Design of Punch and Die for Trimming Operation – Mechanical Projects
Versatility of the Manufacturing sector demands the production of Special Purpose Machines for increasing productivity, reducing machining time and human work force. Raw castings often contain irregularities caused by seams & imperfection in moulds, as well as access ports for pouring material into the moulds. A special purpose trimming machine can be used for removal of fins from castings rather than conventional manual grinding. This requires customized punch and dies according to the workpiece. This paper mainly deals with design of punch and die in a trimming machine for fettling of a differential bearing cap casting. Parameters are selected considering the geometry and material of the fin.
A differential is located between the front and rear axles of an automobile. It is responsible for transmitting appropriate amount of power to the drive wheels during cornering. The differential is supported by a bearing system. Differential Bearing Caps serve as an attachment between the bearings, axle housing and the differential. These Differential bearing caps are mass produced by casting process. After the castings have been removed from the mould, the runners, & gates are removed. But even after shot blasting some extended projections or fins are observed on the finished product.
Trimming is basically a process in which the unwanted, excess or irregular features are removed from a part. Usually trimming is the last operation carried on the part after which a finished part is formed. A trimming machine basically consists of a punch, punch holder, a die, die holder & a hydraulic system to provide the required force to the punch for trimming.
Die is a specialized component of a press, widely used in manufacturing industries to shape or cut the material. A die may be considered analogous to the female part in a complete tool assembly for producing work in a press. Similar to moulds, dies are also custom made according to the component they are used to create. Die block may be considered as a plate or block which encloses a die cavity. A Die set assembly consists of a lower and upper shoe, two or more guideposts and guideposts bushings. The bolster plate is used to support the lower shoe of a die set. The bolster plate is a thick plate mounted on the press bed, which is turn is used to locate and support the die assembly. The dimensions of the bolster plate are generally in the range of 5 to 12.5 cm thickness. The die block is supported by the lower shoe. Also the guide posts are mounted on it. The upper shoe is a part of the die set which contains the guideposts bushings. (Shrama, 2009).
Casting is the process of manufacturing metal or alloy parts. The parts of the desired shape are produced by pouring the molten metal into a prepared mould. Then metal is allowed to cool & solidify. The solidified metal piece is known as casting. Raw castings often contain irregularities caused by seams & imperfections in moulds, as well as access ports for pouring material into the moulds. Further, machining of the raw castings is required which involves cutting, grinding, shaving, or trimming away these unwanted bits this process is known as Fettling.The part i.e. Differential bearing cap is manufactured by casting process. After the castings, have been removed from the mould, the runners, & gates are removed. But even after shot blasting some unwanted thin fin of about 1.5 to 2.0mm thickness along its perimeter is observed. So, it is required to cutoff these extended fins from the component in the finishing process.
Design of Press tool for trimming of Differential bearing cap is developed by following the fundamental die design principles. The output received is;
- Output product having perimeter 440.8 mm and the required cutting force is 29.4 tons. So it suits for above 30 ton press machines.
- It is seen from the calculations of actual cutting forces, that as the shear on the die increases the cutting fore reduces.
- Shear of 1t, 1.5t, 2t and 3t were considered for the die. And by comparing the results a shear of 1.5t is suitable for the die as the cutting force lies within the range of available press tonnage capacity.
- More parts can be trimmed simultaneously if the shear on the die is maximized, as the cutting force required is less, but increasing shear also has some limitations.
- The tools generally made from steel alloys. Based on carbon composition they are classified in P type, D type, H type of all D type is having more carbon percentage which indirectly possess more strength. They are mainly used for making of tools
Reference /Download :https://inpressco.com/wp-content/uploads/2017/05/Paper1250-54.pdf
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