Basics of Milling Machine and its Rigidity

IIT BHU

Metal machining and machine tools

RIGIDITY TEST OF lathe machine 02/03/2016

NAME : Shubham Khatri ROLL NO. : 14135077 CLASS : B. TECH. PART II, Semester IV, Group II MECHANICAL ENGG.

SUBMITTED TO DR. MOHD. ZAHEER KHAN

Effect on Chip Thickness by varying Cutting Velocity in Turning Operation. What is Machining? Machining is a manufacturing term encompassing a broad range of technologies and techniques. It can be roughly defined as the process of removing material from a workpiece using power-driven machine tools to shape it into an intended design. Most metal components and parts require some form of machining during the manufacturing process. Other materials, such as plastics, rubbers, and paper goods, are also commonly fabricated through machining processes.

Types of Machining Process 

Boring Process: In machining, boring is the process of enlarging a hole that has already been drilled (or cast), by means of a single-point cutting tool (or of a boring head containing several such tools), for example as in boring a gun barrel or an engine cylinder. Boring is used to achieve greater accuracy of the diameter of a hole, and can be used to cut a tapered hole. Boring can be viewed as the internal-diameter counterpart to turning, which cuts external diameters.



Cutting process: Cutting is a collection of processes wherein material is brought to a specified geometry by removing excess material using various kinds of tooling to leave a finished part that meets specifications. The net result of cutting is two products, the waste or excess material, and the finished part.



Drilling process: Drilling is a cutting process that uses a drill bit to cut or enlarge a hole of circular cross-section in solid materials. The drill bit is a rotary cutting tool, often multipoint. The bit is pressed against the workpiece and rotated at rates from hundreds to thousands of revolutions per minute. This forces the cutting edge against the workpiece, cutting off chips (swarf) from the hole as it is drilled.



Grinding process: Grinding practice is a large and diverse area of manufacturing and tool making. It can produce very fine finishes and very accurate dimensions; yet in mass production contexts it can also rough out large volumes of metal quite rapidly. It is usually better suited to the machining

of very hard materials than is "regular" machining (that is, cutting larger chips with cutting tools such as tool bits or milling cutters), and until recent decades it was the only practical way to machine such materials as hardened steels. 

Milling process: Milling is the machining process of using rotary cutters to remove material from a workpiece advancing (or feeding) in a direction at an angle with the axis of the tool. It covers a wide variety of different operations and machines, on scales from small individual parts to large, heavy-duty gang milling operations. It is one of the most commonly used processes in industry and machine shops today for machining parts to precise sizes and shapes.



Turning process: Turning is a machining process in which a cutting tool, typically a non-rotary tool bit, describes a helical toolpath by moving more or less linearly while the workpiece rotates. The tool's axes of movement may be literally a straight line, or they may be along some set of curves or angles, but they are essentially linear (in the nonmathematical sense).

Turning Process: Turning is a form of machining, a material removal process, which is used to create rotational parts by cutting away unwanted material. The turning process requires a turning machine or lathe, workpiece, fixture, and cutting tool. The workpiece is a piece of pre-shaped material that is secured to the fixture, which itself is attached to the turning machine, and allowed to rotate at high speeds. The cutter is typically a single-point cutting tool that is also secured in the machine, although some operations make use of multi-point tools. The cutting tool feeds into the rotating workpiece and cuts away material in the form of small chips to create the desired shape. Turning is used to produce rotational, typically axisymmetric, parts that have many features, such as holes, grooves, threads, tapers, various diameter steps, and even contoured surfaces. Parts that are fabricated completely through turning often include components that are used in limited quantities, perhaps for prototypes, such as custom

designed shafts and fasteners. Turning is also commonly used as a secondary process to add or refine features on parts that were manufactured using a different process. Due to the high tolerances and surface finishes that turning can offer, it is ideal for adding precision rotational features to a part whose basic shape has already been formed.

Tooling The various angles, shapes, and sizes of a single-point cutting tool have direct relation to the resulting surface of a workpiece in machining operations. Different types of angle such as rake angle, side rake angle, cutting-edge angle, relief angle, nose radius exist and may be different with respect to the workpiece. Also, there are many shapes of single-point cutting tools, such as V-shaped and Square. Usually, a special toolholder is used to hold the cutting tool firmly during operation.

HEAD STOCK: The headstock carries the headstock spindle and for driving it. The headstock is similar to an automobile transmission except that it has more gear shift combinations and therefore has a greater number of speed changes. On some lathes gears are shifted hydraulically and others are manual.

Various combinations of gears in the headstock transmit power from the drive shaft to the spindle through an intermediate shaft. Use the speed-change levers to shift the sliding gears on the drive shaft and the intermediate shaft to line up the gears in different combinations. This produces the gear ratios needed to obtain the various spindle speeds. Note that the back gear lever has a high and low speed for each combination of the other gears. The headstock casing is filled with oil to lubricate the gears and the shifting mechanism contained within it. The parts not immersed in the

oil are lubricated by either the splash produced by the revolving gears or by an oil pump. The headstock spindle is the main rotating element of the lathe and is directly connected to the workpiece which revolves with it. The spindle is supported in bearings at each end of the headstock through which it projects. The section of the spindle between the bearings carries the pulleys or gears that turn the spindle. The nose of the spindle holds the driving plate, the faceplate, or a chuck. The spindle is hollow throughout its length so that bars or rods can be passed through it from the left and held in a chuck at the nose. The chuck end of the spindle is bored to a Morse taper to receive the solid center. The hollow spindle also permits the use of the drawin collet chuck (to be discussed later in this lesson). At the other end of the spindle is the gear by which the spindle drives the feed and the screw-cutting mechanism through a gear train located on the left end of the lathe. A collar is used to adjust the end play of the spindle.

TAILSTOCK: The primary purpose of the tailstock is to hold the dead centre to support one end of the work being machined between centres. However, it can also be used to hold live centres, tapered shank drills, reamers, and drill chucks. The tailstock moves on the ways along the length of the bed to accommodate work of varying lengths. It can be clamped in the desired position by the tailstock clamping nut. The dead centre is held in a tapered hole (bored to a Morse taper) in the tailstock spindle. The spindle is moved back and forth in the tailstock barrel for longitudinal adjustment. The hand wheel is turned which turns the spindle-adjusting screw in a tapped hole in the spindle. The spindle is kept from revolving by a key that fits a spine, or keyway, cut along the bottom of the spindle. The tailstock body is made in two parts. The bottom, or base, is fitted to the ways; the top can move laterally on its base. The lateral movement can be closely adjusted by setscrews. Zero marks inscribed on the base and top indicate the centre position and provide a way to measure set over for taper turning. Before inserting a dead centre, a drill, or a reamer into the spindle, carefully clean the tapered shank and wipe out the tapered hole of the spindle. After a drill or reamer is placed into the tapered hole of the spindle, make sure that the tool will not turn or revolve. If the tool is allowed to revolve, it will score the tapered hole and destroy its accuracy. The spindle of the tailstock is engraved with graduations which help in determining the depth of a cut when a piece is drilled or reamed.

EXPERIMENT ObjectiveTo measure the rigidity of head stock and tail stock of a lathe.

ApparatusLathe machine, U – Dynamometer, Dial gauge

TheoryRigidity of machine tool is basically the measure of applied load per unit deflection. It is the measure of deflection in various components of machine when they feel some load. Rigidity = load applied / Deflection So, we can conclude that higher the rigidity of machine tools higher the load that it can withstand for lower deflections. If the machine tool is not sufficiently rigid , it may deform and create errors in the dimensions of final product. So it is important that machine tool has to be sufficiently rigid and its rigidity must be check before the operation.

Procedure1. Fix the U- dynamometer and a dial gauge at the tool post, Keep a spherical steel ball in the groove provided for it on the U – dynamometer. 2. Move the cross-slide such that the steel ball just touches the mandrel. 3. Press the feeler of another dial gauge against the mandrel diametrically opposite to the ball position. Set the dial gauge reading to zero. 4. Increase the load by gradually moving the cross slide and note the deflection in both the dial gauges. Repeat the process.

5. Decrease the load gradually by moving the cross slide in the opposite direction in both the dial gauges. Repeat this process. 6. Use the calibration chart and express the deflection of the dial gauge attached to the U-Dynamometer in units of force (kgf).

U DYNAMOMETER (LOAD VS DEFLECTION (in u- dynamometer) LOAD ( kgf) slope = 70 kgf/mm

Deflection X 10^ (-2) mm)

HEAD STOCK POSITION 1 (far away from spindle) LOAD (kgf)

Rigidity = 129.2 kgf/mm

HEAD STOCK POSITION 2 (near to the spindle) LOAD (kgf)

Rigidity=466.67 kgf/mm

TAIL STOCK LOAD (kgf)

Rigidity = 208 kgf/mm

ResultsRigidity near the spindle i.e. position 2 of head stock is more than the position 1 of the head stock which is situated far away from the head stock. This can be easily understood by bending in cantilever at which the point far away from the fixed end suffers more deflection than the nearby point from the fixed end.

Sources of error  

Backlash error in the machine tool. Error may occur when we are not applying the load exactly same that is in the calibration chart. Human error may occur while recording of readings of dial gauges.