Plasma Cutting

Penn Stainless Products utilizes two Koike Aronson Versagraph Millennium Series Plasma Cutting Systems (Model 3100) for all stainless steel plate and sheet plasma cutting. The system features Hypertherm’s HPR800XD HyPerformance ® Plasma technology, which enables powerful precision cutting for superior quality and consistency up to 6.25-inch-thick stainless steel plate. The two machines operating on one shared rail system allows for a cutting envelope of 10 feet wide X 65 feet long. PSP’s Koike Aronson Versagraph Millennium Series cutting solution provides unmatched speed, accuracy, versatility and durability in a plasma cutting system.

Production benefits include optimum cut quality, less dross (cleaner cut edges), less kerf loss (narrow cut), and a smaller heat-affected zone (due to faster cut speeds). Additionally, the system yields a significantly reduced bevel angle on the cut edge (1° to 3° bevel angle compared to 7° to 10° with a standard plasma system).

The plasma cutting machines at Penn Stainless Products are multi-gas capable and utilize highly advanced plasma technology. They are equipped with state of the art Yasukawa Sigma-V motion drives for excellent positioning accuracy. Also, they are equipped with ArcGlide® Torch Height Control, which provides automatic torch height control to enable optimal cut quality.

Plasma Cutting at Penn Stainless Products

• Large cutting size capability
• Thick cutting range capability
• State of the Art plasma cutting technology
• Over 30 years of in house processing expertise
• Two in-house plasma cutting machines for maximum flexibility and fast deliveries.
• Downdraft tables that capture most of the fumes and other pollutants created during cutting

Processing Questions to Consider

• Do you need to add a material allowance for secondary processing?
• Do standard tolerances meet your requirements?
• Does the material need to be marked with part numbers, job numbers, purchase orders, etc?
• Are there special packing or handling requirements?

History and Development of Plasma Cutting

Plasma cutting is based on the technology used for plasma arc welding, which was developed during the 1940’s to provide a more efficient way of joining together metals for the war effort. Plasma, commonly described as the fourth state of matter, is electrically conductive, and composed of ions and free electrons in roughly equal proportions.

The plasma welding process uses this plasma to transfer an electric arc to a work piece.  The metals to be welded are melted by the intense heat of the arc and are fused together. In the 1950’s, scientists discovered that by reducing the inert gas flow opening to the nozzle used for arc welding, both the temperature and the flow speed of the gas increased significantly. At these higher temperatures and flow rate, the resulting arc was found to cut the materials, rather than weld them together.

Plasma Cutting Development

Based on this discovery, the first commercial plasma cutters were introduced in the early 1960’s. Plasma cutters can be used to cut all metals, including stainless steel. Early plasma cutters needed an initial direct contact between the torch and the cutting material to create an electric arc between them.

Now, in their basic form, plasma cutting machines typically include an arc starting circuit, a power supply, a cutting gas, and a plasma cutting torch. The plasma cutting torch contains a cooling mechanism (typically, a secondary gas or water), an electrode in the middle, and a nozzle at the end.

A simplified description is as follows: The power supply and the arc starting circuit are used to generate a high frequency electric arc between the electrode and the nozzle. Additional current from the power supply increases the size of this arc, and gas flow through the torch pushes this arc out of the nozzle orifice. This is the pilot arc.

When the pilot arc touches the work piece (the metal being cut) the positive pole of the arc, which was attached to the nozzle “transfers” to the work piece.,  Gas flow and the amperage of the current flowing through the arc are increased to form the plasma cutting arc. Current flows through this arc between the electrode and the cutting material.

The power supply ensures that enough energy is provided to maintain the plasma arc. The swirling plasma gas that remains un-ionized forms a sleeve around the arc as they exit the nozzle orifice This sleeve of cool un-ionized gas is the primary shaper of the cutting arc. The secondary (shield) gas further constricts the cutting arc as it passes through the shield orifice. The high temperature of the plasma arc melts the material.  The high velocity of the gas flow removes the molten material from the cut.

Plasma Cutting Developments

By the late 1980’s, advanced plasma cutting machines with computer numerical control (CNC) technology were introduced to market. This enabled plasma cutting machines to cut complex two dimensional geometries based on programmed instructions.

As soon as the arc begins to melt the cutting material, torch motion is initiated, and the programmed cutting route is followed. Over the years, many variations of plasma cutting machines have been introduced to the market, include the following:

• Dual Gas PAC: In this process, a shielding gas is used in addition to the cutting gas
• Downdraft Cutting Tables:  – In this process, the cutting table includes exhaust sections that capture most of the fumes and other pollutants produced during cutting and remove them from below the material being cut

Guidance for Stainless Steel Plasma Cutting Selection Process

Plasma Cutting is one of the most versatile and low cost methods to cut stainless steel. And, by utilizing Penn Stainless for your plasma processing, you achieve many additional benefits as compared to using plasma processing options generally available. Still, before selecting this process, it is important to consider many factors, including tolerance requirements, material size and thickness, desired edge quality, lead time, and also any additional processing that will occur after the cutting step.

Benefits:

• Low cost
• Can be used to cut complex 2D geometries, rings and disks, and simple squares and rectangles.
• Quick turnaround times
• Enables efficient material usage when cutting a small shape from a large plate or sheet.

Limitations:

• Use with heat sensitive grades is limited due to risk of cracking.
  • Should not be used with 440C grade stainless steel
  • Should not be used with 410, 416, 420 grades stainless steel over 1.25” thick
• Use with precipitation hardening grades is limited.
  • Should not be used with 17-4 grade stainless steel over 1.5” thick.
• Relies on the use of very high temperatures. Creates heat affected zones (HAZ) around the cut surfaces that may need to be removed by secondary processing. Note, advanced plasma technologies utilized at Penn Stainless produce smaller HAZ than conventional plasma technology, but HAZ area is still larger than encountered with laser.
• Cut quality and tolerances are not at the same level as waterjet and laser cutting. However, given the state of the art plasma technology used at Penn Stainless Products, the levels are much closer than achieved with other standard plasma machines on the market.
• Plasma cutting may lead to dross. Note: At Penn Stainless Products, dross created during plasma cutting is removed in a secondary processing step.
• Not able to cut small holes:
  • A general rule of thumb is that minimum hole diameter when plasma cutting stainless steel is limited to twice the thickness of the cutting material.
• Cannot be used for 3D geometries.
• Plasma cutting can add additional stresses to the part which can lead to distortion in some cases.

Cost Factors to Consider when Comparing Processing Costs

In order to accurately determine the true cost of cutting when comparing processing options, it is important to consider the following:

Cutting Costs

As compared to laser, waterjet and saw cutting, the cost of the plasma cutting process itself is quite inexpensive.

Material Costs

As compared to laser, waterjet, and saw cutting, in most cases plasma cutting will require greater material usage. In order to accurately determine this, it is important to consider extra material that may need to be purchased to account for material that needs to be removed in secondary operations following the cutting process, kerf loss and skeleton loss.

Extra Processing Steps

When determining the economics of choosing plasma cutting, it is important to consider the cost of additional processing steps that may be utilized.

• Plasma cutting may lead to an additional processing step to remove HAZ. It should be noted that removing HAZ areas on stainless plate wears heavily on tool life, which can make this processing step fairly expensive
• May lead to the need for additional processing steps to achieve flatness. Risk of distortion, such as warping, camber and bow, can be high, especially for narrow thin plates. Some flattening methods, such as grinding, can be quite expensive.
• While in certain applications plasma cutting can lead to additional process steps as compared to laser cutting, saw cutting, and Dynamic Waterjet cutting, it should be noted that the state of the art plasma technology used at PSP produces clean, shiny, weld ready edges that can be welded without the need for secondary operations.

Stainless Steel Plate and Sheet Plasma Cutting Benefits

Penn Stainless Products uses state of the art plasma cutting technology. This has many benefits for end user customers as compared to less advanced plasma cutting technologies.

• Better cut quality
• Significantly reduced taper angles on the cut edge.  As a comparison point, this state of the art plasma machine typically produces a 1° to 3° taper angle for the same cutting conditions in which a standard plasma machine would produce a 7° to 10° taper angle.
• Better tolerances
• Cleaner cut edges (less dross)
• Reduced HAZ (due to faster cut speeds)
• Thicker gauge cutting capability; Can cut up to 6.25” thick plate
• Larger size sheet and plate cutting capabilities.  Table sizes can handle material up to 10ft x 65ft
• Ability to use specialty gases.  This enables PSP to deliver weld ready edges that can be welded without the need for a secondary operation.
• Better consistency due to advanced CNC capabilities and automated torch height control systems.
• Downdraft Table, which leads to significantly reduced staining (as compared to underwater PAC) and very minimal fumes.

Huge selection of plate and sheet inventory, including large sizes and over 30 grades are available.  By offering extensive inventory and large size and thick gauge plate cutting capability, Penn Stainless Products is uniquely positioned to provide cost and time savings opportunities to the end user customer as compared to other service centers.

Penn Stainless Products has 30 years of processing experience to help customers select the most cost effective processing options that best meet their needs.

All plasma tables at Penn Stainless Products are controlled by CNC systems.  Penn Stainless Products will accept CAD files in .dxf or .dwg format, PDF renderings of CAD files, PDF scanned drawings, faxed drawings, or textual (i.e. descriptive) dimensions.  PDF and CAD files are preferred over faxed drawings.