Nov. 14, 2023
A CNC grinder is a precision machine tool that utilizes a rotating grinding wheel to gradually remove small increments of material from a workpiece. These machines are primarily employed for the final finishing of components. When dealing with cylindrical workpieces, machinists often perform substantial material removal using a lathe before transferring the piece to a cylindrical grinding machine for the finishing touches.
The essence of CNC grinding lies in the meticulous removal of minute amounts of metal using a high-speed abrasive wheel as the cutting tool. While the grinding wheel remains stationary, the workpiece is firmly secured to the machine and moves along the X-, Y-, or Z-axis. Typically, the grinding wheel necessitates multiple passes to achieve the precise final dimensions, adapting to the specific shape and size of the workpiece.
A CNC grinding machine, also known as a CNC grinder, operates autonomously with minimal intervention from a machinist or operator. It adheres to pre-programmed instructions to attain smooth surface finishes, minimizing distortions and optimizing the grinding process’s efficiency. Flood coolant is employed to uphold the accuracy and finish of the workpiece during machining, with Fanuc controls often ensuring an exemplary CNC system.
Although the term "CNC grinder" denotes a machine that utilizes a grinding wheel to remove material, there exist diverse approaches and machine types to accomplish this task. Here, we discuss four of the most prevalent methods.
CNC grinders come in various forms, each suited for specific machining needs. Common types include surface grinders, cylindrical grinders, precision ID & OD grinders, and centerless grinders.
Surface grinding is a widely used finishing process for flat metal surfaces, aimed at achieving polished appearances or precise dimensions. This grinder comprises an abrasive wheel, a work-holding chuck, and a table that reciprocates or rotates.
The chuck secures the workpiece in two ways: magnetic chucks for ferromagnetic parts and vacuum or mechanical means, like a precision steel vise, for non-ferromagnetic or nonmetallic pieces. The material of the grinding wheel and the workpiece influences the grinding operation, where materials like cast iron and steel typically don't clog the wheel, while aluminum, stainless steel, and brass may require frequent wheel dressing.
CNC surface grinding is efficient for flat, contoured, or irregular surfaces.
Unlike surface grinding, cylindrical grinders focus on round workpieces like rods, shafts, and cylinders. The workpiece rotates between centers while the grinding wheel, spinning in the opposite direction, precisely reduces its diameter. The angle of the grinding wheel in relation to the workpiece can vary during the operation.
Workpieces can be held using various setups like a 3-jaw chuck, 4-jaw chuck, collet chuck, or magnetic chuck. The grinding wheel must be tougher than the workpiece, often made of synthetic compounds with aluminum oxide.
Previously, separate cylindrical grinders handled OD or ID grinding. Modern machines can perform both operations in a single setup, enhancing versatility and efficiency. These grinders provide high-quality surface finishes, accuracy, and concentricity.
ID/OD grinders can handle tapers, steps, contours, and grooves inside and outside a hollow round piece without the need for additional setups.
Centerless grinding involves feeding the workpiece between a grinding wheel and a regulating wheel without the use of centers or fixtures. The grinding wheels push and regulate the workpiece's movement, ensuring accuracy and roundness in cylindrical surfaces.
Two techniques are employed: through-feed grinding, where the workpiece exits through the wheels, and infeed grinding, where the grinding wheel is fed into the part until reaching the correct size. Centerless grinding is suitable for industries requiring high cylindrical surface accuracy and roundness.
CNC grinders play a pivotal role in various automotive applications, handling tasks like grinding brake cylinders, steering pistons, gear shafts, splines, connecting rods, camshafts, and crankshafts. While cylinder heads are often milled, surface grinders excel in precisely grinding their surfaces.
The precise grinding of shaft outer diameters ensures impeccable fittings between gears, bearings, and other mating components. OD grinding guarantees the concentricity of the shaft to its centerline, maintaining concentricity among accompanying diameters.
Specialized crank and camshaft grinders handle offset ODs for non-concentric diameters like crank pin journals and cam lobes. These machines are programmed to grind both on-center and offset diameters on the same shaft. Similarly, ID grinders provide accurate fittings for brake cylinders and connecting rods.
In aerospace, components must withstand harsh engine environments, demanding high-strength materials that can be challenging to machine conventionally. Precision grinding is well-suited for these materials, and components like turbine rings and shafts are commonly precision ground.
Medical equipment requires corrosion and wear-resistant parts, often made from stainless steel and titanium. These materials pose challenges for conventional machining but are efficiently processed using surface grinders, cylindrical grinders, and centerless grinders to achieve the precise results demanded by medical manufacturers.
Machine tool manufacturers rely on CNC grinders due to their exceptional accuracy. Grinders like surface grinders, ID/OD cylindrical grinders, and centerless grinders are utilized to produce spindles, ball screws, linear guideways, couplings, cams, racks, pistons, and valve spools with tolerances as tight as plus or minus 0.0001 inches.
Supporting machine tool production, the tooling industry manufactures precision tools such as chucks, drills, reamers, carbide inserts, gauges, collets, and tool holder shanks. Unlike tooling used in conventional machining, grinding wheels can be dressed multiple times to sustain the shape and edge of abrasives, ensuring accuracy and an excellent finish.
A CNC grinding machine comprises essential components: the grinding spindle head, responsible for securing the workpiece while the grinding wheel removes material from its lateral sides or front. This setup allows for the creation of diverse shapes, including flat surfaces, steps, grooves, and chamfers, accomplished using a surface grinder.
In the case of a cylindrical grinder, it includes four integral parts: the head and tail stocks, one or more grinding wheels, the wheel head, and the table. These versatile grinders enable operations like tapering, profiling, stepping, or achieving straight diameters on both the internal (ID) and external (OD) surfaces of the workpiece. Workpieces can be held in various ways, such as between centers in the headstock and tailstock, utilizing a chuck, or secured in a collet.