centreless grinding wheel change process

what is centerless grinding? | the complete guide to the process

what is centerless grinding? | the complete guide to the process

Centerless grinding is a process that has been a part of manufacturing for nearly 100 years. It helps solve one of the limitations of other types of turning machines such as lathes and mills. The process is better suited to deal with the limitations imposed on lathes and mills with respect to the size, material type, and finishes of different surfaces that may not be as adaptable to other machining processes.

It is different from centered grinding in that there is no spindle used to hold in place the material on which the work is being carried out. Instead, it is secured between a pair of rotary grinding wheels that rotate at pre-set speeds. This determines the speed at which excess material is removed

A combination of the cutting pressure and capability of the grinding wheel and the gravity acting on the workpiece ensures that the work maintains contact with the control wheel and the rest blade. The control wheel (or regulating wheel) is normally made from a rubber bonded material that offers a frictional surface that is constantly advancing. This makes sure there is a steady, continual rotation of the work which is at exactly the same surface speed (or peripheral velocity) as the control wheel.

Centerless grinders dont have a lot of moving parts and instead owe much of their functionality to some basic principles of physics. That makes centerless grinding a relatively simple process thats ideal for finishing the outside diameter of small cylindrical metal parts requiring a tight tolerance.

During grinding, the force of the grinding wheel pushes the workpiece into the regulating wheel which operates at a far slower speed than the grinding wheel, and against the support. This is how the workpiece is held in place, by pressing it between the regulating wheel and the grinding wheel.

The regulating wheel is a critical element in the generation of roundness in centreless grinding, as the regulating wheel supports the workpiece and precisely positions it during the grinding. The workpiece circumference should simultaneously be in line, contact with the grinding wheel, work rest blade, and the regulating wheel. This is why it is very important for the regulating wheel to provide grip to ensure that the workpiece is in the correct position.

The arrangement of these elements can be different on different machines, depending on what type of centreless grinding is being enacted, but no matter which model or type of machine, the principles of the process remain the same.

This is a virtually continuous process, because, compared with grinding between centers, the loading time is relatively small. Even extreme long lengths can be ground continuously and large quantities of small parts can be automatically ground by means of various feeder attachments.

In addition, centerless grinders are capable of performing consistently at high speeds. That makes the process a great choice for high-volume applications in aerospace, automotive, military, medical, and other industries.

In this process, the workpiece is fed through the center of the two grinding wheels. Thru-feed grinding is best used for parts that are cylindrical in shape. The regulating wheel can be set at such an angle that it pulls the material through the grinding process, without the need for any separate feeding mechanism.

In addition to being available in different diameters and widths/thicknesses, grinding wheels come in different grain types and grit sizes, often using super abrasive materials such as polycrystalline diamond and cubic boron nitride.

A companion question to what is centerless grinding is which industries use it? The simplicity and effectiveness of the process mean that it is ideal for use in machining parts for many major industries:

Our wide client base means that the millions of parts that we grind every year end up in some quite extraordinary places. Components and bars that we grind could be used anywhere from at the bottom of the sea to way out in space. They could equally find themselves in a nuclear reactor as on a NASCAR winner. We also provide work for hundreds of precision and general engineering and manufacturing companies all across the US.

The simple answer to this question is No. Precision ground bars are that are further machined using the process to achieve high dimensional tolerances. They are supplied in volume to those clients who require very tight tolerances for their components, such as pneumatic cylinders, valve stems, piston, and pump shafts.

They are a semi-finished product where our clients will not need to further machine the diameter or enhance the surface finish. Our steel bar can be centreless ground to your exact sizes and tolerances, get a quote today.

thrufeed centerless od grinding: parameter relationships and troubleshooting | cutting tool engineering

thrufeed centerless od grinding: parameter relationships and troubleshooting | cutting tool engineering

On many work parts, the outside diameter (OD)needs to be highly accurate. Tight tolerances are required for OD size, roundness, high and low frequency lobe patterns and taper.Thrufeed centerless OD grinding can achieve precise part quality at an economical processing cost.

As the name implies, centerless grinding involves the grinding of cylindrical parts without locating the part on a specific center line between centers. The centerless process is commonly used for high volume production, and its also easily used for low volume production because the machine setups are fairly simple.

In thrufeed centerless OD grinding the workpiece passes between two wheels, a grinding wheel and a regulating wheel (as illustrated in the diagram below). Both wheels rotate in the same direction, but at much different speeds. The purpose of the grinding wheel is to remove material from the workpiece and improve part OD quality.The regulating wheel acts like a brake, controlling the rotational speed and thrufeed rate of the workpeice. An angular-topped workrest blade supports the workpiece as it passes through the grinder between the grinding and regulating wheels.

The abrasive types used in the grinding wheel are determined by the part material to be ground.Aluminum oxide, ceramic aluminum oxide and CBN grains are typically used to grind ferrous materials.Silicon carbide and diamond grains are typically used on non-ferrous materials. These grains are used in vitrified or resin bonds to make a grinding wheel. Generally vitrified bonds are used to grind weak configured parts that may deform when high grind force is applied. Resin bond grind wheels are used to grind stronger parts like bars or solid rollers.

The top angle on the workrest blade helps with the rounding action of the part. With increased angle, quicker rounding occurs, but it also weakens the blade rigidity. The most common top angle used in centerless grinding is30 degrees. As the diagram below indicates, lower angles are used when grinding heavy workpieces, whichhelp minimize vibration.Workrest top angles typically range from 45 degrees down to 20 degrees. Generally speaking, 30 degrees is a good starting point for the majority of parts to be thrufed centerless ground.

A majority of centerless grinders are set up with the work center height above the centerline of both wheels. There are some applications like bar grinding that set up the bar center below the centerline of the wheels to keep bar vibration low during the grinding process. We will focus on setups with the work center above the centerline of the wheels, which iscommonly called work height above center.Part diameters 1"or less should have the height above center dimension set at half the part diameter. Parts greater than 1"should be proportionally less for stability reasons. The purpose of the truing device on the regulating wheel is to have the diamond follow a similar line of contact to the wheel that the parts will follow. This will allow parts to enter and exit the grind zone in a straight line. So there is an important relationship that ties the work height above center dimension to the regulating wheel diamond offset setting. (See images below.)

Typically the diamond offset is set slightly less than the workpiece height above center dimension.It is key to understand that this relationship influences the grind pattern and part contact to the grinding wheel as parts pass through the grinder. It is very important to calculate the ratio of the regulating wheel diameter to the workpeice diameter, or D/d. D is the regulating wheel diameter and d is the workpeice diameter. Once you know this ratio, then you can use the Truing Setting chart (below) to determine the correct truing angle and diamond offset.

The regulating wheel angle of inclination typically is in the +1 degree to +3 degree range. This angle, along with regulating wheel speed (RPMs), determines the part thrufeed rate in inches per minute. This setting also affects the distance a part will travel in one workpiece revolution. A lower angle means a shorter travel distance and this affects grind force on the workpeice. So you can affect how a grinding wheel performs by changing regulating wheel inclination and regulating wheel RPMs. Parts that have a high diameter-to-length ratio, such as bearing rings, should have a lower regulating wheel angle of inclination to help keep the parts stable as they travel through the grind zone.Proper settings allow the workpieces to smoothly enter and exit the grind zone.

Typically there are adjustable guides on the entrance and exit sides of the grind machine. The purpose of theguides is to align the workpeices as the wheel goes in and comes out of the grind zone. (See diagram below.)It is important to correctly align the guides located on the regulating wheel side. The workpeices should smoothly transition between guides and regulating wheel. Even a slight bump during the transition can cause a defect to be ground into your parts.

Proper guide alignment is important to avoid your parts from having a barrel or hour glass diameter across the part length. Theillustration below shows how misaligned guides could affect part quality.

Be sure to inspect all the tooling used in the centerless grinder, and make sure all tooling is in good condition. You can have a good machine setup, but if the diamond tools are worn, they will cause dull dress condition on your wheels and generate poor part quality.Paying close attention toyour tooling condition and machine setup will ensure that your grinder will produce excellent part quality at low manufacturing costs.

top 5 centerless grinding problems & grinding troubleshooting | hindustan abrasives

top 5 centerless grinding problems & grinding troubleshooting | hindustan abrasives

Regular maintenance ofcenterless grindingmachine can help your business alot and reduces number of problems in grinding process. But when your superstar grinder suddenly becomes non-functional, youll start deep diagnosis to find out root cause or problem behind error.

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thrufeed centerless od grinding: parameters and troubleshooting | norton abrasives

thrufeed centerless od grinding: parameters and troubleshooting | norton abrasives

As the name implies, centerless grinding involves the grinding of cylindrical parts without locating the part on a specific center line between centers. The centerless process is commonly used for high volume production, and its also easily used for low volume production because the machine setups are fairly simple.

The abrasive types used in the grinding wheel are determined by the part material to be ground. Aluminum oxide, ceramic aluminum oxide and CBN grains are typically used to grind ferrous materials. Silicon carbide and diamond grains are typically used on non-ferrous materials. These grains are used in vitrified or resin bonds to make a grinding wheel. Generally vitrified bonds are used to grind weak configured parts that may deform when high grind force is applied. Resin bond grind wheels are used to grind stronger parts like bars or solid rollers.

A majority of centerless grinders are set up with the work center height above the centerline of both wheels. There are some applications like bar grinding that set up the bar center below the centerline of the wheels to keep bar vibration low during the grinding process. We will focus on setups with the work center above the centerline of the wheels, which is commonly called work height above center. Part diameters 1" or less should have the height above center dimension set at half the part diameter. Parts greater than 1" should be proportionally less for stability reasons. The purpose of the truing device on the regulating wheel is to have the diamond follow a similar line of contact to the wheel that the parts will follow. This will allow parts to enter and exit the grind zone in a straight line. So there is an important relationship that ties the work height above center dimension to the regulating wheel diamond offset setting. (See images below.)

Typically the diamond offset is set slightly less than the workpiece height above center dimension. It is key to understand that this relationship influences the grind pattern and part contact to the grinding wheel as parts pass through the grinder. It is very important to calculate the ratio of the regulating wheel diameter to the workpeice diameter, or D/d. D is the regulating wheel diameter and d is the workpeice diameter. Once you know this ratio, then you can use the Truing Setting chart (below) to determine the correct truing angle and diamond offset.

The regulating wheel angle of inclination typically is in the +1 degree to +3 degree range. This angle, along with regulating wheel speed (RPMs), determines the part thrufeed rate in inches per minute. This setting also affects the distance a part will travel in one workpiece revolution. A lower angle means a shorter travel distance and this affects grind force on the workpeice. So you can affect how a grinding wheel performs by changing regulating wheel inclination and regulating wheel RPMs. Parts that have a high diameter-to-length ratio, such as bearing rings, should have a lower regulating wheel angle of inclination to help keep the parts stable as they travel through the grind zone. Proper settings allow the workpieces to smoothly enter and exit the grind zone.

Proper guide alignment is important to avoid your parts from having a barrel or hour glass diameter across the part length. The illustration below shows how misaligned guides could affect part quality.

Be sure to inspect all the tooling used in the centerless grinder, and make sure all tooling is in good condition. You can have a good machine setup, but if the diamond tools are worn, they will cause dull dress condition on your wheels and generate poor part quality. Paying close attention to your tooling condition and machine setup will ensure that your grinder will produce excellent part quality at low manufacturing costs.

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grinding wheel: specifications & manufacturing process by norton abrasives

grinding wheel: specifications & manufacturing process by norton abrasives

There are two main methods of metal cutting. Cutting performed using a single point tool and cutting performed using a multi-point cutting tool. We are well aware that while performing cutting using a multi-point cutting tool, if the material to be removed is of a high volume, then milling is performed; while if less material is to be removed and the surface finish is to be improved, then grinding is used.In this article, we are going to learn more details about the grinding wheel.

Apart from grains and bond, the porous construction of the wheel is an important part. The coolant entering deep into this during cutting process does not allow increase in the temperature of the wheel and the job.

In other machining processes, tool wear is a serious problem. But in grinding, that in itself is beneficial, because unless the wear of the wheel takes place, new sharp grains cant be available for work.

Defects like loading in which sometimes the grains and chips becoming free stick onto the grinding wheel or glaze on the wheel surface which has become blunt due to heat, or the distortion in the shape of the wheel due to use arise in the grinding wheel. To repair these, the process of wheel dressing is followed.

Approximately 60-70 years ago, manual or hydraulically operated grinding machines were in vogue. The quantitative and to a certain extent qualitative needs of that time were less as compared to those prevalent today, hence the wheels used in those days were suitable for the needs of that time. Brief information on the expected degree of quality of a job manufactured by grinding is given in the table below.

At present thumb rule which is being followed - go coarser, go faster, go bigger. For this purpose, large size grains are expected to be used. It is expected to attain the maximum possible wheel rotational speed or maximum possible cutting speed.

In this case, the turbocharger fan and the shaft behind are assembled together by friction welding. The hardness and material of these two parts are different. Hence instead of using two different grinding wheels having different properties in two separate grinding set-ups, a single layered wheel was used. A groove is formed by one of the layered wheels while the outside diameter of the fan is ground by the wheel having more width.

Since the wear of the wheel was non-uniform, a taper was forming on the shaft. Also after performing grinding on the shoulder, burn marks and grinding cracks could be seen on the job surface. As a solution for this, instead of VS3 bond, the advanced VT3 (Vitrium) bond was used.

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Born in 1941, in a 40'x40' room at Mora, near MumbaiGrindwell pioneered the manufacture of Grinding Wheels in India. Promoted by two Parsi entrepreneurs, the Company has grown steadilyover the years.Grindwell Norton Ltd. (GNO) came into being when a technical collaboration in 1967 between Grindwell and the then world leader in abrasives Norton Company, USA, grew into a financial collaboration in 1971. In 1990, Saint-Gobain acquired Norton Company, USA, worldwide, and six years later, in 1996 GNO became the first majority-owned subsidiary of Saint-Gobain in India.

We use cookies in order to improve site performance, offer you a better browsing experience and enable you to easily share content. Cookies are pieces of information stored on your computer in simple text files which our server can read and record. These files do not contain any sensitive information. By continuing to browse our site, you agree to the use of cookies.

8 principles of centerless grinding - metal cutting corporation

8 principles of centerless grinding - metal cutting corporation

In the machining world, turning tools such aslathesandmillsare the flashy stars. In fact, theyaremachining to most people. However, the ability to doprecision centerless grindingin addition to machining is a definite advantage.

Centerless grindingis one of several machining processes that use abrasive cutting to remove material from a part (workpiece). The process involves the part being supported on a workpiece rest blade that sits between two rotating cylinders:

The beauty of centerless grinding is that the workpiece is held in place by the pressure of the rotating wheels. No fixturing is required, so the setup is simple and turnaround times are fast. And because the workpiece is rigidly supported, there is no deflection during the grinding operation.

But despite these and other advantages, centerless grinding has fewer practitioners than machining. And although the centerless grinder has been around for almost a century, a lot of people struggle with the fundamentals of the process and how it works.

What else is helpful to know about this somewhat mysterious process? Lets take a look at8 basic principles of centerless grinding things it is helpful (and we hope, interesting) to know about this mature and yet still somewhat unfamiliar process.

A downside of centerless grinding is, unlike machining, you cant have as manymultiple axes operating on the workpieces. However, there are many parts where the centerless process addresses the limitations of machining in terms of dimensions, materials, and surface finishes.

Thats why we like to say that where machining ends, the centerless grinding process begins. For instance, if you have a part that is out of round from a turning machine and the parts diameter is too small or its center is impossible to mount, you can achieve roundness throughcenterless grinding techniques.

Since they owe much of their functionality to some basic principles of physics, centerless grinders dont have a lot of moving parts. That makes centerless grinding a relatively simple process thats ideal for finishing theoutside diameter of small cylindrical metal parts requiring a tight tolerance.

Centerless grinding is virtually continuous because, compared with grinding between centers, the loading time is small. So, long lengths can be ground continuously. Even large quantities of small parts can be automatically ground by means of various feeder attachments.

In addition, centerless grinders can perform consistently at high speeds. That makes the process a great choice for high-volume applications in aerospace, automotive, military, medical, and other industries.

In-feed grinding also calledplunge grinding is used to grind cylindrical parts with notches or complex shapes, such as gear shafts. Here, the workpiece rest blade needs to be tooled to match the shape of the part, and the grinding and regulating wheels must be dressed to match the parts desired profile cut.

With the in-feed method, the regulating wheel spins the part at one speed while pushing it towards the grinding wheel, which is spinning at a faster speed. The greater the difference in speeds, the faster the removal rate.

In addition to being available in different diameters and widths/thicknesses,centerless grinding wheelscome in different grain types and grit sizes, often using superabrasive materials such as polycrystalline diamond and cubic boron nitride.

Generally, the centers of the regulating and grinding wheels are set at the same height on the machine, and the center of the workpiece is situated higher. However, if the workpiece is set too high, it may exhibit chatter. If the workpiece is set too low, it may be out of round.

The goal is to keep the part (1) in contact with the regulating wheel and (2) rotating at a slower speed, while the faster, larger abrasive grinding wheel applies the force that creates the precise roundness of the part. Using the correct wheel angles helps to ensure that the entire surface of the grinding wheel is in use.

If the angle of the regulating wheel is too acute, it can cause the workpiece to go too far into the grinding zone. This can result in uneven wear, tapering, and reduced wheel life. If the regulating wheel is too close to parallel with the grinding wheel, it can cause the parts to stall between the wheels or, worst-case scenario, cause a workpiece/wheel crash.

But with a wheel width of 6 (152.4 mm) or 8 (203.2 mm), that same angle may generate too much pressure toward the grinding wheel and cause chatter. In this case, changing the angle to 20 or 25 will reduce the pressure and eliminate the chatter on the part.

Centerless grinding requires the use of correctly pressurized coolant to overcome the air barrier created between the grinding wheel and workpiece during the grinding process. This allows the coolant to flow in the space between the two.

The coolant step in centerless grinding is critical to preventing heat from returning to the workpiece or the grinding wheel. Otherwise, it can be difficult to hold tolerances for roundness and straightness, and thermal damage can even cause the grinding wheel to blister and crack.

To increase process efficiency and productivity, CNC programmable controls make it even easier to set up and change the equipment from one job to the next. Other newer technologies are making it possible to:

For example,the latest generation of centerless grinding machinesremove the regulating wheel and replace it with stationary wire supports that have a bushing mode option. This option allows for intricately ground shapes and exotic dimensional features by performing similarly to the guide bushings onSwiss-style automatic lathes.

In addition, advances in software controls, direct drive motors, and robotic loading/unloading of workpieces allow the simple concept of centerless grinding to make complex parts that were previously unthinkable.

For example, from the beginning Metal Cutting has been augmenting our cutting capabilities with centerless grinding for the production of glass-to-metal-seal parts. More than 50 years later, we still perform centerless grinding virtually every day and we continue to stay abreast of industry trends and customer demand by using the latest generation of equipment.

In the right hands, centerless grinding is capable of producing a machined surface that a process such as turning simply cannot match both as an Ra value and also on certain metals that are nearly impossible to turn with a cutting tool.

Almost 100 years after its inception, centerless grinding is still not as common as other metal fabrication methods. Yet, the unique qualities of a ground (vs. turned) finish combined with the innovations and variations available with centerless grinding allow it to produce metal parts that are irreplaceable for their applications.

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