The so-called deep hole is a hole whose hole length/diameter ratio is greater than 10. In most cases, the depth/diameter ratio of general deep holes is L/d≥100. Such as cylinder holes, shaft axial oil holes, hollow spindle holes and hydraulic valve holes, etc. Some of these holes require high machining precision and surface quality, and some of the materials to be processed have poor machinability, which often becomes a major difficulty in production. What methods can you think of for treating deep holes? I believe many people will first think of gun drilling – the mainstay of deep hole processing. Today we will look at how barrel drills solve the problem of processing deep holes.
Gun drilling has a wide processing range: from plastics such as fiberglass and Teflon to carbon steel, alloy steel, non-ferrous metals and high strength alloy steel (such than high temperature heat resistant alloys and titanium alloys), it can be used for deep hole processing.
Gun drilling was first used in the processing of gun barrels. Due to its excellent hole processing performance, it is now widely used in industries such as shipbuilding, automobiles, engines, locomotives, military industry, chemical machinery, oil nozzles and pumps, mining machines and. hydraulic parts.
The precision of cannon drilling that must be mentioned
Gun drilling requires forced chip removal. High pressure cutting oil enters the inner hole of the drill bit from the drill shank and reaches the cutting area to cool and lubricate the edge of the drill bit. Iron chips and cutting oil are discharged along the “V” groove of the drill pipe, also called external chip discharge.
By using deep hole processing machine tools and appropriate cutting parameters, the following processing effects can be achieved:
Hole size: IT6 ~ IT611 Inner hole roughness: Ra0.2 ~ Ra6.3 Asymmetry: 1/1000 × hole depth, fixed part, tool rotation 0.5/1000 × hole depth, rotation workpiece, reverse rotation of the tool
Gun drilling is particularly suitable for processing small diameter holes. Usually, holes with a diameter of less than 10mm are more suitable for gun drilling. The most advantageous is that it can discharge iron shavings smoothly.
The lever for efficiency in deep hole machining
Due to the special structure of the gun drilling tool, there is no need to remove chips when processing deep holes, and the depth can be processed in one go. The deeper the depth of the hole, the more treatment efficiency can be reflected. Depending on the material and hole diameter, the processing speed can reach more than 30-100mm/min. Gun drilling is not only suitable for deep hole drilling machines, but also can be used for other traditional machine tools, such as machining centers and CNCs. turns.
(Reminder: Unlike special gun drills, machining centers rarely use drill guides for guidance. Therefore, to use gun drilling on a machining center, you must first pre-drill a pilot hole on the workpiece In order to achieve a better processing effect, the pilot hole must meet the tolerance requirements of hole diameter, hole depth, etc.).
Classification of artillery exercises
Problems to pay attention to during treatment
1. The workpiece clamping must be safe and reliable, and coaxial with the center of the machine tool. The outer circle and end face of the part can be processed, and at least the locating surface must be turned over.
2. When processing long workpieces, the workpiece and the gun drill should use a fixed center frame. Additionally, the drill rod should also have 1-3 movable supports.
3. The center hole of the workpiece should be smaller than the diameter of the drill bit. If the size of the central hole cannot be reduced, a special guide sleeve can be used.
4. When starting drilling, a pilot drill sleeve should be used. The inner diameter of the drill sleeve corresponds to the diameter of the drill bit. The inner diameter of the drill sleeve must be ground to IT6 level. Hole straightness is not required, it can also be used on the workpiece. Pre-drill pilot holes to guide you.
5. The drill sleeve is a wearing part. When the wear of the inner diameter of the drill bush is more than 0.02mm, the drill bush should be replaced.
How to Resharpen a Carbide Pistol Drill
The most common problem faced by barrel drills is wear and tear. As far as wear goes, it’s just resharpening. This is currently the simplest and simplest way. Since carbide gun drill bits are the most commonly used, let’s first talk in detail about how to better use carbide gun drill bits after resharpening.
Re-sharpening carbide drill bits:
The grinding of the gun drill should be forced at regular intervals. When sharpening, the gun drill should be clamped and indexed by a sharpening device, and the tool edge should be sharpened on a special sharpening machine.
Standard for blunting carbide gun drills
When the flank width of the outer edge of the gun drill exceeds the value shown in the table below, the gun drill should be ground to prevent the cutter head from breaking due to the increase in force. cut.
Things to Note When Sharpening Carbide Drill Bits
1. The grinding of the gun drill should be forced at regular intervals. That is, when the degree of wear on the back of the tool reaches the dull grinding level, it must be resharpened.
2. When grinding, you must use a sharpening accessory and a special sharpener. Do not sharpen with a hand drill.
3. When grinding, the force direction of the drill bit should be toward the tool pad to avoid damage to the tool due to swinging of the drill rod. The feeding amount each time should not be too large to avoid the carbide drill bit from cracking and breaking, causing injury.
4. After the five cutting surfaces of the drill bit are ground, the edges and corners between the flank surface of the drill bit and the guiding part of the drill bit need to be manually rounded on the grinding wheel.
5. The gun drill must be resharpened on a special diamond grinding wheel.
6. The dust generated by sharpening the carbide part of the drill bit is harmful to the body. Please wear protective glasses and masks.
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