Brake drums are the main components of automobiles and are consumables. With the rapid development of the automotive
industry, manufacturers of processed auto parts in the downstream industry have risen rapidly. In order to put parts on the
market faster, quality may be neglected. The problem is that the surface roughness of the brake drum is generally within Ra1.6,
resulting in a higher proportion of scrap and defective products, in order to obtain better surface roughness without affecting
the overall processing benefits. Must improve the machining process and tool materials.The following describes in detail the
processing technology of the brake drum and the choice of tool materials.
Ⅰ, the processing technology of the brake drum
At present, the main material of the brake drum on the market is gray cast iron, the gray cast iron has good shock absorption
and wear resistance, and the noise is small, and the processing technology is simple. The general processing technology is
casting - roughing - semi-finishing - finishing - drilling - inspection.
(1) Casting: When the brake drum is being cast, it is necessary to control the quality of the charge, control the chemical composition
of the molten iron, and control the pouring temperature. The ingredients are correct. If the control is notgood,casting defects
may occur. casting defects will bring difficulties to the subsequent processing.
(2) Roughing: After casting, it enters the machining workshop. At present, the processing brake drum often uses a numerically
controlled lathe, the reasons as below:
1 , to reduce the scrap rate of the workpiece,
2, to improve the processing efficiency. The roughing brake drum needs to leave a margin of about 0.5mm for later finishing and
finishing to ensure the finish.
(3) Semi-finishing: In order to obtain a high degree of smoothness of the brake drum, semi-finishing is generally performed after
roughing, leaving a margin of 0.1-0.2 mm, and the finishing process in the latter.
(4) Finishing: In order to obtain a high surface finish, it is generally refined after semi-finishing, to the required dimensions of the
drawing, and the finish of Ra1.6.
(5) Drilling: Drill holes of corresponding size in the required parts of the drawing.
(6) Inspection and storage: Check the surface finish of the brake drum, and whether the dimensional tolerance meets the requirements
of the drawings. If it is qualified, it can be assembled or assembled.
Ⅱ, the tool selection when processing the brake drum.
Since the brake drum processing requires three processes, the rough machining generally requires a margin of about 3 mm,
and the brake drum is required in large quantities, and the brake drum is generally processed by a numerically controlled lathe.
In theprocessing process, it is necessary to ensure the processing size, but also to improve the processing efficiency. The
selected tool material requirements are as follows: one is not sensitive to the line speed and can be cut at high speed; the other
is that the machining allowance can be completed with one knife and the same. Processing time to improve processing efficiency.
At the beginning, the choice of traditional carbide tools, but the carbide tool is sensitive to the line speed, can only cut the brake
drum at low speed, the production cycle becomes longer, affecting the processing efficiency, such as small batch or a small number
of brake drums, without affecting the overall processing efficiency. On the basis of the selection of suitable carbide tools, for large-
volume brake drums, machinery manufacturers will choose cubic boron nitride tool processing, and more will choose Halnn BN-S300
CBN grade inserts and The BN-K20 CBN grade inserts processing brake drum is more effective.
Halnn BN-S300 CBN grade inserts belongs to the solid CBN inserts, suitable for rough machining process. BN-K20 CBN grade
inserts belongs to brazed CBN inserts , which is suitable for finishing process. Due to different processes, different machining allowances,
and different tool grades, the following is a brief introduction to the brake drum for the Halnn CBN inserts.
Ⅲ, select the appropriate Halnn CBN grade inserts for different processes
(1)Roughing process: The margin is generally about 3mm. The BN-S300 CBN grade inserts of Halnn is selected. This grade uses
non-metal (ceramic) as the binder, which is compared with the traditional CBN inserts Compared with the increase of toughness, not
only high hardness and high strength, but also good wear resistance and impact resistance, the brake drum can be turned over with a
large margin, and the remaining amount of the brake drum can be completed by one knife. The picture below shows the picture of the
brake drum of BN-S300 CBN grade inserts of Halnn.
Cutting parameters:
Cutting Depth(ap) = 1-10 mm,
Feed Rate(Fr) = 0.21 mm / r,
Cutting Speed(Vc) = 200 - 800 m / min.
Machining effect: Hann BN-S300 CBN grade inserts tool life is 15 times that of coated carbide tools
(2)Semi-finishing: Within the allowance of 0.5mm, there are two options:
1 ,select the BN-S300 CBN grade inserts, one knife is completed:
2,to select the BN-K20 CBN grade inserts two knives to complete. It is recommended to use the BN-S300 CBN grade inserts to save
processing time.
Cutting parameters:
Cutting Depth(ap) ≤ 1 mm,
Feed Rate(Fr)= 0.05 - 0.3 mm / r,
Cutting Speed(Vc) = 300 - 1500 m / min.
(3) Finishing: Within the margin of 0.3mm, the BN-K20 CBN grade inserts of Halnn is economical, which can guarantee the
smoothness of the brake surface and the smoothness and dimensional tolerance of the mouth. The picture below shows the
smoothnessof the processing surface and the stop of the BN-K20 CBN grade inserts of Halnn.
Cutting parameters:
Cutting Depth(ap) ≤ 1 mm,
Fr = 0.05 - 0.3 mm / r,
Vc = 300 - 1500 m / min.
Processing effect: The smoothness of Halnn BN-K20 CBN grade inserts is guaranteed within Ra1.0, and the tool life is 1-2 times that of other
factory CBN inserts.
(4) Roughing, semi-finishing and finishing select BN-S300 CBN grade inserts: All of the above are different tools for different processes,
and can also be rough, semi-finished and finished with the BN- S300 CBN grades inserts reduce unnecessary tool change time, save time,
reduce processing costs, and ensure the surface finish of the brake drum.