To “Add” or to “Subtract?”

To “Add” or to “Subtract?”

Should I use additive, or subtractive manufacturing processes to make my precision part? That is an important question facing many product designers, engineers, inventors and part buyers these days. It’s also a key question facing manufacturing companies, as they consider equipment investments to diversify their service offerings.

If you didn’t know, additive manufacturing is the process of adding materials, layer upon layer, until the part is completed. And subtractive processes remove material from a solid piece of material, layer after layer, until the part is completed.

Other names for additive manufacturing are: 3-D Printing, Rapid Prototyping and Direct Digital Manufacturing.

If you need a precision part, there are many factors to consider when choosing between additive and subtractive manufacturing processes. The biggest factors to consider are:

• The design of your part
• The material requirement
• Dimensional tolerances needed
• Surface finish needed
• Quantity needed

Subtractive manufacturing processes have been around a long time. In fact, subtractive processes were used to manufacture the first additive machines! That’s ironic.

The same can be said about man-driven (or manually driven) machinery, which was used to make the first automated machines to replace man-driven machines. That’s ironic too.

There is an obvious need for 3-D printed parts, which is why it is becoming main-stream. Very complex part designs can be made with the best additive machines on the market.

However, before you can 3-D Print a part, you must first develop a computer generated solid model. Many software programs are available to generate a solid model. The solid model is required before you can print a part from it. And the same solid model file can also be used during conventional machining, although it isn’t always required.

A majority of parts that come across my desk aren’t overly complex, and can be made by utilizing conventional subtractive type machining processes.
With conventional machining processes, we can manufacture a prototype, and quickly transition into full-scale, cost effective and efficient production output.

The raw materials we can machine from are endless too which generally include aluminum, stainless steel, titanium and plastic. Initially, additive machines could only use plastic materials, but some additive machines are now capable of printing out metal parts.

You don’t always need to choose between additive and subtractive. For certain parts, we can actually 3-D print a part, and then run subsequent machining operations to finish the part.

3-D printers are now sold directly to consumers, but that doesn’t mean that they are a one size fits all solution. Inexpensive 3-D printers are very limited in capability.

I receive many calls from new prospective customers and they are “sure” that they want a 3-D printed part because they’ve seen it in the news recently. And 9 times out of 10, we’ll end up making their part with conventional machining processes.

There are advantages and disadvantages with both methods of manufacturing. It is best to consult with a company like mine that has both additive and subtractive capabilities in-house.

Source: Jason M LaRock
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