China Supplier Custom Gravity Metal Sand Casting

 

1、 Preface

The box is the core component of the transmission system of construction machinery, mainly processing flat and hole systems. The quality of workpiece processing determines the assembly accuracy and working performance of the machine. The following introduces the processing techniques and practical experience of box type parts from the aspects of processing equipment, fixture fixtures, and tool selection, providing reference for the processing of other similar parts.

2、 Workpiece features

The box body is a polyhedral structure with internal cavities, thin walls and uneven wall thickness distribution, and is made of gray cast iron HT250 material. Grey cast iron has good cutting ability, wear resistance, and vibration absorption [1], which can meet the strength and stiffness requirements of the entire machine.

The structure of box type parts is complex and irregular. Figure 1 shows the rear shell structure. One clamping cannot complete the milling and drilling of the bottom large plane, and two clamping affects the precision of plane processing. Figure 2 shows the structure of the rear box. When the bottom hanging area of the machining position is large after the workpiece is positioned, due to the thin wall of the workpiece, it is easy to deform, resulting in the flatness of the large plane and the position of the pin hole exceeding the tolerance. At the same time, when processing such workpieces, the accuracy requirements for the position and coaxiality of each hole should also be ensured.

     

 

Figure 2 Schematic diagram of rear box structure

Generally, a machining allowance of 5mm is left on one side of the casting blank. Considering the pressure installation of the workpiece in the later processing process, it is determined whether to pour out the process boss. After all processes are completed, it is determined whether to mill out the process boss based on the assembly situation. The machining process is divided into rough machining, semi precision machining, and precision machining according to the principle of separating rough and fine machining, first rough and then fine machining, first surface and then hole, and scientific concentration [2]. The machining process is divided into rough machining, semi precision machining, and precision machining, balancing the allowance at each end. Before and after rough machining, there are two lines of marking. Rough marking is the reference line for rough machining, and fine marking is used for aligning the workpiece during precision machining. Leave a finishing allowance of 2mm for rough machining, and a finishing allowance of 0.2-0.5mm for semi precision machining.

In order to reduce or eliminate the influence of internal stress on the workpiece and improve the stability of machining accuracy, aging treatment is required after the blank casting and rough machining processes. The specific processing steps are: rough marking → rough turning of each end → fine marking → semi precision machining, precision machining of both ends → machining of the side. When drilling, half wall cutting should be avoided to ensure the machining accuracy of important holes and arrange the machining sequence reasonably. The valve core hole is shown in Figure 3 and should be machined first φ 18H7 holes, 2 on the side after machining φ 18mm hole.

 

3、 Processing equipment

When formulating processing techniques, process personnel should have a thorough understanding of the performance of workshop equipment and choose appropriate processing equipment based on the overall dimensions of the workpiece and the processing capacity of the equipment. Vertical lathe is selected for rough machining; For semi precision machining and precision machining, CNC vertical lathes are used, vertical machining centers are used for machining both ends, and horizontal machining centers or horizontal milling and boring machines are used for machining the sides. For machining centers, the spindle runout should be verified periodically. For horizontal machining centers, the minimum rotation scale unit of the workbench should also be considered. Some radial hole centerlines and workpiece centerlines have an angle of half degrees, and the minimum rotation scale unit of integer degrees cannot meet the machining accuracy of such holes. When preparing the machining process, the workbench should rotate clockwise or counterclockwise in one direction to complete the machining of all the circumferential surfaces of the workpiece. This helps to maintain the rotational accuracy of the horizontal machining center and improve the service life of the equipment.

 

4、 Tooling Design

Considering the cost of tooling manufacturing, specialized tooling is suitable for mass production. Once the tooling is aligned, the workpiece can be processed according to the line alignment, saving the alignment time for each workpiece and improving production efficiency. After determining the processing equipment, determine the fixture pressing position based on the T-shaped groove spacing of the equipment workbench. The bottom tire of the tooling is made of HT250 material that is not easily deformed, and is processed after aging treatment to eliminate internal stress. The rear shell clamping is shown in Figure 4, and the bottom tire needs to be milled out to pull the front face of the fixture (yellow side in Figure 4) and align the workpiece with the front face (green side in Figure 4), φ 20mm milling cutter milling groove). The positioning components (positioning pins, positioning shafts, and positioning rings, etc.) are made of 45 steel, and their hardness and wear resistance are improved after heat treatment; The pressing plate and cushion block should be made of material Q235 or Q355. The contact area between the tooling bottom tire and the workbench is not too large, and it is designed as a hollow bottom tire with a bottom surface; The use of spacer blocks between the fixture and the workpiece reduces the contact area, which is beneficial for ensuring the flatness of the fixture and workpiece [3]. In addition, the design of the fixture structure should avoid interference with the cutting tool or spindle. When a vertical machining center and a horizontal machining center share a set of positioning fixtures, due to the distance between the horizontal machining center spindle and the workbench, and combined with the distance between the workpiece processing range and the workbench, it is necessary to adjust the height of the bottom tire appropriately.

 

5 、Tool selection

To improve machining efficiency, surface milling cutters with high cutting efficiency should be selected for cutting large flat surfaces of the box. Composite cutting tools should be designed for cutting end holes with sealing slopes to replace small hole milling cutter interpolation milling. If the diameter of the pin hole is ≥ 30mm, it should be processed with a boring cutter, and if the diameter of the pin hole is<30mm, it should be processed with a reamer.

In terms of cutting tools, we mainly consider some uncommon processing tools, such as whether the workpiece needs to process some slender holes, large diameter holes, and some American and British threaded holes. After the part design drawing is signed for, the process personnel should list all the tool details required for the machining process based on the workpiece structure and processing content. Based on the tool ledger of the tool management center, the missing tools should be identified. In addition to purchasing a batch of standard tools, consideration should also be given to whether to extend the rod or customize special tools (such as extended tools, large diameter boring tools, etc.). The extension rod is determined based on the size of the blade and the length used. As the extension rod is too long and can easily vibrate the blade, the selection of the extension rod is not a priority. The production cycle of special tools is relatively long, usually 1-2 months. It is necessary to report the tool plan in advance to avoid delaying use and affecting product delivery.

 

6、 Clamping methods

Clamping is divided into positioning and clamping, as described below.

1）The positioning method of the box is generally divided into mouth positioning, mouth positioning+positioning pin positioning, double pin or double spindle positioning. Lip positioning is known as hole axis clearance fit. To ensure rapid positioning, the positioning length between the workpiece and the positioning pin or spindle is not easily too long, and the general positioning length is set to 8-12mm. In addition, a combination of a cylindrical pin and a diamond pin is often used. The arrangement of cylindrical pins and diamond pins should grasp the following key points: the sharp corner of the diamond pin points towards the center of the cylindrical pin, and the positioning of the double spindle is also the same. For double spindle positioning with height differences, when starting trial processing of each batch of products, the positioning surface is usually milled flat with a milling cutter to ensure the height difference and eliminate processing errors caused by tool wear.

Layout diagram of double spindle (double pin)

2）The edge width of 5mm or more on the back of the box assembly surface can meet the requirements of ordinary pressing plate installation. When the workpiece positioning surface is warped after positioning with the fixture positioning surface, copper sheets, paper scraps, etc. can be used to eliminate the warping before pressing. When the contact surface between the positioning surface and the tooling bottom tire is large, cushion blocks should be used to reduce the contact area. The pressing position should be a solid point (the pressing position of the pressure plate should be consistent with the cushion block) to avoid deformation of the workpiece caused by suspended pressing.

3）The large plane of the workpiece needs to be milled, drilled, and clamped twice to meet the processing requirements. To improve the flatness of the large plane, the method of using transitional threaded holes can be used for one-time clamping and processing. The red bolts at the three windows of the fixture are pulled down and tightened through the pre machined M14-6H threaded holes on the workpiece. After the surface and hole processing are completed, the tension bolts are loosened, and then the processing surface is compressed with a pressure plate to expand the three M14-6H threaded holes to the final required size in the drawing φ 16mm.

7 、Conclusion

In summary, based on the structure and accuracy requirements of box type parts, the following experiences and techniques have been obtained.

1) Leave sufficient machining allowance for the casting blank and separate the rough and fine machining. When casting defects such as sand holes appear on important machining surfaces during rough and semi precision machining of box parts, there is still room for mutual borrowing between the two opposite sides.

2) During the first trial machining of the workpiece, polar coordinate programming is usually not used for holes with strict positional requirements. When the hole positional tolerance is found to be out of tolerance during the three-coordinate inspection, the method of changing the coordinate value can be used for correction.

3) Based on the complexity of the structure and processing content of box type parts, select appropriate cutting tools and processing equipment, design the optimal positioning and clamping fixtures, and analyze specific problems to ensure that qualified products can be processed, greatly improving production efficiency.

 

 

 

 

Basic Information

Total Capitalization	less than US$50,000
Country / Region	China
Year Established	2014
Total Employees	100 to 149
Business Type	Exporter, Manufacturer, Trading Company

 

Trading Capabilities

Total Annual Sales	less than US$50,000
Export Percentage	90 percent to 94 percent
OEM Services	Yes
Small Orders Accepted	Yes
Brand Names	Innolead
Payment Terms	TT
Main Competitive Advantages	Experienced R&D Department, Large Product Line, ODM (Original Designing & Manufacturing), OEM Capability, Production Capacity, Reliability, Reputation
Other Competitive Advantages	NA
Major Customer	Soprano, European Thermodynamics Ltd.
Export Markets	Australasia, Central/South America, Eastern Europe, Mid East/Africa, North America, Western Europe

 

 

 

 

 

 

 

 

 

 

 

 

 

CONTACT US

Alex He

Tel:+86 15989331617

Whatsapp&Wechat:+86 15989331617

Skype ID:alex.ho43

Email: alex.he@innolead.net

 

Web:www.innolead.net

 

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