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V. Process Preparation before Broaching
Published: 2015-11-13

I. Process requirements on workpiecesbefore broaching

①-2138.comThe scale layer or other scale substances on the machining surface shallbe eliminated by sand blasting or acid washing before broaching.

The workpiece shape shall be simple as far as possible with even thickness of hole wall, to avoid the hole surface deformed after broaching and affecting the accuracy.

The reference plane when broaching must be flat and smooth and shall be that of the hole in previous process, or a spherical surface shall be used to support the clamp.

The chilled layer on the surface of workblank shall be avoided todirectly contact with the broach blade against quick wearing or tipping ofbroach teeth. Therefore, it generally needs to be cut with other tools prior tobroaching. However for integrated wheel broach, users can directly broach onthe surface of workblank since such broach has high rise per tooth and the edgeof broach teeth can cut into the surface of the chilled layer.

If the length of a shorter workpiece is less than the pitch of the broach, several such workpieces can be fastened together with a clamp for broaching, however, users must tightly clamp those workpieces without loose, or broach teeth will be damaged..

⑥-1115.comThe surface quality will be better after broaching if the hardness of workpiece is HB180-210; the workpiece must be preheated to change its hardness and the cutting performance if the hardness is lower than HB170 or higher than HB240.

The diameter of holes must have a certain geometric accuracy before broaching, including the concentricity of the diameter of holes and the perpendicularity of end faces. The front pilot of broach shall be able to entirely penetrate into the hole, if fails or half penetrates, broaching shall not be started, or the broach will be bended or broken. In general, the accuracy of hole is required to be H11-H13, and the surface roughness of workpieces before broaching shall not be too small, but commonly be Ra1.6-6.3μm.

Two ends of the hole shall be processed for chamfering before broaching to avoid burrs affecting the passing of the broach and the positioning of workpieces.


2.Speed selection of broach

Since the cutting width and thickness (rise per tooth) are ;;, appropriate selection of broaching speed is important to improve the productivity of broaching.

The broaching speed is generally within 1-8 m/min. So users should alsoconsider the type, size and rise per tooth of broach, the material of workpieceand tool, requirements for the quality of workpiece surface and so on whenselecting. If the rise per teeth of the broach is high, the broaching speedshall be small; for the broach with high heat resistant materials, largebroaching speed can be selected; for broaching hard (HB=280-320) or soft(HB=147-170) workpieces, the broaching speed shall be reduced correspondingly.For workpieces with the broaching hardness of above HB320, the broaching speedshall be reduced more. Workpieces with too low or too high broaching hardnessshall be preheated prior to broaching.-www.44118.com