What is Metal Machining? An Explanation of Machining Types and Selection Points!
What is Metal Machining?
Metal machining refers to the collective processing methods that use metal as a material to manufacture products. There are numerous types of metal machining, with various classification approaches. Based on JIS standards, the representative machining methods are summarized in the figure below.
Metal machining can be broadly classified into “metal forming” and “metal property modification.” The former involves processing sheets, bars, and molten metal to create product shapes. The latter involves heat and chemical treatments to enhance hardness and prevent rust.
Types and Classification of Metal Machining
Let’s explore the various metal machining methods and their characteristics.
Metal Forming
The methods for shaping metal can be divided into the following four main categories:
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Machining
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Plastic Processing
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Casting
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Others
Each method is detailed below.
1. Machining
Machining encompasses three primary methods: cutting, grinding, and special processing.
Cutting
This is a process where blade-shaped tools are used to remove unwanted parts from a workpiece to shape it. It is the most widely used method due to its broad material applicability, good balance between precision and cost, and versatility. Representative equipment includes lathes, milling machines, machining centers, and drilling machines.
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Lathes use chucks to rotate workpieces and cut them with tools for cylindrical and thread processing.
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Milling machines and machining centers fix workpieces on tables and use rotating milling cutters for machining.
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Drilling machines fix workpieces on tables and use drills or taps for drilling and tapping.
This method is widely used in various products, such as home appliances and automotive parts.
Grinding
This process uses grinding wheels to remove unwanted parts from a workpiece. Similar to cutting, it achieves higher precision but at a higher cost and time consumption. Cylindrical and surface grinders are commonly used for machining cylindrical and flat surfaces, respectively, to improve flatness, cylindricity, and surface roughness.
Special Processing
Machining methods that are neither cutting nor grinding are classified as special processing. Notable examples include electrical discharge machining (EDM) and laser processing.
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EDM uses electrical discharges between a workpiece and an electrode to melt material and shape parts. It is suitable for high-precision and micro-machining of hard-to-machine materials.
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Laser processing uses high-energy lasers to melt and evaporate material. It is ideal for micro and precision machining.
2. Plastic Processing
Plastic processing includes stamping, forging, and rolling.
Stamping
This involves cutting or shaping sheet workpieces using significant force with tools and molds. Equipment such as shearing machines, stamping machines, and turret presses are used. Sheet metal processing is also categorized under stamping.
Forging
This process shapes workpieces by applying significant force with hammers and molds. Preheating workpieces facilitates deformation. It is classified by temperature into hot forging, warm forging, and cold forging, and by mold use into die forging and free forging.
Rolling
This method deforms cylindrical workpieces using dies to shape them into the external form of the die. It is commonly used for threading, such as in bolts and screws.
3. Casting
This involves melting raw metal materials in a furnace, pouring them into molds with product-shaped cavities, and solidifying them to create products. It is suitable for mass production of complex shapes. Traditional sand casting and modern low-pressure casting and die-casting are common methods.
4. Others
Other methods include powder metallurgy and metal 3D printing, which can produce complex shapes not achievable with traditional methods.
Powder Metallurgy
This process compacts metal powder in a mold and then heats it in a furnace to bind the particles together. It is used to manufacture products with special properties, such as gears and self-lubricating bearings.
Metal 3D Printing
This method gradually builds up material to form the final product. It allows for complex and unique shapes and is used for rapid prototyping and small-scale, high-value production.
Modifying Metal Properties
Methods to alter metal properties include heat treatment and surface treatment.
Heat Treatment
Heat treatment changes the internal structure of metals to enhance various properties. Common methods include quenching, tempering, normalizing, and annealing.
Surface Treatment
Representative methods include electroplating and chemical conversion coatings.
Electroplating covers metal surfaces with thin metal films to prevent rust, enhance aesthetics, and harden surfaces. It is widely used in household goods and automotive parts.
Chemical Conversion Coatings alter surface properties through chemical treatment. Examples include phosphate coating for rust prevention and chromate conversion coating for screws.
Key Points for Selecting Metal Machining Methods
When selecting metal machining methods, consider the following:
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Understand the characteristics of each machining method: Different methods have varying strengths and weaknesses in terms of shape flexibility, precision, cost, time, mass production, and strength.
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Know available machining options: Be aware of your factory’s capabilities and scheduling.
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Review past cases: Check if similar parts have been machined before.
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Consult with experts: Discuss with experienced individuals in production technology or manufacturing departments. Observing actual machining processes can be highly educational.
In summary, metal machining encompasses various methods, including mechanical machining, plastic forming, casting, and others for shaping metals, as well as heat treatment and surface treatment for modifying metal properties. Choose the appropriate method based on the application and purpose.
