Knowledge

Surface treatment is a process method that artificially forms a surface layer with mechanical, physical and chemical properties different from those of the base material on the surface of the base material. The purpose of surface treatment is to meet the requirements of corrosion resistance, wear resistance, decoration or other special functions of the product. For metal castings, surface heat treatment of lead screws and guide rails is a commonly used surface treatment method.

 

Surface hardening

Surface hardening refers to a heat treatment method that strengthens the surface of a part by rapidly heating the surface to austenitize it and then quenching it without changing the chemical composition and core structure of the steel.

The main methods of surface heat treatment include flame hardening and induction heating heat treatment. Common heat sources include oxygen-acetylene or oxygen-propane flames, induction current, laser, and electron beam, etc.

 

Induction heating

A method that uses alternating current to induce huge eddy currents on the surface of a workpiece, rapidly heating the surface of the workpiece.

Induction heating is classified into the following types:

 

1. High-frequency induction heating, with a frequency of 250-300 KHz, and a hardened layer depth of 0.5-2 mm;

2. Medium-frequency induction heating, with a frequency of 2500-8000 Hz, and a hardened layer depth of 2-10 mm;

3. Power-frequency induction heating, with a frequency of 50 Hz, and a hardened layer depth of 10-15 mm.

 

Flame heating

A method of directly heating the surface of a workpiece using an acetylene flame. It is low-cost but the quality is difficult to control.

 

Laser heating

A method of heating the surface of a workpiece using a laser with high energy density. It is highly efficient and of good quality.

Laser surface strengthening can be classified into laser phase transformation strengthening treatment, laser surface alloying treatment and laser cladding treatment, etc.

Laser surface strengthening is mainly used for parts that require local reinforcement, such as blanking dies, crankshafts, cams, camshafts, splined shafts, guide rails of precision instruments, high-speed steel cutting tools, gears and cylinder liners of internal combustion engines, etc.

Nowadays, driven by the wave of Industry 4.0, the current status of this technology shows a fusion of precision and intelligence. Taking the induction heat treatment of lead screws and guide rails as an example, the core objective is to achieve uniform and controllable hardening layer depth and microstructure under the constraint of micron-level geometric accuracy. Industry 4.0 technology has brought about three major breakthroughs for this purpose.

 

Precision control capability has soared: The combination of all-solid-state IGBT power supplies and adaptive PID algorithms has compressed temperature fluctuations to within ±1℃, and the hardening layer depth tolerance is controlled within ±0.05mm, far exceeding the ±3℃ and ±0.2mm of traditional equipment. After optimization, a certain domestic high-precision ball screw has achieved a surface hardness of 61.5HRC, with a 30% increase in service life and a 12% reduction in scrap rate.

 

Efficient energy-saving path breakthrough: The application of megawatt-level high-temperature superconducting induction devices has doubled the energy conversion efficiency compared to traditional resistance furnaces. For a 500kg metal workpiece, the heating time has been reduced from 9 hours to 10 minutes, with a 50% reduction in comprehensive energy consumption and more than a 50% reduction in carbon emissions.

Intelligent closed-loop formation: An online monitoring system based on machine vision captures workpiece deformation in real time, combined with a digital twin model to predict the stress distribution of the hardening layer, achieving full autonomy in the "perception-decision-execution" process.

 

As the "bones" of precision machinery, the induction hardening and tempering equipment for lead screws and guide rails directly determines the accuracy, lifespan and reliability of high-end machine tools, robots and semiconductor manufacturing equipment. Induction heat treatment equipment is undergoing a qualitative change from "thermal processing tools" to "intelligent systems". Currently, this technology has demonstrated irreplaceability in four high-end fields.

 

1. High-precision machine tools field: The ball screws of CNC machine tools adopt segmented variable-frequency quenching, with the full-travel straightness error ≤ 3 μm/m, reducing the cost of imported products by 50%. After a certain enterprise adopted the AI temperature control model, the fatigue life of the screw exceeded 2 million cycles.

2. New energy vehicle field: The induction quenching equipment for motor rotor shafts integrates a robot loading and unloading system, shortening the production line cycle to 45 seconds per piece, which is four times more efficient than the traditional process. A certain car factory improved the uniformity of shaft heating to ±3℃ through conformal cooling coil design.

3. Railway transportation equipment: The rails for high-speed trains with a speed of over 160 km/h need to meet the strict standards of a hardened layer depth of 4-6 mm and a surface hardness of 58-62 HRC. The dual-frequency quenching technology has been successfully applied to the fastener system of high-speed railway tracks, reducing the wear rate by 70%.

4. Aerospace field: The regulating screws of aircraft engines adopt a vacuum induction quenching + low-temperature plasma nitriding composite process, improving the anti-fretting wear performance by three times and meeting the service requirements under extreme conditions of 1500℃.

 

Despite significant technological advancements, high-end applications still face four major challenges:

 

1. Complex geometric profiles: Structures such as lead screw helical grooves and variable cross-section guide rails can cause magnetic field distribution distortion. Traditional inductors struggle to achieve contour heating, often resulting in insufficient hardening at the tooth root or overheating at the tooth tip. For instance, in the dual-frequency quenching of gears in urban rail vehicles, the failure rate of hardened layer fractures due to sudden changes in tooth profile curvature is as high as 8%.

2. Sensitivity to material property fluctuations: The critical points of phase transformation for high-carbon steel and ductile iron differ, requiring the power supply to respond to frequency band switching within 0.5 seconds. However, the stability of domestic IGBT power supplies in the >100kHz high-frequency band is still lacking, which restricts the uniformity of quenching for thin-walled guide rails.

3. Bottleneck in cooling medium coordination: The temperature control accuracy of the water-oil mixed medium during the quenching stage is insufficient, causing fluctuations in the martensite transformation rate. A certain machine tool enterprise's actual measurement shows that a deviation of 5°C/s in the cooling rate can increase the residual stress of the lead screw by 200MPa, leading to microcracks during service.

4. System integration barriers: Compatibility issues between the communication protocols of old equipment and industrial IoT platforms result in 30% of production lines being data islands.

 

Vigor has the professional supply chain of special treatments for our metal components of castings, die-forgings and CNC machined parts. If you have any question or parts need to be developed, please feel free to contact us at info@castings-forging.com