PowerPoint Presentation

GRINDING MACHINE

What Is Grinding Machine?Thegrinding machine (often shortened togrinder),is amachine toolused for grinding, which is a type ofmachiningusing anwheel as thecutting tool. Each grain of abrasive on the wheel's surface cuts a smallchipfrom the work piece via shear deformation. The grinding machine consists of a power driven grinding wheel spinning at the required speed (which is determined by the wheels diameter andmanufacturers rating, usually by a formula) and a bed with a fixture to guide and hold the work-piece. The grinding head can be controlled to travel across a fixed work piece or the work piece can be moved whilst the grind head stays in a fixed position. Very fine control of the grinding head or table position is possible using a vernier calibrated hand wheel, or using the features of numerical controls. Grinding machines remove material from the work piece by abrasion, which can generate substantial amounts of heat; they therefore incorporate a coolant to cool the work piece so that it does not overheat and go outside its tolerance. The coolant also benefits the machinist as the heat generated may cause burns in some cases. In very high-precision grinding machines (most cylindrical and surface grinders) the final grinding stages are usually set up so that they remove about 200nm (less than 1/100000 in) per pass - this generates so little heat that even with no coolant, the temperature rise is negligibleWhy And When Do We Need To Used It?Grinding is the process of removing metal by the application of abrasives which are bonded to form a rotating wheel. When the moving abrasive particles contact the work piece, they act as tiny cutting tools, each particle cutting a tiny chip from the work piece. It is a common error to believe that grinding abrasive wheels remove material by a rubbing action; actually, the process is as much a cutting action as drilling, milling, and lathe turning. The grinding machine supports and rotates the grinding abrasive wheel and often supports and positions the work piece in proper relation to the wheel. The grinding machine is used for roughing and finishing flat, cylindrical, and conical surfaces; finishing internal cylinders or bores; forming and sharpening cutting tools; snagging or removing rough projections from castings and stampings; and cleaning, polishing, and buffing surfaces. Once strictly a finishing machine, modem production grinding machines are used for complete roughing and finishing of certain classes of work.

How Is The Grinding Process Work?Different types of grinding machine have different kinds of process work:Internal grinding, is used to grind the internal diameter of the work piece. Tapered holes can be ground with the use of internal grinders that can swivel on the horizontal.Pre-grinding, When a new tool has been built and has been heat-treated, it is pre-ground before welding or hard facing commences. This usually involves grinding the OD slightly higher than the finish grind OD to ensure the correct finish size.Center less grinding, is when the work piece is supported by a blade instead of by centers or chucks. Two wheels are used. The larger one is used to grind the surface of the work piece and the smaller wheel is used to regulate the axial movement of the work piece. Types of center less grinding include through-feed grinding, in-feed/plunge grinding, and internal center less grinding.

Electrochemical grinding, is a type of grinding in which a positively charged work piece in a conductive fluid is eroded by a negatively charged grinding wheel. The pieces from the work piece are dissolved into the conductive fluid.Surface grinding, is the most common of the grinding operations. It is a finishing process that uses a rotating abrasive wheel to smooth the flat surface of metallic or nonmetallic materials to give them a more refined look or to attain a desired surface for a functional purpose. The surface grinder is composed of an abrasive wheel, a work holding device known as a chuck, and a reciprocating table. The chuck holds the material in place while it is being worked on. It can do this one of two ways: metallic pieces are held in place by a magnetic chuck, while nonmetallic pieces are vacuumed in place. Cylindrical grinding, (also called center-type grinding) is used in the removing the cylindrical surfaces and shoulders of the work piece. The work piece is mounted and rotated by a work piece holder, also known as a grinding dog or center driver. Both the tool and the work piece are rotated by separate motors and at different speeds. The axes of rotation tool can be adjusted to produce a variety of shapes. The five types of cylindrical grinding are: outside diameter (OD) grinding, inside diameter (ID) grinding, plunge grinding, creep feed grinding, and centerless grinding. A cylindrical grinder has a grinding (abrasive) wheel, two centers that hold the work piece, and a chuck, grinding dog, or other mechanism to drive the machine. Most cylindrical grinding machines include a swivel to allow for the forming oftapered pieces. The wheel and work piece move parallel to one another in both the radial and longitudinal directions. The abrasive wheel can have many shapes. Standard disk shaped wheels can be used to create a tapered or straight work piece geometry while formed wheels are used to create a shaped work piece. The process using a formed wheel creates less vibration than using a regular disk shaped wheel. Tolerances for cylindrical grinding are held within five ten-thousandths of an inch(+/- 0.0005) for diameter and one ten-thousandth of an inch (+/- 0.0001) for roundness. Precision work can reach tolerances as high as five hundred-thousandths of an inch (+/- 0.00005) for diameter and one hundred-thousandth of an inch (+/-0.00001) for roundness. Surface finishes can range from 2 to 125 micro inches, with typical finishes ranging from 8-32 micro inches.

Creep-feed grinding (CFG), was invented in Germany in the late 1950s by Edmund and Gerhard Lang. Unlike normal grinding, which is used primarily to finish surfaces, CFG is used for high rates of material removal, competing with milling and turning as a manufacturing process choice. Depths of cut of up to 6 mm (0.25) inches are used along with low work piece speed. Surfaces with a softer-grade resin bond are used to keep work piece temperature low and an improved surface finish up to 1.6micrometres R max. With CFG it takes 117 sec to remove 1 in.3 of material, whereas precision grinding would take more than 200 sec to do the same. CFG has the disadvantage of a wheel that is constantly degrading, and requires high spindle power, 51 hp (38 kW), and is limited in the length of part it can machine. To address the problem of wheel sharpness, continuous-dress creep-feed grinding (CDCF) was developed in the 1970s. It dresses the wheel constantly during machining, keeping it in a state of specified sharpness. It takes only 17 sec. to remove1 in3 of material, a huge gain in productivity. 38 hp (28 kW) spindle power is required, and runs at low to conventional spindle speeds. The limit on part length was erased.Form grinding, is a specialized type of cylindrical grinding where the grinding wheel has the exact shape of the final product. The grinding wheel does not traverse the work piece.Type Of Grinding Machine The grinding machines are divide into:Belt grinder, which is usually used as a machining method to process metals and other materials, with the aid of coated abrasives. Sanding is the machining of wood; grinding is the common name for machining metals. Belt grinding is a versatile process suitable for all kind of applications like finishing, deburring, andstock removal.Bench grinder, which usually has two wheels of different grain sizes for roughing and finishing operations and is secured to a workbench or floor stand. Its uses include shaping tool bits or various tools that need to be made or repaired. Bench grinders are manually operated.Cylindrical grinder, which includes both the types that usecentersand thecenter lesstypes. A cylindrical grinder may have multiple grinding wheels. The work piece is rotated and fed past the wheel(s) to form a cylinder. It is used to make precision rods, tubes, bearing races, bushings, and many other parts.Tool and cutter grinder and theD-bit grinder.These usually can perform the minor function of thedrill bitgrinder, or other specialist tool roomgrinding operations.

Surface grinder,which includes thewash grinder.A surface grinder has a "head" which is lowered, and the work piece is moved back and forth past the grinding wheel on a table that has a permanent magnet for use with magnetic stock. Surface grinders can be manually operated or have CNC controls. Rotary surface grinders or commonly known as "Blanchard" style grinders, the grinding head rotates and the table usually magnetic but can be vacuum or fixture, rotates in the opposite direction, this type machine removes large amounts of material and grinds flat surfaces with noted spiral grind marks. Used to make and sharpen; burn-outs, metal stamping die sets, flat shear blades, fixture bases or any flat and parallel surfaces.Jig grinder, which as the name implies, has a variety of uses when finishing jigs, dies, and fixtures. Its primary function is in the realm of grinding holes and pins. It can also be used for complex surface grinding to finish work started on a mill.Gear grinder, which is usually employed as the final machining process when manufacturing a high-precision gear. The primary function of these machines is to remove the remaining few thousandths of an inch of material left by other manufacturing methods (such as gashing or hobbing).

Machine Parts And Functions

Grinding Wheel MaterialsAluminum Oxide (A), Silicon Carbide (C), Diamond (D, MD, SD) and Cubic Boron Nitride (B)2.

Available Wheel ShapesStraight wheel (Types1) Straight wheel are the most common style of wheel and can be found on bench or pedestal grinders. They are used on the periphery only and therefore produce a slightly concave surface (hollow ground) on the part. This can be used to advantage on many tools such as chisels. Straight wheels are the kind of generally used for cylindrical, centreless, and surface grinding operations. Wheels of this form vary greatly in size, the diameter and width of face naturally depending upon the class of work for which is used and the size and power of the grinding machine.Cylinder or wheel ring (Types2) Cylinder wheels provide a long, wide surface with no center mounting support (hollow). They can be very large, up to 12" in width. They are used only in vertical or horizontal spindle grinders. Cylinder or wheel ring is used for producing flat surfaces, the grinding being done with the end face of the wheel.Straight cup (Types6) Straight cup wheels are an alternative to cup wheels in tool and cutter grinders, where having an additional radial grinding surface is beneficial.

Tapered wheelTapered wheel is a straight wheel that is tapered outward towards the center of the wheel. This arrangement is stronger than straight wheels and can accept higher lateral loads. Tapered face straight wheel is primarily used for grinding thread, gear teeth etc.Dish cup (Types12) Disk cup is a very shallow cup-style grinding wheel. The thinness allows grinding in slots and crevices. It is used primarily in cutter grinding and jig grinding.Saucer wheel (Types13) Saucer wheel is a special grinding profile that is used to grind milling cutters and twist drills. It is most common in non-machining areas, as saw filers use saucer wheels in the maintenance of saw blades.Diamond wheel Diamond wheels are grinding wheels with industrial diamonds bonded to the periphery. They are used for grinding extremely hard materials such as carbide cutting tips, gemstones or concrete. The saw pictured to the right is a slitting saw and is designed for slicing hard materials, typically gemstones.Diamond mandrelsDiamond mandrels are very similar to their counterpart, a diamond wheel. They are tiny diamond rasps for use in a jig grinder doing profiling work in hard material.Cut off wheelsCut off wheels, also known as parting wheel, are self-sharpening wheels that are thin in width and often have radial fiber reinforcing them. They are often used in the construction industry for cutting reinforcement bars (rebar), protruding bolts or anything that needs quick removal or trimming. Most handymen would recognize an angle grinder and the discs they use.

Others types of wheel shapes available is as following:

Criteria Of The WheelsGrain size, from 8 (coarsest) 600 (finest), determines the physical size of the abrasive grains in the wheel. A larger grain will cut freely, allowing fast cutting but poor surface finish. Ultra-fine grain sizes are for precision finish work.

Wheel grade, from A (soft) to Z (hard), determines how tightly the bond holds the abrasive. Grade affects almost all considerations of grinding, such as wheel speed, coolant flow, maximum and minimum feed rates, and grinding depth.

Grain spacing, or structure, from 1 (densest) to 16 (least dense). Density is the ratio of bond and abrasive to air space. A less-dense wheel will cut freely, and has a large effect on surface finish. It is also able to take a deeper or wider cut with less coolant, as the chip clearance on the wheel is greater.

Wheel bond, how the wheel holds the abrasives, affects finish, coolant, and minimum/maximum wheel speed.Wheel Balancing For satisfactory work, the grinding wheel and its sleeve or mount must be in a reasonably good state of balance. Except for extremely high precision work, the wheel assembly does not need to be in, or corrected to, precise balance. The reason for this is that the well design grinding machine is so rigid that vibrations due to normal wheel imbalance within the close inspection limits are of practically no consequence. Proper design and construction will also have eliminated any possibility of the wheel spindle operating at, or near the resonant or natural frequency of any machine component. While grinding wheels today are held to very close limits with respect to structural uniformity and grade duplication, some manufacturing tolerance, however small, must be observed for grinding wheels, as for any manufactured product, and therefore some imbalance may be present .Besides, even if a wheel conceivably, were in perfect balance when made, some imbalance is inevitable when the wheel is mounted, for the simple reason that if the Standard Safety Code is to be observed, the wheel must not fit tightly on the spindle. Clearance must be provided so that any possible expansion of the spindle or sleeve due to grinding heat or bearing heat cannot exert outward pressure or stress at the hole. This is very important as it has been clearly established that the maximum stresses in a rotating body are tangential at the edge of the hole and any additional stress might lead to breakage. This mandatory hole-to-spindle clearance thus means that any grinding wheel of necessity will be mounted eccentrically - only a few thousandths of an inch, to be sure, but still enough to produce a certain amount of imbalance. If refinement of balance is vital to the success of work regularly ground, then an automatic wheel balancer should be considered for use on cylindrical grinders. Conventional balancing procedures can be time-consuming. In contrast, since the automatic wheel balancer is built into the wheel head, this allows balancing in place on the machine and the operator merely pushes abut on. The balancing cycle is automatically terminated after about 5 seconds. Thus, precise wheel balancing can be accomplished at any time, except during actual grinding, with no special operator skill required. Steps In Balancing A WheelStandard equipment for balancing grinding wheels consists of a balance stand and balancing arbors to fit various sizes of wheel sleeves.The procedure to follow in balancing a wheel is as follows:Mount the wheel on its sleeve. (In case of wheels with arrow markings, the stenciled arrow should point upwards). Tighten the flange bolts evenly and only enough to hold the wheel firmly. True the wheel so that it is in running truth on its own sleeve.Remove the wheel and sleeve assembly from the grinding machine. Insert the proper size balancing arbor and then place the arbor with the wheel on the balancing stand. Remove the two balance weights from the wheel sleeve. Allow the two wheels to turn until it has come to rest with the heavy side down. Draw a chalk mark on the side of the wheel at the exact top (directly opposite the heavy side). Replace the two balancing weights in the flange groove with their adjacent ends meeting under the chalk mark. Tighten the weights just enough to hold them in position temporarily. 6) Give the wheel a quarter turn. The wheel may not remain at rest in this position; move the weights gradually and equally from the chalk mark until the balance is established. 7) Give the wheel a half turn. Test for balance and then keep turning the wheel for a complete revolution, stopping and checking for balance at about eighth of a revolution. 8) Now tighten the balancing weights securely. 9)Carefully rest the wheel on the floor, remove the balancing arbor and mount the wheel in the grinding machine. Finally retrue the wheel preparatory to grinding.

Clamping Techniques Clamping techniques used in the grinding processes. The clamping force of the grinding wheel flanges is an important safety parameter of a grinding operation, the clamping force:Must be high enough to drive the wheel without slippage under the most severe operating conditions of the machine.Must not apply to the wheel an excessive compression stress which could weaken the wheel.Must not distort the flanges. When flanges are clamped by screws it is essential to know the torque to use when tightening these screws to make sure that the needed clamping force is obtained and that each screw is loaded enough to avoid loosening.

Vernier caliper

Parts of a vernier caliper:Outside jaws: used to measure external diameter or width of an objectInside jaws: used to measure internal diameter of an objectDepth probe: used to measure depths of an object or a holeMain scale: gives measurements of up to one decimal place (in cm)Main scale: gives measurements in fraction (in inch)Vernier: gives measurements up to two decimal places (in cm)Vernier: gives measurements in fraction (in inch)Retainer : used to block movable part to allow the easy transferring a measurement

Measuring InstrumentsA variation to the more traditional caliper is the inclusion of a vernier scale; this makes it possible to directly obtain a more precise measurement. Vernier calipers can measure internal dimensions (using the uppermost jaws in the picture at right), external dimensions using the pictured lower jaws, and depending on the manufacturer, depth measurements by the use of a probe that is attached to the movable head and slides along the center of the body. This probe is slender and can get into deep grooves that may prove difficult for other measuring tools. The vernier scales may include both metric and inch measurements on the upper and lower part of the scale. Vernier calipers commonly used in industry provide a precision to a hundredth of a millimeter (10 micrometers), or one thousandth of an inch.

2) Inside caliper

The inside calipers are used to measure the internal size of an object. The upper caliper in the image (at the right) requires manual adjustment prior to fitting, fine setting of this caliper type is performed by tapping the caliper legs lightly on a handy surface until they will almost pass over the object. A light push against the resistance of the central pivot screw then spreads the legs to the correct dimension and provides the required, consistent feel that ensures a repeatable measurement. The lower caliper in the image has an adjusting screw that permits it to be carefully adjusted without removal of the tool from the work piece.

3) Divider caliper

In the metalworking field divider calipers are used in the process of marking out suitable work pieces. The points are sharpened so that they act as scribers, one leg can then be placed in the dimple created by a center or prick punch and the other leg pivoted so that it scribes a line on the work pieces surface, thus forming an arc or circle.