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Frequently Asked Questions

FAQ Category: Prototyping

What are the prototyping options with a design intended for die cast production?

Beyond 3D computer product modeling, there is a wide range of prototyping options for eventual die casting. They include prototype parts produced by conventional machining from stock of the same alloy family; by CNC machining directly from CAD files; by one of several of the new rapid prototyping (RP) techniques including Fused Deposition Modeling (FDM) or 3D printing; and by creating an RP or conventionally modeled master for plaster molded or investment cast prototypes. Gravity cast prototypes are sometimes used. Since only production from an actual die casting die can yield a part with precise die cast characteristics, a single-cavity prototype die is the most thorough approach to critical product performance evaluation, although the alternative requiring the greatest prototype investment and lead time. Today's most widely accepted prototyping for metal parts, CNC machining, and newest RP prototyping process, FDM, are discussed below. The limitations and prerequisites for using various prototyping processes for functional evaluations prior to die casting die design are discussed in Technical Bulletin (No. 022), "Prototyping for Die Casting," (available in the CWM Resource Center), and in the NADCA Product Design for Die Casting Sourcebook, available through CWM. E-mail sales@cwmtl.com or call 630-595-4424 for more information.

What are the advantages of using CNC machined prototypes for a design intended for die casting?

Developments in 3D-CAD, CAM and CNC programming have made the machining alternative increasingly desirable. Parts can be CNC machined from wrought or sheet stock, working directly from customer CAD files, depending on the type and accuracy of the files. After transfer to a CAM program interfacing with specialized CNC workstations, total machined prototype lead times can often approximate rapid prototyping production scheduling. Validation of form and fit is assured and virtually all functional tests can be performed, with the prototype capable of withstanding the most extreme handling. Many multiple prototypes can be produced in the same time frame at reasonable additional cost. CNC machining can produce parts in metal alloys of the type to be die cast, to near identical part weights and to the specified die casting tolerances with precise details. For Al 380 die castings, A1 6061-T6 aluminum plate is generally used for CNC prototypes. For Mg AZ91D die castings, AZ31 Mg plate is recommended. Zamak 3 stock is available to prototype Zamak No. 3 zinc die castings. Planned post-castng coatings and finishes can be applied to machined "hogouts" to closely approximate the appearance of the proposed die casting.

What are the advantages of using Fused Deposition Modeling prototypes for a design intended for die casting?

The rapid prototyping process called Fused Deposition Modeling (FDM) enables the production of far stronger RP prototypes in durable ABS plastic, directly from STL design files. FDM parts are built and bonded, extruded layer by layer, from 3-D computer data. An FDM prototype can be geometrically complex and produced to tolerances of ±0.005 in. (±.127mm). Because of the strength of the ABS plastic part, it can be evaluated rigorously for form and fit and used in many functional tests. Most RP methods often have difficulty reproducing very tight toleranced sections, such as in sections containing ribs, bosses and holes; in these cases precision CNC machining can be performed on the strong FDM ABS part to the required critical specifications. FDM prototypes are being generated by CWM on every new die casting project to expedite production and shorten total lead times: FDM models help assure that die designs result in first-piece success and aid in the simultaneous construction of die cast tooling, trim dies, machining fixtures, finishing masks, and any required subassembly gauges or fixtures. FDM parts can also be used as masters for investment casting in an alloy approximating the properties of the planned die casting.

What exactly is a prototype die and when should it be used?

Prototype dies are usually requested by a customer to produce a small number of castings under precise die cast production conditions where thorough functional product testing is critical before committing to full production dies. Lesser grades of die steel can be used in prototype dies. Where full functional testing is not required, a range of lower cost prototyping options, with lower lead times, are available.

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