 Tooling & Metal Part Technology Comparison Tables...
Injection Molds & Metal Parts
The intent is frequently to fabricate injection molds faster and at lower cost than possible with subtractive technology. Rapid tooling is also sometimes used to get an idea of how production tools will perform. These additively-fabricated molds are used to make thermoplastic parts in quantities ranging from a few dozen for testing or prototyping, to in some cases production quantities of a million or more. Additive technologies are also being used increasingly for the direct fabrication of metal parts. In fact, even though many of these methods arose initially as tooling solutions, the majority of items made with them today are end-use parts.
Why Use Rapid Prototyping for Injection Molds?
Making injection molds by subtractive CNC or spark erosion methods is extremely slow and expensive. Skilled craftspeople are in short supply, product complexity is increasing and product cycles are growing ever shorter. This means that an ever larger number of more precise tools have to be created by a declining population of toolmakers. There is therefore a good deal to gain from a process which provides both great time and labor savings and addresses these limitations. In addition, RP offers the prospect for improvement in mold performance beyond anything that can be accomplished with subtractive technologies. The ability to fabricate complex conformal cooling channels to provide better thermal performance, or to use multiple or gradient materials to optimize each portion of a mold for performance and cost, may ultimately lead to a revolution across the entire field. Decreases in cycle times of 20 to 30%, or more, have been achieved using such techniques, for example. Consequently, this application has provided a strong driving force in the development of additive technologies that produce metal parts, as well as in material transfer processes that use additively-fabricated patterns.
What are the Limitations?
The long-term prospect is for the direct additive fabrication of injection molds with the same level of precision and durability as CNC methods. While great strides have been made in that direction, and important time and labor savings are being realized today by RP methods, the technology is still immature. This means that the benefits realized are not universal and must be evaluated for each case. Rapid prototyping injection mold fabrication methods should be considered for projects in which:
- the reduction of time to market is important,
- for prototype and short to medium volume production runs, and
- for parts which may be very hard to machine because of their geometry.
The general limitations of RP methods compared to CNC today are:
- they produce somewhat less accurate and less durable tools,
- may have part size and geometry limitations,
- don't necessarily produce identical parts to hardened tooling, and
- tools may not easily be modified or corrected using typical toolmaking techniques.
These limitations vary both as function of the specific additive technology used and for each individual case. The inability to modify many tools fabricated by RP technology means that making such a tool is frequently a one-shot deal; if it's not right the first time, it may be necessary to scrap the tool and start over. Rapid tooling may lose its advantage compared to conventional tooling methods under those circumstances.
Selecting a Process
Selection of the optimum RP-based process for each case is complex. Among the factors to consider are the final application, production volume, part size, accuracy and material requirements. The descriptions of the available technologies here provide a general guide for selection, as well as places to learn more. One important thing to keep in mind at the present state of the art is that while direct RP tool generation methods may actually offer faster turn-around, one of the indirect processes may offer lower costs and higher accuracy. Another thing to keep in mind is that it's sometimes appropriate to fabricate part of a tool with CNC technology and part using RP methods. The most economic and appropriate process must be selected for each portion of a tool, and not necessarily for the tool as a whole.
Other Technologies
This is not an all-inclusive listing. Additional technologies are being explored in corporate, university and government laboratories. Indeed, several companies, particularly in Europe, are developing proprietary rapid tooling methods for their exclusive internal use in the hopes of obtaining a competitive advantage. There are also a number of methods which have not succeeded commercially over the course of several years, but are still being pursued on an experimental or limited commercial basis.
The great majority of molds today are still made using subtractive fabrication. Market acceptance for additive fabrication-based methods can be expected to increase, but is likely to remain concentrated where the technology offers specific advantages. However, the increased need for faster time to market, as well as more individualized and shorter run products, means that while additive fabrication won't dominate the field, it can be expected to achieve greater acceptance as existing technical limitations are overcome.
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