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Introduction to a New Method for the Design and Fabrication of Electrodes for Cylinder Head Molds Introduction to a New Method for the Design and Fabrication of Electrodes for Cylinder Head Molds Current Location: Home >> Company News >> Technical Documents >> Main Text Introduction to a New Method for the Design and Fabrication of Electrodes for Cylinder Head Molds I want to print IE Bookmark Add to portfolio I want to leave a message View messages Source: Kunshan Mould Network Added by: binghe_521 Date added: 2006-3-29 10:55:41 I. Characteristics of Molds for Motorcycle Engine Cylinder Heads The cylinder head is a very important component of a motorcycle engine; its function is to create the working volume of the cylinder and to guide the movement of the piston. It operates under conditions of high temperature, high pressure, poor lubrication, alternating loads, and corrosion. To increase the cooling area and ensure adequate heat dissipation, many fins are cast on its outer surface, along with numerous support ribs. The leaves, ribs, etc. create small, deep, and complex grooves on the mold, which cannot be machined using cutting tools; therefore, electrodes must be made through electrical discharge machining to give them the desired shape. Therefore, electrical discharge machining plays an important role in the manufacturing of cylinder head molds. The cooling fins are characterized by being arranged around the cylinder head, in large numbers (ranging from 5 to 14), with a relatively small thickness (around 3 mm) and a small spacing between them (10–12 mm). The mold structure features three-way core extraction. Each mold core has a large number of deep grooves. The main parts of the three-way core pulling are shaped using CNC machines or wire cutting to establish their basic form, while the areas that cannot be reached by the cutting tools are finalized through electric discharge machining. We adopt CAD/CAM/NC machining integration technology, using UG software as the platform for product and mold design as well as CNC programming. The HV45 machining center is used as the primary tool for machining the mold surfaces and blade electrodes, while Beijing Archie spark machining machines are employed to machine the blade grooves. The following describes the design and processing methods for the heat dissipation fin electrodes. II. Traditional design and manufacturing methods for blade electrodes: We take the XX90 cylinder head as an example. To ensure adequate heat dissipation, this cylinder head features 6 cooling fins spaced 12 mm apart, with an outer edge thickness of 2 mm; a draft angle must be added to facilitate demolding. Moreover, the outer edges of each blade are at different distances from the center; therefore, the blade profile is a surface model with a variable draft angle, ranging from 1° to 3°. The mold adopts a parting structure with core extraction from three sides, and electrodes are required for core extraction on all three sides. If a solid electrode is used for each core extraction, only slender cutting tools with a diameter of 5 mm or less and a length of up to 100 mm can be used, making cutting impossible. Therefore, a single-electrode combination method is usually adopted. It is the mold and electrode model for the first blade. Each blade requires three electrodes; therefore, the mold for the XX90 cylinder head, which has 6 cooling blades, needs 18 electrodes. Similarly, the XX250 cylinder head, with 12 cooling blades, requires 36 electrodes. For ease of processing during manufacturing, blanks of the same shape and size are usually used. First, forge 18 identical rectangular blanks, mill all six faces of the blanks to ensure a thickness of 12 mm, and drill and ream two positioning holes with equal diameters and at consistent positions in each blank. Then, a CNC machining program is created in UG, and each blade is machined on a CNC machine. Finally, the six electrodes in each of the three directions are clamped together through positioning holes to form three sets of electrodes, and three different core pullers are machined on an electrical machining machine. When designing the programming, 18 three-dimensional geometric models and 18 blank models are required for the XX90 cylinder head, while 36 three-dimensional geometric models and 36 blank models are needed for the XX250 cylinder head. Each blade electrode requires 3 programs; alone the XX90 cylinder head needs 54 programs. The process of creating numerical controls and carrying out CNC machining is time-consuming, complicated, and prone to errors. Therefore, the design and manufacturing of the blade electrode significantly affect the manufacturing cycle and cost of the mold. III. Improved design and manufacturing methods for blade electrodes 1. Blade electrode design: Based on the characteristics of the cylinder head, we have improved the three electrodes in each layer into a single integrated blade electrode. The rectangular profile is a 12 mm thick blank; a frustum is created in its central portion, and 4 positioning and clamping holes of equal diameter are drilled and reamed, with their centerlines either parallel or perpendicular to the core-pulling direction. After each surface is processed, a complete combined electrode is formed through the positioning and clamping holes. When electrical machining is used for left core pulling, two positioning holes perpendicular to the core pulling direction are used for positioning and clamping. After processing is complete, rotate 90° to machine the lower ejector, and finally rotate 90° again to machine the right ejector. Why is this possible? First, the middle part of the cylinder head blade constitutes the cylinder head matrix; it is a cavity in the mold, and electrode shaping is not actually necessary there. Only the areas surrounding the blade electrodes are functional ； Furthermore, the blades are arranged around it; the core-pulling in the three directions each utilizes a part of the integral electrode, which are connected at the parting line, with no interference between the various parts. During electrical machining, there is no interference or electrocorrosion between the various components. Even if there is slight corrosion near the parting line, since the mold blade grooves in that area are open, it is possible to rectify this issue using hand-fitting techniques; practice has shown that the amount of corrosion is very small. Thus, the die for the XX90 cylinder head with 6 cooling fins requires 6 electrodes, while the XX250 cylinder head with 12 cooling fins only needs 12 electrodes. During electrical machining, as long as proper positioning of the electrode is ensured, it is entirely possible to machine the three core pullers using this integrated blade electrode. The electrode material is **reduced**, and the workload for designing 3D models of the electrodes is also **decreased**. 2. Processing of the leaf electrode: Before CNC machining, the pre-processing of the electrode blank follows the same procedure as before, which involves forging → milling six surfaces → drilling and reaming four holes of equal diameter. It must be noted, however, that aside from the thickness of 12 mm, the size of the electrode, as well as the positions of the 4 holes with equal diameters and the frustum, must be accurately determined in CAD software. The principle is as follows: the minimum length and width of the electrode must accommodate the maximum outline of all blades; the diameter of the frustum must be within the minimum operating outline of all blades; and the 4 holes with equal diameters must be located within the frustum. Finally, four holes with equal diameters were used as mounting and positioning references to install it on the designed fixture, and the blade electrode profile was machined on an HV45 vertical machining center. Unlike the original vertical installation method of the electrodes, the improved blade electrodes are placed horizontally; one side is machined first, and after that, the other side is machined by installing them upside down. Since the 6 blades can use the same blank, machining positioning coordinate system, programming coordinate system, machining method, machining allowance, tools, and cutting parameters, when designing and programming, it is sufficient to replace one blade with another in order to create a new machining program for that blade. This **reduces the amount of programming work and improves machining efficiency, while also lowering the error rate. CNC process planning carried out in UG. It can be seen that when generating the machining program for electrode PIAN-2, it is sufficient to COPY the program for electrode PIAN-1 and place it under PIAN-2, then regenerate it; all blade electrodes require only 30 programs. Let’s use the first one as an example. First, machine the upper surface. First, use a high-speed steel flat-end milling tool with a diameter of Φ20 and a radius of curvature of 1 mm to move along the outer contour of the electrode component once; the PLANAR MILLING machining method is employed, with the cutting trajectory type set to PROFILE. Surface allowance: -0.1 mm (discharge gap); spindle speed: 1000 rpm; feed rate: 100 mm/min; cutting depth: 1 mm. The contour shape of the processed blade. Then, the contour cutting method of CAVITY MILL is used to remove a large amount of material from the blade profile. Machining was performed using a high-speed steel end mill with a Φ20 diameter and a radius of curvature of 1 mm, in conventional FOLLOW cutting mode; the surface finish was set at 0 mm, the spindle speed was 1000 r/min, and the depth of cut was 1 mm. During cutting, the feed rate is 200 mm/min, with tool path simulation. For surface finishing, the FIXED CONTOUR driving method or the RADIAL LINE cutting method is typically used. Due to the low feed rate and high cutting force associated with three-axis simultaneous machining, and because the electrode is clamped in the middle using four screws resulting in a relatively weak clamping force, we adopted the PROFILE mode from the equal-height cutting methods such as CAVITY MILL. The machining path is shown in Figure 10 (the path curve has been scaled down for better clarity). The machining was carried out using a high-speed steel end mill with a Φ20 diameter and a radius of curvature of 1 mm. To meet the discharge gap requirement of 0.1 mm in the electro-etching process, the surface allowance was set at –0.1 mm. The spindle speed was 2000 rpm, the feed rate was 1000 mm/min, and the cutting depth was 0.03 mm. Although the draft angle of the electrode profile is as low as 1°, making the profile very smooth, according to the surface roughness formula in milling theory, surface roughness decreases as the cutting depth is reduced. Therefore, using a cutting depth of 0.03 mm yields excellent results, and a slight amount of polishing subsequently achieves good surface quality. Once one side has been processed, the processing of the opposite side is carried out in the same way as described earlier; since the electrode profile is already in place, only the last two procedures are required. It should be noted that as the clamping contact area further decreases, the cutting depth must be reduced; therefore, 0.5 mm is used for rough machining and 0.03 mm for finish machining. During machining and programming, it is important to note that since the electrode is clamped with only four screws in the middle, the clamping force is low; therefore, the cutting force must be reduced. According to cutting theory, reducing the cutting depth can effectively lower the cutting force, and it can also reduce the surface roughness of the electrode profile. Therefore, we chose a higher cutting speed and a smaller cutting depth, with the finish machining cutting depth being 0.03 mm. The tool material is high-speed steel; compared to cemented carbide, it has lower hardness, but the tool remains sharp and has a greater ability to cut thin materials. Since the workpiece material is copper, hardness is not an issue. Practice has shown that in the machining of copper electrodes, the use of high-speed steel tools along with appropriate cutting parameters can yield better results than those achieved with cemented carbide tools. IV. Conclusion: Electrical discharge machining is widely used in motorcycle cylinder head molds. The traditional design and manufacturing methods for blade electrodes result in material waste and long processing times. By improving the design and manufacturing processes for these cooling blade electrodes, incorporating advanced 3D CAD/CAM technologies, and adopting appropriate processing and installation methods, the efficiency of mold manufacturing can be greatly enhanced. We have already applied this method to multiple cylinder head molds, and practice has proven it to be effective.