Universal welding management software WeldEye is now available for managing the quality of robotic welding. By collecting data from the welding robot and synchronizing it with weld lists in the cloud service, WeldEye provides an effortless way of monitoring robotic welding quality and its compliance with welding procedure specifications (WPS). In addition, the software ensures full traceability down to each weld and welded end product.

Data collection requires that the welding power source is connected to WeldEye’s Digital Connectivity Module. The device then transfers the data wirelessly to the software, where the information can be easily viewed and analyzed further.

In addition to the web browser-based user interface, the WeldEye mobile application can be used e.g. for real-time monitoring of welding parameters, operator identification, or selecting the filler wire material.

“With WeldEye you will know what has been welded, at which welding station, and when it happened. It also reports the used welding parameters, heat input, and any possible deviations in real time and with precision. The logic is based on identifiers, which help us track even a specific filler batch in welding production if it has been faulty,” says Vesa Tiilikka, Product Manager, Software at Kemppi Oy.

Integration with A7 MIG Welder

The development of the WeldEye software has been successfully piloted with Kemppi’s robotic welding system, A7 MIG Welder.

“All setups will be configured case-by-case according to the customer’s needs. If you have been looking for a robotic welding solution that can be monitored in terms of welding quality and traceability, I encourage you to contact us to see what we can do to help out,” says Artturi Salmela, Product Manager, Automation at Kemppi Oy.

WeldEye’s quality control functionalities are available when using WeldEye for Welding Quality Management, which includes the following software modules:

Welding Procedures
Personnel and Qualifications
Quality Management

WeldEye collects data on arc-on time, welding deviations, and reason codes used to report non-welding activities.

Welding runs can be reviewed against the digitally collected, detailed welding parameter data and heat input calculations.

The data from the robot is synchronized with the weld lists and product structure in WeldEye, which enables full traceability down to each weld and welded end product.

For more information contact vesa.tiilikka@kemppi.com or artturi.salmela@kemppi.com

The Aristo Air PAPR (Powered Air Purifying Respirator) system combined with the Sentinel A50 Air helmet, offers heavy-duty protection from welding fume and dust when welding, gouging & grinding. The unit features the latest in PCB Board technology, allowing the welder to adjust the air flow from 170 L/min to 210 L/min to suit the environment and application. This is highlighted by an LED airflow indicator on top of the unit. The Aristo Air is equipped with audio & visual blocked filter and low battery alarms, offering extra safety for the welder.

The strong physical construction of the Aristo Air, makes it extremely robust and suitable for all heavy-duty welding applications.

Aristo Air unit weighs only 1kg, allowing for longer wear time without the user getting fatigued and weighed down.

Sentinel A50 Air Helmet Features

• Crystal clear true colour visibility
• High impact revolutionary shell design
• Colour touch screen control panel
• Hard coated Anti-Scratch front cover lens (clear/amber)
• Halo™ Headgear: Ergonomic, infinitely-adjustable 5 point headgear provides extreme comfort and balance
• Externally activated Grind button. (Shade 3 grind mode)
• Low-profile design, central pivot point allows for maximum head clearance while the helmet is in the up position
• Low amperage TIG rated ≥2amp (DC) (AC)
• Memory – 8 location storage.

Years of welding have trained you to know exactly what you need in a hood: crucial comfort, large lens, and next-generation technology. Every special operation needs special equipment that gets the job done, and when it comes to your helmet, SENTINEL™ is worn by the best.

Aristo Air PAPR Features

• Li-Ion battery pack (up to 8hr duration @ 210L/min)
• P3 filter and pre-filter
• Audio/visual blocked filter and low battery alarms
• LED air flow indicator
• International intelligent charger (interchangeable pins)
• Battery charge LED indicator

The strong physical construction of the Aristo® Air, makes it extremely robust and suitable for all heavy-duty welding applications.

Suitable For

• Plasma Cutting
• Oxy-Fuel Cutting
• SMAW/MMA (Stick)
• GTAW (TIG – Tungsten Inert Gas )
• GMAW (MIG/MAG – Metal Inert Gas / Metal Active Gas)
• Grinding

Find your nearest distributor to order your system now!

The goal of any Australian welding and fabrication company is to create quality products for their customers, while also managing costs and maintaining the desired levels of productivity and quality.

Missed or defective welds can severely affect costs, productivity and quality levels of the company and defects in the welds could also lead to potential safety issues and a loss of company income.

Being able to clearly identify problems early in welding and fabrication activities is crucial — and welding information management systems can help

Detecting problems early

Given that overseas competition can make life tough for Australian fabricators; fabricating quality parts, maintaining high productivity levels all the while seeking ways to reduce costs all become critical factors.

It is therefore important for fabricators and management to consider some of the following questions:

• Is the design overly complex, making it more prone to missed or defective welds?
• Are we able to complete visual inspection – ensuring that all welds are in place and compliant?
• How much risk is our company willing to take that the visual inspection is accurate?
• What are the long-term consequences if a part fails?

In every case, missed or defective welds will lead to cost implications for the company. They could also pose significant safety hazards and even lead to serious personal injury for a site worker or member of the public. The cost implications if a defective weld can result in a failure in the field or in an insurance claim. We all recently heard on the news of the Victorian road sign that fell from its support structure and onto oncoming traffic. So, the earlier in the welding process that companies identify mistakes, the less costly it will be to correct the problem. Generally, the costs of welding fabrication can be identified as:

• Labour: 85%
• Welding consumables: 6%
• Raw materials: 4%
• Gas shielding: 3%
• Utilities: 2%

However, these costs can all go up significantly when a weld is missed or defective.

The methods of reducing these potential cost impacts can be completed during the various stages of the fabrication cycle.

Stage one: welding booth

At this stage, identifying a missed or defective weld is the ideal scenario. A welding supervisor or the welders him/her self can usually spot the missed weld easily and correct the issue. This action would be the most cost-effective method.

Weld defects may pose a slightly more difficult problem as they may require the removal of the weld and its rework. Rework costs would typically be two or three times that of the original fabrication.

Stage two: the shop floor

Fabrications on the larger shop floor and that come together from a series of sub-assembly parts can be visually inspected, with defective welds that are identified or welds that have been missed can be returned to the welding booth if the boilermaker/welder does not have the equipment or qualifications to make adjustments.

If the sub-assembly is large, the company may accumulate downtime for moving it. This will inevitably lead to lost productivity and unnecessary costs. Returning a part to the welding booth could also lead to a welder waiting on a part.

The result is a bottleneck that affects the company’s throughput and profitability.

Stage three: the paint shop

At this stage, and after painting has been completed, the rectification of missed or defective welds that are identified will mean the company will need to remove the paint and return it to the shop floor.

These failures will cause the company to amass extra labour and rework cost, but also for the paint itself. For larger components which require painting all at once, these costs could be significant.

Stage four: final fabrication assembly or site assembly

If a company identifies missed or defective welds in this stage, it will require disassembling the part, removing paint and returning the part to be completely fabricated again. By starting the entire welding process over, costs continue to escalate due to both downtime and labour.

If defects are identified on site, the company might be able to deploy mobile welding equipment to rectify the problem. Correcting a missed or defective weld in this way requires additional labour for an employee dedicated to this site welding, with potential costs of having to use a site welding process (MMAW) and a possible field weld repair procedure. There may also be site induction costs plus the inefficient use of a shop welder. Having mobile welding equipment also requires a capital investment for equipment that is only used periodically.

Stage five: customer identification

If a customer inspection identifies a missed or defective weld, a company could accumulate costs to remove the product and deliver a new one.

In the case of a piece of a heavy fabrication, these costs could be substantial and can lead to warranty claims in addition to having to remove and replace the item. The company’s reputation would be at risk, especially if the problem is reoccurring and becomes known throughout the industry. In some cases, tier one companies who supply welded fabrications could potentially lose job contracts if they generate a poor track record for missed and/or defective welds.

Stage six: insurance claim

Property damage or bodily injury is the most significant consequence of a missed or defective weld. This threat to safety is a very real concern and one that far exceeds the financial ramifications a company could experience as a result. Yet, there are still those financial concerns. Insurance claims can generate significant expenses at this point. Negative — and potentially, permanent — damage to the company’s brand reputation is also possible and could lead to future loss of business and profits. Again, these effects are always secondary to a catastrophic event, but companies must consider them as due course of operating a successful business.

Solution options

For some companies, standard quality control inspections may be enough to protect against missed or defective welds. For example, welding operations with smaller, less complex parts may be easier to evaluate on an ongoing basis. Companies with larger and more complicated welding applications or parts, however, may find the need to implement quality checks throughout the welding process, leading to higher labour costs. Such operations could benefit from alternative other means of quality and cost control.

Advanced welding information management systems are one such option. These systems electronically gather weld data to help companies drive quality and productivity improvements in the welding operation. Among other features, they also provide real-time feedback to the welding operator to help prevent missed or defective welds. Using a human-machine interface (HMI), the system guides the welder through the correct weld sequence and weld placement using visual cues on screen (usually a ruggedised PC monitor), counting each weld as it is completed. Welders must finish each weld correctly and in order before proceeding to the next one.

Advanced welding information management systems also monitor welding outputs to ensure that the welding operator is welding within the weld procedure to create a quality weld. They are capable of tracking multiple factors, including:

• Amperage and voltage
• Gas flow
• Wire feed speed
• Weld duration

Companies can program an advanced welding information management system to respond accordingly if a welder welds outside of the procedure ranges. The system can provide a simple alert or it can disable the welding gun entirely until the welding supervisor or engineer is able to identify the problem and offer a solution.

Many equipment manufacturers can offer welding information management systems. By choosing to monitor weld sequence and parameters, a company that has chosen to invest in such equipment can reduce or prevent productivity loss, product quality failure, and damage to its brand image.

When a company considers that upfront cost compared to the long-term benefits and savings of these systems, the investment starts to make good business sense.

Dynaweld, the welding supply experts, are delighted to announce the launch of the Bossweld TC16 hydrogen controlled, twin coated electrodes.

The Bossweld TC16 hydrogen controlled, twin coated electrodes have been through a rigorous schedule of R&D and testing to produce an electrode that is the equivalent of the market leading 7016 twin coat electrode.

Get your FREE sample pack!

As an Australian Welding Institute member exclusive, Dynaweld is offering a free sample pack to all members.

Follow this link for your free sample or to find out more about the Bossweld TC16 hydrogen controlled, twin coated electrodes.

The ideal choice for all applications where high strength is required

Designed for welding high tensile steels, the TC16 electrodes are ideal for rural maintenance, fabrication and repair of farm machinery.

Other applications include general welding and maintenance welding jobs such as repair of earth moving equipment, root run on pipe butt joints or plates.

And because the TC16 has an extremely stable arc it is more tolerant to rust or paint on the work surface than other electrodes.

The advantages of twin coat

The inner coating of the TC16 electrodes contains the ionising and conducting ingredients that enable a strong and stable arc to be concentrated around the wire.

This inner coating provides excellent arc striking characteristics and superior arc stability.

The outer coating contains the shielding and slag-forming elements and is non-conductive.

It contributes to the x-ray quality weld metal and it is also designed for welding with the new inverter technology.

Many features and benefits

Enjoy the many features and benefits of these easy-to-use low hydrogen twin coat electrodes, including:

• Excellent arc striking characteristics
• Smooth and stable arc
• Easy slag removal
• Tolerance to rust or paint on the work surface
• Delivery of x-ray quality meld metal

The Bossweld TC16 hydrogen controlled, twin coated electrodes are suitable for inverter welding and all positional welding (except vertical down).

And they are guaranteed to do the job, with ABS Approval – Grade 3 H10.

Performing gas tungsten arc welding (GTAW) on anodized aluminium is a bit like trying to poke a hole in a sheet of ice without disturbing the water underneath. In this case, the ice is the hard layer of oxide created by the anodisation process and the water is the soft aluminium underneath.

Anodized aluminium is simply standard aluminium that has been treated to produce a thick layer of oxides on its surface. The aluminium base is a very soft material and melts at approximately 590 °C, but the oxide layer is extremely hard (some types approach the hardness of diamonds) and melts at 1980°C. The difficulty in welding anodized aluminium lies in removing the oxide layer without burning through the aluminium base.

GTAW on anodized aluminium requires different equipment, preparation, and technique than on standard aluminium. Its corrosion resistance makes it ideal for boating accessories, such as this tuna tower, that are exposed to high-salinity environments.

Interestingly, it is these properties of the oxide layer that make anodized aluminium a useful material in the first place. It is relatively inexpensive, visually appealing, lightweight, and corrosion-resistant, making it suitable for high-salinity environments, such as coastal areas.

Without any treatment, aluminium naturally forms a very thin layer of oxides. The process of anodizing aluminium uses an electrolytic chemical application, usually with sulphuric acid, to create a layer of oxides several times thicker than would naturally form —0.005 to 0.025 mm thick.

Anodized aluminium Types

The four types of anodized aluminium are standard, bright-finish, coloured, and hardened.

Bright-finish anodized aluminium can be visually distinguished from standard anodized aluminium by its shiny, chrome-like finish. This type of material has a thicker layer of oxides than standard anodized aluminium, making it more difficult to GTAW, and is used primarily for cosmetic reasons.

Coloured anodized aluminium is also used for cosmetic purposes. This material uses dyes in the anodisation process, which allow the material to take on different hues, but also introduce potential contaminants into the weld.

Hardened anodized aluminium is almost as hard as a diamond and is very difficult to weld. This type of material is usually used only in highly specialized industrial applications.

Bright-finish, coloured, and standard anodized aluminium’s all use much the same equipment, preparation, and technique as standard aluminium, but they have some unique requirements in order to be welded successfully.

Selecting the Right Equipment

Selecting the right equipment is the first step in welding anodized aluminium successfully. Equipment unique to the process includes a torch with a fingertip control and a 5356-class filler metal. An air-cooled torch is suitable for less than 200 amps, but a water-cooled torch should be used for applications requiring more amperage.

Like standard aluminium, anodized aluminium also requires a 100 percent argon shielding gas or an argon/helium mixture and a 2 percent ceriated (orange stripe) or thoriated (red stripe) tungsten. [Note: Thorium is radioactive. Always follow the manufacturer’s warnings, instructions, and the Material Safety Data Sheet for its use.] Pure tungsten (green stripe) also can be used, but only up to about 70 percent the amperage of ceriated or thoriated tungsten.

When preparing the tungsten, grind it to the same type of point that you would when welding steel or stainless steel. Be sure to regrind the tip when it rounds off and causes the arc to become unstable. Repeat this process as necessary.

A power source capable of alternating current (AC) is also necessary because the electrode-positive portion of the current cycle breaks apart the oxide layer.

Although some traditional transformer-based GTAW power sources are capable of successfully welding anodized aluminium, an inverter is highly recommended for its balance and frequency controls.

Balance control allows you to adjust how long the current spends in each part of the AC cycle. For example, a balance control set to 30/70 means that the current spends 30 percent of its cycle in electrode-positive, cleaning the oxide layer from the base material, and 70 percent in electrode-negative, directing the electrical energy into the weld joint and joining the two pieces of material.

Your experience and skill will determine how you set the balance control. A more skilled welder often can use a higher percentage of electrode-negative (80 to 90 percent) in order to work faster.

The frequency control function available on inverter units allows you to determine the length of time that it takes the unit to complete one full current cycle (the combined time spent in electrode-positive and electrode-negative.)

Transformer-based power sources produce an output of 60 Hz, which is the same frequency that comes from a standard outlet. Inverters, however, are able to adjust the frequency from 20 to 400 Hz. For anodized aluminium, a frequency of about 160 to 200 Hz generally produces the best results. The frequency produces a narrower arc cone and, consequently, a narrower weld bead and HAZ. The strength of the weld increases by reducing the area of the base material exposed to the heat of the arc. A narrower weld bead reduces the time and filler metal needed to make the weld.

An inverter machine also eliminates the need for a backhanding technique. Backhanding, also known as backing around the weld, involves making two passes on each weld joint—one pass going forward to clean off the oxide layer and then reversing direction to add filler metal to the area just cleaned. In addition to doubling the time it takes to weld the joint, backhanding requires the workpiece to be heated twice, and this can reduce the strength of the weld.

Material Preparation

Properly preparing the material is critical to ensuring strong and cosmetically appealing welds on anodized aluminium.

The material should be at room temperature for at least an hour before welding, otherwise condensation can form within the aluminium and react with the argon shielding gas, creating porosity and a black, sooty appearance on the weld.

Cleaning any residue, dirt, or other foreign material from the base metal and filler metal with a clean cloth prior to welding helps prevent weld defects such as porosity, inclusions, and lack of fusion.

Although the electrode-positive portion of the AC cycle helps remove the oxide layer that builds up on aluminium, you may want to use a dedicated stainless steel brush to manually clean the material before welding. Using this brush for other purposes will introduce foreign contaminants to the weld joint and compromise the weld’s structural integrity. An oxide layer begins to form immediately after brushing, so it is also necessary to rebrush a piece that sits for an extended amount of time without being welded.

Technique

Anodized aluminium requires a technique known as bumping, which is a way to remove the thick oxide layer without putting too much heat into the weld pool. Because it uses a fingertip control switch, a foot pedal is unnecessary for this technique.

Bumping involves very briefly starting an arc using the finger control switch, adding the filler metal, extinguishing the arc, moving down the weld joint about 1.6mm, and repeating the process. Turning the fingertip switch off gives the weld pool a moment to cool and solidify before you reintroduce the heat with a new arc.

Although easily described, bumping is one of the more difficult GTAW techniques to master. A proficient operator typically can reach a travel speed of about an inch every 30 to 40 seconds.

The amperage range you use will depend on your skill, with a beginner to intermediate welder using around 180 to 190 amps, and a highly skilled welder around 230 amps.

The thickness of the material will require you to adjust the travel speed—thin material requires a faster travel speed than thicker material—but the amperage range typically remains the same regardless of material thickness.

At those amperage levels, a filler metal of 3.2mm diameter should be used. Anything smaller will melt off before it gets to the weld pool. It is also important when adding the filler metal to insert it at the leading edge of the weld pool while the arc is live and to remove it before extinguishing the arc, so that the filler metal doesn’t become trapped in the weld pool as it cools.

The distance between the end of the filler metal and the weld should be no more than the diameter of the torch cup.

Although anodized aluminium certainly poses some unique challenges, its weight, low cost, and resistance to corrosion make it the best option for many applications and environments. Following this advice should help you overcome the difficulties associated with this material and realize its potential benefits.

Copyright © PRACTICAL WELDING TODAY

Written by JACK FULCER

Leading international welding equipment manufacturer, Kemppi, has unveiled its new Kemppi X8 MIG Welder for extreme industrial welding – the ultimate choice for demanding welding. The X8 MIG Welder is a multi-process system for synergic and pulsed MIG/MAG welding, MMA welding, MIG brazing, cladding and gouging. It delivers extreme power and accuracy using the most common electrical network voltages. Developed, designed and made in Finland, the X8 MIG Welder ensures the very best in performance. This intelligent equipment provides users with extremely precise control of the arc, high-duty welding performance up to 600 A, upgradable power sources, digital WPS and native connectivity with WeldEye welding management software so that they can perform, control and manage welding production in a way that was not possible before.

Designed with precision, welding efficiency and quality in mind, the X8 MIG Welder’s welding arc characteristics deliver enhanced performance – particularly on austenitic stainless steels, aluminium and advanced high-strength steels. To improve quality control and eliminate the need for printed WPS, the X8 MIG Welder features an integrated digital WPS (dWPS) function. By connecting the X8 to the WeldEye cloud service, welders can search, view and activate WPS via the Control Pad display and automatically use the right parameters during welding.

Fast and accurate, the digital WPS function ensures quality control, and helps saves time and money during welding production. The X8 MIG Welder also features a sophisticated Control Pad. In addition to allowing the welder to access and view digital WPS, the Control Pad also lets welders set and adjust parameters to control welding. The device can also be used to collect fabrication information to verify that the weld meets WPSs and analyse welding productivity based on arc time and tracking. Ergonomically designed, the welding gun of the X8 MIG Welder has been shaped for maximum comfort. The hand grip, mobility and stability of the gun have been optimised to meet the most demanding welding tasks. Plus, the innovatively designed wire feeder ensures safe and ergonomic loading of the filler wire spool.

Easy to set up and configure when compared to standard welding equipment, the X8 MIG Welder is ideal for use in a range of industrial applications including on oil rigs, process pipelines, and pressure vessels and boilers.

‘Smart, powerful and robust, the X8 MIG Welder adapts easily to any welding environment and meets even the most extreme expectations of industrial welding,’ said David Green, Managing Director, Kemppi Australia.

For more information on the new X8 MIG Welder call Kemppi Australia on (02) 8785 2000 or email sales.au@kemppi.com

It is with great excitement that CIGWELD/ESAB announces the launch of the new Transmig 255i! These units will be available in early February with pre-orders being accepted NOW!

The Transmig 255i is a compact self-contained single phase multi-process welding inverter, capable of welding MIG (GMAW/FCAW), Stick (MMAW) and Lift TIG (GTAW). Ideal for welding plate thicknesses between 0.8mm and 12mm with a range of wires from 0.6mm – 1.2mm (solid).

The Transmig 255i is ideal for onsite repairs and maintenance, medium industrial workshops, car panel repairs or serious welders that want a single phase inverter they can plug in and use around their own home workshop.

Coming standard with a 15amp plug, this machine can easily be upgraded to a 25amp plug and 4mm2 supply lead to increase the duty cycle to an impressive 255A @ 40%.

The Transmig 255i is equipped with an integrated wire feed unit that fits 300mm spools, 2T/4T, Down Slope (in TIG), adjustable Arc Force (in Stick), VRD (which is applicable in stick mode), PFC (power factor correction), and Fan on Demand which minimises power consumption, noise and dust contaminants. The unit is also fully compliant to Australian Standard AS 60974.1-2006 and is ideal for indoor and outdoor use with an enclosure rating of IP23S.

For intricate aluminium welding, users can easily attach and run the Tweco SGT250 Spool Gun thanks to the compatible Euro adapter and 8-pin socket.

PACKAGE CONTENTS (Part# W1005255):

• Transmig 255i Power Source
• Tweco Professional Fusion 250 MIG Torch, 3m
• COMET Professional Argon Regulator/Flowmeter
• Feedrolls: 0.9/1.2mm “V” groove (fitted), 0.6/0.8mm “V” groove, 0.9/1.0mm (U) groove, 0.8/0.9mm “V” knurled
• Contact Tips: 0.9mm (fitted), 0.8mm, 0.9mm, 1.0mm
• Twistlock Electrode Holder with 4m Lead
• Work Clamp with 4m Lead
• Shielding Gas Hose Assembly
• Operating Manual

The precipitation hardening (PH) stainless steels are a family of corrosion resistant alloys some of which can be heat treated to provide tensile strengths of 850MPa to 1700MPa and yield strengths of 520MPA to over 1500MPa – some three or four times that of austenitic stainless steel such as type 304 or type 316. They are used in the oil and gas, nuclear and aerospace industries where a combination of high strength, corrosion resistance and a generally low but acceptable degree of toughness is required. Precipitation hardening is achieved by the addition of copper, molybdenum, aluminium and titanium either singly or in combination.

Stainless Steel Composition

The family of precipitation hardening stainless steels can be divided into three main types – low carbon martensitic, semi-austenitic and austenitic – typical compositions of some of the steels are given in Table 1.

Table 1: Typical Compositions of some commoner precipitation hardening stainless steels

The martensitic PH steels, of which 17/4PH is the most common, transform to martensite at low temperatures, typically around 250°C, and are further strengthened by ageing at between 480 and 620°C.

Austenitic Steels

The austenitic-martensitic PH steels are essentially fully austenitic after solution treatment and require a second heat cycle to 750°C/2 hours before cooling to room temperature to form martensite. Some of these alloys need to be refrigerated (-50/-60°C for eight hours) following this heat treatment to ensure full transformation to a stable austenitic/martensitic structure although the two most commonly used alloys, FV520 and 17/7PH, do not require refrigeration to develop optimum properties.

Ageing of these alloys occurs at temperatures between 500 to 600°C. The austenitic grades are stable down to room temperature, improvements in strength being from the precipitates formed by ageing at 650 to 750°C. These fully austenitic grades can exhibit good toughness and some may be used at cryogenic temperatures.

For best weldability, it is recommended that all three types of alloys are supplied in the annealed, solution treated or overaged condition. Alloys in the form of sheet or strip may be in a cold worked condition and weldability is seriously compromised. As with many precipitation hardening alloys, achieving mechanical properties in the weld and HAZs to match those of the parent material is a problem. Even with matching welding consumables, a full solution treatment and age hardening, the maximum strength of a joint in the semi-austenitic and austenitic alloys is likely to be only some 90% of that of the base metal.

Martensitic Steels

Martensitic PH steels in the solution-treated condition can be welded with most of the conventional arc welding processes although the best toughness will be achieved with the TIG (GTAW) process as this provides the cleanest weld metal. Even better toughness can be achieved using power beam processes (electron beam or laser welding). Matching filler metals are available for most of the steels in this group enabling matching mechanical properties to be achieved by carrying out a post weld ageing heat treatment.

If a joint is very highly restrained then 17/4PH may fail along the fusion line by a form of reheat cracking during the ageing heat treatment. In these circumstances, the component should be welded in the overaged condition and then given a solution heat treatment followed by the PWHT described below. Austenitic filler metals such as 308L or, for higher weld metal strength, a duplex filler metal such as 2205, can be used where lower strength joints can be tolerated or cracking due to high restraint is a problem. PWHT is not possible if a duplex filler metal is used or recommended for austenitic weld metal due to embrittlement.

The martensite in these steels is relatively soft due to the low carbon content so preheat is not generally necessary, although for thick, (above 25mm) highly restrained joints, a preheat of around 100°C has been found to be useful in reducing the risk of cracking. Because of the low temperature at which these steels transform to martensite a maximum interpass temperature of 200°C is recommended.

Maintaining a very high interpass temperature results in the entire weld transforming to martensite on cooling to room temperature and the volume change that occurs when this happens can then lead to a form of quench cracking. The stress raising effect of the notch in the root of fillet welds and partial penetration butt welds has been found to cause cracking. Provided the reduction in strength can be tolerated, a Tp308L root pass can be used to solve this problem. It has also been found that 17/4PH castings may form HAZ hot cracks during welding; for cast items the copper content is therefore limited to 3% maximum.

PWHT generally comprises a 750°C soak and cool to room temperature to ensure that the steel is 100% martensitic followed by ageing at 550°C. This should give UTS of 900 to 1000MPa, yield strength 800 to 900MPa and ductility of some 15% depending upon the composition of the alloy and the temperature of the ageing heat treatment.

The semi-austenitic alloys are generally supplied in the solution treated condition. This means that the steel is fully austenitic and preheat is not generally required although for welding of thick and highly restrained joints a preheat of around 100°C has been found to be helpful. All the common arc welding processes may be used although, as above, TIG (GTAW) will give the best properties.

For alloys containing aluminium, eg 17/7PH, MMA and submerged arc welding should be avoided as a good proportion of the aluminium is lost during welding; inert gas shielded processes are therefore preferred. The weld pool is less fluid than the non-aluminium alloys. Matching composition filler metals for FV520 are readily available but 17/7PH consumables are difficult and expensive to obtain so parent metal sheared from a strip is often used for TIG welding. Alternatively, a 17/4PH or FV520 filler may be used; a preheat of 100°C is advisable if the 17/4PH filler is used. PWHTs are similar to those used for the martensitic steels but, without a full solution heat treatment and matching filler metal, strengths matching those of the parent metal are unlikely to be achieved.

For Best Results

It is recommended that the fully austenitic PH steels are welded in the solution treated condition; a water or oil quench from around 980°C. The ageing process is very sluggish, requiring some 15 hours at 720°C to develop full strength and this means that the HAZ is virtually unchanged from the parent metal. Optimum strength can therefore be developed during the post-weld ageing treatment. These steels, like the austenitic stainless steels, are insensitive to cold cracking and do not require to be pre-heated. They are, however, very sensitive to hot cracking due to them being fully austenitic. This makes the welding of thick sections problematic and requires the welding conditions to be very closely controlled with low heat input, small weld beads and interpass temperature controlled to less than 150°C.

Aerospace alloys such as AMS 5858, equivalent to A286, have been produced with improved weldability. The 17/10P grade is particularly sensitive and cannot be welded with matching fillers; a type 312 (29Cr/9Ni) filler gives the best chance of success, although hot cracking in the HAZ may still occur.

Due to the presence of aluminium and/or titanium in many alloys, only the inert gas shielded arc welding processes should be used. Some matching composition filler metals are available, again in aerospace grades such as AMS 5804 and these can be aged to give strengths close to those of the parent metal. Alternatively, either austenitic, duplex or nickel-based weld filler metals may be used.

As is apparent, the metallurgy of these steels can be complex and if there is any doubt concerning welding or heat treatment the advice of specialists should be sought.

Copyright © TWI Ltd 2014

The content of this article was correct at the time of publication.

This article was written by Gene Mathers.

To confirm that a weld has been made to specification it is usually required to measure and often document the parameters that have been used. For arc welding the main parameters are as follows:

• Welding current
• Arc voltage
• Travel speed

These parameters can be used to calculate the heat input, which is derived from the arc energy. The other parameters which may be measured and recorded are as follows:

• Wire feed speed (for MIG/MAG) and other processes with a filler wire
• Gas flow rate (shielding, backing and plasma)
• Temperature (pre-heat, inter-pass and post-weld heat treatment)

In most cases the mean values of the parameters over the time of the weld can be recorded and used to calculate heat input. A simple meter can be used for this, but it is better for quality assurance to have documented values. A number of instruments exist which have been specifically designed for this purpose. Generally, they provide a paper printout with mean values over a second or so. Some of these instruments allow the length of the weld to be input so that arc energy (kJ/mm) can be calculated.

When measuring voltage and current it is important to do so correctly. Although current can be measured anywhere in the circuit, Figure 1, it is important to ensure that all the current passes through the cable and is not, for example, conducted elsewhere through the component or through a leakage path to earth.

Fig. 1. Current measuring technique, ‘A’ showing the connection for the sensor

Current is normally measured by a Hall effect probe clipped around the cable. The current rating and accuracy of the probe needs to be taken into account.

Voltage measurement is a bit more difficult to get right as the voltage will vary depending where the connections are made. For true arc voltage, it is important to measure as close to the arc as possible, Figure 2. For MIG/MAG, a connection on the drive rolls, back at the wire feeder, will suffice. However, the voltage measured across the arc will be lower than that measured across the power source terminals, possibly by several volts, depending on the length and diameter of the welding cables and the amplitude of the welding current.

Fig. 2. Voltage measuring technique a) Connection to the back of the TIG torch; b) Connection to the back of the MIG gun

Care should be taken when measuring arc voltage in TIG welding as the high voltage used for starting the arc may damage the instrumentation unless it is specifically designed for arc monitoring.

Some standards now require heat input to be calculated from instantaneous values and this requires an instrument that can accurately record the waveform of the voltage and current and perform the calculation up to 5,000 times per second or more. An example of such an instrument is shown in Figure 3. Several other manufacturers provide similar instruments.

Fig. 3. AMV 4000 Data Logger – Triton Electronics Ltd

Such instruments can record and display the current and voltage waveform from pulsed TIG and MIG/MAG processes including controlled dip transfer and multi-pulse techniques.

Wire feed speed can be measured by clipping a tachometer to the wire or by attaching a sensor to the wire feed drive rolls. Temperature is measured using a thermocouple or resistance temperature detector (RTD) probe in contact with the surface or, alternatively, an infrared non-contact device. Although gas flow can be measured with a bobbin type gauge, for recording the value a mass flow type instrument is required.

Limits can be set (typically +/-10%) to indicate if the parameters have deviated outside of the procedure and statistical process control (SPC) can be used to stop or correct a process before problems occur. However, this is a relatively crude technique and TWI is investigating more advanced digital processing.

Copyright © TWI Ltd 2014

The content of this article was correct at the time of publication.