Estimation of Welding Cost
By K.R.Prasanna Venkatesan
Sayings
“ If you cant measure it, you cant manage it” – Peter – Peter Drucker. “If you are not measuring it you are not managing it” corollary
Sayings
“ If you cant measure it, you cant manage it” – Peter – Peter Drucker. “If you are not measuring it you are not managing it” corollary
Types of Companies
Large Scale. Design first, Cost Next.
Small Scale. Cost First, Design Next.
Estimating
It is the process of determining the probable cost of a Product / Process (Welding) before the manufacturing.
Estimation is the Process done by a Technical Person and not by Accountant.
Both Over Estimation and Under Estimation is Dangerous.
Costs
Direct Cost. Material Cost. Labour Cost. Expenses.
Indirect Cost. Over heads. Admin. Expense. Selling and Distribution. Profit, Discount….
Ladder of Cost. Discount Profit Sales and Distribution
Selling Price Total Or
Admin.
Factory Direct Expense,
Work Cost
Prodn. Cost
Ultimate cost
Market Price
Material Cost
It is the cost of Materials required for a Process (Welding)
Example:
Direct: Filler, Flux, Gas, etc.
Indirect: Cotton wastes, Coolant, etc.
Labour Cost
It is the cost spent to the workers who are directly or indirectly involved in Manufacturing.
Examples:
Direct: Operators, Welders…
Indirect: Watchman, Supervisor…
Expenses
All other expenditure other than Material and Labour cost is called Expenses. Examples:
Direct: Power consumption, Welding M/C. cost….
Indirect or overhead cost: Depreciation.
Welding Cost Parameters
Joint Design Type
Weld Size
Weld Type
Welding Process
Electrode Deposition Efficiency
Others (Safety)
Thinking of Welders
“If a little is Good, a lot size is Better, and too big is Just Right.” But this leads to failure of Weld, and increase in cost, which is not preferred.
Butt Weld
Fillet Weld
Factors of Welding Cost •Time for joint preparation. •Time to prepare the material for welding (blasting, removal of oils, etc.). •Time for assembly. •Time to preheat the joint (when required). •Time for tack-up. •Time for positioning. •Time for welding. •Time to remove slag (when applicable). •Time to remove spatter. Time for inspection.
Factors of Welding Cost •Time for changing electrodes. •Time to move the welder from one location to another. •Time to change welding machine settings. •Time spent by personnel for personal purposes. •Time to repair or re-work defective welds. •Costs associated with any required stress relief. •Cost of electrodes. •Cost of shielding materials. •Cost of electric power.
Basic Cost Formula Welding Costs = (L&O) + (Consumables Costs)
The Operating Factor
The ratio of hours spent welding to total hours worked is called the operating factor
Gas Welding & Cutting Cost
Direct Material cost = base material cost + Consumable’s Cost (Filler, O 2 & C2H2)
Direct Labour cost = Preparation or pre welding cost + welding cost + Post welding cost.
Direct expense = Cost of fixture and auxiliaries.
Over heads.
Three Basic Approaches
Cost per unit.
Cost per length.
Cost per weight.
The application will determine which approach is most appropriate.
Cost Per Unit
This method suits for pieces that move through a workstation.
For SMAW
Cost/unit = (L&O/unit) + (filler metal and shielding material cost/unit)
L&O/unit = (welding-related time/unit) x (L&O rate)
Cost Per Unit
- Contd.
For Wire Fed processes:
Filler m etal co st/un it = (w ire feed sp eed) x (w elding t im e) x (w e i g h t o f e l e c t r o d e /m m ) x ( el e c t r o d e c o s t / k g )
Filler m etal co st (SMAW) = [{(electro de m elt off rate) x (w elding tim e) x (weigh t of electr od e/m m )}/(% of electro de used)]
Shielding gas c os t/piece = (flow rate) x (weldin g tim e) x (gas c o s t / m 3 )
S A W f l u x c o s t /p i e c e = (w t . o f f l u x u s e d ) x (c o s t o f f l u x / k g . )
Cost Per Length
This method is appropriate for estimating the cost of long welds Formula:
C o s t / l en g t h = (L & O c o s t / le n g t h ) + (f i l l er m e t al a n d s h i e l d i n g cost/length)
L& O co st/length = (L& O rate)/(travel speed) x (operating factor)
Filler m etal cos t/length (w ire fed pr oc esses) = {(w ire feed sp eed) x (w t. of electro de/(m o r m m ).) x (cos t of electro de/Kg .)}/(trav el sp eed)
Cost Per Length - Contd.
Filler m etal co st/length (SMAW) = (m elt off rate) x (w t . o f e le c t r o d e /l e n g t h ) x (c o s t o f elect ro de/Kg .)/(travel s peed)(% o f electro de u sed )
S h i e l d i n g g a s c o s t / le n g t h = (g a s f l o w r a t e) x ( g a s 3 cost/m )/(travel speed)
S h i e l d i n g c o s t /l en g t h ( f l u x ) = (w t . o f w e ld m e t al /l e n g t h ) x ( r at i o o f f l u x t o w e l d m e t al ) x ( c o s t o f flux/Kg.)
Cost per weight
It is best used in applications in which significant volumes of weld metal must be deposited, such as multi pass applications. Hard facing and overlay welding are ideal applications.
Formula
C o s t / K g . = (L & O c o s t / K g . ) + (f i l l er m e t al a n d s h i e l d i n g cost/Kg.)
L& O Cost /K g. = (L& O rate)/{(depos ition rate) x (operating factor)}
F i l l er m e t al c o s t /K g . (a n y p r o c e s s ) = (c o s t o f f i l l e r m etal/K g.)/(electr od e efficienc y)
S h i e l d i n g c o s t /K g . (g a s ) = (s h i e ld i n g g a s f l o w r a t e) x (c o s t 3 ) /(deposition rate) o f s h i e ld i n g g a s / m
Shielding
t /K g . (f l u x ) = (
t o f f l u x / K g . ) x ( r at i o o f f l u x
Thumb Rule In case of on site welding process, if it is difficult to estimate the weldment weight. for such case, the Universal Thumb Rule is weldment weight is 2% of total structure’s weight.
Power Cost. V x Ax t x 1x1 x 1000 60 η r
c
Where • V – Voltage in volts • A – Current in amps • t – Welding time in min • η – Efficiency of the welding machine, (0.6 – Transformer & 0.25 – Generator) Operating factor
Theoretical Vs Actual
Tooling time.
Fit ups
Fixture non alignment because of spatter deposition
Filler may change, So quality. may change
Skill varies from men to men.
So we should use Digital communication technology
Theoretical Vs Actual
If we increase the size of fillet weld, the area of Fillet will be Doubled, And the cost will increase. And not only that, it leads to Stress.
Weld Area Vs. Cost
Note: Labour Cost is 80% of Total Cost
Tips
Select the cost calculation method that most directly measures the important cost variables for the specific application.
When evaluating the effect on overhead costs, ask: Will the changes in the welding operations affect the company throughout?
Carefully evaluate the impact of the proposed change on the operating factor. Some changes will decrease this variable, others will increase it.
Make sure the data used for cost computations reflect reality.
Some Data Operating Factor
Labor and Overhead percent of Total Cost
10
89
20
81
30
73
40
67
50
62
60
58
70
54
80
51
Steps to Reduce Welding Cost Analyze the delivery of consumable and accessories to welding point. Analyze whether material handling is effective. Look for ways to correct over welding. Enhance current welding process and procedures. Optimize joint preparation. Eliminate any extra welds from design. Look for items that can be welded rather than cast. Look for ways to eliminate costly record keeping
An Example
If we consider a boiler drum, there are linear and circumferential welds.
That can be done by all kind of welding processes.
So here we are going to see some sample calculations.
Given Data Length – 3m Diameter – 1.2m Thickness – 15mm Both side welding. Rate of weld – 2m/hr(outside), 2.5m/hr (inside) Length of electrode required – 1.5m/m of weld.
Given Data Cost of electrode – 2.75/m Power consumption – 4kwhr/m of weld Power charge -45 paise / kwhr
Labour Charge – Rs. 9/hr Over heads – 90% of prime cost Discarded Electrode – 6% Fatigue and setting up time – 5% of weld time.
Calculations Length of weld: = 2 x Π x D + (2 x L) = 13.54m Total electrode length = 1.5 x 13.54 = 20.31m Electrode Discarded = 6% = 1.22m. Total electrode wanted = 1.22 + 20.31 = 21.53m Cost of electrode = Rs.59.21
Calculations
Labour Cost
Length of inside weld = 3m. Time = 1.5hr
Length of outside weld = 10.54m.
Time = 4.216 hr.
Net time = 5.716 hr.
Total time = net + (Fatigue) = 6 hr.
Cost = Rs. 54.
Calculations
Power Consumption = 4 x 13.54 = 54.16 kwhr.
Cost = 0.45 x 54.16 = Rs. 24.37
Prime cost = 59.21 + 54 + 24.37 = Rs. 137.58
Over Heads = Rs. 123.82 (90%)
Total Cost = 137.58+123.882 = Rs. 261.40
In other process the process may vary.
Conclusion
Simplified calculations make this task easier
Can find Alternate means of manufacturing
Company with economy and new technology can and will compete Successfully
References
Process Planning and Cost Estimation – V. Jayakumar. Welding Principles and Applications – Larry Jeffus Design and planning manual for cost effective welding – AWS. www.weldingdesign.com www.weldingdesign.com/323/Issue/Article/False/ 10864/ http://www.weldingdesign.com/323/Issue/Article/ False/10760/Issue
