Types of rental
Factories use different types of rolled products. Technologies differ in the equipment used and the stages of work. To produce steel parts, machines of different designs are used.
Sheet
This is a popular type of metal processing in which the part is first heated and then passed through rotating rolls. The technology can be carried out in two ways:
- Hot rolled - the method involves heating the material to 1700 degrees Fahrenheit. After heating, the metal becomes more ductile and less hard. However, rolling at high temperatures does not allow accurately calculating the size of finished products after cooling. In addition, strong heating promotes the formation of scale, which must be removed.
- Cold-rolled technology involves slightly heating the workpieces before further work. The surfaces of the parts are cleaned of scale. After this, they are subjected to other technological operations.
The first rolling option is more economical. With its help you can work with sheets of large thickness. The second method allows you to create parts that are more accurate in size, but is not suitable for working with metal sheets thicker than 5 mm.
Varietal
This type of technology can be divided into hot and cold methods. With its help it is produced:
- wire, fittings;
- hexagons, squares;
- circles, semicircular details.
Shaped
Small rental group. The technology received its name because of the complex shape of the finished products. The output is large parts. They are made on industrial machines. Shaped products can be divided into two groups:
- For mass use. This includes channels and corner profiles.
- For special purposes. These include rails for railway or tram tracks, floors, beams, industrial stops.
This method of rolling is used in construction.
Shaped products
Workpiece selection
- Home /
- Mechanical restoration /
- Workpiece selection
The following can serve as blanks for the manufacture of mechanism parts:
- Castings obtained by various methods are used for the manufacture of complex-shaped parts from cast iron, non-ferrous metals and special cast steel (the index L is added to the designation of the steel grade). Using casting methods, holes of various shapes can be produced in the workpiece. Casting blanks are characterized by increased surface roughness, increased hardness of the surface layer (crust), large processing allowances and high cost; forgings are used for the manufacture of parts from plastic metals with a configuration that is less complex than that of castings, but has large differences in dimensions (for example, diameters). As a rule, holes are not produced using forging methods. The exception is cases when obtaining a hole by other means is not economically feasible.
- Forging blanks are characterized by lower surface roughness than castings, but greater waviness; increased hardness of the surface layer (crust), large allowances for processing and low cost;
- Stampings are used to produce parts from plastic metals with a configuration that is more complex than that of castings. When stamping, it is possible to obtain holes of any shape and configuration. The stamping blank is characterized by low surface roughness, high accuracy, small processing allowances and the highest cost. Stamping blanks are used in cases where there are surfaces that cannot be processed mechanically, but their high quality is required;
- Long products . Its main advantage is its low cost. It is made of steel and non-ferrous metals in the form of rods with various cross-sectional shapes (circle, square, hexagon, pipe, square, T-bar, etc.). Rolled products are widely used due to their simplicity and low cost. A significant disadvantage is the low material utilization rate.
The very first criterion when choosing the type of workpiece is the material from which the part is made:
steel - rolled, forged, stamped, less often - casting;
cast iron - various casting methods;
color metals - rolled, casting, less often - stamping.
The second criterion is the technological capabilities of each type:
for parts of simple shape, rolling is preferable; for medium and large sized parts of simple shape with large differences in size - forging; less preferable, due to high cost, are casting or stamping; for parts of complex shape - casting or stamping.
Feasibility study of the correct choice of workpiece
The selection of the type of workpiece according to these criteria is approximate. They may be satisfied with several options for blanks at once. For example, a flange ( see fig.
.).
For a more accurate determination, it is necessary to perform an economic calculation - calculation of the technological cost of manufacturing the part. This calculation is quite complex and requires the use of a large number of economic data from a real enterprise. For educational purposes, it is allowed, instead of calculating the technological cost, to determine the cost of the workpiece and add to it the cost of distinctive operations. If the selected methods for obtaining the workpiece are equivalent, preference should be given to the option with a higher material utilization factor g.
It shows what % of the workpiece material is used for its intended purpose, and how much goes to waste, into chips.
Where
q
- mass of the finished part, g
Q
- mass of the initial workpiece, g.
Where
r
— density of the workpiece material, g/mm3;
V
is the volume of the workpiece, mm3.
Before calculating the volume of the workpiece, it is necessary to design it: using the drawing of the part, the values of allowances for processing are calculated, the dimensions of the workpiece are determined, and its drawing is developed. Based on the drawing, the workpiece is divided into elementary figures (cylinder, parallelepiped, ball, etc.), the volume of which can be calculated using known formulas. The volumes of bodies are calculated separately, and the volumes of voids separately. The volume of the workpiece is determined as
If the part is made from rolled products or forgings, then the cost of the workpiece is determined by the weight of the material required for the manufacture of the part and the weight of the chips delivered, rub.
Where
S
— price of 1 kg of billet material (rolled; forgings), rub.;
Soth
— price of 1 ton of waste, rub.
The cost of blanks obtained by other methods, with sufficient accuracy for course design, is determined by the formula:
rub.,
Where
Ci
— basic cost of 1 ton of billets, rub.;
kt, ks, kv, km, kp
- coefficients depending on the accuracy class, complexity group, weight of the workpiece, grade of material and volume of production of parts.
In the case where the choice of the type of workpiece affects the content of the technological process, the cost of distinctive operations is determined:
rub.,
Where
T st - tariff rate of a worker - machine operator, rub./hour; k=1.15 - coefficient taking into account the salary of the machine operator; Tsh.k - piece-calculation time required to perform this operation, min.
The economic effect of comparing methods for obtaining blanks
rub.,
Where
N—annual program, pcs.
| OPTION 1 - forging | OPTION 2 - stamping |
| Mass of the finished part q = 3.058 kg | Mass of the finished part q = 3.058 kg |
| Workpiece mass Q=10.409 kg | Workpiece mass Q=5.794 kg |
| Material utilization factor g = 0.39 | Material utilization factor g = 0.53 |
| = 11.6 rub. | Szag = 18.02 rub. |
| =1.25 rub. | Cost of distinctive operations = 0 |
| Finally we get: | |
| Szag = 11.6 + 1.25 = 12.85 rub. | Szag = 18.02 rub. |
| Annual economic effect Eg = (18.02 - 12.85) · 10,000 = 51,700 rubles. | |
Earth mold casting, Chill casting, Lost wax casting, Open die forgings, Aluminum castings Rolled brass Rolled steel Hot stamping Steel pipes
- Workpiece selection
- Machining allowances
Equipment
To understand how different parts are made, you need to know what equipment is used during technological processes. Rolling is carried out on the following machines:
- Wire mechanisms. With their help, wire with a diameter of up to 10 mm is produced.
- Slabs - designed for processing long rectangular products.
- Bloomings - used in the manufacture of large square products. In addition to square sections, mechanisms can make blanks of various shapes.
- Pipe rolling are industrial machines that are used to create metal pipes of different diameters.
Before rolling begins, the metal is heated using industrial furnaces and fed through cutting shears to rotating shafts.
Choosing a method for producing forgings
The determining factors when choosing a method for producing a workpiece using plastic deformation methods are the type of production, the dimensions of the part, the shape of the forging and the properties of the forging material.
At the first stage of selection, the type of production of the part in question becomes decisive, since the technological process of pressure treatment is based on the use of high-performance and relatively expensive equipment, as well as expensive tools (dies). In single and small-scale production, the equipment must be universal and relatively inexpensive, and its productivity is not as significant as, for example, in mass production. The deforming tool should also have, if possible, universal application, a simple shape and low cost.
These conditions are met by free forging on forging hammers, as well as forging using backing rings and backing dies.
In mass production, it is advisable to use stamping hammers of various types, and the shaping process is carried out in dies, half of which are fixed on the table and on the hammer head and can have up to five grooves of complex shape.
The productivity of stamping and the accuracy of forgings when using a stamping hammer in large-scale and mass production are no longer sufficient. Therefore, the most rational is the use of crank forging and pressing machines: a crank hot stamping press (CGSP), a horizontal forging machine (HCM), a stamping (crank) press, as well as specialized high-performance machines (rolling machine, forging rollers, etc.).
For most small and medium-sized parts used in mechanical engineering, the above considerations are valid, but in a number of cases it is necessary to deviate from the intended recommendations
The trend of modern mechanical engineering aimed at increasing the power of individual machines (pumps, compressors, drilling machines, etc.) leads to the fact that the force developed by hammers and crank machines is not enough to plastically deform a number of parts. Therefore, for large parts (for example, with a diameter of over 1000 mm), it is necessary to use forging or stamping on hydraulic presses, despite their comparative low speed (free forging for individual and small-scale production, and stamping for serial, large-scale and mass production).
If the parts are small in size, but have a complex shape and, due to operating conditions, must have a very dense metal structure, then blanks for them must be made using closed stamping in split dies. It is most convenient for this stamping method to use a screw friction press (in small-scale and mass production) or a specialized crank-type semi-automatic machine (in mass production). A special group in the shape of parts consists of long forgings with a flange, and
also forgings with through and blind holes for parts such as drill strings, rods of deep-well pumping units, bushings, coupling halves, bearing rings, etc. For them, it is recommended to choose the method of stamping on a horizontal forging machine, since the presence of a split matrix in it and the horizontal arrangement of the main slider makes it possible to obtain forgings of complex shapes with minimal metal waste.
The low plasticity of the material, regardless of the type of production and size of the part, requires the use of a hydraulic press, since only it can ensure smooth operation and a sufficiently low rate of plastic deformation at which microcracks and other defects do not form in forgings.
The stamping method also determines the smallest hole diameters that can be obtained by plastic deformation of the workpieces. When free forging on hammers and hydraulic presses, the minimum hole diameter is 80 mm, when stamping on hammers - 50 mm, and when stamping on crank machines - 35 mm.
