Assignment 1 BFF 1811 MACHINING 2
Lecturer : Mr. Shahanzair Bahrom NAME Mohamad Radzi B. Mohd Sojak
MATRIX NO. FB14009
Introduction What is Milling Machine, Milling machines are tools designed to machine metal, wood, and other solid materials. Often automated, milling machines can be positioned in either vertical or horizontal orientation to carve out materials based on a pre-e xisting design. These designs are often CAD directed, and many milling machines are CNC-operated
(computer numerical control),
Although manually and traditionally-automated milling devices are also common. Milling machines are capable of dynamic movement; both of the tool and the work piece, and many milling machines can perform multi-axis machining. Because of variations in orientation, operation and application, milling machines have varying functions and different operating principles. We will focus about milling machine base on these 6 topics:a) Safety b) Types of milling machines and its component’s function c) Processes perform or operation by milling machines d) Cutting Tools for milling operation e) Clamping technique Work piece clamping f) Type and method of cutting fluid use in milling processes g) Relation of the parameter e.g cutting speed, feed rate and depth of cut
SAFETY
List of standard procedure before operate or using the milling machines PRE-OPERATIONAL SAFETY CHECKS 1. Ensure no slip/trip hazards are present in workspaces and walkways. 2. Locate and ensure you are familiar with the operation of the ON/OFF starter and E-Stop (if fitted). 3. Do not leave equipment on top of the machine. 4. Check that machine guards are in position. 5. Ensure cutter is in good condition and securely mounted. 6. Check coolant delivery system to allow for sufficient flow of coolant. 7. Faulty equipment must not be used, immediately report suspect machinery.
OPERATIONAL SAFETY CHECKS 1. Keep clear of moving machine parts. 2. Never leave the machine running unattended. 3. Follow correct clamping procedures- keep overhangs as small as possible and check work piece is secure. 4. Set the correct speed to suit the cutter diameter, the depth of cut and the material. 5. Before making adjustments and measurements or before cleaning swarf accumulations switch off and bring the machine to a complete standstill.
HOUSEKEEPING 1. Switch off the machine. 2. Remove milling cutters and store them safely. 3. Leave the machine and work area in a safe, clean and tidy state.
POTENTIAL HAZARDS
Sharp cutters Moving components - hair/clothing entanglement Eye injury Skin irritation Metal splinters and burrs Flying debris
Before starting, make sure that:
all guards are in place;
work is properly secured in place;
bolts used to hold down work clear the tooling;
tooling and supporting pieces are properly tightened in position;
table stops are secured properly;
handles on all feed screws are in neutral;
table is free of stock, tools or other loose material;
the arbor and arbor support are clear of the work;
the cutter is rotating in the right direction.
Types Of Milling Machines And Its Component’s Function There are several types of milling machines:1. 2. 3. 4. 5. 6.
Knee and Column Type Milling Machines Universal Horizontal Milling Machines Vertical Knee and Column Type Milling Machine Fixed Bed Type Milling Machines Bridge Type Milling Machines Special Milling Machines
Knee and Column Type Milling Machines Column and knee type milling machines are the most common milling machines. The spindle to which the milling cutter is may be horizontal (slab milling) or vertical (face and end milling).
Knee-type milling machines are characterized by a vertically adjustable worktable resting on a saddle which is supported by a knee. The knee is a massive casting that rides vertically on the milling machine column and can be clamped rigidly to the column in a position where the milling head and milling machine spindle are properly adjusted vertically for operation.
The plain vertical machines are characterized by a spindle located vertically, parallel to the column face, and mounted in a sliding head that can be fed up and down by hand or power. Modern vertical milling machines are designed so the entire head can also swivel to permit working on angular surfaces, The turret and swivel head assembly is designed for making precision cuts and can be swung 360° on its base. Angular cuts to the ho rizontal plane may be made with precision by setting the head at any require d angle within a 180" arc.
The plain horizontal milling machine's column contains the drive motor and gearing and a fixed position horizontal milling machine spindle. An adjustable overhead arm containing one or more arbor supports projects forward from the top of the column. The arm and arbor supports are used to stabilize long arbors. Supports can be moved along the overhead arm to support the arbor where support is desired depending on the position of the milling cutter or cutters. The milling machine's knee rides up or down the column on a rigid track. A heavy, vertical positioning screw beneath past the milling cutter. The milling machine is excellent for forming flat surfaces, cutting dovetails and keyways, forming and fluting milling cutters and reamers, cutting gears, and so forth. Many special operations can be performed with the attachments available for milling machine use. The knee is used for raising and lowering. The saddle rests upon the knee and supports the worktable. The saddle moves in and out on a dovetail to control cross feed of the worktable. The worktable traverses to the right or left upon the saddle for feeding the work piece past the milling cutter. The table may be manually controlled or power fed. The universal knee and column milling is very similar to the p lain 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 .
Universal Horizontal Milling Machines
The basic difference between a universal horizontal milling machine and a plain horizontal milling machine is the addition of a table swivel housing between the table and the saddle of the universal machine. This permits the table to swing up to 45 ° in either direction for angular and helical milling operations. The universal machine can be fitted with various attachments such as the indexing fixture, rotary table, slotting and rack cutting attachments, and various special fixtures.
Vertical Knee and Column Type Milling Machine
Ram Style Knee and Column Type Vertical Milling Machine.
A 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.
Fixed Bed Type Milling Machines The most distinguishing aspect of the fixed bed type milling machine is the absence of the knee.
CNC Vertical Spindle Bed-Type Milling Machine. 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.
CNC Vertical Bridge-Type Milling Machine.
Special Milling Machines
Extrusion Screw milling Machine There are a number of types of special milling machines. Special milling machines are designed specifically for one particular part or family of similar parts. Specialty milling machines are used extensively in the automotive and aeronautics industry. The specialty milling machine in Figure 9 is used to mill screws used in large extruding machines.
Processes Perform Or Operation By Milling Machines The three principal machining processes are classified as turning, drilling and milling. Other operations falling into miscellaneous categories include shaping, planning, boring, broaching and sawing.
Turning operations are operations that rotate the work piece as the primary method of moving metal against the cutting tool. Lathes are the principal machine tool used in turning.
Milling operations are operations in which the cutting tool rotates to bring cutting edges to bear against the work piece. Milling machines are the principal machine tool used in milling.
Drilling operations are operations in which holes are produced or refined by bringing a rotating cutter with cutting edges at the lower extremity into contact with the work piece. Drilling operations are done primarily in drill presses but sometimes on lathes or mills.
Miscellaneous operations are operations that strictly speaking may not be machining operations in that they may not be swarf producing operations but these operations are performed at a typical machine tool. Burnishing is an example of a miscellaneous operation. Burnishing produces no swarf but can be performed at a lathe, mill, or drill press.
An unfinished work piece requiring machining will need to have some material cut away to create a finished product. A finished product would be a work piece that meets the specifications set out for that work piece by engineering drawings or blueprints. For example, a work piece may be required to have a specific outside diameter. A lathe is a machine tool that can be used to create that diameter by rotating a metal work piece, so that a cutting tool can cut metal away, creating a smooth, round surface matching the required diameter and surface finish. A drill can be used to remove metal in the shape of a cylindrical hole. Other tools that may be used for various types of metal removal are milling machines, saws, and grinding machines. Many of these same techniques are used in woodworking.
Cutting Tools For Milling Operation The variety of milling cutters available helps make milling a versatile machining process. Cutters are made in a large range of sizes. Milling cutters are made from High Speed Steel (HSS), others are carbide tipped and many are replaceable or indexable inserts.
High-speed steel (HSS) shell end milling cutter.
Periphery milling cutters — Periphery milling cutters are usually arbor-mounted to perform various operations. Common high-speed steel milling cutters include the staggered tooth cutter, side-milling cutter, plain-milling cutter, single-angle milling cutter, double-angle milling cutter, convex milling cutter, concave milling cutter, and corner-rounded milling cutter. •
Light-duty plain mill — A general-purpose
cutter for peripheral milling operations. Narrow cutters have straight teeth, while wide ones have helical teeth. •
Heavy-duty plain mill — Similar to the light
duty mill except that it is used for higher rates of metal removal. To aid it in this function, the teeth are more widely spaced and the helix angle is increased to about 45 degrees. A face-milling cutter with wedge-clamped indexable inserts
Side milling cutter — Has a cutting edge on the sides as well as on the periphery. This allows the cutter to mill slots.
Half-side milling cutter — Same as the one previously described except that cutting edges are provided on a single side. It is used for milling shoulders. Two cutters of this type are often mounted on a single arbor for straddle milling.
Face-milling cutters with indexable inserts and wedgeclamped milling carriages.
•
Stagger-tooth side mill — Same as the side-
milling cutter except that the teeth are staggered so that every other tooth cuts on a given side of the slot. This allows deep, heavy-duty cuts to be taken. •
Angle cutters — The peripheral cutting
edges lie on a cone rather than on a cylinder. A single or double angle may be provided. •
Shell endmill — Has peripheral cutting
edges plus face cutting edges on one end. It has a hole through it for a bolt to secure it to the spindle.
Indexable-insert ball-nosed milling cutters using the screw clamping method
Form mill — A peripheral cutter whose edge is shaped to produce a special configuration on the surface. One example is the gear tooth cutter. The exact contour of the cutting edge of a form mill is reproduced on the surface of the workpiece.
End-milling cutters — End mills can be used on vertical and horizontal milling machines for a variety of facing, slotting and profiling operations. Solid end mills are made from high-speed steel or sintered carbide. Other types, such as shell end mills and fly cutters, consist of cutting tools that are bolted or otherwise fastened to adapters.
Solid end mills — Solid end mills have two, three, four, or more flutes and cutting edges on the end and the periphery. Two flute end mills can be fed directly along their longitudinal axis into solid material because the cutting faces on the end meet. Three and four fluted cutters with one end cutting edge that extends past the center of the cutter can also be fed directly into solid material.
Milling cutter nomenclature — As far as metal cutting action is concerned, the pertinent angles on the tooth are those that define the configuration of the cutting edge, the orientation of the tooth face, and the relief to prevent rubbing on the land. o
Outside diameter — The diameter of a circle passing through the peripheral cutting edges. It is the dimension used in conjunction with the spindle speed to find the cutting speed (SFPM).
o
Root diameter — This diameter is measured on a circle passing through the bottom of the fillets of the teeth.
o
Tooth — The tooth is the part of the cutter starting at the body and ending with the peripheral cutting edge. Replaceable teeth are called inserts.
o
Tooth face — The tooth face is the surface between the fillet and the cutting edge, where the chip slides during its formation.
o
Land — The area behind the cutting edge on the tooth that is relieved to avoid interference is called the land.
o
Flute — The flute is the space provided for chip flow between the teeth.
o
Gash angle — The gash angle is measured between the tooth face and the back of the tooth immediately ahead.
o
Fillet — The fillet is the radius at the bottom of the flute, provided to allow chip flow and chip curling.
Clamping Technique The workpiece should be clamped in the machine vice as shortly as possible above the clamping jaws to prevent the workpiece from being torn out or from changing its position during the milling operation.
Clamping the workpiece in the machine vice 1 vice, 2 workpiece. 3 parallel pieces The following work-holding fixtures are used essentially for milling parallel surfaces:
Machine vice
Magnetic chuck
Direct clamping on table
Clamping fixtures (single and multi-piece clamping)
When clamping the workpieces in the machine vice for milling parallel surfaces it is absolutely necessary to place the contact surfaces on ground parallel pieces. The following prerequisites have to be fulfilled:
The grade of parallelism depends on the planeness of the surface worked first.
The workpiece has to be clean (free from chips) and deburred.
The exact workpiece rest can be checked by the tight seat of the parallel pieces.
Same height of parallel pieces is necessary.
The following prerequisites are to be considered when work-p ieces are clamped and milled on a magnetic chuck:
The surface machined first must be clean, deburred and plane. It serves as contact and reference surface.
To secure the workpiece position, fences having at least 2/3 o f the workpiece height must be available.
The depth of cut must not exceed a maximum of 2.5 mm.
Contact surface width must at least correspond to the height of the workpiece.
Only ferriferous workplaces (steel and cast materials) are permitted to be machined on the magnetic chuck.
Clamping on magnetic chuck No.1 magnetic chuck, No. 2 workpieces, No. 3 parallel pieces,No. 4 fence, No.5 operating elements Due to the geometrical form or the workpiece size, direct clamping on the milling machine table is used as well. In this case, clamping fixtures are employed in the form of clamping bolt, clamping iron and clamping base as well as special auxiliaries (stop rails, work-holding plates, etc.).
Clamping elements No. 1 clamp bolt, No. 2 nut, No. 3 washer, No. 4 clamping iron, No.5 step block (workholding base) Fixtures for milling parallel surfaces are used in those cases where a definite positioning and securing of the position of the workpiece is not possible with common clamping means. When a great number of pieces are produced, the employment of multi-piece clamping fixtures is economically substantiated.
Type and method of cutting fluid use in milling processes Cutting fluids can be broken into four main categories: straight cutting oils, water miscible fluids, gasses, and paste or solid lubricants
Emulsions Emulsion is a term that describes soluble oils. An emulsion is a suspension of oil droplets in water. Soluble oils are mineral oils that contain emulsifiers. Emulsifiers are soap-like materials that allow the oil to mix with water. Emulsions (soluble oils) when mixed with water produce a milky white coolant. Lean concentrations (more water-less oil) provide better cooling but less lubrication. Rich concentrations (less water- more oil) have better lubrication qualities but poorer cooling.
Chemical Fluids Chemical coolants are also miscible cutting fluids. Chemical cutting fluids are preconcentrated emulsions that contain very little oil. Chemical fluids mix very easily with water. The chemical components in the fluid are used to enhance the lubrication, bacterial control, rust, and corrosion characteristics. There are several types of chemical coolants available, including coolants for extreme cutting conditions.
Inactive chemical cutting fluids are usually clear fluids with high rust inhibition, high cooling, and low lubrication qualities. Active chemical fluids include wetting agents. They have excellent rust inhibition and moderate lubrication and cooling properties. Some contain sulfur or chlorine additives for extreme pressure cutting applications.
Semi-chemical Coolants Semi-chemical fluids are a combination of a chemical fluid and an emulsion. They have a lower oil content but more emulsifier. This makes the oil droplets much smaller. They have moderate lubrication and cooling and high rust inhibition properties. Sulfur, chlorine, and phosphorous are sometimes added to improve the extreme pressure characteristics.
Straight Cutting Oils Straight cutting oils are not mixed with water. Cutting oils are generally mixtures of mineral oil and animal, vegetable, or marine oils to improve the wetting and lubricating properties. Sulfur, chlorine, and phosphorous compounds are sometimes added to improve the lubrication qualities of the fluid for extreme pressure applications. There are two main types of straight oils: active and inactive.
Inactive Straight Cutting Oils Inactive oils contain sulfur that is very firmly attached to the oil. Very little sulfur is released in the machining process to react with the work piece. Mineral oils are an example of straight oils. Mineral oils provides excellent lubrication, but are not very good at heat dissipation (removing heat from the cutting tool and work piece). Mineral oils are particularly suited to nonferrous materials, such as aluminum, brass, and magnesium. Blends of mineral oils are also used in grinding operations to produce high surface finishes on ferrous and nonferrous materials.
Active Straight Cutting Oils Active oils contain sulfur that is not firmly attached to the oil. The sulfur is released during the machining operation to react with the work piece. These oils have good lubrication and cooling properties. Special blends with higher sulfur content are available for heavy duty machining operations. They are recommended for tough low carbon and chrome-alloy steels. They are widely used in thread cutting. They are also good for grinding as they help prevent the grinding wheel from loading up. This increases the life of the grinding wheel.
Gasses Cutting oils and water miscible types of cutting fluids are the most widely used. Gasses are sometimes use. Compressed air and inert gasses are sometimes used. Carbon dioxide, Freon, and nitrogen are also used sometimes.
Paste and Solid Lubricants Waxes, pastes, soaps, graphite, and molybdenum disulfide may be used. These are generally applied directly to the work piece or tool, or in some cases, impregnated directly into a tool, such as a grinding wheel. One example would be lard. Many experienced journeymen recommend lard for tapping.
CO2 Coolant Carbon dioxide (chemical formula CO2) is also used as a coolant. In this application pressurized liquid CO2 is allowed to expand and this is accompanied by a drop in temperature, enough to cause a change of phase into a solid. These solid crystals are redirected into the cut zone by either external nozzles or through-the-spindle delivery, to provide temperature controlled cooling of the cutting tool and work piece.[4] The ChilAire system is one of the pioneers in the application of CO2 as a coolant.[citation needed] Existing CNC machines can be retrofitted with this safe and environmentally friendly coolant approach. In applications such as turning, milling or drilling tool life and throughput have been improved substantially; especially in high temperature alloys such as titanium, 4140, steels and plastics.
The Use of Cutting Fluids in Drill Press Operations The coolant should be aimed at the area where the tool contacts the work. It should be flooded so that as much fluid as possible reaches the cutting edges. The operator should withdraw the tool occasionally to remove the chips. The best method is the use of tools that have integral oil holes. This
means that various tools are available that feed the coolant through the tool and directly to the cutting edge. This also helps wash the chips out of the hole.
Relation Of The Parameter e.g Cutting Speed, Feed Rate And Depth Of Cut Cutting Speed
Important factor that affected milling operation efficiency
In order to work efficiently & economically
Its symbol is V. It is expressed in metre/min (m/min)
Formula: Cutting speed = diameter of cutter x π x spindle speed V=dxπxn
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 MILLING MACHINE CUTTING SPEEDS CUTTER MAT. HIGH SPEED STEEL CUTTER m/min RAW MAT. Machine Steel 20 - 30 Tool Steel 18 - 20 Cast Iron 15 - 25 Bronze 20 - 35 Aluminium 150 - 300
CARBIDE CUTTER m/min
100 - 125 40 - 60 40 - 60 60 - 120 150 - 300
Spindle Speed
defined as the speed at which the spindle of a milling machine rotates per minute Its symbol is n. It is expressed in revolution/min (rpm)
Formula:
Selection of proper cutting speed: a) For longer cutter life, use the lower cutting speeds in the recommended range b) Know the hardness of the material to be machined c)
When starting a new job, use the lower range of the cutting speed and gradually increase to the higher range if conditions permit
d) If a fine finish is required, reduce the feed rather than increase the cutter speed e) 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
defined as the distance in millimeters per minute that the work moves into the cutter
Its symbol is f. It is expressed in mm/min
Formula:
Factors on which feed rate depends on a) b) c) d) e) f) g)
The depth and width of the cut. The design or type of the cutter. The sharpness of the cutter. The workpiece material. The strength and uniformity of the workpiece. The type of finish and accuracy required. The power and rigidity of the machine
Machining Time Calculation
Formula:
I = Workpiece length to be milled
lu = Over travel
la = Advance.
L
D = Milling Cutter Diameter
n = r.p.m of the Cutter
Ts = Machining Time (min)
f
= Total Milling Length
= Rate of Feed (mm/min)
Formula: Machining Time = Travelling Distance of the Milling Table (mm) Rate of Feed (mm/min)
ts = L f NOTE: The travelling distance depends on the length of the cut to be milled, the type of cutter used and the type of milling performed.
