Metalforming is the practice of deforming metal stock material which can be in solid bulk, sheet, or profiled form. The origins of metalforming date back to manually operated heated forgings and many of these niche applications are still practiced today by artisans and professions including farriers. Modern metalforming is an automated accurate repeatable set of processes. The classifications of metalforming operations are self-descriptive, generally defining the motion of the tool creating the deformation, such as rolling / spinning / stamping. The range of metal alloys has become vast and this is reflected in the specialisation of equipment and skills sets to process and shape the workpieces.
The market for metalforming products is spread across sectors, applications, metal types, making it difficult to make an accurate estimate of the global market. Market analysts have reported that global value will be $286Bn by 2025. A significant portion of this is into the automotive and train/rail sectors.
Metalforming is often performed at elevated temperatures to soften or increase the malleability of the material. Heating softens the material to increase deformation and reduce required press force, but this introduces distortion and shrinkage as the component cools. There are sophisticated computer modelling tools available to predict and optimize material flow, heating, and manage stress distribution.
An ‘open die’ operation is less accurate than a ‘closed die’ operation but produces a semi-finished part which then requires further processes such as trimming or machining.
Pressings, Stampings and Spinning
Pressings and stampings are components produced from sheet or thin section metal by the axial stroke of a press. Pressings are shaped by sandwiching a pre-defined piece of sheet between dies. Stampings are produced in the same way, but the stroke of the press removes the component from the stock sheet material, which may be fed from coil for mass manufacture. There are many variants on these processes to generate bespoke products. Fine blanking is one of the specialist processes, it is a stamping process with very high accuracy and fine tolerances between the die and punch to generate a finished edge.
Spinning is an incremental process operating in a similar way to a pottery wheel. The metal stock may in sheet or bulk form, the spinning machine rotates the metal piece while tools shape the internal and external form. Large canisters and containers can be made in this way, typically pressure vessels and other demanding applications benefit from this process, the alternative being fabrication.
Cold Rolled Steel
Rolling steel at ambient or near ambient temperature refines the metallurgical structure creating ‘work hardening’ as the molecular structure of the steel is broken into smaller grain size. Although this does introduce significant residual stresses these are computer modelled and managed to ensure the product retains its stability and strength during use. Steel is very strong in tension; cold rolled sections also have high compressive strength due to the work-hardening.
Fasteners are often mass produced with large batch sizes. The manufacturing processes are complex multi-operations.
A simple screw or bolt will be made from wire through cutting, heading, thread rolling across the face of a single press in a fraction of a second. It is quite common for these horizontal progression presses to have upwards of 7 stations across a face, with sets of transfer fingers between each station. Every time the press opens the workpieces are moved from one station to the next. Once set up the press will run continuously at a rapid rate, spitting out the products into large collection bins. As the piece part price is low for fasteners the economics of production requires speed and volume.
There are more complex fasteners including hinges and closures, which are generally more than one part. The automated process generates the basic elements of pins and plates then performs the assembly to output the finished parts.
Economic automatic assembly of metal parts requires bespoke sets of tooling operating in a simultaneous process. Manufacturing companies will tend to focus on families of assemblies to minimise tool change between production batches.
Hot forming is the deformation of metal at elevated temperatures. This process allows significant deformation of the workpiece and with hard alloys it is often the only way to lower the yield strength to allow deformation. Hot rolled products are often subjected to post processing, imparting lower amounts of deformation to straighten or size them to a higher tolerance. The computer modelling of hot forging is essential to control the material flow and prevent defects due to ‘cold shuts’ (where two cooling flows meet in the die causing an inherent weakness) and other structural defects. Hot forged steel alloys form a brittle oxide crust which is generally removed for aesthetic and post processing purposes.
Sheet Metal / Steel Suppliers
Sheet metal can be in the form of flat sheet or rolled coils, depending on the type of metal, the thickness of the sheet, and the application. Thin sheet metal can rupture during processing, requiring a high level of quality control in the sheet manufacture, transport, handling, and processing. The increasing demand for lighter structures means that ever thinner sheet metal sections are being used on space frames of lightweight alloy profiles. Cupping operations to make drinking cans and other containers are highly automated process involving multi-stage deep drawing and blanking operations on a vast scale. This is an example of the economies of scale through employing speed and large production batches.