Laser Cladding has seen success in the additive manufacturing industry. IBC coating now offers a solution that is capable of cladding a host of material to increase the wear performance of components in the food, electrical, energy and agricultural sectors. Continued process development and new technology will improve the quality and variety of applications served, making laser cladding a viable solution in the decades to come.
Material and Application SelectionThe following materials have been used to clad a host of products:
- Stellite 6 – Food applications, magnet dies, die punches
- Stellite 12 – High temperature corrosion/waste treatment
- Inconel 718 – Die punches
- Inconel 625 – Butter passes, corrosion resistance
- 420 SS – Centrifuge hubs, shafts, bearing journals
- Tungsten Carbide – Plow blades, grinding disk manufacturing
- General Wear
- Metal to Metal Wear
- High Temperature Corrosion
- Hot Gas Erosion
- Low Stress Abrasion
Clad ParametersAn overview of the cladding process control is shown in the following figure
If there are any errors/discrepancies in any of the inputs listed, the clad/final product will be compromised. Therefore, careful control of process parameters is a must.
In welding/cladding systems, initial process development revolves around adjusting the following parameters to achieve a stable bead:
- Heat input
- Cool/Wait Times
- Wire/powder feed rate
The heat input is based off of the travel speed and total energy/power being delivered. For laser welding processes the feed rate and heat source are independent of each other. This enable the process to be more controlled than standard gas metal arc (GMA) processes, where the wire feed speed is directly related to the current/power output.
During the printing process, the directional heat flow changes in the printed part. In conventional cladding applications, the cladded areas experience a three-dimensional heat flow where the heat is dissipated fairly quick in the bulk of the printing pad.
In applications of high build-up/additive manufacturing, the heat flow characteristics change. As the layers are built up, the heat flows along the walls of the part, taking on a 2-dimensional form. As the print height increases, the peak temperature increases and the heat dissipation rate decreases, increasing the thermal strain/distortion (see the strain model below). After a given number of layers, the heat flow and process temperatures reach a steady-state where there is no significant change in the thermal strain on the material.
To reduce the amount of strain/distortion in the part, the steady-state condition must be obtained in the shortest number of layers possible. In order to do this, the printing process heat input should be as low as possible while still creating a stable bead. As the heat input is lowered, deposition rates are reduced, bead size decreases, and cycle times are increased.
For high strength steels, the inter-pass temperatures will limit the cooling times, making it more difficult to print successive layers without excessive melting/sag. The heat gradient can be further controlled Part analyses need to be conducted to balance cycle times and distortion effects with the geometry of the component.
From a metallurgical perspective, laser cladding is a localized, high speed heat treatment. The solidification and transformation rates are much higher than conventional heat-treating processes. In the printing process, the heat treatments are further complicated with varying heat flows/gradients. Once a bead layer is printed, it can undergo a variety of tempering/quenching operations due as the welding/printing process proceeds above it. As result, the material properties can vary between layers depending on the geometry and size of the part.
This can present a variety of challenges in the additive manufacturing world. For standard cladding applications, materials with enhanced properties are cladded on to lower-grade materials. The thermal properties of these materials vary greatly, and the large thermal gradients seen in laser cladding can produce a lot of stress in the clad and clad interface.
To prevent cracking, a host of practices are used to prevent failure and ensure quality:
1 Investigate the application - Are micro cracks in the material an issue? Typically, high wear applications in the mining/construction industry don’t focus on cracking as a failure source unless the clad material spalls away from the parent material. Will the clad outlast the component? Can a softer, more ductile material be used?
2 Buffer Layers - To control the stresses in the clad, buffer passes are put between the base material and clad. These are typically made of stainless steels or Inconels.
3 Pre-heating - Preheating the material lowers the temperature gradient, reducing the chances of cracking. Typical methods involve flame, furnace and induction heating, with some method of monitoring the interpass temperature (infrared guns, temperature probes, thermocouples, etc.).
The microstructure of 3D printed parts are also affected by the thermal gradients. To control the microstructure of the printed part, the following steps need to be taken:
1 Develop low heat input process parameters - Reducing the heat input will reduce the peak temperatures and will achieve a steady-state condition quicker, reducing the amount of transient microstructures.
2 Adjust cool/wait times - The inter-pass temperatures need to be made as uniform as possible and as close to the melting point of the material without allowing the process to melt the previous layer(s). Lowering the heat input will allow us to decrease the wait times.
3 Pre-heat treatments to printing pad - Pre-heating the printing substrate will decrease the temperature gradient/heat flow, influencing the cooling rates and microstructure of the material.
4 In-process heating - Applying inductive heating to the printing pad could control the heating and cooling gradients, and could decrease the time needed to reach a steady state and control the microstructure/mechanical properties.
5 Post-process heat treatments - Normalizing the component after the printing is complete will help control the final microstructures. For the titanium and high-strength steels listed, this will be included in the heat treatment processes used to obtain the desired mechanical properties.
In addition to the clad properties, AM and cladding systems have to obtain a high level of accuracy and precision. The process parameters must be controlled to ensure the build height is equal to the offset distance specified in the program. If there is even a difference of 0.01 mm between the two, the focal point of the laser beam will either “dive in” or “pull away” from the part, leading to variations in power density/heat input, erratic melting, uneven layers, and poor clad quality. These effects are magnified as the number of layers increase.
In addition, sharp transitions in part geometries can be challenging depending on the machine controls/capabilities. Many machines have to accelerate/decelerate or round corners to change directions. This could affect the build in those areas and or affect the edge geometry.
Laser Cladding Cell
- 4 kW IPG fiber laser
- Headstock/Tailstock Positioner
- Capacity: 2000 kg
- Maximum Length: 10 ft.
- Wide Selection of clad materials
- Vary depending on alloy selection
- Common applications
- Wear Resistance
- Impact Resistance
- Corrosion Resistance
Cladding Wear Sleeves
ID Laser Cladding
Many laser cladding processes involve cladding the outer diameter of components. A lot of fluid and abrasive wear can occur on the inner surfaces/diameters of rolls and tubes, especially if the medium travelling through is abrasive or caustic.
To combat these types of wear, material can be cladded into the inner diameter of rolls and tubes. This would save on material costs, since the base material of the tube can be fabricated with lower grade material. Depending on the application/tube dimensions, the clad can be left on as-is or machined depending on the clearances/tooling geometry.
IBC materials is integrating a special ID cladding tool from Nittany Laser Technologies. Its small profile is capable of cladding tubes/bores as small as 1.5 inches, with an effective cladding length of 29 inches at the smallest diameter.
Centrifuge Hubs – Stainless Steel
Cladding Steel Mill Rolls
- Base Material – 4140
- Length – 66 in
- Outside Diameter – 7.67 in
- Clad Material – 431 SS
Steel Mill Roll Processing
- Laser Clad
- Final Machine
- Ion Plasma Nitride Final Surface
- Increased hardness
- Increased wear resistance
Wind Turbine Centrifuge Hubs
Wind Turbine hubs and shafts are subjected to wear due to load variation due to changes in wind speed/intensity. Once this happens, the gearboxes can fail prematurely, leading to large replacement costs.
IBC Coatings Technologies has laser cladded worn hubs, journals and shafts, which are then machined back to print specifications. Base materials include a variety of stainless steels (410 SS, 420 SS, 440 SS). The prime cladding material is 420 stainless steel. Careful control of the preheat and process parameters ensures the clad material is free of defects and has similar/improved properties compared to the base material.
In the picture above, a small centrifuge hub from California was repaired using laser cladding and thermal spray technologies.
Centrifuge hubs experience a lot of metal to metal wear/abrasion. IBC Coatings Technologies has laser cladded worn centrifuge hubs, journals and shafts, which are then machined back to print specifications. Base materials include a variety of stainless steels (410 SS, 420 SS, 440 SS). The prime cladding material is 420 stainless steel. Careful control of the preheat and process parameters ensures the clad material is free of defects and has similar/improved properties compared to the base material.
Bottom Punches/Magnet Dies
When produce magnets for motors, the magnet material is combined in a slurry. It is then set into a die, where there are punches that force the slurry into the magnet die and force all the water/contaminants out of the slurry. These punches have to have tips that are non-magnetic so they don’t interfere with the magnet’s polarity. In addition, the dies are subject to high metal to metal wear.
Traditionally, stellite 6 has been applied to the top surface via GTAW. However, the dilution line between the base material (D2 steel) and the substrate (Stellite 6) was choppy, and the manual process was time consuming (roughly 1 hour per punch).
IBC proposed an automated solution to improve productivity. To do this, a coaxial powder feed laser head was used. Custom programming was implemented to map the clad/layer paths.
In conclusion, IBC was able to produce a buildup of stellite 6 that exhibited a very clean dilution line between the parent and clad material, and produce a clad in 15-20 minutes as opposed to 1 hour. Hence, quality and productivity was improved drastically with this automated solution.
Laser cladding is an additive welding process in which wire or powder feed stocks are continuously fed into a high-powered laser beam and melted across a metallic substrate. The process allows the materials to form a complete metallurgical bond with the metallic substrate. The resulting coating is dense with no porosity or voids. Laser cladding is particularly useful as a repair technology for oil and gas industry tooling and aerospace alloy substrates.
- Complete metallurgical bond
- Small heat-affected zone
- No porosity
- High cooling rate
- Can clad with a wide range of materials
- Seal surfaces
- Pump components
- Forging dies
- Best technique for increasing wear resistance
- Metal to Metal
- High Temperature Corrosion
- Hot Gas Erosion
- Low Stress Abrasion
- Remanufacturing Applications
- Maximum Length – 10 ft
- Diameter Limit – 6 ft
- Weight Limit – 2,000 kg
- Offline Capabilities to Model Parts/Determine Feasibility
IBC Coatings Technologies now offers laser cladding as a viable, proven additive cladding operation. Paying careful attention to process parameters, preheating, and program stability has ensured success and repeatability. Looking forward, the invention of new technologies and monitoring capabilities will increase the robustness, quality and diversity of this process, lending itself to more applications in the future.