CNC Machine - Introduction, Working, Parts, Types

CNC Machine –


Computer Numerical control machine is the full form of cnc machine 

It replaced the cnc machine by using mini computer. In cnc machine programme is stored in the computers. It makes the interfaces easy for write, edit or changing the programme completely. Noways in cnc machine we can make port programme which can easily store, edit, download, uploaded and simulation using tool path.

CNC Machine working —


Make the job on cnc machine by following step-

 1.  First we make the drawing of the required job in cod software
     2. Generate the programme through software or manually
     3.  Feed the programme in cnc machine central unit from computer through        USB cable or chip
     4.  Identify the machine tool from machine tool database
     5.  cnc machine will be identify operation, tooling, teed, speed, depth,                 power, by reading programme
     6.  Cheek the simulation using tool path
     7.   Take a trail run 
     8.  Cut the job


CNC Machine

CNC Machine parts – cnc machine has following parts –

1.    Base – All the remains parts of cnc machine is mounted on base. It is made of cast iron

2.    Spindle – It provides the necessary motion and power for the machining

3.    Drive – In cnc machine two types of drive is used

a.     Spindle drive – It provide power to main spindle for cutting
b.    Feed drive – It drive the axis as per programme

Following motor is used in cnc machine for feed drive-

(i)    Dc and Ac servomotor
(ii) Stepped motor

(iii)                       Linear motor

4.    Lead Screw – Lead screw is used to convert the rotary motion into linear motion for operating various axis of machine

5.    Slide way

6.    Feed back devices

7. Sensor

8. Linear scale 

9. Machine control unit – this is the main part of cnc machine in which programme is stored and control the all movement of machine.

10. ATC

Read Also -

CNC Machine Tool - https://www.cncrules.com/2018/12/cnc-machine-tool-characteristics-types.html


Types of CNC Machine - 


CNC Machine has a wide range of application we are given some cnc 

machine name here used in various manufacturing areas-


1. CNC milling machine –

 Cnc milling machine is used widely for manufacturing a lot of product. It can perform a lot of operation line face milling, threading, vertical milling, drilling, boring etc. It is computer interface

2. CNC Lathe machine – 

Cnc lathe machine is used to cut the rotatedjob. It this machine job will be fix in chucke. CNC leathe tool is Controlled by machine control unit. Job will be rotate and tool will be move according to programme in x and z axis. CNC lathe machine works on two axis x and z axis

3. CNC Electric machine (EDM) -

 CNC wire cut EDM machines are common in which relative motion of the work piece with respect to the EDM wire. It is mostly used in sheet metal industry.

4. CNC Laser cutting machine -

CNC laser cutting machine is used to cut the job in two parts. It is widely used in industry.

5. CNC Router - 

CNC router is used to cut word plastic and sheet metal in X,Y and Z direction. It is used for manufacturing large scale products.

6. CNC grinding machine -

CNC grinding  machine is used for finishing  the job. These CNC machine is also controlled by mini computers through using programme.






Milling Machine - Definition, Operations, Parts, Cutter, Process



Milling machine definition


Milling is a machining process which is uses to remove material from the job by using multi point cutting tool. A machine which is used to perform various operations like horizontal milling, vertical milling, angular milling is named milling machine. Milling machine parts is given as 
below :



Milling Machine Parts


1.                Base
2.                Column
3.                Knee
4.                Gearbox
5.                Spindle
6.                Saddle
7.                Table
8.                Over arm
9.        Arbor
10.     Arbor support   


1.              Base:  The base of a machine works as a foundation for all other parts which rests upon it. It is made of cast iron. 

2.             Column:  The column is the main parts of milling machine which is mounted vertically on the base. The column houses have all the driving mechanism for the spindle and table feed. The main motor is incorporated in the column. The top of the column is finished to hold an overarm that extends outward at the front of the machine. The lower part of the column is a sturdy base, which incorporates the cutting fluid tank.

3.             Knee: The knee is of rigid casting that slides up and down along a precision machined guide-ways. The knee houses the speed mechanism of the table and the different controls to operate it. The feed motor and gearbox are usually incorporated in the knee.

4.             Gear box: The gear box for the spindle drive comprises, shafts with bearings and gears, and controls for the setting of the spindle speed.

5.              Spindle: The spindle is housed in the upper part of the column and receives power from the motor and transmits it to the arbor. The front end of the spindle projects from the column face and is provided with a tapered hole into which various cutting tools and arbors may be mounted.The accuracy in machining depends on the rigidity of the spindle. The speed of spindle can be selected by the speed gearbox, and the feeds can be selected through the feed gearbox. The spindle is arranged horizontally in the horizontal milling machine.

6.              Saddle: The saddle is placed on the top of the knee which slides on the guide way set exactly at 900 to the column face. A cross feed screw near the top of the knee engages a nut on the bottom of the saddle to move it horizontally for applying the cross feed.

7.             Table: The table rests on the guide way on the saddle and travels longitudinally. T slots are provided on the table to mount the work pieces directly or to mount the work holding devices. The longitudinal feed stops are located on the front of the table. These disengage the machine feed at a set position. The table is also fitted with a hand wheel for hand feed in the longitudinal direction and a lever for locking the table. There is a gutter around the around the edges of the table to collect the cutting fluid.

8.              Over arm and brace: The over arm is mounted on the top of the column above the spindle and is intended as a support when milling with an arbor. The arm is adjustable so that the bearing support may be provided nearest to the cutter. The brace provides extra stability to the machine. It must be loosened before the table elevation setting is altered.

Milling machine


Milling machine diagram




Milling Machine Cutter

Milling machine cutter can be classified as:

1. Plain milling cutter -

(a) Light duty plain milling cutter -   Helix angle= 25 degree
(b) Heavy duty milling cutter - Helix angle = 25-40 degree
(c) Helical duty milling cutter - Helix angle = 45-60 degree

2. Side milling cutter -

(a) Plain side milling cutter 
(b) Staggered teeth milling cutter - Used for large depth cut

3. Metal slitting saw cutter milling cutter - Suitable for cutting small cut and to divide the job in two parts

(a)  Plain metal saw milling cutter - 0.3 mm - 6 mm
(b) Staggered teeth slitting milling cutter - 6-7.5 mm

4. Angle milling cutter -

(a) Single angle milling cutter
(b) Double angle milling cutter


Milling cutter



5. Formed cutter -

(a) Convex milling cutter
(b) Concave milling cutter

6. Thread milling cutter

7. Wood ruff key slot milling cutter

8. Fly cutter

9. Tap and reamer cutter

10. Corner rounding milling cutter

11. Gear cutter

12. Sprocket cutter

13. Spline cutter

14. bolted cutter



                                                  

Material For milling cutter


1. High carbon steel (H C S) - 

2. High speed steel (H S S) - Tungsten = 14-22 % , Venedium = 4%

3. Sintered carbide- Mixture of tungsten carbide, cobalt and titanium                                carbide 

4. Ceramics

5. Diamond                                              

Angle of milling cutter

  
A milling cutter tooth is more or less identical to that of a single point tool. The rank angle of a milling cutter is the inclination of the tooth face and it is measured from a line joining the cutter of the cutter and the tooth of the tip. The clearance angle of a milling cuter is the relief given to the portion AB of the cutter. This clearance relief is given to from the cutting edge, and it avoids rubbing the rubbing the work piece while machining. It is given two stages. First it is ground to a small angle 0 and this angle is called relief angle. This angle should be very small as any increase in this angle would reduce the strength of the tooth. The portion TP of the tooth up to which the relief angle extends is called the land. After the land the tooth is further relieved t any angle 0 and angle is called the primary clearance angle which is about 150. The angle 02 is called the secondary clearance angle and this defines the shape of the chips space which is call gas. The tooth of the chip is radius to help cutting of the chips. This round portion of the chip space is called fillet. Primary clearance angle, relief angle, secondary clearance angle are all measured from a tangent drawn at the tool tip.
          
The positive rake angle is used for general purpose, and issued specially for milling materials, which produce continuous chips. In the positive rake, the weakest point, the weakest point is presented to cut first. The reaction   forces tends to pull the cutter into the work and the cutter forces tend to lift the work piece .The positive rake cutting edges peal the chip away from the work, and hence there is a likely hood of breakage of cast iron parts, especially those having thin and fragile sections.
         
A negative rake makes the tooth stronger and is suitable for roughing cuts. In the negative rake, the strong area is presented to cut first. The reaction forces tend to push the cutter away from the work, and the cutter forces tend to push the work against the fixture.
          
Zero rake angle is ideal for milling material like cast iron, brass etc. which produce broken chips.


MILLING PROCESSES


Several operations are performed on knee type horizontal milling machine and vertical milling machine .Some are as given

(1)           Plain milling or Slab milling: It is the production of a horizontal flat surface parallel to the axis of the milling machine. The work piece is held in a vice or fixture, or fastened directly on to the table.

(2)          Side milling: It is the process of machining a vertical flat surface perpendicular to the axis of the milling machine arbor. The combined this action of the peripheral and side teeth on a side and facing cutter perform this operation.

(3)          Face Milling: It is done to produce a flat surface perpendicular to the spindle axis of the machine. This is done by means of a face-milling cutter mounted on the vertical milling machine spindle. Face Milling may also be done in a horizontal milling to produce vertical flat surfaces.

(4)          End Milling: It is an operation similar to face milling but done using a much smaller cutter. Cutting is done on the end of the cutter as well as on the periphery. Its operation is used for facing small surfaces, milling slots, grooves, producing internal recesses and for truing the edges of a work piece.

(5)    Straddle Milling: In this type milling two vertical face of job is prepared simultaneously. Two side and face cutter is used on arbor in a single operation.

(6)    Gang Milling: When two or more surfaces is prepared simultaneously in milling machine is called gang milling.

(7)    Angular milling: To prepare the angular face of the job is used angular milling.

(8)   Form milling:   Form cutter is use in this process. Irregular contour is performed by this process.

(9)   Profile Milling 

(10)  Key way and Slot Milling 

(11)  Saw Milling

(12)  Helical Milling

(13)  Gear milling

(14)  Thread Milling

(15)  Cam Milling   



Up milling and - Down-Milling


The two operations differ by the directions in which the teeth of the cutter and the feed of the work piece move.


Up-Milling


The most commonly used method of feeding is to being the work against the direction of rotation of the cutter. This is also known as conventional milling. This is most commonly used method. In up milling the removal of the chip by each citing edge starts at the thinnest part of the chip and progresses to the thickest part. The cutting edge slides in the material before it starts to cut. This scraping causes a good deal of heat and wears on the cutter. The cutter and work pieces suddenly spring apart the machine chatters, and ripples flaw the material surface. The spindle for the milling is pensioned in the direction of feed. It is feasible on any milling machine, Chances of cuter breakage are less.

Up Milling


Down milling

It is also known as climb milling. In it the feed moves in the same direction as the rotation of the cutter. Chip removal starts at the thickest part. The cutter cuts into the material straight way and doesn’t slide. As a result less heat is developed and there is less wear on the cutter. Work piece is pressed down on the worktable by the cutting pressure and thus prevents the work piece from lifting. This Method is not recommended unless the machine table is fitted with a backlash eliminator.

Down Milling


Read Other Milling Topic -

Read About Vernier Caliper -






x

Vernier Caliper - Definition, Principle, Types, Reading, Least count, Diagram


Vernier Caliper


The vernier caliper is precision instrument which can measure upto 1 / 1000th of an inch in british system and 0.02 mm in metric system

Vernier scales are made to read 1 / 1000" in inches and 1/50 mm. in metric size.



Principle of Vernier caliper


Vernier Caliper works on the difference of main scale and vernier scale.
It involves dividing a line of known length into a certain number of equal parts and then comparing the length of these division with those made on a line of the same length but with a number of division which are one more than on the first line.


Vernier caliper diagram

         






If a fixed scale f 1" length is divided into 4 equal parts and sliding scale of 1" length is divided into 5 equal parts, then difference will be 1/4 - 1/5 = 1/20 or 0.05". Now if the sliding scale is moved in such a way that the first line of the sliding scale coincides with the first line on the first scale, the distance moved by the scale will be .05".


Vernier Caliper Least Count 



In Metric System - 0.02 mm

In British System - 0.001 inch


Vernier Caliper Formula [Vernier Caliper Reading]



One parts of main scale is - 1/2 mm
24 main scale division = 1/2 * 24 = 12 mm
25 vernier scale divison = 12 mm
1 vernier scale divison = 12/25 mm
So according to Principle Least count = Main scale - Vernier scale
Least count = 1/2 - 12/25 = 1/50 = 0.02 mm

Parts Of Vernier Caliper



1.Outside Large Jaws -
                                      It is used to measure the outer side of any project.
 
2.Inside Small Jaws -
                                    It is used to measure the inside of any object.
 
3.Depth Rod -
                        It is Used to measure the depth of any project or hole
 
4.Main Scale - 
                         It is made from stainless steel
 
5. Vernier Scale (Metric) -
                                            it shows the measurement in 0.1 mm.

6. Movable Jaw

7. Fixed Jaw
 
8. Lock Screw

9. Sliding Unit

10. Beam


ads

How to Read the Vernier caliper (British System)


(1) Note the number of full inches that show from the zero on the main scale to zero on the vernier. In Fig. 15.30, it will be 3.000".
         
(2) Read the number of division beyond the inch division which we have already taken (3) and note them. In the fig. it will be 5 which will read 0.5".
         



(3) Note the 1/40th division on the main scale. In fig. it will be 2 which will read 2/40 or 0.05".
        
(4) To read the vernier scale, note along the scale until you find the line on vernier coinciding with the main scale line. this may be nicely read with magnifying glass. in fig. we see that line 15 on the vernier scale is coinciding with the line on the main scale, which will read 0.015" because one line on the vernier scale reads 0.001".
          
(5) To get the total reading we add all the readings :- 3.000+0.500+0.050+0.015= 3.565".
The same way the reading on the metric vernier can be had.


Types of Vernier Caliper


1. Flat Edge Vernier Caliper

2. Knife Edge Vernier Caliper 

3. Flat and Knife Edge Vernier Caliper

4. Vernier Caliper Depth Gauge

5. Gear Tooth Caliper

6. Dial Caliper

Read for milling machine- 
https://www.cncrules.com/2018/11/milling-machine.html

Read for Lathe machine operations -
https://www.cncrules.com/2018/11/lathe-machine-operation.html


How to make cnc/ vmc programme -

https://www.cncrules.com/2018/06/how-to-make-cncvmc-programme-with-step.html