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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