Precision Bearings Parts CNC Machining for Robotics Industry

Specific materials are the best options for different types of precision bearings. AISI bearing steel 52100, for example, through-hardens to a hardness of 62 HRC, and exhibits the highest resistance to rolling contact fatigue for millions of cycles. It has a fine carbide structure which ensures smooth raceway finishes, and the carbide structure has proven reliable in bearings used for high performances. 52100 is excellent for machining, cost-efficient, and achieves dimensional stability through appropriate heat treatment and tempering. For these reasons, 52100 has become the number 1 choice for robot joint bearings, bearings for gear reducers, and high-speed spindles. Stainless bearing steel 440C has corrosion resistance which enables safe use in washdown and sterile environments, as well as for robotics in the food processing, pharmaceutical, and cleanroom industries. It has 5360 HRC hardness, which provides adequate wear resistance comparing to 52100, and it has non-magnetic and biocompatible properties which are important for medical robotics. Its corrosion, chemical, and humidity resistance allow safe use without protective coatings. In exchange for environmental durability, 440C has acceptable performance with a sacrifice of 10 to 20 percent reduced life compared to 52100.
M2 high-speed steel and D2 air-hardening steel are custom bearing tool steels due to their extreme temperature stability, wear resistance in high abrasive environments, and complex geometry heat treatment stability. They are also available in smaller quantities for prototypes. Lightweight bearing housings and retainers made from aluminum alloy 7075-T6 decrease rotational inertia in high-speed applications. It also has excellent thermal conductivity for heat dissipation, superior machinability for complex integrated features, and adequate strength for non-raceway bearing components. It is also economically produced for collaborative robots and positioning systems, where improved dynamic performance is realized through weight reduction.

State-of-the-art CNC bearing manufacturing as described in the upcoming sections encompasses the various stages of bearing production. Besides turning for the rough machining of bearing rings, most operations utilize grinding processes. These steps include cylindrical grinding of the inner and outer diameter raceways, achieving tolerances of 0.0001 inches for dimensions and 0.00005 inches for roundness, utilizing CBN grinding wheels; surface grinding of the bearing face surfaces and shoulders, obtaining perpendicularity of 0.0001 inches; grinding of the raceways for the contact surfaces of balls and rollers, achieving the specified radius and a surface finish of less than 4 Ra microinches; superfinishing or honing of the raceway surfaces to reduce friction and increase bearing life to below 2 Ra microinches; grinding of the threads for precision lock nuts used in bearing preload adjustment; EDM wire cutting for thin-section bearing rings and complex profiles in hardened materials; lapping of the bearing faces to achieve flatness 0.0001 inches with mirror finish; boring of the bearing housing bores with H7 or higher tolerances; heat treatment with specified hardness and minimal distortion; and inspection for compliance to bearing grades with specialized machines that measure the bore diameter, outer diameter, width as well as the radial runout, raceway geometry, and radial runout.

We can achieve tolerances within the limits of ABEC 7 or ISO Class 4 bearing industry standards, which include controlling bore diameter to within ±0.00012 inches to accommodate shaft interference or clearance fits, tolerances on outer diameters of ±0.00012 inches for housing fits, width tolerances of less than 0.0002 inches for axial positioning within bearing stacks, raceway roundness to within 0.00005 inches to ensure uniform load distribution on rolling elements, total indicator reading of radial runout to within 0.0001 inches to eliminate vibrational of the bearing during rotation, raceway of the bearing to within 4 Ra microinches for standard applications and for high-speed or ultra-precision requirements to within 2 Ra, face of the bearing within 0.0001 inches to ensure proper contact with shoulders and spacers, bore and outer diameter within 0.0001 inches to maintain alignment of the rotational axes, and controlled raceway with defined geometric, radial, and width tolerance dimensions of ±0.0002 inches for proper ball or roller contact. This allows bearing assemblies to maintain a radial runout of 0.5 microns for precision spindles, standard sizes for friction torque the bearing to be less than 0.01 Newton-meters, noise levels of the bearing to be less than 40 dB at normal speeds, temperature of the bearing to rise less than 15 degrees Celsius above ambient at rated loads, and service life of the bearing to exceed 20,000 hours under ISO 281 bearing life theory.

Yes, Zintilon provides versatile manufacturing options, which includes rapid prototyping for bearing designs and custom application testing with CNC turning and grinding, as well as low-volume production for specialized robotics where size and geometry are non-standard and custom, medium-volume production for research and limited production robots, high-volume production for standardized bearing components which are for robots equipped with sophisticated automation where thousands of races or housings are produced annually to precise tolerances, complete dimensional inspection and external and internal geometric consistency was ensured using bearing measuring machines, CNC measuring machines, and complete process documentation assessed and verified critical components for motion control bearings including dimensional and surface roughness, contours with profilometers, hardness for thermal treatment assessed and verified against control steps, ABEC or ISO tolerance classes were documented for critical motion control applications, and tolerances defined by the customer were verified for motion control application to bearing and housings.

Yes. According to ISO 9001 standards, all components must conform to bearing industry standards. This includes ABEC (Annular Bearing Engineering Committee) tolerance classes, iso 492 Bearing tolerances standards, customer specified dimensional and metallurgical requirements including hardness ranges and case depth specifications, and ASTM standards for bearing steel A295 52100. There must be complete traceability from the material heat lot to the final inspection including bearing metallurgical failure audits for components to be used in high precision applications where failure of the bearing will cause industrial automation to fail, cause production to stop, or pose safety risks.

We provide comprehensive finishing solutions tailored to the needs of each precision bearing component. These include precision cylindrical grinding to attain surface finishes below 4 Ra microinches on raceways with stock removal for dimensional accuracy control, superfinishing with abrasive stones to below 2 Ra microinches to create ultra-smooth surfaces for lower friction and extended life, lapping for bearing faces to attain mirror finishes and flatness within 0.0001 inches, through-hardening heat treatment to attain 58 to 63 HRC hardness on 52100 steel with tempering for toughness, case hardening for selective hardening of raceway surfaces while leaving ductile cores, black oxide coating for light corrosion protection and break-in lubrication retention, phosphate coating for temporary corrosion protection during storage and shipping, passivation on stainless steel to remove free iron and to enhance corrosion resistance, and specialized coatings like titanium nitride (TiN) and diamond-like carbon (DLC) for extreme wear applications or dry running conditions where conventional lubrication is used.

Custom designs for bearings tailored to specific robotic joints? Yes, to conceptualize solutions, our bearing engineers work alongside robotics designers. This collaboration allows us to understand various targeted primary load scenarios, constraints, and motion specificities. We construct large diameter, thin section bearings in hollow robotic joints, allowing routed cables to pass through, and integrated bearing races to be machined directly into aluminum structures of robotic arms to optimize weight and make assemblies more streamlined. We create four-point contact bearings for combined radial, axial, and moment loads capable of functioning in arrays of compact envelopes. We design cross-roller bearings for robotic wrists that require high rigidity in a small axial zone, optimize axial contact bearing preload configurations to reduce friction and achieve required stiffness, and design complete assemblies of face bearing races, rolling elements, cages, and seals to complete assemblies of a bearing. This rotary joint technology has a myriad of applications, including high-speed, friction and inertia delta robots, compact, heavy payload industrial robots, collaborative robots with backdriveability and safety, smooth low friction motion, and precision civil systems with sub-micron runout focus used for optical alignment or handling of semiconductors.

We provide comprehensive finishing solutions tailored to the needs of each precision bearing component. These include precision cylindrical grinding to attain surface finishes below 4 Ra microinches on raceways with stock removal for dimensional accuracy control, superfinishing with abrasive stones to below 2 Ra microinches to create ultra-smooth surfaces for lower friction and extended life, lapping for bearing faces to attain mirror finishes and flatness within 0.0001 inches, through-hardening heat treatment to attain 58 to 63 HRC hardness on 52100 steel with tempering for toughness, case hardening for selective hardening of raceway surfaces while leaving ductile cores, black oxide coating for light corrosion protection and break-in lubrication retention, phosphate coating for temporary corrosion protection during storage and shipping, passivation on stainless steel to remove free iron and to enhance corrosion resistance, and specialized coatings like titanium nitride (TiN) and diamond-like carbon (DLC) for extreme wear applications or dry running conditions where conventional lubrication is used.

The precision of CNC machining provides specific benefits in performance in several areas. For instance, obtaining raceway roundness to within 0.00005 inches guarantees uniform load distribution for all balls or rollers. This prevents localized stress concentration which leads to spalling or pitting failure. With the correct configuration, the designed bearing life can be fully realized or even exceeded in actual service. A raceway surface finish of less than 4 Ra microinches guarantees a 30 to 50 percent reduction of the friction coefficient on the surface. This reduction leads to decreased operating torque and heat generation which extend the lubrication intervals from 2,000 hours to 10,000 hours in continuous operation. Bore and outer diameter dimensions which have been manufactured precisely guarantee either interference or clearance fits as designed radial internal clearance is maintained post mounting. Correct fits also prevents bearing creep on shafts or in housings which leads to fretting corrosion and ultimately, premature failure. A bevelled edge and exact raceway geometry, inclusive of radius dimensions of within ±0.0002 inches, will eliminate optimal ball or roller contact stress distribution limiting maximum Hertzian stress to a level safe below the material fatigue limit. For optimal face grinding the goal is a perpendicularity of within 0.0001 inches, to ensure uniform preload distribution across all rolling elements in back-to-back bearing arrangements. For joint stiffness this provides the required 10 to 50 Newton-metres per millimeter deflection.
Having through-hardened raceways that achieve 60 to 62 HRC hardness provides wear resistance for predicted L10 bearing lives exceeding 20,000 hours under rated loads, as compared to 2,000 hours for inadequately hardened races. This is because the dimension consistency enables predictable bearing performance. A friction torque variation of under 20 percent between friction torque units allows the accurate control of robot motion without the need for individual calibration. A minimum radial runout of under 0.0001 inches provides a mechanical means of preventing the transmission of vibrations to delicate sensors and end-effectors, thus, maintaining positional accuracy. Technological advancements in heat treatment and stress relief minimize ongoing modifications to the mean dimensions of a workpiece, thus, maintaining tolerances through temperature cycling and extended service. Quality surface treatments protect against corrosion during storage and operation.
Contamination that causes 80 percent of premature bearing failures is prevented with clean manufacturing. Maintaining the bearing components that are machined with precision creates the rotational foundation for robotic systems that achieve angular positioning accuracy with minimal friction and backlash of ±0.005 degrees. They enable smooth motion profiles with no stick-slip or cogging and constant velocity for applications such as welding and dispensing that require highly variable total velocity of 1 percent or less. They also support high rotational speeds of over 10,000 RPM for spindle applications where the DN value is over 1 million, support moment loads for cantilevered robot wrist and elbow loads, and support thermal stability with performance from -20 to 100 degrees Celsius. They provide a long service life of over 20,000 hours with maintenance intervals of 5,000 to 10,000 hours and predictable reliability that facilitates the productive automation of several industries for automotive spot welding, electronics assembly, semiconductor wafer handling, medical robotics, and high-speed packaging.