is again, an inverse logarithmic relationship between the pore size and the UTS.26
surface Roughness Overall, the combination of the
unmodified eutectic silicon, porosity and Fe inclusion led to the brittle fracture and poor strength of the aluminium specimens, indicating a poor melt quality rather than the ability of the RP process.
In fact, careful scrutiny revealed that the steel crucible made for magnesium was also used for melting aluminium, due to some constraints in handling metal pouring equipment, and there could have been some contamination of the alloy. Also, the lance degassing was found to be inadequate in effectively handling the gas porosity. Tensile testing conducted on A356 castings produced later with a correct treatment of the mol- ten metal, involving rotary degassing, and the use of cleaning fluxes resulted in strength values at around 142 Mpa.
Table 4 presents the ANOVA for surface roughness and the variations of the corresponding S/N ratios are shown in Fig. 6. The pouring temperature has the least significant effect, and hence is pooled as the error term. It appears that the narrow temperature range and the relatively lower up- per limit for the temperature did not result in any adverse metal mould reactions. On the other hand, the mould mate- rial came out to be the most significant factor at 95% confi- dence level in influencing the surface roughness, and as can be seen in Fig. 6, the ZP131 material is the most favourable in terms of the best surface quality. While this is an obvi- ous result considering the grain size between the two 3D printing materials, the noteworthy point is that this mate- rial is not actually intended for casting as per the manufac-
Figure 6. S/N ratios of surface roughness are shown above. Table 4. ANOVA of Surface Roughness
32
International Journal of Metalcasting/Summer 2011
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 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75