Surface Grinding

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Saturday, April 22, 2023

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SURFACE GRINDING

Surface grinding is used to produce a smooth finish on flat surfaces. It is a widely used abrasive machining process in which a spinning wheel covered in rough particles (grinding wheel) cuts chips of metallic or non-metallic substance from a work piece, making a face of it flat or smooth.


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Work piece is secured on a chuck attached to the worktable of the grinder


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The surface grinder is composed of

abrasive wheel,

a work holding device known as a chuck,

a reciprocating or rotary table.

The chuck holds the material in place while it is being worked on. It can do this one of two ways: magnetic pieces are held in place by a magnetic chuck, while non-magnetic and non-metallic pieces are held in place by vacuum or mechanical means. A machine vise placed on the magnetic chuck can be used to hold non-ferromagnetic work pieces if only a magnetic chuck is available.

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TYPES OF SURFACE GRINDING

• RECIPROCATING GRINDING• CREEP FEED GRINDING• HIGH SPPED GRINDING


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RECIPROCATING GRINDING

reciprocating grinding is a peripheral longitudinal grinding process with a back-and-forth feed motion, in which the feed motion takes place gradually in small steps with a relatively high feed rate.

Reciprocating grinding is used for generating plain surfaces of usually large lateral dimensions. The grinding spindle is parallel to the work piece surface to be machined, the work piece material being cut mainly with the circumferential side of the grinding wheel. The grinding wheel is fed orthogonally to the work piece surface


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Specific Removal RateThe specific material removal rate for reciprocating grinding is calculated from the product of infeed a and feed rate v: Q ′ = ⋅av

Non-productive Timedepends on table speed and acceleration and the non grinding time can be because of the grinding wheel running beyond the work piece, and also because of the reversing table motion.


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• contact length between work piece and wheel is small and the grinding forces are relatively small. There are only a few cutting edges engaged at the sametime

• Increasing the feed rate results in higher average chip thickness and length,and thus in an increase of grinding forces and thermal stress.

• In feed and feed rate (work speed) crucially determine the total machining time in reciprocating grinding. An increase of in feed increases grinding forces and thermal stress. The work piece surface roughness decreases with a higher number of engaged cutting edges.


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ECONOMICS

Low thermal, static, and dynamic stresses are advantages of reciprocating grinding, in contrast to creep feed grinding.

They allow for a more simple machine design in terms of drive capacity,rigidity, and auxiliary units, thus accounting for lower purchase and operating costs.

The generally high total machining times are a disadvantage for the workpiece, as well as higher surface roughness of the workpiece ,


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CREEP GRINDING

The total grinding stock being cut in one or only a few passes.

In this method, the grinding spindle is parallel to the work piece surface to be machined, the work piece material being mainly cut with the grinding wheel circumferential side. The grinding wheel is fed orthogonally to the work piece surface

creep grinding is usually characterized by in feeds larger than 0.5 mm and feed rates smaller than 40 mm/s


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HIGH-EFFICIENCY DEEP GRINDING

High-performance deep grinding, with increased wheel peripheral speed and increased feed rate, is a special case requiring a cooling lubricant supply system

The advantages of high-speed grinding are higher surface quality, shorter machining times, lower wheel wear, and low grinding forces.


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• Due to the large contact length and large infeed in creep feed grinding, grinding forces tend to be high, which, in turn, lead to high thermal stress in the working zone

• An increase of the specific material removal rate by increasing the infeed or the feedrate involves higher grinding forces and elevated thermal stress due to a higher chip thickness

• The chip thickness and thus the cutting force at the single grain are smaller during creep feed grinding than during reciprocating grinding. Additionally, there are no repeat impact loads on the grinding wheel, so that the abrasive grains can be held longer by the bond matrix before the grains are broken out.


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Higher cutting forces require significantly higher static and dynamic rigidity and higher drive performance of the grinding machine and its ancillary units than necessary in the case of reciprocating grinding.

The high thermal stress during creep feed grinding does not only represent a high load for tool and grinding machine, but also damages the workpiece material causing cracks and structural changes.

In creep feed grinding, surface roughnesses are much smaller due to the engagement of a higher number of cutting edges and due to smaller feedrates than in the case of reciprocating grinding.


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ECONOMICS OF CREEP FEED GRINDING

• Lower grinding times and high achievable surface quality with a high removal rate argue for creep feed grinding in contrast to reciprocating grinding

• High process temperatures and large contact lengths require cooling lubricant pumps with increased volume flow and pressure, adapted cooling lubricant nozzles

• High-dimensional accuracy and high forces require high-precision and rigid bearings and guidance, shock-free and precise drives.

• High concentricity and adjustable grinding wheel topography require integrated auxiliary conditioning equipment for diamond grinding wheels


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SPEED-STROKE GRINDING

An innovation of surface grinding driven by the Japanese in the 1980s is a process called Speed Stroke Grinding that involves very high table speeds of 50 to 100 m/min and shallow depth of cuts of the order of 1 µm or less

Offers the ability to remove stock faster and with lower forces and less risk of burn, but roughness will be higher and compensation must be made in bond/gritstrength for increased force/grit


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FACE GRINDING

• Face grinding is surface grinding using the face of a grinding wheel.

• These include segment grinding, double- and single-disc grinding, and double- and single-sided fine grinding


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Surface grinding segments are generally used to grind flat stock or flat surfaces within a workpiece. The segment moves over the workpiece in a flat plane or vice versa. Applications can vary from heavy, rapid stock removal to precision tolerance operations.


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vertical and horizontal double disc grinding machines and single disc grinding machines is available

Double disc grinding is an abrasive machining process that removes material from two sides of a part simultaneously. In a typical double disc grinding machine, the grinding discs are side-mounted on a pair of opposed spindles. Because the process grinds both sides at the same time, it offers a high degree of accuracy and parallelism and reduces stress on the part. The process is suitable for a wide range of materials, including stainless steel, sintered metal parts and high-strength alloys.


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Date post:	29-Jan-2016
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Surface Grinding

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