Fig. 2. Minor shrinkage was predicted in the three areas under the risers.
in permanent mold, a case study on a mounting bracket casting used in medical equipment was conducted. Te component, shown in Fig. 1, is currently produced in A356 in a 4140 steel permanent mold. Te cur- rent design ensures the A356 alloy can be cast without hot tearing. Te A356 component also needed to pass grade C radiographic quality. Te team’s key objectives
were to establish and refine casting processing parameters, including: • Initial mold preheating temperature.
• Pouring temperature. • Mold fill time. • Total die cycle dwell time. Because the casting was
currently in production, tooling was in place, so the research team could not make any changes to the design that would disrupt production during casting trials. Before initial trials, the team used simulation software to ensure the gating system was properly designed before pour- ing. Predictive modeling allowed the research team to ensure the casting could be poured at a reasonable
Fig. 4. Hot tearing was found in the post to journal transition area.
Fig. 3. The simulation showed potential hot tearing in the top cross bar and journal areas.
mold temperature that will avoid hot shortness but still have enough strength to withstand ejection stresses. 3-D CAD models of the
casting with rigging were provided by Eck Industries Inc. to Product Development & Analysis for analysis. Te simu- lation suggested minor shrink- age would be discovered in the areas under risers when the die was opened (shown in Fig. 2). Additionally, hot tearing was likely near the top cross bar and in the transition from the post to the shaft area (Fig. 3). Toward the end of solidification, hot tearing looked to develop where the top post transi- tioned into the journal areas (Fig. 4). Tese problematic locations correlated with observed hot tearing on the bracket component. Hot tearing tended to
Fig. 5. The two thermocouples were attached to the moving half of the permanent mold.
32 | MODERN CASTING September 2014
develop when the fraction solid, the percentage of solid phases in the solidifying metal, ranged from 75-90%. Te defects were reduced or eliminated when the fraction solid was reduced to 65-75%, due to the presence of liquid metal that fed the solidifica- tion shrinkage. Shrinkage underneath the top risers and the junctions
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70