Today's Industrial Products and Solutions March 2019 | Page 16

approach, thin 1-2 mm sheets of metal are bonded but this provides very little control over large parts
in what is essentially an additive process. with more complex geometries.
The layered sheets can be laser cut so that when To compensate, thick graphite pressing plates
combined together create cooling channels, for ex- (10”-15” in height) must be used to mate the layers
ample, used to dissipate heat. The final “sandwich” of metal together at a more consistent pressure.
with all its layers can then be machined using Unfortunately, this takes up furnace space while
traditional CNC turning and milling equipment, if adding to the time to heat up the surfaces of the
needed. metals. 
Heat Treatment Furnaces with Integrated Today, however, leading manufacturers such as
Presses PVA TePla of Corona, California, offer multi-cyl-
Because diffusion bonding is a product of heat inder systems with large pressing plates that can
and pressure, the heating elements and integrated accommodate a variety of parts. The largest, the
hydraulic press play a key role in the quality of the company’s MOV 853 HP can process parts as large
final join. as 900mm (35.43”) x 1250mm (49.21”), which is
For the atoms of two solid, metallic surfaces to in-
tersperse they typically must be at approximately
quite large for diffusion bonding. The pressing
force is 4,000 kN.
50-70% of the absolute melting temperature of the By controlling each cylinder independently, the
materials. To achieve these temperatures, the sur- integrated press provides extremely consistent
faces are heated either in a furnace or by electrical pressure across the entire surface. The MOV also
resistance to temperatures as high as 1400˚C. comes with built-in pressure transducers along the
The pressure is applied by a hydraulic press or
dead weights. Because the two mating pieces must
be in intimate contact with each other, fixtures are
bottom of the pressing plate. Based on the read-
ings, the individual hydraulic cylinders can be ad-
justed to achieve uniformity even over large areas.
often used. Once clamped, pressure and heat are PVA TePla has optimized a physical ink test method
applied to the components, usually for many hours. that can be performed to identify areas on the part
where uneven pressure is being applied.
Since oxidation can also affect bonding, most heat
treatment furnaces operate under a high vacuum. For greater temperature uniformity, the MOV
More Precise Controls mity within the chamber, instead of the usual one
While these are common elements of the process, or two, for a maximum operating temperature up
the missing piece to date has been precise control to 1,400°C. Rapid cooling quickly brings tempera-
of each. tures down so parts can be removed in about half
In the case of the pressure applied, for example,
system utilizes six heaters for temperature unifor-
the time without risk of cracking or other damage.
integrated single cylinder hydraulic presses can With superior temperature control and multiple
apply a consistent, measurable amount of force, hydraulic cylinders in the press, much thinner
14 TIPS Magazine • March ‘19