Turning knowledge of design and precision machining

2020-09-05 11:29:37

三、Turning process

1、Tool handle has a negative front Angle and a positive front Angle, what is the difference between the two? When choosing a turning tool, there are negative front Angle and positive front Angle, how to use it in processing?

Negative front Angle and positive front Angle tool handle performance Negative front Angle tool handles use negative Angle blades. Negative Angle blades are divided into two-sided and single-sided. The single-sided type is used for roughing because of the support at the bottom. Two-sided economy is good, now the most used.

正前角车刀柄多使用正角刀片。因为锋利性好，常用于精加工及小型刀片。

Rake Angle	Shank with negative front corner	Right front corner tool handle
Tool diagram
distinction	Most use negative Angle blades	Most use positive blades
peculiarity	Large anti-collapse edge, suitable for rough machining and other intermittent processing, cutting resistance is large, easy to produce vibration. Depending on the chip-breaking groove, single side or double side can be used.	Sharp cutting edge, small cutting force, suitable for finishing. Suitable for soft material processing. The blade is thin and brittle. The blade can only be used on one side.

The effect of residual deflection Angle mainly affects the load per unit length of the main cutting edge and the cutting force per unit area of the cutting layer.1.Increase the residual deflection Angle, the knife Angle increases, the knife tip strength increases, suitable for intermittent processing.2、The tool residual deflection Angle is 0°, 45°, -5°, etc., how to distinguish the use? There are many types of Angle of residual deflection, I do not know how to choose when processing, and whether there is a difference in performance?

2.With the increase of residual deflection Angle, the cutting force per unit area of cutting layer increases and the cutting thickness decreases.

The selection method of residual deflection Angle

◇When the cutting depth and the feed amount of each edge are certain, the larger the residual deflection Angle, the thinner the thickness of the cutting layer (45 degrees is about 70% of 0 degrees), the cutting force borne by the unit cutting edge length is reduced, and the tool life is extended. However, when the thickness of the cutting layer is too large, the feed component increases, which is easy to cause high-frequency chatter and shorten the tool life.

◇Machine tool and fixture rigidity is good, can choose a large residual deflection Angle.

◇For hard cut material, choose large residual deflection Angle.

◇The shape of the workpiece is complex, which is more suitable for using a larger residual deflection Angle.

3、How to suppress chatter when boring deep holes?Boring deep hole machining surface often produce chatter, headache, excuse me have a solution?

Why is boring more difficult?

1.Machining surface visual observation is difficult.
2.It is very easy to retain chips inside the hole, and it is impossible to process a good surface.
3.The deep hole can not be seen at all, and the bottom position of the hole is difficult to stop, and can only be judged by the handle numbers and sounds.
4.The height of the blade is not adjusted properly, and the machining surface is easily damaged outside the blade.

Cause of flutter

The phenomenon of chatter often occurs when boring deep holes, which leads to the result that the surface finish of the boring holes becomes poor or becomes cone-shaped holes, affecting the accuracy of the holes, shortening the tool life, and easy to break the edge. The main reasons for flutter are: 1. Poor tool rigidity 2. Large cutting force 3. Insufficient clamping force

Increase tool rigidity

To enhance tool rigidity, you can first choose a large diameter boring bar as far as possible, and then shorten the overhang of the tool bar as much as possible. You can also use a carbide tool bar to replace the steel tool bar, or use a boring bar with damping function and vibration reduction function.

Reduce the cutting force during machinin

Select small R Angle blade and positive front Angle blade (chip breaking groove with small cutting force), select small residual deflection Angle tool bar, reduce the cutting depth during processing, reduce the feed amount during processing and other measures.

Strengthen the clamping force of the tool bar

Strengthening the clamping force on the tool bar can first increase the clamping length, generally the diameter of the tool bar is greater than 25mm, the clamping length is not shorter than 2.5 times the diameter, and then the clamping structure can be changed to increase the clamping force, such as the use of bushings.

4、How to control the best chip clearance when selecting the boring bar?

The selection of the inner hole boring tool has the minimum processing size, but if the tool is too small when selecting, the rigidity is not enough, which affects the processing.The selection of large will affect the chip clearance, the chip can not be discharged normally, the processing operation is interrupted, and the processing surface is scratched. Is there any good method?

Chip clearance and tool bar diameter

In order to increase the rigidity of the tool, when selecting the boring bar, the tool bar with the minimum machining diameter and the aperture to be machined is often selected.In this way, the rigidity of the tool is satisfied, but it may have an impact on the chip removal, and may even cause the chip to not be discharged to damage the blade and the tool bar, affecting the accuracy and surface finish of the machined hole.

solution

1.Control chip flow when finishing requires the chip flow to the unprocessed surface, so choose a boring tool with a positive edge Angle, if the processing is blind, in order to discharge the chip from the hole, use a negative edge Angle.2.Maintain the appropriate chip clearance The chip clearance is generally 2 to 2.5 times the cutting depth.

5、What are the factors that affect blade shape selection?The shape of the blade is wide variety, I do not know where to start when choosing, please tell me whether there is a good selection method?

Blade code meaning

Standard blade names are composed of English letters and some numbers, each letter or number indicates the corresponding parameter indicators.

Selection condition	Blade shape
	R circle	S-type 90°	W type 80°	Type C 80°	T-shape 60°	Type D 55°	V-shape 35°
Cutting edge strength
Copying machining
Hardness of the cut
Cutting power
Vibration tendency

6. What are the effects of the blade tip arc radius R on processing?Usually in the choice of blade often in order to determine how much knife tip R Angle and worry, in the end the size of the knife tip R Angle on the processing of some of the impact?

The arc radius of the tool tip R has a great influence on the strength of the tool tip and the finish of the machining surface, and the appropriate r is selected according to the size of the R.

The influence of the tip radius R

◇When the radius of the arc is large, the machining surface accuracy will be improved, and the surface roughness will be reduced.

◇The radius of the arc is large, the strength of the cutting edge is strengthened, and it is not easy to break the edge.◇With large arc radius, the wear of the front and back surfaces of the blade will be reduced.

◇If the radius of the arc is too large, the cutting force in the processing will increase, which is easy to produce vibration, but will affect the accuracy of the machining surface.◇If the radius of the arc is too large, the processing performance of chips will become worse.

Choice of use

Minor circular radius	Large circular radius
Fine shaft	Machining large diameter workpieces
Finishing with small machining allowance	Rough processing, intermittent processing
Machine tool equipment with poor rigidity	Good rigidity machine tool equipment

7、The blade coating has two kinds of CVD and PVD, what is the difference between the two?We often see that the same type of blade has a coating type corresponding to processing different materials, may I ask what is the difference between them?

Action of coating

1.Increase tool wear resistance and extend tool life.

2.Increase the oxidation resistance temperature of the tool surface and improve the processing efficiency.

3.Increase the tool friction coefficient and improve the workpiece surface finish.

Types of coating

There are two types of coatings most commonly used today：
1.CVD(Chemical Vapor Deposition)	Coating name
	MC1020，MC1030 MC1063，MCP3010
2.PVD (Physical Vapor Deposition)
	MT1020Z，MZ2033 MZ2031，MZ3035

Distinction between the use of CVD coating and PVD coating

<CVD coating>
・Machining with high tip temperature

・High speed machining high feed machining high cut deep machining

・Large processing volume

・Continuous processing is effective, and most of the blades are used

<PVD coating>
・High precision machining

・The processing of fusible parts requires sharp blades

・Micro machining low feed machining

・Intermittent machining is effective, milling blade is used more

8、刀What is the function of the chip chute?There are a variety of patterns on the surface of the blade, which is confusing when choosing, and I do not know what the role of these in processing is, how to choose?

Reasons for selecting chip-breaker blades

When machining, the chips are easily wound on the tool and the workpiece, causing the damage of the tool and the damage of the machining surface, especially on the automatic machine tools such as CNC, the processing of the chips is more important.

※Necessary conditions for chip handling

a)To make chip breaking smooth, and does not affect the normal cutting.

b)Control the volume of chips to make it easier for chips to be handled, stored and transported.

c)The chips should be discharged without entangling the workpiece, turning tool or causing the failure of the auxiliary device (automatic feeder, etc.).

Chip breaking principle of chip breaking tank

Chip breaker is an important factor affecting the mechanical strength of chips. This is determined by the "crack" state generated on the inside of the chip.

※Chip chute chip breaking principle

a)Deepen the "grain" inside the chip as much as possible to prevent the chip from bending freely, resulting in a "crack" with a certain degree of rigidity, making it easier to break the chip.
b)The chip break slot part of the blade controls the flow direction of the chip, so that the front end of the chip hits the workpiece or the back tool surface and the chip breaks.

The role of chip-breaker

◇Cut off chips without winding.

◇Control the flow direction of the chips to maintain the precision of the machining surface.

◇Reduce cutting resistance and extend tool life.