Cast iron machining

Surface plates (Fig. 3.7) are smaller reference surfaces and are placed on a bench for use with smaller workpieces. For general use, both surface tables and surface plates are made from cast iron machined to various grades of accuracy. For high-accuracy inspection work and for use in standards rooms, surface tables and plates made from granite are available. 

Fig. 1.21. Coefficient of merit as a function of d/R and y/. (a) Bonded machine, down milling, (b) Bonded machine, up milling, (c) Cast-iron machine, down milling dotted line represents experimental conditions, (d) Cast-iron machine, up milling dotted line represents experimental conditions.

Relative Dynamic Performance of Bonded to Cast-iron Machine under Test and Working Conditions... 

Having explained the technique of dynamic assessment for the case of the bonded machine, for the cast-iron machine all that is needed is a brief summary of experimental and theoretical results. Finally, an evaluation of relative machine quality from the chatter point of view will be given. 

Figure 1.17(b) shows the direct and cross receptances of the cast-iron machine. From these the operative receptances are found, presented in Fig. 1.18(c) for the slot cutter and Fig. 1.18(d) for the helix cutter. The particular conditions to which these refer are specified in Table 1.6. 

The conditions are reversed with the unstable lobes corresponding to the low-frequency mode (chatter frequency between 120 and 150 Hz). For this mode, the only one of practical importance, the negative in-phase amplitude of the bonded machine is substantially smaller than that of the cast-iron machine and hence the former is superior from the chatter point of view. This will become even more obvious from the stability and CoM charts. 

Fig. 1.25. Theoretical and experimental stability charts for cast-iron machine, (a) Theoretical chart (slot cutter), (b) Experimental chart (slot cutter), (c) Theoretical chart (helix cutter), (d) Experimental chart (helix cutter).

As a further illustration, a sample of the cut obtained by the helix cutter, on both the bonded and cast-iron machines, shown in Fig. 1.26, is illustrated in Fig. 1.27, showing large width of cut at which the machine starts to chatter, as compared with the cast-iron machine. 

An inspection of the CoM charts for the bonded and the cast-iron machines shows clearly that the former was dynamically superior to the latter. For instance, in the case of down-milling the CoM of the bonded machine ranged between 12 and 28 N/m as compared to 1-10-5 N/m. For up-milling, the respective ranges of the CoM were 8-29-5 as compared to 1-10-5 N/m. For very shallow cuts and y/ = 60° the cast-iron machine had a slightly better performance but for any other conditions the bonded machine was considerably better. 

Fig. 1.27. Machined specimens for bonded and cast-iron machines, (a) By bonded machine, (b) By cast-iron machine.

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