An Overview of CNC machines

Contents

Various types of machines Why CNC machines, applications & economics Classifications of CNC machines Elements of CNC machines: Mechanical ,

Electronics & accessories CNC features & systems Programming of CNC machines Special terminology Testing of CNC machines Leading makes of Indian & imported CNC machines HSM: High sped Machining.

Types of machines

GPM with conventional or PLC controlGPM with CNC ControlSPM with Conventional or PLC controlSPM with CNC controlTransfer LinesFMS

Definition of a CNC machine

A machine tool , whose movements are controlled by a micro -processor & can be programmed for part cutting.

Applications of CNC machines

CNC machines are used when : Batch size is small Bigger product mix with lot of

variation Part access requires multiple set

ups Referencing not possible by

fixturing

It is a myth that CNC It is a myth that CNC machines can solve all machines can solve all problems !!problems !!

SPM’s give normally better quality , productivity & lower cost of part for mass production environment.

Many industries are doing away with M/C when volumes go higher, for volumes higher than 100 /day , SPM line is preferred.

Advantages of CNC machines

Flexibility of part productionFlexibility of processAccurate reproduction of parts.No operator errorsMinor product changes can be

readily adapted.

Limitations of CNC machines

Higher capital & running cost. Low productivity compared to SPM

‘sRequirement of skilled manpower

for part production & maintenanceless robust compared to SPM &

GPM. Downtime is normally higher.

Summary Slide

Applications of CNC machines

Applications of CNC machines

Typical examples of CNC use For turning applications as variety is high. For multi product set up. For job shops & tool rooms For die making For small size of production & more variety of

operations / parts. E.g. Crankcase set up in Nagpur, John Deere Transmission Set up in Pune etc.

For prototyping For difficult referencing e.g. Dowel hole making in

crankcase & Trans. Case. Etc.

Classifications of CNC Machines

HMC : Horizontal Machining CentreVMC : Vertical Machining CentreCNC turning CentreCNC milling & grinding machinesDrill Tap centersFMSHexapods

Vertical machining Centre

VMC- Hitachi with APC

Horizontal Machining Centre

FMS

Head Changer HMC

Hexapods

Elements of CNC machines - Mechanical

Guideways Hardened & ground type Cast guideways LM guideways Roller guideways Tercite coatings

Ball screws Precision Rolled Dual nut arrangement for backlash elimination

Classification of Ball screws

LM guide ways

Elements of CNC machines - Mechanical

Spindles In-built Cartridge Motorized spindles Gear box

ATC: Automatic Tool Changer Magazine type , e.g. LMW , BFW Corrousal type , e.g. AMS Disc type , e.g. Arrow or Feeler Direct pick up , e.g. AMS HMC

Elements of CNC machines - Mechanical

APC: Automatic pallet Changer: APC enables loading of next part while machining of first part is in progress. Linear type e.g. LMW, PAL Shuttle type , e.g. BFW TMC 630 N Rotary type , e.g. Makino , BFW Maxpro

series Manual type , e.g. UCAM

Rotary Pallet Changers

ATC for VMC

ATC for VMC

ATC for HMC

ATC for HMC

Elements of CNC machines - Mechanical

Table: table is mounted on bed , it receives either fixture or pallet. Table has t -Slots or tapped holes. In case of APC machine,table has pallet

locating & clamping mechanisms. Index table Rotary table : continuos NC table B axis.

Elements of CNC machines - Mechanical

Turret : Turret is used in Turning centers for tool storing , holding & positioning. Unidirectional , Bi-directional Hurth coupling Driven tools

Tail stock Hydraulic, non programmable Programmable

Part catchers & Bar feeders

Elements of CNC machines - Electronic

Control: controls are a combination of hardware & software that decides & monitors machine movements & other functions through program. Fanuc 0-MC , 0-MD, 0-i etc. Siemens : 810 , 840 etc. Mazatrol , Heidenhein , Mitsubishi , Fagor

Drives: Drives are communication hardware & software between machine control to motors.they are called servo drives as they work in closed loop control & monitor movements via. Sensors like encoders. AC /DC drives Analogue / Digital drives

Elements of CNC machines - Electronic

Encoders: Encoders are feed back sensors used for communicating the machine position to the controller. Rotary encoders: they are mounted on the drive

motor shaft & feed the angular position to the controller.rotary encoders do not give feed back on the actual axis position. ( open loop)

Linear encoder : these are nothing but linear scales. They are mounted on the slide itself & give feed back of actual machine position ( closed loop)

Limit / proximity switches: these are sensor elements that give digital signal out put to confirm completion of any movement. They are normally used for axis limit detection , ATC position detection etc.

CNC accessories

Coolant & chip disposal systems Standard coolant system : For bed

wash , Component flooding etc. High pressure coolant : 15 to 125

bars.normally used for coolant through tool feature.

Special rotary unions are required for coolant thru. Spindle : Deublin make.

CNC accessories

Filtration systems Cartridge filtration system Drum filtration system Centrifuge filtration system Magnetic separator Paper band filtration system Oil skimmers

CNC accessories

Chip conveyors: Scraper type Magnetic type Screw conveyor

AC for CNC panel Makes : Sunbeam , Advanced , Rittal etc.

Tool presetter: Ashwini , Optomech , Zoller etc. Used for taking tool offset offline new generation pre-setters allow direct loading of

tool offsets.

CNC accessories

Lubrication systems Centralized auto. Intermittent type:

CENLUBE, Willy Vogal, Used for guideway lubrication

Grease lubrication: Klubber , majorly for spindle but also for guideways.

Eco pack for guidewaysMulti spindle heads , Angle Heads.

Features & Systems

Part seat checkingProbing: Renishaw, Mitutoyo

Spindle mounted probe for work measurement Table mounted probes for tool measurement

Live hydraulicsTool monitoring : Montronix, O-mat,

In-built tool monitoring is done by spindle load &

vibration monitoring against ideal curves.

Programming of CNC machines

Manual programming: through G, M , T codes

CAD, CAMDigitizingWork offsetTool offsetReferencing

Tooling of CNC machines

Different types of spindle tapers ISO-BT 30/ 40 /50 HSK Modular tooling Pull studs Modular fixtures Form A/ B type tooling

HSK taper for Spindle

Special Terminology

MRR - Material Removal RateRS 232Linear motorsInternet connectivityGrid settingMotor specificationsTaper cleaning

CNC specifications

Capacities : like X-Y-Z strokes , table size , motor power etc.

Dimensions : floor space , Spindle to table , floor space

Performance :Spindle taper, Rapid rates, RPM etc.

Accuracies: Positioning error, repeatability etc.

Spindle Motor Characteristics

Testing of CNC machines

Geometrical testing Parallelism , squareness , Spindle run out etc.

Accuracy testing Repeatability , positioning accuracy , Backlash etc. JIS standard, VDI- DGQ 3441 standard etc. LASER Calibration

Performance testing MRR, Part cutting

Other tests Spindle heating, Vibration, idle cycle running etc.

Leading makes of CNC machines

Local : LMW, BFW, HMT, AMS ,PAL , MKL etc.

Imported European: Heller, Grob, Chiron , Huller-

hulle ,Cincinnati, Bridgepart, Warner - Swaccy etc.

Japanese : Makino, Mazac, Hitachi, Yazda , Nigata , Mitsubishi, Mori-seiki etc.

Taiwanese : supermax , Feeler , Hard ford, Tong - Tai etc.

High Speed machining

This technology is created for getting Multi-spindle productivity from single spindled machines.

Features of HSM High rapid rates : upto 100 M/min High spindle speeds : up to 25000 RPM High acceleration >1g Reduced idle times : like tool change : 1.5 sec. ,

Pallet change : 10 secs. Etc. High cutting speeds, reduced loads &

distortions.

High Speed machining

Change in machine elements : Ceramic ball bearings , Hydro-static bearings

for spindles. Linear motors Newer controls Ball screw cooling Spindle core cooling Rotary pallet changers Armless ATC, Direct pick up. High machine rigidity High pressure coolant through Spindle

Demo of Heller MC-16 doing helical Interpolation