3 Types of Manufacturing - Additive, Subtractive, and Forming

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Most of us identify manufacturing processes by the equipment used. But manufacturing is also identified in a broader sense, by the way, the manufacturing is being accomplished. A single way a product is produced can be done by a variety of machines and tools.

This article will describe three types, or ways, of manufacturing a product; additive, subtractive, and forming.

What is Additive Manufacturing?

Think of an artist painting a bear on a canvas. What is the process being used to make the picture of the bear? Paint is being added to the canvas to make the form of the bear. Actually, a variety of colors of paint are being added on top of each other to give the illusion of the different parts and features of the bear. So painting is an "additive" process of creating art.

3D printing is an additive process of manufacturing. That is why it is referred to as additive manufacturing. Material is built up layer by layer until the complete part is made.

Some additive processes use a liquid material, others use material in a powder form. A variety of materials, both plastic, and metal are available to provide the unique attributes needed to satisfy the engineering requirements of the part.

Advantages of additive manufacturing over others are the speed, low labor cost, customization ability, and the ability to make highly complex geometric designs. Disadvantages include the less-competitive cost of high-volume production runs and limited accuracy and tolerances.

What is Subtractive Manufacturing?

Now think of an artist who is a woodcarver. How do they form a bear out of wood? They start out with a block or log, of wood. Then they take a tool, which is sometimes a chainsaw, and remove, or "subtract", wood until they have the form of a bear.

CNC machining is a prominent process of subtractive manufacturing. A product starts out as a block of material large enough to make the part. Through a milling process, cutting tools remove material from the block until the finished part is made.

3-axis CNC machine: A 3-axis CNC uses a combination of three directions, known as the X, Y, and Z axes, to produce a part. The CNC's table moves back and forth, side to side, and the spindle holding the cutting tool moves up and down. Work can only be done on one plane of the block at a time. Then the machine has to be stopped and the block rotated to a new position if the part requires work on another plane.

5-axis CNC machine: A 5-axis CNC machine is able to work on more than one plane without the need to readjust the blank. The table is able to move into a vertical position and the spindle holding the cutting tool can move into a horizontal position. 5-axis CNC can accomplish very intricate work.

One benefit of CNC machining is the cost-competitiveness of producing parts in volumes of several hundred. The making of the same part can accurately be duplicated over and over. Critical tolerances can also be achieved.

Disadvantages include the labor cost involved in the setup process or the repositioning of parts. Skilled machinist and operators are required. Also, you must pay for the amount of material needed to start the process, not the material left after the part is finished. The complexity of part design is also limited.

What is Forming Manufacturing?

Now suppose a toy company wanted to make a collection of little forest animals for kids to play with. The high volume of toy bears needed would be best made through a forming process. A mold with the design of a bear would be filled with liquid plastic, rubbery material. Once cooled, the mold is opened and the toy bear removed.

Injection molding is a way to manufacture goods using the formative process. A mold is made in the form of the part needed. Melted plastic is forced into the cavity of the mold. The material cools and hardens and takes on the form of the mold's design. Then the newly formed part is removed and the mold refilled.

A major advantage of injection molding is the ability to produce thousands of identical parts at a low cost per unit. The downside of injection molding is the time needed and the expense of making a mold. Molds can cost thousands, and even tens of thousands of dollars, depending on the complexity of the part. This would make the production of one or just a few parts extremely expensive.



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