How to improve the smoothness of HT250 brake drum turning

I. Overview

HT250 brake drum turning surface finish is generally required to be within Ra1.6. Due to the roughness limitation of the cutting surface, the brake drum scrap rate and defective rate are directly increased. Moreover, in order to obtain better cutting processing for finishing the car Surface roughness can only increase the frequency of tool change, which not only affects the processing efficiency of the brake drum, but also increases the tool cost. This paper analyzes how to improve the smoothness of HT250 brake drum turning machining from the perspective of machining. The data is compiled by Hualing superhard tool engineer according to the customer's processing site. The shallow experience is shared here with the majority of machining peers.

Second, the influence of tool material on the smoothness of HT250 brake drum processing

1. The first use of CNMA150616 carbide CNC blade to turn the HT250 brake drum, the cutting parameters are: ordinary vertical line speed 130m / min; CNC vertical line speed 300m / min; alloy blade can be processed at each edge After 5 pieces, the roughness began to decrease. The smoothness of the turned surface is shown in the figure:

2. Later, the CBN blade CNMN120416 was adopted, and the linear speed was 300m/min when the CNC was used. The main angle of the turning tool was 95 degrees, the roughness was obviously improved, and the processing surface was very bright. However, after the CBN blade was blunt, the roughness began to decrease. An annular light strip appears on the working surface of the inner surface of the brake drum, and when the mouth portion of the inner surface of the brake drum is cut, the edge of the workpiece is easily torn, resulting in a risk of waste of the brake drum.

3. Based on this, the use of CBN inserts can indeed improve the roughness of the brake drum turning surface, but the tool cost is slightly increased, and there is a risk of tearing the edge of the brake drum when cutting out the mouth.

Third, Valin BN-S30 grade CBN blade and its edge processing.

Valin super-hard BN-S30 grade, non-metallic adhesive, prolongs the life of CBN tool, and uses half-edge processing to solve the risk of tearing the cutting edge of the brake drum due to negative chamfering of conventional CBN inserts. And the tool life is 12 times longer than the life of cemented carbide. Here, it is only the result of the processing of the CBN blade itself (BN-S30 grade) and the blade edge, and this edge treatment is based on the good toughness of the BN-S30 grade tool substrate.

When processing the gray iron parts, the BN-S30 grade can obtain a better surface finish by using the sharp edge treatment in addition to the improved tool life, and solves the tearing of the brake drum mouth portion and the upper end edge when the cutter is cut out. problem. As shown in the BN-S30 grade CBN insert processing HT250 brake drum, the finish is significantly improved, and there is no tearing on the edge of the brake drum.

Fourth, the redesign of the CBN turning tool has greatly improved the finish of the HT250.

Still using the BN-S30 grade CBN insert, the tool model is changed from diamond to square insert, and the insert arc angle is doubled. The effect is: 1. The number of blade edges is increased from 4 to 8, and the tool cost is doubled. 2, the R arc angle of the blade is doubled. Under the same finish requirement, the cutting amount is increased to 0.75mm/r; the production efficiency is increased by 40% (Note: only the loading position and blade shape for the tool bar and the blade) Make adjustments without re-working tooling and fixtures. The original processing technology and the path of the tool are unchanged.)

V. Remarks

1. The redesigned CBN turning tool requires the machine to have sufficient power to withstand the amount of cutting above 0.75mm/r. If the machine power is insufficient, under the premise of the same amount of cutting, because the arc angle of the tool tip is equivalent to the function of the wiper belt, the cutting finish of the HT250 brake drum can reach Ra0.8.

2. Valin BN-S30 grade CBN insert is more inert to cutting temperature due to the use of non-metallic adhesive, so the insert can be cut at any speed of 50-1500m/min, if used in CNC lathe or machining center. The higher cutting line speed not only improves the processing efficiency of the HT250 parts, but also achieves a better finish (roughness).

In this paper, taking HT250 brake drum processing as an example, the cutting finish of gray cast iron is analyzed. This method can be extended to other gray cast iron parts, but it should be noted that the ferrite content and graphite grade of gray cast iron affect machining. The possibility of surface finish is not repeated here.