WELDING ECONOMY &

PRODUCTIVITY

M.P.JayakumarSenior Deputy General Manager

Human Resource Development CentreBharat Heavy Electricals Ltd., Tiruchirappalli 620 014

Email: mpj@bheltry.co.in

WELDING ECONOMY & PRODUCTIVITY

Productivity is a measure of Efficiency

Productivity = Output / Input

Productivity can be improved by improving the capacity utilization or by elimination of waste.

Productivity is an attitude of mind.

Waste is any unnecessary input or any undesirable output from the system.

WORK MEASUREMENT TECHNIQUES

• Time Study

• Production Study

• Work sampling

• Analytical Estimation

• Synthesis from Standard Data

• MTM-PMTS

• METHOD STUDY SHOULD PRECEDE WORK MEASUREMENT

STANDARD TIMEStandard Time for a welding operation is the amount of time that the qualified, properly trained and experienced welder should be take to perform a specific welding operation under specified conditions under normal performance.

• OBSERVED TIME * RATING FACTOR = NORMAL TIME

• NORMAL TIME + ALLOWANCES = STANDARD TIME

• FATIGE ALLOWANCE, PERSONAL NEEDS AND DELAYS.

• STANDARD TIME WILL BE CALCULATED BY BREAK DOWN OF VARIOUS ELEMENTS IN WELDING.

ELEMENTS OF WELDING OPERATION

ARCING – Note down ampere, dia and length of electrodes used.

CLEANING - Chisel / Wire Brush / Pneumatic chipper, No. of layers used

MANIPULATION DURING WELDING – Change electrode, adjust current, getting electrodes, move accessories, Remove and put on helmet, gloves, apron etc.

MANIPULATION OF THE JOB - Turning, lifting, clamping, declamping etc of the job.

Example – Calculation of Standard Time

Sl. No.

Description of the element

Preparati-on Time

Welding Time

Manipul-ation Time

01. Collect documents 2.0

02. Study the Drawing 1.5

03. Connect the plug and disconnect later

0.2

04. Switch on and Stop later

0.3

05. Adjust Current 0.2

06. Clean Work Place 1.5

07. Fill up the Job Card 2.0

08. Handover completed Job Card 2.0

09. Call Crane 3.0

10. Tie and loosen the piece 1.25

11. Bring the job from a distance of 20 Metres

0.9

12. Clamp the earthing cable 0.15

13. Weld 2Metres with basic coated electrode

14.00

14. Complete Weld Ends 0.10

15. Move to side 0.60

Example – Calculation of Standard Time..

16. Call Crane 3.0

17. Rig and Untie 1.25

18. Change through 180 degrees 1.00

19. Weld Next side 2Metre 14.0

20. Complete the weld 0.10

21. Stamp welders Number 0.10

22. Call Crane 3.00

23. Rig and Untie 1.25

24. Take the piece away for 20 Metre distance

0.90

Total time in mins. 9.70 28.20 16.40

Example – Calculation of Standard Time..

ANALITICAL CALCULATION

Introduction:

• In this method, arcing time, welding time, requirement of welding consumables etc. or to be estimated based on the data from

• Direct Time Studies and

• Welding information like are time, rate of deposition, current etc. normally available in electrode manufacturer’s literatures and catalogure.

• Analytically calculated times do not completely replace direct time studies. However, they have a number of advantages like :-

• They reduce the number of studies that must be made.

• They can be used for predicting costs, schedules and delivery periods while estimating and quoting the firms offer.

• Analytical calculations are economical to apply for obtaining Time Standards for a wider coverage of operation in the plant.

ANALITICAL CALCULATION

• Whenever new sizes or new edge preparation

etc. is being introduced, estimates could be

made with accuracy and consistency without

waiting for the job to be taken-up for production.

• Analytical calculation of welding data,

essentially involves first finding out general

expression for the weight of weld metal

deposited for a given edge preparation,

configuration and other welding data, using

previous time study results and secondary

substituting the numerical values (size of the

joint) in the expression to get the require data.

ANALITICAL CALCULATION

WEIGHT OF WELD DEPOSITED

• The area of cross section of the edge preparation when multiplied by the length would give the volume for which the weld metal has to be deposited. To facilitate the calculation, the areas of cross section is divided into sections like rectangle and/or triangle.

• In case of pipe butt joints, circumferential length is the circumference passing through the centre of gravity of the section.

• This volume when multiplied by the

specific gravity of steel would give the

weight of weld metal to be deposited to

complete the joint.

• From the weld metal weight other welding

details like arcing time, welding time,

consumables required can be arrived at using

the data obtained from time studies and

welding data hand book

WEIGHT OF WELD DEPOSITED

• Step by step calculation involved to find out the weight of weld metal to be deposited for a butt joint in pipe by manual arc welding is given below:

• The area of cross section of the edge preparation is divided in to layers depending on the size of electrode used.

• Each layer is further divided in to rectangles and/or triangles.

• The volume for which weld metal is to be deposited in each section (rectangle or triangle) is found as volume of the Section = Area of the section * circumference passing through the centre of gravity of that section.

WEIGHT OF WELD DEPOSITED

• The volumes of all such section in a layer are added to give the volume of metal to be deposited in that layer.

• The volume of weld metal to be deposited in a layer when multiplied by the specific gravity (7.8 gms/cc) would give the weight of weld metal to be deposited in that year.

• The weight of weld metal to be deposited per joint is got by cumulating the weight for all the layers.

WEIGHT OF WELD DEPOSITED

ARCING TIME• The arcing time per joint is the duration of time

for which the are is struck and sustained during

the welding of the joint.

• Arcing Time = Wt. Of weld metal deposited

using a particular size of electrode / Deposition

Rate of Electrode.

No of electrodes burnt per shift 60 with Arcing

time of 120 mins.

ARCING TIME

• The deposition Rate is the weight of weld metal deposited per unit time (e.g. gms/min.). It depends on the type of electrode, size of electrode and the current used. It can be got from Time Study results or it is supplied by the electrode manufacturer themselves (e.g.. Advani Oerlikon Welding Hand Book).

• Since the size of electrodes used changes for each layer, the arcing time has to be found for each layer and added to get total arcing time per joint.

WELDING TIME

The welding time can be found by multiplying the arcing time by a factor. This factor will depend on the type of joint and nature of work can be obtained from the previous time studies on the similar work. Also some welding data Hand Books provides these information.

CONSUMABLES REQUIRED

No. of Electrodes = Wt. Of weld metal deposited using a particular size of electrode /

Wt. Of metal yield per electrode.

The weight of metal deposited by burning an electrodes is not equal to the weight of core material of the electrode. The actual weight of metal deposited per electrode (I.e.) Metal yield depends on the deposition efficiency for the electrode and the length of the stub thrown away after welding.

Deposition Efficiency = Metal yield per electrode / Core Material Wt. Per electrode * 100

The deposition Efficiency will be more than 100 for iron powder electrode and less than 100 for others. If ‘n’ is deposition efficiency of the electrode, ‘L’ is the length of electrode and ‘1’ is the length of throw away stub, then metal yield per electrode.

= (Core Material Wt. Per * n/100 * (L-1)/L Electrode)

CONSUMABLES REQUIRED

This analytical calculation, at the best, can only supplement and at any rate cannot substitute Time Studies. The accuracy of the results obtained by this method largely depends on the norms got from time studies.

CONSUMABLES REQUIRED

FACTORS INFLUENCING WELDING ECONOMY

• Design for Economical use of filler metal

• Plan for Conservation of Material

• Use Setting up Fixtures to eliminate measuring and to facilitate fit up.

• Use Positioning Fixtures/Rotators

• Use the most suitable size and economical type of filler material

• Avoid over welding-use templates

Increasing the operator Factor (Time spent on actual welding)

OPERATOR FACTOR• Represents the percentage of work day spent in

actual welding (ARC Time) .

• Percentage of ARC Time controls the economy of deposition of weld metal .

• ARC Time varies from 10% to 50% depending upon the type of work and handling facilities.

• The average figure of moderately heavy and large fabrication work is approximately 40% of welders working hours.

• High operator factors is an indication of efficiency.

OPERATOR FACTOR

• Jigs, Fixer, Setup, Fit up are directly related to the operator factor.

• Their efficiency will have a great effect upon welding speed and operator comfort and safety .

• Changing from Vertical or Overhead to the flat position can increase the welding speed as much as 400% and increase the operator factor and welder efficiency.

• The use of a helper will increase the operator factor.

COMPUTER AIDED TIME STUDY

The analyst, using an electronic data

collector, can make a time study more accurately

and more quickly than by stop-watch time study

for many kinds of work. However, the greatest

benefits result from having the computer perform

the computations and clerical work after the time

study is completed on the production floor.

COMPUTER AIDED TIME STUDY

The computer deletes noncyclic,

abnormal, and foreign elements and processes

them separately. It determines the average time

for each regular element and for each noncyclic

element and applies the appropriate rating factor,

thus obtaining the normal time for each element.

Compiles the total normal time, adds the

allowance, and calculates time study data showing

the continuous reading and the subtracted time for

each element

Makes an elemental time distribution for each element in the study and shows the number of readings needed for a given degree of accuracy.

This is all done quickly, accurately, and economically. The time required to transmit the data from the data collector to the computer and to obtain the print-out depends upon the available computer facilities and the length and nature of the time study.

COMPUTER AIDED TIME STUDY

FACTORS FOR IMPROVING PRODUCTIVITY

INCREASING THE OUTPUT

Selection of Process (Flux core ARC vs Manual Arc)

• Use of positioners

• Use of Manipulators

• Increasing the operator factor (arc time)

•Use of proper filler metal (for Higher Deposition)

Use of Automation and Semi-Automation wherever possible. Improve layout

• Reducing defect rate

• Use of correct size of electrode and current, WPS

• Reduction of Rework

REDUCING THE INPUT• Proper design of weld Joint

• Proper Edge Preparation

• Reduce Stub End Losses (15% to 20%)

• Reduction in over welding (Number of passes)

• Use of Higher deposition Electrodes

• Reducing the consumables like Gas, Electrodes filer metal etc.

• Reducing the Labour and Overhead Cost

• Proper Estimation

• Recycling of flux