Cast iron and Sintered alloy is a good choice for automotive parts due to its cost-effectiveness, ability to withstand high temperatures and pressures, and resistance to wear and tear. However, Cast iron and Sintered alloy machining can be challenging. MEGA Tech explored the cutting solution from Sumitomo Electric Hardmetal designed to tackle this cast iron and sintered alloy and explained why their new CBN-grade tools are different from others in the market.
Cast Iron and Sintered alloy for Key Industries
The applications of cast iron are common in the engineering world especially the automotive. Essential auto parts like engine blocks, cylinder heads, Caliper Brake, crankshafts, and so on, are made from cast iron, especially the grey cast iron with tensile strength of 20,000 to 25,000 psi. In construction, cast iron is used for columns, beams, and other load-bearing components. In machinery, cast iron is used in parts that experience high stress and wear such as gears, engine blocks, etc.
Why is Cast Iron and Sintered alloy Difficult to Machine?
Cast iron is a class of iron-carbon alloys of about 2 to 4 % and silicon content of around 1 to 3 %. The benefits of cast iron include hardness, toughness ductility, elasticity, malleability, tensile strength, and fatigue strength. When alloying elements like manganese and chromium are applied, cast iron can significantly improve the ability to resist wear, abrasions, and oxidation. Different kinds of cast iron are grey iron, white iron, malleable iron, and ductile iron.
Machining cast iron can be challenging for several reasons. The primary problem encountered when machining cast iron is excessive tool wear due to its abrasive nature where cast iron chips contain graphite flakes which act like tiny abrasives, rapidly wearing down cutting tools if not managed correctly. The second concern is the chip formation issues caused by the brittle material. The brittle nature of cast iron can lead to unpredictable chip formation, causing potential tool damage and poor surface finish.
The third concern is the generation of fine dusty debris that can harm to operators and machines. The dust created from machining cast iron would find its way into the ball screws of the machine. In time, dust could degrade the grease and could harm the machine. So, in machining cast iron it’s recommended to schedule more maintenance and keep the coolant clean. To minimize health problems for operators, an effective dust extraction system is recommended.
The Right Tools for Guaranteed Success
Machining hard metals like cast iron and sintered alloy requires a thorough understanding of the properties of the workpiece material and machining techniques. For instances, in turning and facing process, it’s importance to adjust the right cutting speed and feed rate to avoid excessive vibration and heat that cause premature tool wear. For milling operations, the machinists have to choose cutters with optimal cutting angles to minimize cutting forces and improve surface finish. To minimize surface irregularities, reduce cutting speeds and feeds, and use a larger nose radius on the insert.
With all that said, the key to success lies in selecting the right tools.
New CBN Grade for Hardened Metals Cutting
Sumitomo has developed a CBN Grade “SUMIBORONTM BN7125” for high-efficiency machining of cast iron and sintered alloy and aims to expand its application range to the currently available BN7115. SUMIBORONTM is a CBN material composed of CBN (cubic boron nitride), with a hardness second only to diamond, sintered with improved CBN particle/binder boundary strength due to the special binder and improved binding strength between CBN particles and binders thanks to their proprietary sintering process, excellent fracture resistance is achieved.
This cutting tool is a general-purpose grade featuring balanced excellent wear resistance and fracture resistance while realizing stable performance in high-speed and high-efficiency machining of hardened steel used in automotive components and also supports the machining of exotic alloys such as HSS, heat-resistant alloys, etc.
Cutting Performance
For cast iron milling, the BN7125 has demonstrated a much better performance during the evaluating. With the work material of FC250 (Pearlite), tool : FMU408R, insert: SNEW1203ADTR and cutting conditions of vc = 1,500m/min, fz = 0.13mm/t and ap = 0.3 mm in wet machining, the BN7125, at over 5,000 chip evacuation rate (cm³), the result showed no fractures and was able to continue the cutting while conventional CBN was already damaged and out of use. A similar result was found for interrupted cutting where the BN7125 continued to serve the services while the competitor’s CBN grades found fractures and were unable to continue the task.
The BN7125 is available in four cutting edge treatment types; standard, LF for burr control, LE for surface roughness emphasized, and HS for fracture control.
Examples of Application Ranges
The BN7125 had been used for cutting the grey cast iron cylinder block. The result showed that it can suppress cracking due to heat damage, exhibiting excellent heat damage resistance almost two times comparing to other tools. The BN7125 also exhibits excellent fracture resistance compared to competitor’s CBN, achieving twice the tool life of competitor’s product.
A similar result was realized when use the BN7125 to machine the part that made of sintered ferrous alloy F-08C2 carrier where it achieves 1.5 to 2 times of tool life than the competitor’s tools.
Article by: MEGATech & Sumipol Corporation Limited << Click here