2The study of metal cutting is complex, due to the number of possible variables. Differences in work piece materials and cutting-tool materials, whether or not a cutting fluid is used, the relative speed of the work and cutting tool, the depth of cut, and the condition of the machine all affect the cutting operation.However, certain basic rules apply, and when you know and can apply these you will be in a better position to carry out machining operations effectively.
3Cutting-tool materials 1Red hardness:It is obvious that a cutting tool must be harder than the material being cut, otherwise it will not cut. It is equally important that the cutting tool remains hard even when cutting at high temperatures. The ability of a cutting tool to retain its hardness at high cutting temperatures is known as red hardness.2Abrasion resistance: When cutting, the edge of a cutting tool operates under intense pressure and will wear due to abrasion by the material being cut. Basically, the harder the material the better its resistance to abrasion.3Toughness: A cutting-tool material which is extremely hard is unfortunately also brittle. This means that a cutting edge will chip on impact if, e.g. the component being machined has a series of slots and the cut is therefore intermittent. To prevent the cutting edge from chipping under such conditions, it is necessary that the material has a certainamount of toughness.
4Cutting Tools One of most important components in machining process Performance will determine efficiency of operationTwo basic types (excluding abrasives)Single point and multiple pointMust have rake and clearance angles ground or formed on them
5Cutting-Tool Materials Toolbits generally made of seven materialsHigh-speed steelCast alloys (such as stellite)Cemented carbidesCeramicsCermetsCubic Boron NitridePolycrystalline Diamond
6Cutting OperationNever bring tool point against work that is stationaryAlways use heaviest depth of cut possible for machine and size of cutting toolNever stop machine while feed engagedWill break cutting edgeStop feed and allow tool to clear before stopping machine
7Never continue to use dull cutting tool Dull cutting tool recognized byWork produced oversize with glazed finishRough and ragged finishChange in shape or color of chipsApply cutting fluid only ifCan be applied under pressureCan be directed at point of cutting and kept there at all times
9DrillingDrilling is the operation of producing circular hole in the work-piece by using a rotating cutter called DRILL.The machine used for drilling is called drilling machine.The drilling operation can also be accomplished in lathe, in which the drill is held in tailstock and the work is held by the chuck.The most common drill used is the twist drill.
10Drilling Machine Types :- It is the simplest and accurate machine used in production shop.The work piece is held stationary i.e.. Clamped in position and the drill rotates to make a hole.Types :-a) Based on construction:Portable, Sensitive, Radial, up-right, Gang, Multi-spindleb)Based on Feed:Hand and Power driven
11Sensitive Drilling Machine Drill holes from 1.5 to 15mmOperator senses the cutting action so sensitive drilling machine
12Up-Right Drilling Machine Drill holes upto 50mmTable can move vertically and radially
13Radial Drilling Machine It the largest and most versatile used fro drilling medium to large and heavy work pieces.
15Drill Materials The two most common types are 1. HSS drill - Low cost 2. Carbide- tipped drills- high production and in CNC machinesOther types areSolid Carbide drill, TiN coated drills, carbide coated masonry drills, parabolic drills, split point drill
24Types of cutters Reamers :- Multi tooth cutting tool Accurate way of sizing and finishing the pre-existing hole.Accuracy of 0.005mm can be achievedBoring Tool:-Single point cutting tool.Boring tool is held in the boring bar which has the shank.Accuracy of 0.005mm can be achieved.
25Types of cutters Countersinks :- Special angled cone shaped enlargement at the end of the holeCutting edges at the end of conical surface.Cone angles of 60°, 82°, 90°, 100°, 110°, 120°Counter Bore Tool:-Special cutters uses a pilot to guide the cutting action .Accommodates the heads of bolts.
26Types of cutters Combined Countersinks and central drill :- Special drilling tool to start the hole accurately.At the end it makes countersinks in the work piece.Gun drill :-Machining of lengthy holes with less feed rates.To overcome the heating and short life of the normal drill tool
27Types of cutters Tapping:- For cutting internal thread Multi cutting edge tool.Tapping is performed either by hand or by machine.Minor dia of the thread is drilled and then tapping is done.
30Precautions for Drilling machine Lubrication is important to remove heat and friction.Machines should be cleaned after useChips should be removed using brush.T-slots, grooves, spindles sleeves, belts, pulley should be cleaned.Machines should be lightly oiled to prevent from rusting
31Safety PrecautionsDo not support the work piece by hand – use work holding device.Use brush to clean the chipNo adjustments while the machine is operatingEnsure for the cutting tools running straight before starting the operation.Never place tools on the drilling tableAvoid loose clothing and protect the eyes.Ease the feed if drill breaks inside the work piece.