By: Carlos Ayala, Date: 02/13/2018

• Diffusion bonding is an alternative method to welding metal pieces together. It is accomplished by applying a load to a stack of metals that is then heated to over 50% of the melting point of the material. In doing so, the atoms across the surface of the material are allowed to diffuse. The process produces high quality joints without metallurgical discontinuities. If properly carried out, the joint has equal strength and ductility as the original material.

• The origins of diffusion bonding can be traced back to centuries ago. For example, the bonding of gold and copper used in jewelry would be done by hammering out a certain amount of solid gold into a thin sheet of gold foil. A copper substrate would then be added and the materials were heated in an oven until the gold film was bonded to the copper substrate. To name an example of how old diffusion bonding can be, Samurai swords were created using this technique in which a piece of high carbon iron was hot formed into thin strips and hammered at high temperatures.

• The type of designs that would use the diffusion bonding process are aerospace components, specifically parts such as fuselages, outboard and inboard actuator fittings, and landing gear trunnion.
• Benefits:
  - Conserve expensive materials
  - Reduce manufacturing costs
  - High quality joints produced
  - Joints have equal strength and ductility as parent material
• Components that require high precision are able to be manufactured without subsequent machining so good dimensional tolerances for products are easy to obtain.
• Shortcomings:
  - Excess oxidation or contamination of joint surfaces can lead to weak joint strength.
  - The size of the metals that need to be bonded are restricted to the size of the chamber.
  - The process can be much more time consuming.
  
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• Beginning with two flat surfaces, a pressure is applied so that the two surfaces in contact are as close together as possible. The two surfaces are then inserted into an oven like chamber and heated to at least 50% of their melting points to allow the surface atoms to diffuse into one another. Once a certain amount of time has passed, a newly formed joint is created.
• Initially, the two surfaces in contact and the defects in the surfaces plastically deform and begin to interlink. As temperature is introduced, the grain boundaries and raw materials migrate so the gaps between the surfaces shrink to isolated pores. The material then begins to diffuse across the surfaces and creates a bond.
• Because the process of diffusion bonding is not very complex, (it is essentially inserting two metals in an oven and waiting for diffusion to occur) only one person is needed to operate the equipment. A background in materials science would be useful for determining at what temperature would be ideal to allow for proper diffusion of the atoms.

• Reviewing suppliers of these machines websites, I was not able to obtain a cost for the price of the machine. I was only offered the option for a quote.
• Once the machine is purchased, the tooling cost should not be expensive because the mechanism of the machine is simple and just requires force and heat.
• The typical unit cost depends on the length of time the metals are bonding and the temperature the machine will be using to bond the metals.
• If applicable, provide cost comparison against competitive processes and break even point (e.g. injection molding vs machining).