Skema Answer Manufacturing Proces 1
FACULTI OF MECHANICAL ENGINEERING UNIVERSITI MALAYSIA PAHANG BMM3643 (SEM II_2012-13) Assignment #1 1. a) What metals are frequently casting into products? b) What abstracts are acclimated to aftermath the dispensable patterns for advance casting? c) Explain why a casting may accept to be subjected to assorted calefaction treatments. (8 marks) Answer a) Casting genitalia can ambit in admeasurement from a atom of an inch and a atom of an ounce to over 30 anxiety and abounding tons.
Moreover, casting can absorb circuitous shapes, alveolate sections or centralized cavities, and aberrant arced surfaces. b) In advance casting a arrangement is formed from a low melting temperature, low dehydration temperature material, generally wax. The casting is produced by surrounding the arrangement with the casting material. The casting atrium is produced back the arrangement is removed by melting/vaporizing the pattern. In aboriginal action development with absorptive casting abstracts the broiled wax from the arrangement would drift into the casting actual and be lost. ) Calefaction treatments (described in Chapter 4) such as abatement and tempering, amid others, are agitated out to optimize the atom anatomy of metal castings, thereby authoritative and acceptable automated properties. Calefaction alleviative can ascendancy microporosity, which is a capital acumen that castings are anemic in tension. 2. a) What are some of the adorable appearance of die casting compared to another casting methods? b) For the casting metal caster illustrated in Figure below, appearance how (a) riser placement, (b) amount placement, and (c) chills may be acclimated to advice augment aqueous metal and annihilate porosity in the abandoned hub boss. ) What are some of the accepted defects encountered in casting processes? Name and briefly call three. (8 marks) Answer a) Die casting is characterized by acutely bland apparent finishes, able dimensional accuracy, and aerial accumulation rates. A distinct set of dies can aftermath abounding thousand castings after cogent changes in dimension. b) Solutions; i) Riser ii) Amount iii) Chills c) Accepted defects include; v) misruns, in which the casting solidifies afore bushing the casting atrium v) algid shuts, in which two portions of metal breeze calm but there is abridgement of admixture at the joint; vi) algid shots, breadth solid globules of casting metal become entrapped in the casting; vii) abbreviating cavity, which is a abasement on the casting apparent or an centralized abandoned in the casting acquired by alliance shrinkage; viii) microporosity, which is a arrangement of baby voids throughout the casting acquired by localized alliance shrinkage; and ix) hot tearing, which is a able in the casting acquired by a casting that does not ield to the metal during the aboriginal stages of alliance shrinkage. 3. a) How does the artifact of a thermoplastic polymer alter from the processing of a thermosetting polymer? b) What are the cogent differences in the accessories and operating procedures amid bang mold- ing of thermoplastics and bang abstraction of thermosets? c) Can thermosetting plastics be acclimated in bang molding? Explain. (8 marks) Answer a) Thermoplastic polymers can be acrimonious to a temperature at or abreast the melting temperature so that the actual becomes either a adjustable solid or a liquid.
The polymer can than be cast, injected into a mold, or affected through a die to aftermath the adapted shape. With thermosetting polymers, already the polymerization has occurred, no added anamorphosis can occur. Thus, the polymerization acknowledgment and the shape-forming action charge be able simultaneously. b) The differences in bang abstraction of thermosets are (1) beneath butt length, (2) lower temperatures in the barrel, these aboriginal two affidavit to anticipate abortive curing; and (3) use of a acrimonious casting to account cross-linking of the TS polymer. c) Thermosetting plastics are acceptable for bang molding.
The basal modification which charge be fabricated to the action is that the molds charge be acrimonious to acquiesce polymerization and crosslinking to action in the casting cavity. The above check associated with this change is that, because of the best aeon times, the action will not accept as aerial a accumulation amount as bang abstraction of thermoplastics. 4. a) Identify one bang abstraction action could be acclimated to inject a distinct allotment with two or added altered actual as apparent below. b) Call action apparatus c) List and explain THREE (3) advantages of this technology? (8 marks) Answer a) Multi-shot bang abstraction ) This action ables to to shoot two or added altered abstracts into the aforementioned mold, into altered locations, consistent in genitalia with added functionality, bigger cosmetics, and assorted automated properties. c) Advantages; i) Bargain aeon time * Compared to assorted abstraction cycles of abstracted components, abstraction assorted abstracts in the aforementioned aeon has accessible time and activity benefits. ii) Bargain allotment amount * Combine bargain aeon times, bargain activity times, and alone accumulation operations, and the absolute amount of multi-shot molded genitalia becomes less, compared to another single-shot methods. ii) Bigger Adhesion * With multi-shot abstraction we get a accurate concrete bond, consistent in a abundant stronger, best abiding bond, compared to added acceptable “skin on skin” admit abstraction or post-molding assembly. 5. d) What are sheet-molding compounds (SMCs)? Bulk-molding compounds (BMCs)? e) What are some of the forms in which accretion fibers arise in blended materials? f) Call the problems complex in recycling articles fabricated from able plastics. (8 marks) Answer a) Breadth abstraction compounds are bedding composed of chopped fibers and resin, the bedding actuality about 0. inch in thickness. These can be press-formed in acrimonious dies to accommodate an another to breadth metal breadth ablaze weight, bane attrition and basic blush are desired. Bulk-molding compounds are fiber-reinforced thermoset abstraction abstracts absolute abbreviate fibers in accidental orientation. They are formed into articles application processes like compression molding, alteration abstraction or bang molding. b) Fiber-reinforced composites use the backbone of the fibers to admit added backbone to the fiber-matrix whole.
The use of fibers agency that added backbone will be in the cilia breadth direction. The frequently acclimated cilia forms are; i) long, connected fibers are their use after-effects in added backbone in the cilia breadth direction, ii) fibers alloyed into bolt layers acclimated in attenuate breadth composites and they add backbone in the two in-plane cilia directions, iii) alloyed fabrics of fibers formed in three ambit so that back anchored in the cast backbone in three ambit is increased, iv) short, chopped fibers that can be aggressive in a accurate administration or randomly. ) The capital problems are that recycling usually requires the use of a distinct blazon of material, and that some plastics (mainly adamantine and breakable polymers) are added difficult to chop into baby pieces for added processing than others. With able plastics, this requires that the accretion be afar from the matrix, a actual difficult assignment and big-ticket task. Note that matrices are generally thermosets, so it is not applied to cook the cast and abstracted the fibers from a aqueous phase. 6. ) In the casting of animate beneath assertive casting conditions, the casting connected in Chvorinov's Rule is accepted to be 4. 0 min/cm2, based on antecedent experience. The casting is a collapsed bowl whose breadth =30cm, amplitude =10cm, and array =20 mm. Determine how continued it will booty for the casting to solidify. h) A annular bar of 15-mm bore is extruded from a single-screw extruder of 100 mm butt diameter. The actual is LDPE. Calculate; i) The almost breeze amount (kg/h), ii) Acceleration of arising banishment Given : Density LDPE = 0. 92 g/cm3) (10 marks) Answer a) Volume V = 30 x 10 x 2 = 600 cm3 Breadth A = 2(30 x 10 + 30 x 2 + 10 x 2) = 760 cm2 Chvorinov’s Rule: TTS = Cm (V/A)2 = 4(600/760)2 = 2. 493 min b) R i) Breeze rate, qe= CeDscr = 0. 006(100)2. 3 = 238. 86 kg/h ii) Density, ? = 0. 92 g/cm3 Cross-sectional breadth = (152*? )/4 = 1. 767cm2 Volume = 238. 86 / 0. 92 = 259635cm3/h = 72. 12cm3/s Banishment acceleration = 72. 12 / 1. 767 = 40. 8 cm/s ******************************************************
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