| |JULY 20219resistant nickel alloys prevent this heat transfer. This leads to higher cutting temperatures and increased rates of tool deterioration when compared to common steel machining. Simply stated, the nature of the material and its high amount of elasticity make it difficult to achieve chip formation and induce quite a bit of wear on the cutting tool.Combatting these challenges can be done a few ways--one of those being understanding machine conditions. While machine type does play a small factor, machine condition is more detrimental. Machinists must ask themselves, is the spindle rigid? Is the alignment reasonable or near zero runout on a lathe? Knowing these factors can greatly benefit or cause significant issues when trying to machine stainless steel. Additionally, running through the tool coolant provides significant tool life advantages over flood coolant. Ultimately, due to its alloying elements, more torque and horsepower are required to drill stainless than typical steel or aluminum materials. These challenges in stainless applications can also be resolved by working with a more aggressive geometry to attempt to get the chip to form. In austenitic stainless like 316, it is best to use a geometry with a higher rake angle to produce a more manageable chip; however, when working with a harder material such as PH stainless, this method is not effective. In this instance, increasing the rake angle causes the cutting edge to weaken--in turn reducing tool life. With harder materials, this makes the negatives often outweigh the positives. Nevertheless, the benefits of stainless are so numerous that it is beneficial to overcome these challenges when possible. Corrosion resistance is one of the key benefits of stainless steel. Because a number of grades of stainless are highly corrosion resistant, it is the material of choice in applications where weather or corrosive materials will be in direct contact. For example in the energy industry, electrical wiring that is run through the ocean for offshore wind farms is made out of stainless steel or a high temp alloy material because of its corrosion resistance, which does not allow salt water to negatively impact it as it does other materials. Similarly, offshore drilling utilizes stainless steel because of the corrosive and abrasive materials that are being pumped through these lines.The food industry is another industry where stainless steel is often used. Stainless steel's chromium composition, which must be a minimum of 10%, is highly reactive to oxygen environments. This forms a strong, unreactive barrier on the surface of stainless steel, making it the material of choice for the food industry. Finally, the naturally high strength of stainless steel as well as its resistance to corrosion and weather make it a vital material for the aerospace industry in terms of precision parts, fittings, and other components. All in all, stainless steel is not a material that can be brought into a machine shop to machine straightaway; every aspect must be reviewed prior to machining stainless steel. Not only do machinists need to firmly understand the different grades of stainless and their properties, but they also need to examine machine capabilities. Yes, tool wear and excellent chip formation are challenges that one will face when drilling stainless. Fortunately, these can be managed through proper coolant usage and correct choice of insert geometries, coatings and substrates. Making the best selections can be simplified by consulting cutting tool experts like those at Allied Machine and Engineering as well as coolant specialists. Remember, one cannot get away with just anything when machining stainless steel.
< Page 8 | Page 10 >