CNC CONTROLLED PTA WELDING AND HARD FACING ...

 

INTRODUCTION:

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• 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

• Plasma gas flow & pressure
• Shielding gas flow & pressure
• Carrier or Powder gas flow & pressure
• Powder feed rate
• Powder feed down slope
• Surface speed of the job
• Travel speed of the torch
• Torch Oscillation
• Welding current
• Arc gap

MASS

• Powder feed rate
• Powder feed down slope

MOTION

• Surface speed of the job
• Travel speed of the torch
• Torch Oscillation

POWER

• Welding current
• 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.

 

1. Plasma gas flow & pressure
2. Shield gas flow & pressure
3. Powder or Carrier gas flow & pressure
4. Gas pre flow time
5. Gas post flow time
6. Welding current
7. Welding voltage / Arc gap
8. Rotating speed of the job
9. Linear travel speed of the torch
10. Weld position of the torch
11. Torch oscillation width]
12. Torch oscillation speed
13. Dwell time
14. Weld current down slope
15. Powder flow down slope

A TYPICAL CONTROL SCREEN ON CNC DISPLAY SHALL LOOK LIKE THE FIGURE SHOWN BELOW:

1. Sense the Park or No Weld position of the torch
2. Bring the torch to Weld position above the job
3. Initiate the gas
4. Initiate the pilot arc
5. Start the welding arc
6. Start the job motion
7. Start the torch motion
8. Start the oscillation
9. Start the powder flow
10. Deposit desired bands of weld
11. Deposit desired passes of weld
12. Bring the weld current and powder flow to down slope mode at the end of the job.
13. Stop welding & all the other motions
14. Allow desired post flow of gas.
15. Bring the torch back to park position

TYPICAL JOBS ACHIEVED BY SUCH CNC PTA SYSTEM ARE SHOWN BELOW:

 

 

 

 

 

 

• 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.

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
5. Volumetric control ensures optimized flow rate.
6. Minimal  wastage of powder.
7. Machine is used by Operator not Welder.
8. Increase in the rate of production.

•           Saving in powder

•           No dependency on skilled labor

•           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.

• 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.

 visit us   : www.arcraftplasma.com

If you want to learn more, please visit our website CNC Hardfacing Machine.

us  : 

Waldun CNC hardfacing machine for wear resistant composite plate has the following advantages:

* Multi-purpose.

The flat plate welding can be realized by placing X MM worktable in the wide build-up welding operation platform, or by placing positioner and turntable on the platform, etc. The unique function and various types of welding guns can be used to locate accurately in a wide range. The welding passes of any shape can be built up on the surface of a circle, ring,  cylinder, cone, Inner Circle and plane It is suitable to build up any shape wear-resistant weld bead on the side-by-side central slot plate of coal conveyor.

* High configuration.

The control system, which is composed of PC numerical control motion system and full digital PLC technology control system, is composed of the top-level hardware configuration and the well-functioning programming software It provides a perfect hardware and software system for experimental research. Make the plate more flat and beautiful.

* High Precision.

The 3-d positioning accuracy of the welding torch is 0.1 mm, the arc voltage is automatically stabilized within 0.5 v Range, and the rotating arc current can be controlled at 1A The process parameters such as workpiece rotation and swing can be set and controlled with high precision, which provides the conditions for obtaining high quality surfacing layer. The overlap between Weld Bead and weld bead is smooth, without concave-convex phenomenon.

* Multifunction.

Due to the use of advanced PC motion control system and full digital process control system, as well as complete programming software, it has a variety of control functions, such as: Intelligent Automatic Setting of process parameters; Setting function of electronic pitch for surfacing welding roller surface.

* Welding Large Parts.

Automatic build-up of wear-resistant bead of any shape on large workpiece. For large diameter pipeline, in order to build-up welding directly on the inner wall of the pipeline, it is very convenient to operate the welding torch without moving. In order to weld the pipeline, the software system set up the function of automatic centering.

* Good Control.

Due to the use of a high-definition wide touch screen man-machine interface, well-designed windows and man-machine dialogue, the setting of process parameters and procedures is very simple, one person can control more than one, and in the build-up welding process of the state of the process You can see it through the window. For the numerical control motion system, the running track of the welding torch is set by CAD drawing on the 8-inch computer display screen, and the moving track is displayed in the welding process.

* Easy to maintain.

Because the high wear-resistant compound plate numerical control overlaying welding machine uses the smooth linear guide rail and the simple control system, is easy to install, easy to maintain, the breakdown is almost zero

For more information, please visit Portable Hardfacing Machine.