DESIGN CONSIDERATIONS CAREFUL CONTROL OF LARGE NUMBER OF VARIABLES NEEDED- CHARACTERISTICS OF METALS & ALLOYS CAST METHOD OF CASTING MOULD AND DIE MATERIALS MOULD DESIGN PROCESS PARAMETERS- POURING, TEMPERATURE, GATING SYSTEM RATE OF COOLING Etc.Etc. NITC

Poor casting practices, lack of control of process variables- DEFECTIVE CASTINGS TO AVOID DEFECTS- Basic economic factors relevant to casting operations to be studied. General guidelines applied for all types of castings to be studied. NITC

CORNERS, ANGLES AND SECTION THICKNESS Sharp corners, angles, fillets to be avoided Cause cracking and tearing during solidification Fillet radii selection to ensure proper liquid metal flow- 3mm to 25 mm. Too large- volume large & rate of cooling less Location with largest circle inscribed critical. Cooling rate less shrinkage cavities & porosities result- Called HOT SPOTS NITC

LARGE FLAT AREAS TO BE AVOIDED- WARPING DUE TO TEMPERATURE GRADIENTS ALLOWANCES FOR SHRINKAGE TO BE PROVIDED PARTING LINE TO BE ALONG A FLAT PLANE- GOOD AT CORNERS OR EDGES OF CASTING DRAFT TO BE PROVIDED PERMISSIBLE TOLERANCES TO BE USED MACHINING ALLOWANCES TO BE MADE RESIDUAL STRESSES TO BE AVOIDED ALL THESE FOR EXPENDABLE MOULD CASTINGS. NITC

DESIGN MODIFICATIONS TO AVOID DEFECTS- AVOID SHARP CORNERS MAINTAIN UNIFORM CROSS SECTIONS AVOID SHRINKAGE CAVITIES USE CHILLS TO INCREASE THE RATE OF COOLING STAGGER INTERSECTING REGIONS FOR UNIFORM CROSS SECTIONS REDESIGN BY MAKING PARTING LINE STRAIGHT AVOID THE USE OF CORES, IF POSSIBLE MAINTAIN SECTION THICKNESS UNIFORMITY BY REDESIGNING (in die cast products) NITC

PROPERTIES AND TYPICAL APPLICATIONS OF CAST IRONS, NON FERROUS ALLOYS etc. Tables shall be supplied NITC

General Cost Characteristics of Casting Processes PROCESSCOST PRODUCTION RATE (pc/hr) DIEEQUIPMENTLABOUR SAND LLL-M<20 SHELL L-MM-HL-M<50 PLASTER L-MMM-H<10 INVESTMENT M-HL-MH<1000 PERMANENT MOULD MML-M<60 DIE HHL-M<200 CENTRIFUGAL MHL-M<50 NITC

THIXOTROPIC DIE CASTING Some of the die-cast joints used in the Insight's aluminum body are made using a newly developed casting technology invented by Honda engineers, called Thixotropic Die Casting. Thixotropic Die Casting uses aluminum alloy that has been heated to a semi-solid condition, instead of the molten, liquid state normally used in die casting. Pieces made with molten aluminum must be more highly processed and refined before casting. NITC

However, Thixotropic Die Casting requires less energy for smelting (an important consideration since aluminum is more expensive than steel), and owes much of its strength to the controlled formation of discrete aluminum crystals within the metal casting. Thixotropic casting involves vibratory casting of highly thixotropic slips of very high solids loadings that are fluid only under vibration, using porous or nonporous molds. It is quite different from other conventional and new methods for solid casting ceramics, including vibroforming, vibraforming, in situ flocculation, direct coagulation casting, and gel casting. This is demonstrated in Table 1. NITC

Casting Method and Major FeaturesDifferentiating Properties of Thixotropic Casting Vibroforming – Requires a cement for setting Cement is not required for setting Vibraforming – Requires excess counter ions and centrifugation for settling Addition of organic deflocculant/binder and vibration are the only necessary steps In situ flocculation – requires the addition of urea and heating to control the pH to the isoelectric point No urea additions, heating, control of pH, or attainment of the isoelectric point are required Injection moulding – required large quantities (15-30wt%) of entraining polymer and pressurized mould feeding Only traces (<1%) of binder are needed and no pressure needed for filling of moulds Direct coagulation casting – requires control of the pH through an enzyme catalysed decomposition reaction No enzyme additions or control of pH are required Gel casting – requires use of a neurotoxin to cause polymeric gelling No polymer additive or polymerization are required Table 1. Thixotropic casting in comparison with the alternatives. NITC

Thixotropic casting is a little-known derivative of solid slip casting, having reportedly been used in the refractories industry in the early 1970's. Since then, the refractories industry has since largely embraced low-cement and ultra-low-cement castables. It is also a suitable process for forming ceramic matrix composites and metal-ceramic functionally gradient materials. Thixotropic casting involves vibratory casting of highly thixotropic slips of very high solids loadings that are fluid only under vibration, using porous or nonporous molds. It is quite different from other conventional and new methods for solid casting ceramics, including vibroforming, vibraforming, in situ flocculation, direct coagulation casting, and gel casting. (This is demonstrated in Table 1) NITC