Detail about the milling technology

1. SAFETY

Safe worker : Alwayst keep tidy and neat Alwayst consider the welfare of fellow workers and personnel Alwayst maintain a responsible attitude when doing any work or project Alwayst perform work in a safe and accurate manner

Safety in machine shop : Machining the work piece We must understand all mechanisms of machine before operating it. Keep hand away from spinning tools Stop the machine before doing cleaning and measuring Carrying out machining is prohibited without proper attires , well planning and permission Gloves and cloth must be away from rotating spindle Dont operate the machines with more than 1 user Any injuries should be reported and treated immediately

Personal safety outfit Avoid wearing loose clothes Remove any watches, rings and bracelets Long hair must be protected by hair net Alwayst keep safety googles wearing on when carrying out machining Always wear a proper shoes (Safety boots )

Housekeeping Stop the machine before clean it Always keep the machine clean Do not place the important equipments on machine table Keep the floor free from oil and grease Sweep up the floor frequently

Securing the work piece Remove all burrs and sharps edges Do not attempt to lift the heavy object which are difficult to handle by your own Be sure the work piece are securely clamped on clamping attachment Make sure the cutter are have the safe distance from the work piece before it rotating

Safety for precision equipment Do not put measuring equipment on the machine table Clean the measuring equipment from coolant and chip after being used Dont mix-up precision equipments and cutting tool Keep the safe distance when measuring the work piece to make sure it not hit with cutting tools

When operating a milling machine Understanding the operational and mechanism of milling machine before operating it Clamp all the work pieces solidly Use the suitable arbor for selected cutting tool Ensure all auto-feed levers are in neutral position Dont perform cutting operation on vice or machine table Do not clamp the work pieces too high from vice surfaces Stop the machine immediately if odd noise or vibration develops while you are operating it Plan your work thoroughly before starting work Return all the tools / equipments to proper storage after being use Do not attempt to remove chips with your fingers Do not talk or fooling around ( horseplay ) during machining

2. Types of milling machines and its components function

Milling machines are a very versatile machine tool. Milling machines are capable of machining one or two pieces as well as large volume production runs. The milling machine can produce a variety of surfaces by using a circular cutter with multiple teeth that progressively produce chips as the cutter rotates. The advantage of having a circular milling cutter with multiple teeth has led to the design of a large variety of milling machine types. These different milling machine types can be classified as Knee and Column, Fixed Bed, Bridge Type, and Special. All of these classifications can have either a vertical or horizontal spindle configuration. Further classifications of milling machines are made on the basis of the type of computer numerical control the machine uses. Types of milling machines

Knee and column type milling machines Work table, on which the work piece is clamped using the T-slots. The table moves longitudinally with respect to the saddle. Saddle, which supports the table and can move transversely. Knee, which supports the saddle and gives the table vertical movements for adjusting the depth of cut. Overarmin horizontal machines, which is adjustable to accommodate different arbor lengths. Head, which contains the spindle and cutter holders. In vertical machines the head may be fixed or vertically adjustable.

Differences of knee and column type milling machines

1. Vertical knee and column type milling machinesA vertical type knee and column milling machine has the spindle located vertically, parallel to the face of the column, and perpendicular to the top of the table.The ram style knee and column type milling machine is a light duty milling machine. This type of machine is well suited for a variety of tool room work as well as other light duty operations. The head is mounted on a ram that can be swivelled or brought forward. This allows the head to be brought into an operating position over most of the table.

2. Universal knee and column type milling machinesThe universal knee and column milling is very similar to the plain knee and column milling machine. The largest difference being the swivelling table housing. The swivelling table housing allows the table to be swivelled at an angle to the axis of the spindle.

3. Horizontal knee and column type milling machinesThe most distinguishing characteristic of this type of machine is the knee and column configuration This type of milling machine is unique in that the table can be moved in all three directions. The table can be moved longitudinally in the X-axis as well as in and out on the Y-axis. Since the table rides on top of the knee, the table can be moved up and down on the Z-axis. There are several different types of knee and column type milling machines, but they all have the same characteristic. The knee slides up and down on the column face.

Fixed bed type milling machines The most distinguishing aspect of the fixed bed type milling machine is the absence of the knee. The fixed bed construction of this style of milling machine minimizes deflection and allows very heavy cuts to be taken. Fixed bed style milling machines can be used for general purpose work although many people look upon them as high production machines. The table can move in a longitudinal and a transverse direction. The vertical position of the spindle, with respect to the work table, is obtained by moving the head up and down along the column of the machine.

Bridge type milling machines The construction of the Bridge Type milling machine resembles that of a bridge The table is mounted on the bed. On either side of the bed are two vertical columns connected at the top by a brace. A cross rail is mounted on the brace. The cross rail houses the spindle head. Bridge type milling machines are typically used to machine large pieces such as castings, machine tables and housings.

Planer machines Planer machines are similar to bed type machines but are equipped with several cutters and heads to mill various surfaces.

Rotary table machines Rotary table machines are similar to vertical milling machines and are equipped with one or more heads to do face milling operations.

Tracer controlled machines Tracer controlled machines reproduce parts from a master model. They are used in automotive and aerospace industries from machining complex parts and dies.

Computer numerical control ( CNC ) Machines Various milling machine components are being replaced rapidly with computer numerical control (CNC) machines. These machine tools are versatile and capable of milling, drilling, boring and tapping with repetitive accuracy.

3. Processes perform by milling machines

The time required to produce a given quantity of parts includes the initial setup time and thecycle timefor each part. The setup time is composed of the time to setup the milling machine, plan the tool movements (whether performed manually or by machine), and install thefixturedevice into the milling machine. The cycle time can be divided into the following four times: Load/Unload time- The time required to load the workpiece into the milling machine and secure it to the fixture, as well as the time to unload the finished part. Theload timecan depend on the size, weight, and complexity of theworkpiece, as well as the type of fixture. Cut time- The time required for the cutter to make all the necessary cuts in the workpiece for each operation. Thecut timefor any given operation is calculated by dividing the totalcut length for that operation by thefeed rate, which is the speed of the cutter relative to the workpiece. Idle time- Also referred to as non-productive time, this is the time required for any tasks that occur during the process cycle that do not engage the workpiece and therefore remove material. Thisidle timeincludes the tool approaching and retracting from the workpiece, tool movements between features, adjusting machine settings, and changing tools. Tool replacement time- The time required to replace a tool that has exceeded its lifetime and therefore become to worn to cut effectively. This time is typically not performed in every cycle, but rather only after the lifetime of the tool has been reached. In determining the cycle time, the tool replacement time is adjusted for the production of a single part by multiplying by the frequency of a tool replacement, which is the cut time divided by the tool lifetime.

Following the milling process cycle, there is no post processing that is required. However, secondary processes may be used to improve the surface finish of the part if it is required. The scrap material, in the form of small material chips cut from the workpiece, is propelled away from the workpiece by the motion of the cutter and the spraying of lubricant. Therefore, no process cycle step is required to remove the scrap material, which can be collected and discarded after the production.

4. Cutting tools for milling operation Angles on milling cutting(a) Cutter = Multi-edge cutting tool(b) The teeth remove chips one after another (c) = clearance angle(d) = wedge angle(e) = rake angle

Milling cutterMilling cutters come in several shapes and many sizes. There is also a choice of coatings, as well asrake angleand number of cutting surfaces.(a) Shape:Several standard shapes of milling cutter are used in industry today, which are explained in more detail below.(b) Flutes / teeth:The flutes of the milling bit are the deep helical grooves running up the cutter, while the sharp blade along the edge of the flute is known as the tooth. The tooth cuts the material, and chips of this material are pulled up the flute by the rotation of the cutter. There is almost always one tooth per flute, but some cutters have two teeth per flute.Often, the wordsfluteandtoothare used interchangeably. Milling cutters may have from one to many teeth, with 2, 3 and 4 being most common. Typically, the more teeth a cutter has, the more rapidly it can remove material. So, a 4-tooth cutter can remove material at twice the rate of a 2-tooth cutter.(c) Helix angle:The flutes of a milling cutter are almost always helical. If the flutes were straight, the whole tooth would impact the material at once, causing vibration and reducing accuracy and surface quality. Setting the flutes at an angle allows the tooth to enter the material gradually, reducing vibration. Typically, finishing cutters have a higher rake angle (tighter helix) to give a better finish.(d) Centre cutting:Some milling cutters can drill straight down (plunge) through the material, while others cannot. This is because the teeth of some cutters do not go all the way to the centre of the end face. However, these cutters can cut downwards at an angle of 45 degrees or so.(e) Roughing or Finishing:Different types of cutter are available for cutting away large amounts of material, leaving a poor surface finish (roughing), or removing a smaller amount of material, but leaving a good surface finish (finishing). A roughing cutter may have serrated teeth for breaking the chips of material into smaller pieces. These teeth leave a rough surface behind. A finishing cutter may have a large number (4 or more) tooth for removing material carefully. However, the large number of flutes leaves little room for efficientswardremoval, so they are less appropriate for removing large amounts of material.

(f) Coatings:The right tool coatings can have a great influence on the cutting process by increasing cutting speed and tool life, and improving the surface finish. Polycrystalline(PCD) is an exceptionally hard coating used on cutters which must withstand high abrasive wear. A PCD coated tool may last up to 100 times longer than an uncoated tool. However the coating cannot be used at temperatures above 600 degrees C, or on ferrous metals. Tools for machining aluminium are sometimes given a coating ofTiAlN. Aluminium is a relatively sticky metal, and can weld itself to the teeth of tools, causing them to appear blunt. However it tends not to stick to TiAlN, allowing the tool to be used for much longer in aluminium.

(g) Shank:The shank is the cylindrical (non-fluted) part of the tool which is used to hold and locate it in the tool holder. A shank may be perfectly round, and held by friction, or it may have a Weldon Flat, where aset screw, also known as agrub screw, makes contact for increased torque without the tool slipping. The diameter may be different from the diameter of the cutting part of the tool, so that it can be held by a standard tool holder.

Type of milling cutter (i) End mill cutterEnd mills (middle row in image) are those tools which have cutting teeth at one end, as well as on the sides. The wordsend millare generally used to refer to flat bottomed cutters, but also include rounded cutters (referred to asball nosed) and radiuses cutters (referred to asbull nose, ortorus). They are usually made fromhigh speed steelorcemented carbide, and have one or more flutes. They are the most common tool used in a vertical mill.

(ii) Slot mill cutterSlot drills (top row in image) are center-cutting end mills, generally two- (sometimes three- or four-) fluted cutters that are capable of drilling (plunge-cutting) straight down into the material and then moving laterally to cut a slot. The plunge-cutting action is possible because at least one (diametrically opposite) pair of teeth extend all the way to the centre of the end face. Such a feature of end mills is called "center-cutting". Slot drills are so named for their use in cuttingkeywayslots. The termslot drillis usually assumed to mean a two-fluted, flat-bottomed end mill if no other information is given.

(iii) Roughing end millRoughing end mills quickly remove large amounts of material. This kind of end mill utilizes a wavy tooth form cut on the periphery. These wavy teeth form many successive cutting edges producing many small chips, resulting in a relatively rough surface finish. During cutting, multiple teeth are in contact with the workpiece reducing chatter and vibration. Rapid stock removal with heavy milling cuts is sometimes calledhogging. Roughing end mills are also sometimes known as ripping cutters.

(iv) Ball nose cutterBall nose cutters (lower row in image) are similar to slot drills, but the end of the cutters ishemispherical. They are ideal for machining 3-dimensional contoured shapes inmachining centres, for example inmouldsanddies. They are sometimes calledball millsin shop-floor slang, despite the fact that that term also hasanother meaning. They are also used to add a radius between perpendicular faces to reduceconcentrations. There is also a termbull nosecutter, which refers to a cutter having a corner radius that is fairly large, although less than the spherical radius (half the cutter diameter) of a ball mill; for example, a 20-mm diameter cutter with a 2-mm radius corner. This usage is analogous to the termbull nose centerreferring tolathe centerswith truncated cones; in both cases, the silhouette is essentially a rectangle with its corners truncated (by either a chamfer or radius).

(v) Slab mill cutterSlab mills are used either by themselves or ingang millingoperations on manual horizontal or universal milling machines to machine large broad surfaces quickly. They have been superseded by the use ofcemented carbide-tipped face mills which are then used in vertical mills or machining centres.

(vi) Side-and-face cutter

The side-and-face cutter is designed with cutting teeth on its side as well as its circumference. They are made in varying diameters and widths depending on the application. The teeth on the side allow the cutter to makeunbalanced cuts(cutting on one side only) without deflecting the cutter as would happen with a slitting saw or slot cutter (no side teeth).Cutters of this form factor were the earliest milling cutters developed. From the 1810s to at least the 1880s, they were the most common form of milling cutter, whereas today that distinction probably goes toend mills.

(vii) Involute gear cutterThere are 8 cutters (excluding the rare half sizes) that will cut gears from 12 teeth through to a rack (infinite diameter).

(viii) Face mill cutter

A face mill is a cutter designed for facing as opposed to i.e., creating a pocket (end mills). The cutting edges of face mills are always located along its sides. As such it must always cut in a horizontal direction at a given depth coming from outside the stock. Multiple teeth distribute the chip load, and since the teeth are normally disposable carbide, this combination allows for very large and efficient face milling.

(ix) Formed cutterFormed cutter is a n incorporate the exact of the shape of the part it is suitable for production small parts. There are some type of formed cutter such as concave, convex and profiling.

(x) Angle cutterSingle angle milling cutter (dovetail cutter) {mill guide ways, angle available- 45o, 50o, 60o } Double angle milling cutter { mill guide ways, angle available- 45o, 50o, 60o }

(xi) Relieved cutterRelieved cutter id used for cutting profiling shape. Example involutes gear cutter, twist drill groove cutter, sprocket cutter & radius cutter.

5. Clamping technique ( work pierce and tool ) Clamping technique in toolWhen started work, we must check that the cutter runs true. Direction of spindle must be same with cutting direction. After finish using, must clean the internal taper of milling spindle. Always keep the arbor and collars clean. Last, mount the cutter short as possible.(i) Cutter mounting Direct mountingThe taper of cutting tool fitted directly into the work spindle. I may have morse taper or steep taper shape. Steep taper shape morse taper shape

Indirect mounting Cutter not inserted directly into the taper of the work spindle. Mounted to the correct attachment. Collet chuck collet end-mill

(ii) Mounting attachments(a) Arbor mounting for vertical milling Shell end arbor = mainly use to mount shell end mill and cutter head.

Adapter self-locking chuck = use to reduce the internal taper in the work spindle so that its fits on the required arbor or cutter.

Collect chuck = design to take small cylindrical cutter to various cutter. Widely use at industries' ER40, ER32, ER16 used with BT40 and R8 arbor.

Drill chuck = It use when there is a drilling process ,center drill, deep drilling ,reaming ,counter bore.

(b) Mounting of cutter on vertical milling Cutter should be clamped as near to the collet as possible. This is to minimize overhanging of cutter that lead to cutter deflection. To reduce the vibration during cutting operation that lead to chattering at work piece

(c) Mounting of cutter on horizontal milling Maximum rigidity is an essential of efficient machining. Arbor support permits considerable metal removal. Cutter should be places near to headstock to maintain the maximum rigidity of clamping and to reduce the cutter deflection.

Clamping technique in work piercei. Direct clamping Holding pressure is provided by clamp bolt which should be as close as possible so it can maintain the force applied. Work piece with a surface can be directly clamp on the work table, using variety of clamp and t-bolt. From clamp and t-bolt(a) (b) Clamping kit

(c) Ordinary clamp(d) U clamp (e) Gooseneck clamp(f) Edge clamping(g) Rules of clamping is the hold pressure that provide by the clamp which should be close as possible to workplace

ii. Vise clamping(a) Angular vise (b) Machine vise with swivel base

(c) Vise alignment techniqueIn setting up the vise onto machine table the fix jaw must be parallel to the machine table.

iii. Other clamping attachment(a) Chuck clamping for round wok piece

6. Type and method of cutting fluid used in milling process The major advantage of using a coolant or cutting oil is that it dissipates heat, giving longer life to the cutting edges of the teeth. The oil also lubricates the cutter face and flushes away the chips, consequently reducing the possibility of marring the finish. TypesCutting oils are basically water-based soluble oils, petroleum oils, and synthetic oils. Water-based coolants have excellent heat transfer qualities; other oils result in good surface finishes. The cutting oil compounds for various metals are given in Table 4-3 in Appendix A. In general, a simple coolant is all that is required for roughing. Finishing requires cutting oil with good lubricating properties to help produce a good finish on the work piece. Plastics and cast iron are almost always machined dry. Method of UseThe cutting oil or coolant should be directed by means of coolant drip can, pump system, or coolant mist mix to the point where the cutter contacts the work piece. Regardless of method used, the cutting oil should be allowed to flow freely over the work piece and cutter.

7. Relation of the cutting parameters Cutting speeda. Important factor that affected milling operation efficiencyb. In order to work efficiently and economicallyc. Its symbol is V. It is expressed in meter/min (m/min) d. Formula: Cutting speed = diameter of cutter x x spindle speed V = d x x n

e. Selection of proper cutting speed Type of material to be machined Type of tool material Rigidity and condition of the machine Types of cutting operations

Spindle speedi. Defined as the speed at which the spindle of a milling machine rotates per minuteii. Its symbol is n. It is expressed in revolution/min (rpm)iii. Formula :Spindle speed = Cutting speedDiameter of cutter x n = v d x

iv. Selection of proper cutting speeds For longer cutter life, use the lower cutting speeds in the recommended range. Know the hardness of the material to be machined. When starting a new job, use the lower range of the cutting speed and gradually increase to the higher range if conditions permit. If a fine finish is required, reduce the feed rather than increase the cutter speed. The use of coolant, properly applied, will generally produce a better finish and lengthen the life of the cutter since it absorbs heat, acts as a lubricant and washes chips away.

Feed ratei. Defined as the distance in millimeters per minute that the work moves into the cutter.ii. Its symbol is f. It is expressed in (mm/min).iii. Formula:Feed = no of teeth x rec. feed/tooth x spindle speedf = N x f/t x niv. Factors on which feed rate depends on The depth and width of the cut. The design or type of the cutter. The sharpness of the cutter. The work piece material. The strength and uniformity of the work piece. The type of finish and accuracy required. The power and rigidity of the machine