The CNC machining of die forgings has always been a challenge in the mechanical processing industry, and the nozzle for die forgings used in aircraft is also the same. This article will take the die forging nozzle used on airplanes as an example, starting from analyzing its category and processing status, and propose an adapter for connecting the hydraulic spindle of a CNC lathe with a multi-purpose chuck, as well as a tiger mouthpiece fixture, to solve the problems of low machining efficiency, difficulty in clamping and poor flexibility in the conventional lathe machining of die forging nozzle parts. This will enable the CNC lathe to use a more flexible multi-purpose chuck to clamp die-forging nozzle parts, thus achieving its CNC machining.
1. Current situation
Nozzles are commonly used in aircraft, and these nozzles generally come in two blank forms: one is free forging, which is used in the early stages of development; Another type is dying forgings, used for mass production. According to statistics, AVIC Chengfei has undertaken over 1300 nozzle parts for multiple aircraft models, with their main categories and quantities shown in Table 1.
Table.1 Types and quantities of nozzle parts
|Type of nozzle||Straight nozzle||Angled nozzle||Flat tee nozzle||Three-dimensional tee nozzle||Flat four-way nozzle||Three-dimensional four-way nozzle|
|Picture of nozzle|
|Distribution quantity N/item||403||126||394||95||223||79|
The processing process of free forging joint pijp nozzles generally includes: cutting → milling hexagonal → deburring → rough milling of various pipe nozzle shapes → deburring → precision turning of each pipe nozzle → milling → deburring → marking. During the processing, there is milling hexagonal so that there are reference and clamping surfaces in subsequent processing. Universal two-jaw or single action chucks can be used for clamping, which can be processed on ordinary and CNC lathes.
During the forging process, the nozzle of the die forging produces molded burrs on the blank, the surface is irregular, and the quality is unstable, resulting in no reference plane available. Through years of exploration and the experience of skilled workers, a self-made fixture called Hukou Piece, which can be combined with the surface of the nozzle blank of die forgings, has been designed. The three-dimensional model is shown in Figure 1. The cylindrical surfaces 1 and 2 on the tiger mouth piece are perpendicular. The cylindrical surface can be processed according to the outer circular surface of the nozzle blank and then connected to the nozzle blank by clamping the cylindrical surfaces 1 and 2. The schematic diagram of the blank of the tiger mouth clip nozzle is shown in Figure 2, where the square groove is used to avoid the wrench flat boss of the blank. But this type of tiger mouth piece is a self-made fixture based on the two jaw or single action chuck used on ordinary lathes. The two are assembled through a cylindrical surface and cannot be combined with the hydraulic chuck standard on CNC lathes. This is determined by the structural form of the hydraulic chuck. Moreover, the jaws of the hydraulic chuck are flat and cannot be positioned to clamp the blank surface of the nozzle of the die forging.
Figure.1 3D Model of Tiger Mouth Slice
Figure.2 Schematic diagram of the nozzle for the clamping die forging of the tiger mouth piece
There are two processing methods for the nozzle parts of die forgings: one is on an ordinary lathe, which uses two claws or single action chucks with tiger jaws to grip the parts and manually operates the machine tool to complete the part processing. Its characteristic is that the clamping method is universal, but the processing efficiency is low, the labor intensity of workers is high, and the quality is unstable. The second is carried out on CNC lathes, which have high efficiency, precision, low labor intensity, and stable quality in turning parts. However, the connection method of multi-purpose chucks is different from that of CNC lathes. On CNC lathes, parts can only be clamped using a combination of specialized fixtures, and CNC lathes automatically complete part processing. Its characteristic is that the clamping method has poor universality, and the combined fixture has significant human factors, resulting in extremely unstable accuracy. In actual operation, it often requires multiple adjustments and rework; At the same time, the combination fixture is limited by the combination of components, with a large clamp size and a long pressing plate, resulting in a long cantilever of the machining tool, long clamping time of the parts, and unstable processing quality. The combination fixture has a long cycle, usually requiring more than one day of assembly time, and the waiting time for parts is long. Although specialized fixtures have solved the problems of low stability and reliability, as well as long waiting times, their universality could be better, and a complete fixture is required for each part, resulting in high costs. Therefore, with the increase of aircraft models and batches, the processing of nozzle parts for die forgings has become a major bottleneck in the aviation manufacturing industry.
2. Implementation of CNC lathe machining for die forging nozzle parts
To solve the problem of CNC lathes being able to process die forging nozzles, it is now considered to modify the chuck used in ordinary lathes into a multi-purpose chuck. Two jaws can achieve automatic centering through the action of screw rods, and the other two chuck keyways perpendicular to the automatic centering jaws can be installed with positioning jaws, which can be used to locate parts and achieve eccentric turning of parts. Simultaneously design an adapter (see Figure 3) to connect the multi-purpose chuck to a CNC lathe, thereby achieving CNC turning off the nozzle for die forgings. Figure 4 shows the construction diagram of a multi-purpose chuck used on a CNC lathe through an adapter, and Figure 5 shows a three-dimensional solid model.
The spindle adapter plate 14, shown in Figure 4, is connected to the spindle of the CNC lathe, and then the spindle adapter plate 14 and chuck 1 are connected using screws through adapter 7; The spindle adapter plate 14 and adapter 7 use a cylindrical surface for positioning and orientation, and a conical surface for auxiliary positioning; The adapter 7 and chuck 1 are positioned and oriented using a cylindrical surface; Ensure that adapter 7, chuck 1, and spindle adapter 14 are on the same axis as the centerline of the lathe spindle. Claws 2 and 5 are positioned on chuck 1 through keyways, and jaws 2 and 5 are installed with tiger mouth pieces 3 and 4 through cylindrical surface positioning. The tiger mouth pieces grip the die forging nozzle blank 15. During the clamping process, screw rod 6 applies force to jaws 2 and 5 simultaneously to clamp the die forging nozzle blank 15, achieving automatic centering and ensuring that the axis of the parts is consistent with the axis of the machine tool.
Figure.4 2D Structural Relationship Diagram
1. Chuck; 2. 5. Claw; 3. 4. Tiger mouth slices; 6. Screw rod; 7. Adapter; 8. 10. 12. Screws; 9. Positioning pin; 11. Cylindrical pin; 13. Washers; 14. Spindle adapter plate; 15. Blank of nozzle
Figure.5 3D Structural Relationship Diagram
The adapter is threaded and connected to the spindle adapter and chuck. The adapter has a clearance fit between the spindle adapter and the chuck, while the claw and the tiger blade are equipped with a clearance fit. The cylindrical surface of the spindle adapter plate is positioned and centered, and the screw connection is installed on the CNC lathe; The adapter adopts shaft pin positioning, cone centering, and screw connection to install on the spindle adapter plate; The chuck adopts cylindrical positioning and centering, and is connected and installed on the adapter with screws; The claw is connected to the chuck through a T-shaped groove and automatically centered through screw adjustment; The tiger mouthpiece is positioned and centered through a cylindrical surface, and is connected to the claw with a pin.
Through the above connection and clamping, the nozzle of the die forging can be conveniently, reliably, and accurately positioned on the CNC lathe. The operator can call the CNC program to achieve the CNC machining of nozzle parts.
3. Application of CNC lathe machining for die-forged nozzle parts
After data collection on CNC machine tools and conventional lathes (CA6140, CY6140, CF6140), adapters and multi-purpose chucks suitable for CNC machine tools TALENT8/52 and TALENT10/78 have been designed and manufactured. The adapter is made of 45 steel materials and designed based on the connection method of the hydraulic spindle and multi-purpose chuck of the CNC lathe. It is processed and produced according to the assembly dimensions of the hydraulic spindle and the two-jaw chuck. Through practical trial applications, the adapter has been successfully installed and used to process a certain three-way pipe joint part (metal material: 30CrMnSiA). With the use of existing equipment and accessories, without adding any special tools or fixtures, the processing time has increased from the previous 85 minutes. Shorten it to 25 minutes and improve processing efficiency by 70%. It not only saves costs but also reduces the labor intensity of workers.
This device adopts manual clamping to avoid the problem of difficult control of clamping force. At the same time, it can achieve eccentric positioning of parts through non self-centering claws. Therefore, it can be applied to the CNC machining of die forging pipe nozzle parts and to CNC turning of eccentric parts. It also solves the problem of thin-walled parts that cannot be processed using CNC lathes due to the difficulty in controlling the deformation of hydraulic chuck clamping. The phenomenon of low efficiency, high labor intensity, and unstable quality when using ordinary lathes to process die forged nozzles, eccentric parts, and thin-walled parts.
The implementation and application of CNC machining for die forging nozzle parts is a successful case, which has saved costs, improved efficiency, and reduced labor intensity for the aircraft system parts processing of AVIC Chengfei. Through this case study, we can further consider the implementation methods of converting ordinary machining to CNC machining for other types of parts and the idea of changing the low utilization rate of CNC equipment in China’s aviation manufacturing enterprises.
Author: Dou Haifeng