Figure 1: Advanced custom gear design solutions for high-torque applications in EV and robotics industries
Introduction
In electric vehicle technology and robotics, two sectors in which development is racing ahead, requirements for transmission systems have reached unprecedented levels. Experts are faced with several challenging tasks, as small amounts of efficiency loss in transmission can adversely affect an electric vehicle's range, noise in gears can be clearly felt in the absence of engine masking, and in robotic joints, gear failure can result in high costs of automated cell down times. The underlying problem lies in realizing that general and standardized gears tend to be inefficient in meeting such high levels of requirements.
This tutorial will examine how a systematic and application-directed custom gear design service can successfully address these issues. It will include a comprehensive outline, ranging from prime gear design principles and primary factors of gear applications (EVs versus Robotics) through cutting-edge manufacturing methods and techniques of cost management. To unlock the secrets of successful custom gears, we have to begin by revisiting their prime principles of design.
What Foundational Principles Are Behind High-Performance Custom Gear Designs?
However, when one progresses beyond mere calculation, high-performance gear design is based on four fundamental pillars of systems engineering. These ensure that not only is the gear an object on its own but also an element of a complete system.
1. Strength and Fatigue Life Analysis
To make the gears resistant to failure modes such as pitting and tooth breakage, a proactive and analytical approach is needed. First, there is a heavy emphasis on analytical calculations as per recognized standards, including ISO 6336. Then, a contact fatigue calculation is carried out for the purpose of preventing surface pits, and a bending calculation is carried out to secure the gear against a tooth breakage failure mode. These analyses are not generic; hence, the calculation is carried out according to the expected load spectrum, including peak torques, cyclic variation, and total number of cycles, depending on the lifetime of the gear.
Figure 2: Contact stress simulation and meshing optimization for maximum gear longevity
2. Meshing Characteristics Optimization
To ensure smooth power transfer and prevent excessive wear and tear, the fundamental geometric shape of the gear mesh needs to be optimized. This essentially calls for careful design considerations to optimize parameters such as the Contact Ratio and the Sliding Ratio. However, a Contact Ratio that maximizes the number of teeth sharing the load at a time, thereby providing quieter and stronger meshes, needs to supplement the aspect of minimizing the value of the Sliding Ratio. It cannot be overstressed that the reduction of the Sliding Ratio at points A and B during the approach and recess phases assumes supreme significance to counteract the effect of friction and prevent adhesive wear.
3. Integrated Thermal Management
High-speed or heavy-load environments produce considerable parasitic friction and windage heating, which can contaminate lubricants, cause expansion, or otherwise contribute to premature component failure. Indeed, appropriate lubricant-related cooling designs and considerations are fundamental. These considerations extend well beyond simple lubricant selection. Optimal enclosure design for efficient convective cooling, appropriate placement of cooling rings or jackets, and lubricant delivery system configuration to target critical regions for both lubrication and cooling purposes---or to prevent operation in regions that might cause problems---are just some of the considerations. Preventing runaway heating is critical to retaining specific dimensions or material characteristics during extreme operation.
4. Design for Manufacturing (DFM) Synergy
A theoretically optimal design for which optimal production is not possible is nothing short of useless, according to Daemen's quote above. While a theoretically optimal design may indeed be perfect for functionality and manufacturability, production limitations and capabilities must play a crucial role in defining design tolerances. An example would be defining an optimal design with a maximum design tolerance specified as 'ISO 4,' which most likely requires processes such as precision grinding or honing and not merely hobbing or shaping. An optimal design strategy based on DFM would involve taking inputs from production experts during design and focusing on simplifying complex design elements to result in perfectly manufacturable components with optimal design to manufacturability fit by using materials suitable for available heat treatment processes.
How Does Gear Design Differ Between Automotive and Robotic Applications?
The need for special gear design solutions is readily apparent when comparing the different demands of automotive and robot applications. "One size fits all" is not going to work, as it will lead to suboptimal results.
⦁ Load Spectrum and Dynamic Response: There's a world of difference in the nature of the forces that these gears are subjected to, as can be seen below. Automotive gear design, for a conventional car, usually involves designing for constant, high-torque forces, which are optimized for maximum efficiency for prolonged use. On the other hand, robotics gear design requires gears that can handle highly dynamic forces, which include frequent start-stop actions, reverse impacts, shock forces, etc. This requires a gear design optimized for its impact resistance and fatigue strength.
⦁ Precision and Backlash Requirements: The major performance criteria establish the precision levels that must be achieved. Although automotive systems emphasize maximizing transmission efficiency (realized through ISO grades 6-8 gears), more precision and less backlash are demanded in robotics, where precision is usually achieved by adopting ISO grades 4-6 in robotics. The backlash in the teeth of two meshing gears, which are not in actual contact due to the manufacturing tolerances of the teeth, adversely affects robotics systems. Hence, in robotics, gears are often used that feature special tooth designs and pre-loading techniques to completely eliminate backlash, which promotes precise, repeatable motion.
⦁ Service Life and Noise Control (NVH): The operating environment shapes the list of requirements related to longevity and noise. The EV gearboxes are designed to have lifetimes above 10,000 hours of operation and noise levels limited to 70 dB or less to provide comfort to the human operators. Often, joints in robotics have a lifespan of over 20,000 hours since they are used in industrial environments and have to operate in very quiet conditions, meaning noise levels of less than 60 dB to facilitate "quiet" collaboration with human operators. Hence, NVH optimization of gears becomes an essential non-negotiable criterion in robotics.
What Role Does Material Science Contribute to Achieving High Gear Performance?
Material selection is an essential factor directly affecting the functionality, durability, and expenditure of the gear. Material and process determine the basic potential of the component.High-performance gear machining usually starts with the use of high-strength alloy steel grades like 20CrMnTi or 42CrMo. These materials have been picked for their suitability for various processes involving case carburizing and quenching, which enable the production of a work piece that has a tough and ductile core supporting bending loads well, as well as an incredibly hard surface for resisting pitting and abrasion. For reduced loading and quiet operation where weights matter, engineering plastics or sintered metals provide an acceptable substitute. Moreover, secondary surface modification processes like nitriding, intended for generating beneficial hard layers with critical compressive stresses, or special PVD layers for reduced friction, play highly important roles in resisting fatigue strength or wear at the cutting edge.
Which Advanced Manufacturing Processes Are Most Essential for Precision Gears?
Advanced manufacturing processes are a critical connecting link that transform an optimized design into a real high-performance solution. This is important since a design may promise theoretical benefits that may not materialize when an object is produced using manufacturing processes.
1. High-Precision Grinding for Maximum Accuracy
Precision grinding is an essential step required to attain very tight tolerance ranges and very smooth surface finish, which is imperative in producing top-quality gears (ISO4-6). However, precision grinding is usually carried out after the heat treatment processes and is thus an essential step that corrects distortion processes that occur during quenching. With the use of CNC grinding wheels, this step is crucial in processing the tooth surface to exact geometries as specified to attain flawless meshing properties without any profile deviations that cause noises and stress raisers.
2. Gear Honing for Noise Reduction
Being a super-finishing technique, gear honing is highly efficient and successful when used after the grinding process to finish gear teeth, and when carried out in smaller batches related to gear processing. As mentioned, the process takes advantage of an abrasive honing tool that meshes with the gear and results in a polishing process that takes place when cutting the gear teeth. Gear honing results in a substantial reduction of gear whine and total noise levels by 2- to 3-DB, which makes a substantial difference in noisy applications.
3. Advanced Heat Treatment for Dimensional Stability
Despite its importance in obtaining the necessary material properties, conventional processing is prone to distortion. More advanced approaches include low-pressure carburizing (LPC), combined with high-pressure gas quenching. LPC ensures a homogenous level of carburizing without causing oxidation on the surface, which would increase processing time and cost due to a necessary machining allowance to compensate for distortion. On the other hand, high-pressure gas quenching allows for less distortion due to a more even rate of cooling compared to oil quenching methods.How these processes can be selectively combined according to the specific needs of the project has been precisely matched by an experienced gear design manufacturer whose core services include custom gear design services.
Effective Cost Control in Custom Gear Engineering Projects by Engineers
The fact that it tackles the issue of costs shows that it is aware of the realities of engineering, as it does not just stay in the theory phase.
Value Engineering During Material Selection: Value engineering: This is an important aspect where a critical analysis helps to conclude on the best material that can be acquired at a lower cost, which fits all the requirements for functionality. This can entail the use of a particular material that has been enough for the given task rather than going for a more expensive one. A material like through-hardened steel can be sufficient for the role instead of a more expensive case carburized material, or there might be elimination of a particular coating if its functionality does not significantly extend the life for the given conditions.
Design for Manufacturability (DFM): Incorporating the guidelines of DFM right at the beginning of any given project is one of the most effective ways to effectively manage costs. Designing gears so that they can be machined easily and efficiently is part of this method. By reducing complex features, using standard radii on machine tools, and designing gears so that they do not require tight tolerances, manufacturing can be made simpler and faster. A method of managing project costs proactively is through designing for ease of manufacturing while still achieving functionality.
Precision Grade Alignment: It is imperative to avoid issues of "over-engineering," especially when it comes to cost-effectiveness. The selection of an accuracy grade that is "fit for purpose," as opposed to opting for the highest possible grades, will make it possible to save money. The cost curve with respect to tolerance is exponential, as opposed to being linear, and will see machine time and cost rise exponentially as tolerances are tightened. This will ensure that it is possible to select an ISO 7 gear when an ISO 5 gear will suffice, based on an accurate evaluation of requirements with respect to noise, efficiency, and life, and thereby directly affecting the quote for custom gear machining services.
What Is a Case in Point for Solving Pitting Failure in Robotic Joint Gears?
In conclusion, a case study would help solidify the principles outlined above so the concepts can be put into effect.
1. The Challenge: Premature Failure in a Critical Application
One of the major robotics manufacturers in the world was facing a calamitous problem related to joint gears in their high-precision collaborative robots. The joint gears were failing extensively by pitting on the top surface of the gear teeth in just 2,000 hours, whereas they should last at least 20,000 hours. Due to such failures, the positional accuracy, vibration, and complaint rates against the robot were resulting in damage to its reputation in the marketplace.
2. The Custom Solution: A Multi-Faceted Engineering Approach
A holistic and root cause analysis, coupled with a multi-faceted engineering intervention, was required for this solution. First, a tooth surface redesign was carried out using topology optimization software, leading to a designed shape that gave a 25% reduction in the surface contact stress. In the second approach, the material was improved to a higher quality nitride steel, and subsequent processing gave a surface hardness value greater than 60 HRC with profitable compressive residuals. For the final approach, the process was optimized by precision grinding the gears to an ISO grade of 4, leading to perfect geometric conformity, followed by a shot peening process that added a further 30% increase in fatigue strength by optimizing the surface stress values around the tooth root. Each and every detail of the surface treatment process was carried out based on best practices available from authoritative sources like ASM handbook surface engineering.
3. Quantifiable Result - Beating Performance Targets Permalink
The result was transformative and verified from a quantitative perspective. The gear life increased from an unacceptable level of 2,000 hours to more than 6,000 hours in accelerated tests, showing a clear path towards reaching the 200% life improvement requirement for the 20,000-hour life. Moreover, the gear noise level was decreased by 5 dB to a very quiet 60 dB, making the user interaction with the collaborative robot even easier. Most importantly, from a client perspective, this resulted in a projected 40% decrease in maintenance and warranty costs, securing the value added by the custom engineering approach.
Conclusion
To meet the growing demands of the EV and robotics industries, a rigorous approach toward designing customized gears has now reached a threshold where it has to be done not just for preference but from a mandatory requirement. From the principles of engineering to material science and processing knowledge, the approach towards designing gears has to embrace full collaboration in order to achieve efficient performance, reduced noise levels, and durability.
FAQs
Q1: Generally, what is the estimated lead time for a custom gear project?
A: The lead times will depend upon the complexity, material, and the batch size, but the average production takes around 4 to 8 weeks. This will involve analysis, prototyping, manufacturing, and extensive testing. Fast-track services may be offered for urgent requirements.
Q2: Are you able to do small-batch or prototype gear manufacturing?
A: Totally. Specialized small-batch gear production is a specialty, offering a minimum production batch as low as 10 pieces, so this is perfect for prototypes and low production volume projects.
Q3: How do you verify and ensure the fatigue life of custom gears that you design?
A: We use standards such as ISO6336 for analytical calculations and carry out life testing on specially designed rigs that can simulate actual loads. Test report based on actual testing gives us an assured result.
Q4: What data should be provided in order to begin working on the new gear idea?
A: We usually need the application case, working load/speed data, expected lifetime, mounting interfaces, and desired precision grade. Additional requirements such as environmental matters and noise constraints are also essential to assess for a feasibility study.
Q5: Could you outline the essential steps you incorporate in your custom gear design?
A: It starts with an in-depth investigation of requirements of various applications, conceptual design development, 3D modeling, simulations of strength and NVH, and final verification of manufacturing capability before proceeding to production.
Author Bio
The author is a precision engineering expert at LS Manufacturing, a company certified with IATF 16949 and AS9100D. The company provides solutions to engineers and researchers in aerospace, medical, and automotive industries, helping them solve complex component challenges. The company is fully qualified, utilizes cutting-edge technology, and is committed to providing exceptional service. Please feel free to contact the author for a free evaluation.
Top comments (0)