Wednesday, June 25, 2014

WPS/PQR



First we will discuss about WPS part than we will come to PQR section 

WPS in simple term is Welding Procedure Specification, actually it basically decide the procedure and way of welding so to achieve the desired property in weld and product.
-actually it defines a single common procedure for all welders, so to weld in that manner to achieve the desired properties
-for instance if in WPS its mention that the weld should be welded in horizontal position and rod should be used for all welding , than it means all the welders have to use the above mentioned parameter

So in nutshell we can define WPS is a written procedure for welding which include essential and non-essential parameter and set the range for those in practical so to achieve the desired properties

For making a WPS, we have to follow certain rules and regulation from a accepted Standard.

The used Standard may be ASME Section IX & EN ISO 15614 ,EN ISO 15609,and so many , it’s also depend on the customers specification and the relevant standard agreed by both manufacturer and customer. 

These  standards present guidelines for WPS format, what variables to include in what range and so many.

Here I will discuss more about ASME section IX requirements and its use in preparation of WPS.

 Below you can see the suggested WPS format from ASME section 9, we will discuss more about that format one by one , we will discuss the specific one related to grove welding , but the same thing would apply to other joints also , just you have to refer the ASME section 9 for other details as similar to presented below

WPS FORMAT -1 OF 2

WPS FORMAT-2 OF 2





OK Let’s discuss the WPS format -

1. Put your company name, welding procedure specification number (ex-1,2 etc.)and supporting PQR no.(we will discuss later)
2. What welding process you are using (ex-FCAW, SMAW etc.) and then type like automatic, semi-auto, manual etc.
SMAW is manual and FCAW is automatic or semiautomatic and so on.

3. JOINTS-what joint you going to prepare –grove, fillet, U grove etc., root spacing etc.

4.BASE material-what base material you are going to weld you must include the P NO. and group no so as to qualified many materials with it ,also mention specification type/grade (for ex-ASTM A216 WCB/WCC etc.)
You should also specifies the thickness range for qualification (min and max) , this you can find this in ASME section IX (QW-450) for groove weld , No. of passes etc.

5.Filler material –for Selection of filler material you must refer the Asme Section II C, The filler material should be of equivalent chemistry and mechanical properties as base metal

 From ASME section 9 you can get F no & A no. in QW-430(ASME SECTION IX). it generally indicates the we don’t need to make WPS for all filler metal hence with the help of grouping we can qualified the other filler metal even its name doesn't listed in WPS but it belongs to same group.

 Size of filler metal –like in case of SMAW 3.2 mm, 4 mm, 5 mm and in case of FCAW- 1.2 mm or 1.6 mm

Weld Metal thickness range –min or maximum of thickness range to be weld should be mentioned in WPS.

6.POSITIONS –WPS must record the welding position 1G, 2G, 3G, 4G etc.,

7. PREHEAT-preheat details must be mentioned in WPS,

8. Electrical characteristics-like type of current and polarity, amps, volts, wire feed speed, energy,tavel speed  etc., mode of metal transfer

9. TECHNIQUE-String or Weave bead, cleaning of weld, contact tube to work distance, multiple or single pass

10. POST WELD HEAT TREATMENT – details of post weld heat treatment like SR, Quenching , Solution annealing

11. Gas details –gasses used for shielding process 


This complete the WPS preparation , if you have any doubt please inbox me i will try to give possible solution 

Next we will discuss about PQR




















Wednesday, June 18, 2014

SMAW & FCAW

SMAW  &  FCAW

These two are highly acceptable process of welding in industries as per foundry is concern 
we will discuss more about these two types in details and i will give you some references for more details 

1. SMAW-  It stand for shielded metal arc welding , an arc welding process in which joining takes place between the tip of covered electrode and the surface of the base metal






Shielded Metal Arc Welding (SMAW) or Stick welding is a process which melts and joins metals by heating them with an arc between a coated metal electrode and the work piece. The electrode outer coating, called flux, assists in creating the arc and provides the shielding gas and slag covering to protect the weld from contamination. The electrode core provides most of the weld filler metal.

When the electrode is moved along the work piece at the correct speed the metal deposits in a uniform layer called a bead

The Stick welding power source provides constant current (CC) and may be either alternating current (AC) or direct current (DC), depending on the electrode being used. The best welding characteristics are usually obtained using DC power sources


The power in a welding circuit is measured in voltage and current. The voltage (Volts) is governed by the arc length between the electrode and the work piece and is influenced by electrode diameter. Current is a more practical measure of the power in a weld circuit and is measured in amperes (Amps).

The amperage needed to weld depends on electrode diameter, the size and thickness of the pieces to be welded, and the position of the welding. Thin metals require less current than thick metals, and a small electrode requires less amperage than a large one.

It is preferable to weld on work in the flat or horizontal position. However, when forced to weld in vertical or overhead positions it is helpful to reduce the amperage from that used when welding horizontally. Best welding results are achieved by maintaining a short arc, moving the electrode at a uniform speed, and feeding the electrode downward at a constant speed as it melts

SHIELDED METAL ARC WELDING (SMAW)
PROCEDURE

1. Work piece

Make sure work piece is clean before welding.

2. Work Clamp

Place as close to the weld as possible


3. Electrode

Before striking an arc, insert an electrode in the electrode holder. A small diameter
electrode requires less current than a large one. Follow recommendations of the electrode manufacturer when setting weld amperage or just follow according to your WPS/PQR.


4. Arc Length
Arc length is the distance from the electrode to the work piece. A short arc with correct amperage will give a sharp, crackling sound. Correct arc length is related to electrode diameter. Examine the weld bead to determine if the arc length
is correct.

Arc length for 1/16 and 3/32 in. diameter electrodes should be about 1/16 in. (1.6mm); arc length for 1/8 and 5/32 in. electrodes should be about 1/8 in. (3 mm)


5. Slag

Use a chipping hammer and wire brush to remove slag. Remove slag and check
weld bead before making another weld pass

Striking An Arc − Scratch Start Technique

Drag electrode across work piece like striking a match; immediately lift electrode slightly after touching work. If arc goes out, electrode was lifted too high. If electrode sticks to work piece, use a quick twist to free it.

Striking An Arc − Tapping Technique

Bring electrode straight down to work piece; then lift slightly to start arc. If arc goes out, electrode was lifted too high. If electrode sticks to work piece, use a quick twist to free it

Positioning Electrode Holder

Hold the electrode nearly perpendicular to the work, although tilting it ahead (in the direction of travel) will be helpful

Electrode Movement During Welding
1. Stringer Bead − Steady Movement along Seam

2. Weave Bead − Side To Side Movement along Seam

Conditions That Affect Weld Bead Shape

Electrode Angle


Arc Length

Travel Speed

Poor Weld Bead Characteristics

1. Large Spatter Deposits
2. Rough, Uneven Bead
3. Slight Crater During Welding
4. Bad Overlap
5. Poor Penetration

Good Weld Bead Characteristics
1. Fine Spatter
2. Uniform Beads
3. Moderate Crater During Welding
4. No Overlap
5. Good Penetration Into Base Metal

Typical Weld Joints



Types of Groove (Butt) Joint Welds

1. Tack Welds
Prevent butt joint distortion by tack welding the materials in position before final weld. Work piece distortion occurs when heat is applied locally to a joint. One side of a metal plate will “curl” up toward the weld. Distortion will also cause the edges of a butt joint to pull together ahead of the electrode as the weld cools

 2. Square Groove Weld

3. Single V-Groove Weld

4. Double V-Groove Weld

Materials up to 3/16 in. (5 mm) thick can often be welded without special preparation
using the square groove weld. However, when welding thicker materials it may
be necessary to prepare the edges (Vgroove) of butt joints to ensure good welds.
The single or double V-groove weld is good for materials 3/16 − 3/4 in. (5-19 mm) thick. Generally, the single V-groove is used on materials up to 3/4 in. (19 mm) thick and when, regardless of thickness, you can weld from one side only. Create a 30 degree bevel with oxyacetylene or plasma cutting equipment. Remove scale from material after cutting. A grinder can also be used to prepare bevels.

Groove (Butt) Joint Training Procedure
Practice welding butt joints on 1/8 in. (4mm) or thicker material. (Avoid thinner materials since they require greater skill.) Separate the squared edges of the material about 1/16 in. (1.6 mm) and make a butt weld all the way through with a 1/8 in. electrode. (You may need to adjust the weld current and travel speed to obtain the desired weld.) Perform a similar exercise on 1/4 in. (6 mm) material, depositing a bead on each side of the joint and fusing one to the another (no bevel needed).


Practice making a single V-groove weld on 1/4 in. (6 mm) plate beveled 30°. Start with a 1/8 in. electrode for the first bead and finish with a 5/32 in. (4 mm) electrode. Be sure to penetrate about 1/32 in. (1 mm) beyond the bottom of the “V” or root. Perform a similar exercise on thicker materials. Generally, deposit a bead for each 1/8 in. (3mm) of material thickness, cleaning the joint between layers. On heavier plates, it may be necessary to weave the top layers to fill the groove.

Weld defects and its troubleshooting

Possible cause
Corrective action
 Arc length too long.
Reduce arc length.

Work piece dirty.
Remove all grease, oil, moisture, rust, paint, coatings, slag, and dirt from work surface before welding
Damp electrode.
Use dry electrode.


2. Excessive Spatter

Scattering of molten metal particles that cool to solid form near weld bead.

Possible cause
Corrective action
Amperage too high for
electrode.
Decrease amperage or select larger electrode
Arc length too long or voltage
too high
Reduce arc length or voltage.


3. Incomplete fusion

Failure of weld metal to fuse completely with base metal or a preceding weld bead

Possible Cause
Corrective action
Insufficient heat input.
Increase amperage. Select larger electrode and increase amperage.
Improper welding technique
Place stringer bead in proper location(s) at joint during welding.
Adjust work angle or widen groove to access bottom during welding.
Momentarily hold arc on groove side walls when using weaving technique.
Keep arc on leading edge of weld puddle.
Work piece dirty.
Remove all grease, oil, moisture, rust, paint, coatings, slag, and dirt from work surface before welding.


4 . Excessive Penetration

Weld metal melting through base metal and hanging underneath weld.
Possible cause
Corrective action
Excessive heat input.
Select lower amperage. Use smaller electrode
Improper weld technique.
Adjust travel speed.


 
FCAW-FLUX CORED ARC WELDING

Flux Cored Arc Welding (FCAW) is a welding process by fusion which is widely used on ferrous metal. The consumable electrode can have an interior flux or a mix of flux and metal powder and has a tubular form . It is as semi-automatic or automatic arc welding process












Advantages and applications
·         FCAW may be an "all-position" process with the right filler metals (the consumable electrode)
·         No shielding gas needed with some wires making it suitable for outdoor welding and/or windy conditions
·         A high-deposition rate process (speed at which the filler metal is applied) in the 1G/1F/2F
·         Some "high-speed" (e.g., automotive) applications
·         As compared to SMAW and GTAW, there is less skill required for operators.
·         Less precleaning of metal required
·         Metallurgical benefits from the flux such as the weld metal being protected initially from external factors until the slag is chipped away
Used on the following alloys:
·         Mild and low alloy steels
·         Stainless steels
·         Some high nickel alloys
·         Some wearfacing/surfacing alloys
·         Porosity chances very low

Disadvantages
Of course, all of the usual issues that occur in welding can occur in FCAW such as incomplete fusion between base metals, slag inclusion (non-metallic inclusions), and cracks in the welds. But there are a few concerns that come up with FCAW that are worth taking special note of:
·         Melted Contact Tip – happens when the contact tip actually contacts the base metal, thereby fusing the two and melting the hole on the end
·         Irregular wire feed – typically a mechanical problem
·         Porosity – the gases (specifically those from the flux-core) don’t escape the welded area before the metal hardens, leaving holes in the welded metal
·         More costly filler material/wire as compared to GMAW
·         The equipment is less mobile and more costly as compared to SMAW or GTAW.
·         The amount of smoke generated can far exceed that of SMAW, GMAW, or GTAW.
·         Changing filler metals requires changing an entire spool. This can be slow and difficult as compared to changing filler metal for SMAW or GTAW.
·         Creates more fumes than stick welding.[1]


for more info try those website it will help you to increase your knowledge












Friday, June 13, 2014

Welding

One of the best part of manufacturing engineering is Welding .Welding history is not very old , the experienced gained  during the second world war forced to develop a technique to join the broken parts of equipment , hence form there welding become the essential parts of manufacturing . Now days its utilization ranging from a simpler household to aircraft industry
Let’s defines welding in a very simpler term or say layman language

WELDING- is nothing but a technique of joining similar or dissimilar metals by using heat or pressure
Hence in a layman language it’s a joining process by using heat (current)

Field of application -welding field is very versatile , its find usability in many areas and sectors like

  1. Foundry
  2. Ship manufacturing 
  3. Railways
  4. offshore 
  5. Aircraft industries & Nuclear sector.......................................... and so many   .

Types of welding process

there are so many types and variant of welding process some of them are listed here 

Arc Welding 
  • Flux Cored Arc Welding (FCAW)
  • Shielded Metal Arc Welding (SMAW)
  • Atomic Hydrogen Welding (AHW)
  • Gas Metal Arc Welding (GMAW)
  • Gas Tungsten Arc Welding (GTAW)
  • Plasma Arc Welding (PAW)
  • Submerged Arc Welding (SAW)                           


Oxy-fuel gas welding


  • Air acetylene welding
  • Oxyacetylene welding
  • Pressure gas welding 
Resistance Welding

  • Resistance spot welding
  • Resistance seam welding 
  • Projection welding