Rapid Prototyping Versus Machining
Which prototyping method is best?
Two of the most common prototyping techniques in the industry are rapid prototyping and machining. Here we break down the complexities of each process and what advantages and challenges they bring when developing a prototype.
What is rapid prototyping?
Rapid prototyping is the process of making three dimensional physical objects from a digital file, most often by laying down many layers of material in succession. This process is also known as additive manufacturing.
What is machining?
Machining is a process that creates a desired shape by removing unwanted material from a larger piece of material. This process is also known as subtractive manufacturing.
Types of rapid prototyping
There are multiple techniques available for rapid prototyping, with new technologies becoming available regularly. Here are the top four rapid prototyping techniques we use when building prototypes:
SLA - Steriolithography, or SLA, is an additive manufacturing process where UV light is applied to a photopolymer resin causing it to solidify. SLA has the advantage over other rapid prototyping methods of producing parts that are watertight and clear.
SLS - SLS stands for Selective Laser Sintering and involves using a high power laser to fuse a powdered material, such as nylon, into a 3D shape. Since SLS is commonly done with nylon, the parts produced are very strong.
FDM – Fused Deposition Modeling (FDM), involves extruding thermoplastic resin through a nozzle onto a platform. The layers are applied using a cross-wise pattern that hardens as it cools. FDM is what most people envision when they think of 3D printing as it is the least expensive method and easy to use.
DMLS – DMLS, or Direct Metal Laser Sintering, is similar to SLS in that it uses a laser to fuse powder into a solid material. As the name suggest, the difference lies in that DMLS involves using metallic powders. Parts produced using DMLS are durable enough to work as a functional prototype as well as in end-use production.
Types of machining
Various machining techniques have been around for decades, but most fall into three principle processes each requiring a specific tool and experienced machinist. They are:
Turning – Turning or Lathing involves rotating the workpiece on a machine, while a single edged cutting tool remains stationary. The cutting tool is slowly moved parallel to the workpiece’s rotational axis, removing material as it goes.
Drilling – Drilling results in creating a round hole by rotating a cylindrical tool parallel to the workpiece’s axis of rotation. The hole created is equal in diameter of the tool that was used.
Milling – Milling is the process of removing material, using rotary cutters, from a workpiece in a feed motion perpendicular to the rotational axis of the cutting tool. This is one of the most common forms of machining used today.
How does rapid prototyping work?
Regardless of building material or printing method, in order to make a 3D printed object you need to start with a 3D digital model. Most often this model is in the form of a Computer Aided Design (CAD) file built using Solidworks or ProEngineer software. The CAD file is then run through another software that converts the 3D object into hundreds or thousands of 2D slices. The 3D printer then builds the object, layer by layer, using these 2D slices as blueprints.
How does machining work?
In modern prototype development, machining is most often done using a CNC machine, which stands for Computer Numeric Control. In essence, the machine uses computer software to take CAD design models and map out toolpaths, turning the designs into 3D machined parts. The CNC can create parts from a wide variety of materials, in varying types of finishes, with tolerances created to the nearest .0001” from solid material. Unlike rapid prototyping, parts are machined using real materials reflecting the density, finish, and porosity of the finished design. Machined parts can be used for representative testing, models including sliding components where friction is a factor, and for sealed components requiring 0 rings and gasketed surfaces.
Rapid prototyping pros & cons
- Faster than traditional machining methods
- Can make almost any complicated geometry, including a negative space within your object
- Lower resolution than traditional metal machining
- Grain direction matters as the part is weaker across the grain axis
- Tolerance determined by laser or nozzle size. For FDM parts, this is currently .007” thick
- Size limitation is based on machine platform
Machining pros & cons
- Choice of a variety of finishes and materials
- Tighter tolerances down to .0001”
- Real materials and real densities
- Only works from one side at a time. Object needs to be turned and repositioned manually
- Requires a skilled machinist
- Materials and time to machine can be expensive
In conclusion, both rapid prototyping and machining prototyping techniques offer strong advantages and disadvantages to the design process. Things like material, size, design complexity, and cost are all factors that are considered when creating your prototype. This may mean that there is not one specific solution that fits your design and instead multiple techniques are implemented to create your perfect prototype.
Synectic offers a suite of prototyping capabilities from FDM 3D printing to CNC machining in house to keep your project on budget and on time. For more information on how we can help you with your prototyping and design needs visit our prototyping and design pages. If you have any questions about which prototyping would best suit your design, contact us below.