How it’s made

So, how do you cut a drive sprocket? A machine tool show gives us some idea how spare parts are manufactured.

Consider an excavator, or a bulldozer, or any other piece of construction equipment for that matter. They are each made of tens of thousands of parts, but have you ever wondered those beautifully machined parts come from in the first place?

Of course, most of the structure is either pressed or cast, and most of us have a concept of how this might be done, but what about components that are hewn from a block of solid metal? You might be familiar with the lathe, but how on earth do you cut, say, a gear for a differential?

We were so fascinated by this subject, we hopped on the next available plane to Taiwan, where the world's largest exhibition of machine tools was being held. At the event, around 900 exhibitors showed off their wares. Don't forget, this event was just for machine tools, not actual machines, so clearly manufacturing is still very big business in the Far East, even with the downturn hitting Taiwan like a ‘financial tsunami' in the words of the island's prime minister.

Machining Centres

One of the first principals of shaping metal is that it is all about removing excess material, as precisely and efficiently as possible. It might sound obvious, but very few machines ever try to form a work piece by adding material - with the possible exception of rapid prototyping which involves material being formed by a chemical process.

Principals

The three principal machining processes are classified turning drilling and milling. Other operations falling into miscellaneous categories include shaping, planing, boring, broaching and sawing Turning operations are operations that rotate the workpiece as the primary method of moving metal against the cutting tool. Lathes are the principal machine tool used in turning where the tool stays still and the workpiece turns, while in milling, the tool turns while the workpiece stays still.

Obviously, you will know what a drill does, but in engineering terms a ‘drilling operation' is where holes are produced or refined by bringing a rotating cutter with cutting edges at the lower extremity into contact with the workpiece.

Drilling operations are done primarily in presses but not uncommonly on lathes or mills.

There are other miscellaneous operations that can be done with machine tools, such as burnishing, which is the generally undisarable effect of two surfaces rubbing against each other. However, there are a few instances where burnishing can be used in the manufacturing process. An unfinished workpiece requiring machining will need to have some material cut away to create a finished product.

A finished product would be a workpiece that meets the specifications set out for that workpiece by blueprints. For example, a workpiece may be required to have a specific outside diameter. A lathe is a machine tool that can be used to create that diameter by rotating a metal workpiece, so that a cutting tool can cut metal away, creating a smooth, round surface matching the required diameter and surface finish.

A drill can be used to remove metal in the shape of a cylindrical hole. Other tools that may be used for various types of metal removal are milling machines, saws, and grinding tools. More recent, advanced machining techniques include the electrical discharge machine (EDM), electro-chemical erosion, water jet, or laser cutting to shape metal workpieces.

Although a machine shop can be a stand alone operation, many firms who run and maintain their own heavy equipment maintain their own internal machine shops.

Machining requires attention to many details for a workpiece to meet the specifications set out in the engineering drawings or blueprints. Beside the obvious problems related to correct dimensions, there is the problem of achieving the correct finish or surface smoothness on the workpiece.

The inferior finish found on the machined surface of a workpiece may be caused by incorrect clamping, dull tool, or inappropriate presentation of a tool. Frequently, this poor surface finish, known as chatter, is evident by an undulating or irregular finish, and the appearance of waves on the machined surfaces of the workpiece.

CNC Control

CNC, or computer numerical control, is vital for just about any tool used in component manufacturing in modern times. Systems vary, but the computer will always pinpoint the machining heads to an exact position in the work area.

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