MACHINABILITY1) Dear Sandeep kulkarni sir Please share why machineability issue comes in casting what are possible reasons. 2) Why always foundry shop is blamed for poor machininability of castings while other reasons are also present e.g. Incorrect feed rate, Speed, worn out cutting tool, wrong selection of cutting tool with respect to casting hardness etc.â˜ş 3) I have faced so many times, one machine shop will complaint for poor machininability while the other one is happy with same casting parameters. 4) Yes...They can argue on tool life n we must answer for that... 5) Big machine shop have system to monitored tool life and resharpening and their complaint is genuine but difficult to manage with small machine shop. This make additional cost to foundry production by way of increased inoculation or higher addition of pig iron or change over to costlier Inoculants. 6) There has been a trend these days..customers insisting for higher strength n BHN values within a given range and expect machinability of lower strength material... This is where our knowledge and conviction stands... 7) Hardness and machinability are different 8) but one is dependent largely on the other. Customer has to understand that. We may keep on arguing about that 9) Grade of material is base for tool selection and tool life . There must be base line for tool life for various grades. Besides this if someone insists for tool life equivalent to lower grade then has to be debated with machine shop or customer. 10) In grey iron there are two micro features,both depending on inoculation and rate of cooling. When inoculation is just insufficient D and E graphite with some ferrite forms on surface leading to problem in machining specially when machining allowance is less. Further deformation occurs with this supercooled micro permeates to inside of the casting. Next is formation of steadite in cell walls. With continued deformation of inoculation,cementite forms leading to serious problems. Thus micro shows the degree of lack of inoculation and low CE. 11) In machine shop feed and speed are the two keys important irrespective of material to be machined. 12) Nowadays foundries r reducing machining allowances on tool point for reducing cycle time. This is also one of the cause for less tool life.
13) Yes first layer of 1. To 1.5 mm is always with chilling 14) Imagine machining allowance is 2 mm and casting shift 0.5 mm what we expect 15) Coarse pearlite .... 16) Good morning everybody. Sharing first hand experience on machinability and surface chilling. One of my client foundry with Disa magic line hence getting machining allowance below 2mm was facing a serious problem of machinability coupled with very fine pits on machined faces during machining in own plant as well as customers in many castings. The problems were being tackled thru chemistry changes as the spots were taken to be microporocity before I was called in. Micro examination revealed that the surface had undercooled D and E graphite and steadite eutectic in cell walls both varying in depth and degree but in most castings. In some extreme cases cementite particles were also present.Chemisty and inoculants used was proper. Inoculation was being done at 1500+ during first pouring from Ind fce. Reladling was necessary as mold line is in next bay. Due to poor ladles and delays, pouring temperature varied between 1400 and 1370, specially in last boxes poured. The problem has been solved by practice improvement and re inoculation during pouring and mold inoculation in few castings. Surface chilling and undercooled graphite and ferrite is enhanced by fast cooling and decarburization as my worthy friends have said earlier. In normal practice machining allowance are more and the 'chilled' layer is removed in first cut itself but with some poor machinability 17) For longer pouring times, better go for Barium (2%) base inoculant to avoid fading. Otherwise, simple Ferro- silicon inoculant is sufficient Thanks Dr.Rao. 18) Ferrite forms in the skin (surface) of cast iron because of carbon loss at the surface. Carbon in the iron reacts with oxygen or water vapors in the molding aggregate, resulting in a decarburized surface layer so minimize these. 19) A detailed and careful study of micro will reveal that undercooled graphite role is more in causing machinability and apparent porosity. D and E type undercooled graphite due to deficiency of inoculation leeds to ferrite formation inside the casting too. Time and temperature available is too short for an appreciable amount f ferrite to form. 20) Sir, undercooled graphite pose mcbility problems. Yes Please opine on my yesterday's post. 21) ✔✔Excellent.
And one point to add for those who use bought out boring. Spectro shows everything as usual. Mc shop all of a sudden complains poor mcbility. Foundry gropes in the dark. Any takers for this?