The super-hard centerless grinding wheel is a special grinding wheel for centerless grinding machines. It is used for grinding hard and brittle materials such as tungsten carbide, ceramic, magnetic materials, PDC tools and etc.

Abrasives are diamond or CBN. The types of bond are resin, vitrified and metal bond.

With high efficiency, high precision and long life of diamond or CBN centerless grinding wheel, it is suitable for a large batch of automatic pipe, rod, and trap for external grinding. Whether it is the quality of the processed product, or consistency, both better than the conventional abrasive centerless grinding wheel

Super Hard Centerless Grinding Wheel Working Principle

There is not a headstock and a tailstock for the high precision centerless grinding machine. Instead, a pallet and a guide wheel support the workpiece and is ground by grinding wheel.

The centerless grinding method is that it consists of three mechanisms: a grinding wheel, an adjusting wheel and work support, and the grinding wheel actually serves as grinding, and the adjusting wheel controls the rotation of the workpiece and makes the workpiece have feed speed. The work support can support the workpiece during grinding.

Grinding Method of Centerless Grinding Machine

There are three main types of centerless grinding methods, namely pass-through, plunge-cut and plunge-through.

    There are 3 main types of grinding methods of centerless grinding machine, through-feed, in-feed, and through-feed and in-feed centerless grinding.

• Through-feed centerless grinding: The workpiece is ground in the direction of grinding wheel axis. The workpiece axial feed is done by adjusting the slight inclination of the guide wheel axis. It is suitable for grinding slender cylindrical workpieces, short shafts without center holes, sleeve and etc.
• In-feed centerless grinding: There is an axial positioning fulcrum for the support pallet, and support the workpiece at a certain position pallet, and is ground by a grinding wheel or a guide wheel. It is used for grinding workpiece with shoulder of spindle or convex plate as well as cones, spheres or other rotating parts.
• Through-feed and In-feed centerless grinding: It is compounded by the two. In addition, there are tangential feed grinding and end-feed grinding of the stepped workpiece in the axial direction. With high productivity, centerless cylindrical grinding machines are mostly used for mass production and they are for automation easily.

Centerless Grinding Advantage and Disadvantage

1 Continuous processing, no need to retract the tool, short time for clamping the workpiece, and high productivity.

2 The bracket and guide wheel positioning mechanism has better rigidity than that of the top and center frame of the conventional cylindrical grinding machine, and the stock removal is large, which is good for processing the slender shaft workpiece, and it is easy to realize high speed grinding and strong grinding.

3 The workpiece on the centerless cylindrical grinding machine is positioned on the positioning mechanism by the cylindrical. The grinding amount is the margin on the diameter of the workpiece.

Therefore, the effect of the wear of the grinding wheel, the compensation of the feed mechanism, and the repeated positioning accuracy error of the cutting mechanism on the diameter of the part is relatively little, only half of that of conventional cylindrical grinding machine, no need to drill the center hole.

4 The pass-through the mechanism of wide grinding wheel centerless grinding machine can increase the processing allowance each time, when cutting-in grinding, it can be disposable grinding for the complex profile, high productivity, wide applications.

5 The centerless cylindrical grinding machine has no mechanism that cannot guarantee the relative positional accuracy(coaxial, verticality, etc.) of the grinding surface and non-grinding surface, and the

Roundness is poor when grinding the axial direction to the intermittent external surface.

6 There is odd-numbered roundness for grinding surface. If it is big, it will often cause the illusion that the measured size is smaller than the largest physical size, which will affect the assembly quality and working performance.

7 The adjustment of the machine tool is complicated and time-consuming. It needs to adjust the height of the bracket and the distance and related process parameter when replacing the workpieces of different diameter every time. Therefore, the adjustment technology is difficult, and it is not suitable for small batch and single-piece production.

Types of Superabrasive Centerless Grinding Wheel:

There are resin, vitrified and metal bond diamond centerless grinding wheels, of which resin bond diamond centerless grinding wheel is the most widely used, mostly used for grinding hard alloy rod, tungsten carbide, ceramics, and vitrified bond diamond centerless grinding wheel is mainly used for grinding PDC. Metal bond diamond centerless grinding wheel is often used to grind magnetic materials.

Resin bond centerless CBN grinding wheel can be used for high-speed steel rob. The vitrified bond can be used for various bearing rollers, bearing rings cylindrical, injection nozzles, pump parts, etc.

Specifications of Centerless Grinding Wheels(mm)

Truing and Dressing  of Diamond /CBN Centerless Grinding Wheel:

After grinding a period of time, the grinding wheel may have a channel or unsharp. Usually, the grinding wheel needs to be dressed. The conventional abrasive centerless grinding wheels use single point diamond dresser or diamond rotary dresser to ensure the shape and sharpness. There are truing and dressing processes for super hard abrasive grinding wheel.

The truing is a micro-cutting of the grinding wheel to achieve the required geometry and precision and make the abrasive tip crushed to form a micro-edge. the dressing is removing the bonding agent between the abrasive grains so that there is a certain holding debris space between the abrasive grains. And make the abrasive grains protrude and form cutting edge.

For multi-porous vitrified bond super hard abrasive grinding wheels( diamond and CBN grinding wheel), usually, truing and dressing can be done at one time due to the loose bonding agent. For the dense bonding agent of grinding wheel( such as resin, metal bond), truing and dressing should be done separately.

The most effective truing tool for superhard abrasive grinding wheels is diamond dressing tools. Truing in single grain diamond often affects the accuracy of the profile due to wear of the dressing tool. If it is truing with diamond rotary dresser, it can obtain good grinding wheel shape avoid being worn too fast. The feed accuracy of the truing device is high, and the feed rate should be controlled at the micron level. Excessive truing affects both the quality and life of the grinding wheel.

There are many methods of dressing. Usually, mechanical methods( such as cutting-in sharpening with corundum block, hydraulic jet sharpening method) or electric machining can be used. The latter is mostly used for the metal bond grinding wheel, and the grinding wheel is used as the anode to remove the metal bond by electric spark or electrolysis. If adding the graphite powder to the bonding agent, the method is also suitable for resin and vitrified bond grinding wheel.

Operation notes of centerless grinding wheel :

1 Check the condition of the machine before starting, and do not put the items on the machine table, and place the workpiece neatly.

2. Check whether the oil level of the fuel tank is normal before starting, whether the water level of the cooling water tank, the grinding wheel and the gap between the guide wheel and the supporting blade are normal, whether there is debris in the machine tool;
3. Check the switches before starting the machine, and confirm whether the safety protection such as the protective cover is effective;
4. Turn on the power, start the hydraulic switch, and observe whether the pressure of the hydraulic gauge of the machine is normal, and then see if there is oil flowing through each oil mirror and each oil pipe.
5. Clean the grinding wheel and the guide wheel dressing seat before starting, and fill with the oil for the oil cup.
6. Operators should be trained according to the operation instructions to learn about various work procedures before starting the machine.
7. The above confirmation is correct before starting up.
8. Turn on the main power to the ON position.
9. Turn on the hydraulic switch to the ON position.
10. Check the oil system oil mirror, and start the centerless grinding wheel and guide wheel after the oil meter is stable.
11. Turn on the water pump and adjust to the appropriate amount of water after the grinding wheel and the guide wheel running normally.
12. Test 1-3 pcs of the workpiece after adjusting the machine, first check the size and appearance of the workpiece.
13. Mass production after the test is qualified.
14. Operators should do the self-test and record the first sample according to the operation instructions.
15. Stop the machine immediately when it is abnormal in the production process and fill in the relevant forms.
16. Turn off the water pump motor to the OFF position, stop the water supply, and take out the work substance that is stuck in the machine tool.
17. The grinding wheel and the guide wheel are continuously idling for more than 5 minutes to make dry, so as to avoid unbalanced grinding wheel when turning on the machine again. Turn the grinding wheel and the guide wheel power switch to the OFF position after drying the water.
18. After stopping the centerless grinding wheel and a guide wheel, turn the oil pressure switch to the OFF position. ( Do not stop the hydraulic motor first to avoid oil loss and wear the bearing bush and the main shaft).