cnc cooltool - milling machine - pbworksstsdubai.pbworks.com/w/file/fetch/92339586/module 1 term 2...

1 Prepared By: Tareq Al Sawafta

CNC Cooltool - Milling Machine

Module 1:

Introduction to CNC Machining


Module Objectives:

1. Define machining.

2. Know the milling machine parts

3. Understand safety rules in machining

4. Distinguish between machining cutting tools.

5. Recognize the main machining processes.

Module Contents

1. General Introduction and Definitions

2. Description of Milling Machines

3. Safety precautions on CNC machine tools

4. Types of milling tools

5. Milling operations


1.1 General Introduction and Definitions

Machining is a class of material-working processes that involves using a power-

driven machine tool to shape metal.

The parts shown in Fig.1.1 are made by machining processes.

Fig. 1.1

The two major categories of machining are:

1. Conventional machining.

Also known as "manual machining" is generally regarded as using manually

controlled machines, particularly lathes, mills and drill presses. The tool

moves around the work by mechanical controls that are manually controlled.

2. CNC (computer numerical control) machining.

CNC machining is generally regarded as using lathes and mills (and some

other machine types) in which all tool and workpiece motion is controlled by

a computer.

The actual metal cutting process is the same. The difference is in how the

tool path is controlled as it cuts the workpiece.


1.1.1: History and Development of CNC Technology

The idea of numerical control (NC) of machine tools emerged in 1949/50 at

the MIT (Massachusetts Institute of Technology, Cambridge, USA) in order to

manufacture important airplane parts from full material rather than by

riveting and welding material together.

The templates and patterns needed for form cutting were however very

complicated and could only be manufactured with a considerable time and

cost increase when using conventional technology. Since how-ever the

contours of the large parts could easily be represented as mathematical

functions it was decided to develop a control to control a milling machine on

this basis.

1.1.2: What is CNC?

CNC stands for Computer Numerical Control. It is the technology of

controlling a machining operation using a computer program, which is called

Numerical Control (NC) Program. Fig. 1.1.2

Fig. 1.1.2


1.2: Description of Milling Machines

The most important conventional machine tools that shape materials

to a size by cutting away unwanted portions, are:

a. Turning (Lathe) machine

The primarily function, of the turning machine is to produce a cylindrical

surfaces.

b. Milling machine.

Use a rotating multi toothed cutter into the workpiece to remove material, in

order to make gears, slots, holes, many different shapes.

1.2.1: Milling machines are classified to:

a. Vertical milling machine

in which the spindle positioned perpendicular

to its worktable.


CNC Cooltool vertical milling machine parts


b. Horizontal milling machine shown in Fig.

in which the cutting tool positioned horizontally and parallel to the

worktable.

1.3: Safety precautions on CNC machines

The target of work security is to eliminate accidents and damages to

persons, machines and facilities at work site.

Basically the same work security precautions apply to working on CNC

machines as to conventional machine tools. They can be classified in three

categories:

1. Danger elimination

Defects on machines and on all devices necessary for work need to be

registered at once.

Emergency exits have to be kept free.

No sharp objects should be carried in clothing.

Watches and rings are to be taken off.


2. Screening and marking risky areas:

The safety precautions and corresponding notifications are not allowed to be

removed or inactivated. Moving and intersecting parts must be screened.

3. Eliminating danger exposure

Protective clothing must be worn to protect from possible sparks and

flashes.

Protective glasses or protective shields must be worn to protect the eyes.

Damaged electrical cables are not allowed to be used.

When setting up and operating CNC machines the following is to be taken

into consideration:

• In general, setting-up is allowed only on a machine which has been

switched off.

• The operator should not go to the rotation or work area of the machine

since within this area the machine can automatically rotate the turret head

or feed the tool carrier.

ATTENTION

Milling can be very dangerous, you can be seriously injured !

AVOID

Wrong milling direction (always mill against the turning direction of the

milling head), too thick chips.

The surface of the work piece is not clean

Mill again, less feed, check milling direction

Machine does not work exactly

Check connections, clean and grease slides (they must be easily moveable),

check backlash.

Backlash is the play in the engagement of the spindles for cross and

longitudinal

slide that allows a few hundreds of a mm to be turned on the

handwheel before the leadscrew starts to turn when changing directions.


This is not a fault with the machine but simply a fact of life on any threaded

screw and is accounted for by always making your cuts in the same

direction and keeping track of which way you turned the handwheel last.

We recommend backlash be set to about 0,08 mm to 0,12 mm. Unimat

slides come with adjustable handwheels to recalibrate on change of

direction.

Finishing steps:

1. Shut off the machine.

2. Switch off the power supply.

3. Use a brush to remove chips from the work piece

4. Keep workplace clean and tidy.

1.4: Classifications of milling tools

Details of milling tools are given in the manufacturers´ catalogues and in the

corresponding norm sheets.

1.4.1: Cutting edge materials

In milling, the cutting edges are not in operation all the time. The milling cut

is a discontinuous cut with a changing cutting diameter. Therefore, the

cutting edge is exposed to high impact forces. The cutting edge material has

to be tough and heat resistant, and they are:

1. High-speed steel

2. Hard metals

3. Cutting ceramics

4. Diamond


1.4.2: Cutting oils (coolant)

The major advantage of using a coolant or cutting oil is:

1. It dissipates heat

2. giving longer life to the cutting edges

3. Lubricates the cutter face

4. Flushes away the chips

Types

Cutting oils are:

1. Water-based soluble oils,

2. Petroleum oils

3. Synthetic oils.

In general, a simple coolant is required for roughing. Finishing

with good lubricating properties to help produce a good finish on the

workpiece. Plastics and cast iron are almost always machined dry.


1.5: Cutting Tools function

1.5.1: Cutting Tools for Horizontal milling

a. Slab Mills

For heavy cutting of large and flat surfaces.

Slab Mill

b. Side and Face Cutters

For cutting shoulders and slots.

Side and Face Cutter

c. Slitting Saws

For cutting deep slots or for parting off.

Slitting Saw

1.5.2: Cutting tools for vertical milling

a. End Mills

Commonly used for facing, slotting and

profile milling.

End Mill

b. Rough Cut End Mills

For rapid metal removal.

Rough Cut End Mill


c. Slot Drills

For producing pockets without drilling

a hole.

Slot Drill

d. Face Milling Cutters

For heavy cutting.

Face Milling Cutter

1.6: Milling operations

Milling machine is one of the most versatile conventional machine tools with

a wide range of metal cutting capability. Many complicated operations such

as indexing milling etc. can be carried out on a milling machine. Some of

them are:

1. End milling (Pocket): a milling of a flat surface

with the axis of the cutter perpendicular

to the machining surface. Makes either

peripheral or slot cuts

2. Chamfer milling: a chamfer end mill

makes a peripheral cut along an edge of

the workpiece e to create an angled surface.


3. Face milling: a face mill machines a

flat surface of the workpiece in order to

provide a smooth finish.

4. Drilling: a drill enters the workpiece

axially and cuts a hole with a diameter

equal to that of the tool.

5. Boring:

performed after drilling a hole to

enlarge the diameter or obtain

more precise dimensions.

6. Tapping:

The existing hole is typically drilled

By the required tap drill size that will

accommodate the desired tap.


1.6.1: CNC milling

Cutting process in which material is removed from a block by a rotating

tool. In CNC milling the cutting tool is moved in all three dimensions to

achieve the desired part shape. The cutting tool usually rotates about an

axis that is perpendicular to the table that holds the material to be cut.

A block of material is placed on a moving table below the cutter. While

the cutting tool turns, a computer controls the vertical (Z axis) motion of

the cutter and the horizontal (X and Y axis) motion of the block of

material. The cutter is guided to move through the material, removing

portions to create shapes.

Material is usually removed by both the end and the side of the cutting

tool.

Some common cutter shapes include:

Referring to the above images from left to right:

1. Plain end mill - used for most milling - creates walls with straight

90 deg edges and sharp corners at the bottom of recesses.

2. Chamfer end mill - creates 45 deg bevels on the top edge of a

wall or recess.

3. Grooving end mill - creates rectangular grooves in side walls.

4. Ball mill - creates rounded edges at the bottom edge of a recess.


5. Rounding end mill - creates rounded edges at the top edge.

6. Angle end mill - creates walls at angles other than 90 deg.


Student's Notes

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cnc cooltool - milling machine - pbworksstsdubai.pbworks.com/w/file/fetch/92339586/module 1 term 2...

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