Metal fabrication uses a variety of techniques to shape, form and join metal sheets together to create a new and innovative object. We are going to elaborate on the topic of metal shaping and the techniques associated with it.
What is Metal Shaping?
Metal shaping is the process by which you can bend, cut, shrink or stretch the metal to give it the desired shape.
There are various techniques employed to shape metals depending on the qualities of the metal and the products you want to make. The most common and useful metal shaping techniques are:
A punch and die are used in blanking, which is a shearing process. In blanking the piece that has been punched out is called the blank and is now the new work piece. Punching is also referred to as piercing.
There are many benefits that make this method so popular.
- Metal workpieces are made at a relatively cheap price
- The overall quality is controlled very well by the punch and die
- Makes holes of various shapes quickly
- It is useful for the formation of hollow metal objects like bearings and washers
The clearance of the die is extremely important. The pressure produced at the cutting edge of the tool AKA the point pressure is caused by the die clearance.
Point pressure above the threshold can lead to accelerated wear which will ultimately lead to failure. The clearance also affects the trimmed edges’ surface quality too.
There are various types of blanking: notching, nibbling, shaving, cutoff, and dinking.
- A blank has the sides shaped and sheared to make a more detailed shape. This is called shaving. Its main purpose is to be a finishing process. It helps to achieve better dimensional accuracy and can be used to smooth out edges or just help get the shape you wanted to get
- The final process completed is trimming. It is similar to shaving since, its main function is to shaves off all the excess metal that was not taken off in the other processes
- The cut off process is used to separate a stamping from a strip or stock, it is one of the final parts that occur in blanking
- Fine blanking is an in-depth form of blanking where there is no fracture zone. During this it compresses the whole part. Then the upper and lower punch, extract the blank. This allows the process to hold very tight tolerances, and even at times eliminate secondary operations
Hot unprocessed metal is pressed between two dies. It is usually called hot pressing. It is carried out either using hydraulic presses or mechanical presses. These dies are in the shape of the object we desire to make.
Due to the continuous action of the hydraulic presses, the deformation penetrates deeper. So the entire volume of the work piece simultaneously and uniformly undergoes deformation. The dies are then pressed together to obtain the required shape. Press forging can be used for mass production of rivets, nuts, bolts, valves, break levers, screws, etc.
Advantages of Press Forging
- The speed, pressure and travel of the die are controlled
- More complicated shapes can be forged with better dimensional accuracy
- Has higher productivity levels than drop forging
- The operation is completed in a single squeezing action, saves the time
- The deformation goes deep into the centre of the work piece in one continuous movement, provides uniform and simultaneous deformation throughout the metal
However, there are a few limitations of press forging including the initial overall cost is higher than drop forging, because the cost of a crank press is higher than that of an equivalent hammer. The process is only economically suitable when the equipment is efficiently utilised.
Another commonly used forging process is drop forging. Essentially, in this process a hammer is lifted and after that dropped onto the workpiece. This deforms the work piece to whatever shape the die underneath it is.
During forging the deformation of the metal is done using a hammer, roller or press to compress the metal. The processes are usually carried out cold, although it the metal is hot. The plasticity of a metal increases because of forging. This is great because it reduces the forces to work it.
Drop forging is when, the metal is placed on an anvil and a hammer powered by a pneumatic or hydraulic force repeatedly rises and falls on the metal.
Some of the products produced via drop forging are claw poles, door handles, clamp straps etc.
There are two sub-types of drop forging these are: open-die drop forging and closed-die drop forging. The main difference as hinted by the names is the shapes of the dies used.
Open die forging- When numerous dies are used in the process of deforming some metal where the dies do not fully enclose the metal piece.
However in the closed die drop forging process, the metal bar is heated before being placed in the die and then hammered until the metal completely fills the die cavity.
Rolling and Thread Rolling
The hot metal is passed through the series of rollers thereby compressing it. This increases its length and reduces the thickness. In thread rolling, a thread is applied to machine bolts produced by cold heading.
Sheets and bars are prepared by using the rolling technique. Meanwhile knurled patterns, worm gears, spline shafts etc. are prepared by using thread rolling. Here are some advantages of thread rolling:
- Rolling is unique as it is able to maintain the accuracy of the original setup, during long runs of high speed production
- The thread angle and the lead of the thread on the die is nearly always exactly reproduced onto the material being rolled
- The work piece’s resistance to fatigue failure is increased by thread rolling in several ways. One example of this is that, rolling between smooth dies leaves the thread with smooth burnished roots and flanks, free from tears, chatter or cutter marks that can serve as focal points of stress. Therefore, making starting points for fatigue failures.
In this technique, a hydraulic ram pushes a heated metal of a certain length and cross section through a die of a smaller cross-sectional are and the desired shape. The extrusion method is used to make long objects like bars and tubes.
The advantages that make people choose it over other manufacturing processes are It forms parts with an excellent surface finish, its ability to create highly complex cross-sections, and to work materials that are brittle. This is because the material only encounters compressive and shear stresses.
Bending and Casting
Objects with angles are prepared by using this method. Here the force is applied to a metal sheet to make a curved shape. In the casting method, the metal is given shape by pouring molten metal into a mould (a cavity having the shape of the required object).
Sand is a good material to make mould because it can withstand high temperatures and can be moulded into complex shapes. Various types of casting methods include sand casting, die casting, wax casting and centrifugal casting.
There are some features of this metal shaping process that make it unique:
- Certain light metal alloys because of their respective strength and weakness, can only be produced as castings
- It’s a highly adaptable process for mass production. Large numbers of a given casting can be produced at a much faster rate than the others. One example is that transmission cases and cast blocks are mass produced in the automotive industry
- Some metals due to their physical attributes can only be cast since they cannot be re-modelled into or other shapes
Who Are We?
UK Pressings offers British made, high-quality metal pressings, and welded assemblies at an affordable price. Skilled professional workers from our company make your life easier by manufacturing and supplying of metal pressings in Walsall at the heart of West Midlands in the UK. The industry offers for individual customer specifications for standard and bespoke services.