Metal working – Method of mechanical manufacture – Prime mover or fluid pump making
Patent
1998-05-26
1999-10-19
Cuda, Irene
Metal working
Method of mechanical manufacture
Prime mover or fluid pump making
29888072, 29888075, 29888076, B23P 1506
Patent
active
059668075
DESCRIPTION:
BRIEF SUMMARY
This invention relates to manufacturing piston rings.
Piston rings are currently produced using one of two established methods.
The first method comprises "parting off" a cast tube into individual sections to form piston ring blanks from which piston rings are produced. The second method comprises casting the individual piston ring blanks to near nett shape using the principle of investment casting.
EP-A-0,436,996 discloses a method similar to that of the above mentioned first method, in which a tube is cast, machined and then parted into a plurality of piston rings which are then individually gapped.
An alternative method is disclosed in U.S. Pat. No. 4,713,867 wherein a plurality of individual rings are gapped, compressed, resealed and then assembled in a suitable device whereupon the individual rings are collectively machined.
Certain functional properties of piston rings such as their "diametric load" and "free shape" properties currently require them to be produced from individual blanks to the exclusion of other currently available and cost effective manufacturing techniques.
The main disadvantage of processing the above blanks arises from the need to handle them individually, or in small groups, for a majority of operations. Handling times significantly contribute to the total floor-to-floor time of each batch. Also, in general, many handling activities require a high level of diligence and certain acquired skills which, when relaxed or ignored, can lead to the manufacture of a non-conforming product.
Another disadvantage relates to the total setting and transportation times associated with blank processing and the sequential steps thereof. Discrete machining operations are almost always performed on operation-specific machines, and if a small to medium sized batch is to be processed, a considerable proportion of the total lead time will be spent in setting up the job and preparing it for transportation. This can affect the product delivery dates and profit margins.
Other drawbacks also exist. Numerous machines are required to perform the various machining operations and these in general require relatively high manning levels. Moreover, much of the plant has to be dedicated to specific tasks associated with piston ring production, making it expensive to maintain whilst reducing its potential for flexible manufacture. Furthermore, the planning, scheduling and progressing of work is difficult and time consuming whilst associated control and administration functions require high levels of staffing, thereby significantly contributing toward indirect costs.
The present method seeks to improve manufacturing efficiency, by eliminating, or at least reducing, the disadvantages listed above. In particular, the present method seeks to increase the opportunity for automation of the manufacturing process and to enable large numbers of piston rings to be manufactured on a continuous or small batch production line basis, if required.
In accordance with the present invention, therefore, there is provided a method of manufacturing piston rings from a tube blank, the method comprising the steps of: partially closed and said tube adopts a stressed shape; shape upon removal of said force; stressed shape piston rings;
E. releasing each of said individual stressed shape piston rings such that each of said piston rings returns to its unstressed shape.
In one embodiment, the method further comprises the step of: of said stressed tube.
The skilled man will appreciate that the term "stressed shape" refers to the shape adopted by the slotted tube blank when the force of step (B) is applied to at least partially close the slot. Similarly, the "unstressed shape" refers to the shape of the slotted tube blank when that force has been removed.
As will be further elaborated hereinafter, the present method exhibits a number of advantages over the prior art. In particular, the production and machining of a tube blank is significantly easier than the production and machining of a plurality of individual piston rings. The prior art met
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patent: 4651395 (1987-03-01), Tanner et al.
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