Process, Materials, and Measurements

Manufacturing Processes 73

RAPID PROTOTYPING

Overview

Selecting a method of prototyping a three-dimensional product is depend-

ent on multiple factors, including purpose, cost, and time available to produce it. In

choosing a process, consider if it is for an appearance model, an ergonomic study,

or a mock-up of a mechanism. For many applications, a fast, inexpensive prototype

with low finish level works very well, but in some cases, a realistic representation

is critical.

3D Printing

On a vertically articulating platen, a layer of wax, ink, or glue is printed

on a thin layer of build material such as starch or plaster, which then solidifies and

hardens. The configuration of each printed layer is determined by a 3D CAD data

file. The platen indexes down and another layer of build material is laid across the

previous one, resulting in a thicker combination. This process is repeated many

times until the entire three-dimensional part is built. The print material is usually

available in different colors, and in some devices, multiple colors can be printed

in a single part. Some materials require a secondary process, such as impregnating

the part with wax, glue, or resin. Although these processes are relatively inexpensive

and fast, the finish and resolution can be low.

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A Thermo-Jet wax-based 3D printer

Courtesy of Altitude, Inc.

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74 PROCESS, MATERIALS, AND MEASUREMENTS

Computerized Numerical Control (CNC)

A process in which parts are produced using

a CNC machine tool to cut the part from metal, plastic, or composite stock. Starting

with 3D CAD data, a milling sequence is developed that performs the actual machin-

ing. This sequence may use one tool for the entire milling, or may require tool

changes to achieve finer details and surface quality. Depending on the shape of the

object to be machined, one or more fixtures may be required.

The primary advantage of CNC prototypes is that they can be produced in the exact

material planned for the final product. This process results in the creation of fully

functional prototypes that can be used for testing in the planned product environ-

ment. The primary disadvantage of CNC prototypes is that the time required and

the cost of the prototype is highly dependent on the size and geometric complexity

of the piece.

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Courtesy of Scott Models

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Manufacturing Processes 75

Fused Deposit Modeling (FDM)

This

process is embodied in a small desktop

machine that may run in an ordinary

office environment. Based on a 3D CAD

data file, the machine builds up thin lay-

ers of liquid resin one after another. As

each layer hardens, the next is added.

When the build is complete, the proto-

type is removed from the build platform

and the support material is removed.

FDM systems often allow different mate-

rial and color choices. FDM prototypes

are not suited for highly finished parts

or as master patterns because of the

poor quality and resolution produced.

Laminated Object Manufacturing (LOM)

A process that involves laminating

sheets of paper or plastic that have been

laser-cut to a specific shape based on a

3D CAD data file. The sheet material in

roll form advances to the cutting plat-

form, and a laser beam cuts one layer

of the desired shape. The material

advances, and an uncut layer is heated

or pressure-laminated onto the previous

layer, where it is then laser-cut. The

process is repeated until the object

is formed. The process is inexpensive,

but the finish level is low.

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Roller

Laser Cuts

Sheet Material

LAMINATED OBJECT MANUFACTURING (LOM)

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