INTRODUCTION TO MANUFACTURING PROCESSES-MACHINING-PART 1

Audio: Introduction to manufacturing processes-machining-part 1

In my previous article, we learned what manufacturing is, why it is important, and the general classification of different manufacturing processes. In this article, we will look into the shaping processes involving material removal, also known as machining. We will look into turning, boring, milling, drilling, thread cutting, shaping, planing, broaching, grinding, honing, and lapping. This article is part of the introduction to manufacturing processes series split into multiple parts (articles).

Introduction to material removal process - machining processes

Material removal processes are a family of shaping operations, and as the name says, the final geometry of the workpiece is achieved by removing the excess material from a workpiece. Usually term “machining” or “mechanical machining” is for material removal processes.

Machining is one of the most widely used and important manufacturing processes. It can be divided into cutting, abrasive, and advanced machining processes.

As a mechanical design engineer, there are high chances you will encounter more than one type of machining process. Machining processes like drilling you might perform yourself when working on prototypes. Therefore, it is important to deeply understand different processes, their capabilities, and where you could use them. The selected machining process will require special attention to design so that you can ensure quality and reduce cost through your design.

Some of the advantages of machining processes:

High accuracy,
A wide variety of shapes can be produced,
A wide variety of work materials,
Good surface finishes.

Machining processes, however, have some disadvantages:

Material waste,
Compared to casting and forging, machining can be time-consuming.

Let us know look into the different machining processes.

Machining processes: Turning and boring

Overview

Turning is a machining process in which the workpiece is rotated while moving a non-rotational tool removes material until the desired shape, size, and surface finish is produced. The workpiece is typically round. Turning is performed on the outer side of an existing cylinder. However, boring is similar to turning, but it is performed on the inner diameter of an existing hole.

Turning is carried out on a lathe machine, and boring on a machine called a boring machine. However, a lathe machine can also be used to perform boring operations. Furthermore, on the lathe machine, a wide variety of operations can be performed: turning, boring, taper turning, drilling, profiling, parting, facing, grooving, thread cutting, and knurling.

Turning:

Boring

Variations

Manual: engine lathe, bench lathe, toolmaker’s lathe, turret lathe,
Fully or semi-automated,
CNC machines,
Machining centers.

Production quantities

Production quantities can range from one piece to many millions.

For smaller quantities, manual and CNC machining are commonly used – low tolling cost, high flexibility.

For high quantities, automatic machines are used – high tooling cost, low flexibility.

Tolerances

Turning: Fine: ± 0,025 – 0,13 mm

Rough: ± 0,13 mm

Boring: ± 0,025 mm

Achievable mean roughness value (Ra): 0,2 – 50 µm

Materials

The workpiece is generally made by other processes, such as casting, forging, extrusion, drawing, or powder metallurgy. The workpiece can be made from materials: all metals (free machining ones), some plastics, elastomers, and ceramics.

Application

Any cylindrical workpiece can be machined, from small hinges to large turbine shafts.

Machining process: Milling

Overview

Milling is a machining process in which a rotational tool removes material from the workpiece until desired shape, size, and surface finish is produced. Workpieces can be in different sizes and shapes.

Milling is carried out on a machine called a milling machine. Furthermore, on the milling machine, a wide variety of operations can be performed: end milling, face milling, partial face milling, profile milling, surface contouring, pocket milling, and angle milling.

Variations

Horizontal and vertical milling machines,
CNC machines,
Machining centers.

Quantities

Economic production quantities are low to moderate due to a large amount of waste material. Low tooling cost.

Tolerances: ± 0,013 – 0,025 mm

Achievable mean roughness value (Ra): 0,4 – 25 µm

Materials

Application

Any standard or non-standard parts requiring secondary operations.

Common parts produced include automobile engine blocks and automobile cylinder heads, open-end wrenches and other hand tools, gearboxes, brackets, ribs, fittings, flanges, spars, beams, pumps, printing presses, machine-tool components, aircraft parts, office machines and computer peripheral equipment, and compressors.

Machining process: Drilling

Overview

Drilling is a machining process in which a rotational tool removes material to create a round hole in a workpiece. The boring process can only enlarge the hole, not create it. Drilling is usually done with a drill press machine, but other machines can also be used. Operations that can be performed after the drilling are reaming, tapping, counterboring, countersinking, centering, and spot facing.

Variations

Horizontal and vertical milling machines,
CNC machines,
Machining centers.

Quantities

Economic production quantities are low to moderate. Produce a large amount of waste material. Low tooling cost.

Tolerances: ± 0,075 mm

Achievable mean roughness value (Ra): 1,6 – 50 µm

Materials

All metals (mostly free machining) and some plastics and ceramics.

Application

Any part requiring cylindrical holes (blind or through). Holes are typically used for assembly with fasteners (such as bolts, screws, and rivets, each of which requires a hole). Furthermore, holes are used for design purposes (such as weight reduction, ventilation, or access to the inside of parts), or for appearance.

Machining process: Thread cutting

Overview

Thread cutting is a machining process in which a cutting tool removes material from a workpiece to form thread. Threads are grooves that form a uniform cross-section that follows a spiral or helical cross-section on the outside of a cylindrical (external thread) or the inside of a round hole (internal thread).

External threading:

Internal threading (tapping):

Variations

Single-point threading, threading die, self-opening threading dies, thread milling, and thread grinding for external threading.
Taps for internal threading

Quantities

Economic production quantities are from low to high quantities.

Tolerances: ± 0,025 mm

Achievable mean roughness value (Ra): 0,4 – 25 µm

Materials

The workpiece can be made from all metals and plastics.

Application

Screws, bolts, and other usages where external and internal threads are required.

Machining processes: Shaping and planing

Overview

Shaping is a machining process in which a moveable tool removes material from a stationary workpiece. It is usually used for smaller workpieces, and the process result is a straight and flat surface. Shaping is carried out on a machine called a shaper. The following operations can be performed on the shaper: roughing, slotting, dovetailing, and finishing.

Shaping:

Planing is a machining process in which a stationary tool removes material from a moving workpiece. It is usually used for large workpieces with 25 x 10 m of surface area, and the result of the process is a straight and flat surface. Planing is carried out on a machine called a planer. The following operations can be performed on the planer: roughing, slotting, dovetailing, and finishing.

Planing:

Variations

Horizontal and vertical shapers,
Open-side planer, single-column planer, and double-column planer.

Quantities

Economic production quantities are usually low. Tooling costs are low.

Tolerances:

Shaping: ± 0,05 – 0,08 mm

Achievable mean roughness value (Ra): 0,4 – 25 µm

Planing: ± 0,08 – 0,13 mm

Achievable mean roughness value (Ra): 0,4 – 25 µm

Materials

The workpiece can be made from materials all metals (free machining ones).

Application

Shaping and planning are machining processes used for machinery bases and tool beds, diesel engine blocks, die blocks, ley seats, slots, notches, large gear teeth locomotives, and ship parts. In addition, large, rough castings and welded assemblies are candidates for planing.

Machining process: Broaching

Overview

Broaching is a machining process in which a moveable multiple-teeth cutting tool (broach) removes material from a workpiece. Broaching is carried out on a machine called broaching machine. The following operations can be performed on the shaper: external and internal broaching.

Variations

Horizontal and vertical broaching machines,
Broaching press and continuous broaching machines.

Quantities

Economic production quantities are high, 10 000 – 100 000. Tooling costs are high (high quantities are required to justify the high tooling cost).

Tolerances: ± 0,025 – 0,15 mm

Achievable mean roughness value (Ra): 0,4 – 25 µm

Materials

The workpiece can be made from materials all metals (free machining ones).

Application

Broaching is used to make an internal and external square, circular, and irregular shapes: key slots, splines, holes with straight-sided involute, specially shaped teeth, cam forms, gears, ratchets, and other complex forms.

Machining process: Grinding

Overview

Grinding is a machining process in which an abrasive rotating tool removes a small amount of material from the workpiece at a very high speed. Grinding is carried out on a machine called a grinding machine.

Variations

We can divide grinding into the following categories: surface grinding, cylindrical (external and internal) grinding, centerless grinding, creep feed grinding, and other grinding operations (jig grinders, disk grinders, abrasive belt grinding, snap grinder).

Quantities

Economic production quantities are from low to high quantities.

Tolerances:

Achievable mean roughness value (Ra): 0,025 –6,3 µm

Materials

The workpiece can be made from materials all hard materials.

Application

Grinding is used to create basic geometric surfaces and finishes of various components.

Machining processes: Honing and Lapping

Honing

Overview

Honing is a machining process in which a moveable and rotatable tool removes a small amount of material from a workpiece. The tools consist of a set of bonded abrasive sticks. A cutting fluid must be used. The finishing surface have a hatched pattern.

Variations

Horizontal and vertical honing machines.
It can be used on lathes and drilling machines.

Quantities

Economic production quantities are from low to high quantities.

Tolerances:

Achievable mean roughness value (Ra): 0,012 – 1,4 µm

Materials

The workpiece can be made from materials all metals, including some ceramics and plastics.

Application

Honing can be used for any geometric shape. Still, it is mostly used for holes, like automotive-cylinder or valve-body bore, and other applications where superior accuracy and surface finish are required.

Lapping

Overview

Lapping is a machining process that removes a small amount of material from the workpiece to produce surface finishes of extreme accuracy and smoothness. The tools consist of a set of bonded abrasive sticks. A fluid with abrasive (referred to as lapping compound) must be used.

Variations

Hand lapping,
Horizontal and vertical machine lapping,
Centerless lapping,
Pressure jet lapping.

Quantities

Economic production quantities are from low to high quantities.

Tolerances:

Achievable mean roughness value (Ra): 0,012 – 1,6 µm

Materials

The workpiece can be made from all materials.

Application

Piston rings, piston rings, valve seats, bearing surfaces, gages, and other parts requiring a superior surface finish on a flat, cylindrical, or contoured surface.

Closing words

Knowing the different manufacturing processes available for every mechanical design engineer is extremely important. Based on the chosen manufacturing process, the mechanical design engineer has to adjust the design to reduce costs and ensure quality. In this article, we covered a range of machining processes, and in part 2, we will look into the rest of them.

Now you have an overview of some machining processes you could use as a mechanical design engineer. However, I suggest you go through the text once more and identify areas you think need more understanding and clarity. Then, once you have identified those areas, start building up your knowledge in those areas.

To make it easier for you to find related posts, check the “Further reading” chapter below. Do you have any questions or need something to be clarified better? Leave a comment below, and I will give my best to adjust the post accordingly.

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