In Pursuit of high tech: what foundries must consider to become State-of the-Art: three engineering firms detail their vision of what it takes to be considered a high-tech foundry.

When we think of a high-tech foundry, images of robots and automated (labor-less) molding, pouring and grinding operations jump to mind. While this can be the case, a high-tech foundry might also refer to a plant utilizing the latest management and maintenance techniques combined with an innovative and well-trained workforce.

According to the three consulting firm's MODERN CASTING polled--Vulcan Engineering Co., Mount Co. and Peter E. Macler Assoc.--a high-tech foundry utilizes the latest in technology to support its workforce and to best serve the needs of its customers. The goal, according to these firms, is to ensure that any drive toward high technology that a foundry considers must be driven by a desire to meet a customer's need.

According to Macler Assoc., "Equipment selection should be based upon customer requirements, such as metallurgical specifications, and casting sizes and configurations." New technology for technology's sake doesn't cut it anymore as profit margins continue to fall, the firm said.

The following article dissects the various areas of a foundry and provides the thoughts each of these engineering firms has as to what is some of the best current technology available and what it takes to become a high-tech foundry.

Coremaking

According to Vulcan and Macler Assoc., today's foundry has two main coremaking options--coldbox and shell. From the supplier's perspective, the majority of research and development has been focused on coldbox and the development of better, faster and less expensive binders and production machinery. The terminology "coldbox" refers to any amine, S[O.sub.2] or methyl formate gas-cured processes (including nobake).

Typically, coldbox (also see molding section for more details) is faster and less expensive in operation than shell coremaking. However, said Macler Assoc., there are numerous factors that must be evaluated in making this comparison, including capital equipment required, raw material costs, tooling costs, operational costs, environmental costs, waste disposal costs and reclaimability. Specific considerations include:

* size and shape of the core and whether it is produced solid or hollowed out (producing a shell can affect cycle cure rate and sand consumption) figures into the cost equation and final selection;

* operational differences mean differ any of the coldbox processes as it is with shell, meaning that tooling can be manufactured out of less expensive material (such as wood, plastic, aluminum and cast iron). Shell tooling is constructed for an operating temperature of 425F;

* the lack of heat used also attributes to faster machine set up in the coldbox process due to the fact that there is no heat up or cool down time required during set-up and tear down;

* another key advancement in coldbox technology is the ability to effectively reclaim and reuse large quantities of core sand either mechanically and/or thermally. This technology can greatly reduce the foundry waste stream, which reduces raw material and disposal costs.

While coldbox offers versatility, speed, reclaimability and a lower cost per pound, the shell process continues to be a viable alternative. While equipment and raw material innovation and advancements have not paced that of coldbox, the shell process still offers many distinct opportunities. Surface finish, shakeout (for certain alloys), sand consumption reduction for larger cores and handling strength make the shell process attractive. Additionally, there is less capital equipment to purchase and maintain as there are no sand mixers, gas generators and fume scrubbers required in running the shell process.

Another coremaking option on the horizon for foundries, said Mouat, is the introduction of water-soluble, environmentally friendly binders. These products, which have begun to gain fame in the last five years, "show promise but have not yet proved to be economically practical," said Mouat. Some binders are produced using animal products but require significant modifications to existing equipment and/or new equipment for production.

The newest water-soluble core binders utilize salts, which require heat to drive off moisture used in making the binder. However, the core then is easily dissolved in water, facilitating removal from the casting. This is especially attractive for aluminum components, considering the difficulty in removing cores made from conventional resin binders.

Molding

While the molding processes available to today's foundries have not changed dramatically over the past decade, technology has come a long way, said all three engineering firms.

Green Sand Molding--According to Mouat, this remains the most economical method of high-volume casting for most metals. Green sand control technology also has advanced to the point that excellent and repeatable sand properties can be obtained, as long as the foundry installs the latest technology controls. These controls include screening, metallic separation, cooling of the return sand and accurate metering of additive materials for mixing/mulling with the return sand.

"Green sand molding machines are holding tighter tolerances with better mold quality and at mold rates unheard of just a couple of years ago," said Vulcan. "Coupling these improvements with more efficient sand systems delivering consistently controlled sand should keep green sand as a leader for both ferrous and nonferrous casting production."

In a comparison of vertically and horizontally parted green sand molding, Macler Assoc. states that vertically parted green sand molding has dominated the market for the high production of small to medium size gray and ductile iron castings. The processes relatively low capital cost, high speed, low labor requirement, consistency and compact physical size are key advantages. Its limiting factors include constraints in gating and risering configurations, and setting of complex coring, filters, chills, sleeves and ram up cores. In addition, relatively high metallostatic pressure can cause metal penetration when casting highly fluidic alloys.

From the nonferrous side, high-production vertically parted molding has begun to gain ground with systems designed to accommodate the different casting nature of these alloys. However, until greater production volumes with the necessary mechanical properties are achieved with this method, permanent mold will still be the dominant choice for high-production aluminum castings.

Horizontally parted green sand is one of the dominant processes for low and medium volume casting production, said Macler Assoc. Whether with cope and drag or matchplate technology, horizontally parted molding systems can provide greater flexibility for producing complex castings. In some instances, the systems are able to make pattern changes within one cycle, allowing for efficient output of either short or long production runs. However, manual labor must be replaced by mechanization, and the overall system capability must be optimized to assure superior surface finish and dimensional accuracy.

When selecting green sand molding technology, several considerations are key, including:

* the system's capability to produce high quality molds having uniform hardness;

* provisions for quick tooling changes;

* utilization of automatic/mechanized core setting, mold handling, weight and jacket changing for matchplate, and mechanized flask handling for cope and drag molding.

To achieve uniform mold hardness, a number of different technologies have been employed, according to Macler Assoc. The blow and squeeze method is used on several automatic matchplate machines. It is important that the blow direction be perpendicular to the pattern plate to assure uniform mold density. Some cope and drag machines have incorporated a combination of rapping and squeezing to improve uniformity of mold hardness. Others have used highly compressed gasses to create a sharp impulse to compact the sand against the pattern. Sheep's foot compactors are sometimes used on larger molding machines. Compensating squeeze heads and hydraulic squeeze heads also are used.

However, the fact that there are numerous methods employed to achieve uniform mold hardness suggests that no one solution has proven superior for all applications. Check with current users or have the manufacturer run test molds using the foundry's tooling before making a selection.

Precision Sand--This process focuses on the chemically bonded molds produced via the coldbox processes. It has seen a recent resurgence, said Vulcan, particularly in the casting of aluminum blocks and heads because the process offers users the advantage of using chills for directional solidification along with the ability to cast iron cylinder liners in the blocks.

It emerged in the early 1970s as a means to produce nearer net shape castings and castings having difficult geometry that normally required additional coring when produced in green sand. Today, coldbox molding has become the standard for dimensionally accurate and complex castings, producing a wide variety of alloys in sand molding. As seen in the core room, new innovation in resin chemistry along with new core room equipment is allowing for better quality parts at a reduced cost. Additional equipment improvements in molten metal pinups and robotic automation assembly lines are lowering manpower requirements and contributing to better quality castings at lower costs.

A coldbox molding machine is a larger version of a core machine. Some produce a cope and drag simultaneously, while others produce stack molds having impressions on both sides. A third arrangement utilizes two machines, with one producing the cope and the other producing the drag.

According to Macler Assoc., these machines usually feature constant tooling clamping during the entire cycle to improve dimensional accuracy and minimize parting line fins. Larger machines are entirely hydraulically operated for smooth and reliable operation. Automatic ejection and mold removal is common. Automated manipulators can be installed to wash and dry, set cores, apply adhesives and close the molds. Employing these options reduces labor requirements and can help to assure the highest quality and productivity. With coldbox systems, tooling design is critical as it will impact not only surface geometry and finish, but also the accuracy of core assembly and location in the core prints.

Several types of blowing technology are available for coldbox molding, according to Macler Assoc. Most machines fluidize the sand in the blow head to improve transportation into the tooling. Typically, these machines use lower blow pressure and higher air volume, and can nearly empty the blow head each cycle, A few manufacturers utilize a process called "extruding", which differs from fluidization. Using a proprietary blow head design, lower air volume and higher blow pressure are required. They claim that "extruding" allows the sand to flow easier into complex shapes. The best advice would be to check with current users of both technologies, and if possible have prospective manufacturers run samples using the foundry's own tooling.

While coldbox systems are capable of producing very accurate and complex castings, the cost of tooling, sand, binder and catalyst is substantially higher than the cost of sand and bond for green sand. In addition, production rates are lower for coldbox.

Lost Foam--Lost foam continues to evolve and expand its market share as equipment and raw materials continue to improve, said Vulcan. The latest designs in multi-vector compaction tables and real time feedback sand fill systems offer lost foam users improved quality and faster cycles--translating into dollar savings realized by the end users.

Lost foam advantages still lead the molding process technologies in offering design freedom with the production of complex shapes with no, low or reverse draft, casting weight reduction, reduced or eliminated machining requirements and cast-in features with no core use. This design freedom translates into castings being poured today that were never before possible.

In addition to equipment innovations, new developments in bead composition, coatings and compaction media also are improving quality and productivity and contribute to the expansion of the market.

Melting & Pouring

With today's production requirements calling for foundries to produce a multitude of alloys quickly and with quality, according to Vulcan, nothing fits the bill of versatility better than today's electric melt systems. Current trends show that the coreless induction tilt-pour and the lift-swing or pop-up units fulfill the melting needs of today's foundry pouring numerous alloys.

To select the proper melting unit for an operation, according to Macler Assoc., a foundry must consider the following factors:

* alloys to he poured;

* continuous or batch melting;

* required melting rate;

* characteristics of available charge materials;

* cost of energy and limitations on usage;

* hours of operation;

* skill of labor required;

* safety and environmental issues.

Advances in solid state electrical technology have expanded the utility of induction melting by allowing greater power application using a wide range of frequencies. Additionally, using one power supply to simultaneously melt or melt and hold with multiple furnaces greatly improves utilization and flexibility. Electrical demand charges can also be reduced.

To achieve the highest level of efficiency, mechanized charge weighing and drying equipment, and automatic charging systems should be employed to reduce labor costs and increase productivity and quality while decreasing occupational hazards. For high purity alloys, inert gas shielding during melting and tapping has evolved as a standard practice.

Several specialty foundries use vacuum casting systems, which utilize induction furnaces and chemically bonded molds. The vacuum process features partially immersed molds having bottom gating, drawing clean metal directly from the furnace into the molds. The resulting castings are very clean and have exceptional surface definition.

Foundries pouting one to two classes of iron in large quantity still tend to rely on the cupola for their melt. This method of melting produces large quantities of quality iron delivered at perhaps the lowest cost per ton of any melt system. The cupola can be cost effective provided that the quantity of iron poured covers the larger manpower requirements generally associated with its operation. Ductile iron shops are finding that both electric melt and cupolas deliver good base iron with consumption again playing a part in the selection of the inch system used.

Foundries pouring large quantities of a single aluminum alloy have found that the gas reverberatory furnace provides a cost effective solution for their melt requirements. Although, foundries that are pouring smaller amounts of different aluminum alloys tend to favor smaller lift swing or pop-up electric units for their melting requirements.

A good choice for melting within carbon steel foundries is the are furnace because lower cost charge materials can be used and alloy refinement can be accomplished. However, alloy steel foundries use induction melting extensively.

Regardless of what melt method is chosen, each user must evaluate utility costs, environmental considerations, manpower requirements and raw material requirements associated with each specific melt system and how that will impact the cost effective operation of that facility.

Cleaning and Finishing

According to Macler, it has been said many times over the years, "Castings should be made in time foundry and not in the finishing room." In addition, said Vulcan, foundries must face: a changing workforce that doesn't want to work in manufacturing (much less the cleaning room); new ergonomic and safety, pressures; and casting buyers requiring tighter tolerances, consistency, shorter delivery times, value added validation and/or testing--all at reduced prices.

All of the above leads foundries to explore methods of reducing human intervention for casting finishing to improve efficiency, quality and speed while simultaneously lowering costs. But how can this goal be realized? Through engineering and technology enhancement.

But before committing major capital to more grinding equipment, eliminating the root causes for finishing operations (such as trimming parting line fins, removal of risers and gating, and grinding core prints) is critical. According to Macler Assoc., these root causes can be identified within areas such as: tooling design and maintenance; sand control: mold hardness and uniformity; coating practices; gating; and equipment maintenance.

But improving production practices only can take you part of the way with cleaning and finishing. Technology does play an important role.

According to Macler, for medium to high production foundries, several opportunities for increased efficiency have been developed:

* robots are used in finishing operations to reduce labor, achieve more repetitive results and increase output. Smaller castings are grasped and moved through the same motions that would be performed manually. For large castings, the finishing tools would be moved to the castings;

* in some applications, castings can be removed from gating systems using shears and trim presses;

* trim presses are also widely used to remove parting line fins and flashing. Robots can be used to load and unload trim presses. Smaller castings can be automatically sorted and positioned using vibratory bowl feeders that load the presses;

* multipurpose finishing tools can be installed around a turntable feeder. Operations could include grinding, shearing, trimming and machining. The turntable would have multiple stations for loading, unloading and for the selected operations;

* gates and risers also can be removed using impact hammers, wedges and shears. These operations can be automated if the position of the work is repetitive, and the work is sufficiently restrained to withstand the action of time tools.

For low-volume production, efficiency opportunities include:

* modernization of the finishing work station to increase productivity and quality, while decreasing fatigue and the potential for injury;

* ergonomic improvement through elevating and tilting work tables, work positioners, universal clamping devices, overhead hose reels, tool balancers, and improved lighting and ventilation;

* castings can be conveyed in and away from the work stations;

* bin feeders can be used to present castings at a proper height, eliminating bending and lifting.

According to Mouat, the ramble blast (or barrel blast) is currently the most widely used blast cleaning technology in foundry finishing rooms. These units come in various sizes from 5-100 cu ft. This method of blasting is the most economical due to the ability to completely automate it, minimizing physical handling of the castings.

The design concept allows for fairly efficient cleaning by tumbling the castings under a high velocity stream of abrasive. For years, the tumbling mill was an articulating chain-type conveyor that did create some parts-jamming potential, as well as a significant maintenance cost as the chain and mill components wore.

However, newer technology has replaced the chain-type mill with a fabricated drum with geometry that creates proper tumbling as it rocks back and forth. This concept eliminates the jamming issues, as well as the higher maintenance costs associated with a chain-type mill. This design is also more conducive to continuous, or flow-through, designs for a foundry with a casting mix that can be cleaned on a continuous basis The limiting factor of the throughput is that the flow of castings must be restricted to achieve proper cleaning of the most difficult-to-clean casting.

One of the problems of tumbling is damage to thin-wall castings, as well as smaller ferrous and nonferrous components, that suffer from part-on-part impingement damage. New technology has recently been introduced that combines mass finishing, also known as vibratory finishing, with high velocity shot impingement. This technology utilizes various medias to convey the castings (keeping them from impinging against each other) and provide a gentle scrubbing or burnishing action on the exterior and interior surfaces, while exposing the parts to the abrasive stream for more aggressive cleaning. This approach also eliminates the wasted blast from over-blast since the work is held in close proximity to the blast in the center of the stream.

For larger, more intricately cored castings such as engine blocks and heads and valves, the generally accepted cleaning method has been to hang the castings on a rotating hook, and advance the castings on a monorail type conveyor to one or multiple shot blast wheel locations. This ensures multiple angles of shot impingement for complete coverage, and allows for abrasive drainage to prevent blinding of internal passages.

Newer technology utilizes "grippers" that rotate the castings in front of the shot wheels, sometimes through multiple stations. Other technology can use a robot with a special shielded gripper. This allows for the casting to be manipulated at an infinite number of angles, directly in the blast stream, and eliminates much of the over-blast while allowing for fewer blast wheels.

For finishing, said Mouat, foundries have attempted to find alternatives to hand grinding, turning to the use of trim presses. For years these were simple, manually loaded, single-station units that were slow and of questionable efficiency due to tool design.

Now, trim presses have advanced to "finishing systems" that are automated from load to unload to perform multiple-plane trimming, and incorporate additional functions such as milling, drilling, non-destructive testing and gauging in one automated process. With the advances in tooling design, these systems can now be used for ductile iron, gray iron and aluminum, and process castings at rates in excess of 900 castings/hr, depending on the size of the piece and the complexity of shape.

Due to the cost of tooling, automated finishing systems using trim presses typically are used only in higher run casting configurations. However, at least two manufacturers have introduced automated finishing cells using CNC flexible automation. While these do not provide the speed (usually 1.5 to 3 times slower than trim press systems) they do not require the high-cost tooling and can store many programs to accommodate different castings. Also, these systems utilize material handling resembling a Cartesian manipulator to present the castings to the various tools so they are faster and can withstand higher grinding forces than conventional robots.

According to Vulcan, these systems can come equipped with vision systems and computer validation programs instructing robotic cells to finish the casting only where required. In addition, the robotic cells are being designed to handle multiple parts with easy fixturing and off-line part programming. These cells also are using new complaint grinders, cut-off and deburring units that are designed to work specifically with robots. These new designs maximize G-forces providing for optimum abrasive wear of stones, wheels, cut-off blades, efficient cut speeds, contouring and overall enhancement of the casting finishing process.

For More Information

"GIFA '03: Unveiling New Technology, Advancements," A.T. Spada and R. Petersen, MODERN CASTING, August 2003, p. 39.