FINE GRINDING TECHNIQUE & TECHNOLOGY Ø 810

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Jessie Marshall
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1 FINE GRINDING TECHNIQUE & TECHNOLOGY 7 3 Ø 80

e Grinding: a cost efficient process e Grinding: D & CBN superabrasives e grinding, also known as flat honing, refers to a type of high accuracy grinding operation meant to achieve micron and

2 e Grinding: a cost efficient process e Grinding: D & CBN superabrasives e grinding, also known as flat honing, refers to a type of high accuracy grinding operation meant to achieve micron and submicron flatness and parallelism. The true lapping nature of the process allow surface finishes of equally low values. Advanced machining techniques are carried out on vertical grinders, single-sided or double sided, fitted with segmented or pellet type wheels made out of Diamond or CBN superabrasives. Wheel design can take several forms suitable to grant the highest coverage along with the maximum cutting ability. Nevertheless segments or pellets, glued on supporting cast iron or aluminum blanks, are arranged in arrays or pattern to bear securely the workpieces so much as to prevent them from sticking into the gaps, slots or holes. The main bonding systems of the wheels are vitrified or resin; metal bonds are very seldom used. The stock removal is controlled by the pressure exerted from the upper wheel which is fed downwards, pneumatically or hydraulically or even by mechanical servofeed, at a constant rate. A key factor is the maximum load per cm2 the machine structure is able to stand up to: it is of paramount importance to determine how many parts each load are viable to be ground. The basic analysis to qualify for the feasibility is the height to bearing surface ratio which should not exceed :, and only in few cases 2 : is possible. Despite the relatively low material removal rate (though in compliance with GD&T and roughness required), it is a highly efficient and fast operation. As a matter of fact several parts are machined altogether each load, with a toothed carrier to hold em in between the wheels and to accommodate workpieces at the right position. The carriers are rotating on an outer pin rim which must be lowered to mount loading and unloading attachments. The lower and upper wheels are driven simultaneously by separate motor spindles. Speed and direction of rotation can be set alone as required. The pressure exerted, in conjunction with the relative speed between wheels and carriers it affects the process and results comes accordingly. The kinematics parameters makes the workpieces move along path curves which are stretched or interlaced hypocycloids or epicycloids. Superabrasives like Diamond and CBN suit the purpose perfectly. Their free-cutting, hard and blocky sharp edges make them the best match to develop low cutting forces, thus being able of high material removal at low wear rate. To a lesser extent, superabrasives have a particularly strong likeness for fine grinding: they offer endless reliability and repeatability, effective size control and dimensional stability and, finally, dramatic savings in idle time. To fine tune the process, a correct grit size choice is the easiest way to cope with increasingly demanding expectations. FEPA FEPA 30/40 22/36 20/30 2/22 Macro grit size mesh 20/40 39/07 40/70 6/90 70/200 97/75 200/230 85/65 230/270 75/57 270/335 65/49 325/400 57/4 Micro grit size mesh 40/30 36/22 30/20 22/2 Pre-ground Pre-ground Pre-ground The concentration it influences the service life of the abrasive tool, the stock removal rate, the grit retention, the shape and profile stability, the surface finish and, last but not least, the price. It resembles the amount of abrasive per unit of volume (expressed in carats per cm3) contained into the layer of the disposable rim. Because of the difference in density between Diamond (3,5 g/ cm3) and CBN (3,48 g/ cm3) the volume occupied can vary significantly at the highest concentration Concentration Diamond 2,5% 2,8% 25% 3,25% 37% 43,8% 50% 2,2 3,3 4,4 5,5 6,6 7,7 8,8 2,09 3,3 4,8 5,22 6,26 7,3 8,35 CBN 2% 8% 24% 30% 36% 40% 46%

e Grinding: the devil s in the details e Grinding: segments and pellets Details are sometimes underrated, but as the idiom says, if carefully set, can become important components of a larger task.

3 e Grinding: the devil s in the details e Grinding: segments and pellets Details are sometimes underrated, but as the idiom says, if carefully set, can become important components of a larger task. Neat oil is the preferred fluid in fine grinding (or deionised water with rust inhibitor for ceramics), delivered through bore circles drilled both in the blank as well as in the abrasive. The basic role of the cutting fluid is to control the heat, which develops due to friction in the machining area, and at the same time to flush away polluted waste (chip and abrasive). To accomplish these tasks the oil must flow through the circuitry piping evenly and uninterrupted, moreover coolant temperature must be controlled by chillers. The first aspect has two more faucets: oil flooding may lead to acquaplaning and, secondly, the opposite i.e. shortage, could cause untimely wear and/or burnings on the workpieces. Drainage is carried out by centrifugal forces and the filtering stage must be as accurate as possible to prevent dirt from entering into the hot area and thus worsen the surface roughness. Dressing and conditioning are, among others, crucial for wear correction as well as for tool life. It affects wheels performance as it cleans out the active abrasive layer, exposing freshly points eager to cut. Tip: a heavy dressing pressure is often times much better than a long smooth cycle which makes every single grain dull in return. A convenient approach would mean to be aware of how an accurate pre-machining is essential to make the most out of your process. Stock must be kept as even as possible; workpieces should be screened into selected dimensional ranges. This sharpens the allowance within strictly comparable classes. Since dressing is a time consuming process, the utmost care should be taken for premature wheel wear. To get the best output at the cheapest cost per part, reduced wheel wear each load is paramount, if out of control size-capability is due to poor pre-machining management, costs grow higher for unwanted precious abrasive rim loss. So expand your economic vision to the whole work-flow, it will pay you off. Round Square Hexagonal Segments Segments allow a 00% coverage which entwines flawlessly with the smallest workpieces ever. Square pellets are the cheapest, while hexagonals are universally known for their flexibility and are the most useful. Round pellets account for different sections to be used on a plate. Apart from those simple shapes as shown above, many others, if it s worth, are derived in order to fit any special requirement. For instance, edge protection in case of automatic loading, is secured juxtaposing rectangular type small pellets. Or rather, for reinforcement of inner and outer overrun, hexagonal pellets can be entwined into a single or in a goldfish tail arrangement. Correspondingly, round pellets can be juxtaposed in the distinctive eight outline. Pellets are patterned on the blanks according to layout whose maths definition correspond to the concept of tasselation or tiling. It s 2 mm not just a matter of shape and dimensions, their distribution too counts. The space between each pellets, known as gap, is of paramount importance. It provides good coolant access and/or drainage along with swarf clearance (notwithstanding it is sometimes necessary to close it in with filler), but each pellet side acts like a cutting edge itself. And again: the gap affects the real abrasive footage, and this has drawbacks on the cutting ability of the wheel. By simply changing the gap size you can make a wheel acts harder or softer, all other parameters preset.

4 Serma: maximize your tooling potential! Technical enquiry Machine Builder: Type: Year: Specification: Workpiece Identification: Drawing No.: Material: Hardness: Dimension: Stock: Pieces per load: Roughness: Parallelism: Flatness: Top Wheel Blank type: Alluminum Cast iron Cement Bottom Wheel Blank type: Alluminum Cast iron Cement Pellet: Dimension: Gap: Round Hexagonal Square Pellet: Dimension: Gap: Round Hexagonal Square grinding wheel outer fixed pin ring toothed carrier inner driving pin ring workpiece

Serma services and extras Serma tooling beyond future Dressing/conditioning tools in Al2O3 (aluminum oxide) & SiC (silicium carbide): are the right match for a kick start with no downtime.

Epoxy resin adhesive for do-it-yourself repairs with original spare parts. Geared carriers cut to customer s specification.

e grinding wheels are the ultimate abrasive tool which complete and expands our product range.

5 Serma services and extras Serma tooling beyond future Dressing/conditioning tools in Al2O3 (aluminum oxide) & SiC (silicium carbide): are the right match for a kick start with no downtime. It s only a good dressing tool combined with a smart strategy that can make the cutting action outlast much longer and extend the tool life to unprecedent limits. Epoxy resin adhesive for do-it-yourself repairs with original spare parts. Geared carriers cut to customer s specification. Consulting and engineering fine grinding process; from wheel design through approval drawing up to final inspection sheet with balancing and straightness report for an easy and smooth mounting. e grinding wheels are the ultimate abrasive tool which complete and expands our product range. It s high time for us to provide our resources and knowledge in advanced high-tech abrasive machining to a worldwide arena and thus give free restrain to our concrete attitude towards innovation. No compromise quality standards and limitless warranty set our goal to superior process solution: no matter we have the privilege of starting from scratch or it is process improvement you re aiming at. We strive to solve individual needs with personal engineering support, therefore sealing a long-term partnership. Roughness chart Ra 0,025 0,05 0,06 0,08 0, 0,2 0,6 0, ,3 0,4 0,5 0,63 0,8,25,6 Rt 0,2 0,4 0,5 0,6 0,8,25,5 2 2,5 3, , ,5 Rz 0,6 0,32 0,38 0,5 0,6 0,75,25,6 2 2,5 3, ,3 8 0 CLA 2 2,4 3,2 4, 5 6, , , Grade N N2 N3 N4 N5 N6 N7

6 Serma case studies Sealing discs with Diamond Material: Al2O3... Hardness 8 Mohs Stock... GD&T Load pcs/load MRR... Cycle time... 0,02 min/part GD&T Bearing rings with CBN Material: 00Cr6... Hardness HRc>60 Stock... GD&T Load... 0 pcs/load MRR... Cycle time... 0,5 min/part GD&T Tappet shims with CBN Material: 00Cr6... Hardness HRc>60 Stock... GD&T Load pcs/load MRR... Cycle time... 0,02 min/part GD&T Gerotor pumps with CBN Material: Sintered St... Hardness HRc>60 Stock... GD&T Load pcs/load MRR... Cycle time... 0, min/part GD&T Serma: committed to high-end solution! Milano Via Persicetana Persicetana Via Persicetana Vecchia ecchia Via a Due Portoni A4 Latitude N Via Marco Emilio Lepido Longitude E Via D Della Salute Salute A4 Via Be Bencivenni Firenze nze 4 Via del Triumvirato 4bis Ancona Content & layout: Roberto Giovannini SERMA S.r.l. Via Due Portoni, Bologna (IT) Tel. +39-(0) Fax. +39-(0) info@sermasrl.it - web:

INTRODUCTION TO GRINDING PROCESS

INTRODUCTION TO GRINDING PROCESS GRINDING PART 2 Grinding Grinding is a material removal process accomplished by abrasive particles that are contained in a bonded grinding wheel rotating at very high surface speeds. The rotating grinding