The winners of the Japan Powder Metallurgy Association (JPMA) 2013 Powder Metallurgy Awards once again demonstrate the continuing evolution of Japan’s PM industry. The awards honour companies for the development of new materials, manufacturing processes and component design and evident in this year’s awards are the increasing number of applications for PM in hybrid and electric vehicles.
Development Prize: New Design
Oil-impregnated sintered bearing for the motor of an idle speed control system
Diamet Corporation received an award for an oil-impregnated sintered bearing for the motor in an idle speed control system on small motorcycles. The idle speed control system is widely used in medium to large motorcycles and four-wheeled vehicles. However in order to spread the application to smaller motorcycles a cost reduction and downsizing of the system was needed.
This resulted in the development of a heat resistant oil-impregnated sintered bearing which is able to be easily assembled, achieving a cost reduction through the net shape production process.
A newly developed Fe-Cu-Sn material offers low friction and the required strength. Two upper punches were used for sizing, with the sizing sequence optimised to achieve high accuracy of the products.
Diamet achieved both downsizing of the component and cost reduction in the production of the motor. The oil-impregnated sintered bearing for the motor of the idle speed control system of small motorcycles is now in mass production.
Joint for electric power steering motor
Diamet Corporation also received an award for a joint part which transmits movement from an electric power steering motor to a steering shaft. In recent years, as joint parts with leg sections to improve torque transmission and assembly have increased in popularity, Powder Metallurgy has lost market share to forged alternatives.
The reasons for the reduction in PM’s share was the low strength of the sintered leg sections and the cost to form them. In this component bending strength and hardness of the leg portions were improved through material selection, uniform density distribution and optimised heat-treatment conditions.
The combination of geometries of the lower punches was designed for uniform density distribution of the boss, enabling a 15% weight reduction by utilising the step formed with the lower punches to decrease thickness of the flange.
The scatter of the height of the leg portions was controlled by FEM analysis and optimisation of the production conditions, eliminating the need for machining of the tapered chamfers of the leg portions. As a result, mass production of the joint part was achieved, replacing forged alternatives.
Lightweight shock absorber piston for motorcycles
Fine Sinter Co., Ltd. won an award for a piston used in a motorcycle shock absorber. The piston design has complex thin sections and internal structures.
The thinner portion is essential to ensure that the penetrating holes allow a receiving area for damping force characteristics of more than 65%. Challenges in the development of this new part related to product strength and mould strength, due to the thin sections and complex shape.
For the thin sections of the design Fine Sinter adjusted mould thickness by increasing and decreasing thickness in the part. Mould strength was achieved by selecting high strength and high toughness mould materials. Product strength was ensured by optimising the selected material.
As a result, the production of lightweight pistons with thinner sections was successfully achieved. Damping force characteristics were stabilised and the diameter of the shock absorber and spring lower loading were reduced, The development contributed to an overall cost reduction.
Sintered bearing for HEV and EV battery cooling fan motors
Porite Corporation won an award for an oil impregnated sintered bearing which is used in a battery cooling fan motor for hybrid electric vehicles and electric vehicles.
Previously, ball bearings were used in brushless motors. However this new sintered bearing satisfies the requirements for lower noise and improved durability.
In this development, Porite adopted the “Nakanige” bearing, with close attention paid to the accuracy of tooling and the press, control of powder filling, density balances, and the optimisation of a repressing process. Through these improvements a 1 μm coaxiality between upper and lower sliding surfaces was achieved. Improvement of coaxiality makes the clearance between the bearing and shaft smaller, improving sliding performance and wear resistance and reducing clearance noise.
The motor that uses this new sintered bearing passed the necessary endurance tests at the customer, resulting in the conversion to a PM bearing from conventional ball bearings and offering cost reductions.
Reduced noise oil pump rotors
Diamet Corporation won an award for rotors for oil pumps driven by electric motors. Conventionally, oil pumps for automobiles are driven by the engine so the noise they produce is masked by the noise of engine. With the spread of hybrid electric vehicles and vehicles with stop-start systems, the use of electric oil pumps is increasing. Because electric oil pumps are often used when engines are stopped, oil pump rotors are now required to offer both silent operation and high efficiency.
By focusing on the tooth gap between the inner rotor and the outer rotor, Diamet concluded that the low noise and high efficiency oil pump rotors previously developed generated a loud impact and vibration sound when the teeth engaged.
Based on this, the company developed a new tooth profile which reduced both tooth impact sound and vibrations. The rotors with the newly developed tooth profile exhibited a 25% noise reduction and 5% efficiency improvement compared with previously developed oil pump rotors.
Parking component for PHEV transmission
Sumitomo Electric Industries, Ltd. won an award for a parking component used in the transmission developed for a PHEV (Plug-in Hybrid Electric Vehicle). The component locks the parking gear when the mating component slides on to the taper shaped part of this product.
Since this component was as long as 50 mm in length and its shape required a lot of machining processes, the design was adapted to make it suitable for PM.
In this development, a density increase in the central length of the taper shaped part became a problem. To solve this, a low alloy Fe-Mo-Cu-C material was used, offering high-compressibility and high mechanical strength. The material was optimised and, along with appropriate lubricant, Sumitomo achieved the correct density rise and smooth ejection. The pressing process adopted a floating core and a dummy core, holding the upper side of the core from the upper punch side.
The new component is now in mass production.
Development Prize: New Materials
Oil seal for VVT system
NTN Powder Metal Corporation won an award for a Powder Metallurgy oil seal component used in the hydraulic chamber of a Variable Valve Timing (VVT) system. Characteristic demands of such oil seal parts are sealability, sliding and wear resistance. Resin was used traditionally, however the resin oil seal had lower dimensional accuracy and oil leaks at startup was a problem.
A PM oil seal offered higher dimensional accuracy than resin, however at the start of development there were problems relating to dimensional control. The use of graphite during sintering and a low sintering temperature Fe-Cu-Sn composition helped to resolve this issue.
The microstructure enabled improved accuracy through sizing, and free graphite working as solid lubricant offered excellent sliding characteristics. As a result, mass production of this sintered metal oil seal was achieved.
Process Development Prize
Low cost SMC core for an automotive reactor
Sumitomo Electric Industries, Ltd received an award for a Soft Magnetic Composite (SMC) core used in the boost converter of the motor drive system in a Hybrid Electric Vehicle (HEV).
Soft magnetic cores are smaller and lighter than conventional laminated steel cores, but to expand applications cost reduction is the most important factor.
In developing this part Sumitomo tried to achieve the required performance whilst lowering costs by using cheaper iron based powders, optimising the shape of product, improving the compacting method, and using a laser irradiation process.
The company was able to downsize by using pure and fine iron powders, but the eddy current loss created by the electric current on the component surface became a problem. To overcome this the compacting directions were adapted. In addition, the shape of the product was changed so that it could be compacted with a simple shoulder die, giving no interference with the reactor case.
In the middle core, a problem was that the eddy current travels around the outside of the component. This was overcome by shaping a non-conductive part by laser irradiation, intercepting the eddy current.
As a result, the company developed a pure iron based Soft Magnetic Composite core for an automotive reactor which had previously been made by laminated steel. Excellent performance was achieved as well as cost reductions.
Ring gear manufactured with a segregation-free mixed powder with excellent drilling performance
Sumitomo Electric Industries, Ltd. won an award for this pinion and ring gear used for the rear wheel suspension adjustment of a front-engined, front-wheel drive car. The component is used in the operation of an actuator.
During pre-production, the specification as detailed in the drawings was achieved but operating noise inside the test vehicle failed to meet the target value. Thus, in order to obtain improved precision of the gear and tooth profile a die manufacturing optimisation process was carried out.
Extremely high mould accuracy and improved sintering methods resulted in effectively reducing operating noise.
As a result, it became possible to meet the target value for the operational noise of the actuator and mass production of the ring gear and pinion was achieved.
Sintered hydrodynamic bearing for super thin fan motor
NTN Powder Metal Corporation received an award for this oil-impregnated sintered bearing which has hydrodynamic grooves on the bore.
Mobile devices have become ever more popular and thinner cooling fan motors have had to be developed at a rapid rate. Demands for thinner bearings have therefore also increased. However, the size of the impeller (fan) to maintain cooling characteristics has tended to become larger and loads on the bearings have therefore increased.
To meet these demands, hydrodynamic groove specifications were optimised by improving the accuracy of the hydrodynamic bearing part width and expansion of groove angle, bearing clearance and hydrodynamic groove depth. Groove machining conditions were optimised with improved accuracy of the mould and optimisation of press operation. A lubricating oil able to maintain low evaporation and high rigidity was also developed.
As a result, the new thinner bearing has good oil film forming ability and non-contact support. Mass production of the sintered hydrodynamic bearing with low noise and high reliability for the super thin fan motor was achieved.
High strength planetary gear for stop/start systems
Hitachi Chemical Co., Ltd. won an award for a high strength and high dimensional accuracy planetary gear used in the starter motor of an idling stop/start system.
The increasing use of stop/start engine idling systems has resulted in the need for higher durability planetary gears in the starter motors. High dimensional accuracy reduces stresses and Hitachi developed a sintered material for the planetary gear that provides high strength and high dimensional accuracy.
The density of the newly developed planetary gear reaches 7.4g/cm3 after single pressing with the tool structure optimised for high pressure compacting. A high performance lubricant is used for better ejection.
Sintering conditions were optimised to reduce deformation during sintering and to increase the amount of nickel rich austenite phase in order to obtain high plastic deformation during the sizing of the inner diameter.
As a result, the dimensional accuracy of the newly developed material was improved by 60% and tensile strength was improved by 16% compared to the conventional 4% nickel material.
This planetary gear, which has high strength and high dimensional accuracy without quenching and machining, is already in mass production and contributing to cost savings, downsizing and weight reduction of the units.