The program of CNC special fixture for flexible production line is the foundation of efficient machining. Next, we start from the key structure design of the jig of multi-type engine cylinder block and cylinder head produced by collinear production, and discuss the key design of the jig layout scheme to the efficiency and quality improvement of the production line.
1. Efficient fixture design for rough machining
Finishing the following process positioning datum processing; The main machining surface to the margin, at the same time to reserve a reasonable margin for finishing to ensure the machining surface. Final size and flatness, surface roughness and other requirements. The processing interference, cutting efficiency and quality stability are considered under the same process condition of multiple products. The product coarse datum is different at the same time, needs to realize the compatibility through the innovation design of the fixture.
1. Cylinder block clamping scheme
Rough machining mainly for the cylinder block, combustion chamber surface and other characteristics of processing. After the workpiece is set, the fixture mainly pushes out the pressure bar through the oil cylinder to press the sand discharging process hole of the blank of the cylinder body, and presses the part precisely in the reference direction, but the pressure bar breaks frequently due to the casting allowance, the drawing Angle and the cutting impact load, which seriously affects the production efficiency.
However, the clamping head at a certain point in this direction has never had the problem of fracture. By re-designing the structure of the clamping head reasonably and designing all the auxiliary clamping schemes into the same structure, the problem of fracture caused by impact of the clamping head has been effectively solved.
2. Double fixture scheme is suitable for collinear production
There is a big difference in the crude positioning datum of cylinder head. Three schemes are proposed to realize the collinear production of different products:
1) outsourcing the implementation of rough processing sequence features;
2) add a CNC;
3) processing in the same processing center.
The double fixture scheme is optimized by means of changing the positioning device or setting up the double fixture scheme. The size of the cylinder block cylinder head parts localization design differences: double fixture design Ⅰ design for the small cylinder processing; Ⅱ for large cylinder processing position, to achieve the cost control and quality assurance.
Part.2 design of finishing fixture based on "one side and two pins"
The cylinder block and the cylinder head are processed as typical box parts, and the positioning scheme of "one side and two pins" is adopted to finish 6 planes and holes.
1. Adopt A/B shaft clamp
Based on the b-shaft transmission mode, the original cylinder production line adopts the b-shaft fixture scheme. Some processing features, such as the crankshaft position sensor hole and the main bearing cover bonding surface, must be processed after the parts are turned upright.
After industry investigation and practical application of cylinder head A shaft, the processing load of cast iron cylinder block with A small displacement below 1.5L can completely meet the process requirements through A shaft machining. The series arrangement of axis B and axis A can conveniently realize the positioning surface of the parts is always facing down, without the need to turn over and stand up as A whole, which not only saves the operation time of the employees, reduces the work load, but also avoids the pollution of the working environment caused by the splashy cutting fluid in the process of turning over.
2. Optimize the clamping point design of aluminum alloy clamps
The design of the lever type force increasing clamping mechanism is applied to the processing of the aluminum alloy cylinder head, which not only avoids the deformation of the cylinder head, but also meets the requirements of the processing force. Due to the large distance difference between clamping points, the compatible clamping process cannot be realized. Through the design of quick-changing chuck structure, the compatibility of different parts can be realized.
3. Precise design of stop and stop structure
Based on the low cost design requirements, CNC design for semi-automatic feeding. In order to ensure that employees will push and pull the parts in place, the design of the machine tool jig induction device is particularly important.
After the workpiece is pushed in place, the pressure changes in the channel caused by the connection mechanism's internal air circuit is connected until the set value, and the parts are monitored in place. By writing the signal into the interlock logic of the equipment, the machine does not process the parts when they are not in place to prevent the parts from falling into the processing bin.
4. Structural design of locating pin gas check
Based on the design structure of "one side and two pins", "one side" passes through three or four registration points; The "two pins" are the round pin and diamond pin positioning components.
The air pressure monitoring channel is adopted in the design, when the force is too large, the machine will stop automatically and give an alarm, to prevent the occurrence of tool collision accident.
5. Registration point structure design
Air tightness monitoring and cutting fluid flushing devices are used at each registration point of the fixture. During the positioning process, washing is used to prevent abnormal processing caused by iron filings on the positioning surface. During the process of manufacturing, the whole process of air tightness detection and monitoring whether parts shift.
Part.3 design of key machining fixture
All machining adopts CNC machining, mainly considering production flexibility and the introduction of new products in the future and other factors, but in the key features of the long-term processing capacity can not meet the process requirements, such as curved bore location degree.
1. Fixture design for special station
The curved bore of the cylinder block adopts the line boring tool processing method with special machine characteristics, which not only gives consideration to the flexibility of CNC, but also guarantees the stability of special machine processing. The key point is to add a bearing support at the far end of the tool to prevent the position variation caused by the tool gravity factor and the soft and hard processing materials. However, the line boring cutter is very demanding on the center of the feed, and the positioning scheme based on the pinhole coordination has some influence on the clearance.
In order to eliminate the clearance, a push hydraulic cylinder is added on the side of the part. After the workpiece is seated and positioned, the part is pushed to the side through the push rod to eliminate the potential clearance effect and ensure the moderate alignment. By using a special machine line boring tool scheme on CNC, the difference between front and rear end center of crank hole was successfully improved from 0.025mm to less than 0.01mm.
2. On-line measuring device for key station tooling
The on-line probe is used for the processing of key features of box parts. Such as cylinder block thrust surface, cylinder block cylinder head combustion chamber surface and other important features of machining detection, in order to ensure the machining size ability, tool wear compensation is achieved by measuring tool head. In order to avoid the impact of iron scrap, aluminum scrap and measuring head body fluctuation, a reference part of standard size is installed on the fixture to calibrate and monitor the measuring system regularly to ensure the accuracy of machining size.
Special fixture for box parts has been successfully developed and applied in cylinder block and cylinder head production line. In addition to some clamps and guide components need to be changed manually, positioning devices do not need to be changed, which can realize the collinear production of three categories of products. The mixed use of finishing A/B axis based on one side and two pins effectively shortens the auxiliary production time, improves the application of ergonomics, especially the application of the concept of special machine to the design of CNC fixture, and effectively improves the long-term processing capacity of key features.
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