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The mold frame is the key component of the bottle blowing machine and one of the core components of the beverage packaging machinery. The frame is a key part used to support and guide the moving and fixed die moving parts of the bottle blowing machine die frame, and its machining accuracy directly affects the rotating speed of the bottle blowing machine and the opening and closing performance of the die frame. There are many reasons affecting the machining accuracy of the frame, such as: casting material, frame structure, positioning reference precision, pressing deformation, etc. The precision and compression deformation of the positioning reference will directly affect the coaxiality of the mounting hole (center shaft hole) of the moving and fixed die and the opening and closing performance of the moving and fixed die. As the frame belongs to thin and long parts with thin wall and cantilever box, it deforms greatly during processing, and the dimensional accuracy is difficult to be guaranteed. In the past processing, the key dimensions, such as coaxiality of central shaft hole and distance between swing arm holes, cannot be guaranteed, and the dimension is out of tolerance seriously, which cannot meet the performance requirements of the product. This process research and development solves this problem well and ensures the product quality.

1、 Part process analysis

The material of this part is ZG45, which is casted by the disappear die. From the drawing analysis, the total length is 787mm and the wall thickness is 14mm. The part belongs to thin-wall cantilever casting with poor rigidity and variability. It mainly consists of two groups of holes and three groups of planes. The coaxiality of the fixed circular hole of the central shaft is required to be 0.03mm within a distance of 400mm. The tolerance of the distance between the central shaft hole and the swing arm hole is required to be (128.36 ± 0.02) mm, (81.28 ± 0.02) mm. The perpendicularity of Φ26mm to Datum A is 0.04mm, the symmetry of the plane 70 mm to the center of the part is 0.02mm, and the surface roughness is 3.2ηm. It is high requirements.

2、 Brief Introduction to Frame Machining Process

Parts are inspected after being processed according to the process route, and the series of center shaft holes are: Φ26, Φ40, Φ42mm,coaxiality 0.15~0.25 mm;

Shaft hole Φ26mm and swing arm hole Φ47mm In the X direction, the hole pitch is 128.40~128.55mm; in the Y direction, the hole pitch is 81.36~81.51mm; The symmetry of the 70mm plane to the center of the part is 0.50-0.88mm, which reflects that the positioning of the product is unstable and the dimension is out of tolerance seriously.

The specific reasons are as follows:

• Low workpiece datum accuracy. It can be seen from the machining process that the installation datum plane of the horizontal machining center is machined on the common milling machine X63K at one time. Since the rough positioning datum is the casting blank plane during machining, the flatness of the two datum planes after machining is 0.2mm~1mm. During the subsequent finishing, the workpiece is installed on the horizontal machining center and compacted. Due to the uneven datum surface, the end of the part and the part itself are twisted to different degrees. After the workpiece is machined, the pressing plate is loosened, and the workpiece will rebound, finally making the center shaft hole of the head twist Φ26mm and job-hole Φ40mm cannot be coaxial.

• Unreliable positioning of tooling. During finishing, two planes are taken as the supporting surfaces for installation and positioning, the middle part is suspended, and the vibration of the workpiece during processing is added. At the same time, the protruding part of the suspension is placed on the reference plane in the form of floating support. After installation and clamping, the pressing plate is tightened, and the deformation of the workpiece in the X direction is 0.2-1mm, which indicates that the parts are deformed during pressing, and finally the coaxiality of the two holes is out of tolerance.

• Improper selection of pressing point position. The part belongs to thin and thin box parts with poor rigidity and easy deformation during installation and clamping. In order to prevent deformation and movement, the pressing force must be increased. Therefore, the selection of supporting point is very important.

3、Main measures for solving out-of-tolerance of workpieces

• Improve the machining accuracy of locating surface. It can be seen from the above analysis that the machining accuracy of datum plane is the main factor affecting the machining accuracy of workpiece. Therefore, it can be considered to add a process to process the installation datum plane, specifically: first, process the rough datum plane on the common milling machine X63K, then process the original two rough datum planes on the vertical machining center, and at the same time, increase the positioning datum of the machining head (the original blank surface), The flatness of the datum plane shall be within 0.02mm and the height difference shall be less than or equal to ±0.02mm.

• Change fixture positioning and add floating support. The floating support of the blank surface of the original head part is changed into a fixed support. Meanwhile, several floating positioning supports are added to improve the vibration during processing and enhance the rigidity of the parts.

• By changing the position of clamping point, the deformation of hole pitch and hole diameter caused by pressing force is solved. To sum up, the parts after adjustment of the processing technology have been verified in small batches and have met the technical requirements of the drawings, the performance of the product and the product quality is stable.

4、 Conclusion:

Thin and thin cantilever box parts are prone to two major problems in the processing and production process: deformation under the action of pressing force and distortion caused by the instability of the datum plane. These two factors are the main reasons for unqualified product quality. Therefore, the deformation caused by the installation and clamping of the parts can be effectively avoided by increasing the rough datum, ensuring the machining accuracy of the accurate datum, increasing the fixture positioning, correctly determining the clamping point position of the tooling and other measures, so as to ensure the quality and performance of the product.