Machining Operations in Manufacturing
Let's move a step ahead from Manufacturing
Table of contents
Difference between machining and manufacturing
Lathe machine and its operations
Milling machine and its operations
Horizontal and Vertical Milling
Earlier we have had a look at what are the conventional manufacturing processes. How are various components made by either sand casting process or by extrusion process. These processes are not the only ones in the process of manufacturing. In the journey of manufacturing a product, there are different stages which involved a variety of processes such as
1. Basic modeling - where the basic geometry or profile of the product is achieved. In this step there is minimal attention to detail.
2. Trimming of excess profiles - When preparing the basic geometry, there are certain profiles which are produced as a in time necessity, like a supporting structure. The final product does not require this profile and hence it is trimmed out.
3. Finishing - Finishing involve smoothening and polishing of the surface. Adding details to the profiles. Coating is done to prevent corrosion.
4. Quality and safety assessment - This step is more of a precautionary measure and a functionality test and does not involve any changes to the final product.
We have seen what are the stages in manufacturing process. But what qualifies a process in that specific category? The answer is simple, after the product is passed through a certain process in that stage is the product ready to use? And how many steps away is it from being ready to be used?
In line with the manufacturing processes we have machining operations. Machining operations involve milling, turning, boring, knurling, etc. These are different from the conventional manufacturing processes and provide a greater finish to the product.
How are the machining operations different from manufacturing processes?
In manufacturing process, we build a product from a bulge. Before this process we don't have any geometry, just raw material. The raw material is molded or shaped to look like the final product. On the other hand, in machining operations we remove excess profiles and give dimensional accuracy to the product. In simple words, manufacturing processes are adding material where as machining is removing of excess material.
As the name suggest, machining operation will be requiring a machine. Let's take a look at one of the most popular tool used in machining - Lathe machine
A lathe machine is a tool which supports different machining operations and assists in the material removal process to achieve a desired shape for the product.
Lathe machine is a complex equipment with various parts having specific functionality. The different parts of the machine are:
Headstock - It is located at the left end of the machine and the driving mechanism of the gear assembly is within it. It holds the job (product) in place along the spindle. The rotating force to perform the machine operation is transmitted through headstock.
Bed - It is the base of the lathe machine. The bed has sliders along it's length to assist cutting at different angles and sections. It is important that the bed is rigid and can withstand vibrations during the machining operation. It supports the headstock, tailstock and carriage.
Tail stock - Located at the opposite end of the headstock, tail stock is used to holds and supports the long end of the job to minimize sagging when the job vibrates.
Carriage - The carriage is used for support, guide and feed the tool against the job when the machining is done. It is in charge of holding, moving, and controlling the cutting tool. During operations, it provides stiff support for the tool. It uses an apron mechanism to transfer power from the feed rod to the cutting tool for longitudinal cross-feeding.
Tool post - It is the carriage's highest section, and it holds numerous cutting tools or tool holders.
Lead screw - A lead screw is also known as a translating screw or a power screw. It is a device that converts rotational motion into linear motion. In a lathe machine tool, a lead screw is used for thread cutting.
Feed Rod - Feed rod is used to move the carriage from the left side to the right side and also from the right side to the left side.
Chuck - Chuck is used to holding the workpiece securely.
Main Spindle - The spindle is a hollow cylindrical shaft in which long jobs can pass through it. It is designed so well that the thrust of the cutting tool does not deflect the spindle.
Leg - Legs are carrying an entire load of a lathe machine tool and transfer to the ground. The legs are firmly secured to the floor by the foundation bolt.
A lathe machine is powered by electricity. There are different variations available for the type of lathe machine depending on the applications. But a simple lathe machine can perform all the required operations.
Let us see how the lathe works.
The job or workpiece is clamped onto the spindle and tail stock using chucks. The workpiece is held tightly in place by lead screw. A cutting tool is fixed on the carriage and brought in contact with the workpiece by adjusting the cross slide. Headstock provides the rotational force to the job and the cutting tool is adjusted by feed rod to position the tool according to the required shape.
Some of the operations performed on lathe machine are -
Turning - The operation by which we remove the excess material from the workpiece to produce a cone-shaped or a cylindrical surface.
Chamfering - It is used for beveling the end of a job to remove burrs, to look better, to make a passage of the nut into the bolt.
Knurling - It is the process of producing a rough surface on the workpiece to provide effective gripping. Knurling tool is held rigidly on the tool post and pressed against the rotating job so that leaving the exact facsimile of the tool on the surface of the job.
Thread cutting operation - It is the operation that is used to produce a helical groove on a cylindrical or conical surface by feeding the tool longitudinally when the job revolved between the two centers.
Drilling - It is an operation by which we can make holes in a job. In this operation, the job is rotated at the turning speed on the lathe axis and the drilling tool fitted on the tail-stock spindle. And the tail-stock is moved towards the job by hand feed.
Boring - In this operation, we can enlarge the diameter of the existing hole on a job by turning inside with some farm tool known as a boring tool. The boring tool is also fitted on tail-stock.
Reaming - It is the operation for sizing or finishing a drilled hole to the required size by a tool called reamer. This tool is fitted on tail-stock.
Spinning - In this operation, the job of this sheet metal is held between the former and the tail-stock center rotates at high speed with the former.
Tapping - We use this operation for creating internal threads within a hole by means of a tool called tap.
Parting-off - It is the operation of cutting off a bar type job after complete the machining process.
In this operation a bar type job is held on a chuck, rotates at turning speed, a parting off tool is fed into the job slowly until the tool reaches the center of the job.
The workpiece which undergoes machining in a lathe should be of circular cross section.
The applications of lathe include:
Profiling of cams and shafts in engines.
Adding threading to the pipes for connection.
Knurling to provide grip and textures to pipes and rods.
Milling is a process where a rotating cutter tool is used to remove material progressively.
In milling process, the cutting tool is of circular geometry and is in continuous rotating motion. There are multiple cutting points along the circumference of the tool. The workpiece or job is placed stationary on the work bench.
The milling process removes material by performing many separate, small cuts. This is accomplished by using a cutter with many teeth, spinning the cutter at high speed, or advancing the material through the cutter slowly; most often it is some combination of these three approaches.
Let's take a look at different types of milling processes.
Based on tool orientation
The most common type is a vertical milling machine, which has a vertically oriented cutting head or spindle. A rotating cutting tool is held against the workpiece by the spindle. Along the Y-axis, the spindle moves vertically. To correctly place the workpiece, other machine elements shift along the X-axis or even the Z-axis.
Vertical mills are perfect for jobs that require only one side to be worked on, such as sectioning or finishing operations such as end millwork. Vertical mills are further classified into two categories of vertical milling machines: bed milling machines and turret milling machines. Each one works a little differently than the others and has its own set of benefits.
Horizontal milling machines, like vertical mills, have a rotating spindle. This spindle is horizontally positioned above the bed. The cutting tool, which is usually a disc that looks like a saw blade or a grinder, can travel along the spindle's length. This enables the horizontal mill to remove material along the length of a workpiece or even act as a planer to complete the entire surface. The horizontal mill, when combined with a rotary table, becomes nearly as versatile as a vertical mill.
Horizontal milling machines can make heavier and deeper cuts than vertical milling machines. Horizontal mills often feature higher horsepower motors and wider beds, making them excellent for heavy-duty applications.
Based on operation process
In down milling (climb milling), the cutting tool is fed in the direction of rotation. Down milling is always the preferred method whenever the machine tool, fixture and workpiece will allow for it.
In peripheral down milling, the chip thickness decreases from the start of cut, gradually reaching zero by the end of cut. This prevents the edge from rubbing and burnishing against the surface before engaging in the cut.
In up milling (conventional milling), the feed direction of the cutting tool is opposite to its rotation.
The chip thickness starts at zero and increases toward the end of the cut. The cutting edge has to be forced into the cut, creating a rubbing or burnishing effect due to friction, high temperatures and often contact with a work-hardened surface caused by the preceding edge. All this reduces tool life.
Cutting forces tend to push the cutter and workpiece away from each other and radial forces tend to lift the workpiece from the table.
Around 1751, Jacques de Vaucanson invented the lathe.