Brazing Vs Welding

Both processes produce strong and permanent joints, which are almost similar in efficiency. The obvious question now is that which particular process suits which application. Let's have a look at different key considerations:

• Appearance
  The appearance of the joint should be of the least significance, but when the matter comes to the customer products it becomes important. Brazing produces a tiny, neat fillet, versus the irregular bead of a welded joint. The brazed joints don't need additional finishing operations like welding.
  
  
• Thickness
  If the thickness of both metal sections are relatively thick (say 0.5 inch or greater), in that case either method works well. But thinner sections tip the scales in favor of brazing. As for example, brazing is the better option on a T-joint when a 0.005 inch sheet metal is bonded to 0.5 inch stock. The thinner sections are likely to burn or warped due to the intense heat of welding. Brazing's broader heating and lower temperature joins the sections without distortion.
  
  
• Assembly Size
  Welding is a better option for joining big assemblies. In brazing heat is applied to a broad area often the whole assembly. Larger assemblies have the tendency to dissipate heat and thus can make it difficult to reach the flow point of the filler metal. Welding provides intense localized heating and overcomes this drawback.
  
  
• Joint Configuration
  The performance of welding and brazing differs when making joints of different configurations. Brazing and welding both produce spot joints. Welding offers localized heat, which has some specific advantages. For example, if two metal strips are to be joined at a single point then electrical-resistance welding provides an economical and fast way to make permanent and strong joints by the thousands.
  
  But in case of linear joints, brazing is easier than welding. Welding heats one end of the metal interface to melting temperature and then slowly traveling along the joint line. Then it starts depositing filler metal in sync with the heat. Brazing doesn't require such manual tracing, and filler metal is drawn with same intensity into straight, curved, or irregular joint configurations.
  
  
• Types of Materials
  When it comes to joining of dissimilar metals, brazing holds substantial advantages over welding. Keeping least changes in the properties of base metals, it is able to form strong joints. However the filler material should be metallurgically compatible with both base metals and has a melting point lower than the two. Let's take an example. If you have to weld copper (1981°F mp.) to steel (2500°F mp.), in that case copper would melt before the steel even approached welding temperature. It will also require expensive and sophisticated welding techniques. Brazing has the ability to join dissimilar metals. It lets users select metals best suited for an application's functional requirements, regardless of variations in melting temperatures.
  
  
• Production Volume
  If the job requires only few assemblies to join, it is most likely to be done manually. Then the choice between brazing and welding comes down to thickness, configuration, size, and material considerations.
  
  • When the assembly parts to be joined are in hundreds or thousands then production techniques and cost become vital factors to decide. However both methods can be automated, but they vary in terms of flexibility. Welding allows you to either weld manually, one at a time, or install sophisticated and costly equipment to handle large runs of identical assemblies. There is rarely a practical choice in-between.
    
    
  • In large scale production, brazing lends itself to various degrees of automation. For moderate production runs, simple automation techniques such as pre-fluxed assemblies and pre placed lengths of filler metal can speed up the production process.
    
    

Joining Techniques
Technique of welding and brazing differs from one another and so the strength, quality, and performance of the joints.

• Welding
  In welding, the metals are joined by melting and fusing them, commonly adding a filler material. The fusion of metals needs concentrated heat directly at the joint. The temperature during welding must exceed the melting point of the joining metals and filler material. The joints created by welding are generally as strong or stronger than the base metals.
  
  
  
• Brazing
  The technique used in brazing differs from welding. It also joins two pieces of metal together with a third, molten filler metal. But the main difference is that the base metals aren't melted and fused, instead the joint area is heated above the melting point of the filler metal but below the melting point of the metals being joined. The filler material melts and flows into the gap between the two metal pieces by capillary action and as it cools a strong metallurgical bond is formed.