been developed and a STEP application protocol for casting is in the works, but this is still a long way from the total system.
A computer-based, automated manufacturing system for production of castings will benefit users of castings, as well as improve the competitiveness of the U.S. foundry industry. The automated production scheme envisioned will allow for the first successful production of castings in much shorter time--a few days or a few weeks instead of the several months or years now required--after the design concept is established by the part user.
This will be very close to the rapid prototyping capability desired by U.S. manufacturers. Significant cost savings will result. The castings consumed in the U.S. are worth about $20 billion annually. Even a small portion of this represents a significant savings.
The potential savings in aerospace and defense are probably much greater than in larger-volume applications. Here, the setup and design costs for a casting are spread over a much smaller production volume. For the production of a few hundred or a few thousand pieces, the setup cost may be greater than the production costs, and so significant savings are possible through the use of computer-aided casting.
R. Ryan et al. "Built for Speed," BYTE, vol 17, No. 2 pp. 123-135 (February 1992).
J. Rumble, J. Carpenter, "Materials 'STEP' into the Future," Advanced Materials and Processes, vol 142, No. 4 (October 1992).
A.H. Al-Ashaab, R.I.M. Young, "Information Models: An Aid to Concurrency in Injection Moulded Products Design," ASME Winter Annual Meeting, Anaheim, CA (November 1992).
H. Callihan, R. Henry, C. Orogo, "A Proposed Architecture for Developing a Suite of Application Protocols for STEP on Near Net Shape Processes for Producing Discrete Parts," a working concept paper presented to the Manufacturing Technology Committee of the IGES/PDES Organization, Seattle, WA (April 1992).
C. Orogo, H. Kuhn, H. Callihan, "Concurrent Engineering of Discrete Parts in a STEP Environment," CALS Expo '92 Proceedings, San Diego, CA (December 1992).
A. Paul, C. Wang, O. Huey, "U.S. Navy Program Advances Casting Technology," modern casting, (March 1992).
C.M. Wang, A.J. Paul and R.A. Stoehr, "Modeling Foundry Castings for a Rational Process Design System," Numerical Simulation of Casting Solidification in Automotive Applications, ed. Chongmin Kim and Chung-Whee Kim, The Minerals, Metals and Materials Society, Warrendale, PA, p 139 (1991).
Table 1. Typical Process in Casting a Part Today
1) Customer sends a drawing or blueprint to the foundry.
2) Foundry prepares a quotation and may suggest minor changes to the design that will make the part easier (and less costly) to produce.
3) An order is awarded to the foundry, and the foundry designs (or redesigns) a mold, pattern or die, depending on the casting process to be employed.
4) Foundry prepares a paper drawing of the pattern or mold and cores (if necessary). The drawing is sent to the pattern shop or mold and die maker for fabrication.
5) Foundry pours the first castings. They are inspected for dimensional tolerance, strength and soundness. If problems occur, it may be necessary to redesign the casting by returning to step 3 above.
Author's Note: This project is supported by the CALS Shared Resource Center under U.S. Air Force contract F33600-92-C-0194. The authors thank AFS, Littlestown Hardware and Foundry, Stahl Specialty and CMI for their valuable contributions. Additional acknowledgment to Barry Lerner for his review.
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|Title Annotation:||Computers in the Foundry|
|Author:||Kuhn, Howard A.|
|Date:||Oct 1, 1993|
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