Hardened Steel Machining
Application Examples
Precision Cast Iron Machining
Roll Turning
Valve Seat Machining
Heat Resistent Alloy Machining


Kindly click on the arrows to view the answers
Expand/Collapse ItemQues: What is Hard Turning?
Answer: Hard turning is a term given to machining Hardened steel with CBN (Cubic Boron Nitride) tools for replacing conventional method of finishing by grinding process.
Expand/Collapse ItemQues: What is the advantage of hard turning as compared to grinding?
Answer: Reduction in Machine & man power cost by reduction in cycle time, improved accuracy, flexibility to do intricate shapes and environmentally friendly as chips produced can be recycled as compared to Grinding Sludge & used coolant which is hazardous.
Expand/Collapse ItemQues: What are usual work materials finished by Hard Turning?
Answer: Carbon steel, Chromium Molybdenum Steels, chromium steels etc. In existing customers hard turning is being done on 70% in Case Hardened Steels, 20% to induction Hardened steels & 10% others..
Expand/Collapse ItemQues: What are usual parts machined by Hard Turning?
Answer: Transmission gears, Differential Bevel Gears, Shafts, Bearings, Diesel Pump parts etc. in Automotive. Construction, Machine parts, Oil Pressure parts etc. in Engineering.
Expand/Collapse ItemQues: What are the ideal shapes to be finished by Hard Turning?
Answer: Components with Concave or convex shape, with many surface to be turned like boring, Grooving External diameter & face turning in single chucking, Components with small bores, Components where linear/axial dimension controlling is difficult in grinding Esc are good examples of Hard Turning.
Expand/Collapse ItemQues: For what Hardness range Hard Turning can be applied?
Answer: Hard turning can be applied to Steel having Hardness from 45 to 68 HRc.
Expand/Collapse ItemQues: Can we apply Hard Turning on interrupted components?
Answer: Yes Hard Turning can be applied to any degree of interruption & for That Sumitomo has suitable grades. The components like Splined shaft or bore, Bore with keyway, holes on the face or bore etc. can be Hard turned with Sumitomo Grades BN 250 or BN 300.
Expand/Collapse ItemQues: What surface Tolerance and Surface Finish is achievable by Hard Turning?
Answer: Generally H7 or 7 class Tolerance & Surface Finish of Rmax 3.2 (Ra0.8m) is achievable by Hard Turning. With a rigid set up customers are achieving 6 class (H6) Tolerance & up to Rmax 2.0( Ra 0.5m). With the latest developed wiper edge inserts finish can be achieved even finer than above.
Expand/Collapse ItemQues: What is the difference in the quality of surface turned by hard Turning as compared with that of Grinding?
Answer: Grinding being a operation in which the cutting takes place by abrasion the heat produced is much higher. This heat when goes to the component surface it leads for the problems like surface cracks, Re-hardened & tempered layers, which are no good for the life of the component. Hard Turning being single point turning & CBN being an excellent thermal conductive material negligible heat is transmitted to the component surface. So many a times Hard Turning is preferred to solve the surface Integrity Problems faced in Grinding.
Expand/Collapse ItemQues: Is my machine capable of doing Hard turning?
Answer: Any NC Machine can do the Hard turning which has min. surface speed for the job to be turned about 100Mtr/min. There is no extra power required in the machine to do Hard turning only force as mentioned before higher in case of Hard turning is Trust/radial outward force. To counter that the job chucking & in case of boring carbide shank boring bar is recommended if the overhang of the bar is more than 3.
Expand/Collapse ItemQues: What cutting speed is recommended for Hard Turning?
Answer: Usually 80 to 180 m/min is used in Hard Turning depending on other machining conditions like rigidity, chucking, overhang etc. We also have grades for high efficiency machining on continuous turning where the cutting speed can be as high as 250m/min.
Expand/Collapse ItemQues: How are the cutting forces while doing Hard turning as compared to soft machining & how to counter those?
Answer: In Hard Turning only thrust/radial outward force is higher as compared to soft machining. Rest of the forces i.e. Principal force (downward on tool) & Feed force (axial force pushing tool in opposite direction of feed) remain unchanged. Thrust force affects the dimension in deep boring application (L/D of boring Bar more than 3), to counter this we recommend to use Carbide shank boring bar. Sumitomo has introduced a special series of Boring bars, for Hard Turning, made of 100% carbide. By these boring bars the finish, accuracy & life of the tools can be expected better than the conventional carbide boring bar being marketed. For further details write to us or contact our regional sales team.
Expand/Collapse ItemQues: How does the variation/tolerance in Hardness affect the accuracy in Hard turning & how the same should be countered?
Answer: The Thrust force, which is responsible for the dimension, increases with increase in Hardness after 45 HRc. The variation in hardness by more than 5HRc can result in variation of dimension produced. To counter this variation in Hardness more than 5HRc should be avoided.
Expand/Collapse ItemQues: How does hard turning surface roughness profile different from surface profile generated by grinding operation?
Answer: Grinding is multipoint cutting operation where N number of abrasive particles produce the ground surface by rubbing. This action creates irregular peak and valleys so the surface graph is irregular. In contrast Hard Turning is a process of single point turning which will give regular feed marks and periodic surface profile.
Expand/Collapse ItemQues: Is coolant needed for Hard Turning?
Answer: Generally Hard Turning is recommended in dry condition. Interrupted machining must be used only in dry condition. Some conditions where use of coolant can be helpful are Die Steels, applications where thermal distortion is predicted.
A member of Samvardhana Motherson Group