How to design a suitable gun drill cooling system?

Gun drill deep hole processing has a long history. With the development of machinery manufacturing technology, the gun drill has become an effective method and weapon for processing precision deep holes. Its application has long been beyond the scope of gun manufacturing. Its use in automobiles, molds, and Deep hole processing in various industries such as hydraulics, aerospace, textile machinery, heat exchangers, and machine tool manufacturing.

The three major elements of gun drill processing technology are equipment, tools (gun drill), cooling, and lubricating devices.

Among them, whether the cooling and lubricating device can supply sufficient and clean cutting fluid has an important impact on the tool’s life, the surface roughness of the hole, and the dimensional accuracy.

Cooling and lubrication mainly have the following functions:

  • It can reduce the wear of the tool and the guide sleeve;
  • It can inhibit the formation of built-up edge;
  • It can cool the agency to reduce and eliminate the friction heat and cutting heat;
  • Under the action of pressure, friction, and temperature, a thin layer is formed The oil film prevents the tool and the workpiece from seizing;
  • Continuously eliminates the shoulder.
multi axis gun drilling machine
multi axis gun drilling machine

First, gun drilling needs to choose a good cooling lubricant. The domestically developed high extreme pressure cutting oil (compounds with elements such as sulfur, phosphorus, and chlorine) can meet the gun drilling process requirements. Secondly, there must be a cooling and lubricating device that is reasonably designed, efficient, and environmentally friendly.

The cooling and lubricating device must have the following functions:

(1) Purification function

In the process of gun drilling, a large number of cuttings mix into the cooling lubricant, and the cuttings need to be separated from the oil and purified before they can recycle.

Relevant tests show that when the cutting fluid filtration accuracy is 20um, the tool can drill 100 holes between two sharpenings. When the filter accuracy is 10μm, and other conditions remain unchanged, then 500 holes can drill between two sharpenings. The relationship with the quality of the machined surface is also the same. When the cutting fluid filtration accuracy control at about 50um, the machined surface roughness value is 5μm, and when the filtration accuracy control at 10um, the machined surface roughness value is 0.5~1μm. Therefore, cutting the liquid’s cleanliness is closely related to the quality of the machined surface and the life of the tool.

(2) Pressure and flow of cutting fluid

During the gun drill processing, it is necessary to provide a certain pressure and cooling lubricant flow. If the flow and pressure are insufficient, a chipping edge will occur, and the chips cannot be removed in time, which will directly affect the processing quality, tool life, and equipment safety.

The pressure and flow setting of the cutting fluid are mainly related to the machining hole’s size and depth. The hole diameter and hole depth determine the pressure, the same hole diameter, the deeper the spot, the larger the pressure; the flow rate is related to the gun drill’s center oil diameter. The oil pump’s output characteristics adjustment require during processing. During the processing, the user can adjust the set pressure appropriately according to the different processing effects.

(3) Oil temperature control

In the process of gun drilling, the deformation of metal chips, the friction between the drill support pad and the whole pad, and the friction of the chips on the forward inclined surface of the tool will generate a lot of heat, which is difficult to dissipate quickly.

According to relevant information, when the drilling hole diameter is less than 20mm, the heat generated is 17x×106J/h, and when the 40mm hole diameter drill, the heat generated is 46×106J/h. Only 3.75% of this heat radiate through the workpiece. 96.25% of the heat depends on the cutting fluid for cooling, so the cutting fluid temperature rises quickly and must control.

Generally, the weather should keep between 20~45℃, and the maximum temperature should not exceed 50℃. Not only can the tool be in a good cooling state for cutting, but the nature of the cutting fluid will also deteriorate, thereby affecting the Lubrication effect. When the temperature is lower than 20℃, the low temperature will encounter the high-temperature cutting zone, which will easily lead to the formation of small foam on the tool’s surface, which will damage the cutting tool and cause adverse consequences. Therefore, the cutting fluid tank volume should have sufficient work, but a temperature control device is also required to maintain good cutting performance.

(4) During the processing of the gun drill with the protective device, due to the tool’s wear, the increase of the discharge resistance, and the change of working conditions, the cutting fluid pressure will also produce certain fluctuations.

To make the pressure fluctuation not affect the normal cutting process, the user must monitor the cutting fluid pressure during the entire deep hole drilling process. When the pressure exceeds or falls below the set range, the machine tool can automatically retract the mechanism or take corresponding protective measures. Ensure the safety of workpieces, tools, and equipment.

Based on the above requirements for the gun drill cooling and lubricating device, you can design a suitable gun drill cooling system for your products.

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