Application of Automatic Compensation in the Process of Finishing in Mainstream Automotive Engine Works in China

This article briefly introduces the automatic compensation technology for precision boring, which is successfully applied in the modern automobile manufacturing industry. Taking engine cylinder bore machining as an example, based on the investigation of the actual application of mainstream automobile engine plants in China, the company is planning to The different process choices made during the process. The article also combines examples to introduce typical compensation patterns.

1 Precision Automatic Compensation Technology

(1) Overview Automatic compensation of fine files is a mature technology that has been in existence for many years. It is a very important and representative type of control technology known as “auto-adjustment” in modern mechanical manufacturing. In the engine's main components, such as the cylinder, connecting rod and other hole processing has been more widely used. Taking the cylinder machining as an example, the fine bore of the cylinder bore is one of the most important steps. The dimensional accuracy and shape error involved will directly affect the quality of the engine. The actual use effect indicates that if the automatic compensation link is added in the fine boring process, the operation quality of the process can be significantly improved, mainly reflected in the following aspects:
1 Because the automatic compensation system can compensate for tool wear and the influence of temperature and other unstable factors, and the compensation amount of the cutting edge can reach 1 μm, the effect of improving and improving the quality of the workpiece is obvious.
2 It can reduce the number of knife adjustments and improve process efficiency (especially when combining semi-finished and fine boring in the same process).
3 By improving machine tool performance, ordinary machine tools can be upgraded to precision machine tools.

(2) Realization of automatic compensation function for fine boring The automatic compensation system consists of three parts: random detection, (signal) feedback compensation and boring head with fine adjustment function. In the main parts of the engine, in addition to the outside of the cylinder, there are many automatic countersink compensation systems used in connecting rod machining, but the compensation principle and system composition are exactly the same. The work cycle is: After the file is boring, the file exits, and the electronic plug gauge (measurement head) measures the workpiece; then the probe exits and the test information is sent to the measuring instrument, which is sent to the compensation control after amplification and A/D conversion. The unit, after performing calculations in the unit, makes appropriate judgments. If compensation is required, a corresponding instruction is issued to the compensation actuator; the compensation actuator can have different forms. Figure 1 shows the servo motor. Conversion of the coupling into axial movement of the tie rod sometimes requires the use of a coolant supply device; finally, displacement is generated by the tie rod and the diameter of the guillotine cutting edge (blade tip) is caused by a boring head (knife) with a fine adjustment function. Displacement to complete the tool's automatic compensation during boring.
Among the three elements that make up the system, the random detection part made up of the probe/electronic plug gauge and measuring instrument is actually the same as the commonly used off-line detection device. In controllers, execution units and auxiliary components of the (signal) feedback compensation system, the controller has been manufactured and is generally provided by a randomly detected supplier. When a servo motor or a stepping motor is used as an actuator, the controller is also provided. To configure the drive power. The famous measuring instrument company MARPOSS uses this method to cooperate with the machine tool factory to meet the needs of users. Therefore, in the process selection of automatic compensation of cylinder bores by engine plant planners, in addition to the execution mode of compensation, the last element of the three elements of the system—the selection of steamed bread (knife) with fine-tuning function is particularly important. It must be pointed out that in recent years, the measuring instrument and the compensation control unit in the above system have been integrated and replaced by a common computer-aided measurement system based on an industrial control computer (for example, MARPS company's E9066 product).
So far, in the fine boring compensation system, the proportion of fine grooving boring tools using the wedge mechanism is still the largest. Although the actual application of the tool will have some differences in the specific structure, and even the way the rod is driven is completely different, but its basic The working principle is the same. This file is shown in Figure 2. As can be seen from the figure, the front end of the pull rod in the middle part has a small angled wedge, and the close contact with the oblique wedge is a short column at the upper part of the lever, and the fine boring blade is installed at the front end of the lower part of the lever. In this way, when the pull rod moves back and forth, it will cause a slight radial displacement of the tool tip. Based on the knowledge of the angle of the wedge and the ratio of the lever, the mathematical relationship between the axial displacement of the rod and the radial displacement of the tool nose can be established to achieve quantitative tool trimming.

(3) The compensation mode for fine compensation automatically However, the measurement information output after random detection is converted to the corresponding compensation command and the radial displacement of the tool tip is determined. This is achieved by the control unit (compensation controller) calculating and processing the detection result, and making a corresponding judgment to issue instructions to the drive device. Only the mode of operation and processing (that is, the mathematical model for performing compensation) must be decided by the user's craft department and quality department according to their own conditions.
Of course, there are some engine manufacturers that use a simpler compensation model. For example, in a certain cylinder block production line with a large production volume, the cylinder bores adopt the “compulsory compensation” method. The specific approach is: each hole of the precision boring insert machining 10 holes, The tool wear amount is automatically compensated by 1 μm.
The fine boring compensation system described above is a kind of feedback automatic compensation of closed-loop control, but in fact, in the automobile, diesel engine and other industries, when it is actually used in the cylinder hole boring process, there is a manual adjustment/compensation mode, and this situation is not only existed The engine factory built early in the country is still used by some companies. Built in the late 1980s, Shanghai Volkswagen Engine No. 1 Plant is one of the first modern automobile engine plants in China. Its cylinder production line is a rigid automatic line composed entirely of combination/special-purpose machine tools. Manual compensation. A cylinder "rigid" production line of Chery Automobile Engine Plant No. 1 also adopted a similar approach in cylinder bore machining. However, this is not just a kind of technological choice in the early stage of the enterprise. The well-known private company Geely Automobile Co., Ltd. in the cylinder hole boring process of the 3 cylinder production lines built in recent years all have fine-grained compensation functions, but they are all "open-loop". Manual control. However, even if it is "manual" control, there are differences in specific practices. In the cylinder line of the Shanghai Volkswagen Engine 1 Plant, there is actually only a small number of drive devices c compared to the system configuration shown in FIG. In the automatic line, the random detection instrument and control unit for full inspection can still automatically give the compensation amount according to the preset compensation requirements, but it only needs manual operation (usually performed on the machine control panel). The model of Geely Automobile is much simpler. No random inspection station is set in the production line. Operators only determine the compensation and compensation amount according to the measurement results obtained during each sampling cycle based on the inspection tool set outside the line. The specific method is also to establish a warning (control) area within the tolerance range. When it is found that one (or 3-5) measured value (or average value) of one cycle (for example, one hour) exceeds the warning line, Manually perform the compensation operation and adjust to the middle of the tolerance.

2 cylinder hole fine boring process selection

In the machining of the cylinder block, the fine bore of the cylinder bore is one of the most important steps. The dimensional accuracy and shape error involved will directly affect the quality of the engine. Therefore, the company will take a very cautious approach when planning this process. It is necessary to ensure the physical quality and process quality of the parts, and to use the most appropriate solutions in combination with the actual conditions of the products and the company. The process selection of cylinder bore fine boring involves many factors such as processing equipment, boring technology, boring burrs (including blade material, whether with compensation function, etc.).
In the automotive industry is facing an increasingly fierce market competition environment, the company has accelerated the speed of product replacement, pay more attention to reducing costs and increasing efficiency, and strengthen the flexible production methods. Indeed, since the mid-1990s, machining centers have become more and more widely used, and automated lines (including cylinder lines) consisting entirely of machining centers have emerged. But is this a development trend? It turns out that this is only a desirable mode. In recent years, the internationally renowned machine tool suppliers and auto enterprise groups have been very optimistic and have given priority to the adoption of “hybrid flexible auto lines”. This is a kind of flexible automatic line combining a special machine tool and a machining center. Its advantages are high production efficiency, and at the same time it is quite flexible. It can adapt to mass production and variant product production, while the investment is relatively small (by parts The structural characteristics and process analysis are determined). When the cylinder is machined in this mode, the boring process of the cylinder bore is performed by a dedicated machine tool. The fine boring automatic compensation that has been configured and used many years ago further improves the machining quality of the borehole boring. However, although the effectiveness of this measure has been confirmed, as a process option, enterprises will still consider economical aspects, applicability, etc. in their planning and implementation, and finally make decisions based on their actual conditions.
Through the investigation of more than 60 cylinder production lines of more than 20 mainstream automobile engine plants (including diesel engine plants) in the country, we have a relatively clear understanding of the process technology used for the cylinder bores. Among the more than 60 cylinder lines, nearly half (47.5%) of the new lines put into operation after 2002 were produced. However, among these lines, the proportion of the use of machining centers in the borehole boring process has increased to 45%. This shows that in recent years, the application of flexible automatic lines composed of machining centers in the manufacture of major engine parts has expanded.
However, relatively speaking, the above-mentioned "hybrid flexible automatic line" is still slightly dominant. According to this manufacturing method, the borehole boring process is completed on the plane. In fact, China has built a number of advanced and representative cylinder lines after 2005, such as Dongfeng Cummins, Shanghai GM L850, Volkswagen Powertrain (Shanghai), Dalian Diesel Engine Plant, and Volkswagen FAW Engine (Dalian). Such models have been adopted.
As for the equipment with automatic compensation function for cylinder bores, it accounts for 54% of all the more than 60 production lines surveyed; among them, when the boreholes are machined by special planes, 64% with this function; When the center processes, only 25% of the processes have this function.
In fact, even though automatic compensation is a mature technology that has been applied for many years (in the past it was also referred to as “auto-adjustment”), with the continuous development of related technologies such as numerical control and inspection, especially in the core position of the compensation system. The improvement and perfection of the micro-adjustable mast, the effectiveness of compensation has been greatly improved and expanded, fully reflects the continuous progress of this mature technology.