Things to Consider When Choosing a Metal Assembly

Metal assembly is always a challenge, no matter what you design. Whether your specialty is cars,
computers, airplanes or roofing, you should be focused on assemblies that offer the lowest cost and
highest possible performance.
Unfortunately, there is no one size fits all approach to choosing an ideal assembly. Here are some key
factors to consider.

High Quality Materials

The metal fabrication industry involves the use of various materials for creating reliable products for
diverse applications and industries. When it comes to developing these products, the selection of
material is critical. With all you have to choose from, including steel, stainless steel, aluminum, and
other alloys, you need to select the metal that has the unique properties and benefits for your specific
application.
Here is how to choose the perfect material for your metal assembly that ensures optimal performance.

Ductility

Ductility refers to how pliable the material happens to be. Can you draw it into a wire or form it into a
variety of shapes? Stainless steel has high ductility, while aluminum is on the lower side of the scale.

Weldability

You next should consider how easy it is to solder the metal. Will preparation be necessary, or do you
require advanced welding techniques and tools? The latter may increase your project costs, so be wary.
Steel, on the other hand, is very weldable, whereas stainless steel is on the medium side of weldability.

Machinability

This attribute refers to the ability to cut the metal with a blade. Highly machinable metals are those that
can be cut at higher speeds. Steel has medium-range machinability while stainless steel exhibits a bit
harder machinability.

Tensile Strength

Tensile strength is the force required to snap the metal. In other words, how strong is the material?
Stainless steel can handle higher levels of tension while aluminum, on the other hand, cannot.

Corrosion Resistance

This refers to how well a substance can withstand damage caused by chemical reactions and oxidation.

Cost

The cost of the material is a significant consideration. How expensive or inexpensive is the metal
compared to other alloys? Will the metal perform just as well as another material for your specific
project?

Which Metal is Right for Your Assembly

Aluminum

Aluminum is preferred for many assemblies for its lightweight and corrosion-resistant properties. The
metal can be powder coated or left unfinished as a bare metal or can contain a grained finish.
If electrical contact is required with aluminum, the metal must be chem-filled, otherwise known as
chromate coated. It can also be anodized, which affixes it with a durable and hard protective oxide
coating.

Since aluminum has a lower stiffness than some metals like steel, a thicker gauge may be required if
strength is necessary for the overall design.

Cold Rolled Steel

This metal is used almost as often as aluminum, as it is both cost-effective and nearly as stiff as steel.
Cold rolled steel is preferred for metal assemblies due to its long-term durability. The metal is not
naturally corrosion resistant. If corrosion resistance is needed, the best bet is to go with stainless steel,
galvanneal, or aluminum.

Stainless Steel

This metal is strong and as stiff as cold rolled steel. The difference is that stainless steel actually is
corrosion resistant. That’s because of its makeup, which consists of chromium and nickel. Stainless steel
can be powder coated or left unpainted as a bare metal. The metal can also be affixed with a grain finish
to give it a brushed appearance.

Galvanneal

This low carbon steel is first coated with zinc before it is annealed so that the zinc bonds to the substrate
via diffusion. This prevents the metal from flaking. The coating also makes it highly durable, especially in
wet environments, though galvanneal isn’t as durable as aluminum or stainless steel.

Copper

Copper is preferred for its soft, flexible, and ductile properties. The metal is also highly thermal and has
high electrical conductivity. Copper can pose some issues. For example, when torquing fasteners into
tapped holes, great care must be taken. This is because the metal is very soft when compared to other
alloys, so self-clinching fasteners should be used with copper whenever possible.

Sheet Metal Thickness

The choice of metal is highly important, but so is the thickness. Selecting the proper gauge can be
challenging, as they all seem the same when viewed on paper. Only those with experience will know
which metals perform best at certain thicknesses.

Choose a Finish Method

Powder Coating

This is a type of dry, thermoplastic powder that is applied to the metal electrostatically. It is then fused
and bonded to the metal in an oven. Powder coating can come in a variety of colors and gloss levels, as
well as textures. This method of coating metal is widely recognized for its cost-effectiveness and high
durability.

Digital Printing

This finishing technique gives the metal a professional appearance and can be applied to flat panels and
parts.
Chemical Conversion Coating
This method of finishing metal is sometimes referred to as chem-film or chromate coating. When
applied to the metal substrate, the chromate creates a corrosion-resistant surface that is nearly as
durable as stainless steel. Chemical conversion coating also exhibits high levels of electrical conductivity.

Anodizing

This electro-chemical process is used to prepare non-ferrous metal surfaces. The goal is to make the
surface of the metal harder and less likely to corrode, such as aluminum. The anodized surface becomes
an aspect of the aluminum, which means that it will never chip, peel, or flake off.

Tin Plating

This simple immersion technique deposits pure tin onto copper sheets. The tin plating is used to
improve the resistance to corrosion, electrical conductivity, and solderability.

Bare Metal Finishes

Bare metal finishes come in three types for metals like aluminum and stainless steel.

No Finish

With this method, the metal is deburred with no additional finishing. This means that the metal may
exhibit small swirl marks or scratches. The non-finishing method can be cost-effective but is best used
for functional parts that will not be on display.

Grained Finish

Like the no finish method, the grained finish involves deburring the metal before it is given a linear grain
direction by way of brushing.

Tumbled Finish

This method smooths and imparts a non-directional finish to the metal via tumbling in an abrasive
medium. With this method, you get the same overall effect as frosted glass.

Selecting a Joining Method

Joining refers to the process of attaching components together. You may be joining two metals together
or a metal and different materials. You also have different kinds of joints during the joining process,
including temporary and permanent joints.

Adhesives

Adhesives are a good choice if you plan to keep costs to a minimum. The biggest costs with this method
come from the consumable adhesives, labor costs, adhesive applicators, and the fixtures to hold the
parts during the adhesion process. You may also select this route if you have products that are going to
be assembled in limited volumes and speed, and without the need for assembly automation.
In addition, adhesives are ideal for plastic parts that are incompatible with plastic welding.

Mechanical Joining

Mechanical joining methods can include snap and press-fit joints, rivets, and screws. Mechanical joining
is ideal for products like appliances and electronic devices, as well as those that are subject to
disassembly for repair or replacement of internal components like batteries, bulbs, circuits, or switches.

Mechanical fasteners are also excellent for low-volume or products that are initially run. This is
especially true when the cost of equipment for joining parts exceeds the fastener and labor costs for the
expected volume of production. The major costs with mechanical joining come from consumable
fasteners, assembly tools and labor.

Plastic Welding

Plastic welding is the process of bonding assembly parts together using pressure and heat. This method
may be ideal when plastic parts are compatible with one another and volume production is high. Plastic
welding is also used when the goal is hermetic sealing and permanent bonding with the highest level of
consistency.
Plastic welding can refer to a few different technologies, including ultrasonic welding, vibration welding,
laser welding, and infrared welding.

Ultrasonic Welding

Ultrasonic plastic welding is the process of joining thermoplastics with the use of heat that is generated
from high-frequency mechanical motion. This is accomplished by converting electrical energy of a higher
frequency into an equally higher frequency mechanical motion. This motion, when combined with applied force, creates the necessary frictional heat at the joints. As the plastic melts, it forms a
molecular bond between the assembled parts.
In order to bond two thermoplastic parts, the materials being connected must be chemically compatible.
Otherwise, there will be no molecular bond. The joint design of the mating process is critical to the
process. The joint design depends on the type of plastic, requirements of the weld, and the parts’
geometry.

Vibration Welding

Linear vibration welding is the process of moving one or two parts horizontally under pressure. This
creates heat through surface friction that successfully melts and welds the parts together. Unlike
ultrasonic welding that operates at a high frequency, vibration welding operates at much lower
frequencies with higher amplitudes and greater clamping force. This method of welding uses
electromagnetic heads that eliminate lubrication and wear that is typically associated with bearing
surfaces.
Vibration welding can join all known thermoplastics together, including materials that contain 45% filler
content. Welders can also join dissimilar materials with compatible melting points, such as composite
materials and fabrics.

Laser Welding

Laser welding is the process of joining together metals or thermoplastics using laser beams to form the
weld. The laser welder delivers a controlled amount of energy to precise locations. This gives the welder
more precision in controlling the heat input, making it easier to adjust the beam size and giving more
options as far as the range of methods available for precise positioning and moving the beam.
Nearly all thermoplastics can be welded together using a laser source and the appropriate joint design.

Infrared Wedding

This welding process makes use of infrared radiation which is then absorbed by the thermoplastic before
it is transformed into heat. This results in the melting of the faying surface of the plastic. The
components are then joined by pressing the two halves together. This method is preferred for its fast,
particulate-free, and non-contact form of welding.

Spot Welding

This fast and efficient welding method is inexpensive and useful for permanently joining two sheets of
metal in one or additional spots. Unlike other joining methods, spot welding leaves behind minuscule
traces of the joint.

Seam Welding

This method is useful for continuously joining two or more pieces of sheet metal together so that they
appear seamless in shape and form. Many metal assemblies use Cold Metal Transfer (CMT) seam
welding, which transfers the filler metal via sputtering at higher temperatures. Since CMT only generates
a tenth of the heat when compared to MIG welding, there is no warping of the metal or melt back, even
on thinner sheets of metal. Excess metal is then removed by grinding, which results in continuously
joined seems that are useful for EMI leakage and weatherproofing.

Tack Welding

Tack welding is similar to seam welding but is performed in discrete segments.

Do You Have the Right Cmponents for Your Metal Assembly?

You now have much to consider when selecting the right components and materials for your metal
assembly process. Not only do you have to choose the proper metals, finishes, and joining methods, but
you need to make sure the entire assembly matches the volume you are aiming for, as well as the costs
to fit your budget.
For more information on metal assembly considerations, contact Flex Fit Host, where we provide quality
services that can assist with all your production challenges. With our help, we can help you choose the
metal assembly for the highest quality and the production outcomes you desire. Call us to learn more.

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