Honing is a secondary operation employed to improve and/or control the geometric form of a bore, to maintain close size tolerances & surface finish.
A rotating tool, using either a diamond-coated sleeve or stone abrasive, is used to remove metal from inner diametric surface of a part - to achieve closely controlled diameter, circularity, cylindricity & surface roughness.
Longer stroke and variety of type & grit sizes of the abrasives - accord honing the advantage over internal grinding of workpieces with an L/D of 2 or higher.
Single Pass Honing & Multi Pass Honing, are typically the most widely used types across the manufacturing shop-floors today.
Relative to Multi-stroke type, Single Stoke Honing accords a gamut of operational benefits such as faster cycle times, lower cost per component, ease of equipment maintenance, much lesser need of operator skill, and so forth.
Take a quick look at the following videos for a visual understanding of Single Stroke Honing Process. If you already know this, skip to the 'Contents' section.
Eight Spindle Single Pass Honing Machine
[Current version of iHones]
Six Spindle Single Pass Honing Machine
[1st version of iHones - launched over half a decade back]
[Also known as Single Stroke Honing or Diamond Bore Sizing]
Single pass honing, is a high-productivity bore-finishing process, that imparts high-precision form, tight size control and high surface finish consistently and precisely.
The process involves passing a series of tools with pre-set sizes, progressively through the bore, in a single in-and-out stroke.
Either Tool, or Part, or both can be rotating.
The number of tools that are used, depend on (i) Amount of Stock to be removed (ii) Geometrical or Form Tolerances (iii) Surface Finish required and (iv) Material Composition of the work-piece.
Single Pass Honing, is apt for high production rates, ensuring very close bore size & geometric repeatability over a large batch size of order of tens of thousands of parts, reaching as high as 4,00,000~5,00,000 parts in one setting.
Production rates may go as high as 600 parts per hour, being a function of Bore size & Length.
Conventional Honing is done by a tool that expands and contracts as the tool reciprocates in the bore during the honing cycle. Simultaneous radial and axial movements of the Tool, make it difficult to precisely and consistently control the bore size and geometry within shorter ranges of tolerance bands. Although conventional honing does offer excellent bore finishing, batch sizes and bore controllability are limited by the nature of the process.
Insight’s Single Pass Honing Machines, use fixed pre-set sizes of Tools, that have expandable abrasive Sleeve embedded with Diamond or CBN grit. These tools hone the bore in one pass only, removing a certain specific amount of material per Tool. With a set of Tools working on the bore progressively (each tool progressively increasing in size and finer grit size), bore size & geometry are controlled precisely and consistently, over a large batch size.
Since the tool stroke is only once in Single Pass Honing, cycle time achieved is greatly reduced, of order of 40~70% relative to conventional honing, as a function bore size and length.
Single Pass Honing, as a process is an economical process, consuming 40~60% lesser cost per piece, relative to Conventional methods.
The tool, a Single Pass Hone, is a size adjustable 2-piece unit, made of:
(i) An expandable abrasive Sleeve that has embedded Diamond or CBN grit
(ii) A Tapered mandrel / arbor, on which the Sleeve is mounted and affixed
The Sleeve is set to size during the set-up; Once set, further adjustment or movement (as in case of Conventional Honing) is not necessary, during the cutting cycle.
The Sleeve, is diamond impregnated / electro-plated and exhibits the property of high hardness of cutting points, which in-turn accords very slow wear rate of the Sleeve, thereby according large component-batch-sizes in one setting. After a certain batch size, the Sleeve can be expanded (owing to being mounted Tapered mandrel) to compensate the reduced size due to wear, and then again according next batch size, that can go as high as half a million parts.
The Sleeve can be expanded to increase its diameter, to compensate for diamond sleeve wear, over time. The mandrel may contain path-ways for coolant flow into the grooves in the sleeve.
Since Single Pass Honing Tools, are fundamentally diamond reamers, conventional tool holders suffice, be it collet holder, side lock holder, etc. In short, Tool holding is as simple as it gets.
As a function of amount of (i) stock removed per tool (ii) material composition & hardness of the part (iii) bore-size & length, tool life can go as high as 4,00,000~5,00,000 parts. This is further enhanced by super-precision Spindles of Insight’s iHone series of Single Pass Honing Machines, that impart clean and smooth rotation to the Tool, thereby enhancing Tool life expectancy to as high as a million parts. This reinforces a key tangible benefit of low cost of operation and thereby low cost per component through Single Pass Honing process in comparison to Conventional ways of super precision bore finishing.
Insight’s iHone Series of Single Pass Honing Machines, achieve tolerances that are typically in order of 0.0005mm (0.00002in) to 0.002mm (0.00008in) in terms of Bore size repeatability and Cylindricity (Circularity + Straightness). Surface finish typically achieved, is in order of 0.05~0.15 Ra. The process offers consistent SPC, of order of Cpk greater than 2.
iHone’s super precision spindles, meticulously engineered Fixturing and best-in-class build of the machines, definitively guarantee a reliable & consistent process over tens of thousands of cycles, for one setting of Tool size.
Typically Single Pass Honing process, can remove stock of 0.025mm ~ 0.075mm (0.0001in ~ 0.0003in) using three or four progressive tools.
Insight’s iHone series of Single Pass Honing Machines, range from Single Spindle Machines to Twelve Spindle Machines. Stock range that can be removed ranges from 0.01mm ~ 0.2mm (0.00004in ~ 0.008in).
Insight’s iHones, owing to stock-distribution over successive tools, offer rapid cycle times as low as 6 seconds per part, translating to nearly 600 parts per hour. It is important to note through, that the Cycle time is directly proportional to diameter and length of the bore. As an example, a part with bore size of dia. 22mm x 40mm length, removing a total stock of 0.04mm (0.0016in) is being produced at the rate of 10 seconds per part (360 parts per hour), on Insight’s iHone-500-6s, a CNC Six Spindle Single Pass Honing Machine.
Insight’s iHone series, is built to keep operator skill level to zero. Axes & Spindle interlocks are comprehensively integrated into machine controls, to eliminate unintended mismanagement of operational parameters.
Insight’s Automation division offers fully automated systems (Robotic or Pick & Place) that include Auto Load/Unload, Pre-honing component gauging & Post-honing final quality check, effectively ensuring end-to-end no-skill operation of the machine or the production line.
CNC system, Servo Z-axis and Spindles with speed variability, offer complete flexibility in setting or changing the parameters at the click of a few buttons. Further tweaking is also possible by use of standard CNC programs (G-codes & M-codes), wherein hundreds of programs can be prepared and kept ready for quick change-over.
Indexer axis being Servo-controlled precise Rotary Table, any indexing configurations and position set-points are possible.
iHone’s standard Spindles and easy to change Fixturing on the 4th Axis indexer, offer flexibility of change of Tools and Fixtures, effectively making it a standard General Purpose Machine.
Single pass honing process can be tailored to meet the requirements of a verity of applications, to achieve different results.
For example, whilst certain applications may require very critical bore geometry and allow longer cycle times; others may call for less critical geometry, but require a higher production rate at the lowest possible cost per piece.
Insight’s Machine building division, Tooling division & Automation division, accord a single source of build of entire system, end-to-end, effectively enhancing productivity, quality consistency, and thereby reduce overall ownership cost of the system.