Metal Processing

Mills Products Rollformer

One of the first fields I got involved with in automation in the early 1990s was metal forming. Presses, slitters and rollformers with their associated unwinds, cutoffs and punches were a big part of my business for the first few tears of ACS. Since I was just getting started in business, packaging and metal processing lent itself to fairly quick mostly discrete I/O based systems that were straightforward to program. I am very appreciative of Mills Products and NAS for helping me when I was starting out.

Since it is the time of the year to be thankful I thought I’d cover a bit from the Primer on one of my early areas of experience.

From the Primer: Metal Processing

Once a metal has been alloyed into its final constitution it must be brought into a useful form. It is common to cast the raw alloy into ingots for further treatment or use a continuous process to form it into sheets or plates. This is often done at the smelter prior to shipping using extrusion or rolling mills.

If metals are rolled thin enough they may then be re-rolled for shipment. Larger rolls are then often slit into smaller rolls by other facilities. The smaller rolls may then be further processed using cutting, punching or pressing techniques.

Ingots may be melted back into liquid form and poured into molds or castings to form a shaped piece. These cast or formed pieces are then finished in various ways using presses or machine tools.

Like the smelting industry metal processing uses automation extensively. Thicknesses and lengths must be accurately measured and roll speeds controlled and monitored.

Following are just some of the forming processes for metals:

• Investment casting (also called lost wax casting)
• Centrifugal casting
• Die casting
• Sand casting
• Shell casting
• Spin casting

Plastic Deforming
• Cold sizing
• Extrusion
• Forging
• Hot metal gas forming
• Powder metallurgy
• Friction drilling

Sheet metal forming
These types of forming process involve the application of mechanical force at room temperature.
• Bending
• Coining
• Decambering
• Deep drawing
• Drawing
• Spinning
• Flow turning
• Raising
• Roll forming
• Roll bending
• Repoussé and chasing
• Rolling
• Rubber pad forming
• Shearing
• Stamping
• Wheeling using an English wheel (wheeling machine)

Cutting is a collection of processes wherein material is brought to a specified geometry by removing excess material using various kinds of tooling to leave a finished part that meets specifications. The net result of cutting is two products, the waste or excess material, and the finished part. In cutting metals the waste is chips (or swarf )and excess metal. These processes can be divided into chip producing cutting, generally known as machining. Burning or cutting with an oxyfuel torch is a welding process not machining. There are also miscellaneous specialty processes such as chemical milling.
Cutting is nearly fully represented by:
• Chip producing processes most commonly known as machining
• Burning, a set of processes which cut by oxidizing a kerf to separate pieces of metal
• Specialty processes
Drilling a hole in a metal part is the most common example of a chip producing process. Using an oxy-fuel cutting torch to separate a plate of steel into smaller pieces is an example of burning. Chemical milling is an example of a specialty process that removes excess material by the use of etching chemicals and masking chemicals.
There are many technologies available to cut metal, including:
• Manual technologies: saw, chisel, shear or snips
• Machine technologies: turning, milling, drilling, grinding, sawing
• Welding/burning technologies: burning by laser, oxy-fuel burning, and plasma
• Erosion technologies:by water jet or electric discharge.
Cutting fluid or coolant is used where there is significant friction and heat at the cutting interface between a cutter such as a drill or an end mill and the workpiece. Coolant is generally introduced by a spray across the face of the tool and workpiece to decrease friction and temperature at the cutting tool/workpiece interface to prevent excessive tool wear. In practice there are many methods of delivering coolant, but it is usually recaptured, filtered and cooled before being introduced to the workpiece again.

I will be out of the country visiting Central America for the next month. I am going to take that opportunity to feature some of Doug Alward from Wright Industries’ writing. Doug is an Applications Engineer who has done some fascinating work on the evolution of automation and machine building companies in the US.

Hope everyone has a great Christmas and a wonderful New Year!


Electrical Engineer and business owner from the Nashville, Tennessee area. I also play music, Chess and Go.

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