U3 p4 casting defects
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This document provides an overview of various manufacturing processes, with a focus on casting processes and defects. It defines common casting defects such as cold shuts, shrinkage cavities, sand blows, and pin holes. It also discusses additional steps after solidification like trimming, removing cores, cleaning, inspection, and heat treatment. Various casting processes are introduced like sand casting, shell molding, and use of chills. Causes of casting defects include issues with casting design, mold design, gating system design, sand choice, melting temperature, and composition. Quality inspection methods for castings include visual inspection, dimensional measurement, and metallurgical/chemical testing.
U3 p4 casting defects
- 1. Manufacturing Technology II (ME-202) Overview of Manufacturing Processes Dr. Chaitanya Sharma PhD. IIT Roorkee
- 2. Title of slide Lesson Objectives In this chapter we shall discuss the following: Learning Activities 1. Look up Keywords 2. View Slides; 3. Read Notes, 4. Listen to lecture Keywords:
- 3. ©2007 John Wiley & Sons, Inc. M P Additional Steps After Solidification • Trimming • Removing the core • Surface cleaning • Inspection • Repair, if required • Heat treatment
- 4. ©2007 John Wiley & Sons, Inc. M P Trimming Removal of sprues, runners, risers, parting-line flash, fins, chaplets, and any other excess metal from the cast part • For brittle casting alloys and when cross sections are relatively small, appendages can be broken off • Otherwise, hammering, shearing, hack-sawing, band-sawing, abrasive wheel cutting, or various torch cutting methods are used
- 5. ©2007 John Wiley & Sons, Inc. M P Removing the Core If cores have been used, they must be removed • Most cores are bonded, and they often fall out of casting as the binder deteriorates • In some cases, they are removed by shaking casting, either manually or mechanically • In rare cases, cores are removed by chemically dissolving bonding agent
- 6. ©2007 John Wiley & Sons, Inc. M P Surface Cleaning Removal of sand from casting surface and otherwise enhancing appearance of surface • Cleaning methods: tumbling, air-blasting with coarse sand grit or metal shot, wire brushing, buffing, and chemical pickling • Surface cleaning is most important for sand casting – In many permanent mold processes, this step can be avoided
- 7. ©2007 John Wiley & Sons, Inc. M P Heat Treatment • Castings are often heat treated to enhance properties • Reasons for heat treating a casting: – For subsequent processing operations such as machining – To bring out the desired properties for the application of the part in service
- 8. ©2007 John Wiley & Sons, Inc. M P Casting Quality • There are numerous opportunities for things to go wrong in a casting operation, resulting in quality defects in the product • The defects can be classified as follows: – General defects common to all casting processes – Defects related to sand casting process
- 9. Casting Cleaning : •The casting is separated from the mold and transported to the cleaning department. •Burned-on sand and scale are removed. •Excess metal is removed (Fins, wires, parting line fins, and gates). •Subsequently the casting can be upgraded using welding or other such as procedures. •Final testing and inspection to check for any defects Advantages: •Improves the surface appearance and finish of casting •Improves overall quality and functionality by removing impurities, such as sand, scale and excess metal Finally the sand from the mold is separated and processed through a reclamation system for further use.
- 10. • Defects may occur due to one or more of the following reasons: Fault in design of casting pattern • Fault in design on mold and core • Fault in design of gating system and riser • Improper choice of molding sand • Improper metal composition • Inadequate melting temperature and rate of pouring
- 11. • Classification of Casting Defects • Surface Defects Blow, Scar, Blister, Drop, Scab, Penetration, Buckle • Internal Defects Blow holes, Porosity, Pin holes, Inclusions, Dross • Visible Defects Wash, Rat tail, Swell, Mis run, Cold shut, Hot tear, Shrinkage/Shift
- 12. • Discontinuities in castings that exhibit a size, shape, orientation, or location that makes them detrimental to the useful service life of the casting • Some casting defects are remedied by minor repair or refurbishing techniques, such as welding • Other casting defects are cause for rejection of the casting Casting Defects
- 13. • Metallic Projections: fins (flash), swells, and scabs – Fins are excessive amounts of metal created by solidification into the parting line of the mold Fins are removed by grinding or sandblasting – Swells are excessive amounts of metal in the vicinity of gates or beneath the sprue – Scabs are surface slivers caused by splashing and rapid solidification of the metal when it is first poured and strikes the mold wall Casting Defects — Metallic Projections
- 14. • Blowholes, pinholes, shrinkage cavities, & porosity – Blowholes and pinholes are holes formed by gas entrapped during solidification – Shrinkage cavities are cavities that have a rougher shape and sometimes penetrate deep into the casting Shrinkage cavities are caused by lack of proper feeding or non-progressive solidification – Porosity is pockets of gas inside the metal caused by micro-shrinkage, e.g. dendritic shrinkage during solidification. Casting Defects — Cavities
- 15. • Cracks in casting and are caused by hot tearing, hot cracking, and lack of fusion (cold shut) – A hot tear is a fracture formed during solidification because of hindered contraction – A hot crack is a crack formed during cooling after solidification because of internal stresses developed in the casting – Lack of fusion is a discontinuity caused when two streams of liquid in the solidifying casting meet but fail to unite Rounded edges indicate poor contact between various metal streams during filling of the mold Casting Defects — Discontinuities
- 16. • Casting surface irregularities that are caused by incipient freezing from too low a casting temperature • Wrinkles, depressions and adhering sand particles Casting Defects — Defective Surfaces
- 17. • Particles of foreign material in the metal matrix • The particles are usually nonmetallic compounds but may be any substance that is not soluble in the matrix – Slag, dross, and flux inclusions arise from melting slags, products of metal treatment, or fluxes They are often deep within the casting – Mold or core inclusions come from sand or mold dressings and are usually found close to the surface Casting Defects — Inclusions
- 18. ©2007 John Wiley & Sons, Inc. M P A casting that has solidified before completely filling mold cavity Figure 11.22 Some common defects in castings: (a) misrun General Defects: Misrun
- 19. ©2007 John Wiley & Sons, Inc. M P Two portions of metal flow together but there is a lack of fusion due to premature freezing Figure 11.22 Some common defects in castings: (b) cold shut General Defects: Cold Shut
- 20. ©2007 John Wiley & Sons, Inc. M P Metal splatters during pouring and solid globules form and become entrapped in casting Figure 11.22 Some common defects in castings: (c) cold shot General Defects: Cold Shot
- 21. ©2007 John Wiley & Sons, Inc. M P Depression in surface or internal void caused by solidification shrinkage that restricts amount of molten metal available in last region to freeze Figure 11.22 Some common defects in castings: (d) shrinkage cavity General Defects: Shrinkage Cavity
- 22. ©2007 John Wiley & Sons, Inc. M P Balloon-shaped gas cavity caused by release of mold gases during pouring Figure 11.23 Common defects in sand castings: (a) sand blow Sand Casting Defects: Sand Blow
- 23. ©2007 John Wiley & Sons, Inc. M P Formation of many small gas cavities at or slightly below surface of casting Figure 11.23 Common defects in sand castings: (b) pin holes Sand Casting Defects: Pin Holes
- 24. ©2007 John Wiley & Sons, Inc. M P When fluidity of liquid metal is high, it may penetrate into sand mold or core, causing casting surface to consist of a mixture of sand grains and metal Figure 11.23 Common defects in sand castings: (e) penetration Sand Casting Defects: Penetration
- 25. ©2007 John Wiley & Sons, Inc. M P A step in cast product at parting line caused by sidewise relative displacement of cope and drag Figure 11.23 Common defects in sand castings: (f) mold shift Sand Casting Defects: Mold Shift
- 29. ©2007 John Wiley & Sons, Inc. M P Foundry Inspection Methods • Visual inspection to detect obvious defects such as misruns, cold shuts, and severe surface flaws • Dimensional measurements to insure that tolerances have been met • Metallurgical, chemical, physical, and other tests concerned with quality of cast metal
- 30. Shell molding • Advantages • • Better surface finish • Better dimensional tolerances. • Reduced Machining. • Less foundry space required. • Semi skilled operators can handle the process. • The process can be mechanized. Disadvantages The raw materials are relatively expensive. •The process generates noxious fumes which must be removed. •The size and weight range of castings is limited.
- 31. CHILLS
- 32. Manufacturing, Engineering & Hot Tears in Castings Figure 10.12 Examples of hot tears in castings. These defects occur because the casting cannot shrink freely during cooling, owing to constraints in various portions of the molds and cores. Exothermic (heat-producing) compounds may be used (as exothermic padding) to control cooling at critical sections to avoid hot tearing
- 33. Manufacturing, Engineering & Common Casting Defects Figure 10.13 Examples of common defects in castings. These defects can be minimized or eliminated by proper design and preparation of molds and control of pouring procedures. Source: After J. Datsko.