Who needs surface grinders?

Posted on Aug 14, 2020

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Surface Grinders

Surface grinding is generally the most common grinding technique. The abrasive wheel rotates on a spindle and extends generally over a piece of material, metal or non-metal. This gives the desired surface finish together with the ability to grind to extremely high tolerances. Typically + / -0 .0001 ”or + / - 0.002mm. The workpiece is held on a chuck, usually magnetic, another version is the use of a vacuum chuck for non-magnetic parts.

The grinding wheel required will depend on the type of component being ground, and there are many different mixtures available for different grinding materials. After selecting the correct circle, you can either sand with a flat disc to get a flat surface or you can place the mold outside the circle for a specific shape, it will be a mirror image of the shape on the wheel.

Cylindrical grinding is another type of grinding. This allows the grinding of external and internal diameters. The main difference between the two methods is that when cylindrical grinding, both the workpiece held in the chuck or between the centers and the grinding wheel will rotate. The same level of tolerance is achievable as with the surface finish.

Surface grinding is used to obtain a smooth finish on flat surfaces. It is a widely used abrasive machining process in which a rotating disc coated with rough particles (grinding wheel) cuts a shavings of a metallic or non-metallic substance from the workpiece, making the surface flat or smooth.

:: Read More : The Critical Chain Component in Metal Machining: CNC Surface Grinder

 

Process

Surface grinding is the most common grinding operation. This is a finishing process that uses a rotating abrasive wheel to smooth the flat surface of metallic or non-metallic materials to give them a more refined appearance by removing an oxide layer and debris from the surface of the workpiece.

The surface grinder consists of an abrasive wheel, a working handle called a handle and a reciprocating or rotary table. The gripper holds the material in place during processing. This can be done in two ways: ferromagnetic components are held in place by a magnetic chuck, while non-ferromagnetic and non-metallic components are held in place by a vacuum or mechanical means. A machine vise (ferromagnetic steel or cast iron) placed on a magnetic chuck can be used to hold non-ferromagnetic components if only a magnetic chuck is available.

Factors to consider when grinding a surface are the material of the grinding wheel and the material of the workpiece.

Common workpieces are cast iron and mild steel. These two materials do not tend to clog the wheel during machining. Other materials include aluminum, stainless steel, brass and some plastics. When grinding at high temperatures, the material tends to become weakened and is more inclined to corrode. This can also result in a loss of magnetism in materials where this is applicable.

The grinding wheel is not limited to a cylindrical shape and can have countless options that are useful in transferring various geometries to the workpiece. The operator can dress simple wheels to create custom geometries. When grinding the surface of the workpiece, please bear in mind that the shape of the disc will be transferred to the workpiece material like an inverted image.

Spike is the term used when searching for precision values ​​and literally means "until the sparks disappear (no more)". It consists in the fact that the workpiece under the disc is moved, without resetting the depth of cut, more than once and generally more than once. This ensures that any non-conformities in the machine or workpiece are eliminated.

:: Read More : Rotary Surface Grinder and Processing Quality

 

Equipment

Surface grinder with electromagnetic chuck, the inset shows a manual magnetic chuck

A surface grinder is a machine tool used to precisely grind a surface of a critical size or to finish a surface.

Typical accuracy of a surface grinder varies by type and application, however, for most surface grinders, ± 0.002 mm (± 0.0001 inch) should be achieved.

The machine consists of a table that moves both along and across the face of the wheel. The longitudinal feed is usually hydraulically powered, as is the cross feed, however, any mixture of manual, electric or hydraulic may be used depending on the end use of the machine (ie, Manufacturing, workshop, cost). The grinding wheel rotates in the spindle head and can also be adjusted in height by any of the methods described above. Modern surface grinders are semi-automatic, the cutting depth and sparkout can be pre-set to the number of passes, and once set, the machining process requires little operator intervention.

Depending on the material of the workpiece, machining is usually held by a magnetic chuck. It can be an electromagnetic chuck, or a manually operated, permanent magnet type chuck; both types are shown in the first image.

The machine has provision for the application of coolant as well as the extraction of metal dust (metal and grinding particles).

Types of surface grinders

 

Surface grinders with a horizontal spindle (circumferential)

The periphery (flat edge) of the wheel is in contact with the workpiece to form a flat surface. Peripheral grinding is used for precise work on straight flat surfaces; conical or curved surfaces; slots; flat surfaces by the shoulders; recessed surfaces; and profiles.

 

Vertical spindle grinders (disc)

The face of the wheel (cup, cylinder, disc or segment wheel) is used on a flat surface. Face grinding is often used to remove material quickly, but some machines can perform high-precision work. The workpiece is held on a reciprocating table that can be changed depending on the task, or on a rotary table machine with continuous or indexed rotation. Indexing allows one station to be loaded or unloaded while grinding operations are performed on the other. An alternative term is snow grinding.

 

Disc and double-disc grinders

Disc grinding is similar to surface grinding, but with a larger contact area between the wheel and the workpiece. Disc grinders are available with a vertical and horizontal spindle. Double disc grinders work simultaneously on both sides of the workpiece. Disc grinders are able to achieve particularly close tolerances.

 

Grinding wheels for surface grinders

Aluminum oxide, silicon carbide, diamond and cubic boron nitride (CBN) are four commonly used abrasives for grinding wheel surfaces. Of these materials, alumina is the most common. For reasons of cost, diamond and CBN grinding wheels are usually manufactured with a less expensive core material surrounded by a diamond or CBN layer. Diamond and CBN wheels are very hard and are suitable for the economical grinding of materials such as ceramics and carbides that cannot be ground with aluminum oxide or silicon carbide wheels.

As with any grinding operation, the condition of the disc is extremely important. Abrasive dressers are used to maintain the condition of the grinding wheel and can be bench mounted or mounted in the grinding wheel head where they can be easily applied.

:: Read More : Surface Grinding Machines in the Automotive Industry

 

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