In manufacturing, producing a perfect part is not just about creating the correct shape; it’s about producing a perfect surface. Consider a car’s engine cylinder, for example.
It needs to be extremely smooth, but it also needs to have a specific texture that holds oil, allowing the engine to run for thousands of miles. How do manufacturers achieve this level of detail? The answer usually lies in a machining process by the name of honing.
It’s a finishing touch that transforms a part from good to great, allowing everything from hydraulic cylinders to gun barrels to perform as expected. It’s the magic behind the dependability and lifespan of many of the high-performance components we utilize every day.
In this article, we will focus on and explain the fun world of the honing process. We will define honing, discuss its value, and explain the steps and functionalities of the honing process, as well as list the tools of honing tools and discuss their applications in many different environments.
What is Honing in Manufacturing?
So, what is honing in business? Put simply, honing is an abrasive machining process that produces a precision surface on a metal workpiece. The honing process is specialized for the geometric form of a surface; however, its most notable attribute is the fantastic surface finish it leaves behind.
Unlike grinding, which generally uses a single high-speed rotating wheel to process the workpiece, honing machining uses a specialized honing tool that rotates and strokes. This equipment is equipped with small abrasive stones (often called a honing stone).
Honing processes change the inside features of a hole or bore. Honing is considered a finishing process because it is done after other machining processes (such as drilling or boring) have created the hole. Honing takes a small amount of material off the part to geometrically fix a bore for problems like out-of-round, waviness, or taper.
The honing process leaves a cylindrical surface geometry with amazing precision and cylindrical surface finish – a specification of cross-hatch patterns is required and very important for honing performance.
Why Use Honing for Machined Parts?
With the many finishing combinations available to an engineer or designer, it is questioned why honing is chosen as a finishing process over many others that can be done? The answer is more than just a smooth surface. Honing has a unique combination of fine precision, versatility, and efficiency for several very important applications.
Accuracy
For the honing process, the most obvious answer for the process is for high accuracy. The previous machining steps may have left some subtle bore shape or surface imperfections.
The honing process will correct the bore, i.e., round and straight for their length, with both size control (the honing process is capable of low tolerances +-.00025), and corrective action in the bore geometry is very important for parts that have to create a proper seal or close clearances, such as hydraulic parts.
Versatility & Compatibility
The honing process is incredibly useful and versatile! It can be applied to a wide range of materials, from hard metals like steel and cast iron to softer metals like aluminum and brass.
The abrasive material on the honing stone can be specific to the material of the workpiece. In addition, honing operations can be conducted on bores with almost any diameter and length, and on anything from tiny fuel injector nozzles to large industrial cylinders.
Faster and More Efficient Production
Honing is inherently a precision process, but it can also be very efficient. Many new honing machines – particularly fully automated machines – can achieve the desired surface finish and dimension through honing more quicker than with other types of finishing, such as lapping.
Specialized production finishing systems can be set up to hone multiple parts with very little operator input, producing parts with a shorter cycle time and lower costs per part.
Keeping Safety in Mind
As compared to high-speed grinding, honing is low-speed and low-pressure. The process generates much less heat, which is extremely helpful. Without going down a huge rabbit hole: heat is an enemy, and excessive heat can damage the surface of the metal (altering its properties), and in some cases, lead to micro-fissuring of the surface.
Honing allows operators to achieve a low enough temperature that the integrity of the workpiece material is retained. This ensures the final surface finish is smooth, while being stronger and more durable.
How Does Honing Machining Work?
What makes the honing process unique is the combination of movements. While honing may seem like a complicated process, it is simply a sequencing of easy steps that, when followed properly, will produce a great surface.
Mounting the Workpiece
The first step is to securely mount the workpiece to be honed in the honing machine. The workpiece must not move at all while the honing is carried out when correcting the bore geometry.
Inserting the Honing Tool
The honing tool (a mandrel with one or more honing stones mounted to it) is inserted into the bore with the stones pulled back.
Honing Motion
The machine is turned on, and at a slow rotational speed, the honing tool begins to rotate and reciprocate (back and forth) over the length of the bore. This special motion is the key advantage of honing over all other manufacturing processes.
Expanding the Stones
As the tool is showing motion, the honing stones are forced outward against the bore surface in their full length with controlled pressure, causing very tiny and sharp abrasive particles on the honing stones to start shearing off microscopic amounts of material.
Creating the Cross-Hatch
As the rotating and reciprocating honing tool works its way through the bore, the paths traced by the abrasive particles create an apparent pattern of fine scratches across the surface, or the iconic cross-hatch pattern so often referenced in honing.
Final Sizing and Finishing
The honing continues until the bore achieves the final diameter and the final portion of surface finish is achieved. Once the bore is complete, the stones are retracted, the tooling is removed, and the part is cleaned to remove any residual abrasives and ferrous metal particles.
Typical tools used in the Honing Process
The honing process relies on the use of a variety of specialized tools and materials that are selected to produce a precise machining outcome. For honing to take place, each tool is vital to the overall process- to the abrasive honing stones, which, by cutting action, produce the honing, or the fixtures used to hold the part still.
Honing Stones
The honing stone is the heart of the honing process. The honing stone is a small rectangular block of material that is made from abrasive material (abrasive grains) held together with some type of bonding agent.
The honing stones are mounted to a mandrel or tool holder. The shape, size, and grade of the honing stone are selected to suit the workpiece (material) being honed and the surface finish being pursued.
Abrasives
The honing process removes material through the cutting action of the abrasive materials. The abrasives selected for the operation must be well-made. Typical abrasives used in honing include silicon carbide when honing cast iron or non-ferrous metals.
If the workpiece material is harder, such as hardened steel or ceramics, special abrasives known as superabrasives are utilized. These can include diamond or cubic boron nitride (CBN).
The size of the abrasive grains is also important—the coarseness of the grain can impact the cutting action the tool has on the workpiece. Coarse grains cut material much faster, while finer grains are only used for the final smooth surface.
Coolant and Lubricant
The axial force used in the honing operation and typically requires a typical flow of a specialized liquid to be directed at the workpiece. This is a dual-purpose liquid, acting as a coolant to cool the part and protect the surface, and a lubricant to smoothly allow the stones to travel along the surface, flushing away the tiny metal chips and broken down abrasives and leaving a clean cut.
Fixtures and Work Holding Devices
In order to achieve high precision, the workpiece needs to be held absolutely still in space. Fixtures are custom-made devices that clamp the part securely and accurately in the intended orientation. Fixtures allow the honing tool(s) to get to the bore exactly, ensuring good surface geometry or dimensional accuracy.
Dressers and Truing Tools
Over literally thousands of parts and potentially many years, the honing stones can become clogged with metal or the stones can wear unevenly. Dressers and truing tools will sharpen and reshape the stones. The dresser breaks off the bonding material, disclosing new, sharp abrasive grains, bringing the stone to a cutting condition and the same surface quality throughout the stone.
Applications of Honing in Different Industries
Because honing can provide incredibly high precision and functional surfaces, the honing process is used in most industries where performance must meet prevailing safety requirements. Below are a few examples of how you may encounter honed surfaces in industry.
Automotive Industry
The most classic example of honing. The inside cylinder walls of an engine block have to be honed to a specific cross-hatch pattern. The cross-hatch pattern is needed to hold a thin layer of oil to lubricate the piston rings as they move up and down millions of times until the next routine service or end of use. An engine would wear out very quickly without a specific surface.
Aerospace Industry
In aerospace, safety and reliability are most critical. Honing is used to manufacture critical high-accuracy tolerances. This includes the bores of hydraulic components for landing gear and flight control systems, as well as parts for jet engines. The accuracy of honing allows those parts to perform at extreme pressures, tolerances, and temperatures.
Mold Making
When manufacturing plastic parts, the quality of the mold is everything. Most likely, the inside surfaces of injection molds are honed to a nearly mirror finish. There are good scientific reasons that injection-molded parts come out with a perfect finish, are easily released from their mold, and have a polished, imperturbable, uninterrupted finish without defects.
Medical Industry
The medical field requires instruments and implants made with the utmost precision. Honing is not even that common, but we have it, for example, in the finishing of surgical instruments, orthopedic implants, such as artificial joints, and for precision medical pump bores.
The honed surfaces are extremely smooth and clean, making them easy to sterilize; in the case of implants or surgical instruments, it is vital that they exist in a precise, functioning surface finish for them to work properly.
Conclusion
The honing process is not just a final operation. It is a machining process that can demonstrate the highest level of performance and precision.
Honing corrects the geometry of the bore and applies a custom surface finish that provides the part reliability under extraordinary stress. Besides that, it also provides a perfect seal, and continues to be functional far into the future.
From your car’s engine to an airplane’s landing gears, evidence of this careful process is everywhere. It’s a process that silently does its bit to improve the safety and reliability of our world.
It’s a perfect combination of power and delicacy, removing microscopic amounts of material to obtain a colossal gain in function.
FAQs
Q: How much stock can be removed through honing?
A: Honing usually removes very little stock, given that it is a finishing process. Honing is typically used to remove stock in the range of 0.02mm to 0.25mm in diameter from a bore, although the amount depends on the intended use of the bore and its original condition.
Q: What do you mean by honing?
A: Honing is an abrasive machining process that uses a honing tool with abrasive stones to produce a very accurate surface finish in the inside of a bore, altering the diameter and geometry of the bore while leaving a characteristic cross-hatch pattern on the operative surface.
Q: What does honing product mean?
A: Honing Product is any commodity that has completed the honing process. It could be an engine cylinder, hydraulic cylinder, gear, or any other component, or the finished internal surface has undergone honing to produce very high accuracy while adopting a surface structure of some sort.
Q: What is the honing method?
A:The honing method uses a unique tool to both rotate and alternatively reciprocate or oscillate in a bore. During honing, the abrasive stones will expand against the operating surface to remove a small amount of material to improve the bore geometry and create a specific surface finish.