Metal Fabrication 101
Metal fabrication is a very common manufacturing process that combines various types of processes. For a broad description, metal fabrication is the combination of cutting, bending, joining, finishing and the final assembly of metal material that ends with an end part or product. If you have a customized metal part, then the fusion of these steps are important to the successful creation of your unique product.
The first step of the metal fabrication process is to receive rolled metal sheets. These rectangular sheets are flat, while the thickness and composition depends on the specifications from your given product. The first step is to take these sheets and cut them down into smaller pieces that will be processed.
There are two primary types of cutting, cutting with a shear and cutting without a shear. Shearing is when a physical object applies force to something. For metal fabrication, shearing means a force that is applied to a sheet in order to break off a specified shape in a sheet.
Cutting With Shears
There are three basic operations for shear cutting:
Shearing: In short this process is cutting larger sheets into smaller sheets in preparation for other processes. The most common cuts will be squares, but angled cuts are also possible.
From the diagram above, you can see that there is a shearing force being applied to the sheet metal that breaks up the sheet metal into a smaller piece. The removed piece can be looked at as a smaller piece that’s more manageable to process.
Blanking: This process is when a specific shape is removed from the sheet metal by large force that’s called the punch. For this process the piece that is removed, the blank, is not scrap, but the actual part that will be used for additional processes. The blank that is used in production depends on the thickness of the sheet metal and the dimensions of the punch. The blanking process consists of laying a piece of sheet metal over a die. The die has a little cutout that’s a little larger than the size of the punch which is applied to the sheet metal to break off the blank. Since the blank is just a piece of sheet metal, there are usually burs and some minor surface flaws. Therefore, a secondary process, such as polishing, treatment and a coating that is required.
Punching: This process is similar to blanking. However, the main difference is that instead of the removed material being used, the removed material in punching is scrapped. Therefore, the sheet metal will be processed further. Punching can be used to create holes, cutouts and various shapes and sizes in the workpiece. The punching process, which is exactly the same as blanking, consists of laying a piece of sheet metal over a die. The die has a little cutout that’s a little larger than the size of the punch which is applied to the sheet metal to break off the scrap.
Since the piece of sheet metal will be processed further, there are a number of secondary processes, such as milling, grinding, etc.
Cutting Without Shears
Cutting without shears means that there is no physical weight that is applied to the sheet metal. Instead of weight, the material is removed by different means, such as energy, water, etc.
Plasma Cutting: Material is removed using a plasma torch which is when gas is being blown out of a nozzle at a high speed.
Laser Cutting: A beam of high density energy is focused on the workpiece which cuts away parts.
Water Jet Cutting: Instead of heat being used, high pressure water is shot out of the nozzle and can provide cutouts with sharp edges. The common materials are aluminum, copper, brass, stainless steel and steel.
Wire Electric Discharge Machining (EDM): Instead of heat or water, an electrically energized wire is used to slice through the material. The process uses repetitive spark discharge from the wire to the electrically conductive material. The material is then eroded away which ends with a cut.
After the cutting stage is completed, you will most likely have a part that needs to be machined further. There are a number of processes that can be used to remove material which will take you a step closer to the final part. The processes at the removing material stage are the following:
Milling This is the most common process for removing material. The milling processes includes a rotating drill bit that removes material from the part. CNC milling has become a popular process which can remove material using a pre existing design that is programmed into the machine.
The process is usually used when there is a need for parts that aren’t symmetrical and have many different types of features.
The benefits of using milling is that they offer short lead times, keep tight tolerances, lower tooling cost and more.
The main drawbacks of using milling is that parts might require several operations in order to machine the final part and large amount of scrap (the material that is removed).
Turning This is another form of machining which is used to create rotational parts by cutting away excess material. This process is used to create a circular outer part or that needs a hole in the middle of the part. This process for removing material needs a lathe or turning machine along with a workpiece, fixture and cutting tool.
This process is used when either the work piece or the turning tool is rotating which removes material from the part. For this process you can either remove material on the outside and also on the inside of the part. If you are removing material from the inside then it will usually be used as a hole for internal threads.
The benefits of the turning process is the same as milling which is good for tight tolerances, short lead time and more.
The disadvantages are also similar to milling as you might need several different operations in order to machine one part and a high scrap rate.
Drill (Hole Making)
This is the most commonly known type of process. This process simply removes material that ends with the part having a hole in it.
BENDING & FORMING
This process doesn’t necessarily follow the previous step, removing material, but can be processed after the cutting. Bending and Forming is when a force is applied to a piece of sheet metal which causes it to bend and form into another shape. Bending is typically done on a press machine which has the punch come down onto the die and causes the sheet metal geometrics to change. In order to calculate the desired bend, the material, force and die, all need to be taken into account.
The most common method of bending is called V-bending. This is when the punch and the die are both V shaped. The die has an inner V shape and the punch has an outer V shape, so the punch is able to fit into the die. If the force of the punch is not great enough and there is space between the punch and the die then that is known as air bending. You can think of it as there being air between the bottom of the punch and the top of the die. On the other hand, if the force of the punch is great enough so the punch is able to touch the bottom of the die is known as bottoming. Bottoming is used when more control is needed.
In a majority of projects, there is also a need for two or more pieces of various metal sheets to be joined together. There are multiple ways for two sheets to be joined together. The following are the most common types of joining sheet metal.
Screws: The most common ways of joining to pieces of sheet metal is using a screw. Usually, you pre-drill holes into the sheet metal and then drill in the screw. This process is convenient and as the screws aren’t permanent, can be taken out.
Rivets: This is a common operation of joining two plates. For this method, holes are punched into two sheets of metal plates and a rivet is inserted inside to connect those two sheets. Usually, there are multiple rivets per sheet that are able to permanently fasten the joints.
Welding: This is the most commonly used process for permanently joining two metal sheets. The two main types of welding are TIG welding and MIG welding.
Brazing: This method is when a filler material is used to bond two metals together. It is similar to welding but is a cheaper alternative.
Adhesives: This method doesn’t join two materials together as well as other techniques, but it still can be an effective method that’s cheaper than the alternatives. The most common adhesives are epoxy, silicone, polyurethane and tape.
Metal finishing is important to solve two main issues. The first is to ensure that the part doesn’t corrode or rust using a number of different finishes. The second is improving its appearance or aesthetic qualities, making it more attractive to buyers. Depending on the product and materials, finishing has the ability to make a part or product much more aesthetically appealing with the use of color, textures and finishes.
When planning your finishing, there are a number of things that need to be taken into account. You will need to consider the process used, the materials (what are the chemical properties of that material), the texture and the overall desired finish. Below are the main types of finishes used in metal fabrication, please note that these are not in any special order.
Anodizing: This finish is used only for aluminum and is the most commonly used finish for resisting corrosion. While the coat is uniform, it doesn’t smooth out any imperfections, damages or scratches on the raw material. Therefore, a process before anodizing is most likely needed to smooth or eliminate these flaws.
Sand Blasting: This is a surface treatment process widely used to smooth out flaws or create a desired texture. Sand blasting is the process by which an abrasive media (grit or sand) is accelerated through a blasting nozzle by means of compressed air. Different types of abrasive media is used depending on the desired finish or texture.
Brushed Metal: This is when a wire or belt brush creates parallel grain surface to smooth out the surface. This is a good way to remove surface flaws.
Buffing & Polishing: This process removes excess material and smooths out the parts surface.
Electroplating: This is a type of metal plating that involves depositing a thin layer of metal onto the surface of your part. The main purpose of electroplating is to improve resistance to corrosion and wear.
Powder Coating: This process is both corrosion resistant and also provides the surface with a very smooth paint like surface. Powder coating is applied as a free-flowing powder in a completely dry form. Think of it as paint with the solvent part removed. The coating is applied electrostatically and then cured under heat which causes it to form a kind of “skin.”
The final step of the metal fabrication process is final assembly. This last step consists of bringing together the various finished parts so they can be assembled into the final product. During the assembly process, there can be multiple sub assembly processes that add extra value to the process. For example, if you’re looking to apply a logo then there are multiple options, such as laser etch, silk screen print, pad print and more.
Depending on the complexity of the product, the manufacturer might incorporate a flow line which will have the material flow from one station to another station. This limits the amount of work that is done by one individual. Therefore, one operator takes responsibility for one part and then they move that part on to another operator that’s responsible for something else.
The process of getting a piece of raw sheet metal into a final product can be a bit complex, but for the most part follows the steps outlined here. We will be going into a more detailed review of each step in the process in future articles so subscribe here to receive email alerts. If you have any questions or would like to discuss an upcoming project, please contact us to schedule a call or meeting.