Category: Welding Techniques

When you think of ground-breaking and game changing, a lot of things undoubtedly come to mind. For welders, it might be titanium welding. In its early days, all titanium welding used to be carried out inside glove boxes – significantly limiting the size of projects a titanium welder could undertake. Not anymore.

The Limitations of an Emerging Science

Titanium is a difficult material that is especially sensitive to contamination. To shield titanium from the embrittling effects of elements like nitrogen, hydrogen and oxygen, virtually everyone in the industry used to conduct all titanium welding inside of glove boxes. These are airtight boxes filled with inert gas and fitted with rubber gloves, which the welder engages with while standing outside of the box. This limited manufacturers to welding only parts that were small enough to fit inside of these boxes, which is horribly insufficient for larger critical-use applications.

The Titanium Welding Revolution

Through brainstorming, experimentation and a whole lot of trial and error, a few crucial discoveries were made that would go on to liberate titanium welders from the confines of glove boxes, including:

• It is possible to create high-quality welds in the open-shop environment.
• Welds must be protected while they are solidifying, and the reverse side of welds must also be shielded.
• Trailing shields that use inert gases like argon or helium can protect welds from contamination.
• Local purges offer more flexibility than purging large volumes.
• Shielding gases must be clean and devoid of moisture.
• Titanium welding requires a higher degree of cleanliness than is required for other metals. Lint-free paper towels and acetone works best.
• Ductile welds cannot be produced by oxygen acetylene welding, or any method using active gases, coated electrodes or traditional fluxes.
• The best results usually come from gas tungsten-arc welding, laser beam welding or electron beam welding, however, gas metal-arc, spot, seam and flash welding may all be used depending on the demands of the application.
• There should be no surface colors on finished welds, and different colors indicate different severities of problems that corrupted the welding process. Under no circumstances should a welder make a second pass if the first pass resulted in surface discoloration until the problem has been corrected.

Industry-Wide Impact

When these discoveries were shared with welders across the world, the practices developed quickly became standard in the industry. The entire industry benefits from shared knowledge. Firms that don't regularly work with titanium can continue to design inferior shields, fail to clean well enough and produce low-quality welds, which are unreliable and prone to failure in the field. Anyone who works with titanium is encouraged to learn about the history of the craft and the evolution of techniques that are now considered common best practices.

Gone are the days of being forced to limit your welding to what can fit inside a certain space. With the knowledge and skills available today, titanium welders are able to think outside the (glove) box.

There are many reasons to use preheating when welding. In some applications, manufacturers preheat materials prior to welding. Sometimes preheating is required by specifications, sometimes it is an elective technique that conforms to best practices. Either way, it is critical to work with a manufacturer that understands this process and knows how to incorporate it into planning.

The 3 Reasons for Preheating

Manufacturers generally preheat for one of three reasons:

1. It is required: Welding codes or standards sometimes require preheating. Certain materials — such as high carbon or alloy steels — are prone to cracking during welding. Cracking, which is the worst kind of welding flaw, can occur when metal cools too fast. Preheating slows cooling of both liquid weld metal and base metals.

2. It increases productivity: Manufacturers sometimes choose to preheat steel because it increases productivity in three ways. First, it can reduce weld distortion. Second, it encourages weld metals to blend more fluidly into the surrounding areas, which can reduce the amount of required grinding. Finally, it reduces porosity by slowing the cooling enough to prevent gas bubbles from getting trapped as the metal solidifies.

3. It reduces stress: Preheating can work in conjunction with post-weld heating to bolster stress relief efforts. Some materials are especially prone to cracking, and the best results are achieved when post-weld stress-relief heating is preceded by major preheats of 500-600 degrees Fahrenheit.

Preheating and the Planning Process

Since it can take considerable time to heat a massive amount of steel, preheat requirements must be accounted for during planning. Since preheating involves several variables and complicated considerations, it is better for planners to flag this requirement early.

Planners must consider if the steel needs to cool overnight, or if teams will have to maintain the temperature so that less preheating is required the next morning. In some cases they will have to maintain a high temperature, finish welding and then, if necessary, move straight into post-weld stress relief without first letting it cool.

Often, manufacturers preheat because it is mandated by a welding code. Sometimes preheating is conducted by choice to achieve a benefit in productivity or stress relief. Either way, the need to preheat must be identified early in the planning process to enjoy optimal results.

Exotic metals fall outside the list of materials that are common to most manufacturing projects. Since they are rare and unfamiliar, they can be expensive and difficult to obtain. But the performance requirements of some projects can only be satisfied by these unusual materials. Most manufacturers avoid the risk associated with these projects, and the bold few who are willing to work with exotic metals have to leverage their experience and expertise to get it right the first time.

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Titanium welding is a specialty within a specialty. This remarkable metal has unusual properties and offers unique benefits — especially for critical-use aerospace and marine applications.

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Manufacturers use objective quality evidence (OQE) to ensure that critical-use parts will perform as intended throughout their life, to provide transparency to the customer and to trace the source of a problem in the rare case that a failure occurs in the field. Businesses based on manufacturing parts for critical-use projects must build an extremely high level of OQE into their standard fabrication processes.

High Standards as the Default Setting

Look for a manufacturer whose basic OQE standards are remarkably high, and can be increased even further upon customer request. Even if a contract explicitly states a low standard, the seasoned manufacturer generally defaults to their regular high standard.

This is because OQE practices are so ingrained in their process and day-to-day activity, it would be risky to lower standards for a single project and then raise them back for the next. It is safer and more consistent to maintain an extra-high standard across the board.

The Components of Objective Quality Evidence Standards

Sure, everyone will have some form of quality control. But when standards for a manufacturer’s basic OQE surpass most firms in the industry, they will include:

• 100 percent dimensional inspection: Every single dimension on every single drawing is measured and recorded as acceptable or unacceptable.
• Material heats and lots are tracked to each serial number of each component.
• Special tasks are limited only to qualified personnel, and their qualification records are kept on file.
• Nondestructive Examination (NDE) reports are created for in-process and final inspections.
• All data is recorded, filed and archived whether or not it is required to be delivered with the components.
• Weld maps with unique joint identification can be created so that welding parameters and inspections can be tracked to a specific weld on a specific serial numbered weldment.
• Weld pass records are maintained so the parameters used are recorded along with individual sign-offs for inspections performed on each pass.

When Customers Require Even Higher Standards

Some contracts may require a higher level of OQE. During contract review, seasoned manufacturers flag anything that is not standard or that may require a higher OQE than normal. When they identify these special requirements — or when a customer specifically requests higher standards — they include steps in their process to accommodate.

Instead of just recording each dimension as acceptable or unacceptable, a contract with higher OQE may require their partner to measure every dimension as normal, and then also record the actual value of every single dimension.

For example, say a hole was designed to have a diameter of 1.000", with a tolerance of +/- .005", and the hole measured at 1.001" in diameter. Instead of just recording it as acceptable, the team would take the extra step of documenting its actual value (1.001") for extra proof that parts will function as designed.

Layers and Checks to Assure Accuracy

A thorough OQE process travels through several checks — from design to inspection — to ensure nothing is lost in translation.

First, the person with technical responsibility — usually the project engineer or quality engineer — reviews the project requirements. That person then establishes the check points and inspection points necessary for each of the OQE requirements, which the teams will work off of and record.

Next, it is reviewed by the quality manager, who makes sure the plan includes all requirements necessary to fulfill the contract.

Finally, it is passed to the actual people who will conduct the inspection, so they can see the first-hand, verbatim language of what is required and how to achieve those requirements.

The Value of Strict OQE

High-standard OQE is not just a formality. It protects and insulates both parties, and provides a tracking mechanism should a failure occur in the field.

If a customer is concerned that a piece of equipment is incorrect, the manufacturer can refer to the OQE — complete with inspection reports, signatures, dates and recorded values — during an audit. If the client wants to probe deeper, a seasoned manufacturer maintains supplementary data, including coordinate measurement machine inspections, which saves records from old inspections.

In the rare case that a part fails or breaks in the field, clients need to be able to trace the process from the origin of the material through the entire manufacturing process. If a screw fails, for example, the exact origin of that screw can be traced, as can any other locations where similar hardware was used to prevent future failures.

Strict OQE protects all parties, ensures quality, provides a complete record and tracks the source of a problem should a failure occur in the field. New technology and paperless processes have been applied to control the flow of sensitive information, but the basic principles of sound OQE have not changed.

After spending time, effort, and resources to bring an idea to life, the last thing you want is to have your project stalled because of contaminated materials. Manufacturers must develop strict protocols to prevent contamination of any manufacturing process, welds, or finished surface. Failure to plan can have catastrophic effects on the functionality of the finished product.

Contamination vs. Cross Contamination

Contamination occurs when a foreign substance, such as oil or rubber, is inadvertently introduced into the manufacturing process. Cross contamination, on the other hand, occurs when metal from one application — carbon steel, for example — is accidentally transferred onto a non-compatible metal, such as stainless steel.

Both contamination and cross contamination can negatively impact the finished part's performance, durability and lifespan. Among the possible consequences of contamination and cross contamination are:

• Unexpected corrosion.
• Weld failure or cracking.
• Liquid metal embrittlement in elevated temperature services.
• Contamination of sensitive final-use products in industries where cleanliness and purity are critical. If oil or rust contaminates a part made for a pharmaceutical freeze dryer, for example, then the drugs produced on that equipment are contaminated.
• Spread of detrimental materials throughout a larger system of equipment. If a contaminated part were to enter a nuclear reactor, for example, that contaminant could quickly spread throughout the entire reactor.

Best Practices for Preventing Cross Contamination

There are six different approaches to keeping the wrong materials from being introduced into manufacturing processes:

1. Conduct high-risk activities away from sensitive parts: Operations like grinding are especially prone to generating airborne particles, which can settle on sensitive materials. Grinding equipment should be used and housed away from vulnerable materials.

2. Use color-coding to classify tools: A well-accepted industry practice is to assign colors to tools based on their purpose or previous contacts. Abrasives are painted with one color so employees are alerted not to move them from carbon steel to stainless steel. Another color distinguishes tools for grinding that haven't been (and cannot be) used on a different type of material.

3. Develop strict handling practices: Employees should refrain from sliding parts along surfaces or other parts made of incompatible materials. A stainless steel part should never be dragged across a carbon steel table, for example. Installing shims between clamps and parts can prevent unwanted contact.

4. Segregate sensitive materials: Materials like titanium are especially vulnerable to cross contamination and must be totally pure. Some applications require these hyper-sensitive materials to be completely segregated in storage.

5. Purify the machines themselves: Manufacturers who know their machines inside and out can go even further in preventing unwanted exposure. For example, coolant is used to prevent tools from wearing out, and that coolant can collect contaminants. When working with sensitive materials like titanium, it may be necessary to flush out and replace the coolant to avoid any particulate matter from metal that was machined earlier that day.

6. Cover materials with plastic: Simple plastic wrapping can go a long way in preventing airborne grit and dust from settling onto components tools or materials.

Contaminants can devastate an otherwise perfect manufacturing process. In order to avoid contamination and cross contamination, manufacturers must be strict and methodical in developing and following a non-negotiable series of preventative measures to maintain absolute control over what goes into — and doesn't go into — each and every step of manufacturing.