A key connection is one of the basic methods of mounting the hub on the shaft journals. A specially prepared key is used for this purpose, which is placed in a groove made. The grooves are made both in the hub and in the shaft of the elements connected by means of milling processing. Milling of keyways, channels with specific parameters can be done in different ways, depending on the geometric features of the groove. Keyway connections should be made in accordance with the accepted standards of geometric tolerances and surface roughness, e.g.: DIN 6885-1.
Spline connections are characterized by the possibility of greater load and allow the centering of the connected elements in relation to key connections. One of the methods of making a spline is its milling. Splines can be made both on lathes with a C and Y axis or on machines multi-tasking milling machines with a dividing head are also suitable for this. Splined shafts are made of hardened steel, cast iron or cast steel.
The first method of milling a keyway involves the use of standard shank cutters. Using this type of tool, we will make keyways characterized by closed geometry (non-through), with dimensions larger than the tool diameter. The technologically correct approach is the one in which the machining is divided into two stages: roughing and finishing. The main advantage of this approach is obtaining high accuracy of the made groove.
Roughing is characterized by the need to determine the method of tool entry into the material, e.g. oblique plunge, as well as defining the path profile. Trochoidal milling can be used, allowing for quick material removal, leaving only an allowance for the final achievement of the assumed keyway profile. The use of a long cutting edge cutter enabling efficient volumetric milling, combined with technology generating trochoidal paths, enables effective milling of difficult-to-cut materials such as titanium, heat-resistant steels, and steels with hardening coatings.
The second stage consists in finally obtaining the keyway geometry. A properly defined technological process containing machining parameters matched to the tool used allows for obtaining keyways that meet specific standards. Obtaining the intended shape and dimensional tolerance is possible by using a small radial cutting depth, eliminating the tendency of the cutting tool to vibrate and to deviate from the milling cutter axis.
The second way to make a groove concerns the possibility of using disc milling cutters. Depending on the characteristics of the groove, we are able to make long and relatively deep countersinks using a disc tool, and we can also adjust the width of the undercut. By providing a tolerance in the technological documentation for making a groove, we can divide the processing depending on the accuracy of the execution and the type of processing, analogously to using shank milling cutters, e.g. roughing and finishing milling of the keyway. Using disc milling cutters, we will make all kinds of through grooves. Depending on the blank material used, this type of tool can be used for both forward and reverse milling.
The third method of making keyways (or splines) involves using both milling and turning machining centres and using special attachments that enable chiselling. The entire process is very similar to the standard execution using chiselling machines. The machining cycle consists of entering a fixed single-edge tool into the workpiece (shaft, sleeve), then sinking into the material with a full cross-section of the cutting layer and withdrawing the tool in the axis of the detail with the cutting insert leading out into the groove.
The next layer is cut with a given tool offset. The shape of the groove depends on the profile of the cutting insert mounted in the tool holder and provides great freedom. Using the tool exit in the Z axis in the case of a vertical milling centre with a centrally mounted detail and simultaneous rotation in the C axis allows you to obtain a groove with a helical surface. The method allows for the production of external and internal grooves. The main advantage of the chiseling method is the possibility of obtaining very high dimensional and surface accuracy of the keyway.
Tip
Lack of the required manufacturing tolerance can negatively affect the entire keyway connection. Excessive clearances in the case of heavily loaded connections result in the breakage of the grooves and significant wear of the keys. In such a case, the connected parts tend to undesirable vibrations and rapid wear of the device, which is why it is so important to correctly select the right manufacturing method, tools and technological process.
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