A continuing challenge in implementing Friction Stir Welding (FSW) in an industrial environment is the lack of a trained or informed workforce. Many of the companies that have implemented FSW as a joining process have had to make a significant investment not only in the capital equipment – but in training their work force internally.  Unlike fusion welding – there is no ready trained FSW work force – in fact there are comparatively few institutions that address FSW training at any level.    Several universities have started quality programs that cover FSW – typically in the engineering disciplines (Mechanical, Metallurgical  etc.).   At the undergraduate and graduate level – an increasing number of universities are offering experience in friction stir welding – producing engineers that have a good understanding of FSW basics and are able operators.  The Welding Institute (TWI) in the UK has developed and provides a course that covers the basics of FSW - http://www.twitraining.com/world/courses/index.jsp?coursecode=ATC210. 

At a technical or vocational level there is no substantial FSW “operator” training programs available to supply the growing industrial market.  As an increasing number of engineers graduate with FSW background – there is still a void not yet filled for a production line operator/welder.  In all but the most expensive applications – using engineers in the role of an operator presents an additional fiscal challenge for a small to moderate size company.  Long debated in FSW circles is what the ideal candidate would look like.  Many consider starting with a trained welder and training them on machine operations is the best approach – these individuals already come with an understanding of metal joining and the process (WPS/PQR) requirements necessary to for a solid joint.  Others believe that starting with a machinist and teaching them the basics of materials joining is a better approach – the machinist already understands the fundamentals of machine operations, tool path planning etc.  Whichever approach is adopted – there is a significant amount of training that is necessary to fill the void of knowledge as it exists today.

One of the major impediments to broader industrial implementation of FSW has been the affordability and suitability of FSW equipment. Current FSW equipment presents implementation challenges – due to either high cost or lack of adequate performance feedback to ensure quality of the joint.  Many of the current systems that are available for fielding, which possess adequate system feedback and control, can be extremely expensive and are typically custom designed and built.  While these machines have the ability to perform the welds to high standards – their cost imped broad implementation within the larger industrial base.  These machines range from approximately $1 million to upwards of $3 million – making use impractical for all but the most expensive components. Aerospace has been a primary customer of these machines – providing a very high quality joint and the process control, feedback and “process records” that are essential in that industry. However; industry at large cannot justify the acquisition of these systems unless the component to be manufactured or repaired are extremely valuable and can achieve an overall return on their investment.  The systems that are more affordable, often lack adequate sensing and control feedback – making verification and adherence to process parameters (WPS/PQR) very difficult. The only way to determine that the joint has the required characteristics is expensive and time consuming NDI or destructive techniques. The key to overcoming these limitations is advanced control software.  HF Webster has formed an alliance with MTS Systems Corporation to address these issues.  This alliance combines the quality, experience and global support of MTS Systems with the production process experience and high-value engineering of HF Webster.  This solution is being implemented on a family of high quality CNC mill platforms – providing  a low cost platform married with  very high quality control and feedback systems.  This CNC series of friction stir welding machines is aimed at a very broad range of production applications.  The new high value FSW line will provide the sensing, control and feedback necessary to ensure adequate quality is maintained while reducing the equipment costs by an order of magnitude. 

Industrial Standards

One of the major roadblocks to widely implementing Friction Stir Welding in US industry has been the lack of industrial standards. Without this foundation, limited information has been available for general design,  manufacturing and fabrication.  Industries that selected FSW as a primary joining technique have played a significant role in overcoming this obstacle.  Extensive progress has been made in addressing this void. The AWS D17.3 Subcommittee began development work on a FSW standard in 1998, targeting aerospace applications.  In December 2009 the AWS published D17.3, Specification for Friction Stir Welding of Aluminum Alloys for Aerospace Applications.  This AWS specification represents a significant body of work and will provide the foundation from which additional standards can be built.  These family of specifications, when released, will provide post weld acceptance criteria for both continuous friction stir welds and friction stir spot welds.  Additionally, they will provide guidance for  design requirements, equipment, operator and procedure qualification and certification requirements. In the meantime, many FSW users have developed internal specifications for application to their products. As outlined in “Friction Stir Welding and Processing” (Mishra & Mahoney), in 2002, the American Bureau of Shipping (ABS) issued approval to use FSW in marine applications.  Additionally, NASA, the FAA and SAE have accepted FSW production items as meeting their internal standards.  The DOD is heavily involved in developing several guidelines for FSW joints – including ship building, ballistic joints for armor and evaluating aerospace fabrication and repair applications. 

This is the first part of a series to discuss Friction Stir Welding’s (FSW) barriers to Industry and bridging those barriers for a quality and robust joining method.

Currently, the bulk of US Industrial Friction stir welding development dollars have been spent in the aerospace industry. As a result, the broader automotive, marine, heavy & light manufacturing and construction markets for FSW implementation are still evolving. Several issues have been identified as barriers to more extensive FSW implementation in US markets:

• Lack of industry standards and specifications
• High cost of capital equipment
• Lack of trained work force
• Lack of design guidelines
• Overcoming industrial traditions (rivets, fusion welding, other mechanical joining methods)

Industrial Benefits of FSW

FSW is a solid state joining (non-melting) process thus avoiding the inherent issues associated with melting and solidification of conventional fusion welds. Typically, FSW reaches approximately 80% of the material’s melting temperature; the lower heat input leads to significantly reduced Heat Affected Zone (HAZ) resulting in a 2000% decrease in horizontal contraction and over 1000% decrease in distortion. The FSW process is less operator dependant thus significantly reducing defects. The higher quality and process stability leads to a reduced need for post weld inspection – saving time and money.

• FSW has the ability to join thicker, difficult to weld and higher strength aluminum alloys
• FSW joints retain parent metal chemistry
• Allows the ability for joining dissimilar alloys more efficiently 
• Environmentally and ergonomically friendly
• Reduced health hazards – no toxic fumes and gases
• Reduce/eliminate shielding gas requirements
• No filler required & No consumables

FSW can dramatically improve manufacturability by reducing part counts, production time and defects. Additionally, surface preparation time is reduced along with post weld finishing requirements (grinding or brushing). When compared directly FSW vs. Fusion welding, FSW has:

• Higher production rates,
• Better quality; FSW produces repeatable and predictable results
• A very robust process envelope
• Increased impact and ballistic properties (1.7 x better than the parent metal)

Increasingly, many companies are turning to extruded aluminum structures to house sensitive electronic assemblies.   The auto, marine, automotive and aerospace industries have increased the use of low cost extrusions to provide a cost effective method of protecting sensitive control and sensing units. One of the major challenges in developing these assemblies in a cost effective manner is sealing them. Many of these assemblies require a hermetically sealed structure. Current methods of sealing some of these containers range from developing complex extrusions that provides a “hinged” self-sealing option, special adhesives or mechanical fastening methods.  Since most of the internal contents are sensitive to heat inputs – traditional joining or welding methods are impractical.  Companies in both the automotive and aerospace industries have turned to a solid state method of joining aluminum that provides a low cost method of sealing these containers – Friction Stir Welding (FSW). 

The use of friction stir welding to seal these types of containers provides a high quality hermetically sealed enclosure.  The reduced production costs, high quality assurances and highly automated production method allows them to meet high quality and volume rates necessary.  FSW sealed enclosures provides a solid state joint that has mechanical properties similar to the parent material that the extrusion is made  of – resulting in a monolithic structure with a very strong hermetic seal. You eliminate problems of costly extrusions, adhesive failures or mechanical failures.  Since there is very low heat input and distortion, the electronic equipment housed in the container remains safe and well protected. 

The DOD is currently investigating using these methods on both aerospace and land vehicles.  The harsh environment that the land vehicles are subjected to in both the Iraq and Afghanistan theaters has lead to an increased failure rate in some of the electronic components.  Enclosing some of the equipment in a more ruggedized structure may alleviate this problem. 

The animation posted on July 22^nd
on our videos page shows how simple aluminum extrusions are used to replace
existing bulky, corrosion-prone structural-members and plywood flooring to
become a single monolithic structure. This structure can be tailored to fit
many applications; the deck shown is just one of many possibilities for the
marine industry. In addition to the benefits for boats to replace problematic
decks, flying bridges, hull structures, weather-shields, railing, and frames,
this methodology can also improve seawalls, offshore structures, docks, and
shoreline buildings. By using friction stir welding, any aluminum alloy can be
considered for design purposes to create a strong tailored structure.   H.F. Webster’s manufacturing methods will
reduce materials, weights, and manufacturing lead times- simultaneously
increasing strength, rigidity, product quality, product life, and customer satisfaction.
Our animations and videos give excellent examples showing how HF Webster can
tailor products to fit your manufacturing and supplier’s needs.

The need for Process Qualification Procedures continues to perplex current commercial and DoD elements in both the repair and manufacturing areas.  The bane of technology infusion into both repair and manufacturing is the lack of design specifications, repair qualification standards and affordably changing designs to accept a new process.  There is a strong need for a systematic, objective, and scientific procedure to take a promising technology from possibility to actuality.  For our DOD customers the HF Webster procedure to qualify technologies is a hallmark our business – actual repairs qualified on actual parts – yielding a limited – but focused point qualification.  While there are many ways of describing this process used over the past 80 years with great success in many industries, we will use the framework of the popular Six Sigma quality approach to describe our qualification process: Define-Measure-Analyze-Improve-Control (DMAIC).

One of the technologies used in our repair and manufacturing processes is Friction Stir Welding (FSW).  FSW represents a perfect fit for designing quality into the repair or manufacturing. Each of the parameters that go into a friction stir weld can be measured, monitored and more importantly controlled – rotation speed, travel speed and load (there are many other parameters but these are among the most important).  This ability to get feedback and control provides a strong foundation for designing quality in – using DMAIC and the associated tool box (SPC and DOE methods).  Other traditional fusion welding methods do not readily lend themselves to this approach.

In Define, HF Webster identifies the problem, defines the requirements and set goals. We further identify the quality characteristics that are important to the customer for the particular part, repair technology, and failure mechanism.  Sources may be diverse including original requirements, specifications, technical orders, drawings, reverse-engineering the part, and identifying typical failure mechanisms.  The quality characteristics for the repair, defined by the original equipment manufacturer may include weld quality, weld strength and hardness, to name a few.  We also define the steps in the repair or manufacturing process, along with key sources of possible variation in product  consistency. 

Under Measure, we validate problem/process – we refine problems, goals, and measure key steps.  We physically measure the characteristics of the repaired part and compare the measured values to the standard developed in the first step.   An important subcomponent of this step is to assess how accurate our measurements are and improve their accuracy if required – as a minimum understand any limits that are present.

In the Analyze step, we use a variety of tools to compare the measured values to the standard and possibly brainstorm ways of closing the gap between what we now have and what is required, including reducing variation in the repaired parts.  Possible tools include expanded flow charts, check sheets, Ishikawa diagrams (fishbone diagrams), design of experiments, statistical process control, and other tools. 

Improve means to bring the output of the repair or manufacturing process closer to the goal.  If the problem is unanticipated variations in an otherwise healthy process, we employ Statistical Process Controls (SPC) to identify and eliminate special causes of variation such as worker qualifications, uncontrolled process parameters, or variations in raw materials or parts.   We might also employ Design of Experiments (DOE) to bring the outcome closer to the target value or reduce variation, and optimize processes for key responses.  For a given part we may use a series of designed experiments on coupons and surrogate parts to develop the needed weld strength, and proved the resulting weld parameters by repairing and testing actual parts. 

Finally, Control – We establish standard metrics to maintain performance and correct problems as needed.  This means we will define the current state and capability of the process, using the established process parameters.  The control step ensures the process is repeatable and capable of consistently producing quality parts that return t satisfactory values.  The qualification process does not end here, but would be continued in qualifying an industrial company to conduct the repairs.  To qualify the corporation, we would supply the parameters and tolerances along with requiring the company to demonstrate their capability by repairing or manufacturing a statistically significant number of actual parts, which would then be tested and measured to prove the process has the capability to conduct the specified repair or produce the part. 

The quest for improved repair qualities then branches back to other steps in the cycle in a never-ending pursuit of improved and more consistent performance, at lower costs.  The hallmark of HF Webster is that we have not merely shown such repairs may be possible, but that we have proved the technical and practical feasibility of such repairs on real-world applications and parts. 

Existing manufacturing methods for pontoon style boats,
houseboats, small aluminum hulls and larger yachts in the U.S. utilize mostly
traditional fusion welding and mechanical fasteners such as rivets. These
traditional methods can have several drawbacks including susceptibility to
corrosion thereby decreasing the life of the structure, reduced strength, low impact
resistance, increased weight thus reducing fuel efficiency, In addition, fusion
welding and mechanical fastening can have long manufacturing and fabrication
times. Transitioning to a stiffer, more cost-effective and higher strength deck structure, companies can eliminate the bulky structural
cross members, the inevitable-rotting plywood flooring, and all the individual
fusion-weldments that come with these problematic sub assemblies. Manufacturers should be utilizing all the
benefits and advantages of FSW. FSW has the capability of joining smaller
extrusions to form tailored load-bearing structures and decking-platforms, all
in one assembly. H.F.Webster’s manufacturing methods will reduce materials,
product weights, manufacturing lead times, as well as increasing product
quality, product life, and customer satisfaction.

• Reduction in weight
• Increased payload
• Increased fuel efficiency due to reduced weight and aerodynamics
• Decreased corrosion problems
• Longer trailer life
• Higher resale value
• Lower cost for manufacturing
• Reduced manufacturing time
• Reduced number of parts in manufacturing process
• Increased rigidity – higher strength structure

To put things into perspective – on an average over the road flat bed trailer – substituting aluminum for steel and wood decking  and  implementing Friction Stir Welding in the manufacturing process would result in over 20% reduction in weight, reducing number of manufacturing parts by almost 60% and increasing corrosion resistance significantly.  Lower weight, better fuel economy, more payload, simplified manufacturing processes and lower costs – FSW is a smart fit for trailer manufactures – big or little.