LEAN WELDING – AN APPROACH TO BEST WELDING PRACTICE.

105


S. K. Gupta.
B.E., C.E., FIE.,FIIW., MISNT.,
MAE., MITD.

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INTRODUCTION   

Today product innovators and entrepreneurs want the designers, technologists and engineers involved in manufacturing and fabrication to produce the intended marketable product in the shortest possible time with superior quality and at the least cost.

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Welding today can claim the second best meteoric growth next to IT in Technological perspective. It is all pervasive – from minor household equipment  to gigantic structures in buildings, bridges, tunnels, rail road, motorways, mining sea faring  ships, air ships, inter planet voyage vehicles, satellites and not to speak of IT equipment, welding is used as the major assembly process and technique. Products differ from manufacturer to manufacturer and products have different models and variations of design.

This has been the outcome of years of toil of Innovators, entrepreneurs, technologists and engineers covering a wide range of design, technology, machineries, equipment, process, consumables and automation. In association of these developments, codes and specifications, quality management systems, testing and inspection, operator training and testing are also developed.

The outcome of these efforts and toil cannot be articulated and documented in this limited scope. But at least an attempt can be made to frame the overall scenario prevailing at present.

  1. DESIGN

Product design in respect to weld design has become a sophisticated process. In place of manual design and use of empirical formulae applicable over a wide range of materials and service conditions with standard consumables, computer soft wares have been developed for specific material, specific service condition, specific loading condition and other factors. It is of course essential for the designers to have in depth knowledge of materials and their behavior, structural stress analysis, computer soft wares and of course practical applicabilty of design.

  1. WELDING PROCESS

Starting from the year 1887 (?) when Lavoisier discovered use of Oxygen and used it in industry for welding; and later on  with the introduction of coatings on bare rod electrode in 1907, welding processes have been innovated to cover a very wide range of application. Soldering and Brazing, Gas welding. SMAW, MIG/MAG, TIG, Electro Slag welding, SAW, PLASMA, Electron Beam welding, Resistance welding, Friction Stir Welding, Orbital Welding  are only a few to name.

3. WELDING MACHINES

Gas welding Torch, Transformers, Rectifiers, Inverters, Pulsed Welding sets, Spot and seam Welders, Plasma welding setup, Electro Slag Machine, All these Welding equipment have again multi variation models in Moving Core, Fixed Core, Thyristor Controlled, Engine driven Motor Generator sets.

Manufacturers of these machines are very many and capacities and range of parameters covered are wide. Obviously, the parts of these machines manufactured by different manufacturers are of different shapes, sizes and designs.

4. MECHANIZATION AND AUTOMATION

Along with the technological advance of the processes dependence on manual operation is being reduced with a target of eliminating it altogether. Use of Templates, Jigs and Fixtures, Manipulators, Rotators, Positioners, Hydraulic Clamping, Electronic Indexing, Robotic welding are the outcomes applied for increasing production and productivity.

5. MANUFACTURING SET UP – PREPARATION

Efficiency and Effectiveness of a welded joint in a job executed by any process or technology solely depend upon the accurate preparation of the joint and the fitment prior to welding. Shearing, Machining, Gas Cutting, Plasma Cutting, Bending, Sawing manually conducted before are being  done by CNC machines to  conform to the Joint Specification as accurately as possible as per WPS.

6. INSPECTION/ QUALITY CONTROL/QUALITY ASSURANCE – CODES & SPECIFICATIONS

Possible defects in a weld conducted by any process are more or less same with less or more in extent. In order to attain the ultimate objective of defect free welding (Six Sigma?)  it is necessary to use proven Codes and Specifications. These codes and specifications direct the weld producing organizations to formulate Inspection procedures, Quality Control and Quality Assurance Guidelines. IS, BS, ISO, DIN, ASME, AWS are a few only to mention from a large contingent

7. OPERATORS AND SUPERVISORS – KNOWLEDGE AND SKILL

Whatever may be the welding process, machineries and equipment, automation in use, knowledge and skill of the supervising staff and most importantly of the operators or welders are of prime importance. Today, skill development through structured National Operational Specification curriculum, National Certification of Vocational Training are available at a minimum or no cost at all to willing young generation and experienced workforce.

8. WELDING MANAGEMENT SYSTEM

Welding as an operational entity covers a plethora of subjects and that to in great details. It starts with the customer contract and covers the total supply chain till customer satisfaction. The need for a Welding Management System like ISO 9001 has been felt earlier and now in a position to accept and implement.

All the above mentioned scopes, criteria, variables, implications are in one hand opened up opportunities to the knowledgeable to access for the best, but on the other hand creates confusion to others not so well equipped.

                                         
RESULTING FIRE FIGHTING AT ALL STAGES

          WHAT WE NEED TO APPROACH FOR THE BEST WELDING PRACTICE

                                     

The BEST PRACTICE in welding can be simply defined as the most EFFECTIVE and EFFICIENT method to weld a joint.  The term “EFFECTIVE” refers to the method which utilizes the resources to the optimum extent and the term “EFFICIENT” refers to the method of Right First Time with minimum wastage. In addition an approach for Continuous Improvement will pave the way for adopting the BEST PRACTICE in Welding.

CONCEPT OF “LEAN WELDING” IN RELATION TO THE BEST PROCESS

“Lean” is a manufacturing concept designed to provide the optimum framework for efficient and effective production. The lean production system focuses on the reduction of waste from the value stream in order to remain competitive. Lean manufacturing is lean because it provides a way to do more and more with less and less—less labor, less equipment, less time, and less space—while coming closer to providing customers with exactly what they want.

Standard, Uniform and Single Welding Process

The Approach to Best Welding Practice may start with lean welding becoming the Focal Point when the organization may commit to use a Standard Single Process for all criteria described above starting from design to welding management system in the whole of the supply chain in operation. The steps may be stated in the following order:

  1. Welding Management System – ISO 3834 is the ideal to adopt for global application.
  2. Standardize the Design Codes, Specification and Auto Cad system. Eliminate manual and Rule Of Thumb processes.
  3. Standardize the Welding Procedure Specifications and WPR in single format.
  4. Standardize the Welding Process – the most difficult decision to make. Selection of a single welding process apparently is not possible in a manufacturing situation. Even if we select two or three processes out of many for specific applications still it is acceptable. But there must be a rationale behind the selection by calculating percentage use of different types of weld, positional approach and productivity factor. Selection of SMAW or MIG/MAG, SAW, Resistance Welding, TIG, FSW, Plasma or Electron Beam Welding for specific application may definitely be selected, but should be confined to the specific application only.
  5. Once the welding process/processes are identified and selected, the next important part is to Standardize Machinery and Equipment for that specific process. For example, if 80 percent of the weldment need MIG then we must select one make, one model, one capacity specific units of single type of Power Packs, Wire Feeders, Torches for all the weldment to be covered by MIG irrespective of current and voltage requirement for different joints.
  6. Once the machinery and equipment are standardized, all consumables are also to follow suit – one brand, one type, one size of electrode from one supplier, one type of gas or gas mix, one type, one brand and one size of slag from one vendor.
  7. Standardizing Jigs, Fixtures, Rotators, Manipulators, Positioners, Clamping devices and arrangement should run parallel. It is understood that for each specific job or part or subassembly different types of Jigs-Fixtures are needed, but locating, holding positioning means and devices must be standardized.
  8. Lean Welding requires minimum wastage of materials and consumables, less labour, low production time. As the correct Fitment for a Joint depends solely upon the preparation process and accuracy, standardization and automation is desirable to eliminate manual preparatory methods and introduce CNC Gas, Plasma, Shearing, Bending, Slotting, Punching, Drilling, Edge Planning operations.
  9. Calibration of machinery. Output of Machines and equipment diminishes with use and age; meters on the machines and the Regulating Knobs will not indicate correct setting of parameters. Such a condition impedes productivity quality, and operator’s morale, increases degree of supervision, delivery period and cost. Outputs of all the Welding Sets in terms of steady current and voltage is essential. Any fluctuation or variation in these parameters will adversely affect quality production and productivity. Even a skilled worker working with such variations will not be able to produce a good weld.
  10. Safety, Maintenance and Inspection of Arc Welding Equipment in Use. Standardized Welding Machinery, Equipment and Accessories after calibration needs regular inspection and maintenance to sustain exposure to optimum uses with minimum probability of failure. In addition, the health and safety of the operators are ensured by this process of Inspection and maintenance of work equipmentProcess related benefitsAs welding is standardized through standard fit ups, single process with, in standard positional set ups on new welding technology, numerous process-related benefits are generated, such as:
    • Eliminating variability in primary power fluctuation (with Grouping as in Auto-Line technology)
    • Ability to limit or “lock-in” functionality within scope of specific requirements
    • Multi-MIG process capability using one type of wire and one type of gas mixture.
    • Ability to weld thick or thin metal with same set up.
    • Improved travel speed with lock in function.
    • Less heat input through pulse(recommend Pulsed MIG, if MIG is selected) operation
    • Better puddle control with locked in current and voltage
    • Reduced distortion due to low heat input
    • Less spatter with current control
    • Improved arc stability through reduction of controlled parameters locked in.
    • Operators are confident to produce high quantity weldment with quality.
    • Welding Training will be simplified and of shorter duration on knowledge and use of limited brand machines and accessories focusing more on techniques and productivity.
    • Provide flexibility to deploy welders with Standard productivity in different Work Stations having Standardized Set Ups.
    • Immediate improvement of operator performance (higher production rates with fewer errors and better morale).
    • Eliminate sources of variability in quality and productivity between welding stations in different shifts.
    • Maintenance planning and execution is greatly simplified and streamlined by drastically reducing parts count; maintaining 200 to 300 Welding Sets of the same design enables maintenance to become very proficient.
    • Change the typical vendor-supplier relationship into a vendor-partner relationship where each party contributes more to the value chain and benefits accordingly.

Vendor – Partner Relationship

The traditional relationship between a Manufacturer and the suppliers of Machineries, Accessories and Consumables is just a buyer and a seller for a particular transaction. The main interest common to both the parties is the PRICE and the payment. Instead, understanding each other’s needs, goals and long-term objectives must be given priority over price and delivery

Once such a relationship starts it should develop into a joint venture of Lean Journey to include:

  • Supplier-managed inventory for accessories and spares at Vendor’s stores.
  • Planning and building inventory to customer requirement for a long span, rather than to a short forecast.
  • Daily on-line inventory replenishment for delayless supply.
  • Ability to build and ship even customer specific products in one day
  • Same-day shipping of replacement parts
  • Building facilities for some circuit boards to be built in-house.
  • A flat, responsive and reactive organizational structure.
  • Employees at supervisory levels empowered to make decisions.
  • Line employees/ operators engaged in production, inspection and maintenance empowered to manage their own business areas.

Welding system performance is important, but more value should be placed on finding a responsive welding partner with similar organizational philosophies, structures, objectives and goals. This type of relationship, where both parties are aligned for mutual success, enables the parties to manage better the challenges that arise with any product’s use.

Making of a Welder

The most important part in the approach to best welding practice is making of an Welder and his performance on the job. Today most of the fabrication and production work with welding as a major or minor process are outsourced. Work is contracted out to contractors. Engagement of a Contractor must be based on his knowledge of welding and fabrication and an attitude towards continuous improvement

In most of the Manufacturing Workshops we will find:

  1. Skilled Welders, qualified as per ASME / EN / AWS / IS standard and performing welding to the best of their knowledge and ability producing good quality welds to the specified productivity norms – very few in number !
  2. Skilled Welders, qualified as per ASME / EN / AWS / IS standard and performing welding in a lackadaisical attitude producing average quality welds with some rectifications to production norms – many in number!
  3. Semi-skilled Welders without formal qualifications through tests and certification engaged in welding producing good quality welds to the productivity norms – quite a few in number!
  4. Semi-skilled Welders without formal qualifications through tests and certification engaged in welding producing poor quality welds with large number of rectifications and naturally with below par productivity norm – few only in number!
  5. Unskilled workmen engaged mainly as Manual Welder for tacking work in the fitment of parts and components in Jigs and Fixtures prior to welding – quite a few in number !

In an IDEAL situation the percentages of the above categories working with strict supervision should be:

CATEGORY IDEAL SITUATION
I 60
II 25
III 10
IV 3
V 2

In addition to “Off The Job Training”, to sustain continuous improvement in weld quality and productivity it is imperative and absolutely necessary to facilitate a continuous “On The Job Training” to all the Welders. The Training Contents at different stages of Welding are outlined below:

  1. ON THE JOB – Functions, Operations, Safety
  • Setting the Welding Set Up
  • Striking the Arc
  • Maintaining the Arc for Welding
  • Gas Flow – Setting, Regulating, Adjusting

2.INSPECTION – Before Welding – Check

  • The JOB
  • Jigs / Fixtures / Rotators / Manipulators
  • Safety at Work – Follow up

3.During Welding – To Carry out welding properly

  • Welding to start on the extension piece or on the joint itself.
  • In Butt welding electrode should be forced for penetration
  • For Root welding, a 2.5 dia. Electrode in SMAW and 1.2 mm wire in MIG/MAG are effective.
  • Correct weaving motion and direction of travel to be selected for effective Bead shape and form.
  • Craters to be removed by back tracking weld beading.
  • Ends of joint should be locked.
  • Welding size must as per WPS – No oversize beading should be encouraged / entertained
  • Torch angle to be maintained at 90 deg. to horizontal and 20 deg. to vertical in the direction of travel for best result.
  • At the beginning of the working shift it is better to make a trial run on a scrap plate for adjustment of settings.

                                                  

4. AFTER WELDING – CHECK

  • Visual Checking
  • Size of Weld
  • Defects on the surface
  • Appearance of Beading
  • P. Test procedure and conduction
  • Rectification of defects                                                                                                                                                                                                      5.PERFORMANCE EVALUATION – SELF AND PEER – 12 POINT ANALYSIS

  • Starting Time of Work
  • Finishing Time of Work
  • ARC ON Time
  • Length of Welding / Vol of Weld Deposit made
  • Weld Position worked
  • Volume of Consumables used
  • Scrap / Wastage / Rework
  • Supervision Needed
  • Cleanliness of Machines and Workplace
  • Safety Awareness
  • Team Working
  • Making Reports

CONCLUSION

Welding Technology is advancing at a very fast pace. For every welding process innovators are introducing newer sub processes every day with special applications as well as for generalized techniques. Welding engineers must take lead to introduce a systematic approach for the Best Process of Welding applicable for the product. Lean Welding as defined in this article is a vast subject covering all the aspects of product manufacturing through the special process – WELDING. Organizing such an approach initially may cost time, energy and money, but in the long run it will pay back with rich dividends.

 DIAGRAMS TO SHOW A FEW WELDING PROCESSES, POSITIONERS & FIXTURES

                                Few Welding Processes

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                       Rotators Positioners  & Fixtures

 

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