Milling machine & Milling work Unit 4 Milling machine & Milling work

Types of Milling Machine Column & Knee type milling machines. Fixed Bed type or Manufacturing type milling machines. Planar type milling machines. Production milling machines. Special Purpose machines.

Column and Knee type milling machines. These machines are of general purpose machines and have single spindle only. They derive their name ‘column & knee’ type from the fact that the work table is supported on a knee like casting, which can slide in vertical direction along a vertical column. Depending upon the spindle position and table movement, they are further classified as Hand milling m/c. Plain or Horizontal milling m/c. Vertical milling m/c. Universal milling m/c. Omniversal milling m/c.

2. Fixed bed or Manufacturing type milling m/c. These machines, in comparison to column and knee type, are more sturdy and rigid, heavier in weight and larger in size. They are not suitable for tool room work. Most of these machines are either automatic or semi automatic type in operation. They may carry a single or multiple spindles. The common operations performed on these machines are cutting, grooving, gang milling and facing. They are further classified as: Plain type(having single horizontal spindle). Duplex head(having double horizontal spindle). Triplex head(having 2 horizontal & 1 vertical spindle). Rise & fall type(for profile milling).

3. Planar type milling m/c. They are used for heavy work. Upto a maximum of 4 toolheads can be mounted over it, which can be adjusted vertically. It has a robust & massive construction like a planar. 4. Production milling m/c. They are also manufacturing machines but differ from the above, as they do not have a fixed bed. They include the following machines: Rotary table or continuous type. Drum type. Tracer controlled. 5. Special Purpose milling m/c. These machines are designed to perform specific type of operations only.

Horizontal/Plain milling m/c. Its principal parts are shown by means of a block diagram. The vertical column serves as a housing for electricals, the main drive, spindle bearing etc. The knee acts as a support for the saddle, worktable and other accessories like indexing heads.

Over arm provides support for the yoke which, in turn, support the free end of the arbor. The arbor carrying the cutter rotates about a horizontal axis. The table can be given straight motions in three directions: longitudinal, cross and vertical(up and down). For giving vertical movement to the table the knee itself, together with the whole unit above it, slides up and down along the ways provided in front of the column. For giving cross movement to the table, the saddle is moved towards or away from the column along with the whole unit above it Both hand and power feed can be employed for work.

Vertical Milling m/c. It derives its name from the vertical position of the spindle. The major difference is that the spindle head is of swivelling type, i.e. the head can be swivelled to any desired angle to machine the inclined surface. Every other function is same as horizontal milling.

Milling Methods: The following two methods are generally used for performing milling operations. Up or Conventional milling. Down or Climb milling

Milling Cutters: The milling cutters may have either straight teeth, i.e. , parallel to the axis of rotation or helical in shape. The helix angle may be right hand or left hand and this will decide the direction of rotation of the cutter for cutting operation. Further, a milling cutter may be made of single piece of steel or having the cutting portion welded to a tough shank. The broad classification of milling cutters is according to the shape of teeth they carry, such as plain, inserted, formed or saw teeth, etc.

Common types of milling cutters are the following : Plain milling cutters. Side milling cutters. End milling cutters. Face milling cutters. Metal slitting cutters. Angle milling cutters. Formed milling cutters. Woodruff key milling cutters. T-slot milling cutters. Fly cutters.

Plain milling cutters: These milling cutters may have the cutting teeth on their periphery. The teeth may be either straight, i.e., parallel to the axis, or helical. Their end faces are either ground square with the axis or slightly concave to reduce friction. Thus, no cutting action is provided by the side faces. These cutters are employed for milling flat surface parallel to axis of rotation.

Side milling cutter: These cutters, apart from having teeth on the periphery, also have cutting teeth on one or both sides. They are always provided with a central hole for the purpose of mounting them on the arbor. They are also called straddle mills when used in pairs. The main types of side milling cutters are 1.Plain side milling cutters 2.Half side milling cutters 3.Staggered teeth side milling cutters 4.Interlocking side milling cutters

End milling cutters: These are solid circular cutters which are manufactured in two different varieties; those having the shank and others which do not have the shank. They carry teeth on the periphery as well as on the end. These teeth may be straight i.e., parallel to the axis of rotation, or helical. Helical teeth may be right hand or left hand. End milling cutters are used for milling slots, keyways, grooves and irregular shaped surfaces.

Face milling cutters: These cutters are made in two common forms. The smaller type almost resembles a shell end milling cutter and is known as shell type face milling cutters. It carries teeth on the periphery as well as the end face. Maximum cutting is done by the teeth on the periphery and those on the end face perform finishing operations. The larger type of cutter, called the built up face milling cutter, consists of a steel body, along the periphery of which are inserted the cutting teeth. The former type is used for small work whereas the latter for larger surfaces.

Angle milling cutters: These cutters carry sharp angular teeth which are neither parallel normal to their axes. Their specific use is in milling V-grooves, notches, dovetail slots, reamer teeth etc. they are of following two types: 1.Single angle cutters 2.Double angle cutters

Metal slitting cutters: These cutters are frequently called metal slitting saws. They are used for cutting thin slots or for parting off. They are manufactured in following two varieties: 1.Plain slitting saws 2.Staggered teeth milling cutter

Form milling cutters: They are also known as form relieved milling cutters or radius cutters. This category includes fairly large variety of milling cutters used for producing different shape contours. Their teeth are provided with certain angle of relief so that their form and size are retained even after resharpening.

Woodruff-Key milling cutter: It is a small type of end milling cutter which resembles with plain and side mills. Smaller sizes, say upto 50mm diameter, are made to have solid shank, to be fitted in machine spindle, whereas the larger sizes are provided with a hole for mounting the same on arbor. Smaller sizes have straight teeth whereas the larger sizes are usually made up of staggered teeth.

T-slot milling cutter: It is a single operation cutter which is used for cutting T-slots. In smaller sizes it is made to have the shank integral with the cutter. Large sizes are mounted on a separate shank. In operation, the narrow groove at the top is first milled by means of a slotting cutter or end milling cutter.

Fly cutter: It is actually a single point cutting tool. It is either mounted on a cylindrical body or held in a bar, in a same way as boring tool. Screws are used for tightly holding the tool in above holders.

No. of teeth in a cutter There is no standard rule which can be straightaway applied to determine the number of teeth in a cutter. Moreover, the number of teeth do not have any direct influence. The only effect they produce is on a chip thickness and hence the power, efficiency. A milling cutter with coarse pitch, i.e., having less number of teeth will have thicker and therefore stronger teeth. Against this, cutters having more no. of teeth, will remove chip of less thickness and are used for finish milling operations. The main advantages offered by a coarse teeth are: Its teeth can be made stronger by increasing the are of cross-section. The chip gets more space for its flow and exit. The requirement of power for driving is less. Its has more life than the fine pitch cutter because it can stand more regrind. Lesser heat is developed at the metal cutting area due to smaller sliding friction.

Milling Operations: A large variety of components are machined on a milling machine involving various types of operation. These operations are widely classified as : Plain or slab milling Face milling Angular milling Form milling Straddle milling Gang milling

Plain Milling: It is the process employed for machining a flat surface, parallel to the axis of the cutter, by using a plain or slab milling cutter. When a very wide surface is to be machined, it is advisable to use the interlocking teeth plain milling cutter instead of simple slab mills.

Face milling: The milling is employed for machining a flat surface which is at right angles to the axis of rotating cutter. The cutter used in this operation is the face milling cutter. In face milling, the feed can be either horizontal or vertical.

Angular Milling: Angular milling, or angle milling, is milling flat surfaces which are neither parallel nor perpendicular to the axis of the milling cutter. A single angle milling cutter is used for angular surfaces, such as chamfers, serrations, and grooves. Milling dovetails is a typical example of angular milling.

Form Milling: Form milling is the process of machining special contours composed of curves and straight lines, or entirely of curves, at a single cut. This is done with formed milling cutters, shaped to the contour to be cut. This operation is accomplished by using convex, concave, and corner rounding milling cutters ground to the desired circle diameter. 

Straddle Milling: When two or more parallel vertical surfaces are machined at a single cut, the operation is called straddle milling. Straddle milling is accomplished by mounting two side milling cutters on the same arbor, set apart at an exact spacing. Two sides of the workpiece are machined simultaneously and final width dimensions are exactly controlled.

Gang Milling: Gang milling is the term applied to an operation in which two or more milling cutters are mounted on the same arbor and used when cutting horizontal surfaces. All cutters may perform the same type of operation or each cutter may perform a different type of operation. For example, several workplaces need a slot, a flat surface, and an angular groove. The best method to cut these would be gang milling

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