The Application of Automatic Compensation Technology in Mainstream Automotive Engine Factory in China

Cylinder hole fine boring automatic 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, when planning the process, the company will take a very cautious attitude. It is necessary to ensure the physical quality and process quality of the parts, and to use the most suitable solution 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.).

Since the mid-1990s, machining centers have become more and more widely used. There are also automatic lines that consist entirely of machining centers, including cylinder lines. But is this a trend of development? It turns out that this is only a desirable mode.

In recent years, the world-famous machine tool suppliers and auto enterprise groups have been very optimistic and have given priority to the "hybrid flexible automatic line", which is a kind of combination/specialized machine tool and machining center mixed flexible line, its advantages are high production efficiency At the same time, it is quite flexible and can be suitable for mass production and production of variant products. When the cylinder is machined in this mode, the boring process of the cylinder bore is performed by a dedicated machine tool.

At the same time, the fine boring automatic compensation that has been configured and used many years ago has further improved 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 the economy and applicability in planning and implementation, and finally make decisions based on their actual situation.

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, a clear understanding of the process technology used for the fine-hole drilling of cylinder bores has been obtained. Proved the proportion distribution of combined/specialized machine tools and machining centers in the borehole boring process.

Of the more than 60 cylinder lines we surveyed, the new line completed and put into operation after 2002 accounted for one half of the weak (47.5%), but in these new lines, the proportion of machining centers used in the borehole boring process increased. 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 special 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 Factory, and Volkswagen FAW Engine ( Dalian, etc., adopt this model.
As for the equipment with the automatic compensation function for cylinder bores, it accounted for 54% of all the more than 60 production lines surveyed. Among them, when the cylinder bores are machined in special planes, 64% are equipped with this function. With the machining center, only 25% of the processes have this function.

Fig.1 Composition and working principle of automatic compensation system

In fact, although precision compensation is a mature technology that has been applied for many years (it was also referred to as “automatic compensation” in the past), with the continuous development of related technologies such as digital control and testing, especially at the core of the compensation system. The improvement and improvement of the tunable masts have greatly improved and expanded the effectiveness of compensation, reflecting that this mature technology is continuously improving.

Realization of automatic compensation function

The automatic compensation system consists of three parts: random detection, (signal) feedback compensation, and boring head with fine-tuning function. In the main engine parts, in addition to the cylinder body, there are many automatic boring hole compensation systems used in connecting rod machining. The principle of compensation and system composition are exactly the same, see Figure 1.

The working cycle is: After the file is boring, the file exits and the workpiece is measured by the electronic plug gauge (measurement head); then the probe exits and the test information is sent to the measuring instrument, which is then compensated after amplification and A/D conversion. The control unit, after performing the operation therein, makes a corresponding judgment. If compensation is required, a corresponding command is issued to the compensation actuator. The compensation actuator may have different forms. The servo motor shown in FIG. 3 is used at this time. It is necessary to convert the axial movement of the tie rod through the coupling, and sometimes it is also necessary to match the coolant supply device; finally, the lever is displaced and the cutting edge of the boring tool is caused by a boring head (knife) with a fine adjustment function. The radial displacement of the tool thus completes the automatic compensation of the tool 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 generally provided by a randomly detected supplier. When a servomotor or stepper motor is used as an actuator, it is also equipped with a drive power supply.

The famous measuring instrument company MARPOSS used this method to cooperate with the machine tool factory to meet the needs of users. Therefore, in the selection of the process for the automatic compensation of cylinder bores by engine plant planners, besides the execution mode of compensation, the last one of the three elements of the system—the selection of boring heads (knives) with fine-tuning functions is important. Now.

It must be pointed out that in recent years, the measurement instrument and the compensation control unit in the above system have been integrated and replaced by a universal computer-aided measurement system based on an industrial control computer, such as MARPOSS'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 be different in the specific structure, and even the rod drive method is completely different, but basically The working principle is the same.

Fig. 2 is a schematic view of a trowel of this type, in which the front end of the tie rod has a small angled wedge, and the wedge that is in close contact with the wedge is the upper column of the lever, and the front end of the lower part of the lever is equipped with a fine boring blade. In this way, when the rod is moved back and forth, it will cause a slight radial displacement of the tool tip. Based on the known 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, thereby realizing the quantitative tool trimming.

But how does the measurement information output after random detection change to the corresponding compensation command and determine the radial displacement of the tool tip? As can be seen from FIG. 1 , it is achieved by the control unit (compensation controller) calculating and processing the detection result, and making a corresponding judgment to issue an instruction to the drive device. It is 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 circumstances. The following is a representative example.

1. Set the value:
(1) T is the aperture tolerance and can be expressed as ±T/2;
(2) k‧T is a controlled range and can be expressed as ±1/2k‧T, ie the tolerance T is compressed (k<1), “+1/2k‧T” and “-1/2k‧T” Control line or cordon;
(3) Xi is the measured value of the aperture, which can be regarded as the deviation of the nominal diameter of the relative aperture when using the comparative measurement method;
(4) n is the number of workpieces that are continuously detected at a time and is the base of the calculation process.
2. Compensation conditions:
(1) The control unit executes a processing mode in which five workpieces are continuously measured at a time and then averaged;
(2) At that time, compensation was needed;
(3) When compensation is needed, the compensation amount is taken, that is, the position of the tip of the boring tool is adjusted to the nominal value of the aperture, which is the midpoint of the tolerance;
In general, n takes 5 and k takes 0.5.

Of course, there are also more simple compensation models used by engine plants. For example, in a certain cylinder block production line with a large production volume, the cylinder bores adopt the “compulsory compensation” method. Compensation tool wear 1μm.

The fine boring compensation system introduced above is a kind of feedback automatic compensation of dead-cycle control, but in fact, in the industries such as automobiles and diesel engines, when it is actually used in the process of fine hole drilling, there is a manual adjustment/compensation mode. Exist in the early domestic engine factory built, still used by some companies.

Completed in the late 1980s, Shanghai Volkswagen Engine 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 combined/specialized machine tools. It uses manual compensation. A cylinder "rigid" production line of Chery Automobile Engine Plant No. 1 also takes a similar approach in cylinder bore machining. However, this is not just an early choice of technology for the company. Geely Automobile's borehole boring process in the three cylinder production lines built in recent years all have fine-grained compensation functions, but they are all “open-loop” manual controls.

Figure 2 Slant wedge micro-adjustment

However, even if they are all "manual," there are differences in specific practices. In the cylinder line of Shanghai Volkswagen Engine No. 1 Plant, compared with the system composition shown in Figure 1, there is actually only a small number of drive devices. The random detection instrument and control unit used for full inspection in the automatic line 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. The operator only determines 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 approach is to establish a guard (control) area within the tolerance range first. When it is found that one (or three to five) measured values ​​(or average values) of a single cycle (for example, one hour) exceed the warning line, Manually perform the compensation operation and adjust to the middle of the tolerance.

Development of fine-tuning fine boring tool and improvement of quality of cylinder bore boring process

1. Application of deflection mechanism for fine tuning boring tool

Although the fine-tuning boring tool adopting the wedge working principle still has a wide range of applications, the late-appearing deflection mechanism fine-tuning boring tool has gained more applications in the engine industry due to its superior performance. In recent years, there are examples of the use of this novel boring tool in some of the most advanced fine-boring processes in the new connecting rod and cylinder production lines in China. Figure 3a shows the working principle of this fine-tuning file.

In short, the radial adjustment r of the blade cutting edge is brought about by the deflection mechanism. The deflection mechanism is mainly composed of an adjustment fork, a pad (sliding) block and a yaw axis. As can be seen from FIG. 3a, the axial displacement “s” of a tie bar (not shown in the figure) connected with the adjustment fork coaxially enables adjustment in the housing. The fork moves with it, and the inner surface of the adjusting fork has an angle “α” with the centerline.

The yaw shaft, which acts as a transmission, is fixed on the housing by means of a pivot axis and cooperates with the inner surface of the adjusting fork by means of two spacers. Therefore, when the adjusting fork is moved axially, the yaw axis generates a corresponding radial displacement. The length L is fixed to the left side of the yaw shaft by the end face connection, and the cutting edge of the insert is located at the front end of the boring bar. In the state of the figure, the following relationship exists between the radial displacement “r” of the blade and the axial movement “s” of the tie rod:

r=(A/BX tgα) X s

Fig.3 The working principle and structure diagram of the fine adjustment boring tool of the deflection mechanism

Where A = L + k1, k1 is a structural parameter of the yaw axis, k1 = 10mm in Figure 3b.
Fig. 3b is a schematic diagram of the structure of the cylinder hole fine-tuning boring tool. The working principle of the deflection mechanism is adopted. According to the icon structure parameters, when the compensation drive device has an axial displacement of 1 mm, the corresponding radial displacement of the tool tip is 16.25 μm. In other words, in order to obtain a radial compensation amount of 1 μm at the tool tip, it is necessary to move the tie rod axially by 0.062 mm, which is very easy for a reliable servo system.

The fine-tuning boring tool using the deflecting mechanism has some technical advantages compared to the mature “wedge type” introduced in the previous section. The radial displacement of the former tool tip is caused by the movement of the deflection mechanism. As can be seen from FIG. 3 , in the process of converting from the axial movement of the tension rod to the radial compensation of the cutting edge, no fitting clearance exists, so the transmission and conversion accuracy is relatively high.

The "clear wedge" mechanism's existing fit clearance will have some impact on the accuracy of the compensation. On the other hand, the determination of the latter structure, together with the objectively existing slight fit clearance, results in poor sealability of the guillotine blade. Once oil, dust, and even minute cutting enter the tip, it is particularly adhered to the fit. Parts, will reduce the effectiveness of compensation. On the contrary, as can be seen from the structure of the yoke of the deflection mechanism shown in FIG. 3, the sealing effect is better.

2. The fine-tuning function of the boring knife in the "semi-precision / fine boring integrated" application

In recent years, in the processing of cylinder bores and connecting rod holes, semi-finishing/finishing boring has been combined into one process, and semi-finishing boring and boring boring have successively been completed in one station. The fine-tuning function plays an important role in it.

For this purpose, the end of the mast in FIG. 3 will not only have a fine boring insert located below, but also one or more semi-finished boring inserts on the top. FIG. 4 is a schematic diagram of a boring head for processing a cylinder bore. The three blades in the upper half of the left-hand side of the left-hand side are used for semi-finishing.

When machining in this integrated manner, the adjusting fork in Figure 3a is first placed in the ejected position so that the two pads on the yaw axis are located at the rear of the fork, the yaw axis is upturned, and the mast is biased. The value "r" is set so that the cutting edge of the blade 1 reaches the semi-finishing position. At this time, the cutting edge of the fine boring blade must be within the semi-finishing diameter to form a "knife."

Afterwards, the boring tool finishes the semi-finishing of the hole during the advancement, and the tie rod in Figure 3a retreats so that the 3 cutting edge is moved back to an offset value "r". The boring process is completed when the boring tool is returned. As for the value of the "r" value, it depends on the nominal value of semi-finishing and fine boring, and the tolerance given by the process and other factors must also be considered.

When the fine-tuning boring tool is a "wedge" type, the process of semi-finishing and fine boring is similar to the above description except that the semi-fine boring insert is a fixed, non-deflecting boring bar. on. When the boring tool advances and the semi-finishing process is performed, it is first moved by the pull rod, and the cutting edge is retracted by the oblique wedge mechanism to complete the "knife" of the fine boring blade.

The superiority of the integration of semi-finishing/fine boring is very obvious. There are two main aspects. (1) Saved one station of the production line, reduced the input, including hardware and workshop site such as equipment; (2) Due to the implementation of two processing operations in the same station and the same clamping state, which greatly reduced the traditional The two-station machining method may produce manufacturing errors and improve the precision of the workpiece finishing.

3. Cylinder hole fine boring machine automatic compensation application in machining center

As we all know, semi-finishing and fine boring of the large and small headed holes of connecting rods are all based on special machining methods, but cylinder bores are not. From the previous introduction, we know that the proportion of machining centers in recent years has exceeded 40%. However, another obvious fact is that only a quarter of the automatic compensation systems equipped with precision boring are used in this case, which is far less than nearly two-thirds of the time when using special machines. What are the reasons?

Fig. 4 Schematic diagram of automatic compensation of cylinder bores in machining centers

From a technical point of view, this is generally not as rigid as a special machine tool in machining centers. The process of achieving tool nose compensation is more complicated, and its use is less effective than that of a special machine.

However, in recent years, the automatic compensation technology for the borehole boreholes developed by the companies such as (Germany) SANtech and Valenite (USA) has gradually increased its application ratio due to better solutions to some difficult problems. After comparing the working principle and implementation process of the above two products, it can be found that there are many similarities. Figure 5 is a schematic diagram of the system.

In diagram a of FIG. 4 , the left side is a fine-tuning trowel, which is placed in the magazine like other tools. It can be seen from the figure that the boring knife adopts the "wedge" type working principle and has two kinds of semi-finished and fine boring blades. At the beginning of the process, the tool changer first removes the boring tool from the magazine directly to perform automatic tool change, and then the machine tool spindle moves with the tool and positions it to the specified position.

Before the work feed is performed, the cooling fluid enters the front end of the tool at a certain pressure, and after the pressure is applied, a beveled piston (right) is moved back, so that the fine boring blade IV is retracted. Then, the spindle of the machine tool advances and the semi-finishing of the cylinder bore is completed by the blades I, II, and III at the same time.

Immediately after the coolant discharged inside the tool is discharged, a powerful compression spring moves the piston (left) forward through a pull rod, and the lower slanted surface of the latter expands the fine boring blade IV. As for the lever and the piston can be linked, because there is a thread between the two to pay for the connection. The bulging amount of the above-mentioned blade IV is equivalent to the finished boring size, and FIG. 4a shows the swelled state of the fine boring blade. Afterwards, the spindle of the machine tool retreats and the work feed is completed again.

When a workpiece has been machined, an on-line gage is used to measure the finely-divided cylinder bore. If an error change is found—mainly due to blade wear causing a decrease in bore diameter—and the control unit will incorporate fine-tuning when compensation needs to be applied. The actual structural parameters of the boring tool enter the corresponding compensation amount into the CNC system of the machine tool.

The spindle of the machining center is then moved to the front of an adjustment device (see Fig. 4b) as if the robot was carrying a trowel. The adjustment device is fixed on a certain position on the table. The spindle allows the front end of the tool to be inserted into one of the holes in the unit and then starts to rotate.

Since the front end of the tool is integrated with the pull rod in the boring tool, the pull rod and the piston with the wedge mechanism are connected with the thread (see Fig. 4a), so when the tool spindle rotates the boring tool housing together with the piston, the piston There will be an axial displacement at the same time, so that the cutting edge of the fine boring blade will swell in the required amount to complete the compensation.
As for the relationship between the spindle rotation angle and the blade tip expansion amount, depending on factors such as the angle of the bevel and the thread lead, according to SANTECH's product specifications, the cutting edge will generally produce a radial displacement every 20 degrees of rotation. 1μm.

Figure 5 Process Capability Analysis of Cylinder Hole Refinement Process

4. Cylinder hole fine boring compensation improves process quality

Regardless of whether it is a special plane or a machining center, after the cylinder hole fine-pickup compensation system is arranged, it has a significant effect on improving the processing quality of the parts, and in particular it can effectively improve the quality of the production process operation.

Fine boring is not the last step of a cylinder bore, but it has very high technical requirements. The bore diameter tolerance is ±0.01mm and the cylindricity needs to be controlled to 0.01mm. For this purpose, the random inspection station set up after the semi-finishing and finishing work positions simultaneously measures 100% of the upper and lower cylinder sections and the two directions of each section. And at any time, according to some trends reflected by the data processing results of detected values, signals are sent out for targeted fine compensation. In order to verify the quality of parts after finishing, high-precision electronic inspection tools are also set up online to evaluate the quality of physical processing and the quality of process operations.

Figure 5 shows an example of a cylinder hole boring process from a cylinder block production line of an engine plant using Grob's special machine, SANtech's fine-tuning boring tool, MARPOSS's random measuring device and off-line detection device. According to the normal production period during the week, the data collected according to the specified sampling method and statistical analysis based on this.
In Fig. 5, a is a single-value process diagram, also called a "scatter diagram," which reflects the trend of the size of the cylinder bore to be machined during this period. b is a histogram, on the basis of which the process capability indices Cp, Cpk — two indicators for evaluating the quality of the production process during this period can be calculated. From the results obtained (Cp=1.72, Cpk=1.71), the level of process quality that can be achieved with this type of finishing station is quite high.