Blog 34: Metal Machining its Types

Introduction:

Manufacturing’s main goal is to turn raw materials or waste into useful products. To meet this requirement, various manufacturing procedures are available. Casting is the process of melting the raw material or trash and pouring it into a cavity that has already been created to create the impression. When two or more parts are combined to create one whole, the process is known as joining. By using external pressure, raw material is shaped into a certain shape as needed throughout the forming process. Casting, forming, and joining are all essentially the same kind of manufacturing process. Another example of this is metal machining, which involves cutting (shearing) material from the job in order to obtain the desired object.

The following section offers a typical definition of machining. Machining is the regulated process of chopping a piece of raw material into the desired end shape and size. Metal machining creates shapes in a wide range of metals using milling machines, lathes, drill presses, and other tools. Different materials, sizes, and geometric shapes require the employment of various machining techniques.

Definition of metal machining or metal cutting operation

To obtain the correct shape, polish, and tolerance, surplus material is sheared off a pre-formed blank in the form of chips during one of the secondary production processes known as machining.

Although cutting materials other than metals, such as plastics, wood, and ceramics, is often known as a “metal cutting operation,” or “machining,” is a process. Solid materials can be broadly categorised into three categories: metal, polymer, and ceramics. Metal is one sort of solid material. Polymers and ceramics are the other two. By the way, metals are used in the bulk of engineering applications, therefore the alternate name is appropriate.

The conventional machining process is schematically shown in the above figure. The figure is drawn on Orthogonal Plane, and thus the suffix ‘O’. It must be noted that the uncut chip thickness (a1) is always lesser than the chip thickness (a2). Also, the clearance angle must have a non-zero positive value (usually ranges between 3º to 15º) and the rake angle may be positive, negative, or zero (usually ranges between –30º to +15º).

Types of the metal machining process

Both standard and unconventional methods are used in metal machining. The removal of material by either a heat or chemical process is a part of unconventional machining methods. On the other hand, metals are widely employed in conventional machining operations, which fall into three groups. These include abrasive machining, multi-point cutting, and single-point cutting machining.

Each machining operation employs a particular kind of cutting tool and method on a workpiece. A metal object would need to be machined using a variety of processes carried out in a predetermined order in order to produce the desired design and features.

Here are the different metal material removal processes:

1. Mechanical machining

Single-point cutting

In this, the workpiece’s metal material is removed using a single cutting tool with a sharp edge. A common single-point cutting technique is turning, which involves rotating the workpiece while feeding the cutting tool into it to remove material.

A variety of characteristics are produced by turning operations including boring, grooving, cut-off (parting), facing, and thread cutting. Slots, tapers, flat surfaces, threads, and intricate curves are a few of these traits. Other single-point cutting techniques that don’t need rotating the workpiece are planning and shaping.

Multi-point cutting

Multiple cutting tools with pointed tips move against the workpiece during multi-point cutting to remove material. The most popular multi-point cutting techniques, in which a cylindrical cutting tool has a sharp tooth that rotates at a very high speed, are milling and drilling. When milling, a rotating tool is inserted into the workpiece to produce various features using various rotating depths and routes.

On a milling machine, the various milling operations include chamfer milling, face milling, and end milling. Milling techniques can produce chamfers, smooth surfaces, complicated curves, slots, and pockets. Additionally, milling machines are capable of drilling and other hole-making tasks. Milling processes like sawing and broaching will be covered in more detail later.

2. Abrasive machining

Abrasive machining is a mechanical procedure that eliminates metal materials from a workpiece using an abrasive tool. Although a workpiece’s features can be shaped and formed with this method, it is primarily employed to enhance a part’s surface quality.

A popular abrasive machining technique is grinding, in which the cutting tool’s abrasive grains are bonded to a wheel that rotates against the workpiece. A surface grinding machine or a cylindrical grinding machine can be used for grinding. Lapping, abrasive jet machining, ultrasonic machining, and honing are some of the further abrasive machining techniques.

3. Chemical machining

Chemical machining, such as electrochemical machining, or ECM, employs chemicals to remove material. It is a method of mass-producing an electrochemical procedure to remove metal. Additionally, it is used to work with electrically conductive materials that are very tough or challenging to manufacture using traditional techniques.

4. Thermal machining

Electrical discharge machining, often known as EDM, torch cutting, and high-energy beam machining are all examples of thermal machining. EDM is a non-traditional machining technique that uses heat energy to remove a workpiece. EDM is similar to laser cutting in that it doesn’t involve using mechanical force to remove material.

Example of metal machining processes

To meet the always-changing market demand, there are hundreds of various machining procedures that can be used to machine a wide range of materials in diverse ways. All of these machining techniques have varying degrees of ability to produce surfaces with various properties. Here are a few frequently used machining techniques.

Facing

It is done to make a surface considerably smooth and level. Facing can be done using a milling machine or a lathe (but only for cylindrical workpieces). No matter whether a machine tool is used, facing always results in a level surface.

Turning

In this type of metal CNC machining, undesirable metal materials are taken out of rotating parts. A workpiece is fed into a turning or lathe machine at a high rate of rotation. The two types of turning are single-point cutting and multi-point cutting, as was already mentioned above. Depending on the needs of the product, various tools are utilised.

You can always improve or add features to metal components since turning increases the precision of rotating metal part features with an existing shape. This process can be used to create metal objects such as shafts and fasteners with unique designs.

For turning, you can use a variety of raw materials, including titanium, magnesium, steel, brass, aluminium, nickel, and nickel. When choosing a material, factors like cost, strength, machinability, and wear resistance are crucial to take into account. Aim for a substance that will provide your metal products with the best surface polish. The efficiency of turning also encourages a longer tool life.

Here are the different specs or features you can create with turning:

  • Holes
  • Grooves
  • Different diameter steps
  • Contoured surfaces
  • Tapers

Milling

Symmetric metal pieces can be produced, including slots, holes, pockets, and three-dimensional surface features. Milling is frequently used to create metal tools. Fasteners and brackets with a specific design are more examples.

Carbide, high-speed steel, high-speed cobalt steel, and carbon steel are all possible materials for milling cutting tools. The attributes of the cutter, such as resistance to wear, toughness, and hardness, as well as the material of the workpiece, will determine the type of cutting tool material you’ll need.

Reaming

A device called a reamer with one or more cutters is used for reaming. It is applied to increase a hole’s size. The same machine is used for drilling, and different-sized HSS or carbide reamers may be employed.

Grinding

When executing an abrasive machining operation, grinding involves the use of grindstones, grinding wheels, hand-cranked knife-sharpening, or grinders. When temporary binders and bond materials are combined, metal is cut with abrasive particles, and the metal is then shaped by applying pressure to the grinding wheels. The mechanical form of machining used in this procedure is part of CNC machining.

Boring

Enlarging existing cast or drilled holes is done via boring. The several types of boring include lathe boring, back boring, and line boring, with one of the ends held by a boring bar (enlarging a hole with a single-point cutting tool to create tapered or square holes).

Honing

It is a type of abrasive machining that tries to produce an accurate metal surface. The spinning abrasive tool is a stone that is scrubbed in a regulated pattern against the workpiece to remove undesirable material, hence enhancing surface form and texture. In order to get the appropriate diameter of the metal component, honing is utilised in surface finishing.

Broaching

Precision machining and the creation of unusual shapes are done via broaching. Unwanted material is removed during this machining process using a broach, which is a toothed tool. On the surfaces of a workpiece, linear broaching applies to broach linearly. Rotary broaching is done on a lathe machine.

Shaping

Of course, you’d want to mould metal parts to meet your needs or those of your clientele. Metal shaping is one method for doing this. It includes hot forging, which involves hammering, pressing, and upsetting a pliable metal component to get the desired shape. It entails heating the substance 75% above its melting point in order to mould it as required.

Laser engraving

Flexible, quick cycle times, high-precision labelling, permanent marking with laser technology, and production line integration. It is an affordable method of marking metal components.

Laser technology can be used for laser engraving to perform precision metal stamping. Metal items can be accurately and uniformly labelled with the proper serial numbers, identity codes, brand names, and model numbers using metal precision stamping. Use laser technology to impress your customers and investors.

ECM/EDM

These non-mechanical methods of material removal employ chemicals or erosive sparks. An electrode sparks at the surface of a conductive workpiece using an electric discharge machine, which transmits the spark through a dielectric fluid. This technique can be used to machine very tiny features such as small diameter holes, die cavities, etc. Hardness does not typically affect the discharge rate; instead, the metal’s thermal conductivity and thermal characteristics do.

An electroplating process in reverse, electrochemical machining creates burr-free holes with excellent surface finishes. Since it is a cold machining procedure, the workpiece experiences no thermal stresses.

Advantages of the Machining Process:

The advantages of the machining process are as follows.

  • A high surface finish can be obtained.
  • Machining is not only performed on metal but also performs on wood, plastic, composites, and ceramics.
  • A variety of geometry features are possible, such a Screw threads, Very straight edges, Accurate round holes, etc. 
  • Good dimensional accuracy.

Limitations of the Machining Process:

The limitations of the machining process are as follows.

  • The accuracy of the components produce is dependent on the efficiency of the operator.
  • Consistency in manufacturing is not present. Hence 100% inspection of the component is required.
  • The personal needs of the operator are reducing the production rates.
  • Because of the large amount of Manpower involved, the labor problem will also be high.
  • Complex shapes like parabolic Curvature components, Cubicle Curvature components are difficult to manufacture.
  • Frequent design changes in the component cannot be incorporated into the existing layout.

Applications of Machining Process:

The applications of the machining process are as follows.

  • Machining can be performed on various components in the form of either conventional or unconventional processes.
  • The machining can be performed on a lathe machine, milling machine, ultrasonic machining, etc.
  • The advancement of machining can be performed on CNC Machines where there is no intervention of humans.

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