The honing process is a micro-finishing process used to obtain perfect hole geometry. Industries today see the great importance of honing machines as the process offers final sizing and creates the desired finish pattern on the interior of tubing or cylinder bores.
This process may be considered a machining process because the removal of microchips occurs. The honing process uses a tool called honing stone to perform its operation. Today you’ll get to know the definition, function, applications, operations, components, types, diagram, and working of honing as an industrial process. You’ll also get to know the advantages and disadvantages of this process as well as the difference between honing and lapping.
What is honing?
Honing is a process developed to make the perfection of bore geometry, size control, surface structuring, and final surface finish. The honing process offers final sizing and produces the desired finish pattern on the interior of tubing or cylinder bores.
The term “honing” was developed from the word “hone”. It is an abrasive method used for finishing previously machined surfaces like drilled or bored holes. The tool used for the process is called a hone or honing stone. It is a bonded abrasive stone used for the correction or modification of diameter, surface finish, shape, and positional tolerances of bores.
Honing is a low-velocity abrading process, that is, the removal of material is accomplished at lower cutting speeds. Therefore, heat and pressure are reduced, resulting in excellent size and geometry control. It has the capacity of machining holes to within less than 0.001 in. in diameter and keeps true roundness and straightness with finishes less than 20(mu) in. This is one of the most difficult operations in manufacturing.
However, finish boring or internal grinding may perform this task, but spindle deflection, variation in the harness of the material, and difficulties in precise work-holding make the result unperfect and slow the work. Honing, on the other hand, uses rectangular grinding stones rather than circular grinding wheels to eliminate these irregularities.
The honing process can consistently produce finishes as fine as 4μ in. Finer finishes are even possible because they can remove as little as 0.0001 in. of stock and as much as 0.125 in. of stock. Although 0.002 in. to 0.020 in. stock is usually left on the diameter for honing.
Applications of the honing process
The primary function of the honing process is for achieving accurate dimensions of cylindrical holes. It is ideal for finishing the internal surfaces of I.C. engine cylinders, hydraulic cylinders, and other cylinders where retention of lubricant film over the surface is necessary.
Applications of honing in industries include automotive, aerospace, oil and gas, aviation, agricultural engineering, etc. The honing process is used in the production of the following parts:
- Hydraulic valves
- Fuel injectors
- Cartridge valves
- Connecting rod
- Crankshafts journals
- Engine blocks
- Gun barrels
- Round holes, etc.
Read more: Working principles of CNC machines
The function of honing as a cost-effective machining method includes:
- Bore tolerance
- Stock removing
- Generating exacting
- Bore polishing
- Finishing bores of almost all material including CGI, ceramics, sprayed coatings, etc.
Components of honing machine
The various parts of honing are mentioned below in the diagram and they are explained in the working principle.
Diagram of honing machine:
Honing machine operations
The honing machine has the capacity of performing three major tasks in includes:
- Stock removal
- A finish pattern is produced to offer the best possible surface for promoting optimum lubricating conditions.
- It ensures extremely accurate straightness, roundness, and size of a cylindrical surface.
Read more: Hot and Cold Rolling Process
Types of honing machine
Below are the two types of honing.
The manual types of honing are rarely used nowadays. In its working, the hone continuously rotates and the workpiece is moved front and back manually.
In machine types of honing, the hone combines both rotary and reciprocating motion and there is less manual interaction. Machine honing is further classified into two types.
Horizontal spindle machine:
The horizontal-spindle honing machine is one of the most used. It rotates the hone from 100 to 250 fpm. The operator moves the work back and forth (to stroke it) over the rotating hone. The operator must float the work, that is, not press it against the hone or the hole will be slightly oval. In some cases, the workpiece must be rotated. Horizontal-spindle honing machines are made with power stroking.
Vertical spindle machine:
The type honing machine is specially designed for heavier and larger work. It has power stroking at speeds from 20 to 120fpm. The length of the stroke is also machine-controlled by stops set up by the operator. Vertical honing machines are made with multiple spindles which allow several holes to be machined at once.
Just as earlier stated, the honing stone is a tool used in honing operations, consisting of various abrasive grains. The size of the grains differs depending on the desired surface texture. For example, for a rough surface texture, a low-grit honing stone may be used. And for a smooth surface texture, a high-grit honing stone should be used.
Nevertheless, all honing operations must make use of a honing stone. since honing stones are made from many small grains bound together, the tool is somewhat friable and susceptible to breaking. Therefore, it is often treated with wax so that its lifespan can be increased.
The hone body is made in several styles using a single stone for small holes, and two to eight stones as the size get larger. These honing stones are available in different sizes and shapes. A cutting fluid must be included in the honing process for several purposes. Fluid will help to clean the small chips from the stones and the workpiece. It will also cool the work and hone, and also lubricate the cutting action.
Working principle of the honing process
The work of honing is less complex and can be easily understood. The process is accomplished by expanding abrasive stones of suitable grit and grade against the work surface. The stones are rotated and reciprocated in the workpiece with the hone abrasive under controlled pressure and velocity. A cross-hatch pattern is produced on the surface of the part when rotation and reciprocation movement is combined.
This abrasive stone is used in the form of sticks, mounted on the mandrel. Although some other materials like diamond and carbon boron nitride, aluminum oxide, and silicon carbide grit are used nowadays. In fact, they can accomplish the operation in just one stroke. These grains are bonded in resinoid or vitrified bonds to form the honing stone.
The honing stone is forced away by mechanical or hydraulic pressure against the surface of the bore. The stone moves back and forth, typically at a slow rate of speed to remove material from the workpiece’s surface.
Watch the video below to learn more about the working honing process:
Advantages and disadvantages of the honing process
Below are the benefits of honing process in their various applications:
- The process is highly accurate.
- It is less complex
- Both long and short bores can be processed.
- Regardless of hardness, any material can be finished.
- It maintains the original bore centerline.
- The workpiece does not require rotation by power.
- The central shaft is used to drive the hone, which causes tapered holes to be eliminated.
Despite the good benefits of honing the process, some limitations still occur. Below are a few disadvantages of honing in their various applications:
- It is a slow process, though new machines and stones have reduced the time rate.
- Oval holes might be created if work is not rotated or supported.
- The initial machine cost is high.
Difference between honing and lapping
The difference between honing and lapping can be discovered in their final applications. Though honing and lapping are similar in some aspects like working on low velocity, improving the surface texture of working, and working at precision. They are both used for the final finishing process.
The difference between honing and lapping is that honing is used for tubing and cylindrical surfaces whereas, lapping is used on flat surfaces.
Honing is a machining process that helps to obtain perfect bore geometry, size control, surface structuring, and final surface finish. The process allows final sizing and produces the desired finish pattern on the interior of tubing or cylinders. That is all for this post where we give the definition, function, applications, components, diagram, types, and working of the honing process. We also explain the advantages and disadvantages of the process.
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