Agricultural machinery manufacturing process

For each machine in the field there are a series of people and processes involved in the manufacturing, selection and assembly of each component that together form equipment of all types and with the most diverse technologies available.

In relation to mass, iron is the most abundant element in the Earth's crust. In 2014 alone, 3,22 billion tons of iron ore were extracted, of which 320 million tons were produced in Brazil, representing almost 10% of world production, behind only China (47%) and Australia (20,5%). .XNUMX%). The high production is not surprising, iron has a varied number of applications in different fields. Iron is durable, resistant, hard, malleable, withstands tensile and compression efforts well, weighs a lot and most importantly: it is cheap. These characteristics make iron the perfect material for agricultural machinery. From the iron ore extracted by mining companies to the metal part working in the most diverse mechanisms and structures, there is a range of processes responsible for this transformation, some of these, with an emphasis on mechanical processes, will be covered in this article.

FOUNDRY

It is likely that in volume most tractor components will be manufactured through casting, mostly from iron, since aluminum, being a lighter metal, is not as interesting a material for agricultural machinery as it is for other sectors of the industry. Auto Industry. In casting, a metal in liquid state, completely molten in a furnace, is poured into a mold with the desired shape and, after solidifying, it shapes the metal.

The most commonly used method, and also the cheapest, is sand mold casting, where common sand mixed with a binder is compacted around the part model. In this process, the mold is destroyed and the sand is reused. Engine blocks, pistons and crankshafts for low power applications are some examples of components cast in sand molds, in addition to ingots used in mechanical forming processes.

Casting with a metal matrix allows for much more complex parts with thinner walls than those processed by sand molds. However, it is not used to melt steel, being used in the casting of metals with a melting temperature lower than that of steel, such as aluminum, lead and zinc alloys, with the metal being able to be injected by gravity or pressure. The matrix, after casting, is cleaned and lubricated, making it ready for a new process and can be used hundreds or thousands of times. Parts such as heads, connecting rods, pistons and gearboxes are cast in dies.

CONFORMATION

In mechanical forming processes such as rolling, forging, drawing and extrusion, parts are obtained by applying pressure forces to solid metals, which through their plastic deformation are molded into the desired product. They can be executed hot, facilitating the process as it requires less mechanical energy to shape the metal or to modify its mechanical properties, or cold, resulting in a better final finish in addition to hardening the material, increasing mechanical resistance, but reducing the ability of the material to deform without breaking.

Some of the mechanical forming methods are necessary before the part goes to the final forming process, such as rolling, a process in which an ingot passes between the cylinders of the rolling train that compress it, reducing the thickness and increasing the width and length . This method produces plates, sheets or bars that can be used in other forming, machining or welding processes.

EXTRUSION

Extrusion is the forming process in which an ingot coming directly from a forge or a billet from a rolling mill is intensely compressed and forced to pass through a die. Regarding the movement of the material, extrusion can be classified as direct and indirect: in direct, the plunger compresses the material, forcing it to pass through a matrix attached to the chamber, on the side opposite the plunger; In indirect (or inverse) mode, the die is attached to the piston and advances towards the billet. Bars with different shapes can be made using extrusion, such as tubes and rails.

STAMPING

Hoods, rims, fenders and metal bodywork in general are manufactured using metal sheets (thickness between 0,15mm and 6,3mm), while cabin supports and couplings, for example, are sheets (thickness greater than 6,3mm ) shaped by stamping. To manufacture a sheet or plate, an ingot goes through the hot or cold rolling process. Having the sheet or plate, it goes to the stamping process, where it is subjected to a compression load between a punch and a die, which can be used to shape, bend or cut. The metal used must be ductile and malleable, such as low-alloy steels (from 2% to 5% of other elements) and aluminum. Stamping is used for series production due to the cost of molds or dies, which are not economically viable for small runs. Cold stamping offers greater dimensional precision and a better finish, however with hot stamping curves can be obtained that would not be possible with cold stamping.

FORGING

Forging is one of the oldest methods of working with metals. In its process, the metal undergoes compression deformation and can be hammered or pressed into the mold, giving the desired shape. For the most part, operations are carried out hot (requiring less compression force from the press, but with finishing and dimensional accuracy not as good as cold), although in some specific cases the metal can be forged cold.

In the hammer forging process, a punch suddenly exerts an impact force on the metal surface. In the pressing forging process, the material is subjected to a progressive compression force.

Forging can also be characterized according to the type of die: open die (also called free forging), used for the production of small-scale parts such as bars with special shapes and in general simple shaped parts that require little elaboration, such as lower arms of the hydraulic lift; and closed die (also known simply as die forging), used for large quantities of parts, a process through which connecting rods, crankshafts, bearings, transmission shafts and screws can be manufactured, however, almost all parts require some subsequent machining work .

MACHINING

Machining processes consist of achieving the desired shape and dimensions of a part by removing material, called chips. Through machining, a series of advantages are achieved, such as great dimensional precision in operations, execution of a wide variety of formats, no alteration of the physical and chemical properties of the material, in addition to being processes that can be easily automated. On the other hand, machining processes demand more energy than other processes, have long production times and therefore may not be economically viable for large batches of parts, the size of the parts is limited by the capacity of the machine tool and also the material removed from parts in many cases is not recycled.

It can be said that most commercial parts have some machining process in their production. Machining can be done with different processes, such as electroerosion, laser, water jet, etc. But the most common processes are mechanical using machine tools, such as drills, lathes, milling machines. A revolution in machining processes were CNC (Computer Numerical Control) machines, which, through programming codes, can machine more complex profiles, facilitating the creation of parts with machining in three dimensions, in addition to reducing working time and dimensional errors.

The use of metals, mainly iron, in agricultural machinery is essential and elementary. Knowing the processes involved in its refinement, from the raw ore to the worked piece, is important in evaluating these machines that are so present and useful to the producer.

Factory vocabulary

As in all work environments, some words make up a specific vocabulary that is widely used in the processes that are part of that location, as is the case of factories producing metallic components that serve as raw materials for the construction of agricultural machinery.

Cavaco: pieces of material removed from the part by a tool in machining processes.

Ductility: property that represents how much a material deforms before fracturing. The opposite of ductile is brittle.

Hardening: phenomenon that only occurs when cold, increased hardness due to plastic deformation.

Ingot: blank piece of metal, block or bar, which, after melting, is poured into a mold to facilitate handling.

Machine tool: machine used to manufacture parts through machining, such as drills, lathes and milling machines.

Billet: solid object, usually solid cylinders, used as raw material for processes such as rolling and machining.

Drawing: is the mechanical forming process that makes thin metal wires and bars.

Gabriel Silveira Chagas, Airton dos Santos Alonço, Tiago Rodrigo Francetto, DautoPivetta Carpes, Laserg/UFSM

Article published in issue 159 of Cultivar Máquinas.