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Laser hardening involves surface heating of the hardened element with a focused laser beam. The material is very quickly heated above the austenitizing temperature and then undergoes rapid cooling.

 Characteristics

Cooling by itself results from the temperature difference between the hardened surface and the core of the element and does not require any external coolant. The depth range of the hardened layer is 1 – 1.5 mm, depending on the type of hardened material and the size of the element. Compared to conventional hardening methods (induction hardening, flame hardening), laser hardening causes the formation of hardening structures of higher hardness and less deformation of the element during the hardening process.

Laser pad welding is a process where the source of heat necessary to melt the filler and the substrate is a focused coherent light beam. Filler, in powder or wire form, is fed continuously to a pool of liquid metal, which forms the padding when solidified. The entire process, due to the need to maintain extreme precision and comply with occupational health and safety requirements, occurs in a fully robotized manner.

Compared to conventional pad welding methods, laser pad welding offers a number of advantages:

• small width of the heat affected zone,
• minimum mixing of the filler and the substrate,
• high process speeds can be achieved,
• low deformation of the parent material after the pad welding process,
• low thickness padding (~ 0.5 mm) can be achieved,
• preferred fine-grained structures in the padded material due to the solidification rate can also be achieved

Most common materials used in laser pad welding are:

• iron-based alloys,
• nickel-based alloys,
• cobalt-based alloys,
• copper alloys,
• alloys containing hard carbides,
• bearing alloys.

MIG/MAG (GMA) pad welding involves an arc between the consumable electrode and the welded object in a gas atmosphere which melts the electrode material and the substrate creating the padding.

Solid wires with diameters of 0.5 – 2.4 mm and powder core wires with diameters of 1.2 – 4.3 mm. Pad welding capacity of 4 – 10 kg/h can be achieved with DC pad welding with with positive polarity and arc metal spraying. A potential drawback of this solution is the high proportion of substrate metal in the padding, which is 20-40%. It is possible to limit metal weld penetration to below 5% by pad welding with thin wires with a diameter of 0.5 – 1.2 mm, so-called short-arc with coarse metal transfer through the arc.

The process is robotized to achieve maximum repeatability with minimum number of defects. The MIG/MAG process is used by Plasma System S.A. in all situations where the required precision is lower than in the case of laser or PTA pad welding, and the economic factor or high layer thickness are of decisive importance. This method is very versatile and can be applied to a wide range of padding materials.

PTA pad welding is a process where the source of the heat is a plasma arc, which is a stream of highly ionized gas. The material in powder form s fed directly into the stream of hot plasma, where it is melted and then flows into a pool of liquid metal. Plasma pad welding enables a higher power density and efficiency in the case of the TIG method, while maintaining top quality of the padded layer and low mixing with the substrate.

Additionally, using a concentrically fed stream of powder ensures full repeatability of the process. Some of the padded materials are:

• cobalt-based alloys,
• nickel-based alloys,
• iron-based alloys,
• copper alloys, alloys containing hard carbides.

TIG (GTA) pad welding is arc pad welding with a non-consumable electrode in a gas shield which involves feeding the filler to the arc area between the non-consumable tungsten electrode and the padded substrate in inert gas shielding.

The filler can be fed in the form of solid wire, powder wire, strip or powder melted directly on the padded substrate. The protective gasses in this process are generally argon and helium; 5-10% hydrogen or nitrogen additive is sometimes used to increase the temperature (hydrogen additive is not acceptable in the case of welding aluminium, copper and and their alloys). The non-consumable electrode is made of tungsten with the additive of thorium, zirconium, lanthanum, cerium or nir to increase the durability, ease of ignition and stability of the arc.

High repeatability and stability of the arc provide exceptional quality of padding with almost no defects. The TIG method is used by Plasma System S.A. in all situations where the filler is available only in wire form, and the technical conditions prohibit the use of laser or CMT technology.

Items made of steel, cast iron, cast steel, copper alloys and aluminium alloys can be padded. Padding welds are applied with high-alloy steels, lead, nickel alloys, cobalt, copper, aluminium and ceramics.

Advantages of TIG Pad Welding:

• Inert metallurgical process ensuring full penetration of alloying elements into the padding weld
• High concentration of heat which provides a narrow heat affected zone, little liquid metal bath and low proportion of native material in the padding
• No splashing or slag

Application:

• Components made of various types of steel and non-ferrous metals can be refurbished
• This method is recommended while padding abrasion resistant layers with stellite sticks with dynamic loads
• The method is used for plating carbon steel items with high-alloy steels and non-ferrous metals

The CMT (Cold Metal Transfer) technology is an innovative system developed by Fronius for welding and padding with a minimum amount of heat input. This system, due to its specific nature, causes up to 75% less mixing of the filler with the native material compared to other pad welding methods. The CMT method makes it possible to combine materials with extremely different melting points, such as steel and aluminium. The filler is fed into the pool in wire form. Owing to the low degree of mixing, the top layer gains the required properties with the first layer already, and the low heat impact limits component deformation.