cnc pta hardfacing and cladding system
TRANSCRIPT
CNC CONTROLLED PTA WELDING AND HARD FACING OF COMPONENTS
ARCRAFT PLASMA EQUIPMENTS (I) PVT.LTD.
◦ An extension to plasma welding when used for hard-facing
or cladding using powder as a filler material is known as
Powder Plasma welding. Also commercially known as PTA
i.e. Plasma Transferred Arc welding. Being a welding
process the advantages of the PTA are enormous compared
to other Flame or Arc spraying processes. Also as compared
to the commonly available welding methods the PTA scores
well above processes like SMAW, TIG, MIG.
◦ However all the advantages come at a cost in form of
“Automation”. PTA is a process which is not meant to be
used manually and call for an automation is to certain level
mandatory.
◦ The level & topology of the logic for the control of
automation may differ from manufacturer to manufacturer
however the automation can be broadly in 3 categories.
1. Semi automated with timers
2. Numeric controlled (NC) with micro
controller, alpha numeric display, keypad
3. Fully computer based CNC system
• The basic differences can be judged from the working
capacity, the flexibility of the operation, repeatability of
the job, skill level of the operator etc.
• As the subject of automation is very vast and beyond the
scope the article, only the insight into high end
automation has been focused here in next few pages.
• The PTA process has multiple set of parameters to be handled which can be broadly grouped into gas, mass, motion
& power. The parameters covered by each group are as under.• GAS
Ø Plasma gas flow & pressure
Ø Shielding gas flow & pressure
Ø Carrier or Powder gas flow & pressure
• MASS
Ø Powder feed rate
Ø Powder feed down slope
• MOTION
Ø Surface speed of the job
Ø Travel speed of the torch
Ø Torch Oscillation
• POWER
Ø Welding current
Ø Arc gap
• Although the conventional method of handling certain
parameters like gas, powder flow, welding current can be
handled manually but it calls for the skill & the
experience of the welder / operator.
• Exploiting the advantage of the CNC topology,
practically all the parameters involved in the process can
be programmed and by allowing the computer to handle
the process the need for the skilled welding or operator
can almost be eliminated. As in any welding
qualification the initial setting of parameters can be done
under the expert’s guidance. Once set the operator job is
only limited to the loading & unloading of the job on the
system. It is to be noted that any pre or post weld process
required to achieve the desired result have to completed
in any case.
• A typical CNC based system can be wired around high
grade of components which include.
1. Industrial mother board
2. High speed PLC configurable with external add on
modules.
3. High resolution graphic display with Touch Screen
facility.
• Other supporting devices like interlocks, sensors,
measuring devices are to be compatible with the CNC
configuration.
• To achieve the desired result, the compatible mechanical
system with high degree of accuracy is required typically
employing Ball screw mechanism, planetary gear boxes
etc. is a must to squeeze maximum benefits out of CNC
system.
CNC controlled Plasma Transfered Arc (PTA) Welding system
oWith the necessary support of interfacing devices for signaling, measurement, control & correction a complete fail safe PTA
CNC base system can control literally all the parameters involved in the process which are listed as under1. Plasma gas flow & pressure2. Shield gas flow & pressure3. Powder or Carrier gas flow & pressure4. Gas pre flow time5. Gas post flow time6. Welding current7. Welding voltage / Arc gap8. Rotating speed of the job9. Linear travel speed of the torch10. Weld position of the torch11. Torch oscillation width]12. Torch oscillation speed13. Dwell time14. Weld current down slope15. Powder flow down slope
Display screen for Welding current
Display screen of motion control
o Other than the control of parameters the system employs typically single touch operation which controls the sequential
flow of operation automatically which is as under.
1. Sense the Park or No Weld position of the torch2. Bring the torch to Weld position above the job3. Initiate the gas4. Initiate the pilot arc5. Start the welding arc6. Start the job motion7. Start the torch motion8. Start the oscillation9. Start the powder flow10. Deposit desired bands of weld11. Deposit desired passes of weld12. Bring the weld current and powder flow to down slope mode at the end of the job.13. Stop welding & all the other motions14. Allow desired post flow of gas.15. Bring the torch back to park position
TYPICAL JOBS ACHIEVED BY SUCH CNC PTA SYSTEM:
Engine valve HardfacingID Cladding
◦ By allowing the CNC to virtually control all the activity of the process there is an endless list of advantages of such system
◦ Saving in Time
The time saved is what otherwise would be lost in activities like
1. Adjust the torch over the job every time the new job is placed
2. Manually raise the torch every time the job is finished
3. Manually adjust the powder flow rate for every new job.
4. Manually adjust the current for every new job
5. Manually adjust the speed of job, torch, oscillation of every new job.
◦ Saving in powder
1. Volumetric control ensures optimized flow rate.
2. Minimal wastage of powder.
• Uniformity of weld deposit
1. Highly uniform weld deposit
2. No crater at the end of the weld
3. Optimum gas flow ensure no blow holes and no oxidation of the job.
4. Highly repeatable results
• The bottom line
As required by any industry is fulfilled in the form of
1. Reduced cost of deposit per job or per square inch
2. Reduced cost of labor
3. Reduced cycle time hence increase in the production rate
4. Very low rate of rejection
5. Reduced inventory of powder & gases.
• No dependency on skilled labor
1. Machine is used by Operator not Welder.
2. Increase in the rate of production.
◦ As general conception goes that CNC machines demand high capital investment does not really hold ground
here in the case of CNC based PTA machine.
◦ Carefully designed with optimized use of high quality of raw material, choosing the right option for the
electronics involved can make a highly efficiency system at much affordable price.
Arcraft Plasma Equipments (I) Pvt Ltd., 124, Diamond Industrial Estate, Ketkipada, Dahisar (East), Mumbai- 400068.
INDIA.
Visit us : arcraftplasma.com
Email us: [email protected]
Contact us:
Ph : 00-91-22-28965890, 28965745, 28963247 Fax: 00-91-22-28966418