Investigation of Causes of Scrap Occurrence in Thread Cutting on Steel Sleeves for Motorcar Industry

Nonconforming, and for their purpose unusable castings, not fulfilling the requirements of the standard and/or with customer agreed delivery conditions represent scrap [1, 2]. Scrap is manifested in foundries as waste in material, energy and labor. its efficient monitoring and supervision is possible only when the quality criteria have been unequivocally established, not only for the final product but also for single operations. Taking into account harsh market competition, only top quality product can be sold, and that at prices acceptable to customer. Scrap can significantly influence the profitability of production. Therefore, it is of the utmost importance, that causes of scrap occurrence are discovered as soon as possible. The biggest waste is when scrap occurs in final stage of casting production. Steel sleeves for carriers of motor components in car industry have been taken as an example of unforeseen increase in production cost. during the process of die casting of aluminum carriers, steel sleeves have been cast into them, and additionally threads have been cut. it was This paper studies causes of scrap occurrence, wear and breakage of cutters during thread cutting of steel sleeves poured in Al die castings of motor car engine components. It was concluded that the reason for occurrence of problems with thread cutting of sleeves most probably should be attributed to the fact whether hardness value reaches 200 HB or over 250 HB. The most probable reason for over wear and consequently to breakage of cutters and scrap occurrence, although castings display top quality, lies in the fact that the internal diameter of sleeves frequently falls down under minimally allowed tolerances for threaded sleeves.