information process and strengthened the combination between information process and physical  process。 This resulted in numerical controlled (NC) design and manufacturing such as computer numerical control (CNC) processing technology, flexible manufacturing systems (FMS) technology, computer-integrated manu- facturing system (CIMS) technology, and digital simu- lation technology。

However, as illustrated in Fig。 2, the NC design and manufacturing only achieves digital information proc- ess and numerical controlling of tools in the forming process。 The transfer of forming materials in the physi- cal process is still completely passive, not numerical controlled。 Therefore, from this point of view, this ap- proach is still a type of analog forming, or numerical controlled analog forming。

Fig。 2    Illustration of digital manufacturing and anolog manufacturing

Comparatively, RPM technology not only realizes the digital information process, but also the digital physical process。 In RPM, the material-transferring process is based on the piling ability of materials。 Con- trolled by digital information, forming materials are added on-demand, and gradually step-by-step accumu- lated in forming area to shape up the final part which further enhances the flexibility of the forming process。

Thus, from the material-transferring features in the forming process, RPM can be regarded as a complete digital forming technology。 The data processing is very important in RPM process。 Figure 3 illustrates the flow chart of this process。 In the data processing, layered process and algorithm is the kernel for all rapid proto- typing and manufacturing techniques。

1。3RPM family

RPM is a great family, in which each member is defined

Fig。 3    Data processing in RPM process

with a special name according to its special function and application of the formed pieces such as rapid pro- totyping (RP), rapid manufacturing, rapid tooling (RT)[3], rapid moulding (RM), and biomanufacturing (BM)[4,5]。

RP is the first emerging technology in the RPM family。   Its  formed  pieces  are  mainly  used  for    the

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evaluation of the structure, assembly, and color of the designed models, as well as for the customer quoted prices, academic discussions, and in vitro models of prosthetic organs。

When the RP-formed pieces contain other functions (performances) besides the above-mentioned functions such as special mechanical properties, electromagnetic properties, and biological properties, they can be ap- plied into many other fields such as forming mould, di- rect parts manufacturing in aerospace, automotive, household appliances fields, and bio-medicines。 And thus they derive many technical branches in RPM such as rapid manufacturing, rapid tooling, rapid moulding, and biomanufacturing。 Although these branches are in dynamic development, some would be eliminated while some would emerge out, it should be emphasized that all of them are based on the same dispersed- accumulated forming principle。

There are also many other names for RPM technol- ogy in the international community, all are defined from different points of view to emphasize a particular aspect of its features such as: (1) free forming fabrica- tion, or solid freeform fabrication, which means that this forming method needs no special fixtures and moulds; (2) dispersed-accumulated manufacturing, which denotes its fundamental guiding principle; (3) layered manufacturing, which emphasizes the impor- tance of layers in piling up process; (4) material in- crease manufacturing, which denotes the accumulating forming process; (5) direct CAD manufacturing, which denotes that it is directly controlled by CAD    models;

(6) instant manufacturing, which emphasizes its rapid response; and (7) e-manufacturing。 Among all of the features, the most  important  is  that  this  technology is fast and flexible in whole forming process which makes its common name as rapid prototyping and manufacturing。