At the beginning of the eighteenth century they also succeeded in obtaining cast iron by using pit coal and then compensating, especially in nations like England with scarcity of woods, to the shortage of wood. In any case the productivity was very good but the obtained material very fragile. It was used for castings but it was unusable for the plastic deformation. They were facing an opposite problem to that found in the previous centuries, it was necessary to decarbonize the obtained product through refining.
Numerous solutions were tested starting from the seventieth century, but none of then were particularly productive and economic.
The most interesting was certainly the so called puddling. The cast iron was heated up to the liquefaction in reverberation furnaces where the material did not come into contact with combustion products but it was exactly heated by the flame reverberation. The metal was continuously puddled by an operator, in presence of a hot air flow, to make it loose carbon and then to transform it into steel.
Fundamental was, in , the introduction of the Bessemer converter Figure 1 used in the industrial production of steel starting from the melted cast iron produced in the blast furnace. It was the first furnace that permitted the production of steel in a single machining phase. The operation is conceptually simple: a great quantity of air that crosses the bath is pumped from the bottom.
The high carbon percentage, the high bath temperature and the oxygen contained in the air provoke characteristic blasts in which carbon is burnt thus diminishing the content in the bath and thus obtaining steel without adding further fuel! In the first times the process was not usable for the cast irons with high phosphor percentages the majority! This technology remained in use until the Sixties when it was supplanted by an analogous one that uses oxygen breathed into the bath from above, the BOF Basic Oxygen Furnace process.
Other developments were achieved with Martin-Siemens, electrical and continuous casting furnaces and many others but we have in the meantime arrived at our age. At present the most used technology to refine cast iron are the BOF process for the blast furnace cast iron and electrical furnaces to remelt the scrap iron, eventually mixed with cast iron.
Soft iron was only hot workable, then arousing particular problems for the attainment of thin thicknesses. The real turning point in the sheet metal production took place with the introduction of the rolling mill. Also in this case it was provided for the cold machining of ductile materials, especially for lead, tin etc but it is not certain that it was ever built. There are reports of two rolling mills in the sixteenth century: one used to obtain gold sheets with uniform thickness from which to draw coins, the second to cut already formed sheets into strips.
The first industrial plant of which we have certain news was used in , to obtain lead and tin plates Figure 3. Others followed, driven by animal or hydraulic force. Due to the increased possibility of obtaining ferrous material, the cold rolling of steel is simultaneously started. In a cold rolling mill of notable sizes was present in Newcastle in England. Galles will remain the main European producer of thin sheets until the end of In the eighteenth century they also started rolling more complex shapes: rounds, squares, rails, double-T beams etc.
It is essential to observe how the rolling complies with the demands of that age producing the requested materials: in lead sheets for the roof covers were highly requested and this possibility is then developed, at the end of , in the middle of the industrial revolution, they needed rails and semi-finished steel products that therefore the rolling promptly satisfies. At the beginning of the nineteenth century the rolling mill structure was essentially the current one: a sturdy cast iron cage with two steel cylinders and the possibility of adjusting, through a screw, the roller distance Figure 5.
Already at that time they understood that the rolling was a very productive process able to satisfy the enormous quantity of semi-finished products, among which obviously metal sheet, which the historical time requested, even if the process still needed a conspicuous human labour use Figure 6. The driving force used evolves in time: after the hydraulic wheel, the steam engine and then the electric motor. Up to the four-cylinder configuration already hypothesized by the genius Leonardo da Vinci with the two more external cylinders acting as support to the two internal ones that accomplish the machining, up to implementing the configuration with even 20 cylinders.
It is anyway worth making a clarification: rolling, as we know it today, cannot be attributed to a single inventor neither to our genius Leonardo! The study aimed to investigate the whole-structure response up to and including eventual failure. The experimental and numerical simulation results confirmed that the introduction of an adhesive into the clinched joint increases the joint strength.
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While it is commonly believed that adding an adhesive layer to clinched joints is beneficial, there is uncertainty about negative effects on the mechanical properties of the joints. Several researchers, e.
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The results of their work show that including an adhesive layer increases both the strength and energy absorption capacities of joints. They found that the adhesive layer can act as a lubricant between the two sheets during the clinching process but that after curing, the glue introduced strong adhesive forces between two sheets. However, in tensile shear load tests the adhesive layer failed in a brittle manner after peak load. At this point, the clinch keeps sheets connected but the joint can bear only a small additional load. Friedrich et al. Specimens of PA6-GF15 plastic and DC04 steel were clinch-joined in various combinations and then subjected to peel and tensile shear loads.
The authors were able to demonstrate that appropriate clinching and hot-gluing can result greater joint strength compared to clinching or hot-gluing alone. FE methods are commonly used to simulate the failure of clinch-bonded joints. Cohesive zone CZ models can also be used to simulate damage and failure in clinched joints that incorporate an adhesive layer.
Excessive distortion of the elements can be avoided by using arbitrary Lagrangian—Eulerian ALE adaptive meshing and the minimum time increment in explicit analyses can be increased by using mass scaling. On this basis, Pirondi and Moroni [ ] began their analysis with 3D modeling of clinching processes. They then derived the values for GTN and DD model parameters by an inverse method, comparing the results from simulations of simple clinched joints with data from experiments or published literature.
Finally, the adhesive layer was introduced into the model as a layer of cohesive elements. The results of the simulations agreed well with values obtained experimentally with respect to the stiffness, peak load and the energy absorption capacity of the joints. The purpose of Lee et al.
The failure behavior of hybrid clinching was described by multi-CZMs to evaluate the crash resistance of hybrid clinched structures. Cohesion parameters of mechanically joined and adhesive bonded parts in hybrid joining were determined by a numerical-experiment approximation technique. The crash-worthiness of top-hat specimens joined by hybrid clinching was designed based on the crash analysis with multi-CZMs.
Also, the crash tests were performed to verify the effectiveness of multi-CZMs.
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Ultrasound-assisted clinching applies ultrasonic energy to the punch during the process. Current research focuses on the possibility of using the ultrasonic softening mechanisms in clinching of high-strength steel and aluminum. Heeln and Wanner [ ] described the integration of the ultrasonic unit in the clinching process. The research results focusing on verification of the concept were also presented. Mucha et al. The authors described joining S GD sheet metal using this combination of joining technologies.
This material is used in the construction of light gauge steel frames for residential and commercial buildings. The authors discussed the results achieved for joints arranged in parallel and perpendicular to the load for specified joint spacing and for various combinations of joint types. The test results for rivet-clinched joints were compared with those for clinching alone.
Joint strength can be increased by using rivet-clinching technology. Rivet-clinching allows for greater flexibility in sheet joining as the extensible die can be used in this new technology.
Another new clinching method, namely die-less rivet-clinching, has also been introduced by Neugebauer et al. The die-less rivet-clinching works with a flat anvil as a counter tool. When joining materials by forming with a flat counter tool the crack-inducing tensile stresses in the bottom part are very low. High-strength steels can be clinched if the ductility at the site of the joint can be improved by localized heating.
Reich et al. With this new method, the overlap section is heated locally by a laser during the clinching process. As long as the heating is confined to the joint area, the properties of the material away from the joint should be unchanged by the joining process. In this context, Osten et al. The mechanical properties of samples were studied by thermo-mechanical analysis in a deformation dilatometer.
The results showed, for the first time, the feasibility of laser-assisted clinching between sheets of 22MnB5 press-hardened steel.
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Conventional clinching technology has no thermal effect on the materials being joined and does not introduce complementary joining elements such as rivets that add weight to the structure. On the other hand, the process causes a protrusion jutting out of the sheet plane on the die side. For this reason, conventional clinching cannot be used for visible and functional surfaces such as automotive body shells and sliding parts [ 56 ]. Also, access to both sides of the joint is essential and the technique cannot be used on brittle substrates.
To overcome these problems, some modified clinching methods have been developed. Flat clinching was introduced in the s [ ].
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In this process, the joined sheets are deformed after press clinching by being sandwiched between a punch and a flat die. This creates a new joint configuration which is flat on the bottom surface. Because at the end of the process one surface is flat, the technology can be applied even on functional surfaces. In a further variation, the second step was performed by pressing the joint between two flat dies and this has been shown to be very effective. The authors carried out FE simulations to optimize the process and the results for joint strength were verified by experimental tensile tests.
Some joints were cut to show the changing of the contact line and how its characteristics influenced the bonding performance. Wen et al.
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This compression controlled the local plastic deformation of the joint, reducing the height of the protrusion.