So you need a "Prototype" sample; What’s right for you?

Product designers, application engineers, and entrepreneurs are often in need of initial samples for 3D visual representation of a new component, or to test new components in the application prior to finalizing designs.  These early samples are commonly referred to as "prototype" samples.  Many prototype options are available when the prototype samples are needed. 

The first question you should ask is:  "Do I need samples that are representative of the form and fit of the component I am planning, or do I need samples that are representative of the form, fit and function of the component?" The second question you should ask is:  "How many prototype samples do I need?"

To provide you with guidance for the relative cost of each option, the symbol ($) means the cost is lower with respect to the other options. The symbol ($$$$$) means this option is higher when compared to the other options. Every project is unique and each must be evaluated individually for an accurate cost assessment.  The generic cost estimate is for reference only.

"Form and Fit" Prototype Options  

Commonly referred to as Rapid Prototyping, several alternative methods are used to develop a 3D sample of the component.  These samples are generally for:

• Touch and feel
• Confirm the component features integrate with other components in an assembly 
• Demonstrate new concept samples to a client 
• To verify CAD files prior to tool build 

Products from these fabrication methods are typically made from materials or processes that will not be used for the volume production that is planned for later.  Because of this, a limited level of functional and performance analysis can be performed on the form and fit samples.  Depending on the tolerances, a significant level of flexibility may be needed for dimensional tolerances on form and fit prototype samples. 

SLA (made from a Stereolithography Apparatus). Sometimes called optical fabrication, photo-solidification, solid free-form fabrication, and solid imaging.  It is today the most popular choice for rapid prototypes. 

Stereolithography is an additive fabrication process utilizing a vat of liquid UV-curable photopolymer "resin" and a UV laser.  A 3D digital file (CAD) is used to guide the building of the object one cross sectional layer at a time.  On each layer, the laser beam traces a cross-sectional pattern on the surface of the liquid resin.  Exposure to the UV laser light cures, or, solidifies the pattern traced on the resin and adheres it to the layer below.  Layer upon layer are then completed until the object is fully formed.  SLA samples can be fairly brittle. New developments in material options are becoming more available; one such option resembles Polypropylene as the makers have migrated from acrylic based to epoxy based resin.  Liquid resin costing several hundred dollars per gallon can result in a significant expense for more than one or two samples. One sample  $$ 100 samples  $$$$$

SLS (Selective Laser Sintering) like SLA, is a layering rapid prototyping technique.  It is the second most popular method for obtaining rapid prototype samples.  It uses a high power laser to fuse small particles of plastic, metal, or ceramic powders to create an object.  The laser selectively fuses powdered material by scanning cross-sections generated from a 3D digital file of the part on the surface of a powder bed.  After each cross-section is scanned, the powder bed is lowered by one layer thickness, a new layer of material is applied on top, and the process is repeated until the object is completed.

Compared to other rapid prototype methods, SLS can produce parts from a relatively wide range of commercially available powder materials, including polymers (nylon, also with glass-filler or with other fillers, and polystyrene), metals (steel, titanium, alloy mixtures, and composites) and green sand.  Fine features may not be as crisp as those seen on SLA samples.  If the SLS sample can be made from a similar material as the component being designed, some analysis of chemical and temperature compatibility expected in the application can be studied.  Injection molding includes a high level of packing pressure during the curing phase to promote a greater level of density in the finished product. This packing pressure is something the SLS process will not currently replicate, and performance characteristics of SLS samples made from plastic resins can be much different than samples made from the injection molding process. One sample $$  100 samples $$$$$

FDM (Fused Deposition Modeling) Like SLA and SLS, this method operates on a "layering" principle. A plastic or metal filament is unwound from a coil and supplies material to an extrusion nozzle, which can turn on and off the flow. The nozzle is heated to melt the filament and can be moved in both horizontal and vertical directions by a numerically controlled mechanism, directly controlled by a 3D CAD file.  

At the time of this writing, the greatest selection of materials is available for FDM. Optional materials include a variety of metals, Acrylonitrile butadiene styrene (ABS), Polycarbonates, Polycaprolactone, Polyphenylsulphones, and waxes.  For more delicate features or samples, a water-soluble material can be used for making temporary supports while forming is in progress.  Once the object is formed, this soluble support material is then dissolved in a solution with the assistance of ultrasonic agitation. One sample $$ 100 Samples $$$$$

LOM (Laminated Object Manufacturing) is another rapid prototyping method using a layering system.  In it, layers of adhesive-coated paper, plastic, or metal laminates are successively glued together and cut to shape with a knife or laser cutter.  LOM products are typically lager and more bulky with thicker z-axis wall sections.  It is virtually impossible, for instance, to make a drinking glass using LOM techniques.  LOM samples are sometimes used as casting molds to create a larger number of cast prototype samples.  LOM is being replaced by advancements made in other rapid prototyping methods described here.  One sample n/a 100 samples n/a

3D Printing is another "layering" type of rapid prototyping that is gaining considerable popularity due to its greater speed to create an object, and significantly lower cost of the equipment than other rapid prototype methods.  This type of fabrication uses a device closely resembling an inkjet printer.  Layers of material are "printed" in cross sectional layers using 3D CAD information. These Photopolymer Phase machines use an ultraviolet (UV) flood lamp mounted in the print head to cure each layer as it is deposited until the object is fully formed.  This, technology, is the only rapid prototyping method that allows for creating full color prototypes. It also is recognized as the fastest and least expensive of all rapid prototype methods.  The trade-off is fewer material options at this time.  One sample $   100 samples $$$

"Form, Fit, and Function" Prototype Samples

Sometimes called Rapid Injection Molding, this fabrication method often uses 3D CAD data to create a mold for producing the injection-molded prototype.  The resin used to create the samples can be same as the material intended for the application, or groups of alternate resins can be used for performance comparisons.  This method is preferred when: functional test performance is needed or large groups of assembly system pilot samples are required.  

Steel, aluminum, and a variety of plastics can be used for the mold.  We see little relative difference between the cost for steel, aluminum, and plastic mold stock.  We therefore prefer steel as it more closely replicates the conditions seen in the production mold, and steel is much more durable if additional unplanned samples become necessary.  Initial mold costs are greater than a single SLA or SLS sample, but once initial mold costs are invested the incremental cost of molded samples is significantly less than rapid prototype samples.  Rapid injection molded samples can be used for much more detailed form, fit, and function analysis.  Injection molding process information can also be captured from the prototype samples that may be valuable for enhancing the design and performance of the production process and the production mold. 

The mold is generally developed to fit in a multi-use frame unless size constraints dictate otherwise.  Mold development can be as little as one week to as much as six weeks based on complexity of the project.  A significant trade-off exists between tolerances and the mold construction timeline.  High precision tolerances may complicate the mold development, significantly increase mold costs, or may require additional time to "fine-tune" dimensions prior to samples being available. 

One sample $$$  100 samples $

Pull-Ahead Production Mold

When a multiple cavity production mold is planned, the production mold is constructed but only one of the cavity inserts is completed.  Once testing and design validation are complete, the remaining production cavities are then finished to complete the production ready mold. This option essentially eliminates much of the cost of a separate prototype tool, but increases the cost and delivery for the production tool. 

Summary

Many prototype options are available to you, and every project is unique; so, it makes sense to partner with a company that has the experience to discuss the advantages and disadvantages of each option with you. 

We can get started today.  If you would like to talk to one of our project support staff, please call us at: 806-474-1000 or e-mail us at sales@indmolding.com.

Industrial Molding Corporation
616 East Slaton Road
Lubbock, Texas 79404