What determines the quality of prototypes?
How is CNC machining different from other rapid-prototyping processes?
What are other benefits of CNC machining?
Can I specify special materials for CNC machining?
What are the disadvantages with CNC machining?
With the benefits in CNC machining, why is it not as common as other RP processes?
How do I know if CNC machining is suitable for my application, and will it cost me an arm and/or leg?
What are the differences in various rapid-prototyping processes?
Most rapid-prototyping (RP) processes involve the building of a model in layers (imagine an object being sliced into thin layers like ham, and then assembled together). When a CAD file is input into the software controlling the rapid-prototyping machine, it calculates the profile and area of each layer, and then duplicates the layer in the RP machine.
Generally, the major difference is in the material used to create the models. SLA (Stereolithography) uses liquid polymer resins and cures them into solids with ultraviolet rays. FDM (Fused-Deposition Modeling) lays each layer with strands of near-molten ABS or PC, and SLS (Selective Laser Sintering) uses a CO2 laser to fuse powder based materials together to create a solid prototype.
What determines the quality of prototypes?
The quality of the prototypes created is dependent on the thickness of the layers created (the thicker it is, the less accurate) and the properties of the material used (dimensional stability, reflection of actual material etc.) SLA creates somewhat fine and accurate layers, but the resins are susceptible to shrinkage and warpage over time. FDM parts have better dimensional stability, but the surfaces created are less refined due to the thickness of the ABS strands laid. SLS creates rather porous models due to the powder based material it uses. In addition, the materials used in typical RP methods are only approximate to the actual materials used in production.
How is CNC machining different from other rapid-prototyping processes?
Unlike the building of layers in other RP processes, CNC machining cuts away at a solid block of material to create the final model. The material used in CNC machining can range from soft materials like foam and plastic to hardened steel. Therefore, it is by far the best method for functional testing of prototypes when actual materials used for eventual mass production are utilized during the machining.
What are other benefits of CNC machining?
The most evident advantage is the tolerance and accuracy exhibited by CNC machines. The paths taken by the tool bits do not have to follow a 2D profile like other RP processes. For example, it can cut away at a material up and down a sloping profile in any degree specified. Each cutting path can also be programmed to be as close as 0.1mm apart (in comparison, SLA creates only horizontal layers of 0.25 mm at best). The implications are profound- CNC parts require little or no secondary finishing work, and parts fit together the way they are designed.
Can I specify special materials for CNC machining?
If the plastic material requested is not common ABS, PC, Acrylic, Nylon or Delrin, or if a specific color is requested, it is still possible by injection molding a block of your specified material and then CNC machining the block. Contact us for details.
What are the disadvantages with CNC machining?
In essence, the only disadvantage of CNC machining compared to other RP processes is in the lead-time. Since CNC machining involves CAM programming, much time is spent programming toolpaths- the more complex a part is, such as deep 3D surfaces, bosses and snap details, the longer it takes to program. Also, if materials harder than plastics are used, longer periods of machining time are required. An item such as a cellphone requires only a few hours on an SLA machine, but may take up to a full day to complete with CNC machining. However, with the quality and accuracy of the prototypes produced, this is only a minor inconvenience.
With the benefits in CNC machining, why is it not as common as other RP processes?
Unlike CNC machining, the entire prototyping process in other RP methods is controlled by the machines and their software. It is efficient without much human input, and models are created quickly and predictably. They can be operated in an office environment, as they are 'clean' in their processes, without generating dust, particles and waste typical in CNC machining. Therefore, most companies in the U.S. prefer the use of these modern RP methods in creating prototypes.
CNC machining, on the other hand, is a more traditional prototyping method. It requires plenty of care and expertise in order to create good prototypes. Factors like CAM programming- such as the types of milling bits to use, travel and spindle speed for cutting different materials, methods to reach undercuts and various other issues have to be controlled by experienced machinists and programmers with years of training specific to CNC prototyping.
Along with the transfer of most production and assembly of consumer and industrial products to countries with lower labor costs, the tool and die industry which supplies CAM programmers and machinists is gradually dwindling. This is perhaps the main reason for the shortage of CNC machining in America.
How do I know if CNC machining is suitable for my application, and will it cost me an arm and a leg?
If you want a prototype that is as close a reflection to the actual production part as possible, then CNC machining is definitely the choice. However, if all you require is a prototype for general design verification, then other RP processes with shorter turnaround times are probably more suitable. It is important to note that SLA parts require much more hand finishing (post processing) to create a part. Small details or features are easily sanded down or completely removed during this process. Parts which are CNC machined require very little to no post processing, so small features stay on the part and do not end up as dust on the floor.
It is difficult to gauge the cost of your part without reviewing the design. A simple 2D machining of a flat piece of material can be cheaper than SLA, whereas a part with plenty of details can be twice as much. Unlike other RP methods where cost is calculated at the prototyping time and amount of materials used, cost for multiples of the same part for CNC machining is discounted, as time is saved in CAM programming. Send us your file or images, and we'll gladly send a quote right away.
*For a limited period of time, we are giving away $1000 worth of CNC prototypes free (excluding material and shipping costs) for first time customers. Limited to registered companies.
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