Drilling knowledge for design and precision machining II

2020-09-05 11:31:21

8, hope more rapid hole processing

I tried to calculate the time spent on hole processing and found that the time spent was beyond imagination, accounting for 60% of the total processing time. Want to improve the processing speed to achieve the efficiency of processing, but where is the key point to improve the processing conditions?

The necessary conditions for high-speed drilling
In order to achieve high-speed hole machining, the movement time between holes (feed speed and agility) is the key, and the following conditions need to be met in terms of tools.
(1)	High rigidity tool material If the rigidity of the tool material itself is insufficient, the speed can not be increased for processing. The first step is to choose a highly rigid material such as ultrafine particle carbide.
(2)	Best fit for slot length Compared with the end mill, the drill core thickness is thin, if the groove length is too long, the tool rigidity will be significantly reduced. In order to implement high-speed machining, it is necessary to select the drill bit with the right groove length according to the depth of the machining hole and improve the rigidity as much as possible.

	Using a bit with the right groove length can greatly improve the efficiency of hole processing. By extending the length of the regrinding section, although the number of regrinding times can be increased to extend the service life of the bit, the processing efficiency will be affected as the processing speed increases. When setting the regrinding part, careful study is needed to avoid affecting the processing efficiency.
(3)	High precision and high rigidity tool handle It is also important to use a highly rigid shank that holds the bit with high precision and does not vibrate even when rotating at high speeds. Thermal expansion tool handle best.

9, hope to shorten the processing time through stepless processing

In order to prevent the chips from becoming longer, no matter what holes are processed, they are graded in units of 1mm.

Want to switch from graded machining to stepless machining, but what is the maximum machining depth of stepless machining?

Also, what are the main points of stepless processing?

Effect of graded processing (advantages and disadvantages)

Graded machining has an excellent chip removal effect, and on the other hand, there are also disadvantages such as the phenomenon of cutting edge and cutting surface colliding with each other during graded machining, which can lead to reduced tool life and longer processing time, thereby reducing processing efficiency. Especially in the processing of workpiece with low thermal conductivity such as stainless steel, it may lead to a sharp reduction in drill life.

Key points of stepless processing

Stepless machining is an effective solution in both tool life and machining efficiency. The technical conditions required for stepless machining are described below.

(1)

Processing condition

The effective means of chip breaking are to increase the feed rate (mm/ revolution), increase the drill speed (cutting speed), and ensure sufficient cutting fluid supply.

When stepless machining is used, the machining depth of the standard drill bit is about 5 to 10 times the drill diameter, and the machining depth of the drill bit for deep hole machining is about 10 to 20 times the drill diameter.

(2)

The application of the internally cooled bit because the internally cooled bit can effectively supply the coolant (including the mist coolant) to the tool, if the use of the extended bit, the maximum can be achieved about 15 times the diameter of the bit stepless machining.

In addition, it is better to use a bit with a polishing treatment that improves the surface roughness of the coating and a mirror groove treatment that improves the surface roughness of the groove.

10. It is hoped that the hole processing of high-hardness steel will be converted from EDM to cutting

The hole processing of high hardness steel above 50HRC is carried out by fine hole EDM and wire cutting, but the processing time is too long.If the drill can be used for hole machining of high-hardness steel, the processing time can be greatly reduced. Consult high hardness steel tool selection, conditions, etc.

Effect of graded processing (advantages and disadvantages)

The use of high-hardness steel machining with a drill, instead of EDM (wire cutting) machining

Traditional high speed steel bits with a hardness of about 60HRC can not process hardened high hardness steel. However, the coated carbide drill bit, which has become a mainstream product, is capable of drilling high-hardness steel above 50HRC。
Among them, with the high surface hardness of silicon coating, and small spiral Angle and large core thickness to improve the rigidity of high-hardness steel processing with carbide drill bits as a new tool to replace EDM has attracted attention.

11, hope to drill and chamfer at the same time to improve processing efficiency

The drawings indicate that chamfering must be carried out after hole machining. If there is a tool that can carry out hole machining and chamfering at the same time, it can not shorten the processing time?

Use step drill to reduce machining processes

A step bit can usually be used for simultaneous machining of the bottom hole and chamfer. The step bit is a compound tool with both a small diameter part for machining the bottom hole and a large diameter part for chamfering.

12, hope to use a drill to process the bottom hole and countersunk hole to improve the processing efficiency and chamfering processing, in the processing of hexagonal bolt mounting holes, if there is a tool that can simultaneously carry out hole processing and countersink processing, it can not shorten the processing time?

Use step drill to reduce the process

A step drill can usually be used for simultaneous machining of bolt and countersink holes. A step bit is a compound tool with both a small diameter part for machining the bottom hole and a large diameter part for sinking the hole.

13. It is hoped that the positioning of the hole and the chamfer will be carried out at the same time to improve efficiency

The current hole processing procedure is in accordance with(1)Use a center drill for positioning → (2)Hole machining with drill → (3)The process of chamfering using chamfering drill is carried out, and it is wanted to reduce the process to improve efficiency. Is there a good way?

Improve machining efficiency by positioning and chamfering at the same time. The center drill with a center hole Angle of 60° can be positioned, but it cannot be chamfered at 90°/120° at the same time. However, by using a NC positioning drill with a 90°/120° tip Angle and a 90° chamfer center drill, the positioning bottom hole machining with chamfer machining can be achieved. (1)Tip Angle 90°/120°NC with positioning drill

(2)90° chamfer center drilling

14, deep hole processing time, low efficiency

In the past, deep hole machining of more than 10 times the diameter of the tool was drilled with a gun, but the processing was very time-consuming.

If you want to use the integral drill for high-speed machining, what kind of tool to choose and what steps to process is better?

Correct deep hole machining method When using a solid drill bit for deep hole machining, you need to use a long deep hole drill designed for deep hole machining.

However, the groove length and total length of the extended drill for deep holes are relatively long, and the tool rigidity is low, so it is necessary to pay attention to the occurrence of vibration.

Different from the usual hole processing, the main points of deep hole processing with extended drill bits are high-precision pre-processing and adjustment of cutting conditions. The following are typical deep hole machining steps.

(1)Guide hole machining
	When machining the guide hole, select a bit with the same diameter as the machining hole or about 0.05mm larger. For high-precision drilling, it is also important to improve the accuracy of the guide hole, so the reamer finishing of the guide hole is also very effective.

(2)Low speed insertion
	Until it reaches near the bottom of the guide hole, it is not rotated at the cutting speed, but inserted at a stopped or low speed state.

(3)Cutting speed
	Increase the speed to the cutting speed and start machining.

(4)After processing
	After the machining is complete, remove the drill bit from the bottom of the hole and pull it out when the rotational speed drops to low.