Redefining core competencies

abstract:

Even today, experts have to solve many problems in core production based on their experience or by trial and error. In an interactive MAGMAacademy workshop carried out by MAGMA Inc., USA, and Laempe-Reich, attendees had the opportunity to discuss various technical challenges in the core shop related to core shooting, gassing, and binder hardening.

 

Fig. 1: The parallel coordinates plot shows the impact of process design modifications on core density

Fig. 1: The parallel coordinates plot shows the impact of process design modifications on core density

The typical degrees of freedom available to the core maker such as tool design, modification of vent types and locations, using different nozzle/blow tube strategies and cavity layout were examined. The enriching environment spanning both hands-on real core production and core simulation provided a unique experience for the attendees to assess the impact of the most common variables on core making in real time.

All proposed vent and nozzle combinations for the investigated core summed up to a theoretical total of 262,144 possible designs. Finding the best combination with a trial-and-error approach was simply not possible – neither with real trials nor with the help of traditional simulation tools. With the use of Autonomous Engineering in MAGMA C+M (Core + Mold), a total of 160 designs were automatically created and simulated. Today, this technology can evaluate these 160 different design scenarios in less time than it would take to make 2 real physical trials.

A parallel coordinates plot in MAGMA C+M made it easy to assess the effects of the different variables on the defined main objective: a core with the highest possible density (Fig. 1). Each line in the plot corresponds to one of the simulated designs, and a different color is assigned to each design/line depending on its quality. Blue lines lead to a poor or low density, whereas bright yellow ones lead to better compaction and higher density in the core.
A positive relationship was determined between the total shooting area of the blow tubes and the core quality at the end of the shooting process. As the number of nozzles increased, along with the appropriate venting conditions, the core density increased.

Shooting a sand-binder mixture into a cavity and achieving its maximum compaction is half of the battle in obtaining a defect-free core. For coldbox cores, after this phase the gassing manifold introduces amine into the core box cavity through the nozzles and sometimes through the top vents.
Typically the operator will start with an initial amount of amine and increase it until an acceptable core is made. Similarly, the operator may repeat this approach with an extended cycle time to allow more time for the amine to cure the core.

The real-life cores produced using the process set-up which led to a dense core after shooting in the simulated Design of Experiments (DoE) proved: the core quality increased with an increasing amine amount. However, the workshop teams also found that even with a 63% increase in amine content, a good quality core was not possible (Fig. 2).

Fig. 2: Increasing the cycle time reduces the amount of non-hardened core areas (left). Defect assessment of non-hardened areas in produced cores (right)

Fig. 2: Increasing the cycle time reduces the amount of non-hardened core areas (left). Defect assessment of non-hardened areas in produced cores (right)

In a second iteration, the gassing time was increased, which is also a common practice to reduce defects in core making, even if it lengthens the cycle time and leads to lower productivity. However, after 45 seconds of curing time, the core still showed un-cured areas (Fig. 2, (right)).
To provide the attendees with further understanding of defect resolution for an uncured core, an alternative venting layout was presented with the original starting conditions (cycle time 15 seconds, 19cc of amine). This combination was simulated and produced, and the modified venting layout turned out to be the key element to success. All previous un-cured areas had been fully cured and the core had achieved all objectives for shooting and gassing (Fig. 3).
MAGMA C+M had provided critical information for the cost-effective manufacture of a quality core in the early stages of tooling design.

Fig. 3: Final result after optimizing the venting configuration

Fig. 3: Final result after optimizing the venting configuration

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