What is CNC grinding introduction?

Abrasive cutting tool for grinders

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This article is about the modern abrasive cutting tool. For the traditional tool, see Grindstone . For millstones as grinding wheels, see Millstone . For the 2017 Overkill album, see The Grinding Wheel

Various types of grinding wheels

Grinding wheels are wheels that contain abrasive compounds for grinding and abrasive machining operations. Such wheels are also used in grinding machines.

The wheels are generally made with composite material. This consists of coarse-particle aggregate pressed and bonded together by a cementing matrix (called the bond in grinding wheel terminology) to form a solid, circular shape. Various profiles and cross sections are available depending on the intended usage for the wheel. They may also be made from a solid steel or aluminium disc with particles bonded to the surface. Today most grinding wheels are artificial composites made with artificial aggregates, but the history of grinding wheels began with natural composite stones, such as those used for millstones.

The manufacture of these wheels is a precise and tightly controlled process, due not only to the inherent safety risks of a spinning disc, but also the composition and uniformity required to prevent that disc from exploding due to the high stresses produced on rotation.

Grinding wheels are consumables, although the life span can vary widely depending on the use case, from less than a day to many years. As the wheel cuts, it periodically releases individual grains of abrasive, typically because they grow dull and the increased drag pulls them out of the bond. Fresh grains are exposed in this wear process, which begin the next cycle. The rate of wear in this process is usually very predictable for a given application, and is necessary for good performance.

Characteristics

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There are five characteristics of a cutting wheel: abrasive material, grain size, wheel grade, grain spacing, and bond type. They are indicated by codes on the wheel's label.

Abrasive Material

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The abrasive aggregate is selected primarily according to the hardness of the material being cut. Chemical compatibility is also a concern. For example because carbon alloys with iron, silicon carbide is not suitable for use with iron-based metals like steel.[citation needed]

Grinding wheels with diamond or CBN grains are called superabrasives. Grinding wheels with aluminum oxide (corundum), silicon carbide, or ceramic grains are called conventional abrasives.

Grain size

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From 10 (coarsest) to 600 (finest), determines the average physical size of the abrasive grains in the wheel. A larger grain will cut freely, allowing fast cutting but poor surface finish. Ultra-fine grain sizes are for precision finish work. Generally, grain size of grinding wheels are 10-24 (coarse), 30-60 (medium), 80-200 (fine), and 220-600 (very fine).

Wheel grade

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From A (soft) to Z (hard), determines how tightly the bond holds the abrasive. A to H for softer structure, I to P for moderately hard structure and Q to Z for hard structure. Grade affects almost all considerations of grinding, such as wheel speed, coolant flow, maximum and minimum feed rates, and grinding depth.

Grain spacing

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Spacing or structure, from 1 (density) to 17 (least dense). Density is the ratio of bond and abrasive to air space. A less-dense wheel will cut freely, and has a large effect on surface finish. It is also able to take a deeper or wider cut with less coolant, as the chips clearance on the wheel is greater.

Wheel bond

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How the wheel holds the abrasives; affects finish, coolant, and minimum/maximum wheel speed.

Bond name Bond symbol Bond description Vitrified V Glass-based; made via vitrification of clays and feldspars Resinoid B Resin-based; made from plants or petroleum distillates Silicate S Silicate-based Shellac E Shellac-based Rubber R Made from natural rubber or synthetic rubber Metal M Made from various alloys Oxychloride O Made from an oxohalide Plated P Made by Electro / Electroless bonding of metal to hold abrasive

Types

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Straight wheel

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Straight wheel

To the top is an image of a straight wheel. These are by far the most common style of wheel and can be found on bench or pedestal grinders. They are used on the periphery only and therefore produce a slightly concave surface (hollow ground) on the part. This can be used to advantage on many tools such as chisels.

Straight Wheels are generally used for cylindrical, centreless, and surface grinding operations. Wheels of this form vary greatly in size, the diameter and width of face naturally depending upon the class of work for which is used and the size and power of the grinding machine.

Cylinder or wheel ring

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Cylinder wheels provide a large, wide surface with no center mounting support (hollow). They can be very large, up to 12" in width. They are used only in vertical or horizontal spindle grinders. Cylinder or wheel ring is used for producing flat surfaces, the grinding being done with the end face of the wheel.

Tapered wheel

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A straight wheel that tapers outward towards the center of the wheel. This arrangement is stronger than straight wheels and can accept higher lateral loads. Tapered face straight wheel is primarily used for grinding thread, gear teeth ...

Straight cup

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Straight cup wheels are an alternative to cup wheels in tool and cutter grinders, where having an additional radial grinding surface is beneficial.

Dish cup

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A very shallow cup-style grinding wheel. The thinness allows grinding in slots and crevices. It is used primarily in cutter grinding and jig grinding.

Saucer wheel

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A special grinding profile that is used to grind milling cutters and twist drills. It is most common in non-machining areas, as sawfilers use saucer wheels in the maintenance of saw blades.

Diamond wheels

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Diamond wheel

Diamond wheels are grinding wheels with industrial diamonds bonded to the periphery.

They are used for grinding extremely hard materials such as carbide cutting tips, gemstones or concrete. The saw pictured to the right is a slitting saw and is designed for slicing hard materials, typically gemstones.

Mounted points

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Mounted points are small grinding wheels bonded onto a mandrel. Diamond mounted points are tiny diamond rasps for use in a jig grinder doing profiling work in hard material. Resin and vitrified bonded mounted points with conventional grains are used for deburring applications, especially in the foundry industry. Mounted points is a small handle with a general name, used in electric mill, hanging mill, hand drill. Many of the main types of ceramic mounted points, rubber mounted points, diamond mounted points, emery cloth and so on.

Ceramic mounted points: granular sand (usually corundum, white jade, chrome corundum, silicon carbide) made of ceramic binder sintering, the central supplemented by metal handle. Mainly grinding all kinds of metal, for the diameter of the inner wall of the grinding, mold correction. Rubber mounted points: finer particle size sand combined by rubber binder Into, for the polishing of the mold. sandpaper mounted points: Multi-piece rectangular sand cloth, bonding around the metal handle. Granularity is generally in the 60 # -320 #, for the diameter of the inner wall of the polishing. Diamond mounted points: A grinding tool for non-metallic materials such as stone, porcelain and the like, and more particularly to a grinding tool using a diamond alloy as a grinding body comprising a substrate and a plurality of grinding bodies, And the substrate is preferably made of an adhesive material having a certain toughness, and the grinding body is preferably made of a diamond alloy material, and the substrate is preferably made of a diamond alloy material, The utility model has the characteristics of high grinding performance, simple manufacture and low cost, high grinding quality and can be applied to large-scale grinding.

Cut off wheels

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Cut off wheels, also known as parting wheels, are self-sharpening wheels that are thin in width and often have radial fibres reinforcing them. They are often used in the construction industry for cutting reinforcement bars (rebar), protruding bolts or anything that needs quick removal or trimming. Most handymen would recognise an angle grinder and the discs they use.

Use

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Grinding produces sparks and little fragments of metal, called swarf.

To use the grinding wheel it must first be clamped to the grinding machine. The wheel type (e.g. cup or plain wheel below) fit freely on their supporting arbors, the necessary clamping force to transfer the rotary motion being applied to the wheels side by identically sized flanges (metal discs). The paper blotter shown in the images is intended to distribute this clamping force evenly across the wheels surface.

Dressing

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Grinding wheels are self-sharpening to a small degree; for optimal use they may be dressed and trued by the use of wheel or grinding dressers. Dressing the wheel refers to removing the current layer of abrasive, so that a fresh and sharp surface is exposed to the work surface. Trueing the wheel makes the grinding surface parallel to the grinding table or other reference plane, so that the entire grinding wheel is even and produces an accurate surface.

Grinding wheels and grinding tools are used extensively in industry and manual trades for treating surfaces and for separating and cutting objects and have to withstand massive mechanical stress. Mostly centrifugal forces can cause a break, but also flexural and shear forces. Since a break or failure of the grinding tool can present a severe hazard to people and machinery due to the high levels of energy released, high standards are placed on the mechanical and breaking strength of grinding tools in the European safety standards. The Institute for Occupational Safety and Health of the German Social Accident Insurance conducts tests based on the "Rules of Procedure for Testing and Certification carried out by the Testing and Certification Bodies in DGUV Test".[1]

See also

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References

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A CNC grinding machine, also known as a CNC grinder, is an automatically operated grinding machine. This machine is in charge of the refining of the surface finishes on the final products, which are made of metals, by removing the materials from the workpieces with the assistance of the grinding wheels.

To begin with, grinding is one of the machining processes that remove the materials by turning the grinding wheels as they come in contact with the surfaces of the workpieces, instead of directly cutting through them with the actual cutters.

A grinding machine consists of a spindle head that holds the workpieces in place, with the grinding wheels grind the workpieces from the lateral sides or the front, in order to achieve a wide variety of configuration on the products, which range from tapering, stepping, grooving, profiling, or chamfering, etc. on the internal and external radius or diameter of the workpieces.

When it comes to accuracy and precision, the machine must be maneuvered by the CNC system. The CNC system refers to the computerized numerical control system, which utilizes the computerized technology to cover the designing of the products and the controlling of the operation.

With the automatic operation that performs the precise works by following the preset instructions that are programmed to be numerals, the CNC grinding machine is able to create the smoothest surface finishes on the products that are ground, minimize deformation on the products, and maximize the efficiency of the grinding processes for the manufacturers.

What types of CNC grinding machines are there?

Depending on the required geometries of the grinding products, there are several types of CNC grinding machines that are specialized in different grinding techniques or grinding different parts on the products, including:

● CNC Universal Internal Grinders

This type of grinders are capable of conducting the grinding works on either the inside diameter or outside diameter, which means with the special arrangement of the grinding wheels, these grinding tools can achieve the steps, tapers, grooves, chamfers, or profiles on the inside and outside of the holes.

● Cylindrical Grinders

The cylindrical grinders are used to grind the workpieces that are made as cylindrical shapes. The grinding wheels can be either angular or parallel to the workpieces during operation.
With the plunge type of grinding wheels, the tools grind on the cylindrical workpieces by pressing down the workpieces from above, and traveling through the surfaces of the workpieces, in order to fulfill the required shapes on the products.

● Surface Grinders

Based on the different configurations on the grinding wheels, the surfaces of the workpieces can be ground directly as the wheels travel on them according to the instructions.

● Centerless Grinders

This type of grinders are not equipped with the machining centers, which allows for multiple working stations to be managed in the same production line, and thus improves the efficiency and productivity of the works.

● High Precision Rotary Grinders

This type has rotary table on the base of the machine, which allows the grinding wheels grind the workpieces around the circular surfaces or edges as the workpieces rotate with the table during operation.

● Center Hole Grinders

As the name implies, this type of grinders are used to grind the existed center holes on the products, so that the grinding wheels are specially designed as conical shapes, which allows them to be fit into the holes of the products.

● Double-sided Fine Grinders

This type grinds the workpieces on two sides at the same time. These grinders are equipped with the upper and lower discs or plates, which perform the grinding works on the top and bottom respectively.

What can a CNC grinding machine achieve in the finishes of the products?

As far as we know, there are several types of grinding machine that are available for being applied to achieve the different requirements of the manufacturers, and these achievements can be categorized into some perspectives based on the grinding direction, the grinding parts, and the grinding geometries.

● Grinding direction

In general, most grinding machines can achieve the grinding works with the grinding wheels turns axially or radially, which means they grind the workpieces from the sides and the front.
With the differentiation of the grinders, the plunge type is specialized in grinding the workpieces from the top to the bottom of the product surfaces. In addition, there are also the double-side finer grinders that grind the works from above and under the works respectively.

● Grinding parts

With the various types of grinding machines, they are capable of attaining the grinding works on a variety of parts, including the inside diameter, outside diameter, or the faces of the products.

● Grinding geometries

Through the varied grinding tools and techniques on the different types of grinders, more grinding geometries can be achieved accordingly, including steps, tapers, chamfers, profiles, or grooves.

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