Authored by:
Jörg C. Sturm
Magma Giessereitechnologie
GmbH
Aachen, Germany
Christof Heisser
Magma Foundry Technologies
Inc.
Schaumburg, Ill.
Edited by Leslie Gordon
Resources:
Magma Foundry Technologies Inc.

In general, foundries effectively recycle their materials. More than 90% of all cast parts in Germany are made from remelted scrap metal. And the reuse of molding materials such as sand and water means almost no waste.

However, foundries spend a lot on energy and materials — on average 40% of all costs. Physical laws dictate that an average energy input of 2,000 kW-hr per metric ton of final casting product is needed. This adds up to a total energy consumption of 11 billion kW-hr in the German foundry industry per year. Over 50% of this energy is used just to fill gates and risers.

Fortunately, casting-simulation software helps foundry engineers optimize casting parameters, often before the first part is poured. Simulation helps to minimize the amount of material cast and, thereby, the amount of energy needed for the melting process.

Simulation also plays a role in cutting CO2 emissions by helping users slash process and cycle times for high-production castings. Engineers can use simulation to optimize heat-up and temperature distribution in permanent molds, plan layouts that maximize the number of parts molded at one time, and reduce or eliminate preproduction trial-and-error runs.

Here are a few example of how simulation software such as Magmasoft can help optimize casting operations.

Outside-of-the-box casting techniques
New ways of doing things usually pose potential risks and rewards. Simulation lets engineers take more risks because they can predict the results of changes they make. Engineers are free to make unusual design changes and see what will happen virtually without waiting until multiple different castings are poured.

For example, one company detected a shrinkage defect in its complex ductile-iron carriers late in the machining process. Simulation showed the root cause: The pass feeding molten metal to the critical area was getting cut off prematurely. Engineers changed the riser layout to eliminate the defect.

They also took design chances by making unusual changes to the gating system. This slashed the pouring weight by 13 kg, a savings of 13 metric tons of melt and 12,272 kW-hr energy used to melt the raw material per year. The redesign also reduced the riser neck cross section by 25%, resulting in lower riser-removal costs. The modified layout shortened pouring time by 2.5 sec and slashed solidification time by 11 min, increasing productivity by 15%. The original job was to eliminate the defect. The final design, based on simulation, resulted in significantly lower production costs.

In another example, simulation results encouraged pump manufacturer Otto Junker in Germany to cast a steel pump housing that had direct-pour top risers instead of the typical side risers. This lowered the amount of liquid metal needed by 81%, reduced molding time by 79%, and minimized the time needed to burn-off the risers by 87%. The company reduced its total production costs for the part by 12%.

Additionally, a South American iron foundry increased the casting yield for a ductile-iron differential-case housing from 62 to 67% by using simulation to develop a nontraditional gating system. The design lowered the overall scrap rate from 17 to 7%, saved 700,000 kW-hr/yr to produce 24,000 parts and slashed total costs by $500,000.

Simulation boosts quality
Equipment manufacturer John Deere, Moline, Ill., cut the scrap rate of a gray-iron part from 10.3 to 1.4% and saved $66,936/yr by modifying the part and gating system. The company also boosted its casting yield from 58 to 64% for an additional savings of $66,600/yr. The foundry claimed that if it had used simulation at an earlier stage, it could have potentially saved $140,000 more in the first year of production and would have avoided casting design and pattern changes that cost $120,000.

In another case, mechanical-engineering company Heidelberger Druck AG in Germany relocated a mold gate based on simulation results and thereby significantly reduced the amount of repair welding it had to perform on a cover. Temperature losses in the original part had led to incomplete filling of a rib. Simulation let engineers see how material flow was affected by moving the gate to different locations.

Energy savings in heat treatment
Many castings obtain their final mechanical properties after the casting process during heat treatment. The optimal layout and energy input during heat treatment strongly relates to when a necessary microstructure develops. Magmasoft lets users model the entire heat-treatment process and the resulting microstructures.

The software also lets users simulate residual stresses. Designers previously added large safety margins to each heat-treatment step because the way heat-treatment furnaces transmit energy to parts was not well understood. Simulation does away with these safety margins.

New models even let users predict the amount of local carbon saturation in cast iron and steel. Say the total austenitization time for a wind-energy part was 6 hr. Reducing this time by 1.5 hr saves 128 kW-hr/metric ton of product without sacrificing final properties or microstructure. For 500 heat-treated parts, savings add up to 100,000 KW-hr/yr.

Aluminum molds
Energy savings in mass-produced castings that use metal molds rather than sand molds are comparatively high because metal molds can be used for more parts. The number of degrees of freedom in permanent molds is much lower than in sand casting, but it is still possible to cut costs using simulation.

In one case, the original gating system for a motorcycle fork produced using the tilt-pour casting process resulted in several quality issues. Worse yet, casting yield was only 49%. Simulation helped engineers eliminate filling turbulence, and a hotspot and its related defect. They used smaller gates, which boosted the casting yield by 18.5%. In addition, the faster filling of thin walls shortened solidification time to cut cycle times by 10%.

Savings in high-pressure die casting
In high-pressure die casting, 40 to 60% of process energy goes to melting metal. The remainder is used for the actual casting process. The energy input needed for melting depends on the amount of scrap (typically 5 to 7%), melting losses (2 to 5%), and casting yield, the ratio between casting weight and total pouring weight (30 to 70%).

Raw metal is usually melted with natural gas, but the amount needed can vary by a factor of seven, depending on the equipment and environmental policies of different foundries. And the amount of electricity used can vary by a factor of two, for an average value of 5,603 kW-hr per metric ton of final castings. With these uncertainties, simulation can help designers better design and place gating systems, which can significantly reduce the amount of energy needed.

Optimizing gating systems and remelt
Using a gearbox housing as an example, a research project evaluated the energy savings possible by switching from an oil-based die-cooling technique to a water-based technology without affecting casting quality. A comprehensive design of experiments study (DOE) was conducted using casting simulation to evaluate the effect of several process parameters and gating designs. The software compared all of the calculated trial runs and showed the best solutions.

Here, simulation netted a 25% reduction in runner volume, which meant that 12% less material was needed per shot. The better design, in combination with the lower pouring weight, slashed cycle time by 8%.

© 2011 Penton Media, Inc.