A guide to Metal Fabrication techniques
At Wisconsin Metal Tech we work with many types of companies in the metal fabrication sector. The common factor to all these companies is that the part we machine or metal we supply will be used as a component of a larger machine or structure. The part can be integrated into the larger whole using various fabrication techniques.
Cutting in Metal Fabrication
Metal cutting is a very basic and most essential part of metal manufacturing.
This is also known as die-cutting. The process of shearing cuts stock without the formation of chips, it does not require heating in the form of burning or melting, therefore making it a very cost-effective and environmentally friendly process. Sheet metal or plates are best cut with this metal, although rods can also be sheared.
Band Sawing or Cold Sawing
Bandsawing involves the saw band (a continuous saw blade) traveling at speeds of up to 5000 feet per minute to provide a clean-cut, even when the part has been previously coated, therefore preventing damage to the part surface. The process also leaves a precise squared or angle cut to any specification.
Laser cutting is used to cut metal when a very precise and complex shape is required. The laser cutter works by directing the output beam of a high-powered laser through various optics. A CNC program is used to control the position of the laser beam. This position is controlled using a motion-controlled system moving in various axis around the work surface. Depending on the material the laser beam will either melt, burn or even vaporize the material away, usually any excess material is blown away by a gas jet. This leaves a very high-quality surface finish and a cut to very high tolerances.
The process of oxyfuel cutting is the most widely used industrial thermal cutting process. This is mainly due to the fact that the process allows the cutting of material from 0.019685inches to 9.84252 inches in thickness. The equipment itself can be used manually or through a mechanized process. Unlike the other cutting processes this form of metal fabrication requires that certain criteria are met first:
The ignition temperature of the material to be cut has to be lower than it’s melting point. The oxide melting point has to be lower than the surrounding material, this is so that the material can be blown away from the oxygen cutting jet.
The oxidation reaction between the oxygen jet and the material has to be sufficient enough for the ignition temperature to be maintained.
A minimum of gaseous reaction products must be produced so that the cutting oxygen is not diluted.
When cutting stainless steel, cast iron or other non-ferrous metals, the powder must be injected into the oxygen flame to form a low melting point, fluid slag, because in these materials the melting point is higher than the materials.
Plasma Arc Cutting
This process of metal fabrication is used as an alternative to the oxyfuel process as it is not as restricted in its use, particularly for stainless steel, cast iron or other non-ferrous metals. The process of plasma arc cutting requires that the arc formed between the electrode and the workpiece is constricted by a fine boring copper nozzle. By doing this the temperature and velocity of the plasma coming out of the nozzle are increased by a very large amount. The temperature is in excess of 36,032 Fahrenheit and a speed approaching the speed of sound. This means that the molten residue of the cutting process is expelled by the exiting plasma.
Water Jet Cutting
The process of water jet cutting uses an ultra-high pressure jet of water, with abrasive grit in solution with it. It is the abrasive carried by the water which does the actual cutting, almost like a mechanical sawing action. This leaves a very precise, smooth cut with no surface marks.
Unlike Oxyfuel and Plasma Arc Cutting, which are primarily for metals, water jet cutting is a far more versatile process, allowing it to cut through almost any material. The only limitations are highly brittle materials such as tempered glass and certain ceramics.
Water jet cutting is a very precise method of metal fabrication. It has a very narrow kerf width, allowing fine contours and the ability to produce high tolerance parts. But due to its nature, the process is slow and expensive on most metals in comparison with plasma cutting.
Perhaps the most basic of metal fabrication methods. Metal folding or simply, sheet metal bending, has been around as long as metal has been used. From the most basic hand-folding machines to complex CNC controlled folding machines, although a basic process there are many different types of folding:
Air Bending Metal
This bending method forms material by a die punch being pressed into the material. This forces the material into the bottom die mounted on the press. This forms the V shape most common with folding. Either V-shaped or square opening may be used on the bottom fixed die. The process of air bending requires less bending force so air bending tools tend to be smaller than other folding methods.
Some forms of the bottom die are adjustable, meaning that a single set of dies can create different profiles for folding, making it a quicker, more cost-effective method.
In this method, the sheet metal is forced against the opening in the bottom die. This leaves space between the sheet metal and the bottom of the V opening. The disadvantage of this is that a different die set is needed for each bend angle, the thickness of the sheet and even the material being used. This does have the advantage of having greater accuracy and less spring back. In general, though, air bending is the preferred method.
The least known method of bending, in coining the top die forces the material into the bottom die at a force of between 5 to 30 times that of air bending, this causes permanent deformation of the sheet metal. Due to the force, this method can produce very small radiuses. Even though the method has a very high precision it’s higher costs mean that it is used very little.
There are also other processes in bending, including Folding, Three-Point Bending, Wiping, Rotary Bending, Roll Bending, Elastomer Bending, and Jogging.
Metal Punching / Stamping Fabrication
Metal punching is often termed as stamping. This process involves the use of a large, heavy machined to punch or stamp out a shape from sheet steel. The shape can be quite complex and include very precise holes. The principal is actually very simple:
- The sheet metal being punched is sandwiched between the punch and a die.
- The punch moves downward and into the die. This causes the sheet metal underneath the punch to be sheared away from the surrounding material.
- Any cut metal is collected into a container for later use/recycling.
The quality of each punch is determined by some critical factors:
- The size/shape of the die and punch press;
- The amount of force applied
- The condition of the die and punch press (punching tools are only useful for so many “strokes” before becoming too worn to make clean punches);
- The thickness of the metal being punched
- The type of metal being punched (harder metals are more difficult to punch).
For example, when punching a round hole, it is generally recommended that the minimum diameter of the hole should be larger than the thickness of the metal. However, for especially sturdy metal alloys, the size of the hole may need to be even larger than that general recommendation states.
The ultimate and perhaps the most difficult manual form of metal fabrication is considered to be welding, in fact, it is considered somewhat of an art form. There are many types of welding:
Known as the beginners choice, MIG welding is actually 2 different types of welding. The first of these types use a bare wire and the second uses a flux core. The Bare wire method is used to join thin pieces of metal together. Flux core MIG welding is mostly used outdoors away from the workshop as it does not require a flow meter or gas supply. Due to its ease of use and low cost of machines, MIG welding is a favorite of DIY enthusiasts and hobby welder.
This method of welding is the most versatile but also one of the most difficult techniques to learn. It requires both hands to work; one hand feeding the rod whilst the other holds the TIG torch. The torch creates the heat and the arc, allowing the welding of aluminum, steel, nickel and it’s alloys, copper and it’s alloys, titanium, and cobalt.
Also known as Arc Welding. This is the old fashioned way of welding, a little more difficult to master than MIG welding but still accessible and the accessibility of it is increased by the low cost of purchasing the equipment. This method uses a stick electrode welding rod.
Plasma Arc Welding
The high precision of this method of welding lends itself to particular use in the aerospace industry, where metal thicknesses can be as low as 0.015 of an inch. For instance, the jet turbine blade or an air seal require plasma arc welding. The process is very similar to TIG welding but here the electrode is recessed and the ionizing gases in the arc are used to create the heat.
As well as these popular methods of welding, the following are used rarely in day-to-day welding throughout various industries.
Electron Beam and Laser Welding
The most precise, highest energy welding techniques.
Very rarely used now and also largely superseded by TIG welding. This method requires oxygen and acetylene. Its advantage is that it is highly portable. Used primarily in the car exhaust repair industry.