metal work in China


Centrifugal Casting

Centrifugal casting, sometimes called rotocasting, is a metal casting process that uses centrifugal force to form cylindrical parts. This differs from most metal casting processes, which use gravity or pressure to fill the mold. In centrifugal casting, a permanent mold made from steel, cast iron, or graphite is typically used. However, the use of expendable sand molds is also possible. The casting process is usually performed on a horizontal centrifugal casting machine (vertical machines are also available) and includes the following steps:


  1. Mold preparation – The walls of a cylindrical mold are first coated with a refractory ceramic coating, which involves a few steps (application, rotation, drying, and baking). Once prepared and secured, the mold is rotated about its axis at high speeds (300-3000 RPM), typically around 1000 RPM.
  2. Pouring – Molten metal is poured directly into the rotating mold, without the use of runners or a gating system. The centrifugal force drives the material towards the mold walls as the mold fills.
  3. Cooling – With all of the molten metal in the mold, the mold remains spinning as the metal cools. Cooling begins quickly at the mold walls and proceeds inwards.
  4. Casting removal – After the casting has cooled and solidified, the rotation is stopped and the casting can be removed.
  5. Finishing – While the centrifugal force drives the dense metal to the mold walls, any less dense impurities or bubbles flow to the inner surface of the casting. As a result, secondary processes such as machining, grinding, or sand-blasting, are required to clean and smooth the inner diameter of the part.

Centrifugal casting is used to produce axi-symmetric parts, such as cylinders or disks, which are typically hollow. Due to the high centrifugal forces, these parts have a very fine grain on the outer surface and possess mechanical properties approximately 30% greater than parts formed with static casting methods. These parts may be cast from ferrous metals such as low alloy steel, stainless steel, and iron, or from non-ferrous alloys such as aluminum, bronze, copper, magnesium, and nickel. Centrifugal casting is performed in wide variety of industries, including aerospace, industrial, marine, and power transmission. Typical parts include bearings, bushings, coils, cylinder liners, nozzles, pipes/tubes, pressure vessels, pulleys, rings, and wheels.

Centrifugal Casting


Typical Feasible
Shapes: Thin-walled: Cylindrical
Solid: Cylindrical
Thin-walled: Complex
Solid: Complex
Part size: Diameter: 1 – 120 in.
Length: Up to 50 ft.
Weight: Up to 5 tons
Materials: Metals
Alloy Steel
Carbon Steel
Cast Iron
Stainless Steel
Surface finish – Ra: 63 – 500 μin 32 – 500 μin
Tolerance: ± 0.01 in. ± 0.002 in.
Max wall thickness: 0.1 – 5.0 in. 0.1 – 5.0 in.
Quantity: 100 – 10000 1 – 10000
Lead time: Weeks Days
Advantages: Can form very large parts
Good mechanical properties
Good surface finish and accuracy
Low equipment cost
Low labor cost
Little scrap generated
Disadvantages: Limited to cylindrical parts
Secondary machining is often required for inner diameter
Long lead time possible
Applications: Pipes, wheels, pulleys, nozzles

Sheet Metal Cutting (With out Shear)

Cutting processes are those in which a piece of sheet metal is separated by applying a great enough force to caused the material to fail. The cut being formed may follow an open path to separate a portion of material or a closed path to cutout and remove that material. The geometric possibilities for a cutting process depend on the technology used, but most are capable of cutting out any 2D shape. Some of the most common sheet metal cutting processes use shearing forces to separate the material. A description of those processes can be found in the previous section. In this section, cutting processes that use other forces, such thermal energy or abrasion, will be discussed. Some common methods of sheet metal cutting that use such forces include the following:

Laser cutting

Laser cutting uses a high powered laser to cut through sheet metal. A series of mirrors and lenses direct and focus a high-energy beam of light onto the surface of the sheet where it is to be cut. When the beam strikes the surface, the energy of the beam melts and vaporizes the metal underneath. Any remaining molten metal or vapor is blown away from the cut by a stream of gas. The position of the laser beam relative to the sheet is precisely controlled to allow the laser to follow the desired cutting path.

This process is carried out on laser cutting machines that consist of a power supply, laser system, mirrors, focusing lens, nozzle, pressurized gas, and a workpiece table. The laser most commonly used for sheet metal cutting is a CO2 based laser with approximately 1000-2000 watts of power. However, Nd and Nd-YAG lasers are sometimes used for very high power applications. The laser beam is directed by a series of mirrors and through the “cutting head” which contains a lens and nozzle to focus the beam onto the cutting location. The beam diameter at the cutting surface is typically around 0.008 inches. In some machines, the cutting head is able to move in the X-Y plane over the workpiece which is clamped to a stationary table below. In other laser cutting machines, the cutting head remains stationary, while the table moves underneath it. Both systems allow the laser beam to cut out any 2D shape in the workpiece. As mentioned above, pressurized gas is also used in the process to blow away the molten metal and vapor as the cut is formed. This assist gas, typically oxygen or nitrogen, feeds into the cutting head and is blown out the same nozzle as the laser beam.

Laser cutting can be preformed on sheet metals that are both ferrous and non-ferrous. Materials with low reflectivity and conductivity allow the laser beam to be most effective – carbon steel, stainless steel, and titanium are most common. Metals that reflect light and conduct heat, such as aluminum and copper alloys, can still be cut but require a higher power laser. Laser cutting can also be used beyond sheet metal applications, to cut plastics, ceramics, stone, wood, etc.

As previously mentioned, laser cutting can be used to cut nearly any 2D shape. However, the most common use is cutting an external profile or complex features. Simple internal features, such as holes or slots are usually punched out using other sheet metal processes. But highly complex shapes and outer part boundaries are well suited for laser cutting. The fact that laser cutting does not require any physical contact with the material offers many benefits to the quality of the cuts. First, minimal burrs are formed, creating a smooth edge that may not require any finishing. Secondly, no tool contact means only minimal distortion of the sheet will occur. Also, only a small amount of heat distortion is present in the narrow zone affected by the laser beam. Lastly, no contaminates will be embedded into the material during cutting. Although not a quality issue, it is worth noting that the lack of physical tool wear will reduce costs and make laser cutting cost effective for low volume production.

Laser cutting machineLaser cutting


  • Sheet thickness: 0.02-0.50 in.
  • Cutting speed: 30-500 IPM (1000 IPM feasible)
  • Kerf width: 0.006-0.016 in. (0.004 in. feasible)
  • Tolerance: ±0.005 in. (±0.001 in. feasible)
  • Surface finish: 125-250 μin

Design rules

  • Edges – Burrs are minimal, but can be further reduced by using a thinner sheet stock.
  • Corners – Rounded corners are preferred to sharp corners. Interior corners must have a minimum radius equal to the laser beam radius.
  • Holes – Minimum hole diameter should be approximately 20% of sheet thickness, down to 0.010 inches. Laser-cut holes will have a slight natural taper.
  • Multiple sheets can be cut at once to reduce cost

Plasma cutting

Plasma cutting uses a focused stream of ionized gas, or plasma, to cut through sheet metal. The plasma flows at extremely high temperatures and high velocity and is directed toward the cutting location by a nozzle. When the plasma contacts the surface below, the metal melts into a molten state. The molten metal is then blown away from the cut by the flow of ionized gas from the nozzle. The position of the plasma stream relative to the sheet is precisely controlled to follow the desired cutting path.

Plasma cutting is performed with a plasma torch that may be hand held or, more commonly, computer controlled. CNC (computer numerically controlled) plasma cutting machines enable complex and precision cuts to made. In either type of plasma torch, the flow of plasma is created by first blowing an inert gas at high speed though a nozzle pointed at the cutting surface. An electrical arc, formed through the flow of gas, ionizes the gas into plasma. The nozzle then focuses the flow of plasma onto the cut location. As with laser cutting, this process does not require any physical tooling which reduces initial costs and allows for cost effective low volume production.

The capabilities of plasma cutting vary slightly from laser cutting. While both processes are able to cut nearly any 2D shape out of sheet metal, plasma cutting cannot achieve the same level of precision and finish. Edges may be rough, especially with thicker sheets, and the surface of the material will have an oxide layer that can be removed with secondary processes. However, plasma cutting is capable of cutting through far thicker sheets than laser cutting and is often used for workpieces beyond sheet metal.

Plasma cuttingsheet metal cutting

Water jet cutting

Water jet cutting uses a high velocity stream of water to cut through sheet metal. The water typically contains abrasive particles to wear the material and travels in a narrow jet at high speeds, around 2000 ft/sec. As a result, the water jet applies very high pressure (around 60,000 psi) to the material at the cut location and quickly erodes the material. The position of the water jet is typically computer controlled to follow the desired cutting path.

Water jet cutting can be used to cut nearly any 2D shape out of sheet metal. The width of the cuts is typically between 0.002 and 0.06 inches and the edges are of good quality. Because no burrs are formed, secondary finishing is usually not required. Also, by not using heat to melt the material, like laser and plasma cutting, heat distortion is not a concern.

Water jet cuttingWater jet cutting

Sheet Metal Cutting (Shearing)

Cutting processes are those in which a piece of sheet metal is separated by applying a great enough force to caused the material to fail. The most common cutting processes are performed by applying a shearing force, and are therefore sometimes referred to as shearing processes. When a great enough shearing force is applied, the shear stress in the material will exceed the ultimate shear strength and the material will fail and separate at the cut location. This shearing force is applied by two tools, one above and one below the sheet. Whether these tools are a punch and die or upper and lower blades, the tool above the sheet delivers a quick downward blow to the sheet metal that rests over the lower tool. A small clearance is present between the edges of the upper and lower tools, which facilitates the fracture of the material. The size of this clearance is typically 2-10% of the material thickness and depends upon several factors, such as the specific shearing process, material, and sheet thickness.

The effects of shearing on the material change as the cut progresses and are visible on the edge of the sheared material. When the punch or blade impacts the sheet, the clearance between the tools allows the sheet to plastically deform and “rollover” the edge. As the tool penetrates the sheet further, the shearing results in a vertical burnished zone of material. Finally, the shear stress is too great and the material fractures at an angle with a small burr formed at the edge. The height of each of these portions of the cut depends on several factors, including the sharpness of the tools and the clearance between the tools.


Sheared edge


A variety of cutting processes that utilize shearing forces exist to separate or remove material from a piece of sheet stock in different ways. Each process is capable of forming a specific type of cut, some with an open path to separate a portion of material and some with a closed path to cutout and remove that material. By using many of these processes together, sheet metal parts can be fabricated with cutouts and profiles of any 2D geometry. Such cutting processes include the following:


  • Shearing – Separating material into two parts
  • Blanking – Removing material to use for parts
  • Conventional blanking
  • Fine blanking
  • Punching – Removing material as scrap
  • Piercing
  • Slotting
  • Perforating
  • Notching
  • Nibbling
  • Lancing
  • Slitting
  • Parting
  • Cutoff
  • Trimming
  • Shaving
  • Dinking
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