The difference between 3D printing and other manufacturing methods

To produce an object from a 3D CAD model there are 3 manufacturing methods to choose from; Additive manufacturing (3D printing), Subtractive manufacturing (CNC Milling) and Formative manufacturing (Injection moulding). All of these manufacturing methods are CNC controlled and computer monitored with little to no human interaction.

3D printing is another name for additive manufacturing technologies. The toolhead of a 3D printer lays down material only when needed, layer by layer as per the outer surface of the digital 3D model. The process typically works from the bottom and works its way up, building upon each layer.

Almost any shape can be 3D printed when configured correctly for the appropriate technology. Additive manufacturing is typically used to make prototypes and end products, however its possible to use AM to produce low yield mould tools. Setup costs for 3D printing are relatively low compared to other manufacturing methods. 3D printed parts can be manufactured from a variety of material choices like that of other manufacturing processes. 3D printed parts are not as strong as a counterpart manufactured using subtractive manufacturing due to an infill percentage meaning the part is not completely solid. 3D printing using layers would also mean that the object is weakest in the same direction as the print direction.

(AM process line artwork)

Subtractive manufacturing such as CNC milling involves starting with a solid block of material which is larger than the intended physical 3D object. The material is machined away at, material is subtracted from the block to generate the end object. Multiple operations are involved to get the required end result and more complex objects require more operations with different tools. A lot of the material removed from the original block is wastage, however in some cases this can be recycled. A variety of materials such as polymers and metal can be machined with Subtractive manufacturing. This is also used to produce the prototypes and end products with tight tolerances, however it can also be used to produce tooling for production. Tool paths need to be generated by the user using CAM software, this is a time consuming process to program each step increasing the overall lead times. Some end parts can’t be manufactured since the tool must have access to the surface which it’s cutting without colliding with the rest of the part.

(Subtractive process line artwork)

Formative manufacturing such as injection moulding, forming and stamping is used for high volume production of the same part, where each part is identical. This involves the use of a mould tool or stamping tools in combination with robotics to provide unattended automation. Mould or forming tools provides a template for the material that is shaped under heat and/or pressure. Formative materials can be both metals and plastics, with the formative process generating thousands of parts at a low cost in a small amount of time. The start up of costs for formative production is very high due to the complexity of the mould tool and equipment required, however as the units manufactured increases overtime the cost per part reduces. The design of the mould tool has to be carefully considered and design elements such as deep drawn walls and inconsistent wall thickness needs to be redesigned.

(Formative process line artwork).

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