New Core Technology for Light Metal Casting

Abstract

A new concept for lost cores for gravity castings is presented. In contrast to the conventional principle of thermally breaking down binder strength, demolding of the new cores is based on a mechanical collapse of parts of the filler material. For this purpose, the usual sand filler is substituted for hollow microspheres with defined isostatic compression strength. After casting, the core is subjected to high hydrostatic pressure, leading to destruction of the hollow filler and a resulting loss of core structural strength and volume, allowing it to be washed out easily. In the present study, phosphate-, gypsum-, and cement-bonded cores with additions of hollow glass microspheres and cenospheres are produced and their bending strength and surface quality are determined. The core behavior during the casting process is evaluated using permanent mold gravity and low pressure aluminum casting experiments. Phosphate bonded materials containing 62 vol% of glass microspheres exhibit the best combination of surface quality and collapse behavior while reaching strength levels comparable to conventional sand cores. The study contributes to a deeper understanding of the collapse mechanisms, suggesting a major role of 1) open porosity of the matrix phase, 2) sufficient strength of the filler-matrix interface, and 3) filler particle shell integrity. Due to a lack of the latter, cenospheres are proved unsuitable for the new demolding approach.

Advances in Metal Casting Technology: A Review of State of the Art, Challenges and Trends—Part II: Technologies New and Revived

“…Similarly, cores may be employed to realize undercuts. Technologies for core production as well as core materials are closely linked to cast materials and casting processes and too diverse to cover in full here; thus, a focus is set on lost cores for HPDC, as well as new developments in decoring represented by the concept of collapsible cores [169], while the additive manufacturing of cores is discussed further below in Section 2.3.3 (note that general links to studies in this field may also be found among the entries in Table 3…”

“…Via this porosity, it is possible to exert sufficient pressure on the hollow filler particles to make them collapse. The core can then simply be washed out as slurry in a batch process utilizing cold isostatic pressing (CIP) to build up the required levels of pressure [169]. The fundamental principle of this approach is illustrated in Figure 7 below.…”

“…In this case, the building material is transferred to the focal point of a laser entering the open porosity of the matrix in which the microspheres are embedded exerts pressure on the latter, making them collapse. The integrity of the core is lost, and its remainders can easily be washed out [169,188].…”

Effects of Boehmite on the Calcination Shrinkage and Mechanical Properties of Gypsum‐Bonded Molds

“…[ 1–5 ] The advantages of using gypsum‐bonded molds include their high forming ability, high surface quality, and low cost. [ 6–10 ] The combination of additive manufacturing technologies and gypsum‐bonded molds proved its feasibility in trial production. [ 11–13 ] To date, this technology (relatively mature) has been widely used in the manufacture of handicrafts.…”

A Comparative Analysis on Organic and Inorganic Core Binders for a Gravity Diecasting Al Alloy Component

“…The research to date has addressed the properties of organic and inorganic binder-based cores, considering their mechanical and thermomechanical properties, [8][9][10][11][12][13][14] their environmental compatibility, [15][16][17][18] the employment of new compositions 5,[19][20][21][22][23][24] as well as new production technologies. [25][26][27] Attention has also been paid to the humidity resistance of sodium silicate bonded sands and to the curing of the binder. [28][29][30][31][32][33][34][35][36] Although extensive research has been devoted to binders systems, few studies have directly investigated their direct employment in the foundry, 37 also considering the effects of moisture absorption on their performances.…”