One of the oldest machining technologies is surface grinding. Over the years, it has changed with the evolution of technology. As technology improved, so did grinding method.
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And with time, different techniques have evolved, too. They include cylindrical, surface, centerless, and internal grinding. These four types all serve their purpose. Although our focus today will be on surface grinding.
Read on to find out more.
Surface grinding is a widely used technique done using an abrasive machine such as CNC machine. Industries prefer this technique as it helps provide precise dimensions.
One important component needed while surface grinding is the rotating abrasive wheel. Without it its impossible to achieve a smooth surface finish.
You can also use this technique to remove dirt or rust. It is popular in many industries like metalworking and job shops.
Now that you understand surface grinding let's assess why you may need to use this technique.
In this section, we will look at why industries choose to grind surfaces.
This is possible because surface grinding effortlessly removes impurities in a controlled way.
The good thing about using surface grinding is that you are open to use any material you want. You can use plastics, ferrous and non-ferrous materials, and ceramics.
It is a cost-effective solution when it comes to getting better surface finishing.
Most industries' dream is to have techniques that help improve production. Surface grinding helps these industries achieve this dream.
By removing impurities on the workpiece, surface grinding helps improve the materials' longevity and durability.
You can easily surface grind manually or automatically. You do not necessarily need an operator if you run the machine manually.
From this section, it is evident that grind surfacing is a beneficial technique. However for this method to benefit you, you must pick the right type of surface grinder.
Did you know there are five types?
Let's have a look at them;
The five common types of surface grinders include;
A common technique used in most if not all machine operations is the horizontal spindle. It can easily accommodate small and large work pieces as the surface grinders come in different sizes.
During the process the grinding wheel usually moves back and forth. For you to achieve this technique you need to place the wheel horizontally as it works its magic on the work piece's edges.
The wheel is also horizontally mounted as it cuts its perimeters. For you to achieve the rotatory table technique you need to mount the workpiece in a way that it can easily rotate 360 degrees.
Notice that while using this method, the workpiece should be under the wheel head. Doing so helps the wheelhead easily do cross-feed movements.
This kind of grinder is best when you wish to grind narrow and long castings. It is good to use when removing materials. For the vertical spindle to work it is best to always place the workpiece on the reciprocating table.
Doing so makes it easy to make adjustments when needed. Alternatively if you wish to achieve an index rotation you could place the workpiece on the rotatory table machine.
Note one property that makes this type of grinder unique is that you can use it to cut heavy metal or remove impurities on it. You'll need segmented or cup wheels for this method to function well.
The other good thing about using this method is that their spindles can finish large castings.
As much as we classify disc grinders as a type of hydraulic surface grinding, in actuality, they are quite similar. This is because it also involves a great area of the disc and workpiece in close contact.
From its design, a surface grinder offer flexible grinding system. Usually, you can work on both sides of your workpiece.
Knowing these types will come in handy when using surface grinding for your product. However, choosing the right surface grinder is not enough to get outstanding results.
You'll also need to choose a good grinding wheel to help you achieve your needs. So before you decide to buy your next grinding wheel, make sure to read this section.
The grinding machine has different parts that all play an important role. A grinding wheel is an important component of the grinding machine that always needs to be the right one.
If you wind up using the wrong wheel you may not achieve the best results. There are a couple of grinding wheels on the market. This way, it is important to look at a few factors before settling on one. They include;
You'll need to know what you are grinding and assess if it is a soft or hard material. Knowing this will help you choose the right abrasive and grain type.
If the material you choose to use is easy to grind then you could settle for a durable grain. In the case where you end up with a hard material then a mild grain is a good option for you.
Before choosing a grinding wheel always ensure that you always know the amount of grinding pressure you'll use. This is because not all grinding wheels can handle the high extremity of an operation.
Knowing the severity of the project will also help you know the type of grain you'll use. For a high-pressure operation, you'll need a tough grain.
It is important to know if you need a fine finish or stock removal. Understanding this need will make it easier to choose the right grinding wheel.
You need to know the operating wheel speed you'll use for your operation. Knowing this will help you choose the right wheel specification and also know the wheel grade you need to choose.
You can use this equation to calculate the surface speed.
Surface speed = π×Diameter (inch) × RPM÷12
Surface Speed (M/s) = π×Diameter (mm) × RPM÷
This is an important factor that you should never overlook as it will guide you in knowing the type of hardness the wheel should have.
If the operation will use a high horsepower, then you'll need a hard wheel. A softer-grade wheel will do the job if the horsepower is low.
Using these factors will help you in choosing the right grinding wheel. However, finding the right grinding wheel doesn't solve the puzzle as there are more pieces to tackle such as which grinding method to use.
For some they get confused on whether to use cylindrical or surface grinding symbol. Knowing how these two compare will help you make the right decision. Let's have a look at them.
The simplest way to compare these two is by assessing the shape of the results. Surface finishing helps the operator to get a flat surface finish on the workpiece. On the other hand, a cylindrical grinding process will get the best round cut.
Here are a few reasons why industries may choose to use either of the two
Surface GrindingIt is easy to specify the tolerance thickness when need be
Achieving smooth finishing on flat surface is easier
Recommended for both metallic and non-metallic parts
You either choose to use automatic or manual operations
Cylindrical GrindingPerfect for producing very precise and outer surfaces
A better alternative for processing hard materials
This method is easy as you do not require heavy machines or hire skilled operators.
Most cylindrical machines have high productivity rates as they can run for hours without breaking down.
The method you wind up choosing solely depends on your needs, as they all offer different results and benefits. If you choose to use surface grinding, you'll need to solve another puzzle before grinding the surface.
Let's dive deep into it.
The following tips are facts you need to keep in mind before starting your grinding project.
Observing these guidelines will reduce the chances of having a failed surface grinding project. Although these tips may not be of much help if you do not have an idea on how to surface grind. So, stick around to find out how the process starts and ends.
Industries seeking to have their metallic or non-metallic materials have a smoother finish often settle with surface grinding. This is possible as the grinding wheel removes impurities such as an oxide layer on the material.
Before you start grinding a surface it is important to have a good workpiece material such as iron or steel. Choosing these materials is great as they do not block the grinding wheel.
Make sure that you have all the surface grinder components. They include a reciprocating table, an abrasive wheel, and work holding device. Lastly, there are occasions when you may need a lubricant to cool the machine.
Make sure to check the material you are working with, as it will help you choose the right lubricant. Once you cross-check that you have everything then you can start the process.
When you wish to grind a surface, you first need to mount the workpiece on the reciprocating table. After mounting the workpiece, you'll notice that it will slowly moving across the grinding wheel.
Also, the workpiece is always in a back-and-forth motion until the desired finish gets achieved. Note that you'll need to set the machine's temperatures high when you intend to remove materials on the workpiece.
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Although this excessive heat can affect the surface finishing so its good to introduce coolants here. Doing so will help ensure the machine remains cool.
You can as well use lubricants on the moving parts. If you do not know the lubricant you should use here's a guide you can follow;
There are a few times when you may need to use a lubricant to cool the wheel and workpiece. Using lubricants also helps remove chips. While applying the lubricant, make sure you apply it directly to the cutting area.
This will help ensure that the grinding wheel does not carry the lubricant away. Note that the type of lubricant you choose solely depends on the material you work with.
Knowing the right lubricant to use will always ensure that your machines are up and running in order to create a perfect workpiece. Although in most cases the workpiece created often differs from the original material. And in some cases, it can affect its properties. Let's have a look at some of these effects.
During the process, the material is often exposed to high temperatures, and due to these changes, it creates residual stresses. Also, the part's surface is likely to form a hard crystalline form. This in turn will reduce the fatigue strength.
If you are surface grinding a magnetic material often it may lose its magnetic properties when exposed to extreme temperatures. Lastly, the materials are prone to corrosion.
Always check the wheel's RPM. Note that the wheel RPM always remains constant while surface grinding. In case the wheel RPM is high it may cause material burn.
Lastly, you need to assess the material you are grinding, as it will help you know the wheel speed you need to use.
This is the back-and-forth movement of the workpiece on the wheel. Having a faster feed rate helps remove impurities faster although it causes chatter marks. Therefore in order to get a finer finish it is best to use a slower feed rate.
Having a deeper cut allows you to remove more materials although it can cause wearing out of the grinding wheel. So it is best to stick to lighter cuts as they will give you a fine and smooth finish.
If you are grounding a hard material, wheels types ranging from CBN, aluminum oxide, and silicone carbide can get used. Cork wheels are great options for operators who wish to burnish or polish their workpieces.
When you poorly dress the wheel, you are likely to lead to fast tears, glazing, and vibration. Also an, improper dressing does not create a good finish.
Using coolants helps in cooling the wheel, and workpiece, flush chips, and prevent loading of the wheel.
Always ensure that you securely mount the workpiece to improve accuracy and prevent chatter. You can use clamps, chucks, vacuum, or magnetic tables to achieve a strong work hold.
Having a knowledgeable operator will help ensure that they choose the right parameters and ascertain great results.
Assessing these factors will help ensure your next grinding project is a success. But as we all know, everything has its limitations, and so does the surface grinding process. Let's have a look at some of these limitations.
Here are some limitations for using surface grinding;
Although do not let these limitations sway you away from using surface grinding. This is because there are so many things you can achieve while using this type of grinding. They include:
Here are some key areas you can take advantage of surface grinding technique;
Surface grinding is an ideal method to use when you wish to have a reference surface due to its ability to produce distinct flat surfaces. Making it the best method to use when flattening valves, gauges, machine ways and bearings.
The abrasive grinding wheel helps remove imperfections on the workpiece. This, in turn, will help you achieve a polished finish.
You can dress the grinding wheel with different profiles and create unique shapes for workpieces like cutting tools or gauges.
Not only can surface grinding help in removing materials but it also helps in squaring up blocks. This feature makes it a favorite for operators using rough machines.
Surface grinding helps remove burrs, armoury imperfections, welds, and flashes from casting.
The edge of wheel makes it possible for the operator to either deburr holes or even create a radius on the edge of the workpiece.
If you are looking for highly efficient and affective surface grinding service machines, TSINFA, has the best solution for you. Whether you want to upgrade or invest in a new machines, we will help you get the best surface grinder for your business ' contact us now.
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Surface Grinding Machine ' Source: TSINFA
Surface Grinding ' Source: WIKIPEDIA
Grinding, or abrasive machining, once performed on conventional milling machines, lathes and shapers, are now performed on various types of grinding machines.
Grinding machines have advanced in design, construction, rigidity and application far more in the last decade than any other standard machine tool in the manufacturing industry. Grinding machines fall into five categories: surface grinders, cylindrical grinders, centerless grinders, internal grinders and specials.
Surface grinding
Surface grinders are used to produce flat, angular and irregular surfaces. In the surface grinding process, the grinding wheel revolves on a spindle; and the workpiece, mounted on either a reciprocating or a rotary table, is brought into contact with the grinding wheel.
Four types of surface grinders are commonly used in industry: the horizontal spindle/reciprocating table; the horizontal spindle/rotary table; the vertical spindle/reciprocating table; and the vertical spindle/rotary table.
Horizontal spindle/reciprocating table. This surface grinder is the most commonly used type in machining operations. It is available in various sizes to accommodate large or small workpieces. With this type of surface grinder, the work moves back and forth under the grinding wheel. The grinding wheel is mounted on a horizontal spindle and cuts on its periphery as it contacts the workpiece.
Horizontal spindle/rotary table. This surface grinder also has a horizontally mounted grinding wheel that cuts on its periphery. The workpiece rotates 360 degrees on a rotary table underneath the wheelhead. The wheelhead moves across the workpiece to provide the necessary cross feed movements.
Vertical spindle/reciprocating table. This type is particularly suited for grinding long and narrow castings, like the bedways of an engine lathe. It removes metal with the face of the grinder wheel while the work reciprocates under the wheel. The wheelhead assembly, as on most other types of surface grinders, moves vertically to control the depth of cut. The table moving laterally accomplishes cross feed.
Vertical spindle/rotary table. This grinding machine is capable of heavy cuts and high metal-removal rates. Vertical spindle machines use cup, cylinder, or segmented wheels. Many are equipped with multiple spindles to successively rough, semi-finish, and finish large castings, forgings, and welded fabrications.
Workholding devices. Almost any workholding device used on a milling machine or drill press can be used on surface grinders. However, the most common workholding device on surface grinders is a magnetic chuck.
Cylindrical grinding
Cylindrical grinding is the process of grinding the outside surfaces of a cylinder. These surfaces may be straight, tapered or contoured. Cylindrical grinding operations resemble lathe-turning operations. They replace the lathe when the workpiece is hardened or when extreme accuracy and superior finish are required. As the workpiece revolves, the grinding wheel, rotating much faster in the opposite direction, is brought into contact with the part. The workpiece and table reciprocate while in contact with the grinding wheel to remove material.
Workholding devices. Workholding devices and accessories used on center-type cylindrical grinders are similar to those used on engine lathes.
Independent, universal and collet chucks can be used on cylindrical grinders when the work is odd-shaped or contains no center hole. These also are used for internal grinding operations.
Centerless grinding
Centerless grinding machines eliminate the need to have center holes for the work or to use workholding devices. In centerless grinding, the workpiece rests on a workrest blade and is backed up by a second wheel, called the regulating wheel. The rotation of the grinding wheel pushes the workpiece down on the workrest blade and against the regulating wheel. The regulating wheel, usually made of a rubber-bonded abrasive, rotates in the same direction as the grinding wheel and controls the longitudinal feed of the work when set at a slight angle. By changing this angle and the speed of the wheel, the workpiece feed rate can be changed.
Intemal grinding
Internal grinders are used to finish straight, tapered or formed holes accurately. The most popular internal grinder is similar in operation to a boring operation in a lathe: The workpiece is held by a workholding device, usually a chuck or collet, and revolved by a motorized headstock. A separate motor head in the same direction as the workpiece revolves the grinding wheel. It can be fed in and out of the work and also adjusted for depth of cut.
Special grinding processes
Special types of grinders are grinding machines made for specific types of work and operations, for example: Tool and cutter grinders. These grinding machines are designed to sharpen milling cutters, reamers, taps and other machine tool cutters. The general-purpose cutter grinder is the most popular and versatile tool-grinding machine. Various attachments are available for sharpening most types of cutting tools. Jig grinding machines. Jig grinders were developed to locate and accurately grind tapered or straight holes. Jig grinders are equipped with a high-speed vertical spindle for holding and driving the grinding wheel. They utilize the same precision locating system as do jig borers. Thread grinding machines. These are special grinders that resemble the cylindrical grinder. They must have a precision lead screw to produce the correct pitch, or lead, on a threaded part. Thread grinding machines also have a means of dressing or truing the cutting periphery of the grinding wheel so that it will produce a precise thread form on the part.
Creep-feed grinding
Traditionally, grinding has been associated with small rates of metal removal and fine finishing operations. However, grinding also can be used for large-scale metal-removal operations, similar to milling, broaching, and planning. In creep-feed grinding, developed in the late s, the wheel depth of cut is as much as 0.25 in. and the workpiece speed is low.
Its overall competitive position with other material-removal processes indicates that creep-feed grinding can be economical for specific applications, such as in grinding shaped punches, twist-drill flutes, and various complex super alloy parts. The wheel is dressed to the shape of the workpiece to be produced. Although generally one pass is sufficient, a second pass may be necessary for improved surface finish.
Grinding wheel wear
The wear of a grinding wheel may be caused by three actions: attrition or wearing down, shattering of the grains, or breaking of the bond.
In most grinding processes, all three mechanisms are active to some extent. Attritions wear is not desirable because the dulled grains reduce the efficiency of the process, resulting in increased power consumption, higher surface temperatures, and surface damage. However, attrition must go on to some extent, with the forces on the grit being increased until they are high enough to shatter the grit or break the bond posts holding the dulled grit. The action of particles breaking away from the grains serves to keep the wheel sharp without excessive wear. However, the grains must eventually break from the bond or the wheel will have to be dressed. Rupturing the bond post that holds the grit allows dull grains to be sloughed off, exposing new sharp edges. If this occurs too readily, the wheel diameter wears down too fast. This raises wheel costs and prohibits close sizing on consecutive parts.
G-ratio. The G-ratio is the ratio of the amount of stock removed versus the amount of wear on the wheel, measured in cubic inches per minute. This ratio will vary from 1.0 to 5.0 in very rough grinding, and up to 25.0 to 50.0 in finish grinding.
Even though grinding wheels are fairly expensive a high G-ratio is not necessarily economical, as this may mean a slower rate of stock removal. It often takes some experimenting to find the wheel-metal combination, which is most economical for a job.
Attritions wear. Attritions wear is responsible for the so-called "glazed" wheel that occurs when flat areas are worn on the abrasive grains but the forces are not high enough to break the dull grains out of the wheel face. Attritions wear of the wheel occurs most often when fine cuts are taken on hard abrasive materials. Taking heavier cuts or using a softer wheel that will allow the grains to break out can often avoid it.
Grain fracture. The forces that cause the grain to shatter may arise from the cutting forces acting on the wheel, thermal conditions, shock loading, welding action between the grit and the chip, or combinations of these factors. In finish grinding, this type of wheel wear is desirable, because it keeps sharp edges exposed, and still results in a low rate of wheel wear. In time, the wheel may become 'loaded' and noisy, and require dressing.
A loaded wheel should be dressed by taking a few deep cuts with the diamond so that the metal-charged layer is removed, and the chips are not just pushed further into the wheel. Then, it should be finish-dressed according to the application requirements.
Bond fracture. It is desirable to have worn grit break out of the wheel so that new cutting edges will be exposed. This breaking down of the bond should progress fast enough so that heat generation is sufficiently low to avoid surface damage. On the other hand, bond breakdown should be slow enough so that wheel costs are not prohibitive. Normally, this means choosing the proper wheel grade for the job. Certain bond hardness is required to hold the grain in place. Softer wheels crumble too fast, while harder wheels hold the dull grit too long.
Coated abrasives
Typical examples of coated abrasives are sandpaper and emery cloth. The grains used in coated abrasives are more pointed than those used for grinding wheels. The grains are electrostatically deposited on flexible backing material, such as paper or cloth. The matrix or coating is made of resin.
Coated abrasives are available as sheets, belts and disks and usually have a much more open structure than the abrasives on grinding wheels. Coated abrasives are used extensively in finishing flat or curved surfaces of metallic or nonmetallic parts, and in woodworking. The surface finishes obtained depend primarily on the grain sizes.
Abrasive belt machining. Coated abrasives are also used as belts for high-rate material removal. Belt grinding has become an important production process, in some cases replacing conventional grinding operations such as the grinding of camshafts. Belt speeds are usually in the range of 2,500 to 6,000 ft/min. Machines for abrasive-belt operations require proper belt support and rigid construction to minimize vibration.
Grindability
Grindability, in a like manner as machinability, may be thought of as the ease with which material can be removed from the workpiece by the action of the grinding wheel. Surface finish, power consumption, and tool (wheel) life can be considered as fundamental criteria of the grindability of metals. In addition, there are the important factors of chip formation and susceptibility to damaging the workpiece. Chip formation, which leads to a 'loaded' wheel, is detrimental.
The most important machine setting affecting machinability, the cutting speed, is not as important an influence on grindability because grinding is done at more or less constant speed. Instead, the important factor becomes the nature of the grinding wheel. The type of grit, grit size, bond material, hardness and structure of the wheel all influence the grindability of the workpiece. The problems of tool material and configuration variables were discussed in connection with machinability.
In grinding operations like snagging and cut-off work, the surface finish, and even the metallurgical damage the workpiece, may become relatively unimportant. Wheel life and the rate of cut obtainable then become the criteria of grindability.
The best way to determine grindability is to start with the selection of the proper wheel. Beginning with the manufacturer's recommended grade for the conditions of the job and then trying wheels on each side of this grade will do this. Any improvement or deterioration in the grinding action, as evidenced by wheel wear, surface finish, or damage to the workpiece, can be noted. After the proper wheel has been chosen, wheel life data may be obtained. Usually, this can be done during the production run.
Some of the factors to consider in establishing grindability ratings are discussed in the following examples relative to the performance metals.
Cemented carbide material cannot be ground with aluminum-oxide grit wheels. Although it can be ground with pure silicon-carbide wheels, the grinding ratio is very low and the material is easily damaged. Carbide is easily ground with diamond wheels if light cuts are taken to prevent damage to the workpiece material. However, diamond-grit wheels are quite expensive, and the overall grindability of this material is very low.
High-speed steel can be ground quite successfully with aluminum-oxide grit wheels. The grinding ratio is low, the relative power consumption is high, and the possibility of damage to the workpiece is always present. Overall grindability is quite low.
Hardened steel (medium hard alloy or plain carbon steels) is easily ground with aluminum-oxide wheels. The grinding ratio is good, and damage to the workpiece is not a serious problem. The grindability rating is good.
Soft steels (annealed plain carbon steels) grind with relatively low power consumption. Aluminum-oxide wheels are satisfactory, and the grinding ratio is quite high, but surface damage may be encountered. As a group, these materials are rated as having good grindability.
Aluminum alloys (soft) grind with quite low power consumption, but they tend to load the wheel quickly. Wheels with a very oven structure are needed. Grinding ratios are good. Silicon-carbide grit works well, and belt grinding outperforms wheel grinding in many cases.
George Schneider, Jr., is the author of Cutting Tool Applications, a handbook to machine tool materials, principles, and designs. He is the Professor Emeritus of Engineering Technology at Lawrence Technological University, and former Chairman of the Detroit Chapter of the Society of Manufacturing Engineers.
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