Honing Process | Types of Honing Machines

Honing process

The honing process is an abrasive procedure that is used to polish previously machined surfaces. It’s often used to smooth out drilled or bored holes. A “hone,” also known as a “bonded abrasive stone,” is a stick-shaped bonded abrasive stone used in this technique.

Many geometric defects or distortions caused by grinding, heat treatment, forming, or other manufacturing processes, such as out-of-roundness, bellmouth, axial straightness, waviness, undersize, barrel, taper, bored marks, reamer chatter, rainbow, and misalignment, can be eliminated.

The expanding reamer and the honing tool both function in the same way. The honing stones are pushed away from the bore’s surface by mechanical or hydraulic pressure. To make honing stones, aluminum oxide, silicon carbide, or diamond grains of appropriate grit are joined in resinoid or vitrified bonds. The honing procedure may be used to polish both interior cylindrical and flat surfaces.

Rough honing, finish honing, micro honing (or superfinishing), and free form honing are some of the many types of honing (or abrasive flow machining). Freeform honing is also referred to as a superfinishing technique. The grit ranges and surface finish capabilities of the processes may be compared to provide insight into their suitability for different applications.

What is honing?

Honing machines are metal abrasive tools and methods that use hard tooling and consumable abrasive stones to fix flaws in metal parts of:

• Diameter
• Shape
• Surface finish
• Positional tolerances of bores

The honing method was created to enable bore geometry, size control, final surface quality, and surface structuring to be perfected. On the inside of tubing or cylinder bores, the honing process gives the final size and develops the required finish pattern. Finishing is done by rubbing abrasive stones with the appropriate grit and grade against the work surface. Under regulated pressure, the stones are rotated and reciprocated in the section with the hone abrasive. The surface of the honed portion has a cross-hatch pattern created by combining rotation and reciprocation.

Why Honing?

Method of machining that is both cost-effective and efficient for:

• Stock removal
• Producing precise results
• Tolerances in the bore
• Sanding the bore
• Sprayed coatings, CGI, ceramics, and other materials can all be used to finish bores.

How does the honing process work?

The honing tool’s abrasive action removes material from the inside diameter of the workpiece. While the workpiece reciprocates (strokes) back and forth, the tool spins and expands. Special fixturing, for example, can achieve round and straight tolerances of 0.003mm (0.0001″) in manufacturing. The workpiece must be permitted to “float” or move in three axes in order to attain such tight tolerances. This is the single most critical step in achieving the tighter tolerances necessary in today’s industry.

The workpiece must be positioned against a flat face plate perpendicular to the machine spindle axis in order to rectify out-of-squareness. This, of course, limits the amount of movement, or “float,” by diminishing one of the three axes of movement.

Honing is done using tiny, bonded abrasive stones or super abrasive sticks fixed in a fixture that spins and reciprocates (strokes) when they are applied to the surface or hole to be completed. The hone may reciprocate or oscillate while the workpiece spins on larger surfaces. For manual stroke honing machines, an operator controls oscillation. A basic variant of a manual stroke honing machine is a honing head fitted into a drill press.

What is the Honing Process’s History?

Leonardo da Vinci was the first to use a tool to smooth the inside walls of a wooden pipe with the use of a stick linked to abrasive paper on it in the 16th century. This stick has the ability to move in both linear and radial directions.

To sharpen the internal components of internal combustion engines, honing tools were invented in the early twentieth century.

The first five-bladed honing tool with a stick and spring was created and patented in 1924. After a few years, the honing method was adopted by industries for production reasons.

Three operations are carried out by honing machines.

• It is, first and foremost, a stock removal procedure that removes ruptured metal and reaches basic metal.
• Second, a finish pattern is created to give the greatest possible surface for lubricating conditions.
• Third, honing ensures that the cylinder surface is exceedingly exact in terms of straightness, roundness, and size.

What is the purpose of a single-pass honing machine?

A diamond abrasive, boring bar-type honing tool is used for single-pass honing. In one pass through the workpiece, this sort of honing tool creates a straight, round, and un-tapered bore. Single-pass honing is excellent for honing the engine crank and cam bores. The completed portion has no crosshatch pattern since the size is accomplished in one pass. With a cone identical to normal tooling, the adjustable single-pass tool widens the hone stones.

However, unlike traditional honing, the stones are not enlarged and retracted. The stones are just enlarged to reach their final size. The honing tool is much longer than typical equipment, and the extremely abrasive layer covers the whole length of the tool. The single-pass hone has a final size section of 2.5 inches and is tapered for roughly seven inches. On the following page, there is a picture. Because the single-pass tool has no in-process hone expansion, it must be adjusted while the machine is stopped.

Tools for Hone & Honing

The following are the various honing tools:

1. Flexible hones
2. Sharpening stones
3. Honing sticks
4. Hand hones

Flexible Hones

Hairbrushes are used as sharpening instruments. Abrasive beads are attached to the bristle ends. They’re utilised to refine the metal’s interior and exterior surfaces, as well as to smooth the surface. Flex tool is another name for this sort of honing tool.

Sharpening Stones

Sharpening stones are typical abrasive stones used to sharpen metal edges or surfaces. The sharpening stone is a common abrasive stone used to sharpen the edges or surface of a metal.

Honing Sticks

It’s used to give the inside bores a final polish. The diameter of the wheels used for abrading on the metal surface is smaller with this type of tool. It’s often employed in these situations to polish or finish the inner surface of a metal’s inner diameter.

Hand Hones

Diamond hones are another name for hand hones. The edges of ground cutting tools are honed with these honing tools. In the sharpening process, this is an off-hand method.

Honing Tool Material

The materials used to make the honing tool are as follows:

1. Abrasive material
2. Bonding material

Abrasive Material

The most frequent grit particles include aluminium oxide (Al2O3), silicon carbide (SiC), diamond, and others. For roughing, use 150 to 180 grit, and for finishing, use 600 grit.

Bonding Material :

It should be firm enough to hold the grit during its cutting life, but not so hard that it rubs against the bore and slows down the cutting motion. To regulate the cutting action and extend the life of the abrasive bond, it is frequently filled with wax, sulfur, resin, and other materials.

Hard grit and bond are utilized to endure vigorous dress action if the item to be completed is interrupted by ports, voids, cut-ways, out of roundness, etc. Grit is a tool for cutting edges. It must be shattered and sharpened in order to penetrate, and it must be sturdy enough to sustain the pressure necessary. We employ friable and porous bonding on hard materials. The porosity of the stick is determined by the grit combination, bond, technique, and pressure utilized in its formation. The stick’s motion is influenced by porosity, which facilitates chip clearing and reduces heat buildup.

Honing Tool Bonds

• Softer Bonds should be used with harder materials like steel, chromium, and so on, whereas intermediate bondsnds should be used with Cast Iron and Harder Bonds should be used with softer materials like aluminum, brass, and bronze.
• Abrasive content is retained for a period of time to allow efficient usage of the abrasive substance, but not for so long that the abrasive becomes dull or useless.

Features of Honing tool abrasives

Abrasive grain type and grit size are important considerations when selecting hones and honing tools. Choices for abrasive grain include:

• aluminum oxide
• boron carbide
• ceramic
• emery or crocus
• Silicon carbide
• cubic boron nitride (CBM)
• synthetic diamond
• tungsten carbide
• zirconia

When choosing hones and honing equipment, the abrasive grain type and grit size are key factors to consider. Aluminum oxide, boron carbide, ceramic emery, and crocus are all options for abrasive grain.

Abrasive items with abrasive grains contained in a matrix or glued to a surface are referred to as grit size. Coated abrasives, dressing sticks, super abrasives, vitrified grinding wheels, and honing stones or grit dressers are all examples of this type of abrasive.

Grit size applies to abrasive products with abrasive grains held in a matrix or bonded to a surface. Examples include coated abrasives, dressing sticks, super abrasives, vitrified grinding wheels, and honing stones or grit dressers.

Honing Coolants

Honing need a large quantity of coolant. The coolant is utilized for two different things:

1. To dissipate the heat.
2. To get rid of the chips.

Animal fat oil combined with kerosene might be used for this. Turpentine, soap, and a water solution are also utilized.

Honing Coolant Considerations

The following are the roles of coolants:

• Chips should be carried away to maintain the tool free-cutting
• Tool life is extended by lubricating the cutting region.
• Heat is dissipated, while the size and shape of the object are maintained.
• Rust resistance
• Oil-based coolants offer better lubricity than water-based coolants, but they don’t disperse heat well and have negative disposal needs.
• Water-based coolants effectively remove heat and are compatible with diamond abrasives. Vitrified abrasives do not function well with water-based coolants.
• Emulsions (mixed water-oil), synthetics (water-soluble compounds), and semi-synthetics are all examples of water-base (water and chemistry combined)
• The coolant should be kept at a temperature of 68-72 degrees Fahrenheit.

What Type of Coolant Should You Use?

• To minimise tearing, we provide a coolant with sulphur content and high lubricity additives for steel and other stringy chip materials.
• We provide a mild honing oil with just enough lubricity to assure clean cutting for Cast Iron and other easy-to-hone materials.
• We provide a light honing oil with a high fat content for aluminium and brass to enable clean cutting on soft materials.
• Many customers have previously installed honing coolants in their facilities. We can work with any coolant that has the cutting properties they want and the finish they want.
• Many clients request that we utilise a cutting fluid that they already have on hand for boring or other operations. These are typically insufficient for honing.

Honing Process Parameters

The hole’s precision and surface polish are largely determined by a number of process parameters, which are detailed below.

1. RPM of tool:

When the tool speed is increased, the metal removal rate increases and the surface roughness reduces.

2. Honing time:

Increased honing time reduces surface roughness to some amount before gradually increasing it. It is chosen in such a way that it produces the least amount of surface roughness while removing the most metal.

3. Honing stick pressure:

The graph depicts the change in metal removal rate and surface roughness as a function of unit pressure. The honing stick pressure is chosen to provide the least amount of roughness while removing the most metal.

4. Stroke Length:

The stroke length must be sufficient to span the whole working length.

Types of Honing Process

There are two types of honing processes.

1. Manual Honing
2. Machine honing
   1. Horizontal honing
   2. Vertical honing

Manual honing process

Along with the honing stone, a proper amount of coolant is utilised in this operation. As a result, this procedure is known as the “wet process.” The hone is continually turned during this operation, and the workpiece is pushed front and back with the assistance of the hand.

Machine honing

Honing may be done on a variety of devices, including lathes and drilling machines. The fixed type of machine is ineffective for sharpening. By replacing the drill bit with an honing tool head, a portable, tiny drilling machine may also be used for honing. In large manufacturing, these little machines will fail to produce precise results. To get a nice outcome, you’ll need to utilise a normal honing machine. There are several different types of sharpening machines available. The most prevalent kinds are described in the following sections.

Horizontal honing machines

With the aid of these equipment, longer operations may be manufactured. The honing tool is positioned on a horizontal spindle on these devices. The workpiece is mounted on the table and moves back and forth on various machines. The honing revolves and oscillates slightly around its own axis. This oscillation is mechanically or hydraulically regulated. The honing tool may be mounted on a moving head and rotated as well as reciprocated in some circumstances.

The workpiece is rotated along its own axis while being held horizontally. This machine is designed for jobs that take a long time to complete. Gauges are used to ensure that the machining sizes are correct. In certain machines, there are two spindles.

Vertical honing machines

The tool, as well as the workpieces, are held vertically in this machining operation. More spindle types are available for these machines. The tool reciprocates and the workpiece is steady. Fixtures are used to keep the workpiece in the right place. Hydraulic drives are used to control the tool and the workpiece in contemporary machinery.

Vertical honing machines are suitable for jobs that aren’t too long. When compared to horizontal honing machines, these machines are more extensively employed.

Explain the Honing Process:

1. The workpiece is firmly fastened on the bench. The bore must be kept parallel to the axis of the honing spindle with extreme caution.
2. Aluminum oxide or silicon carbide abrasive sticks are attached on a mandrel or fixture.
3. There is a floating motion between the work and the tool, so any pressure applied to the tool is distributed evenly on all sides.
4. Finally, the stroke and working length must be adjusted, as well as the hone, in order to get a nice cylindrical bore.
5. As the honing tool spins, it is provided a slow reciprocating motion, resulting in an honing speed of 10 to 30 m/s. This movement results in quick stock removal and the creation of a straight and round surface at the same time.
6. A lubricant such as paraffin or hard oil mixed with kerosene is poured into the hole to be polished, and the metal is removed using an honing stick. The following are the two uses for lubricant:

(i) To dissipate the heat.

(ii) To flush away the chips.

It’s possible to hone a pair of interior cylindrical and flat surfaces. However, the honing process/method is mostly used on interior cylindrical surfaces. The diagrams depict an honed and simplified version of a cylindrical hole honing procedure.

Applications of honing process

The primary purpose of the honing procedure is to get exact cylindrical hole diameters. It’s perfect for polishing interior surfaces of I.C. engine cylinders, hydraulic cylinders, and other cylinders where a lubricant layer must be maintained across the whole surface.

Automotive, aerospace, oil and gas, aviation, agricultural engineering, and other sectors use honing. The following items are manufactured using the honing process:

• Hydraulic valves
• Fuel injectors
• Cartridge valves
• Gears
• Connecting rod
• Crankshafts journals
• Engine blocks
• Gun barrels
• Round holes, etc.

Advantages And Limitations Of Honing Process

Honing has evolved into a viable industrial technique with distinct benefits and drawbacks:

Advantages of Honing Process:

There are no chucking or locating mistakes because the workpiece does not need to be turned by power, and no chucks, faceplates, or rotating tables are required. Because the hone is powered by a central shaft, bending the shaft will not result in tapered holes like it does when boring. If the prior processes left enough stock for the hone to clear out all the imperfections, the result is a completely round hole with no taper or high or low regions.

When compared to grinding or fine boring, which employs a tiny contact area at a high speed, honing uses a big contact area at a moderate speed. The crosshatched pattern formed by the simultaneous rotating and reciprocating action is good for retaining lubricant. Diamond stones, which are comparable to diamond wheels, may be used to sharpen diameters with 0.001 to 0.0001-inch accuracies and closer accuracies.

• Fixtures that are less complicated or inexpensive.
• It is really precise.
• It’s appropriate for both long and short bores.
• It keeps the bore’s original centerline.
• Any material, regardless of its hardness, may be completed.

Limitations of Honing Process:

Honing is regarded to be a time-consuming procedure. New machinery and stones, on the other hand, have significantly reduced honing times. Unless the piece is turned or supported, horizontal honing might result in oval holes. Even mild hand pressure might result in a somewhat oval hole if the workpiece is thin.

Conclusion

Honing is a machining process that aids in bore geometry, size control, surface structuring, and final surface quality. On the interior of tubing or cylinders, the technique enables for final sizing and provides the required finish pattern. This concludes our discussion of the honing process’ definition, function, applications, components, diagram, types, and operation. We also go over the advantages and drawbacks of the procedure.

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