Centering of the sheet metal trough a circular hole Washers can have different designs, and feature of the washers from the fig. 11 is that it provides three rows of set- ting of screws or pins. 

Contexts in source publication

Context 1

... step is planning of every clamping device in order to gain a full insight into the setup plan of the current setup station. It is necessary to eliminate (command hide ) all work-holders except sheet from the fig. 4 and the current work-holder. The display will present the situation as shown in fig. 6: Fig. 7 shows a simple device with the corresponding elements: 1. The clamp that is in contact with sheet metal has been processed on a NC machine in order to obtain a matching shape that reduces the possibility of errors. This clamp station is a stationary part. 2. This clamp contact surface was also processed on a NC machine, but in contrast to clamp 1, this is a movable element, and opens in correlation with hand element number 6. 3. The console on which the stationary clamp is mounted and purchased clamping work-holder 4. 4. Purchased pneumatic clamping device that comes together with the hand element 6. 5. Element that connects the clamp 2 and hand of the work- holder 6. For the clamp it is not necessary to be connected through this element, but it is possible to directly connect to the hand. Clamp has been connected in order to achieve the connection between the arms and clamps. Clamp can also be designed in order for the element 5 to become unnecessary, but on how and why it will be discussed further in the text. 6. Hand of the clamp 4 comes together with the work-holder 4. 7. Open position shows all the movable parts. They are usually shown with a transparent color. Method of used setup plan for the construction of the work-holder has 4 important positions (fig. 7): – Position 1). There is gravitation toward smaller dimensions of clamp values, especially in direction of clamping. – Position 3). The console is mounted on the work desk. Surface contact of the console and the desk (board) on which the console is installed must be of fine processing treatment. Other elements if necessary can be mounted on the console. In the event of shear stress occurring in the clamping space (the place of contact of clamps and the sheet metal) it would be desirable to further stiffen the console element which is perpendicular to the console. – Position 4). This is about a pneumatic clamping work- holder of the Tuenkers brand. Also, there are still manual, hydraulic and electrical clamping work-holders. For the work-holder the most important is the opening angle. – Position 7). Open position must be show how it looks like when the sheet is not in the clamped position. Open position represents a state where the sheet metal can be placed or removed from the work holder. Fig. 8 shows a clamped (closed) position of the work- holder. The same figure shows a part of the sheet by which the clamps were NC processed in order to obtain the exact form of the corresponding clamp surface which corresponds to the surface area of the sheet metal, where clamps perform the tightening, one specific shape is shown in fig. 5. In order to reduce the costs for the construction of work- holders there is a trend of buying prefabricated parts. Percentage of purchased parts use increases with the proper construction of parts that are made, i.e., elements must be made in a way that facilitates the use of a purchased element as an attachment, and thus avoiding manufacture of special construction parts. In order to obtain correct position while assembling the construction it is necessary to connect every element with a pin that is made with a tolerance of H7. For smaller elements such as clamps it is sufficient to achieve the two screws for connecting. Two screws also represent a mini- mum, although in some cases one screw is enough, then it is usually a very small tolerance values of the structural elements. It is important to emphasize the tolerances of the drill hole. With holes for pins they amount to ± 0.01 mm and in all other holes (threaded or passing) the amount of tolerance is ± 0.1 mm. All contact surfaces of structural elements must be processed to a fine surface roughness. Fig. 9 represents the work-holder and the sheet metal griper. Sheet metal that is to be clamped must be aligned with two holes, with one hole to be circular and the other with a wider aperture. In fig. 10 a centering of the circular hole is shown. Centering through a circular hole allows stopping of the sheet meal motion in two directions, but it still is not enough as the plate can rotate around such a centering, so it is necessary to center the sheet through another hole with a wider aperture which centers the sheet in a way that stops the sheet metal movement in one direction, thus the plate motion is completely disabled. Also, during construction of the centering pin attention should be paid so that the cantering pin can be adjusted in two directions with the use of shimplates fig. 11, in our case it is about X and Y direction. This is necessary because it is almost impossible to make perfectly work-holders, i.e., there are always some variations in construction. To the mentioned work-holder belongs also the device (INI), which registers the presence of sheet metal, in our case at this work-holder it is located just on the right side as shown in fig. 12. Checks of referent weld points with the use of computer simulation ensure correct distribution of weld guns in process planning. In this manner validation of whole production project is possible before contacting suppliers or start of production process. Good clamping of two sheet metals given in this example requires the following conditions: – Supports must be constructed in a number of places in order to facilitate resting of sheet metal in such a way that deformations because of it’s own mass are avoided. – Clamps must be set in all the places that are selected as critical and that assure for the sheet metal to be firmly clamped. – It is necessary to center each sheet metal with two centering pins, one of which is centers trough a circular hole and the second trough an extended hole. In our case there are two sheet metal plates that are welded together, which means that it is necessary to set up a total of four centering units. – For each sheet it is necessary to set up a two-INI, which register the presence of the sheet metal plates, in our case it means the existence of at least four INI-a. – On the margins of sheet metal plates it is necessary to set delimiters. Careful account of welding robot motions in accordance with welding targets must be taken into account and all other devices involved in the process of welding to avoid collision. Interaction design knowledge about the characteristics of the environment and operator has to be included in the design. Improvements of constructed work station will be fo- cused on quantity of products, shorter processing cycle times while maintaining product quality. Further investi- gation should be concentrated on process control of gauge errors, and stability of constructed work station. The handling system can also display virtual obstacles in an assembly operation; this is useful in order to avoid collisions and also guidance to the target assembly position. Some consideration on pressures applied to the sheet metal plates during welding are also to be addressed. Control with ap- plication of external sensors is needed for stable and safe interaction when handling robot welding and work-holder station. In long-term solutions the design of intrinsically safe interaction of work-holder station and robots will focus on safety and sophisticated control will provide ...

Context 2

... 11 Centering of the sheet metal trough a circular hole Washers can have different designs, and feature of the washers from the fig. 11 is that it provides three rows of set- ting of screws or pins.  ...