20 questions about machining

Machining is the process of using a machine tool to cut, shape or remove material from a workpiece by cutting off chips. Machining is called subtractive manufacturing, in contrast to additive manufacturing (3D printing). 

The three main machining operations are drilling, milling and turning. 

Drilling

Milling

Turning

Yes, provided the operator has been properly educated and the machine is stable enough to run safely with carbide insert tools of good quality.

Computer Numerical Control (CNC) uses a computer program to control the sequence of operations of the machine. 

Cutting data for machining is available in SSAB’s machining brochures.

Material hardness is the ability to resist indentations by the pressure of other objects. 

The term machinability refers to the ease with which a material can be machined to give a satisfactory result, including the machined surface, tool life and costs.  

A harder steel will shorten tool lifetime. A lower cutting speed will do the opposite.

You can use a column or radial drilling machine for very hard steel, like wear plates, provided the drilling machine is stable and robust enough, and sufficiently powerful.

Drilling is a chip-forming machining method where a bit or insert with a cutting edge mounted on a rotating spindle is forced into a workpiece, to create a round hole. In most cases the workpiece is clamped, and the drill rotates but the opposite arrangement is also possible.

It is possible to drill into very hard steel, like wear plates. For Hardox grades up to Hardox 500, you can drill single holes into a stationary drilling machine with high-speed steel drill/you can use a stationary drilling machine with a high-speed drill to drill single holes together with low cutting speed and a lot of cooling. For even harder steels, a solid carbide drill or a carbide tipped drill must be used. 

It is not recommended to use hand drilling machines when drilling in hardened steels.  A human operator using a hand-held machine are not very stable and do not have the power necessary to get a satisfactory result.

To increase stability, use as short a drill as possible. The center insert will take more punishment, so choose a softer insert, while a harder peripheral insert is recommended where the wear is higher.

When used in a stable and powerful machine with good clamping facilities, a solid carbide drill is the optimum choice for drilling into all Hardox^® wear plate grades.

Use countersinking tools with carbide inserts in a stable machine. SSAB has recommendations on tools and suppliers.

If you have access to a CNC machine, you can spiral interpolate the shape of the chamfer with a solid carbide end mill. However, this approach takes much longer and becomes more expensive. See question number 15 for appropriate countersinking tools. 

Milling is a cutting process producing chips. Cutting inserts are rigidly mounted on a rotating tool (milling body). The milling body cutting edges can have various shapes. The workpiece is clamped onto a table. Both the table and the tool can be moved independently in one or more spatial dimensions. The movements can be controlled manually or by a computer program (CNC). 

The machine must be stable, and the workpiece must be well clamped. Use only a milling body equipped with carbide inserts for wear plates harder than 400 HBW. Use cutting feed provided by the tool manufacturer.  It is worth trying a gradual increase in cutting speed to save time. Start from a low cutting speed. 

Roughing is mainly to remove a large amount of material from the workpiece. Finishing is to improve surface finish and the tolerance of the workpiece.

Turning is a chip-forming cutting process where the workpiece rotates in a lathe. The resulting shape will have rotational symmetry.