ⅠOverview
FC250 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 cutting 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 FC250 brake drum turning machining from the perspective of machining. The data is compiled
by Halnn superhard tool engineer according to the customer's processing site. The shallow experience is shared here
with the majority of machining peers.
Ⅱ the influence of tool material on the smoothness of FC250 brake drum processing
1, the first use of CNMA150616 carbide CNC blade for turning FC250 brake drum, cutting parameters: 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 using the CBN inserts CNMN120416, using the CNC vertical line speed of 300m / min; the tool nose angle of 95
degrees, the roughness is significantly improved, the processing surface is very bright, but after the CBN inserts is blunt,
the roughness begins to decline ,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 CBN inserts can indeed improve the roughness of the turning surface of the brake drum, 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.
Ⅲ, Halnn BN-S30 CBN grade inserts and its edge processing.
Halnn BN-S30 CBN grade inserts, non-metallic adhesive, prolongs the life of CBN inserts 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 traditional carbide inserts. Here, it is only the result of the processing of the
CBN inserts itself (BN-S30 CBN grade inserts) and the cutting edge, and this edge treatment is based on the good toughness
of the BN-S30 CBN grade inserts substrate.
When processing the gray iron parts, the BN-S30 CBN grade inserts 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 FC 250 brake drum,
the finish is significantly improved, and there is no tearing on the edge of the brake drum.
Ⅳ,the redesign of the CBN inserts has greatly improved the Surface finish of the FC250 brake drum.
Still using the BN-S30 CBN grade 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 position of the arbor and the blade and the shape of the blade are adjusted, no need to rework tooling and
fixtures. The original processing technology and the path of the cutter are unchanged.)
Ⅴ. Remarks:
1, redesigned CBN turning tools, the machine needs to have enough 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 FC250 brake drum can reach Ra0.8.
2,Halnn BN-S30 CBN grade insert is more inert to cutting temperature due to the use of non-metallic adhesive, so the blade
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 FC250 parts, but also achieves a better finish (roughness).
3, this paper takes FC250 brake drum processing as an example to analyze the cutting finish of gray cast iron. 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.