GM Unveils Latest Lost Foam Success: Setting the bar for lost foam casters, GM's newest venture at Saginaw Metal Casting Operations has ramped up in record time to produce cylinder heads and blocks for the firm's award-winning SUVs. (Cover Story).

To say General Motors Powertrain (GMPT) has taken a leadership position in lost foam casting is an understatement.

Since the development of the process as an "art" in the 1950s. and its entrant into "production" casting in the early 1980s, no other foundry group--jobbing or captive--has had greater success than GMPT with lost foam as a high-volume production casting process.

Leaders in Lost Foam History

In the early 1980s, GMPT developed lost foam casting for full-scale production at its Massena, New York facility for aluminum cylinder heads for a 4.3L, V6 automotive diesel engine. Although this project was shortlived, it paved the way for Massena's 2.2L inline lost foam four-cylinder head in 1986. This head is still in production today for GM's highest volume four-cylinder engine. More than 5 million have been produced.

In 1986, GM sent the automotive and foundry worlds into shock when it announced that the 4-valve aluminum cylinder blocks and heads and ductile iron crankshafts and differential cases for its new car company, Saturn, would be produced via lost foam casting.

"Saturn's entire fleet of vehicles and fortunes depended on the lost foam process for all of its aluminum engine blocks and cylinder heads and iron crankshafts and differential carriers," said Al Steffe, manufacturing engineering director--castings for GMPT. Steffe stated that the Saturn project didn't have any backup alternatives. Saturn's success or failure rode with lost foam.

As history proved out, Saturn was a rousing success for GM ever since the cars first rolled off the line in 1990.

Since Saturn, GMPT has further built on its success with the 1999 production start-up of lost foam cylinder heads and blocks for GM's global Ecotec four-cylinder program. These components are being produced at a rate of more than 1400/day.

The result for GMPT from these successes is the desire to push the envelope even further and faster.

In January, production officially began for the lost foam cast aluminum cylinder blocks and heads for GM's new Vortec 4200 Inline 6 engine. This production was begun at GMPT's newest lost foam family member--Saginaw Metal Casting Operations (SMGO).

A Lost Foam Engine

From 1995-97, GM was developing the new Vortec 4200 engine for a line of high-performance sport-utility vehicles to introduce for the 2002 model year. In 1997, the decision was made that the 88-lb block and 49-lb head designs were to be produced via the lost foam process. This manufacturing method was going to assist designers in achieving the necessary performance, fuel economy and reduced noise/vibration and emissions from the Inline 6, 4.2L, 270 horsepower engine at a reasonable total system cost.

"GM wanted a 'top in class' engine with horsepower, fuel efficiency, peak torque and mass efficiency," said Ronald Kociba, GM's chief product engineer for the new engine. "This engine design was developed specifically for lost foam casting."

Lost foam allowed the designers to cast-in various features into the cylinder block and head, including:

* integrated crankcase ventilation system oil/air separator (eliminating an additional bolt-on);

* oil galleries (significantly reducing machining effort and cost);

* intricate water jacket design, which eliminated oil cooler costs and potential for leaks, allowing maximum cooling efficiency;

* intricate convoluted oil drain-backs that provide structural stiffness for low noise and vibration as well as providing large, functional oil drain returns to the oil sump;

* coolant passages (which traditionally require drilling or external plumbing) are cast directly into the block, resulting in less machining and fewer opportunities for assembly error.

Although lost foam was the manufacturing process for the engine block and head, designers had to determine the material for the components.

Initially, the goal was to use 319 aluminum because this material had been successful at both Saturn and Massena facilities with heads and blocks. In addition, the material is friendly to machine and less expensive from a raw material standpoint when compared to the alternative, 356 aluminum. But GM ran into a problem in the initial testing with 319.

The 319-cast lost foam blocks and heads couldn't consistently achieve the necessary high-cycle fatigue strengths the new engine required. GMPT switched to A356 for its durability, specifically increased elongation and high cycle fatigue properties, and was forced to develop alternatives in the machining process to increase its efficiency.

Once the design for the engine's block and head were finished, the components had to be sourced and produced.

SMCO = Green Sand + Lost Foam

In 1999, most of the employees at SMCO knew little about the lost foam process, much less casting GM's latest engine design innovation using it. It was a green sand foundry (see "SMCO: Also a Green Sand Foundry" sidebar).

"In early 1999, the SMCO plant was focused only on green sand; lost foam wasn't even on the radar," said Richard Sutton, plant manager-SMCO.

However, due to the foundry's ability to conquer aluminum green sand casting earlier in the decade, its proximity to GM's research hub at the Casting Development and Validation Center (CDVC) in Saginaw, and the fact that some of its current iron block production was being replaced by these new aluminum blocks, it became the logical choice for expansion when the decision was made to go with lost foam for the Inline 6 blocks and heads. CDVC was the group responsible for producing the "recipe for success" for manufacturing these castings (see "Development of Inline 6 at CDVC" sidebar). The close proximity of the two groups provided SMCO with guidance every step of the way.

"Development for the heads and blocks from a manufacturing perspective was performed just a few feet away at the CDVC," said Sutton, who was brought from the GM Massena facility to the green sand foundry to lead its adoption of lost foam. "This was and is critical to our success during this aggressive program because we have onsite experts to work with on any obstacles during production."

Although Sutton is quick to recognize the invaluable service provided by CDVC during the ramp-up, he also stated that "production on the scale of CDVC and production for 2000 blocks and heads a day are totally different ballgames." Cluster and casting handling, cleaning and finishing, and extensive robotics pose daily challenges the foundry has and must continue to overcome.

Lost foam production at SMCO officially began in January with the startup of the engine program.

"This ramp-up to full-scale production in lost foam at SMCO is three times larger than any other ever," said Sutton. After four weeks of production, the foundry was delivering 1500 net good blocks and 1500 net good heads per week. After six months of production, the foundry was delivering 1500 blocks and 1500 heads--each day. By October 2002, the foundry will be capable of meeting the engine plant potential requirement of 2100 blocks and 2100 heads per day.

The reason behind this aggressive ramp-up was that GM determined the demand for the SUVs (GMC Envoy, Oldsmobile Bravada and Chevrolet Trailblazer) using the Inline 6 engine would be one of the highest ever. Normally, an engine is introduced at a low volume of 30-40,000 in the first year. The Inline 6 program is expected to produce close to 300,000 engines its first year.

"We know we are succeeding with the ramp-up and casting production," said Sutton. After nine months, he said, internal scrap was less than 10% and overall scrap (after leak tests) was 12%.

SMCO's Lost Foam Casting

The "white side" or foam mold production at SMCO has five bead expanders--one for each lost foam casting cell (three cells for blocks and two for heads). Once expanded, the beads are delivered to 29 different foam molding machines. The head foam molds are composed of five different foam slices and the block foam molds are composed of four different slices. (For a complete list of lost foam equipment at SMCO, see For More Information at www.moderncasting.com.)

After gating one-on for the block and two-on for the head, the mold clusters are dipped by robot for coating.

"These components are some of the largest ever on a high-volume production line in lost foam," said Mark Dickman, SMCO superintendent-lost foam manufacturing. "With that much polystyrene the coating plays a critical role."

SMCO had its mica-based refractory mold coating specifically developed for it. The keys to the coating are:

* to cover the foam pattern cluster completely and uniformly;

* to evaporate quickly during coating drying so as not to impede production;

* to be strong enough to not buckle from the pressure exerted by the sand during sand compaction in the flask;

* to be permeable to the polystyrene gas as the mold is poured to ensure efficient venting;

* to insulate the aluminum immediately after pouring to keep it molten while allowing it to solidify free of internal shrink porosity.

Different coating formulas are used on the head and block to account for differences in metallostatic head pressure. With two-on gating on the head, the cylinder head foam molds are aligned vertically in the flask and are closer to the top of the flask than the one-on block that is aligned horizontally. The result is greater metallostatic head pressure on the cylinder head during filling, requiring a "stronger" refractory coating.

"Refractory coating is the single biggest control parameter our process engineers must watch to make quality castings," said Brian Smith, engineering group manager-GMPT. "We have and will continue to work at CDVC with the refractory coatings."

After passing through an oven for drying, the dipped clusters are delivered to one of five 31-flask lost foam casting cells. In preparation for pouring, the foam clusters are placed automatically inside of the lost foam flasks and "rained" with silica sand during a three-stage horizontally clamped compaction process.

In the design of its lost foam casting cells, SMCO faced one dominant measure--cycle times. To be able to produce more than 2100 heads and blocks/day, cycle time was critical. For cylinder block production, this cycle time didn't pose a problem. On the two cylinder head lines, however, this presented a challenge.

SMCO was using a bottom-fill gating system for the blocks and heads to provide a low turbulence, quiscent mold fill. In addition, the plant was using a solid foam gating system to reduce metal turbulence flow and resultant entrapped gas from the evaporating polystyrene. When CDVC attempted to speed up the fill rate to achieve target cycle times, the result was increased porosity problems with the heads.

The solution was the development of the "leap frog" pouring process for the cylinder head lines. In this process, a pouring cup is automatically placed on the flask (positioned above the sprue) to receive the pour. Then, a robotically-controlled ladle pours the A356 aluminum, and, before the metal has vaporized and displaced the entire solid gating system and polystyrene mold, the flask transfers to the next station on the mold loop with the pouring cup still feeding metal.

"Initially, the belief was that moving the flasks while pouring would hurt casting quality," said Dickman. "The truth is that it has had no effect."

Once feeding is complete, the pouring cup is removed from the flask and returns to a position to receive metal for another flask. This design allows SMCO to accommodate its target cycle and pour times to maintain both cylinder head casting quality and required production rates. For the cylinder block pouring, the pour cup remains with the pouring robot and the flask travels to the next station alone.

For melting, SMCO's A356 is delivered to the foundry molten at a rate of 30,000 lb every 3 hr by an off-site supplier. The melt makes its way through one of the five lost foam cell's identical melt systems. These systems are composed of a 70,000-lb reverberatory receiving furnace, a 70,000-lb reverberatory holding furnace and a 22,000-lb ladle furnace from which the pouring robot at the casting line ladles.

These furnaces are connected by launder systems to quiescently transfer molten aluminum while maintaining temperature and minimizing the aluminum's interaction with the atmosphere. In addition, the ladles on the pouring lines have slits in their sides so that when they are submerged in the molten metal bath, they are drawing aluminum from below the melt surface to ensure the cleanest metal possible for pouring.

After casting, the heads and blocks are machined, 100% leak tested and T6 heat-treated at the two dedicated offsite supplier facilities in Saginaw. These components then are delivered to GM's Flint Engine South operation, Flint, Michigan, where they undergo further machining before cast iron sleeves (after being chilled with liquid nitrogen to shrink them to fit) are inserted into the block prior to assembly. Depending on market demand, this greenfield engine assembly facility is capable of producing 2100 engines/day.

Rewarding Success

The ultimate reward for GMPT's successful lost foam ramp-up at SMCO and dedication to lost foam is the recognition the firm has received from its peers for the block and head castings, the Vortec 4200 engine and the vehicles they power.

This year, GMPT was named a winner in the Engineered Casting Solutions magazine/AFS Marketing Div. Casting Contest for its Inline 6 engine cylinder block. In addition, Motor Trend magazine named the GMC Envoy as the 2002 Sport/Utilility of the Year, Sport Truck magazine named the Envoy its Sport Truck of the Year, and the Trailblazer was named the top Midsize Sport Utility Vehicle in the 2001 J. D. Power Automotive Performance Execution and Layout (APEAL) study.

For GMPT, success breeds more success. The future currently has the foundry group beginning to ramp-up lost foam casting at its Defiance, Ohio facility for Inline 4 and 5 blocks and heads.

Beyond that, the foundry world will have to wait. But a good bet is the casting future will have something to do with lost foam.

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General Motors Powertrain Saginaw Metal Casting Operations Saginaw,
Michigan


Market             Automotive and light
                   truck.
Products           Engine cylinder blocks
                   and heads.
Metals             A3556 aluminum and
                   GM232 and GMG250
                   gray iron.
Mold Processes     Lost foam and
                   green sand.
Melt Processes     Reverberatory
                   and cupola.
Core Processes     Coldbox.
2001 Projected
Production         Aluminum--288,000 lost
                   foam cylinder heads,
                   288,000 lost foam
                   cylinder blocks, and
                   1,925,000 green sand
                   cylinder heads; Iron--
                   1,970,000 green sand
                   cylinder blocks.
Year Founded       1918 (Chevrolet Motor
                   Div.).
Total Employees    2310 (546 lost foam)
Plant Size         1,871,000 sq ft. (150,000
                   sq ft for lost foam).
Senior Management
Officials          Rick Sutton, plant
                   manager, Gene Tuohy,
                   production manager; Chuck
                   Morello, engineering
                   manager; Mark Dickman,
                   manufacturing
                   superintendent; John
                   Evans, engineering
                   superintendent; Cy
                   Pilkington, launch
                   manager.

CDVC Develops Inline 6 Head and Block for Lost Foam

Development of the lost foam casting process used to produce the Inline 6 block and head castings began at GMPT's CDVC.

"Once the initial engine design was complete and materials and manufacturing processes were selected, it was up to us to develop the lost foam process to make the components," said Barry Priem, CDVG validation/facilities manager--GMPT. Priem points to the simultaneous engineering effort between the CDVC, product engineering and machining as critical in the development of the castings for production.

The CDVC is more than just a research facility for GMPT. It is a production development center that proves out processes and controls on a level that will equate to full-scale manufacturing. The center has production-ready equipment for every lost foam manufacturing step (molding, coating, casting, etc.) on only a slightly smaller scale to that at SMCO.

"Our goal was to develop a process control plan for lost foam manufacturing of the blocks and heads that included everything from bead sizes to pouring times," said Brian Smith, engineering group manager-GMPT. "We wanted a recipe for SMCO to follow."

Now that the castings are in production at SMCO, the CDVC is available as consultants when a "hiccup in manufacturing occurs," said Smith. "We take a SWAT team approach with not only SMCO, but with GM's other lost foam casting plants. We are available to help when anything is stopping our manufacturing plants from producing acceptable lost foam castings."

The CDVC was formed in 1999 as a combination of the Advanced Development Lab and Advanced Materials Development Center, two of GMPT's facilities that performed "research-type" development and validation of potential casting processes and materials. The difference between the CDVC and its predecessors is that it is more focused on materials and processes "a year or two away from production," said Smith.

Current projects under development at the CDVC include various lost foam process developments, such as bottom- and side-pour rollover systems as well as low-pressure counter-gravity casting. In addition, the center has a lost foam pouring cell set up in an X-ray chamber to perform modeling and video inspection of the lost foam mold filling process.

SMCO: Also a Green Sand Foundry

SMCO was born in 1918 as part of Chevrolet Motor Div., producing gray iron castings in green sand. After reaching record-high employment of 6846 in 1971, the gray iron foundry became part of Central Foundry Div. and began to contract throughout the 1980s before becoming part of GM Powertrain in 1991.

Aluminum was introduced to the foundry in 1993 when it was awarded a contract to produce aluminum cylinder heads in green sand. The plant's ability to cast both gray iron and aluminum in green sand allowed it to grow while other GM foundries have continued to contract.

Currently, on the green sand side in both gray iron and aluminum, SMCO casts 9 different engine blocks (14, V6 and V8) and three different heads (V8) for a variety of engines including the Vortec 4300, 4800, 5000, 5300, 5700, and 6000, the 2.2L, the 3800 and the 3800 (Super-Charged). These are cast on two cope and drag green sand lines for gray iron fed by three cupolas and one dedicated cope and drag green sand line for aluminum fed by 3 gas-fired reverberatory furnaces.