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Joining techniques for permanent metal connections

Welding & Brazing-Soldering

Joining techniques are among the fundamental processes of industrial manufacturing. They enable permanent connections between metallic components and parts. Without these technologies, modern production in many industries would be inconceivable.

In welding, materials are fused together by heat or pressure. Brazing-soldering, by contrast, uses filler materials with a lower melting point. Both joining methods offer specific advantages for different applications.

Quality assurance plays a central role in joints. Testing technology monitors the execution quality already during manufacturing. Failure analysis identifies defects and helps prevent future problems.

Modern service providers combine all three areas under one roof. They support industry and trade with procedure qualifications and materials engineering assessments. Their range of services extends from planning to final evaluation.

National and international standards form the basis for all activities. They ensure uniform standards and comparable results. Expertise in materials engineering is essential for safe and durable constructions.

Fundamentals of joining techniques in materials engineering

To guarantee the reliability of joints, various testing methods are used. These procedures help to detect defects at an early stage and to secure the quality of the connections. In accredited testing laboratories, both non-destructive and destructive testing is carried out in accordance with national and international standards.

The choice of the appropriate testing method depends on several factors. These include the component size, the material used and the required quality standards. Standards such as ISO, EN and ASTM provide the framework here.

Welding procedures and their fields of application

In welding, the materials are melted at the joining points by heat. In some procedures, additional pressure is used. After cooling, a firm, permanent connection is created. This technique is particularly suitable for metallic materials.

Arc welding is one of the most frequently used methods. An electric arc generates the necessary heat. This procedure works reliably and economically. Steel structures in building and bridge construction are often joined with it.

TIG welding stands for tungsten inert gas welding. It offers the highest precision and quality. Thin sheets and stainless steels can be perfectly joined with it. The automotive industry and apparatus engineering prefer this procedure.

MIG welding uses metal inert gas as a protective atmosphere. It works quickly and productively. Aluminium alloys are frequently processed with this procedure. The aerospace industry relies on this reliable technique.

MAG welding uses a metal active gas mixture. Steel construction benefits particularly from this method. Thick sheets can be joined efficiently. Mechanical engineering constructions are often created using this procedure.

The most important welding procedures at a glance:

  • Arc welding for general steel structures and robust connections
  • TIG welding for high-quality stainless steel and thin-sheet connections
  • MIG welding for aluminium materials in aviation
  • MAG welding for thick-walled steel components in mechanical engineering
  • Spot welding for serial sheet metal connections in automotive production

Brazing-soldering procedures in materials engineering and fields of application

In brazing-soldering, an essential difference from welding remains. Only the filler material melts, while the base materials stay solid. The molten filler flows into the joint gap by capillary action. This gentle method is suitable for temperature-sensitive components.

Soldering works at temperatures below 450 degrees Celsius. Electronics uses this technique for printed circuit boards and fine connections. Tin-lead alloys or lead-free alternatives serve as filler material. Low thermal stress protects sensitive components.

Brazing requires temperatures above 450 degrees Celsius. These brazing-soldering procedures in materials engineering create mechanically loadable connections. Copper-phosphorus alloys or silver fillers are used. Heating and air-conditioning technology uses this method regularly.

The fields of application of brazing-soldering procedures extend across many industries:

  • Electronics industry: assembly of printed circuit boards with electronic components
  • Sanitary engineering: connection of copper pipes in drinking water systems
  • Refrigeration technology: joining of refrigerant lines in air-conditioning systems
  • Jewellery industry: connection of precious metals in pieces of jewellery
  • Dental sector: manufacture of dentures and bridges

The choice between welding and brazing-soldering depends on several conditions. The type of material plays a central role. The required strength must be taken into account. The thermal load capacity of the components limits the choice of procedure.

The component size also influences the decision. Economic considerations enter into the planning. Both procedures have their justification in modern manufacturing. They complement each other and cover different requirements.

Key findings

  • Joining techniques are indispensable procedures for permanent metal connections in industrial manufacturing
  • Welding procedures and brazing-soldering procedures differ fundamentally in temperature and field of application
  • Quality control through testing procedures secures the reliability of connections during production
  • Failure analysis enables the identification of weak points and optimises future manufacturing processes
  • Specialised service providers offer holistic support from procedure development to evaluation
  • A standard-compliant approach guarantees uniform quality standards across all projects

Welding & brazing-soldering in materials engineering, testing technology and failure analysis: modern testing procedures

Joining materials permanently requires specialised techniques that are used differently depending on the requirement. Joints are created by two proven methods: welding and brazing-soldering. Both procedures create permanent connections, but differ fundamentally in their execution.

The qualification of these joining techniques follows strict standards. EN ISO 15614-1 to -14 governs the procedure qualifications in welding. EN ISO 17660 and AD2000 set further standards. The materials engineering assessment of components forms an important part of quality assurance.

Non-destructive methods for seam testing

Non-destructive testing procedures offer a major advantage: the examined components remain intact and can be reused after testing.

These methods are particularly suitable for expensive or safety-relevant components. Weld seam testing with non-destructive procedures is standard in many industries.

Visual testing is the simplest form of weld seam testing. A trained inspector examines the surface with the naked eye or with aids such as magnifying glasses. In doing so, defects such as cracks, pores or incomplete weld seams become apparent. This method is well suited for an initial assessment.

In radiographic testing, X-rays or gamma rays are used. The radiation penetrates the material and produces an image on a film or digital detector. Internal defects such as cavities or inclusions thus become visible. This technique delivers meaningful results for thick-walled components.

The ultrasonic testing procedure works with high-frequency sound waves. A probe sends the waves into the material. At defects, the waves are reflected and captured by the device. Weld seam testing by ultrasound enables the location and sizing of defects. This method is mobile and can be carried out without radiation protection.

Magnetic particle testing only works with ferromagnetic materials such as steel. The component is magnetised and sprayed with a fine iron powder. Cracks and surface defects interrupt the magnetic flux. The powder collects at these points and makes them visible.

Dye penetrant testing is suitable for all materials. A coloured liquid is applied to the cleaned surface. It penetrates into open defects. After a dwell time, the excess liquid is removed. A developer draws the penetrated dye out of the defects and makes them recognisable.

Each of these methods has its strengths and limitations. Radiographic testing delivers detailed images but requires radiation protection. Ultrasound is fast and flexible but needs trained personnel. The choice depends on the specific task.

Quality assessment of brazed-soldered joints

Brazed-soldered joints require special testing approaches. Both non-destructive and destructive methods are used here. The decision depends on the type of component and the quality requirements.

In the non-destructive procedures, optical inspections play an important role. Microscopes and magnifying glasses help to examine the joint precisely. The wetting, the seam shape and possible surface defects are assessed. For complex components, X-ray examinations are suitable, which also reveal internal structures.

Electrical function tests ensure that the joint fulfils its task. Resistance measurements and continuity tests reveal faulty connections. These tests are particularly widespread in electronics manufacturing.

Destructive testing delivers detailed information about the mechanical properties. The tensile test is one of the most important procedures. On a universal testing machine, the specimen is loaded to fracture. The applied test force can be very high and depends on the specimen geometry and the material. Electronic strain measurement records the deformation precisely.

Important characteristic values can be determined from the tensile test. These include the yield strength, the tensile strength, the elongation and the modulus of elasticity. These values show how well the joint withstands mechanical loads.

Shear tensile tests test the connection for shear stress. The force acts parallel to the joining plane. Peel tests simulate the pulling-off of a connection. Both methods are particularly relevant for brazed-soldered joints.

Metallographic examinations offer a look inside the connection. For this, a microsection specimen is taken from the component and prepared. The specimen is ground, polished and often etched. Under the microscope, microstructure, heat-affected zone and seam formation become visible.

This analysis reveals possible bonding defects such as incomplete wetting or cavities. The metallographic examination is part of the comprehensive materials engineering assessment of joints. It delivers insights that other procedures do not offer.

Hardness tests according to Vickers and Brinell determine the strength properties at various points of the connection. A test body is pressed into the material with a defined force. The size of the indentation gives the degree of hardness. Differences between base material, heat-affected zone and seam thus become measurable.

Notched bar impact bending tests assess the fracture behaviour at different temperatures. The specimen is broken with a pendulum hammer. The energy consumed in the process shows how brittle or tough the material reacts. Tests at temperatures down to -196°C examine the low-temperature strength.

The combination of various testing procedures delivers a complete picture of the joint quality. Standards such as ISO, EN and ASTM define the execution and assessment. Accredited testing laboratories guarantee compliance with these standards and the comparability of the results.

Failure analysis of welded joints: systematic troubleshooting

When weld seams or brazed-soldered joints fail, a thorough failure analysis provides valuable answers. The systematic examination reveals weak points and shows how similar problems can be avoided in the future. Metallographic examinations and mechanical testing procedures complement the visual inspection here.

A professional failure analysis of welded joints follows structured methods. It combines various testing techniques and evaluates the results in context. This produces clear recommendations for action for practical use.

Common defects in weld seams

Cracks are among the most critical defects in welded joints. Hot cracks form during the solidification of the weld metal, when the material contracts. They arise particularly in materials with a wide solidification range or under unfavourable stress conditions.

Cold cracks, by contrast, develop after cooling. They often occur in the heat-affected zone, where the material was altered by the welding heat. Hydrogen in the material considerably intensifies this crack formation.

Stress corrosion cracking only shows up under operating conditions. The combination of mechanical load and corrosive environment leads to gradual failure. These cracks grow slowly but can suddenly lead to fracture.

Pores and gas bubbles significantly reduce the strength of the weld seam. They arise when gases are trapped during welding. Insufficient shielding gas flow or moist electrodes favour this defect.

Bonding defects occur when no complete fusion takes place. The base material and the weld metal do not properly bond with each other. Welding temperatures that are too low or incorrect seam geometry frequently cause this problem.

Inclusions of slag or other foreign materials weaken the seam. They remain behind when the slag was not completely removed or when several layers are welded on top of each other. A thorough welding defect analysis reliably identifies such flaws.

Shape defects impair the function and appearance of the connection:

  • Insufficient seam reinforcement weakens the strength
  • Undercuts act as stress concentration
  • Edge misalignment leads to uneven load distribution
  • Seam overlap complicates later processing steps

Typical problems with brazed-soldered joints

Incomplete wetting is one of the most common brazing-soldering defects. The filler does not distribute evenly over the base materials and does not form a continuous connection. Contaminated surfaces or incorrect temperature control cause this flaw.

Flux residues remain after brazing-soldering and can trigger corrosion. They attract moisture and attack the material. Particularly with electronic components, this leads to failures.

Gaps in the filler joint arise from incorrect gap dimensions. If the distance between the joining partners is too large, the filler does not completely fill the gap. The capillary action then no longer works properly.

Overheating damage to the base material occurs at too high brazing-soldering temperatures. The material loses its original properties or warps. Thin sheets react particularly sensitively to heat exposure.

Electrical conductivity problems show up in electronic connections. Too little filler material or impurities increase the resistance. Mechanical weak points due to the wrong filler also impair the function.

Cause determination and measures

The systematic failure analysis begins with precise documentation. Photographs capture the condition before further examinations take place. A detailed description records all visible features.

The operating conditions provide important clues to possible causes. What loads acted on the component? Under what environmental conditions did it work? The load history often shows the path to failure.

Metallographic examinations provide deep insights into the microstructure. Sections through the weld seam make microstructural changes visible. The heat-affected zone can thus be precisely assessed and compared with target values.

Mechanical tests complement the analysis with measurable data:

  1. Hardness measurements show local strength differences
  2. Tensile tests determine the actual load-bearing capacity
  3. Bending tests examine the ductility of the connection
  4. Impact tests assess the toughness

The comparison with standard requirements reveals deviations. Where do the values lie outside the tolerance? Which test criteria were not met? This welding defect analysis shows concrete fields of action.

From the examination results, targeted improvement measures emerge. For welded joints these can be: optimisation of amperage, voltage and feed speed. The seam preparation also plays a major role.

The selection of suitable filler materials often improves the quality considerably. Sometimes an adjusted preheating temperature helps to avoid crack formation. Post-weld heat treatment can also reduce residual stresses.

For brazed-soldered joints, other measures apply. The temperature control can be steered more precisely. A different flux wets the surfaces better. Optimised gap dimensions or improved surface preparation eliminate many problems.

A thorough failure analysis of welded joints serves not only to remedy problems. It also delivers valuable insights for upcoming projects. The documentation of damage cases and their causes drives continuous improvement forward.

Frequently asked questions about welding and brazing-soldering

What is the fundamental difference between welding and brazing-soldering?

In welding, the materials to be joined are melted at the joining points by heat and often additional pressure, so that after cooling a firm, permanent connection is created. In brazing-soldering, by contrast, only the filler material (filler) is melted, while the base materials stay solid. This fundamental difference determines the respective fields of application and properties of the connections.

Which welding procedures are most frequently used?

The most important welding procedures include arc welding, TIG welding (tungsten inert gas), MIG welding (metal inert gas), MAG welding (metal active gas) and spot welding. TIG welding is particularly suitable for high-quality connections in thin sheets and stainless steels, while the MAG procedure is frequently used in steel construction. Each procedure has specific properties, advantages and typical fields of application.

What is meant by soldering and brazing?

In soldering, temperatures below 450°C are used, while in brazing temperatures above 450°C are applied. Soldering is frequently used in electronics and for filigree connections, while brazing is used for mechanically more loadable connections, for example in heating and air-conditioning technology. The choice between the two procedures depends on the mechanical requirements and the thermal load capacity of the components.

Which non-destructive testing methods are available for weld seam testing?

The most important non-destructive testing methods include visual testing for detecting surface flaws, radiographic testing with X-rays or gamma rays for revealing internal defects, the ultrasonic testing procedure with sound waves, magnetic particle testing for ferromagnetic materials and dye penetrant testing for all materials. These procedures enable comprehensive quality control without damaging the tested components.

Which destructive testing procedures are used for brazed-soldered joints?

In destructive testing procedures for brazed-soldered joints, tensile tests are carried out on universal testing machines with electronic strain measurement in order to determine mechanical characteristic values such as yield strengths, tensile strength, elongation and modulus of elasticity. Further procedures are shear tensile tests, peel tests, metallographic examinations of microsection specimens, hardness tests according to Vickers and Brinell as well as notched bar impact bending tests for assessing the fracture behaviour at different temperatures down to -196°C.

What are the most common welding defects and how do they arise?

The most common welding defects include cracks (hot cracks during the solidification process, cold cracks after cooling, stress corrosion cracking), pores and gas bubbles due to trapped gases, bonding defects in case of incomplete fusion between base material and weld metal, inclusions of slag or foreign materials as well as shape defects such as insufficient seam reinforcement, undercuts or edge misalignment. Their formation depends on welding parameters, material preparation and environmental conditions.

Which typical problems occur with brazed-soldered joints?

Typical problems with brazed-soldered joints are incomplete wetting, in which the filler is not distributed evenly over the base materials, flux residues, which can cause corrosion, gaps in the filler joint due to incorrect gap dimensions, overheating damage to the base material at too high brazing-soldering temperatures as well as electrical conductivity problems with electronic components and mechanical weak points due to too little or the wrong filler material.

How is a systematic failure analysis of welded joints carried out?

A systematic failure analysis is carried out in several steps: first, the damage is documented through photography and description. Then the operating conditions and load history are examined. Material analyses by means of metallographic examinations provide information about microstructural changes and the heat-affected zone. Mechanical tests such as hardness measurements, tensile tests and bending tests deliver information about the actual material properties. Through comparison with target values and standard requirements, deviations are identified and measures for defect avoidance are derived.

Which measures can be taken to avoid welding defects?

To avoid welding defects, various measures can be taken: optimisation of the welding parameters such as amperage, voltage and feed speed, improvement of the seam preparation, selection of more suitable filler materials, adjustment of the preheating temperature or change of the post-weld heat treatment. For brazed-soldered joints, measures concern the temperature control, flux selection, gap dimension optimisation or surface preparation. A thorough documentation of damage cases contributes to continuous process improvement.

On which parameters does the choice between welding and brazing-soldering depend?

The choice between welding and brazing-soldering depends on several parameters: the type of material, the required strength of the connection, the thermal load capacity of the components, the component size and economic considerations. Welded joints generally offer higher strength, while brazed-soldered joints are advantageous with lower thermal load on the base materials and for filigree components. Both procedures have their justification and complement each other in modern manufacturing.

What role do standards play in joining technology and failure analysis?

National and international standards form a central basis for all activities in joining technology, testing technology and failure analysis. They establish requirements for procedures, materials, testing methods and quality assurance. Compliance with these standards ensures consistent quality and enables the comparability of results. Accredited testing laboratories orient themselves towards these standards and thus represent reliable partners for industry and trade.

Why is the combination of joining technology, testing and failure analysis so important?

Only the combination of sound knowledge of joining techniques, modern testing methods and systematic failure analysis ensures a permanently high quality of the connections. Testing technology enables the quality control of the manufactured connections, while failure analysis serves not only to remedy defects but also delivers important insights for process optimisation. These three areas are closely linked with each other and can only guarantee reliable product quality in their entirety.

Our conclusion

Welding & brazing-soldering in materials engineering each offer specific advantages for different applications. The choice of the right procedure depends on the material, the mechanical requirements and the economic framework conditions. Both joining techniques require sound expertise for proper execution.

Modern testing procedures form an indispensable part of quality assurance. Non-destructive and destructive testing methods deliver reliable results for material acceptance and qualifications in accordance with national and international standards. Systematic weld seam testing and inspection of brazed-soldered joints ensure the required reliability.

Failure analysis serves not only to remedy defects. It delivers important insights for continuous process optimisation. Through the identification of defect causes, manufacturing processes can be specifically improved and repeated errors avoided.

The combination of methodological competence in joining technology, modern testing methods and systematic failure analysis secures permanently high quality. Accredited testing laboratories with a comprehensive range of services represent reliable partners for industry and trade. Continuous further training enables specialists to keep pace with technological developments and to steadily improve the quality of connections.

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