AMMTIAC Quarterly, Vol. 2, No. 1 - Advanced Materials ...

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Table 1. Chemical Compositions of Various Grades of Titanium.Chemical Composition, max wt.%ASTM Designation Ti (min) C H O N Fe OthersGrade 2 98.885 0.10 0.015 0.25 0.03 0.30 0.30Grade 3 98.885 0.10 0.015 0.35 0.05 0.30 0.30Grade 5 Remainder 0.10 0.015 0.20 0.05 0.30 6.75 Al, 4.50 VGrade 7 99.005 0.10 0.015 0.25 0.03 0.30 0.12-0.25 PdGrade 12 Remainder 0.10 0.015 0.25 0.03 0.30 0.2-0.4 Mo, 0.6-0.9 NiGrade 38 Remainder 0.00 0.00 0.25 0.00 1.50 4 Al, 2.5 VCHARACTERISTICS OF CAST TITANIUMIn Corrosive EnvironmentsThe majority of titanium alloys (wrought or cast) are very resistantto corrosive attack and virtually immune to many oxidizing andreducing environments. This is due primarily to a tenacious oxidefilm that is formed when titanium is exposed to the atmosphere.The oxide film acts as a barrier to the surrounding corrosive environmentand thereby protects the titanium alloy from furtheroxidation and corrosion. By combining titanium with smallamounts of palladium or molybdenum and nickel, the corrosionresistant properties of the titanium alloy can be improved further.Strength and Structural IntegrityUnlike aluminum and steel alloys, which tend to lose structuralintegrity and strength when cast, titanium tends to maintainstructural integrity and strength that is comparable to wroughttitanium products. Table 2 illustrates this point by comparingtensile and yield minimums for wrought and cast titanium alloyscommonly used in chemical processing and defense applications.Dimensional Control of Titanium Rammed Graphite CastingsRammed graphite castings made with titanium alloys are eitherstatic or centrifugally cast, depending on the shape and size ofthe cast part. Common tolerances for titanium rammedgraphite castings are listed below; tighter tolerances can beachieved with additional trials and correction efforts:• Minimum Section Thickness: 3/16", 1/8" if less than onesquare inch of surface• Base Tolerance:• Up to one linear inch: ± 1/32"• 1 inch up to 10 inches: ± 1/16"• 10 inches up to 20 inches: ± 1/8"• 20 inches up to 60 inches: ± 3/16"• Additional Tolerances:• For dimensions across the parting line: ± 1/8"• Added tolerance for dimensions affected by parting line andparallel to the parting line (mismatch):• Less than 10 inches: ± 1/16"• 10 inches and above: ± 1/8"• Radius Dimensions:• General radius conforms to base dimensions• Sharp to 1/8" radius ± 1/32" (convex)• Up to 1/2" fillet radius ± 1/32" (concave)• Finish Stock:• Nominal 1/8" on all machined surfaces on dimensions lessthan 12"• Nominal 3/16" – 1/4" on all machined surfaces greaterthan 12"• Angles: ± 1 degreeThe Basicsof MetalCastingBenjamin D. CraigAMMTIACRome, NYCasting is a manufacturing process that has been in use for several millennia; cast metals, for example, have beendated back to 4000 B.C. There have been advancements in the process over the years, but the basic principles haveremained. A molten or liquid material (either a metal, polymer, or ceramic) is poured into a mold, where it conformsto the shape of the cavity, and then is solidified to create a finished or nearly finished product. The processis often used to efficiently form complex parts and is typically a cheaper route compared to the alternativefabrication methods, such as forming or machining from a solid. The size of the castings can range from hand heldpieces (and smaller) to multi-ton items such as ship propellers.A pattern is the three dimensional model that is designed and used to create a mold cavity, which will ultimatelyform the final casting product. Patterns can be reusable or expendable. The reusable patterns are typically made fromwood, metal, plastic, or a composite material and can be used to make duplicate molds. Expendable patterns, on theother hand, are made of materials such as wax, polystyrene, or other plastics and are disposed of after making themold. In the case of the lost Styrofoam ® method, the pattern is vaporized during casting process.*Traditionally, the molds for casting metals have been made with prepared sand (called green sand casting becauseit is unfired), although other materials can be used. Typically these mold materials include a binding material (clay)and a small percentage of water so that after molding the sand retains the exact inverse of the pattern shape. Theprepared sand retains an imprint of the pattern to create the casting cavity that will eventually host the moltenmetal. A common practice of casting metals is to create the mold in two parts. The top part of a mold is calledthe cope and the bottom part is called the drag. These two components are separated at what is referred to as aparting line. Molds are held in place and supported during the casting process using a frame called a flask, whichis typically made of wood or metal. A core is a separate solid material within the mold cavity that is used to makean internal void or passageway in the final product. The pattern is modified to allow for the positioning and retentionof the core in an exact location. Figure 1 illustrates some of the common components of a mold.* Styrofoam is a registered trademark of the Dow Chemical Company.6The AMMTIAC Quarterly, Volume 2, Number 1
Table 2. Comparison of Strength Specifications for Cast andWrought Forms of Various Grades of Titanium [1], [2].Titanium Grade Tensile Strength, min. Yield Strength0.2% Offset, min.Ksi MPa Ksi MPaCast Grade 2 50 345 40 275Wrought Grade 2 50 345 40 275Cast Grade 3 65 450 55 380Wrought Grade 3 65 450 55 380Cast Grade 5 130 895 120 825Wrought Grade 5 130 895 120 828Cast Grade 38 130 895 115 794Wrought Grade 38 130 895 115 794Size and WeightsWhile the size and weight of titanium rammed graphite castingscan vary depending on the manufacturer, 1 to 1300 pounds is acommon weight range for cast titanium alloys. Larger castingscan be produced by fabricating several castings into a singlecomponent. In certain configurations, casting weights in excessof 1300 pounds are possible but they should be evaluated on acase by case basis.CONCLUSIONWhile titanium rammed graphite castings are not new to themilitary, they are often overlooked as an alternative to traditionalmanufacturing processes and wrought products utilized inthe production of defense components. Today, design engineerscan realize many military objectives by utilizing titaniumrammed graphite castings to ease the burden of assembly, reducecomponent weight, maintain structural integrity, increasecorrosion resistance, cut back lead times and reduce long termmaintenance costs. While titanium rammed graphite castingsmay not be the newest technology available, it certainly could bethe best choice – especially when weighed against the militaryobjectives of today and tomorrow.NOTE AND REFERENCES* Melt stock raw materials are more readily available than mill productsbecause mill products must be manufactured from the ground up,whereas melt stock raw materials can be taken from mill products thathave already been produced and are in the inventory.[1] “ASTM Designation B 367 – 06,” Standard Specification forTitanium and Titanium Alloy Castings, ASTM.[2] “ASTM Designation B 265 – 06b,” Standard Specification forTitanium and Titanium Alloy Strip, Sheet, and Plate, ASTM.GENERAL REFERENCESM. Guclu, I. Ucok, and J.R. Pickens, “Effect of Oxygen Content onProperties of Cast Alloy Ti-6Al-4V,” Symposium on Cost-AffordableTitanium, Charlotte, NC, March 2004, The Minerals, Metals &Materials Society, Inc., pp. 135-143, DTIC Doc.: AD-P016696.D. Eylon, F.H. Froes, and L. Levin, “Effect of Hot Isostatic Pressingand Heat Treatment on Fatigue Properties of Ti-6Al-4V Castings,”Proceedings of the Fifth International Conference on Titanium, 1985,pp. 179-186, DTIC Doc.: AD-D135659.R.D. Williams and J. Dippel, “Comparisons of Titanium Investmentand Rammed Graphite Castings,” Titanium Net Shape Technologies,The Metallurgical Society of AIME, 1984, pp. 193-199, DTIC Doc.:AD-D134602.More Titanium Rammed Graphite Castings reports available throughPrivate STINET and TEMS. Qualified users can access these databasesthrough the DDR&E Research Portal (https://rdte.osd.mil/).The mold cavity in the cope and drag can be formed using different types of patterns, such as a standard loosepattern or a match plate pattern. The match plate has a pattern mounted on both sides of the pattern plate andconforms to the parting line between the cope and the drag parts of the mold. The match plate system typicallyuses an interlocking feature that surrounds the exterior edge ofthe pattern. This ensures a very accurate registration of the moldhalves and restricts movement of the mold during solidificationof the metal.During the casting process, shrinkage of the casting material canoccur during solidification. To account for this, risers are usedwhich act as a molten metal reservoir to fill any voids created whenthe casting shrinks inside the mold cavity. Risers that do not havean outlet on the topside of a cope are called blind risers. Vents areused to allow for gases to escape in order to reduce the occurrenceof voids in the casting. A sprue is the vertical channel in the moldthat connects the pouring basin to the gating system. Some moldsdo not have a pouring basin, in which case the molten metal ispoured directly into the sprue. The gating system is a series of passagewaysthat distributes the molten metal between the sprue andthe casting cavity. Design of a proper gating system is importantbecause it allows the liquid to flow and enter the casting cavity properly in order to avoid defects in the final casting.The use of so called green (unfired) or fused sand allows for the easy removal of the sand from the solidifiedmaterial. Additionally, the sand can be reprocessed, and when clay and water are added it can be used for the nextseries of castings.PartingLineFlaskSpruePouring BasinGating SystemBlind RiserCompacted Green SandVent HoleFigure 1. Components in a Green Sand Casting Mold.CopeCoreMoldCavityDraghttp://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 2, Number 1 7
Page 2 and 3: Named after the Titans in Greek myt
Page 8 and 9: Calendar of EventsSeptember 2007Cor
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Page 15 and 16: AMMTIAC DirectoryTECHNICAL MANAGER/

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