Enhanced Technology in Crankshaft Machining

The application of shot blasting technology can effectively improve and improve the anti-fatigue life and corrosion resistance of key automotive components. At present, many of the world's leading automotive OEMs and component manufacturers have already enhanced their inclusion in the standard production process. At the same time, strengthening equipment also forms a complete modern manufacturing line as does other manufacturing equipment.

With the continuous development of shot peening technology, its use in the automobile manufacturing field to improve and improve the anti-fatigue life of key automotive components has become an increasingly important focus of attention, and in the initial design of cars, trucks, motorcycles, etc. It has been fully considered and valued. At present, most of the engine parts design will have spray / shot blasting technology and process applications, including: crankshaft (descaling and strengthening), connecting rod (enhanced), transmission gear and other shaft parts, ring gear, Pistons, sun and planet teeth, and leaf springs and springs. A large number of automotive parts, whether cast/forgings, die castings, or mechanical cutting and welding parts, require different types of spray/throw equipment for surface treatment such as descale, deburring, sand cleaning, and cleaning of other surfaces. Impurities.

There is conclusive data to prove that through shot peening, the fatigue life of the leaf spring can be extended by 600%, the fatigue life of the transmission gear can be extended by 1500%, and the fatigue life of the crankshaft can be extended by 900%. Effectively improving the anti-fatigue performance and corrosion resistance of components is of great significance for their useful life and safety of use. Rely on shot peening technology, parts can be designed to be more lightweight, some of the original parts that had to use expensive materials due to process specifications can now also be replaced with low-cost materials, and can achieve equal or even better performance standards through shot peening.

Blast cleaning in crankshaft manufacturing process

As a part of the manufacturing process, the heat-treated crankshaft needs to remove the surface thermal oxide skin by shot blasting. The crankshaft is placed on a rotating roller. When rolling, all the surfaces of the crankshaft are fully exposed to a plurality of jets ejected by the throwing head. The multi-angled shot impact completely cleans the outer surface of the crankshaft.

The size of the crankshaft determines the type of shot blasting machine used. For large engines, the crankshaft size may be as large as 762 mm and length 6096 mm. The crankshaft is placed between a set of rollers mounted on a trolley. There are several ways of working. Customers can choose fixed heads according to the actual conditions of their factory workshops. They can not only allow the trolley to move under the head, but also fix the trolley and move the heads above. Whichever way is chosen, the crankshafts placed between the rollers are constantly rotating so that all surfaces are fully blast cleaned.

The smaller crankshafts, such as φ152-203mm and 914mm long, are usually shot blasted using a spin-on shot blasting machine. The crankshaft is hung on a hook, and then it is sent to a blasting chamber equipped with a plurality of throwing heads through the rotation of the catenary to perform blast cleaning. The hook rotates in the shot blasting chamber, allowing the workpiece to be fully exposed to the flow of high speed pellets and passing while rotating. Its cleaning speed can reach 250 pieces/h, and the cleaning effect is very good.

Although the requirements for process control are less stringent than fortification, modern crankshaft shot blasting equipment also ensures the quality of the cleanup by monitoring the process parameters.

Crankshaft reinforcement

As the crankshaft works under the action of alternating stress, the risk of stress fatigue and strain failure at the transition radius at the variation of the journal surface is extremely high. At present, the anti-fatigue performance of the crankshaft has been widely applied through shot peening, and the effect is satisfactory.

The defect of the traditional rolling technology is that, due to the limitation of the machining technology of the crankshaft, the roundness of each journal is difficult to match with the roller, which often results in the round-cut phenomenon, and the crankshaft after the rolling is greatly deformed, and the effect is not significant. good. The mechanism of shot peening is the use of pellets with strictly controlled diameter and certain strength. Under the action of high-speed air flow, the pellet flow is formed and continuously jetted onto the metal surface of the crankshaft. It is like hammering with countless hammers to generate the surface of the crankshaft. Extremely strong plastic deformation forms a cold hardened layer. In short, because the crankshaft is affected by various mechanical cutting forces during machining, the stress distribution on the surface of the crankshaft, especially the change in the cross section of the crankshaft, is extremely uneven, and it is easily subjected to alternating stress during operation. Stress corrosion reduces the fatigue life of the crankshaft. The shot peening process is to offset the tensile stress that the part will receive in the later working cycle by introducing a pre-compression stress, thereby improving the fatigue resistance of the workpiece and the safe service life.

There are two most critical parameters for the shot peening process. One is the stress intensity, which is usually measured using the "Almen test piece". A plurality of test strips are fixed on different surfaces of the crankshaft, in particular the transition fillets of the crankshaft sections with the most concentrated stress, and the shot peening is performed together. The compressive stress generated on the test strips causes the test piece to bow. The change in curvature is proportional to the impact energy of the pellets. Another major parameter determining the quality of shot peening is the coverage rate, which mainly refers to the ratio of the area occupied by the reinforced surface craters to the total reinforced surface. This parameter is defined by the design engineer of the crankshaft and usually requires 100% to 200%. Some crankshaft applications may require a coverage of more than 200%.

According to the hardness of the crankshaft and the ideal introduced compressive stress strength, the hardness of the pellets used for crankshaft shot peening is usually 50 to 55 HRC and the size is S 280 to S 330 (0.7 mm to 0.84 mm). This results in an intensity range of about 0.008 to 0.010 C (0.025 on the A scale) on the "Almen test piece." Compared with shot blasting, the monitoring of process parameters for shot peening is more demanding. For crankshaft hardening applications, the parameters that need to be monitored include: shot peening speed, shot peening strength, pellet diameter, shot peening distance, time of fortification, and coverage. Changes in any one of these parameters will affect the effect of crankshaft surface hardening to varying degrees.

The correct application of controlled shot peening technology can greatly improve the fatigue strength of the crankshaft and other parts that work under high load conditions, thereby greatly prolonging the fatigue life of the part. The advanced and precise shot peening equipment with computer program control technology can closely monitor the shot peening process to ensure the constant quality and repeatability of shot peening. At present, many of the world's leading automotive OEMs and component manufacturers have enhanced their inclusion in the standard production process. Strengthening equipment also forms a complete modern manufacturing line as does other manufacturing equipment.