Machining: Buying Guide

General Information

Machining is a broad category that encompasses a range of processes, materials, and terms. In its most basic form, machining involves the use of a machine tool, such as a mill or a lathe, to mechanically alter a material to create the desired end-product. Materials can include wood, plastic, and various types of metal, and process machines can range from basic manual turning devices to complex computer numerical controlled outfits. Modern machining can be broken down into several common types: chemical machining, conventional machining, electrical discharge machining (EDM), and screw machining.

Types of Machining

Chemical Machining

Chemical machining can refer to processes such as photo-chemical machining (PCM) and metal etching and finishing.

Processes and Applications:

• PCM can be used on an array of metals and alloys, under 0.100 inches in thickness, to produce products and prototypes such as linear encoders, laser mirrors, and screened meshes.
• Etching and finishing can be applied to gaskets, metal spacers, and a wide range of aerospace components.

Materials and Other Services:

Common materials include stainless steel, aluminum, bronze, copper, and brass. Other services can include computer numerical control (CNC) precision engraving, and customized processes, as offered by specific companies. Typically, chemical machining can produce components with very tight tolerances.

Conventional Machining

Conventional machining typically refers to manual machining processes, wherein an operator oversees lathe, mill, or drill press. Computer numerical controlled (CNC) processes, sometimes referred to as non-conventional machining, are termed such because of their dependence upon a computer in place of an operator.

Processes and Applications:

Basic machine processes, such as milling and drilling, can be conducted with conventional machining.

Materials:

Conventional machining materials include a wide range of wood and metals, and work specifications vary according to machine type and company services.

Electrical Discharge Machining (EDM)

Electrical discharge machining uses electrical discharge as the primary tool with which to shape or otherwise alter a workpiece. There are two general types of EDM: sinker and wire.

Processes:

• Sinker EDM takes place when both the workpiece and the primary electrical discharge source (an electrode) are submerged in insulating fluid, and connected to a power source. As the two components are moved closer together, the power source causes the electrode to generate sparks, which cut away at the workpiece.
•  Wire EDM involves feeding a brass wire through the workpiece. The workpiece is then submerged in dielectric fluid and connected to a power source, which induces electrical discharge.

Applications:

EDM is commonly used in mould-making, as well as to generate prototypes in industries that require highly specific parts, such as aerospace and automobile industries. EDM is also used for small hole drilling. Short product runs are well-suited to EDM.  Sinker EDM is typically used to achieve 3D geometries. Unlike sinker EDM, wire EDM is not typically used to create 3D geometries but can yield intricate and precise parts. It is also a preferred EDM process for generating products with low residual stress.

Screw Machining

Screw machining is a metalworking process used to generate high-volume runs of small parts. Essentially, screw machines are automated, CNC lathes, that create turning components, such as threads and screws.

Processes:

Applications and Materials:

Relevant Terms

Tolerances or Specificity:  These terms indicate the margin of precision for a given product. Some products require less specificity, and thus have a greater margin of precision; others require precision manufacturing because the end-product’s measurements or geometry must fall within a very slim margin, and are said to have tight tolerances.

Product Runs: With certain kinds of custom and precision machined parts, only a small amount of the designated product needs to be manufactured, so a short production run is appropriate. However, when products need to be mass produced, a long production is typically preferred.

Measurement: Depth, width, length and thickness are key measurements to consider in terms of material and a given workpiece. Additionally, certain machines may be designed to only work within certain ranges of these measurements, so it’s important to predetermine machine parameters before committing to a specific kind of machining.

Material Considerations

Equally important as determining the kind of production run, a product’s material can greatly influence the kind of machining used to generate a given process. Some machining processes are more well-suited to metal work, where as others favor wood or plastic. Knowing how a material responds to machining can also aid in proper material selection, resulting in an end-product that can meet tight tolerances.