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[November 26, 2019] Through Advanced Precision Machining’s blog, we make a concerted effort to keep readers and customers informed with regards to the various precision milling and machining techniques we employ on a daily basis at our Colorado machine shop. In our latest installment, we want to present a primer and compare two time-tested, yet very effective high-speed machining methods our shop relies on; CNC grinding and CNC turning. Recent technological advances have made substantial strides for machinists utilizing either technique, and there have been many discussions about their pros and cons, but the bottom line remains the same; machine shops need both capabilities to address today’s ever-changing workflow.
In any precision manufacturing environment, the tried and true machining process of CNC grinding versus turning a part with a cutting edge has been hotly debated, with the merits and drawbacks of both deserving attention. But, we’ll begin our discussion with grinding because it often turns out to be the better choice. Simply stated, a CNC grinding machine uses an abrasive form of cutting to finish a precision part, and is considered to be one of the oldest and most accurate of the conventional machining services. Depending on the type of machine used, CNC grinding systems can be adapted to manufacture a myriad of precision machine components, especially when working with more exotic materials requiring tighter tolerances.
At a typical CNC machining operation, the grinding process is often used following more aggressive removal of material produced through traditional CNC milling and machining methods. A power driven high-speed grinding wheel, often outfitted with diamond cutting heads, is mounted on a bed with a fixture to hold the workpiece in place. The grinding head then either travels across the fixed workpiece or depending on the machine, remains stationary while the piece travels. Modern grinding systems rely on CNC for exacting control of the grinding head or table position, creating a finish on precision parts to exacting geometric tolerances. Thus, they are able to take on different forms and function. Considered by many to be the most “craftsman-like” of all machining processes, grinding requires highly skilled CNC machinists at the helm with years of experience.
Surface, cylindrical and internal grinding make up most grinding methods and account for the majority of CNC grinding machines found in a machine shop. Surface grinding is a basic finishing technique and involves smoothing a machined part's surface with a grinding wheel via abrasion to produce a highly refined look. Instead of finishing, cylindrical grinding machines are used to externally shape a work piece by removing material and are typically applied to more rounded surfaces. A part is held in place on both ends and spun while a rotating grinding wheel is passed along its length. Internal CNC grinding essentially finishes a previously drilled or reamed hole on a workpiece to a high degree of accuracy with a small grinding wheel rotating at very high RPMs. This metal boring technique is typically applied mainly along the centerline to cylindrical work pieces. As new technology continues to advance and increase the capabilities of modern CNC grinding machines, there is some debate in the precision machining sector comparing the merits of grinding versus hard turning for particular applications.
Hard turning is an alternative method of grinding using a CNC turning machine and can be a cost-effective alternative for machine shops looking to streamline precision part production. It’s defined as the process of single point cutting of part pieces with hardness values over 45 Rc. Hard turning is often considered as a replacement for grinding operations or as a pre-grinding process. Parts can be manufactured with accuracies arguably comparable to the tolerances produced by CNC grinding machines. When compared directly with CNC grinding, other benefits include shorter cycles, less time to load and unload, better energy efficiency, less chip production, and lower machine costs.
So, herein lies the debate! With hard turning methods holding the possibility of eliminating grinding operations altogether. Why grind when you can hard turn? Okuma, a manufacturer of CNC lathes, CNC grinders and machining centers offers some fresh perspective on reasons to grind rather than hard turn. Wherever your loyalties lie, there is no debate that accurately finishing a precision machined part is a crucial step in the high speed machining process. At Advanced Precision Machining, our certified CNC machinists are happy to discuss any grinding, hard turning, or any other milling and machining project with you. Call us today at 303.776.1910 for a free consultation or quote, or learn more about our Colorado machine shop.
Gerry Dillon is a co-founder, current owner and certified CNC machinist at Advanced Precision Machining (APM), a full-service machine shop located in Longmont, Colorado. Before making his home in the United States in 2000, Gerry was born and raised on the emerald isle of Ireland and took an interest in milling and machining from an early age, ranking #1 in the Irish National Apprenticeship Program. In 2005, he and a partner began what’s grown into a leading Colorado machine shop. Gerry brings over 30 years of machining experience to the shop floor, and is certified in all aspects of geometric dimensioning and tolerancing.