Clinching as a Nonconventional Method to Join Drawing

The most common methods for joining the galvanized steel sheets in automotive industry is resistance spot welding. These methods require some consuming pretreatment of joined materials and the protective layer is destroyed which lead to decreasing of corrosion resistance. Therefore, it is necessary to utilize the other joining methods. The contribution deals with analysis of properties of clinched joints. There were made samples with single press joint and various sheets orientation due to punch and die and also samples with double press joints. Deep drawing quality steels of U.S.Steel Košice, Ltd. productions of various thicknesses a quality were used. The steels are also used in automotive industry. Moreover carrying capacity of press joints was evaluated.


INTRODUCTION
In materials joining technologies, the development of the automotive industry in recent years has been conducive to the development of new joining techniques and the modification of the joining techniques, which are already in use [1]. The trends of materials and energy savings are being increasingly applied to car body production. The production of cars with lower weight and thus with lower fuel consumption follows the environmental requirements of reducing emissions in the air. On the base of these demands, the need of joining of materials with different thicknesses and qualities (formerly known as the @ IJTSRD | Available Online @ www.ijtsrd.com | Volume -2 | Issue -1 | Nov-Dec 2017 The most common methods for joining the galvanized steel sheets in automotive industry is resistance spot specific timeconsuming pretreatment of joined materials and the protective layer is destroyed which lead to decreasing of corrosion resistance. Therefore, it is necessary to utilize the other joining methods. The contribution rties of clinched joints. There were made samples with single press joint and various sheets orientation due to punch and die and also samples with double press joints. Deep drawing quality steels of U.S.Steel Košice, Ltd. productions of various s a quality were used. The steels are also used in automotive industry. Moreover carrying : clinched joints, double clinched joints, In materials joining technologies, the development of the automotive industry in recent years has been conducive to the development of new joining techniques and the modification of the joining techniques, which are already in use [1]. The trends of als and energy savings are being increasingly applied to car body production. The production of cars with lower weight and thus with lower fuel consumption follows the environmental requirements of reducing emissions in the air. On the base of these s, the need of joining of materials with different thicknesses and qualities (formerly known as the Ultralight Steel Auto Body ULSAB project), coated or non-coated, and joining ferrous and non as well [2][3]. Their application in the automoti industry opens new possibilities for designers. These consist in the optimal use of the properties of different types of sheets, which can be combined into one complex construction and thus affect its strength, stiffness or corrosion resistance in vario drawn parts. The above requirements lead to the need for further research in the field of material joining, with particular emphasis on the load joints, their lifetime or corrosion resistance [4 One of the joining methods utilized in the automotive industry is a mechanical joining technique The mechanical clinching is considered as one of the possible alternatives to replace resistance spot welding, especially when galvanized steel sheets are welded a also where no conventional welding can be used, e.g. when joining combination of aluminium parts and steel parts [6][7][8].
The clinching process does not build any thermal stresses into the work-piece, so a clinched joint performs well where there is the fatigue or heat [9].
The paper deals with the analysis of the properties of joints created by the method of mechanical clinching. For the experiments, hot-dip galvanized steel sheets of drawing quality were used.

Scientific (IJTSRD)
International Open Access Journal

Clinching as a Nonconventional Method to Join Drawing
Ultralight Steel Auto Body ULSAB project), coated or coated, and joining ferrous and non-ferrous metals 3]. Their application in the automotive industry opens new possibilities for designers. These consist in the optimal use of the properties of different types of sheets, which can be combined into one complex construction and thus affect its strength, stiffness or corrosion resistance in various areas of the drawn parts. The above requirements lead to the need for further research in the field of material joining, with particular emphasis on the load-bearing capacity of the joints, their lifetime or corrosion resistance [4][5].
g methods utilized in the automotive industry is a mechanical joining technique -clinching. The mechanical clinching is considered as one of the possible alternatives to replace resistance spot welding, especially when galvanized steel sheets are welded and also where no conventional welding can be used, e.g. when joining combination of aluminium parts and steel The clinching process does not build any thermal piece, so a clinched joint performs well where there is the potential of thermal The paper deals with the analysis of the properties of joints created by the method of mechanical clinching.
dip galvanized steel sheets of Clinching as most used method of mechanical joining is a metalworking process which can connect steel sheets effectively without any splashes, flashes or harmful light. The principle of this technique consists in pressing the bonded sheets into a specially shaped die (Fig. 1). With increasing pressure, the joined materials are forced to flow into the sides of the specially shaped die (Fig. 2). Two or more metal sheets should be joined (made of the same or different materials and up to a total joint thickness of about 5-6 mm) regardless of surface condition and without any edge preparation [9]. After the joint has been made, there is no need for repainting the sheets or performing stress relieving treatments [10][11].
In recent years, it is said that this method of materials joining will largely replace spot welding in car body production. In comparison with resistance spot welding, the clinching has the following advantages:  from 30 to 60% of cost savings compared to resistance spot welding,  simple, non-destructive quality control of the joint is possible,  the material is reinforced at the joint place; no surface cracks occur,  the clinched joint reaches about 50% of the static strength in comparison with resistance spot weld strength,  higher lifetime of active tool parts (250,000 to 300,000 joints) in comparison with resistance spot welding electrode tips (1000 to 5000 welds).

IV. RESULTS AND DISCUSSION
The average values of the load-bearing capacity of the clinched joints are shown in Fig. 3. The samples with double clinched joints were formed only with a thinner sheet on the die side.
Average values of load-bearing capacity of clinched joints (*thinner sheet on the die side) The highest values of load-bearing capacity were achieved with double clinched joints, followed by the samples with a single clinched joint when the thin sheet was oriented on the die side and the lowest loadbearing capacity was achieved with single clinched joints where the thinner sheet was on the punch side.
As can be seen in Fig. 4, the failure of the clinched joints depends on the orientation of the steel sheets relative to the punch and die. A deformed part of the top steel sheet along with a crack in the clinched joint is visible on the sample along the circumference of the joint - Fig. 4a. This part was torn from the lower, thinner plate. Figure 4b shows the sample breakage occurred by rupturing the thinner bottom in the critical area of the joint, i.e. in the place with the largest thinning. The critical area of the joint is shown in Fig.  5. A typical example of a double clinched joint failure is shown in Fig. 6.  The measured and the computed values show that the higher values of the load-bearing capacity of one clinched joint with the thinner sheet on the die side reached the samples II and IV, where the difference in the joined thicknesses of the materials was most significant. Figure 7 shows a cross section of the part of pressure joint of the sample I (DC01, thickness of 0.8 mm + DC01, thickness of 0.62 mm). In the place A, the structures of the two joined materials are visible without grain deformation caused by joining process. In the place B, where the clinched joint starts to be created, the deformed grains of the joined materials are visible, with greater deformation on the top sheet. In the place C, the deformation of the grains of both materials is almost the same. In the bottom of the clinched joint in the place D, a considerable deformation of the grains of both materials was observed. There is more than 50% of the thinning in both joined steel sheets. At the bottom of the clinched joint and in the critical area of the clinched joint, the largest amount of thinning of the joined materials occurred.

Conclusion
The mechanical clinching is a relatively new method of material joining. Its usage in the automotive industry is increasing as an alternative to resistance spot welding or in cases where conventional joining method cannot be used. Research into properties of clinched joints in the automotive industry is mainly focused on their impact on the load-bearing capacity of the resulting parts. Since the 1990s, the tailored blanks consisting of materials of different qualities and thicknesses are investigated by the ULSAB (UltraLight Steel Auto Body) project. This also closely relates to the need for research into the joining of materials of different thicknesses and qualities using various joining methods.
On the basis of the conducted experiment, the following conclusions can be formed:  the results of the tensile test as well as the metallographic observations confirmed the mechanical clinching as a suitable method for joining the tested combination of materials,  the highest values of load-bearing capacity were achieved with double clinched joints,  load-bearing capacity of the clinched joints varies significantly depending on the orientation of the sheets in the testing sample,  when clinching materials of different thickness, it is advantageous to orient the joined materials so that the thinner sheet is on the die side and the thicker sheet on the punch side.